Showing papers on "Active vibration control published in 1987"

An approach to structure/control simultaneous optimization for large flexible spacecraft

Abstract: This paper presents an approach to the simultaneous optimal design of a structure and control system for large flexible spacecrafts based on realistic objective function and constraints The weight or total cost of structure and control system is minimized subject to constraints on the magnitude of response to a given disturbance involving both rigid-body and elastic modes A nested optimization technique is developed to solve the combined problem As an example, simple beam-like spacecraft under a steady-state white-noise disturbance force is investigated and some results of optimization are presented In the numerical examples, the stiffness distribution, location of controller, and control gains are optimized Direct feedback control and linear quadratic optimal controls laws are used with both inertial and noninertial disturbing force It is shown that the total cost is sensitive to the overall structural stiffness, so that simultaneous optimization of the structure and control system is indeed useful

Active vibration control of a simply supported beam using a spatially distributed actuator

Abstract: The application of a spatially shaped distributed actuator for the vibration control of a simply supported beam is studied both analytically and experimentally. The actuator consists of a layer of polyvinylidene fluoride (PVF 2 ) bonded to one face of the beam. A summary of the underlying theory is presented, with emphasis on how controllability requirements affect the choice of the film's spatial distribution. The requisite film controller has a linearly varying spatial distribution that facilitates the control of both even- and odd-order vibrational modes. Experimental results are presented for the control of the beam's first three modes, using both the linearly varying as well as a uniform spatial distribution. The linearly varying distribution is shown to be effective in controlling both even- and odd-order modes, serving to increase the modal loss factors by up to a factor of 4.5. In addition, the experimental results are found to corroborate a simplified computer model of the controller.

Nonlinear Control of a Distributed System: Simulation and Experimental Results

Abstract: A nonlinear active vibration damper has been developed which uses a spatially distributed piezoelectric actuator, polyvinylidene flouride, to achieve active vibration control of a cantilever beam. The control algorithm was derived using Lyapunov’s Second Method. All modes of the beam can be controlled simultaneously if the angular velocity of the tip of the beam is known. A simulation algorithm was developed to predict the effect of the control on the free decay of a single mode. A parameter study for the first mode was performed and compared to experimental results. The active damper has been tested successfully on two different scale structures.

Control of Oscillating Transmitted Forces in Axial-Thrust Bearings with a Secondary Magnetic Bearing@

Abstract: In certain applications, axial pulsating forces in a machine need to be isolated so as to reduce the vibration or transmitted force of the main support. This paper illustrates the trade-offs that must be considered for such vibration isolation. It considers tile use of active feedback control and duly notes the control algorithm difficulties that are anticipated in the use of a magnetic bearing as the means for implementing the isolation. Complete vibration isolation is theoretically possible in a machine over certain frequency ranges for a sinusoidally varying exciting force, but at the cost of large vibration amplitudes of the shaft or very large control forces at low frequencies. Conversely, optimum (reduced) transmitted forces may be determined on the basis of a maximum prescribed amplitude of vibration that is acceptable for a particular machine. Presented at the 41st Annual Meeting in Toronto, Ontario, Canada May 12–15, 1986

A New Concept of Generalized Structural Filtering for Active Vibration Control Synthesis

Abstract: A new concept of generalized structural filtering and its application to active vibration control synthesis are presented. The concept is a natural extension of the classical notch and phase lead/lag filtering, and emphasizes the use of a nonminirnum-phase filter which has zeros in the right-half s-plane. Application of this concept to single-input/single-output systems with many oscillatory modes results in a robust feedback compensator with much physical insight. The concept also enables the control designer to understand the inherent nature of an "optimal" compensator, and to modify the optimal design to be more robust and meaningful. This paper shows that for certain cases, nonminimum-phase structural filtering provides the proper phase-lag to increase the closedloop damping of the flexible modes, while maintaining good performance and robustness to parameter variations.

Method and apparatus for measuring weight by means of piezoelectric vibrator

Abstract: PURPOSE: To enable the measurement of a change in weight in a short time, by driving a piezoelectric vibrator to vibrate intermittently and by measuring vibrations. CONSTITUTION: On the occasion when a piezoelectric vibrator is driven to vibrate, it is driven in a manner of intermittent vibration wherein a cycle of vibration and stop of vibration is repeated so that a vibration time width is within 0.1W100sec and that a vibration stop time width subsequent thereto is 10 times as long as or longer than the vibration time width. In the case when a quartz vibrator of AT-Cut of 14mmϕ and 6MHz is made to vibrate at the temperature of 400°C near 573°C of an α-β transformation point, for instance, temperature control is conducted with the precision of 0.1°C and an intermittent vibration method of 5sec drive and 5min stop is adopted, and thereby a measured value having reproducibility for a change in temperature is obtained. COPYRIGHT: (C)1988,JPO&Japio

Vibration control apparatus for vehicles

Abstract: A vibration control apparatus for vehicles to be installed on the vehicle wherein a vehicle body is supported on a truck through springs and damping mechanisms, for suppressing the vibrations of the vehicle body and enhancing the riding quality of the vehicle, comprising a vibration detector which detects the vibration of the vehicle body, a compensator circuit which compensates the detection output of the vibration detector and produces a control output for suppressing the vibration of the vehicle body, a fluid operating mechanism which controls the relative displacement between the vehicle body and the truck and which is connected to the vehicle body on one side and to the truck on the other side, a fluid control device which controls the fluid operating mechanism by the use of the control output produced by the compensator circuit, and damping control means to suppress the damping function of the damping mechanism upon sensing the state under which the vibration of the vehicle body is suppressed by the fluid operating mechanism.

Workshop on Structural Dynamics and Control Interaction of Flexible Structures

Abstract: The Hubble Space Telescope features the most exacting line of sight jitter requirement thus far imposed on a spacecraft pointing system. Consideration of the fine pointing requirements prompted an attempt to isolate the telescope from the low level vibration disturbances generated by the attitude control system reaction wheels. The primary goal was to provide isolation from axial component of wheel disturbance without compromising the control system bandwidth. A passive isolation system employing metal springs in parallel with viscous fluid dampers was designed, fabricated, and space qualified. Stiffness and damping characteristics are deterministic, controlled independently, and were demonstrated to remain constant over at least five orders of input disturbance magnitude. The damping remained purely viscous even at the data collection threshold of .16 x .000001 in input displacement, a level much lower than the anticipated Hubble Space Telescope disturbance amplitude. Vibration attenuation goals were obtained and ground test of the vehicle has demonstrated the isolators are transparent to the attitude control system.

Vibration absorbing and vibration isolating device

Abstract: PURPOSE:To prevent a device easily damaged by vibration from earthquake vibration and environmental vibration, by a method wherein, by mounting a vibration isolating bed on a foundation bed, supported on rolling balls, through lamination rubber structures, vibration during earthquake is absorbed and fine vibration, e.g. environmen tal vibration, are enoughly absorbed. CONSTITUTION:Vibration of micron order, e.g. environmental vibration, is transmitted to a foundation bed 16 through rolling balls 12, 12... and support seats 14, 14.... Fine vibration in a horizontal direction and vertical direction generated to the foundation bed 16 is absorbed by means of lamination rubber structures 32, 32.... Thereby, fine vibration is not transmitted to a vibration isolating bed 34, and a device easily dam aged by vibration on the vibration isolating bed 34 is hardly influenced by fine vibra tion. When earthquake occurs, the rolling balls 12, 12... are rolled on a foundation bed floor 10, and vibration of the foundation bed 16 generated by earthquake is re placed with low frequency through the force of springs 20 and 20. The foundation bed 16 and the vibration isolating bed 34 are widely resonated approximately in an equal phase, slow and high swing is generated on the vibration isolating bed 34, and the vibration is gradually absorbed. Thus, the device easily damaged by vibration on the vibration isolating bed 34 is widely swung in a horizontal direction, but a fear of the device falling down is eliminated.

Accuracy of derivatives of control performance using a reduced structural model

Abstract: The sensitivity of control system performance to structural changes is calculated for a multi-span beam with direct-rate feedback vibration control. Reduced models based on the natural modes of the structure are formed and derivatives of the damping ratios of the closed-loop eigenvalues are calculated. The convergence of the derivatives of the damping ratios with increasing number of modes is shown to be slower than the convergence of the damping ratios themselves. In particular, in some cases the convergence of finite-element approximations to the derivatives is much faster than the convergence of the modal approximations. The results indicate that the use of reduced models based on natural vibration modes may be ill-advised for calculating the sensitivity of control system performance to changes in the controlled structure.

On a New Concept of Active Vibration Damping of Elastic Structures

Abstract: In this paper we deal with flexible, continuous systems, which for the sake of simplicity are assumed to be undamped; this does not however represent a limiting restraint. The active vibration damping of such distributed parameter systems, i.e., the attenuation of vibration by means of active control devices, was first studied in the last decade mainly with a view toward potential applications in aeronautics and astronautics. A typical application in aeronautical engineering is the case of active flutter control.

Active control of sound fields in elastic cylinders by vibrational inputs

Abstract: An experiment is performed to study the mechanisms of active control of sound fields in elastic cylinders via vibrational outputs. In the present method of control, a vibrational force input was used as the secondary control input to reduce the radiated acoustic field. For the frequencies considered, the active vibration technique provided good global reduction of interior sound even though only one actuator was used.

Active vibration control synthesis for the cofs-i: a classical approach

Abstract: Pole-zero modeling and active vibration control synthesis for the COFS Mast Flight System (COFS-I) are discussed. An analytical transfer function from the tipmounted actuator force to the beam deflection at various sensor locations is derived for preliminary control synthesis. A new concept of generalized structural filtering for flexible-mode stabilization is applied to the COFS-I. The simplicity and practicality of the classical transfer-function approach to active structural control are demonstrated for the COFS-I. In particular, nonminimum-phase compensation is proposed for the noncolocated control experiment of the COFS-I. The effects of proof-mass actuator dynamics and control-loop time delay on the phase stabilization of the COFS-I flexible modes are also discussed.

A comparison of active vibration control techniques - Output feedback vs optimal control

Abstract: The paper presents analytical and experimental comparison of two control laws for a laboratory structure designed to simulate large space structures. The first control law is the standard linear quadratic law, which is optimal but requires model reduction for practical implementation. The second control law is a new simple direct feedback control law designed to minimize control forces while guaranteeing stability. The optimal control law was found to be only slightly better than the direct feedback law even in terms of the quadratic performance index. Moreover, the optimal control law provided almost no margin of stability for the unmodeled modes while the direct feedback law provided significant stability margins to all modes. The above results were verified experimentally using a digital implementation of the control laws. Excellent agreement between the analytical prediction and experimental measurements was observed.

On the Vibration Control of Superstructures of Ships by Means of a Dynamic Vibration Absorber with an Adjustable Mass

Abstract: The reduction of superstructure vibration is essential for securing comfortable accomodation space and for preventing damage of delicate equipment in ships. Superstructure vibration is divided into three categories. The first is the local vibration where decks and walls vibrate locally. The second is the fore-aft vibration of the superstructure where the whole superstructure vibrates in the fore and aft direction at its resonant frequency. And the third is the vibration which is caused by hull girder vibrations. The prevention of fore-aft vibration is the most important, because the cure is difficult and expensive in many cases.The authors have developed a dynamic vibration absorber of which the natural frequency can be controlled by adjusting the location of the mass. The reduction of the superstructure fore-aft vibration by means of the dynamic vibration absorber were studied, and are presented in this paper. Scale model tests and full scale tests were performed. The superstructure and the dynamic vibration absorber were modelled into two degrees of freedom systems with the help of FEM analyses. The experimental results were compared with the results calculated by the simple formula of two degrees of freedom systems. They generally showed good correlation.The vibration of the superstructure of a 40, 000 DWT cargo ship was reduced to one forth of the original vibration level by using the dynamic vibration absorber with a 800 kg weight.The dynamic vibration absorber has the following advantages : (1) The installation requires little change in the vibrating structure, so the installation is economical.(2) The dynamic vibration absorber itself generates no vibration, nor noise, because it requires no power sources.(3) The effect of vibration reduction is constant and reliable.

Practical Experiences in Passive Vibration Control of Chimneys (Conclusions from Wind Tunnel and Full Scale Tests)

Abstract: Cylindrical chimney structures with low structural damping are very susceptible to wind induced oscillations. It is well known that chimneys under wind loading respond dynamically in the across-wind as well as in the along-wind direction. For such structures the dynamic response in the across-wind direction is often greater than along-wind.

Active Control of Flexible Space Structures Using the Nitinol Shape Memory Actuators

Abstract: : Summarizes research progress in the feasibility demonstration of active vibration control using Nitinol shape memory actuators. Tests on straight wire and helical actuators to characterize their dynamic response are described. The experimental set-up and the range of parametric variation used in a beam vibration control are also described.

Vibration suppression by stiffness control

Abstract: The feasibility of using piezoelectric ceramics as both sensors and actuators for vibration suppression in a lightweight, flimsy structure was demonstrated. Multimode control was achieved using one sensor and actuator pair. The Positive Position Feedback control strategy requires only knowledge of the natural frequencies of the structure. Implementation of the Positive Position Feedback used only strain measurements to achieve damping, no velocities, or acceleration are needed. All spillover is stabilizing for sufficient small gains.

EVIS: The First General Purpose Active Vibration Isolation System

Abstract: EVIS is the first commercial active vibration control system suitable for general purpose application. It's design closely follows the guidelines and principles described by Sandercock in the previous paper. We First present quantitative operating data For the system, and then discuss some of the unique qualitative aspects of that performance. Some examples of specific applications which are particularly well suited for active control technology are discussed. We have found that the usual models for understanding the operation of conventional passive vibration control systems are not adequate when considering the corresponding active systems. Therefore we discuss a simplified model which has proved useful for estimating the operational benefits of active systems in actual applications.© (1987) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Optimum mix of passive and active control of space structures

Abstract: The objective of this research was to test vibration suppression (settling time and jitter) of a large space structure (LSS) characterized by low frequency high global vibration modes. Five percent passive damping in a large truss was analyzed, tested and correlated. A representative system article re-target analysis shows that modest levels of passive damping dramatically reduce the control energy required. LSS must incorporate passive damping from the outset. The LSS system performance will not be met by either active or passive damping alone.

Experimental and theoretical investigation of passive damping concepts for member forced and free vibration

Abstract: Potential passive damping concepts for use in space structures are identified. The effectiveness of copper brush, wool swab, and silly putty in chamber dampers is investigated through natural vibration tests on a tubular aluminum member. The member ends have zero translation and possess partial rotational restraints. The silly putty in chamber dampers provide the maximum passive damping efficiency. Forced vibration tests are then conducted with one, two, and three damper chambers containing silly putty. Owing to the limitation of the vibrator used, the performance of these dampers could not be evaluated experimentally until the forcing function was disengaged. Nevertheless, their performance is evaluated through a forced dynamic finite element analysis conducted as a part of this investigation. The theoretical results based on experimentally obtained damping ratios indicate that the passive dampers are considerably more effective under member natural vibration than during forced vibration. Also, the maximum damping under forced vibration occurs at or near resonance.