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31 December 1992
4.5 DEVELOPMENT BIAS
4.5.1 Basic Concept
When the drum is exposed, most of the negative charge is eliminated from
the areas where light strikes the drum. This leaves a negative charge pattern
corresponding to the dark areas of the original. After exposure however, a
small residual charge of about –100 volts (for white paper) remains in the
exposed areas. This residual charge could attract positively charged toner
from the development roller and result in dirty background on the copy.
The development bias prevents such dirty background. A negative bias a
little larger than the residual charge is applied to the development roller. This
prevents the positively charged toner from being attracted to the background
areas of the latent image.
Manual ID Bias
Bias
(Volts)
-280
-260
-240
-220
-200
-190
-180
-170
-160
-140
-120
1
4.5.2 Manual Image Density Bias
When in manual image density mode, the development bias is applied as
shown by the above chart.
In addition to the development bias, the image density is also controlled by
varying the exposure light intensity. (See the exposure section.)
3
4
5
2
Manual ID Setting
6
7
9
8
2-25
DEVELOPMENT
10
11
12 - 26
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