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(11) | EP 0 066 471 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Sheet feeding apparatus |
| (57) Disclosed herein is a vacuum transport means for feeding sheets along a predetermined
path into abutment with a registration member. To minimize damage to the leading edge
of the sheet by the registration member, yet assure reliable transport of the sheets
to the registration member, the vacuum transport means is provided with two vacuum
plenums (82, 84), one upstream in the sheet path relative to the other. Vacuum control
means are provided to control the relative level of vacuum supplied to the respective
plenums so that the upstream plenum applies a relatively high vacuum force to a sheet
presented to the transport means for feeding, and so that the downstream plenum applies
a lesser vacuum force to the sheet during transport, whereby a sheet can slip relative
to the vacuum transport belt when the sheet's leading edge engages the registration
member (34). The vacuum control additionally functions to decrease the vacuum supplied
to the upstream plenum at a time when a sheet is transported under the influence of
the downstream plenum. |
[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, Hampshire, 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 desireable 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 as been stopped by the registration member. However, when this occurs the vacuum transport2:may encounter difficulty in initially liftihg 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. The vacuum transport means of the invention comprises 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 between the 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 sheets and the belt upon such contact. In this manner, any damage to the leading edge of the sheet by the registration member is minimized.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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,
[0010] 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.
[0011] 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 these 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 diagramatically 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.
[0012] 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.
[0013] 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.
[0014] 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 lower most 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.
[0015] 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 plenums 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.
[0016] 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.
[0017] 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.
[0018] 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 l12 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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 guage in plenum 82 with an air flow rate of about 0.4 cubic meters per minute. This changes to about 20 cm. water guage 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 guage with an air flow rate of .09 cubic meters per minute. This changes to about 7.6 cm. water guage 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 guage 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.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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 l16 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 than rotated counterclockwise to its original position.
[0035] 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.
[0036] 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.
1. 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 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.
2. An apparatus as claimed in claim 1 characterized in that the vacuum plenum means
comprises a first and a second plenum over which the belt passes, the first plenum
being upstream of the second plenum, and the control means as arranged initially to
apply the first level of vacuum to the first plenum, the second level of vacuum to
the second plenum, and, before the sheet engages the registration member, to remove
the first level of vacuum from the first plenum.
3. An apparatus as claimed in claim 1 or 2 further characterized in that a vacuum-operated
feed means is provided'for presenting sheets to the vacuum transport, the feed means
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 and to
the feed means.
4. An apparatus as claimed in claim 3 characterized in that the vacuum control means
comprises a first control valve for regulating the flow of air from the vacuum operated
feed means 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 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.
5. An apparatus as claimed in claim 4 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.
6. An apparatus as claimed in claim 4 or 5 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.
7. A method of feeding a sheet along a predetermined path into abutment with a sheet
registration member using a vacuum belt comprising 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.