Studyon Tolerance Design Ofaerostatic Bearing System Based On Global Sizes

Aerostatic spindles are the key components of precision machine tools and measuring instruments,which are the key of industrial production,and have been widely applied in precision machining and measurement,aeronautics and astronautics,and other fields.At present,the mass production of the high precision aerostatic spindle has not been achieved in our country,which restricts the development of precision machine tools and measuring instruments.The tolerance design of the bearing and the rotor based on the global size and the performance of the aerostatic bearing under the skin model were studied in this paper,and the related experimental analysis was carried out.On the basis of the analysis of the aerostatic spindle bearing and rotor structure,the cylinder's global sizes is used to analyze the radial fit clearance of the aerostatic bearing system.Through the influence factors analysis of the bearing and rotor(hole and shaft)fit,not only do the dimensional deviations of the bearing and rotor have much influence on their fit,their geometric errors,such as roundness error,cylindricity error,perpendicularity error and so on also have influence on their fit.The dimension chain with dimension deviations and geometric error is used to analyze the fit between bearing and rotor and the fit base on global size,and Monte-Carlo simulation is used to simulate the radial clearance between bearing and rotor under global size distribution.Through the analysis of bearing and rotor fit,the dimensional tolerance and geometric tolerance of hole and shaft for the aerostatic spindle were determined,and for the bearing and rotor fit,the genetic algorithm was applied to allocate the tolerance values to roundness,cylindricity and perpendicularity error based on the cost tolerance function.Through the simulation of cylindrical cross-section data,the skin models of cylindrical surface of bearing and rotor fit were established by using UG(including porous aerostatic spindle and orifice compensated aerostatic spindle),and the assembly model of the established the skin models was processed by using ANSYS Workbench,the physical model of bearing performance simulation was obtained and its bearing capacity was calculated.The bearing capacity of orifice compensated aerostatic bearing was tested on the modular spindle testbench,and the bearing performance under the ideal condition and the skin model was compared and analyzed.Combined with theoretical research and simulation results,the process of tolerance design for aerostatic radial shaft system is given,through the simulation of the bearing performance of the skin model,it lays the foundation for the radial film thickness design of the aerostatic spindle based on the global sizes.