Research On Axial Trajectory Control Technology Based On Controllable Hydrostatic Bearing

It is of great significance to realize the active control of the axis trajectory.Through active control,the spindle vibration and external disturbance can be suppressed,the rotation error can be reduced,and the machining accuracy of the rotating equipment can be improved.In addition,the non-circular axis trajectory can be realized by active control,which provides a new way for the precision machining of non-circular shaped inner holes.However,in the current research of controllable hydrostatic bearing-spindle system,there are still some problems,such as complex system model,long solution time,not suitable for controller design,low controller accuracy and limited application scenarios.Therefore,based on the controllable hydrostatic bearing,this paper studies the modeling,identification and controller design of the controllable hydrostatic bearing-spindle system for the spindle axis trajectory control problems such as non-circular axis trajectory forming and disturbance suppression.(1)Based on the existing test bench and hardware control system,the system detection and control software is developed,and the system characteristics are tested and analyzed.(2)The second-order linear model of the system is obtained by system identification,and the repetitive controller is designed to realize the non-circular axis trajectory forming.Firstly,a second-order linear decoupling system of the controllable hydrostatic bearing-spindle system is established,and the transfer functions of the system in the horizontal and vertical directions are obtained by system identification.Then,aiming at the periodic characteristics of noncircular axis trajectory forming,a repetitive controller is designed to realize the non-static error tracking of the spindle axis to the periodic reference target.Finally,the repetitive controller is compared with the PID controller through simulation and experiment.The results show that the repetitive control has higher tracking accuracy for the periodic reference trajectory,and by adjusting the gain parameters,the repetitive control system can obtain a suitable stability margin and suppress the interference caused by modeling errors and random disturbances.(3)The nonlinear state space model of the system is established.Through the flow equation of controllable hydrostatic bearing and piezoelectric thin film restrictor and the oil film force equation of oil chamber,the strict feedback nonlinear state space equation suitable for controller design is derived.The discrete system equation for parameter identification is obtained by the second-order Euler method.The error criterion function of the system is established by the prediction error method,and the minimum value of the error criterion function is solved by the particle swarm optimization algorithm to obtain the system model parameters.In order to verify the accuracy of the nonlinear model of the system,different input signals and their system responses are used as verification data sets to verify and compare the simulation accuracy of the nonlinear model.The results show that the nonlinear model has high accuracy.(4)A nonlinear controller and an extended high-gain observer are designed to suppress different types of disturbances.Based on the strict feedback nonlinear state space equation of the controllable hydrostatic bearing-spindle system,the state feedback controller of the system is derived by backstepping method.An extended high-gain observer is designed to estimate the unmeasured states and external disturbances of the system,and a saturation function is used to suppress the adverse effects of the peak phenomenon of the high-gain observer.The feasibility of the extended high gain state observer is verified by simulation.Then,simulation and experiment are designed to verify the control effect of nonlinear control system under random disturbance and steady disturbance.The results show that the nonlinear state feedback control system based on extended high gain observer can suppress different types of disturbances and improve the spindle rotation accuracy.