Direct Velocity Feedback Control Research Articles

Velocity sensor with an internal feedback control loop

This paper presents a new velocity sensor whose output is directly proportional to velocityat low frequencies, but has a well damped resonance after which it has a controlled roll-off.It is designed to be used in a feedback loop with a closely located piezoelectric patchactuator to form a sensor–actuator pair for the implementation of active damping.The velocity sensor consists of a principal spring–mass seismic sensor with aninternal direct velocity feedback control loop. This internal feedback loop uses aseparate control spring–mass seismic sensor and a reactive actuator, which are fixedon the seismic mass of the principal sensor. The control gain is tuned to obtaintwo effects: first, the output signal from the principal sensor becomes directlyproportional to the velocity at the base of the sensor itself and second, the fundamentalresonance peak is reduced by the active damping effect of the internal feedback loop.The practical feasibility is then studied by considering a prototype model. Thestability of the internal feedback control loop has been assessed first, followingwhich the frequency response function of the sensor with and without the internalfeedback loop has been measured. The experimental measurements have shown thatthe internal feedback loop is conditionally stable but guarantees sufficient gainmargins to obtain the desired velocity output from the sensor. The sensor hasbeen successfully tested with a closed loop, and shows the desired velocity outputwith no resonance at the fundamental natural frequency of the seismic sensor.

Smart panels with velocity feedback control systems using triangularly shaped strain actuators

In this paper we present a theoretical study on the active structural acoustic control of a new smart panel with sixteen triangularly shaped piezoelectric patch actuators, having their base edges evenly distributed along the perimeter of the panel, and velocity sensors positioned at the vertices opposite the base edges. The performance is assessed and contrasted with that of a conventional smart panel using a 4 x 4 array of square piezoelectric patch actuators evenly distributed over the surface of the panel with velocity sensors at their centers. For both systems the control effectiveness and stability of MIMO decentralized or SISO direct velocity feedback control architectures have been analyzed. The two control systems are arranged to generate active damping which reduces the response and sound radiation of the panel in the lightly damped and well separated low-frequency resonances. In particular the new control system can be seen as a set of sixteen "active wedges" which absorb energy from the incident flexural waves to the borders of the panel so that the panel could be considered anechoic. This study shows that the new arrangement with triangularly shaped actuators can achieve better control than the corresponding system using square actuators.

The optimum structural control method – neutral equilibrium mechanism

Traditional structure was used as an active control mechanism and structure system under the stable situation in the time history of dynamic response. In order to attain the energy dissipation, the additional applied work depends on the deformation of control elements. The new control mechanism, Neutral Equilibrium System (NES), will be introduced in this paper. NES is composed of unstable control mechanism and stable structure frame. It has advantages of all functions; a merit of active control method and it does not require the extra energy supply. The earthquake record or the histories of harmonic loading are used as input data to discuss the results of numerical simulation in investigating the stability, usability and effect of this control mechanism. The results indicate that this mechanism should be controlled thoroughly. Under appropriate control law, the control state is nearly perfect. Nevertheless, the external energy is required for control system to operate by using the control law of related displacement. Thus, NES should match with the control law of related velocity. The entire capability of active control can be performed under the condition of direct velocity and control feedback control method when no power energy is supplied.

보의 능동진동제어을 통한 직접속도 피드백의 적용성 연구

Direct velocity feedback (DVFB) control is known that it offers an unconditional stability with very high performance when the control strategy is applied at a point collocated sensor and actuator pair. because the sensor-actuator pair has strictly positive real (SPR) property In this paper, two types of collocated sensor-actuator pairs are considered for practical active vibration control of a structure. They are a Point collocated sensor-actuator pair and a point sensor-distributed actuator pair. Both pairs with DVFB show robust stability and performance. It is noted that the collocated point sensor-actuator ultimately acts as a “skyhook” damper, hut the point sensor-distributed actuator pair with DVFB acts as a “skyhook” rotational damper pair.

Active Vibration Control Methods of Axially Moving Materials - A Review

In this paper we provide a review of the state of the art for active vibration control of axially moving materials (string and beam, etc.) in the past ten years, with particular regard to the subjects of some important active control methods of axially moving strings. First, an introduction is given to explain the aims and scope of this paper. This is followed by a comprehensive discussion of the active wave control methods presented by many investigators in the past ten years, including feedback control methods (such as the modal control method, the direct velocity feedback control method and the control method via transfer function formulation), active wave control methods combining transfer function, boundary control methods using the Lyapunov function, the variable structure control method, the adaptive control method, the vibration control of an axially moving beam and the active control of a moving material with arbitrarily varying length, etc. Finally, we conclude with a discussion of several issues for future research in this area.

능동음향진동제어를 위한 센서와 액추에이터의 동위치화 연구

The problem considered in this paper is about the collocation of sensor and actuator for the active control of sound and vibration. It is well-known that a point collocated sensor-actuator pair offers an unconditional stability with very high performance when it is used with a direct velocity feedback (DVFB) control, because the pair has strictly positive real (SPR) property. In order to utilize this SPR characteristics, a matched piezoelectric sensor and actuator pair is considered. but this pair suffers from the in-plane motion coupling problem with the out-of-plane motion due to the piezo sensor and actuator interaction. This coupling phnomenon limits the stability and performance of the matched pair with DVFBcontrol. As a new alternative, a point sensor and distributed piezoelectric actuator pair is also considered, which provides SPR property in all frequency range when the pair is implemented on a clamped-clapmed beam. The use of this sensor-actuator pair is highly expected for the applications to more practical active control of sound and vibration systems with the DVFB control strategy.

Nonlinear and Robust Control Schemes for Offshore Steel Jacket Platforms

This paper presents two control schemes to control the dynamicresponse of an offshore steel jacket platform due to wave-inducedforces. The objective of the controllers is to greatly reduce theinternal system oscillations and to obtain a smooth response ofthe steel jacket platform when subjected to nonlinear self-excitedhydrodynamic forces. The first controller is a nonlinearcontroller whose design is based on Lyapunov theory. The secondcontroller is a robust state feedback linear controller whosedesign is based on an optimal control approach. Both controlschemes guarantee the asymptotic stability of the system. Thetheoretical developments are illustrated through simulationresults of the proposed control schemes. Furthermore, theperformance of the offshore steel jacket platform is presentedwhen a direct velocity feedback controller is applied to thesystem. It is found that the performance of the system with theproposed controllers is better than the performance of the systemwith the direct velocity feedback controller.

Matched piezoelectric double sensor/actuator pairs for beam motion control

This paper presents a study of an arrangement consisting of two matched pairs ofpiezoelectric transducers bonded on a cantilever beam for vibration control. Asingle pair of transducers when used as a matched actuator and sensor inpractice, is known not to have a strictly positive real (SPR) response due tocoupling between in-plane motion and out-of-plane motion. The stabilityand performance of the matched single pair are thus limited when directvelocity feedback control is applied. An arrangement using four piezoelectrictransducer layers arranged as two matched pairs has been suggested toovercome this problem. Theoretically, when the actuator pair and thesensor pair are connected out-of-phase, the response becomes SPR sincein-plane motion cannot be excited. A smart beam with matched doublepiezoelectric sensor/actuator pairs has been implemented. Triangularly shapedsensors and actuators were bonded on each side of the beam. However, thismatched double sensor/actuator pair could not excite pure out-of-planeflexural motion of the beam, due to the direct inter-layer coupling betweenthe sensor and actuator which were bonded directly on to each other.Therefore, the four-layer smart beam does not provide an SPR response.

Experimental validation of a collocated PVDF volume velocity sensor/actuator pair

The active control of sound transmission through a rectangular panel is experimentally verified. The control system is based on a collocated volume velocity sensor/actuator pair which measures and excites the first radiation mode of the panel. Suppression of the first radiation mode is an efficient strategy to control the low frequency sound radiation from the panel. This configuration leads to a simple single-input single-output control system, to which feedback control can be applied. Two implementations of the volume velocity sensor/actuator pair are tested. First, a polyvinyledene fluoride polymer (PVDF) volume velocity actuator foil with shaped electrodes is used in combination with an identical PVDF volume velocity sensor foil. Due to the mechanical coupling between the PVDF sensor and actuator foil, it is shown that a direct velocity feedback control scheme is not feasible because higher order structural modes will be destabilized. Instead integral force feedback is applied, such that the open-loop transfer function has a roll-off towards higher frequencies. Experiments show that this control strategy results in a reduction of the sound pressure in the receiving room of 10 dB at the first structural resonance without spillover to higher order modes. Due to the roll-off towards high frequencies, the control over higher order modes remains limited. Second, a discrete volume velocity sensor is constructed by summing the signals from 12 point sensors placed on the panel. The volume velocity actuator consists of two PVDF foils, glued on each side of the panel and driven in opposite phase. Direct volume velocity feedback is applied to this system, which is minimum phase. This control system is capable of reducing the sound pressure in the receiving room below 300 Hz by 10–15 dB without spillover to higher order modes.

Coupling analysis of a matched piezoelectric sensor and actuator pair for vibration control of a smart beam.

This paper presents a theoretical and experimental study of the in-plane and out-of-plane coupling of a matched piezoelectric sensor/actuator pair bonded on a beam. Both the sensor and actuator are triangularly shaped polyvinylidene fluoride (PVDF) transducers and are intended to provide a compact sensor/actuator system for beam vibration control. The measured sensor-actuator frequency response function has shown an unpredicted increase in magnitude with frequency, which was found, to be due to in-plane vibration coupling. An analytical model has been developed to decompose the sensor-actuator response function into an in-plane contribution and an out-of-plane contribution. This in-plane coupling can limit the feedback control gains when a direct velocity feedback control is applied. A method called the j omega s compensation method is proposed to identify the effect of the in-plane vibration coupling at low frequencies. Even after this compensation, however, there was unexpected strong out-of-plane coupling at even modes, which may have been caused by a lack of accuracy in the shaping of the PVDF sensor and actuator. Numerical simulations have confirmed the sensitivity of the matched sensor/actuator pair with shaping errors.

Comparisonof low-frequency piezoelectric switching shunt techniques forstructural damping

In this paper, the performances of two novel low-frequency piezoelectric switching shunt techniques forstructural damping are compared to the traditional passive tunedresonant shunt circuit technique. The first novel technique,state switching, is a semi-active variable stiffness techniquein which bonded piezoelectric elements are switched from theshort circuit to open circuit states. This technique changesthe stiffness of the structure for two quarters of its vibrationperiod, thus dissipating energy. The second novel technique,pulse switching, is a semi-active continuous switching techniquein which a resistor/inductor shunt circuit is periodicallyconnected to the bonded piezoelectric elements. This techniqueapplies charges to the piezoelectric elements in a mannersimilar to the direct velocity feedback and bang-bang timeoptimal control techniques. A brief description of each of thedamping techniques is given. Numerical simulations of theswitching techniques are shown and compared to the resonantshunt damping technique. Finally, preliminary experimentalresults are presented for the resonant shunt, state switching, and pulseswitching techniques on a simply supported beam.

Analysis and measurement of a matched volume velocity sensor and uniform force actuator for active structural acoustic control

This paper presents a theoretical and experimental study of the frequency response function of a matched volume velocity sensor and uniform force actuator for active structural acoustic control. The paper first reviews the design of a volume velocity sensor and uniform force actuator on a panel, using piezoelectric film with quadratic shaping of the electrodes. The frequency response function of a matched volume velocity sensor and uniform force actuator bonded on either sides of a panel is then studied in detail. This analysis shows that below 100 Hz the sensor–actuator response is controlled by the bending vibration of the panel and a good estimate of the volumetric component of the transverse vibration of the panel is achieved. At higher frequencies, however, the sensor–actuator response is controlled by the in-plane longitudinal and shear vibration of the panel, which causes the real part of the frequency response function to be not strictly positive and to be characterized by large amplitudes at higher frequencies. These two phenomena are important since they limit the possibility of implementing a stable direct velocity feedback control system using these transducers.

Energy Dissipation Analysis of Piezoceramic Semi-Active Vibration Control

In this paper, the performances of two novel low frequency piezoceramic shunt techniques for structural damping are compared to the traditional passive resonant shunt circuit technique. The first novel technique is a semi-active variable stiffness technique in which bonded piezoceramic actuators are switched from the short circuit to open circuit states. This technique changes the stiffness of the structure for two quarters of its vibration period, thus dissipating energy. The second novel technique is a semi-active pulse switching technique in which a resistor-inductor shunt circuit is periodically connected to the bonded piezoceramic actuators. This technique applies charges to the piezoceramic actuators in a manner similar to the well-known Direct Velocity Feedback control technique. The energy dissipated from the structure depends on the magnitude of the applied charge. A description of energy dissipation mechanisms is shown for each switching method and for the traditional passive resonant shunt technique applied to a simple single degree of freedom system.

A panel with matched polyvinylidene fluoride volume velocity sensor and uniform force actuator for the active control of sound transmission

This paper presents a theoretical and experimental study of a smart panel designed for active structural acoustic control. The system consists of a clamped aluminium panel 1 mm thick with dimensions 414 mm X 314 mm. Polyvinylidene fluoride films 0.5 mm thick with a quadratic electrode shape are bonded to either side of the plate, to form a matched volume velocity sensor and uniform force actuator pair. In this paper the design of the smart panel is described in detail. The main properties of the frequency response from distributed actuator to distributed sensor are then discussed with reference to the requirements for direct velocity feedback control. In particular, three problems encountered in the measurement of the transfer function between the sensor and actuator are addressed: first, the unwanted coupling between the sensor and actuator via in-plane plate vibration; second, the high-frequency effects produced by the non-perfect shaping of the actuator and sensor electrodes; third, the phase delays due to the measurement equipment chain.

MULTICHANNEL FEEDBACK CONTROL FOR THE ISOLATION OF BASE-EXCITED VIBRATION

This paper describes the implementation of an independent two-channel controller based on absolute velocity feedback and its performance in improving the isolation from base vibration of a mounted rigid equipment structure characterized by two-degrees of freedom. A single-channel controller is also investigated. If the base structure were rigid, a collocated control strategy based on feedback of the equipment absolute velocity reduces the vibration transmission by skyhook damping. In this study, the vibrating base is flexible so that no rigid ground is available to react the secondary forces off. The direct velocity feedback (DVFB) control implemented here is shown to be very stable, however, so that high control gains could be applied. Effective damping ratios of up to 600% in the modes of the suspended system could be introduced by the two control channels. The passive isolation performance is thus dramatically improved by the two-channel controller: the heave mode is reduced by up to 40 dB, whereas the amplitude of the pitching mode is attenuated up to 26 dB. The experimental results also show a global improvement in the vibration caused by the resonances of the base plate over the frequency range of control [0–200 Hz]. The control effect decreases with frequency as a consequence of the increasing efficiency of the passive isolation. It is also shown that if the feedback gains are equal for the two control channels, the control effect is the same as adding equal damping terms to the two modal responses of the mounted equipment. Finally, the control is shown to be robust to changes in the plate support dynamics, since adding masses at various positions on the base plate did not destabilize the system.

Microvibration Control of Surgical Microscopes with Active Dynamic Vibration Absorbers.

It has been a problem in some hospitals that operations using surgical microscopes for brains and eyes bacome more difficult due to microvibrations of the microscopes caused by human wolks and building equipment such as air conditioning machines. For a practical solution to it, a microvibration control system was developed, in which an active dynamic vibration absorber using a small mass of 0.34 kg driven by an electromagnet and an accelerometer were collocated for vibration control in each direction. The system was attached on the point of the arm of the microscope. A direct velocity feedback control law was developed for the microscopes having various dynamic characteristics corresponding to their attiudes. Furthermore an active-passive switching law was developed to manage large vibrations of the microscopes due to doctors' handling of them. Tests showed that the microvibration control system was effective and reliable enough for real application.

DVFC-Based Identification and Its Application to Robust Vibration Suppression Control of Flexible Structures

This paper proposes direct velocity feedback control (DVFC)-based identification along with its application to robust vibration suppression control of flexible structures. At first, a flexible structure is modified by pseudo-passive control which is realized by DVFC. This DVFC behaves just like a mechanical damper if the sensor and actuator are collocated. Next, system identification is applied to the modified structure. Through this procedure, the accurate structure model for vibration suppression control is more easily derived without paying regard to a sampling time, an identification model and its order. Consequently, the uncertainty such as parameter errors and unmodeled dynamics can be expressed. Finally, the effectiveness of this identification method is verified through the experimental results primarily for a typical earthquake loading and additionally for vibration suppression control of a flexible structure.

Vibration Control of a Beam with Piezoelectric Film Sensors/Actuators.

Vibration control of a flexible beam with piezoelectric film sonsors/actuators is investigated. Triangular-shaped piezoelectric films are bonded on the both surfaces of a flexible beam, and are treated as collocated sensor/actuator pairs. Equations of motions of the beam and sensor output are derived for two boundary conditions: 1) fixed-free, 2) both ends simply supported. Direct velocity feedback (DVFB) control law is employed, and closed-loop stability is analytically checked using Lyapunov's direct method. Forced vibration responses of the beams are calucutated under the condition that the system is harmonically excited. Analytical results show that first several bending modes can be controlled with reasonable feedback gains. In the simply supported case, anti-symmet-rical modes (even modes) are also efficiently controlled, and thus it is shown that the proposed control scheme is valid for multi-mode vibration control' of flexible beams.

Intelligent Material and Fluid Systems. Vibration Sensing and Control of a Flexible Beam Using Piezoelectric Films.

Multimodal vibration control of a cantilever beam using bonded piezoelectric film sensors and actuators is studied both theoretically and experimentally. Equations of motion of the Bernoulli-Euler beam with collocated bonded piezoelectric sensors / actuators are derived. Then, direct velocity feedback control is employed as the vibration control law, and applying Lyapunov's direct method, it is shown that this control law is stable for arbitrary vibration mode. Transient responses of the beam, with control and without control, are studied for the cases in which an impact force is applied to the tip of the beam. Numerical results and experimental results show good agreement, which shows the validity of the proposed control scheme. It is also shown that first three bending modes are efficiently controlled, and that in order to achieve more broadband vibration control, it is necessary to consider the dynamics such as extensional vibrations of the beam which is not considered in the present study.

Vibration Control of a Cantilever Beam Driven with a Piezoelectric Actuator Using Dynamic Compensator.

Unless the collocation requirement is satisfied, it is difficult to control the vibration of a mechanical system with direct velocity feedback control. In the control of a cantilever beam with a piezoelectric actuator and a displacement sensor, state-space methods are usually used because the actuator and sensor cannot be collocated. Though state-space methods are very useful, a large number of sensors at least equal to the number of eigenvalues concerned are needed to fulfill observability conditions. In this paper, a simple design for a stable dynamic compensator with which modal damping ratios of the mechanical system are greatly increased using a noncollocated actuator and sensor is proposed. Experimentally it is found that three natural frequencies of the cantilever beam are well damped with the designed compensator and calculated results of the mechanical system poles and forced response are consistent with experimental ones.