A Control Strategy of a Two Degrees-of-Freedom Heavy Duty Parallel Manipulator

The motion accuracy of a heavy duty parallel manipulator is usually low due to time lag and the difficulty to real-time measure the position of the end-effector. In this paper, a dynamic modeling of this system with consideration of the link flexible deformation is proposed, and a double-feedforward control is presented. The link deformation is considered in the kinematic model. Taking link deformation into account, the dynamic model is derived for real-time application, and the inverse dynamic compensator is designed. The zero phase error tracking controller (ZPETC) is introduced as the second compensator. The system stability is investigated by simulations. The control method is compared with the kinematic-based control without consideration of link deformation. The results show that the maximum contouring error reduces from 7.5mm to 10 mu m. Thus, the tracking performance is improved when using the method proposed in this paper.