Study On Ultra-Precision Motion System Based On Hydrostatic Screw And Hydrostatic Guideway

The precision and ultra-precision machining technology have been the support of national defense and advanced technology. Many high-technology products have higher requirements on the machining accuracy of parts. As a result, the performances of machine tools need to be improved. The linear motion components are the important parts of ultra-precision machine tools to achieve high precision motion. A structure composed of linear motor and hydrostatic guideway is widely used nowadays. This structure has its own advantages such as high stiffness, fast response, but it also has the problems, such as the anti-interference performance and the damping performance. Different from linear motor, the hydrostatic screw and nut has its own advantages, including high stiffness, low friction, good damping and so on because of fluid lubrication between screw and nut. And it can make up for the lack of hydrostatic guideway damping in motion direction. However, few hydrostatic screws were used in the field of ultra-precision machining tools. Therefore, in order to explore the performances of the ultra-precision motion systems driven by hydrostatic screw, this article constructed an ultra-precision motion system based on the hydrostatic screw and hydrostatic guideway.Firstly, according to the theory of hydrostatic bearing, this article developed the software which can calculate the performance of hydrostatic guideway. Based on the result of calculation, the structure of inner-type hydrostatic guideway and the structure of driving system based on hydrostatic screw have been designed. The factors of hydrostatic guideway deformation have been analyzed through experiments and simulation, and the methods to reduce the deformation of hydrostatic guideway were proposed. Besides, a control system based on PMAC was constructed. And in order to support the normal work of hydrostatic parts, the hydrostatic station based on the feedback of oil pressure was developed.This article studied the static and dynamic performances of inner-type hydrostatic guideway. The pressure distribution in the pockets of hydrostatic guideway was analyzed through experiments and simulation. The relationship between the stiffness of guideway and the structure coefficient was verified according to the experiments. And this paper proposed that the reasonable range of structure coefficient is 0.707 to 1. In order to investigate the dynamic performance of hydrostatic guideway, the dynamic equation of oil film extrusion effect influenced by orifice restrictor is developed. Besides, the modal of hydrostatic guideway was simulated and measured.After finishing the designing and constructing the whole system, this article tested the coaxiality of hydrostatic screw and hydrostatic guideway by monitoring the output current of motor. And then the damping of system was analyzed through the theory and experiments, and it was verified that the hydrostatic screw nut and hydrostatic bearing have larger damping than the hydrostatic guideway. Then this article designed and analyzed the control system, and the torque control mode based on current loop was selected. Then the test of motion resolution has been done in the condition with different feedback resolution, and better than 10 nm resolution of motion can be achieved. However, the vibration which the frequency is 9Hz was found in the motion system. After experimented and analyzed, it was verified that the vibration is caused by the base. Therefore, the base must be optimized for the next research.