Study On Control Method Of Oil Film Thickness Of Hydrostatic Rotary Worktable

With the advantages of high accuracy,high rigidity,low wear and long working life,hydrostatic rotary table is widely used in CNC machine tools,being one of the important components of vertical CNC machine tools.The rigidity and the bearing capacity of the hydrostatic worktable oil film mainly depends on its thickness.For the traditional constant pressure oil supply system,the oil pr essure being constant,the thickness of the worktable oil film would vary due to the change of worktable load and the viscosity of hydraulic oil,thus affecting the machining accuracy of the worktable and reducing the operation stability of the rotary table.In our country,rotary worktable with high accuracy,high rigidity and adaptive regulation capability almost all relys on imports.To solve this situation,it’s of great significance to improve the existing oil supply method and obtain progress in the automation level of wor ktable oil film thickness control.In the hydraulic system of the hydrostatic worktable,based on the basic principle of hydrostatic worktable rail and its hydraulic oil supply system,the structure of open hydrostatic rail and the characteristics of constant current oil supply are analyzed,a hydrostatic worktable with an open constant current oil supply system is identified as our research object,and ahyd raulic oil supply system is designed to control the thickness of the worktable oil film.In the control of oil film thickness,according to the existing working environment and research req uirements,A complete closed-loop oil film control scheme composed of Siemens 840Dsl universal numerical control system and frequency converter combined with asynchronous motor,multi-head pump,hydrostatic rotary table and eddy current displacement sensor is proposed.which is based on the control system hardware selection basis and significance,to improve the accuracy of oil film thickness control.And a mathematical model of the corresponding control link is established,a relationship between the frequency and the theore tical model of oil film thickness is deduced as well.To verify the accuracy of the motor frequency and the theoretical model of the oil film thickness,a human-computer interaction intelligent control system software based on the Siemens 840Dslnum erical control system was designed and developed.An experimental platform was established based on the oil film thickness detection method,and the feasibility and accuracy of the oil film thickness adjust method based on the theoretical model was verified.Meanwhile,an oil film thickness adjust method based on the least squares was put forward based on the data measured.The experimental results further validated the theoretical model,corrected the error of the theoretical model,indicated a higher control accuracy of the oil film thickness,and provided support for the practical project application as well.