Trajectory tracking control of space robot actuated by control moment gyroscopes

A new design concept of space robotic system was proposed, as well as a trajectory tracking control approach. Unlike traditional manipulator arms, the space robot employs free ball joints as manipulator link connections. A group of control moment gyroscopes (CMGs), serving as torque actuators, was mounted on each link and the base. The modified Rodrigues parameters (MRPs) were employed to describe the attitude of the base and the links, and the equations of motion were derived by using Kane's equations. To accomplish trajectory tracking control of both the base position/attitude and the end effector position, a control law was designed using the inverse dynamics method. A steering law with null motion was adopted for each group of CMGs to achieve simultaneous desired torque output and singularity configuration avoidance. The simulation results based on a two-joint space robot system with pyramid-configuration CMGs demonstrate the effectiveness of the proposed control law and steering law, as well as the ball joint advantage in increasing the degrees of freedom of the end effector and decreasing the system dynamical coupling.