Control Of Planar 2-DOF Redundant Parallel Manipulators

With the advantage of high precision and heavy load capacity, parallel robot has been widely used on the occasion of less demanding work space and high precision motion. Parallel manipulator is composed of a number of parallel moved chains. The complexity of its structure and the existence of the singularity problem limit the parallel manipulator to maximize its applications. Redundant drive can eliminate the singularity of parallel manipulator, and improve the performance of the kinematics and dynamics of the system.Based on planar two degrees of freedom redundant parallel robot, this thesis introduces a nonlinear saturation function to improve the typical augmented PD controller and computed torque controller, and two new controllers named nonlinear augmented PD and nonlinear computed torque are proposed. Lyapunov direct method and La Salle invariance principle are employed to prove the global asymptotic stability of the closed-loop system. The effectiveness and improved performances of the proposed controllers are verified through numerical simulations.In order to obtain higher control precision and coordination, based on cross coupling strategy, a synchronous control is proposed by selecting the contour error as synchronous error, to realize the synchronized motion of the end effector along X and Y direction. In this thesis a sliding mode item has been introduced to realize the global asymptotic stable tracking. Global asymptotic stability of the closed-loop system is proven. The sliding mode item is discontinuous, which leads to the existence of the chattering of the torque in the active joints. So, a class of continuous sliding mode control strategy is modified. Numerical simulations are presented to demonstrate the effectiveness of the proposed controllers.