| 摘要 |
PURPOSE:To keep the recording dot interval on a drum constant by detecting scanning speed in response to the turning position of a polygon mirror from the detection output of a turning speed detection means and a start point detection means so as to change the period of a clock in response to the fluctuation of the scanning speed. CONSTITUTION:The frequency divider 11c of a PLL oscillator 11 divides a high oscillation frequency in the MHz order by 1/N and the result is fed back to a phase comparator 11a and the division number N decides the frequency of a clock signal. The turning speed detection means detects the scanning position changing timewise from the output of a charging element 7 and a pulse generator 10 and switches the division number N sequentially depending on the scanning position. Then the frequency is made lower at the scanning start point and the scanning end point (thus, the period of clock signal is increased), and the frequency is increased at the middle part conversely (the period of clock signal is decreased). Through the processing above, although the scanning speed is changed actually, the recording dot (latent image dot) interval on the drum is kept constant.
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