Abstract: Sliding mode control is applied in space robot capturing floating target with soft-hard grasping. Capturing operations become quite complicated and important for the nonlinear characteristics such as the dynamic coupling between the arm and the base, the impact excitation during grasping when the space robot captures a floating object. The dynamic model of the space robot and floating target is established, and then the impact dynamic model in grasping is introduced. The dynamic grasping area and the sliding mode control is applied for the arm grasping control to reduce the impact interference to the space robot, while the attitude control of the base with the error quaternion method is used to keep the base stable. The sliding mode surface parameters denote the impact-resistance ability of keeping and tracking status, which can be changed for various grasping characteristics: hard grasping as touching and soft grasping as colliding. The simulation results indicate that hard grasping as continuous contact can keep the arm rigidity as the joints change little, while the soft grasping can make the arm moving for energy dissipation as the joints change a lot, but the impact to the attitude of target and the position of base is little, about 50% that of the hard grasping. The results have important academic value and engineering significance.

Key words: Dynamic grasping area, Grasping impact, Sliding mode control, Soft-hard grasping, Space robot, Analytical formulae, High-speed train, Residue theorem, Root mean square value of vibration response, Secondary vertical suspension system