Motion Capability Optimization of Space Manipulators with Free-Swinging Joint Failure

Space manipulators are usually used to assist or replace the astronaut to execute on-orbit tasks. However, due to the burdensome tasks and harsh space environment, free-swinging joint failure is prone to happen. Because the faulty joint cannot provide torque, the motion capability of the manipulator will degrade, easily causing the task to be unable to continue. To satisfy the task requirement, a motion capability optimization method is proposed. First, we establish the kinematics and dynamics model of the faulty manipulator. Second, the dexterity and load operation ability indexes of space manipulator with free-swinging joint failure (SMFSJF) are constructed. Third, by using a sixth-order polynomial function with superfluous parameter to describe the trajectory of the active joint and end-effector, a trajectory optimization model is established. Through solving the optimization model based on the particle swarm optimization (PSO) algorithm, the optimal trajectory of SMFSJF is obtained. The simulation experiments are carried out with a 7-degree of freedom (DOF) space manipulator, verifying the correctness and effectiveness of the optimization method. The method has two advantages: (1) the motion capability of space manipulators with free-swinging joint failure is analyzed for the first time; and it is pointed out that compared with the faultless manipulator, the motion capability of the faulty manipulator is greatly degraded; and (2) by constructing the trajectory optimization model with superfluous parameter, the trajectory optimization is realized based on the PSO algorithm. It ensures that the task can be executed successfully by the manipulator with the optimal motion capability.