Disturbance-observer-based motion control of redundant manipulatorsusing inertially decoupled dynamics

In this paper, a robust motion control method for kinematically redundant manipulators is addressed to control the motion of the end-effector, as well as the null-space motion. To reduce the disturbance effects on the system performance, a new disturbance observer is proposed to improve the performance of the conventional structure. A minimal parametrization of the null space is performed to visualize the null-space motion explicitly using the weighted decomposition of joint space. Augmenting this null motion with conventional velocity relations, an extended task space formulation is obtained. The proposed disturbance observer is adopted in the extended task space formulation and a motion control method is devised based on the passivity concept. The performance of the proposed controller is verified through experiments with a three-link planar direct-drive manipulator     

Performance tuning of robust motion controllers for high-accuracy positioning systems

This paper presents a structural design method of robust motion controllers for high-accuracy positioning systems, which makes it possible to tune the performance of the whole closed-loop system systematically. First, a stabilizing control input is designed based on Lyapunov redesign for the system in the presence of uncertainty and disturbance. And adopting the internal model following control, robust internal-loop compensator (RIC) is proposed. By using the structural characteristics of the RIC, disturbance attenuation properties and the performance of the closed-loop system determined by the variation of controller gains are analyzed. Next, in order to design a robust motion controller for a high performance positioning system, dual RIC structure is proposed and it is shown that if the synthesis of the robust motion control law is performed in the RIC framework, the robust property of RIC can be naturally implanted in the feedback controller. The proposed structural design of robust motion controller provides a systematic approach to the problem of robust stability and performance requirement in the face of uncertainty. Furthermore, by allowing the tradeoffs between robust stability and performance to be quantified in a simple fashion, it can illuminate systematic design procedure of the robust motion controllers. Finally, the proposed method is verified through simulation and the performance is evaluated by experiments using a high-accuracy positioning system.     

Wideband Force Control by Position-Acceleration Integrated Disturbance Observer

Motion control is widely used in industry applications. One of its key components is the disturbance observer, which estimates a disturbance torque of a motion system and realizes a robust acceleration control. A disturbance observer observes and suppresses the disturbance torque within its bandwidth. Motion systems have started to spread in society and they are required to have the ability to interact with unknown environments. Such a haptic motion requires much wider bandwidth. However, since the conventional disturbance observer attains the acceleration information by the second-order derivative of a position response, the bandwidth is limited due to the derivative noise. To enlarge the bandwidth of a disturbance observer, this paper proposes a position-acceleration integrated disturbance observer (PAIDO). Since an acceleration sensor is implemented in it, the control performance of the PAIDO is superior to the conventional one. In this paper, the PAIDO is applied to force control and the viability of the proposed method is confirmed by fast Fourier transformation analyses. The experimental results show the viability of the proposed method.     

Robust learning control of a high precision planar parallel manipulator

End-point positioning accuracy and fast settling time are essential in the motion system aimed at semiconductor packaging applications. In this paper, a novel robust learning control method for a direct-drive planar parallel manipulator is presented. A frequency-domain system identification approach is used to identify the high frequency dynamic of the manipulator. A robust control design method is employed to design a stable, fast tracking response feedback controller with less sensitivity to high frequency disturbance and the control parameters are determined using genetic algorithm. A Fourier-series-based iterative learning controller is designed and used on the feedforward path of the controller to further improve the settling time by reducing the dynamic tracking error of the manipulator. Experimental results demonstrate that the planar parallel manipulator has significant improvements on motion performance in terms of positioning accuracy, settling time and stability when compared with traditional XY-stages. This shows that the proposed manipulator provides a superior alternative to XY-motion stages for high precision positioning.     

Robust performance of the multiloop perturbation compensator

A novel perturbation attenuation method is proposed for robust performance of mechanical systems. First, we give a unified view on a class of existing perturbation observers and define the residual perturbation. In terms of the view and the definition, a new perturbation compensator with multiloop structure is developed. It effectively compensates the perturbation (i.e., model uncertainty and external disturbance) to the plant in a hierarchical and recursive fashion. In the multiloop perturbation compensator (MPEC) proposed, as the number of loops increases, the external disturbance condition for system stability is greatly relaxed and the perturbation attenuation performance is gradually enhanced but the robust stability margin on the modeling error becomes more strict. A recursive algorithm for general n-loop case of the MPEC is derived. By combining the developed robust perturbation compensator with a nominal feedback controller, a robust motion controller is synthesized. Experimental results for XY positioner and 2-DOF robot arms demonstrate the excellent robust tracking performance in spite of arbitrary large perturbation inputs     

压电定位系统的自耦PID控制

针对一类存在非线性迟滞特性的纳米定位压电驱动器的控制问题,使用了一种与被控系统无关的自耦比例积分微分(ACPID)控制方法。该方法将系统内部所有复杂因素及外部扰动定义为一个总扰动,建立了以总扰动为激励的受控误差系统,进而设计了基于ACPID控制理论的压电定位控制系统。理论分析了ACPID控制系统的鲁棒稳定性和抗扰动鲁棒性。仿真结果表明,ACPID控制系统的有效性不仅具有更快的响应速度、更高的控制精度,且具有良好的抗扰动鲁棒性,在压电定位系统控制领域具有较大应用价值。     

Torque sensorless control in multidegree-of-freedom manipulator

A torque sensorless control for a multi-degree-of-freedom manipulator is described. In the method, two disturbance observers are applied to each joint. One is used to realize a robust motion controller. The other is used to obtain a sensorless torque controller. A robust acceleration controller based on the disturbance observer is shown. To obtain the sensorless torque control, it is necessary to calculate the reaction torque when the mechanical system performs a force task. The calculation method for the reaction torque is explained. Then the method is expanded to workspace force control in the multi-degree-of-freedom manipulator. Several experimental results are shown to confirm the validity of the proposed sensorless force controller     

Nonlinear control of mechatronic systems with permanent-magnet DC motors

The current trends in development and deployment of advanced electromechanical systems have facilitated the unified activities in the analysis and design of state-of-the-art motion devices, electric motors, power electronics, and digital controllers. This paper attacks the motion control problem (stabilization, tracking, and disturbance attenuation) for mechatronic systems which include permanent-magnet DC motors, power circuity, and motion controllers. By using an explicit representation of nonlinear dynamics of motors and switching converters, we approach and solve analysis and control problems to ensure a spectrum of performance objectives imposed on advanced mechatronic systems. The maximum allowable magnitude of the applied armature voltage is rated, the currents are limited, and there exist the lower and upper limits of the duty ratio of converters. To approach design tradeoffs and analyze performance (accuracy, settling time, overshoot, stability margins, and other quantities), the imposed constraints, model nonlinearities, and parameter variations are thoroughly studied in this paper. Our goal is to attain the specified characteristics and avoid deficiencies associated with linear formulation. To solve these problems, an innovative controller is synthesized to ensure performance improvements, robust tracking, and disturbance rejection. One cannot neglect constraints, and a bounded control law is designed to improve performance and guarantee robust stability. The offered approach uses a complete nonlinear mechatronic system dynamics with parameter variations, and this avenue allows one to avoid the conservative results associated with linear concept when mechatronic system dynamics is mapped by a linear constant-coefficient differential equation. To illustrate the reported framework and to validate the controller, analytical and experimental results are presented and discussed. In particular, comprehensive analysis and design with experimental verification are performed for an electric drive. A nonlinear bounded controller is designed, implemented, and experimentally tested.     

Robust H∞ control with multiple constraints forthe track-following system of an optical disk drive

In this paper, the authors design a tracking controller which satisfies transient response specifications and maintains tracking error within a tolerable limit for the uncertain track-following system of an optical disk drive. To this end, a robust H_∞ control problem, with regional stability constraints and sinusoidal disturbance rejection is considered. The internal model principle is used for rejecting the sinusoidal disturbance caused by eccentric rotation of the disk. The authors show that a condition satisfying the regional stability constraints can be expressed in terms of a linear matrix inequality (LMI) using the Lyapunov theory and S-procedure. Finally, a tracking controller is obtained by solving an LMI optimization problem involving two LMIs. The proposed controller design method is evaluated through an experiment     

双机拖动系统的鲁棒调节器的设计

在线性系统设计中,需要设计一种调节器使系统具有闭环系统稳定且达到无差调节的性质,在系统参数发生微小扰动时,仍然要求保持这两种性质。设计具有这种性质的调节器的问题,称为鲁棒调节器问题。本文以双机拖动调速系统为例,说明鲁棒调节器的结构及设计方法,这种方法在鲁棒调节器设计中起着重要作用。     

Nonlinear adaptive torque control of electro-hydraulic load system with external active motion disturbance

This paper develops a high performance nonlinear adaptive control method for electro-hydraulic load simulator (EHLS). The tracking performance of EHLS is mainly affected by the following factors: actuator’s active motion disturbance, flow nonlinear and parametric uncertainties, etc. Most previous studies on EHLS pay too much attention on actuator’s active motion disturbance, while deemphasize the other two factors. This paper concerns EHLS as a motion loading system. Besides actuator’s motion disturbance, both the nonlinear characteristics and parametric uncertainties of the loading system are addressed by the present controller. First, the nonlinear model of EHLS is developed, and then a Lyapunov-based control algorithm augmented with parameters update law is developed using back-stepping design method. The stability of the developed control algorithm is proven via Lyapunov analysis. Both the co-simulation and experiment are performed to validate the effectiveness of the developed algorithm.     

A motion control strategy based on equivalent mass matrix inmultidegree-of-freedom manipulator

This paper describes a decoupling motion control strategy based on an equivalent mass matrix in operational space. In the conventional approach, the equivalent mass matrix is defined as a function of Jacobian matrix and inertia of manipulator. Therefore, it is difficult to know the variation of the equivalent mass matrix precisely and to select it arbitrarily. This makes it difficult to realize the decoupling motion controller in the operational space. To improve the above problem, the authors introduce a robust control strategy based on a disturbance observer. In the observer-based approach, the equivalent mass matrix is determined arbitrarily independently of configuration and inertia variation of the manipulator. First, the equivalent mass matrix based on robust control is derived. Second, a simplification method of an operational space controller is discussed by using the equivalent mass matrix. Several experimental results are shown to confirm the validity of the proposed methods     

Robust sliding-mode tip position control for flexible arms

In this paper, we consider the robust tip position control problem for flexible arms by using the sliding-mode method. The higher order modes of the flexible arm are treated as disturbances, and are compensated by introducing a disturbance observer. The remaining disturbance and the model uncertainties are considered as the system uncertainty. The robustness of the sliding-mode control is effectively employed to cope with the system uncertainty, where the upper and lower bounds of the uncertainty are adaptively updated. The stability of the closed-loop system is analyzed by using the fact that a part of the control input is the approximate estimate of the uncertainty. Experimental results show that the robustness and superiority of the proposed method, where only the strain moment at the root and motor angular position of the arm are measured     

Global Robust Sliding Mode Control for Time-Delay Systems with Mismatched Uncertainties

A novel robust sliding mode control method for time-delay systems with mismatched uncertainties is presented, taking into consideration of both the norm-bounded mismatched uncertainties in the input matrix and the unknown input disturbance. First of all, an original time-delay system is changed into a new form without time delay via a nonsingular transformation, based on which, an integral sliding mode controller is then designed in the form of linear matrix inequalities, to guarantee the existence of the sliding motion from the initial time. In order to estimate the upper bound of unknown input disturbance, a new adaptive law is also proposed. Finally, a numerical simulation case is given to show the effectiveness of the proposed method.     

Control of redundant manipulators considering order of disturbanceobserver

A manipulator control method using a disturbance observer with no inverse dynamics has been proposed. The order of the disturbance observer affects the performance of control system, because nominalization of plant is dependent on the control object and the order of the disturbance observer. This paper proposes a unique choice of disturbance observers of different order in joint and task space to improve system performance of hybrid position/force control of redundant manipulators. Also, it has been shown that a proper selection of a coefficient of the disturbance observer is capable to improve robust stability, while not influencing basic performance. The proposed strategy can realize acceleration control and second derivative of force control in the task space, which realizes robust and precise control of manipulators. Experimental results using a redundant manipulator show the effectiveness of the proposed strategy     

Robust independent joint controller design for industrial robotmanipulators

A novel approach is presented for the design of simple robust independent joint controllers for industrial robot manipulators. In this approach, each joint actuator is treated as a simple inertial system plus a disturbance torque representing all the unmodeled dynamics. By a very simple algorithm, the disturbance is instantly estimated and rejected, thus allowing a simple proportional-derivative (PD) control scheme to be used. The stability of the proposed control law is analyzed. Experimental evaluations of the controller on a microcomputer-controlled PUMA 560 arm were performed. It is shown that the control scheme is simple and practical and that it can be easily implemented on an industrial manipulator presently in use     

Robust Explicit Solution of Multirate Predictive Control System with External Disturbances

This paper considers the problem of robust predictive control for a class of uncertain multirate systems, in which the output sampling period is several times larger than the one of input updating. By means of dynamic programming and multiparametric quadratic programming (mp-QP) techniques, this work proposes a novel robust explicit model predictive control (REMPC) algorithm such that the higher on-line updating speed of input can be attained. Firstly, the optimization problem is decomposed into several subproblems. For each subproblem, a constraint condition only involving current state and input is constructed. Then taking current state and future inputs as parameter variables we can obtain a robust explicit solution for the new reformulated optimization subproblem by mp-QP method. Especially, by choosing a maximal robust positive invariant set as the terminal constraint set of the optimization problem, closed-loop robust stability of the multirate control system subject to external disturbance can be guaranteed. Finally, a numerical simulation is given to show the effectiveness of the proposed method.     

Observer-Based H<Subscript>∞</Subscript> Controller for Perturbed System with State and Input Delay

This paper deals with the robust stability problem for continuous-time linear systems with external perturbation and time delay in state and control input. We derive a sufficient condition that guarantees the closed-loop delayed system stability and a prescribed H norm bound of the closed-loop transfer matrix from the disturbance to the controlled output. Based on this derivation, the proposed observer-based robust controller not only reduces the influence of the disturbance, but also guarantees the closed-loop system stability. An example is given to illustrate the availability of the proposed design method.     

舰载导弹的小扰动抑制优化制导控制技术研究

舰载导弹在大气小扰动下容易出现控制失稳,通过控制优化设计,提高导弹制导的稳定性。针对传统的PID神经网络模糊控制精度较低的问题,提出一种基于小扰动抑制和参数自整定误差修正的舰载导弹制导控制优化算法,首先构建舰载导弹的被控对象模型和纵向运动数学模型,根据控制约束参量进行舰载导弹制导控制约束参量分析,然后采用小扰动抑制方法进行扰动误差和控制参量的自整定修正,实现控制算法优化设计。最后通过仿真实验进行性能测试,仿真结果表明,采用该控制方法进行舰载导弹的小扰动抑制和制导控制设计,降低了导弹的轨迹输出误差,俯仰角等运动参量的跟踪性能较好,提高了控制品质。     

Adaptive positioning control for a LPMSM drive based on adapted inverse model and robust disturbance observer

The adaptive robust positioning control for a linear permanent magnet synchronous motor drive based on adapted inverse model and robust disturbance observer is studied in this paper. First, a model following two-degrees-of-freedom controller consisting of a command feedforward controller (FFC) and a feedback controller (FBC) is developed. According to the estimated motor drive dynamic model and the given position tracking response, the inner speed controller is first designed. Then, the transfer function of FFC is found based on the inverse model of inner speed closed-loop and the chosen reference model. The practically unrealizable problem possessed by traditional feedforward control is avoided by the proposed FFC. As to the FBC, it is quantitatively designed using reduced plant model to meet the specified load force regulation control specifications. In dealing with the robust control, a disturbance observer based robust control scheme and a parameter identifier are developed. The key parameters in the robust control scheme are designed considering the effect of system dead-time. The identification mechanism is devised to obtain the parameter uncertainties from the observed disturbance signal. Then by online adapting the parameters set in the FFC according to the identified parameters, the nonideal disturbance observer based robust control can be corrected to yield very close model following position tracking control. Meanwhile, the regulation control performance is also further improved by the robust control. In the proposed identification scheme, the effect of a nonideal differentiator in the accuracy of identification results is taken into account, and the compromise between performance, stability, and control effort limit is also considered in the whole proposed control scheme.