Study On The Control Scheme Of Oil Film Thickness Adjustment Of Opened Hydrostatic Slideway

With advantages of high accuracy and large rigidity as well as low attrition, the hydrostatic slideway is widely applied in the field of CNC Machine Tools. Its rigidity, bearing capacity and operating performance mainly lie on its oil film thickness. It is essential to guarantee the optimum value of oil film thickness in order to improve its performances. The existing hydrostatic slideway uses proportioning oil supply system, which can not adjust oil film thickness. In the working process, oil film thickness changes along with the time-varied load bearing. Sometimes it even has surpassed the stipulation scope, which not only reduces rigidity of oil film and bearing capacity but also cuts down the processing precision and the processing scope of numerical machine tools. Therefore, it is necessary to improve existing oil supply system and take control measures to enhance rigidity and bearing capacity of the hydrostatic slideway. Based on the analysis of existing oil supply system and the characteristic of vector variable frequency velocity modulation technology, mathematical model of induction motor is proposed. An improved oil supply system is proposed which consist of Converter, induction motor, proportioning pump. This system can adjust the oil film thickness to the optimum value through the rotate speed adjustment of motor and flux adjustment of pump.In order to reduce oil film thickness dithering due to the varied load bearing, the open-loop and closed-loop control scheme are proposed. Based on the control flow of the controller and executor, the performances of control schemes are emulated and analyzed.When the closed-loop control scheme is used to adjust oil film thickness, the phenomena of lagging adjustment is emerging. An improved closed-loop control scheme based on matching arithmetic and its control flow is designed which can avoid lagging adjustment effectively.