Robust force/motion control of constrained robots using neural network

A robust neural network (NN) controller is proposed for the simultaneous force/motion control of constrained rigid robots. The NN weights here are tuned on‐line, with no off‐line learning phase required. Most importantly, we can guarantee the boundedness of constraint force errors, joint position tracking errors, and NN weights. When compared with adaptive controllers, we do not require linearity in the unknown parameters, and the tedious computation of the regression matrix. Novel passivity properties of the NN controller are stated and proven. ©1999 John Wiley & Sons, Inc.     

Sliding-mode motion/force control of constrained robots

A sliding-mode controller is proposed for the simultaneous position and force control of constrained robot manipulators with parametric uncertainties. Based on this controller, the trajectories of the closed-loop system can reach a stable sliding surface in finite time. Under this condition, the asymptotic convergence of the motion error and force error can be successfully ensured with improved results compared to previous studies     

Force/motion control of constrained manipulators without velocitymeasurements

In this paper the authors deal with the problem of force/tracking control of constrained manipulators without velocity measurements interacting with an infinitely stiff environment. They use a reduced-order model for which the coordinate space is restricted to a subset R where the Jacobian constraint is guaranteed to be nonsingular. In contrast to other similar approaches, the authors do not assume that the generalized trajectories belong to the subset Ω all the time, thus our contribution is to prove that if the trajectories start within the subset Ω they remain in it. Furthermore, we prove uniform asymptotic stability considering only position and force measurements     

多关节机器人的神经滑模控制

针对含有建模误差和不确定干扰的多关节机械臂轨迹跟踪控制,提出了一种神经滑模控制方法。该方法采用全局快速终端滑模面保证了系统状态能够在有限时间内到达滑模面和平衡点。采用径向基函数神经网络自适应地补偿系统的建模误差和外界干扰,保证了滑模控制在滑模面的运动。利用李亚普诺夫稳定性判据推导出了控制器的控制律和神经网络的目标函数,通过神经网络的在线学习,削弱了滑模控制的抖振。仿真结果表明了其有效性。     

Decentralized sliding mode control for flexible link robots

A technique using augmented sliding mode control for robust, real-time control of flexible multiple link robots is presented. For the purpose of controller design, the n-link, n-joint robot is subdivided into n single joint, single link subsystems. A sliding surface for each subsystem is specified so as to be globally, asymptotically stable. Each sliding surface contains rigid-body angular velocity, angular displacement and flexible body generalized velocities. The flexible body generalized accelerations are treated as disturbances during the controller design. This has the advantage of not requiring explicit equations for the flexible body motion. The result is n single input, single output controllers acting at the n joints of the robot, controlling rigid body angular displacement and providing damping for flexible body modes. Furthermore, the n controllers can be operated in parallel so that compute speed is independent of the number of links, affording real-time, robust, control.     

串联机器人的双模糊自适应滑模控制

提出了一种串联机器人的改进控制算法。采用一自适应模糊控制器,根据滑模到达条件对滑模切换增益进行估算,消除滑模控制中输出力矩的抖振现象,增强其对不确定性因素的适应能力。采用另一自适应模糊控制器对指数趋近律系数进行修正,改善由于大范围初始位姿产生的偏差而引起的大力矩和速度跳变问题。该方法无需确定被控对象的具体数学模型,具有强鲁棒性和高跟踪精度。基于Lyapunov方法进行了稳定性证明,保证控制系统的稳定性与收敛性。实验结果表明,该方法应用于串联机器人,跟踪效果良好并产生了平滑的力矩输出和速度输出。     

Perfect position/force tracking of robots with dynamical terminal sliding mode control

According to a given performance criteria, perfect tracking is defined as the performance of zero tracking error in finite time. It is evident that robotic systems, in particular those that carry out compliant task, can benefit from this performance since perfect tracking of contact forces endows one or many constrained robot manipulators to interact dexterously with the environment. In this article, a dynamical terminal sliding mode controller that guarantees tracking in finite‐time of position and force errors is proposed. The controller renders a dynamic sliding mode for all time and since the equilibrium of the dynamic sliding surface is driven by terminal attractors in the position and force controlled subspaces, robust finite‐time convergence for both tracking errors arises. The controller is continuous; thus chattering is not an issue and the sliding mode condition as well the invariance property are explicitly verified. Surprisingly, the structure of the controller is similar with respect to the infinite‐time tracking case, i.e., the asymptotic stability case, and the advantage becomes more evident because terminal stability properties are obtained with the same Lyapunov function of the asymptotic stability case by using more elaborate error manifolds instead of a more complicated control structure. A simulation study shows the expected perfect tracking and a discussion is presented. © 2001 John Wiley & Sons, Inc.     

多自由度机器人自适应滑模迭代学习跟踪控制

机械臂可代替人工完成繁重工作、降低生产风险、提高生产效率,被广泛应用于制造业和生产业中.工业生产的高质量需求对机械臂的操作精度提出了较高要求,考虑有色金属工厂中铸锭打磨的应用场景,该任务的作业轨迹均具有较强重复性.此外,实际应用环境复杂,存在如环境干扰及系统参数变化等多种不确定性,固定的控制参数难以保证系统持续稳定运行.基于上述考虑,针对多自由度机械臂系统,设计一种自适应滑模迭代学习跟踪控制方法,控制器包含参数自整定的比例-微分项、基于滑模的符号函数项和上一次迭代的控制输入,其中PD项的控制参数通过模糊逻辑系统实时调整,在保证控制系统正常运行的情况下提高系统的鲁棒性.同时,在理论上证明迭代域闭环系统的稳定性和跟踪误差的收敛性.最后通过仿真验证所提出控制方法的有效性和鲁棒性.     

Adaptive sliding mode trajectory tracking control for wheeled mobile robots

This paper discusses the problem of adaptive sliding mode trajectory tracking control for wheeled mobile robots in the presence of external disturbances and inertia uncertainties. A new fast nonsingular terminal sliding mode surface without any constraint is proposed, which not only avoids singularity, but also retains the advantages of sliding mode control. In order to implement the trajectory tracking mission, the error dynamic system is divided into a second-order subsystem and a third-order one. First, an adaptive fast nonsingular terminal sliding mode control law of the angular velocity is constructed for stabilising the second-order subsystem in finite time. Then, another adaptive fast nonsingular terminal sliding mode control law of the linear velocity is designed to guarantee the stability of the third-order subsystem. Finally, a simulation example is provided to demonstrate the validity of the proposed control scheme.     

漂浮基空间机器人自适应RBF 网络终端滑模控制

主要研究漂浮基空间机器人对工作空间连续轨迹跟踪控制问题．针对系统动力学模型中非线性项未知，以及参数不确定性和外界扰动无法估计的情况，提出了基于自适应RBF网络终端滑模控制方法．该方法结合了非线性滑动流形与径向基函数特性，利用自适应RBF网络在线学习系统中的不确定性，使得无需精确的动力学模型亦能保证系统在有限时间内快速稳定．根据Lyapunov方法设计的自适应增益保证闭环控制系统具有全局稳定性，并且有效抑制抖振现象．针对6关节空间机器人的轨迹跟踪控制仿真表明，提出的自适应RBF网络终端滑模控制方法能够基于不完整动力学模型实现高精度轨迹跟踪，且误差在有限时间内快速收敛，系统抖振也得到了有效抑制．     

Visual motion and structure estimation using sliding mode observers

The problem of estimating motion and structure from a sequence of images has been a major research theme in machine vision for many years and remains one of the most challenging ones. In this work, we use sliding mode observers to estimate the motion and the structure of a moving body with the aid of a change-coupled device (CCD) camera. We consider a variety of dynamical systems which arise in machine vision applications and develop a novel identification procedure for the estimation of both constant and time-varying parameters. The basic procedure introduced for parameter estimation is to recast image feature dynamics linearly in terms of unknown parameters and construct a sliding mode observer to produce asymptotically correct estimates of the observed image features, and then use the observer input to compute parameters. Much of our analysis has been substantiated by computer simulations and real experiments.     

Chattering reduction using multiphase sliding mode control

For the system with sliding mode controllers operated by on/off switches, ‘chattering’ appears in the output of the system when its switching frequency is restricted. In power systems, the switching frequency is commonly limited to prevent power losses, and chattering or ‘ripple’ appears especially in the system current. Common methods to decrease such ripple are based on ‘harmonic cancellation’ using the multiple number of phase channels having the desired phase shift that brings cancellation in the sum of outputs from the individual channels. In this article, a design principle of sliding mode control for a multiphase controller is proposed. The methodology is originated from the concept of multidimensional sliding mode and provides desired phase shifts between phases with the help of adaptive width for the hysteresis loops in switching elements. The chattering suppression effect is demonstrated by simulations for the DC–DC converter systems in various situations.     

Robust formation control of electrically driven nonholonomic mobile robots via sliding mode technique

This paper proposes a sliding mode formation control method for electrically driven nonholonomic mobile robots in the presence of model uncertainties and disturbances. We use the kinematic model based on the leader-following approach for the formation control of multiple robots. Unlike many researches considering only the kinematic model, we also consider the dynamic model including actuator dynamics to obtain the voltage input because it is more realistic to use the voltage as input than the velocity. Then, the sliding mode control method is used to deal with model uncertainties and disturbances acting on the mobile robots. The stability of the proposed control system is proven using Lyapunov stability theory. Finally, we perform computer simulations to demonstrate the performance of the proposed control system.     

基于Terminal 滑模的高超声速飞行器姿态控制

针对高超声速飞行器六自由度再入模型,考虑模型参数不确定和外界干扰对再入姿态控制的影响,基于Terminal滑模对再入过程中姿态角的跟踪控制问题进行研究.为了减少外界高频噪声对系统性能的影响,首先,利用多时间尺度技术将姿态模型划分为双环结构;然后,分别针对各环路设计Terminal滑模控制器,并通过Lyapunov理论和奇异摄动理论对系统的稳定性进行证明.仿真结果表明,对于六自由度再入模型,该控制方法能够很好地跟踪再入制导指令.     

基于滑模变结构的倒立摆系统稳定控制

利用滑模变结构控制对一级倒立摆系统进行了有效控制.首先对一级倒立摆系统的模型进行线性化处理,再利用滑模变结构控制方法对此模型中摆的镇定、台车位置的调节和系统参数不确定性设计了具体的控制规律,并使用饱和函数的方法抑制系统的抖振.最后在Matlab/Simulink上进行了仿真实验,实验结果说明滑模变结构控制方法是有效的.     

基于终端滑模机器人模糊自适应路径跟踪控制

对质心位置未知的移动机器人系统设计了基于快速终端滑模的模糊自适应路径跟踪控制方法。该方法采用模糊逻辑系统逼近控制器中的未知函数,基于李亚普诺夫稳定性分析方法对未知参数设计自适应律,并设计鲁棒控制器来补偿逼近误差。该方法不但可以保证闭环系统中的所有信号有界,而且可使跟踪误差在有限时间内收敛到原点的小邻域内。仿真结果验证了方法的有效性。     

Adaptive cruise control of a HEV using sliding mode control

This paper presents adaptive cruise control of a hybrid electric vehicle. First, the mathematical model of the vehicle is formulated. Next, a classical controller is applied to the vehicle model. Swarm optimisation is implemented for self parameter tuning of the controller. The model is simulated and the result of the response to a variable speed is analysed. The results reveal that the controller is not a powerful means to manage the rapid transformation of the desire set point. Accordingly, a sliding mode controller is developed next. The performance of this controller is compared with the classical controller.     

Decentralized sliding mode control design using overlapping decompositions

This paper discusses overlapping decentralized sliding mode controller design for large-scale continuous-time systems. Design issues, like connective reachability of the sliding manifold and the stability of the sliding mode equations in the expanded and original state spaces are examined. Application of the results to automatic generation control is also discussed briefly.     

Sensor fault tolerant control using sliding mode observers

Previous work has considered the use of sliding mode observers for fault detection and isolation (FDI) in uncertain linear systems whereby the unknown faults are reconstructed by appropriate processing of the so-called equivalent output error injection. The paper builds on this work and considers such a scheme within the broader context of fault tolerant control. Specifically, by correcting the faulty measurement by an estimate of the fault obtained from the sliding mode FDI scheme, good closed-loop performance is still maintained. An example of such a scheme, which has been implemented in real-time on a laboratory dc motor rig, is described.     

Finite time convergent control using terminal sliding mode

A method for terminal sliding mode control design is discussed. As we know, one of the strong points of terminal sliding mode control is its finite-time convergence to a given equilibrium of the system under consideration, which may be useful in specific applications. The proposed method, different from many existing terminal sliding model control design methods, is studied, and then feedback laws are designed for a class of nonlinear systems, along with illustrative examples.