Research On The Low Velocity Movement Of The Electro-Hydraulic 6DOF Parallel Platform

For its high load carrying capacity, good dynamic performance and precise positioning, the electro-hydraulic 6dof parallel platform is used to all kinds of fields by generating general motion in space such as motion simulator, parallel machine, parallel manipulator, and so on. With the development of its application, how to improve the trajectory tracking precision of the platform in low velocity motion becomes more important in the field. The platform is a MIMO nonlinear system. There are all kinds of influencing factors that influence the smooth running and trajectory tracking precision of the platform in low velocity such as motion asynchrony, coupling disturbance force among the linear hydraulic actuators, the frictions of each pairing element and so on. So the low velocity characteristic of the platform is more complex. Through the general research on each aspect of the low velocity motion of the platform, the dissertation discloses the low velocity characteristic and regularity of the platform to improve the trajectory tracking precision of the platform in low velocity motion from control issue and design methods two sides.The dissertation consist of eight chapters, the main content of each chapter is as follow:The first chapter of the dissertation generally discusses the correlative background of the research. The low velocity crawl of mechanical servo system, electrical servo system and hydraulic servo system and the friction compensation research are introduced. At the same time, the each aspect research about the low velocity movement of the electro-hydraulic 6dof parallel platform is respectively summarized. At the end of this chapter, the support, significance of the research and main research content of the subject is illustrated.In the second chapter, the whole dynamics of the platform is deriving to found the theoretical basis of the research. In this processing, the frictions of each pairing element and the inertia of each cylinder take into account to build the system dynamic model. The third chapter has analyzed the each influencing factor about the low velocity characteristic of the joints and the platform based on the dynamics. The input/output transmission relationship of the platform in space is shown to disclosure low velocity characteristic of each degree of freedom of the platform. The simulation results of the low velocity characteristic of the system are shown to validate the analysis and the accuracy of the model by AMESim and MATLAB/Simulink tool.In the fourth chapter, a new design method is proposed to optimize each degree motion performance in the low velocity according to the low velocity characteristic of each degree of freedom of the platform in space. According to the characteristic, the global indices of each degree motion performance and the correlate cost function are present. At the same time, a new kinematic calibration method based on generalized force principle is proposed to improve the setting accuracy.In the fifth chapter, friction compensation research of cylinders based on LuGre model and closed loop gain scheduling of the whole platform in space are present to improve the trajectory tracking performance in the low velocity motion according to the friction characteristic of cylinders and the transmission relationship characteristic of the platform in space.In the sixth chapter, according to the disturbance force characteristic include the friction during the low velocity trajectory tracking process for the electro-hydraulic 6dof parallel platform, a mix compensator of the disturbance force is proposed in the chapter. Through analyzing the source and effect of the disturbance force, an adaptive robust compensator and the classical compensator based on structure invariance principle are designed to separately deal with the influence of different disturbance force.In the seventh chapter, according to the non-synchronization and coupling disturbance force among the hydraulic cylinder of the platform in low velocity motion, the position synchronization errors is investigated by considering motion synchronization between each actuator joint and the synchronization errors of cylinders. The position disturbance errors of each degree motion are investigated too. According to the compositive tracking errors which consist of the position errors and the synchronization errors, the robust controller is proposed to guarantee asymptotic convergence to zero of both the position errors and the synchronization errors in low velocity trajectory motion by backstepping design methodology. The adaptive law is deduced to deal with the unknown parameters of the platform. Finally, the low velocity performance of the platform is measured in space with the controller. The result validated the analysis of the third chapter. At the same time, the low velocity performance is measured in different pressure condition to express the influence of the system pressure of the oil. According the results and the analysis, the low velocity performance of the platform in whole design space can be known.In the eighth chapter, main research work, conclusion and innovation points of this dissertation are summarized. At the same time, future development of the platform about the low velocity motion research is predicted in order to provide references for the further research on this project.