Recent Developments in Multibody Dynamics

Cable-driven parallel robots (CDPRs) have larger workspace, simple design, are easy to transport, assemble and disassemble, and hence, possess a great potential in on-site 3D printing of large structures. However, they are prone to collision of cables with the preceding layers of structures being 3D printed. Therefore, this work proposes an analytical approach to determine the boundary of the collision-free workspace of planar over-constrained cable robots. This workspace is composed of poses that can be reached while avoiding the collision of lower cables with the structure being printed. The analytical expressions of the collision-free workspace have been obtained for both cases, i.e., considering zero platform orientation and variable platform orientation. These analytical expressions have been utilized for rapid computation of collision-free workspace. Simulation results have been obtained for both cases, and the effect of orientation on the collision-free workspace is analyzed. Additionally, the optimal design problem of CDPR is presented to achieve the desired collision-free workspace while minimizing the installation space of the robot. The results show a significant reduction in installation space by considering the variable orientation of the platform.

The current article describes the modeling and positional control of a flexible tube manipulator intended for medical applications. The flexible tube is made of polyamide material and its tip is controlled via a calibration-based controller. The configuration is made compact with Shape Memory Alloy (SMA) spring pair as the prime actuators. Two antagonistically connected SMA spring pairs manipulate the flexible tube in 2D and the amount of current required to control the spring is delivered via the controller. The dynamics of the SMA spring pair along with the flexible tube dynamics are presented and the simulation predicts the force transmission capability of the actuator. Thereafter, experimental analysis shows the positional tracking ability of a flexible tube manipulator.

Virtual Motion Simulators are electro-mechanical systems that are used to create an immersive environment for virtual reality applications, like gaming platforms for the entertainment industry, flight training simulators, vehicle testing systems, etc. A Gough-Stewart parallel manipulator is one of the most widely used platforms to support these applications’ human handling cockpits, along with its integrated controls. Most of these motion platforms were originally proposed with hydraulic jacks [7], which later on, with advancement in electrical controls, were reported with electrical actuators [8]. Hydraulic actuators find their application in robust and huge load capacity moving platforms, whereas electrical actuators are applied mainly for applications with high stiffness and precision, like telescope mounts [14]. Both hydraulic and electrical actuators pose a trade-off of being expensive for non-critical applications like gaming platforms or training simulators where a high degree of precision is not much of a concern. On the contrary, pneumatic actuators are inexpensive, fast and offer a long linear actuation. Reckoning this, we propose using pneumatic piston linear actuators for all six legs of a Gough-Stewart platform for a Virtual Motion Simulator. However, due to the compressibility of air in the linear cylinder, the actuators are prone to external disturbances in their position due to the dynamically varying load while the platform is moving. The paper proposes to use Continuous Integral Sliding Mode Control for the precise positioning of six pneumatic actuators of the Virtual Motion Simulator. The first part of the paper will discuss the mechanical design, the kinematics and physical assembly of the motion platform. Secondly, the paper will discuss the hardware integration of the electro-pneumatic system, which implements the controller for all the six linear actuators of the Gough-Stewart platform. Next, the paper will discuss the control approaches for precise positioning of the pneumatic actuator, namely, the continuous integral sliding mode control technique. Finally, the hardware integration to the PC-based gaming engine is discussed, and the methods for extracting the data, pose, velocity and acceleration from the gaming engine are discussed. The paper will conclude with results and a discussion on the performance of the motion simulator as a whole.

Robots are getting deployed at home and in industries, becoming an integral part of our daily lives. Sophisticated mechanisms are required to make the joints of the robots compact and simple. In this paper, we have developed a flexure joint for the fingers of the robotic hand. The flexure joint is arranged in series to make a three-DOF underactuated finger. Five fingers are arranged to make a robotic hand. Castigliano’s theorem is used to develop the deformation related to the applied loads, using the equation the flexure mechanism was designed. Pseudo-rigid model is developed to determine the stiffness of the flexure mechanism. A virtual model of the flexure mechanism is developed in a CAD environment. Finite Element (FE) simulation is conducted to the different loading conditions to evaluate the performance of the flexure mechanism. It was seen that the flexure mechanism is flexible about the rotational axis and stiff about the other axes. The stiffness model developed using the pseudo-rigid model has a good correlation with the FE simulation model.

This paper presents a novel rotary actuator's design concept based on shape memory alloy (SMA) springs and permanent magnet systems. The proposed actuator is so designed that it can operate even in a vacuum. The presence of permanent magnets leads to efficient and quick rotation motion without any direct contact between the actuation system and passive disc rotation. The presence of a smart actuator (SMA) system helps build a lightweight actuator. The presented actuator converts the translational motion of the SMA springs in the bi-directional rotation of the passive disc. The contraction of the SMA could directly control the rate of rotation.

Multirotor Unmanned Aerial Vehicles (UAVs) and their ability to hover and maneuver in the air make them the best vehicle for applications requiring quick package deliveries. Our assumed example system is a collaboration of a UAV and a land vehicle capable of storing multiple packages and charging the UAV’s batteries. Another example is quickly exploring some unknown region where the UAV scans the unexplored region and returns to the moving vehicle when required knowledge is gathered. An active research problem in such systems is about takeoff and landing the UAV on the moving vehicle. The landing problem, however, is quite challenging without unique markers like visual tags, hard-coded trajectory targets, etc. We present a markerless controller that uses only computer vision and calculates the optimum trajectory to land the UAV on the moving platform. This paper presents the work in a two-stage implementation process. First, the detection of a moving vehicle and finding the centroid by applying optical flow and contour technique on image feed from an RGB camera, and secondly, following the ground vehicle by matching the velocity by utilizing a visual servoing process followed by simple PID controller to descend in the smooth trajectory towards the landing point.

A mechatronic two-axle rail vehicle with only one suspension step is introduced in the Shift2Rail project Pivot2. This vehicle design reduces the vehicle weight in comparison to standard bogie vehicles. However, having only one suspension step drastically decreases passenger comfort. Thus, hydraulic actuators are introduced instead of passive dampers and active modal sky-hook control is applied. Due to the strong interaction between the running gear frame and the carbody, a blended modal solution is applied where a percentage of the acceleration of the frame is used in the feedback loop in addition to the acceleration of the carbody. To assess the performance of the controllers, simulations are carried out with the vehicle running at constant speeds from 10 km/h to 120 km/h on tangent track with high level of track irregularities. First, multiplicative dimensional reduction method (M-DRM) sensitivity analysis is applied to determine the importance of the control variables and subsequently a genetic algorithm (GA) optimization is performed to identify the control gains for each speed. The blended control proposed here can improve passenger comfort with respect to a standard modal control while maintaining similar energy and force usage.

The contribution presents a complete frequency solver workflow applied to automotive transmissions modeled as multi-body systems consisting of mechanical components like rotating rigid and elastic shafts interconnected by gear contacts and supported by bearing joints. Solving the equations of motion in frequency domain based on a linearized model yields the periodic steady-state results very fast compared to transient time integration methods, where fast oscillating components may decay slowly. The frequency domain solver workflow is described in detail from getting a loaded state of the model, which is used for linearization, up to solving linear equation systems for each non-negligible frequency load component. The presented solver workflow is applied to a simple gearbox model. Resulting vibrations from the linear frequency domain solution are compared against results of a transient time domain solution, where the frequency domain solution matches well the time domain results but is obtained within a fraction of CPU time.

The proposed fuel handling scheme of the future Indian fast reactors (FBR 1 and 2) envisages the use of a dedicated flask called subassembly transfer flask (STF) for handling of subassemblies out of the reactor vessel. The STF transfers the fuel subassembly (SA) between fuel transfer port (FTP-I) on roof slab and fuel transfer position 2 (FTP-2) on RCB floor and vice versa. This machine consists of a flask mounted over a self-propelled carriage, which moves between the fuel transfer port of reactor vessel at one end and fuel transfer port of inert gas filled SA transfer carriage cell (STC cell) at another end. STF transfer/receives transfer pot holding irradiated/FSA (Fresh Subassembly) to/from the transfer carriage through the transfer ports. STF traverse between the two ports on rails and raises/lowers the transfer pot by wire ropes, Multibody dynamics approach is used to study the dynamic behavior of the STF under an earthquake loading. The present work is a detailed MBD investigation of the performance of STF under seismic events to evaluate the forces experienced by the different components of the machine and to study the motion of SA inside STF during a seismic excitation. Rigid body dynamic behaviour is considered for the docked STF at FTP loaded with SA, but the locking pins are modelled as flexible elements. Nonlinear contact behaviour between STF and rails during seismic excitation is observed and the functionality effectiveness of locking mechanism provided for the machine is verified through MBD investigation using RecurDyn solver for analysis.

Recent developments in the area of single-point incremental forming process deal with the study of forming accuracy. In general, the forming tool is assumed to be rigid, contrary to what exists in real experiments. This paper presents the simulation results of the effect of tool stiffness in the single-point sheet incremental forming process. A finite element method-based analysis was adopted for this study. The analysis is carried out using tools having different compliance. The nodal displacement of the deformed profile of the truncated cone was measured and compared with the results from the numerical trials with a rigid and deformable tool. The study indicates that using a deformable tool results in considerable geometric errors in the formed component.

Virtual Environments (VE) need large workspaces. On the other hand, haptic devices are mostly grounded and typically have small workspaces compared to the VE. The main objective of this work is to extend the smaller workspace of haptic devices for Virtual Reality (VR) applications without affecting the haptic perception of the user. A position drift-based robotic approach has been proposed in which a redundant kinematic Degree of freedom (DOF) is added to the haptic device by moving its base using a mobile robot to expand the workspace of the haptic interface point (HIP) in the VE. In order to validate the proposed approach, a psychophysical study measuring stiffness Just Noticeable Difference (JND) has been conducted to compare the user perception before (Stationary Robot) and after the proposed approach (Moving Robot). Two experiments were conducted separately, one for a single axis (Experiment I) and another for a two-axis (Experiment II). The %JND for Experiment I is 21.08% and 24.59% for stationary and moving haptic devices. The %JND for Experiment II is 20.55% and 26.56% for stationary and moving haptic devices. One-way ANOVA was performed to test whether the difference in the %JND between the two cases is insignificant. With the insignificant %JND difference (p = 0.32 for Experiment I, p = 0.34 for Experiment II), the proposed method could be considered as not affecting the user haptic perception while expanding the haptic workspace for the interactions in VE. The stability of the haptic device has been analyzed, including robot dynamics. The current study implements up to two axes of workspace expansions for the 3D systems Touch haptic device; however, the algorithm is extensible to three axes and any grounded haptic devices.

Due to advancements in the area of robotics and automation, there is a need of skills for engineers. They are obtained through various workshops, seminars, conferences and participating in various competitions. Apart from the practical work skills, there is a requirement of proper software-based skills to get an idea of the performance of final tasks on the field. This paper presents the use of such a multi-body dynamics software for simulating the game of a robotics competition to check the effectiveness and completeness of the intended tasks. In this work, MSC ADAMS, a multi-body dynamics software, has been used for simulations. The tasks that have been performed are the tasks for ABU Robocon 2022. The theme was “Lagori” that is based on Indian game called as “Pithu”. Two tasks of the game were considered here to demonstrate the use of a software. One is Lagori breaking and the other is hitting the Ball on Head. The simulation was performed for several speeds and angles at which the ball was thrown. The effectiveness of the tasks was checked with the real situations when the games were actually played.

Gearbox is frequently utilized as a power transmitting device due to its adaptability to operate at a wide range of speed and loads. Any gearbox defect may lead to total failure or even seizure of the machine. Therefore, predictive maintenance is adopted to find the health state of gear train. Modelling of a physical system is economical due to the cost involved in experiments. In the current work, a dynamic model of 9-degrees of freedom (DOFs) spur gear model is taken into consideration to determine the status of gear in both healthy and faulty conditions. In modelling, a high contact ratio spur gear system is considered for analysis. The model comprises of a loader, a motor, and a gear-pinion pair. The equations of motion from the planer block diagram model of the gear pinion system are solved in the MATLAB-Simulink environment. Time and frequency domain analysis is used to compare the health of gear train under different operating conditions.