Patent ID: 6350006
Filing Date: 2002-02-26
Classification: B41J

Abstract:
A method for monitoring operation of an ink jet printing mechanism including a plurality of print nozzles, the method comprising the steps of:a) providing predetermined control signals to the ink jet printing mechanism, the printing mechanism responding to the control signals to actuate a continuous row of the plurality of print nozzles so as to eject a curtain of ink drops through a predetermined gap; b) providing a source of illumination for projecting a beam through the gap at substantially a right angle to the path of the curtain, whereby the intensity of the beam downstream from the gap is reduced proportionally to the curtain's optical density; c) sensing the beam downstream from the gap to generate an optical density signal representative of variation in intensity of the beam, whereby the optical density signal is representative of the optical density of the curtain; d) comparing the optical density signal to a first reference signal; and e) if the comparison indicates that the curtain is insufficiently dense, generating a printhead malfunction signal.