一种自移动空间机械臂末端执行器的研制

针对中小型自移动空间机械臂在轨操作和"换位行走"的任务需求,研制了一种小型化、大容差、高刚度可靠连接的末端执行器及其相应的目标适配器.末端执行器采用单一驱动实现捕获、拉紧锁合、解锁和电连接器插拔等多种功能.考虑捕获容差条件及锁合性能要求,对末端执行器的关键机构参数进行设计.通过ADAMS建立虚拟样机,对捕获容差及锁合的功能性能进行验证.最后通过样机实验对末端执行器的功能进行验证,验证了设计的可行性及仿真的准确性.     

空间大型末端执行器抓捕容差优化及其仿真

为了使空间大型末端执行器的抓捕操作性能得到最大程度的发挥,不同于传统的从机构设计角度得到末端执行器固定抓捕容差的方法,本文从优化设计学的角度出发,根据末端执行器的工作过程及其原理,将抓捕容差划分为捕获容差和拖动容差两部分,通过分析影响大型末端执行器抓捕容差的结构因素,分别建立了末端执行器捕获容差和拖动容差的数学优化模型,并基于线性加权法和惩罚函数法获得了抓捕容差最优值(128.58mm,128.58 mm,100 mm,15.12,15.12,16.32)T,同时得到了末端执行器本体相对应的结构参数.最终,采用仿真研究方法进行了抓捕容差优化及抓捕性能实验研究.实验结果验证了理论分析的正确性,证明本文提出的末端执行器数学优化模型合理,优化算法正确.     

空间网状捕获接口的等效抓捕控制

在空间大型机械臂在轨抓捕过程中,其关节柔性及长臀杆的变形会产生较大的末端跟踪及定位误差,因此很难实现成功抓捕.为此,本文研制了一种空间应用的网状捕获对接接口,提高了大臂末端执行器在大定位误差下的抓捕能力.同时,为了提高末端执行器与目标之间的非相对零速情况下的抓捕性能,利用等效抓捕的思想避开了抓捕过程中捕获接口对目标抓钩纠偏力建模复杂的问题,将问题简化为对目标抓钩端点在捕获面上投影的位置跟踪问题,实现了在末端执行器与目标具有一定的相对逃逸速度的情况下的成功抓捕.实验表明,利用本文提出的控制策略增大了网状捕获接口的抓捕容差范围,从而验证了本文提出的控制策略的何效性.     

空间大型末端执行器柔性钢丝绳的建模与捕获动力学

针对大容差软捕获这一空间捕获操作的重要准则,研制了基于钢丝绳的末端执行器大容差柔性捕获机构.针对钢丝绳具有较大柔性,在窄间应用环境下难于快速连续建模控制的问题,提出丁柔性钢丝绳的离散控制模型,解决了钢丝绳的建模问题.通过钢丝绳的离散模型,分析了末端执行器钢丝绳柔性机构捕获空间自由飞行载荷舱的动力学问题.实验证明钢丝绳模...     

线驱动柔性机械臂的运动学分析

与传统的由连杆和关节构成的刚性机械臂不同,设计的柔性机械臂无任何刚性结构,外围驱动装置通过嵌在机械臂内部的拉线与柔性机械臂相联系,控制拉线长度的变化量即可调整柔性机械臂末端执行器的位置和姿态。柔性机械臂由弹性材料制作而成,拥有无穷多个自由度,在确保了高安全性、高灵活性的同时,随之也带来运动学和动力学建模复杂、控制难度大等问题。基于分段常曲率的假设,提出了一种运动学建模方法,通过建立3个空间,即驱动空间、虚拟关节空间、任务空间,以及两个映射,即驱动空间-虚拟关节空间映射、虚拟关节空间-任务空间映射,将拉线长度的变化量和柔性机械臂末端执行器的位置和姿态关联起来。仿真结果表明,提出的线驱动柔性机械臂的运动学模型,能较为真实地模拟柔性机械臂在拉线长度变化时的形态,计算末端执行器的位置和姿态。     

基于分布式控制系统的空间大型末端执行器抓捕策略

针对空间大型机械臂冈其关节和臂杆柔性带来的抓捕前定位问题,为一种具有柔性捕获接口的新型末端执行器设计了分布式控制系统,并建立了以捕获环收缩速度为主要控制对象的抓捕策略,可实现稳定且高效的抓捕.其中,该控制系统由传感器单元、上层控制单元和3个模块化的底层驱动单元组成.传感器单元和底层驱动单元集成在末端执行器内部,采集系统...     

基于力/位混合算法的7自由度机械臂精细操控方法

为了使冗余机械臂在具有良好的自治性和灵活性的同时保证末端的执行精度,提出一种基于力/位混合控制的冗余机械臂精细控制方法.通过建立准确的运动学模型,分析机械臂系统的运动特性,利用固定角度与梯度下降相结合的方法求动力学逆解.在对机械臂的力/位混合控制律建模的基础上,利用位置控制和力控制对机械臂末端的运动轨迹进行规划.针对受环境约束的机械臂的控制问题,提出冗余自由度机械臂的适从坐标系建立方法,使得末端执行器能够在任意曲面完成作业任务.在仿真分析和实验中,令机械臂末端跟随任意设定的曲线轨迹到达给定点.通过多次测量得出,力精度误差小于2%,并且在保证作用力方向精确的条件下,机械臂末端轨迹的偏离值小于5%.结果表明,所设计的力/位混合控制方法对7自由度机械臂控制精度效果良好.     

空间机械臂操控技术研究综述

考虑到空间机械臂在执行在轨维修、在轨组装、在轨加注等复杂危险的空间任务时,其精准、灵巧的操控技术的重要性,从不同类型空间机械臂构形、末端执行器出发,分析了空间机械臂的发展趋势。综述了空间机械臂操控过程中涉及的5项关键技术,包括：交会对接与捕获技术、自主规划与智能控制技术、传感与感知技术、智能协同与操控技术及系统安全保障技术。最后,就现有的空间机械臂在操控过程中面临的问题,提出未来的发展方向及展望。     

三手指空间机器人末端执行器的柔顺抓握策略

空间机器人在抓握物体时,末端执行器与目标物体之间因接触碰撞而产生的扰动力可能会造成机械臂抖动和位姿改变,甚至将日标物体弹出捕获区,造成捕获失败,针对这一问题,首先介绍了哈尔滨工业大学(HIT)自行研制的三于指窄间机器人末端执行器,对末端执行器抓握日标物体过程中的碰撞扰动力进行了分析,提出了一种柔顺抓握策略以削弱抓握目标...     

基于伪逆的导轨机械臂关节速度纠偏运动规划方案

针对导轨机械臂在任务执行过程中出现的关节速度偏离期望值的问题,提出了一种基于伪逆算法的导轨机械臂关节速度纠偏运动规划方案。首先,根据机械臂的关节角状态和末端执行器的运动状态,运用伪逆算法对导轨机械臂在速度层上进行冗余度解析。然后,设计时变函数对关节速度进行约束调整,使偏离后的关节速度收敛于期望值。接着,针对末端执行器出现的位置误差设计了误差修正方法以保证轨迹跟踪任务的顺利执行。最后,将运动规划方案在Matlab软件上以基座直线移动和弧形移动的四连杆冗余度机械臂为例进行了仿真实验。仿真结果表明了该方案能纠正导轨机械臂在任务执行过程中偏离期望值的关节速度,且能使末端执行器的轨迹跟踪达到较高的精度。     

自由飞行空间机器人系统的协调运动控制

考虑由载体和机械臂组成的空间机器人系统的协调控制问题,提出了一种新的协调 控制策略.该策略首先利用简单的变结构控制器粗略控制载体的运动,进而设计机械臂控制 器以保证手端精确跟踪其期望的运动轨迹.应用该策略分别对手端自由运动和受限运动设计 了相应的控制器,并对两杆平面空间机器人系统进行了仿真,证实了控制策略的有效性.     

Fault-tolerant motion planning and control of redundant manipulator

One important issue in the motion planning of a kinematic redundant manipulator is fault tolerance. In general, if the motion planner is fault tolerant, the manipulator can achieve the required path of the end-effector even when its joint fails. In this situation, the contribution of the faulty joint to the end-effector is required to be compensated by the healthy joints to maintain the prescribed end-effector trajectory. To achieve this, this paper proposes a fault-tolerant motion planning scheme by adding a simple fault-tolerant equality constraint for the faulty joint. Such a scheme is then unified into a quadratic program (QP), which incorporates joint-physical constraints such as joint limits and joint-velocity limits. In addition, a numerical computing solver based on linear variational inequalities (LVI) is presented for the real-time QP solving. Simulative studies and experimental results based on a six degrees-of-freedom (DOF) redundant robot manipulator with variable joint-velocity limits substantiate the effectiveness of the proposed fault-tolerant scheme and its solution.     

Path-constrained control of a redundant manipulator in a task space

This study addresses the problem of controlling a redundant manipulator with both state and control dependent constraints. The task of the robot is to follow by the end-effector a prescribed geometric path given in the task space. The control constraints resulting from the physical abilities of robot actuators are also taken into account during the robot movement. Provided that a solution to the aforementioned robot task exists, the Lyapunov stability theory is used to derive the control scheme. The numerical simulation results, carried out for a planar manipulator whose end-effector follows a prescribed geometric path given in a task space, illustrate the trajectory performance of the proposed control scheme.     

Position referenced force augmentation in teleoperated hydraulic manipulators operating under delayed and lossy networks: A pilot study

Position error between motions of the master and slave end-effectors is inevitable as it originates from hard-to-avoid imperfections in controller design and model uncertainty. Moreover, when a slave manipulator is controlled through a delayed and lossy communication channel, the error between the desired motion originating from the master device and the actual movement of the slave manipulator end-effector is further exacerbated. This paper introduces a force feedback scheme to alleviate this problem by simply guiding the operator to slow down the haptic device motion and, in turn, allows the slave manipulator to follow the desired trajectory closely. Using this scheme, the master haptic device generates a force, which is proportional to the position error at the slave end-effector, and opposite to the operator’s intended motion at the master site. Indeed, this force is a signal or cue to the operator for reducing the hand speed when position error, due to delayed and lossy network, appears at the slave site. Effectiveness of the proposed scheme is validated by performing experiments on a hydraulic telemanipulator setup developed for performing live-line maintenance. Experiments are conducted when the system operates under both dedicated and wireless networks. Results show that the scheme performs well in reducing the position error between the haptic device and the slave end-effector. Specifically, by utilizing the proposed force, the mean position error, for the case presented here, reduces by at least 92% as compared to the condition without the proposed force augmentation scheme. The scheme is easy to implement, as the only required on-line measurement is the angular displacement of the slave manipulator joints.     

Path following by the end-effector of a redundant manipulator operating in a dynamic environment

This paper addresses the problem of generating at the control-loop level a collision-free trajectory for a redundant manipulator operating in dynamic environments which include moving obstacles. The task of the robot is to follow, by the end-effector, a prescribed geometric path given in the work space. The control constraints resulting from the physical abilities of robot actuators are also taken into account during the robot movement. Provided that a solution to the aforementioned robot task exists, the Lyapunov stability theory is used to derive the control scheme. The numerical simulation results for a planar manipulator whose end-effector follows a prescribed geometric path, given in both an obstacle-free work space and a work space including the moving obstacles, illustrate the trajectory performance of the proposed control scheme.     

On the dynamics and control of flexible joint space manipulators

Space manipulator systems are designed to have lightweight structure and long arms in order to achieve reduction of fuel consumption and large reachable workspaces, respectively. Such systems are subject to link flexibilities. Moreover, space manipulator actuators are usually driven by harmonic gear mechanisms which lead to joint flexibility. These types of flexibility may cause vibrations both in the manipulator and the spacecraft making the positioning of the end-effector very difficult. Here, both types of flexibilities are lumped at the joints and the dynamic equations of a general flexible joint space manipulator are derived. Their internal structure is highlighted and similarities and differences with fixed-base robots are discussed. It is shown that one can exploit the derived dynamic structure in order to design a static feedback linearization control law and obtain an exact linearization and decoupling result. The application of such controllers is desired in space applications due to their small computational effort. In case of fixed-base manipulators, the effective use of a static feedback controller is feasible only if a simplified model is considered. Then, the proposed static feedback linearization control law is applied to achieve end-effector precise trajectory tracking in Cartesian space maintaining a desirable non-oscillatory motion of the spacecraft. The application of the proposed controller is illustrated by a planar seven degrees of freedom (dof) system.     

Canonical parameterization of excess motor degrees of freedom withself-organizing maps

The problem of sensorimotor control is underdetermined due to excess (or "redundant") degrees of freedom when there are more joint variables than the minimum needed for positioning an end-effector. A method is presented for solving the nonlinear inverse kinematics problem for a redundant manipulator by learning a natural parameterization of the inverse solution manifolds with self-organizing maps. The parameterization approximates the topological structure of the joint space, which is that of a fiber bundle. The fibers represent the "self-motion manifolds" along which the manipulator can change configuration while keeping the end-effector at a fixed location. The method is demonstrated for the case of the redundant planar manipulator. Data samples along the self-motion manifolds are selected from a large set of measured input-output data. This is done by taking points in the joint space corresponding to end-effector locations near "query points", which define small neighborhoods in the end-effector work space. Self-organizing maps are used to construct an approximate parameterization of each manifold which is consistent for all of the query points. The resulting parameterization is used to augment the overall kinematics map so that it is locally invertible. Joint-angle and end-effector position data, along with the learned parameterizations, are used to train neural networks to approximate direct inverse functions.     

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．     

Data-Driven Human-Robot Interaction Without Velocity Measurement Using Off-Policy Reinforcement Learning

In this paper, we present a novel data-driven design method for the human-robot interaction (HRI) system, where a given task is achieved by cooperation between the human and the robot. The presented HRI controller design is a two-level control design approach consisting of a task-oriented performance optimization design and a plant-oriented impedance controller design. The task-oriented design minimizes the human effort and guarantees the perfect task tracking in the outer-loop, while the plant-oriented achieves the desired impedance from the human to the robot manipulator end-effector in the inner-loop. Data-driven reinforcement learning techniques are used for performance optimization in the outer-loop to assign the optimal impedance parameters. In the inner-loop, a velocity-free filter is designed to avoid the requirement of end-effector velocity measurement. On this basis, an adaptive controller is designed to achieve the desired impedance of the robot manipulator in the task space. The simulation and experiment of a robot manipulator are conducted to verify the efficacy of the presented HRI design framework.      

Study on Non-holonomic Cartesian Path Planning of a Free-Floating Space Robotic System

The non-holonomic characteristic of a free-floating space robotic system is used to plan the path of the manipulator joints, by whose motion the base attitude and the inertial pose (the position and orientation with respect to the inertial frame) of the end-effector attain the desired values. First, the kinematic equations of a free-floating space robot are simplified and the system state variables are transformed to another form composed of base attitude and joint angles. Then, the joint trajectories are parameterized using sinusoidal functions, whose arguments are seven-order polynomials. Third, the planning problem is transformed to an optimization problem; the cost function, defined according to the accuracy requirements of system variables, is the function of the parameters to be determined. Finally, the Particle Swarm Optimization (PSO) algorithm is used to search the solutions of the parameters that determine the joint trajectories. The presented method meets three typical applications: (i) point-to-point maneuver of the end-effector without changing the base attitude, (ii) attitude maneuver of the base without changing the end-effector's pose and (iii) point-to-point maneuver of the end-effector with adjusting the base attitude synchronously. The simulation results of a spacecraft with a 6-d.o.f. manipulator verify the performance and the validity of the proposed method.