Dynamics and Control of a Flexible-Link Flexible-Joint Space Robot with Joint Friction

Multi-DOF flexible space robots play a significant role in the on-orbit service. The flexibility of the robots is mainly caused by the flexible links and some flexible drive elements in joints. The vibration generated by the component flexibility can affect the accuracy of control. In this paper, the dynamics and control issues of flexible-link flexible-joint (FLFJ) space robots considering joint friction are studied. Firstly, the Spong’s model is employed to depict flexible joints, and the Coulomb friction model is adopted to describe joint friction. Then based on the single direction recursive construction method and velocity variation principle, dynamic equations of the system are derived. Secondly, a trajectory of joint motion is given and a trajectory tracking controller with friction compensation is designed with the computed torque method. Finally, several numerical simulations are carried out to verify the accuracy of the dynamic model and illustrate the effect of joint friction and joint flexibility on the dynamic characteristics of space robots. Besides, simulation results suggest that the controller designed in this paper could effectively achieve the trajectory tracking control for the 6-DOF FLFJ space robot with joint friction.