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基于Clamped B样条的空间非合作目标抓捕策略研

AN OPTIMAL GRASP PLANNER FOR SPACE ROBOTS USING CLAMPED B-SPLIE

  • 摘要: 空间机械臂技术是未来实施在轨服务与维护任务的关键技术之一. 利用机械臂对空间非合作目标, 特别是翻滚目标的抓捕仍然存在巨大的挑战. 本文提出一种基于Clamped B样条的空间非合作目标抓捕策略方案. 在对非合作目标与空间机械臂运动学与动力学分析的基础上, 结合非合作目标被空间机械臂抓捕后的动静态对偶性分析, 构建抓捕后的力可操作度椭球作为抓捕策略设计的优化指标. 其次, 考虑目标的运动预测和空间机械臂的抓捕能力图谱构建, 确定空间机械臂应对目标的最优抓捕时机与抓捕终端状态. 基于Clamped B样条对空间机械臂各关节轨迹进行时间归一化参数描述, 并对抓捕过程中的机械臂关节角、速度、避撞、抓捕走廊等约束进行数学变换, 最终将抓捕策略转换为多约束、多目标的非线性优化问题, 利用自适应惯性权重的粒子群优化算法进行求解. 将所设计的抓捕策略应用于空间七自由度运动学冗余机械臂, 实现了对空间中翻滚目标的成功捕获, 验证了所提抓捕策略的可行性与有效性.

     

    Abstract: Space manipulator is one of the key technologies to carry out on-orbit servicing and maintenance missions in the future. Until now, it is still a vast challenging mission to capture a non-cooperative target satellite by using a space robot, especially when the motion of the target satellite is tumbling. How to design a feasible and optimal grasping strategy is very important for the successfully capturing of non-cooperative target. Based on the concept of the Clamped B Spline, this paper investigates an optimal grasp planner for a kinematically redundant space manipulator to capture an arbitrarily rotating target, such as space debris, dysfunctional satellites, etc. The kinematics and dynamics of the space robotic system and non-cooperative target in pre- and post-capture phases are firstly introduced as the foundation for designing the grasp planner. With consideration of the kineto-statics duality of the non-cooperative target captured by a space robot, the concept of the force manipulability ellipsoid was derived and employed as an optimization index in the following grasp planning strategy design. Subsequently, the space robotic optimal grasping time and the target's terminal motion states are determined with consideration of the robotic capability map, the target motion prediction and the grasping direction of the space robotic end-effector. Furthermore, the joint trajectories are parameterized with time normalization using the clamped B-spline curves. The grasp planner of the space robot is then transformed as a multi-constraint, multi-objective nonlinear optimization issue with consideration of the space robotic joint angle, velocity, collision avoidance and end-effector's grasping cone limits, and solved by a constrained particle swarm optimization algorithm with adaptive inertia parameters. The designed grasp planning strategy is applied to a seven degree-of-freedom kinematically redundant manipulator mounted on a free-floating spacecraft base, and the successful capturing of a tumbling target satellite in space is realized. Simulation results are presented and demonstrated the feasibility and effectiveness of the proposed method.

     

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