Perfect tracking control based on multirate feedforward controlwith generalized sampling periods

In this paper, a novel perfect tracking control method based on multirate feedforward control is proposed. The advantages of the proposed method are that: (1) the proposed multirate feedforward controller eliminates the notorious unstable zero problem in designing the discrete-time inverse system; (2) the states of the plant match the desired trajectories at every sampling point of reference input; and (3) the proposed controller is completely independent of the feedback characteristics. Thus, highly robust performance is assured by the robust feedback controller. Moreover, by generalizing the relationship between the sampling period of plant output and the control period of plant input, the proposed method can be applied to various systems with hardware restrictions of these periods, which leads to higher performance. Next, it is shown that the structure of the proposed perfect tracking controller is very simple and clear. Illustrative examples of position control using a DC servomotor are presented, and simulations and experiments demonstrate the advantages of this approach     

Precise position control of shape memory alloy actuator using inverse hysteresis model and model reference adaptive control system

Position control of Shape Memory Alloy (SMA) actuators has been a challenging topic during the last years due to their nonlinearities in the governing physical equations as well as their hysteresis behaviors. Using the inverse of phenomenological hysteresis model in order to compensate the input–output hysteresis behavior of these actuators shows the effectiveness of this approach. In this paper, in order to control the tip deflection of a large deformation flexible beam actuated by an SMA actuator wire, a feedforward–feedback controller is proposed. The feedforward part of the proposed control system, maps the beam deflection into SMA temperature, is based on the inverse of the generalized Prandtl–Ishlinskii model. An adaptive model reference temperature control system is cascaded to the inverse hysteresis model in order to estimate the SMA electrical current for tracking the reference signal. In addition, a closed-loop proportional–integral controller with position feedback is added to the feedforward controller to increase the accuracy as well as eliminate the steady state error in position control process. Experimental results indicate that the proposed controller has great accuracy in tracking some square wave signals. It is also experimentally shown that the suggested controller has precise tracking performance in presence of environmental disturbances.     

Short track seeking of hard disk drives under multirate control-computationally efficient approach based on initial value compensation

This paper proposes a design method for short track-seeking control based on one degree of freedom (ODOF) control and initial value compensation (IVC). IVC uses nonzero initial values of the feedback controller to improve the step reference response of the ODOF tracking control system. This makes feedforward control unnecessary to shape the transient response of short track seeking. As a result, the amount of computation during short track seeking may be minimal. The proposed design method minimizes tracking errors in multirate control framework for a step reference input taking into account the inter-sampling behavior. The effectiveness of the proposed method is shown by simulation and experiment.     

Intersample ripple-free multirate control with application to a hard disk drive servo

This paper discusses the intersample ripple problem in multirate control design. Supplementations and corrections have been made to the multirate control scheme proposed in . Moreover, the proposed method is applied to a 5.25-in hard disk drive servo system. The experimental results show that the proposed method can handle the intersample ripples existing in the conventional design very well and that the new multirate control design demands a much smaller control input profile than the conventional design.     

Dual Servo Control of a High-Tilt 3-DOF Microparallel Positioning Platform

This paper presents a precise positioning control of a microparallel positioning platform using a dual-stage servo system. The result of the research can be applied to dual-stage-type parallel machines for improving the positioning accuracy. The proposed platform adopts a dual-stage system that consists of three coarse actuators and three fine actuators to realize 3 degrees of freedom (DOF) motion. The 3-DOF motion of the end-effector is measured by a set of three linear sensors. Dynamic models for the coarse and fine actuators are derived by the system identification approach. The gain-scheduled multi-input multi-output (MIMO) controllers are synthesized based on the modeling. The MIMO controller is designed with a mixed-sensitivity criterion on tracking performance and positioning capability, and the design of the gain scheduler is based on the kinematics change. By integrating the controllers for two kinds of actuators, a dual servo controller can be developed based on the master-slave with decoupling structure. An antiwindup controller and a feedforward compensator are adopted to improve the performance. The successful performance of the synthesized dual servo controller is validated through experiments on tracking to guarantee submicrometer accuracy.     

Interaction control of an industrial manipulator using LPV techniques

This paper presents the design and implementation of a hybrid force/motion control scheme on a six-degrees-of-freedom robotic manipulator employing a gain-scheduled linear parameter-varying (LPV) controller. A nonlinear dynamic model of the manipulator is obtained and the unknown parameters are estimated. The manipulator is decomposed into an inner and a wrist submodel, and a practical way is proposed to investigate the coupling between them. The motion control part of the hybrid controller which is the main focus of this paper is formed by a combination of an LPV controller and a model-based inverse dynamics controller for the inner submodel and the wrist joints, respectively. A quasi-LPV model with a reduced number of scheduling parameters is derived for the inner submodel, and a polytopic LPV gain-scheduled controller is synthesized in a two-degrees-of-freedom structure including feedback and feedforward parts, which is augmented by a friction compensation term. A PD controller with a feedforward path is designed to control the interaction force. The proposed hybrid force/motion scheme is implemented on the 6-DOF CRS A465 robotic manipulator to perform a writing task. Comparison of the results with those of a hybrid force/motion controller with a plain model-based inverse dynamics motion control and the same force control shows that the proposed controller improves the position tracking performance significantly.     

Positive acceleration,velocity and position feedback based damping control approach for piezo-actuated nanopositioning stages

This paper proposes a new damping control approach with positive acceleration, velocity and position feedback (PAVPF) scheme for piezo-actuated nanopositioning stages to implement high-bandwidth operation. To achieve this objective, the intrinsic hysteresis nonlinearity of the piezoelectric actuator is firstly handled by a feedforward compensator with a modified Prandtl–Ishlinskii model. Afterwards, the PAVPF controller with the pole-placement method is implemented to suppress the lightly damped resonant mode of the hysteresis compensated system. With the PAVPF controller, the poles of the damped system in a third-model can be placed to arbitrary positions with an analytical method. Finally, for accurately tracking a predefined trajectory, a high-gain proportional-integral (PI) controller is designed, which could deal with the disturbance and the unmodeled dynamics. For verifying the proposed PAVPF-based control approach, comparative experiments with positive velocity and position feedback controller and with PI controller are conducted on a piezo-actuated nanopositioning stage. Experimental results demonstrate that the developed control approach with PAVPF controller is effective on damping control and improves the control bandwidth of the conventional PI controller from 111 Hz to 766 Hz, which leads to the significant increase of the tracking speed.     

Position control of shape memory alloy actuator based on the generalized Prandtl–Ishlinskii inverse model

Hysteresis and significant nonlinearities in the behavior of Shape Memory Alloy (SMA) actuators encumber effective utilization of these actuator. Due to these effects, the position control of SMA actuators has been a great challenge in recent years. Literature review of the research conducted in this area shows that using the inverse of the phenomenological hysteresis models can compensate the hysteresis of these actuators effectively. But, inverting some of these models, such as Preisach model, is numerically a complex task. However, the generalized Prandtl–Ishlinskii model is analytically invertible, and therefore can be implemented conveniently as a feedforward controller for compensating hysteresis nonlinearities effects in SMA actuators. In this paper a feedforward–feedback controller is used to control the tip deflection of a large deflected flexible beam actuated by an SMA actuator wire. The feedforward part of the control system is based on the generalized Prandtl–Ishlinskii inverse model while a conventional proportional–integral feedback controller is added to the feedforward controller to increase the accuracy together with eliminating the steady state error in position control process. Experimental results show that the proposed controller performs well in terms of achieving small overshoot and undershoot for square wave tracking as well as small tracking errors for sinusoidal trajectory. It has also great capability for tracking hysteresis minor loops.     

Adaptive gain scheduling with feedforward control system based on system model for PMSM

A feedforward controller for permanent magnet synchronous motor (PMSM) has been proposed in this study, and proportional and integral gain could be self-adaptive under different operating conditions. The control structure used in the feedforward system is the same as in the feedback control system. This control structure could guarantee independence of the speed command input to output with the disturbance input to output, which makes the system have better reference trajectory tracking and disturbances rejection. In order to obtain optimal control performance when the parameters are uncertain, a gain scheduling adaptive controller is used in the feedforward system. The proposed controller has been verified by the experimental and simulation results with less steady-state error and better dynamic response than the controllers without it under the condition of external load torque disturbance and PMSM parameter uncertainties.     

Random vibration test control of inverter-fed electrodynamic shaker

The random vibration control of an inverter-fed electrodynamic shaker is presented in this paper. First, the dynamic model of the shaker is found and a current-controlled pulsewidth modulation inverter is designed and implemented. The feedback controller is augmented with a command feedforward controller and a disturbance feedforward controller to let the armature exciting current have low harmonic content and possess excellent waveform tracking performance. Then, an acceleration controller and its random vibration command are arranged. In the proposed acceleration control scheme, a command feedforward controller and a robust disturbance feedforward controller are also employed to let the shaker have close random acceleration command waveform tracking control performance, and the performance be insensitive to the system parameter variations. It follows that the acceleration control with desired frequency response in a vibration test could be achieved through properly setting the command signal. The effectiveness of the proposed control scheme is verified by simulation and measured results     

Multirate Control in Internet-Based Control Systems

One of the major challenges in Internet-based control systems is how to overcome the Internet transmission delay. In this paper, we investigate the potential of using the multirate control scheme and the time-delay compensation to overcome the Internet transmission delay. A two-level hierarchy is used for the Internet-based control systems. At the lower level, a local controller is implemented to control the plant at a higher frequency. At the higher level, a remote controller is employed to remotely regulate the desirable set-point at a lower frequency for the local controller. A compensator located at the feedback channel is designed to overcome the time delay occurring in the transmission from the local site to a remote site. Another compensator in the feedforward channel is designed to compensate the time-delay occurring in the control action transmission. The simulation and experimental application results illustrate that the multirate control scheme with the time delay compensation offers a promising way to efficiently reduce the effect of Internet time delay on control performance     

Integral resonant damping for high-bandwidth control of piezoceramic stack actuators with asymmetric hysteresis nonlinearity

This paper presents a novel control scheme for high-bandwidth control of piezoceramic stack actuators (PSAs). For this purpose, we first characterize and compensate for the asymmetric hysteresis nonlinearity of the PSA. A linear integral resonant controller is then designed as a means for damping the resonant modes of the dynamic system with the hysteresis compensation. Finally, a tracking controller and feedforward input are developed to minimize the tracking errors and improve the closed-loop tracking bandwidth. To verify the effectiveness and efficiency of the proposed control scheme, a PSA-actuated positioning platform is built and comparative experiments are conducted. Experimental results demonstrate that the proposed controller achieves robust broadband nanopositioning of the PSA by improving the tracking bandwidth from 22 Hz (with an integral controller) to 657 Hz.     

A neural-network-based controller for a single-link flexiblemanipulator using the inverse dynamics approach

This paper presents an intelligent-based control strategy for tip position tracking control of a single-link flexible manipulator. Motivated by the well-known inverse dynamics control strategy for rigid-link manipulators, two feedforward neural networks (NNs) are proposed to learn the nonlinearities of the flexible arm associated with the inverse dynamics controller. The redefined output approach is used by feeding back this output to guarantee the minimum phase behavior of the resulting closed-loop system. No a priori knowledge about the nonlinearities of the system is needed and the payload mass is also assumed to be unknown. The network weights are adjusted using a modified online error backpropagation algorithm that is based on the propagation of output tracking error, derivative of that error and the tip deflection of the manipulator. The real-time controller is implemented on an experimental test bed. The results achieved by the proposed NN-based controller are compared experimentally with conventional proportional-plus-derivative-type and standard inverse dynamics controls to substantiate and verify the advantages of our proposed scheme and its promising potential in identification and control of nonlinear systems     

永磁同步电机伺服系统自抗扰控制器设计

对永磁同步电机(PMSM)调速系统中的时变输入提出具有更高跟踪精确度的改进型自抗扰控制策略.传统的自抗扰控制主要针对阶跃信号进行快速和无静差追踪,对时变信号存在较大的跟踪误差,使自抗扰控制的应用受限.文中对稳态误差的存在原因进行了理论分析,进而设计带有微分前馈和并联线性扩张状态观测器(P-LESO)的改进型转速自抗扰控...     

Disturbance modeling and control design for self-servo track writing

The major disturbances in self-servo track writing are identified and modeled. Based on the disturbance models, an H/sub 2/ controller together with a feedforward compensator is designed via linear matrix inequality approach to minimize the propagation tracking error from one track to the next. Furthermore, the error propagation containment effectiveness of the optimal H/sub 2/ control is compared with that of proportional-integral-derivative (PID) and proportional-derivative (PD) feedback controls with the feedforward compensators. Our results show that the propagation tracking error is improved by 27% with the H/sub 2/ control compared with that by PID control.     

A Repetitive Model Predictive Control Approach for Precision Tracking of a Linear Motion System

In this paper, a new model predictive control (MPC) approach suitable for high precision linear motion drive operating with repetitive tracking tasks is presented. For the proposed predictive controller, the feedforward controller of the conventional MPC has been modified to provide zero-phase learning property. This is achieved by augmenting the reference trajectory with a phase-compensated term that is updated with the historical tracking error. The proposed approach attempts to combine the merits of both the conventional MPC and repetitive control schemes. Experimental results have demonstrated that the system effectively reduces the tracking error from the periodic disturbance caused by the friction. Its performance under varying reference conditions and different loadings shows that the system is robust.      

Robust tracking servo system considering force disturbance for the optical disk recording system

This paper proposes a new robust tracking servo system for the optical disk recording system with feedforward controller based on the prediction of the tracking error. In optical recording systems, the feedback servo system must suppress the influence of force disturbance and parameter variation. To overcome this problem, this paper designs the robust feedback control system by using coprime factorization and disturbance observer. The detecting signal of the optical disk recording system is only a tracking error. Hence, the feedforward controller of the proposed tracking control system is constructed based on both the "zero-phase-error tracking" control theory and the prediction of the tracking error. The experimental results point out that the proposed tracking servo system has a quick and precise tracking response and keeps the residual tracking error below its tolerance.     

Tracking control of a piezoceramic actuator with hysteresis compensation using inverse Preisach model

This paper presents the classical Preisach hysteresis modeling and tracking control of a curved pre-stressed piezoceramic patch actuator system with severe hysteresis. The actuator is also flexible with very small inherent damping. It has potential applications in active antennas. A series of tests are conducted to study the hysteresis properties of the piezoceramic actuator system. The numerical expressions of the classical Preisach model for different input variations are presented. The classical Preisach model is applied to simulate the static hysteresis behavior of the system. Higher order hysteresis reversal curves predicted by the classical Preisach model are verified experimentally. The good agreement found between the measured and predicted curves showed that the classical Preisach model is an effective mean for modeling the hysteresis of the piezoceramic actuator system. Subsequently, the inverse classical Preisach model is established and applied to cancel the hysteresis the piezoceramic actuator system for the real-time microposition tracking control. In order to improve the control accuracy and to increase damping of the actuator system, a cascaded PD/lead-lag feedback controller is designed with consideration of the dynamics of the actuator. In the experiments, two cases are considered, control with major loop hysteresis compensation, and control with minor loop hysteresis compensation. Experimental results show that RMS tracking errors are reduced by 50% to 70% if the hysteresis compensation is added in the feedforward path in both cases. Therefore, hysteresis compensation with the feedback controller greatly improves the tracking control accuracy of the piezoceramic actuator.     

RRO Compensation of Hard Disk Drives With Multirate Repetitive Perfect Tracking Control

In this paper, novel repetitive controllers are proposed based on perfect tracking control (PTC) in order to reject high-order repeatable runout (RRO) of hard disk drives. First, the feedback approach of the repetitive PTC (RPTC) is developed with internal model of periodic disturbance. Although this method has performance robustness against small plant variation, the internal model worsens the stability robustness for big modeling error. Then, the feedforward (FF) approach of RPTC is introduced with switching mechanism such that the high-order RRO can be rejected without any sacrifice of the closed-loop characteristics. In both approaches, multirate FF control is utilized to overcome the unstable zero problem of discrete-time plant. Finally, the advantages and disadvantages are demonstrated through simulations and experiments.     

Piecewise affine modeling and compensation in motion of linear ultrasonic actuators

Ultrasonic actuators used in high-precision mechatronics possess strong frictional effects, which are among the main problems in precision motion control. Traditional methods apply model-based nonlinear feedforward to compensate the friction, thus requiring closed loop stability and safety constraint considerations. In this article, model-based parametric controllers are developed to obtain an optimal positioning control for these motors. A systematic approach which uses piecewise affine models greatly simplifies the friction model compared to the traditional methods. Issues about the nonlinear effects of the friction are addressed by designing a robust control law near zero speed. These developments result in a gain-scheduling optimal input, which is simple to carry out in real-time applications. The controller is expected to improve the safety constraints and the tracking performance for actuator operation.