Adaptive trajectory/force control scheme for constrained robot manipulators

An adaptive control scheme for the trajectory/force tracking of robot manipulators is presented. Asymptotic stability of state variables and convergence of constraint forces to any prespecified set are proven. The design procedure avoids the restrictive solvability condition of the constraint equation in the whole space of robot co-ordinates. A fairly accurate bound of the tracking error is derived by means of a Lyapunov analysis.     

Adaptive fault-tolerant tracking control for nonlinear systems with unknown control coefficient and input saturation

In this article, the tracking control problem is investigated for a class of nonlinear systems in the presence of unknown disturbance, input saturation, actuator fault, and unknown control coefficient. A novel disturbance observer-based adaptive fault-tolerant tracking control strategy is proposed with regard to nonlinear systems. Based on the Gaussian error function, the auxiliary dynamic system is designed to offset effects caused by the input saturation. Moreover, the Nussbaum-type function is employed to avert control singularity and deal with the unknown control coefficient. A theoretical analysis indicates that the boundedness of all signals in the closed-loop system can be guaranteed. Finally, two examples with one concerning the dynamic point-the-bit rotary steerable drilling tool system are given to confirm the validity of the method.     

Fuzzy adaptive two-bits-triggered control for nonlinear uncertain system with input saturation and output constraint

In this work, a fuzzy adaptive two-bits-triggered control is investigated for the nonlinear uncertain systems with input saturation and output constraint. The considered systems are more widespread. Without sufficient transmission resources, how to resolve the constraint issues while guarantee the control performance is difficult and challenging. Then, hyperbolic tangent function and barrier Lyapunov function are integrated with the designed auxiliary system to solve input saturation and output constraint. Meanwhile, faced with the transmission resources limitation, this work both considers the triggering condition and the control signal transmission bits. A two-bits-triggered control is proposed to economize the transmission resources. Furthermore, improved fuzzy logic systems are established to further promote the control performance. It combines with the time-varying approximation error for processing. The boundedness of all the system signals can be proved. Simulation results illustrate the validity of the proposed approach.     

Adaptive finite‐time actuator fault‐tolerant coordinated attitude control of multispacecraft with input saturation

In this study, for nonrigid spacecraft formation, a distributed adaptive finite‐time actuator fault‐tolerant (FTAFT) coordinated attitude tracking control (CATC) issue is addressed. Aiming at stabilizing the spacecraft formation flying system during a limited time, two distributed adaptive FTAFT CATC strategies are presented. Initially, on basis of distributed finite‐time observer (DFTO), adaptive control, consensus approach, graph theory, and finite‐time theory, we develop a distributed adaptive FTAFT coordinated attitude tracking controller to repress the impact of the external state‐dependent and state‐independent disturbance, unknown time‐varying inertia uncertainty, and actuator fading or fault. Then, combining with the proposed controller, a distributed adaptive FTAFT control law with input saturation subjected to physical limitations of actuator is further designed. In addition, a self‐adjusting matrix (SAM) is proposed to improve the actuators' performance. With the two proposed CATC strategies, the followers can synchronize with the leader. Simulations demonstrated the validity of the designed control laws.     

Adaptive multi-dimensional Taylor network funnel control of a class of nonlinear systems with asymmetric input saturation

In view of the result and performance of control are affected by the existence of input constraints and requirements, adaptive multi-dimensional Taylor network (MTN) funnel control problem is studied for a class of nonlinear systems with asymmetric input saturation in this paper. Firstly, the effect of asymmetric input saturation can overcome by introducing the Gaussian error function, namely, the asymmetric saturation model is represented as a simple linear model with a bounded disturbance. Secondly, MTNs are employed to approximate the unknown functions in the controller design. Then, an adaptive MTN tracking controller is developed by blends the idea of funnel control into backstepping, which can guarantee that the tracking error always meets the given prescribed performance regarding the transient and steady state responses as well as the output of system tracks the give continuous reference signal. Finally, the effectiveness of the proposed control is demonstrated using two examples.     

Fixed-time fault-tolerant control of uncertain MIMO switched interconnected systems subject to state delay,unknown control directions,and quantized nonlinear inputs

This paper investigates design of an adaptive fixed-time fault-tolerant decentralized controller for a class of uncertain multi-input multi-output (MIMO) switched large-scale non-strict interconnected systems under arbitrary switching subject to unknown control directions, quantized nonlinear inputs, actuator failures unknown external disturbances, and unmodeled dynamics. In addition to interconnected terms, time-varying delayed interconnected terms have been considered in the system model which makes it more general than previous works in the literature. The proposed controller can handle switched systems with unknown switching signal and different types of input nonlinearities including, saturation, backlash, and dead-zone. The singularity problem in designing the fixed time controller has been solved. The quantizer and actuators fault parameters are assumed to be unknown. The Razumikhin lemma has been used to deal with the delayed interconnected terms. To cope with the system unknown dynamics, neural networks (NNs) have been applied and by updating the maximum norms of the networks weight vectors the computational load has been reduced. The explosion of complexity occurring in the traditional back-stepping technique has been avoided by applying dynamic surface control (DSC). Finally, by defining an appropriate common Lyapunov function (CLF), fixed-time convergence of system outputs and the closed-loop system stability have been established. The effectiveness of the proposed controller has been shown via simulation study.     

A simplified adaptive tracking control for nonlinear pure-feedback systems with input delay and full-state constraints

This article investigated the adaptive backstepping tracking control for a class of pure-feedback systems with input delay and full-state constraints. With the help of mean value theorem, the system is transformed into strict-feedback one. By introducing the Pade approximation method, the effect of input delay was compensated. Radial basis function neural networks are utilized to approximate the unknown nonlinear functions. Furthermore, in order to reduce the computational burden by introducing backstepping design technique, dynamic surface control technique was employed. In addition, the number of the adaptive parameters that should be updated online was also reduced. By utilizing the barrier Lyapunov function, the closed-loop nonlinear system is guaranteed to be semi-globally ultimately uniformly bounded. Finally, a numerical simulation example is given to show the effectiveness of the proposed control strategy.     

基于摩擦模型的机器人力/位安全控制方法研究

针对机器人力/位控制应用的安全问题,提出一种基于动力学模型的快速实用机器人碰撞检测算法.首先,设计机器人力/位安全控制方案,建立基于动力学的碰撞检测数学模型;然后,基于静态LuGre摩擦模型辨识和补偿机器人关节摩擦力,设计简化的机器人力/位控制碰撞检测模型;最后,以轻型工业机械臂为实验平台,让机器人执行力/位控制与人类...     

神经滑模控制在机器人轨迹跟踪中的应用

针对滑模控制在机器人轨迹跟踪中应用时出现的抖振问题,提出了基于滤波器的神经滑模趋近律控制方法.根据滑模变结构和径向基函数(RBF)神经网络控制理论,并结合滤波器,对两关节机器人的轨迹跟踪控制进行了仿真研究.通过对单纯的滑模变结构加滤波器的控制方法、RBF神经滑模等效控制和RBF神经滑模趋近律控制这三种方法进行对比仿真分析,结果表明设计的神经网络滑模趋近律控制系统具有良好的跟踪性、鲁棒性和较高的控制精确度,同时有效地消除了抖振,实现简单.     

Adaptive switching control of uncertain fractional systems: Application to Chua's circuit

Since the introduction of fractional‐order differential equations, there has been much research interest in synthesis and control of oscillatory, periodic, and chaotic fractional‐order dynamical systems. Therefore, in this article, the problem of stabilization and control of nonlinear three‐dimensional perturbed fractional nonlinear systems is considered. The major novelty of this article is handling partially unknown dynamics of nonlinear fractional‐order systems, as well as coping with input saturation along the existence of model variations and high‐frequency sensor noises via just one control input. The method supposes no known knowledge on the upper bounds of the uncertainties and perturbations. It is assumed that the working region of the input saturation function is also unknown. After the introduction of a simple finite‐time stable nonlinear sliding manifold, an adaptive control technique is used to reach the system variables to the sliding surface. Rigorous stability discussions are adopted to prove the convergence of the developed sliding mode controller. The findings of this research are illustrated using providing computer simulations for the control problem of the chaotic unified system and the fractional Chua's circuit model.     

Iterative learning control for non‐repetitive trajectory tracking of robot manipulators with joint position constraints and actuator faults

In this work, we present a novel iterative learning control (ILC) scheme for a class of joint position constrained robot manipulator systems with both multiplicative and additive actuator faults. Unlike most ILC literature that requires identical reference trajectory from trail to trail, in this work the reference trajectory can be non‐repetitive over the iteration domain without assuming the identical initial condition. A tan‐type Barrier Lyapunov Function is proposed to deal with the constraint requirements which can be both time and iteration varying, with ILC update laws adopted to learn the iteration‐invariant system uncertainties, and robust methods used to compensate the iteration and time varying actuator faults and disturbances. We show that under the proposed ILC scheme, uniform convergence of the full state tracking error beyond a small time interval in each iteration can be guaranteed over the iteration domain, while the constraint requirements on the joint position vector will not be violated during operation. An illustrative example on a two degree‐of‐freedom robotic manipulator is presented to demonstrate the effectiveness of the proposed control scheme. Copyright © 2016 John Wiley & Sons, Ltd.     

基于RBF神经网络的永磁同步电机无位置传感器控制

本文通过分析永磁同步电机Id=0控制策略及其间接位置检测原理,提出了基于径向基函数(RBF)神经网络的无位置传感器控制方法.该方法首先构建一个隐层节点数为零的四输入两输出RBF网络,网络的输入为电机α-β轴上电压和电流,输出为转子转角和转速,然后在离线训练过程中按照自适应算法不断添加和删除隐层节点,形成一个结构简单、紧凑的RBF网络,最后采用梯度下降纠正误差法在线训练更新网络参数.该方法通过对电机α-β轴上电压和电流的映射,得到了电机转子的转角和转速,取代了传统的位置传感器.实验结果表明了该控制方法的有效性.     

Adaptive parallel simultaneous stabilization of a set of uncertain port‐controlled hamiltonian systems subject to actuator saturation

This paper investigates adaptive parallel simultaneous stabilization (APSS) of a set of uncertain nonlinear port‐controlled Hamiltonian (PCH) systems subject to actuator saturation and proposes a number of results on the design of the APSS controllers. First, the case of two PCH systems is studied. Using both the dissipative Hamiltonian structural and saturated actuator properties, the two systems are combined to generate an augmented PCH system, with which, some results on the control designs are then obtained. When there are external disturbances in the two systems, an H _∞ APSS controller is designed for the systems. Second, the case of more than two uncertain PCH systems subject to actuator saturation is investigated, and several new results are proposed for the APSS problem. Finally, an illustrative example is presented to show that the adaptive stabilization controllers obtained in this paper work very well. Copyright © 2013 John Wiley & Sons, Ltd.     

基于ELM的机器人自适应跟踪控制

针对刚性臂机器人系统,提出基于极限学习机(ELM)的两种自适应神经控制算法。极限学习机随机选择单隐层前馈神经网络(SLFNs)的隐层节点及其参数,仅调整其网络的输出权值,以极快的学习速度可获得良好的推广性。在自适应控制算法中,ELM逼近系统的未知非线性函数,附加的鲁棒控制项补偿系统的逼近误差。ELM神经控制器的参数自适应调整律及鲁棒控制项由Lyapunov稳定性理论分析得出,所设计的两种控制算法均不依赖于初始条件的约束且放松对参数有界的要求,同时保证闭环系统跟踪误差满足全局稳定而且渐近收敛于零。将所提出的ELM控制器应用于二连杆刚性臂机器人跟踪控制实例中,并与现有的径向基函数(RBF)神经网络自适应控制算法进行比较,仿真结果表明,在同等条件下,ELM控制器具有良好的跟踪控制性能,显示出其有效性和应用潜力。     

Adaptive motion/force tracking control of holonomic constrained mechanical systems: a unified viewpoint

This paper proposes a robust adaptive motion/force tracking controller for holonomic constrained mechanical systems with parametric uncertainties and disturbances. First, two types of well‐known holonomic systems are reformulated as a unified control model. Based on the unified control model, an adaptive scheme is then developed in the presence of pure parametric uncertainty. The proposed controller guarantees asymptotic motion and force tracking without the need of extra conditions. Next, when considering external disturbances, control gains are designed by solving a linear matrix inequality (LMI) problem to achieve prescribed robust performance criterion. Indeed, arbitrary disturbance/parametric error attenuation with respect to both motion and force errors along with control input penalty are ensured in the L₂‐gain sense. Finally, applications are carried out on a two‐link constrained robot and two planar robots transporting a common object. Numerical simulation results show the expected performances. Copyright © 2006 John Wiley & Sons, Ltd.