Apparatus for detecting tape on sheets

Claim 1

Apparatus for sensing the condition of the surface of a moving printed document, comprising: (a) illuminating means (A) including a plurality of optical fibres for guiding light to the surface of the document, said fibres having laterally spaced light-emitting ends with a low numerical aperture to direct collimated beams of light at a plurality of adjacent regions in a line across the document in a direction transverse to its movement; (b) a pair of first and second light receivers for each illuminated region of the document, each pair including individual first and second photoelectric means and associated optical fibres leading to the individual photoelectric means; (c) light-receiving ends of the optical fibers of the first light receivers (D) being laterally spaced across the path of document movement for receiving light specularly reflected from the plurality of adjacent illuminated regions, and the associated first photoelectric means providing corresponding first electrical signals; (d) light-receiving ends of the optical fibers of the second light receivers (B) being laterally spaced across the path of document movement for receiving light diffusely reflected from corresponding ones of said regions, and the associated second photoelectric means providing corresponding second electrical signals; and (e) signal-analyzing means (10-14) for receiving the signals from each pair of first and second light receivers and responsive, for each pair, to an increase in the ratio of the instantaneous values of the first and second signals, representing respectively light reflected specularly and diffusely from the corresponding illuminated region, to provide a signal output indicative of the presence of shiny tape on the illuminated surface of the document.