Showing papers on "Dynamic Vibration Absorber published in 2003"

A broadband controller for shunt piezoelectric damping of structural vibration

Abstract: In this paper a broadband active shunt technique for controlling vibration in piezoelectric laminated structures is proposed. The effect of the negative capacitance controller is studied theoretically and then validated experimentally on a piezoelectric laminated simply supported plate. The 'negative capacitance controller' is similar in nature to passive shunt damping techniques, as a single piezoelectric transducer is used to dampen multiple modes. While achieving comparable performance to that of the passive shunt schemes, the negative capacitance controller has a number of advantages. It is simpler to implement, less sensitive to environmental variations and can be considered as a broadband vibration absorber.

Energy-Recycling Semi-Active Method for Vibration Suppression with Piezoelectric Transducers

Abstract: *A novel energy-recycling method is studied that enables effective semi-active vibration suppression with piezoelectric transducers embedded or bonded to a structure. In this method, the energy converted from the mechanical energy of a vibrating structure is collected in the capacitor of a piezoelectric transducer as an electric charge, and to suppress vibration, rather than dissipate the energy, the polarity of the charge is changed according to the state of vibration. With this method, no energy is supplied to the total system of the structure and transducers with shunt circuit, which means that the system is stable. A simple electric circuit and a control law for multiple-degree-offreedom systems with multiple piezoelectric transducers are proposed for this method based on energy recycling. Numerical simulation of vibration suppression of a truss structure shows that this method is more effective in suppressing vibration than both a semi-active method without energy-recycling and that based on the use of an optimally tuned passive system. A preliminary experiment with a truss structure also shows that this method can effectively suppress vibration in an actual structure. However, there was some discrepancy in the experimental results compared to the results of the numerical simulation performed assuming ideal linear characteristics of the piezoelectric transducers estimated from a static test. Nomenclature

Properties of a magnetorheological semi-active vibration absorber

Abstract: A tuned vibration absorber (TVA) is a spring-damper-mass system used in many industries for the suppression of a specific vibration frequency. A state-switched absorber (SSA) is similar to a TVA, except that one or more components in the SSA is able to instantaneously and discretely change properties, thus increasing the effective bandwidth of vibration suppression. The components responsible for bandwidth increase are called switching elements. In order to design a replacement SSA for the classic TVA, the SSA must operate in the appropriate frequency range, be lightweight and compact. An optimal SSA will also have a maximal frequency range that it can switch between. This paper discusses the development of a magnetorheological (MR) silicone gel used as the SSA switching element, the SSA geometry selected to maintain a magnetic flux path, and the contribution of the magnet-mass to frequency shifting. The MR gel is iron-doped silicone, cured in the presence of a magnetic field. During operation, the applied magnetic flux is modified to change the natural frequency. Since a flux path through the switching element is required, a steel flux path was incorporated as part of the SSA design. The SSA is desgined to operate below 100 Hz. An MR elastometer with 35% iron by volume yielded the most tunable results, where the minimum natural frequency was found to be 45 Hz, and the natural frequency was tunable up to 183 Hz.

Passively minimizing structural sound radiation using shunted piezoelectric materials.

Abstract: Two methods are presented to determine optimal inductance and resistance values of the shunt circuit across a piezoceramic material, which is bonded to a simply supported plate in order to minimize sound radiation from the plate. The first method (DH) makes use of den Hartog's damped vibration absorber principle. The second method (SM) uses the Sherman Morrison matrix inversion theorem. The effectiveness of each method is compared with regard to minimizing total acoustic sound-power radiation and acoustic pressure at a point. Optimization algorithms and case studies are presented using a linearized model for the piezoceramic and using a nonlinear model for the piezoceramic that accounts for the inherent dielectric hysteresis. Case studies demonstrate that the second method (SM) results in superior performance, under both linear and nonlinear system assumptions. Studies also illustrate that, if the nonlinearity in the system is significant, it must be incorporated in the optimization process.

Modeling the Bifilar Pendulum Using Nonlinear, Flexible Multibody Dynamics

Abstract: This paper deals with the modeling of the bifilar pendulum, a hub-mounted self-tuning vibration absorber used on certain rotorcraft. The bifilar consists of a tuning mass that acts as a pendulum and is connected to a support frame by means of two cylindrical tuning pins. The tuning pins roll without sliding on curves of cycloidal shape machined into the tracking holes on the support frame and tuning mass. In this work, a detailed model of this device is presented, which involves nonlinear holonomic and nonholonomic constraints. The formulation is developed within the framework of finite element based dynamic analysis of nonlinear, flexible multibody systems, and features energy preserving and decaying time integration schemes that provide unconditional stability for nonlinear systems. Numerical examples are presented that demonstrate the efficiency and accuracy of the proposed approach.

On the need for control of nonlinear oscillations in machine systems

Abstract: Oscillations in machines are invariably nonlinear. This is either because of inertial coupling effects between different motions of the moving components, material and constitutive phenomena giving rise to stiffness modifications, nonlinear dissipation mechanisms, large deflections, or, as is most likely, some sort of combination of all of these. The net effect of nonlinear vibrations is that at best the machine may well behave a little differently from the way the designer intended, or at worst, in a manner which renders it completely unsuitable for the job. The extent of such problems depends on the nature and the scale of the nonlinearities that are present but it is safe to say that nonlinear oscillations can rarely be completely overlooked in precision machinery analysis and design. The unifying theme in this paper is pendulum motion, firstly in the case of a mobile gantry crane for container stacking where we wish to minimise such motion and converge on a target, and then secondly in the case of a vibration absorber in which we choose to initiate pendulum motion within a special absorber, for the purposes of vibration minimisation. The third example involves the potential for pendulum motion at a very much larger scale and summarises the main control problem that is likely to be encountered in a fully deployed momentum exchange propulsion tether operating in space. The paper discusses the general mathematical issues that pertain to pendulum motion in each of the three cases. This motion is investigated initially in the context of the mobile gantry crane, in the form of a basic three dimensional dynamical model. A feedback linearised controller is shown to offer some advantages for the control of such a system and then a simulation based on data from a practical implementation of this within a real-time control system on a 1/10 laboratory scale model is discussed. It is recalled that the real-time effectiveness of the controller can be compromised by relatively slow sensing and data logging hardware but that despite this some useful performance gains can still be obtainable using this sort of control strategy. The second example comprises an autoparametric vibration absorber and here it is shown how even a simple hunting controller can exploit the mode-locking and wide detuning region effects inherent in autoparametric systems. Further experimental results are discussed in the case of a hunting controller for detuning a vertically oriented parametrically excited pendulum in order to exploit and enhance the powerful and persistent absorption available during autoparametric interaction. The paper concludes with a summary review of the third problem in which the theoretical attitude dynamics of a motorised momentum exchange space propulsion tether are summarised and it is shown that they need to be controlled for reliable and optimal payload velocity boost from both circular parking orbits and elliptical transfer orbits about the Earth.

Damping Effects on the State-Switched Absorber Used for Vibration Suppression:

Abstract: A state-switched device is conceptually capable of instantaneously changing its mass, stiffness, or damping. Such a device will exhibit different dynamical response properties (modes and resonance frequencies) depending on its current state. A state-switched vibration absorber exploits the state-switching concept for the purposes of enhanced vibration suppression. Between each state switch, it is fundamentally a passive vibration absorber, but one which exhibits a different tuning frequency for each possible state. A state-switched vibration absorber therefore has a greater effective bandwidth than a classical passive absorber. This paper considers the role of damping in the state-switching concept for a simple one-degree of freedom system and for a two-degree of freedom system. Certain values of damping in the system improve performance, while other values hinder the performance of the state-switched absorber, as compared to classical absorbers. The predicted performance of the system also depends upon t...

Double adjustable shock absorbers utilising electrorheological and magnetorheological fluids

Abstract: Double adjustable shock absorbers allow for independent adjustment of the yield force and post-yield damping in the force versus velocity response. To emulate the performance of a conventional double adjustable shock absorber, an electrorheological (ER) and magnetorheological (MR) automotive shock absorber were designed and fabricated at the University of Maryland. For the ER shock absorber, an applied electric field between two tubular electrodes, located in the piston head, increases the force required for a given piston rod velocity. For the MR shock absorber, an applied magnetic field between the core and flux return increases the force required for a given piston rod velocity. For each shock absorber, two different shaped gaps meet the controllable performance requirements of a double adjustable shock absorber. A uniform gap allows for control of the yield force of the shock absorber, while a nonuniform gap allows for control of the post-yield damping. Force measurements from sinusoidal displacement cycles, recorded on a mechanical damper dynamometer, validate the performance of uniform and non-uniform gaps for adjustment of the yield force and post-yield damping, respectively.

Experimental and Numerical Analysis of a Nonlinear Vibration Absorber for the Control of Plate Vibrations

Abstract: We investigate a nonlinear active vibration absorber to control the vibrations of plates. The absorber is based on the saturation phenomenon associated with dynamical systems with quadratic nonline...

Vibration absorber assembly

Abstract: A vibration absorber assembly including a disc shaped housing having a central rotational axis and a plurality of radially elongated cavities, and a plurality of movable masses, each movable mass being housed in, and movable within, one of the plurality of radially elongated cavities. The plurality of movable masses are movable in the plurality of radially elongated cavities to absorb torsional vibration, and/or alter moment of inertia of the vibration absorber assembly.

Self-tuning vibration absorber system and method of absorbing varying frequency vehicle vibrations

Abstract: A system and method for absorbing vehicle body vibrations is described. The mechanical self-tuning vibration absorber system is utilized to absorb a body vibration with a varying frequency. In a particular application the absorber system provides for absorbing varying frequency vibrations of a helicopter aircraft body. The vibration absorber system utilizes asymmetrical damping to tune the resonant frequency of the system.

Performance comparison of vehicle suspensions featuring two different electrorheological shock absorbers

Abstract: This paper proposes a novel type of semi-active electrorheological (ER) shock absorber for a small-sized passenger vehicle. The field-dependent damping forces of the proposed orifice type of ER shock absorber are experimentally evaluated and compared with those of a conventional cylinder type of ER shock absorber. The governing equations of motion for a vehicle suspension system equipped with ER shock absorbers are derived and an optimal controller is designed to attenuate vibration due to bump and random road excitations. Control responses such as vertical acceleration of the vehicle body are evaluated in time and frequency domains, and comparative work is done between the orifice type and cylinder type of ER shock absorbers.

Vibration-proof tool holder

Abstract: PROBLEM TO BE SOLVED: To provide a vibration-proof tool holder capable of suppressing chatter vibration and highly precisely machining. SOLUTION: The tool holder for mounting a boring tool, a milling tool or the like at the tip has a dynamic vibration absorber formed inside a weight supported by a viscoelastic substance or the like. A hole of a body and the weight are tapered, and the cross-sectional area becomes larger as closer to the tip of the tool holder. Thus, a rigidity of the tool holder body is improved while the volume of the weight is increased. The viscoelastic substance supporting the weight has its spring constant variable by preload, thereby enabling the properties of the dynamic vibration absorber to be controlled. COPYRIGHT: (C)2005,JPO&NCIPI

直列二重動吸振器の最適設計と制振効果(機械力学,計測,自動制御)

Abstract: The multiplication of Dynamic Vibration Absorbers (DVAs) has been studied for several years to improve its performance. However, the optimal regulation of DVA becomes practically difficult for increasing of number of DVAs. In this paper, two-series-mass DVA has been studied to improve vibration control performance and regulation easily. The optimal parameters of two-series-mass DVA have been calculated from compliance optimization, accelerance optimization and mobility optimization, so that optimal design diagrams and approximately formulas shall be conducted. The performance of vibration control is analyzed through the simulation and experiment. The results show that the two-series-mass DVA improves its performance, in the same total mass ratio, by about 20% than the one-mass DVA, and also it shows better results than even the four-parallel-mass DVA.

Vibration absorber, and vibration control structure using the same

Abstract: A vibration absorber (7) comprises a hollow outside long-sized body (21) in the form of a cylindrical member, a hollow inside long-sized body (22) also in the form of a cylindrical member, a viscous body (26) disposed in a cylindrical clearance (25) defined between the inner surface (23) and outer surface (24) of these long-sized bodies (21, 22) so that the viscous body is in contact with the inner and outer surfaces (23, 24) of these long-sized bodies (21, 22), rectangular attaching plate members (31, 32) respectively fixed to the other end (29) of the long-sized body (21), which has one end (28) on the side of an open end (27), on the closed side in the axial direction (X), and to one end (30) of the long-sized body (22) on the closed side, and a holding means (33) for holding the clearance (25) between the inner surface (23) of the long-sized body (21) at one end (28) of the long-sized body (21) and the outer surface (24) of the long-sized body (22).

Design and analysis of high-frequency periodically layered isolators for helicopter gearbox isolation

Abstract: Vibration generation by meshing gear pairs is a significant source of vibration and cabin noise in rotorcraft transmissions. This tonal, high-frequency gearbox noise (500 Hz – 2000 Hz) is primarily transmitted to the fuselage through rigid connections, which do not appreciably attenuate vibratory energy. Because periodically-layered elastomer and metal isolators exhibit transmissibility “stop bands”, or frequency ranges in which there is very low transmissibility, they may provide an elegant passive vibration control solution. Realistic design constraints associated with helicopter gearbox isolator mass, axial stiffness, and elastomeric fatigue are estimated. An optimization routine is then used in concert with design constraints and an axisymmetric isolator model to determine layered isolator passive performance limits. The optimization results suggest that layered isolators cannot always be designed to meet target frequencies given a certain set of constraints. Therefore, passive performance enhancements to layered isolators are considered. The use of embedded fluid elements in the metal layers results in a combination of advantageous performance benefits, including motion amplification and vibration absorber effects. The enhanced layered isolators are capable of passively providing broadband noise attenuation, as well as dramatic attenuation at discrete problematic tones. INTRODUCTION Dynamically-tuned flexible mounts are frequently used for passive isolation of mechanical components subject to vibration. Elastomeric materials are incorporated into many mounts to provide a combination of low stiffness and moderate damping. Typical isolation mounts are designed to attenuate motion or force at low frequencies, usually below 100 Hz. The principles of vibration isolation in this frequency range are well understood. Elastomeric mounts employed for low frequency isolation may be simultaneously subjected to higher-frequency, machine-generated vibro-acoustic energy. Standard isolation techniques, however, may not be appropriate for forcing frequencies much higher than the fundamental system frequency, due to the presence of wave effects. Wave effects occur at high frequencies when the elasticity and the distributed mass of the mount interact to create sharp transmissibility peaks (Ref. 1). Refs. 2 and 3 report that periodically-layered metallic and elastomeric mounts are potential attenuators of dynamic stresses at high frequencies. The impedance difference between layers is the attenuation mechanism, in which an incident wave is scattered and essentially split into a reflected and refracted wave (Ref. 4). The device becomes increasingly effective with a larger impedance mismatch between the isolator materials. A one-dimensional analysis of periodicallylayered isolators in compression is presented in reference (Ref. 4). Motivation for the research effort was isolation of reactor components and structures from seismic, impact, or other accident-induced loads. A time-domain solution was obtained for plane stress 44th AIAA/ASME/ASCE/AHS Structures, Structural Dynamics, and Materials Confere 7-10 April 2003, Norfolk, Virginia AIAA 2003-1784 Copyright © 2003 by Joseph Szefi. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. 2 American Institute of Aeronautics and Astronautics wave excitation through layered composites. The analysis makes use of continuity of stress and displacement at the layer interfaces. Plane longitudinal stress waves with particular wavelengths are attenuated in periodically-layered elastic mounts, whereas no attenuation is exhibited by an undamped homogeneous elastic medium. A one-dimensional analysis of layered isolators, based on the theory of shear waves in infinite, periodically layered media is presented in Refs. 2 and 3. Floquet theory is used to solve the equations for the propagation of plane waves through a laminated system of parallel plates. The plates consist of two alternating materials, and the direction of propagation is normal to the plates. The theory predicts high frequency “stop bands” within which vibratory energy is attenuated. The analysis includes a method for predicting the beginning and end frequencies of stop bands. Thus, the layered isolator behaves as a mechanical notch filter. The existence of the predicted stop bands was corroborated by testing of layered specimens in shear. The test specimens were of finite length, and therefore edge effects and reflections from the top and bottom layers were observed in the experiment. These effects, however, did not obscure the basic physical phenomenon of stop bands. The effects of three-dimensional elasticity on periodically layered isolators in compression were examined in Ref. 5. A detailed finite element analysis of periodically layered isolators was conducted to gain an improved understanding of three-dimensional effects on isolator performance. The isolator models consisted of alternating, cylindrical layers of elastomer and metal. Axisymmetric solid elements were used to model each layer of cylindrical isolators. Each element had eight nodes and forty-eight degrees of freedom. The first four mode shapes of a typical three-celled isolator are shown in Figure 1, where a cell is a single elastomer and metal layer combination. The mode shapes of the isolator were then examined (Refs. 5, 6). For an isolator with n cells, there are (n-1) isolator modes below the beginning of the stop band. The stop band frequency range begins at the n isolator mode and continues until the (n+1) isolator mode. In the first n modes, each elastomer layer associated with these frequencies undergoes approximately uniform axial strain. In fact, the metal layers behave essentially like n discrete masses supported by n axial springs in series. Invariably, in the first mode, every elastomer layer exhibits either uniform tension or compression. In the next (n-1) modes, the mode shapes of the individual layers are observed to contain different combinations of layerwise compression and tension. The (n+1) mode (e.g., mode 4 in Figure 1) is the first mode in which an elastomer layer exhibits a ‘thickness’ mode. Physically, this mode involves both tension and compression within the elastomer layer and minimal net axial motion of the constraining metal layers. This mode is associated with the end of the stop band frequency range. The first three modes in Figure 1 also exhibit significant lateral motion of the middle of each elastomer layer. This is due to fact that the upper and lower surfaces of each layer are constrained and that elastomeric materials are nearly incompressible. Consequently, the effective three-dimensional stiffness of each layer differs from that predicted by onedimensional theory, which only addresses axial motion. Figure 1. First four axisymmetric mode shapes of a cylindrical three-celled isolator in compression. Stop Band Mode 1 Mode 2 Mode 3 Mode 4

Dynamic vibration absorber

Abstract: PROBLEM TO BE SOLVED: To provide a dynamic vibration absorber with relatively simple setting of parameters, and in which a large vibration restricting effect to a subject structure. SOLUTION: The subject structure (of a mass M) is supported through a spring (of a spring constant K) and a damper (of a damping coefficient C) to the ground vibratablein a vertical direction (with a displacement x). A first additive mass body (of a mass m1) is supported through a spring (of a spring constant k1) and a damper (of a damping coefficient c1) to the subject structure in a vibratable state ain a vertical direction (with a displacement y1). A second additive mass body (of a mass m2) is supported through a spring (of a spring constant k2) and a damper (of a damping coefficient c2) to the first additive mass body in a vibratable state in a vertical direction (with a displacement y2). Where natural frequencies of the subject structure, the first additive mass body, and the second additive mass, in the vertical direction, as sole systems, are respectively referred to as f M , f m1 , f m2 , then they are set to satisfy f m1 >f M and f m2 M . COPYRIGHT: (C)2004,JPO&NCIPI

Motor-driven road vehicle for improving driving economic efficiency has vibration absorbers fitted between wheel axles and a vehicle's structure or other parts moving in relation to each other

Abstract: A steering stub axle (12) supports a vehicle wheel's (10) axles (11). Fitted like a conventional hydraulic telescopic shock absorber between a fastening device (13) on a vehicle's structure and the steering stub axle, a vibration absorber (20) has a piston (22) that slides on-axis in a guide cylinder (21) and links to a piston rod (23).

Experimental evaluation of magnetorheological dampers for semi-active tuned vibration absorbers

Abstract: The main purpose of this study is to experimentally evaluate the dynamic performance of a semi-active Tuned Vibration Absorber (TVA) with a Magneto-Rheological (MR) damper. To this end, a test apparatus was built to represent a two-degree-of-freedom primary structure model coupled with a MR TVA. The primary structure mass, which is modeled with steel plates, was excited by a hydraulic actuator through four air springs. The air springs represent the stiffness of the primary structure and offer the ability to change the stiffness. The semi-active TVA consists of a steel plate, a MR damper, and four coil springs for physical representation of the mass, the damping element, and the stiffness of the TVA, respectively. Mounted on top of the primary structure, the TVA is connected to the primary structure plates by hardened linear bearing shafts. A series of transducers along with a data acquisition system was used to collect sensory information and implement real time control of the MR TVA. Using this test rig setup, a parametric study was performed to analyze the dynamics of the semi-active TVA and to compare the performance of the semi-active TVA with a passive TVA. Displacement based on-off groundhook (on-off DBG) control was used as the control policy for the semi-active TVA. In the parametric study, the effects of on/off-state damping of the MR damper were investigated and compared with a passive TVA to analyze the relative benefits of a semi-active TVA. When damping increased in the passive TVA, the two resonant peaks merge into one peak, and the peak grows. This indicates that the primary structure and TVA are linked together, disabling the TVA, and it eventually magnifies the vibrations. For a semi-active TVA, however, the two resonant peaks decrease as on-state damping increases (keeping low off-state damping), indicating reduction of vibrations. It is shown that semi-active TVAs outperform passive TVAs in reducing the peak transmissibility, implying that semi-active TVAs are more effective in reducing the vibrations of the primary structure.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Roll, in particular middle roll of a calendar, and calendar

Abstract: Roll and calender including the roll that includes a roll jacket structured and arranged to surround an interior space. Roll also includes an absorber arrangement having at least one passive vibration absorber located within the interior space. The instant abstract is neither intended to define the invention disclosed in this specification nor intended to limit the scope of the invention in any way.

Output regulation of robot manipulators with a constantly revolving arm

Abstract: This paper presents analysis and experiment results on regulation of a two-link robot with a constantly revolving arm. The rotating member imposes a harmonic excitation on the system. A control algorithm inspired by passive dynamic vibration absorber is devised to turn the base link to a target position asymptotically. The displacement of the base link is the only state variable required in the feedback loop. Asymptotic stability is proved using a tool based on the center manifold theory. Real-time experiments are conducted to verify the performance of the proposed method.

Dynamic response in the low-khz range and delta-e effect in ferromagnetic shape memory ni-mn-ga

Abstract: Recent work on ferromagnetic shape memory nickel-manganese-gallium (Ni-Mn-Ga) has demonstrated several characteristics which make this material attractive as an active element for the next generation of intelligent transducers. Alloys of martensitic Ni-Mn-Ga can strain up to 6% as a result of the rotation of twin variants and associated twin boundary motion which occur in these materials in response to magnetic fields. The magnetic actuation holds promise in transducer design because it can lead to enhanced frequency response compared with shape memory alloys with comparable strains. In this paper, we report on experimental measurements collected from a Ni50 Mn28.7 Ga21.3 sample which has been tested in a solenoid transducer by means of a novel drive configuration consisting of a collinear uniaxial field-uniaxial stress pair. We have observed that the elastic modulus of a Ni-Mn-Ga sample driven in these conditions changes substantially in response to varying bias field. In this paper, we further investigate the dependence of the elastic modulus on ac field intensity and mechanical load as well as bias field. Quasistatic, white noise, and swept-sine excitations were employed to examine the behavior of Ni50 Mn28.7 Ga21.3 driven under various combinations of magnetic fields and mechanical loads. Mechanically free quasi-static tests demonstrate reversible strains of 6300 μe which are consistent with prior measurements on samples with similar composition near the Heusler stoichiometry. Dynamic measurements reveal a significant stiffness increase, of up to 209%, with dc bias field. This frequency shift or ΔE effect is shown to originate in the Ni-Mn-Ga sample and is believed to stem from the reorientation of twin variants in response to varying dc field. These results might facilitate a new class of solenoid-based Ni-Mn-Ga transducers for tunable vibration absorber applications, and lay the ground work for developing methods and criteria for the implementation of broadband Ni-Mn-Ga transducer technologies.Copyright © 2003 by ASME

Torsional dynamic tuned absorber for vehicle steering system

Abstract: A vibration absorber for a vehicle steering system that suppresses torsional vibrations that would otherwise be felt by a driver holding the steering wheel. At least two energy absorbing units are mounted to a steering shaft at locations equidistant from the shaft's axis of rotation. The energy absorbing units may be attached to the spokes of the steering wheel, and are preferably located at diametrically opposite positions on the steering wheel so that they do not adversely affect the balance of the wheel as it is turned. Each energy absorbing unit comprises a mass supported for reciprocal movement along a path of movement perpendicular to a radius of the steering shaft and at least one kinetic energy absorption device acting on the mass along the path of movement. A case houses the mass and kinetic energy absorption device, and a rod is supported at either end by the case and passes through a hole in the mass to guide the mass along the path of movement. The kinetic energy absorption device preferably comprises two coil springs, one located on either side of the mass and encircling the rod. Secondary springs are disposed on opposite sides of the mass along the path of movement and are spaced from the mass by a distance such that the mass contacts the secondary springs when the mass has moved a predetermined distance from a neutral position. The secondary springs serve as travel stops and apply a progressing centering force to the mass when it nears the limits of its movement, thereby producing a dual-rate spring effect to improve the vibration absorbing performance of the absorber units.