Modeling And Active Control Of Hydrostatic Spindle Center Motion Embedded With Control Recess

Spindle rotation error is important for machine tool machining accuracy.Indirect compensation of rotation error and direct control of rotation error are two effective ways to improve machining accuracy.Indirect compensation often requires complex compensation actuator and is not able to reduce the rotation error itself.This thesis researches on active motion control of the spindle supported by the hydrostatic bearing embedded with control recess with the aim of reducing the spindle rotation error itself.The influence of different working parameters and spindle system parameters on the active control results was studied,which has reference value for the design of spindle rotation error active control system.Firstly,based on Reynolds equation and flow conservation equation,the motion model of the spindle supported by the hydrostatic bearing embedded with control recess was established.The basic principle of spindle center motion active control was described.Then,the PID controller for spindle center motion active control was designed to verify the feasibility of spindle motion active control.The position of spindle balanced without external load was took as reference value.The active control of spindle center motion under different loads,oil supply pressure and oil viscosity were studied.The results show that under the fixed load,the deviation of spindle center increases with the increase of load and the settling time of controlling back to reference values also increases.Under the periodic load,the frequency of spindle motion is the same as that of external load and the amplitude of spindle motion increases with the increase of external load.Controlled spindle motion amplitude is effectively reduced compared with uncontrolled case.Different spindle rotation speeds have no significant effect on the control effect.As the oil supply pressure increases,the stiffness of oil film increases,and the settling time of active control decreases to some extent.When the oil viscosity increases,the damping of oil film increases,which is helpful to reduce the motion amplitude of controlled spindle motion.Next,the hydrostatic spindle system model was locally linearized and the state space model was established to facilitate the implementation of the designed spindle motion active control system.On this basis,LQR and MPC controllers were designed and applied to the nonlinear model to study the active control of spindle center motion.The results show that the two controllers based on state space model have ideal control effect.Under fixed load,the settling time is reduced by more than 70.6%compared with PID;Under periodic load,the amplitude of spindle center motion is reduced by more than 72.2%compared with PID.Last,the platform which has the ability of spindle center motion signal acquisition and control was built based on the existing sliding bearing test bench in the laboratory.Spindle motion control experiments were carried out.The results show that,under the experimental conditions of the thesis,the amplitude of spindle center motion in x and y directions decreases by 2μm and 4.5μm respectively,which verifies the feasibility of the proposed active control scheme.