Showing papers on "Active vibration control published in 1988"

Active Vibration Control of Large Civil Structures

Abstract: This survey of vibration control methods for safety and comfort in large civil structures (LCS), reviews the application of control theory to LCS, and discusses a class of vibration suppression algorithms that avoid the major difficulties encountered in the application of modern control techniques to building structural systems. Two simple, efficienct methods are presented for the on-line pulse control of linear as well as nonlinear, multi-degree-of-freedom systems responding to arbitrary dynamic environments. The latter method is suitable for situations in which detailed knowledge of the system structure is not available. Digital computer simulation studies, electronic analog computer investigations, and experimental tests with several mechanical models of different size and configuration demonstrate the feasibility, reliability, and robustness of the proposed pulse-control methods.

Controlling velocity-limited systems to reduce residual vibration

Abstract: To avoid vibration of robot arms when they are moved very rapidly, a set of shaped force profiles have been developed to minimize the excitation energy at the system's first natural frequency during motion. The system is assumed to be velocity-limited. The force profiles are constructed from a versine (one-cosine) function and its harmonics, with coefficients chosen to minimize the spectral magnitude near the system natural frequency. The profiles can be tuned to the closed-loop natural frequency of a closed-loop system with motor position and velocity feedback. When integrated twice, the force profile becomes a reference trajectory which serves to bring the system to peak velocity with minimum excitation at the first natural frequency. Using a suitable dwell time between acceleration and deceleration, a specified position can be reached quickly with minimum residual vibration and within while never exceeding the velocity limit. >

Microprocessor controlled force actuator.

Abstract: The mechanical and electrical design of a prototype force actuator for vibration control of large space structures (LSS) is described. The force actuator is an electromagnetic system that produces a force by reacting against a proof-mass. The actuator has two colocated sensors, a digital microcontroller, and a power amplifier. The total weight of actuator is .998 kg. The actuator has a steady state force output of approximately 2.75 N from approximately 2 Hz to well beyond 1000 Hz.

Vibration absorbing apparatus

Abstract: A vibration absorbing apparatus for reducing vibrations of a vibration damping objective comprises a vibration member excited by a piezo-ceramic element. The voltage applied to the piezo-ceramic element is controlled in accordance with the vibration state of the objective.

Active vibration control synthesis for the control of flexible structures mast flight system

Abstract: Pole-zero modeling and active vibration control synthesis for the Control of Flexible Structures Mast Flight System (COFS-I) are discussed. An analytical transfer function from the tip-mounted actuator force to the beam deflection at various sensor locations is derived for 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 vibration control are demonstrated for the COFS-I. In particular, nonminimum-phase structural filtering 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/gain stabilization of the flexible modes are also discussed.

Automatically controlled dynamic absorber

Abstract: An automatically controlled dynamic vibration absorber in which the characteristic frequency of the vibration absorber is adjusted automatically to the frequency of vibration from a vibrating source to dissipate the vibration by mating a response vibration with a forced vibration.

Active Control for Vibration Damping

Abstract: Active control laws are developed for an LSS-type structure to damp vibrations. High frequency modelling uncertainties lead to the necessity for a robust control design. The Linear Quadratic Gaussian with Loop Transfer Recovery (LQG/LTR) control design technique is a particular robust design technique selected for use in designing a damping control system. A summary of LQG/LTR is given and numerical example using a two bay truss is presented.

Drive controller for ultrasonic motor

Abstract: PURPOSE: To escape an ultrasonic motor rapidly from a vibration deviating state and to recover it to a normal vibrating state by altering the applied pressure of a rotor by an actuator if the ultrasonic motor becomes the vibration deviating state. CONSTITUTION: When a high frequency voltage is supplied from a power supply circuit 20 to a piezoelectric element 1b, the piezoelectric element 1b is vibrated to form a traveling vibration wave at an elastic element 1a. When a rotor 2 is brought into pressure contact with a stator 1 in which the traveling vibration wave is generated by a pressurizing unit 100, the rotor 2 is rotated by a frictional drive while vibrating. When a vibration deviating state discrimination circuit 40 judges the vibration deviating state, it inputs a vibration deviating state signal to a vibration recovering unit 50. The vibration recovering unit 50 elongates or contracts a piezoelectric actuator 51 by its drive circuit 52 to alter an applied pressure by an energizing member 6 thereby to vary the resonance characteristic of an ultrasonic motor MT. Thus, the ultrasonic motor MT is recovered from the vibration deviating state to a normal vibrating state. COPYRIGHT: (C)1990,JPO&Japio

Active damping of spacecraft structural appendage vibrations

Abstract: An active vibration damper system, for bending in two orthogonal directions and torsion, in each of three mutually perpendicular axes is located at the extremities of the flexible appendages of a space platform. The system components for each axis includes: an accelerometer, filtering and signal processing apparatus, and a DC motor-inertia wheel torquer. The motor torquer, when driven by a voltage proportional to the relative vibration tip velocity, produces a reaction torque for opposing and therefore damping a specific modal velocity of vibration. The relative tip velocity is obtained by integrating the difference between the signal output from the accelerometer located at the end of the appendage with the output of a usually carried accelerometer located on a relatively rigid body portion of the space platform. A selector switch, with sequential stepping logic or highest modal vibration energy logic, steps to another modal tip velocity channel and receives a signal voltage to damp another vibration mode. In this manner, several vibration modes can be damped with a single sensor/actuator pair. When a three axis damper is located on each of the major appendages of the platform, then all of the system vibration modes can be effectively damped.

An expository overview of active control of machinery mounts

Abstract: The author considers the isolation of vibration originating in a comparatively compact, rigid machine. The machine can be an internal combustion engine, a turbine, compressor, etc. The machine is mounted in a structurally flexible vehicle using several machinery mounts. A machinery mount should be capable of transmitting low-frequency forces and supporting the machine against static loads due to vehicle accelerations but incapable of transmitting high frequency vibratory force. Past approaches have been passive, involving 'soft springs' and, occasionally, dynamic effects. Advances in electronics, materials and to a lesser degree control theory, suggest the possibility of accomplishing these tasks more effectively with active or combined active/passive techniques. The author attempts an overview and classification of the problem and of potential active approaches. >

Reduction of interior sound fields in flexible cylinders by active vibration control

Abstract: The mechanisms of interior sound reduction through active control of a thin flexible shell's vibrational response are presently evaluated in view of an analytical model. The noise source is a single exterior acoustic monopole. The active control model is evaluated for harmonic excitation; the results obtained indicate spatially-averaged noise reductions in excess of 20 dB over the source plane, for acoustic resonant conditions inside the cavity.

Optimal Placement of Piezoceramic Sensors and Actuators

Abstract: Bonded and embedded piezoceramic sensors and actuators can be used for active vibration control of flexible structures. Development of optimal control procedures require a consideration of design variables such as the size of the piezoceramic devices, types of devices, number of such devices, control gains, signal conditioning options, weights to be used on state and control, decentralization and placement of the transducers. In this paper the effect of the location or placement of the sensors and actuators and the question of centralization and decentralization has been discussed with reference to a selected flexible structure and selected piezoceramic sensors, actuators and a strain rate feedback.

Smart Components for Structural Vibration Control

Abstract: A vibration control strategy for multi-component structures has been developed in which the structural components are actively damped beam members Each component element is smart in the sense that it is an active vibration control system which is autonomous of all other structural components Distributed sensor and actuator transducers constructed from polyvinylidene fluoride (PVF 2 ) are embedded in each beam element Lyapunov's direct method was used to develop a vibration control strategy for a generalized system consisting of an arbitrary number of smart beam members rigidly joined at a common boundary The analysis leads to a smart component control law which guarantees stability to the global system A universal spatial film distribution is proposed which has the potential of providing active damping to all components irrespective of boundary conditions The control methodology was validated experimentally on a structure constructed from three rigidly joined autonomous smart components Frequency response data for the first three modes demonstrate that the smart structure control strategy provides active damping simultaneously to multiple vibrational modes

An active air bearing. Ultra-precision control of floating position and vibration.

Abstract: This paper introduces an active air bearing. In the conventional passive type, for example, in an air slide, a table is supported by the pressurized air film which can be considered as a spring and damper system. Thus, disturbances, i. e. various kinds of external force cause the table vibration as well as the change of the air film thickness and that of the table floating position. Moreover, motion accuracy of the table depends on accuracy of guideways. These suggest necessity of a mechanism capable of floating position and vibration control of an object. In the active air bearing, a PZT actuator is used for controlling floating characteristics ; floating position and vibration of the object. The actuator is arranged in series to the air film not to damage its property ; free of mechanical contact. Two degrees of freedom control system (PID-PD or PID-PDD2) is adopted for obtaining desired characteristics of floating position control and active damping of vibration. In experiments, a 9 kg mass object is floated under control with 20 nm vibration amplitude, and is positioned with 20 nm positioning accuracy, 500 Hz bandwidth and no-overshoot.

Vibration proofing method and device thereof

Abstract: PURPOSE:To obtain an excellent vibration-proofing effect in a short time, by converting vibration of an object for vibration-proofing into an electric signal to be detected, and providing inverse vibration to the object for vibration- proofing by means of a vibrator, the inverse vibration which is oriented inversely of vibration of the object, and the magnitude of which is determined in accordance with that of vibration thereof. CONSTITUTION:When external force is exerted on an object 3 for vibration- proofing and vibration is generated therein, the vibration is transmitted to a piezoelectric element 2, so that the piezoelectric element 2 stretches or shrinks in accordance with the vibration, to thereby output voltage signals to a detector 5. The detector 5 outputs the signals thus detected to a controller 7, which outputs voltage being inverse of the output voltage of the piezoelectric element 2 of its sign and having its magnitude determined in accordance with that of the output voltage to the piezoelectric element 2. Vibration of the piezoelectric element 2 is thus rapidly attenuated and vibration of the object 3 for vibration-proofing is also rapidly attenuated. Thus the controller 7 controls vibration positively in accordance with the quality of vibration, so that vibration which is temporally variable can be controlled in a shorter time.

Advanced Joining Concepts for Passive Vibration Control

Abstract: Passively damped joints, in which the conventional adhesives are replacedby high damping viscoelastic materials, have the potential of being effective practical means for passive vibration control of dynamically loaded civil and aerospace structures. However, this potential cannot be realized unless the associated structural penalties are reduced to acceptable limits. This paper describes a rational methodology for the development of advanced joining concepts for structural systems capable of providing enhanced dissipation of vibrational energy without serious penalties in strength, stiffness, or weight characteristics. One such configuration is that of a rhombic-type joint, which provides a beneficial deformation coupling between the direction of load transfer and less critical offset directions. A comprehensive parametric study has been carried out in order to establish design guidelines for favorable trade-offs between damping benefits and the associated stiffness, strength, and weight penalties in a rhombic joint. The results are compared with the corresponding trade-offs for a double-lap joint made of the same materials.

Active vibration control of flexural power flow in beams

Abstract: Active control of flexural power flow in infinite and semi‐infinite thin elastic beams by point force inputs is analytically studied. Various forms of terminating impedances or discontinuities positioned on the beam are also considered. The influence of system parameters such as the discontinuity impedance and effects such as bending nearfield generation on the location and number of control actuators and error sensors is investigated and discussed. The mechanisms by which control is achieved are considered. It is demonstrated that these types of boundary conditions strongly influence the choice of optimal controller format. For example, if the error signal only contains information from the propagating wave component, then only one control actuator is needed for complete attenuation of flexural power flow. Finally, preliminary results of a companion experimental investigation will be discussed and compared with the theoretical developments. [Work supported by NASA Langley Research Center.]Active control of flexural power flow in infinite and semi‐infinite thin elastic beams by point force inputs is analytically studied. Various forms of terminating impedances or discontinuities positioned on the beam are also considered. The influence of system parameters such as the discontinuity impedance and effects such as bending nearfield generation on the location and number of control actuators and error sensors is investigated and discussed. The mechanisms by which control is achieved are considered. It is demonstrated that these types of boundary conditions strongly influence the choice of optimal controller format. For example, if the error signal only contains information from the propagating wave component, then only one control actuator is needed for complete attenuation of flexural power flow. Finally, preliminary results of a companion experimental investigation will be discussed and compared with the theoretical developments. [Work supported by NASA Langley Research Center.]

Active vibration control in microgravity environment

Abstract: An active control process to reduce vibration transmitted from the Space Station structure to the vibration sensitive payload is evaluated. A low-friction air-bearing table is used to approximate zero gravity in the horizontal plane. An analog control system is described which activates calibrated air jets when displacement of the test mass is sensed. The air jet control system is found to introduce an effective damping factor in controlling the oscillatory response. The air-jet control system is designed such that the thrust force produces less than 10 to the -5th g acceleration of the payload. An analytical model has verified the amount of damping in addition to flow parameters such as the pressure drop across the valve and the air flow rate.

Output Regulation in Active Dynamic Vibration Absorber Systems

Abstract: An output regulation problem of an active dynamic vibration absorber system is considered, where the object is to reject completely the effects of a sinusoidally varying external force on the main mass by manipulating the motion of a auxiliary mass in an absorber attached to the main mass. The theory of output regulation with internal stability is applied in designing the control system of an active dynamic absorber system which consists of a main mass to be regulated, an auxiliary mass generating inertial reaction, an actuator driving the auxiliary mass and sensors detecting the diplacements of the masses. A new control method is presented which is enable to remove completely the vibration of the main mass at a particular frequency and to attenuate well the vibration in a wide range of frequency as well. Moreover the obtained condition of output regulation includes the tuning condition of a passive vibration absorber without damping as a special case; that is to say, at the natural frequency of the absorber the vibration of the main mass is completely removed automatically. The effectiveness of the control method is confirmed by numerical simulation and analysis of the frequency characteristics of the designed control system.

Distributed parameter active vibration control of smart structures

Abstract: A vibration control strategy for multi-component structures has been developed in which the structural components are actively damped beam members. Each component is mart in the sense that it is an active vibration control system which is autonomous of all other structural components. Distributed sensor and actuator transducers constructed from polyvinylidene fluoride (PVF 2) are embedded in each beam element. Lyapunov's direct method was used to develop a vibration control strategy for a generalized system consisting of an arbitrary number of smart beam members rigidly joined at a common boundary. The analysis leads to a smart component control law which guarantees stability to the global system. The distributed transducer electric fields may be varied to provide controllability to all modes or to specific modal subsets of a structure. Guidelines are presented for choosing film electrode spatial distributions to meet design goals. A universal spatial film distribution is proposed which has the potential of providing active damping to all modes of many structures with nearly arbitrary boundary conditions. To develop the control methodology, theoretical models for spatially distributed transducers on flexible beam components were derived. An analytical model for spatially distributed sensors on flexible beam elements was developed without the necessity of modeling the beam in terms of its component vibrational modes. The model provides insight into the observability of beams with nearly arbitrary boundary conditions. The sensor electrode surface may be spatially distributed so as to function similar to point sensors or to produce a signal in which certain vibrational modes of the structure are weighted more than others. A previously derived model for PVF2 actuators is presented in terms of its duality with the distributed sensor analysis. The sensor model was verified experimentally for spatially uniform and linearly-varying sensors applifed to a clamped-free beam. The signals provided by the distributed sensors were compared to the outputs of corresponding point sensors. PVF 2 sensors and actuators situated on the same structural component developed radiative noise problems which were effectively compensated with noise reduction circuitry.

Method for the testing of vibration dampers (shock absorbers)

Abstract: Method for the testing of vibration dampers of a vehicle in the built-in condition, in which at least one wheel resting at the time on a wheel stand plate is caused to vibrate and the amplitudes of the vehicle body are evaluated. For the evaluation of the effectiveness of a vibration damper, the amplitude of the maximum resonant frequency of the vehicle body is ratioed to the amplitude of the resonant frequency multiplied by the factor @2. The value thus obtained yields a measure of the degree of damping of the vibration damper.

Experimental Demonstration of the Maximum Entropy/Optimal Projection Design Theory for Active Vibration Control

Abstract: Based on a recent survey of Large Space System concepts and the identified characteristics of ground-based experiments needed to demonstrate capability for future systems, a sequence of vibration control experiments have been designed and are being performed at Harris Corporation. The experiments involve a progression of structural configurations ranging from relatively simple one and two dimensional strctures to a large aperture, multi-segment optical structure. The experiments have been designed to evaluate a variety of control design methods including the Maximum Entropy/Optimal Projection method. This paper reviews the concepts and status of these experimental activities.

Vibration control in a tower structure by a two-dimensional active mass damper with an LQ control system.

Abstract: This paper proposes a two-dimensional active mass damper which is controlled by a software servo system in order to reduce the vibration of tower structures caused by strong winds or earthquake. The purpose of the two-dimensional active mass damper is to control effectively the two-dimensional 1st vibration modes of the structure. In designing the software servo system, LQ control theory is applied. The results of experirental examination on the design show that although the 1st vibration modes are well controlled, a resonance peak at the 2nd mode increases as a resonance peak at the 1st mode is decreased and runs into spillover instability. It is also shown that the spillover instability can be prevented easily by a dynamic absorber attached at the maximum amplitude point on the 2nd vibration mode.