Detection of ink or fixer on selected locations of a fluorescent print media by irradiation of the locations and detection of the reflectivity thereat

摘要

To check that nozzles of printheads 11-15 which apply fixer or an ink to a print media 22 are operating correctly, the fixer or ink is applied to selected locations on a print media including a fluorescent substance which is then subjected to ultra-violet radiation. The method involves: irradiating the media at a first wavelength which causes the media substance to fluoresce to produce radiation at a second wavelength; detecting the reflectivity of a portion of the media at the second wavelength; providing a reference reflectivity; and comparing whether the detected reflectivity with the reference reflectivity to detect whether fixer or ink is present at the portion of the media. In an ink-jet printer, applied fixer may be irradiated with ultra-violet light 31 by a source 30 and applied inks may be irradiated with visible light, with a common detector 40 in the visible light which may detect blue light 41 reflected from the media mounted on a printhead carriage 10. The arrangement, which may also be used with page wide printheads, photocopiers, fascsimile machines and scanners, permits the detection of ink or fixer which is not normally optically detectable and also the checking of individual nozzles of the printhead.