To obtain an automatic gap control head which can enhance the detecting accuracy of a foreign matter without lowering the detecting efficiency of the foreign matter by a method wherein a ring-shaped back pressure face is formed around an air blowoff port and a pressure release groove by which the blown-off air is set free is formed in the outer circumference of the back pressure face.
While the air is being blown off onto a glass substrate (w) from an air blowoff port 3, an automatic gap control head 10 used to detect a foreign body is scanned on the glass substrate (w). The air is reflected by the surface of the glass substrate (w), and a back pressure is generated on a back pressure face 6. The area of the back pressure face 6 is small, and the very small pressure of the air is detected. The blown-off air is received by a pressure release groove 8 so as to be released, and it is set free to the outside of a gap from an air relief groove 7. Therefore, the detecting accuracy of the back pressure is enhanced, the position of a detecting head 1 is controlled by a gap servo control part, and a foreign matter on the glass substrate (w) can be detected precisely. When a foreign matter having a size of 15 μm or higher exists on the substrate (w), the foreign mater is guided by an introduction groove 1e so as to creep into the lower part of the head 1, the gap between the substrate (w) and the head 1 is expanded, and the foreign matter is detected.
TACHIKAWA SHIGERU
MORITA MASARU
ISHIKAWAJIMA SYST TECH
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