Document feeder with vacuum system having two control valves in series

In a sheet feeder for feeding a sheet along a path extending from a storage position to a work station, the improvement comprising:

• a vacuum blower;
• vacuum operated means coupled to said blower and effective to at least partially remove a sheet from the storage position and feed the sheet into the path;
• vacuum transport means for receiving a sheet from the vacuum operated means and for advancing the sheet along the path to the work station, the vacuum transport means comprising a vacuum belt located along the path, and first and second vacuum plenums adjacent the belt, the second plenum being coupled to said blower, the vacuum transport being operable to apply a first level of vacuum through said first plenum to a sheet as the sheet travels along a first part of the path and to apply a second and lower level of vacuum through said second plenum to a sheet as the sheet travels along a subsequent part of the path;
• and
• first and second control valves for regulating the flow of air from the vacuum operated means and the first plenum to the blower, the first valve being connected to the blower and the vacuum operated means and the second valve being connected to the first plenum and the first valve so that operation of the first valve controls vacuum in the vacuum operated means and operation of both valves is required for control of vacuum in the first plenum.

In a vacuum system for a document feeder, the feeder being useful for feeding seriatim a plurality of document sheets along a path having (1) a first portion extending from a stack of such sheets to an exposure position, wherein the sheets are registered and copied, and (2) a second portion leading away from the exposure position, the feeder having an oscillating vacuum member for removing a sheet from the stack and initiating movement of the removed sheet along the first portion of the path, and a vacuum transport for receiving a sheet removed by the vacuum member and for advancing the sheet along the first portion of the path toward the exposure position, the vacuum transport comprising at least one vacuum belt, a first vacuum plenum and a second vacuum plenum positioned adjacent said belt along the first portion of the sheet path so that a sheet can be attracted to the belt for transport along said path when a partial vacuum exists in at least one of said plenums, the first plenum being located along said path between the second plenum and the vacuum member;

• the improvement comprising:
• a vacuum blower;
• a first conduit directly interconnecting said blower and said second plenum;
• a first control valve having an inlet port connected to said blower and having first and second outlet ports, the first outlet port being connected to the vacuum member, said control valve being adjustable between (1) a first open position wherein the second outlet port is closed and the first outlet port is open to the passage of air from the vacuum member to the blower so that a partial vacuum can be established in the vacuum member and (2) a second open position wherein the first outlet port is closed to the passage of air from the vacuum member to the blower to allow the vacuum member to return to atmospheric pressure and the second outlet port is open;
• a second control valve, the second valve having (a) an inlet port connected to the second outlet port of the first valve, (b) an outlet port connected to the first plenum and (c) a vent, said second valve being adjustable between (1) a closed position wherein the inlet port is closed to the passage of air from the first plenum to the first valve and the vent is open to allow the first plenum to reach atmospheric pressure, and (2) an open position wherein the vent is closed and the inlet port is open to the passage of air from the first plenum to the first valve so that a partial vacuum can be established in the first plenum;
• and
• control means for operating said valves in a programmed sequence wherein (1) the first valve is adjusted to its first open position to temporarily establish a vacuum in the oscillating vacuum member for feeding a sheet from a stack and into the first portion of the path and the second valve is in its closed position, and then (2) the first valve is adjusted to its second open position and the second valve is adjusted to its open position to allow the oscillating vacuum member to return to atmospheric pressure and to temporarily establish a partial vacuum in the first plenum to hold the sheet against the belt while the belt moves the sheet along the first portion of the path until the sheets come under the influence of vacuum in the second plenum and then the second valve is closed.

In a sheet feeder for feeding a sheet along a path extending from a storage position to a work station, the improvement comprising:

• a vacuum blower;
• vacuum operated means coupled to said blower and effective to at least partially remove a sheet from the storage position and feed the sheet into the path;
• vacuum transport means for receiving a sheet from the vacuum operated means and for advancing the sheet along the path to the work station, the vacuum transport means comprising a vacuum belt located along the path, and first and second vacuum plenums adjacent the belt, the vacuum transport means being operable to apply a first level of vacuum through said first plenum to a sheet as the sheet travels along a first part of the path and to apply a second and lower level of vacuum through said second plenum to a sheet as the sheet travels along a subsequent part of the path, the second plenum being coupled directly to said blower;
• a first control valve for regulating the flow of air from said vacuum operated means to said blower, the first valve having an inlet port coupled to said blower, a first outlet port coupled to said vacuum operated means and a second outlet port;
• a second control valve for regulating the flow of air from the first plenum to the blower, the second valve having an inlet port coupled to the second outlet port of the first valve and an outlet port coupled to said first plenum, and
• logic and control means connected to said control valves and operable to regulate the operation of said valves in a programmed sequence calling for (1) operation of the first valve to provide vacuum to said vacuum operated means to initiate feeding of a sheet into the path and (2) then operating the first and second valves to interrupt the vacuum supply to the vacuum operated means and to establish a vacuum in the first plenum, thereby to tack a sheet to the belt so the belt can transport the sheet, followed by interruption of the vacuum supply to the first plenum after the sheet comes under the influence of vacuum supply to the second plenum.