Research On The System Characteristics And Attitude Control Method Of Hydraulic Driving Spherical Wrist

In this dissertation,taking the hydraulic driving spherical wrist as the research object and the high-performance attitude control of the full hydraulic driving spherical wrist as the goal,the system characteristics and high-performance attitude control strategy of the three degree of freedom spherical wrist drive by hydraulic are studied.Firstly,the mechanism composition and working principle of hydraulic driving spherical wrists are analyzed in detail,and the hydraulic driving scheme and motor driving scheme are compared and analyzed.The feasibility of adopting hydraulic driving scheme for spherical wrist is analyzed theoretically,and the three-dimensional mechanism model of hydraulic driving spherical wrist is established in SOLIDWORK.Secondly,considering the characteristics of the electro-hydraulic driving system and the dynamic characteristics of the wrist mechanical structure,a nonlinear comprehensive dynamic model of the independent motion of each joint of the wrist is established.And the comprehensive description of the overall dynamic behavior of each joint of the full hydraulic driving wrist is realized.At the same time,the system model of the wrist output attitude tracking is established,and the reasons of strong nonlinearity,strong unmatched uncertainty disturbance and strong coupling in the established comprehensive dynamic model are analyzed theoretically.Based on the established comprehensive dynamic model,the effects of electro-hydraulic driving system dynamics and wrist mechanical structure dynamics on the dynamic performance of wrist joints were studied.Thirdly,a sliding mode back-stepping recursive control method is proposed to solve the problems of strong nonlinearity,strong unmatched uncertain disturbance and strong coupling in the hydraulic spherical wrist system.The combination of sliding mode control theory and back-stepping recursive controller design method gives full play to the advantages of sliding mode control and back-stepping recursive control method,which can effectively suppress the unmatched disturbance in the case of unknown accurate model.In the design process of sliding mode back-stepping recursive control algorithm,a new smooth continuous sliding mode control law is proposed,which not only solves the design conflict between sliding mode theory and back-stepping control method,but also improves the high-frequency chattering phenomenon in the switching process.The stability of the sliding mode back-stepping control algorithm and the convergence of tracking error are analyzed by Lyapunov theory.Finally,sliding mode back-stepping controller is designed for wrist attitude control when each wrist joint acts separately and simultaneously.Based on the co-simulation platform composed of Recur Dyn,AMESim and Matlab/Simulik,a virtual prototype of the full hydraulic driving spherical wrist is established,and the control performance of sliding mode back-stepping controller and PID controller to the virtual prototype is compared.The results show that: the sliding mode back-stepping controller can effectively suppress the uncertainty in the system,and achieve high performance tracking performance of the wrist to the reference attitude trajectory.Compared with PID controller,the tracking performance of sliding mode back-stepping controller is significantly improved and has stronger robustness.