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.     

Energy-efficient joint path-following for attitude-fixed space manipulators with bounds on completion time and motor voltage/current

This paper investigates the minimum-energy joint path-following problem for space manipulators whose base attitude is stabilized by reaction wheels. In the problem, manipulator joint path is specified for rest-to-rest motion and constraints are imposed as the upper bound on both motion completion time and the voltage/current limits of DC motors in manipulator joints and reaction wheels. We suggest a simple two-stage algorithm to address this problem. The algorithm first tries to find a global optimal solution by solving a relaxed convex problem. If the convex relaxation is not successful, then the algorithm solves subproblems iteratively to find a suboptimal solution. Since both problems are formulated as second-order cone programming (SOCP) form, they can be solved efficiently using dedicated SOCP solvers. The effectiveness of the proposed method is verified by numerical experiments.     

Optimal path planning of redundant free-floating revolute-jointed space manipulators with seven links

The path planning of free-floating manipulators is of great interest in space operations. The manipulators in the free-floating mode exhibit nonholonomic characteristics due to the nonintegrability of the angular momentum, which makes the problem complicated. This paper analyzes the path planning of redundant, free-floating space manipulators with revolute joints and 7 degrees of freedom. The primary task of manipulators is to move the manipulator arms so that the desired end-effector position and orientation can be achieved. The motion of the manipulators can produce an attitude disturbance of the base, which has an adverse impact on the spacecraft operation. Thus, it is necessary to minimize the base attitude disturbance in order to reduce the fuel consumption for attitude maintenance. Practically, the path planning of redundant free-floating manipulators with higher degrees of freedom (7 degrees of freedom in this paper) in three-dimensional space is more complicated than path planning with fewer degrees of freedom, including planar or fixed base cases. This paper provides a tractable planning method to solve this problem, which could avoid the pseudo inverse of the Jacobian matrix. The sine functions, whose arguments are the polynomial functions with unknown coefficients, are used to specify the joint paths. The PSODE algorithm (particle swarm optimization combined with differential evolution) is applied to optimize the unknown coefficients of the polynomials in order to achieve the desired end-effector position and orientation and simultaneously minimize the base attitude disturbance. The simulations demonstrate that this method could provide satisfactory smooth paths for redundant free-floating space manipulators.     

Singularity robust path planning for real time base attitude adjustment of free-floating space robot

This paper presents a singularity robust path planning for space manipulator to achieve base (satellite) attitude adjustment and end-effector task. The base attitude adjustment by the movement of manipulator will save propellant compared with conventional attitude control system. A task-priority reaction null-space control method is applied to achieve the primary task of adjusting attitude and secondary task of accomplishing end-effector task. Furthermore, the algorithm singularity is eliminated in the proposed algorithm compared with conventional reaction null-space algorithm. And the singular value filtering decomposition is introduced to dispose the dynamic singularity, the unit quaternion is also introduced to overcome representation singularity. Hence, a singularity robust path planning algorithm of space robot for base attitude adjustment is derived. A real time simulation system of the space robot under Linux/RTAI (realtime application interface) is developed to verify and test the feasibility and reliability of the method. The experimental results demonstrate the feasibility of online base attitude adjustment of space robot by the proposed algorithm.     

自由飘浮空间机器人系统基座姿态调整

规划机械臂的运动以调整作为其基座的卫星的姿态，既节约姿控燃料，又可作为常规姿控系统的备份手段．首先，建立自由飘浮空间机器人系统的状态方程，其状态变量为关节角和卫星姿态角，输入变量为关节角速度．基于系统能控性理论，规划连接系统初始状态和期望状态的路径，实现了仅通过机械臂关节的运动同时控制基座姿态和机械臂关节角的目的．从理论上分析了机械臂的能量消耗，给出了使能量指标最小的近似最优算法．仿真结果表明了该方法的有效性．     

自由漂浮空间机器人的笛卡尔连续路径规划

对于自由漂浮空间机器人,位置级逆运动学方程不适合于笛卡尔连续路径的规划,而且机械臂的运动会对基座产生扰动.为此提出了基于速度级逆运动学方程的方法,可实现5个目标:1)惯性空间连续位姿跟踪;2)基座姿态无扰动的连续位置跟踪;3)基座姿态无扰动的连续姿态跟踪;4)基座姿态调整的连续位置跟踪;5)基座姿态调整的连续姿态跟踪.采用阻尼最小方差法回避动力学奇异,所规划的路径连续平滑.仿真结果表明了该方法的有效性.     

空间机械臂本体与末端抓手协调运动的自适应控制方法

讨论了载体位置不受控制的漂浮基空间机械臂本体与末端抓手协调运动的自适应控制问题. 对系统的运动学、动力学分析表明, 结合系统动量守恒关系得到的系统动力学方程及协调运动的增广广义Jacobi矩阵可以表示为适当选择的组合惯性参数的线性函数. 以此为基础, 对于系统存在未知参数的情况, 设计了本体姿态与机械臂末端抓手惯性空间轨迹协调运动的自适应控制方案. 上述控制方案的显著优点在于: 不需要测量、反馈飞行器本体的位置、移动速度及移动加速度. 仿真运算, 证实了上述控制方案的有效性.     

Mobile robot with a self-positioning system

This paper describes a general method using configuration space for planning a collision-free path of a manipulator with 6 degrees of freedom (DOF). The basic approach taken in this method is to restrict the free space concerning path planning and to avoid executing unnecessary collision detections, based on the idea that a collision-free path can be planned using only partial information of the configuration space. The configuration space is equally quantized into cells, and the cells concerning path planning are efficiently enumerated based on a heuristic graph search algorithm. A heuristic function which characterizes the search strategy can be defined to give priority to the gross motion using the first few joints. A bi-directional search strategy is also introduced to improve efficiency. The memory is allocated only to the portion of the configuration space concerning path planning, and the data of the free space defined in the 6-dimensional configuration space can be efficiently stored. This algorithm of free space enumeration is independent of the kinematic characteristics of the manipulator. Therefore, this method is generally applicable to any type of manipulator. It has actually been implemented and has been applied to a 6-DOF articulated manipulator.     

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.     

Motion planning in velocity affine mechanical systems

We address the motion planning problem in specific mechanical systems whose linear and angular velocities depend affinely on control. The configuration space of these systems encompasses the rotation group, and the motion planning involves the system orientation. Derivation of the motion planning algorithm for velocity affine systems has been inspired by the continuation method. Performance of this algorithm is illustrated with examples of the kinematics of a serial nonholonomic manipulator, the plate-ball kinematics and the attitude control of a rigid body.     

Autonomous Path Planning and Experiment Study of Free-floating Space Robot for Target Capturing

Space robotic systems are expected to play an increasingly important role in the future. The robotic on-orbital service, whose key is the capturing technology, becomes research hot in recent years. In this paper, the authors propose an autonomous path planning method for target capturing. The task is described in Cartesian space and it can drive the manipulator to approach the target along the closest path. Firstly, the target feature is extracted based on the measured information via the hand-eye camera, and the target pose (position and orientation) and velocities (linear velocity and angular velocity) are estimated using Kalman filtering technology. Then, a numerically feasible approach is presented to plan the manipulator motion and avoid the dynamic singularities, which are transformed into real-time kinematic singularities avoiding problem. Thirdly, the potential disturbance on the base due to the manipulator’s motion is estimated, and the joint rates are autonomously adjusted to reduce the disturbance if it is beyond the allowed bound. At last, a ground experiment system is set up based on the concept of dynamic emulation and kinematic equivalence. With the experiment system, the autonomous target capturing experiments are conducted. The experiment results validate the proposed algorithm.     

基于最小二乘法的桥式起重机机械臂关节控制系统设计

机械臂关节控制过程存在姿态误差,提出基于最小二乘法的桥式起重机机械臂关节控制系统设计;设计机械臂总体架构,达到级联组成末端位姿目的,使用全驱动灵巧手,包含1手掌和3手指,采用多个连杆串并联混合的形式传递运动和力矩,借助AT89C51单片机设计电路结构;采用最小二乘法构建机械臂的响应面模型,通过H-D参数法计算机械臂末端运动关节间位姿误差,建立误差模型,利用DETMAX算法分析运动参数,实现最小姿态选取,将机械臂运行速度数据记录在控制系统平台中,根据机械臂运行速度信息获取其均匀性控制状况,实现控制;激光测振仪的输出单位为1 mm/V,柔性机械臂的振动周期200ms,训练样本集大小为300,测试集样本大小为100,实验结果可表明,该方法机械臂关节运动拟合度与实际情况基本一致,位置跟随误差见效时间需要0.05～0.2 s,之后位置跟随误差便能够保持在较小的范围之内.     

Motion Planning Strategy for Finding an Object with a Mobile Manipulator in Three-Dimensional Environments

In this paper, we investigate the problem of minimizing the average time required to find an object in a known three-dimensional environment. We consider a 7-d.o.f. mobile manipulator with an 'eye-in-hand' sensor. In particular, we address the problem of searching for an object whose unknown location is characterized by a known probability density function. We present a discrete formulation, in which we use a visibility-based decomposition of the environment. We introduce a sample-based convex cover to estimate the size and shape of visibility regions in three dimensions. The resulting convex regions are exploited to generate trajectories that make a compromise between moving the manipulator base and moving the robotic arm. We also propose a practical method to approximate the visibility region in three dimensions of a sensor limited in both range and field of view. The quality and success of the generated paths depend significantly on the sensing robot capabilities. In this paper, we generate searching plans for a mobile manipulator equipped with a sensor limited in both field of view and range. We have implemented the algorithm and present simulation results.     

Disturbance rejection for space‐based manipulators

Most industrial manipulators operate from a fixed base. Hence, there are no disturbances from the environment to alter the position of the end‐effector. On the other hand, manipulators that are mounted on mobile platforms are subject to disturbances emerging from unwanted motion at the base. Similarly, manipulators that perform delicate operations in space while on board in‐orbit spacecraft experience disturbances. This article describes the design and implementation of a disturbance rejection controller for a 6 degree‐of‐freedom (DOF) programable universal manipulator for assembly (PUMA) manipulator mounted on a 3‐DOF platform. A control algorithm is designed to track the desired position and attitude of the end‐effector in inertial space, subject to unknown disturbances in the platform axes. Experimental results are presented for step, sinusoidal, and random disturbances in the platform rotational axis and in the neighborhood of kinematic singularities. ©1999 John Wiley & Sons, Inc.     

Dynamic modeling and vibration characteristics analysis of flexible-link and flexible-joint space manipulator

With the development of space technology, lighter and larger space manipulators will be born, of which flexible characteristics are more obvious. The manipulator vibration caused by the flexibility not only reduces the efficiency of the manipulator but also affects the accuracy of the operation. The flexibility of space manipulator mainly comes from structural flexibility of links and transmission flexibility of harmonic gear reducer in joints. The vibrations generated by these two kinds of flexibility are coupled and transformed mutually, making the dynamics characteristics of space manipulator system complicated. Therefore it is difficult to assess respective effects of these flexibilities on vibrations of the manipulator tip. And the characteristics of integrated vibration of manipulator tip with different link and joint stiffnesses are not very clear. In this paper, the dynamic equations of multi-link multi-DOF flexible manipulator are established. Then, vibration responses of the tip under different elastic modulus, damping and joint stiffness were studied, and vibration characteristics of the tip with both link and joint were also analyzed. Moreover, the effects of motion planning on the vibration of the tip were analyzed. Finally, the vibration characteristics of the manipulator with flexible joints and links are verified by a two-degree-of-freedom manipulator experimental system. Dynamics analysis results presented some useful rules for the path planning and control to suppress the vibration of the flexible space manipulator.     

空间机器人捕获运动目标的协调规划与控制方法

针对目标以任意轨迹运动且其轨迹可能与``有保证工作空间'不相交的问题, 提出了空间机器人捕获运动目标的协调规划与控制方法. 首先, 根据手眼视觉测量数据, 预测目标的运动路径, 由此确定空间机器人对目标的最优交会姿态及最佳捕获臂型; 其次, 规划基座姿态及机械臂关节角的轨迹; 最后, 采用协调控制的方法, 实现空间机器人系统对运动目标的最优捕获(以最优交会姿态及最佳捕获臂型对目标进行捕获). 仿真结果表明了该方法的有效性.     

基于hp自适应伪谱法的空间机器人路径规划

针对空间机器人运动过程中基座姿态产生较大扰动的问题,基于hp自适应高斯伪谱法提出了一种以基座所受反作用力矩最小为目标函数的空间机器人路径规划方法.首先,综合考虑空间机器人运动过程中存在的关节角度约束、关节角速度约束、控制力矩约束及初始状态和终端状态约束等约束条件,将空间机器人路径规划问题看成满足一系列约束条件和边界条件并实现特定性能指标最优的最优控制问题.其次,结合hp自适应高斯伪谱法（hp-AGPM）与非线性规划技术,求解带有边界约束和路径约束的优化控制问题,得到满足约束且性能指标最优的空间机器人运动轨迹.最后,以平面2自由度空间机械臂为例对所设计方法进行仿真验证,并与其他伪谱法进行对比分析.仿真结果表明：本文算法能在10.6 s的时间内规划出满足各约束条件且容许偏差低于10^-6的最优运动轨迹,并且在计算速度和配点数量上都优于其他伪谱法.     

基于速度修正项的机械臂避障路径规划

针对机械臂运行过程中存在的碰撞问题, 提出一种基于速度修正项的机械臂避障路径规划方法. 利用B 样条曲线进行机械臂关节空间规划, 使机械臂能够在特定时刻运行到指定构型. 在运行过程中, 利用碰撞检测算法实时计算机械臂与障碍物的最小距离, 在碰撞即将发生时引入积分为零的避障速度修正项改变机械臂运行轨迹, 使得机械臂能够在实现障碍回避的同时, 保证其在特定时刻通过指定构型的要求. 仿真实验表明了所提出方法的正确性和有效性.     

空间机器人目标捕获过程中的载体姿态扰动优化

针对自由飘浮空间机器人在捕获目标的过程中会对其载体姿态产生扰动的问题,提出了一种新的笛卡儿轨迹参数化方法.建立了反映载体姿态变化的日标函数,该函数既可以限制机器人关节角的运动范围,也可以避免动力学奇异的影响.利用遗传算法进行目标函数的优化,有效降低了空间机器人末端执行器在跟踪笛卡儿轨迹时对载体姿态的影响.仿真结果验证了...     

Analysis and acceleration of TORM: optimization-based planning for path-wise inverse kinematics

Autonomous Robots - A redundant manipulator can have many trajectories for joints that follow a given end-effector path in the Cartesian space, since it has multiple inverse kinematics solutions...