Direct Velocity Feedback Control Research Articles

Acoustic scattering from spherical shells and its active control

The scattering of sound by a thin spherical shell is considered using an analytic formulation involving spherical harmonics. The integral of the far field scattered intensity, termed the scattered power, can then be expressed in a simple form. At low frequencies the scattered power can be minimised by an appropriate choice of material properties and shell thickness, which is illustrated for both a steel shell and for one in which the mass and stiffness of the shell are equal to those of the displaced fluid. Simulations of feedforward active control are then used to investigate the best possible performance in attenuating the scattered power, although this approach requires knowledge of the incident and scattered sound fields. Feedback control of the shell vibration using structural actuators and sensors is a more practical control strategy since it does not involve the need to separate the incident and scattered contributions. Direct velocity feedback control is considered using collocated and distributed actuators and sensors that spread the applied force and sensed velocity over spherical caps on the surface of the shell. This approach shows effective suppression of the structural shell modes that give rise to significant scattering at their resonant frequencies.

Fluid–structure–control interaction simulation of flutter control problems

Flutter is an aeroelastic instability and can lead to destruction of structures, and thus its control is important in engineering. A flutter control problem is classified into fluid–structure–control interaction (FSCI) problems. Conventionally, flutter control has been investigated using simple FSCI models. However, these models are sometimes insufficient because of their many simplifications (e.g., potential flow, simple geometry, small deformation). For control problems with severe nonlinearity, high-fidelity FSCI modeling, where control systems are incorporated into models that couple computational structural dynamics and computational fluid dynamics, may be required. Although high-fidelity modeling has a high computational cost, recent improvements in machine power have made the use of FSCI models feasible. In FSCI analysis, control forces are dealt with as external forces that can be treated implicitly or explicitly. Although the treatment of control forces influences the damping of controlled systems, it has not been discussed in previous studies on FSCI analysis. Furthermore, there has been no study in which high-fidelity FSCI simulations of flutter control problems were conducted. The present study evaluates the difference between the implicit and explicit treatment of control forces using stability analysis. The stability analysis results show that explicit treatment cannot capture the damping of controlled systems, especially for high-order modes. Therefore, implicit treatment is required for FSCI analysis. In numerical examples, we consider flutter of a cantilevered beam in axial flow. Control laws designed using conventional approaches are tested using the developed FSCI analysis. Reasonable results are obtained in terms of the improvement in flutter velocity. • Fluid–structure–control interaction (FSCI) analysis is proposed by incorporating control systems into FSI analysis. • The difference between implicit and explicit coupling of control systems is investigated using stability analysis. • Implicit coupling is required to accurately evaluate the damping of the controlled systems. • Direct velocity feedback control and state feedback control with an identity observer are tested in the proposed FSCI analysis. • The FSCI analysis reproduces the improvement in flutter velocity predicted at the control design stage.

Computational control for strongly coupled structure, electric, and fluid systems

Piezoelectric-structure interaction (PSI) and fluid-structure interaction (FSI) are multi-physics coupled systems. These interactions affect the vibration characteristics of coupled systems and thus such complex coupled systems must be controlled. This paper proposes computational control based on the finite element method for strongly coupled multi-physics analysis of the PSI of a thin flexible piezoelectric bimorph actuator. The vibration characteristics and the effect of direct velocity and displacement feedback (DVDFB) control in coupled systems are investigated. The displacement and velocity feedback gains are used together as well as separately. DVDFB control is extended to the FSI of stiff and soft structures to study vibration characteristics using active control and compare the stability of the two types of structure. The results of PSI show a reduction in actuator displacement amplitude and a shift in the resonance frequency due to DVDFB control. For FSI, the results for a stiff material show a reduction in displacement. The velocity feedback gain has no effect for a stiff material and leads to instability due to a large control force. The results for a soft material show a reduction in displacement and amplitude and more stability compared to the case for the stiff material.

Experimental comparison of different automatically tuned control strategies for active vibration control

Chatter is the main limiting factor affecting the material removal rates of machine tools and is caused by the machine's most flexible structural mode shapes. The use of active vibration control systems can damp the structural mode shapes and, in turn, significantly increase the chatter-free depth of cut. In order to reduce the commissioning effort, previous publications have introduced methodologies to automatically tune various control strategies for active damping. This paper presents a new automatic tuning approach for a robust model-based controller, which uses particle swarm optimization to find the best-performing control parameters. The proposed method was tested on both a 5-axis milling machine and a vertical lathe, together with an automatically tuned direct velocity feedback controller and an adaptive controller. The performance was evaluated by conducting extensive cutting tests under industrial operating conditions. All controllers and automatic tuning methodologies led to notable increase in chatter-free material removal rates, reduced vibration amplitudes, and improved surface roughness.

Investigation on nonlinear dynamics and active control of boring bar chatter

This article deals with identification of nonlinear dynamics and active control of boring bar chatter. A control system with unidirectional actuation is proposed, which consists of an accelerometer sensor that monitors the cutting tool vibrations as well as an electrodynamic shaker that exerts a controllable force to a boring bar in the radial direction. The forward path model for actuator–boring bar assembly is identified using the fundamental concepts of system identification. A novel parameter-varying transfer function is suggested to model the nonlinear dynamics of forward path, which originally stems from the cutting tool structure. The proposed model describes the variations of system’s output response with respect to frequency and amplitude of input excitation. The identified dynamic model is then utilized for model-based controller tuning. The chatter control system utilizes a Direct Velocity Feedback (DVF) controller, and the optimal control gain is computed based upon the disturbance rejection criterion. It is confirmed that the performance of optimally tuned DVF controller does not depend on variations of forward path dynamics. The practical performance of optimal controller is experimentally verified by conducting impact tests as well as cutting tests on Aluminum alloy 6063-T6. According to the obtained results, the dynamic stiffness of active cutting tool is significantly improved by 20-fold. Moreover, chatter is perfectly attenuated around the fundamental mode of boring bar. The DVF controller efficiently attenuates the vibrations by 70 dB. Finally, the viability of using an active cutting tool with embedded electromagnetic damper is studied for industrial applications.

Preventing stroke saturation of inertial actuators used for active vibration control of floor structures

Active vibration control techniques using inertial-mass actuators have gained some level of acceptance in civil structures. Recent research indicates the effectiveness of this technique in mitigation of human-induced excitation in pedestrian structures such as floors and footbridges. However, there are some drawbacks associated with the use of inertial-mass actuators which needs to be dealt with. One of the main disadvantages of using inertial actuators is their stroke saturation non-linearity. When the stroke saturation phenomenon happens, excessive movement of inertial mass along the stroke hits the ends of actuator and can destabilize the system or even damage the actuator. This paper presents a novel velocity feedback control strategy to robustly prevent stroke saturation of inertial actuator. Two inner loops are added into a direct velocity feedback (DVF) control loop. First inner loop is a proportional-derivative (PD) controller based on the measured displacement of inertial mass. The second inner loop is implemented as a DVF gain modifier based on the actuator mass displacement over-range. This adaptively reduces the DVF gain, by an amount proportional to the over-range by displacement ratio, when inertial mass displacement is predicted to exceed the certain limit. Theoretical and experimental study of the control strategy is examined on a laboratory scale floor structure using an inertial-mass actuator. Both the results demonstrate the effectiveness of the proposed control strategy. The displacement of actuator's mass is kept within the stroke limits while satisfactory control performance is maintained.

Design, analysis, and implementation of a new adaptive chatter control system in internal turning

In this article, the adaptive control of chatter vibrations in internal turning operations is addressed. The single-input and single-output (SISO) control system is composed of an electrodynamic shaker as the controllable actuator, an integrated electronics piezoelectric (IEPE) accelerometer as the feedback sensor, and a newly proposed control algorithm. A novel adaptive direct velocity feedback (DVF) controller is developed on the basis of the energy balance concept. The suggested gain adaptation algorithm dynamically adjusts the value of controller gain by considering the mutual interaction between the control system and the cutting process. The aim of the adaptive DVF controller is to maintain a reasonable balance between the rate of positive energy generated by the actuator and the rate of destructive energy absorbed by the boring bar due to chatter phenomenon, such that the stability of cutting process is remarkably improved with minimized actuation cost. The performance of the proposed adaptive chatter control system is experimentally verified during the internal turning of Aluminum alloy 6063-T6. The value of critical limiting depth of cut is anticipated to be nearly 0.2 mm for the slender boring bar. During the impact experiments, it has been observed that the adaptive DVF controller enhances the dynamic stiffness of boring bar by 11.4-fold. In addition, with the help of the presented adaptive controller, the stable cutting process is successfully performed with the maximum cutting depth of 2 mm. It has been observed that the amplitude of chatter vibrations is efficiently attenuated by at least 60 dB, adjacent to the dominant bending mode of the boring bar. The periodic chatter waviness is eliminated from surface texture and the roughness of cut surface is remarkably improved. Finally, it is proved that the presented control system can be effectively utilized in order to enhance the stability of active boring bar in deep internal turning operations.

A Design Method of Active Damping for Gyroscopic Systems Using Direct Velocity Feedback

For gyroscopic dynamic systems, active damping using direct velocity feedback control with collocated actuator/sensor pairs is discussed in this paper. The proposed method of designing the damping is actually to assign the negative real parts of the poles for specific modes of the uncontrolled system. The targeted values of the negative real parts are determined by desired damping ratios to be gained for the specific modes. The procedure is formulated as solving constrained nonlinear equations or a constrained nonlinear least squares problem with elements of the control gain matrix as variables. Finally, it is illustrated via an example rotor system that the presented method is effective and easier to implement.

Boring Bar Chatter Control using Feedback Filtered-x Normalized Least Mean Square Algorithm

Abstract This paper deals with the adaptive control of chatter vibrations in boring operations. A novel feedback control method is suggested based upon the well-known filtered-x normalized least mean square (FxNLMS) algorithm. The proposed feedback controller is implemented on the developed active boring bar that is equipped with electrodynamic shaker and accelerometer. The adaptive digital control algorithm utilizes two finite impulse response (FIR) filters in order to efficiently drive the electromagnetic actuator and successfully minimize the mean square of the chatter vibrations. Feasibility of the proposed control algorithm is verified for boring of Aluminum alloy 6063-T6. The performance of feedback FxNLMS controller is compared with the constant-gain direct velocity feedback (DVF) controller. It is observed that both control algorithms attenuate the chatter by more than 70 dB. In addition, the actuator cost is reduced by 50 percent for the optimally tuned adaptive digital controller. As a result, the proposed adaptive controller provides a robust and efficient solution for chatter suppression.

Parametric study on the optimal tuning of an inertial actuator for vibration control of a plate: Theory and experiments

This paper presents a theoretical and experimental tuning of the velocity feedback gain of a plate with an inertial actuator. The objective of the study is to analyse a direct velocity feedback control unit, which can be tuned locally and yet providing a global vibration reduction. This is achieved through the knowledge of the velocity signal and the actuator dynamics, without information on the plate dynamics. In practice, an electrical input is provided to the actuator, proportional to the local velocity of the structure, in such a way to generate active damping. The tuning is performed by maximising the power absorbed by the inertial actuator from the structure, and this is shown to be equivalent to the minimisation of the global level of vibration, estimated through the kinetic energy of the structure. Nine accelerometers have been used, and the performance for several values of different feedback gains has been investigated. Moreover, the influence of the frequency range of integration in the tuning of the velocity feedback gain is considered, and it is found experimentally that a broadband reduction up to 5 dB can be achieved, as expected from the numerical model. The absorbed power from the plate by the control unit is found to be negative below the first natural frequency of the inertial actuator, when the feedback control is implemented. This is due to the fact that, although a collocated velocity feedback is implemented, the control system is only conditionally stable because of the actuator dynamics. The performance of active control is found to reduce dramatically, if instability occurs for gains lower than the optimal one. For this reason, the work is enriched with a parametric study on the plate-actuator pair, in which the influence of the dynamic properties of the plate and the inertial actuator are investigated. The effectiveness of the active control is found to depend on the mass ratio between the actuator and the plate. In particular, for low mass ratios, the system well approximate the ideal case, in which a control force is proportional to the velocity of the plate, but for high mass ratios, a small amount of active damping can be introduced.

High-performance controller design and evaluation for active vibration control in boring

High quality manufactured components with fast production rate is an increasing demand of modern machine tool industry. Internal machining operations due to the large length to diameter ratio are most prone to intolerable chatter vibrations and proved to be an extremely challenging process. This paper presents a new method for proper design of direct velocity feedback (DVF) controller in order to extend boundaries of stable cutting for internal turning with minimum control effort. Control effort and active damping performance are two counteracting parameters that affect the results of active vibration control. After properly implementing the DVF active control algorithm on the internal turning setup, stable boundaries for different control gains of DVF controller are thoroughly studied. The comparison shows that although high DVF gains may considerably improve dynamic stiffness of the tool, it leads to the maximum control effort and actuator saturation and consequently process instability. The proposed gain selection method results in a significant increase in stable machining over the desired range of cutting conditions. The suggested design approach of the DVF controller can considerably improve limitations of rough machining on long over hang boring bars.

Velocity Feedback for Controlling Vertical Vibrations of Pedestrian-Bridge Crossing. Practical Guidelines

Active vibration control via inertial mass actuators has been shown as an effective tool to significantly reduce human-induced vertical vibrations, allowing structures to satisfy vibration serviceability limits. However, a lot of practical obstacles have to be solved before experimental implementations. This has motivated simple control techniques, such as direct velocity feedback control (DVFC), which is implemented in practice by integrating the signal of an accelerometer with a band-pass filter working as a lossy integrator. This work provides practical guidelines for the tuning of DVFC considering the damping performance, inertial mass actuator limitations, such as stroke and force saturation, as well as the stability margins of the closed-loop system. Experimental results on a full scale steel-concrete composite structure (behaves similar to a footbridge) with adjustable span are reported to illustrate the main conclusions of this work.

Compact and Efficient Active Vibro-acoustic Control of a Smart Plate Structure

An effective wide band active control law through one kind of the Dynamic Vibration Absorber (DVA) is proposed and studied in this paper. With the help of mechanical impedance method, active DVA control law is formulated based on the passive mechanical model. The electrical DVA can generate multi-mode active damping to the structure. The host structure is an aluminum plate and acceleration signal is feedback through the controller to a collocated piezoelectric actuator. Experimental systems are setup and the open loop analysis shows that the control system has better roll-off property than the Direct Velocity Feedback (DVF) controller does. Furthermore, real time control results demonstrate that the multiple vibration modes can be suppressed simultaneously. Meanwhile, the measured sound isolation performance below 1 kHz can be up to 6 dB. The proposed method is simple and effective, which is applicable to other types of structures.

Cluster filtering/control of bending/torsional vibrations of a tape tether using smart-film sensors/actuators

Tape tethers show great promise for application in space debris removal because they possess a large collecting area, which is crucial for the collection of electrons from a plasma environment in space. Tape tethers are therefore preferred over string tethers in electrodynamic tethered systems (EDTS), which operate based on the Lorentz force derived from the interaction between the electric current on the tether and the Earth's magnetic field. Vibrations of the tether may disturb the attitude of the mother satellite and the subsatellite, and are difficult to damp in space because the damping would be minimal owing to the almost zero drag force in space. Due to their relatively large width, tape tethers experience torsional deformation and therefore cannot be treated as a string tether. If torsional deformation of tape tethers is not avoided, the advantage of tape tethers as the materials for EDT systems will be deteriorated. Point-type sensors and actuators are usually used to sense and control vibrations. However, it is difficult to apply such sensors and actuators to tape tethers because of the substantial length of the tether as well as the need for a deployment mechanism, such as a reel. In order to overcome the difficulties related to vibrations, the use of smart-film sensors and actuators for sensing and controlling vibrations of tape tethers is considered in this study. In a previous study, we presented an application of smart film for sensing vibrations of tape tethers, but the actuation of tape tethers using smart-film actuators has not yet been reported. In the present paper, we mathematically derive suitable configurations of smart-film attachment to a tape tether for cluster filtering and actuation of bending and torsional vibrations of the tape tether, and carried out cluster actuation experiments. The experimental results reveal that the bending and torsional vibrations of a tape tether can be reduced by cluster actuation control based on direct velocity feedback control (DVFC) using smart-film sensors/actuators attached to the surface of the tape tether with the derived configurations.

Active control of sound transmission using a hybrid/blind decentralized control approach

This paper presents a theoretical and experimental analysis of broadband sound transmission control of an aluminum panel in the frequency range between 30 Hz and 1 kHz. Based on the analysis of characteristics of sensor-actuator pairs, piezoelectric patches bonded on the structure are used as actuators, and collocated accelerometers are used as sensors. Then a hybrid decentralized control law is derived, which has a broad control band and puts more control authority on the most sound radiation effective mode. This control law comprises two parts: one is the direct velocity feedback controller, and the other one, relatively new, is called the negative acceleration feedback (NAF) controller. The control architecture is decentralized, which means each controller works independently. Due to the second-order dynamic property of the NAF controller and the fact that the structure’s frequencies may shift, the Hilbert-Huang method is used for quick and automatic identification of the natural frequency. Finally, open loop and closed loop experiments are presented to support the theoretical analysis. The active control results demonstrate that the panel’s vibration level can be suppressed by 16.7 dB and the broadband sound pressure level could be lowered by more than 7 dB.

The Analysis of a Smart Jeffcott Rotor with Direct Velocity Feedback Control in the Supercritical Range

The paper discusses the analysis of the active control of a Jeffcott rotor with the rotational speed in the supercritical range. By the application of collocated sensors and actuators and a suitable control algorithm it has been possible to influence the internal damping of the rotor, which is the origin of self-induced vibrations. By this approach it is possible to increase the range of the stable operation of the rotor. In the paper, a classical analytical two-degree-of-freedom Jeffcott rotor model has been extended to account for the presence of piezoelectric patch sensors and actuators. The applicability of this model has been positively verified through the comparison with the finite element results derived using the Ansys software. Plots have been obtained by both the analytical approach and the finite element method that demonstrate the applicability of velocity feedback to increasing the threshold of instability of the rotor.

A low density, high stiffness flat loudspeaker with combined feedback-feedforward response correction

This paper presents a novel perforated flat loudspeaker with improved sound frequency response by applying velocity feedback control. Flat loudspeakers provide advantages of compact dimensions and high durability. Known flat loudspeaker technology is based on high model density. However, the resonances in the panel are complex and difficult to control, which often leads to complicated computations and insufficient low frequency response. The flat loudspeaker in this paper comprises a novel panel structure, which offers low density, high stiffness, and efficient space utilization. Direct velocity feedback control provides a simple and stable control loop. We apply the multiple direct velocity feedback control method to obtain flat sound frequency response. Furthermore, a Linkwitz filter is applied to our system to increase response at very low frequencies. Experimental results show that a multiple combined feedback-feedforward control method effectively improves the performance of the flat loudspeaker with extended low-frequency response.

Active vibration control of clamped beams using positive position feedback controllers with moment pair

This paper investigates the active vibration control of clamp beams using positive position feedback (PPF) controllers with a sensor/moment pair actuator. The sensor/moment pair actuator which is the non-collocated configuration leads to instability of the control system when using the direct velocity feedback (DVFB) control. To alleviate the instability problem, a PPF controller is considered in this paper. A parametric study of the control system with PPF controller is first conducted to characterize the effects of the design parameters (gain and damping ratio in this paper) on the stability and performance. The gain of the controller is found to affect only the relative stability. Increasing the damping ratio of the controller slightly improves the stability condition while the performance gets worse. In addition, the higher mode tuned PPF controller affects the system response at the lower modes significantly. Based on the characteristics of PPF controllers, a multi-mode controllable SISO PPF controller is then considered and tuned to different modes (in this case, three lowest modes) numerically and experimentally. The multi-mode PPF controller can be achieved to have a high gain margin. Moreover, it reduces the vibration of the beam significantly. The vibration levels at the tuned modes are reduced by about 11 dB.

Active vibration control of beam structures using acceleration feedback control with piezoceramic actuators

In this study, the active vibration control of clamped–clamped beams using the acceleration feedback (AF) controller with a sensor/moment pair actuator configuration is investigated. The sensor/moment pair actuator is a non-collocated configuration, and it is the main source of instability in the direct velocity feedback control system. First, the AF controller with non-collocated sensor/moment pair actuator is numerically implemented for a clamped–clamped beam. Then, to characterize and solve the instability problem of the AF controller, a parametric study is conducted. The design parameters (gain and damping ratio) are found to have significant effects on the stability and performance of the AF controller. Next, based on the characteristics of AF controllers, a multimode controllable single-input single-output (SISO) AF controller is considered. Three AF controllers are connected in parallel with the SISO architecture. Each controller is tuned to a different mode (in this case, the second, third and fourth modes). The design parameters are determined on the basis of the parametric study. The multimode AF controller with the selected design parameters has good stability and a high gain margin. Moreover, it reduces the vibration significantly. The vibration levels at the tuned modes are reduced by about 12 dB. Finally, the performance of the AF controller is verified by conducting an experiment. The vibration level of each controlled mode can be reduced by about 12 dB and this value is almost same as the theoretical result.

Filtered Velocity Feedback 제어기를 이용한 평판 능동진동제어

This paper reports a filtered velocity feedback(FVF) controller, which is an alternative to direct velocity feedback(DVFB) controller. The instability problems at high frequencies due to non-collocated sensor/actuator configuration with the DVFB can be alleviated by the proposed FVF controller. The FVF controller is designed to filter out the unstable high frequency response. The dynamics of a clamped plate under forces and moments and the FVF controllers are formulated. The stability of the control system and performance are investigated with the open loop transfer function(OLTF). It is found that the FVF controller has a higher gain margin than the corresponding DVFB controller owing to the rapid roll-off behavior at high frequencies. Although the gain margin cannot be fully utilized because of the enhancement at the high frequencies, the vibration at the modes lower than the tuning frequency is well controlled. This performance of the FVF controller is shown to be improved from that of the DVFB controller. It is, however, noted that the stability around the tuning frequency is very sensitive so that the enhancement in vibration level should be followed. The reduction performance at low frequencies using the FVF controller should be compromised with the enhancement in the vibration at high frequencies while designing the controller.