Advances in Mechanism, Machine Science and Engineering in China

Twisted and coiled polymer fiber (TCPF) is a new type of artificial muscles featuring large stroke and high loading capacity that can be benefited in soft robotic actuation. However, due to the multi-step fabrication process with various parameter, the existed TCPF suffers from an inconsistent actuation performance, which hinders its further application. The current paper studies the mechanics of TCPF actuation, revealing the significance of coiling and annealing procedure. Effect of twisting weight, annealing temperature and pre-stretch as mechanical and thermal training, are experimentally investigated, and the contraction forces are characterized. With these mechanical and thermal training, consistent and hysteresis-free contraction force is attain. The findings offer a guidance for the high-performance artificial muscle in compliant structures and tensegrity robot.

In this paper, the statistical calculation formulas of gear transmission error are put forward to predict total transmission error of a gear train. Gear transmission errors come from a number of complex factors and those factors are hardly considered together on gear models. In order to analyze transmission error considering multiple factors, a three-layer coupling relationship model of each factor influencing the transmission error is investigated. Then, the influence of the third layer factor on the second layer factor and the influence of the single factor in the second layer on the gear transmission error are analyzed. Furthermore, the synthetic expression of transmission error for a gear train and the statistical calculation formula is obtained.

Traditional independent meter-in and meter-out hydraulic systems have been widely used in industry because of their energy saving characteristics and control flexibility. However, the control accuracy is limited by the strong nonlinearities and parametric uncertainties. In addition, independent metering systems suffer from safety problem due to complex hydraulic mechanical structures. The conventional solutions to guarantee safety are using mechanical mechanisms to limit the system’s states which increase complexity further. This paper proposes a novel two loop control strategy which regards the physical limits as state constraints to alternative mechanical structures. A conventional adaptive robust controller (ARC) is utilized in the inner loop to achieve high tracking accuracy and handle the nonlinearities, uncertainties and disturbances. A third order trajectory algorithm is synthesized to modify the original severe trajectory to a modest one which will make sure that the state constraints are not violated. Simulations are carried out and the results demonstrate the effectiveness of the proposed control strategy.

In order to study the influence of joint clearance and flexible component on axisymmetric vectoring exhaust nozzle (AVEN) mechanism, the rigid flexible coupling dynamic equation of simplified AVEN mechanism is established based on the finite element method. Specifically, the Lankarani-Nikravesh contact force model is used to analyze the clearance impact force, and the flexible component is established by the absolute node coordinate method (ANCF). The dynamic equation is derived by Lagrange multiplier method, and solved by EULER IMPLICIT and MINRES combined. The influence of clearance and flexibility on the dynamics of AVEN mechanism are analyzed, which implies that the clearance and flexibility will cause nonlinearity of the AVEN dynamics. With the increase of joint clearance, the accuracy and stability of mechanism motion decrease and the reaction force of joint increases. Moreover, the flexibility would compensate the nonlinearity caused by the clearance.

Based on the basic principle of statistical energy analysis, the concept of equivalent SEA is put forward and the equivalent SEA model of gear box is established. The vibration response and radiation noise of the gearbox under the gear dynamic load excitation are studied. The modal density and loss factor of each subsystem are determined by the virtual test method and the numerical calculation method of backflow of power flow. The modified statistical energy parameters are assigned to the SEA model, obtaining the structural vibration responses and the radiation noise spectrum of each subsystem of the gearbox.

Hybrid joint-space control strategy, where some redundant cables are force control, while other cables perform the length control, has the ability to control the robots with small pose errors, and maintain all cables tensioned at the same time. In the cable-driven parallel robots with redundant drives, all the cable tensions have a predicable range, we called cable adjustable force (CAF) in this study. This work aims at investigating the relationships between the CAF of target force-controlled cables, and the pose errors under the hybrid joint-space control strategy. A simulation framework, considering interfering cable length and cable forces, is developed to analysis the characters of hybrid-input control strategy, based on a cable suspended with one redundant layout. We found that the CAF is related to the pose control error of the end-effector, and can be regard as a selection criteria for the target cable for the force control in the hybrid joint-space control strategy.

In this study, the gear backlash of the common 3K planetary gear train is studied in depth. After the coupling analysis of various factors affecting the gear backlash of the gear, the calculation formula of the gear backlash under various factors is derived, and the probability statistical method is innovatively introduced into the calculation to analyze the influencing factors of gear backlash in gear train closer to the design and manufacturing process. Finally, the numerical analysis example reveals the importance and influence of some parameters that may make the gear backlash larger. The research has a certain guiding significance for the parameter pre-optimization in the design and manufacturing of the gear.

Spur gear has a large impact and low load-carrying capacity and will lead to greater vibration, while helical gear will produce axial force. In order to improve the transmission performance, the transmission principle of one novel high-order phasing gear is proposed in this paper. The staggered phase angle of the high-order phasing gear is defined, the calculating method of the contact ratio of the high-order phasing gear. The influences of design parameters on dynamic properties, such as mesh stiffness and dynamic response as well as transmission error, are studied. The results show that when the staggered phase angle of the second-order phasing gear equals to 1/2 pitch angle, that is ϕ = π/z, the time-varying mesh stiffness fluctuation of the phasing gear is much smaller than that of the spur gear. Meanwhile, the second-order phasing gear’s fluctuation of dynamic meshing force is the smallest. This novel phasing gear could reduce vibration and has superior transmission performance, and verified through experiments.

The over-constrained parallel manipulators have drawn a lot of attention, and their application potential is constantly being explored. To improve the performance of the over-constrained mechanism, the actual structural parameters need to be calibrated. The calibration methods of the non-over-constrained mechanism cannot be applied to the over-constrained mechanism because of the existence of the over-constrained force. Therefore, the calibration methods which utilize a complex model to calculate the deformation and the over-constrained force are proposed. These methods need complex modeling and calculation, and the calculation errors of the forces and deformation may affect the calibration accuracy. To follow the trend of perceptual intelligence and simplify the calibration process, a kinematic calibration method of the over-constrained mechanism is proposed, utilizing the measured force data to calibrate the actual structural parameters. This method can avoid complex modeling and eliminate the impact of the calculation errors of the forces and deformation on the calibration accuracy. To verify the feasibility of this method, a 2-DOF over-constrained parallel manipulator is designed and developed. Each chain of this mechanism contains a force sensor, which is utilized to measure the over-constrained force. The kinematic error model is established in this paper, and it is identified using the Newton–Raphson iteration, the Regularization method, and the least-square method. Finally, a group of experiments is conducted to verify the validity of this method. The experiment results show that this method can reduce the root mean square error of the over-constrained mechanism from 1.243 to 0.028 mm.

In order to alleviate the problem of the temperature rise, thermal deformation and unreasonable local distribution of equivalent stress which will cause fatigue damage and reduction of the service life of the disc brake. In this study, the friction-thermal-mechanical multi-dimensional coupling analysis of the disc brake of belt conveyor is carried out, and the distribution of the transient temperature field and stress field of the disc brake under the emergency braking condition is obtained. The structural parameters of brake disc and brake shoe are taken as design variables, and the maximum temperature and maximum equivalent stress of the brake disc are taken as the optimization objectives. The Kriging response surface proxy model of the maximum temperature and maximum equivalent stress of the brake disc is constructed by using the optimal space filling to collect the data sample points. According to this, the multi-objective genetic algorithm (MOGA) is used to optimize the design, and the optimized structural parameters are obtained, such as thickness and diameter of the brake disc, thickness, length and width of the brake shoe. The maximum temperature, maximum equivalent stress and maximum deformation are reduced, and the fatigue life cycle is improved, which provides a theoretical basis and reference basis for the improvement of relevant technologies of the disc brakes.

The identification and solution of NVH problem is the main way to continuously improve the comfort in the mechanical field. With the application of 350 bar high pressure fuel supply system, the solution of noise problem of high-pressure system has become an important work content in the development of sound quality of automobile cab. This paper studies the noise reduction of high-pressure direct injection engine, comprehensively analyzes the key factors of high-pressure direct injection system noise, and provides new ideas and references for the system to solve the high-pressure direct injection noise problem. The main path solutions for high-pressure direct injection noise and vibration problems in the mechanical field are to optimize the structural mode, increase vibration isolation, change the pipeline direction, and optimize the injection strategy.

An intramedullary lengthening nail avoids complications frequently found in the external fixator and shows remarkable clinical results. The magnetic drive is the mainstream actuation method for intramedullary lengthening nails which shows good results, but clinicians claim insufficient distraction torque of the intramedullary lengthening nail will occur occasionally. In this paper, we investigate the optimal parameters for magnetic drive intramedullary lengthening nail based on parametric modeling to ensure the rotor magnet is rotated synchronously and the distraction torque is sufficient for bone lengthening. The driver-rotor magnet model is established, and parametric optimization of the angular position of the driver magnet local coordinate system, the angular velocity of the driver magnet, the number of driver magnets, and the number of pole pairs of the driver magnet to determine optimal values. Optimal parameters are selected and verified by experiments. The results show that a pair of single-pole pairs of the driver magnet rotating with an angular speed of 50 rpm can meet the minimal distraction torque of 1.5 N mm, which is around 5.6 N mm.

In order to improve the meshing performance of non-orthogonal helical face-gears, a designation of double-crowned tooth modification with high-order transmission error (HTE) is constructed in this paper. First, the double-crowned tooth modification is designed based on the tooth profile modification of the rack-cutter and the motion relationship between the rack-cutter and the processed pinion, and then, the designation of high-order tooth modification is verified by using tooth contact analysis (TCA). Second, a parameterized 3D grid of modified gears is generated based on MATLAB programming, and a simulation of loaded tooth contact analysis for modified non-orthogonal helical face-gears is carried out by using ABAQUS software. Third, the calculation results of the standard tooth, second-order parabolic modified tooth and high-order parabolic modified tooth are compared with and without the assembly errors. Ultimately, an example is presented and the results show that the geometric transmission error of the newly designed high-order modified non-orthogonal helical face-gears conforms to the expected design. Compared with the second-order parabolic tooth modification, the newly designed high-order tooth modification pair shows a better meshing performance with and without assembly errors. The research of this paper can provide ideas and methods for the tooth modification design of non-orthogonal helical face-gear.

Reconfigurable parallel mechanisms have more than one motion pattern and facilitate complex and compound manipulations. However, it is still a challenge to describe all the motion patterns by an integrated expression, which leads to difficulties in the analysis of transformation process. Furthermore, performance model of each motion pattern is always constructed individually in spite of their coupled relationship. In this paper, a reconfigurable parallel robot with spatial translational (3T) and rotational (3R) motion patterns is presented for on-orbit manipulation of cabins, including target capture, racemization, screwing and plugging. The integrated topology description, transformation process and whole kinematic modeling of this robot are investigated in-depth. Firstly, the topologies of two motion patterns are described in finite screw format and combined by defining a transformation factor. In this way, the transformation process is analyzed algebraically. Then taking advantage of the differential mapping of finite and instantaneous screws, the Jacobian matrix is derived from the motion equations directly. Finally, a numerical example is given to show the on-orbit manipulation process of the reconfigurable robot, involving inverse kinematics and workspace analysis. The method proposed in this paper could connect the topologies under different motion patterns algebraically, which facilitates to investigate the motion and performance of reconfigurable parallel mechanisms as a whole.

A parallel robot mechanism with two parallel links is proposed. It can realize the motion characteristics of synchronous telescopic in the swing state by employing a set of constraints of a synchronous belt drive system. Further, the moving platform can have 2-DOF translational motion and no singularity in its workspace by integrating the special synchronous belt drive system into the parallelogram mechanism. The kinematics analysis of the mechanism includes position-forward solution, position-reverse solution, velocity analysis, and workspace analysis. Moreover, the trajectory planning of the robot and one of its trajectory routes are presented. The distribution mode of velocity and acceleration on the trajectory is set, and the position, velocity, and acceleration of the trajectory interpolation points are obtained. Finally, the prototype manufacture is completed, and relevant tests are carried out.

Straightness measurement needs to be performed before straightening. In this paper, considering the rationality of structural design and protecting the sensor, we used the lever structure to measure the straightness of the regular hexagon section shaft. However, due to lever parameters and the contact mode between the lever and the shaft and between the lever and the sensor, the lever model has measurement errors. Two kinds of lever-type measuring mechanisms are discussed to improve the measuring precision in this paper. The error correction method is proposed through strict mathematical derivation. At the same time, sensitivity analysis of lever parameters was carried out. Finally, the validity of the error correction is proved through experimental verification. The experiments indicate that the error of measurement results of two lever models after error correction is controlled within ± 0.006 mm, which improves the measurement accuracy significantly. At the same time, after correcting the measurement results of deflection of the regular hexagon section shaft, the length error of deflection vector is reduced to 0.01 mm basically.

The wheel-legged hybrid structure has been utilized by ground mobile platforms in recent years to achieve good mobility on both flat surface and rough terrain. However, many designs of the obstacle-crossing part and transformation driving part of this structure is highly coupled, which limits its optimal performance in both aspects. This paper presents a novel wheel-legged robot with rim shape changeable wheels, which has the bi-directional and smooth obstacle-crossing ability. Based on the kinematic model, the geometric parameters of the wheel structure and the design variables of the driving four-bar mechanism are optimized separately. Experiments show that the prototype installed with the novel transformable wheel can overcome steps with the height of 1.52 times of its wheel radius with less fluctuation of its centroid and performs good locomotion capabilities in different environments.

This paper proposes a new numerical approach called Forward and Backward Cyclic Coordinate Descent (FBCCD), which is based on the Cyclic Coordinate Descent (CCD) algorithm. A specific set of solutions can be found from infinite solutions of multi-segment continuum robots using the iterative numerical algorithm. Inspired by the Forward and Backward Reaching Inverse Kinematics (FABRIK) algorithm, the inverse kinematics (IK) of a multi-segment continuum robot is divided into two phases: a forward iteration of end coordinates and a backward iteration of end direction. Forward and backward iterations correct and compensate each other, making the end pose close to the target. By altering the goal function of a single iteration, the FBCCD algorithm can also be applied to the continuum robot with a movable base. The numerical experiment results illustrate that this algorithm is with higher convergence rate and effectiveness compared with some of the most popular IK approaches. The average operating time for a five-segment continuum robot is 361 ms and the average number of iterations is 22.89.

The problem of low reproduction accuracy of road spectrum of wheel-coupled vehicle durability test bench needs to be solved. From the perspective of mechanism innovation, a fully decoupled two-rotation parallel mechanism with large load-bearing capacity for vehicle durability testing is proposed in this paper. This kind of parallel mechanism can solve the problem of low-bearing capacity of fully decoupled parallel mechanisms. Based on the requirement of reproduction accuracy of real road spectrum, the degree of freedom required by the mechanism is analyzed. Due to the requirements of fully decoupled and large load-bearing, the configuration design of the parallel mechanism is carried out. In order to further improve the bearing capacity of the mechanism, based on the kinematic analysis results of the mechanism, the size parameters of the mechanism are optimized by using the graph method. The research results show that the bearing capacity of the mechanism is increased by 50% after adding the closed-loop unit and optimizing the size. The finite element simulation verifies that the load-bearing capacity of the optimized fully decoupled two-rotation parallel mechanism satisfies the design index requirements. This research lays a theoretical foundation for the application of fully decoupled parallel mechanisms with large bearing capacity.

This work proposes a hybrid machining robot RPR/RP + RR + P based on a planar parallel mechanism. Based on the screw theory, the characteristics of the degree of freedom of the hybrid robot are analyzed, and then the inverse and forward kinematics are solved by geometric methods. And size optimization is carried out by taking the workspace and driving forces as the objects. Then the working space of the hybrid robot is calculated by the Monte Carlo method. Finally, the three-dimensional model of the mechanism is established, and through ADAMS simulation, the accuracy of the inverse kinematics solution was verified.

This paper presents a force modulation (FM) mode harmonic atomic force microscope (AFM) for enhanced cell scanning quality. Compared with tapping mode AFM, FM mode AFM has less contact force and less damage to biological samples. Harmonic AFM has been widely applied to characterize the local mechanical properties of the specimens. In this paper, we integrate FM mode AFM and harmonic AFM to scan Hela cells. Experimental results show that the comprehensive scan mode can perform better image resolution than the conventional tapping mode AFM. Our comprehensive scanning strategy is a powerful and proper technique to study the complete mechanical properties of cells and improve the sensitivity of nanometer detection.

The legged robot has better adaptability to terrain in the process of moving and has been considered for future planetary exploration missions. As the part of direct contact with planet soil, the foot will directly affect movement performance and control effect of the legged robot. In this paper, the advantages and disadvantages of various foot configurations of ground legged robot are analyzed, and a coronal foot configuration is proposed. Based on the foot-terrain interaction mechanics model, the size of the coronal foot is optimized with the goal of anti-sinkage, anti-slip and light weight. Then, a high-performance coronal foot with two-stage buffering and touch sensing functions is designed. And the finite element analysis is carried out to verify the reliability of strength and stiffness of the foot in the ultimate working conditions. Finally, the anti-sinkage and tangential traction performance of the coronal foot is verified by quasi-static loading, loading with impact and tangential slip experiments.

A unified uncertainty analysis method for estimating uncertainty distribution is proposed to deal with the uncertain propagation problem involving probabilistic, evidence, fuzzy and interval uncertainties. First, the unified moment analysis based on dimensional reduction integral and efficient global optimization is performed to calculate the first four statistical moments. Then, based on these moments, a family of Johnson distributions fitting to the distribution function of response are obtained using the moment matching method. Afterwards, the uncertainty distribution bounds of the response function are obtained by using optimization techniques. Finally, three numerical examples are investigated to demonstrate the validity of the proposed method. The results show that the proposed method can not only be applied to the uncertain propagation analysis under probabilistic, evidence, fuzzy and interval uncertainties, but also be suitable for general application problems with strong nonlinearity and implicit response function.

This paper deals with the conceptual design and kinematic analysis of a novel six degrees of freedom (DOF) parallel mechanism. The newly invented mechanism is a modified version of the F-200iB industrial robot, achieved by integrating the universal joints of a pair of limbs into a two-in-one part. The mobility of the proposed parallel mechanism is analyzed with the aid of the theory of mechanism topology. The inverse and forward kinematic models of the proposed parallel mechanism are derived in brief and validated by numerical simulation.

A nursing bed is helpful for patients confined to the bed for a long period of time and rigid origami is a potential source for designing support mechanism of nursing beds. This paper presents a rigid origami nursing bed support mechanism that is able to fit into human body curve. Firstly, the relation between degree-4 origami vertex and spherical 4R linkages is introduced, together with the kinematics of spherical 4R linkages. Secondly, the origami pattern of the support mechanism is proposed, and the kinematics of the back board, which can be folded to fit into human body curve, is analyzed. Finally, the back-lifting, turning and leg-lifting mechanism of the support mechanism is introduced together with their kinematics. The mechanism proposed in this paper provides multiple choices for the design of nursing beds.

The non-probabilistic convex model describes uncertainty of parameters in the form of a bounded set rather than the probability distribution and is generally applied to interval uncertainty analysis based on the fluctuation ranges of structural parameters. When performing the structural response bounds analysis or uncertain optimization design, too many interval parameters is not beneficial in most circumstances. It may lead to problems such as inefficient computation and non-convergence of the optimization process. This paper proposes an interval principal component analysis method for the non-probabilistic multidimensional ellipsoid convex model, which aims to reduce the dimensionality of the uncertainty domain of correlated intervals, while retaining as much as possible of the variation present in the bounded uncertainty. Firstly, the mathematical mapping between the coordinate axes and the marginal intervals of the multidimensional ellipsoid convex model on these axes is established for an arbitrary coordinate system. Secondly, the difference index is introduced to describe the differentiation degree of the group of marginal intervals, the maximizing of which yields the principal axes of the multidimensional ellipsoid convex model. With the magnitudes of the marginal intervals, the most critical axes and corresponding interval components in uncertainty quantification can then be identified. By neglecting those axes with small marginal intervals, the dimensionality can be thus reduced. An error index is also suggested to indicate the accuracy of uncertainty quantification under the dimensionality reduction representation. Finally, two numerical examples are presented to show the dimensionality reduction representation procedure by the proposed interval principal component analysis.

In this article, a new six degrees-of-freedom (DOF) deployable parallel manipulator (DPM) with three straight scissors legs is briefly described. The configuration design method of the DPM is proposed by means of GF set theory, using this method the mechanism configuration can be determined. The decoupling of the proposed kinematic chains is discussed, a new deployable parallel manipulator is designed. Its position only depends on the elongation of three deployable legs, there such legs are employed to build 6-DOF DPM manipulator. And the effect factors of error were investigated, its accuracy and precision are verified by checkout location errors and clearance and driving errors, and the kinematic accuracy models are proposed for the proposed manipulator.

Cable-driven continuum robots, inspired by natural biologies such as elephants and octopuses, have countless numbers of degrees of freedom, permitting them to carry out special tasks in confined space. However, the slender manipulator driven by cables also results in a significant number of driving motors integrated at the end of manipulator, which complicates the control of continuum robot. In this paper, to solve the problem, we optimize the cable layout based on the analysis of the cable length variation principle. First and foremost, a cable layout method of the shared motor is proposed, which can achieve the complete control of a continuum robot by employing half the number of motors. And then, the kinematics for the proposed cable layout is established based on the assumption of piecewise constant curvature. Finally, the experimental platform is constructed to evaluate the effectiveness of the proposed methods. The experimental results suggest that the optimized cable layout method can achieve the control of a double-section continuum robot by employing four motors. Moreover, it is worthy to be noted that, to some degree, the proposed cable layout method can effectively decrease the influence of gravity, which maximally improves 92.16% of the tip position accuracy.

Force feedback in robot-assisted surgery is important to enhance the immersion of intraoperative operations. In this paper, a miniaturized small-range three-dimensional force sensor is designed for surgical robots. We presented the elastomer structure design and performed mechanical modeling analysis, finite element force and deformation verification as well as the analysis and comparison to choose a better elastomer structure. According to the optimized elastomer structure, the strain gage arrangement method is carried out to ensure higher sensitivity and better dynamic performance. Finally, the calibration experiment verifies that the designed miniature three-dimensional force sensor has high sensitivity, high resolution and low-dimensional coupling, resulting in potential application in surgical robotic instruments.

A type of parallel driving mechanism (PDM) is proposed in this paper. PDM is different from parallel mechanism and hybrid mechanism, which is composed of the operating mechanism, driving mechanism, and connecting joint. Both the operating mechanism and driving mechanism are connected to the frame which can reduce the inertia at the end of the mechanism and improve the dynamic response. Based on the PDM’s concept, configuration design process of lower-mobility PDM is proposed. In this process, the matching procedure between the driving mechanism, operating mechanism and connecting joint in PDM during configuration design is presented. On this basis, the configuration design of 3–5 degrees-of-freedom (DOFs) PDM is carried out. PDM can enrich the types of mechanisms and provide more configuration options for mechanical equipment. The configuration design process provides theoretical support for developing new PDMs and three PDMs has good potential to be used in different application.

In this paper, a kind of simulated “soft” mechanical adaptive grasper (GXU-Grasper) with the characteristics of adaptive object shape, uniform grasping force, single-degree-of-freedom drive and full rigid structure is taken as the research object, and the dimensional of its transmission mechanism is analyzed. The correlation model between the motion parameters and dimensional parameters of the transmission mechanism of each knuckle element under different constraints is established, and the linkage correlation model of the transmission mechanism between adjacent knuckle elements is established. The relationship diagram of all feasible solution of the transmission mechanism dimensional of each knuckle unit of the grasper is obtained through the analysis of the example. A prototype was made and the grasping experiment was carried out. The experiment showed that the GXU-Grasper can relatively smoothly and softly grasp the objects that are variable, fragile, brittle and uneven in shape, which verifies the effectiveness of the dimensional analysis of the grasper transmission mechanism.

Compared to other types of robots, snake robots have many advantages and are able to work in special environments such as narrow spaces. In this paper, we design a remote-controlled snake robot with orthogonal connections by investigating the structural design and motion planning algorithms according to performance requirements. Experiments have shown that the snake robot designed in this paper can move quickly on flat surfaces and can also enter narrow environments for detection. In post-disaster rescue, the snake robot can be used to enter through narrow passages, detect trapped people and improve rescue efficiency.

This paper presents a design of a 3DOF XYZ precision positioning platform using novel Z-shaped flexure hinges. In the platform, bridge-type mechanism and leverage mechanism are adopted to amplify its output displacement. Besides, a new type of Z-shaped flexure hinge is proposed to achieve the amplification of the displacement in Z-axis. The bi-directional motion in the X-axis of the platform is realized using the differential moving principle. Kinematics and statics analysis of the proposed platform are carried out by pseudo-rigid-body-modeling method and matrix-based compliance modeling method, respectively. In addition, finite element method is used to verify the validity of theoretical analysis. The simulation results show that the maximum displacement of the platform in the XYZ-axis are ± 535.25 μm, 439.98 μm and 1578.7 μm, respectively.

Aiming at the problem of cleaning and transportation of muck at the bottom of the tunnel, a new muck cleaning, and transportation scheme is proposed, and the effectiveness of the scheme is verified. Firstly, according to the construction requirements, the design boundary conditions of the robot are extracted, and a new mechanism of muck removal robot with redundant degrees of freedom is designed. Secondly, combined with the actual operation process, the mechanism model is simplified and established. The kinematics model of the robot is established based on the D-H parameter method. The operation parameters in the robot workspace are obtained by using forward kinematics analysis results and the Monte Carlo method. Thirdly, according to the different requirements for trajectory accuracy in different working processes of the robot, the circular interpolation algorithm and B-spline function algorithm are used for trajectory planning in Cartesian space and joint space respectively, and the results are introduced into the simulation platform to obtain the motion trajectory and joint motion of the robot in the workspace. The results show that the robot has no collision with the tunnel ground, and can meet the requirements of muck removal and transportation.

The legged robot can adapt to challenging terrains such as stairs and debris. The hexapod robot has better stability, payload capability, and fault-tolerant ability than the biped and quadruped robot. This paper proposes a novel hexapod robot composed of two walking platforms and an actively actuated waist joint. The mechanical topology of the robot is determined by comprehensively considering the walking stability, energy consumption, and operating dexterity. The kinematics of the modular leg mechanism and the robot body are analyzed. The robot dimension, including the leg and body dimensions, affects terrain adaptability. The requirements on the robot dimension to cross a ditch with target width and traverse a step barrier with target height are proposed, respectively. The leg and body dimensions are determined by simultaneously considering these two scenarios. Virtual simulations and prototype experiments are conducted to verify the feasibility of the robot dimension design.

In the imaging process of a multi-frequency atomic force microscope (AFM), the higher harmonics of the tapping cantilever probe are collected to ensure an accurate estimation of material property information, such as elasticity. But the higher harmonics have the disadvantages of low amplitude and rapid decay, which reduce the sensitivity of multi-frequency AFM. According to the vibration theory, assigning resonance frequencies to integer harmonics can significantly improve the detection sensitivity of higher harmonic frequencies. This paper demonstrates a hard-kill based structural optimization method for assigning resonance harmonics of an AFM cantilever. The sensitivity number of void elements is calculated by the interpolated displacement. The ABAQUS is integrated into the code as the finite element analysis (FEA) solver, which can provide an accurate FEA result. Numerical results show that the proposed method is efficient and can obtain a convergent solution satisfying the resonance harmonics assignment.

Based on flexible slider mechanisms and triangular amplification mechanisms, a symmetric micro-displacement amplification mechanism (MDAM) is proposed combined with a fixed guide flexible segment and a parallel guide mechanism. The dynamic performance of the mechanism is analyzed through finite element method, and the modal analysis is carried out through ANSYS. Finally, the different effects of the main structural parameters of the mechanism on the natural frequency are obtained.

Low stiffness characteristic of robotic machining equipment makes it prone to vibration during machining. It is a practical and feasible way to improve robot’s machining performance through dynamic design. This paper built the dynamic model of a 5-DoF parallel robot based on the finite element method (FEM). The dimension and structure parameters involved in optimization are selected through sensitivity analysis, and their effects on main global vibration modes (GVMs) are analyzed. The appearance of local vibration modes (LVMs) is mentioned. Then the robot’s uniformity of stiffness, uniformity of first order main GVM frequency and mean value of first order main GVM frequency within workspace are optimized based on the multi-objective genetic algorithm. Finally, a 5-DoF parallel robot with small performance fluctuation and high first order main GVM frequency is designed.

Piezoelectric actuator is a critical component of piezo-actuated compliant mechanisms, especially for the precision positioning stage. To design and optimize a stage with high bandwidth and proper motion range, it is necessary to establish a kinetostatic and dynamic model for the piezo-stack widely used in nano-positioning stage. Based on piezoelectric vibration theory and dynamic stiffness method, a new modeling method for compliant mechanisms actuated by piezo-stack has been proposed in this work. The planar dynamic stiffness matrices of the piezo-plate, the piezo-stack, and the piezoelectric actuator with insulating plates are deduced by considering PEA as several beam components with external forces equivalent to piezo-actuated forces. To verify the proposed modeling method, the dynamic models of piezoelectric actuator and two piezo-actuated compliant mechanisms are deduced based on the proposed method and validated by the finite element method.

Although various advanced anthropomorphic hands have been proposed, the design and fabrication of thumb joints to achieve dexterity function in a limited space is still a great challenge. To promote the dexterity of the anthropomorphic thumb joints in the cramped space of the palm, we present a fabric-based flexible actuator used for thumb joints to realize two degrees of freedom (DOFs): circumduction and adduction. First, we introduce the design concept inspired by muscle groups of the human palm. A kind of pneumatic small-scale actuators that relies on fabric-crease to produce deformation is proposed. Then the properties of flexible lightweight actuators are characterized. The actuators just need ± 10 kPa pressure to realize a flexion range of 90°. Finally, we modularly assemble the actuators to construct a compact two DOFs thumb joints. Experimental results show that the applied fabric-based thumb joints can achieve dexterous manipulation like sliding the smartphone screen.

The three-dimensional fabric fabricated by three-dimensional braiding technology can remedy the defects of poor interlayer bonding of continuous fiber reinforced polymer composites, but the traditional three-dimensional braiding machines are not applicable for the braiding of small special-shaped structures. Therefore, a small aperture braiding technology based on truss structure is proposed in this paper, which can fabricate small special-shaped structures. Firstly, based on 3D printing continuous fiber reinforced polymer technology and 3D braiding technology, this paper given definitely basic project for solving problem and integrated techniques flow. Then, according to the size of the required braided structure and referring to the cable-driven interventional catheter technology applied to the treatment of cardiovascular diseases, the principle of 3D braiding technology is introduced and the structural design of 3D braiding head is completed. Finally, according to different fabric structures, the trajectory planning of each braiding mechanism is realized, and their simulated motions are imitated by the software of Adams to obtain motion trajectory figures.

An end-traction lower extremity rehabilitation robot named ETLER is designed to meet the rehabilitation needs of patients with lower extremity dysfunction at all stages of recovery, while taking into account the ease of operation for the patient. A single robot can meet the needs of a hemiplegic patient on either side for the designed end-change structure. The robots can also be used in pairs for patients with spinal cord injuries. Meanwhile, the adjustable ankle joint limit design provides customized training programs for the ankle joint. To carry out the trajectory planning of the rehabilitation robot, kinematic analysis and control strategy modeling of the robot and human–machine system are carried out. The functionality and universality of the rehabilitation robot are verified through comparative tests.

Variable stiffness mechanisms perform better compliance during forceful interactions with uncertain environments. This paper proposes a novel disc-spring-based cable-driven variable stiffness joint. Considering the elastic cable and variable stiffness device, stiffness model of a general cable-driven joint is established. Mechanical property of a disc spring is analyzed. A variable stiffness device is obtained by stacking disc springs with different modes. Influence of cable tensions on stiffness of a revolute joint and a Hooke joint is evaluated. Two cases, a RR serial chain and an UR serial chain, are studied to verify the feasibility of stiffness adjustment through regulating cable tensions. Structure of the proposed variable stiffness joint is simple and compact, which can be utilized in cable-driven mechanisms widely.

With its advantages of high flexibility, high efficiency and low cost, industrial robots play an important role in the transformation and upgrading of aviation manufacturing technology. However, due to uncertain parameters after the assembly, the industrial robot has low absolute positional and trajectory accuracy, which indicates robots designed based on traditional kinematics are far from meeting the high precision requirements. The purpose of this paper is to develop a dynamic accuracy analysis method of industrial robot considering uncertainty and provide theoretical guidance for the design and manufacturing stage of industrial robot. Sobol' global sensitivity analysis method is adopted to obtain the sensitivity data of uncertain parameters. 10 main parameters are extracted from 54 uncertain parameters and the residuals of the simplified model compared with the completed model are ± 0.05 mm.

The hydraulic cover support and walking structure are the main parts of cover robot for coal mining. Through the analysis of moving path of four connecting rods which simplified from cover support of cover robot and the pressures from falling down of coals and rocks, the new cover support structure is designed. The pedrail of robot adapted to different terrains are designed. The structure of pedrail is designed from the moving path of connecting rods which simplified from pedrail. The auxiliary parts such as dangerous gas and temperature identifications are added. From the experiments of excavation of coal, the pressures of cover robot are collected form sensors. The results show that the new designed cover robot can adapt well to the coal terrain, and the pressure of working robot is reasonable.

The autonomous underwater vehicle (AUV) has become important means of ocean observation. In this paper, we have based on the characteristics of AUV to design an ARMs 2.0 autonomous vehicle that satisfies requirements for water surface and underwater operations. It adopts a modular cabin structure design to easily replace or add equipment required for different missions. The new rim driven propeller is used as the stern main thruster. Through comparative test analysis, the different characteristics such as roll and noise brought by the rim propulsion AUV are verified, and the experimental basis conditions for the subsequent design optimization algorithm are provided. The vehicle has perfect navigation, communication and perception capabilities, as well as safe self-rescue capabilities in emergency and dangerous situations, and can reliably carry out path search and target detection missions in a harsh marine environment.

Due to the excitation of sea environment such as waves, wind and current, complex motions can occurs on floating platform such as vessels, offshore rigs and so on, which will affect seriously the performance of operation on the platform. The motion compensation platform can effectively reduce effects. In this paper, a novel motion compensation platform based on 3SPS-RPS-PS parallel mechanism is designed for marine ship with a dynamic positioning system. It can compensate motion in heave, pitch and roll dimensions induced by wave. The structure and working principle of the device are introduced. After that, the working performance of the device is analyzed, mainly including the establishment of the mathematical model of the device, and then the kinematics and compensation space of the device are analyzed. Numerical simulation suggests that the mechanism can implement the function of motion compensation. The motion compensation experiment of 3SPS-RPS-PS mechanism is carried out. Experimental results show that the motion in 3 degrees-of-freedom (DOF) such as heave, roll and pitch of the motion simulation platform can be compensated effectively, and the compensation accuracy can reach 85%. The factors that affect the accuracy of compensation are also analyzed based on experiment test.

High power density is a development trend in legged robots. However, the huge weight and size of the hydraulic power unit is a major obstacle to improving the performance of robots, and heat dissipation is also an important issue for the power unit. As the core power component of the legged robot, the integration of the motor pump unit can reduce the volume and weight. This paper designs a coaxial motor pump unit with embedded cooling channels, which has the performance advantages of small envelope size, light weight, and high efficiency. Aiming at the heat dissipation problem of the motor pump, a spiral cooling flow channel is designed in the motor pump housing, and the temperature field inside the housing is simulated to verify that the oil cooling flow channel can realize the heat dissipation function.

In order to improve the terrain adaptability and enrich the locomotion modes of the mobile platform with single-DoF leg, a multi-mode wheel-leg mechanism is proposed, and wheel mode and leg mode correspond to two motion branches of the spatial reconfigurable mechanism, respectively. The obstacle-climbing expectation of leg mode is obtained by theoretical calculations, and a series of dynamic simulations are conducted and analyzed to test the cruising ability, flexibility and climbing ability of the platform. This study provides a new reference for multi-mode wheel-leg platform development.

A fully compliant bistable mechanism is capable of steadily staying at two distinct positions without power input. The maximum stress in forward and backward directions is a critical parameter influencing the life of the bistable mechanism, and the out-of-plane deflections can significantly influence the kinetostatic behavior. In this paper, we propose a bistable mechanism based on the circular beam. The circular beam has a better stress distribution compared to the traditional straight beam, therefore, it can reduce the maximum stress during the stress transition of the mechanism, and improve the life of the mechanism. Meanwhile, the out-of-plane bending resistance of circular beams will be improved, when the presence of off-axis or eccentric loads in the bistable mechanism. Through the finite element simulation analysis results, it is concluded that the maximum stress of the compliant circular beam bistable mechanism is reduced 39.3%, the compliant circular beam bistable mechanism resistance to out-of-plane deformation increased by 16%.

Compliant motion reverser plays a significant role in the field of micro-electromechanical systems, micro-measurement, and biological engineering. Traditional motion reverser is designed based on topology optimization, which is complicated and time-consuming. This paper presents a new compliant monolithic motion reverser by resorting to the rigid-body replacement method to realize the inversion of displacement and force. The rhombic four-bar linkage is replaced with double-layer leaf-shaped compliant hinges, and the structure layout has been designed to reduce the stiffness of the whole mechanism. Then, the geometric advantage, mechanical advantage, and natural frequency of the motion reverser have been derived based on pseudo-rigid-body model. To validate the performance of the designed motion reverser, finite element analysis simulation has been conducted with ANSYS software. The simulation results show that the developed mechanism has a good working performance with a geometric advantage of − 0.9904, a mechanical advantage of − 0.9903, and a natural frequency of 377.05 Hz. The proposed motion reverser is promising to act as the inverter of displacement and force in micromanipulation.

To meet the increasing requirements for high-performance machine tools in manufacturing industry, a 5-axis hybrid kinematic machining unit (HKMU) is proposed with a topology of 2UPR&1RPS&1RPU-XY. Firstly, the inverse/forward position of the HKMU is analyzed by using the closed-loop vector method. Secondly, based on the position analysis, a 3-axis and a 5-axis reachable workspace are defined to demonstrate the motion capabilities of the proposed HKMU. And a ‘hierarchical’ searching algorithm is proposed to calculate the above two types of reachable workspace. Finally, the relationship between dimensional parameters and reachable workspace is graphically revealed by using an illustrative example of the proposed HKMU.

A new quasi-zero stiffness isolator based on the motion singularity characteristics of parallel mechanism in the passage is proposed, which can solve the problems of poor low-frequency vibration isolation performance and small vibration isolation bandwidth of linear passive vibration isolation technology. The planar horizontal 2-RRR parallel mechanism and the vertical single-degree of freedom mobile mechanism in parallel to construct a P/2(2-RRR)RR parallel vibration isolation mechanism. The quasi-zero stiffness characteristics of the system are constructed by the superposition of the following two characteristics that the planar 2-RRR parallel mechanism can output the negative stiffness near the motion singular point and the positive stiffness generated by the spring in the vertical direction. Firstly, the nonlinear force–displacement model of planar 2-RRR parallel mechanism is established, and the stiffness characteristics of P/2(2-RRR)RR parallel vibration isolation mechanism are analyzed. Then the dynamic model of P/2(2-RRR)RR parallel vibration isolation mechanism is established, and the influence of excitation force amplitude and system damping on the vibration isolation performance of the system is analyzed by harmonic balance method. The results show that the P/2(2-RRR)RR parallel vibration isolation mechanism has lower resonance peak and wider vibration isolation bandwidth than the traditional linear vibration isolation system when the amplitude of vibration excitation force is small and the damping ratio is appropriate.

The fault-tolerant control is regarded as the main method to improve the reliability of the parallel robot, which has the important value. For the 3-PRS parallel robot, the redundant design procedures are provided by using the redundant design method of the parallel mechanism. The redundant kinematic chain is designed according to the structure characteristics and then the 3-PR(P)S redundant parallel robot is obtained. The degrees of freedom (DOF) of the overall robot and the moving platform relative to the fixed platform are analyzed and calculated by making use of Screw Theory and the modified Kutzbach-Grubler formula. A fault-tolerant control strategy is proposed based on the position control model. The motion equations of the control input parameters are deduced under the master control and the master–slave control. The terminal trajectory is set and simulated through MATLAB. The results further show that the designed parallel redundant structure is reasonable and the fault-tolerant control of the 3-PRS parallel robot can be realized. So the method is effective and the expected trajectories of the motion are accomplished.

Bionic flapping-wing flying robot can fly by imitating the flight action of birds in nature and generating lift force through regular flapping of wings. Compared with traditional fixed-wing aircrafts and rotorcrafts, bionic flapping-wing flying robots have the advantages of flexibility, lightness and good camouflage, and have an important significance in natural environment observation, war reconnaissance and other fields. Therefore, this paper presents a new bionic flying robot based on two-stage wing. Firstly, the bionic principle of the flying robots was introduced in detail. Secondly, the mechanism of a bionic flying robot was designed based on the two-stage flapping wing, including the flapping component, fuselage component, and tail wing component. Meanwhile, the model of the flying robot’s mechanism was established using SolidWorks. Finally, kinematic analysis of the flapping mechanism was carried out to verify the feasibility of the design by simulation. The results show that the presented flying robot has the advantages of more flexibility, lightness and heavy load. Hence, it could be used for natural environment observation, aerial photography and other occasions.

Aiming at the problem that traditional rehabilitation equipment cannot provide immersive training mode, resulting in low training effect, a multi-joint lower limb rehabilitation robot is designed that uses virtual reality technology to improve the perception strength of the nervous system. The robot can realize the continuous posture adjustment function of the patient’s supine position-standing position, and can realize the unilateral/bilateral active training of the affected limb at the same time. The structure design scheme of the robot is introduced in detail, the kinematics and dynamics are analyzed, and the correctness of the theoretical analysis is verified by simulation experiments. By analyzing the rehabilitation needs, a virtual reality immersion training program and active training control strategy were designed, and the training process of the patients was tracked and evaluated. Finally, the safety, feasibility and stability of the control system of the robot design are verified through the prototype platform, and the human–machine synergy and training effect of the virtual reality training mode are also tested.

Aiming at the on-orbit assembly task requirements of large space structures, a space cable-driven parallel mechanism (CDPM) is proposed, and its available wrench set (AWS) and workspace are studied. By mapping the tension space (TS) to the wrench space, the AWS of the CDPM is obtained, and the influence of the moving platform position and cable tension on the AWS is analyzed. Then, based on the hyperplane shifting method, a algorithm for solving the feasible wrench workspace (FWWS) of CDPM is established. Considering the complex assembly reaction force on the moving platform in the assembly process and the acceleration requirements during the movement process, the FWWS in the assembly process and dynamic feasible workspace (DFWS) are solved respectively. Finally, for the on-orbit assembly task of the CDPM, the feasible workspace (FWS) is proposed and calculated. The FWS can meet the requirements of the assembly reaction force in the assembly process and the acceleration requirements in the movement process at the same time, and has strong application value, which plays a guiding role for the design of the CDPM.

As space antenna tends to be large-scale, deployable antenna is more and more widely used. As a key part of antenna structure, the antenna profile will be deformed due to uneven heating during on-orbit operation, which affects the service performance of the antenna. In this paper, the thermal effect mode of space environment on the on-orbit antenna is analyzed firstly, and the differential heat conduction equation is obtained by taking the profile as research object. Then, thermal simulation of the ring truss-type deployable antenna in the sun-synchronous orbit is carried out by using the NX-TMG software. The temperature characteristics of the antenna profile and the influence law of material parameters on the profile temperature during on-orbit operation are analyzed. It is concluded that temperature of antenna profile changes in one orbital period. The selection of low absorption rate and high density materials can reduce the profile temperature difference, which provides the reference for ring truss-type deployable antenna design.

Elastodynamic model of parallel mechanism is important to elastodynamic optimization. Long prismatic pairs composed of tube structure are very common in the parallel mechanism. This work uses the kinematic pair equivalent method to simulate the surface contact of outer and inner tubes. Corresponding mass and stiffness matrix are derived through the strain energy minimization method with matrix structural analysis. The reconfigurable legged lunar lander has been used as an example to verify the effectiveness of the method. Equivalent static loads and desirability approach are introduced and modified to optimize the elastodynamics of parallel mechanism. The optimization is implemented on the lander and the result shows a good reduction in mass and an increase in natural frequency.

In dealing with the shortage of traditional fossil energy, climate change and environmental pollution, wave energy has great potential. A wave energy converter is a device that converts wave energy into electrical energy. In this paper, the motion equation of a fully enclosed inertial mass wave energy converter is deduced, and a dynamic model of the fully enclosed inertial mass wave energy converter is established. Then, the average power of the wave energy converter at different frequencies is analyzed. Finally, the system mechanical parameters of the fully enclosed inertial mass wave energy converter are optimized based on the Moth-flame algorithm.

In view of the limited configuration of spacecraft docking posture adjustment equipment, a ground closed six degree of freedom (6-DOF) parallel attitude adjustment configuration library is constructed. Firstly, the single branch chain configurations with six degrees of freedom are enumerated, which are screened based on local degrees of freedom and mechanical property constraints, and the single branch chain pedigree is constructed. Secondly, the configuration synthesis is carried out by using GF set, the topology optimization and load carrying performance of the chain are analyzed, and the isomorphism identification of the configuration is completed by graph theory. Finally, the configuration library of the parallel posture adjustment platform is constructed. Taking 4-PPPS (P: prismatic pair, S: spherical joint) mechanism as an example, the configuration equivalence and performance evaluation are carried out. The results show that the mechanism has unique position inverse solution, large workspace and no singular configuration. The configuration library of parallel posture adjustment platform provides the basis and idea of configuration design for the design of docking posture adjustment equipment, and has guiding significance for the engineering design of posture adjustment equipment.

Joint bearing can make spherical motion in a certain angle range because the contact surface is spherical in shape. And the clearance of the joint bearing is necessary for the bearing to realize oscillation, tilting and rotating motion. In order to determine the best original clearance of the joint bearing, simulation analysis of the joint bearing under different original clearances is carried out based on the theoretical calculation analysis of the mating clearance. The analysis results show that when the clearance between the inner and outer rings increases, the maximum contact stress between the inner and outer rings of the bearing increases. Under the premise of satisfying the original clearance, mating clearance and working clearance of this spherical bearing, the clearance value of this model of spherical bearing is selected as the smaller clearance in the clearance range.

Based on the analysis of existing ankle rehabilitation devices, a new ankle rehabilitation mechanism based on 3-UPU parallel mechanism is proposed in this paper. The mechanism has three degrees of freedom, and can achieve ankle pronation/supination, inversion/eversion, and stretch movement. The rotation axis of the mechanism can be adjusted according to the ankle height and the position of the movement axis of the human body. In this paper, the inverse kinematics and DOF of the mechanism are solved. According to the ankle rehabilitative requirements, the size of the mechanism is determined, and the workspace of the mechanism is further solved. Finally, the kinematics of the mechanism is simulated and verified by the prototype. Therefore, the rotation axis of the mechanism can match with the motion axis of the human ankle joint better and bring better rehabilitation effects to the patients.

Large-area space deployable antennas require very high folding efficiency. Since plane-symmetric Bricard linkage has a large folding efficiency, its networking becomes a potential scheme to meet the demand. However, complex geometry makes networking a very difficult problem. This paper studied the closure equations of plane-symmetric Bricard linkage from the perspective of biquadratic curve and proved several propositions that can be applied to networking. The basic motivation is that the compatible conditions between linkages are equivalent to their biquadratic curves having a common branche under Mobius transformation. Using the propositions proved in this paper, a kinematically compatible network of plane-symmetric Bricard linkages was constructed, and the motion simulation was carried out with a CAD model. Results shown that the theories proposed in this paper are correct, having a reference significance for the invention of new deployable mechanisms.

Large-area flexible roll-out solar array system has huge application potential in space structure especially for the Space Solar Power System (SSPS) due to the advantages of the lightweight, high area to mass ratio, excellent folding and deployable capabilities. For SSPS to operate economically, solar array system must operate at power levels greater than MW, while the commercial SSPS should operate at power levels no less than GW. Therefore, advanced flexible solar array systems with areas up to 104 m2 and 107 m2 are essential. In this study, a modular large-area flexible roll-out solar array system with several subarrays is proposed, in which Composite lenticular boom is used as the load-carrying structure, and inflation constrained with Velcros is designed as the drive mechanism. The single array can be expanded to more than 1000 m2, while the specific power is expected to reach more than 500 W/kg. In this paper, structural dynamics, inflation deployment dynamics and on-orbit thermal performances of the subarray are analyzed, the result show that the proposed solar array system is reasonable and feasible for SSPS application.

The cascade thrust reverse device is widely used in the civil aircraft. In order to realize the two-stage motion of blocker door, a small pull rod is added between large pull rod and blocker door, which results in a two degree of freedom under-actuated mechanism. Based on the cascade thrust reverse device, this paper studies the effect of joint clearance on the dynamic response of under-actuated cascade thrust reverse mechanism. The results show that the increase of clearance value and driving speed brings larger reaction force and vibration, while the increase of aerodynamic load on blocker door can effectively weaken the vibration fluctuation, therefore, increase the stability of block door movement.

The Eight-degree-of-freedom (8-DOF) serial redundant manipulators are considered more suitable for performing special tasks in unstructured environments due to their higher flexibility and larger workspace. The 8-DOF tunnel shotcrete manipulator is a kind of construction machinery that is applied to the concrete spraying support in the process of tunnel excavation. Since the mechanism itself is a redundant manipulator with link offset, it is difficult to solve its inverse kinematics. Aiming at the problems that the traditional inverse kinematics solution of a redundant manipulator is difficult to solve analytically and the numerical algorithm needs multiple iterations and error accumulation, a combinational optimization inverse kinematics algorithm based on the weighted least-norm (WLN) method and joint angle parameterization (JAP) method is proposed to overcome these defects. Firstly, a set of optimized joint angle approximation solutions is obtained based on the WLN method of joint angle limit avoidance optimization function. Secondly, the two joint variable parameters in the set of approximate solutions are taken as known parameters, and the analytical expression of the remaining joint angle is derived by using the algebraic equation of the homogeneous transformation matrix based on the JAP method. Finally, Numerical simulation results show that the algorithm has the advantages of avoiding joint angle limits, high computational accuracy, and no cumulative error.

In order to solve the problems of insufficient motion accuracy and stalling of the variable stator vanes adjustment mechanism in the compressor, a three-dimensional modeling of the variable stator vanes adjustment mechanism test bench is carried out, and a multi-body kinematic dynamics simulation analysis considering nonlinear factors is performed. A physical experiment system is built based on the model and the simulation results are compared and verified. The results show that the kinematic simulation of the variable stator vanes adjustment mechanism is reasonable and the simulation results are more suitable for the experimental results when considering friction. As the clearance increases, the vane hysteresis time t and the maximum rotation deviation Δ increase. The clearance at the head of the motor and the 0-stage crank has a greater effect on the hysteresis time. The joint bearing clearance at the end of the motor and at the 0-stage crank produces a larger maximum rotation deviation Δ. The simulation results provide useful references for subsequent studies.

Several approaches, such as the pseudo-rigid-body model and beam constraint model, are available for nonlinear analysis of moderately large-deformation compliant mechanisms, but most focus on the kinetostatic issue. Although these methods have also been combined with Lagrange’s equation for dynamic modeling, some key characteristics like the amplitude-dependent resonance frequencies were ignored. Complementary to previous works, the current study introduces a dynamic beam constraint model (DBCM) on the frequency domain for nonlinear analyses of both the kinetostatics and dynamics of beam flexures in compliant mechanisms with moderately large strokes. Particularly, the DBCM enables the existing BCM to insightfully formulate the nonlinear dynamics of beam flexures in a pseudo-static and closed-form manner. Based on the DBCM, some nonlinear dynamic behaviors are found. Interestingly, the presented DBCM can be directly degenerated into the traditional BCM by letting the dynamic frequency to be zero.

Aiming at the development needs of large-scale, modular and on-orbit assembly of satellite antenna, a hexagonal prism modular truss deployable antenna structure with strong topology and good adaptability is proposed. The structure composition and deployment principle of the antenna are expounded. In order to improve the stiffness of the configuration antenna, two types of tension cable configurations are proposed based on the structural characteristics of the hexagonal prism module. Firstly, the static analysis model of the antenna deployment state is established based on the node method, and the mechanical influence relationship between the tension cable and the antenna beams is established, and the value range of pretightening force of the tension cable is derived. Secondly, based on the coordinates of the key nodes of the antenna structure, the dynamic analysis model of the three-layer 19-module antenna support structure is established. Finally, by comparing and analyzing the dynamic characteristics of no cable, cross tension cable and parallel tension cable, the influence of tension cable configuration on antenna stiffness is verified. The analysis results show that the overall stiffness of the antenna support structure can be increased by more than 2.6 times by the two tension cable configurations, and the parallel tension cable is more indigenous to the increase of the antenna stiffness.

The structural design of constrained joints is an effective way to realize the type synthesis of constrained metamorphic mechanism. In previous studies, constrained joints are often represented in the form of kinematic diagrams of mechanism, which doesn’t provide enough reference to the practical application of metamorphic mechanisms. On the basis of summarizing the constraint forms and resistance characteristics of the commonly used variable-constraint constrained joints, and according to the force analysis of the augmented Assur group with constrained joints, a new constrained revolute joint with combined variable-constraint of spring force and geometric constraint is designed, which has advantages such as simple structure, reliable working ability and passive adaptive capability to operational conditions. Based on this constrained joint, a two-configuration constrained metamorphic mechanism with under-actuated is designed, the force analysis of the mechanism is completed, and the effectiveness and feasibility of design approach proposed in this paper is verified for the constraint parameters of the invented metamorphic joint. The novel combinatorial variable-stiffness constrained joint can obtain stable and reliable configuration switching ability, which provides a feasible way for promoting the engineering application of metamorphic mechanism.

3-RPS parallel mechanisms have an extensive effect on many industries such as the chemical industry, iatrology, and aviation. Its dynamic model is a multi-parameter coupled and highly nonlinear complex system that is difficult to obtain a closed-form expression, and this problem has not been solved completely at present. In this paper, a novel Udwadia-Kalaba (U-K) modeling method for the 3-RPS parallel mechanism (PM) is proposed. Such an approach abstracts the physical connection into system constraints. Based on this, the constraint force generated by the constraints is obtained. As a result, the dynamic equations, which are in analytical form, can be obtained. In the dynamic modeling process, our method does not require auxiliary variables which is the most brilliant advantage. Furthermore, the results of the numerical simulation and verification obtained via Adams and Matlab have shown that our dynamic modeling method could solve the dynamic analytical decoupling equation of the 3-RPS PM efficiently, systematically, and quickly.

The 3-R(SRS)RP multi-loop Mechanism is regarded as one module of a multi-stage manipulator for space manipulation operations, such as capturing free-flying objects. The mechanism has two rotational and one translational degrees of freedom, as well as includes coupled kinematic chains, which can be constructed to the modular system for space operation. The dynamics analysis of the mechanism is the basis of its structural design and actuation control. In this paper, the twist shaping matrix between the twists of links and the input rate array is derived by decoupling the mechanism and motion analysis. Based on the Newton–Euler equation, the dynamics model of the mechanism is established. the theoretical values of actuation power consumption on the certain motion modes is calculated via programming, then being compared with the simulation values obtained through ADAMS model. The results are basically consistent, which verifies the correctness of the dynamics analysis of the mechanical system.

A seamless deformation structure that changes the curvature of the main airfoil has a positive effect on improving the aerodynamic performance of long-range aircraft and reducing noise. Aiming at the problems of obvious wrinkles and heavy weight of rigid mechanism driven skin, this paper describes a compliant mechanisms-based leading-edge of morphing wing with a seamless deformation structure. In order to avoid the wrinkling of the wing skin, the driving points and the driving forces on the deformed skin were designed. In addition, the leading-edge flexible rib designed by the topology optimization method of flexible mechanism can make the wing leading-edge deflect downward by 17°. Finally, a set of experimental prototypes and experimental platforms were manufactured for the wing load-bearing deformation experiment. Experiment shown that the aerodynamic performance of the variable camber morphing wing was improved and can resist aerodynamic loads well.

Based on the pseudo-rigid body model theory, the bistable characteristics and driving performance research of four-link compliant mechanism with one and two flexible joints are carried out using the energy method. Firstly, according to the modified pseudo-rigid body model, the kinematics and potential energy of a general four-link compliant mechanism are analyzed. Secondly, the bistable characteristics of the four-link compliant mechanism with one flexible joint are deduced, and the conditions for the existence of bistable characteristics of the four-link compliant mechanism with one flexible joint are proposed. Then, the bistable characteristics of the four-link compliant mechanism with two flexible joints are analyzed, and it is found that the bistable characteristics of the four-link compliant mechanism with two flexible joints are closely related to the selection of the driving links of the mechanism, the geometric parameters of the mechanism and the initial motion position of the mechanism. Finally, taking the four-link compliant bistable switch as an example, the relationship between the driving performance of the mechanism and the initial motion position of the mechanism and the parameters of the flexible joint is explored.

Joint clearance, which is always being viewed as a negative factor in most machine operations and hoped to be eliminated in previous studies, can be used to release some constraints in mechanisms, especially in overconstrained linkages. It is expected to prevent the movement of the developable structure constructed with overconstrained linkages from being stuck due to the deformation of the components. In this paper, we propose a general comprehensive model of 3D clearance for revolute joints (R-joints) and focus on the kinematic performance. From a kinematical perspective, contact modes of journal and bearing are divided into four cases by treating the point (or line, surface) contact as a single-point contact. Then, the relative motion of journal and bearing is analysed and derived by D-H method. Using the model, we present a method to study the kinematic characteristics of overconstrained mechanisms with joint clearances. The correctness of the proposed method is verified by the comparison with a numerical case.

A semi-active vibration reduction method using internal resonance is proposed to decrease the nonlinear vibration of a flexible antenna with large flexibility. The dynamic model of a large space antenna with an absorber is established by the Kane method. The approximate analytical solutions of the system's nonlinear vibration equation are studied using the multi-scale method. The damping as well as frequency of vibration absorber are controlled by the PD feedback control method. By adjusting parameters of the vibration absorber, an energy channel between the fourth-order vibration mode of the large space antenna and the vibration mode of the vibration absorber is established, and a 2:1 internal resonance is formed between these two mode. The numerical simulation verifies the existence of energy interaction and the effectiveness of the vibration absorber.

With the potential advantages of slender structures and vast degrees of freedom, redundant manipulators have attracted the attention of numerous researchers. However, existing redundant manipulators normally depend their dexterity on a large number of motors. In this paper, the size of the drive system of the redundant manipulator has the potential of miniaturization with the participation of variable stiffness mechanisms and the matched driving strategy. By activating the variable stiffness mechanisms on different elements, any element on the manipulator can be directly controlled with a few motors. The matched driving strategy is described in detail while the kinematic and static analyses of the cable-driven redundant manipulator is carried out. As verification, a prototype of a planar redundant manipulator is constructed, which equips variable stiffness mechanisms utilizing the principle of force amplification near the dead point position of the crank slider mechanism. This work provides a novel potential approach to miniaturize redundant manipulators.

This paper investigated the movement of a close chain five-bow-shaped-bar linkage when tracking an acceleration profile. The mechanism is constrained to remain vertically upright and accomplish rolling motion through adjusting its own shape. The objective is to design trajectories of driving joint angles that enable the mechanism to track an acceleration profile. Firstly, the symmetrical structure of close chain five-bow-shaped-bar linkage was designed which’s mechanical centroid and geometrical center are in the same position when the mechanism has a circular outline. Secondly, the relationship between the mechanical centroid and driving joint angles is obtained by building a rolling kinematics. Then, the trajectories of driving angles through both strategies of constant potential energy and variable potential energy were figured out. On this basis, an available approach to tracking an acceleration profile is figured out and some simulation results are provided.

Larger deformation and higher bearing capacity is a worthwhile goal for designing the compliant mechanism. By virtue of the anisotropy, variable stiffness and superior designability, fiber reinforced composite material is effective way to solve the contradictory problem. There are several reports to design compliant mechanism with composites and improve its performances. But adding directly stress constraints in topology optimization process is very complex and difficult to establish the explicit expression of stress constraints for compliant mechanism with composites. This paper investigated the topology optimization and performance prediction of compliant mechanism with composites by neural network. Topology configurations, output displacements and maximal stress in matrix materials of compliant mechanism under different fiber laying angles were firstly implemented. Subsequently, neutral network models were built to predict the output displacement and maximal stress. Examples of compliant inverter and gripper were used to verify the proposed method.

Tetrahedral mechanisms are mechanisms whose architectures constructed based on tetrahedron. Take the vertex as a ternary link, and the edge as a binary link respectively, the generalized mechanism is built. To describe the tetrahedral generalized mechanism, the topological graph is drawn and is expressed by configuration matrix. Possible types of tetrahedral mechanisms are listed using enumeration method. After setting axes of P and S pairs, the effective tetrahedral mechanisms results are obtained by G–K criterion.

Reconfigurable structures are considered promising candidates for high-adaptability and multi-functionality due to their variable topology and have thus gained thriving progress in recent years. To date, most studies on reconfigurable linkages focus on innovative design and reconfiguration mechanism of a single unit, yet the possibility of forming larger structures is rarely investigated. In this paper, we develop a multi-loop origami pattern with flat foldability and rigid foldability formed by four 4-crease vertices, which can be utilized as a platform for constructing reconfigurable 6R linkages. Through the analysis of kinematic compatibility of equivalent networks of spherical linkages, three types of reconfigurable 6R linkages are obtained with the kirigami technique, including a double spherical linkage, a planar-spherical linkage, and a parallel 6R linkage. The explicit closure equations and bifurcation behaviors of obtained parallel 6R linkage have been derived. Connecting the linkage under bifurcation paths, the tessellation of this parallel 6R linkage forms a series of structures with complex shapes with one DOF, e.g., arch shapes, “m” shape, and closed-loop tube, whose reconfigurability is achieved simply by switching some mountain and valley creases. This work provides a promising perspective for constructing reconfigurable 6R linkages from origami and kirigami, which can be applied in deployable structures, architectures, homogeneous or heterogeneous metamaterials.

The planetary rovers are important devices in nowadays planetary exploration missions. However, the uneven and soft terrain on Lunar and Martin surfaces is challenging to the rovers and leads to hazards in extreme situations. This paper proposes an index of Actuation Margin. It can indicate a wheel’s residual ability of generate traction which is influenced by both terrain physical features and normal load situation. Based on such an index, a traction control method is proposed for planetary rovers. By the allocation of wheel force conditions, the excessive slippage is avoided and the maximum traction ability is increased. Therefore, the proposed method realizes the adaptation of terrain physical features and improves the rover mobility in extreme terrain which is uneven and soft. The proposed control algorithm is applied to a rover prototype and validated experimentally.

Single degree-of-freedom (DOF) mechanisms have been widely used as motion executers for their compact structure and simple control. However, a single-DOF mechanism can only lead through one specific motion trajectory. Thus, they usually cannot handle multiple tasks well, i.e., realizing a good fit of multiple trajectories. In order to solve such problems, this paper proposes an approach to design multi-mode single-DOF six bar mechanisms, which could individually realize multiple task trajectories using only one driving input via an optimized structure with a selected adjustable parameter (A-Parameter). First, a source mechanism for multi-mode watt-I six bar linkage is designed with 9 candidate adjustable parameters (link lengths, location of pivots, etc.), which enables the same mechanism to fit multiple trajectories by selecting only one parameter to be adjustable. Next, to select the optimal A-Parameter, a multi-objective optimization algorithm NSGA-II + ARSBX is used to demonstrate and analyze the Pareto front optimization under different A-Parameters. Then, we use an example of three different human gait trajectories to show how the synthesis multi-mode single-DOF six bar mechanism is conducted with our approach. In the end, the comparison of task trajectories and the resulting trajectories are presented, which show that the method proposed in this paper is feasible.

Kinematic calibration is an effective way to improve the kinematic accuracy of hybrid machine tools. Conventional calibration methods require position and attitude measurements for each measurement pose, and the measurement process, especially the attitude measurement, is extremely complicated. In this paper, a calibration method that only requires position measurement and alignment is proposed. Measurement process can be done using only three dial indicators. Based on this measurement method, a constrained least squares identification method based on the regularization solution is proposed to solve the ill-posed problem. The proposed calibration method is verified by simulation and experiment. The proposed method can complete the calibration with a small measurement cost, which greatly improves the calibration efficiency.

The hybrid machine tool based on parallel spindle heads can efficiently process complex parts, but the load of the feed axes of the spindle head has the characteristics of nonlinear and coupling, which brings difficulties to the control. In this paper, the contour error of the tool center point (TCP) is greatly reduced by the method of dynamic modeling and feedforward. Specifically, the kinematic modeling is performed using the vector loop method, the dynamic modeling is performed using the virtual work principle, and the frictional force modeling is performed using the Stribeck model to obtain the dynamic model of the spindle head. The servo system of the feed axis is modeled and then the torque feedforward module is designed. Finally, in MATLAB/Simulink simulation, torque feedforward effectively reduces the contour error of TCP. Based on the analysis of the simulation results, the load torque of the parallel spindle head has the characteristics of nonlinearity and coupling. The evaluation index LCE (load caused error) is proposed, and the load torque mainly causes errors during acceleration, deceleration and commutation.

For topology optimization in additive manufacturing, the support structures have a significant impact on production cost and can be minimized by choosing the optimal print orientation, where model voxelization plays an important role on the computing accuracy and efficiency. To overcome the inherent insufficiency of the cube voxelization, we propose a new voxelization modeling method based on the Delaunay Triangulation to match arbitrary shapes with fewer voxels at arbitrary angle, and speed up the computing efficiency by the gradient descent method for the optimal voxelization. Our method can be widely used in the future for accurate modeling and result optimization in the case of solving the optimal orientation.

The winding origami structure allows the panels to be wrapping folded to achieve a very large deployable ratio. However, the existing winding origami patterns are non-rigidly foldable or multi-degree-of-freedom rigidly foldable. In this paper, a new single-degree-of-freedom rigidly foldable winding origami pattern is designed based on a non-rigidly foldable winding origami pattern. The new pattern is obtained by removing the creases in the area of concentrated panel deformation under non-rigidly folding and then converting the generated virtual creases into actual creases. The panel deformation and folding energy are reduced through the crease transformation. The kinematic analysis by the truss transformation method proves its rigidly foldable characteristics with one degree of freedom. Therefore, this pattern design has an application prospect in aerospace engineering and emergency equipment. In addition, it provides an idea for the transition from non-rigid structures to rigid ones which also has universal significance.

Compliant constant-force mechanisms (CCFMs) are widely used in overload protection, surgical manipulation and polishing/deburring to provide a near constant-force output over a range of displacement. This work proposes a novel CCFM that comprises a diaphragm mechanism and a bistable mechanism using the building block method. The diaphragm mechanism and bistable mechanism are employed to provide the positive and negative stiffness over the range of the displacement, respectively. The positive and negative stiffness modules are connected in parallel so that to output a constant-force in a large range of displacement with less variation. The chained spatial beam constraint model (CSBCM) is developed to model the spatial deflection of the initially curved beams in the diaphragm mechanism and the chained beam constraint model (CBCM) is used to derive the load–displacement relation and stress properties of the bistable mechanism. To eliminate the force variation, the realized optimization of the geometric parameters, and the optimal geometric parameters are employed to form the CCFM to output a constant-force in a large range of displacement with very small variation.

This paper proposes a geometric modeling and algebraic solution method for the displacement analysis of the three seven-link Baranov trusses based on conformal geometric algebra (CGA). Under the frame of CGA, a coordinate-free formulation for the basic four-link kinematic chain is derived in terms with the area sign of the triangle and CGA operation. Then, based on the aforementioned formulation and the distance relationship, two constraint equations for the displacement analysis problem are formulated. Finally, a high-degree univariate equation is derived by one-step resultant elimination. The contribution of the paper is that the derivation of two constraint equations is free of coordinate and the elimination procedure is greatly simplified to only one-step due to the reduction of the number of equations using CGA. At last, numerical examples are given to confirm the correctness of the method. The proposed method offers a new sight for solving the displacement analysis problem of other Baranov trusses.

With the continuous development of aerospace industry in recent years, space manipulator has attracted much attention because of its excellent performance in aerospace operation. In this work, the topology of space manipulator is obtained through configuration evolution based on the Canadarm2 serving in the international space station. By analyzing the configuration characteristics, a new topological configuration of space manipulator is further optimized, then the structural design and prototype construction are completed. The kinematic model of space manipulator is established by D-H method. By comparing the theoretical calculation results with simulation data obtained from SolidWorks and MATLAB, the effectiveness of the established kinematic model is verified. Based on the kinematic model, the workspace analysis of the new space manipulator is completed by Monte Carlo method.

To meet the requirements of lightweight structure and effective space utilization in vehicle side door latch, the structural synthesis of novel spatial over-constraint mechanism is proposed based on position and orientation characteristics. The mechanism decoupling feature synthesis of mechanism is carried out based on topology and dimension constraint types, and two clusters of mutually perpendicular rotating pairs are constructed in single loop mechanism. The dimension characteristics of spatial decoupling over-constrained mechanism are optimized, and a compliant pair composed of groove and compliant joint with torsion spring is added to construct a single loop compliant spatial mechanism RRUPRR with multi-mode motion. To meet the requirements of electric cinch function, a novel electric cinch mechanism with avoidance function is proposed. The compliant single loop variable mode power release mechanism and the novel electric cinch mechanism are embedded into the door latch, with different driving modes and limit stoppers, the mechanism realizes a variety of motion modes. The dynamic simulation results shows that the gear crank rotates only a small angle of 0.042° in the manual release condition, which verifies the motion compatibility between the power release branch and the manual release branch. And through the simulation to explore the torque change of the cinch motor and the sweeping track of the push rod in the process of electric cinch, it is verified that the integrated cinch mechanism can reduce the contact force of the ratchet and pawl in the process of the door latch from the half lock to the full lock position, and improve the working life of the ratchet and pawl mechanism.

Cable-driven parallel mechanisms, also known as cable-suspended parallel mechanisms attract lots of attention in recent years. Intensive studies on three-degree-of-freedom planar cable-driven parallel mechanism and six-degree-of-freedom spatial cable-driven parallel mechanism have been carried out. The above-mentioned two kinds of mechanisms have full degrees of freedom respectively in planar and spatial manner. It is noted that few research has been conducted on lower-mobility cable-driven parallel mechanisms. This paper presents a new cable-driven parallel mechanism having four degrees of freedom which contain one translational motion and three rotational motions. The mobility of the proposed mechanism is analyzed by instantaneous screw-based method. Meanwhile, a finite displacement screw-based method is also employed for mobility analysis of this lower mobility cable-driven parallel mechanism.

This paper presents a new redundantly actuated parallel mechanism with a configurable platform for haptic use. The novelty of the proposed redundant mechanism is that the two rotations around the X- and Y-axis are compounded of the rotational movements of two rods in the configurable platform, instead of the conventional methods in which the rotational motions are produced by the relative translations between two sub-platforms. The rotational feature of the proposed mechanism is explored. Subsequently, a multi-objective optimization is carried out to obtain a compact geometry with sound kinematic performance and no interference. Two different objective functions are taken into account: the overall height and width of the redundant mechanism. The constraints of interference and kinematic performance are analyzed and established. The optimization results reveal that the proposed mechanism can rotate continuously about the X- and Y-axis up to large angles, and is suitable for haptic application.

In this paper, based on the non-smooth dynamics method, a dynamic modeling method for spatial multi-body systems with spherical clearance joints is proposed in the framework of Lie group. A Lie group time stepping algorithm is presented by extending the Moreau’s time-stepping algorithm to three-dimensional special Euclidean group. The differential measures of velocity and impulse are introduced to describe impact-free dynamics and impact dynamics in a unified framework at the velocity-impulse level. Based on Newton’s collision law, the constitutive relationship of a spherical joint with clearance is described as a linear complementarity problem (LCP) at the velocity-impulse level, and it is embedded in the Lie group time stepping algorithm to solve it. This method can uniformly describe a large range of rigid body motion and joint clearance motion on SE(3), and no local parameterization of rotational variables (such as Euler angles, quaternions, etc.) is introduced, which has the advantages of avoiding singularity and coordinate invariance. Finally, a space four-bar mechanism with two spherical clearance joints is given as an example to illustrate the feasibility and effectiveness of the modeling and calculating methods proposed in this paper.

This paper investigates the time-varying formation control problem for multi-agent systems and uses algebraic graph theory to abstract topological relationships between agents. Unlike conventional time-varying topologies, we consider a more challenging situation where agents may be destroyed during the maneuvering process. To cope with this problem, firstly we propose the time-varying target formation based on the rigidity graph theory. Then the double-integrator dynamics are addressed and the distributed multi-agent control laws based on the consistency theory and stress matrix are developed during at different stages of formation. Finally, the stability of the system is given and simulation results demonstrate the validity of the proposed formation control algorithm under time-varying topology.

The parallel robot is a multivariable nonlinear and strongly coupled system, which is difficult to apply to controller design. In order to improve the trajectory tracking accuracy and anti-disturbance ability of the parallel robot, a control method based on improved dynamic integral sliding mode is proposed. Firstly, the dynamic model of the parallel robot is decoupled and simplified. Secondly, considering the errors caused by the decoupling and simplification of the dynamic model and the existence of external disturbances in the actual system, a sliding mode controller is introduced to improve both the trajectory tracking accuracy and the robustness of the system. The traditional sliding mode control method, however, will produce large chattering, which may damage the robot. Therefore, by constructing the second-order dynamic sliding mode surface based on the first-order linear sliding mode, the chattering can be suppressed to a great extent, while maintaining the strong robustness of the sliding mode control. Then, a Lyapunov function is constructed for stability analysis, followed by stability analysis of the closed-loop control system. Finally, an experimental platform is built for comparative experiments to verify the effectiveness and practicability of the proposed controller.

This paper presents an approach for optimizing the posture of a friction stir welding robot with a redundant degree of freedom. After a brief introduction of the robotized equipment, an index that evaluates the translational stiffness performance along the tool axis is defined. Then, by maximizing this index, the robot posture optimization is summarized as a single-objective optimization problem in consideration of the robotic dexterity and the position, velocity, and load-carrying capacities of actuated joints. In addition, a discretization search algorithm is proposed for solving this optimization problem. Both computer simulations and experiments are carried out to demonstrate the validity of the proposed approach.

Due to the presence of joint clearance, the end accuracy of the serial robot deteriorates as the number of joints increases. For diverse activities in medical contexts, the robot has different requirements for end position accuracy and operation space. We are intended to trade less operation space for higher local end-point accuracy. Therefore, a kinematic error model that incorporates joint errors via virtual links is established. Then the expression of the auxiliary constraints to serial manipulator’s intermediate joints is discussed. The variation and spatial distribution of the serial manipulator’s errors is investigated under the constraints of various joint points. The simulation results demonstrate that when point constraints are on joints 1, 2, 3, and 4, the mean value of the end position repeatability error is reduced by 41.05%, 67.78%, 92.55%, and 96.25%, respectively, and the repeatability of the end position is improved. The repeatability error of the end position is positively related to its distance from the center. According to the results of physical experiment, the position repeatability error under the constraint of the 2nd and the 3rd joints are decreased by 81.71% and 88.17% respectively, compared to the unconstrained xArm manipulator which confirms the results of the simulated experiments on the trend. Auxiliary point constraints that match the requirements of operating space range and accuracy index, can be designed based on the obtained rules. Thereby, the application range of the serial robot will be extended.

In order to solve the problem that the traditional trajectory planning method does not consider the uniformity of paint film thickness in the spraying process, a trajectory planning method of spray-painting robot based on the thickness uniformity of the paint film is proposed. Firstly, the spray path of the spray gun is designed. By setting buffer areas on both sides, the spray gun can spray the flat parts to be sprayed at a uniform speed; Secondly, according to the designed spraying path, a spraying trajectory planning method based on the uniformity of paint film thickness is proposed. Taking the uniform spraying area as the middle trajectory, the head and tail variable speed buffer area are designed by quintic polynomial to ensure the continuity of velocity and acceleration between segmented trajectories. The correctness and feasibility of the trajectory planning method are verified by simulation; Finally, the robot spraying system is built, and the spraying experiment is carried out based on the trajectory planning algorithm. Spraying experiments show that the proposed method ensures the stability and continuity of the robot spraying process. The actual spraying trajectory is completely consistent with the simulation trajectory, and effectively improves the uniformity of paint film thickness.

For the requirements of multi-modal man–machine interaction between astronauts and robots in lunar surface exploration, research on three interaction modes and test system based on speech, body posture and tactile recognition are carried out. An improved speech feature classification and recognition algorithm based on Mel-scale Frequency Cepstral Coefficients (MFCC), a three-stage body posture recognition algorithm based on target detection—node recognition—skeleton action recognition, and a tactile recognition algorithm based on Radial Basis Function network (RBF) are proposed. In the body posture recognition algorithm, a lightweight CVC-Net model is developed based on the classical HourglassNet algorithm. Deep separable convolution, attention mechanism and improved up-sampling method are introduced. A lightweight network and adaptive graph convolution module for skeleton action recognition are designed by introducing the information of human body joints and skeleton vectors. Above algorithm is suitable for the embedded computing platform and can greatly reduce the number of module parameters while ensuring the detection accuracy. Based on the simulated lunar surface environment, lunar robot and simulated space suit, the ground test verification of three modes of command recognition is realized, which can meet the low power consumption, lightweight and real-time requirements of lunar robot for recognition algorithms and the embedded computing platform.

The traditional assembly process reuse method for a single product is not efficient in the product family due to the similarity between the products in the family. Therefore, an assembly process modelling and reuse method oriented to product family is proposed in this article. The assembly process correlation is quantitatively analysed based on grey correlation analysis and minimum spanning tree algorithm to establish assembly process unit model. Based on the cluster analysis and sequence analysis of the assembly process route, the typical assembly process route model of the product family is established. Compared with the modelling and reuse of the assembly process route based on the structural hierarchical relationship of the product, the proposed modelling and reuse method based on the assembly process correlation considers the assembly process features of the product family, which is helpful to improve the quality and efficiency of assembly process planning.

Compared with electrically driven dual-arm robots, the hydraulic dual-arm manipulator in constrained motion is currently more difficult to accurately track the desired contact force and motion trajectory, because of its highly nonlinear property and parameter uncertainties. In this study, a hybrid motion/force controller in constrained motion is proposed for the hydraulic dual-arm cooperative manipulator. First of all, for the held object, a hybrid motion/force controller is designed to control the contact force with the environment, the object’s motion and the internal force control of the closed-loop chain. An adaptive control method is designed for unknown dynamic parameters of the held object. Then, the virtual decomposition control (VDC) method is established to enable the end-effector of each manipulator to track the desired trajectory accurately, considering the closed-loop kinematic structures and nonlinear valve characteristics of hydraulic manipulators. Compared with impedance control, the simulation results indicate the force and position errors are both reduced by the proposed method under different contact stiffness.

Trajectory scheduling helps improve the input quality of the machining system, thereby meliorating machining quality. By taking a newly developed 5-DOF (degree of freedom) hybrid robot named TriMule as an exemplar, this paper presents an effective trajectory scheduling method for flank milling of the S-shaped test piece. Firstly, a C3 continuous toolpath corner smoothing method is applied to address the five-axis toolpath generated by the CAD/CAM software. Then, based on kinematic and dynamic analysis of the robot, a rapid yet smooth movement of the robot can be achieved through feedrate scheduling. The results of both simulations and experiments on a prototype machine show that the machined S-shaped part meets the ISO standard in terms of surface profile tolerance.

Underwater manipulator plays a huge role in the exploration and obtainment of marine resources. However, the working attitude of underwater manipulator forms different angles with the ocean flow direction, leading to changes in the hydrodynamic performance and flow field characteristics. Therefore, this paper focuses on the flow characteristics of underwater manipular several operating attitudes with different flow directions in the subcritical range. Simulation results show that the position of the section in the flow field is not related to the trend of hydrodynamic coefficients. With the increase of the incoming flow direction angle γ, the lift and drag coefficients increase and the velocity of the flow field accelerates.

Robots are widely used in machining tasks for their great flexibility. In this paper, a cooperative robotic grinding system consists of a cooperative robot, a binocular camera and a 3D laser scanner. An unavoidable issue is the unknown transformation relationships between the frames of the robot and measurement equipment (robotic frame, camera frame and scanner frame). In this paper, an approach for unifying multi-equipment frames is proposed, which composes two steps calibration that calibrating the pose transformation matrices from the camera frame to robot base frame and 3D laser scanner frame to the camera frame individually. The multi-equipment frames’ unifying is achieved by converting all measured point coordinates from the camera and the scanner to the robot base frame. In the experiment, a workpiece was ground to shows the performance of the cooperative robot machining system.

To acquire the rapid numerical simulation iteration with sufficient precision for the space manipulator, and resolve the contradiction between the force-closure properties elimination and vibration suppression, a parametric modelling method for the flexible space manipulator system was proposed in this paper. Based on this method and by adopting the Adams software, a rigid-flexible dynamic model for the space manipulator applying in the space station was developed, which contained the cabin, adapter and end-effector. Especially, the flexibility of the manipulator was introduced by employing the modal superposition method. Also, the stiffnesses of the harmonic reducer and torque sensor were respected in order to simulate the flexibility of manipulator joints. Then a typical working task represented as shifting the load module by using the space manipulator was selected to analyze its dynamic behavior during the docking and capturing process. Results showed that the joint error could be reduced by the flexibility deformation of the space manipulator. And it was found the contact force and joint load were positively related with joints stiffness. In general, the modeling method and dynamic model proposed in this paper could provide a reference for the design and operation setting for the space manipulator.

Defect identification on the surface of aircraft radome is an important issue of the radome remanufacturing. This paper radome surface defect recognition for a robotic lacquer removing system. An improved Canny operator is proposed, and the curvature operator with an adaptive Gaussian filter can effectively locate the location of radome surface defects. Finally, the algorithms are verified by radome example pictures, The result shows that the improved Canny operator improves the evaluation index by 10.17% compared with the traditional operator. It proves the effectiveness of the enhanced operator in detecting defects, and the operator can also be applied to interfering situations such as image exposure, blurring, and much noise, which has better practicality.

Inverse kinematics (IK) is a significant theoretical foundation for the real application of redundant manipulators. In existing methods, the Denavit-Hartenberg (DH) conversion and screw-based IK sub-problems have been utilized to calculate the inverse solution, but would be limited by some special manipulators’ configurations or cannot obtain exact solutions. In this paper, an exact inverse solution for a 7R manipulator is modeled based on screw theory. In the modeling, firstly assuming that the first joint is known, the total motion of all joints are divided into three steps of operational motions: Rotation about the second, third and fourth joints; Rotation about the five and six joints; And rotation about the last joint. Problems for the first two rotations can be both modeled based on a novel screw-based sub-problem. Finally, the angular displacements of six joints are formulated explicitly in terms of the redundant joint angle. Using the proposed method, all exact solutions can be obtained by traversing values of the redundant angle. The effectiveness and efficiency of the proposed technique is validated using a simulation in MATLAB.

According to the detection requirements of foreign objects in the aircraft oil and gas pipeline, and also based on the characteristics of the aircraft oil and gas pipeline, such as small inner diameter, variable diameter, large length, and complex spatial attitude. This paper proposes a foreign object detection robot based on the principle of helical propulsion, which can adapt to the change of the inner diameter of the pipeline. First of all, the legs of the robot are retractable structures designed based on the linkage mechanism. The built-in motors and sensors can realize the self-adaptive telescopic motion of the legs, so that when the diameter of the pipe changes, the legs can be supported at a constant pressure on the on the inner wall of the pipe. Second, the robot adopts the driving principle based on helical propulsion. Only one motor can realize the forward, backward and stop motion of the robot in the pipeline, and actively adapt to the bending and spatial posture of the pipeline to ensure the walking ability of the robot in the pipeline. The third is that the robot is equipped with a camera to realize video detection inside the pipeline, and at the same time, it can autonomously detect foreign objects based on Faster R-cnn. Finally, the pipeline walking experiment and foreign object detection experiment are designed.

Along with the development of the automated techniques, construction robots are developed rapidly. This article proposes a brick-laying robot, which automatically detects the poses of the bricks and lays the bricks on the wall. Firstly, the mechanism structure of the robot is proposed. There are four modules in the robot, including a mobile chassis, a lifting system, mechanical arm and grippers. The problem of laying the brick is investigated from the viewpoint of application. The finite state machine is used to predict and control the robot’s movement in a semi-structured environment. Software structure and the sensor system are discussed subsequently. Finally, a prototype experiment of this brick-laying robot is shown.

This paper presents a general method for dynamic modeling of three-dimensional flexible manipulator with multiple degrees of freedom based on Lagrange’s second kind of dynamic equation. Firstly, the dynamic model of flexible joint considering joint stiffness, joint damping, joint friction and joint clearance is deduced, and the dynamic model of flexible rod considering internal structural damping of flexible rod is deduced by using hypothetical modal method. Secondly, the overall dynamic model of flexible manipulator is obtained by comprehensively considering the flexibility of joint and rod. The joint pair has two settings: rotating pair and moving pair. Finally, the simulation experiment of five degree of freedom series flexible manipulator is carried out to verify the correctness of the dynamic modeling method of multi degree of freedom flexible manipulator.

This paper addresses torque control and disturbance compensation for a load simulator used in hardware-in-the-loop simulations of robot manipulators. Focusing on the characteristics of a wide range of output torques and frequent accelerating and decelerating following motions of the load simulator, an active disturbance rejection control-based torque regulator is designed according to a mechatronic model. To reduce the negative effects of the inertia force, a feedforward compensator with inertia compensation is designed. The comprehensive feedback and feedforward control strategy gives the load simulator a desirable tracking capability despite the significant nonlinear disturbance in a highly accelerating and decelerating following motion. Experiments on a prototype machine were carried out to verify the effectiveness of the proposed control strategy.

Because of their variation of dynamic performance versus configurations, hybrid robots suffer from multi-axis motion errors that degrade their trajectory accuracy. A controller tuning method is presented in this paper for enhancing the multi-axis motion performance of these hybrid robots. After modelling analytical expressions of P-PI (P—proportional control, I—integral control) controller parameters considering joint elasticity and the variation of equivalent inertia to motor versus configurations, a controller tuning method with the goal of minimizing the maximum response time difference between each actuated joint in the workspace is proposed. Simulation results on a TriMule-800 hybrid robot show that the trajectory accuracy of the end effector is remarkable improved.

This paper proposes a new self-calibration method for a 5-DOF hybrid robot, which involves two successive steps: (1) an error model of the hybrid robot is built based on the kinematic equivalent limb for simple structure and easy identification; (2) a self-calibration method is proposed based on vision measurement for the convenience of automation. Experimental verification shows that the mean position errors of the robot can be reduced by 92.32% after calibration. Moreover, the method is simple, efficient, and convenient for automatic application.

Fault-tolerant gaits can effectively improve the reliability and prolong the service life of legged robots in unmanned environments. However, few stability-guaranteed fault-tolerant gaits are available for quadruped robots to traverse rough terrains. This paper proposes a fault-tolerant walking and turning gait planning method for quadruped robots with one locked leg on rough terrains. First, a quadruped robot with serial-parallel leg mechanism is introduced and the inverse kinematics is built. Then, the fault-tolerant gait is designed for both walking and turning. The gait trajectory planning method is proposed for both gaits on rough terrains with slopes and steps. Finally, simulations are carried out to visually illustrate and validate the fault-tolerant gaits. The results prove the correctness of the gaits planning.

Differential driven mobile robots are typical nonholonomic systems, involving system nonlinearity, which brings challenges to trajectory tracking control. We propose a kinematics control strategy based on backstepping to solve the nonlinearity of the system in this paper, in which the system is divided into three subsystems and two virtual control variables are derived to design the controller. Benefiting from this improvement, the design of the Lyapunov function is simplified and the nonlinearity is solved effectively. In terms of LaSalle invariance theorem, global asymptotic convergence of the provided control scheme is achievable. Furthermore, the effectiveness of the derived control method is validated in both the co-simulation of MATLAB and ADAMS (performed on a differential driven wheeled mobile robot) and the experiment (implemented on a tracked mobile robot). Results indicate that the controller is effective to make the nonholonomic mobile robots converge to reference trajectories in finite time.

On the basis of the momentum conservation equations and recursive least squares with forgetting factor, a new adaptive reactionless planning algorithm is proposed for the reaction null-space motion of the free-floating space manipulator after capturing an unknown rotating target. First, the Lagrange dynamic model of the manipulator is established. Second, the adaptive reactionless planning algorithm is designed to update the null-space solutions for joint rates in online manner. To go to a step further, the desired motion generated by adaptive reactionless planning is produced by driving joints with the PID controller. Finally, on the basis of Lyapunov method, the stability of the proposed scheme is proved theoretically, and the effectiveness of the designed scheme is verified by computer simulation.

In recent years, digital twin, as an enabling technology to realize intelligent manufacturing, has attracted more and more attention, but there is relatively few landing research on it. In order to realize transparent and real-time monitoring without dead angle, this paper proposes a remote 3D visualization monitoring framework based on digital twin. According to the framework, this paper constructs a virtual model of a kinematically redundant (6 + 3)-dof hybrid parallel mechanism, and uses real-time data, which is transmitted through OPC UA protocol and Socket, to drive the virtual model to move the same as reality. This paper realizes the mapping from physical layer to virtual layer. It is hoped to provide some references for the landing application research of digital twin.

Complex structural parts with large aspect ratio are extensively used in the aviation field. Such parts usually have the characteristics of large size, large aspect ratio, and thin-walled structure. To realize high-efficiency and high-precision machining of such kinds of parts, a gantry hybrid machining robot has been designed. To investigate and reveal the potential of this robot, the motion/force transmissibility and static stiffness are comprehensively analyzed. On this basis, an optimal workspace of this robot is identified with excellent motion/force transformation performance and high-quality stiffness characteristics. The identification of this optimal workspace is fundamental to fully exploring the potential of this robot, and helpful to ensure its machining performance. In this workspace, both excellent kinematic transmission performance and high structural rigidity of this robot can be guaranteed. Consequently, the high-efficient and high-precision machining of complex structural parts with large aspect ratio can be realized.

Model-based kinematic calibration is feasible to improve robot accuracy by compensating for the geometric errors. However, non-geometric errors such as backlash and deformations cannot be eliminated via this approach since they are difficult or impossible to fully model. This paper proposes a two-stage calibration method to comprehensively compensate for the geometric and non-geometric error sources for a 5-DoF parallel machining robot. In the first stage, the geometric error propagation model of the parallel robot is established using the vector loop method. On this basis, a kinematic calibration algorithm to compensate for geometric errors is presented by employing the truncated singular value decomposition technique (TSVD) from an ill-posed identification matrix problem. To further improve the accuracy of the robot, in the second stage, an artificial neural network (ANN) is designed and applied to eliminate the residual non-geometric errors by integrating it into a kinematic calibration model. As a result, an augmented pose error model with computational efficiency is developed to accurately describe the comprehensive error characteristics of the parallel robot. Finally, simulation experiments are conducted. The results demonstrate that the presented approach is effective and robust, with average position and orientation errors reduced by 68.6% and 93.5%, respectively, compared with model-based kinematic calibration.

Due to the effects of wind, waves and currents, floating platforms such as vessel inevitably produce multi-degree-of-freedom motions, causing equipment and personnel on ships to fail to work normally. With the continuous development of my country’s ocean engineering, the construction of offshore operations and offshore platforms is also increasing, and the development of deeper and farther sea areas is considered, and combined with the background of China’s “building a maritime power”, for the above problems, this paper introduces the multi-degree-of-freedom motion compensation device based on series mechanism and parallel mechanism, and the key technologies required to apply the mechanism to the field of offshore motion compensation. It proves that the series mechanism and the parallel mechanism play an important role in the field of marine engineering and have broad application prospects.

Time series data of rolling bearing vibration is an important resource in the field of industrial systems, yet it is difficult to be exploited because of the large amount of noise that can be mixed into the acquired signal, the signal generally has the characteristics of nonlinear and non-stationary and the inability of usual methods to handle time series data. To solve the above problems, a method based on GRU convolutional denoising Auto-Encoder for rolling bearing fault diagnosis is proposed in this paper. Firstly, Gaussian noise is added to the original vibration signal of the rolling bearing and fed into the GRU convolutional denoising Auto-Encoder model for training. Secondly, the characteristics extracted by the neural network are used as input to the Softmax classifier for fault diagnosis. The CWRU dataset were used for the analysis. The results show that the proposed method achieves an average fault diagnosis rate of 99.8%. The advantage of the method proposed in this paper over traditional fault diagnosis methods is that effective characteristics can be learned from time-series data mixed with noise, better greater robustness and diagnostic results.

Compared with traditional mobile robots, legged robots have a larger workspace and higher flexibility, which can meet peoples demands in various disciplines such as manufacturing, transportation, reconnaissance and rescue. However, all practical applications depend on the stable movement of legged robots. In order to improve the adaptability of legged robots on rough road, this paper proposes a strategy of foothold planning and body posture adjustment of hexapod robots based on its own state in complex terrain. The algorithm calculates the robot state according to the sensors’ information, evaluates the walking environment, and then selects the appropriate foothold and dynamically adjusts the body posture of the robot to adapt to the terrain, so as to improve the walking stability of the hexapod robot on complex terrain. In this paper, the strategy is implemented on hexapod robots Qingzhui-II to prove its effectiveness.

Grasping force control is important to realize safe and reliable robotic manipulation. In this paper, a semi-closed-loop constant grasping force control strategy of the multi-modes rigid-flexible underactuated gripper is designed to eliminate the influence of full-closed-loop control system on the grasping dexterity. For the two-point grasping mode and enveloped grasping mode, the inverse static model of gripper were established based on the forward static models proposed in our previous research and the numerical fitting. A semi-closed-loop PID constant grasping force control strategy was designed using the established statics models. Matlab Simulink was utilized to verify the proposed control strategy. Further, the multi-modes grasping force control system was built, and the effect of deformation for the flexible linkages on the equivalent size of grasped object was considered to correct the proposed control strategy by the analysis of balance position and numerical fitting. Finally, the rapidity, accuracy and stability of corrected control strategy were verified by experiments.

FF HSE protocol has become one of the most popular fieldbus technologies under the industrial scene. However, even though it has many advantages, the communication quality is still restricted with different type of faults caused by complicated real-time environment, undetermined time delay and random electromagnetic interference. In order to overcome the defect in traditional troubleshooting methods, the design of a new FF HSE protocol fault analyzer based on deep network is proposed. Utilizing the powerful representation ability of deep network, the fully-trained storage monitor can auto-parse all kinds of FF HSE faults and predict possible reply messages from each ends. It can also be transplanted into other similar scenes where diverse protocols are adopted. The analyzer, as a functional tool, is competent at various fieldbus tasks in regard with fault diagnosis and communication quality analysis.

The polishing process for composite curved parts is currently done by hand or by machine-assisted semi-automatic grinding. In the process of polishing operation, a large amount of composite dust will be generated, which will cause great harm to the body of the polishing operator. And this manual way of working will lead to poor product consistency and low production efficiency. In this regard, this paper designs and builds a set of robot automatic grinding system for the surface characteristics of parts and the requirements of the grinding process. The kinematics model of the robot is established, and the position-based adaptive impedance control method is used to realize the smooth control of the robot grinding force, and the polishing force is optimized according to the polishing surface quality through experimental verification, and the tracking control effect of the polishing force is verified.

Leg calibration of the quadruped robot is of great significance to improve the positioning accuracy. However, the encoder used to represent the real pose of the quadruped robot often exhibits zero-point drift, which reduces the positioning accuracy. The traditional calibration method is to manually calibrate each joint angle by technicians, which is time-consuming and labor-intensive. This paper proposes an online intelligent kinematics calibration method for quadruped robots based on machine vision and deep learning to simplify the calibration process and improve the calibration accuracy. The method includes two parts: identifying the marker fixed on the legs through target detection and calculating the center coordinates of the markers, and solving each joint angle by establishing an inverse kinematics neural network based on deep learning. We conducted a series of experiments to verify the accuracy of the method. The experimental results show that compared with the traditional manual calibration, the proposed method can greatly improve the calibration efficiency on the premise of meeting the calibration accuracy.

Large-space manipulations require robots can work in large or even infinite space. As for the robot manipulator, the large-space can be defined that the working range of the task exceeding the workspace of the manipulator. This paper proposes a large-space manipulation skill learning approach based on the mobile manipulator. In the skills extraction stage, the trajectories as well as the endpoint stiffness of the human arm are recorded simultaneously by using the motion and surface electromyogram (sEMG) capture devices. In the skills encoding stage, Gaussian Mixture Model and Gaussian Mixture Regression (GMM-GMR) approaches are applied to encode and reproduce the demonstrated skills. In the skills reproduction stage, the mobile manipulator platform with the developed weighted whole-body Cartesian impedance controller is used to reproduce the demonstrated large-space manipulation skills. The experiment results show that the mobile manipulator successfully inherits the human skills, and successively completes the large-space manipulation task.

In the task of path planning, the unmanned surface vessels (USV) are required to reach the destination while avoiding obstacle. However, it is difficult for USV to prioritize the two sub-target tasks of destination arrival and obstacle avoidance in a complex dynamic environment using traditional path planning methods. Based on the above considerations, a path planning method for USVs based on strategy integration is proposed. Firstly, the path planning scenario containing dynamic obstacles and two sub-target scenarios are set up. In order to strengthen its ability to reach the destination and avoid dynamic obstacles, the dynamic obstacles and the destination are removed separately in the two sub-target scenarios. Furthermore, the model for strategy selection is trained on action decisions in sub-target scenarios through double deep Q-Network with prioritized experience replay. Finally, a framework for strategy integration is designed to optimize strategy selection for USV. The simulation results show that the proposed method achieves a good overall performance and a higher path planning success rate than the traditional path planning method.

To improve the path following control performance of autonomous underwater vehicle (AUV) and ensure AUV can track the target path quickly and accurately, a tracking control algorithm based on model prediction theory is presented in this paper. Firstly, the adaptive line-of-sight distance and acceptance circle are integrated to the framework of line-of-sight guidance (LOS). Then, under this framework, a kinematic adaptive LOS guidance algorithm is constructed to convert target path tracking into dynamic heading tracking. Subsequently, an incremental state-space equation is derived from the AUV horizontal plane’s three-degree-of-freedom dynamic equation. Finally, the optimal feedback control command considering multiple constraints is obtained based on the model prediction principle’s idea of prediction, optimization, and correction. In comparison with the traditional LOS + PID control scheme, the simulation results illustrate that the proposed scheme not only reduces control error but also improves convergence speed, and the turning performance is also greatly improved, proving the effectiveness of the control algorithm. The designed control strategy can complete the AUV path following task and serves as a baseline for the future application of model prediction theory to the study of AUV tracking control technology.

In this paper, a method for SMP-KK RF coaxial connector assembly using a vision system and impedance control is presented. An end-effector is designed to grasp the connector easily, avoiding complicated picking processes. To capture the header (Female part of the connector) directly without the searching process, a robot error compensation method based on spatial similarity is adopted to improve robot positional accuracy. Then, a strategy with improved impedance control is proposed to overcome the remaining position/orientation errors caused by the vision system. The improved impedance control using reinforcement learning is adopted to suppress contact force overshoot and minimize position/orientation errors. The performance of the proposed method is evaluated by a series of experiments using a six-degree freedom robot equipped with the designed end-effector. The experimental results show that the average absolute error of robot positioning is reduced by 70.9% from 0.6898 to 0.2006 mm after precision compensation, and the proposed strategy can reduce the pose error to within 0.5°.

Contact detection is the key part in the unified event-based motion control framework of hydraulic quadruped robots. Without the use of an external force sensor, this process usually requires estimating the contact force, which is then compared with a certain set threshold to judge whether contact occurs. But there are some challenges when applied to hydraulic robots, due to the inherent complexity of the hydraulic system, such as high-order, non-linearity, strong interference, etc. The typical threshold method uses only single force information, which is easy to make incorrect inferences when the feedback hydraulic signal has a large unknown perturbation. What’s more, the dynamic model of a hydraulic robot is more complex and difficult to establish accurately, making some ways of estimating force based on complete dynamics inapplicable. To tackle such problems, this paper introduces the method of probabilistic model fusion for contact estimation, and applies it to our hydraulic single-leg platform. As far as we know, it may be the first time that this probability method is applied to a hydraulic legged robot. The method fuses multiple available information and makes optimal estimation, which can reduce the misjudgment caused by the interference of single information. Moreover, a simplified method for estimating contact force through impedance relationship is proposed. Since the method does not require complex dynamic modeling and torque feedback, it is computationally simple and effective and suitable for hydraulic robots. The above theory is tested in a general framework combined with an event-based state machine, and the experimental results verify the effectiveness. The work of this paper can provide a basis for the quadruped robot to cross the unstructured terrain without external perception in the follow-up work.

With the increasing demand for offshore USV-UAV cooperation, the autonomous safe landing of UAV on USV has become a key issue. The USV bears multi-dimensional swaying motion under the influence of wind, waves and currents when sailing, which poses a great challenge to the take-off and landing of UAV. Aiming at the above challenge, this paper proposes a stable tracking robot consisting a PM (Parallel Mechanism) and a planar CDPM (Cable-Driven Parallel Mechanism). Firstly, according to the DOF (degree of freedom) requirements of the stable tracking robot, a hybrid mechanism with 2R1T PM and 1R2T planar CDPM was constructed on the basis of the principle of DOF distribution and the existing mechanism. Secondly, the process of assisting the take-off and landing of the UAV was determined, and the kinematics and dynamics of the stable tracking robot were carried out based on the screw algebra. Finally, the simulation experiment of the rigid-flexible hybrid stable tracking robot to assist the take-off and landing of the UAV was carried out, which verifies the correctness of the kinematics and dynamics models established, and lays a foundation for the subsequent prototype design and control.

Mobile robots have gradually become indispensable in environmental monitoring. They are more flexible and cost effective than conventional static sensor networks. However, current unmanned mobile robots suffer from limited power supply onboard, which results in short endurance and hinders their applications in large-scale environmental monitoring. One feasible solution is to enable adaptive sampling, in which the essential is to generate effective moving trajectory for mobile robots. This paper presents an informative path planning algorithm for mobile robot adaptive sample using double deep Q-learning network (DDQN). The sampling objective is to efficiently locate the extreme feature in a relatively large region that could not be fully sampled or covered by the robot. Numerical simulation has been carried out to seek the extreme feature described by the Gaussian model. Results indicate feasibility of the proposed path planning algorithm and its superiority to conventional lawn-mower pattern and random sampling.

In recent years, the number of patients with impaired hand function caused by stroke and other diseases has increased gradually. Proper rehabilitation training can improve hand disability recover performance effectively, which is of great significance to patients’ daily life. In view of the shortage of domestic medical resources, insufficient attention to rehabilitation training and high cost, we developed an active rehabilitation training system based on data gloves by combining flexible sensors with a glove. The data glove consists of flexible pressure sensor array, stretchable bending sensors, an inertial sensor, and data acquisition circuit. The sensors are used to measure pressure values applied to fingers and palm, bending angle of each finger, and motion status of hand respectively. For this project, virtual reality technology was adopted for rehabilitation treatment, and we developed interactive games for hand rehabilitation training based on Unity3D platform. The platform receives and processes sensor data, use the data to generate interactive gaming environment, so that patients can perform rehabilitation training by playing games in the virtual world without leaving home. The platform can save historical training data to database, so that patients and doctors can evaluate the effectiveness of rehabilitation training performance any time, and make adjustment to training strategy timely.

This paper proposes a recognition system of ankle movement patterns with two channels of surface electromyography (sEMG) signals. Six parts of shank muscles are selected as primary sEMG channels, and the optimal channel set is determined according to the proposed channel evaluation index. Linear discriminant analysis (LDA) is utilized in training and recognition. The optimal feature set is determined from six primary features in the time domain. The experimental result shows that the proposed method achieved an average recognition rate of 98:04%.

Unlike the streamlined structure of existing underwater gliders, the disc structure can glide in all directions by controlling its center of gravity and buoyancy center, and it is expected to use it to design a new underwater gliding robot. By changing the position relationship between the center of gravity-buoyancy center and the center of gravity-point buoyancy, this paper simulates the falling and rising motion of thin disks, and derives the quasi-steady-state equations for falling and rising of thin disks. Studies have shown that a smaller center of gravity—buoyancy center offset $$e$$ and center of gravity—point buoyancy offset $$\delta$$ can result in a large net horizontal displacement of a thin disk. In this paper, the least squares method fitting of the offset is further performed, indicating that when the offsets $$e$$ and $$\delta$$ change within a certain range, the net horizontal displacement is positively correlated with $$e$$ and $$\delta$$ respectively. The analysis conclusions of this paper have certain guiding significance for the design of thin disc underwater gliders in the future.

Mobile robots have been widely used in military and other fields. By observing the path of the mobile robot, it is easy to infer the destination of its path. However, in some special situations, the user of the mobile robot does not want to reveal its purpose information, such as carrying out military attacks, sneak reconnaissance missions, etc. In order to protect the mobile robot's path information from being leaked, we combine the reinforcement learning path planning method to propose a computationally efficient deceptive reinforcement learning mobile robot path planning method. The path planned by this method balances the path cost and the target deception weight, making it difficult for observers observing the mobile robot path to predict the real target of the mobile robot, while ensuring a lower path cost for the mobile robot.