SHEET-FEEDERS

Abstract: Sheet-feeding apparatus with a sheet support tray (10), a rear vacuum plenum chamber (19) adapted to acquire the rear portion of a sheet, a front vacuum plenum chamber (18) positioned over the front of the tray and adapted to acquire the front portion of a sheet, a sheet transport (27) associated with the front vacuum plenum to transport a sheet acquired in a forward direction, and an air knife (29) positioned at the rear of the stack of sheets to inject air between the trail edge of the top sheet in a stack and the remainder of the stack. The trail edge of a sheet in a stack is separated by the air knife, acquired by the rear vacuum plenum then acquired by the front vacuum plenum and transported in a forward direction. As the trailing edge clears the rear plenum, the rear plenum, which together with the air knife is continuously actuated, acquires the next sheet in the stack. In this way, the speed of the sheet feeder can be very high, since sheets are separated and acquired by the feeder simultaneously with transporting them off the stack. Preferably, the air knife includes preacquisition fluffer jets to loosen the top few sheets in the stack initially and lateral converging air streams to facilitate separation of the topmost sheet in the stack. The front vacuum plenum includes sheet acquisition tunnels over virtually its entire sheet contact surface in order to accommodate a wide variety of sheet sizes.

Description: The present invention relates to sheet-feeding apparatus, and in particular to high-speed sheet separating and feeding apparatus. A specific embodiment is directed to a top vacuum-corrugating feeding apparatus with two vacuum plena, one for top sheet acquisition, and the other for top sheet transport. With the current high speed xerographic copy reproduction machines wherein copies can be produced at a rate in excess of several thousand copies per hour, the need for a sheet feeder to feed cut copy sheets to the machine in a rapid, dependent manner was recognized to enable full utilization of the reproduction machine's potential copy output. In particular for many purely duplicating operations, it is desired to feed cut copy sheets at very high speeds where multiple copies are made of an original placed on the copying platen. In addition, for many high speed copying operations, a document handler to feed documents from a stack to a copy platen of the machine in a rapid dependable manner is also necessary to enable full utilization of the machine's potential copy output. These sheet feeders must operate flawlessly to eliminate the risk of damaging the sheets and generate minimum machine shutdowns because of uncorrectable misfeeds or sheet multifeeds. It is in the initial separation of the individual sheets from the sheet stack where the greatest number of problems occur. Since the sheets must be handled gently but positively to ensure separation without damage through a number of cycles, a number of separators have been suggested, such as friction rolls or belts used for fairly positive document feeding in conjunction with a retard belt, pad, or roll to prevent multifeeds. Vacuum separators, such as sniffer tubes, rocker type vacuum rolls, or vacuum feed belts, have also been utilized. While the friction roll-retard systems are very positive, the action of the retard member, if it acts upon the printed face, can cause smearing or partial erasure of the printed material on the document. With single-sided documents, if the image is against the retard mechanism, it can be smeared or erased. On the other hand, if the image is against the feed belt it smears through ink transfer and offset back to the paper. Moreover, with documents printed on both sides, the problem is compounded. Additionally, the reliable operation of friction-retard feeders is highly dependent on the relative frictional properties of the paper being handled. This cannot be controlled in a document feeder. One of the sheet feeders best known for high speed operation is the top vacuum corrugation feeder with front air knife. In this system, a vacuum plenum with a plurality of friction belts arranged to run over the vacuum plenum is placed at the top of a stack of sheets in a supply tray. At the front of the stack, an air knife is used to inject air into the stack to separate the top sheet from the remainder of the stack. Air is blasted by the air knife at the stack to separate the top sheet, which becomes sucked into contact with the belts. Following acquisition, the belt transport drives the sheet forward off the stack of sheets. In this configuration, separation of the next sheet cannot take place until the top sheet has cleared the stack. In addition, acquisition of the next sheet in the stack cannot occur until the top sheet has cleared the vacuum plenum. In this type of feeding system every operation takes place in succession or serially and therefore the feeding of subsequent sheets cannot be started until the feeding of the previous sheet has been completed. This procedure takes time and therefore limits the potential operational speed of the sheet feeder. In such a system, in order to try to increase the throughput speed, it has been proposed to activate the vacuum and the transport belts continuously. This frequently results in a difficulty in acquiring the top sheet in a stack, since it must be acquired by a suction applied through moving friction belts. In addition, the second sheet can be prematurely acquired as the trail edge partially clears the vacuum plenum. An overlay multifeed may occur that must be separated with another device. Thus the inherent structure in such a system limits its potential operational speed. In addition, in this type of system the air knife may cause the second sheet to vibrate independent of the rest of the stack in a manner referred to as "flutter". When the second sheet is in this situation, if it touches the top sheet, it may tend to creep forward slightly with the top sheet. The air knife then may drive the second sheet against the first sheet, causing a 'shingle', or double feeding of sheets. A sheet feeder in answer to the above-mentioned problem is US-A-4,451,028, in which a rear air knife vacuum corrugation feeder is disclosed that uses a moving carriage to position an air knife assembly, as well as a rear vacuum assembly, with respect to the trail edge of a copy sheet stack, but the moving carriage applies a cost burden to the apparatus. Relevant prior art can be summarized as follows: EP-A-0,155,475 describes a sheet-feeding mechanism which employs a guide block having a groove with a flat floor cut into it, in which an endless belt containing perforations travels. A vacuum, when periodically applied by a valve, operates through the perforations so that the topmost sheet of the stack is sucked against the endless belt. The guide block is adjustable for regulating the distance a sheet is forwarded along a sheet receiving apparatus, such as an alignment table. US-A-3,158,367 describes a sheet feeding system employing a sheet separating head the bottom surface of which is provided with a groove which terminates in an enlarged portion. Vacuum is applied through a hose creating a low pressure in the enlarged portion which low pressure extends along the groove causing the top sheet of an underlying stack to "peel" progressively from the stack. US-A-2,979,329 describes a sheet-feeding mechanism useful for both top and bottom feeding of sheets, wherein an oscillating vacuum chamber is used to acquire and transport a sheet to be fed. In addition, an air blast is directed to the leading edge of a stack of sheets from which the sheet is to be separated and fed to assist in separating the sheets from the stack. US-A-3,424,453 illustrates a vacuum sheet separator feeder with an air knife, wherein a plurality of feed belts with holes are transported about a vacuum plenum and pressurized air is delivered to the leading edge of the stack of sheets. This is a bottom sheet feeder. US-A-2,895,552 illustrates a vacuum belt transport and stacking device wherein sheets which have been cut from a web are transported from the sheet supply to a sheet stacking tray. Flexible belts perforated at intervals are used to pick up the leading edge of a sheet and release the sheet over a pile for stacking. US-A-4,157,177 illustrates another sheet stacker wherein a first belt conveyor delivers sheets in a shingled fashion, and the lower reach of a second perforated belt conveyor, which is above the top of the stacking magazine, attracts the leading edge of the sheets. The device has a slide which limits the effect of perforations depending on the size of the shingled sheet.. US-A-4,268,025 describes a top sheet feeding apparatus wherein a sheet tray has a vacuum plate above the tray which has a suction hole in its bottom portion. A feed roll in the suction hole transports a sheet to a separating roll and a frictional member in contact with the separating roll. FR-A-2,461,668 discloses a sheet unstacking and dispensing machine having a rear air nozzle and an overhead vacuum plate. The rear air nozzle forces the top sheet of a stack into contact with the overhead vacuum plate. A roller located at the front of the vacuum plate then dispenses the top sheet from the vacuum plate. US-A-4,184,672 shows a sheet-feeding apparatus that includes a rear air blast nozzle and a rear suction cup mechanism. Means for controlling the supply of vacuum and compressed air to the sheet feeding apparatus is also included. A sheet is separated from the top of a stack by the rear air blast nozzle. The rear suction cup grips the trail edge of the sheet and forces the sheet forward into contact with a transport mechanism. US-A-4,470,589 is directed to a sheet-feeding apparatus that includes a primary rear air nozzle, a secondary rear air nozzle and a rear air suction cup mechanism. The primary rear air nozzle separates the trail edge of the top sheet from a stack. The rear suction cup mechanism grips and lifts the trail edge of the sheet. The secondary rear air nozzle injects pressurized air between the sheet and the stack, thereby forcing the sheet into contact with a transport path. SU-A-138,184 discloses a sheet-feeding mechanism having a rear air jet and overhead suction members. The rear air jet forces the top sheet of a stack into contact with overhead suction members. The front suction member then dispenses the top sheet from the stack. The present invention provides a sheet-feeding apparatus, comprising a sheet stack support tray, a rear vacuum plenum chamber positioned over the rear portion of the tray and adapted to acquire the rear portion of a top sheet, when sheets are in the tray, a front vacuum plenum chamber positioned over the front of the tray and adapted to acquire the front portion of a top sheet when sheets are in the tray, sheet transport means associated with the front vacuum plenum to transport the sheet acquired by the front vacuum plenum in a forward direction out of the tray, and an air knife positioned at the rear of the tray and adapted to inject air between the trail edge of the top sheet in a stack of sheets and the remainder of the stack when a stack of sheets is in the tray, characterised in that said tray includes an adjustable front edge guide adapted for movement to a first position in order to accommodate the feeding of small size sheets and to a second extended position in order to feed large size sheets and the front vacuum plenum chamber is provided with openings that are positioned with respect to the first position of the adjustable front edge guide to lie closely spaced from the adjustable front edge guide and just inside the lead edge of the smallest sheet to be fed, the openings being adapted to induce a sub-atmospheric pressure above the sheet stack, thereby causing a separated sheet to adhere to the front vacuum plenum chamber and the transport means, and acquisition tunnels connected to the openings to allow suction to be applied successively to all areas of the acquired sheet. For a better understanding of the invention as well as other features thereof, reference is made to the accompanying drawings, in which: Figure 1 is a cross-sectional side view of an exemplary sheet feeder of the present invention; Figure 2 is an enlarged partial cross-sectional side view of the sheet feeder of Figure 1, showing an acquisition tunnel in a front vacuum plenum; Figure 3 is an enlarged partial cross-sectional side view of the sheet feeder of Figure 2 after a B5 size sheet has been acquired; Figure 4 is an enlarged partial cross-sectional side view of the sheet feeder of Figure 1 in position to feed A3 size sheets, and Figure 4A is an enlarged partial cross-sectional side view of the sheet feeder of Figure 4, showing an A3 sheet having been acquired by front and rear vacuum plena. The invention will now be described with reference to a preferred embodiment. As used herein, the term "high-speed sheet feeding" is intended to mean the feeding of sheets at a speed greater than one per second. Typically, apparatus according to the present invention is capable of feeding sheets in excess of four sheets per second, and has achieved sheet feeding rates as high as seven to ten sheets (8½ x 11", long edge feed) per second. Referring more particularly to Figure 1, there is illustrated an exemplary sheet separator feeder for installation adjacent to the exposure plates of a conventional xerographic reproduction machine for feeding of documents to the platen for copying. Alternatively, or in addition, the sheet feeder may be mounted at the beginning of the paper path for the feeding of cut sheets of paper. In either situation, the feeder illustrated is merely one example of a sheet separation feeder according to the present invention. The sheet feeder is provided with a sheet stack supporting tray 10 which may be raised and lowered through electric power screws 11,12 by means of motor 13 from the base support platform 14. The drive motor is actuated to move the sheet stack support tray vertically upward by stack height sensor 17 when the level of sheets relative to the sensor falls below a first predetermined level. The drive motor is deactuated by the stack height sensor 17 when the level of the sheets relative to the sensor is above a predetermined level. The stack height sensor is located at the rear and at a side of the stack of paper to sense height level. In this way the level of the top sheet in the stack of sheets may be maintained within relatively narrow limits to ensure proper sheet separation, acquisition and feeding. The illustrated device provides both a front and a rear vacuum plenum arrangement to perform separate functions in the steps of sheet acquisition and transport. The front vacuum plenum 18 and the rear vacuum plenum 19 are kept at sub-atmospheric pressure through conduits 20,21 by means of vacuum pump 24. When the pump 24 is activated, air is pulled from both the front and rear vacuum plena through the pump to exhaust 25. A valve 16 is placed in the air conduit 20 supplying the front vacuum plenum. The front vacuum plenum also has associated with it a belt transport assembly for transporting the top sheet in the stack from the stack. At the rear of the stack of sheets is an air knife 28 having at least one nozzle 29 directed to the rear of trailing edge of the top sheet in a stack of sheets to be fed. The air knife serves to direct a continuous blast of air at the trailing edge of a sheet to separate the top sheet from the remainder of the stack by inserting a volume of air therebetween. In this embodiment, the air knife performs two functions, preacquisition separation of sheets, and if necessary, a post-acquisition separation of the top sheet from the remainder of the stack. In operation, the sheet stack support tray 10 is elevated by power screws 11, 12 and advances the topmost sheet to the sheet-feeding level. The vacuum pump 24 is actuated and continuously exhausts air from lines 21 and 20, it being noted that line 20 is periodically closed by valve 16. In addition, the air knife is continuously actuated to inject air between the top sheet and the remainder of the stack and serves to separate the top sheet from the remainder of the stack. Once separated, the trailing portion of the top sheet is readily acquired by the rear vacuum plenum 10. With the valve 16 open, the front of the topmost sheet is acquired by the front plenum 18 as the air knife 28 continues to direct air into the space formed between the top sheet and the remainder of the stack, and forces a separation of the top sheet from the remainder of the stack. The belt transport assembly is actuated and the top sheet which has been acquired by both vacuum plena, is driven forward from the stack. The sheet is fed forward since the driving force on the sheet from the belt transport and front plenum assembly is greater than the drag force exerted on the sheet by the rear plenum. For both plenum chambers the force exerted F is controlled by the suction applied, times the area of the sheet exposed to the suction, times the coefficient of friction. Since the suction applied may be the same in both plenum chambers, it does not have to be the controlling factor. The area of exposure and the coefficient of friction, with reference to the rear plenum, are relatively low, and hence the drag force is also relatively low. In contrast, the belt assembly associated with the front plenum provides a relatively large area of contact with the top sheet and has a surface with a relatively high coefficient of friction. Thus, the frictional driving force exerted on the sheet by the front vacuum and by the belt transport assembly is greater than the drag force exerted on the sheet by the rear vacuum plenum. Typically in operation, the air knife 28 and the rear vacuum plenum 19 are constantly actuated, while the front vacuum plenum 18 and belt transport 27 are pulsed for each sheet that is fed to ensure an intercopy gap between the sheets being fed, and to avoid the possibility of sheets shingling out with the top sheet, and giving rise to shingle sheet feeding or multisheet feeding. Generally, the belt transport and the front vacuum plenum are pulsed simultaneously to start and stop the suction and the belt drive. Alternatively, the belt transport assembly may be continuously driven while the front vacuum plenum is pulsed on and off for each sheet feed. This is a possible alternative because if the suction in the front plenum is turned off, the transport belt may continue to advance the top sheet since its leading edge may have already been captured by the output feed rolls 32, 33 which will extract the top sheet from the tray. Output feed rolls continuously drive separated sheets onto the next operating station in the process. At the nip of the output feed roll pair is a sensor 34 for sensing the lead edge of the sheet. This sensor, by its location, automatically determines that a sheet has been separated and fed and is under a different drive system. Accordingly, the front vacuum plenum and the belt transport may be deactuated. Reference to Figures 2-4A will schematically illustrate how the sheet feeder of the present invention is an improvement over the sheet feeder in US-A-4,451,028. In Figure 2, the front vacuum feedhead assembly includes a vacuum plenum 18, vacuum ports 50 and one of a plurality of acquisition tunnels or channels 51 that allow the feedhead assembly to acquire and feed A4 and A3 sheets with equal ease and with fewer mechanical parts than the '028 feeder. Sheets are acquired and separated at the stack trail edge precisely as is done with the '028 feeder, however, the air knife assembly and the rear vacuum plenum in the '028 patent have to be positioned at the trail edge of a sheet stack for various sheet sizes. To eliminate the cost associated with moving both the air knife assembly and rear vacuum plenum, and in accordance with the present invention, air knife 28 and rear vacuum plenum 14 are stationary and sheets 30 are rear edge registered against tray end stop 41. Openings in front vacuum plenum 18 lie just inside the lead edge of B5 sheets. These openings permit suction flow which induces a negative pressure gradient above the stack, causing a sheet to tack to the feedhead assembly and belt transport 27, as shown in Figure 3. For larger sheets (A3), stack front edge guide 40 is moved from the solid line position in Figure 1 to the solid line position in Figure 4 and as shown in Figure 4A, a sheet is first acquired at the vacuum port opening 50. However, the presence of continuous acquisition tunnels 51 allows suction flow to be continually drawn over the stack, as indicated by the arrows in Figure 4, thereby enhancing the front vacuum plenum in acquiring the whole sheet as in Figure 4A. Because of the acquisition tunnels 51, B5 size sheets are continually held and driven by transport belt 27 until each reaches a set of take-away rolls 32,33. The rear air knife vacuum corrugation feeder of the present invention provides a very high speed reliable sheet feeder at lower cost. The feeder employs a stationary rear air knife and rear vacuum plenum in conjunction with a sheet stack tray having a rear edge registration member. A front vacuum plenum has sheet acquisition tunnels therein in order to increase the size of sheets that can be accommodated by the apparatus without movement of the air knife or front and rear plena. The continuous acquisition tunnels are positioned over the entire feedhead assembly, which ensures acquisition of a whole sheet area. While the present invention has been described with reference to a stationary feedhead and a elevating sheet stacking tray, a stationary tray and moving feedhead could be employed.

Claims: Sheet-feeding apparatus, comprising a sheet stack support tray (10), a rear vacuum plenum chamber (19) positioned over the rear portion of the tray (10) and adapted to acquire the rear portion of a top sheet, when a stack of sheets is in the tray, a front vacuum plenum chamber (18) positioned over the front of the tray and adapted to acquire the front portion of said top sheet, sheet transport means (27) associated with the front vacuum plenum chamber, to transport the sheet acquired by the front vacuum plenum in a forward direction out of the tray, and an air knife (28) positioned at the rear of the tray and adapted to inject air between the trail edge of said top sheet and the remainder of the stack in the tray, characterised in that said tray (10) includes an adjustable front edge guide (40) adapted for movement to a first position in order to accommodate the feeding of small size sheets and to a second extended position in order to feed large size sheets and the front vacuum plenum chamber (18) is provided with openings (50) that are positioned with respect to the first position of the adjustable front edge guide (40) to lie closely spaced from the adjustable front edge guide (40) and just inside the lead edge of the smallest sheet to be fed, the openings being adapted to induce a sub-atmospheric pressure above the sheet stack, thereby separating said top sheet from the stack and adhering it to the front vacuum plenum chamber (18) and the transport means (27), and acquisition tunnels (51) connected to the openings to allow suction to be applied successively to all areas of the acquired sheet. Sheet-feeding apparatus, comprising: a support tray (10) for supporting a stack of sheets for feeding therefrom; an air knife (28) positioned in the rear of the tray (10) to separate the top sheet in the stack from the remaining sheets in the stack; rear vacuum plenum means (19) adapted to acquire the trail edge of the sheet separated from the stack by the air knife (28), and front vacuum plenum means (18) adapted to acquire the lead edge of the sheet separated from the stack by the air knife (28), said tray (10) including a rear edge registration means (41) for registering the stack of sheets thereagainst, characterised in that said tray (10) includes an adjustable front edge guide (40) adapted for movement to a first position in order to accommodate the feeding of small size sheets and to a second extended position in order to feed large size sheets and wherein the front vacuum plenum has openings (50) at are positioned with respect to the first position of the adjustable front edge guide (40) to lie closely spaced from the adjustable front edge guide (40) and just inside the lead edge of the smallest sheet to be fed, the openings allowing suction to be applied to the top sheet to cause it to adhere to the front vacuum plenum, and acquisition tunnels (51) connected to the openings (50) to allow suction to be applied to all areas of the sheet, and feed heads (27) for forwarding the sheet away from the stack of sheets for further processing. A sheet feeding apparatus of any preceding claim, characterised in that each vacuum plenum includes means for corrugating sheets adhered thereto. A sheet feeding apparatus of any preceding claim, characterised in that the air knife (28) and the rear vacuum plenum (19) are stationary. A sheet feeding apparatus of any preceding claim, characterised in that the stack of sheets is rear edge registered. Sheet-feeding apparatus, comprising a sheet stack support tray (10), a vacuum plenum chamber (19) positioned over the rear portion of the tray (10) and adapted to acquire the rear portion of a top sheet when a stack of sheets is in the tray, a vacuum plenum chamber (18) positioned over the front of the tray and adapted to acquire the front portion of a sheet, the vacuum plenum chambers (18, 19) each having a portion positioned in its bottom to provide a corrugation member parallel to the sheet-feeding direction, means (27) associated with the front vacuum plenum to transport the sheet acquired by the front vacuum plenum in a forward direction out of the tray, and an air knife (28) positioned at the rear of the tray (10) and adapted to inject air between the trail edge of the top sheet in a stack of sheets and the remainder of the stack, characterised in that said tray (10) includes an adjustable front edge guide (40) adapted for movement to a first position in order to accommodate the feeding of small size sheets and to a second extended position in order to feed large size sheets and the front vacuum plenum chamber (18) having openings (50) that are positioned with respect to the first position of the adjustable front edge guide (40) to lie closely spaced from the adjustable front edge guide (40) and just inside the lead edge of the smallest sheet to be fed, the openings being adapted to induce a sub-atmospheric pressure above the sheet stack, thereby causing said top sheet to adhere to the front vacuum plenum chamber, and acquisition tunnels (51) connected to the openings to allow the sub-atmospheric pressure to reach all areas of the acquired sheet. A sheet-feeding apparatus of claim 6, characterised in that the acquisition tunnels (51) are of D-shaped cross-section

Inventors: ROLLER, GEORGE J.
Applicants: XEROX CORPORATION
Application year: 1987
Main classification: B65H3
IPC codes: B65H3