Adaptive Feedforward Control System Research Articles

An adaptive feed-forward active vibration isolation algorithm for input disturbance unbalanced MIMO systems

Multi-axis active vibration isolation systems often encounter order-of-magnitude differences in the perturbations in each input direction. This causes adaptive feedforward control systems to converge at a relatively slow rate, or possibly even diverge. To solve this problem, we propose an improved adaptive feedforward vibration isolation technique based on the classical FxLMS algorithm. Our approach constructs a weighted transformation matrix based on singular value decomposition, attenuates the uneven influence of the input perturbations, and effectively avoids the problems of slow convergence and poor stability faced by existing adaptive algorithms. This paper first describes the parameter update algorithm and the structure of adaptive feedforward algorithms. The convergence of the proposed algorithm is then analyzed, and the method for constructing the weighting matrix is introduced. Finally, the feasibility of the algorithm is verified using a multi-axis vibration isolation system simulation model. The simulation results show that the power spectrum of acceleration in the frequency domain from 0.1 to 100 Hz is attenuated by up to 70 dB under the condition of no excitation in a specific direction, demonstrating the vibration isolation effect of the algorithm. The relative deviation between the predicted and actual parameter error is no more than 6 %, which shows that the algorithm achieves good convergence. The proposed algorithm has potential applications in the active vibration isolation of space telescopes and high-precision optical equipment.

Predicting the performance and optimizing the control parameters of an active vibration control system by pre-identifying the secondary path

In an active vibration control (AVC) system, the secondary path can generally only be identified when the system has been built. The performance of a typical adaptive feedforward control system using the filtered-x least mean square (FxLMS) algorithm is heavily dependent upon the dynamic characteristics of the secondary path. It would, therefore, be helpful for engineers to have knowledge of this behavior early in the design process. In this paper, pre-identification of the secondary path is proposed, which means its offline identification model can be obtained without installing the AVC equipment. This can save both time and money. In the pre-identification process, the secondary path is split into three parts. The first part includes the actuator and related electrical equipment. The frequency response function of this part can be identified after the hardware has been selected. The second part involves the dynamic behavior of the structure to be controlled, which is identified by impact excitation using a specially developed pneumatic impact harmer. The third part concerns the analogue/digital and digital/analogue converters whose effect on the secondary path is offset by a phase shift corresponding to half the sampling time. In this paper, the pre-identification process of the secondary path components is described, and some experiments are conducted to verify the feasibility of the approach and to demonstrate the significance of the pre-identification results. This mainly involves predicting the control performance and optimizing the parameters of the control system. Combined with the simulation of the control system, the approach proposed can improve the work efficiency of large-scale engineering projects and reduce the cost of testing.

Active control of road noise considering the vibro-acoustic transfer path of a passenger car

This paper presents an efficient approach to select the reference sensor position in active control of road noise by considering the vibro-acoustic transfer path of a passenger car. To ensure sufficient noise attenuation in active road noise control, the reference signals should be correlated with vehicle interior noise signals. To achieve this aim, the vibro-acoustic transfer path delivers promising options. An appropriate number of reference signals have generally been obtained by principal component analysis. Then reference sensor positions have been determined by evaluating a large number of candidate locations on a car from a coherence perspective. However, this task is time-consuming and inefficient in the actual vehicle development process. Furthermore, in practice, it is challenging to obtain a highly coherent reference signal for road noise with broadband noise characteristics without understanding the characteristics of the road noise transmitted to the interior of the vehicle. In this study, a structural transfer path analysis was conducted to derive the primary vibro-acoustic paths of structural road noise, and the optimum positions of the reference sensors were determined through the analysis of path contribution and vibro-acoustic transfer function. A practical active noise control system was implemented with the remote microphone technique based on a vehicle audio system to validate the noise attenuation performance. The experiments demonstrated an average attenuation of 3.4 dB at the driver and rear right-hand-side seat positions for up to 400 Hz frequencies. This approach is expected to increase the efficiency in developing active road noise control systems based on adaptive feedforward control systems.

Adaptive feedforward control of closed orbit distortion caused by fast helicity-switching undulators.

A new correction algorithm for closed orbit distortion based on an adaptive feedforward control (AFC) has been developed. At SPring-8, two helicity-switching twin-helical undulators (THUs) had been implemented with conventional feedforward corrections. However, the validity of these corrections turned out to be expiring due to unforeseen variation in the error magnetic fields with time. The developed AFC system has been applied to the THUs dynamically updating the feedforward table without stopping the helicity switching amid user experiments. The error sources in the two THUs are successfully resolved and corrected even while the two THUs are switching simultaneously with the same repetition period. The actual operation of the new AFC system enables us to keep the orbit variations suppressed with an accuracy at the sub-micrometre level in a transparent way for light source users.

Removing SPR-Like Conditions in Adaptive Feedforward Control of Uncertain Systems

This paper considers the problem of designing adaptive feedforward control (AFC) systems for uncertain single-input single-output linear systems perturbed by multisinusoidal disturbances of known frequencies. The proposed approach removes the longstanding assumption that either the sign of the real part or the imaginary part of the transfer function of a stable plant at the frequency of excitation is known for AFC to be applicable, which is referred to in this paper as a strictly positive real (SPR)-like condition. Notable features of the solution are that persistence of excitation is not required, and stability analysis tools based on averaging are avoided; hence, the requirement of an exponentially stable equilibrium for the closed-loop system is circumvented.

Reweighted adaptive bilinear filters for an active noise control system with a nonlinear secondary path

The nonlinearities of active control systems are the main factors that deteriorate noise-reduction performance. To improve the performance of a control system with a nonlinear secondary path, a filtered-x least mean square algorithm using reweighted bilinear filters is proposed in this paper and a generalized filter to model different nonlinear secondary paths is explored. Within the controller of an adaptive feedforward control system, the proposed algorithm uses trigonometric expansions to achieve high-order nonlinearities and combines the cross terms between the controller output, sine and cosine functions of the input with the reference signal. As a result, satisfactory control performance can be achieved with a shorter memory length of the controller compared to certain control algorithms. It is also found that the introduction of a reweighting factor in the weight-updating process can effectively reduce the interference produced by the small coefficients of the control filter and accelerate the convergence rate. The computational complexity of the proposed algorithm is analyzed and its control performance is verified through simulation experiments with different nonlinear secondary paths and input noises. Simulation results show that the proposed algorithm outperforms four other widely accepted algorithms in terms of convergence rate and residual error.

An Adaptive Fuzzy Feedforward-Feedback Control System Applied to a Saccharification Process

Abstract In industrial bioprocess control, disturbance sources typically influences process variable regulation. These disturbances may reduce a system control performance or even affect the final bioproduct quality. Therefore, feedforward control is desired because it anticipates the effects caused by these disturbances in an attempt to keep the process variable at the setpoint value. However, designing a feedforward control law requires process modeling, which can be a tough task when dealing with bioprocesses that are intrinsically nonlinear and multivariable systems. Thus, an adaptive feedforward control law or other advanced control system is needed for satisfactory disturbance rejection. For this reason, a general fuzzy feedforward control system is proposed in this paper to replace the classical feedforward control, making it easier to implement the feedforward control action by avoiding nonlinear and multivariable process modeling. The adaptive fuzzy feedforward-feedback (A4FB) system was applied to a product concentration control loop in an enzymatic reactor, to reject disturbances caused by variations in the substrate and enzymatic solutions feed concentration. The results showed that the A4FB controller rejected much more disturbance effects than classical feedforward control law, demonstrating its advantage, supported by not only its simple implementation, but also its improved disturbance rejection.

Active vibration control of smart flexible piezoelectric beam with a tip mass using hybrid FX‐VSSLMS algorithm

This study concerns adaptive feedforward and hybrid (combined feedback and feedforward) control systems for active vibration suppression of smart flexible beam with a tip mass. By analysing traditional feedforward filtered-X least mean square (FXLMS) algorithm and filtered-X variable step size least mean square (FX-VSSLMS) algorithm, a new hybrid FX-VSSLMS algorithm is developed to improve the control performance of feedforward controllers. A stainless steel beam with a tip mass is employed to simulate flexible robot arm with varying loads. Piezoelectric actuators and sensors are attached to the surface of the beam. Comparison experiments show the effectiveness and benefits of the proposed hybrid FX-VSSLMS method.

Wave-filter-based approach for generation of a quiet space in a rectangular cavity

Abstract This paper is concerned with the generation of a quiet space in a rectangular cavity using active wave control methodology. It is the purpose of this paper to present the wave filtering method for a rectangular cavity using multiple microphones and its application to an adaptive feedforward control system. Firstly, the transfer matrix method is introduced for describing the wave dynamics of the sound field, and then feedforward control laws for eliminating transmitted waves is derived. Furthermore, some numerical simulations are conducted that show the best possible result of active wave control. This is followed by the derivation of the wave filtering equations that indicates the structure of the wave filter. It is clarified that the wave filter consists of three portions; modal group filter, rearrangement filter and wave decomposition filter. Next, from a numerical point of view, the accuracy of the wave decomposition filter which is expressed as a function of frequency is investigated using condition numbers. Finally, an experiment on the adaptive feedforward control system using the wave filter is carried out, demonstrating that a quiet space is generated in the target space by the proposed method.

Analysis and experiments of adaptive feedforward and combined vibration control system with variable step size and reference filter

An adaptive feedforward and combined vibration control system with variable step size and reference filter is analyzed and implemented to suppress the vibration of a kind of thin-walled structure. The theoretical analysis and experiments of adaptive feedforward and combined vibration control algorithms are presented. The experimental setup of a flexible plate bonded PZT (Lead Zirconate Titanate) sensors/actuators is constructed. The control algorithm combines an adaptive feedforward controller and an adaptive feedback controller together, which has shown a superior control performance in the experiments. Considering the disadvantages of fixed step size used in the conventional filtered-U least mean square (FULMS) control algorithm, a variable step-size (VSS) method is applied. Also, a reference filter is used to extract the desired signal from the positive feedback and measurement noise. A proportional derivative (PD) feedback control algorithm is also applied as comparison. The experimental results demonstrate that the adaptive combined control algorithm has better control performance than the adaptive feedforward and PD feedback control algorithms.

A simplified adaptive feedback active noise control system

In the adaptive feedback active noise control system based on the internal model control (IMC) structure, the reference signal is regenerated by synthesizing the error signal and the secondary signal filtered with the estimation of the secondary path, hence more computation load and extra programming are required. Motivated by the engineering truth that the primary noise cannot be completely cancelled in most practical active noise control applications and the error signal still contains some portions of the primary noise, a simplified adaptive feedback active noise control system is proposed in this paper, which adopts the error signal directly as the reference signal in an adaptive feedforward control system and utilizes the leaky filtered-x LMS algorithm to update the controller. The convergence properties of the proposed system are investigated and its advantages are discussed by comparing with other feedback control systems as well as the weakness. Finally, simulations and experiments are carried out to demonstrate the effectiveness of the proposed system.

시스템 상태 및 입력 외란을 고려한 하이브리드 방식의 적응형 피드포워드 제어시스템

AFC (Adaptive Feedforward Control) is significantly employed for improving control performance of dynamic systems particularly involving periodic disturbance signals in engineering fields. This paper presents a novel hybrid AFC approach for discrete-time systems with multiple disturbances in terms of control input and state variables. The proposed AFC mechanism is hierarchically composed of a conventional feedforward control framework and PID auxiliary control configuration in parallel. The former is generic to decrease periodic disturbance excited to control actuators and the latter is additionally constructed to overcome control deterioration due to time-varying uncertainty under given systems. We carry out numerical simulation to test reliability of our proposed hybrid AFC system and compare its control performance to a well-known conventional AFC method with respect to time and frequency domains for proving of its superiority.

Active Feedforward Wave Control of a Rectangular Panel Using a Wave Filter Constructed with Smart Mode Sensors

This paper is concerned with an active wave control method of a rectangular panel. It is the purpose of this paper to present a wave filtering method for the panel using smart modal sensors and its application to an adaptive feedforward control system. Firstly, a wave solution of a rectangular panel is derived to describe the wave dynamics of the structure. This is followed by the proposition of the design procedure of the wave filter using smart mode sensors. Then, from a viewpoint of numerical analyses, accuracy of the proposed method is verified using condition numbers of a filtering matrix. Furthermore, a multi-rate technique is introduced for approximation of the sub-filters in the wave filter, which reduces the computational burden. Finally, experiment on an adaptive feedforward control system using the proposed method is carried out. It is found that the reflected wave absorbing control enables the inactivation of vibration modes.

Active Feedforward Wave Control of a Rectangular Panel Using a Wave filter Constructed with Smart Mode Sensors

This paper is concerned with an active wave control method of a rectangular panel. It is the purpose of this paper to present a wave filtering method for the panel using smart modal sensors and its application to an adaptive feedforward control system. Firstly, a wave solution of a rectangular panel is derived to describe the wave dynamics of the structure. This is followed by the proposition of the design procedure of the wave filter using smart mode sensors. Then, from a viewpoint of numerical analyses, accuracy of the proposed method is verified using condition numbers of a filtering matrix. Furthermore, a multi-rate technique is introduced for approximation of the sub-filters in the wave filter, which reduces the computational burden. Finally, experiment on an adaptive feedforward control system using the proposed method is carried out. It is found that the reflected wave absorbing control enables the inactivation of vibration modes.

Adaptive feedforward control of a rectangular panel using a wave filter constructed with point sensors

This paper presents the wave filtering method for a rectangular panel, which is necessary for a feedforward wave control system, and clarifies its validity in the control system. Firstly, a wave solution of a rectangular panel is derived to describe the wave dynamics of the structure. This is followed by the derivation of the wave filtering equations that indicates the structure of the filter. It is found that the proposed wave filter consists of a modal filter, a rearrangement filter and a wave decomposition filter. Then, from the viewpoint of numerical simulations, the characteristics of the wave propagation in a rectangular panel as well as the accuracy of the wave fitter are verified. For the evaluation of the filter accuracy, the condition number is used as a performance index. Finally, an experiment on the adaptive feedforward control system using the wave filter is carried out, demonstrating that the reflected wave absorbing control enables the inactivation of vibration modes.

Smart wave filtering method of a rectangular panel using Hilbert transformers and itsapplication to an adaptive control system

This paper concerns the active vibration control of a rectangular panel using smart sensorsfrom the viewpoint of an active wave control theory. The objective of this paperis to present a new type of filter which enables the measurement of the waveamplitude of a rectangular panel in real time for the application of an adaptivefeedforward control system which inactivates vibration modes. Firstly, a novel wavefiltering method using smart PVDF sensors is proposed. It is found that the shapingfunction of smart sensors is a complex function. To realize the smart sensor in apractical situation, a Hilbert transformer is utilized to implement a phase shifter of90° for broadband frequencies. Then, from the viewpoint of a numerical analysis, thecharacteristics of the proposed wave filter and the performance of the adaptive feedforwardcontrol system using the wave filter are discussed. Finally, experiments implementing theactive wave control theory which uses the proposed wave filter are conducted,demonstrating the validity of the proposed method in suppressing the vibration of arectangular panel.

Supervisory control of automatic pouring machine

This paper presents supervisory control of a total molten-metal pouring system to improve the productivity of the factory, the safety of workers, and the quality of the product. Through the pouring processes model, a forward tilting control input was calculated by an adaptive feedforward control system to hold the liquid in the sprue cup at a constant level considering the change effected by the accumulating slag in the ladle. A backward tilting input was obtained by means of the hybrid shape approach applied to suppress the slosh. The supervisory control system reasonably switches from the forward tilting motion to the backward tilting motion by using model predictive control to achieve the accurate poured quantity. The validity of the proposed total control system was demonstrated through experiments.

Combined feedback/feedforward active control of vibration of beams with ACLD treatments: Numerical simulation

This paper concerns the numerical simulation of feedback, adaptive feedforward and hybrid (combined feedback/feedforward) control systems on the active control of vibrations of beams with Active Constrained Layer Damping (ACLD) treatments. For the simulation a 1-D beam finite element (FE) model with an arbitrary number of elastic, piezoelectric and viscoelastic layers attached to both sides of the beam is utilized. The damping behavior of the viscoelastic layers is considered by a Laplace transformed Anelastic Displacement Fields (ADF) method. The analyzed case study regards the disturbance rejection of an aluminium beam with a pair of surface mounted ACLD patches. In the design and simulation of the control system a Single-Input Single-Output (SISO) configuration with the output being the velocity at one point of the beam and the input being the control voltage applied into the piezoelectric constraining layers is considered. The case study allows to assess and discuss the outcomes and drawbacks of the feedback and feedforward controllers when used individually and the advantages of the hybrid controller.

Adaptive feed-forward control of flexural waves propagating in a beam using smartsensors

This paper concerns the active vibration control of a flexible beam using smart sensorsfrom the viewpoint of an active wave control theory. The objective of this paper is topresent a new type of sensor which enables one to measure the wave amplitude of a flexiblebeam in real time for the application of use in an adaptive feed-forward controlsystem. Firstly, a novel wave filtering method using distributed parameter PVDFsensors is proposed. It integrates an infinite number of point sensors and has anintegral calculation ability based on a proposed shaping function. Furthermore, thecharacteristics of the wave filter and the performance of the adaptive feed-forward controlsystem using the wave filter are discussed. Finally, experiments adopting the activewave control theory which use the wave filter are conducted, demonstrating thevalidity of the proposed method in suppressing the vibration of a flexible beam.

Active Wave Feedforward Control of a Flexible Beam Using Smart Sensors

This paper deals with active wave control of a flexible beam using a wave filter constructed with smart sensors. It is the purpose of this paper to present a novel wave filtering method using PVDF film sensor and its application for adaptive feedforward control system. Firstly, the design procedure of the wave filter using shaped PVDF sensors is presented. When introducing PVDF sensor, shaping function is defined as a complex function. In this case, multiplying an imaginary unit is equivalent to making the phase difference of 90 degree. Next, from a viewpoint of numerical analysis, the accuracy of the wave filter and the performance of the control system is clarified. Finally, an experiment of the active wave feedforward control system is carried out, demonstrating the validity of the proposed method.