Showing papers on "Active vibration control published in 1995"

Use of active constrained-layer damping for controlling resonant vibration

Abstract: The work described in this paper is concerned with controlling the strain of the constraining layer of a composite structure in such a way as to enhance the shear generated in the viscoelastic material and hence improve the overall damping of the composite structure. The results have indicated that this concept of active damping produces very effective levels of vibration suppression. In the case of cantilever beams the vibration levels in the first two modes can be almost eliminated when velocity feedback of the beam tip is used. The results show that the addition of active control and passive damping in a single structure combines the advantages of passive damping in the higher modes and active control in the lower modes. In addition active damping as defined in this paper produces a fail-safe mechanism in case of instability occurring in the feedback loop since a considerable level of passive damping is always present.

Adaptive-passive vibration control system

Abstract: A passive-adaptive vibration control system is provided wherein various elements of the system may be adapted on-line in response to sensed vibrations. A spring/weight vibration absorber (160, 165) is attached to a vibrating body, such as the drum (115) of a laundry machine (100), to absorb energy generated by the drum, to minimize the transmission of vibrations to a structure, such as the body of the machine (100) in mechanical communication with the drum. The mass of the weight (160) of the vibration absorber may be adjusted, on-line, to compensate for sensed vibrations. A vibration sensor (170) is connected to the vibrating body so as to sense the level of vibration above a desired level and to send a signal representative of that vibration to an electronic controller (180). The electronic controller (180) is designed to instruct an actuator arrangement (182, 184) to adapt the mass of the weight to compensate for the sensed vibration. For example, the weight (160) may be a chamber, the mass of which may be adjusted by adding or releasing a fluid to or from the chamber via the actuator arrangement (182,184) under the control of the controller (180).

Silica-containing vibration damper and method

Abstract: A method for vibrationally damping an article that is subject to resonant vibrations comprises the steps of providing a vibration damper and applying the vibration damper to the article to damp the resonant vibrations. The vibration damper comprises an acrylate viscoelastic vibration damping material and an effective amount of hydrophobic silica. The invention also relates to vibration dampers that utilize the acrylate viscoelastic vibration damping material as well as articles that incorporate the vibration dampers.

Active vibration control and actuation of a small cantilever for applications in scanning probe instruments

Abstract: The deflection control of a small cantilever is described, which operates using a single active piezoelectric element and optical vibration sensing, so that unwanted vibrations in the cantilever are removed, and yet it remains possible to deflect the cantilever statically or dynamically as required. Such a control system is directly applicable to the very small cantilevers found in scanning probe microscopes, such as atomic force and magnetic force microscopes, the resolution of which is limited by unwanted vibration.

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 Actuation (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 bench-mark 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 parasit...

Influence of Piezo-Actuator Thickness on the Active Vibration Control of a Cantilever Beam:

Abstract: The effect of piezo-actuator thickness on the active vibration control of a cantilever beam is investigated. The vibration field of the beam is theoretically estimated using the Euler-Bernoulli beam theory. Based on a static analysis, it is shown that there exists an optimal piezo-actuator thickness which maximizes the static beam deflection. Results indicate that the optimal thickness is a strong function of the Young's modulus ratio of the actuator/beam configuration, becoming thinner with stiffer piezo-actuators. For comparison, strategies for choosing piezo-actuator thickness based on a dynamic analysis are also investigated. Results suggest that the thickness choice for near-resonance excitation is similarly determined with the static analysis assuming structural damping. It is shown that lighter and stiffer piezo-actuators generally perform better. It is also shown that there exists a piezo-actuator thickness which maximizes the beam deflection for off resonance excitation with single-sided piezo-ac...

Self-sensing Active Vibration Control using the Moving-Coil-Type Actuator

Abstract: Active vibration control requires a velocity signal which is fed back to the force actuator to produce the damping force to the structure. Usually a gap sensor is used to detect the displacement and a differentiator is needed to produce the velocity signal. Moreover, it is very difficult to install the sensor at the same position of the actuator. Setting the gap sensor close to the magnetic actuator may cause an undesirable interaction between them. Sometimes there is no space for installing the sensor. This paper introduces a method of using a moving-coil-type actuator as a two-port sensing and driving device. Four types of velocity identification algorithms are tested and their capability of reducing structural vibrations is compared.

Vibration control of plates by plate-type dynamic vibration absorbers

Abstract: In this paper, a new plate-type dynamic vibration absorber is presented for controlling the several predominant modes of vibration of plate (mainplate) under harmonic excitation, which consists of a plate (dynamic absorbing plate) under the same boundary condition as the main plate and with uniformly distributed connecting springs and dampers between the main and dynamic absorbing plates. Equations of motion of the system in the modal coordinates of the main plate become equal to those of the two-degrees-of-freedom system with two masses and three springs. Formulas for optimum design of the plate-type dynamic vibration absorber are presented using the optimum tuning method of a dynamic absorber in two-degrees-of-freedom system, obtained by the Den Hartog method. Moreover, for practical problems regarding large-scale plates, an approximate tuning method of the plate-type dynamic absorbers with several sets of concentrated connecting springs and dampers is also presented. The numerical calculations demonstrate the effectiveness of the plate-type dynamic absorbers.

Determination of Design of Optimal Actuator Location and Configuration Based on Actuator Power Factor

Abstract: In this paper, a new design algorithm is proposed for optimization of the inducedstrain actuator location and configuration for active vibration control based on an actuator performance index, namely the actuator power factor. The concept of actuator power factor, developed recently by the authors, describes the capability of an integrated induced strain actuator, such as PZT or Terfenol, to transfer the supplied electrical energy into structural mechanical energy (kinetic or potential energy of the mechanical system). A system optimized based on the actuator power factor will guarantee the highest energy efficiency for single frequency and broad-band applications. This paper will also show that a higher energy efficiency corresponds to higher mechanical performance. The approach introduced in this paper is much more convenient to use than the conventional modal domain optimization approach. Furthermore, since the power factor approach can include the electrical parameters from the power system, it will a...

Vibration type motor device

Abstract: A vibration type motor device excites a vibration member by applying frequency signals to piezoelectric elements so as to obtain a driving force. A vibration state detection piezoelectric element is arranged on the vibration member, and when a vibration state is determined by detecting the phase difference between the output from the detection piezoelectric element and a driving frequency signal, a predetermined signal is superposed on the output from the detection piezoelectric element, thus allowing accurate detection of the vibration state even when the output from the piezoelectric element includes noise.

Active vibration control system for aircraft

Abstract: An active noise and vibration reduction system for canceling noise in aircraft or other passenger carrying transportation systems (10) which utilizes a series of seat mounted microphones (6) and trim mounted speakers (4) in conjunction with a digital controller (15) with a class-D stage power amplifier (5) and which is synched to the aircraft alternator (16).

Some Recent Advances in Linear and Nonlinear Dynamical Modeling of Elastic and Piezoelectric Plates

Abstract: A previous review has covered our early efforts in dynamics and vibration of homogeneous and layered elastic plates and shells, including sandwiches. As an update, the present review summarizes our recent efforts in the same general area, now further including laminated composite and piezoelectric plates. These reflect the increasing importance of laminates, the growing interest in distributed active vibration control through the use of piezoelectric layers and often a combination of both. The main purpose of this paper is to again provide a systematic overview of linear and nonlinear dynamical modeling of both homogeneous and layered plates. As many of our contributions have been made by means of the variational equations of motion in three-dimensional elasticity and piezoelectricity, an extended discussion of these equations is included as an integral part of this review. Recent applications of these to the linear and nonlinear dynamical modeling of elastic laminates and piezoelectric layers are described.

Vibration control of a cylindrical shell used in MRI equipment

Abstract: One major problem in magnetic resonance image (MRI) equipment is the high-level noise borne by the vibration of the cylindrical shell to support the coils for gradient magnetic fields. The vibration of the shell is excited by the Lorentz force between the pulse current applied to the coils and the main magnetic field. In order to suppress the noise inside the cylindrical shell, it is aimed to control the vibration of the shell. In this paper, simulation is carried out on the vibration control of the shell by using distributed piezoelectric actuators. The actuators produce a bending moment or an in plane force when pulse voltages are applied synchronously with the pulse current of the coils. Coupling of actuators and vibration modes, and parameter optimization are also discussed. The simulation results show that the vibration level is successfully reduced in the frequency range of 400-1200 Hz.

Active piezo-electric vibration isolation and directional systems

Abstract: Piezoelectric actuators bonded on S-shaped brackets extending between a support and a payload, improve vibration isolation therebetween by attenuating resonant vibrations under computer dynamic control relying on predetermined dynamic resonant characteristics and H-Infinity control methods. The system can also be used for pointing the attitude of a payload on a supporting platform. Bonded piezoelectric ceramic actuators bend aluminum portions of the brackets to adjust the attitude and position of the payload respecting the support well suited for improved optical communications, observation and telemetry. The system is enables concurrent vibration isolation and directional control.

Vibration Control of a Cylindrical Shell Using Piezoelectric Actuators

Abstract: This paper presents a method to control the vibration of a cylindrical shell system. The cylindrical shell system consists of a layer of plastic film and two layers of piezoelectric film, a part of which is used as the actuator. This study presents the analysis of vibration problem caused by periodic excitation. The problem is solved by means of the modal expansion method. A numerical simulation and an experiment of vibration control are performed by applying H∞ control theory to the cylindrical shell system. The result shows the effectiveness for the suppression of the forced vibration of the cylindrical shell system by using this control method.

Measurement of the modal shapes of inhomogeneous cantilevers using optical beam deflection

Abstract: The study of free vibrations of systems such as simple cantilevers has been mainly concerned with the determination of the eigenvalues (frequencies) and eigenfunctions (modal shapes). A technique has been developed, using optical beam deflection, to measure the modal shape of a cantilever non-invasively at each modal frequency. A knowledge of the modal shapes of very small cantilevers incorporating suitable actuators is important in the application of active vibration control to micromechanical structures.

High-performance piezo-based self-sensor for structural vibration control

Abstract: Over the past several years Eastman Kodak Company has been developing technologies in the area of active vibration control for space structures. The basic goal is to keep the structure as still as possible during operation using active and/or passive damping and isolation. Inherent in these space structures are many of the qualities that make a system difficult to actively control. They are lightly damped, modally dense, and are sensitive to weight increases, as well as thermal loads that a powered actuator might apply to the structure. Further, any system must be fully space qualifiable. To overcome these hurdles, Kodak has investigated several schemes to apply in a multitier approach to achieve maximum benefit from an active system. This paper will present the theory of operation and test results for one of these technologies called `Self-Sensing Active Vibration Elimination'. We will elaborate on a collocated active damping technique using self-sensing piezo-ceramics. The term `self-sensing' is used to describe the phenomenon of simultaneous actuation and sensing using the same device, in this case piezo- ceramic wafers. This work is an extension of Dosch et al. (1992). The key differences lie in the geometry in which the self-sensor must operate. We parallel the theoretical development given in Dosch et al., but present the development in more of a tutorial form. Research in this area is plentiful, however, less than desirable results have often been reported on systems more complex than a cantilever beam. A strain-rate self-sensor with > 60 dB dynamic range and nano-strain sensitivity in the 10 to 200 Hz frequency band is detailed below, proving that self-sensing can be made to work on large structures. Closed loop results are presented that show performance improvements of over 30 dB reductions in the structural resonance response. It should be mentioned that the system described below could easily be applied to extremely small systems (such as a disk drive read/write arm). The self-sensor would allow an entire controller to be placed on a single 14-pin DIP chip, and since the actuator is also the sensor, less instrumentation loading will occur.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Design of a smart material actuator for rotor control

Abstract: The results of a study to conceptually define an on-blade smart material actuator for primary and active control on a servoflap rotor are presented. Actuator design drivers, goals, and requirements are defined. For a previously developed hybrid actuator concept, the design of the cyclic and active (high speed) control actuator and feasibility of the collective (low speed) actuator and stroke multiplier are investigated. Sizing of actuator components based on AH-64 servoflap requirements shows that collective control using shape memory alloys is well within the capability of the material. Cyclic and active control using magnetostrictive material, leads to a reduced maneuver envelope due to weight and volume constraints. The promise of smart materials can be realized incrementally as the materials and actuator design approaches mature. Future improvements in smart material performance and actuator technology, and additional rotor system design changes to reduced load and motion requirements should provide the full AH-64 maneuver envelope.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Optimal Active Vibration Absorber: Design and Experimental Results

Abstract: An optimal active vibration absorber can provide guaranteed closed-loop stability and control for large flexible space structures with collocated sensors/actuators. The active vibration absorber is a second-order dynamic system which is designed to suppress any unwanted structural vibration. This can be designed with minimum knowledge of the controlled system. Two methods for optimizing the active vibration absorber parameters are illustrated: minimum resonant amplitude and frequency matched active controllers. The Controls-Structures Interaction Phase-1 Evolutionary Model at NASA LaRC is used to demonstrate the effectiveness of the active vibration absorber for vibration suppression. Performance is compared numerically and experimentally using acceleration feedback.

Linear vibration actuator utilizing combined bending and longitudinal vibration modes

Abstract: A vibration driven actuator includes a vibration member for causing an electro-mechanical energy conversion element to excite bending and longitudinal vibrations, and producing a driving force by using specific vibrations obtained by synthesizing the bending and longitudinal vibrations, and a projection portion formed at a position, on at least one of the energy conversion element and the vibration member, which corresponds to a node of the bending vibrations. The projection portion is used for supplying a signal to the energy conversion element.

Adaptive active vibration control using genetic algorithms

Abstract: This paper presents an investigation into the development of an adaptive active control mechanism for vibration suppression using genetic algorithms (GAs). Active vibration control (AVC) consists of artificially generating cancelling source(s) to destructively interfere with the unwanted source and thus result in a reduction in the level of the vibration (disturbances) at desired location(s). This is realised by detecting and processing the vibration by a suitable electronic controller so that, when superimposed on the disturbances, cancellation occurs. Due to the broadband nature of the disturbances, it is required that the control mechanism in an AVC system realises suitable frequency-dependent characteristics so that cancellation over a broad range of frequencies is achieved. In practice, the spectral contents of the disturbances as well as the characteristics of system components are, in general, subject to variation, giving rise to time-varying phenomena. This implies that the control mechanism is further required to be intelligent enough to track these variations so that the desired level of performance is achieved and maintained (Tokhi and Leitch, 1991).

Active Vibration Control of Rotating Machinery Using Piezoelectric Actuators Incorporating Flexible Casing Effects

Abstract: The modern trend toward lighter and more flexible designs in rotating machinery brings with it increasing demands for ways to dissipate the excess energy transferred to such structures by the action of dynamic forces. The present study incorporates the use of active feedback control mechanisms to suppress this unwanted vibration. The basic active damping scheme involves the introduction of a control force on the structure from a feedback network whose input is dictated by the motion of the structure. The control force is applied to the rotor bearing support housing via a piezoelectric actuator attached to the rotor casing. The current research extends previous electromechanical simulations by incorporating a flexible finite element shell model of the casing to support the actuator and sensors. Actuator and feedback loop dynamics are included in the stability and response simulation

The design of LQG and H/sub /spl infin// controllers for use in active vibration control and narrow band disturbance rejection

Abstract: This paper develops an H/sub /spl infin// design method for narrow band disturbance rejection The method is based on the LQG approach via disturbance modelling given in De Nicolao (1992) These LQG and H/sub /spl infin// approaches to the narrow band disturbance rejection problem are then applied to a helicopter active vibration control problem

Reduced order modeling and vibration control methods for flexible structures arranged in parallel

Abstract: This paper proposes reduced order modeling and vibration control methods for flexible structures arranged in parallel. Due to the reduction of vibration brought about by strong winds the higher floors of tall buildings equipped with active dynamic absorbers have become popular habitats. The higher a tall building the lower its natural frequency. Since obtaining sufficient force to control the lower frequency vibrations of tall buildings is a difficult task, controlling the vibration of ultra-tall buildings using active dynamic absorbers is nearly impossible. According to the proposed method, a pair of flexible buildings are controlled actively by controlling each other by means of actuators placed between them. Therefore, it is possible to obtain enough control force under the low frequency. In this paper LQ control theory is applied to the design of such a control system. Using two flexible structures with distributed parameters arranged in parallel, the effectiveness of this method is demonstrated theoretically as well as experimentally.

Results of investigation of an electropneumatic active vibration control system for a driver's seat

Abstract: The aim of this paper is to present some results of a study of an electropneumatic active vibration control system (AVCS) utilizing a pneumatic spring and a proportional electropneumatic transducer. It is treated as a one degree of freedom linear oscillatory system, working predominantly in the vertical direction. A discussion of various AVCS models and respective linear control laws is followed by a short description of the full-scale dummy system aimed for the driver's seats of heavy earth-moving machines and trucks. Some experimental results are presented too.