Lloyd A. Williams

Strategy for tandem color registration

This writing describes a strategy for color registration and motion control for tandem xerography. The strategy is based on an intelligent closed-loop controller which automatically calibrates the machine against repeatable errors and compensates for long term errors due to drift. Registration errors are measured by means of a dedicated sensor. Repeatable steady and periodic, errors are characterized at long intervals and compensated by feedforward techniques. Long term drifting errors are periodically detected and corrected. Feedback control is used to counteract unexpected and uncalibrated disturbances. Measurements taken on an experimental breadboard show that registration of four xerographic engines can be maintained to within 45 microns, and that color and gray banding can be eliminated. This limit of registration accuracy is mostly due to stretch of the intermediate belt under the action of image dependent transfer forces.