Showing papers on "Active vibration control published in 1983"

Method of and apparatus for active vibration isolation

Abstract: Vibration isolation between a source (1) and a mounting (3) is provided by means of a vibration-cancelling actuator (4a) with a shear isolator (5) placed in series with the source (1). Mechanical and magnetic actuators are disclosed, a preferred mechanical actuator including its own shear isolation with a ratio of compliance in shear and axial directions of at least 50:1.

Vibration studies of a lightweight three-sided membrane suitable for space application

Abstract: Vibration studies carried out in a vacuum chamber are reported for a three-sided membrane with inwardly curved edges Uniform tension was transmitted by thin steel cables encased in the edges Variation of ambient air pressure from atmospheric to near vacuum resulted in increased response frequencies and amplitudes The first few vibration modes measured in a near vacuum are shown to be predictable by a finite element structural analysis over a range of applied tension loads The complicated vibration mode behavior observed during tests at various air pressures is studied analytically with a nonstructural effective air-mass approximation The membrane structure is a candidate for reflective surfaces in space antennas

Piezoelectric vibration wave motor with sloped drive surface

Abstract: In a vibration wave motor, a plurality of electrostrictive elements are phase-differentially arranged or polarized on a ring-shaped vibration member having a thickness which increases as it radially goes from a center to an outer circumference, periodic voltages are applied to the electrostrictive elements to generate a travelling vibration wave in the vibration member, and a movable member press-contacted to the vibration member is friction-driven by the travelling vibration wave.

Active Vibration Control of a Single Mass Rotor on Flexible Supports

Abstract: This paper considers vibration control of a single mass flexible rotor on damped flexible supports with active feedback control. Both proportional and derivative feedback control are utilized. Free vibrations and unbalance response of the rotor-control system are determined. The effect of proportional control is to increase the critical speed of rotating machinery while the effect of derivative control is to reduce the amplitude of vibration. Generally larger ratios of support stiffness to shaft stiffness require larger values of control parameters to produce given amplitudes of vibration.

Active Vibration Control of Simple Beam

Abstract: An experiment on active vibration control of structures is studied. A tendon control mechanism (“King-post Truss”) is used to reduce the vibration of a simple beam, subjected to a sinusoidal driving force. Experimental results are compared with theoretical ones. Conclusions about the efficiency of the control scheme are drawn and practical difficulties are pointed out.

The Control of Engine Vibration Using Squeeze Film Dampers

Abstract: This paper describes the following roles of a squeeze-film damper when used in gas turbine applications as a means of reducing vibration and transmitted force due to unbalance: (a) as an element in parallel with a soft spring in a vibration isolator; and (b) as an element in series with the stiffness of the engine pedestal. The effects of cavitation on performance are elucidated, and the dangers of jump phenomena and subsynchronous response are discussed. Experimental work is described in which both roles of the squeeze-film damper are investigated and the results are compared with theoretical predictions.

Longitudinal vibration type piezoelectric vibrator

Abstract: PURPOSE:To obtain a small-sized longitudinal vibration-type piezoelectric vibrator with highly stable performance and low cost by fixing a supporting base of a vibrator with a lead terminal having elasticity. CONSTITUTION:The main vibration part 9 of a longitudinal vibration type piezoelectric vibrator 100 and a support 13 comprising a support connection part 10, a supporting arm 11 and a supporting base 12 are formed incorporatedly. Main electrodes 9'a, 9'b are formed as electrode pairs at both side faces of the main vibrating part 9. External extraction electrodes 13'a, 13'b are formed on the support 13. Moreover, the electrodes 13'a, 13'b are fixed directly with the side face of lead terminals 17a, 17b penetrating a hermetic terminal 16 and having elasticity. Then the vibrator 100 is sealed to a case 18. Through the constitution above, since the vibration obtained by the main vibrating part 9 is attenuated sufficiently by the lead terminals 17a, 17b, the mass of the terminal 16 and the case 18 is reduced.

Vibration Control of Beams by Ball Screw Type Dampers : Case in which Dampers Possess Viscous Damping

Abstract: The effects of vibration isolation of a ball screw type damper applied to a simple beam, a clamped-clamped beam or a cantilever beam are discussed theoretically. The damper is composed of a ball screw, a flywheel and a dashpot. Numerical examples are given for a simple beam with one or two ball screw type dampers. It is demonstrated that, when the locations of the dampers are chosen suitably, the first, second and third resonant frequencies can be lowered considerably and the amplitude response factors of the beam at the points of attachment of the dampers are about 1 except in a narrow range of resonant frequencies.

Vibration suppression in large space structures

Abstract: The problem of potential instability caused by actuator dynamics is examined. Two ways of overcoming it are discussed: rate feedback with compensation and position feedback with tuning filters.

Vibration and acoustic radiation of piezoelectric transducers——fem—equivalent circuit

Abstract: In this paper, by using the finite element discrete equation, it is shown that the vibration displacement and electric field in piezoelectro-elastic body can be expanded in terms of its free vibration modes Then a multimode equivalent circuit with lumped parameters, which is of universal significance, is presented A FEM-equivalent circuit method is developed to compute the performances of vibration and acoustic radiation of piezoelectric transducers This method has some advantages of both FEM and classical equivalent circuit analysis The calculated results of a composite rod and a concave flexteusional transducer conform with the measured ones

Experimental implementation of parameter adaptive control on a free-free beam

Abstract: A method for identifying modal parameters has been integrated with a modal control scheme and implemented on an experimental beam at the NASA Langley Research Center. This work is the culmination of several studies to develop adaptive control schemes for large flexible spacecraft. The identification scheme is an equation-error technique which generates modal frequency and damping estimates on-line from a set of distributed displacement measurements. The control law is a modal pole placement technique with the objective of vibration suppression. Integration of the identification and control schemes is achieved through a series of tests which validate the identified parameters before they are used for control gain updating. Results using a low order controller show that control gains can be updated in real time based on the validated parameters to improve the performance of the closed loop system. Important factors in the implementation are the test criterion and the a priori assumption of mode shapes.

Experimental Study of Active Vibration Control.

Abstract: : Complementary experimental-theoretical studies were conducted on three separate topics, all of which are related to the dynamics and control of highly flexible large space structures (LSS) in Earth orbit: (1) active damping of vibrations; (2) structural wave propagation; and (3) development of small, flexible laboratory structures having a maneuverable rigid body mode. In the active damping study on a laboratory structure of moderate modal complexity, very good agreement was achieved between experimental measurements and theoretical predictions. The type of active damping applied, output feedback with dual (colocated) control sensors and actuators, should be considered as a candidate for implementation on first-generation LSS because of its stability robustness. The study of wave propagation is focused primarily on transient flexural response of a two-dimensional grid structure to a suddenly applied sinusoidal force at one point. The study is not completed, so results are not presented. New laboratory structures with a maneuverable rigid body mode were build and analyzed. They were relatively simple planar structures composed of thin-walled beam members. They exhibited some unusual dynamic characteristics such as variable natural frequencies, snap buckling, and other nonlinearities. Finite element modeling generally failed to predict the measured vibration modes and the unusual characteristics.

Minimum angular vibration design of airborne electro-optical packages

Abstract: Low-level angular vibration disturbances to airborne electro-optical packages can sometimes severely degrade the accuracy of such systems. This paper is an investigation into the possibility of minimizing the angular vibration response of selected points on an optical bench by redistributing the mass. The governing equations are presented in a form suitable for application of the Pontryagin maximum principle with the beam cross-sectional area playing the role of the control function. Angular vibration reduction at the ends of a pinned beam of an order of magnitude are demonstrated.

On the Suppression of Ground Vibration by Active Force Controller : Suppression of Exciting Force by Feedforward Control

Abstract: For the purpose of suppressing the ground vibration as public nuisance produced by vibrating machines such as a forging machine, a press machine, etc., this paper presents a new type active force controller. First, the principle of the active force controlling method is shown, and the system equations are derived. Secondly, the characteristics and the design parameters of the active force controller are presented. Thirdly, from a point of view of feedforward control method, three kinds of the dynamic compensators are designed so as to obtain sufficient effectiveness of suppressing the exciting force. Finally, in order to demonstrate the control effect, an experiment is carried out, and then the active force controller is proved to be applicable for suppressing the ground vibration as public nuisance.