| 摘要 |
PURPOSE:To improve an S/N and to perform an accurate detection by a method wherein only a high frequency component generated in a moment when a spot light and a mark meet each other or separate from each other is taken out through a filter to be converted into a mark detection signal. CONSTITUTION:When a spot light L is irradiated on a body 1, a photoelectric conversion element 4 receiving the reflection light outputs an electric signal (a) in accordance with a variation of a quantity of reflected light and a signal (b) is entered into a high pass filter 6 through a buffer amplifier 5. A signal (c) output from the filter 6 is a signal for which only a high frequency signal component generated in a moment when the spot light L meets with marks 2, 2' and the spot light L separates from the marks 2, 2' is differentiated. Next thereto, a signal (c) passes through the 2nd buffer amplifier 7, pulse extract circuits 9, 10 and shaping circuits 11, 12 and is applied to an FF circuit 13. The FF circuit 13 is set at a moment when the spot light L and marks 2, 2' meet, and it is reset at a moment when both separate from each other. On this account, its output signal (i) can detect the marks 2, 2'. With this constitution, an S/N can be shown on a figure to perform an accurate detection. |
