欠驱动冗余度空间机器人优化控制

欠驱动控制是空间技术中容错技术的重要方面.本文研究了被动关节中有制动器的欠驱动冗余度空间机器人系统的运动优化控制问题.从系统动力学方程出发,分析了欠驱动冗余度空间机器人的优化能力和控制方法;给出了主、被动关节间的耦合度指标;提出了欠驱动冗余度空间机器人系统的“虚拟模型引导控制”方法,在这种方法中采用与欠驱动机器人机构等价的全驱动机器人作为模型来规划机器人的运动,使欠驱动系统在关节空间中逼近给出的规划轨迹,实现了机器人末端运动的连续轨迹运动优化控制;通过末关节为被动关节的平面三连杆机器人进行了仿真,仿真的结果证明了提出算法的有效性.     

Adaptive neural control for an uncertain robotic manipulator with joint space constraints

In this paper, adaptive neural tracking control is proposed for a robotic manipulator with uncertainties in both manipulator dynamics and joint actuator dynamics. The manipulator joints are subject to inequality constraints, i.e., the joint angles are required to remain in some compact sets. Integral barrier Lyapunov functionals (iBLFs) are employed to address the joint space constraints directly without performing an additional mapping to the error space. Neural networks (NNs) are utilised to compensate for the unknown robot dynamics and external force. Adapting parameters are developed to estimate the unknown bounds on NN approximations. By the Lyapunov synthesis, the proposed control can guarantee the semi-global uniform ultimate boundedness of the closed-loop system, and the practical tracking of joint reference trajectory is achieved without the violation of predefined joint space constraints. Simulation results are given to validate the effectiveness of the proposed control scheme.     

欠驱动机械手的非线性补偿控制的实现

以具有欠驱动关节的水平两自由度机械手为对象,建立了其动力学数学模型。对具有非完全约束机器人的特点进行了分析。利用解非线性方程的有效方法一平均值法对模型进行了处理,得到平均值系统,使模型得到简化。含有非驱动关节的平面二自由度机械手具有不可积分的速度和加速度束。因而是一个二阶非完整系统。通过分析系统的动力学机构,设计了一种非线性补偿控制的方法来对欠驱动关节实现控制。实验结果表明。该控制方法在控制模型、控制算法和反馈控制方法上都是十分有效的。     

Disturbance observer-based robust control for underwater robotic systems with passive joints

Underwater exploration requires mobility and manipulation. Underwater robotic vehicles (URV) have been employed for mobility, and robot manipulators attached to the underwater vehicle (i.e. rover) perform the manipulation. Usually, the manipulation mode takes place when the rover is stationary. The URV is then modeled as a passive joint and joints of the manipulator are modeled as active joints. URV motions are determined by inherent dynamic couplings between active and passive joints. Furthermore, the control problem becomes complex since there are many hydrodynamic terms as well as intrinsic model uncertainties to be considered. Tocope with these difficulties, we propose a disturbance observer-based robust control algorithm for underwater manipulators with passive joints. The proposed control algorithm is able to treat an underactuated system as a pseudo-active system in which passive joints are eliminated. Also, to realize a robust control method, a non-linear feedback disturbance observer is applied to each active joint. A four-jointed underwater robotic system with one passive joint is considered as an illustrative example. Through simulation, it is shown that the proposed control algorithm has good position tracking performance even in the presence of several external disturbances and model uncertainties.     

The dexterity and singularities of an underactuated robot

Underactuated robots are robotic systems with more joints than actuators. A robot may be underactuated by design as in the case of a hyper‐redundant robot with passive joints or may become underactuated as a result of an actuator failure. In this article, we examine the dexterity of underactuated robots whose passive joints operate in either a locked or free‐swinging mode. The ability to an analyze the dexterity of an underactuated robot has important applications especially for the control of passive joints with brakes and for the fault tolerance analysis of an otherwise fully actuated kinematically redundant robot. The approach applied here is to use kinematics and dynamics‐based formulations of manipulator dexterity. We then characterize passive‐joint singularities, i.e., configurations where full end‐effector control is lost because one or more joints are passive instead of active. Lastly, we introduce a new characterization of joint‐limit singularities, which are configurations where full end‐effector control cannot be achieved because one or more joints are at their joint limits. © 2001 John Wiley & Sons, Inc.     

Neural-network-based two-loop control of robotic manipulators including actuator dynamics in task space

A neural-network-based motion controller in task space is presented in this paper. The proposed controller is addressed as a two-loop cascade control scheme. The outer loop is given by kinematic control in the task space. It provides a joint velocity reference signal to the inner one. The inner loop implements a velocity servo loop at the robot joint level. A radial basis function network （RBFN） is integrated with proportional-integral （PI） control to construct a velocity tracking control scheme for the inner loop. Finally, a prototype technology based control system is designed for a robotic manipulator. The proposed control scheme is applied to the robotic manipulator. Experimental results confirm the validity of the proposed control scheme by comparing it with other control strategies.     

Robust robot manipulator control with autonomous consideration algorithm of torque saturation

As each joint actuator of a robot manipulator has a limit value of torque, the motion control system should consider the torque saturation. Conventional motion control based on robust acceleration controller cannot consider the torque saturation and it often causes an oscillated or wrong response. This paper proposes a new autonomous consideration method of joint torque saturation for robust manipulator motion control. The proposed method consists of three on-line autonomous algorithms. These algorithms are the torque limitation algorithm in joint space, the adjustment algorithm of motion control in Cartesian space, and the adjustment algorithm of motion reference in Cartesian space. The robot motion control using the proposed algorithms realizes smooth and robust robot motion response.     

Motion equations and control of the free-flying space manipulator in the reconfiguration mode

The problem of constructing a mathematical model of the planar motion of a free-flying space manipulator meant for maintenance of the surface of manned orbital station was examined. Consideration was given to the design of an algorithm of economic control of the manipulator configuration on the basis of self-braking drives with allowance for substantial mobility of the base. Some results of modeling the space robot dynamics in the mode of manipulator configuration control with subsequent suppression of the carrying body orientation error which corroborate efficiency of the proposed algorithms were presented.     

Some issues of controlling the free-flying manipulative space robot

A brief review of the state-of-the-art in the control of free-flying space robots in the modes of manipulative target lockon by planning the gripper trajectory was presented. For the class of feedback systems, an alternative approach to this problem was proposed. Within the framework of this approach, consideration was given to the problems of constructing the working zone of the space manipulative robot and generating an algorithm to control the manipulative positioning of the load at the desired point of the inertial space with the availability of information about the direction to the target and the distance to it which is acquired using a camcorder mounted at the end link of the manipulator. Examples were presented of computer-aided construction of the working zone and modeling the space robot dynamics which corroborate operability of the proposed algorithm.     

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.     

Control of multimode manipulative space robot in outer space

Some issues of safe motion of the space robot free-flying near the surface of a manned orbital station and generation of the algorithm for initial orientation to the target using a TV camera installed at the end link of the manipulator were discussed. A procedure for construction of the domain of “creeping” speeds of the manipulator where the original model may be replaced by a simplified one was proposed. Consideration was given to the design of an algorithm for installation by the manipulator of a useful load at the given point of surface of the serviced station in the presence of information about the distance to the target. Examples of modeling the robot dynamics were presented to corroborate the efficiency of the proposed algorithms.     

Parametric sensitivity and control of on-orbit manipulators during impacts using the Centre of Percussion concept

During capture of a free-flying object, a robotic servicer can be subject to impacts, which may separate it from the object or damage crucial subsystems. However, the reactions can be minimized using the Centre of Percussion (CoP) concept. Following a brief introduction of the two- and three-dimensional cases, the performance of a robot under impact is assessed when the CoP concept is employed. The effects of the parametric uncertainties on manipulator joint reactions are studied. Α control method to compensate for the reaction forces is proposed. Implementation guidelines are discussed. Simulations of a planar space robot validate the analysis.     

Task space control of a welding robot using a fuzzy coordinator

This paper introduces a fuzzy coordinator as a novel application of fuzzy controller. A control transformation from the task space to the joint space is required to control a robot manipulator in the task space. Because the actuators operate in the joint space while the manipulator is controlled in the task space. A conflict between two spaces is produced due to using an imprecise transformation. Fuzzy coordinator coordinates two spaces by modifying the control transformation affected by uncertainties. The fuzzy coordinator is designed simply and operates as a robust controller. The role of fuzzy coordinator is analyzed and illustrated in the robust control of a welding robot in the task space. A circular trajectory is planned for a welding task performed by a SCARA robot. The fuzzy coordinator is then used to improve the performance of control system affected by imprecise transformations including the imprecise path transformation and the approximated feedback linearization.     

Robust trajectories following control of a 2-link robot manipulator via coordinate transformation for manufacturing applications

A common idea concerning trajectory control of robot manipulators is to tackle the motion of the end-effector. According to traditional trajectory designs, a prescribed profile in a work space is first decomposed into independent joint positions such that the success in a contouring task lies with good tracking capability of individual joints. To advance trajectory control precision without relying on high tracking performance, a contour control strategy for a robot manipulator is presented in this paper. Different from the traditional concept of trajectory control, a contour following control strategy is developed via a coordinate transformation scheme. The main advantage of the proposed control architecture is that the final contouring accuracy will not be degraded in case the tracking performance of the robot manipulator is not good enough. Moreover, using a concept of variable structure control theory, a smooth robust control algorithm is realized in the form of proportional control plus an integration term. The robustness of the control algorithm is also demonstrated. A number of experiments are conducted to demonstrate the advantage of the trajectories following control framework and validate the feasibility of the proposed controller.     

空间机器人捕获航天器操作的避撞柔顺复合自抗扰控制

讨论空间机器人在轨捕获非合作航天器过程避免关节受冲击力矩破坏的避撞柔顺控制问题.在机械臂与关节电机之间配置一种弹簧类柔顺装置——旋转型串联弹性执行器(RSEA),其作用在于:1)在捕获碰撞阶段,可通过其内置弹簧的变形吸收碰撞产生的能量;2)在镇定运动阶段,结合避撞柔顺策略适时开、关电机,以保证关节所受冲击力矩受限在安全范围.首先,应用拉格朗日方法和牛顿-欧拉法分别得到捕获前空间机器人及目标航天器系统动力学方程;然后,结合整个系统动量守恒关系,捕获操作后速度约束关系及力的传递规律,建立捕获后两者形成联合体系统的动力学方程;最后,针对失稳的联合体系统提出一种基于复合误差的避撞柔顺自抗扰控制方案以实现其镇定控制.系统数值仿真结果表明了上述避撞柔顺策略的有效性.     

A scheme for robust trajectory control of space robots

This paper presents a scheme for robust trajectory control of free-floating space robots. The idea is based on the overwhelming robust trajectory control of a ground robot on a flexible foundation and robust foundation disturbance compensation presented elsewhere. No external jets/thrusters are required or used in the scheme. An example of a three-link robot mounted on a free-floating space platform is considered for demonstrating the efficacy of the control scheme. Bond graph technique has been used for the purpose of modeling and simulation. Robustness of the control scheme is guaranteed since the controller does not require the knowledge of the manipulator parameters.     

Real-time implementation of a robust adaptive controller for arobotic manipulator based on digital signal processors

Presents an approach to the design and real-time implementation of an adaptive controller for a robotic manipulator based on digital signal processors. The Texas Instruments DSP (TMS320C31) chips are used in implementing real-time adaptive control algorithms to provide enhanced motion control performance for robotic manipulators. In the proposed scheme, adaptation laws are derived from the direct model reference adaptive control principle based on the improved Lyapunov second method. The proposed adaptive controller consists of an adaptive feedforward and feedback controller and PI-type time-varying auxiliary control elements. The proposed control scheme is simple in structure, fast in computation, and suitable for real-time control. Moreover, this scheme does not require any accurate dynamic modeling nor values of manipulator parameters and payload. Performance of the proposed adaptive controller is illustrated by simulation and experimental results for an industrial robot with four joints in the joint space and Cartesian space     

Nonlinear Feedback Control of a Gravity-Assisted Underactuated Manipulator With Application to Aircraft Assembly

A nonlinear feedback scheme for a gravity-assisted underactuated manipulator with second-order nonholonomic constraints is presented in this paper. The joints of the hyper articulated arm have no dedicated actuators but are activated by gravity. By tilting the base link appropriately, the gravitational torque drives the unactuated links to a desired angular position. With simple locking mechanisms, the hyperarticulated arm can change its configuration using only one actuator at the base. This underactuated arm design was motivated by the need for a compact snake-like robot that can go into aircraft wings and perform assembly operations using heavy end-effectors. The dynamics of the unactuated links are essentially second-order nonholonomic constraints for which there are no general methods to design closed-loop control. We propose a nonlinear closed-loop control law that is guaranteed to be stable in positioning one unactuated joint at a time. We synthesize a Lyapunov function to prove the convergence of this control scheme. The Lyapunov function also generates estimates of the domain of convergence of the control law for various control gains. The control algorithm is implemented on a prototype three-link system. Finally, we provide some experimental results to demonstrate the efficacy of the control scheme.     

基于神经网络的自由漂浮空间机器人关节空间鲁棒跟踪控制

针对存在不确定性以及干扰的自由漂浮空间机器人关节空间轨迹跟踪问题,提出了一种基于鲁棒控制思想的神经网络鲁棒控制方法.对于控制器中由系统惯性参数不确定性引起的非线性不确定项,利用径向基函数(RBF)神经网络进行逼近,并且利用鲁棒控制器使系统镇定并保证从干扰到跟踪误差的增益小于或等于给定的指标.最后,对本文提出的控制方案进...     

Differentially Flat Designs of Underactuated Open-Chain Planar Robots

A fully actuated system can execute any joint trajectory. However, if the system is underactuated, not all joint trajectories are attainable. For such systems, it is difficult to characterize attainable joint trajectories analytically. Numerical methods are generally used to characterize these. This paper investigates the property of differential flatness for underactuated planar open-chain robots and studies dependence on inertia distribution within the system. It is shown that certain choices of inertia distributions make an underactuated open-chain planar robot with revolute joints feedback linearizable, i.e., also differentially flat. Once this property is established, trajectory between any two points in the state space can be planned, and a controller can be developed to correct for errors. To demonstrate the proposed methodology in hardware, experiments with an underactuated 3-DOF planar robot are also presented.