Study on Aerostatic Guidance: Discussion of Flux Coefficients of Orifice

In recent years the aerostatic guidance has been used as a precision positioning apparatus in the Integrated Circuit manufacturing or bioengineering field. The purpose of this study is to examine the relationship between the squeeze part of aerostatic guidance and the mass flux, and to make the theoretical calculation on the aerostatic guidance more accurate, when designing an aerostatic guidance. In this study we produced a measurement device to obtain the flux characteristics of the compressed air passing through an orifice with 0.4mm diameter. We used this measurement device to obtain the flux coefficient of the orifice where the air is blowing out in a direction vertical to the guidance surface. The pressure distribution of the guidance surface was measured and the static load characteristic experiment was carried out. Then the experiment values obtained thereby were compared with theoretical values. The results show that although the flux coefficient could be dealt with a fixed value in the region of orifice-squeeze¹⁾ when the flux coefficient was calculated from the flux characteristics, it was no longer a fixed value in the region of self-squeeze¹⁾. This is considered a cause of the remarkable error in the above-mentioned design calculation result. Thus, in this study the influence of the inner surface roughness (of the orifice) affecting the flux characteristics was clarified and a novel flux formula, where the flow in the boundary layer is taken into account, is devised and formed. As a result, we have established an improved design scheme and theory by which the theoretical computation on the aerostatic guidance can be performed with more sufficient accuracy.