Study on Positioning Accuracy of Aerostatic Lead Screw

The aerostatic lead screw is a non-contact type lead screw in which the contact surface of a male screw and a female screw is supported by a pressurized air film. It is characterized by the features that: (1) there is no degradation in accuracy due to friction wear; (2) no environmental pollution is caused by a leak and scattering of lubrication fluid; and (3) maintenance is easy and simple. However, drawbacks are that vibration is liable to occur and therefore the static rigidity is low. The aerostatic lead screw is useful for semiconductor fabrication and also effective in positioning a table on which a sample is placed in a biomicroscope. This study relates to a drunkenness analysis of the aerostatic lead screw. The drunkenness of a contact-type lead screw represented by the ball screw is generally transferred directly from the male screw to the female screw. In the aerostatic lead screw, the drunkenness based on machining accuracy error of each screw flank is not directly transferred onto the female screw and is instead averaged out by balancing of load capacities among each screw flank, so that the enhanced accuracy in positioning lead screws is expected. In this paper, a balance of the load capacity of each screw flank was computed using the aerostatic guidance theory, so as to carry out a drunkenness analysis. It is found that the balancing effect plays the vital role in improvement on drunkenness of an aerostatic lead screw used in this study.