Showing papers on "Active vibration control published in 1994"

Six degree-of-freedom active vibration control using the Stewart platforms

Abstract: Multiple degree-of-freedom (DOF) vibration control systems are essential for precision control of a wide range of Space-borne structures as well as earth-based systems. This paper studies the design and control problems of a class of multiple DOF vibration isolation systems using the concept of a Stewart truss and Stewart platform mechanism. A novel geometric arrangement of a Stewart platform, called the "cubic configuration" is developed and used. A new design and analysis of actuators employing magnetostrictive material Terfenol-D is presented. Robust adaptive filter algorithms for active vibration control are formulated. Prototype hardware for a six degree-of-freedom active vibration isolation system with the "cubic configuration" of the Stewart platform has been implemented and tested. About 30 dB of vibration attenuation is achieved in real-time experiments. >

Hybrid damping through intelligent constrained layer treatments

Abstract: This paper is to propose a viable hybrid damping design that integrates active and passive dampings through intelligent constrained layer (ICL) treatments. This design consists of a viscoelastic shear layer sandwiched between a piezoelectric constraining cover sheet and the structure to be damped. According to measured vibration response of the structure, a feedback controller regulates axial deformation of the piezoelectric layer to perform active vibration control. In the meantime, the viscoelastic shear layer provides additional passive damping. The active damping component of this design will produce adjustable and significant damping. The passive damping component of this design will increase gain and phase margins, eliminate spillover, reduce power consumption, improve robustness and reliability of the system, and reduce vibration response at high frequency ranges where active damping is difficult to implement. To model the dynamics of ICL, an eighth-order matrix differential equation governing bending and axial vibrations of an elastic beam with the ICL treatment is derived. The observability, controllability, and stability of ICL are discussed qualitatively for several beam structures. ICL may render the system uncontrollable or unobservable or both depending on the boundary conditions of the system. Finally, two examples are illustrated in this paper. The first example illustrates how an ICL damping treatment, which consists of an idealized, distributed sensor and a proportional-plus-derivative feedback controller, can reduce bending vibration of a semi-infinite elastic beam subjected to harmonic excitations. The second example is to apply an ICL damping treatment to a cantilever beam subjected to combined axial and bending vibrations. Numerical results show that ICL will produce significant damping.

Bending-vibration control of composite and isotropic plates through intelligent constrained-layer treatments

Abstract: Intelligent constrained-layer (ICL) damping treatments are applied to control bending vibration of composite and isotropic plates. The treatment consists of a viscoelastic shear layer sandwiched between a piezoelectric constraining cover sheet and the structure to be damped. According to the measured vibration response, a feedback controller regulates axial deformation of the piezoelectric layer to perform active vibration control. The equation of motion and boundary conditions governing the bending vibration with bending-stretching coupling stiffness are derived. Two examples are illustrated in this paper. The first example considers an infinite composite plate consisting of a +or-45 degrees angle ply laminate subjected to plane harmonic wave excitations. The second example considers bending-vibration control of a simply-supported, rectangular, isotropic, classical plate.

Active control of helicopter vibration

Abstract: The reduction of helicopter vibration is of great importance to the helicopter industry and considerable effort has been devoted to research into active methods for vibration reduction. The article describes how active control techniques can offer good vibration reduction over significant areas of the fuselage and also provide the capability to adapt to changing speed, rotor conditions and structural dynamics. There are three main areas on the helicopter where active vibration control techniques can be applied: at the rotor; at the main gearbox to fuselage interface, and within the fuselage itself. The last area is termed the active control of structural response (ACSR) and is considered in more detail. Finally, the performance of the ACSR technique in minimising vibration in helicopter structures is analysed using results which demonstrate the performance potential under differing conditions.

Engineering feasibility of induced strain actuators for rotor blade active vibration control

Abstract: Rotor blade vibration reduction based on higher harmonic control - individual blade control (HHC-IBC) principles is presented as a possible area of application of induced strain actuator (ISA). Recent theoretical and experimental work on achieving HHC-IBC through conventional and ISA means is reviewed. Though the force- displacement and power-energy estimates vary significantly, some common-base values are identified. Hence, a benchmark specification for a tentative HHC-IBC device based on the aerodynamic servo-flap principle operated through ISA means is developed. Values for the invariant quantities of energy, power, and force-displacement product are identified, along with actual displacement and force values of practical interest. The implementation feasibility of this specification into an actual ISA device is then discussed. It is shown that direct actuation is not feasible due to the large required length of the ISA device, resulting in excessive compressibility effects (displacement loss and parasitic strain energy). Indirect actuation through a displacement amplifier was found to be more feasible, since it allows for matching the internal and external stiffness. A closed-form formula was developed for finding the optimal amplification gain for each required value of the closed- loop amplification ratio. Preliminary studies based on force, stroke, energy, and output power requirements show that available ISA stacks coupled with an optimally designed displacement amplifier might meet the benchmark specifications.

Active control of vibrations in helicopters via pole assignment techniques

Abstract: This paper is motivated by the problem of active control of vibrations in helicopter A129 of Agusta S.p.A. Taking into account the specific features of the A129 rotor, whose model is characterized by two nonminimum phase zeros, a new method for active control is proposed. Based on simple pole-placement considerations, the method presents a number of advantages. First, it enables harmonic cancellation without perturbing the low frequency dynamics. In other words, the control system does not affect the overall dynamics of the flight as decided by the pilot. Moreover, it supplies a stable controller. Second, the controller design computations are extremely simple. The performances achievable with such a controller are tested by a number of simulations on an A129 rotor model. >

Self-Tuning Active Vibration Control of Flexible Beam Structures

Abstract: This paper presents the design and performance evaluation of an adaptive active control mechanism for vibration suppression in flexible beam structures. A cantilever beam system in transverse vibration is considered. First order control finite difference methods are used to study the behaviour of the beam and develop a suitable test and verification platform. An active vibration control algorithm is developed within an adaptive control framework for broadband cancellation of vibration along the beam using a single-input multi-output (SIMO) control structure. The algorithm is implemented on a digital processor incorporating a digital signal processing (DSP) and transputer system. Simulation results verifying the performance of the algorithm in the suppression of vibration along the beam, using single-input single-output and SIMO control structures are presented and discussed.

Active/passive piezoelectric vibration suppression

Abstract: The use of piezoelectric materials simultaneously as passive modal devices and active elements to suppress structural vibrations is discussed. A simple modal model is developed which predicts the behavior. Experimental studies are then conducted to verify the model. The results show a reduction of 20 dB in the second mode of the structure is possible via passive shunting while simultaneously commanding the piezo-actuator. The results indicate that for vibration problems involving a few modes, piezoelectric devices combining active and passive techniques can significantly reduce the broadband structural response to disturbances.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Active Vibration Control of Structures Arranged in Parallel

Abstract: This paper proposes a new method for the vibration control of structures arranged in parallel. Recently, active dynamic absorbers have been used widely in the field of vibration control, but in the case of vibration control for several structures which stand independently this method is not advisable. In our method, both structures are controlled actively at the same time with a single actuator placed between them. Since supplementary masses are not necessary, the equipment can be simple and light. Here, the optimal design method of the controller for a 1-1 degree-of-freedom system by LQ control theory is shown. Moreover, the problem on the vibration control of the flexible structures is spillover, and this paper shows the application of the reduced-order model which suppresses the spillover in the controller design and its extension to a multi-degree-of-freedom system. Effectiveness of this method is demonstrated by the experiment.

Active vibration control of structures undergoing bending vibrations

Abstract: An active vibration control subassembly for a structure (such as a jet engine duct or a washing machine panel) undergoing bending vibrations caused by a source (such as the clothes agitator of the washing machine) independent of the subassembly. A piezoceramic actuator plate is vibratable by an applied electric AC signal. The plate is connected to the structure such that vibrations in the plate induced by the AC signal cause canceling bending vibrations in the structure and such that the plate is compressively pre-stressed along the structure when the structure is free of any bending vibrations. The compressive prestressing increases the amplitude of the canceling bending vibrations before the critical tensile stress level of the plate is reached. Preferably, a positive electric DC bias is also applied to the plate in its poling direction.

Active vibration control method and apparatus

Abstract: An improved active vibration control system using feedback and pseudo-feedforward sensor inputs is provided for solving the problem of random and repetitive active vibration control and noise cancellation in a system In a first embodiment of the invention, an artificial neural network is used for learning the dynamics of a structure and for providing output signals that follow the state variables of the structure In one implementation of the neural network, a plurality of neurons obtain biasing inputs derived from sensor inputs, as well as inputs from the other neurons in the network Further, each neuron obtains a feedback input from itself Each input to a neuron is weighted using a weighting function derived on-line The neural network supplies structure parameters and state variables to an optimal controller which derives and provides a control signal to the actuators so as to counteract vibrations and/or noise sensed in the system In a second embodiment an optimal controller utilizing a modified generalized predictive control algorithm is used to to consider the limitations on the physical characteristics of the actuator(s), on-line, in terms of the output level and the rate of change of the output in the system Additional embodiments wherein an optimized control signal is sent to the actuator(s) to minimize vibration incident to the structure are provided

Self-Tuning Active Vibration Control in Flexible Beam Structures:

Abstract: This paper presents the design and performance evaluation of an adaptive active control mechanism for vibration suppression inflexible beam structures. A cantilever beam system in transverse vibration is considered. First-order central finite difference methods are used to study the behaviour of the beam and develop a suitable test and verification platform. An active vibration control algorithm is developed within an adaptive control framework for broadband cancellation of vibration along the beam using a single-input multi-output (SIMO) control structure. The algorithm is implemented on a digital processor incorporating a digital signal processing (DSP) and transputer system. Simulation results verifying the performance of the algorithm in the suppression of vibration along the beam, using single-input single-output and SIMO control structures, are presented and discussed.

Feedforward Control of Gear Mesh Vibration Using Piezoelectric Actuators

Abstract: This paper presents a novel means for suppressing gear mesh-related vibrations. The key components in this approach are piezoelectric actuators and a high-frequency, analog feed-forward controller. Test results are presented and show up to a 70-percent reduction in gear mesh acceleration and vibration control up to 4500 Hz. The principle of the approach is explained by an analysis of a harmonically excited, general linear vibratory system.

Cryogenic cooling system with active vibration control

Abstract: A cryogenic cooling system having a mechanism for canceling vibration at a fundamental frequency and at harmonics thereof. The inventive system includes a first apparatus (28, 32) for cooling a mass. The first apparatus (28, 32) creates a vibration at a first frequency and a second frequency. In a typical application, the first frequency is a fundamental frequency and the second frequency is a harmonic of the first frequency. Often several harmonics are present. The invention includes a second apparatus (30, 34) for substantially eliminating vibration at the first frequency and a third apparatus (48, 50) for substantially eliminating vibration at the second frequency. The second apparatus includes a mass (30) and a motor (34) for driving same. The mass (30) is disposed to counter the vibration created by the first apparatus when the motor (34) is driven by a first current. The third apparatus includes a sensor (48) for detecting the vibration at the second frequency and providing an output in response to a sensed force F resulting therefrom. The third apparatus further includes a feedback circuit (50) for providing a second current for driving the motor. The second current is the sum of the first current and a feedback current I b2 . The feedback current I b2 is equal to -G f (s)F, where -G f (s) is a feedback transfer function. The feedback transfer function is a product of a first transfer function H I (s) representing dynamics of the second apparatus required to cancel the vibration at the first frequency and a second transfer function G D (s) representing the dynamics of the second means required to cancel the harmonic vibration.

An analysis of vibration control using piezoceramics in planar flexible-linkage mechanisms

Abstract: The authors present a finite-element analysis of vibration control in planar mechanisms consisting of flexible links provided with nearly collocated piezoceramic sensors and actuators. Euler-Bernoulli-theory-based beam finite elements with p-convergence capabilities have been cast into a total Langrangian formulation in order to represent large rotations of the links. A simple control strategy based on the placement of closed-loop poles has been applied. Numerical predictions of active vibration control in links undergoing geometrically non-linear deflections of the von Karman class are presented.

Active Vibration Control of a Flexible Cantilever Beam by Applying Thermal Bending Moment

Abstract: Digital vibration control of a flexible cantilever beam using a thermal bending mo ment caused by the temperature gradient across the section of the beam is attained both by experi ments and simula...

Adaptive schemes for the active control of helicopter structural response

Abstract: This paper describes a new method for the design of an adaptive controller for the reduction of vibration in helicopter structures. Two known approaches are described which can be used to implement an active vibration control system-a frequency domain controller or a time domain controller. Both strategies have a number of advantages and disadvantages, which are discussed in the paper. A new approach to the design of an adaptive controller for the reduction of helicopter vibration is described. This new technique is a hybrid time/frequency domain solution combining the advantages from both the time domain linear quadratic feedback controller and the frequency domain quasi-static controller. Both fixed gain and adaptive control designs have been implemented, and comparisons of the performance of the various control approaches to the problem of minimizing vibration in helicopter structures is made. The hybrid strategy has been studied extensively using computer simulations and its performance has been shown to equal that of the frequency domain approach, providing up to 90 percent vibration reduction at the blade-passing frequency. Results from experimental validation on a helicopter airframe test rig confirm the effectiveness of the strategy. >

Active vibration control of rotor systems

Abstract: A study is presented in which the vibrations of a rotor are controlled under both synchronous and transient conditions. In this paper sliding mode control theory has been adopted to minimise rotor vibration due to mass imbalance e.g. blade loss. The system gain matrix is obtained by choosing the desired pole position and solving the Riccatti equation. Control forces are applied to the system via a feedback loop. Multiprocessor hardware is used to apply the controller algorithm on line to an experimental rig consisting of a rotor and two journal bearings with a magnetic actuator to apply the control force. Experimental work has been carried out to show the effectiveness of the proposed control method.

Vibration cancellation device

Abstract: The invention provides a vibration cancellation device for rigidly mounting to or forming part of an apparatus subject to vibration. The device comprises a mass supported by magnetic levitation but which is magnetically driven to provide vibration cancelling relative movement, movement sensors controlling the application of power, in a relative motion cancellation direction.

Disturbance Cancellation Control for Vibration of Multi-Degree-of-Freedom Systems (Case of Using Active Vibration Absorber and Active Dynamic Vibration Absorber)

Abstract: This paper describes a control system design method concerning feedback and feedforward control to cancel disturbance forces, for two kinds of active vibration control devices. One is the active vibration absorber (AVA) utilizing a fixed point for a civil structure such as a bridge, and the other is the active dynamic vibration absorber (ADVA) utilizing an auxiliary mass for a buildinglike structure. We have built two test rigs to simulate large structures with an AVA or an ADVA. In order to carry out fast computation, including the estimation of disturbances, we have used a digital signal processor (DSP). In conclusion, we found that the disturbance forces are perfectly cancelled and the output zeroing is actually realized when the disturbance frequency is exactly equivalent to the design frequency of the observer. We have confirmed that the proposed disturbance cancellation control is very useful for active vibration control.

Development of CMG Active Vibration Control Device for Gondola

Abstract: For reduction of the low-cycle vibration of vehicles such as gondolas which are suspended flexibly, the authors studied the utilization of the control moment gyro (CMG) as an active vibration control device. The CMG is a moment generator using the gyroscopic moment effect and it is applied to attitude control of spacecraft. Particularly in the very-low-frequency region (less than 1 Hz), it is effective and requires no reaction support.

A Multiobjective Design Optimization Procedure for Control of Structures Using Piezoelectric Materials

Abstract: Piezoelectric materials can be used as sensors and actuators for structures that re quire active vibration control and lack sufficient stiffness or passive damping. Efficient implementa tion of these actuators requires that their optimal locations on the structure be determined and that the structure be designed to best utilize the properties of the actuators. A formal optimization pro cedure has been developed to address both of these issues. A gradient based multiobjective optimiza tion technique is used to minimize multiple and conflicting design objectives associated with both the structure and the control system design which is also coupled with the actuator location problem. Objective functions such as the fundamental natural frequency of the structure and energy dissipated by the piezoelectric actuators are included in this study. Constraints are placed on the mass of the structure, displacements and applied voltage to the piezoelectric actuators. Design variables include parameters defining both t...

Experimental Study on Active Vibration Control of Structures by means of H∞ Control and H2 Control

Abstract: This paper describes an experimental study on H∞ control for vibration in multi-degree-of-freedom systems. An H∞ controller designed by using the reduced-order model makes a closed loop system, not only causing no spillover phenomena, but also controlling the vibration on the four-degree-of-freedom experimental model. The experimental results are very similar to the simulation results, and the efficiency of the H∞ control system is confirmed. Also experiments on frequency-shaped cost function LQG (H2) control design are performed in comparison with the H∞ optimal control. Because the H∞ optimal control has strong robust stability against the parameter variations, it can construct a more useful control system than H∞ control for a real control object.

H2 Approach for Optimally Tuning Passive Vibration Absorbers to Flexible Structures

Abstract: : PASSIVE damping by vibration absorbers has been proven both reliable and successful in many areas of vibration control. Research into the optimal tuning of vibration absorbers has received increased attention lately; however, these tuning methods have only been practical on low-order systems (one or two modes). The design of a vibration absorber system is an optimization problem. In the general case, it is desired to couple multiple vibration absorbers to a structure with multiple vibrational modes. If the total mass of all of the actuators is fixed to some small value compared to the mass of the structure, then the design parameters are the set of absorber stiffnesses and damping coefficients.

Active Vibration Control Using the Modified Independent Modal Space Control (M.I.M.S.C.) Algorithm and Neural Networks as State Estimators

Abstract: This article presents a numerical study related to the active control of the vibrations of a cantilevered beam with piezoelectric actuators using the Modified Independent Modal Space Control (M.I.M.S.C.) algorithm coupled with a neural network for state estimation. Among other control strategies, the M.I.M.S.C. algorithm has been shown to have excellent closed-loop structural damping. Such an algorithm requires as input data the modal displacements and velocities of the vibrating beam. A Neural Network is proposed in this paper as an alternative approach to classic estimation structures for the on-line estimation of the modal parameters. The results of a numerical case study are presented and discussed.

Active vibration control of a 2-mass spring system using μ-synthesis

Abstract: A 2-mass system connected by a non ideal shaft has resonance modes and it is difficult to design a controller suppressing the vibration in the face of parameter variation. In this paper, we propose a method of μ-Synthesis based on the descriptor form representation to deal with parameter uncertainties independently. We first consider a class of parameter uncertainty given in the descriptor form and show how to achieve robust stability and robust performance for this class of perturbed systems. Then we apply this method to the 2-mass spring system with parameter uncertainties of the torsional constant and the load inertia. By using this method these two physical uncertainties are treated independently and a controller is designed to achieve not only robust stability but also robust disturbance suppression. In addition, we also use two-degree freedom control scheme to achieve a good transient response.Simulation results are presented to demonstrate the control effects.

Unbalance compensation of magnetic bearings

Abstract: In a rotational machine, unbalance of the rotor is formidable since it causes resonance synchronized with the rotation of the rotor. In order to suppress this unfavorable vibration, an active vibration control system, which accommodates changes of rotor dynamics is desired. In this paper we propose a vibration control system using active magnetic bearings to cope with a sudden sinusoidal disturbance, which simulates a turbine blade loss. Experimental results reveal that our vibration control system is effective enough to suppress the whirling motion of the rotor caused by a sudden disturbance. >