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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.
Figure 4-206
COPYRIGHT
©
1997 CANON INC. CANON NP6218 REV. 0 MAY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)
CHAPTER 4 IMAGE FORMATION SYSTEM
4-27
Developing DC bias
Copy density 9
(equivalent)
Copy density 7.5
(equivalent)
Copy density 5
(equivalent)
Test Sheet Density of original
Newspaper