Over-platen document registration apparatus

In an original document sheet feeding and registration apparatus for a copier, in which a document sheet is fed with a document feeding belt having a diffusely light reflective surface over a transparent platen imaging station of the copier, said imaging station having a document illumination exposure system and a copying lens system under the platen, the improvement comprising:

• at least one minor spectrally reflective patch on said otherwise diffusely light reflective surface of said document belt,
• means for feeding the document sheets onto said belt in synchronism with said spectral patches such that at least one edge of the document sheet only partially overlies said patch and a portion of said spectral patch is exposed,
• and a photosensor system for detecting an edge of the document sheet while the document sheet is over said platen and within said imaging station and within the field of view of said lens system, said photosensor system being optically invisible to said copier,
• said photosensor system comprising sensor illumination means distinct from said exposure illumination system and photosensor means aimed at a registration position on said platen for detecting changes in the light level from said sensor illumination means reflected from said spectral patch,
• and wherein said photosensor system detects the arrival of a document sheet edge at said registration position by sensing the transition in intensity of the reflected illumination from a spectral patch at said registration position versus the reflected illumination from a document sheet partially overlying said spectral patch at said registration position.