| 摘要 |
PROBLEM TO BE SOLVED: To detect the edge position accurately even when samples have different thicknesses by detecting a relative moving position where the output of an optical detector begins to change at the maximum inclination, in a relative moving process between a sample and an optical system. SOLUTION: In a moving process between a sample and an optical system, the output signal of an optical detector 9 is converted into a voltage signal V through a convertor 16, and further the signal V is differentiated by a first differentiation circuit 101. Then the outputted signal A is differentiated into a pulse signal C and it is inputted into an AND gate 106. The signal A is compared with a reference voltage Th through a comparator 103, and when it becomes higher than the voltage Th, a signal B is inputted into the AND gate 106. That is, the relative moving position where the output of the detector 9 begins to change at the maximum inclination is detected. On the other hand, a sample hold circuit 105 is driven by the output signal D of the AND gate 106 so as to hold the signal V. A comparator 107 compares the signal V with a half of a reference signal, and when they become equivalent to each other, an output E is outputted therefrom. |
