Techniques for robust dot placement error measurement and correction

Abstract

Techniques to compensate for random and systematic errors when measuring dot placement errors. Error accumulation due to scan axis irregularities during printhead calibration is minimized by swapping alignment block positions on the print medium from swath to swath. Print media advances during the calibration are minimized by the use of a moving reference instead of a constant reference; adjacent groups of nozzles are used to calibrate the following group. Only a small media advance is needed to print alignment blocks using adjacent nozzle groups one beside the other to be calibrated. To prevent paper slip accumulative errors when using moving references, the order of the groups of nozzles is swapped from one paper advance to the other. This randomizes for small, unavoidable slips when advancing the paper and prevents error accumulation. No further paper advances are used at all for the rest of the dot placement calibration (odd to even columns in a print-head, pen to pen correction and bidirectional correction). When calibrating X-axis position for a group of nozzles, a group of nozzles located at the same Y-axis coordinate is used, so that no paper advances are needed to print them one beside the other.