Study on Aerostatic Guidance

The aerostatic guidance is used as a super precision positioning device in the fields of semiconductor production and measurement machine, and its performance is expected to be improved. Although the study on the small guidance clearance region by which the high positioning precision may be expected is very important, there is almost no research papers published in this area to date. The purpose of this study is to enhance the calculation accuracy in the region of which the guidance clearance is comparatively small in the aerostatic guidance design. This is accomplished by considering the influence of the cutting surface roughness upon the air flow. More specifically, the amount of air flux passing through the orifice which is principal constituent of an aerostatic guidance is calculated in two separated parts. One part is the calculation done on the boundary layer flow whereas the other part on the potential flow. In this case, the calculation of the boundary layer flow is attempted using a theory in which the surface roughness is taken into account. That is, the calculation is done based on a virtual cylinder which has the same area as that of the rough inner surface of the orifice calculated based on the measured result of the surface roughness of an orifice cut surface. The truth inner surface area is calculated from the inspection result of the inner surface roughness measured by using a 3D surface roughness measuring machine. Through this method, the velocity distribution in the boundary layer is made clear where the diameter of the orifice is comparatively small, and a technique for calculating intrarubular flow is newly established. In addition, experimental apparatus to evaluate this theoretical calculation were designed and produced to confirm the flow characteristics and the load characteristic of the squeeze structure used in this study. As a result, the boundary layer velocity in the small diameter orifice which plays an important role in obtaining a high static rigidity and the pressure of the downstream side of the orifice can be calculated with precision. Thus, an attempt is made to improve the calculation precision of static rigidity in the small guidance clearance region where a high positioning precision can be expected. All of these calculation results are in a fairly good agreement with the experimental results.