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中文核心期刊

一种改进 RRT* 结合四次样条的协调路径规划方法

COORDINATED PATH PLANNING BY INTEGRATING IMPROVED RRT* AND QUARTIC SPLINE

  • 摘要: 针对空间机器人抓捕空间非合作目标的在轨服务任务,同时考虑机器人运动学约束和动力学约束,提出一种分层式的自由漂浮双臂空间机器人协调路径规划方法. 首先,在路径规划层面上基于 RRT* 算法分别规划双臂末端执行器在笛卡尔空间下的初始可行路径,为双臂设置独立的采样空间,保证路径规划过程中双臂系统不发生自身碰撞. 然后,在轨迹规划层面上利用四次样条曲线平滑 RRT* 算法生成的初始路径,设计满足样条曲线的一阶、二阶及三阶微分连续约束,同时考虑机械臂末端执行器的初末速度约束条件、初始加速度约束条件,得到适合于空间机器人执行的动力学可行的平滑 轨迹.最后,计算所规划路径的最大速度、最大加速度与机械臂末端执行器物理极限值的比值,取最小上限,即为最少路径规划时间. 所提路径规划方法能够设计出满足特定路径点约束的协调路径,且所设计的路径考虑了机械臂的物理限制条件,通过对自由漂浮双臂空间机器人进行仿真试验,验证了所提路径规划算法的有效性.

     

    Abstract: In order to perform an OOS (on-orbit servicing) mission of capturing a space non-cooperative target by space robot, this paper proposes a hierarchical coordinated path planning method for the free-floating dual-arm space robot, in which we consider the robot's constraints both kinematic and dynamic at the same time. First of all, a feasible end-effectors' path is initially planned via a state-of-the-art sampling-based method, named RRT* algorithm, in the Cartesian space, in which the sampling space is separated for two arms for the sake of possible self-collision avoidances of the dual-arm system during the high level of the path planning stage. Secondly, quartic splines are employed to smooth the path planned by RRT* algorithm during the low level of the trajectory planning stage. By designing the first-order derivative, the second-order derivative as well as the third-order derivative of these quartic splines, continuous differential constraints of the robot's path are well guaranteed. More importantly, we should integrate the robot's dynamic constraints within the design of differential constraints, such as the initial velocity, the initial acceleration and the final velocity of the end-effectors. After that, a smooth trajectory considering certain boundary constraints is obtained, which is dynamically feasible for the robot execution. Finally, the time of the whole path execution is calculated by considering the maximum physical limitation of the end-effectors. The minimum upper limit of maximum velocity and maximum acceleration of planned path of the end-effectors over its physical limitation is the minimum execution time. The proposed path planning method could design a coordinated path satisfying certain waypoints constraints for the robot. Besides, the physical limitation of the robot is also considered for the planned path. Moreover, the proposed path planning method is successfully validated on a free-floating dual-arm space robot and simulation results demonstrate the effectiveness of the proposed path planning method.

     

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