Performance Improvement of Tracking Control for a Planar Parallel Robot Using Synchronized Control

In order to improve trajectory tracking accuracy for a three degree-of-freedom (DOF) planar parallel robot, in this paper, we develop a new control approach based on adaptive control with the use of the so-called synchronization error. Similar to the contour error proposed for machine tools, the defined synchronization error represents the degree of coordination amongst the active joints in the parallel robot, which is substantially different from the traditional tracking errors. By using the synchronization error, all active joints in the parallel robot are controlled to move in a synchronous manner so that the trajectory tracking accuracy of the robot end-effector is substantially improved. In addition, with the use of adaptive control, the synchronization error and the pose error of the platform are guaranteed to converge to zero simultaneously, while uncertain parameters in the system dynamic model are guaranteed to converge to their true values. Experiments conducted on the planar parallel robot verify the above claims and evaluate performance of the proposed control approach, compared with conventional PID control