Process and apparatus for the singling of the sheets of a paper stack

Apparatus for singling of sheets of a paper stack comprising:

• a magazine for holding the stack;
• a perforated endless conveyance band disposed under said magazine for individually transporting the sheets of the stack;
• a suction box disposed below said conveyance band having an upper cover member supporting said conveyance band, said cover member having a concave surface transversely positioned relative to the transporting direction of said conveyance band, suction openings being provided in said cover member facing said magazine, said cover member being disposed below the lowest sheet of the stack positioned in said magazine;
• first means through which a vacuum is applied to said suction box to provide a subpressure therein;
• second means for grasping the lowest sheet when the lowest sheet is being transported but before the lowest sheet uncovers said suction openings of said suction box, at which time the vacuum is switched off to decompose the subpressure in said suction box;
• third means through which a blast of air is introduced into said suction box when the vacuum is switched off so that the next sheet of the stack is not sucked onto the conveyance band at this time;
• and
• said conveyance band being guided over a plurality of conveyance rolls, at least one of said conveyance rolls being driven, one of said rolls being a front roll disposed in front of said magazine in the conveyance direction, at least said front roll being crowned on its running surface, the radius of said running surface of said crowned front roll corresponding to the radius of said concave surface of said cover member of said suction box, with a highest point of said crowned front roll being in alignment with a lowest place of said concave surface of said cover member.