| 摘要 |
PURPOSE:To enable deflection correction in both horizontal and vertical directions to be performed with one set of two-channel detectors by performing scanning in the vertical direction for detecting the errors in the vertical direction at the scanning start end part. CONSTITUTION:5A, 5B are two-channel type derectors near the start end of scanning and the outputs thereof input to a differential amplifier 5C. A position detecting signal generating circuit 10 receives the synchronizing pulse 9 from the driving system of a rotary polyhedral mirror and generates the Y scanning signal of a fixed gradient. A comparator 11 generates a hold signal when the output of the amplifier 5C changes over from negative to positive and therefore when the synchronizing pulse 9 enters, the light beam is also deflected in the vertical direction by a deflector 7, thereby scanning the scanning plane. As a result, the Y scanning waveform may be corrected of vertical errors because the beam spot is held at a certain value on the centerline of the detectors 5A, 5B. Since the spot can be made to enter from the left end of the detector 5B, the scanning start point pulse 13 of good detection accuracy may be obtained as the output of a pulse shaping circuit 12. |
