Showing papers on "Dynamic Vibration Absorber published in 2005"

A shape memory alloy adaptive tuned vibration absorber: design and implementation

Abstract: In this paper a tuned vibration absorber (TVA) is realized using shape memory alloy (SMA) elements. The elastic modulus of SMA changes with temperature and this effect is exploited to develop a continuously tunable device. A TVA with beam elements is described, a simple two-degree-of-freedom model developed and the TVA characterized experimentally. The behaviour during continuous heating and cooling is examined and the TVA is seen to be continuously tunable. A change in the tuned frequency of 21.4% is observed between the cold, martensite, and hot, austenite, states. This corresponds to a change in the elastic modulus of about 47.5%, somewhat less than expected. The response time of the SMA TVA is long because of its thermal inertia. However, it is mechanically simple and has a reasonably good performance, despite the tuning parameters depending on the current in a strongly nonlinear way.

Application of voice coil motors in active dynamic vibration absorbers

Abstract: A dynamic vibration absorber reduces the influence of a force whose excitation frequency nearly coincides with the natural frequency of a rotating machine. However, the performance of this type of passive absorber can be affected by changes in the environment. In this paper, we describe a voice coil motor (VCM) that can serve as the actuator in an active dynamic vibration absorber which can be regulated for different conditions. With a VCM, suitable controllers can be designed for periodic excitation force rejection by using the characteristics of the notch filter in combination with the root-locus theorem. We have evaluated the performance of the active vibration absorber by both simulations and experiments.

Extending Den Hartog’s Vibration Absorber Technique to Multi-Degree-of-Freedom Systems

Abstract: The most common method to design tuned dynamic vibration absorbers is still that of Den Hartog, based on the principle of invariant points. However, this method is optimal only when attaching the absorber to a single-degree-of-freedom undamped main system. In the present paper, an extension of the classical Den Hartog approach to a multi-degree-of-freedom undamped main system is presented. The Sherman-Morrison matrix inversion theorem is used to obtain an expression that leads to invariant points for a multi-degree-of-freedom undamped main system. Using this expression, an analytical solution for the optimal damper value of the absorber is derived. Also, the effect of location of the absorber in the multi-degree-of-freedom system and the effect of the absorber on neighboring modes are discussed.

Vibration control using an adaptive tuned vibration absorber with a variable curvature stiffness element

Abstract: An adaptive tuned vibration absorber (ATVA) with a variable stiffness element is capable of retuning itself in response to a time-varying excitation frequency, enabling effective vibration control over a range of frequencies. One way of adjusting the stiffness is by shape change, and this paper presents the design for an ATVA that exploits this principle. The stiffness element is formed from parallel curved beams whose curvature can be adjusted and hence the stiffness can be changed in real time. The performance of a prototype ATVA with piezo-actuated curved beams is analysed and good correlation is achieved between theoretical and experimental results. The device is shown to be tunable over the frequency range 36–56 Hz, with the maximum tuned frequency being limited by inertia effects of the curved beams. The tests demonstrate the efficacy of this design in vibration control, particularly with respect to its agility in tracking rapidly varying forcing frequencies.

Real-time control of a shape memory alloy adaptive tuned vibration absorber

Abstract: The tuned vibration absorber (TVA) is a well established vibration control device. An adaptive TVA (ATVA) is one whose properties can be continuously adapted to maintain optimal tuning. This paper concerns an ATVA with shape memory alloy (SMA) elements: heating or cooling the SMA changes its elastic modulus and hence the effective stiffness and tuned frequency of the ATVA. The emphasis of this paper is placed on control algorithms for real-time adaptation of the ATVA. An error signal is defined in terms of the phase between the velocities of the ATVA mass and the host structure. Various control algorithms are discussed, including proportional, proportional-plus-derivative (PD) and fuzzy control. Discrete and continuous-time implementations are considered, together with control parameter optimization. Numerical simulations and experimental results are presented and compared. The SMA ATVA is seen to be able to adaptively re-tune in the face of a changing disturbance frequency within a fixed range, although the adaptation time is limited primarily by the thermal time constant of the system. The PD controller gives close to the optimum performance while being very simple to implement.

Designs for an adaptive tuned vibration absorber with variable shape stiffness element

Abstract: An adaptive tuned vibration absorber (ATVA) with a smart variable stiffness element is capable of retuning itself in response to a time-varying excitation frequency, enabling effective vibration control over a range of frequencies. This paper discusses novel methods of achieving variable stiffness in an ATVA by changing shape, as inspired by biological paradigms. It is shown that considerable variation in the tuned frequency can be achieved by actuating a shape change, provided that this is within the limits of the actuator. A feasible design for such an ATVA is one in which the device offers low resistance to the required shape change actuation while not being restricted to low values of the effective stiffness of the vibration absorber. Three such original designs are identified: (i) A pinned–pinned arch beam with fixed profile of slight curvature and variable preload through an adjustable natural curvature; (ii) a vibration absorber with a stiffness element formed from parallel curved beams of adjustable curvature vibrating longitudinally; (iii) a vibration absorber with a variable geometry linkage as stiffness element. The experimental results from demonstrators based on two of these designs show good correlation with the theory.

Modelling and control of friction-induced vibrations

Abstract: Friction-induced vibrations in technical applications are usually unwanted, as they create noise, diminish accuracy and increase wear. This article intends to give insight into basic excitation mechanisms of friction-induced vibrations and to show possible ways of avoidance. Excitation mechanisms under investigation are a friction characteristic decreasing with increasing relative velocity, fluctuating normal forces, non-conservative restoring forces and sprag slip. They are treated using mechanical models with up to two degrees of freedom. Analytical and numerical stability analysis as well as numerical time step integration is used to show the influence of model parameters on the excitation of friction-induced vibrations. In the second part of the article, measures to avoid friction-induced vibrations are presented and explained. Such measures are an increase in external damping, additional external excitation as well as active and passive vibration control.

Stick-Slip Behavior of Torque Converter Clutch

Abstract: The chief objective of this paper is to study the non-linear behavior of torque converter clutch within the context of an automotive drivetrain. An analytical procedure to(minimum) slip TCC [4]. The resulting stickdetermine the pure stick to stick-slip motions isexcite several vibration problems in the driveline system, developed based on the linear system analysis. This procedure can efficiently and accurately identify the frequency ranges where linear or non -linear studies are needed. Stick-slip behavior can be clearly observed as a result of the engine torque irregularity and nonlinear friction characteristics. In particular, the effect of the friction disc inertia is studied.Both analytical and numerical results show that this inertia significantly affects the system dynamics. Our predictions comparestudy the dynamic effects of stickwell with prior measurements on a passive vibration absorber experiment. INTRODUCTION Friction elements are commonly found in many mechanical and structural systems. For example, consider the automotive torque converter clutch (TCC) sub-system that consists of a fluid torque converter and in parallel a mechanical wet friction clutch as shown in Figure 1a. When the engine speed

Bi-axial seismic activation of civil engineering structures equipped with tuned liquid column dampers

Abstract: Tuned liquid column dampers (TLCD) considerably increase the effective damping of vibration prone civil engineering structures in horizontal motion. A single-degree- of-freedom (SDOF) basic system with a TLCD attached is analyzed under horizontal and vertical base excitations in order to prove its sensitivity with respect to the vertical parametrical forcing. The main result is cast in a sufficient condition for the linearized damping coefficient of the fluid motion to ensure its stability under the most critical, time harmonic forcing conditions. The output of computer simulations when varying the damping of the TLCD tuned with respect to frequency only, are verified experimentally by means of a novel model setup. The scaled Friuli 1976 earthquake is applied horizontally and vertically to an SDOF-shear frame with optimally tuned TLCD. A three-DOF-bench- mark structure, equipped with two passive TLCD in parallel connection, optimally fine-tuned in state space, is analyzed by nonlinear computer modeling. Two different relevant earthquakes are alternatively applied in both, horizontal and vertical directions. In all cases it is verified, that sealed TLCD, (with the air-spring effect taken into account) are stable, since the optimal linear damping coefficient exceeds by far the required cut-off value of parametric resonance: the vertical component of the earthquake load remains ineffective. Hence, taking into account this sufficient condition with the maximum vertical ground (floor) acceleration assigned and the maximum amplitude of the fluid motion estimated, saves the consideration of the vertical seismic activation at all.

Internal Resonance of a Nonlinear Vibration Absorber

Abstract: An approach for implementing an active nonlinear vibration absorber is presented. The strategy uses the saturation phenomenon that is exhibited by multi-degree-of-freedom systems with cubic nonlinearities possessing one-to-one internal resonance. The proposed technique consists of introducing a second-order controller and coupling it to the plant through a sensor and an actuator, where both the feedback and control signals are cubic. Once the structure is forced near its resonances, the oscillatory response is suppressed through the saturation phenomenon. We present theoretical results of the application of the proposed vibration absorber. The structure consists of a cantilever beam, the feedback signal is generated by a strain gage, and the actuation is achieved through piezoceramic patches. The equations of motion are developed and analyzed through perturbation techniques and numerical simulation. We use the method of multiple scales to obtain an approximate solution of these equations and investigate the vibration stability. There are two cases of fixed points. In the first case, the response amplitude is symmetric about the origin and divided into two branches with increasing magnitudes for decreasing and increasing the natural frequency ω and the coefficient of external excitation f respectively. In the second case, the response amplitudes are symmetric about the origin for variation of all parameters but the symmetry disappeared for increasing detuning parameter σ.

Vibratory pile driver/extractor with two-stage vibration/tension load suppressor

Abstract: A method and apparatus for driving and extracting piles that includes a vibration/tension load absorber assembly mounted between a housing and the vibratory unit which includes shear-type vibration absorbers connected between the housing and the vibratory unit and operating in combination with at least one compression-type vibration absorber positioned to be compressed between first and second compression plates when the tension load reaches a predetermined level.

Forced vibration response of thin plate with attached discrete dynamic absorbers

Abstract: Forced vibration response of a rectangular thin plate with single discrete mass and patch placed at the centre of plate has been determined using finite element method. The effects of varying thickness or area of patch on the dynamic vibration absorption has been analysed. Results show that single discrete mass/patch at the centre of the plate may act as dynamic vibration absorbers over certain frequency range. Simply increasing the weights of discrete mass/patch does not improve the vibration absorption over the entire frequency range of 0–1000 Hz. Further, a few discrete masses are better than discrete patches for vibration absorption over the entire frequency range. Also, there is optimal weight of the discrete mass for which vibration absorption is optimum. There exists optimal thickness of patch for a given area as well as an optimal area of patch for a given thickness, for which patches behave optimally as dynamic vibration absorbers.

Improving robustness of tuned vibration absorbers using shape memory alloys

Abstract: A conventional passive tuned vibration absorber (TVA) is effective when it is precisely tuned to the frequency of a vibration mode; otherwise, it may amplify the vibrations of the primary system. In many applications, the frequency often changes over time. For example, adding or subtracting external mass on the existing primary system results in changes in the system’s natural frequency. The frequency changes of the primary system can significantly degrade the performance of TVA. To cope with this problem, many alternative TVAs (such as semiactive, adaptive, and active TVAs) have been studied. As another alternative, this paper investigates the use of Shape Memory Alloys (SMAs) in passive TVAs in order to improve the robustness of the TVAs subject to mass change in the primary system. The proposed SMA-TVA employs SMA wires, which exhibit variable stiffness, as the spring element of the TVA. This allows us to tune effective stiffness of the TVA to adapt to the changes in the primary system's natural frequency. The simulation model, presented in this paper, contains the dynamics of the TVA along with the SMA wire model that includes phase transformation, heat transfer, and the constitutive relations. Additionally, a PID controller is included for regulating the applied voltage to the SMA wires in order to maintain the desired stiffness. The robustness analysis is then performed on both the SMA-TVA and the equivalent passive TVA. For our robustness analysis, the mass of the primary system is varied by ± 30% of its nominal mass. The simulation results show that the SMA-TVA is more robust than the equivalent passive TVA in reducing peak vibrations in the primary system subject to change of its mass.

Order-Tuned Vibration Absorbers for Cyclic Rotating Flexible Structures

Abstract: This paper investigates the use of order-tuned absorbers to attenuate vibrations of flexible blades in a bladed disk assembly subjected to engine order excitation. The blades are modeled by a cyclic chain of N oscillators, and a single vibration absorber is fitted to each blade. These absorbers exploit the centrifugal field arising from rotation so that they are tuned to a given order of rotation, rather than to a fixed frequency. A standard change of coordinates based on the cyclic symmetry of the system essentially decouples the governing equations of motion, yielding a closed form solution for the steady-state response of the overall system. These results show that optimal reduction of blade vibrations is achieved by tuning the absorbers to the excitation order n, but that the resulting system is highly sensitive to small perturbations. Intentional detuning (meaning that the absorbers are slightly over- or under-tuned relative to n) can be implemented to improve the robustness of the design. It is shown that by slightly undertuning the absorbers there are no system resonances near the excitation order of interest and that the resulting system is robust to mistuning (i.e., small random uncertainties in the system parameters) of the absorbers and/or blades. These results offer a basic understanding of the dynamics of a bladed disk assembly fitted with order-tuned vibration absorbers, and serve as a first step to the investigation of more realistic models, where, for example, imperfections and nonlinear effects are considered, and multi-DOF and general-path absorbers are employed.Copyright © 2005 by ASME

Broad-band Viscoelastic Rotational Vibration Control for Remote Sensing Applications

Abstract: The ability to eliminate, or effectively control, vibration in remote sensing applications is critical Any perturbations of an imaging system are greatly magnified over the hundreds of kilometers from the orbiting space platform to the Earth's surface Space platforms, such as the International Space Station, are not as predictable or stable as many other spacecraft Therefore, an effective vibration isolation and/or absorber system is needed that operates over a wide range of excitation frequencies A passive system is also preferred to reduce the resources required, as well as to provide a reliable and self-contained system To accomplish these goals, a vibration amplitude limiting system has been developed that uses both vibration isolation and absorber components Viscoelastic structural elements that act as both a spring and a damper in a single element are implemented in the design This configuration also demonstrates a favorable frequencydependent response and produces a system with improved dyna

Planar vibration absorber

Abstract: A tuned mass damper for attenuating vibrations in a selected plane of a mechanical structure, by magnetically induced eddy current damping. A moving damper mass is coupled to a vibrating mass through one or more flexures that confine relative movement of the damper mass substantially to the selected plane. A magnet structure is rigidly attached to either the vibrating mass or the damper mass, and a conductor plate is attached to the other of these masses. Movement of the damper mass relative to the vibrating mass induces eddy currents in the conductor plate and thereby generates a damping force that attenuates vibration in the selected plane.

Comparison of two auto-tuning methods for a variable stiffness vibration absorber

Abstract: A tunable vibration absorber is developed and its stiffness can be varied on-line. The absorber system is mounted on a clamped-clamped beam acting as a primary system. The objective is to suppress vibration of the primary beam subject to a harmonic excitation whose frequency may vary. A system modeling is conducted. The frequency response of the system is given to show the operating range of the absorber system. Using a simplified two-degree-of-freedom model, two auto-tuning methods are studied. The methods differ in the way of how to identify the exciting frequency. The first method follows a common practice that uses the frequency of the maximum peak in the response spectrum as the exciting frequency. The second method makes use of information of both the response spectrum and the natural frequencies. An experimental study is conducted to compare the two methods. The study has shown that the second method performs better than the first method in terms of frequency tracking ability and robustness to dist...

Inkjet recording head having dynamic vibration absorber

Abstract: An inkjet recording head includes a base member, an ink channel unit, a plurality of piezoelectric elements, and a dynamic vibration absorber. The ink channel unit is formed with a plurality of nozzle holes and a plurality of ink pressure chambers. The ink channel unit includes a diaphragm that defines part of each ink pressure chamber. Each piezoelectric element has one end fixed to the base member and another end attached to the diaphragm. Each piezoelectric element generates displacement in a displacement direction for deforming the diaphragm to eject ink droplets through a corresponding one of the plurality of nozzle holes. The dynamic vibration absorber is mounted on the base member for damping vibrations of the base member due to a resonance, the resonance occurring in a frequency range less than or equal to a predetermined frequency.

Electronic apparatus having a vibration absorber

Abstract: An optical access apparatus is provided. The optical access apparatus includes a mounting plate, characterized in that the mounting plate has a bent portion acting as a balance plate of the optical access apparatus.

Vibration absorber with dynamic damper

Abstract: In an engine mount (A) whose axis (X) is oriented in the front to rear direction of a vehicle, a damper weight ( 12 ) is embedded within a toroidal stopper rubber ( 10 ) fixed at its inner periphery to the rear end of an inner cylinder ( 2 ). The damper weight ( 12 ) is made of, for example, steel plate to have a spiral form and placed to surround the inner cylinder ( 2 ), thereby itself functioning as a spring in the direction of the axis (X). This structure can ensure a necessary mass for the damper weight while saving space, and prevent the occurrence of an uncomfortable shock when a stopper works.

Robust Design Method of Multi Dynamic Vibration Absorber

Abstract: To improve the vibration control performance of dynamic vibration absorber (DVA), various multi dynamic vibration absorbers have been introduced for several years. Although the multi DVAs are better than single-mass DVA in vibration control performance with the same mass ratio, their vibration control effects are also very sensitive to the change of natural frequency of the controlled object same with single-mass DVA. In this paper, a new robust optimal design method has been proposed for improving the robustness of multi DVAs in vibration control performance. Optimal parameters of the two-series-mass DVA, two-parallel-mass DVA and four-parallel-mass DVA have been calculated and optimal design diagrams and approximate formulas are conducted. Robustness of vibration control performance is analyzed with the simulation and experiment. The results show the robust design method is better than conventional compliance optimal design method in robustness of vibration control performance.