| 摘要 |
PURPOSE:To enable the autofocusing of an air micrometer at a high speed by obtaining the output of the air micrometer acquired when the edges of a pattern become most sharp and setting the origin of the air micrometer. CONSTITUTION:A pattern image formed by an optical system 3 is detected by a CCD 5. From a pattern detection signal, the deviation of the original of an air micrometer 4 obtained from an optical image is calculated by a CPU 12 and the calculated result is applied to an adder 9 through an offset register 13. On the other hand, a differential pressure due to a meter 4 is detected by a differential pressure sensor 6 and a signal indicative thereof is applied to a linearizer 8. Thus, an automatic air micrometer control circuit 7 operates a Z-axis drive motor 11, drives the optical system 3 and the meter 4 in a Z-axis direction and optically correct the autofocusing position of the meter 4, thereby being able to automatically set the origin.
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