Modeling and control for a long-stroke 4-PPR compliant parallel mechanism

Long-stroke compliant parallel mechanisms (CPMs) are widely used in precision applications. However, stress stiffening and sensitivity to external disturbances in CPMs present challenges in the design of controller. In this paper, the nonlinear stiffness model of the stage is established which is incorporated into the dynamic model. In particular, the method of adaptive nonsingular fast terminal sliding mode control (ANFTSMC) is developed based on the dynamic model. This method addresses the problems of the system parameter uncertainty and the slow convergence of traditional sliding mode control (SMC) at the equilibrium point. The stability of the presented ANFTSMC strategy has been proved based on the Lyapunov analysis. Finally, the proposed control architecture is implemented on the designed 4-prismatic-prismatic-revolute (4-PPR) CPM. The results demonstrate that the developed method exhibits excellent tracking accuracy and robustness compared to the traditional linear sliding mode control (LSMC) and proportional-integral-derivative (PID) control.