D. Automatic Control of Copy Density1. OutlineThe copier has an automatic density adjustment mechanism (AE), whichautomatically controls the DC component of the development bias according to thedensity of originals. As long as the original is more or less uniform in density, the AEmechanism varies the DC component of the development bias accordingly to ensurefogging-free copies.The DC component controlled in AE mode is indicated in the copy density display ofthe control panel.2. Control MethodDuring initial rotation (INTR), the scanning lamp (FL1) is turned on at a specificintensity 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 theDC controller PCB.In response, the DC controller PCB computes the optimum value of the developmentDC bias for copying operation, and generates the result to the microprocessor on thecomposite power supply. Figure 4-206 shows the changes in the DC component of thedevelopment bias caused by the changes in the density of an original.The graph is based on the amount of exposure that brings optimum density withoutfogging when copies are made of a newspaper or a Test Sheet.Figure 4-206COPYRIGHT © 1997 CANON INC. CANON NP6218 REV. 0 MAY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)CHAPTER 4 IMAGE FORMATION SYSTEM4-27Developing DC biasCopy density 9(equivalent)Copy density 7.5(equivalent)Copy density 5(equivalent)Test Sheet Density of originalNewspaper
