Patent ID: 6585346
Filing Date: 2003-07-01
Classification: B41J

Abstract:
A printing apparatus, comprising:a print head including a nozzle row having a plurality of nozzles for ejecting ink drops, the plurality of nozzles being aligned in a direction of sub-scanning; an ink drop detector having a light emitter for emitting light and a light receiver for receiving the light emitted by the light emitter, the ink drop detector being configured to generate detection pulses in response to blockage of the light by the ink drops; a feed mechanism configured to move the print head and/or the ink drop detector in order for the print head and the ink drop detector to move relative to each other; a detection pulse analyzer capable of: (i) measuring a time interval of two consecutive detection pulses which are detected by the ink drop detector while the print head and the ink drop detector are relatively moving in a constant speed; (ii) judging that the two consecutive detection pulses are associated with a same nozzle if the time interval is less than a first threshold value, while judging that the two consecutive detection pulses are associated with two different nozzles if the time interval is greater than the first threshold value; and (iii) counting a number of operative nozzles capable of ejecting ink drops based on the judgment; and a nozzle condition determiner configured to determine presence of an inoperative nozzle incapable of ejecting ink drops if the number of operative nozzles is less than a number of test nozzles being subject to the ink drop detection.