Abstract: The multiple-order dynamic mathematical models of the multiple-input-multiple-output (MIMO) parallel manipulator driven by pneumatic muscles are developed, which comprise the dynamic model of parallel manipulator in task-space, the pressure dynamic model of pneumatic muscles and the average flow rate model of fast switching valves. In order to achieve highly accurate posture trajectory tracking with the guarantee of good transient performances in the parallel manipulator driven by pneumatic muscles, a discontinuous projection-based adaptive robust control strategy is proposed. The control strategy utilizes the parameter adaptation to eliminate the large parametric uncertainties, which arise from unknown parameters of dynamic mathematical models, and the robust feedback term to attenuate the rather severe nonlinear uncertainties, which arise from muscle force errors and time-varying friction forces of pneumatic muscles and unknown disturbances of parallel manipulator. Moreover, the proposed controller is based on backstepping design technology and so is fit for the MIMO multiple-order coupling dynamics system. Experimental results indicate that the parallel manipulator has strong self-adaptability and robustness with the steady error of step response being less than 0.09° and the average tracking error of continuous trajectory tracking being less than 0.15°.

Key words: Adaptive robust control, Discontinuous projection, Parallel manipulator, Pneumatic muscle, Trajectory tracking