Showing papers on "Active vibration control published in 1999"

Passive Vibration Control

Abstract: The Response of Structures to Harmonic Forces. Receptance and Dynamic Stiffness. The Response of Structures to Prescribed Harmonic Motions. The Response of Structures to Non-Harmonic Excitation. Factors Controlling Beam and Plate Vibration. The Control of Vibration by Structural Design. The Control of Vibration by Localized Additions. The Control of Vibration by Added Damping. The Control of Vibration by Resilient Isolation. The Control of Vibration by Combined Methods. Index.

Piezoelectric vibration damping for disk drives

Abstract: The present invention provides passive and active damping systems for reducing or substantially eliminating undesirable vibrations from components of data storage and retrieval systems. The passive and active damping systems incorporate piezoelectric materials, and make use of an advantageous property of these materials, namely the ability to convert mechanical strains into electric potentials and vice versa. The passive systems of the present invention dissipate vibrational energy through an electrical shunt circuit. The active systems seek to cancel an existing vibration in a component by generating and applying an additional vibration to the same component, where the applied vibration is out of phase with the existing vibration and the two vibrations tend to add destructively. Active systems, in certain circumstances, may also be able to anticipate predictable vibrations and proactively cancel them, rather than merely reacting to vibrations after they arise.

Modelling and optimal placement of piezoelectric actuators in isotropic plates using genetic algorithms

Abstract: Theoretical modelling of the vibration of plate components of a space structure incorporating piezoelectric actuators is presented. The equations governing the dynamics of the plate, relating the strains in the piezoelectric elements to the strain induced in the system, are derived for isotropic plates using the Rayleigh-Ritz method. The developed model was used for a simply supported plate. The results show that the model can predict natural frequencies of the plate very accurately. Two criteria for the optimal placement of piezoelectric actuators were suggested using modal controllability and the controllability Grammian. The model was then used to predict the closed-loop frequency response of the plate for active vibration control studies with optimal locations of actuators successfully obtained using genetic algorithms. Significant vibration suppression was demonstrated using optimal actuator placement algorithm developed.

Boundary Control of an Axially Moving String Via Lyapunov Method

Abstract: This paper presents the active vibration control of an axially moving string system through a mass-damper-spring (MDS) controller at its right-hand side (RHS) bound-ary. A nonlinear partial differential equation (PDE) describes a distributed parameter system (DPS) and directly selected as the object to be controlled. A new boundary control law is designed by sliding mode associated with Lyapunov method. It is shown that the boundary feedback states only include the displacement, velocity, and slope of the string at RHS boundary. Asymptotical stability of the control system is proved by the semigroup theory. Finally, finite difference scheme is used to validate the theoretical results.

Experimental investigation of different actuator technologies for active vibration control

Abstract: In a smart structure, where the objective is active vibration control, there is a requirement for actuators, sensors and an electronic controller. Although there have been significant advances in controller design, in terms of software, hardware and control algorithms, this has not been matched in the design of the transducers. This note is concerned with the various actuator technologies for active vibration control. A set of experiments is conducted on five actuators, three of which use piezoelectric driving elements and the other two are magnetostrictive and electrodynamic. The experimental data for each of the actuators are compared by using a simple two-port model which facilitates a comparison of the actuators' mechanical and electrical properties that are important for vibration control actuators. A method of comparing the mechanical output from both voltage and current driven actuators on a composite graph is proposed. It is also shown that with present technologies, actuators that can deliver large displacements generally have a low stiffness and can only generate moderately low forces. The opposite is also true.

Active control of a beam using a piezoceramic element

Abstract: A model is developed to predict the dynamic response of a mechanical stack called a `piezoceramic element' which is composed of a piezoelectric sensor, a viscoelastic damper and a piezoelectric actuator of which the applied voltage is fed back by the sensor voltage. This stack works by stretching: a model based on Euler-Bernoulli beam equations is chosen. This model is then used to investigate the effect of the `piezoceramic element' on the active vibration control of a cantilevered beam. An optimal control law is determined by using a state observer and the Riccati equation. Finally, the theoretical results are simulated and compared with the results obtained in the open-loop condition.

Vibration control of rotationally periodic structures using passive piezoelectric shunt networks and active compensation

Abstract: This paper proposes a multi-mode vibration suppression scheme for rotationally periodic structures. Identical active-passive hybrid piezoelectric networks are applied on each of the substructures, where active charge and current feedback is used together with passive piezoelectric shunts to optimize the network performance. By exploiting the rotational periodicity, a new algorithm is synthesized to analytically determine the control parameters. It is shown that this hybrid approach can suppress all the spatial harmonics, which cannot be achieved by purely passive piezoelectric shunts. It is also observed that such a configuration requires much less control effort (voltage and power) when compared to a purely active approach.

Design and analysis of a high bandwidth disk drive servo system using an instrumented suspension

Abstract: Resonance modes in the suspension of hard disk drives limit the closed-loop bandwidth. The bandwidth of the servo can be increased by active vibration control of the resonance modes. This paper considers the optimal placement of strain gauge sensors on a suspension to observe the vibration states of the suspension. Using a finite-element simulation of an actual suspension, a state-space model is identified for the two normal strains and the shear strain at each finite element. The state-space model includes the dynamics of the three primary resonance modes. A numerical search algorithm is used to determine the sensor location and orientation which maximizes the minimum singular value of the observability grammian. With the strain gauge output signal, a multirate inner loop controller is designed to be used with the existing head-positioning system. Simulations and analysis results suggest that use of an instrumented suspension is a viable candidate method for improved disk drive servo performance.

Active vibration isolation device and its control method

Abstract: A hybrid active vibration isolation device has an intermediate plate inserted between a vibration damping subject and a setting surface on which the vibration damping subject is set, and laminated rubber and electromagnetic motors are interposed between the vibration damping subject and intermediate plate. A piezoelectric element is interposed between the intermediate plate and setting surface. In order to detect vibrations of the vibration damping subject, intermediate plate, and setting surface, velocity sensors are provided to them. The active vibration isolation device has a feedback mechanism for controlling the electromagnetic motors on the basis of signals from the velocity sensors provided to the vibration damping subject and setting surface, and controlling the piezoelectric element on the basis of a signal from the velocity sensor set on the intermediate plate.

Active Vibration Control of Flexible Robots Using Virtual Spring-damper Systems

Abstract: When using robots for heavy loads and huge operating ranges, elastic deformations of the links have to be taken into account during modeling and controller design. Whereas for conventional rigid multilink industrial robots modeling can schematically be done by standard techniques, it is a massive problem to obtain an accurate analytic model for multilink flexible robots. But an accurate analytic model is essential for most modern controller design techniques, and modeling errors can lead to instability of the controlled system due to spillover since the eigenvalues of the system are only slightly damped. A new approach to active damping control for flexible robots is presented in this paper where the actuators act like virtual spring-damper-systems. As the spring-damper-element is a passive energy dissipative device, it will never destabilize the system and thus the control concept will be very insensitive to modeling errors. Basically, the two parameters, spring stiffness and damping constant of this system, are arbitrary and model independent. To satisfy performance requirements they are adjusted using knowledge of the system model. The more it is known about the system model, the better these parameters may be adjusted. The new input of the controlled system is a virtual variation of the spring base. The paper illustrates this technique with the help of a simple and easy to model one link flexible robot which is also available as a real laboratory testbed.

Self-powered active control applied to a truck cab suspension

Abstract: A method of active vibration control using regenerated vibration energy, i.e. self-powered active control, applied to the cab suspension of a heavy duty truck. In the proposed system, an electric generator that is installed in the suspension of the chassis regenerates vibration energy and stores it in the condenser. An actuator in the cab suspension achieves active vibration control using the energy stored in the condenser. Numerical simulations and basic experiments demonstrate better isolation performance of the self-powered active vibration control system than that of a passive and a semi-active control.

Active vibration control of large optical space structures

Abstract: The paper describes techniques for designing and implementing active damping systems for large optical support structures. Each step in the design process is illustrated with results from the Advanced Composites with Embedded Sensors and Actuators (ACESA) vibration control system. The system is installed on a space based laser structural simulator at the Air Force Research Laboratory's Advanced Space Structure Research Experiments facility. The ACESA system consists of three large tubular active members; embedded bad zirconate-titanate (PZTs) wafers in each strut, which allows control of deformation axially and in two bending planes; 400 V drive electronics for each active member; and a nine-channel, digitally programmable, analogue control electronics unit. Design begins with the determination of the critical modes through a gain factor analysis. Actuators are located through modal strain energy analysis. Using piezostructural analysis methods, sensing and actuation functions are included in the open- and closed-loop dynamic simulations. The simulation includes local strain feedthrough effects through a static correction. Damping is applied to all modes in the frequency range up to 100 Hz, with fundamental modes achieving 20% damping, two orders of magnitude greater than the intrinsic damping level. The actuator PZTs used for active damping were also experimentally shunted with resistive elements in an attempt to introduce passive damping, although the effect was barely measurable. This demonstrates that active damping gives three orders of magnitude better performance than a passive resistive shunt in a controlled comparison.

Adaptive Active Control of Machine-Tool Vibration in a Lathe - Analysis and Experiments

Abstract: In the turning operation the relative dynamic motion between cutting tool and workpiece, or vibration, is a frequent problem, which affects the result of the machining, and in particular, the surface finish. Tool life is also influenced by vibration. Noise in the working environment frequently occurs as a result of dynamic motion between the cutting tool and the workpiece. The research study includes the analysis of the statistical and dynamic properties of tool vibration in external turning, a foundation in optimal and adaptive signal processing that enables the active control of tool vibration in a lathe. It was found that the adaptive feedback control enables a broad-band attenuation of the tool vibrations, and is able to reduce the vibration level by almost 40 dB simultaneously at 1.5 kHz and 3 kHz. Further, the adaptive control reduced the acoustic noise level and it enabled a broad-band attenuation of the sound pressure in the frequency band 1.5 kHz to 25 kHz, with up to approximately 35 dB sound pressure level at 3 kHz. A significant improvement in the workpiece surface was also observed with the adaptive control. (Less)

Vibration actuator to control pitching vibration

Abstract: An ultrasonic actuator to suppress or eliminate pitching vibration arising in a vibration element when driving the ultrasonic actuator and to increase driving efficiency and reduce noise. The ultrasonic actuator includes a vibration element; an electromechanical conversion element mounted on the vibration element to generate a drive force in the vibration element by excitation of the electromechanical conversion element; drive force output members to extract a drive force obtained by excitation of the electromechanical conversion element; a relative motion member in contact with the drive force output members and driven in relative motion with respect to the vibration element by the drive force; a base member; and a fixed member to fix the vibration element to the base member. The vibration element generates, by excitation of the electromechanical conversion element, a first vibration in a first direction, and a second vibration in a second direction different from the first direction, and the fixed member is located in at least two (2) positions along the vibration direction of the first vibration and includes a first restriction member to restrict the vibration element in a vibration direction of the first vibration, and a second restriction member to restrict the vibration element in a vibration direction of the second vibration.

Active vibration control system of smart structures based on FOS and ER actuator

Abstract: An active vibration control system based on fiber optic sensor (FOS) and electrorheological (ER) actuator is established in this paper. A new intensity modulated fiber optic vibration sensor is developed following the face coupling theory. The experimental results show that this new type of intensity modulated fiber optic vibration sensor has higher sensitivity in measuring the vibration frequency. At the same time, experimental investigations are focused on evaluating the dynamic response characteristics of a beam fabricated with ER fluid. It is noted that the most significant change in the material properties of ER fluid is the change of material stiffness and damping which varies with the electric field intensity imposed upon the ER fluid. Finally, the structural vibration of the smart composite beam based on ER fluid, fiber optic sensor and piezoelectric transducer has been monitored and controlled actively utilizing a fuzzy-logic algorithm.

Piezothermoelastic Modeling and Active Vibration Control of Laminated Composite Beams

Abstract: A generalized piezothermoelastic finite element formulation of a laminated beam with embedded piezoelectric material as distributed actuators/sensors is presented. Electromechanical and electrothermal couplings are incorporated using the linear equations of piezothermoelasticity. Inclusion of temperature and electric potential as state variables along with mechanical displacement permits a unified representation of multiple fields coupling in finite element formulations. A two noded 3-D beam element is derived using first order shear deformation theory to model direct and coupled effects. Eigenstructure assignment technique using output feedback is employed in the controller design, which is subsequently adopted to actively control the first three modes of a cantilever PZT/Steel/PZT beam. The desired eigenfrequencies are placed exactly and the tip motion of the beam is significantly reduced by shaping the eigenvectors of the closed-loop system. Control spillover effect is minimized by optimally selecting the actuator/sensor locations and optimizing the damping factors of the desired closed-loop eigenvalues.

Automotive applications of active vibration control

Abstract: This paper presents results of an unique active absorber system for broad band vibration compensation where the used controller is based on an adaptive feedforward/feedback control scheme. The experimental results show that an enhanced ride comfort can be achieved by eliminating fatigue from low frequency noise and vibrations.

Implications of using colocated strain-based transducers for output active structural acoustic control

Abstract: Piezoceramic transducers have become popular elements of smart structures that are used for active vibration control and active structural acoustic control. A spatial differentiation is performed by the piezoceramic transducers since they couple into the strain field of the piezostructure. This differentiation causes higher-frequency modes to be emphasized more heavily, causing the effective compliance of the structure as seen by the piezoceramic transducer to increase with frequency. This nonuniform compliance has significant impact on the performance that can be achieved through colocated direct rate feedback control. It is shown that the rectangular piezoceramic transducer is a low-pass wave number filter with a cutoff frequency inversely proportional to the aperture size. Thus DRFB performance can be greatly improved simply by making the size of the piezoceramic transducer large relative to the size of the structure. The resulting increase in coupling to the lower-frequency modes, which are generally targeted by the control system, results in a much reduced control effort. In the event that a large aperture is not practical, it is shown that dynamic compensation can be used to obtain good performance at the cost of much increased computational complexity. Analytical open and closed loop results for an acoustically radiating simply supported plate piezostructure are presented.

Active vibration control of multiple buildings connected with active control bridges in response to large earthquakes

Abstract: Proposes an active vibration control method for multiple high-rise buildings arranged in parallel. According to the proposed method, some flexible buildings connected with control devices called "active control bridges", are controlled through active interaction among them. This method has the merit of obtaining sufficient control force under low frequency. By this method, it is possible to control vibration of the super tall buildings against strong winds and large earthquakes. Four model buildings are connected with four actuators. The objective of this research work is to control the first bending and the first torsional mode of each building by this method. The control effect is evaluated by exciting the base of the structures with earthquake waves and measuring the response of the structures. Both simulation and experimental results show that fairly good control performance has been gained by this method.

Vibration reducing system for internal combustion engine

Abstract: A vibration reducing system of an internal combustion engine for an automotive vehicle. The vibration reducing system comprises a roll vibration system which generates a roll vibration of an engine main body, the roll vibration having a first vibration mode. Additionally, a rotational vibration system is provided to generate a rotational vibration having a second vibration mode, and includes a crankshaft of the engine, for generating a rotational driving force, a main flywheel fixedly connected to the crankshaft, a driving force transmitting mechanism through which the rotational driving force of the crankshaft is transmitted, the driving force transmitting mechanism being movably secured to the engine main body, and an inertial mass member drivably connected to the driving force transmitting mechanism and rotatable to generate an inertial force upon receiving the rotational driving force transmitted through the driving force transmitting mechanism. In the vibration reducing system, the first and second vibration modes cause antiresonance at an antiresonance frequency. Additionally, the rotational vibration system is adjusted to cause the antiresonance frequency to be generally coincident with one of frequencies which are obtained respectively by multiplying an engine-revolutional frequency at a predetermined engine speed by values each being represented by (a natural number/2).

Active and passive vibration confinement using piezoelectric transducers and dynamic vibration absorbers

Abstract: In this paper, a numerical simulation is presented that shows active and passive vibration confinement of a pinned- pinned beam. The beam is divided into three regions: an isolated, a transition, and a localized region. Two dynamic vibration absorbers are used in conjunction with two pairs of piezoelectric transducers with a feedback law to reduce the displacement amplitudes in the isolated region and to confine the vibrations to the localized region. The development of an eigenvector shaping technique is also shown. This technique shapes the eigenvectors of the uncontrolled beam to confine vibrations to the localized region. Finally, the numerical results of a randomly forced and a harmonically forced controlled pinned-pinned beam are presented. These results show that the combination of active and passive vibration confinement reduces the total power required for active vibration confinement and demonstrate that piezoelectric transducers are viable actuators for vibration confinement applications.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Ultrasonic vibration mode for wire bonding

Abstract: A method and apparatus for creating second order vibrational modes. The apparatus includes a signal generator, a piezoelectric transducer, a plurality of wave propagating beams and reflecting boards. An electric field applied by the signal generator to the piezoelectric transducer induces a unidirectional vibration of the transducer. The vibration is propagated through the beams and reflected by the reflecting boards in a closed polygonal loop. The final reflection direction is perpendicular to the original vibration. A circular or elliptical vibration of the apparatus results. The circular or elliptical vibrational energy can be imparted to the wire bond of an integrated circuit to add strength to the connection.

Optimal Actuator Placement for Active Vibration Control With Known Disturbances

Abstract: Two cost functions, based on the disturbance sensitivity grammian, are presented that can be used to find the optimal position of an active vibration control actuator. The disturbance sensitivity g...

Three-axis, six degree-of-freedom, whole-spacecraft passive vibration isolation system

Abstract: The excitations from the engines of launch vehicles and the aerodynamics of flight produce large vibrations which are highly detrimental to spacecraft during launch. Significant dynamic loads often exist in all three translations and for rotations as well, therefore, complete six degree-of-freedom vibration load isolation is often desired. The disclosed device utilizes a previously disclosed passive axial vibration isolation device to simply and effectively create a passive three-axis vibration isolation device suitable for effecting a six degree-of-freedom whole-spacecraft passive vibration isolation system. The vibration isolation system design can be simply tuned to address various dynamic load frequency bands of concern, including isolation for pyrotechnic shock. The resulting system is compact and lightweight and can be easily utilized with existing launch vehicle-to-payload support structures.

Active damping device

Abstract: PROBLEM TO BE SOLVED: To suppress horizontal relative displacement in the vertical position of an equipment caused by vibration, particularly horizontal relative displacement due to the vibration of an equipment body caused by an exiting source in the mounted equipment. SOLUTION: This active damping device is constituted including a base 4 supported by active damping mounts 3 each formed by integrating a passive damping member comprising a cylindrical elastic body 23 and a viscous elastic body 30a, a vertical actuator 32a supported by a height adjusting mechanism 55 disposed in the cylindrical elastic body 23, and a horizontal actuator 32b, an active mass damper 20 provided at an equipment 50 mounted on the base 4, a vibration sensor 17 for detecting the vibration of the base 4 and equipment 50, an equipment controller 9 for driving an exciting source mounted in the equipment 50, and a vibration damping controller 18 for controlling the actuators 32a, 32b, 32c on the basis of the output of the vibration sensor 17.