Printhead-to-platen spacing variation along scan axis due to carriage guide, measured by simple sensor on carriage

摘要

PPS variation along a scan axis is found by shining a light beam from pen carriage to print-medium position and back to detector, and applying a pathlength/intensity correlation. Sensing is done while scanning, to find relative PPS profile along the track. With no medium in place this measures mechanical imperfections-and can be corrected by later deducting thickness of a medium. If medium is present, adjustment is omitted. For absolute values a plural-lamp sensor is calibrated for each lamp, at the PPS design point. Pagewide/webwide variants are included.