Grooved vacuum belt document handling system

For a document handling apparatus in which documents are moved with a vacuum belt to an imaging station of a copier, where the documents are imaged against a light reflected document imaging surface on a first side of said belt, and in which the documents are attracted to said first side of said belt by an air flow applied from a vacuum manifold at the second side of said belt through multiple vacuum apertures extending through the belt and opening on said first side, the improvement in said vacuum belt wherein:

• said openings of said vacuum apertures are limited to areas of said first side of said belt coverable by the smallest document to be imaged thereagainst, to avoid show-around exposure of said apertures during said document imaging,
• said first side of said belt has a multiplicity of vacuum channels recessed slightly below said light reflective document imaging surface thereof,
• said vacuum channels have sufficiently gently sloping walls to avoid imaged edge shadows thereof at said imaging station and light reflective characteristics substantially equal to or better than said document imaging surface to avoid show-around imaging of said channels,
• said openings of said vacuum apertures at said first side of said belt are recessed witin said vacuum channels substantially spaced below said document imaging surface, and said vacuum channels pneumatically connect with said vacuum apertures and extend unapertured outwardly from and beyond said vacuum apertures over said document imaging surface of said belt,
• said vacuum apertures are sufficiently large to provide a low impedance relatively unrestricted airflows therethrough into said vacuum channels, to provide airflows along said vacuum channels into said vacuum apertures from the direction of the edges of a document, and to thereby generate vacuum holddown forces along said channels between said document and said belt, whereby different sizes of documents may be vacuum retained on said document imaging surface without either said vacuum apertures or said vacuum channels being substantially imagable;
• and
• in which said vacuum apertures are provided only in discrete plural spaced minor areas of said belt, each of which spaced minor areas is smaller in dimensions than the dimensions of the smallest document to be held by said belt over that area, to provide plural document holding areas along said belt, and in which said vacuum grooves have depths of less than approximately one millimeter, and said vacuum channels have transverse dimensions of less than approximately four millimeters to avoid excessive deformation of thin documents therein by the vacuum applied through said vacuum apertures to said vacuum channels, and said vacuum channels comprise a plurality of elongated and pneumatically separated grooves in said imaging surface, with discrete said groove containing discrete said vacuum apertures in said limited areas thereof, said vacuum grooves are pneumatically separated from one another by being spaced apart on said document imaging surface between ungrooved document imaging surface areas of said belt, so that individual grooves with their respective vacuum apertures provide independently operating vacuum holding forces under an overlying document, and the total cross-sectional area of the vacuum apertures in a said groove is sufficiently greater than the cross-sectional area of said groove so that the airflow restriction along said groove under a document is significantly greater than the airflow restriction through said apertures into said groove.