Showing papers on "Active vibration control published in 1993"

Active Vibration Control of Laminated Composite Plates Using Piezoelectric Devices: A Finite Element Approach

Abstract: A finite element formulation is presented for modeling the behavior of laminated composites with integrated piezoelectric sensors and actuators. This model is valid for both con tinuous and segmented piezoelectric elements that can be either surface bonded or embedded in the laminated plate. The present model takes into account the mass and the stiffness of the piezoelectric patches. The formulation is based on the first-order shear deformation theory, which is applicable for both thin and moderately thick plates. An additional feature of the present model is that it does not introduce the voltage as an additional degree of freedom. The charge/current generated by the sensor and the response of the plate to an actuator voltage can be computed independently. These features are then coupled with a constant-gain negative-velocity/positive-position feedback control algorithm to actively control the transient response of the plate in a closed loop. Numerical results are presented which indicate the increase in...

Active vibration control system for attenuating engine generated vibrations in a vehicle

Abstract: An active vibration control (AVC) system is disclosed for attenuating vibrational frequency components generated by an engine and transferred through an engine mounting unit to vibrate a motor vehicle body. The motor vehicle is characterized by sprung mass and unsprung mass natural resonant frequencies at which the body also vibrates when the vehicle is driven over an undulating road surface. The AVC system operates by generating input signals representing different vibrational frequency components generated by the engine based upon sensed changes in engine rotation. Each input signal is filtered by an adaptive filter to produce a respective output signal. The output signals are summed to produce a canceling signal for driving an inertial mass shaker mounted on the body. The shaker inversely vibrates the body with respect to the different vibrational frequency components transferred to the body from the engine. A vibration sensor mounted to the body proximate the shaker monitors body vibration and develops a representative error signal. Vibrational components associated with the sprung and unsprung mass natural resonant frequencies are substantially removed from the error signal using a dual notch filter. The filtered error signal is then used to adjust the filtering characteristics of the adaptive filter to minimize vibration of the body caused by the different vibrational frequency components transferred to the body from the engine.

Active Vibration Control of the Axially Moving String by Wave Cancellation

Abstract: Active vibration control of an axially moving string by wave cancellation is presented. The control problem is formulated in the frequency domain. An exact, closed-form expression for the transfer function of the controlled system, consisting of the flexible structure, a feedback control law and the dynamics of the sensing and actuation devices, is derived. It is shown that all vibration modes can be stabilized and that the controlled system has no resonance. Moreover, the designed controller is applicable to the control of the string transverse vibration under various kinds of loading and constraint conditions. Results for the response of the controlled string under different excitations are presented and discussed along with the wave propagation and cancellation characteristics

Implementing Modified Command Filtering to Eliminate Multiple Modes of Vibration

Abstract: The requirements for large robots in waste management and space applications necessitate active vibration control algorithms. The use of long, flexible links provides the needed range of motion but their inherent flexibility can generate undesirable vibrations making both control and endpoint positioning difficult. This paper presents two shaping algorithms, the impulse shaping method and the modified command filtering technique, to eliminate the first two modes of vibration in a flexible manipulator. The vibration suppression capabilities are demonstrated using a large elliptic trajectory that produces a significant change in the system properties of the two-link robot. The acceleration response of the tip of the manipulator provides a means of comparison for the different shaping algorithms.

Vibration damping system for vehicle

Abstract: A vibration damping system for a vehicle includes a vibration sensor (7) which detects vibration of a particular vibrating element and a controller (8) which receives the output from the vibration sensor (7) and controls an actuator (3) such as a loudspeaker or engine mount, to apply to the particular vibrating element such vibration that damps the vibration detected by the vibration sensor. The controller is provided with a circuit which changes the sensitivity of the vibration sensor according to a particular condition of the vehicle, such as vehicle speed, acceleration or deceleration, engine speed or load, number of passengers, condition of audio system, windows, air-conditioner or transmission, vibration sensor noise, fuel load or curve travelling.

Eliminating multiple modes of vibration in a flexible manipulator

Abstract: Vibration suppression is often difficult to achieve in systems whose parameters are a function of configuration. A modified command filtering technique is proposed that eliminates the first two modes of vibration in a large, flexible manipulator with position-dependent parameters. The elimination of residual vibration is demonstrated using a circular trajectory located in the workspace of the manipulator so that a change in system properties occurs. The modified command filtering technique is compared to previous control methods in order to demonstrate its effectiveness in eliminating residual vibration. >

Vibration reducing device for vehicle

Abstract: PURPOSE: To effectively reduce an arithmetic quantity and travel vibration by weighting plural pieces of travel vibration information as specified in advance and performing arithmetic operation for generating a control signal according to the respective pieces of specifically weighted travel vibration information. CONSTITUTION: A 1st vibration detecting means 13 detects travel vibration information on wheels and a 2nd vibration detecting means 10 detects the travel vibration of the wheels at a specific position in the cabin. The output signals of those 1st and 2nd vibration detecting means 13 and 10 are inputted to a control means 25, which generates the control signal for reducing the travel vibration detected by the 2nd vibration detecting means 10 by the arithmetic operation. This control signal is inputted to a vibration generating means 11, which generates a noise; and this vibration and the travel vibration detected by the 1st vibration detecting means 13 cancel each other, and consequently the travel vibration detected by the 2nd vibration detecting means 10 at the specific position in the cabin is reduced, thereby obtaining reduction effects on the vehicle vibration. COPYRIGHT: (C)1994,JPO&Japio

Active Vibration Control in Structures Using Magnetostrictive Terfenol with Feedback and/or Neural Network Controllers:

Abstract: Experimental results are described in which a rod of magnetostrictive terfenol was used in the dual capacity of a passive structural support element and an active vibration control actu ator and artificial neural networks were used for the adaptive real-time control algorithm. Tests were performed on a three-legged table, where the terfenol actuators mentioned above are the table legs. For the table experiment, shaker vibrations generated in the ground and transmitted to the tabletop (via the legs) were attenuated by counter vibrations synthesized in the table leg actuators. The goal of this experiment was to maintain a quiescent tabletop in the presence of floor vibrations. Utilizing a proportional-integral derivative and a neural network controller, actuated forces were used to cancel applied disturbance forces. The neural network architecture identifies (learns) and adapts to the tabletop forced disturbance through a fast adaptation law known as Adaptive Back Propagation, generating the required counte...

Damped vibration isolation system

Abstract: An improved vibration isolation system utilizes a damped elastic structure loaded to approach a point of elastic instability to reduce the stiffness of the structure and to increase the damping. The system provides very low amplification at system resonant frequencies and effectively isolates at higher frequencies.

Combined Piezoelectric-Hydraulic Actuator Based Active Vibration Control for Rotordynamic System

Abstract: Previous research by the authors concentrated on using piezoelectric actuators for active vibration control (AVC) of rotating machinery. The current work extends this by positioning the piezo-actuator remotely from the controlled structure and transmitting the control force via a hydraulic line and two pistons. Liquid plastic (LP) is employed as a transmission “fluid” to obtain a high bulk modulus and low leakage. The paper presents results for bulk moduli measurement, and bench and rig tests for the entire actuator system. These results show the high effectiveness of the hybrid actuator for controlling vibrations on a laboratory rotor test rig.

Active vibration isolation on an experimental flexible structure

Abstract: The paper describes experimental research in the area of active vibration isolation. The objective of the research is to quantitatively assess the performance gained by augmenting a passive isolator with an active stage. Vibration isolation experiments were carried out on a flexible structure utilizing a proof-mass shaker as the disturbance source and a newly developed active member as the isolator. Broad band force feedback control demonstrated more than 20 dB reduction in force transmissibility over passive isolation alone. The broad band controller was augmented with notch filters which resulted in reducing force transmissibility by 40 dB over the passive stage in select narrow bands.

Stabilization of beam parametric vibrations

Abstract: A theoretical investigation of dynamic stability for linear elastic beams due to time dependent harmonic anal forces is presented. The concept of intelligent structure is used to insure the active damping. In the present paper the applicability of active vibration control is extended to linear continuous systems with parametric harmonic excitations. The study is based on the application of distributed sensors, actuators, and an appropriate feedback and is adopted for stability problems of system consisting of beam with control part governed by uniform partial differential equations with time, dependent coefficients. To estimate deviations of solutions from the equilibrium state (the distance between a solution with nontrivial initial conditions and the trivial solution) a scalar measure of distance equal to the square root of the functional is introduced. The tyapunoy method is used to derive a velocity feedback implying nonincreasing of the functional along an arbitrary beam motion and in conseqiaeftce to balance the supplied energy by the parametric excitation and the dissipated ejiergy by the inner and control damping. In order to calculate the energetic norm of disturbed solution as a function of time the partial differential equation is solved numencally. The numerical tests performed for the simply supported beam with surface bonded actuators and sensors show the influence of the fedback constant on the vibration decrease.

A vibration driven motor or actuator

Abstract: A vibration driven motor or actuator has a piezoelectric element, arranged in a vibrating member, for generating a vibration in a first direction, and another piezoelectric element, arranged in the vibrating member, for generating a vibration in a second direction different from the first direction. In the motor or actuator, the vibrating member has a recess portion which shaved e.g., by a laser, or a portion added with a mass, so that the natural frequencies of a given vibration mode of the vibrations in the first and second directions coincide or substantially coincide with each other.

Active vibration control device and its manufacturing method

Abstract: PURPOSE:To obtain a preferable vibration eliminating performance corresponding to a transfer characteristic of vibration covering a vibration source to a vibration eliminating position using an adaptable filter having low resolution and a low cost by restricting a reference signal to the prescribed frequency region being preferable for processing by an adaptable filter. CONSTITUTION:This device is a signal input system transmitted from a detecting microphone to an adaptable filter 22. That is, a fixed filter 24 consisting of analog filter in which the prescribed signal waveform is written is connected in series to the adaptable filter 22 between an amplifier and an A/D converter 21 in the stream side of the adaptable filter 22. A signal waveform of the prescribed frequency region different form a reference signal previously processed by the adaptable filter, that is, a signal waveform of the prescribed frequency which cannot be written in the adaptable filter 22 is written in this fixed filter 24, and this fixed filter 24 restricts the reference signal processed by the adaptable filter 22 so as to be within the prescribed frequency region.

Active vibration damping system for a vehicle

Abstract: A vibration damping system for a vehicle has a vibration sensor which detects vibration of solid elements on the vehicle and vibration of air inside the vehicle. A first vibrator supports a power unit relative to the vehicle body and directly vibrates the vehicle body. A second vibrator directly vibrates air inside the vehicle body. A drive control unit performs calculation on the basis of a detecting signal from the vibration sensor and controls the first and the second vibrators on the basis of the result of the calculation so that the vibration of the solid element and the vibration of air inside the vehicle body are damped. The vibrator control ratio of the first and second vibrators is changed according to the condition of a predetermined factor of the vehicle.

Welding Characteristics of Ultrasonic Wire Bonding Using High-Frequency Vibration Systems

Abstract: Welding characteristics of ultrasonic wire bonding using 60 kHz and 90 kHz complex vibration as well as 120 kHz linear vibration welding systems are studied. The locus shapes of the complex vibration welding tip are controlled from linear to elliptical or circular. Aluminum wire specimens of 0.1 mm diameter are welded successfully using the welding equipment. The required vibration amplitudes of these complex vibration systems are about one-half to one-third and required weld time is shorter than those for a conventional system of linear vibration. The required vibration velocity of a higher-frequency system is smaller than that of a lower-frequency system.

Vibration detection and reduction system and vibration sensors for use in micro-gravity environment

Abstract: The invention is to detect vibrations which would destroy a micro-gravity environment, to grasp factors of the vibrations, to detect and grasp a position and a scale of meteoroid/debris collisions, and to establish a counter-measure. Vibration sensors are disposed in a matrix array on a vibrating body placed in a micro-gravity environment. A computer analyzes a spectrum of the vibration, in a neural network section a vibration source is specified on the basis of the analyzed spectra, in a fuzzy control section, actuators are driven so as to reduce harmful vibrations in response to the vibration energy and the energy source specified by the neural network section, and if necessary, a vibration factor is eliminated. The computer takes in the result of driving for the actuators, the results are learnt in the neural network section and in the fuzzy control section to be ready for generation of vibrations at the next time. The vibration sensor comprises a reflector or a transparent refractor disposed as floating in a micro-gravity space, output means fixed to the vibrating body for emitting energy towards the reflector or transparent refractor, and a receiver fixed to the vibrating body for receiving energy sent from the reflector or transparent refractor and measuring the nature of vibrations of the vibrating body on the basis of movement of the reflected or permeated energy.

Active Vibration Control of a Motor System by Using H∞ Control Theory

Abstract: This paper considers the vibration control of a motor system which has a motor and a load connected with a flexible shaft. However, this system often generates a shaft torsional vibration. Traditional methods of treating this problem to adjust the PID controller so that the closed-loop frequency response is slower than that of the vibration mode. On the other hand, one method has already been proposed in which the vibration is suppressed by a disturbance observer. This paper proposes a new approach based on H∞ control theory. For comparison, a PI control system based on classical control theory also is constructed. The results of several experiments show that compared with the PI control system, the H∞ control system is effective in suppressing the vibration. Further, the H∞ controller obtained in the study consists of a PI controller and a series compensator that functions as an active vibration controller.

Method and apparatus for in-flight shake testing of an aircraft fuselage

Abstract: A force-generating actuator connected at or across points of a structure capable of relative motion at an exciting frequency is operated to input a predetermined load into the structure and the response of the structure is measured for analysis In one form of the invention the actuator is one of a plurality of actuators of an active vibration control system which is isolated and operated independently in a shake test mode Advantageously, especially in a helicopter application, the remaining actuators can continue to be operated to reduce background vibration

Stirling-cycle cryocooler active vibration control

Abstract: A cryogenic cooler capable of continuously maintaining the required cryogenic temperature is one of the critical elements enabling space-borne surveillance sensors to detect cold objects against a space background or warm objects against an Earth background. The performance of these sensors, however, can be greatly degraded by the vibration of typical mechanical cryocoolers. "Balanced" Stirling-cycle cryocoolers produce significant residual vibration at the harmonics of the fundamental drive frequency due to various nonlinearities which are not compensated by a simple oscillating balance mass. Techniques to sufficiently suppress these vibrations are required for high performance surveillance sensors. This paper examines two very effective control techniques in dealing with the residual vibration force suppression. The first technique uses the narrowband feedback principle to design a force servo compensator which produces a notch filtering effect at each of the harmonic frequencies. The second technique uses the adaptive feedforward principle to inject harmonic signals into one of the cryocooler motor drives to produce a complete force cancellation. The concepts and designs of both control techniques are discussed, and test results of the vibration suppression performance on the Hughes IR&D cooler are presented. >

Multilayer Piezo-Ceramic Actuators and Their Applications

Abstract: Actuators are devices which control a displacement, a force and a velocity of a mechanical load, converting electric, fluidic or other input power to mechanical output power. Presently, the input power, extensively used, may be electric, pneumatic or hydraulic.

New Terfenol-D actuator design with applications to multiple DOF active vibration control

Abstract: A linear actuator system for multi-dimensional structure control using the magnetostrictive material Terfenol-D has been designed, built, and tested by the Intelligent Automation, Inc. The actuator assembly incorporates an instrumented Terfenol-D rod, an excitation coil to provide the magnetic field, a permanent magnet assembly to provide a magnetic bias field, and a mechanical preload mechanism. The prototype of the actuator is 2.0 inches in diameter and 8 inches long, and provides a peak-to-peak stroke of 0.01 inches. A linear model was also established to characterize the behavior of the actuator for small motion. Based on the prototype of the actuator, we have performed a study of a six degree-of-freedom active vibration isolation system using a Stewart Platform in a new configuration. IAI's final system is intended for precision control of a wide range of space-based structures as well as earth- base systems.

Active vibration control in automotive chassis systems

Abstract: For over 100 years, comfort in road vehicles has been linked to the introduction of passive components that isolate passenger compartments from mechanical vibration. Near-optimal performance has been achieved by years of experimentation and testing, careful selection and shaping of individual component characteristics, and the development of ingenious mechanisms intended to minimise the effect of inherent design constraints associated with passive systems. It is now apparently the case that only a technological leap can significantly improve vibration suppression in automotive chassis systems over that achieved to date. This article considers the analysis and design of active control solutions for two automotive chassis subsystems susceptible to mechanical vibration phenomena.