| 摘要 |
PROBLEM TO BE SOLVED: To detect a sync detection signal surely by switching the operation to a follow-up mode for controlling the LD forced emission timing of sync detection signal detection of next scanning line when pixel density is altered. SOLUTION: When a switching is made from 600 dpi to 400 dpi, a normal mode is altered to a follow-up mode upon ending the plot of 600 dpi (1), a difference (ΔM) is calculated from the count (M) of a sync detection counter and the count (M0) of a previous scanning line being held in a register, and the set value in the period C of next scanning line is reset from C0 of the previous scanning line to (C0+ΔM). When the clock of a polygon motor is switched to 400 dpi in the follow-up mode (2), scanning time of one line is prolonged gradually and settled at the scanning time of 400 dpi. Since the set value in the period C is reflected by the variationΔM of scanning time from that of the previous scanning line, the LD does not emit light during an extra interval (on the photosensitive body). At the settling point (3) of the r.p.m. of the polygon motor, switching is made to a normal mode and the pixel clock and a main scanning state counter are set with a value of 400 dpi and then switching is made to the operation of 400 dpi from next scanning line. |
