Design Of Planar 3-RRR Parallel Positioning Platform And Control System

As a typical parallel mechanism, three-DOF parallel positioning platform has broad application prospects. In this thesis, a planar 3-RRR parallel positioning platform and its control system are designed, which can provide the basis experimental platform for the following vibration suppression development of precision positioning platform system.First of all, the inverse and forward kinematics models of the planar 3-RRR parallel positioning platform are presented, and through using the Broyden method, the forward kinematic numerical solution is conducted. Based on the first-order influence coefficient method, the singular configuration of the platform is studied. The maximum and fixed pose workspaces are derived, as well as the workspace with different structure parameters and poses are analyzed.Secondly, modal characteristics of the active and collecting rod are theoretically analyzed and simulated using finite element method, and results of theoretical calculation and finite element simulation turn out to have similar results; The modal characteristics of the platform are analyzed by using FEM, as well as the variation under designed trajectory, from which some useful suggestions that contribute to the motion control are obtained.Thirdly, an economic and open hardware system consisting of PC, motion control card, step motor and detection system is constructed. The influence of subdivision number of motor driver on the vibration of step motor is analyzed and tested experimentally. A position detection system, a control system developed by Lab VIEW and the closed-loop PID algorithm is designed. According to the results of the modal analysis, the approach to avoid the singular point and vibration are put forward.Finally, test experiments of the parallel positioning platform and its active rod’s modal characteristic are carried out, compared to the simulation results, the error of first four order natural frequencies is small than 10%, which indicates that the results of the simulation model and experimental model are well consistent. The control system is also tested experimentally, and the results reveal that the closed-loop control system has a good tracking performance.