Patent ID: 8317292

Claim:
A method for monitoring relative position of a carriage and a recording medium in an inkjet printing system having a cylindrical roller for advancing the recording medium along a recording medium advance direction, the method comprising: (a) sending light from a light source mounted on the carriage toward at least a portion of the cylindrical roller; (b) receiving reflected light from the at least the portion of the cylindrical roller in a two-dimensional sensor mounted on the carriage, wherein the two-dimensional sensor is displaced from the light source, and the two-dimensional sensor is oriented to receive specularly reflected light from the at least the portion of the cylindrical roller; (c) sending a signal from the two-dimensional sensor to a controller, wherein the signal indicates the pattern of reflected light received by the two-dimensional sensor; (d) comparing the received signal by the controller to a signal stored in memory; (e) calculating a shift between the received signal and the signal stored in memory; (f) calculating a distance the carriage has moved based on the shift.