User manual

95.08.23.11.30
Color LaserWriter 12/600 PS Basics & Theory 1–86
Density Calibration System
Density
Control
Maximum density control is performed to stabilize the maximum
density for each color. This determines an optimum developing bias.
Halftone
Correction
Control
The gate array (IC109) in the DC controller contains the halftone
correction table (see below) used to correct the laser output in order to
obtain an ideal halftone image. The halftone correction control modi-
fies the halftone correction table to accommodate changes in the
present environment, the total number of prints, or the condition of the
toner and the photosensitive drum.
Halftone
Correction
Table
The laser output and the image density of the printer do not change in a
linear relationship. Therefore, when the laser image is output according
to the halftone specified with the video data signal sent from the I/O
controller, an ideal halftone image is not obtained on the actual prints.
In order to obtain an ideal halftone image, the DC controller halftone
correction table is used to correct the output value of the laser diode.
Density Circuit Maximum density and halftone correction are controlled using the cali-
bration density sensor (PS14).
Laser Output
Image Density
Ideal Halftone Curve
Real Halftone Curve
Density Patches
Density Sensor Assembly
P/N 922-1310
Calibration Density
Sensor (PS14)
Transfer Drum