Showing papers on "Active vibration control published in 1989"

New generalized structural filtering concept 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 nonminimum-phase filter, which has zeros in the right-half s plane. Application of this concept to single-input/singleoutput 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, nonminimumphase structural filtering provides the proper phase lag to increase the closed-loop damping of the flexible modes while maintaining good performance and robustness to parameter variations.

Active vibration control of flexible rotors: an experimental and theoretical study

Abstract: This paper develops the authors' earlier work on vibration control of multi-mode rotor-bearing systems. It shows how a single magnetic actuator can be used to estimate system characteristics and apply the optimum control force needed to minimize synchronous vibration. In the application considered here, a rotor is supported on oil-film bearings. The algorithm determines the optimum control force without prior knowledge of the bearing or rotor characteristics or the distribution of out-of-balance forces. A rig is described and used to illustrate the application of the theoretical work.

Integrated distributed sensing and active vibration suppression of flexible manipulators using distributed piezoelectrics

Abstract: Structural oscillation of flexible robot manipulators would severely hamper their operation accuracy and precision. This article presents an integrated distributed sensor and active distributed vibration actuator design for elastic or flexible robot structures. The proposed distributed sensor and actuator is a layer, or multilayer of piezoelectric material directly attached on the flexible component needed to be monitored and controlled. The integrated piezoelectric sensor/actuator can monitor the oscillation as well as actively and directly constrain the undesirable oscillation of the flexible robot manipulators by direct/converse piezoelectric effects, respectively. A general theory on the distributed sensing and active vibration control using the piezoelectric elements is first proposed. An equivalent finite element formulation is also developed. A physical model with distributed sensor/actuator is tested in laboratory; and a finite element model with the piezoelectric actuator is simulated. The distributed sensing and control effectiveness are studied.

Piezoelectric Pushers for Active Vibration Control of Rotating Machinery

Abstract: The active control of rotordynamic vibrations and stability by magnetic bearings and electromagnetic shakers have been discussed extensively in the literature. These devices, though effective, are usually large in volume and add significant weight to the stator. The use of piezoelectric pushers may provide similar degrees of effectiveness in light, compact packages. Tests are currently being conducted with piezoelectric pusher-based active vibration control. Results from tests performed on NASA test rigs as preliminary verification of the related theory are presented.

Experimental active vibration damping of a plane truss using hybrid actuation

Abstract: Hybrid actuation is defined in the context of active vibration control as the simultaneous functioning of two or more types of structure-borne actuators, each type having a frequency band of greatest effectiveness that is different from the bands of the other types. This paper describes and analyzes, both experimentally and theoretically, a simple active damping system that applied hybrid actuation with air-jet thrusters and reactionmass actuators. The former were highly effective at low frequencies but, due to mechanical time delays, lost effectiveness and were even potentially destabilizin~ at higher frequencies; the latter had the character of a hlghpass filter and, hence, were most effective at f reque~~cies above a certain threshold. Active damping was imposed on a %bay, 7.07-m-long plane truss, the hardware and mathematical models of which are described. The structure's vibration modes considered are the first four, a t 1.56, 10.0, 24.7 and 43.0 Hz. The active damping system consisted primarily of two pairs of back-to--back air-jet thrusters, two reaction-mass actuators, four servo accelerometers, and two small analog computers.

Coordinate measuring machine with vibration dampening system

Abstract: A vibration dampening system particularly for use in a gantry-type coordinate measuring machine. The vibration dampening system includes a vibration damper in the gantry structure, a vibration damper in the Z-rail, and means in the supports for the base for dampening vibrations, all of which work together cooperatively to damp vibrations in the coordinate measuring machine. The vibration damper in the gantry structure and in the Z-rail each comprises a substantial mass suspended by pads of material having high energy absorbence and a low rebound resilience. The vibration dampening means in the table means includes a layer of material which is highly energy absorbent and has a low rebound resiliency, and which is disposed between two rigid plates positioned between each supporting leg of the table and an underlying floor. The vibration dampening system is tuned to provide maximum energy absorbency at major modes of vibrations in the machine during acceleration and deceleration.

Active control of sound fields in elastic cylinders by multicontrol forces

Abstract: An unstiffened cylindrical model was used to study the control of sound transmission into aircraft cabins by the use of multi-control forces applied directly to the cylinder wall. External acoustic monopoles were located on each side of the cylinder to approximate the propeller noise source. This allowed the study of a dual control system utilizing multi-control forces in conjunction with synchrophasing of the twin acoustic monopole sources. For acoustic resonant conditions within the cavity, a spatially averaged noise reduction of approximately 30 dB was achieved using the active control system for both in-phase and out-of-phase monopoles; however, effective reduction of the sound field was dependent upon judiciously positioning the control forces for optimal control of the sound field.

Method and apparatus for sensing and damping vibration

Abstract: A shape memory alloy used for both sensing and damping vibration of a structure. In one embodiment, a flat bar (12) is mounted from one end on its edge so that its other end vibrates from side-to-side at its natural resonant frequency. A vibration damping wire (30) extending longitudinally along one surface of the bar is mounted under tension between spaced apart standoffs (32); a sense wire (42) is similarly mounted along the opposite surface of the bar. The vibration damping wire and sense wire comprise a nickel-titanium (Nitinol) alloy, having a relatively high specific damping coefficient. Absorption of kinetic energy by the vibration damping wire when it is stretched by deflection of the bar greatly reduces the time required to passively damp vibration of the bar, compared to its undamped resonant time. the vibration damping wire is heated above a transition temperature by an electrical current pulse while relaxed to restore it to its unstretched length. The sense wire changes resistance in proportion to stress applied to the wire so that a voltage drop across the sense wire corresponds to the vibrational displacement of the bar. The voltage drop signal is used to control application of the current pulse in synchronization with the vibratory motion of the bar. To actively damp vibration of the bar, the pulse of electrical current is applied to heat the Nitinol alloy above its transition temperature so that it resumes a foreshortened memory shape as the bar's vibratory deflection tries to stretch the vibration damping wire. The vibration damping wire thus applies a force to the bar in opposition to its vibration. Other embodiments include a cylinder (52) and a vibration damped strut assembly (80). In these latter two embodiments, vibration damping wires and sense wires are disposed internally within the structure. A digital control (110) or analog vibration damping control (200) controls the application of current pulses to heat a selected vibration damping wire above the transition temperature in phase with the signal produced by the sensor wire.

Active vibration control through sensing and controlling forces on an intermediate body

Abstract: A method and mounting for active vibration control of a vibrating body mounted to a supporting body, or vice versa, via a mounting which includes an intermediate body, wherein the intermediate body is substantially passively decoupled from the vibrating body and the supporting body, at least over part of the frequency range over which vibrations are to be controlled, and over said at least part of the vibration frequency range compensating forces are applied to the intermediate body in response to vibrations detected within it

Coordinates input apparatus with plural pulse train whose phases differ

Abstract: There is provided a coordinates input apparatus comprising: a vibrator drive controller to output a vibrator drive signal obtained by synthesizing a plurality of pulse trains whose phases differ; a vibration pen to generate a vibration from a vibrator which generates the vibration in response to the vibration drive signal output from the vibrator drive controller; a vibration propagating plate made of a transparent acrylic or glass plate to propagate the vibration generated by the vibration pen; a plurality of vibration sensors, attached to the vibration propagating plate, for detecting the vibration generated by the vibration pen at a plurality of positions; and a coordinate value calculation/control circuit for calculating the vibration propagating times from the vibrations detected by the vibration sensors at a plurality of positions, thereby obtaining the coordinate values on the vibration propagating plate on which the vibration pen is located from the propagating times calculated. With this apparatus, the influences of noise such as reflected waves on the vibration propagating plate can be eliminated, so that the vibration detecting point or a special point on the waveform can be accurately set.

Active Vibration Isolation by Cancelling Bending Waves

Abstract: Active forces applied to a vibrating beam structure may be driven to cancel propagating and evanescent waves entering the region beyond their point of application, thereby preventing those waves from carrying the effects of an external disturbance into that region. The application of this concept to the problem of vibration isolation has great potential; a system designed to detect bending waves as they pass a sensor and then inject an antidote further downstream can achieve total isolation of the entire structure beyond the point of application of just two point forces. The feedforward configuration ensures that the effectiveness of active isolation is limited only by the accuracy of implementation of the control system. Synthesis of the controller in terms of flexural waves suggests that the compensation required would contain irrational terms resulting from the dispersive nature of the waves; the inaccessibility of individual wave components to any measurement system in a finite structure, where vibrations are the superposition of waves in both directions, would complicate implementation and make accurate identification of the system impractical. These difficulties were removed by including the effects of waves generated by the active forces and detected at the controller input in the control system synthesis, and a simple, stable, active isolation system emerged. We show that the compensation required may be expressed in a rational polynomial form, and that identification of the optimal compensation in a noisy environment may be made using input-output response measurements on the structure to be isolated. The same response data can be used to predict limits imposed on the achievable isolation by inaccuracies in implementation. This work culminated in the application of these techniques to the problem of isolating a cantilever beam from vibrations caused by a random, broadband disturbing force near the fixed end. Although component inaccuracies in the particular apparatus used in the experiment allowed only 6 dB of attenuation to be achieved over a bandwidth of 200 Hz, good agreement between predicted and experimental results was shown.

Active control system and method for reducing engine noise and vibration

Abstract: Noise and vibration in a structure is reduced through application to the structure of an oscillatory torque. An electromechanical energy converter provides the oscillatory torque when the input signal to the electromechanical energy converter has a frequency and harmonics thereof required to counteract the noise and vibration desired to be attenuated.

Modified independent modal space control method for active control of flexible systems

Abstract: A modified independent modal space control (MIMSC) method is developed for designing active vibration control systems for large flexible structures. The method accounts for the interaction between the controlled and residual modes. It incorporates also optimal placement procedures for selecting the optimal locations of the actuators in the structure in order to minimize the structural vibrations as well as the actuation energy. The MIMSC method relies on an important feature which is based on time sharing of a small number of actuators, in the modal space, to control effectively a large number of modes. Numerical examples are presented to illustrate the application of the method to generic flexible systems. The results obtained suggest the potential of the devised method in designing efficient active control systems for large flexible structures.

Active vibration suppression for the mast flight system

Abstract: Active vibration suppression of a large flexible space structure is addressed. The system (experimental test bed), performance requirements, and system simulations and models are described. The structures is a 60-m truss beam attached to the Shuttle orbiter. A baseline control system is required to provide 5% structural damping for the first ten structural (flexible) modes of the truss beam. The control design approach used to achieve the damping is a decentralized velocity feedback type. Collocated actuator and sensor locations are given, with details of the model for the proof-mass actuating device, the linear DC motor. >

A planar comparison of actuators for vibration control of flexible structures

Abstract: The methods and results of an analytical study comparing the effectiveness of four actuators in damping the vibrations of a planar clamped-free beam are presented. The actuators studied are two inertia-type actuators, the proof mass and reaction wheel, and two variable geometry trusses, the planar truss and the planar truss proof mass (a combination variable geometry truss/inertia-type actuator). Actuator parameters used in the models were chosen based on the results of a parametric study. A full-state, LQR optimal feedback control law was used for control in each system. Numerical simulations of each beam/actuator system were performed in response to initial condition inputs. These simulations provided information such as time response of the closed-loop system and damping provided to the beam. This information can be used to determine the 'best' actuator for a given purpose.

Demonstration Of A Smart Material With Embedded Actuators And Sensors For Active Control

Abstract: A novel class of 'Smart' materials utilizing embedded actuators and sensors has been developed and demonstrated at Virginia Polytechnic Institute & State University This class of adaptive material with sensing capabilities utilize a shape memory alloy (Nitinol) in a laminated, fiber reinforced composite as the embedded distributed actuators and embedded optical fiber sensors for evaluating the dynamic response of the structure Shape Memory Alloy (SMA) reinforced composites have the capabilities to: change their material properties, induce large internal forces in the material, modify the stress and strain state of the structure and alter its configuration, all in a controlled manner The SMA reinforced composite adaptive abilities has resulted in two new concepts for active vibration control; i) Active Strain Energy Tuning, and ii) Active Modal Modification, both of which will be briefly explained in this paper Results from the experimental demonstration of 'Active Strain Energy Tuning' using the first known composite material containing embedded distributed actuators and sensors will be presented The variation and controllability of the dynamic response of a beam made of shape memory alloy reinforced composites was determined from a single optical fiber sensor embedded in the material with the distributed actuators The optical fiber sensing method used was modal domain sensing and the experimental results are compared to accelerometer data Fast Fourier Transforms (FFT) of both the optical fiber and the accelerometer outputs were performed to compare the two methods for deducing the natural frequency of the structure

Control cable system with device for reducing vibration

Abstract: A control cable system with a device for damping vibration comprising a control cable an end of which is connected to a vibration source, a vibration member connected to another end of the control cable and a dynamic damper The dynamic damper is attached on an element of the control cable and is tuned to have a special frequency characteristic That is, the tuned damper vibrates when it receives a vibration having a frequency in a range including a plurality of resonance frequencies of the vibration member, and the damper resonates in response to a special resonance frequency in the range

Control method for active system dynamic vibration reducer

Abstract: PURPOSE: To prevent an excessive force from being exerted on machineries, when the vibration in a main vibration system is fed back to the control device for an active system dynamic vibration reducer, by reducing the feedback gain in response to the increase in amplitude of an added mass. CONSTITUTION: After detected by an acceleration sensor 14, the vibration of a main vibration system 10 is fed back to a damping controller 18, and a control signal is output, via a multiplier 40 and a displacement controller 20, to a servo valve 22, a hydraulic cylinder 24, and an auxiliary vibration system (added mass) 12 constituting an active system dynamic vibration reducer, so as to damp the vibration. In this case, the amplitude of the added mass 12 is detected by a displacement sensor 26, and a given value C1 is subtracted from the absolute value of the amplitude calculated by a computing element 28, and further thereto a given value C2 is added via a limiter 32, and a smoothing circuit 34, and the feedback gain in the multiplier 40 is decreased by a reciprocal computing element 38 in response to the increase in amplitude of the added mass 12. Thus, an excessive force can be prevented from being exerted on machineries, and even if the vibration increases, operation can be continued. COPYRIGHT: (C)1991,JPO&Japio

Active control of panel‐radiated noise using multiple piezoelectric actuators

Abstract: The potential for active control of structurally radiated nosie by two‐dimensional piezoelectric patches bonded to the surface of thin elastic panels is analytically investigated. A previously presented approximate model for the loads induced by piezoelements bonded to the plate surface is employed for the calculation of the vibration and sound radiation from simply supported rectangular panels. The piezoelectric action modifies the vibration and hence effects the noise radiated by the panel when excited by constant distributed external forces. The complex amplitude of the voltage applied to the piezoelectric is estimated via an optimization scheme that minimizes the total radiated acoustic power into the farfield. Results have been obtained for a single as well as for multiple independently controlled actuators. It is seen that quite significant control is possible in some cases with a single appropriately taylored actuator. The effectiveness, however, deteriorates as control of higher vibration modes is attempted. Much better results are achieved with two or more independently controlled actuators bonded to the plate. It is clearly shown that multiple, appropriately positioned actuators drastically reduce undesired control spillover to the residual modes. [Work supported by ONR.]

Predefined container level measurement and/or monitoring device - has vibration system with vibration elements in centres of parallel membranes acting as restoring spring

Abstract: The mechanical vibration system contains two vibration elements at a distance from each other and each in the centre of two parallel membranes acting as a restoring spring. Both vibration elements are coupled to the facing sides of two wts. via a spring with high stiffness perpendicular to the vibrating element's axial direction and low stiffness parallel to this direction. USE/ADVANTAGE - For determining and/or monitoring a defined level in container. Exactly equal and opposite amplitude vibrations of the vibration elements are maintained under all operating conditions, including when detector rod has deposits attached.

Torsional vibration damping device for marine drive shaft

Abstract: PURPOSE: To surely damp torsional vibration in no relation to a rotational speed of a drive shaft by providing a torsional vibration sensor for detecting the torsional vibration of the drive shaft and a torque generating means for giving torsional vibration, in a phase reverse to that of the torsional vibration, to the drive shaft. CONSTITUTION: A torsional vibration sensor 8 for detecting torsional vibration of a drive shaft 3 is mounted on it. A control part 9 analyzes a detection signal of the torsional vibration sensor 8 to generate a current synchronized with a waveform of the torsional vibration. A torque generating means 10 is mounted on the drive shaft 3 in order to give torsional vibration, in a phase reverse to that of the torsional vibration, to the drive shaft 3 by an output signal of the control part 9. In this way, the torsional vibration can be effectively damped in no relation to a rotational speed of the drive shaft. COPYRIGHT: (C)1991,JPO&Japio

Optimal Linear Active Suspensions with Vibration Absorbers and Integral Output Feedback Control

Abstract: SUMMARY The bandwidth of the body response to a road input in an active suspension may be considerably reduced if the axle motions are independently controlled and if, at the same time, the effects of static and dynamic loads are counteracted by integral action in the body force control system. The paper presents a further application of the Ferguson-Rekasius method, leading to optimal output control with incomplete state feedback. To achieve narrow bandwidth body response the support springs are replaced by hydraulic actuators, and vibration absorbers or active wheel dampers are employed for the control of the axle motions. Active wheel damping is the more effective and gives good results. Proportional-plus-integral control action is shown to reduce the transient body displacements due to external forces.

Active Vibration Damping in Beams

Abstract: The traveling wave approach is discussed of the active vibration control of beam. First an active vibration control for the TIMOSHENKO-beam is designed using external control forces. Then vibration control by means of internal forces. i.e. force systems forming equilibrium groups is discussed. Finally an unexpected resonance phenomenon occuring in this approach is explained.

Active Vibration Control for Flexible Space Environment Use Manipulators

Abstract: A new dynamic control system for flexible space environment use manipulators has been developed from the practical viewpoint. The key concept in the proposed method is that the local position and torque PD feedback loop at each joint should be used for position and structural vibration control. First, the authors derived manipulator dynamics, and then feedback control was developed, using an appropriate potential function. Secondly, an experimental setup using an air suspended SCARA flexible manipulator is described. The effectiveness of this method has been verified by experimental results, adapting it to automatic payload handling.

On the Hybrid Vibration Isolation Method

Abstract: For the purpose of isolating the vibration transmission from machines to soil and vice versa, this paper presents a new active vibration isolation method, that is, a hybrid vibration isolation method capable of isolating the vibration in the whole frequency range. The hybrid isolation method contains the following three characteristics: (1) a low-pass filter of a conventional elastic support method; (2) a high-pass filter of an active vibration isolation method; (3) suppression of a resonant peak due to an elastic support by a servo damper method; First, this paper presents the principle of the hybrid vibration isolation method and shows a fundamental structure of the system. Then by making the active isolator work as a damper, the suppression of a resonant peak due to an elastic support is achieved. Next, taking into consideration both the control effect and the stability of the system, the design procedure of the hybrid vibration isolation system is shown. Moreover, a control chart to estimate the control effect for suppressing the force transmissibility is presented. Finally, an experiment is carried out, demonstrating that the hybrid isolation method is capable of suppressing the exciting force in almost all the frequency range.

Active vibration control device

Abstract: PURPOSE:To make it possible to suppress generation of vibration at a low level by movably providing balance weights in an annular balance groove which is provided on a balance adjusting face of a rotary body, and controlling the balance weights to move according to the vibrating condition of the rotary body CONSTITUTION:An annular balance groove 1 is provided on respective balance adjusting faces 4 of a rotary body 3 in such a rotary machine as a steam turbine, etc Three balance weights 2, which have motors 5, batteries 6, receivers 7 and relays 8 and which are movable in the groove 1, are housed in the groove 1 Tooth shape is formed on outer peripheral faces of the balance weights 2 and is meshed with tooth shape which is formed on an inner side face of the groove 1 A vibration sensor is provided to a bearing of the rotary body 3, and modal analysis is performed from a detected signal thereof in an operator Most suitable positions of the balance weights 2 are decided in consideration of an influence coefficient, so that a command signal is output The motor 5 is controlled by the command signal, so that the balance weights 2 are moved