Showing papers on "Active vibration control published in 1990"

The Effects of Variable Speed Cutting on Vibration Control in Face Milling

Abstract: This paper discusses the use of variable speed cutting for vibration control in the face milling process. Both simulation and experimental results show that the self-excited vibrations that can occur during constant speed cutting, and hence put limitation on the possible size of cut, can be suppressed by continuously varying the spindle speed. Through both analytical and experimental studies, the shape of variable speed trajectory has been examined, in terms of both the trackability by the spindle servo system and performance in terms of vibration suppression. It was found that a sinusoidal wave because of its acceleration and jerk characteristics can be tracked more precisely than some other periodic waves. The dynamic face milling force model was used to study the effects of speed trajectory parameters, namely, the frequency and amplitude. The results, in general, show the method to be fairly robust to the specific nature of the machining situation in terms of both processing conditions and system dynamics. Speed trajectory design was, however, shown to be somewhat dependent upon the nominal cutting speed and dominant frequencies of the system.

The Positioning of Sensors and Actuators in the Vibration Control of Flexible Systems

Abstract: A method is presented for the determination of sensor and actuator positioning and feedback gains for the active vibration control of flexible structures. This method is based on the minization of the minimum quadratic cost functional in the standard optimal control. The optimal criterion is determined via Riccati equations, and it is minimized with a recursive quadratic pfogramming algorithm with respect to sensor and actuator positioning parameters. The application of this method to a cantilever beam yields several dislocated sensor and actuator locations which are locally optimal. An extension to a case in which modal filters are used is also examined. In this case, the location of the actuator is found to be more sensitive than that of the sensors. This method has clear physical meaning and the flexibility to allow varying of the weighting matrix.

Ground-borne noise and vibration damping

Abstract: A ground-borne noise and vibration damping system in which is a track bed formed with rails for a railway vehicle and generating noise and vibration, a structure is to be protected against the noise and vibration; and a damper for ground-borne noise and vibration is embedded vertically in the ground and interposed between the track bed and the structure. The damper has two upright rigid concrete plates defining a vertical gap between them, and an elastic mat sandwiched between the concrete plates and in contact therewith.

Active Vibration Control Using NiTiNOL and Piezoelectric Ceramics

Abstract: The results of a study recently completed by Boeing Aerospace & Elec tronics to investigate the use of NiTiNOL Shape Memory Metals as the sensor and actua tor components of active vibration suppression systems are presented. Two different test set-ups consisting of aluminum cantilever beams with NiTiNOL wires fastened along both sides were developed. The test article for the first set-up was a very flexible, low frequency beam which utilized NiTiNOL wires for both sensing and actuation. The test article for the second set-up was a much stiffer, high frequency beam which utilized NiTiNOL wires for sensing and piezoelectric ceramics for actuation. The settling times of both beams were significantly reduced through the use of the NiTiNOL wire sensors and actuators. Analytical simulations were developed which correlated well with the experimental results. The results of the study demonstrated the feasibility of using NiTiNOL sensors and actuators for active vibration control of structural members.

Active Control of Sound Radiation Pressure

Abstract: This paper is concerned with the problem of suppressing the acoustic radiation pressure generated by a structure vibrating in air. The approach is to control the vibration of the modes of the structure most responsible for the radiation pressure. This control is carried out by active means, i. e., by feedback control. As a numerical example, the problem of active control of the far-field radiation pressure generated by the vibration of a simply-supported rectangular elastic plate is considered. The influence on the control effectiveness of various design parameters, such as the number of controlled modes, the choice of controlled modes, the number of actuators and the location of the actuators, is investigated. The conclusion is that, depending on the magnitude of the excitation frequency, satisfactory control can be achieved by using a sufficient number of actuators and by controlling a relatively large number of modes.

Piezoelectric transducer and an ultrasonic motor using the piezoelectric transducer

Abstract: In the piezoelectric transducer, the elastic member vibrates, being excited by the first electromechanical transducing element. The impedance element on the second electromechanical transducing element is adjusted so that the vibration frequency and the resonance frequency of the elastic member should be almost the same. In the ultrasonic motor using the piezoelectric transducer, the vibration having the same frequency as that of the vibration of the elastic member is applied to the elastic member. This applied vibration has a direction differnt from that of the viration of the elastic member. The applied vibration and the vibration of the elastic member form approximate elliptical vibration, thereby rotating the rotor. The piezoelectric transducer of variable structure can control the resonance frequency in a wide range without electric power. The piezoelectric transducer can efficiently transduce applied electricity into approximate elliptical vibration of the elastic member, thereby generating great mechanical drive power. The electromechanical transducing element and the impedance element can compose a simple and compact vibration control unit. Since the electromechanical transcuding element and the impedance element form a closed circuit consuming no electric power, no power source circuit is required. The vibration control unit adjusts the resonance characteristic of the closed circuit, thus quantitatively controlling the frequency distribution and the amplitude of the mechanical vibration.

Active-type vibration control apparatus

Abstract: An adaptive-type vibration control apparatus for actively controlling vibration of an object (3) mounted on a movable base member (1,210) with vibration-isolating means therebetween. The apparatus includes a vibration sensor (13) secured to the object (3) for detecting vibration thereof, an actuator (12) secured to the object (3) for applying an inverse vibration thereto, and a digital filter (8) with an input (R) connected to the vibration sensor (13) and an output (S) connected to the actuator (12). The digital filter (8) is adapted to generate an output signal for controlling the actuator such that the vibration of the object (3) is at least suppressed by the inverse vibration applied to the object by the actuator (12). The vibration is actively controlled and reduced without being affected by resonance peak frequencies, particularly when the object (3) is applied with vibration over a wide frequency range, or with vibration of a random or periodic nature.

Vibration control of band saws: theory and experiment.

Abstract: Active vibration control is a key to the improvement of the cutting performance and productivity of band saws. In this paper a new method is presented for active control of band saw vibration. The transfer function of a closed-loop system consisting of the band saw, a feedback control law and the dynamics of the sensing and force actuation devices is derived. Analysis of the root loci of the closed-loop system gives two stability criteria. Stabilizing controller design is carried out for both collocation and dislocation of the sensors and actuators. It is found that vibration in all the modes can be damped through use of only one sensor and one actuator and that the control algorithms presented are realizable in practice. The theory presented is experimentally verified.

Method of controlling positions and vibrations and active vibration control apparatus therefor

Abstract: A method of controlling level lateral positions of a vibration control base (2) suspended by air springs (3e) to be returned to its standard level and lateral positions and to keep their positions by utilizing analog integration or a feedback compensation in combination thereto so as to control an air pressure or air pressures of air springs for driving the vibration control base and also controlling vertical and horizontal vibrations of the vibration control base (2) and an apparatus for carrying out the said method.

Device and method for active vibration damping

Abstract: A device and method for active vibration damping of an object which comprises a beam with two free ends comprises a vibration sensor, a control circuit, and an actuator. The sensor is located near the first end of the beam and the actuator is located near the second end of the beam. The control circuit converts input signals from said vibration sensor into control signals for controlling the actuator. The damping device is particularly useful where it forms part of a precision coordinate measuring machine which has a beam of varying length. In this instance, the sensor is located on a sliding spindle of the measuring machine.

Damping coefficient control device for vibration damper

Abstract: A damping coefficient control device, for use in a vibration damper of the type which is disposed between a vibration source and a vibration receiving section to be isolated from the vibration of the vibration source and which has a plurality of small liquid chambers charged with an electrorheologic fluid and communicated through an orifice, includes electrodes disposed in the orifice to receive a voltage which is suitably controlled so as to cause a change in the viscosity of the electrorheologic fluid, thereby controlling the damping coefficient provided by the fluid. The damping coefficient control device has sensors for sensing the velocities of the vibration source and the vibration receiving section. When the direction of the velocity of the vibration receiving section is the same as the direction of the relative velocity of the vibration receiving section relative to the vibration source, the voltage applied to the electrodes is controlled such as to increase the damping coefficient provided by the electrorheologic fluid, whereas, when these directions are different, the voltage is controlled such as to decrease the damping coefficient. This arrangement enables the vibrations of different frequencies to be damped without any risk that resonance will occur.

Piezoelectric sensors and actuators for active vibration damping using digital control

Abstract: Light-weight, rapid, multimode control of a vibrating structure is possible by the use of piezoelectric sensors and actuators and feedback control algorithms. The results of vibration control experiments on a prototype structure such as a cantilever beam using PZT sensors and actuators are presented. Different types of position feedback control and steady-state quadratic optimal control were implemented. Particular attention was paid to the control of low-frequency vibration modes. To extend the applicable range of the control algorithms, signals from the partially distributed sensors and actuators were converted to those from the point concept sensors and actuators. >

Bridge feedback for active damping augmentation

Abstract: A method is described for broadband damping augmentation of a structural system in which the active members (with feedback control) were developed such that their mechanical input impedance can be electrically adjusted to maximize the energy dissipation rate in the structural system. The active member consists of sensors, an actuator, and a control scheme. A mechanical/electrical analogy is described to model the passive structures and the active members in terms of their impedance representation. As a result, the problem of maximizing dissipative power is analogous to the problem of impedance matching in the electrical network. Closed-loop performance was demonstrated for single- and multiple-active-member controlled truss structure.

An investigation of vibration isolation systems using active, semi-active and tunable passive mechanisms, with applications to vehicle suspensions

Abstract: In this dissertation, an analytical investigation on active, semi-active and passive vibration control mechanisms is presented in order to achieve improved shock and vibration isolation of mechanical systems, especially ground vehicle applications. A hybrid active vibration isolation system, incorporating an electro-magnetic force generator along with passive damping and spring elements, is mathematically modeled based on fundamental physical laws and taking into account the generator dynamics. Complete vibration isolation characteristics of the hybrid active control system are evaluated for various feedback variables and control schemes, using numerical simulations. Influence of the force generator dynamics on vibration isolation performance is illustrated through the simulation results. A concept of tunable pressure limiting modulation is proposed in hydraulic damper systems. A hydraulic orifice damper is modified by using the proposed tunable pressure limiting modulation to achieve variable damping in vibration isolation systems, without requiring any external energy source, sophisticated control devices and feedback instrumentation that are essential for active and semi-active isolators. The fluid flow equations are employed to develop the nonlinear mathematical model of the hydraulic damper, incorporating the fluid and mechanical compliance, and the dynamics of the pressure limiting mechanism. The computer simulation reveals that the shock and vibration isolation performance of the tunable pressure limited hydraulic damper systems is comparable to that of the semi-active 'on-off' vibration control systems. A generalized harmonic linearization technique, based on a principle of energy similarity of dynamic elements, is proposed to derive equivalent linear representations of both nonlinear damping and spring elements, in the frequency domain. An analysis of the nonlinear in-plane vehicle model, with air-springs, orifice damping and pressure limiting modulation due to tunable hydraulic shock absorbers, is carried out to establish the stochastic response to random road inputs in terms of power spectral density, and to illustrate the improved vehicle ride performance due to tunable shock absorbers. An interconnected hydro-pneumatic suspension with tunable pressure limiting mechanism is presented to achieve improved vehicle ride and handling performance. Analysis of a roll plane model of a vehicle employing the tunable interconnected suspension shows that the connections of fluid flow within the interconnected suspension provide an enhanced static roll stability; while the tunable pressure limiting modulation between the strut and the accumulator of each suspension unit offers an improved vehicle ride performance

Design and Implementation of Robust Decentralized Control Laws for the ACES Structure at Marshall Space Flight Center

Abstract: Many large space system concepts will requir active vibration control to satisfy critical performance requirements such as line-of-sight accuracy. In order for these concepts to become operational it is imperative that the benefits of active vibration control be practically demonstrated in ground-based experiments. This report describes an experiment conducted by Harris as part of the NASA CSI Guest Investigator Program. The results of this experiment successfully demonstrate active vibration control for a flexible structure. The testbed is the ACES structure at NASA Marshall Space Flight Center. The ACES structure is dynamically traceable to future space systems and especially allows the study of line-of-sight control issues.

Vibration-Isolation Characteristics of an Active Electromagnetic Force Generator and the Influence of Generator Dynamics

Abstract: Vibration-isolation characteristics of an active vibration control system incorporating an electromagnetic force generator (actuator) are investigated. The electromagnetic force generator is modeled as a first-order dynamical system and the influence of dynamics of the force generator on the vibration-isolation performance of the active isolator is investigated via computer simulation. It is concluded that the dynamics of the force generator affect the vibration-isolation performance significantly. An active control scheme, based upon absolute position, velocity, and relative position response variables, is proposed and investigated. In view of the adverse effects of generator dynamics, the proposed control scheme yields superior vibration isolation performance. Stability analysis of the active vibration control system is carried out to determine the limiting values of various feedback control gains.

Distributed transducer control design for thin plates

Abstract: There is a growing interest in the use of distributed actuators and sensors for the active vibration control of thin plates. Recent efforts in this area have been resthcted to the control of plates with cantilevered boundary conditions. This paper presents an energy based analysis of distributed transducer design issues related to the observation and control of thin plates applicable to more general boundary conditions. The particular class of distributed transducers is limited to those which are separable in space and time, i.e. degenerate distributed transducers. The analysis exploits plate mode symmetry and boundary integral representations of key parameters to choose appropriate spatial weiglitings for distributed sensors and actuators. The technique may be used to simultaneously control multiple plate modes as well as target selected modes. While the results presented here are applicable to a broad class of distributed transducers, for the purposes of illustration models based on the piezoelectric polymer film polyvinylidene fluoride (PVF2) are used.

Analysis of dual control vibration testing

Abstract: Analysis of dual control vibration testing is conducted using a two-degree-of-freedom system to represent the interaction between a vibration mode of a test item and a mode of a mounting structure. The results indicate that exact dual control based on specification of the source free acceleration and blocked force is strictly valid only if phase is taken into account. However, extremal dual control without phase alleviates overtesting without risk of undertesting, when the limit acceleration and force specifications are chosen to envelope the coupled system results. Several approaches to deriving appropriate force specifications are explored. Random vibration parametric results from the literature are used to estimate the limit force between coupled oscillators with different source and load masses.

Shape memory alloys and fiber optics for flexible structure control

Abstract: This work investigates the development of Shape Memory Alloy (SMA) actuators and a fiber-optic Mach- Zehnder interferometric dynamic motion sensor as components of an active vibration control system The test set-up consisted of a graphite-epoxy flexible cantilever beam with distributed SMA wires and optical fibers attached along both sides A constant amplitude dead-band control algorithm was used to provide a rate feedback force to actively control transient vibrations The SMA actuators were also used to demonstrate static shape control The settling time of the beam was reduced by more than a factor of 24 through the use of the SMA actuators and fiber optic dynamic motion sensor Analytical models were developed for the integrated structure/actuator/sensor system which helped understand the dynamic effects and the results correlated well with the experimental results This investigation demonstrated the feasibility ofusing SMA actuators and fiber optic dynamic motion sensor for control of flexible structures The work described in this paper was sponsored by the Astronautics Laboratory AL(AFSC) as a part of the "Advanced Composites with Embedded Sensors and Actuators (ACESA)" program

Vibration and control of a flexible rotor supported by magnetic bearings : (control system analysis and experiments without gyroscopic effects)

Abstract: This paper is on the subject of active vibration control of flexible rotors supported by magnetic bearings. Using a finite element method for the mathematical model of flexible rotors, we have formulated the eigenvalue problem taking into account the interaction between the mechanical system of a flexible rotor and the electrical system of magnetic bearings and a controller. However, gyroscopic effects are disregarded in this paper for simplicity. We will be able to adapt this formulation to a general flexible rotor/magnetic bearing system. Controllability with and without collocation is discussed for the higher order flexible modes of the test rig. In conclusion, we have proposed that it is necessary to add new active control loops for the higher flexible modes even in the case of collocation. Then, it is possible to stabilize for the case of uncollocation by means of this method.

Experimental demonstration of active vibration control for flexible structures

Abstract: Active vibration control of flexible structures for future space missions is addressed. Three experiments that successfully demonstrate control of flexible structures are described. The first is a pendulum experiment. The structure is a 5 m compound pendulum and was designed as an end-to-end test bed for a linear proof mass actuator and its supporting electronics. Experimental results are shown for a maximum-entropy/optimal-projection controller designed to achieve 5% damping in the first two pendulum modes. The second experiment was based upon the Harris Multi-Hex prototype experiment apparatus. This is a large optical reflector structure comprising a seven-panel array and supporting truss which typifies a number of generic characteristics of large space systems. The third experiment involved control design and implementation for the ACES structure at NASA Marshall Space Flight Center. The authors conclude with some remarks on the lessons learned from conducting these experiments. >

Adaptive vibration control of vibration isolation mounts, using an LMS‐based control algorithm

Abstract: : This thesis investigates the possibility of actively controlling a two-stage vibration isolation mount so as to minimize the transmissibility through the mount. Based on the least-mean squares (LMS) algorithm, an adaptive control system is developed which performs both system identification and control in real-time. The algorithm is generalized to be applicable for systems with multiple actuators and/or sensors. To demonstrate its performance, the adaptive controller is applied to a two-stage isolation mount to actively control vibration transmission through the mount. Experimental results are presented for both narrowband and broadband excitation signals. To demonstrate the capability of the controller to track changing systems, results are shown for several cases where the parameters of the two-stage isolation mount change in time. It is shown that adaptive control presents an excellent means of achieving optimal control at low frequencies where conventional passive control methods fail. The issue of stability is investigated for several LMS-based algorithms, and it is demonstrated that narrower stability restrictions occur as a result of the transfer function between the control filter and the error sensor which exists in a physical system. The result is that in order to maintain stability, the algorithms have a smaller maximum convergence parameter for noise or vibration control applications than for corresponding signal processing applications with the same input. Keywords: Active vibration control; Mounting; LMS; Real-time; Theses; Narrowband; Broadband; Low frequencies. (kt)

Vibrations, Dynamics and Structural Systems

Abstract: Introduction Free vibration of single degree of freedom system Forced vibration of single degree of freedom system Numerical methods in structural analysis: Applied to SDF systems Vibration of two degrees of freedom system Free vibration of multiple degrees of freedom system Free vibration analysis of continuous systems Forced vibration of continuous systems Dynamic direct stiffness method Vibration of ship and aircraft as a beam Finite element method in vibration analysis Finite difference method for the vibration analysis of beams and plates Nonlinear vibration Random vibration Computer program in vibration analysis The stiffness matrix Table of spring stiffness Index.