Research On Pose Tracking Control Of Four Degree Of Freedom Parallel Platform

In a simulation of the actual motion of the vehicle, the tracking control of the platform target pose is one of the important performance indexes, and it is also a hot spot in the research of the motion control of the parallel platform in recent years. Due to the parallel platform is a typical nonlinear, strong coupling and multi-input multi-output(MIMO) time-varying system, therefore, in the motion process of the platform, it is often affected by the uncertain disturbance(joint system internal parameter perturbation, nonlinear joint coupling force and external disturbance force etc). so, the traditional control method is difficult to meet the fast, stable and high precision motion control requirements. This paper, basing on four degree of freedom parallel platform as its research object and designing good robustness, good control performance as the goal, does a thorough research on platform motion control technology. The main research contents are as follows:Firstly, the kinematic model of the platform is established. By using the method of additional displacement sensor, the forward kinematics equation of the platform is obtained. Based on the principle of spatial coordinate transformation, the inverse kinematics equation of the platform is obtained.Secondly, considering the complexity, economy and stability of the system control, the decentralized control method, which realizes the fast, stable and high accuracy pose tracking control of the platform through the high precision tracking of each joint branch, is proposed. On the basis of decentralized control method, the control method and mathematical model of joint branch are established, and the design of hardware and software of the control system is completed.Thirdly, the joint branch controller is designed. Considering the influence of the internal parameter perturbation, unmodeled dynamics of the joint servo system on the tracking effect, using a variable gain reaching law sliding mode algorithm to design the joint controller, which can effectively weaken the jitter of sliding mode controller output, improve the dynamic response and the tracking precision of the system; Considering the insensitivity of sliding mode variable structure control for mismatching external uncertainty interference(load disturbance and joint coupling force, etc.), the variable gain sliding mode joint controller based on nonlinear disturbance observer(NDO) is designed, which improves the anti-disturbance and robustness abilities of the system, and realize the fast, stable, high precision tracking control of the joint branch.Finally, on the basis of distributed control, the simulation of multi-freedom pose tracking of platform was carried out by using the joint controllers(variable gain sliding mode joint controller and SMC-NDO joint controller). The simulation results show that, in the case of internal parameter variations of servo system and external different disturbances exist, the SMC-NDO joint controller, still be able to achieve fast, stable, high precision of pose tracking of platform, and achieve a good control effect.