Sensing head assembly for multi-color printing press on-line densitometer

In sensing head assembly for multi-color printing press on-line densitometer comprising a sensing head housing movably mounted on cross support members extending across the width of a material being printed by a multi-color press together with means for traversing the sensing head housing back and forth across the width of the material being printed and the material being printed having printed thereon a plurality of spaced-apart color bars extending across the width of the material at predetemined intervals along its length, the color bars comprising a plurality of aligned discrete areas each printed with an elemental color such that each color bar includes all of the elemental colors appearing on the material;

• the improvement comprising a multiplicity of high luminance lamps mounted within the sensing head housing adjacent respective reflectors for projecting light emanating from each lamp through window means formed in the underside of the sensing head housing and onto a specimen plane of material being printed to thereby define an inspection zone for illuminating selected color bars at any point along the width and length of the material, receptor objective lens means for viewing an area on the printed material passing through the inspection zone and illuminated by said high luminance lamps and projecting an image of a selected color bar onto an image plane located within the sensing head housing, means defining an aperture plane located substantially at the image plane and having respective aperture openings therein corresponding in position to each elemental color area comprising the color bar, opto-electric conversion means positioned in back of the respective aperture openings in said aperture plane and responsive primarily only to a respective elemental color light corresponding to the discrete elemental color area of the color bar being imaged through a respective aperture opening, additional small area light responsive opto-electric conversion devices positioned on each side of a selected traverse positioning guide point defined by a particular discrete elemental color area with said additional small area light responsive opto-electric conversion devices being selectively responsive to elemental color light that defines the selected traverse positioning guide point, and feedback circuit means responsive to the output from the additional small area light responsive opto-electric conversion devices for deriving feedback positioning signals for supply to the drive means for traversing the sensing head housing back and forth across the cross support member whereby precise positioning of the sensing head housing at a desired point relative to a color bar can be achieved.

In a sensing head assembly for a multi-color printing press on-line densitometer comprising a sensing head housing movably mounted on cross support members extending across the width of a material being printed by a multi-color press together with means for traversing the sensing head housing back and forth across the width of the material being printed and the material being printed having printed thereon a plurality of spaced-apart color bars extending across the width of the material at predetermined intervals along its length, the color bars comprising a plurality of aligned discrete areas each printed with an elemental color such that each color bar includes all of the elemental colors appearing on the material;

• the improvement comprising a multiplicity of high luminance lamps mounted within the sensing head housing adjacent respective reflectors for projecting light emanating from each lamp through window means formed in the underside of the sensing head housing and onto a specimen plane of material being printed to thereby define an illuminated inspection zone for selected color bars at any point along the width and length of the material, receptor objective lens means for viewing an area on the printed material passing through inspection zone and illuminated by said high luminance lamps and projecting an image of a selected color bar onto an image plane located within the sensing head housing, means defining an aperture plane located substantially at the image plane and having respective aperture openings therein corresponding in position to each discrete elemental color area comprising the color bar, opto-electric conversion means positioned in back of the respective aperture openings in said aperture plane and responsive primarily only to a respective elemental color light corresponding to the discrete elemental color area of the color bar being imaged through a respective aperture opening, and differentiating circuit means coupled to the outputs from a plurality of said light sensitive opto-electric conversion means for differentiating the output pulses produced thereby and providing at least a leading edge and/or trailing edge signal pulse indicative of the movement of the leading and/or trailing edge of a plurality of elemental color areas of the color bar into the inspection zone for use as registration control signals.

In a sensing head assembly for a multi-color printing press on-line densitomter comprising a sensing head housing movably mounted on cross support members extending across the width of a material being printed by a multi-color press together with means for traversing the sensing head housing back and forth across the width of the material being printed and the material being printed having printed thereon a plurality of elemental color areas located at different points extending across the width of the material and at predetermined intervals along its length;

• the improvement comprising a multiplicity of high luminance lamps mounted within the sensing head housing adjacent respective reflectors suitably designed for projecting light emanating from each lamp through window means in the underside of the sensing head housing and onto the specimen plane of material being printed to thereby define an inspection zone for illuminating selected color areas at any point along the width and length of the material, receptor-objective lens means having a maximum numerical aperture for viewing an area on the printed material passing through the inspection zone and for projecting an image of selected color area onto an image plane located within the sensing head housing, means defining an aperture plane located near the image plane and having respective aperture openings therein corresponding in position to each discrete elemental color area, opto-electric conversion means positioned in back of the respective aperture openings in said aperture plate means and responsive primarily only to a respective elemental color light corresponding to the discrete elemental color area being imaged through a respective aperture opening, said opto-electric conversion means each comprising a small area, high impedance semiconductor photodetector cell, and photo-metric scale standardizing means viewed by said receptor objective lens means during each traversal of said sensing head housing across the width of the printed material being inspected for providing a background data reference reflectance level, said opto-electric conversion means viewing the photometric scale standardizing means at the end of each traversal of the sending head housing and deriving output calibration signals for use in calibrating the response of the opto-electric conversion means while viewing the color areas.