Bk is used to detect the reference BD signal and, as such, laser light is directed to the surface of the polygon mirror. In other words, the write start position in main

scanning direction for Bk is determined based on actual measurement and, for this reason, the possible presence of variation in the angle of the polygon mirror

surface will not lead to variation of Bk write start position.

The laser driver for C is found directly under the Bk laser driver and, for this reason, the C laser driver directs laser light against the same polygon mirror surface

as the Bk laser driver, eliminating the effects of variation in the angle of the polygon mirror surface. The write start position of C, for this reason, is also free of

variation as in the case of Bk.

6.2.2 Controlling the Intensity of Laser Light

6.2.2.1 APC Control

/ / / / iR C3380i / iR C3380 / iR C2880i / iR C2880

The machine uses APC control to make sure that the intensity of laser light remains at a specific level.

The machine uses 2 laser driver PCBs, each with a laser driver IC taking care of 2 colors and performing APC control for individual colors.

The following is an outline of APC control operation, executed each time the machine is turned on and for each print job:

1) The DC controller sends the laser control signal (LC_CTL_X(0)=0, LC_CTL_X(1)=1) to the laser driver IC on the laser driver PCB. (X differs depending on

the color.)

2) The laser driver IC is set to APC mode, thus forcing the laser diode (LD) to go on.

3) The laser driver IC monitors the laser diode (LD) by means of a photo diode (PD), adjusting the output of the laser diode until its light is a specific level of

intensity.

4) The laser driver IC stores the laser output in memory for use in the next print job.

START

BD interval

measurement

BD1

value computation

BD1

Write start

position correction

BD1

END