Robust decentralized joint control of a 3-PRS parallel mechanism based on a simplified model

In this paper, a simplified dynamic model is proposed for a 3-PRS (Prismatic, Revolute, Spherical) parallel mechanism. The dynamic model is formulated in the joint space where three holonomic constraint equations are constructed to specify the coupling relationships between the actuated legs. Since the symbolic expressions of the dynamics for the moving platform are complicated in the joint space, they are simplified and only the gravity force is considered. Based on the simplified model, a robust decentralized joint control algorithm is proposed where a disturbance observer is embedded in the control loop to compensate the disturbance resulted from the simplification. Computer simulation is performed on a circular cutting trajectory to investigate the effectiveness of the proposed simplified dynamic model.