Patent ID: 7729611

Claim:
A method of detecting a position of an optical recording medium on which a printing is performed, the method comprising: providing an optical sensor comprising a photo emitter operable to emit light and a photo receiver operable to receive light and output a first signal in accordance with an amount of the received light; transporting the optical sensor to a position above a marker provided on the tray: emitting light from the photo emitter to irradiate the marker; receiving light reflected from the marker with the photo receiver; determining a reference value based on a first value of the first signal outputted when the marker is irradiated; executing a predetermined calculation with respect to the reference value to determine a threshold value; transporting the optical sensor above the tray, while emitting light from the photo emitter and comparing the first signal outputted from the photo receiver with the threshold value; identifying a position of the marker based on the comparison of the first signal and the threshold value; determining a position at which the printing begins based on the identified position of the marker; transporting the optical sensor to positions at which the marker is assumed to be placed; emitting light from the photo emitter at the respective positions to irradiate the tray; receiving light reflected from the tray at the respective positions to generate detection signals; and judging at least one of whether a position of the tray is normal and whether a state of the marker is normal, based on the detection signals.