Patent ID: 7296792

Claim:
A sheet-actuated vacuum assisted sheet conveyor for the continuous transfer of sheets delivered in serial spaced relation, said conveyor comprising: a pair of laterally spaced, parallel driven flat coplanar conveyor belts operating over a flat surface of a vacuum plenum, the flat plenum surface between the belts recessed from the coplanar flat belts to define a shallow vacuum channel; a plurality of vacuum control valves in said flat surface spaced in a direction of conveyor belt movement and providing vacuum communication between the plenum and the vacuum channel; said control valves operative to be held closed in the absence of a sheet on the conveyor, by a negative pressure in the plenum sufficient to create a first pressure differential across the valves, said valves including means for biasing the valves to open for vacuum communication at a second pressure differential across the valves less than the first pressure differential; means for moving sheets into planar contact with the conveyor belts in a manner that progressively covers said vacuum channel; and, means for applying plenum vacuum to an upstream end of the vacuum channel upstream of the upstreammost valve such that, as a sheet moves to progressively cover said vacuum channel, vacuum pressure in the channel moves in a downstream direction with the sheet to cause the first pressure differential across each valve in succession to decrease to said second pressure differential and said valves to serially open, thereby applying the plenum vacuum directly to the sheet to hold the same against and to move with the conveyor belts.