Decentralized Velocity Feedback Control Research Articles

Virtual absorbed energy in decentralized velocity feedback control of a plate with piezoelectric patch actuators

Feedback gain is a key factor in decentralized velocity feedback control. It is known that an optimal feedback gain value exists with which the active damping effect could be maximized. In this paper, a method of finding suitable feedback gains for decentralized velocity feedback control with piezoelectric patch actuators is investigated. The energy absorption of piezoelectric patch actuators is calculated. The concept of virtual energy absorption of the piezoelectric patch actuator is proposed, through which the optimal feedback gain can be got conveniently. Numerical investigations are performed to explore the relationships between the virtual energy absorption by piezoelectric patch actuators and the kinetic energy of the structure. The results show that maximizing the broadband virtual energy absorption is nearly equivalent to minimizing the kinetic energy. A robust self-tuning algorithm is also proposed with maximizing the broadband virtual energy absorption. This algorithm can simultaneously update feedback gains of more than one control units, and find the optimal feedback gains automatically.

A novel decentralized velocity feedback strategy of plate vibrations using piezoelectric patch actuators

Previous studies have shown that, similar feedback gains are required to minimize the kinetic energy of a plate and to maximize the absorbed energy by each force actuator in a wide-band excitation. The energy absorption of a force actuator is easy to measure, but it is hard to get the energy absorption by a moment actuator such as a piezoelectric patch actuator which needs the angular velocity at the mounting point of the actuator. In this paper, the energy absorption of piezoelectric patch actuators for decentralized velocity feedback control of plate vibrations is investigated numerically. A kind of virtual energy absorption of the piezoelectric patch actuator is proposed, which is the multiplication of the torque produced by the piezoelectric patch actuator and the velocity at the mounting point of the actuator. Numerical investigations are performed to explore the relationship of the virtual energy absorption by the piezoelectric patch actuators and the kinetic energy of the structure. The results sho...

Comparison of decentralized velocity feedback control for thin homogeneous and stiff sandwich panels using electrodynamic proof-mass actuators

Theoretical and experimental work is presented to compare the effect of decentralised velocity feedback control on thin homogeneous and sandwich panels. The decentralised control system consists of five control units, which are composed of a proof-mass electrodynamic actuator with an accelerometer underneath its footprint and an analogue controller. The stability of the feedback loops is analysed by considering the sensor-actuator open-loop frequency response function of each control unit and the eigenvalues of the fully populated matrix of open-loop frequency response functions between the five sensors and five actuators. The control performance is then analysed in terms of the time-averaged total kinetic energy and total sound power radiated by the two panels. The results show that for a stiff sandwich panel higher stable feedback gains can be implemented than on a thin homogeneous panel of comparable weight per unit area. Moreover the implementation of decentralised velocity feedback can offset some of the undesirable sound transmission properties of lightweight sandwich structures by efficiently reducing structural vibration and sound power radiation in the mid audio frequency range.

Double panel with skyhook active damping control units for control of sound radiation

This paper presents an experimental study on decentralized velocity feedback control on a double panel consisting of an external aluminum panel and a honeycomb trim panel. The decentralized feedback loops are formed by a 3x3 array of coil-magnet electrodynamic actuators that react off the trim panel and a lightweight stiff frame structure located in the air gap between the two panels. Microelectromechanical systems (MEMS) accelerometers are located on the opposite side of the trim panel in correspondence to the electrodynamic actuators. The grid structure is designed to provide an inertial reference to the actuators. In this way the velocity feedback control loops produce skyhook active damping on the double panel, which minimizes the vibrational response and sound radiation of the trim panel at low audio frequencies. Two configurations are considered where the grid structure is either weakly coupled or strongly coupled to the external panel. Both stability and control performance of the two configurations are analyzed experimentally. The study shows that the control configuration with the weakly coupled grid structure enables the implementation of larger stable feedback control gains, which lead to reductions of the sound radiated by the trim panel between 10 and 30 dB for the first seven resonance peaks.

Downscaling of proof mass electrodynamic actuators for decentralized velocity feedbackcontrol on a panel

This paper presents a simulation study on the downscaling of multiple electrodynamicproof mass actuators for the implementation of decentralized velocity feedback controlloops on a thin panel. The system is conceived to reduce the panel response andsound radiation at low resonance frequencies. In the first part of the paper, theprincipal downscaling laws of a single proof mass actuator are revisited. In particular,the scaling laws are given for: (a) the fundamental natural frequency, (b) thedamping factor, (c) the static displacement, (d) the maximum current that can befed back to the actuator, (e) the maximum stroke of the proof mass and (f) themaximum control force that can be produced by the actuator. The second part of thepaper presents a numerical study concerning the control performance produced bydecentralized control systems with an increasing number of control units, whichare scaled down in such a way as to keep the total base surface occupied by theactuators constant. This study shows that the control performance tends to riseas the number of control units is increased. However, this trend is reversed forlarge arrays of small scale actuators since the gain margin of the feedback loopstends to decrease with downscaling and incrementation of the actuators density.

Homogeneous and sandwich active panels under deterministic and stochastic excitation

In this paper an element-based model is used to predict the structural response and sound radiation of two smart panels excited by (a) an acoustic plane wave, (b) a stochastic acoustic diffuse field, and (c) a turbulent boundary layer. The first panel is made of aluminum, while the second is a composite sandwich panel with equivalent static stiffness but four times lower mass per unit area. The panels are equipped with 16 decentralized velocity feedback control loops using idealized point force actuators. In contrast to previous studies on smart panels, the analysis is extended to the upper end of the audio frequency range. In this frequency region the response and sound radiation of the panels strongly depend on the spatial characteristics of the excitation field and the sound radiation properties with respect to the bending wavelength on the panels. Considerable reduction in structural response and sound radiation is predicted for the low audio frequency range where the panel response is dominated by well separated resonances of low order structural modes. It is also found that some reduction can be achieved around acoustic and convective coincidence regions.

Smart panel with active damping units. Implementation of decentralized control

This paper contains the second part of a study on a smart panel with five decentralized velocity feedback control units using proof mass electrodynamic actuators [Gonzalez Diaz et al., J. Acoust. Soc. Am. 124, 886 (2008)]. The implementation of five decentralized control loops is analyzed, both theoretically and experimentally. The stability properties of the five decentralized control units have been assessed with the generalized Nyquist criterion by plotting the loci of the eigenvalues of the fully populated matrix of frequency response functions between the five error signals and five input signals to the amplifiers driving the actuators. The control performance properties have been assessed in terms of the spatially averaged response of the panel measured with a scanning laser vibrometer and the total sound power radiated measured in an anechoic room. The two analyses have shown that reductions of up to 10 dB in both vibration response and sound radiation are measured at low audio frequencies, below about 250 Hz.

Smart Double Panel with Decentralized Active Dampers for Sound Transmission Control

This paper presents a theoretical study of decentralized velocity feedback control systems for the reduction of sound transmission through double panels. The system studied consists of two plates which are coupled acoustically by the air in the cavity between them and structurally by four elastic mounts. The geometrical and material properties of the double panel have been chosen so as to approximate a section of an aircraft fuselage skin. The outer panel of the skin (the source panel) is excited by oblique plane waves and the consequent sound power radiated from the inner panel (the radiating panel) is calculated. First, a parametric study of passive sound transmission of double panels with different geometrical and material properties is carried out. Second, active vibration control is implemented using 16 decentralized direct velocity feedback loops. Performance of such a control system is assessed for four control cases. The first two cases deal with skyhook force actuators with collocated velocity sensors, which implement active damping either on the source panel or on the radiating panel. In the third case, skyhook actuators and collocated velocity sensors are located on both panels. Finally, an approach using actuators that react between the two panels with collocated relative velocity sensors is considered.

Experimental tests on smart panels for the reduction of sound radiation

This paper presents a comparative experimental study carried out on four types of smart panels for the reduction of sound radiation. The four panels are equipped with decentralized velocity feedback control units that are designed to generate active damping. In this way the frequency averaged response and sound radiation produced by stochastic disturbances can be effectively reduced at low audio frequencies. The first smart panel is composed of a 4×4 array of square piezoelectric patch actuators with accelerometer sensors at their centres. The second smart panel is composed of sixteen triangularly shaped piezoelectric patch actuators with base edges evenly distributed along the perimeter of the panel and accelerometer sensors located on the top vertices of the actuators. The third panel is composed of five electrodynamic inertial actuators with accelerometer sensors located under their footprints. The fourth panel is equipped with a light honeycomb trim panel mounted on four stiff mounts. A set of nine reactive electrodynamic actuators is located in the shallow cavity between the two panels. Accelerometer sensors are mounted at the two footprints of each actuator. The sensor-actuator pairs mounted in the four panels are used to implement analogue local feedback loops.

Rectangular plate with velocity feedback loops using triangularly shaped piezoceramic actuators: Experimental control performance

This paper presents experimental results on the implementation of decentralized velocity feedback control on a new smart panel in order to produce active damping. The panel is equipped with 16 triangularly shaped piezoceramic patch actuators along its border and accelerometer sensors located at the top vertex of the triangular actuators. The primary objective of this paper is to demonstrate the vibration and sound radiation control using the new smart panel. Narrow frequency band experimental results highlight that the 16 control units can produce reductions up to 15 dB at resonance frequencies between 100 and 700 Hz in terms of both structural vibration and sound power radiation.

Optimal centralized and decentralized velocity feedback control on a beam

This paper considers the optimization of a velocity feedback controller with a collocatedforce actuator, to minimize the kinetic energy of a simply supported beam. If the beam isexcited at a single location, the optimum feedback gain varies with the position of thecontrol system. It is shown that this variation depends partly on the location of the controlforce relative to the exciting force. If a distributed excitation is assumed, that is random inboth time and space, a unique optimum value of the feedback gain can be found for a givencontrol location. The effect of the control location on performance and the optimalfeedback gain can then be examined and is found to be limited provided thecontrol locations are not close to the ends of the beam. The optimization can alsobe performed for a multichannel velocity feedback system. Both a centralizedand a decentralized controller are considered. It is shown that the difference inperformance between a centralized and a decentralized controller is small, unlessthe control locations are closely spaced. In this case the centralized controllereffectively feeds back a moment proportional to angular velocity as well as a forceproportional to a velocity. It is also shown that the optimal feedback gain can beapproximated on the basis of a limited model and that similar results can be achieved.

Smart panels with SISO or MIMO velocity feedback control systems

This paper summarizes and contrasts the research work that has been carried out on two types of smart panels with ASAC control systems: first, a SISO velocity feedback control system with a sensor that detects the volumetric component of the vibration of the panel and an actuator that exerts a uniform force over the surface of the panel and, second, a MIMO decentralized feedback control system using a grid of sensors that measure the point velocities of the panel and a grid of actuators that generates point excitations in the locations of the sensors. Both theoretical predictions and experimental results are presented for a reference problem of control of sound radiation by a rectangular panel clamped along the perimeter. The simulations carried out for the two systems have shown that the smart panel with the volume velocity sensor and uniform force actuator can in principle give better control performance than the smart panel with the sixteen decentralized control units. However, the practical implementation of the smart panel with the volume velocity sensor and uniform force actuator is limited by stability problems which are instead a minor issue for the panel with 16 decentralized velocity feedback control units.

Active isolation of a flexible structure from base vibration

This paper presents a theoretical and experimental investigation into an active vibration isolation system. Electromagnetic actuators are installed in parallel with each of four passive mounts, which are placed between a flexible equipment structure and a base structure which is either flexible or rigid. Isolation of low-frequency vibration is studied, so that the passive mounts can be modelled as lumped parameter springs and dampers. Decentralized velocity feedback control is employed, where each actuator is operated independently by feeding back the absolute equipment velocity at the same location. Good control and robust stability have been obtained both theoretically and experimentally for the multichannel control systems. This is to be expected if the base structure is rigid, in which case the actuator and sensor are, in principle, collocated and the control system implements a skyhook damper. With a flexible base structure, however, collocation is lost due to the reactive actuator force acting on the base structure, but the control system is still found to be robustly stable and to perform well. Attenuations of 20 dB are obtained in the sum of squared velocities on the equipment structure at the rigid-body mounted resonance frequencies. In addition, attenuations of up to 15 dB are obtained at the resonance frequencies of both the low order flexible modes of the base structure and the equipment structure.

Decentralized control for multichannel active vibration isolation

This paper describes a theoretical and experimental investigation into an active four-mount vibration isolation system, in which electromagnetic actuators are installed in parallel with each of the four passive mounts placed between a three-dimensional piece of equipment and a vibrating base structure. Decentralized velocity feedback control is applied, where each actuator is operated independently by feeding back the corresponding equipment vibration velocity at the same location. Although one end of the actuator acts at the sensor position on the equipment, the system is not collocated because of the reactive force at the other end acting on the flexible base structure, whose dynamics may be strongly coupled with the mounted equipment. The investigation of this actuator installation and its practical implementation are the motivation of this research. Isolation of low-frequency vibration is considered where the equipment can be modeled as a rigid body and the mounts as lumped-parameter springs and dampers. A general theoretical formulation for analysing multiple-mount vibration isolation systems using the impedance method is presented and is used to investigate the control mechanisms involved. Experimental results show that up to 14 dB reduction in the kinetic energy of the equipment can be achieved in practice. If very high gains are used in the experiments, however, instability occurs at low frequencies due to phase shifts in the transducer conditioning electronics.