| 摘要 |
PROBLEM TO BE SOLVED: To detect each of plural laser beams with one photodetecting element by detecting plural laser beams, outputting a superposable detection signal, inputting the detection signal and outputting the rising differential pulse of the detection signal. SOLUTION: The distance in a scanning direction between the laser beam is set so that it may be larger than a spor diameter on the light receiving surface of the photodetecting element and it may not be equal to the width of the light receiving part of the photodetecting element. A plural-beam detection circuit 3 is constituted of an RC differentiation circuit 3a in which a laser beam detection signal outputted from the photodetecting element is inputted and a schmidt trigger circuit 3b of the poststage. Analog differential waveform is obtained at a stage Y and the rising differential pulse is obtained at a stage Z. Namely, detection pulse rising at each laser beam detection start position is obtained at the output stage Z. Thus, the start timing of the image signal is adjusted for every laser beam. |
