Research On Servo Control Method Of Hydraulic Wrist Joints

Robot has been widely used in the fields of national defense equipment,aerospace,nuclear industry,etc.Wrist as an important component of robot determines the attitude of the end actuator,and the structure and control performance of wrist joint directly affect the flexibility and positioning accuracy of wrist.The research object of this paper is a kind of hydraulic 3-DOF spherical wrist.Its pitch and side swing joints are driven by single rod hydraulic cylinder,the rotation joint is driven by hydraulic motor and the motion of three joints is decoupled.The 3D model of wrist is built and the motion simulation is carried out by UG simulation platform,which verifies the feasibility of wrist joint structure.Based on the spatial geometry of the ball wrist,the mapping relationship between the driving space and the joint space is analyzed.Through the analysis of the mapping relationship between the joint space and the working space,the kinematic relationship between the wrist workspace and the driving space is established,which is prepared for the angle control of the spherical wrist joint.The hydraulic drive three degree of freedom spherical wrist joint is driven by the asymmetrical hydraulic cylinder controlled by the servo valve.The valve controlled electrohydraulic servo system has the characteristics of uncertainty and nonlinearity,and the wrist joint may be subject to external random interference during the rotation.In view of the above problems,an output feedback control strategy based on disturbance observer is adopted to control the angle of wrist pitch and side sway joint.By reducing the order of the joint hydraulic drive system model,the system model is simplified and the system mismatch interference is solved.The disturbance observer can be designed to estimate the disturbance caused by parameter uncertainty and unknown interference.Then,the backstepping controller is designed based on the displacement feedback signal to control the wrist joint angle.In order to solve the complex disturbance caused by parameter uncertainty and random disturbance of the hydraulic drive system of wrist joint,a backstepping sliding mode control method based on extended state observer is proposed to control the wrist joint angle.Brunovsky standard model is used to model the valve controlled electro-hydraulic servo system of wrist joint,which can adjust the disturbance caused by parameter uncertainty and random disturbance into a composite disturbance function.The extended state observer can estimate the speed,acceleration and composite disturbance of the equivalent load of wrist joint on-line,and then the backstepping sliding mode controller can be designed to enhance the performance.The anti-interference ability of the system.Based on the above control strategy,AMESim,Matlab / Simulink and Recur Dyn are used to co simulate the wrist joint angle control.Compared with PID controller,the proposed control method has higher joint angle tracking accuracy and stronger robustness.Aiming at the problem of large throttling loss in valve controlled electro-hydraulic servo system,a kind of pump valve combined electro-hydraulic servo system is adopted to control the wrist joint angle based on the characteristics of high energy utilization efficiency of pump control system and high dynamic and high control precision of valve control system.The structure and principle of pump valve joint electro-hydraulic servo control system are introduced.Based on the control method,the tracking effect and energy-saving effect are analyzed.The purpose of reducing system energy consumption while ensuring joint angle tracking accuracy is achieved.The servo control method of the hydraulic spherical wrist joint studied in this paper has a certain significance for solving the compound disturbance problem caused by the parameter uncertainty and unknown disturbance of the hydraulic wrist joint drive system,and has a certain reference value for the attitude control of the hydraulic spherical wrist end effector.