Non-inverse kinematics of free-floating space robot based on motion planning of sampling

自由漂浮空间机器人无逆运动学基于采样的运动规划

¹ School of Astronautics, Northwestern Polytechnical University, Xi’an 710072, China
² National Key Laboratory of Aerospace Flight Dynamics, Xi’an 710072, China

Received: 9 November 2020

Abstract

Motion planning is one of the fundamental technologies for robots to achieve autonomy. Free-floating space robots composed manipulators and base satellite that do not actively control its position and attitude has nonholonomic characteristics, and there is a first-order differential relationship between its joint angle and the base attitude. In addition, the planning framework which first converts the goal end-effector pose to its corresponding target configuration, and then plan the trajectory from the initial configuration to the goal configuration still has the following problems: the goal configuration and the initial configuration may not be in the same connected domain. Based on the RRT framework, the motion planning of a free-floating space robot from the initial configuration to the goal end-effector pose is studied. In the algorithm design, in order to deal with the differential constraints of the free-floating space robot, and the requirement that the attitude disturbance of its base cannot exceed its limit, a control-based local planner for random configuration guiding growth of the tree and a control-based local planner for goal end-effector pose guiding growth of the tree that can adjust the attitude of the base when necessary are proposed. The former can ensure the effective exploration of the configuration space, and the latter can avoid the occurrence of singularity while ensuring that the algorithm converges quickly and the base attitude disturbance meets the constraints. The present algorithm does not need to solve the inverse kinematics, can successfully complete the planning task, and ensure that the base attitude disturbance meets the requirements. The simulation verifies the effectiveness of the algorithm.

摘要

自由漂浮空间机器人（free-floating space robot，FFSR）是进行在轨服务的重要工具，其基座姿态和关节角间存在复杂的一阶微分约束关系，进行运动规划时需直接考虑微分约束，这让其运动规划问题充满挑战。"先求逆运动学，再规划轨迹"的运动规划框架，存在目标构型与初始构型未必在同一连通域的隐患，为克服这一隐患，基于有目标偏置的RRT（GB-RRT）研究了FFSR从初始构型到目标末端位姿的运动规划问题。对于算法中的目标末端位姿导引生长，考虑到因FFSR执行机构自由度不足，而导致的末端位姿误差收敛与有效调节基座姿态相互矛盾的问题，提出适时调节基座姿态的目标末端位姿导引局部规划器，该局部规划器在保证末端位姿误差能够收敛情况下，兼顾基座姿态调节。此外，还设计了用于探索构型空间的随机构型导引生长局部规划器。将上述2种局部规划器与GB-RRT结合，可实现在不求解逆运动学的情况下，完成规划任务，且保证基座姿态扰动满足要求。仿真验证了算法的有效性。