Analysis On The Static And Dynamic Characteristics Of A Novel Dual-drivable Hydrostatic Lead Screw-nut Pair

As a key component of the machine tool,the large-stroke high-precision drive feed system has become one of the main shortcomings that restrict the quality of ultra-precision machining.The drive feed system based on the traditional rolling contact component is difficult to achieve large-stroke and high-precision displacement feed due to disadvantages such as contact wear and low-speed crawling;although the drive feed system based on the macro-micro composite drive technology can meet the requirements of large-stroke and high-precision,there are problems like the nonlinear hysteresis;although the unique high rigidity,high precision and low friction transmission characteristics of hydrostatic transmission components can compensate for the defects of rolling contact components,they cannot solve the inherent low-speed crawling problem of the drive end,and at extremely low-speed feeds,the friction of hydrostatic transmission components can exacerbate this problem.The low-speed creeping phenomenon of the drive-end motor due to nonlinear friction only occurs in the certain low-speed range.When the motor works at a speed out of this certain range,this phenomenon will disappear.Therefore,based on the principle of differential speed,the author proposed a "novel micro-feed unit based on the dual-drivable hydrostatic screw-nut pair".In principle,the screw and nut can be driven synchronously with two high but close speeds to realize large-stroke and extremely low-speed displacement feed.This paper focuses on the analysis of the static and dynamic characteristics of the dual-drivable hydrostatic screw-nut pair.To achieve that,the oil film flow model of the dual-drivable hydrostatic screw nut pair is established,the algorithm for solving the oil film flow model based on the finite difference method is designed,and the analysis for the static and dynamic characteristics are implemented considering multiple influencing factors including the nut offset and tilt,different restrictors and design parameters of the nut and the restrictor.The main contents are as follows:(1)The oil film flow model of the dual-drivable hydrostatic screw-nut pair is established.In order to compare the static and dynamic characteristics of dual-drive hydrostatic screw nut pairs with different restrictors,dual-drivable hydrostatic screw-nut pairs restricted by the capillary restrictor and the PM restrictor are designed.Based on the equivalent sector plane,the spiral oil film flow problem is transformed into the annular oil film flow problem.Using the simplified Navier-Stokes equation,combined with the principle of mass conservation and the non-slip boundary conditions,the generalized governing equation of the spiral oil film is derived,and the static and dynamic characteristics of the dual-drivable hydrostatic screw-nut pair are calculated.(2)The oil film flow model solving algorithm based on the finite difference method is designed.Iterative formulas or equations based on finite difference method,finite volume method and finite element method to solve the Reynolds equation numerically are deduced.Considering the advantages and disadvantages of different numerical methods,the algorithm for solving the oil film flow model is designed based on the finite difference method,and the algorithm is realized using the MATLAB program.The effectiveness of the iterative program was verified by comparing the calculation results with historical literature and the simulation results using the Fluent.(3)The static and dynamic characteristics of the dual-drivable hydrostatic screw nut-pair with different restrictors considering the nut offset and tilt are analyzed.The homogeneous transformation matrix is used to establish the oil film thickness model including the nut offset and tilt,and the static and dynamic characteristics of the dual-drivable hydrostatic screw-nut pairs restricted by the capillary restrictor and PM restrictor are analyzed under different combinations of the nut offset and tilt.The dual-drivable hydrostatic screw-nut pair and the traditional single-drivable hydrostatic screw-nut pair are compared on the axial load capacity,the axial stiffness,and the axial damping.(4)The influences of design parameters of the nut and the restrictor on the static and dynamic characteristics of dual-drivable hydrostatic screw-nut pairs are studied.The effects of the number of oil recess,thread pitch,half-angle of tooth profile and oil recess wrap angle on the axial load capacity,the axial stiffness,and the axial damping are studied.The influences of oil supply pressure,restricting coefficient,initial flow rate and specific flow rate of the capillary restrictor and the PM restrictor on the axial load capacity,the axial stiffness,and the axial damping are analyzed.