Research On Mechanism Characteristic And Adaptive Control Of Stewart Platform

Since the Stewart parallel mechanism was born, its structure has been widely applying to the field of motion simulator, by virtue of its advantages of high loading capability, high stiffness, high force-to-weight ratio, compact structure and so on. In this paper, a type of 6-UCU Stewart is designed according to the performance index, and the Stewart platform mechanism characteristics and control strategy are studied.Firstly, according to the motion parameters, the trajectory along unidirection of top platform is determined. Then, the inverse kinematics of the Stewart parallel mechanism is carried out by using the influence coefficient method, and the single rigid body dynamic equation is established. Based on the pose inverse kinematics, the Stewart parallel mechanism satisfying motion performance index is designed. The 3D modeling of the structure is carried out, and the kinematic simulation is achieved under Adams software.Secondly, in consideration of its small working space comparing to the series mechanism, the work space of Stewart parallel mechanism is analyzed under consideration of link length limitations, joint angle constraints and link interference constrains. At the same time, the vibration mode of the mechanism based on Adams is established and analyzed to recognize its structure characteristics among links and the top platform.Thirdly, according to asymmetric cylinders driving Stewart parallel mechanism are controlled by the symmetrical valve, the transfer function is educed. In Accordance with the control system transfer function and inverse kinematics, the Simulink model is built and co-simulation is accomplished with Adams. Because damping ratio along unidireciton is small according to co-simulation results, and considering structural characteristics along each degree of freedom, the pressure feedback correction is implemented and the typical response characteristics of each degree of freedom are analyzed.In view of the fixed value of ordinary PID parameters, it is difficult to adapt to Stewart nonlinear, variable parameter etc. In this paper, adaptive tuning PID parameters based on model reference adaptive control is implemented, making it has certain adaptability and anti-interference performance. In the end, the Adams and Simulink cosimulation of the control strategy is verified.