Study On Characteristics Of Axis Locus Of Hydrostatic Spindle Based On Pinhole Throttling

Hydrostatic spindle is a high-speed motorized spindle system supported by hydrostatic bearings.Because of the self-adaptability of oil film thickness of hydrostatic bearing,it overcomes the irreversible defect of rotating precision of rigid bearing motorized spindle,and has the characteristics of high rotating precision,high bearing capacity and high rigidity,so it has been widely used in modern precision and ultra-precision machine tools.In the cutting process of the hydrostatic spindle,its axis trajectory is a dynamic reflection of the spindle rotation accuracy and the minimum oil film thickness of the hydrostatic bearing.Therefore,it is possible to judge whether the spindle system is stable or not according to the axis trajectory of the spindle,and then to judge whether the design parameters of the hydrostatic bearing are reasonable.Although a lot of theoretical and experimental studies have been done on the axis trajectory of hydrostatic spindle at home and abroad,how to ensure full oil film lubrication of hydrostatic bearing at high speed and make it have the characteristics of high rotation accuracy,high load-carrying capacity and high stiffness has not been discussed in detail.In order to solve this problem,based on the thin-walled small-hole hydrostatic spindle system,this paper establishes a non-linear mathematical model of the spindle system’s axis trajectory.Based on the analysis of the influence of the structural parameters of hydrostatic bearing on the motion law of the spindle axis trajectory,the influence of cutting force on the axis trajectory of the hydrostatic spindle system is discussed in detail.The specific contents are as follows:Firstly,taking thin-walled orifice throttle four-chamber hydrostatic sliding bearing-spindle rotor system as the research object,the fluid Reynolds equation of hydrostatic bearing is established,and the fluid flow continuity equation is set up.Combining with five-point discrete method,the oil film force distribution of hydrostatic bearing is calculated.Based on the dynamic equation and Euler method,the mathematical model of the hydrostatic bearing-spindle system’s axis trajectory is established.Secondly,based on the established mathematical model of hydrostatic bearing-spindle system,aiming at the mass eccentricity existing in the spindle system under actual machining,the influence law of system parameters such as bearing structure parameters and working conditions parameters on the spindle center trajectory under mass eccentricity is studied by using the control variable method.At the same time,based on the mathematical model ofcutting force,the actual adding is studied.In the process of construction,under the combined action of mass eccentricity and cutting force,the influence of cutting parameters such as the number of cutter teeth and spindle speed on the spindle center trajectory is studied.Finally,the above theory is simulated and analyzed by using matlab/Simulink software.The results show that the thin-walled orifice throttle hydrostatic bearing-motorized spindle system has the optimal bearing structure parameters and cutting parameters under different processing accuracy requirements when the spindle rotation accuracy at high speed is taken as the control objective,which provides a theory for the structural design and control of hydrostatic spindle.On the reference basis of simulation analysis.Finally,this paper uses MATLAB to simulate and analyze the above theory.The results show that the thin-walled orifice throttle bearing-spindle system has the optimal bearing structure parameters under the cutting process when the spindle rotation accuracy is taken as the control target at high speed,which provides theoretical support for the structure design of hydrostatic spindle.