| 摘要 |
PURPOSE:To improve the accuracy of a mark detection by providing two photodetectors, applying waveform shaping to an addition signal between the 1st mark detection signal and the 2nd mark detection signal delayed for a prescribed time so as to detect a rotary synchronizing mark thereby eliminating a narrow flaw. CONSTITUTION:When a rotary synchronizing mark 30 is turned in the direction of arrow X on a mark detector 29 comprising a light emitting source 11b consisting of a light emitting diode and two photodetectors 24, 25 and the mark crosses the photodetector, waveforms shown in (b-1), (b-2) appear as the output of the photodetector. Each signal is added and amplified by a summing amplifier circuit 26 and a signal waveform (b-3) is obtained. When the signal is binary- coded by a waveform shaping circuit 27 at the voltage of DC voltage V2 (b-4) generated from a DC voltage generating circuit 28, a signal waveform shown in (b-5) is obtained, and the binary-coded signal (b-5) becomes a rotary synchronizing signal and a discrimination signal. When a flaw 31 on the disc surface has a width narrower then the interval of the detectors 24, 25, it is not detected. |
