Canon FY8-13EX-000, NP6218 service manual Automatic Control of Copy Density, Control Method

CHAPTER 4 IMAGE FORMATION SYSTEM

D. Automatic Control of Copy Density

1. Outline

The copier has an automatic density adjustment mechanism (AE), which automatically controls the DC component of the development bias according to the density of originals. As long as the original is more or less uniform in density, the AE mechanism varies the DC component of the development bias accordingly to ensure fogging-free copies.

The DC component controlled in AE mode is indicated in the copy density display of the control panel.

2. Control Method

During initial rotation (INTR), the scanning lamp (FL1) is turned on at a specific intensity and the scanner is moved forward about 65 mm to expose the original.

With the scanner in this position, the reflected light over the area shown in Figure 4- 207 is measured by the AE sensor (photodiode), and the measurements are sent to the DC controller PCB.

In response, the DC controller PCB computes the optimum value of the development DC bias for copying operation, and generates the result to the microprocessor on the composite power supply. Figure 4-206 shows the changes in the DC component of the development bias caused by the changes in the density of an original.

The graph is based on the amount of exposure that brings optimum density without fogging when copies are made of a newspaper or a Test Sheet.

Developing DC bias

Copy density 9 (equivalent)

Copy density 7.5 (equivalent)

Copy density 5 (equivalent)

	Newspaper
Test Sheet	Density of original
Figure 4-206

COPYRIGHT © 1997 CANON INC. CANON NP6218 REV. 0 MAY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON) 4-27