Patent ID: 8651613

Claim:
A method of calibrating a transport roller of an image forming apparatus, the method comprising: ejecting fluid through a plurality of nozzles of a fluid ejector unit arranged in an array having an array height traverse to a substrate transport path to form a reference image on a substrate having an image height during a single pass of the fluid ejector unit across the substrate; moving the substrate a distance along the substrate transport path by a transport roller having a circumference equal to or less than the image height of the reference image and a radius; detecting at least one portion from the reference image to obtain an actual distance of substrate travel along the substrate transport path; detecting an amount of angular movement of the transport roller to obtain an expected distance of substrate travel along the substrate transport path; and determining an offset value based on a difference between the actual distance and the expected distance of the substrate travel, wherein the reference image includes a plurality of lines corresponding to actual distance reference values of substrate advancement, wherein the plurality of lines allow determining the actual distance of the substrate advancement corresponding up to at least a full rotation of the transport roller.