Control System Design Of High Precision 6-DOF Parallel Platform

To ensure the imaging quality of large telescope,secondary mirror adjustment mechanism is needed to adjust the pose of secondary mirror.The 6-DOF parallel platform is widely used in secondary mirror adjustment mechanism because of its high accuracy and high rigidity.However,due to the small size and high precision of the secondary mirror adjustment mechanism,the domestic 6-DOF parallel platform has not yet met the requirements.At present,the high precision parallel platform in China still depends on the import.In order to change this situation and realize the localization of the secondary mirror adjustment mechanism,our laboratory has collaborate with CIOMP(Changchun Institute of Optics,Fine Mechanics and Physics)to develop a high-precision parallel platform.In this thesis,kinematics and inverse kinematics,motion control and zero point determination of parallel platform are studied,and the software and hardware design of control system is completed.The main contents are as follows:Firstly,the structure of the parallel platform is introduced,and its kinematics model is established,and the analytical form of the inverse position solution is given.Next,two positional forward solutions,Gauss Newton method and neural network method,are introduced.According to their respective characteristics,the two solutions are applied to the precise pose calculation and the real-time display of the 3D model of the platform respectively.Secondly,the control strategy of parallel platfcrm is introduced.Track the platform in workspace to ensure smooth operation of the platform without exceeding the workspace.In the joint space,the speed voltage relationship of the outrigger is modeled and identified.The obtained model information is introduced into the linear extended state observer to obtain the linear expansion state observer assisted by the model,which speeds up the convergence rate of the observation state.The ADRC(Active Disturbance Rejection Control)is adopted in the speed loop,and good control effect is achieved.The P + feed-forward compound control strategy is adopted in the position loop,which achieves better tracking accuracy for the planning curve and is able to stabilize the target location at a faster speed.Then,the software and hardware implementation of the parallel platform control system is introduced.The hardware design of the lower machine,the design of the incremental encoder interface circuit in FPGA and the velocity measuring circuit of T method,the design of the software of the lower computer in DSP and the design of the host computer software using the LabVIEV are introduced in detail.Next,the method of determining zero point by using the special designed incremental encoder interface circuit,with the limit signal and the zero reference signal,is introduced.Experiments show that this method can greatly reduce the risk of zero point offset in traditional method with limit signal and zero reference signal.Finally,a parallel platform motion control experiment is carried out.The experiment shows that the motion of the platform is stable under the control of the control system designed in this thesis,and it can be stable in the target rapidly.