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The EUROMECH Colloquium "Dynamics of Vibro-Impact Systems" was held at th th Loughborough University on September 15 _18 , 1998. This was the flrst international meeting on this subject continuing the traditions of the series of Russian meetings held regularly since 1963. Mechanical systems with multiple impact interactions have wide applications in engineering as the most intensive sources of mechanical influence on materials, structures and processes. Vibro-impact systems are used widely in machine dynamics, vibration engineering, and structural mechanics. Analysis of vibro-impact systems involves the investigation of mathematical models with discontinuities and reveals their behaviour as strongly non-linear. Such systems exhibit complex resonances, synchronisation and pulling, bifurcations and chaos, exCitation of space coherent structures, shock waves, and solitons. The aim of the Colloquium was to facilitate the exchange of up-to-date information on the analysis and synthesis of vibro-impact systems as well as on the new developments in excitation, control and applications of vibro-impact processes.

Inhaltsverzeichnis

Frontmatter

Vocal Folds as a vibro-impacts system

A model for human vocal folds in the form of two spring-suspended plates, which can collide with one another, is considered. It is shown that due to air flow between the plates excitation of chaotic self-oscillations occurs. In this process the shape of oscillations of air flow volume velocity was found to be close to observed experimentally.

Polina S. Landa

Behaviour of granular materials in the field of vibration

Vibration has been widely used in various industrial operations dealing with granular materials. Classification, conveying and packing provide typical examples of the vibration technique. In spite of these actual uses, the behaviour of granular materials is poorly understood. Most of the knowledge related to handling of particulates is empirical and no generalized approach for the analysis of the response of granular materials to external forces exists. This paper presents an investigation into the development of a numerical method for size segregation, which is the typical behavior of granular materials in the field of vibration. This numerical method is modified on the basis of the discrete element method proposed by Cundall. In order to consider the shape anisotropy of particles, they are first treated as elliptic models. Then mechanical units such as spring, dashpots and friction sliders are used to express the contact forces. The effect of the size ratio and the shape of each particle on the response of granular materials is considered.

M. Saeki, E. Takano

To the general theory of hand-held percussion machines

The generic approach for the analysis and synthesis of a hand-held percussion machine as a discrete nonlinear converter is presented. The optimisation of the interaction of the machine with the operator and load is formulated and solved as a problem of optimal control. For the simplification of design, the sequence of estimations is developed for the series of possible quasi-optimal excitations.

V. I. Babitsky

Free manifolds of dynamical billiards

A mechanical system with impacts is called a mathematical billiard if it may be reduced to a mass point moving in a plane and reflecting from a bounding curve [1]. A billiard is called dynamical if an external force field is imposed [2–6]. The objective of this work is to suggest a new method of representation of dynamical billiards as generalized mathematical billiards on curved surfaces, or free manifolds embedded in R3. The trajectories of the mass point on a free manifold consist of segments of geodesies. The mass point moves on a free manifold with no external forces acting on it. The free manifolds of dynamical billiards in the constant and Newtonian force fields are shown to be surfaces of revolution in the three-dimensional Euclidean space. The parabolic case is of particular interest, because it is equivalent to the classical planar mathematical billiard.

V V Beletsky, E I Kugushev, E L Starostin

Vibro-impact processes in systems with multiple impact pairs and distributed impact elements

This paper is a brief review of some interesting, and perhaps surprising, phenomena often encounterd in the discrete and distributed systems which vibrate with impacts. We examine such systems in some cases where we have multiple collisions of subsystems or the sizes of objects require the consideration of wave processes. Such systems are: Mechanical objects, which elements are subjected to impacts;Various extended constructions, vibrating near pointwise, gridwork and continuous movement obstacles;Vibro-conductive and vibro-arresting constructions equipped with facilities with solitary and multiple breaks, etc.Original calculation methods have been presented which are based on the frequency-time analysis and other methods of the modern nonlinear mechanics. Multiple nonlinear effects are theoretically described, which are related to the formation of specific nonlinear waves of trapezoidal profiles; advent of localization of intensive impacts in some areas of constructions; generation of higher harmonic components; generation of non-synchronic and chaotic movements, etc.

V L Krupenin

The impact based transportation process in a vibratory feeder

Vibratory feeders are used in automatic assembly to feed small parts. They are capable to store, transport, orient, and isolate the parts. An oscillating track with frequencies up to 100 Hz excites the transportation process,that is mainly based on impact and friction phenomena between the parts and the track. This paper presents a complete mechanical model of part feeding dynamics, based on unilateral constraints with Coulomb friction. This model enables a theoretical investigation and consequently an improvement of the transportation process. The developed impact model was verified by measurements,that were carried out using a special experimental setup with laser distance measurement.

Peter Wolfsteiner, Friedrich Pfeiffer

The effectiveness of the impact damper with granular material

The multiple -particle impact damper consists of a bed of granular materials moving in a container fixed to the resonantly vibrating system. This type of impact damper substitutes for the solid impact damper that causes excessive noise in its operation, and deteriorates the damping performance under gravity. The problem is to determine the effectiveness of the impact damper with granular materials as a damper mass, for reducing the vibration of a single degree-of-freedom system to a prescribed value when the excitation is simple harmonic. In the analysis, the particle bed is assumed to be a mass which moves uni-directionally in a frictionless container and collides plastically with the ends of container. The solutions for some possible types of the steady state impact motions, and frequency response are obtained. This study deals with the two different cases, i.e., the dampers are applied to a vertical and a horizontal vibrating systems. Experimental models were tested to verify the analysis, and further to modify them for the case of the horizontal system.

I Yokomichi, Y Araki, M Aisaka, H Kusano

Dynamics of gear-pair systems with backlash

Dynamics of gear-pair systems involving backlash and time-periodic stiffness is investigated. First, the equation of motion is presented in a strongly nonlinear form, with periodic stiffness and external forcing terms. Then, several types of periodic steady-state response are identified and determined by applying a methodology, that is suitable for piecewise linear systems with time-periodic coefficients and excitation. This methodology is complemented by appropriate analytical procedures, revealing the stability properties of the located periodic solutions. In the second part of the work, numerical results are presented. First, typical series of response diagrams are shown, illustrating the effect of the damping and the forcing parameters on the periodic response. These response diagrams are accompanied by results obtained by direct integration of the equation of motion. These results demonstrate that for some parameter combinations the dynamical system examined can exhibit more complicated and irregular response, including crises and intermittent chaos.

S. Theodossiades, S Natsiavas

Nonlinear stability analysis of a single mass rotor contacting a rigid backup bearing

This paper investigates the steady-state response of a rigid, single mass rotor with imbalance eccentricity supported by an active magnetic bearing with nonlinear characteristics. The rotor may have intermittent contact with an axially collocated, fixed, rigid and circular backup bearing. A radial offset position of the backup bearing center with respect to the magnetic bearing center is assumed. Parameter studies are carried out, especially for the excitation frequency and the friction conditions at the contact point. For frequencies ranging from the onset of contact up to the critical speed various kinds of periodic, non-periodic and quasi-periodic solutions can be observed. Within the parameter range investigated, a two-periodic orbit with one contact was found to be the dominant stable orbit for low excitation frequencies.

Horst Ecker

Influence of contact and impacts on the dynamics of an elastic rotor with an elastic retainer bearing

This study deals with the nonlinear vibrations of a Jeffcott-rotor with an elastic retainer bearing with particular emphasis on the influence of impacts between rotor and retainer bearing.Impacts occur during the non-stationary transitions between states of motion with and without contact and also if the retainer bearing is misaligned towards the rotor axis. Experimental results are compared to computer simulations. For the computer simulations impacts were taken into account by contact models which approximate the force-deformation-relation in the contact point by means of simple linear or nonlinear springs and dampers. Impacts turn out to be particularly important if the retainer bearing is heavy in comparison to the rotor or if the retainer bearing is strongly misaligned.

Georg Wegener, Richard Markert

Wavelets transform in analysis and control of a piezoelectric vibroconverter with impacts

Wavelets provide a new tool for the analysis of vibrations especially for localized phenomena as resonance or impact, i.e. discontinuous actions. The study is exemplified on a piezoelectric vibroconverter with an impact rheological model It consists of a piezoelectric body and another rigid body prestressed to each other by means of a connecting element. During the vibrations of the piezoelectric vibroconverter between its rigid hand and the rigid body the impact interaction takes place. The impact stationary regime and the shock phenomena are analyzed by means of Haar wavelet method. We suppose that the vibrations can be controlled by a feedback system. By means of Haar wavelets we arrive to a signal flow graph of a position control system.

V. F. Poterasu

Stability improvement of the vibro-impact discrete systems

In this work a control of the one- and two-degree-of-freedom vibro-impact systems with a delay loop is presented and analysed. The aim of the delay loop application is to make the return to the vibro-impact periodic motion after the occurrence of disturbances quicker than in the case without the loop. The proposed analytical approach yields the required delay loop coefficients. The original vibro-impact map is described which allows to solve the problem analytically for near resonance case in the one-degree-of-freedom system. The numerical calculations have supported our theoretical investigations. In addition, an efficient delay loop control applied to two-degree-of-freedom system is proposed.

J Awrejcewicz, K Tomczak

Stability of periodic motions in systems with unilateral constraints

Unilateral constraints form a vast class of restrictions which are met in mechanical engineering: it includes rigid obstacles, elastic dampers, tethers, supports, and so forth. From a physical point of view, any existing mechanical constraint is a combination of one-side ones. However, a favorite topic in text-books is the theory of (ideal) bilateral constraints, while very important in practice unilateral problems are considered in scientific journals only. The reason is a number of mathematical difficulties which are met in unilateral dynamics and which may be called discontinuities m one or another sense.Generally speaking, there exist two basic kinds of the discontinuities in finite freedom mechanical systems. First of all, due to the imposed constraints the equations of motion can have different form in different regions of the phase space. Though the right-hand sides of the equations are discontinuous, the solution curves are continuous (non-differentiable in general). Many results on dynamics of such systems were obtained by numerous authors (see [1] for review and references). The second kind is constituted with the systems which have discontinuous solution curves. These breaks are caused by the collisions of rigid bodies. Some special tricks are needed to define usual topological concepts, such as vicinity, for disconnected sets [2].To study periodic motions in discontinuous system, one should define a concept of stability (some definitions were given in [3-5]). As a rule, such concept agrees with stability of fixed point of the Poincaré map, associated with the phase flow. As far as such flow is differenti ab le, it is possible to solve the stability problem by calculating the Floquet multipliers. In this case the main difficulty is to calculate the monodromy matrix. To do it one can use formulas proposed in [6-8].In the present paper we discuss stability problem for two cases which have not been considered in detail previously. The first of them is related to visco-elastic one-side constraints, the second - to multiple ”rigid” constraints. The last case is shown to be rather singular, as in general the corresponding Poincaré map is piecewise-differentiate. Some stability conditions for such maps are obtained. They are applied to certain mechanical systems.

A P Ivanov

On the calculation of resonance oscillations of the vibro-impact systems by the averaging technique

The averaging technique is applied to calculation of resonance processes in the vibro-impact systems. In distinction from the method given in [1, 2], based on use of outcomes [3], this technique based on use some results given in [4]. The small periodic perturbations by time of conservative vibro-impact systems with one degree of freedom are considered. The theorems of existence and stability the periodic solutions are proved.

V Sh Burd, V L Krupenin

Systems with high degree of nonlinearity as vibro-impact ones - asymptotic approaches

Method of “small δ” is proposed and tested. It gives asymptotic for large n (n →) of non-linear dynamical equation with power nonlinearity Xn. Method is based on the nontrivial changing of variables and on the method “small δ” proposed by CM.Bender et aL

Igor V. Andrianov

Simulation of liquid sloshing impact in moving stractures

This paper examines the nonlinear modal interaction between liquid hydrodynamic impacting with an elastic support structure. The liquid impact is modeled based on a phenomenological concept by introducing a power nonlinearity with a higher exponent A special saw-tooth time transformation (STTT) technique is used to analytically describe the in-phase and out-of-phase strongly nonlinear periodic regimes. Based on explicit forms of analytical solutions all basic characteristics of the nonlinear free and forced response regimes such as time history, amplitude-frequency dependencies and nonlinear parametric resonance curves are estimated. The response behavior reveals that high frequency out-of-phase nonlinear mode takes place with a relatively small tank amplitude and is more stable than the in-phase oscillation mode under small perturbations. The in-phase mode has relatively large tank amplitudes and does not preserve its symmetry under the periodic parametric excitation.

V N Pilipchuk, R A Ibrahim

Exact solutions for a discrete systems undergoing free vibro-impact oscillations

Non-smooth transformations are applied to study strongly nonlinear, periodic free oscillations of a two degree-of-freedom system undergoing purely elastic vibro-impacts. The imposition of suitable boundary conditions at the instants of impacts eliminates the singularities introduced by the transformations, and the smoothened problem is solved numerically. Numerical analysis reveals vibro-impact solutions of complicated form and interesting bifurcation structures of nonlinear modes of three types. Because the system supports a reach structure of periodic motions the study was focused on solutions with periods smaller than twice the period of in phase normal mode. Higher-period solutions can be studied similarly.

L. I. Manevitch, M. A. F. Azeez, A. F. Vakakis

Asymptotic study of damped one-dimensional oscillator with close to impact potential

Dynamics of linearly damped oscillator with strongly nonlinear elastic potential is ivestigated. The description of the oscillator dynamics is provided by means of matching asymptotic expansions for strongly nonlinear and quasilinear vibrations. The quasilinear vibrations are investigated by standard methods whereas the strongly nonlinear vibrations require special asymptotics based on exactly integrable partial case. The coincidence of the results with numerical simulation data is satisfactory for any combination of the regimes.

O. V. Gendelman, L. J. Manevitch

Interaction between impulses and impacts in the nonlinear dynamics of an impacting system: a non-classical bifurcation

This work is aimed at studying a non-classical bifurcation arising in the dynamics of mechanical systems subjected to impulses and impacts. It is shown that when the impulses (which are applied at known times but at unknown positions) and the impacts (which are applied at known positions but at unknown times) synchronize, i. e., occur simultaneously, then a previously existing periodic solution is suddenly destroyed. These local bifurcations are detected analytically and it is discussed how they contribute to the determination of the overall bifurcation scenario of an investigated class of periodic subharmonic solutions. The theoretical results are illustrated and checked by some numerical simulations.

Stefano Lencif, Giuseppe Rega

Dynamics of an impact unit for percussion machines

A percussion machine impact unit has been studied as a vibro-impact system. The development of this concept involved the application of various techniques in a co-operative manner. The techniques included are periodic Green’s functions, Matlab-Simulink models and the use of laser vibrometry. The dynamic characteristics revealed by the analytical and numerical studies are compared with those found by experiments on a simple mechanical model and a laboratory model of an impact drill

S A Kember, V I Babitsky

The influence of asymmetries on the double impact oscillator dynamics

The dynamics of the double impact oscillator, as the model of a forming machine, is studied in the paper. The mechanical model is composed from two symmetrically arranged simple impact oscillators, the masses of which are periodically excited and can mutually impact. The influence of asymmetries of own frequencies and amplitudes of exciting forces in both impact oscillators is investigated. Asymmetries do not affect considerably the optimal periodic regime, which is useful for practical purposes. Results of theoretical analysis and numerical calculations are discussed.

F Peterka, O Szőllős

Dynamics of non-linear vibro-impact systems

Dynamical systems with unilateral constraints, turning on and off in their motion, have peculiarities associated with successive variation of their kinematical structure and change of their number of degrees of freedom. Description of their periodical vibrations should be performed via joint consideration of constitutive differential equations and a set of inequalities transformed into equalities at the times of impact interactions unknown in advance. So it is proposed for the system solution to introduce additional unknown variables characterizing the time values when the impacts occur and magnitudes of the velocities discontinuities. For non-linear vibro-impact systems this approach permits to transform the starting two-boundary in time problem for a system of differential equations and inequalities into the multi-boundary in time problem for differential equations without inequalities. In this case, the intermediate boundaries are displacing with the vibration intensity change and additional unknown variables variation.To construct periodical solutions to the gained systems of non-linear differential equations and to study their stability method of continuation by parameter is used jointly with Newton’s method and Liapunov’s and Floquef’s theory of stability. The approach includes sequential linearization of the equations and construction of a transfer matrix at each step of the leading parameter variation. Applied problems are solved with the use of the elaborated technique.

P. Z. Lugovoy, V. I. Gouliaev

Subharmonic response of a single-barrier vibroimpact system to a narrow-band random excitation

Sensitivity of sub harmonics to imperfect periodicity of the excitation is studied for a vibroimpact system with a single barrier, slightly offset from the system’s equilibrium position. The system is excited by a periodic force with random phase modulation, so that small random temporal variations of the excitation frequency are present, which make the force a narrow-band random process. Mean value of the excitation frequency is close to an even integer multiple of the system’s natural frequency without a barrier. Analytical study is performed, based on the Zhuravlev transformation, which effectively removes velocity jumps from the equations of motion, combined with the Krylov-Bogoliubov averaging over the period. The reduced stochastic differential equations of motion are solved then by the method of moments for the mean square response amplitude. The solution is exact for the case of zero offset and approximate, using perturbation-based moment closure scheme for the general case. The results are verified by Monte-Carlo simulation, which was used also to demonstrate possibility for incorporating moderately large impact losses through the use of previously derived equivalent viscous damping factor. The results indicate possibility for significant reduction of peak resonant amplitudes of subharmonics due to imperfect periodicity of excitation, depending on the value of the excitation/system bandwidth ratio. Applications to dynamics of moored bodies under ocean wave’s excitation are discussed

M. F. Dimentberg, D. V. Iourtchenko

Strain solitons in Solids: physics, numerics and Fracture

Nonlinear elastic features of solids result in generation of new type of elastic waves — localized strain waves (solitons) even under short-run and weak reversible (elastic) loading. Based on continuum mechanics approach, the mathematical theory of long nonlinear strain waves in elastic wave guides was developed to provide the successful generation and observation of evolution of strain solitons in a rod. It was shown both in theory and experiments that the soliton propagates along the uniform waveguide without changing of its shape, while there is an amplification of the soliton in a tapered rod.

A. M. Samsonov, G. V. Dreiden, A. V. Porubov, I. V. Semenova

Multiple impacts of a bar with external dry friction

Vibration due to impact of an elastic bar interacting with surrounding in accordance to the Coulomb dry friction law is considered. Qualitative analysis of the non-linear equations governing the problem is given. Multiple impacts of a finite and semi-infinite bars are studied.

L. V. Nikitin

Solving wave propagation problems symbolically using computer algebra

Wave propagation analysis of longitudinal impacts of rods has fascinated many famous scientists over centuries like Newton, Cauchy, Poisson and St. Venant. In this paper, it is shown that such complicated problems can be solved much more easily using computer algebra systems. As an example, the program MAPLE is used to analyze the wave propagation in a thin rod struck by a moving rigid body. Using only a few of MAPLE’s powerful commands, we can get analytical results about time responses of physical quantities such as displacements and stresses which has taken years of research in the past. It is found that some data appearing in a number of textbooks are not correct and fairly restricted. Moreover, amplitude bounds for the maximum displacements of the rod with one fixed end are presented.

B. Hu, P. Eberhard, W. Schiehlen

Stiction modeling: first order differential equation approximation for nonholonomic inequality constraint

Current trends in computational multibody dynamics address stiction between rigid bodies by using the complementarity conditions of optimization theory to develop the unilateral constraint. This paper presents an alternative Newtonian approach employing a nonhomogenous first order differential equation to approximate joint kinematics of a nonholonomic inequality constraint. A stiction algorithm is developed as a function of joint displacement, velocity and a kinematic state variable defined by the first order dynamic equation. System topology remains constant during stiction as the formulation computes proper stick-slip reaction loads. The technique is demonstrated for contacting bodies in lateral motion and offers a smooth approximation for stiction in mechanical systems analyzed by standard ODE and DAE stiff integrators.

A. P. Kovacs

Vibro-impacts induced by non-linear resonances in hertzian contacts

A single-degree-of-freedom non-linear oscillator modelling a loaded sphere-plane Hertzian contact is studied. Dynamic responses are induced by an external harmonic normal force. Non-linear resonances which lead to vibro-impact responses are investigated. Effects of the non-linear Hertzian contact stiffness and effects of some non-linear damping laws are also considered.

J. Perret-Liaudet, J. Sabot

Effect of prestressing on durability at repeated impacts

In present time, there is considerable interest in the durability of some steels and alloys loaded by repeated impacts, phenomenon known under the name of “impact fatigue” So, we can mention a lot of researches regarding the influence upon durability at impact fatigue of the dimensional factor, the shape and dimensions of stress concentrators, the impact speed, the temperature, thermal treatments. But very few studies approach the influence of prestressing on durability at impact fatigue in the light of initiation and propagation of a fatigue crackIn this way the authors made a study regarded of effect of prestressing on durability at repeated impacts, using Charpy V — notch specimens in the same bearing conditions as at a Charpy test — the impacts being applied on the opposite side of the notch.The prestressing of Charpy V notch specimen has been performed by repeated compression tests corresponding to some levels that have represented certain percentages of static compression strength.For certain values of the compression forces as well as for certain number of cycles applied there has been studied the influence of prestressing upon the durability at impact fatigue, having in view both the periods of fracture initiation and the period of propagation the crack. There has been pointed out that prestress level and the number of cycles applied have significant influence upon the periods of initiation and propagation the crack

I. Dumitru, T. Babeu, S. Babeu, L. Marşavina

Identification of damage in bars using PZT sensors and regression techniques

A methodology is developed for the identification of defects in solid bars using longitudinal stress wave propagation data in conjunction with regression techniques. For the experimental study, a series of notches of different depths are cut at a fixed acial location of bars. Longitudinal waves are generated within the bars by means of the indirect collinear impact of a surface hardened spherical steel ball on one of the plane ends of the bars. In order to prevent local plastic deformation of the bar ends and to ensure that the waves induced in the bars are plane longitudinal waves, anvils are attached to the impacted ends of the bars. PZT (lead zirconium titanate) tiles of dimensions 5 X 3 mm, which are cut from standard PZT patches of dimensions 30 X 30 mm, are bonded on the surface of the bars and used as strain sensors. It is shown that the use of PZT sensors has several advantages over the use of conventional resistance strain gauges. A regression anaylysis technique is used to relate the strain histories from the notched bars to the strain history form the defect free bar. It is shown that the technique readily indicates the presence and size of a structural defect. In particular, it is shown that the area enclosed by the regression curve increases as the defect size increases.

K. T. Feroz, S. O. Oyadiji

Laser vibrometry for impact measurements

Since the advent of the laser in the early 1960s the field of optical metrology has provided accurate experimental data in situations in which, hitherto, it would have been considered unobtainable. The vibration engineer requires a time resolved measurement of solid surface motion and in an impact situation this can cause problems for contacting transducery and may often preclude their use. This paper examines the use of laser vibrometry to provide an insitu measurement of vibration velocity when solid surfaces impact. After a brief review of the theory of the measurement the limitations of this technology are addressed before practical examples of successful measurements are provided and discussed.

N. A. Halliwell, S. A. Kember, S. J. Rothberg

On the attainable performance of shock control by visco-elastic bumper

Modern visco-elastic materials, composed of energy absorbing alloys are used widely for shock control The simplest visco-elastic bumper may provide the low-rebound and soft trim of undesirable mechanical deflections without generation of dangerous impact accelerations.In the present paper, the simplified model of a single collision of a free lumped body with the both linear and nonlinear “Kelvin-Voigt” bumper was considered. The analytical solution, describing the dynamics of impact in the linear case was obtained. The parameters of the optimal linear shock absorber along with the attainable performance were estimated.The enhancement of the capability of shock control was achieved by the use of nonlinear visco-elastic bumper. With the help of the numerical simulation it was shown that the use of the damped softening nonlinear bumper might improve the ability of the bumper to control the peak acceleration and restitution ratio. The approach to the problem of synthesis of the optimal nonlinear bumper was made.

A. M. Veprik, V. I. Babitsky

Interaction analysis of mechanical system and hydraulic impact buffer

Hydraulic impact buffers (brakes and shock absorbers) are used to damp the impulse forces afflicting the mechanical systems.

Vladimír Čech

Dynamics of the impact force generator

During the last years the interest of scientists in multibody mechanical systems in which the phenomenon of impact occurs has been still growing. Numerous investigations are carried out on the possibility of employing this phenomenon to increase the efficiency of operation of industrial machines or to eliminate those phenomena which are undesirable during machine operation. In the present paper a principle of operation of the impact force generator being an element of the rotor of the heat exchanger has been presented. Step disturbances of the rotational velocity of the rotor caused by the generator are aimed at intensification of the heat exchange process.

Barbara Błażejczyk-Okolewska, Krzysztof Czolczynski

Driver seat suspension design and identification for commercial vehicles

In commercial vehicles the secondary suspension (seat, driver’s cabin) is responsible for the driver’s comfort. The fatigue caused by long termed vibrations to which the truck driver’s are exposed, can be very severe: spinal hernia, dislocation of the spinal disks, etc. This paper reports on the results of an industrial contract work, optimizing the parameters of a pneumatically suspended seat suspension system. The design problems of the measurement system will be described. The paper introduces the parametric identification process of the seat suspension, and analyzes the measured results from point of view of the human discomfort.

I. Szepessy, I. Wahl

Two-grooved automatic nail machine

An original technological two-grooved nail production scheme has been developed, researched, and introduced to industry.

Sergei VasiIishin, Vilen Roizman

Analytical and numerical methods for the analysis of the stitch forming devices of blindstitch sewing machine

This paper presents a new approach in making models of stitch forming devices in a blindstitch sewing machine. A mathematical model of stitch forming devices is proposed. In this first part of the work a kinematical analysis using Denavit and Hartemberg’s parameters is done. This model is not unique for the sewing machine but with slight modifications could be used to make analysis ofmultibody system with the same number of bodies. An optimal model for the impact of the needle with the fabric is proposed. To solve the problem, MATLAB computational software is used.

Deltchev, Z. Tcherneva-Popova

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