Research On Control Strategy And Performance For Planar 2-DOF Parallel Manipulator

For the multiple kinematic chains, the mechanism structure of parallel manipulator is much more complex than serial manipulator. The kinematics and dynamics of parallel manipulator are very complex. The coordinated manipulation of the end-effector with multiple kinematic chains makes the motion control of parallel manipulator challenging. In this dissertation, based on a planar 2-DOF parallel manipulator, theory and experiment of the motion control for the parallel manipulator were studied from three aspects, including torque transmission, friction compensation and controller design. The main work is as follows:(1) Based on the inverse kinematic, relations between the torque transmission and the kinematic configuration of the planar 2-DOF parallel manipulator were studied with the condition number of velocity Jacobian matrix, and the optimal kinematic configuration was solved.(2) Considering the nonlinear friction in the planar 2-DOF parallel manipulator, a nonlinear model with exponential functions was used to construct the friction of the parallel manipulator, and a nonlinear friction compensation method was proposed. The friction compensation performances were compared between the proposed friction compensation method and the existing friction compensation methods.(3) By combining the nonlinear PD (NPD) control with the typical augmented PD and computed torque controller of the robot manipulator respectively, two new dynamic controllers of augmented NPD and computed torque NPD were proposed. The two new controllers were used to control the planar 2-DOF parallel manipulator, and the asymptotic stability was proved in theory. In the actual trajectory tracking experiment of the parallel manipulator, the proposed controllers were compared with the two typical controllers.(4) A nonlinear adaptive controller in the task space was designed for trajectory tracking of the planar 2-DOF parallel manipulator. The parameter adaptation law was derived with the gradient descent algorithm, and the control law was designed based on the augmented PD controller. The stability of the parallel manipulator system was proved by the Lyapunov stability theorem, and the convergence of the tracking error and the error rate were proved by the Barbalat lemma. The designed controller was implemented in trajectory tracking experiments of an actual planar 2-DOF parallel manipulator, and the experiment results were analyzed in detail.(5) Considering the coordinated motion of the multiple kinematic chains in parallel manipulator, two synchronization controllers were proposed for the planar 2-DOF parallel manipulator with the synchronization control idea. Firstly, the active joint-synchronization (AJ-S) controller was proposed. The dynamic model of the parallel manipulator was formulated in the active joint space, and the AJ-S control law was designed based on this dynamic model, then the asymptotic stability of the parallel manipulator was proved in theory. The AJ-S controller was implemented in the trajectory tracking experiments of an actual planar 2-DOF parallel manipulator. When designing the AJ-S controller, the constraint force between the kinematic chains must be considered, and the acceleration using for the calculation of the constraint force was difficult to be measured. Thus, the contour error-synchronization (CE-S) controller was proposed, the compensation item of the constraint force was not contained in this controller. At first, contour error was introduced to define the synchronization behavior of the parallel manipulator; then the CE-S controller was designed based on the dynamic model in the task space; finally, the asymptotic stability was proved in theory, and the experiment results of trajectory tracking were compared between the AJ-S controller and the CE-S controller.