空间机器人可有效地执行风险较高、不易到达及常规性的任务，尤其空间机械臂的使用更为广泛，在过去三十年间已有许多关于空间机器人的理论发展与验证。在空间机械臂执行任务时，手臂末端与目标物的相对速度不为零，故手臂末端与目标物的接触点上会产生碰撞力。空间机械臂的基座与手臂有着耦合关系，碰撞力除了造成基座姿态扰动之外，若关节间的接触力过于集中于某一关节，则空间机械臂的关节处会因为无法承受过大的接触力而损坏。本文以冗余空间机械臂为模型，建立平面的运动学模型与动力学方程，并将关节处视为非理想的。由于间隙存在，空间机械臂的关节处有接触力的产生。本文结合他人研究成果推导出新的接触力模型，仿真间隙存在与间隙大小对空间机械臂的影响，并且考虑间隙速度项得到动量守恒与角动量守恒方程。间隙存在会降低空间机械臂之稳定性与精确性，本文考虑关节处接触力，推导出的带间隙空间机械臂控制器，可以解决这个问题。空间机械臂抓取目标物时，假设关节处为理想的情况下，只能计算出两者碰撞后的初始状态，若将关节处视为非理想的情况下，可视为瞬间完成的碰撞过程还原为非瞬间完成。藉由还原碰撞过程模拟不同欲碰撞构型之关节处接触力，可以寻找更适合抓取目标物的欲抓构型。本文基于平均分布碰撞后最大接触力与降低抓碰撞的最大总接触力，分别给出两个优化指标。除此之外，由模拟结果证明广义直臂抓取策略比直臂抓取策略更能减少关节处的最大接触力。由于近似弹簧的手臂构型更能平均分布抓取后之最大接触力，本文比较四个相同手臂与五个手臂的冗余空间机械臂抓取同一目标物之关节处接触力，并且采用结合广义直臂抓取及软接触方法的抓取策略，由上述两种优化指标与抓取后基座姿态扰动最小的优化指标选取欲碰撞构型。由模拟结果可知，即使近似弹簧的手臂构型能够平均分布抓取后的最大接触力，尚无法有效地降低末关节处的最大接触力。
Space robots can effectively perform tasks that are more risky, unreachable and routine, especially space manipulators are used more widely. Over the past three decades, there have been many theoretical developments and validation of space robots. When a space manipulator performs a task, because of the relative velocity between the end effect and the contact point of the target is non-zero, it generator an impact force in the end effect and the contact point of the target. The base of the space manipulator has a coupling relationship with the arms. Except the impact force causing an attitude disturbance of the base, if contact forces at joints is too concentrated at certain joints, the joints of the space manipulator will be damaged by bearing oversized contact forces.In this paper, a redundant space manipulator is used to create a planar kinematics model and a dynamics equations, and the joints are treated as non-ideal joints. Due to the presence of the clearance at joints, there are contact forces at the joints of the space manipulator. In this paper, a new contact model is derived from the results of others and simulates the influence of the existence and size of clearance. Considering the velocity terms of the clearance, the momentum and angular momentum equations will be conserved. The existence of the clearance will reduce the stability and accuracy of the space manipulator, this paper considers contact forces at joints to derive a controller for solving above problems.When a space manipulator captures a target, it can only calculate the initial state of post-phase in the situation which considers joints as ideal joints, but in the case of joints as non-ideal joints, it can restore the impact process deemed instantaneously to a non-instantaneous completion. By restoring the impact process to simulate contact forces at joints in different configurations, it can find the pre-impact configuration which is more suitable for grasping the target. Based on the average distribution and total of the maximum contact force after impact, this paper gives two optimization index respectively. Otherwise, the simulation results show that the generalized straight capturing strategy can reduce the maximum contact force at joints more than the straight capturing strategy.Because a spring-like arm configuration can average the maximum contact force more than others, this paper compares contact forces at joints in a redundant space manipulator with four same arms and five arms to grasp the same target and uses a combined strategy of generalized straight capturing strategy and soft contact method. Choosing a pre-impact configuration by above two optimization index and optimization index of minimum attitude disturbance of base, the simulation results show that even spring-like arm configuration can more average the maximum contact force, but it can’t reduce the maximum contact force at the end joint effectively.
