Xerox Phaser 7500 Service Manual page 135

Theory of Operation
Regi Measuring Cycle (Diag)
The Color Registration is measured to determine the periodical shifts generated by
the Drum and belt operations, which is one of the causes for color shift.
The patch for the Color Registration Control is measured to detect the amount of
color shift. The difference between the average value and the maximum/minimum
values of the relative color shift amount against Black in the fast scan and slow
scan directions, which are detected by the MOB Sensors (x2), is calculated and
becomes the measurement result. In addition, this measurement result is
compared with the target value to perform OK/ NG judgment. The measurement
and judgment results are displayed but corrections are not performed.
Registration Control Sensor Check Cycle (Diag)
The Registration Control Sensor Check Cycle checks the functions of the MOB
Sensors (x2), which are used to measure the Color Shift.
This is a self diagnosis cycle for checking whether the detection systems are
operating normally. A single color - Cyan in the patch for the Color Registration
Control is measured to detect the amount of Color Shift. In addition, the detected
shift amount result is compared with the target value to perform OK/NG
judgment. The detected shift result amount at each sensor and judgment result
are displayed but corrections are not performed.
Registration Control Setup Cycle (Diag)
The Registration Control Setup Cycle is the same control operation as the one
performed in Closed Loop Regi Con, but performed in Diag Mode.
This process is to be performed during printer installation, parts replacement, and
NVM initialization to correct the Color Registration to be within the pre-defined
range.
Control Shift Detection/ Correction Process
This section describes an overview of the Color Shift Detection and Correction
operations at the controls that use patches.
Patch Shape
The patch for the Color Registration Control comes in three "<" patterns - A, B, and
C, which go approximately one round on the belt.
Each pattern is made up of 2 patterns that have the same shape at the front and
the rear. The formation positions in the fast scan direction, as well as the positions
relative to the center of the ideal image at the front and the rear are the same.
Phaser 7500 Printer Service Manual 2-75