Sheet feeding apparatus

Abstract: A top vacuum corrugation feeder with optimized performance for a large variation in sheet sizes is obtained by adjusting the vacuum port area of a vacuum chamber by the action of adjusting paper guides (43,44) in the paper tray (40) for different sheet sizes.

Description: This invention relates generally to a sheet feeding apparatus for an electrophotographic printing machine. Present high speed xerographic copy reproduction machines produce copies at a rate in excess of several thousand copies per hour, therefore, the need for a sheet feeder to feed cut copy sheets to the machine in a rapid, dependable manner has been 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 also been reorganized to enable full utilization of the machine's potential copy output. These sheet feeders must operate flawlessly to virtually eliminate the risk of damaging the sheets and generate minimum machine shutdowns due to 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. 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. In operation, air is injected by the air knife toward the stack to separate the top sheet, the vacuum pulls the separated sheet up and acquires it. 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 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. 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 forwardly 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. Also, some current top and bottom vacuum corrugation feeders utilize a valved vacuum feedhead, e.g., US-A-4,269,406 and 4,451,028. At the appropriate time during the feed cycle the valve is actuated, establishing a flow and hence a negative pressure field over the stack top or bottom if a bottom vacuum corrugation feeder is employed. This field causes the movement of the top sheet(s) to the vacuum feedhead where the sheet is then transported to the take-away rolls. Once the sheet feed edge is under control of the take-away rolls, the vacuum is shut off. The trail edge of this sheet exiting the feedhead area is the criteria for again activating the vacuum valve for the next feeding. A top vacuum corrugation feeder with a valveless vacuum system is shown in US-A-4,699,369. Current customer requirements for middle volume machines include the furnishing of sheet feeders that handle sheets ranging in size from A6 to 30.5x46CM (12"x18"). If the port area of a vacuum feedhead of a top vacuum corrugation feeder is designed for the A6 size sheets, there may be insufficient flow and pressure to acquire and feed the larger sheets. However, if the air system is designed for the larger sheets, smaller sheets will not cover all of the port openings, allowing air leakage and reducing feeder performance. Therefore, an improved feeder is needed that will reliably feed a wide variety of sheet sizes. US-A-4,157,177 (Strecker) 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-5,037,079 (Siegel et al.) is directed to a vacuum platen transport system that includes a shutter mechanism which is connected to a side guide of a document handler. Movement of the side guides closes off holes in the vacuum plenum in accordance with the size of documents placed in the document handler. EP-A-446,889 describes a sheet feeding apparatus comprising a sheet stack support tray and transport means for said sheets including a vacuum chamber wherein a mechanism is incorporated to reduce air leakage associated with the vaccuum chamber. An object of the present invention is to provide an improved feeder that will reliably feed a variety of sheets. Accordingly, the present invention provides a sheet feeding apparatus as defined in any of the appended claims. In accordance with one embodiment, a top sheet feeding apparatus is provided comprising a sheet stack support tray for supporting a stack of sheets within the tray, air knife means positioned immediately adjacent the front of said stack of sheets for applying a positive pressure to the sheet stack in order to separate the uppermost sheet in the stack from the rest of the stack, and feedhead means including a vacuum plenum chamber positioned over the front of the sheet stack having a negative pressure applied thereto during feeding, said vacuum plenum chamber having perforated feed belt means associated with said vacuum plenum chamber to transport the sheets acquired by said vacuum plenum chamber in a forward direction out of the stack support tray, characterized by said sheet stack support tray including adjustable side guides with hard or soft cover members attached thereto that are adapted to cover overlying port areas of said vacuum plenum chamber in order to optimize the performance of the sheet feeding apparatus for a large variation in sheet sizes. The present invention will be described further, by way of examples, with reference to the accompanying drawings, in which:- FIG. 1 is an enlarged partial cross-sectional view of the exemplary feeder which is employed in accordance with the present invention; FIG. 2 is a partial rear end view of the paper tray shown in FIG. 1 with 30.5x46cm (12"x18") sheets stacked therein and showing flexible vacuum port cover members outside the vacuum port area of the vacuum feedhead; FIG. 3 is a partial rear end view of the paper tray shown in FIG. 2 with A6 sheets stacked therein and showing flexible vacuum port cover members closing off portions of the area around the vacuum feedhead; FIG. 4 is a partial rear end view of the paper tray shown in FIG. 2 with 30.5x46cm (12"x18") sheets stacked therein and showing rigid vacuum enhancing members outside the vacuum port area of the vacuum feedhead; and FIG. 5 is a partial rear end view of the paper tray shown in FIG. 2 with A6 sheets stacked therein and showing rigid vacuum enhancing members moved closer to the vacuum feedhead. Referring now to a particular embodiment of the present invention, FIGS. 1 to 5 show a system employing the present invention in a copy sheet feeding mode. Alternately, or in addition, the sheet feeder may be mounted for feeding document sheets to the platen of a printing machine. The sheet feeder is provided as shown in FIG. 1 with a conventional elevator mechanism 41 for raising and lowering either tray 40 or a platform 42 within tray 40. Ordinarily, a drive motor is actuated to move the sheet stack support platform 42 vertically by a stack height sensor positioned above the rear of the stack 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 when the level of the sheets relative to the sensor is above a predetermined level. In this way, the level of the top sheet in the stack of sheets may be maintained within relatively narrow limits to assure proper sheet separation, acquisition and feeding. Tray 40 in FIG. 2 includes adjustable side guides 43 and 44 that are laterally or transversely movable with respect to the direction of transport of the sheets in any suitable conventional manner. The side guides have flexible members 45 and 46 attached to their upper ends adjacent to vacuum feedhead 70 such that the flexible members are adapted to abut against or not abut against support 49 when the side guides are moved toward or away from each other and vacuum pressure is applied through ports 72 of belts 71. Vacuum corrugation feeder 70 and a vacuum plenum 75 in FIG. 1 are positioned over the front end of a tray 40 having copy sheets 31 stacked therein. Belts 71 are entrained around drive rollers 24, as well, as plenum 75. Belts 71 could be made into a single belt if desired. Perforations or ports 72 in the belts allow a suitable vacuum source (not shown) to apply a vacuum through plenum 75 and belts 71 to acquire sheets 31 from stack 13. Air knife 80 applies a positive pressure to the front of stack 13 to separate the top sheet in the stack and enhance its acquisition by vacuum plenum 75. Corrugation rail 76 is attached or molded into the underside and center of plenum 75 and causes sheets acquired by the vacuum plenum to bend during the corrugation so that if a second sheet is still sticking to the sheet having been acquired by the vacuum plenum, the corrugation will cause the second sheet to detack and fall back into the tray. A sheet captured on belts 71 is forwarded through baffles 9 and 15 and into forwarding drive rollers 17 and 19 for transport to transfer station D. In order to prevent multifeeding from tray 40, a pair of restriction members 33 and 35 are attached to the upper front end of tray 40 and serve to inhibit all sheets other than sheet 1 from leaving the tray. It is also possible to place these restriction members or fangs on the air knife instead of the tray. Vacuum plenum 75 is preferably equipped with a negative pressure source that is ON continuously during the feed cycle, with the only criteria for sheet feeding being that the motion of vacuum feedhead 70 is ceased prior to the trail edge of the acquired sheet exposing all of the vacuum ports. The next sheet is then acquired in a "traveling wave" fashion as shown in FIG. 2. This feeding scheme affords a reduction in noise due to the elimination of the valve associated with cutting the vacuum means ON and OFF. The addition of flexible members 45 and 46 to adjustable side guides 43 and 44 enable the reliable feeding of a wide variety of sheet sizes through the sheet feed apparatus. Feeding of large sheets, such as, 30.5 x 46 cm (12" x 18") as shown in FIG. 2, is assured since sufficient flow and pressure to the vacuum feedhead is maintained by flexible cover members 45 and 46 being outside the influence of the vacuum port areas of the belts. However, when small sheets, e.g., A6 size, are in tray 40 as shown in FIG. 3, the side guides are moved into position toward each other and the flexible covers will be pulled up by the vacuum feedhead to abut against support member 49 and effectively close off some of the vacuum originating through some of the holes in the belts that are not covered by a sheet. Thus, air leakage is blocked and feeder performance is enhanced. Alternatively, as shown in FIGS. 4 and 5, rigid plates 47 and 48 could be integral with or attached to adjustable side guides 43 and 44, respectively, if desired. In FIG. 4, rigid plates 47 and 48 are positioned outside the vacuum port area of belts 71 and have no effect on the vacuum pressure of feedhead 70 while inwardly positioned side guides 43 and 44 in FIG. 5 shows plates 47 and 48 closer to the vacuum ports 72 of belts 71 and serving to thereby minimizing the leakage of air that would normally occur with smaller size sheets in the tray. In conclusion, a modification to the side guides for a top vacuum corrugation feeder is disclosed which allows improved feeding performance for a wide variety of sheet sizes from 30.5 x 46 cm (12" x 18") to A6. Either flexible or rigid material is added to the upper ends of the side guides to seal or partially block off any air leakage that might be exposed when small sheets are in the feeder. This allows the use of a feedhead which has been optimized for larger sheets, because the port size will be customized for smaller sheets through the movement of the side guides. This will reduce the air leakage for the smaller sheets which in turn will improve performance of the feeder. It should be understood that instead of both side guides being adjustable, only one side guide could be adjustable, if desired.

Claims: A sheet feeding apparatus comprising a sheet stack support tray (40) for supporting a stack of sheets (13) within the tray (40), and feedhead means (70) including a vacuum plenum chamber positioned over the front of the sheet stack having a negative pressure applied thereto during feeding, and perforated feed belt means (71,72) associated with said vacuum plenum chamber to transport the sheets acquired by said vacuum plenum chamber in a forward direction out of the stack support tray (40), wherein said sheet stack support tray (40) includes adjustable side guides (43,44), and wherein said adjustable side guides (43,44) have end portions (45,46) extending laterally therefrom that are adapted to restrict air leakage associated with said vacuum chamber when they are adjusted to accommodate small sheet sizes, characterised in that said end portions (45,46) extending laterally from said side guides (43,44) are flexible members. A sheet feeding apparatus as claimed in claim 1, characterised in that said adjustable side guides (43,44) having the end portions (45,46) extending substantially orthogonally from a vertical portion of the side guides positioned adjacent the side of the stack of sheets, said orthogonal end portions (45,46) are adapted to restrict air leakage from said vacuum chamber when the vertical portions of said side guides (43,44) are positioned in substantial sheet stack contacting relationship with predetermined sheet sizes. A sheet feeding apparatus, as claimed in claim 1 or claim 2, characterised in that the adjustable side guides (43,44) extend along the height of the sheet stack, said adjustable side guides having their end portions (45,46) extending substantially orthogonal thereto and adapted to restrict the leakage of air from said perforated feed belts when said side guides (43,44) are moved a predetermined distance towards each other to thereby enhance the ability of said vacuum chamber to attract a wide variety of sheet sizes to said perforated feed belts. A sheet feeding apparatus according to any of claims 1 to 3, characterised in that said vacuum plenum chamber includes a sheet corrugation member (76) located in the center of its bottom surface. A sheet feeding apparatus according to any of claims 1 to 4, characterised in that said end portions (45,46) extending laterally from said side guides (43,44) partially close off vacuum pressure through perforated feed belt means. A sheet feeding apparatus according to any of claims 1 to 5, characterised by air knife means (80) positioned immediately adjacent the front of said stack of sheets for applying a positive pressure to the sheet stack in order to separate the uppermost sheet in the stack from the rest of the stack. A sheet feeding apparatus according to any of claims 1 to 6, characterised by a support member (49) positioned adjacent said vacuum chamber, and wherein said flexible members are attracted to said support member (49) by said vacuum chamber when predetermined sheet sizes are fed by said top sheet feeding apparatus. A sheet feeding apparatus as claimed in claim 1, characterised in that the adjustable side guides (43,44) are adapted to close off an area around said vacuum chamber when they are adjusted to accommodate small sheet sizes.

Inventors: MARTIN KATHLEEN M, MARTIN, KATHLEEN M.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1995
Main classification: B65H3
IPC codes: G03G15, B65H3, B65H1