A strategy to decelerate and capture a spinning object by a dual-arm space robot

With the increasing requirement of grasping the non-cooperative objects in space by space robots, this paper introduces a new strategy operated by a dual-arm space robot. The strategy includes path planning to capture a spinning target, hybrid control of the motion and the contact force for the end-effectors, coordinated control of the base attitude, and parameter identification of the spinning target during the capture phase. Notably, a pair of proper contact forces can be applied to the two grasp points of the spinning target by the two manipulators, which can decelerate the spinning speed of the target and be utilized to identify the target's moment of inertia around its spinning axis. Considering the non-cooperative situation with the spinning target like a defunct satellite, the uncertainties of the space robot and the target, such as parameters of mass and moment of inertia, are concerned in the design of the Sliding Mode Controller (SMC) with good robustness. Moreover, due to the coupling movement of the base and arms of a dual-arm space robot, the base attitude will be simultaneously maintained by the mounted reaction wheels during the capture operation for good communications and effective solar energy collection. The post-capture process is also presented in the paper to bring the entire system of the space robot and the target into stationary status. To compare the system performance against the uncertainties by different controllers, PID-type Computed Torque Controller (CTC) and SMC are designed together for comparison. When the uncertainties of the mass and the moment of inertia are applied to the system, the simulation results show that SMC has better performance against the uncertainties by delivering higher accuracy of the tracking errors to the desired trajectories than CTC.