Analysis of dynamics and design of sliding mode controller for a 3-DOF translational parallel robot mechanism

For a 3-DOF translational parallel robot mechanism 3-RRC, firstly, the position analysis is done in order to rind out in real time the desired angular displacements of active joints in terms of the movement requirement for the mechanism's moving platform. Secondly, the dynamics of the mechanism is analyzed and simplified in order to calculate in real time the main equivalent torques of the robot mechanism on active joints. On the basis of the above, the control scheme is proposed and the system model considering the main equivalent torques of the robot mechanism on active joints is developed. Then, a practical chattering-free sliding mode controller is designed. Its requirement for guaranteeing the sliding condition is analyzed. Finally, the motion control of the mechanism is implemented by simulation. It is shown from the simulation results that the parallel robot system using the designed controller, in digital implementation, does not have the chattering problem. The controller is robust to the torque action of the robot mechanism on active joints and the plant parameter variation, has good performance in tracking and is easy to implement.