Compliant grasp strategy for three-fingered space robot end-effector

When space robot is capturing an object, the disturbance force produced by interactive collisions may induce the robot arm dithering and distortion; moreover, it may also pop-up the target object away from the capture zone, which will lead to the failure of capturing operation. To solve this problem, the design of three-fingered space robot end-effector of Harbin Institute of Technology (HIT) is introduced firstly, and then the disturbance force produced by interactive collisions during the progress of grasping a target object is analyzed. A compliant grasp strategy is proposed to weaken the interactive collisions disturbance force, and a new structure of controller based on the combination of feed-forward compensation and fuzzy-sliding mode control is proposed. The deterministic disturbance, the linear part of the friction, and the part associated with end-effector's structure itself can be gained by modeling and off-line testing, which can be controlled effectively by feed-forward compensation, and the fuzzy mode control rules can compensate the external uncertain disturbance, nonlinear part of friction, grasp force and so on. Using satellite on-orbit self-servicing manipulator and three-fingered space robot end-effector designed by Harbin Institute of Technology, some grasp experiments are performed on micro-gravity platform. Experimental results show that the proposed strategy and the designed controller can effectively eliminate the disturbance force during grasping.