Electrophotographic color printer apparatus and method with improved registration of colors

A multicolor non-impact printer comprising:

• a photoconductive image receiver;
• means for uniformly charging said receiver;
• means for imagewise exposing said receiver to cream a first electrostatic image;
• means for applying a toner of a first color to said first electrostatic image to create a first toner image of said first color;
• means for imagewise exposing said receiver to create a second electrostatic image in the same general area as said first toner image;
• means for applying toner of a second color to said second electrostatic image to create a second toner image which, with said first toner image, forms a multicolor toner image;
• wherein said means for exposing includes a line printhead device for recording a line of pixels;
• an encoder roller associated with said line printhead device and the roller rotates with movement of said receiver and generates encoder position pulses;
• a look-up table of data;
• means responsive to the encoder position pulses for generating an address to the look-up table;
• and means responsive to data output from the look-up table for generating adjusted encoder position pulses for adjusting for nonuniformities in roller diameter and/or a variation in roller diameter from an ideal diameter.

A method for improving the registration of color images in a nonimpact printer, the method comprising:

• rotating a peripheral surface of a roller that is engaged with a receiver that is to receive the color images;
• generating encoder position pulses in response to rotation of said roller;
• in response to the encoder position pulses generating an address to a look-up table;
• in response to data output from the look-up table generating adjusted encoder position pulses that adjust for nonuniformities in the roller diameter and for a variation in roller diameter from an ideal diameter;
• and
• in response to said adjusted encoder position pulses enabling recording of a line of picture elements on said receiver.