Showing papers on "Active vibration control published in 1991"

Vibration wave driven motor

Abstract: In a vibration wave driven motor, an elastic body of an elliptic shape is provided where different degrees of stiffness or rigidity are available with the arcuate portions and the straight portions, and the ratio between the distortion energy and the vibration energy that part in the generation of the natural frequency for the A vibration mode is arranged virtually equal to that ratio for the B vibration mode, thus enabling the matching of frequencies for both A and B modes.

Optimal design of piezoactuators for active noise and vibration control

Abstract: A generalized approach for the optimization of piezoactuator/substructure coupling is studied. The effective bending moment induced by twin, rectangularly shaped piezoactuators surface-bonded to the upper and lower surfaces of a thin, flat plate is estimated from a static analysis of the composite structure.

Test and Theory for Piezoelectric Actuator-Active Vibration Control of Rotating Machinery

Abstract: The application of piezoelectric actuators for active vibration control (AVC) of rotating machinery is examined Theory is derived and the resulting predictions are shown to agree closely with results of tests performed on an air turbine driven-overhung rotor The test results show significant reduction in unbalance, transient and sub-synchronous responses Results from a 30-hour endurance test support the AVD system reliability Various aspects of the electro-mechanical stability of the control system are also discussed and illustrated Finally, application of the AVC system to an actual jet engine is discussed

Vibration driven motor

Abstract: In a vibration driven motor or actuator, which has members for generating a first bending vibration and a second bending vibration in a direction different from the first bending vibration therein, and in which a combined vibration of the first bending vibration and the second bending vibration is caused, rigidities in two directions of the vibration member are set to be equal to or substantially equal to each other.

Active Vibration Control of the Axially Moving String in the S Domain

Abstract: A new method is presented for active vibration control of the axially moving string, one of the most common models of axially moving continua. The control is formulated in the Laplace transform domain. The transfer function of a closed-loop system, consisting of the plant, a feedback control law and the dynamics of the sensing and actuation devices, is derived. Analysis of the root loci of the closedloop system gives two stability criteria. Stabilizing controller design is carried out of both collocation and noncollocation of the sensor and actuator. It is found that all the modes of vibration can be stabilized and that in principle the spillover instability can be avoided. Also, the steady-state response of the stabilized string to periodic, external excitation is presented in closed form.

Hybrid Active Vibration Control of Rotorbearing Systems Using Piezoelectric Actuators

Abstract: The vibrations of a flexible rotor are controlled using piezoelectric actuators. The controller includes active analog components and a hybrid interface with a digital computer. The computer utilizes a grid search algorithm to select feedback gains that minimize a vibration norm at a specific operating speed. These gains are then downloaded as active stillnesses and dampings with a linear fit throughout the operating speed range to obtain a very effective vibration control.

Fluid mount with active vibration control

Abstract: A fluid mount with the capability of actively controlling the amount of vibrational energy transmitted thereacross. An actuator is provided in series or in parallel with the inertia track passageway of a double pumper isolation mount to permit the dynamic stiffness of the mount to be varied so as to control the amount of vibrational energy transmitted in a desired manner. A control system for permitting frequency-shaped force feedback control of the device is also disclosed. Utilization of the device as a tuned absorber is also described.

Full-scale demonstration tests of cabin noise reduction using activevibration control

Abstract: We report the results of tests conducted to demonstrate the effectiveness of active vibration control techniques in reducing structure borne noise in aircraft cabins. A prototype active vibration control system was tested in the Douglas Aircraft Company Fuselage Acoustic Research Facility, using the aft section of a DC-9 aircraft as the test article

Active vibration control system for the driver's seat for off- road vehicles

Abstract: The paper deals with an electrohydraulic active vibration control system for the driver's seat for off-road vehicles. After a general description of the problem a serial electrohydraulic active vibration control system, working on the compensation principle, is mathematically analyzed. Results of computer simulation, based on an analogue model, indicate, that the system could effectively absorb vibrations in a chosen frequency band. The evaluation method, based on the ISO 7096-82 Standard, is described and the experimental results are presented as well. These indicate, that a 3-fold (or 10 dB) improvement in the vibration absorption, as compared with the passive seat only (based on the weighted rms acceleration values), can be attained. The vibration exposure time can be increased considerably too. The rather large energy consumption is the only drawback.

Vibration device for a vibration driven motor

Abstract: In an ultrasonic vibrator of structure in which an electro-mechanical energy conversion element for generating a vibration is held by and between electrically conductive blocks and in which a mechanical-electrical energy conversion element for detecting the vibration state of the vibrator is inserted between the blocks, the potentials of the blocks are made different from each other by various means. Therefore, the detection of the vibration state becomes possible, for example, by a detecting element.

Modeling of a Shape Memory Integrated Actuator for Vibration Control of Large Space Structures

Abstract: Martin Marietta is developing a shape memory material actuator to pro vide active vibration and shape control for large, adaptive space structures. An important facet of this work is the development of analytical modeling capabilities for shape memory material behavior. These alloys exhibit a very interdependent force-length-temperature (FLT) response, which must be understood to best exploit their behavior for the efficient and timely conversion of heat into mechanical work. Also, the modal response of large, flexible space structures will be affected by the use of inherently non-linear, hysteretic shape memory actuators, and specialized control methodologies need to be developed spe cific to this application. In this work, Cory and McNichols' theory of non-equilibrium thermostatics (NET) was modified to account for the multiple quadrant (i.e., tension and compression) hysteretic behavior of shape memory alloys. Experimental results were used to provide the basis for spatial mapping of the austenite-to-m...

Bidirectional variable reluctance actuator and system for active attenuation of vibration and structure borne noise utilizing same

Abstract: A bidirectional variable reluctance linear actuator and force control system by which one or more bidirectional linear actuators can be operated to produce a linear relationship between the net force on the armature structure and an applied flux linkage variation signal, as well as an actuator system by which the transmission of vibration through a structure can be blocked by applying forces and/or moments to the structure so as to cancel out its vibratory velocity. An adaptive control system, which is synchronized to machine speed, is able to determine the proper forces that will cancel the vibration of the structure and automatically null out each harmonic of the structure vibration, and cancels the vibration in up to six degrees of freedom of structural motion. The system can provide active attenuation system with a variety of noise sources and transmission paths, i.e., radial (lateral), axial, and torsional, including those associated with propeller shafts, turbine generator sets, pumps, compressors, and other machinery.

Active Wave Control of a Flexible Beam. Proposition of the Active Sink Method.

Abstract: This paper deals with the flexural wave control of a flexible beam with an infinite number of vibration modes. It is the purpose of this paper to present a new vibration control method, the active sink method, which makes it possible to suppress all vibration modes of the flexible beam. Unlike a conventional vibration control method which attempts to suppress several vibration modes already excited, the active sink method seeks to keep all the vibration modes inactive. First, this paper presents the principle of the active sink method and shows a means of realizing its system. Next, in order to describe the principle of the active sink method mathematically, transfer matrices of a beam using a progressive wave solution to the wave equation are obtained. Then, the optimal conditions for the active sink system are derived, and the fundamental characteristics of the system are discussed. Finally, from the vdewpoint of vibration intensity analysis, the validity of the active sink method is clarified.

Active vibration control system for an elevator, which reduces horizontal and rotational forces acting on the car

Abstract: A method and apparatus for actively counteracting a disturbing force acting on a platform moving vertically in a hoistway is disclosed. A manifestation of the disturbing force such as rotational acceleration or translational accelerations indicative thereof is sensed and counteracted, for example, by effectively adding mass to the platform in proportion to the sensed acceleration. The rotations of the platform may be about a vertical axis, one or more horizontal axes or equivalents thereof. Counteraction may but need not be accomplished using an electromagnet actuator for actuating the platform in response to a control signal from a control means which is in turn responsive to the sensed signal. Whatever type of actuator is used, it may be used as well to bring the platform to rest with respect to a hoistway sill prior to transferring passengers. The control means may be analog or digital or a combination of both. A preferred analog-digital approach is disclosed in which the digital part is responsive to accelerometer signals, the analog part is responsive to a force command signal from the digital part and provides a position feedback signal in return. In a preferred embodiment, four electromagnet actuators are situated near the bottom of the platform. Each actuator may act along a line which intersects the walls of the car at a forty-five degree angle. A single axis embodiment is also disclosed.

Piezoelectric strain rate sensor and actuator designs for active vibration control

Abstract: A series of piezoelectric sensors which measure the strain rate of a structyre directly arc dcvclopcd hy recognizing the fact that'due to the high output irnpedancc nature oS piczoclectric scnsors the measured signal i.; strongly influenced by the impctlancc matching circuit. tlxperimentnl data which verifies thc performance of a local strain ratc sensor is presented. A uniaxial strain ratc sensor which cornplctely eliminates the cross-axis sensitivity is developed, as well as a pure shcar strain rate scnsor which measurcs the in-planc shcar rate. T o achieve rnorc clTcctivc distributed control, a singlc-input singlc-output multi-modc scnsor/actuator dcsign approach is prcscntcd for controlling N > I modes of a bcam type stlucturc which docs not exhibit any o r the spillover phcnomcnon into tlic uncontrolled modes typically fourid in othcr flcxihlc structure vibration control approaches. It is shown that tlic two-mode scnsor/actuator case is capahlc of achieving critical damping for both rnodcs undcr control. 'I'hc pcrformance of this sensor/actuator approach [or controlling rnorc than two modes are also prcscnted. Even though negative vclocity fccdback has traditionally been the primary fccdhack variablc uscd in flexible structure vihration control 11-31, in many cases velocity feedback is closely related to strain ratc control [4-61. Strain gagcs havc bccn used successf~illy Tor strain measurement during the last half century, but scnsors or gagcs that measure the local strain ratc of a structurr directly havc not been avaiiablc. Tratlitionallv,

Active vibration control

Abstract: A method of and a system for active vibration control of an extended mechanical structure having a point or region at which unwanted vibrations are to be reduced or suppressed, wherein a plurality of uni-axial inertial actuators (4, 5) are disposed to act on a rigid intermediate part such as a flange (1) attached to the point or region of the structure. The actuators may be controlled by an electronic controller (35, FIG. 3) to which are fed control signals from accelerometer sensors (27, 28) adjacent the flange (11).

Active control of vibration

Abstract: A method of and system for active vibration control in an elongate member such as a pipe (2), wherein an actuator which comprises at least one constrictive element (3) capable of changing its length is attached between flanges (1) spaced along the member and is controlled to produce deformations of the member which inhibit the transmission of unwanted vibration from the member to one side of the attached actuator to the other side.

Active Parametric Damping of Distributed Parameter Beam Transverse Vibration

Abstract: An active vibration control for a modified, non-linear, dynamic, simply supported, Bernoulli-Euler beam is introduced using one of the distributed, time-dependent parameters of the system. The control is carried out by observing the axial velocity of the end point of the beam and applying a modified bang-bang variation of beam tensile stress to control beam transverse stiffness. Numerical simulation of the closed-loop system of partial differential equations demonstrates the effectiveness of the control. Two cases representing initial value problems are given as examples. This active control applied to a undamped system model yields an asymptotically stable system which loses its total system energy to a level that is 0.26% of its initial value in five and one half cycles.

Integrated hydraulic mount for active vibration control system

Abstract: An active-controlled vibrating mount (142) permits static forces from a machine (23) to support while decoupling the transmission of dynamic vibrational forces. The mount provides a reduction of force losses from a first generating area (152) to a second force applying area (130, 132) to actively control vibrations of a vibrating element (23). These force losses are minimized due to minimization of the mass and velocity of fluid pumped by pumping the fluid through the short large cross-sectional area passageways (144, 146). The device provides for proper channeling of the forces to the vibrating element (23) in a uniaxial direction (x) and constrains the application of forces in non-working directions.

Thermal and mechanical considerations in using shape memory alloys to control vibrations in flexible structures

Abstract: Laboratory tests have been performed illustrating the potential for control of vibration in a driven cantilever beam by using a shape memory member driven at an out-of-phase amplitude to cause significant attenuation of the forced vibration. The paper explores the basic properties of shape memory alloys (SMAs) which are suitable for active control devices. Heat transfer, strain rate, force output, and coupling factors involved in engineering the interface between the damping element and the structure are discussed in the context of vibration control. Methods of incorporating SMAs as control elements in composite structures are discussed.

Vehicle vibration damping force control system

Abstract: In a vehicle vibration damping force control system, rolling, pitching and bouncing motions are detected independently in a predetermined priority order; each detected motion is compared with respective predetermined levels; if each detected motion exceeds each predetermined level, hydraulic switch valves are controlled so that operating fluid energized by stroke changes of the hydraulic cylinders due to the detected vibration motion is passed through damping force generating mechanisms to increase a damping force against only the detected vibration motion, without generating any other damping forces against other non-detected vibration motions. Since only the necessary damping force is generated against only the detected vibration motion, the damping force is minimized to maintain vehicle riding comfort.

Sizing of active piezoelectric struts for vibration suppression on a space-based interferometer

Abstract: The present paper concerns itself with the active suppression of mechanical vibrations on a representative future spaceborne optical interferometer This is accomplished by the incorporation of a set of piezoelectric struts into the truss structure of the interferometer and the use of these active struts to modify the damping and stiffness characteristics of the truss It is shown that vibration propagation can be significantly reduced through the use of very simple control laws It is further shown that the force and stroke requirements for the active struts for this application are rather modest and fall well within the capabilities already demonstrated by prototype hardware in ground testing

Control device for a vibration wave motor

Abstract: The present invention relates to a vibration wave motor of the type in which an electro-mechanical energy conversion element is disposed on a vibration member and a frequency voltage is applied to the element to form a travelling vibration wave on the vibration member and a moving member is driven by the vibration wave. In the present invention, when the motor has assumed a resonance or the vicinity thereof when speed adjustment is being effected with the frequency of the periodic voltage changed, the change of the frequency to any frequency exceeding the then frequency is inhibited so that the drive frequency is not changed to a value exceeding the resonance frequency.

A design method for achieving weak radiator structures using active vibration control.

Abstract: A general strategy is devised for achieving minimum radiation of sound from structures subjected to a harmonic excitation force. A quadratic expression is written for the total sound power radiated from a structure in terms of the primary excitation and actuator (control) forces. Using quadratic optimization of this expression, a single control force vector is found that minimizes the radiated sound power (weak radiator). A general formulation is presented for the single‐frequency excitation case. This formulation is then extended to the case of a structure subjected to a broadband excitation force; i.e., the magnitude and the phase of the excitation force remain constant as the excitation frequency changes. The numerical implementation of these formulations is described for a baffled beam controlled by forces and moments generated by piezoelectric actuators. Results for a single‐frequency weak radiator show that the radiation efficiency of the beam response with control is drastically lower than that of the beam response with no control. Also, when the response of the structure with control is compared to that of the structure without control, three important observations can be made. First, the controlled structure exhibits lower response amplitudes at frequencies near structural resonances. Second, the controlled structural response amplitude decreases near the boundaries. Third, the wave number content of the controlled structural response shifts from supersonic to subsonic regions. These observations are confirmed experimentally using a clamped–clamped beam excited at a single frequency with a shaker and four PZT actuators bonded to its surface.

Disturbance cancellation control for vibration of multi-degree-of-freedom systems with harmonic excitation.

Abstract: This study is to derive a general design method of disturbance cancellation control systems which completely strike out harmonic excitation forces for a vibration system with multi-degree-of-freedom. In this paper, the output regulator theory with internal stability based on feedback and feedforward control in applied to a design of control system. First, the feedback control system is designed using modal co-ordinates after modeling the dynamics of a vibration system and a disturbance system. Two models are used for harmonic excitation forces. Next, the feedforward control system is designed for two disturbance models. Finally, some simulation results are described. The important conclusion of this study is following: The disturbance cancellation control for actual use is to design as if the disturbance frequencies were equivalent to natural frequencies on each mode. This means near-zero amplitudes at any position and any frequency.

An application of genetic algorithms to active vibration control

Abstract: A genetic algorithm is developed for the calculation of the time-optimal control force for flexible systems. The algorithm is a robust random-search method which uses a simple and compact coding of the control signal as a binary string of maximum positive and negative forces. A random population of admissible strings is allowed to evolve through the three processes of selection, reproduction and mutation to produce strings with increasing fitness and optimality. The introduction of stop characters allows the time optimal control problem to be solved in one procedure. A simulation is presented to illustrate the behavior of the algorithm. 10 refs.

Active vibration control using fixed order dynamic compensation with frequency shaped cost functionals

Abstract: An approach for the design of controllers for active suppression of helicopter vibration that combines recent developments in the design of fixed-order dynamic compensators with the frequency-shaped cost functional approach is presented. A robust compensator that provides loop shaping at the plant input is used in conjunction with frequency-shaped cost functionals to arrive at a controller for vibration reduction. The effectiveness of this technique is demonstrated by a detailed case study for the design of an active vibration controller. >

Method and apparatus for minimizing vibration

Abstract: Vibration of a system such as a motor and pump on a platform or a transformer is minimized by applying a compensating force to the system. The optimum compensating force is determined by measuring the initial vibration and using that measurement in one of three algorithms to determine an adjustment to be made to the compensating force applied to the system at the time the initial vibration was measured. The adjusted compensating force is applied to the system which changes the vibration. That vibration is measured and applied to the selected algorithm to determine a second adjustment to the compensating force. The process is repeated until a compensating force is found which produces zero vibration, minimum vibration or a desired vibration. A plurality of sensors for measuring vibration and a plurality of actuators for applying a compensating force are preferably used.