考虑铰间间隙和重力影响的空间机械臂轨迹跟踪控制

以在轨服务高精度操控任务为背景,研究了铰间间隙和重力对空间机械臂末端轨迹跟踪精度的耦合影响,并设计了间隙补偿控制器.通过分析不同重力环境下含铰间间隙机构的运动特性,基于铰间间隙的Kelvin-Voigt线性弹簧阻尼假设,建立了地面装调及空间服役两种不同工况下的近似间隙等效模型.以二自由度空间机械臂为例,利用牛顿欧拉法推导了重力及重力释放条件下的含间隙机械臂动力学模型,并分离出了间隙补偿项.最后,通过轨迹跟踪控制仿真研究,给出了含间隙机械臂在不同重力环境下的动力学行为差异,同时验证了间隙补偿控制器的有效性.     

六自由度机械臂约束预测控制系统的设计

本文提出了一种基于约束预测控制的机械臂实时运动控制方法.该控制方法分为两层,分别设计了约束预测控制器和跟踪控制器.其中,约束预测控制器在考虑系统物理约束的条件下,在线为跟踪控制器生成参考轨迹;跟踪控制器采用最优反馈控制律,使机械臂沿参考轨迹运动.为了简化控制器的设计和在线求解,本文采用输入输出线性化的方式简化机械臂动力学模型.同时,为了克服扰动,在约束预测控制器中引入前馈策略,提出了带前馈一反馈控制结构的预测控制设计.因此,本文设计的控制器可以使机械臂在满足物理约束的条件下快速稳定地跟踪到目标位置.通过在PUMA560机理模型上进行仿真实验,验证了预测控制算法的可行性和有效性.     

大型挠性空间机械臂振动抑制的一种关节控制策略

大型空间机械臂在操作过程中,一个突出的问题是超低频挠性,不仅存在机械臂的弯曲振动,而且还存在关节的扭转变形振动;另外一个不能忽视的问题就是减速器的扭矩传递特性,以及机械臂关节运动与基座扰动（空间站）之问的耦合特性,这就要求根据关节结构和传感器配置实现关节位置控制,同时稳定和衰减机械臂及其关节的低频挠性振动．本文运用集中参数法对空间机械臂的挠性动力学进行建模,设计了工程可实现的单个关节控制策略及其控制律,分析和数值仿真了其稳定性,对未来空间站的大型挠性空间机械臂设计、动力学与控制的研究具有一定的参考价值．     

地面装调的空间机械臂在空间应用时的自适应鲁棒控制

针对空间机械臂在轨操控过程中,重力加速度不同于地面装调阶段的重力加速度,会随着空间位置的改变而变化的问题.本文提出了一种自适应鲁棒控制策略,用于空间机械臂的末端控制,从而使在地面重力条件下装调好的空间机械臂能够在空间微重力条件下实现在轨操控任务.通过分析重力项对空间机械臂轨迹跟踪控制的影响,设计自适应律在线估计重力加速度,从而得到重力项的估计,系统的不确定性通过鲁棒控制器来补偿.基于李雅普诺夫理论证明了闭环系统的稳定性.仿真结果表明,在地面装调阶段的重力环境下和空间应用阶段的微重力环境下,该控制器对空间机械臂的末端控制均能达到较高的轨迹跟踪精度,具有重要的工程应用价值.     

空间机械臂全局反作用优化及其地面试验研究

针对空间机械臂在运动过程中对其基座产生力／力矩反作用这一问题进行了分析,并提出一种关节轨迹参数化的全局反作用优化方法,用于减小机械臂的反作用力／力矩．基于气浮轴承方法,建立了3自由度空间机械臂反作用优化地面实验系统．最后,采用3自由度机械臂验证了该方法的有效性．     

柔性空间机械臂捕获卫星过程的鲁棒镇定与自适应抑振复合控制

分析漂浮基柔性空间机械臂捕获运动卫星过程的碰撞动力学,及受碰撞冲击后的不稳定空间机械臂系统的控制.首先,利用假设模态法近似描述柔性杆的弹性变形,并结合第二类拉格朗日方程建立柔性空间机械臂多体系统动力学模型.而后,基于动量守恒原理,利用动量冲量法分析空间机械臂捕获卫星的碰撞动力学.针对受碰撞冲击后不稳定运动空间机械臂,设计鲁棒镇定与自适应抑振复合控制以维持空间机械臂与被捕获卫星组合体系统稳定.最后,数值仿真揭示了碰撞冲击影响效应,并验证了上述控制算法的有效性.     

单臂式空间机械臂捕捉空间目标问题研究

以空间机械臂系统的动量守恒关系式为基础,对空间机械臂抓取空间目标过程中的碰撞问题进行了分析,提出了“直臂抓取”与“广义直臂抓取”概念,详细推导了满足基座质心、系统质心及工作端点共线的机械臂构型,得到了碰撞力方向矢量与基座、系统质心重合的角度关系式．满足关系式的空间机械臂构型可有效的减少碰撞力对于系统角动量的影响,进而避免混合体控制问题的关节限制与力矩限制．通过仿真验证了方法的有效性．     

空间机器人捕获非合作目标后的消旋策略及阻抗控制

针对空间机器人捕获自旋目标卫星后的消旋与稳定操作提出了一种阻抗控制方法．首先,基于正序链和逆序链方法推导出空间机器人系统在操作空间中的动力学方程．然后,基于归一化时间设计了目标卫星的快速消旋策略,最优消旋时间由末端执行器的约束条件决定．最后,基于所推导操作空间下的动力学方程,提出了一种消除目标旋转运动并同时稳定基座的阻抗控制方法．在利用7自由度冗余机械臂消除自旋卫星并稳定其基座的案例中给出了仿真结果,验证了所提方法的性能及有效性．     

基于等效惯量模拟的空间站转位机械臂承载性能测试

由于地面模拟真实舱体大惯量负载较为困难,且实现体积庞大,本文提出了一种基于等效惯量模拟的空间站转位机械臂承载性能测试方法,设计了一种基于气浮增速机构的惯量模拟器,并根据等效动力学原理建立了惯量模拟器等效负载数学模型,减小了负载惯量,降低了其空间微重力运动环境模拟难度,实现了空间机械臂承载性能的有效测试.最后通过仿真计算验证了测试方法与空间转位过程的一致性.仿真结果表明,腕关节和肩关节输出力矩与空间转位时输出力矩最大误差分别为4.61%和1.33%,腕关节和肩关节的惯量模拟误差分别小于4.52%和1.03%,证明该方法可有效地对转位机械臂进行承载性能测试.     

基于任务空间的无标定视觉机械臂自适应跟踪控制

针对动力学参数不确定的无标定视觉机械臂系统,研究基于任务空间的自适应控制问题。对于控制器的设计,首先研究机械臂动力学参数不确定情况下基于任务空间的控制问题,然后设计自适应摄像机标定控制器,最后根据任务空间信息和图像空间信息的一致收敛关系统一两部分控制器,设计整个闭环系统控制信号和自适应控制律。实验结果表明了所提出的控制方法的有效性。     

An adaptive fuzzy strategy for motion control of robot manipulators

This paper makes an attempt to develop a self-tuned proportional-integral-derivative (PID)-type fuzzy controller for the motion control of robot manipulators. In recent past, it has been widely believed that static fuzzy controllers can not be suitably applied for controlling manipulators with satisfaction because the robot manipulator dynamics is too complicated. Hence more complicated and sophisticated neuro-fuzzy controllers and fuzzy versions of nonlinear controllers have been more and more applied in this problem domain. The present paper attempts to look back at this widely accepted idea and tries to develop a self-tuned fuzzy controller with small incremental complexity over conventional fuzzy controllers, which can yet attain satisfactory performance. The proposed controller is successfully applied in simulation to control two-link and three-link robot manipulators.     

Passivity based adaptive Jacobian tracking for free-floating space manipulators without using spacecraft acceleration

Most research so far on trajectory tracking of free-floating space manipulators has assumed that the kinematics of the space manipulator is exactly known. However, when a space manipulator picks up different tools of unknown lengths or unknown gripping points, its kinematics and dynamics change and are difficult to derive exactly. Thus, in this paper, we have proposed a passivity based adaptive Jacobian controller for free-floating space manipulators. The proposed controller consists of a transposed Jacobian feedback and a dynamic compensation term, and the parameter adaptation laws are derived by Lyapunov-like stability analysis tools. It is shown that the end-effector motion tracking errors converge asymptotically. To avoid using spacecraft acceleration, we define a new reference velocity, which is called spacecraft reference velocity. In addition, we have also conducted passivity interpretation of the proposed controller to obtain some physical insight into its properties. Simulation results are presented to show the performance of the proposed controller.     

微重力环境下空间机械手的动力学建模新方法

未来空间作业将需要机械手在微重力的环境下完成各种复杂的任务．由于机械手与其本体的动态耦合，给机械手带来了许多运动学、动力学及控制方面的问题．本文提出了一种空间机械手动力学的建模新方法，对空间机械手的正、逆动力学进行了分析．应用该方法，建立了一种基于解出加速度的空间机械手的控制策略．本文所提出的方法不仅适合于单机械手系统，而且适合于多机械手的系统．     

Control of Underactuated Manipulators using Fuzzy Logic Based Switching Controller

This paper introduces a new concept for designing a fuzzy logic based switching controller in order to control underactuated manipulators. The proposed controller employs elemental controllers, which are designed in advance. Parameters of both antecedent and consequent parts of a fuzzy indexer are optimized by using evolutionary computation, which is performed off-line. Design parameters of the fuzzy indexer are encoded into chromosomes, i.e., the shapes of the Gaussian membership functions and corresponding switching indices of the consequent part are evolved to minimize the angular position errors. Such parameters are trained for different initial configurations of the manipulator and the common rule base is extracted. Then, these trained fuzzy rules can be brought into the online operations of underactuated manipulators. 2-DOF underactuated manipulator is taken into consideration so as to illustrate the design procedure. Computer simulation results show that the new methodology is effective in designing controllers for underactuated robot manipulators.     

Adaptive variable structure controller of redundant robots with mobile/fixed obstacles avoidance

In this paper, a variable structure adaptive controller is proposed for redundant robot manipulators constrained by moving obstacles. The main objective of the controller is to force the model states of the robot to track those of a chosen reference model. In addition, the controller is designed directly in Cartesian space and no knowledge on the dynamic model is needed, except its structure. The parameters of the controller are adapted using adaptive laws obtained via Lyapunov stability analysis of the closed loop. The performances of the proposed controller are evaluated using a 3 DOF robot manipulator evolving in a vertical plane constrained by a mobile obstacle. The obtained results show its effectiveness compared to other tested variable structure controllers.     

多移动机械臂系统动力学建模以及稳定性分析

随着社会生产力的发展和发展需求的提高,移动机械臂凭借着自身优势,受到学术界和工业界的广泛关注.但在许多工作场景下,单个移动机械臂有着自由度数以及载荷的限制,无法顺利完成任务.为了更好地满足任务需求,多移动机械臂系统应运而生.在上述工业背景下,本文建立了多移动机械臂系统的动力学模型,并针对该动力学方程进行了稳定性分析.首先通过拉格朗日方程建立单个移动机械臂的动力学方程,将多体动力学软件仿真结果同动力学模型数值计算结果进行对比,验证了模型的正确性.随后联立多个移动机械臂的动力学方程和操作对象的动力学方程,得到封闭形式的多移动机械臂系统的动力学方程.再利用关节位置误差和速度误差设计李雅普诺夫函数,通过反步法获得了关节力矩的控制律.最后在多体动力学软件仿真中,察看轨迹是否能跟踪上期望信号来检验控制律的有效性.     

Integrated Environment for Modelling, Simulation and Control Design for Robotic Manipulators

In this paper an integrated environment for the design of robotic controllers implemented on a PC is described. It is based on the Planar Manipulators Toolbox for dynamic simulation of redundant planar manipulators. The tools are fully integrated in the MATLAB/SIMULINK and hence, a lot of standard tools are available for the analysis and control design. Using the real-time simulation it is possible to apply the developed controllers to a real robot manipulator, which can be included in the system via corresponding interfaces, without any additional coding. The main advantage is the flexibility in fast prototyping of different algorithms in the field of control of robotic systems, especially for redundant manipulators.     

Adaptive force and position control of manipulators

The article presents simple methods for the design of adaptive force and position controllers for robot manipulators within the hybrid control architecture. The force controller is composed of an adaptive PID feedback controller, an auxiliary signal, and a force feedforward term, and achieves tracking of desired force setpoints in the constraint directions. The position controller consists of adaptive feedback and feedforward controllers as well as an auxiliary signal, and accomplishes tracking of desired position trajectories in the free directions. The controllers are capable of compensating for dynamic cross-couplings that exist between the position and force control loops in the hybrid control architecture. The adaptive controllers do not require knowledge of the complex dynamic model or parameter values of the manipulator or the environment. The proposed control schemes are computationally fast and suitable for implementation in online control with high sampling rates. The methods are applied to a two-link manipulator for simultaneous force and position control. Simulation results confirm that the adaptive controllers perform remarkably well under different conditions.     

Switched adaptive tracking control of robot manipulators with friction and changing loads

A switched adaptive controller is designed for robot manipulators with friction and changing loads. The nonlinear friction is depicted by a nonlinear friction model, and a switched nonlinear system is used to model the parameter jump caused by load change. Hyperstability theory is used in the designing procedure, which provides more options for adaptive laws than Lyapunov theory. In the presence of friction and changing loads, asymptotic tracking is achieved under arbitrary switching, which is not able to accomplish by a non-switched adaptive controller. The proposed method is validated by a simulation of a 2 degree of freedom manipulator.     

Distributively controlling two robots handling an object in thetask space without any communication

Two distributed cooperation controllers are presented for trajectory tracking of two manipulators which are cooperatively handling an object. The controllers control the positions of the robots distributively by using the trajectory error of the object in the task space. In the first controller, the internal force between the object and a manipulator is controlled only by a feedforward of the desired force. The second controller uses a force feedback. No communication is required between the manipulators in both the controllers. Their globally and exponentially asymptotic stabilities are guaranteed by Lyapunov functions