Content uploaded by Xu Chen
Author content
All content in this area was uploaded by Xu Chen on May 03, 2015
Content may be subject to copyright.
A preview of the PDF is not available
New Repetitive Control With Improved Steady-State Performance and Accelerated Transient
Abstract and Figures
In repetitive control (RC), the enhanced servo performance at the fundamental frequency and its higher order harmonics is usually followed by undesired error amplifications at other frequencies. In this paper, we discuss a new structural configuration of the internal model in RC, wherein designers have more flexibility in the repetitive loop-shaping design, and the amplification of nonrepetitive errors can be largely reduced. Compared to conventional RC, the proposed scheme is especially advantageous when the repetitive task is subject to large amounts of nonperiodic disturbances. An additional benefit is that the transient response of this plug-in RC can be easily controlled, leading to an accelerated transient with reduced overshoots. Verification of the algorithm is provided by simulation of a benchmark regulation problem in hard disk drives, and by tracking-control experiments on a laboratory testbed of an industrial wafer scanner.
Figures - uploaded by Xu Chen
Author content
All figure content in this area was uploaded by Xu Chen
Content may be subject to copyright.
... In general AFM scanning, it is observed that the dominant coupling effect from the fast axis to the slow axis shows a periodic behavior and can be regarded as the periodic output disturbances [17]. As a consequence, due to the excellent performance in periodic trajectory tracking and periodic disturbance suppression, the repetitive control (RC) is becoming one of the most attractive methods in this field [18][19][20]. For instance, Li et al. ...
... Moreover, its implementation is simple. Similar to the PDOB, combinations of the DOB and repetitive control were proposed (Chen and Tomizuka , 2014;Linlin et al. , 2022), which amplify the nonperiodic disturbance also but less than the repetitive control. Nevertheless, the band-stop bandwidths of the DOB based repetitive control and PDOB are narrow; thus, the suppression performance is not robust against variation of periodic disturbance. ...
Repetitive motions of automatic machines induce a periodic disturbance, and the periodic disturbance deteriorates precision of motion control of the machines. A periodic-disturbance observer (PDOB) was proposed to suppress the periodic disturbance, but variation of the periodic disturbance frequency deteriorates the periodic disturbance suppression because its band-stop bandwidths in the sensitivity function for harmonics elimination are narrow. This paper proposes an infinite impulse response (IIR)-PDOB. The IIR-filter realizes wider frequency bandwidths in the sensitivity function than the PDOB, which achieves robustness against the variation of the periodic disturbance frequency. We confirmed that the IIR-PDOB was robust against the variation of the periodic disturbance frequency using a parallel robot.
In this paper, a robust composite control strategy in the framework of unified infinite-dimensional H∞ optimal control is developed to support nano-scale periodic tracking with improved non-harmonic disturbance attenuation of piezo-actuated nano-stages with sensor-induced measurement delays. In particular, we analyze the electromechanical coupled dynamics and derive a multi-perturbation model, where an extended Youla–Kucera parameterization-based repetitive controller with a disturbance observer is constructed to optimize control performances on high-precision tracking and perturbation rejection. The controller parameters are solved by using a unified infinite-dimensional H∞ optimization method. Comprehensive experiments on a piezo-actuated stage are conducted, where comparative results with representative methods, such as the conventional repetitive control and proportional-integral-derivative control, demonstrate significant performance improvements in hysteresis compensation, trajectory tracking, and disturbance suppression of the proposed method.
Linear Parameter-Varying concept has been formulated decades ago for model linearization and control. This fundamental result of control theory has been used to develop theoretical tools solving many control problems as closed-loop stability, robustness, and optimized performance. This review is dedicated to the LPV switching/interpolating control techniques that have been investigated in the literature. It collects the recent works and classifies them according to the use of gain-scheduling, switching, or interpolating, providing the latest advances with main applications in different control fields. A final discussion gives the timeline from the past to present trends in the field.
Repetitive control (RC) can perfectly attenuate disturbances that are periodic in the time domain. The aim of this article is to develop an RC approach that compensates for disturbances that are time-domain nonperiodic but are repeating in the position domain. The developed position-domain buffer consists of a Gaussian process (GP), which is learned using appropriate dynamic filters and nonequidistant data. This approach estimates position-domain disturbances resulting in perfect compensation. The method is successfully applied to a substrate carrier system, demonstrating performance robustness against time-domain nonperiodic disturbances that are amplified by traditional RC.
Modern production requires shorter measuring cycles of measuring machines, which can be achieved with highly dynamic references causing dynamic deviations of the actual tool-center-point (TCP) position. To minimize the TCP tracking error, the considered measuring machine is extended with a redundant axis and a modular control concept is proposed. For this dual-stage actuation setting, a higher-level reference allocation module exploits the resulting redundancy and yields suitable position references for the lower-level controlled subsystems. On the higher-level, two dual-stage control concepts are presented, yielding both significantly reduced tracking errors in experiments compared to using only the main axis. Furthermore, to deal with strongly spatially varying friction of the main axis of the considered measuring machine, its lower-level control system is improved.
Optical image systems are inevitably affected by disturbances, especially in a segmented lightweight large-scaled diffractive telescope (SLLDT), which is developed by our laboratory. The image-based control method is usually used to compensate disturbances caused by a long optical path in the SLLDT. However, a limited control bandwidth because of time delay degrades the disturbance suppression. An error-based observation control method is proposed for the SLLDT to rejection disturbances. Due to both the accurate disturbance model and additional sensors not required, this proposed method can relax the constraint between disturbance suppression and control stability. Simulations and experiments demonstrate that the proposed method has a significant improvement of sub-aperture image disturbance suppressions.
In repetitive control, the enhanced servo performance at multiple repetitive frequencies is usually followed by undesired error amplifications at other frequencies. This paper presents a new structural configuration of the internal model principle in repetitive control, wherein designers have more flexibility in the repetitive loop-shaping design, and amplification of non-repetitive errors can be greatly reduced. The proposed algorithm is particularly advantageous when repetitive control is required in environments where large amounts of non-repetitive disturbances exist. Verification of the algorithm is provided in a benchmark regulation problem of hard disk drives.
A linear feedback control is applied in high accuracy tracking of a periodic reference input. Asymptotic tracking of an input with a given period is achieved by locating the imaginary poles of the controller's transfer function to suit the period of the input. A frequency-domain analysis of the transient and noise characteristics leads to a simple controller design principle. The method was applied to the computer control of the 27-MVA thyristor power supply to the three main ring magnets of a proton synchrotron. The 10⁻⁴ tracking accuracy required of the exciting current control was achieved after 16 cycles of a pulsed operation.
Periodic disturbances are common in control of mechanical systems. Such disturbances may be due to rotational elements such as motors and vibratory elements. When the period of a periodic disturbance is fixed and known in advance, repetitive control can be used for attenuating their effect. The most popular repetitive controller is based on the internal model principle. When the period is not fixed and unknown, adaptation capability must be introduced. This paper presents some fundamental issues and new challenges in the design of controllers to deal with periodic disturbances along with applications to mechanical systems.
This paper proposes a path-tracking algorithm to compensate for path deviation due to torque limits. The algorithm uses a disturbance observer with an additional saturation element at each joint of n degrees of freedom (DOF) manipulator to obtain a simple equivalent robot dynamic (SERD) model. This model is represented as an n independent double integrator system and is designed to ensure stability under input saturation. For an arbitrary trajectory generated for a given path in Cartesian space whenever any of the actuators is saturated, the desired acceleration of the nominal trajectory in Cartesian space is modified on-line by using SERD. An integral action with respect to the difference between the nominal and modified trajectories is utilized in the nonsaturated region of actuators to reduce the path error. To verify the effectiveness of the proposed algorithms, real experiments were performed for a two DOF SCARA-type direct-drive arm.
This paper discusses linear iterative learning and repetitive control, presenting general purpose control laws with only a few parameters to tune. The method of tuning them is straightforward, making tuning easy for the practicing control engineer. The approach can then serve the same function for learning/repetitive control, as PID controllers do in classical control. Anytime one has a controller that is to perform the same tacking command repeatedly, one simply uses such a law to adjust the command given to an existing feedback controller and achieves a substantial decrease in tracking error. Experiments with the method show that decreases by a factor between 100 and 1000 in the RMS tracking error on a commercial robot, performing a high speed trajectory can easily be obtained in 8 to 12 trials for learning. It is shown that in engineering practice, the same design criteria apply to learning control as apply to repetitive control. Although the conditions for stability are very different for the two problems, one must impose a good transient condition, and once such a condition is formulated, it is likely to be the same for both learning and repetitive control.