Patent ID: 8169454

Claim:
A scanning beam printing system, comprising: a printing medium holder to hold a printing medium on which images are projected and printed onto the printing medium; a laser array comprising lasers to produce laser beams having optical pulses to carry image information to be projected on the printing medium held by the printing medium holder; a scanning and projection module that directs the laser beams from the laser array onto the printing medium holder and simultaneously scans the laser beams along different horizontal scan lines at the printing medium holder and to sequentially scan the laser beams in different vertical regions at the printing medium holder, wherein the scanning and projection module comprises a horizontal polygon scanner to scan the laser beams horizontally, and a vertical scanner to scan the laser beams vertically; one or more servo detectors located to receive feedback light from the printing medium holder caused by the laser beams; and a control that controls the laser array, and the scanning and projection module in response to information in output from the one or more servo detectors, wherein: the printing medium holder holds an alignment plate and has a medium holding position which holds the printing medium, wherein the alignment plate is disposed in an optical path of the laser beams between the scanning and projection module and the medium holding position so that the laser beams transmit through the alignment plate to reach the printing medium, and the alignment plate comprises a central transparent printing area that comprises stripe reflectors that define image pixels and reflect light to the one or more servo detectors to indicate a spatial alignment error of each laser beam along a horizontal scan line.