Sheet feeding apparatus

Description

[0001] This invention relates to sheet feeding apparatus, such as that used to feed document sheets to an exposure platen of a copier/duplicator. More particularly, the invention relates to an improved vacuum transport for feeding sheets along a predetermined path.

[0002] Various types of document feeders for copier/ duplicators are well known in the art. For example, commonly assigned U.S. Patent No. 4,169,674, entitled Recirculating Sheet Feeder, which issued on October 2, 1979 in the name of Matthew J. Russel discloses a recirculating sheet feeder wherein a stack of document sheets to be fed to a platen of a copier/duplicator is placed in a tray. An oscillating vacuum feeder removes the sheets seriatim from the bottom of the stack for transport of each sheet by various rollers to a registration position on the platen for copying. After exposure the sheet is returned to the stack on top of the other sheets remaining in the stack.

[0003] It is also known to provide recirculating document feeders with vacuum sheet transports for movement of a document sheet across the platen to a registration position. In this regard, see commonly assigned U.S. Patent No. 4,179,215, entitled RECIRCULATING DOCUMENT FEEDER, which issued on December 18, 1979 in the name of C. T. Hage. A combination recirculation document feeder and positioner with a platen vacuum transport is disclosed in Item 18540 at pages 526 and 527 of the September 1979 edition of Research Disclosure, a publication of Industrial Opportunities, Ltd., Homewell, Havant, Hamp- shire, P091EF, United Kingdom.

[0004] In some of the prior art devices described above drive rollers are used for advancing sheets across the platen and against a registration member. The drive rollers continue to be driven after the sheet reaches the registration point and thereby slip on the sheet. This allows the sheet to adjust itself into a registered position and thereby eliminate skew that may have developed in the sheet as it was moved from the stack of sheets to the registration member. Generally, this continued driving of the sheet against the registration members does not adversely affect the sheet. However, in vacuum platen transports as disclosed, for example, in the beforementioned Research Disclosure Publication, the sheet may be gripped against the vacuum belt with a relatively high vacuum force. If the belt continues to drive the sheet after the sheet reaches the registration member, there may be some damage to the leading edge of the sheet, depending upon the nature of the sheet and driving force applied to the sheet. Even so, vacuum transports are desirable because they tend to minimize or eliminate skewing of the sheet as it is transported across the platen toward the registration position. Damage to the sheet can be minimized by reducing the level of vacuum applied to the vacuum belt so that the belt can move relative to the sheet after the sheet has been stopped by the registration member. However, when this occurs the vacuum transport may encounter difficulty in initially lifting the sheet off the platen and onto the belt of the vacuum transport.

[0005] In view of the foregoing discussion, an object of this invention is to provide an improved vacuum transport means for reliably advancing sheets along a predetermined path into abutment with a sheet registration member without damaging the sheet's leading edge.

[0006] According to the invention, the method of feeding a sheet along a predetermined path into abutment with a sheet registration member using a vacuum belt is characterized by the steps of feeding a sheet onto the path, applying vacuum at a first level through the belt to tack the sheet to the vacuum belt and to draw the sheet along the path, and applying vacuum through the belt at a second lower level to transport the sheet along the path into abutment with the registration member so as to permit relative slipping between the sheet and the belt.

[0007] Also according to the invention, the sheet feeding apparatus including a vacuum transport means for advancing a sheet along a predetermined path to a sheet registration member which is arranged to abut the leading edge of the advancing sheet to remove any skew of the sheet relative to the path, the vacuum transport means comprising a vacuum belt, drive means forad- vancing the belt along the path, and vacuum means for tacking sheets to the belt and drawing the sheets along the path, the vacuum means including a source of vacuum and vacuum plenum means coupled to the source and positioned adjacent the belt, is characterized in that the vacuum means comprises control means for controlling the level of vacuum applicable through the belt between a first level for initially tacking a sheet to the belt and a second lower level sufficient for the belt to transport a sheet into contact with the registration member and yet to permit relative slipping between the sheet and the belt upon such contact.

[0008] In the detailed description of the preferred embodiment of the invention presented below, reference is made to the accompanying drawings, in which:

Fig. 1 is a generally schematic view illustrating a sheet feeding apparatus embodying the vacuum transport of the present invention; and

Figs. 2 and 3 are schematic views of different vacuum systems for the sheet feeding apparatus illustrated in Fig. 1.

[0009] Referring now to Fig. 1, a sheet feeder embodying the present invention is generally designated 10 and is shown in an environment in which it is used to present document sheets to an exposure platen 12 of a copier/duplicator or the like, a portion of which is shown at 14. In some respects the sheet feeder 10 and copier 14 are the same as, or similar to, the disclosures in the beforementioned Research Disclosure Publication and in the commonly assigned U.S. Patents.

[0010] The feeder 10 has a tray 16 spaced above the platen 12. The feeder is open at the top so that a set of document sheets S arranged in stack can be placed on the tray 16 for removal seriatim beginning with the lowermost sheet in the stack. Removal of the sheets from the stack is effected by a sheet feeder 18 comprising an oscillating vacuum tube. The feeder tube has a series of ports 19 arranged in a row as shown in Fig. 2. The ports are located beneath an opening 20 in the tray so that when vacuum is applied to the feeder 18 the lowermost sheet in tray 16 is attracted to the tube. Then the tube is rotated in a clockwise direction as viewed in Fig. 1 to bring the leading edge of the sheet into a nip between drive rollers 22 and rings 24. The rings are rotatably mounted on the tube 18 and recessed into the tube so that the outer surface of the rings and tube are substantially aligned. After the sheet is fed into the nip between the rollers 22 and rings 24, the tube oscillates in a counter clockwise direction back to its original position sliding relative to the surface of the sheet. The vacuum supply to the feeder is shut off during return movement as explained in more detail later.

[0011] The removed sheet is then fed through a guide slot 26 onto the platen 12. The guide slot 26 is defined by the surface of the tube 18, by an arcuate guide 28 adjacent to the tube, and by a flat plate 30 which is located above the platen and limits upward movement of the sheet away from the platen. The recirculating feeder structure described hereinbefore is disclosed in more detail in the beforementioned U.S. Patent No. 4,169,674.

[0012] As a sheet S is advanced across the platen 12 from right to left as viewed in Fig. 1, it reaches a platen vacuum transport generally designated 32 which will be described in more detail later. Transport 32 is effective to advance the sheet across the platen and into engagement with a registration gate member 34. Registration member 34 can be of any suitable construction and may, for example, be constructed as disclosed in commonly assigned U.S. Patent No. 4,243,316, entitled Registration Mechanism, which issued January 6, 1981 in the name of G. B. Gustafson. Preferably, transport 32 continues to urge the sheet against the registration member 34 even after initial contact therebetween so that any skew or misalignment that may exist in the sheet will be removed by allowing the driven sheet to adjust its relative position on the platen until all the leading edge of the sheet is aligned with the gate member 34. When the sheet is properly aligned it is exposed by flash lamps (not shown) located beneath the platen 12 or by a scanning mechanism. An image of the document sheet is formed on a photoconductor and a copy of the document is produced in a conventional manner.

[0013] After exposure of the document sheet, gate member 34 is lifted to its dotted line position above the sheet path. Transport 32 then drives the sheet off the platen and into the nip between a pair of rollers 36 and 38. Ordinarily those rollers drive the sheet into a guide path 40 defined by a pair of stationary guide members 42 and 44 and a movable guide member 46. Normally the movable guide member 46 is urged into the position illustrated by a spring shown diagrammatically at 48. When a sheet is to be removed from the feeder 10 after exposure (i.e., not recirculated), the movable guide member 46 is swung about a pivot 50 away from its solid line position into its dotted line position. This movement can be accomplished by any suitable moving means, such as a solenoid (not shown). When guide member 46 is in its dotted line position the sheet is deflected out of the feeder along a path shown by arrow 52.

[0014] The sheet is driven along guide path 40 by rollers 36, 38 and by two additional pair of rollers 54, 56 and 58, 60 located along the path. The sheet leaves the upper end of guide path 40 above the tray 16 and above the sheets S resting in the tray. Thus the sheet is returned to the stack of sheets on top of other sheets remaining in the stack. The result of one complete circulation of a sheet as described is that a sheet is inverted once after it is removed from the stack and before presentation for copying on the platen 12, and then inverted a second time after removal from the platen and before being returned to the tray 16. As to the set of document sheets, a sheet occupies the same position, relative to other sheets, before and after seriatim circulation of the entire set of document sheets.

[0015] The feeder has a document positioner mode of operation wherein a document sheet is fed to the platen along a non-recirculating path for copying one or more times. In this mode the sheet is fed to the feeder along a path shown at 62 in Fig. 1. The sheet is driven onto the platen 12 and into path 26 by a pair of nip rollers 64, 66. When the sheet reaches the platen vacuum transport 32, it is advanced against the registration member 34 and copied as explained hereinbefore. Then when the registration member is raised the movable guide member 46 is swung to its dotted line position and the transport 32 drives the sheet off the platen and into the nip between rollers 36, 38. Then the sheet is driven along path 52 and removed from the feeder. This document positioner mode of operation is disclosed in more detail in the beforementioned Research Disclosure Publication and in U.S. Patent No. 4,176,945.

[0016] Referring now to Figs. 1 and 2, the platen vacuum transport 32 preferably comprises a pair of endless vacuum belts 70 and 72 which are trained about three rollers 74, 76 and 78. Roller 74 is coupled to a motor 80 as shown schematically in Fig. 1 so that the roller 74 is driven in a clockwise direction as viewed in Fig. 1. Movement of roller 74 is effective to rotate the belts 70 and 72 about the various rollers, thereby moving the lowermost reach of the belts in a right-to-left direction as viewed in Fig. 1 for advancing a sheet toward the registration member 34. Preferably the belts 70 and 72 are of a white material and have a multiplicity of small holes therethrough through which air can be drawn for attracting a sheet to the belt. The belts are shown in Fig. 2 as being spaced from each other but they can be closely adjacent to each other or a single belt can be used if desired.

[0017] Located inside the endless belts are a first vacuum plenum 82 and a second vacuum plenum 84. Plenum 82 is located along the sheet path upstream with respect to plenum 84 so that a sheet being moved along the portion of the path 26 leading from the tray to the registration member first comes under the influence of vacuum in the plenum 82 and then under the influence of vacuum from plenum 84. The plenums are closely adjacent the lower reach of the belts 70 and 72 and the plenums have openings on the lower side thereof. When air is evacuated from the planums a partial vacuum is created in the plenums, and this partial vacuum is transferred through the openings in the bottom of the plenums and through the openings in the belts to attract a sheet to the belts.

[0018] Vacuum is provided by a single vacuum blower 86 (Fig. 2). The inlet to the blower is connected to a T-shaped coupling 88. One branch of the coupling is coupled by a conduit 90 directly to the second vacuum plenum 84. In this manner anytime the blower is operated there is a partial vacuum established in plenum 84. Preferably a series of vents 92 are provided in conduit 90 so that when the blower is shut off the conduit 90 and plenum 84 will promptly return to atmospheric pressure. These vents also serve to limit the level of vacuum applied to the plenum 84.

[0019] The application of vacuum to the oscillating vacuum feeder 18 and to the first plenum 82 is regulated by a control valve 94. Valve 94 has an inlet port 96 that is connected to another branch of the coupling 88 by a conduit 98. Valve 94 has two outlet ports 100 and 102. Outlet port 100 is coupled by a conduit 104 to the oscillating vacuum feeder 18. A plurality of vents 106 allow the vacuum tube to return to atmospheric pressure when the blower 86 is stopped or the valve 94 shuts off communication between the blower and the vacuum feeder. These vents also serve to limit the level of the vacuum in the oscillating vacuum feeder. Similarly, a conduit 108 is coupled to the outlet port 102 of valve 94 and to. the first vacuum plenum 82. This conduit also has vents 110 therein for allowing the plenum 82 to return to atmospheric pressure and for limiting the level of vacuum applied to the plenum.

[0020] Control valve 94 preferably is operated by a solenoid 112 which is energized and deenergized by the control mechanism for the feeder. The control mechanism may comprise for example, a logic and control unit (LCU) 113. The valve has a lever 114 pivoted intermediate its ends. Solenoid 112 has an armature connected to one end portion of the lever 114, and the other end portion of the lever is connected to a slider 116.

[0021] When the solenoid is deenergized the lever and slider occupy the positions illustrated in Fig. 2. At this time the left end of the slider 116 blocks the passage of air through conduit 108 into the control valve by closing off the outlet port 102 of the valve. However, port 100 is open so blower 96 is effective to provide a partial vacuum in the oscillating vacuum feeder 18 through the control valve 94 and conduit 104. The blower also provides a partial vacuum in plenum 84 through conduit 90.

[0022] When the solenoid 112 is energized lever 114 pivots in a counterclockwise direction to move the slider 116 to the left. The effect of this movement is that the slider 116 now blocks the outlet port 100, thereby interrupting the supply of vacuum to the vacuum feeder 118 and the feeder returns to atmospheric pressure by air flowing through the vents 106. At the same time, the slider 116 opens the outlet port 102 of the valve 94 to allow air to be drawn through conduit 108 from the vacuum plenum 82, thereby establishing a partial vacuum in the plenum 82. Blower 86 continues to apply vacuum in plenum 84. When the solenoid 112 is deenergized lever 114 returns to its original position, as shown in the drawings, port 100 is uncovered and port 102 is again blocked. Plenum 82 can then return to atmospheric pressure by air entering the vents 110. Vacuum again is provided to the oscillating vacuum feeder.

[0023] Conduits 90,104 and 108 can be provided with breakable couplings 120,122 and 124, respectively along the interface between the copier 14 and feeder 10. These couplings facilitate assembly and repair of the feeder.

[0024] Preferably, plenum 82 is smaller than plenum 84. Also, a higher level of vacuum is established in plenum 82 than in plenum 84. A principal function of plenum 82 is to lift the sheet from the platen onto the lower reach of belts 70 and 72. This function is more likely to be successfully accomplished by a relatively high level of vacuum. On the other hand, a principal function of plenum 84 is to hold the sheet against the belts without damaging the leading edge of the sheet when it is driven against member 34. Once a sheet is tacked to the belts by plenum 82, a lower level of vacuum is needed to hold the sheet to the belts. Because the belts 70, 72 preferably continue to move after the leading edge of the sheet strikes member 34, the lower level of vacuum in plenum 84 allows slippage between the belts and the sheets without damaging the leading edge of the sheet.

[0025] LCU 113 is shown connected to solenoid 112. As is known in the art, the LCU can receive signals from various sensors in feeder 10 and copier 14 and furnish control signals to not only the solenoid 112 but also to blower 86, motor 80 and other parts of the feeder and copier to provide a controlled sequence of operations.

[0026] Operation of the apparatus will now be described. Assume initially that control valve 94 is in the position shown in Fig. 2, i.e., port 100 is open and port 102 is closed so that the vacuum blower 86 can provide a vacuum in the oscillating vacuum feeder and in vacuum plenum 84, but not to vacuum plenum 82. Vacuum applied to the vacuum feeder 18 causes the lowermost sheet S in the tray 16 to be attracted to the ports 19 of the vacuum feeder. Then, in response to a signal from the logic and control unit of the apparatus, the oscillating vacuum feeder rotates clockwise to partially withdraw the lowermost sheet S from the tray and to feed the leading edge of the sheet into the nip between the drive rollers 22 and the rings 24. Immediately after the document is fed into this nip solenoid 112 of the control valve 94 is energized to move the slider 116 to its second position wherein port 100 is blocked, thereby allowing the oscillating vacuum feeder to return to atmospheric pressure. This releases the sheet from the oscillating vacuum feeder and allows it to be transported along the first portion of the feeder path by the rollers 22 and rings 24.

[0027] When solenoid 112 is energized valve 94 connects the vacuum blower 86 to the first vacuum plenum 82 to establish a partial vacuum in that plenum. Thus when the leading edge of the sheet is furnished into the space beneath the lower reach of belts 70 and 72 and beneath the vacuum plenum 82, the relatively high level of vacuum in the plenum 82 causes the sheet to be lifted up onto the belts and tacked to the belts. At this time, the belts are being driven in a direction to advance the sheet along the platen towards the registration member 34. Thus the sheet travels beneath the first vacuum plenum 82 and ultimately is delivered into the area beneath the second vacuum plenum 84. As noted previously, air is continuously evacuated from plenum 84 through conduit 90 and the blower 86, the level of vacuum in plenum 84 being somewhat lower than the level of vacuum in plenum 82.

[0028] For a period of time the sheet is held against the belts 70 and 72 by vacuum from both plenums 82 and 84. However, before the leading edge of the sheet reaches the registration member 34, solenoid 112 in valve 94 is deenergized to allow the slider 116 to return to the position illustrated in Fig. 2. This opens the valve to port 100 and closes the valve to port 102, thereby interrupting the flow of air from plenum 82 through the valve to the vacuum blower 86. The vacuum in plenum 82 is vented through holes 110 so that the plenum promptly returns to substantially atmospheric pressure. At this time the sheet is transported under the influence of vacuum from plenum 84 only. The lower level of vacuum in plenum 84 is sufficient to retain the sheet against the belts for movement across the platen and into engagement with the registration member 34. As a result, the sheet leading edge strikes the registration member 34 with a relatively low force. The sheet can be stopped by the registration member even though the belts continue to move toward the registration member, thereby allowing any misalignment of the sheet to be corrected by continued movement of the belts. The relatively low force applied by the belts prevents any damage to the sheet.

[0029] After the sheet is properly aligned on the platen it is illuminated to provide an image to the copier. Then the registration member is moved out of the path of the sheet and the sheet is advanced past the registration position and into the nip formed by rollers 36 and 38 under control of vacuum in plenum 84 and the movement of the belts 70 and 72.

[0030] When the first sheet enters the nip between rollers 36 and 38, it is normally advanced through sheet path 40 and returned to tray 16 on top of any sheets remaining in the tray as previously explained. Alternatively, the movable guide member 46 can be swung to its dotted line position to allow removal of the sheet along the path designated 52. As noted earlier, when the valve 94 returns to the position illustrated in Fig. 2, vacuum is again applied to the oscillating vacuum feeder 18. The vacuum thus applied attracts the leading edge of the second sheet in the stack to the oscillating vacuum feeder. Once the registration member is raised the oscillating vacuum feeder can be oscillated clockwise again to initiate feeding movement of the second sheet.

[0031] After the trailing edge of the first sheet passes the registration member, the registration member is returned to the position shown in solid lines in Fig. 1 so that it can be engaged by the second document sheet to register that sheet. The cycle is repeated as required until the document sheets have all been circulated one or more times for copying.

[0032] The level of vacuum in plenums 82 and 84 can be varied as required, depending upon the type and weight of document sheets to be handled. By way of example, 21 x 28 cm sheets of 6, 9, and 15 kilogram weight per thousand sheets can be transported with an initial vacuum level equal to about 2.5 cm water gauge in plenum 82 with an air flow rate of about 0.4 cubic meters per minute. This changes to about 20 cm water gauge with an air flow of .03 cubic meters per minute when the document sheet fully covers the bottom of the vacuum plenum. Similarly, the level of vacuum in plenum 84 can initially be about 1.3 cm water gauge with an air flow rate of .09 cubic meters per minute. This changes to about 7.6 cm water gauge and an air flow rate of .01 cubic meters per minute when the document sheet fully covers the bottom of the plenum. A vacuum level of about 43 cm water gauge has been found sufficient for the oscillating vacuum feeder. The inside diameters of conduits 90, 104 and 108, respectively can be about 1.6 cm. 4.5 cm and 2.5 cm.

[0033] As noted earlier, plenum 82 preferably is smaller than plenum 84. The apertures in the bottom of each plenum can comprise about 9.7 sq. cm. The belts can be about 3.8 cm wide with .5 cm diameter holes therethrough arranged on 1.3 cm center lines in three staggered rows.

[0034] The ability of the first plenum 82 to pick up a sheet being moved across the platen can be improved by increasing the port area of the plenum to allow a greater air flow and thereby produce more lift.

[0035] One of the advantages of the present invention is that the platen vacuum transport provides a high gripping and lift force in the area of the first vacuum plenum 82. This assures lifting of the sheet onto the belts and also prevents skew of the document sheet. At the same time, when the document sheet leading edge reaches the registration gate, it is being advanced only by the relatively lower vacuum pressure applied through plenum 84 so that lower gate registration forces are encountered, thereby minimizing damage to the leading edge of the sheet due to contact with the registration member. Fig. 3 illustrates an alternative vacuum system for use in the sheet feeding apparatus described above, and like reference numbers designate like parts. This vacuum system differs from that already described in that it includes a second control valve 123 connected as shown in the conduit 108 connecting valve 94 and plenum 82. Like valve 94, valve 123 operates under the control of LCU 113, and it comprises a solenoid 130 and a mechanical linkage 134 for controlling the position of a slider 128. The purpose of valve 123 is to minimize vacuum line fluctuations caused by the opening and closing of valve 94. The elimination of such fluctuations enhances the reliable operation of the oscillating vacuum feeder 18.

[0036] Operation of the apparatus shown in Fig. 3 will now be described. Assume initially that control valves 94 and 123 are in their respective positions as shown in Fig. 3. At this time, vent 125 of valve 123 is open and the plenum 82 is at atmospheric pressure. As to valve 94, ports 96, 100 are open and port 102 is closed. Thus when the vacuum blower 86 is operated, a vacuum is established in feeder 18 and vacuum plenum 84. In response to a signal from LCU 113, the blower is started and vacuum is applied to the vacuum feeder 18. This causes the lowermost sheet S in the tray 16 to be attracted to the ports 19 of the vacuum feeder. Then, in response to a signal from the logic and control unit of the apparatus, the oscillating vacuum feeder rotates clockwise to partially withdraw the lowermost sheet S from the tray and to feed the leading edge of the sheet into the nip between the drive rollers 22 and the rings 24. Immediately after the document is fed into this nip solenoid 112 of the control valve 94 moves slider 116 to the left to block port 100, thereby allowing the oscillating vacuum feeder to return to atmospheric pressure. This releases the sheet from the oscillating vacuum feeder and allows it to be transported along the first portion of the feeder path by the rollers 22 and rings 24. The oscillating vacuum feeder then rotated counterclockwise to its original position.

[0037] When port 100 of valve 94 is closed, port 102 is opened. Shortly after port 102 is opened, and before the sheet reaches a position under plenum 82, the LCU signals the solenoid 130 to move slider 128, thereby closing vent 122 and opening port 119 so that vacuum can be applied to plenum 82. When the leading edge of the sheet reaches the space beneath the lower reach of belts 70 and 72 and beneath the vacuum plenum 82, the relatively high level of vacuum in the plenum 82 lifts the sheet up against the belts and tacks the sheet to the belts. At this time, the belts are being driven in a direction to advance the sheet along the platen towards the registration member 34. Thus the sheet travels beneath the first vacuum plenum 82 and ultimately is delivered into the area beneath the second vacuum plenum 84.

[0038] For a period of time the sheet is held against the belts 70 and 72 by vacuum from both plenums 82 and 84. However, before the leading edge of the sheet reaches the registration member 34, solenoid 130 drives the slider 128 back to the left as illustrated in Fig. 3. This closes the valve port 119 and opens the vent 122, thereby interrupting the flow of air from plenum 82 through the valves 123 and 94 to the vacuum blower 86. This vacuum in plenum 82 is vented through vent 122 so that the plenum promptly returns to substantially atmospheric pressure. At this time the sheet is transported under the influence of vacuum from plenum 84 only. The lower level of vacuum in plenum 84 is sufficient to retain the sheet against the belts during further movement across the platen and into engagement with the registration member 34.

[0039] An alternative approach to avoiding variations in the vacuum applied to the vacuum feeder 18 as a result of varying the vacuum supplied to plenum 82 would be to utilize separate vacuum sources, one for vacuum feeder 18, and one for the vacuum transport 32.

[0040] The invention has been described in detail with particular reference to a preferred embodiment thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and defined in the appended claims.

Claims

1. A method of feeding a sheet along a predetermined path into abutment with a sheet registration member using a vacuum belt characterized by the steps of feeding a sheet onto the path, applying vacuum at a first level through the belt to tack the sheet to the vacuum belt and to draw the sheet along the path, and applying vacuum through the belt at a second lower level to transport the sheet along the path into abutment with the registration member so as to permit relative slipping between the sheet and the belt.

2. A method according to claim 1 characterized in that said first and second levels of vacuum are applied to a sheet being fed along said sheet path through separate first and second vacuum plenums, respectively, said first vacuum plenum being arranged further upstream in the sheet path than said second vacuum plenum, and further characterized in that the vacuum applied to said upstream vacuum plenum is controlled to be ineffective at the time when a sheet reaches the registration member.

3. Sheet feeding apparatus including a vacuum transport means for advancing a sheet along a predetermined path to a sheet registration member which is arranged to abut the leading edge of the advancing sheet to remove any skew of the sheet relative to the path, the vacuum transport means comprising a vacuum belt, drive means for advancing the belt along the path, and vacuum means for tacking sheets to the belt and drawing the sheets along the path, the vacuum means including a source of vacuum and vacuum plenum means coupled to the source and positioned adjacent the belt, characterized in that the vacuum means comprises control means for controlling the level of vacuum applicable through the belt (70, 72) between a first level for initially tacking a sheet to the belt (70, 72) and a second lower level sufficient for the belt (70, 72) to transport a sheet into contact with the registration member (34) and yet to permit relative slipping between the sheet and the belt (70, 72) upon such contact.

4. An apparatus as claimed in claim 3 characterized in that the vacuum plenum means comprises a first (82) and a second plenum (84) over which the belt (70, 72) passes, the first plenum (82) being upstream of the second plenum (84), and the control means as arranged initially to apply the first level of vacuum to the first plenum (82), the second level of vacuum to the second plenum (84), and, before the sheet engages the registration member (34), to remove the first level of vacuum from the first plenum (82).

5. An apparatus as claimed in claim 3 or 4 further characterized in that a vacuum-operated feed means (18) is provided for presenting sheets to the vacuum transport, the feed means (18) being operatively coupled to the vacuum source and in that the vacuum control means is effective alternately to apply vacuum at the first level through the belt (70, 72) and to the feed means (18).

6. An apparatus as claimed in claim 5 characterized in that the vacuum control means comprises a first control valve for regulating the flow of air from the vacuum operated feed means (18) to the vacuum source, the first control valve having an inlet port coupled to the vacuum source, a first outlet port coupled to the feed means (18) and a second outlet port for regulating the flow of air from the plenum means at the first level to the vacuum source, and a valve member for alternately connecting the inlet port to the first and the second outlet port.

7. An apparatus as claimed in claim 6 characterized in that a second control valve is connected between the second outlet port of the first control valve and the plenum means, the second control valve having a first position, alternate with the first control valve connecting the inlet port with the first outlet port, in which the first level of vacuum is not applied to the plenum means and a second position, in which the inlet port of the first control valve is connected with the second outlet port thereof, in which vacuum at the first level is applied to the plenum means.

8. An apparatus as claimed in claim 6 or 7 characterized in that vacuum control means further comprises logic and control means operatively coupled to the first control valve or the first and second control valves to regulate the operation of the valve or valves in a programmed sequence calling for operation of the-valve or the first valve to provide vacuum to the feed means to initiate the presentation of a sheet to the vacuum transport means and then operating the valve or the first and second valves to interrupt the vacuum supply to the feed means and to establish a vacuum at the first level in the plenum means, thereby to tack a sheet to the belt so the belt can transport the sheet, followed by interruption of the vacuum supply at the first level to the plenum means after the sheet comes under the influence of the vacuum applied at the second level.

Revendications

1. Un procédé pour avancer une feuille sur une trajectoire prédéterminée, en butée avec un organe de mise en repérage de feuille, à l'aide d'une courroie à dépression, caractérisé par les étapes suivant lesquelles on avance une feuille sur la trajectoire, on établit une dépression d'un premier niveau à travers la courroie pour plaquer la feuille sur la courroie à dépression et pour tirer la feuille sur la trajectoire, et on applique un dépression d'un deuxième niveau, plus bas, à travers la courroie pour transporter la feuille sur la trajectoire jusqu'à sa mise en butée avec l'organe de mise en repérage, de manière à autoriser un glissement relatif entre la feuille et la courroie.

2. Un procédé conforme à la revendication 1, caractérisé en ce que ces premier et deuxième niveaux de dépression sont appliqués à une feuille circulant sur ladite trajectoire de feuille, par l'intermédiaire de première et deuxième chambres à dépression distinctes, respectivement, ladite première chambre à vide étant disposée plus en amont de la trajectoire de feuille que ladite deuxième chambre à dépression, et caractérisé en outre en ce que la dépression appliquée à la chambre à dépression amont est commandée de manière à être privée d'effet à l'instant où la feuille atteint l'organe de mise en repérage.

3. Appareil d'alimentation en feuille comprenant un moyen de transport à dépression pour avancer une feuille sur une trajectoire prédéterminée jusqu'à un organe de feuille qui est agencé pour buter sur le bord d'attaque de la feuille qui s'avance pour supprimer toute inclinaison de la feuille sur sa trajectoire, le moyen de transport à dépression comprenant une courroie à dépression, des moyens d'entraînement pour avancer la courroie au long de la trajectoire, et un moyen à dépression pour plaquer des feuilles sur la courroie et pour tirer les feuilles sur la trajectoire, le moyen à dépression comprenant une source de dépression et un moyen de chambre à dépression raccordé à la source et adjacent à la courroie, caractérisé en ce que le moyen de dépression comprend un moyen de commande pour commander le niveau de dépression applicable à travers la courroie (70, 72) entre un premier niveau pour plaquer initialement une feuille sur la courroie (70, 72) et un deuxième niveau suffisant pour que la courroie (70, 72) entraine une feuille au contact de l'organe de mise en repérage (34) tout en autorisant un glissement relatif entre la feuille et la courroie (70, 72) une fois ce contact établi.

4. Un appareil conforme à la revendication 3, caractérisé en ce que le moyen de chambre à dépression comprend une première (82) et une deuxième chambre (84) sur lesquelles passe la courroie (70, 72), la première chambre (82), se trouvant en amont de la deuxième (84), en ce que le moyen de commande est agencé initialement pour appliquer la dépression du premier niveau à la première chambre (82), la dépression du deuxième niveau à la deuxième chambre (84), et, avant que la feuille ne touche l'organe de mise en repérage (34), pour supprimer la dépression du premier niveau dans la première chambre (82).

5. Un appareil conforme à la revendication 3 ou 4, caractérisé en outre en ce qu'un noyen d'alimentation (18) fonctionnant par dépression est prévu pour présenter des feuilles au transporteur à dépression, le moyen d'alimentation (18) étant couplé fonctionnellement à la source de dépression, et en ce que le moyen de commande de dépression fonctionne alternativement pour appliquer une dépression du premier niveau à travers la courroie (70, 72), et au moyen d'alimentation (18).

6. Un appareil conforme à la revendication 5, caractérisé en ce que le moyen de commande de dépression comprend une première vanne de commande pour régler le courant d'air du moyen d'alimentation (18) fonctionnant par dépression vers la source de dépression, la première vanne de commande étant munie d'un premier orifice d'entrée raccordé à la source de dépression, d'un premier orifice de sortie raccordé au moyen d'alimentation (18) et d'un deuxième orifice de sortie pour règler le courant d'air du moyen de chambre à dépression au premier niveau vers la source de dépression, et un organe de vanne pour raccorder alternativement l'orifice d'entrée au premier et deuxième orifice de sortie.

7. Un appareil conforme à la revendication 6, caractérisé en ce qu'une deuxième vanne de commande est connectée entre le deuxième orifice de sortie de la première vanne de commande et le moyen de chambre à dépression, la deuxième vanne de commande ayant une première position, alternée avec celle de la première vanne de commande raccordant l'orifice d'entrée au premier orifice de sortie, dans laquelle la dépression du premier niveau n'est pas appliquée au moyen de chambre à dépression, et une deuxième position, dans laquelle l'orifice d'entrée de la première vanne de commande est raccordée au deuxième orifice de sortie de celle-ci, de manière à appliquer, au moyen de chambre à dépression, une dépression du premier niveau.

8. Un appareil conforme à la revendication 6 ou 7, caractérisé en ce que le moyen de commande de dépression comprend en outre un moyen de commande et de logique relié fonctionellement à la première vanne de commande, ou aux première ou deuxième vannes de commande, pour régler le fonctionnement de la vanne, ou des vannes, suivant une séquence programmée actionnant la vanne, ou la première vanne, de manière à fournir une dépression au moyen d'alimentation pour amorcer la présentation d'une feuille au moyen de transport à dépression et actionnant ensuite la vanne, ou les première et deuxième vannes, pour couper l'alimentation du moyen d'alimentation avec une dépression et pour établir une dépression du premier niveau dans le moyen de chambre à dépression, de manière à plaquer une feuille sur la courroie pour que celle-ci puisse entraîner la feuille, suivie par l'arrêt de la fourniture de la dépression du premier niveau au moyen de chambre à dépression après que la feuille arrive sous l'influence de la dépression du deuxième niveau.

Ansprüche

1. Verfahren zum Fördern eines Blattes längs einer vorbestimmten Bahn bis zum Anschlag an einem Blattanlegeelement unter Verwendung eines Vakuumbandes, gekennzeichnet durch die Verfahrensschritte, daß der Bahn ein Blatt zugeführt wird, Unterdruck in einer ersten Stärke durch das Band hindurch angelegt wird, um das Blatt an das Vakuumband anzusaugen und entlang der Bahn zu ziehen, und Unterdruck einer zweiten geringeren Stärke durch das Band hindurch angelegt wird, um das Blatt längs der Bahn bis zum Anschlag an dem Blattanlegeelement zu transportieren und dabei eine relative Verschiebung zwischen Blatt und Band zu ermöglichen.

2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß der Unterdruck in der ersten und der zweiten Stärke an das über die Bahn transportierte Blatt mittels einer ersten bzw. zweiten Unterdruckkammer angelegt wird, wobei die erste Unterdruckkammer auf der Transportbahn weiter oberhalb angeordnet ist als die zweite Unterdruckkammer, und weiterhin dadurch gekennzeichnet, daß der an die weiter oben angeordnete Unterdruckkammer angelegte Unterdruck so gesteuert wird, daß er zu dem Zeitpunkt, zu dem das Blatt das Anlegeelement erreicht, unwirksam ist.

3. Blattfördervorrichtung mit einer Vakuumtransporteinrichtung zum Fördern eines Blattes über eine vorbestimmte Bahn bis zu einem Blattanlegeelement, das so angeordnet ist, daß es mit der Vorlaufkante des sich vorwärtsbewegenden Blattes in Berührung kommt und dabei jede schiefe Lage des Blattes relativ zu der Bahn beseitigt, wobei die Vakuumtransporteinrichtung ein Vakuumband, Antriebsmittel zum Bewegen des Bandes über die Bahn und eine Vakuumeinrichtung zum Ansaugen von Blättern an das Band und zum Weiterziehen der Blätter über die Bahn umfaßt und die Vakuumeinrichtung eine Vakuumquelle und an diese Quelle angeschlossene Unterdruckkammern aufweist und benachbart dem Band angeordnet ist, dadurch gekennzeichnet, daß die Vakuumeinrichtung eine Steuereinrichtung aufweist, mit der die Höhe des durch das Band (70, 72) hindurch anlegbaren Unterdrucks zwischen einer ersten Stärke einstellbar ist, bei der das Blatt zunächst an das Band (70, 72) angesaugt wird, und einer zweiten geringeren Stärke, die ausreicht, um ein Blatt mittels des Bandes (70, 72) mit dem Anlegeelement (34) in Berührung zu bringen, dabei aber während dieser Berührung eine relative Verschiebebewegung zwischen Blatt und Band (70, 72) ermöglicht.

4. Vorrichtung nach Anspruch 3, dadurch gekennzeichnet, daß die Unterdruckkammern eine erste (82) und eine zweite Kammer (84) umfassen, über die das Band (70, 72) hinwegläuft, wobei die erste Kammer (82) in der Bewegungsrichtung des Bandes vor der zweiten Kammer (84) liegt und die Steuereinrichtung so angeordnet ist, daß sie zunächst in der ersten Kammer (82) Unterdruck der ersten Stärke und in der zweiten Kammer (84) Unterdruck der zweiten Stärke erzeugt, und, bevor das Blatt an dem Anlegeelement (34) zur Anlage kommt, den Unterdruck der ersten Stärke in der ersten Kammer (82) wieder aufhebt.

5. Vorrichtung nach Anspruch 3 oder 4, dadurch gekennzeichnet, daß eine vakuumbetätigte Fördereinrichtung (18) vorgesehen ist, um Blätter dem Vakuumtransport zuzuführen, wobei die Fördereinrichtung (18) mit der Vakuumquelle in Wirkverbindung steht, und daß die Vakuumsteuereinrichtung abwechselnd Unterdruck der ersten Stärke durch das Band (70, 72) hindurch und an die Fördereinrichtung (18) anlegen kann.

6. Vorrichtung nach Anspruch 5, dadurch gekennzeichnet, daß die Vakuumsteuereinrichtung ein erstes Steuerventil zum Regeln der Luftströmung von der vakuumbetätigten Fördereinrichtung (18) zu der Vakuumquelle aufweist, wobei das erste Steuerventil eine mit der Vakuumquelle verbundene Einlaßöffnung, eine mit der Fördereinrichtung (18) verbundene erste Auslaßöffnung und eine zweite Auslaßöffnung zum Regeln der Luftströmung von den Unterdruckkammern mit Unterdruck der ersten Stärke zur Vakuumquelle aufweist, sowie ein Ventilelement, mit dem die Einlaßöffnung abwechselnd mit der ersten und der zweiten Auslaßöffnung verbunden werden kann.

7. Vorrichtung nach Anspruch 6, dadurch gekennzeichnet, daß zwischen die zweite Auslaßöffnung des ersten Steuerventils und die Unterdruckkammern eine zweites Steuerventil geschaltet ist, das eine erste Stellung besitzt, die mit der Verbindung der Einlaßöffnung mit der ersten Auslaßöffnung bei dem ersten Steuerventil alterniert, bei der kein Unterdruck der ersten Stärke an den Unterdruckkammern anliegt, und eine zweite Stellung, in der die Einlaßöffnung des ersten Steuerventils mit dessen zweiter Auslaßöffnung vebunden ist, und in der Unterdruck der ersten Stärke an den Unterdruckkammern anliegt.

8. Vorrichtung nach Anspruch 6 oder 7, dadurch gekennzeichnet, daß die Vakuumsteuereinrichtung außerdem logische Schaltungs- und Steuermittel umfaßt, die mit dem ersten Steuerventil oder dem ersten und dem zweiten Steuerventil so in Wirkverbindung stehen, daß damit der Betrieb des Ventils oder der Ventile in einer programmierten Reihenfolge so gesteuert wird, daß das Ventil oder das erste Ventil angesteuert werden muß, damit an die Fördereinrichtung Unterdruck angelegt und damit die Zuführung eines Blattes zu der Vakuumtransporteinrichtung eingeleitet werden kann, und dann das Ventil oder das erste und das zweite Ventil so betätigt werden, daß die Unterdruckzufuhr zu der Fördereinrichtung unterbrochen und Unterdruck der ersten Stärke in den Unterdruckkammern erzeugt wird, wodurch ein Blatt an das Band angesaugt wird und das Band das Blatt transportieren kann, und daß anschließend die Unterdruckzufuhr der ersten Stärke zu den Unterdruckkammern unterbrochen wird, wenn das Blatt unter den Einfluß des Unterdrucks der zweiten Stärke gelangt.

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