CA1103739A - Transfer - fusing speed compensation - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
In an electrostatographic copier wherein the fuser rolls are positioned closer than the dimensions of the copy sheet from the image transfer area, speed mismatch compensation between the fuser roll nip and the initial image support surface is provided by intentionally driving the fuser roll nip at a different velocity to form a buckle in the intermediate portion of the copy sheet controlled by selective cyclic reductions in the vacuum applied to a configured manifold guide surface.
The guide surface may be divided into segments, through one of which the vacuum is continuously maintained.

Description

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The present invention relates to el~ctrostatographic image reproduction wherein an image of fusable material is fusable on a support surface before transfer of the image thereof is completed with compensation for variations between the velocity of the support surface for transfer and its velocity for fusing.
In a transfer electrostatographic process such as conventional transfer xerography, in which an image pattern of dry particulate unfused toner material is transferred to a final image support surface, e.g., a copy sheet from an initial image bearing surface, e.g., a charged photoreceptor surface developed with toner, the transferred toner is typically only loosely adhered to the final support surface after transfer, and is easily disturbed by the process of stripping t~ final support surface away from the initial support surface and by the process of transporting the final support surface to the toner fusing station. The final support surface preferably passes through a fusing station as soon as possible after transfer so as to permanently fuse the toner image to the final support surface, thereby preventing smearing or disturbance of the toner image by mechanical agitation or electrical fields. For this reason and also for r~asons of simplifying and shortening the paper path of the copier and space savings, it is desirable to main-tain the fusing station as close as possible to the transfer station. A particularly desirable fusing station is a roll type fuser, wherein the copy sheet is passed through a pressure nip between two rollers, preferably at least one of which is heated and at least one o~ which is resilient. An example of a

- 2 -xerographic transfer stripping, transporting and fusing system of this type is described in U.S. Patent No. 3,578,859, issued May 18, 1971, to W. K. Stillings.
However, when such a fuser roll nip for the final support surface is located close enough to the transfer station so that a lead portion of the final support surface can be in the fuser roll nip simultaneously with the rear or trailing portion of that same final support surface still being in contact with the photoreceptor, then a serious problem can arise, to which the present invention provides a solution. This problem is that of smears or skips in the unfused toner image which has been, or is being, transferrred to the trailing portion of the final support surface. This condition is caused by relative movement or slippage between the initial support surface and the final support surface in those areas where they are still in contact, i.e., those areas of the final support surface which ha~e not yet been stripped ~ away from the initial support surface. A source of such ; slippage is a speed mismatch between the nip speed of the fuser rolls (the speed at whlch the fuser is pulling the lead edge of the paper through the fuser) relative to the surface speed of the initial support surface. If the fuser roll nip speed is slower, the final support can slip backwards relative to the initial image support surface. If the fuser roll is faster, the final support material can be pulled forward relative to the image on the initial support surface. In either case this can cause the aforementioned smears Gr skips in the toner image being transferred to the trailing area of the final support, or image elongation.

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~ n exactly e~al velocity drive connection between the initial support surface and the fuser rolls is difficult to maintain. Also, there is a further complication that the actual sheet driving velocity of the fuser roll nip can change witlh changes in the effective diameter of the driving roll in the nip.
This can occur from replacement of the rollers, or changes in the resilient deformation of the rollers due to changes in the applied nip pressure, materials aging, temperature effects, etc. Thus, equal speed is difficult to maintain between the fuser roll nip and the photorecepter surface in a commercial apparatus and may require increased maintenance and speed acljustment mechanisms.
Where the spacing between the fusing stati.on and the transfer station is greater than the dimensions of the copy sheet, and a separate two-speed sheet transport is provided therebetween, then substantially different fuser roll nip speeds can be provided, as in U.S. Patent 3,794,417, issued February 26, 1974, to J~ A. Machmer. ~owever, this has the noted disadvantages of requiring additional space, increased unfused image sheet handling~ and also the additional complexity and expense of the additional transport mechanism.
It is known in the electrostatographic copying art to form a buckle in a copy sheet in its movement through the copier at other locations and for other functions~ For example, it is known to interrupt the forward movement of a copy sheet with registration fingers and to form a buckle in the copy sheet by its continued feeding by upstream feed rollers, to provide regi.stration of the lead edge of -the copy sheet before the copy shee-t is fed into the image transf~r static~ll, e.y., 3~ ~
r U, S, Patent 3,601,392, issued August 24, 1971, to Merton R~
Spear, Jr., et al. It is also known to provide or pre-form a buckle in a web o~ copy material to compensate for th~
braking of the web duriny a cutting operation in which the web is cut into individual sheets, e.gO, U. S. Patent No.
3,882,744, issued May 13, 1975, to Alan F. McCarrollO The later patent also illustrates that the copy web may be pre-formed into an initial convex buckle over an apertured surface and that air pressure may be utilized to expand the buckle when the web is stopped downstream thereof.
77't q~ 7 A~ u. s. Patent ~7 ~4r~ issued November 27, 1973, to Stephen Borostyan illustrates a vacuum sheet stripping device for removing copy sheets rom the initial image support member and advancing them to a roll fuser, wherein the copy sheets assume a convex shape. A rotating cylindrical apertured vacuum member is utilized, to which the copy sheet is attracted.
During a portion of its rotation, the vacuum is automaticlly cut-off to the vacuum stripping member to release the copy sheet.
U. S. Patent ~o. 3,508,824, issued April 28, lg70, `-- to R. K~ Leinbach et al. describes a conductive curved guide plate for attracting a copy sheet at the stripping area and guiding it towards a fusing station.
The present invention provides a speed mismatch com~ensation system which allows the fusing roll nip to be closely spaced from the transfer station o~ an electrostato-gxaphic copier, by a distance less than the movement dimension of an individual copy sheet, to provide the above-stated advantages of such a system, yet overcome or substantially , : '' ,' . :
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reduce the above-stated disadvantages thereof. The inter-mediate portion of the copy sheet is selectivel~ supported and guided in a manner which accommodates a speed differe~tial between.the fuser roll nip velocity and the velocity of the i.nitial support surface. A speed variation and differential is accommodated between the leading edge and trailing edge areas of the same final image support surface, in a manner which avoids disturbance of the unfusèd toner ima~e in any area thereon.
In accordance with one aspect of this invention ~here 0 i5 provided in a copying system in which an unfused image of imaging material i5 transferred ~rom a moving initial image supportsurface means onto one side of a copy sheet while said copy sheet overlies the initial image support surface and moves ~ therewith, and in which a lead area of the transferred unfused i 15 image-bearing copy sheet is then engaged by a moving sheet transport means spaced from the initial image support surface whi~e a trail area of the same copy sheet is still moving with the initial image support surface, with the copy sheet extending therebetween, the improvement comprising:
speed control means for moving said initial image support surface and said sheet transport means at a pre-set speed differential- for moving the lead area and the trail area of the same copy sheet at different speeds when said lead area of the copy.sheet is engaged by said sheet transport means.
vacuum guide surface means for vacuum supporting the copy sheet against a vacuum guide surface from the side of the copy sheet opposite from the side bearing the transferred unfused ma~e t said vacuum guide surface means being positioned 3~ between said initial image support surface and said sheet transport means for guiding the copy sheet therebetween, and 3~`~

vacuum control means cyclicly actuab]e for reducing the vacuum applied to said vacuum .guide surface in coordination with the extension of the copy sheet between said initial image support surface and said sheet transport means for movement o~ the copy sheet away from said vacuum guide surface by said pre-set speed differential from said speed control means for speed variation compensation.
Further objects, features, and advantages of the present invention pertain to the particular apparatus, steps, 10 and details whereby the above-mentioned aspects of the invention are attained. Accordingly, the invention will be better under-stood by reference to the followiny description of an exemplary embodiment thereof, and to the drawings forming a part of that description, which are approximately to scale, wherein:
Fig. 1 is a cross-sectional side view of an exemplary xerographic copying apparatus in accordance with the present invention, illustrating those portions thereof relevant to the description of the present invention;
Fig. 2 is a top view of the vacuum manifold unit of 20 the embodiment of Fig. 1, with the top cover thereof shown removed to the right side for clarity;
Fig. 3 is a bottom view of the va~uum manifold of Figs. 1 and 2;
Fig. 4 is a view similar to Fig. 1 of a different 25 embodiment;
; Fig. 5 is a top view of the vacuum manifold system of the embodiment of Fig. 4; and Fig~ 6 is a bottom view of the manifold ~f Fig. 5.

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Referring now to the drawings, and specifically to the embodiment 10 of Figs. 1-3, it may be seen that the xero-graphic transfer, stripping, vacuum manifold transport, and roll fusing system illustrated therein is generally similar in many respects to that of the Xerox 4000 and 4500 xerographic copiers. The above-cited disclosure o~ U. S. Patent 3,578,859 or its equivalents, or other references, may be referred to for additional descriptions of examples of appropriate or conventional details o~ such systems. Accordingly, the following description will be directed speciEically to the novel aspects of the embodiment providing the above-discussed speed mis-match compensation.
However, briefly first describing the conventional aspects of the disclosed system 10 in Fig. 1, it may be seen that a copy sheet 12 is sequentially brought into contact with, and transported at the same speed as, the initial image bearing sur~ace 14 of a moving photoreceptor drum 16. The copy sheet 12 passes under a transfer corona generator 18 which applies electrostatic transfer charges to the back of a copy sheet and electrostatically tacks the copy sheet against the photoreceptor surface 14. The copy sheet 12 is then transported on the photoreceptor surface 14 under a detacking corona generator 20 which substantially reduces the transfer charges thereon, preferably with an alternating current corona emission. The lead edge of the copy sheet 12 is then stripped from the photo-receptor sur~ace 14 here by a mechanical strippin~ finger 24.
~It will be appreciated that ot.her stripping means may be provided). The position of the copy slleet lead edge 22 just as stripping is initiated as illustrated here by the dashed line posi~ion 22a.
A~ soon as the copy sheet lead edge 22 has been stripped from the photoreceptor surface 14, it i5 attracted to and guided over the generally planar, smooth stationary yuide surface 26 here ~ shown in a bottom view of Fig. 3. It may be seen that it contains a plurality of vacuum apertures 30 capable of attracting and retaining the copy sheet 12 in intimate, shape conforming contact with the guide sur~ace 26 as shown by the solid line position of the copy sheet 12.
The continuous electrostatic attachment of a (changing) intermediate segment of the copy sheet 12 behind its lead edge to the surface 14 provides a driving force for the copy sheet 12. The copy sheet i9 driven forward (downstream) at a velocity equal to that of the photoreceptor surface. The copy sheet 12 slides downstream over the guide surface 26, and past any further sheet guide members, such as the guide 32 shown here, toward the nip 34 of the roll fuser unit 36. The additional guide 32 would not be needed if the manifold guide surface 26 or an extension thereof extended sufficiently close to the fuser roll nip. In the solid line position of the copy sheet 12 illustrated in Fig. 1, the copy sheet is shown with its lead edge 22 just entering the fuser nip 34. It may be seen that in this position that the copy sheet 12 is fully engaged by and contiguous with substantially the entire guide surface 26 of the vacuum manifold unit 28.
Considering now some of the major areas of diference between the system 10 and prior systems of this type, the relationship of the driving velocity of the fuser nip 34 and the photoreceptor drum 16 will be discussed first. A common direct mechanical drive interconnection 38 is illustrated between the axis of one of the fuser rolls and the axis of the photoreceptor drum 16. However, rather than being designed to provide an equal surface velocity for the fuser roll nip 34 as that of the photoreceptor surface 14, the drive interconnec-tion 38 is arranged with suitable different pulley or gear diameters to provide a slightly slower speed for the fuser roll nip 34 than for the photoreceptor surface 14 in the txar,sfer station. Thus, as the copy sheet 12 is advanced through the fuser nip 34, the lead edge 22 thereof is moving downstream at a slightly slower velocity than the intermediate and trailing areas of the same CQpy sheet are being advanced downstream by the photoreceptor surface 14. This would cause a potential force for slippage between the copy sheet 12 and the surface 14, which would cause toner image smears or skips, except that the system 10 provides means to allow the inter-mediate portion of the copy sheet 12, between the fuser roll nip and the transfer station, to form, with a low mechanical resistance, a buckle or bridge position away from the vacuum manifold unit guide surface 32. This buckle or bulge is allowed to freely expand out to a maximum position to take up or absorb the full accumulated speed differential of the entire copy sheet 12 until the trail edge 23 of the copy sheet is removed from the photoreceptor surface 14c This buckled or bridged position of the copy sheet 12 is illustrated by its dashed line position 12' in Fig. 1. The leading and trailing edge positions of the copy sheet in its position 12' are illustrated here respectively at 22' and 23'. The buckle is always convex and expands further convexly as the copy sheet advances, relative to the fixed and generally planar guide sur~ace 26.
The loose toner image bearing side o the copy sheet faces away from the vacuum manifold 28.
Since in this system 10 the speed mismatch is com-pensated for by the buckle formed by the copy sheet backing up behind the slower fuser roll nip, and since the buckle expands away from the generally planar guide path 26, the buckles maximum dimensions can increase to compensate for an increase in speed mismatch, or decrease to compensate for a decrease~
in speed mismatch~ Thus, the preset speed differential between the fuser roll nip and the photoreceptor surface is not critical and can vary during operation to accommodate for variations in the radius of the driven fuser roll, variations in the length of a copy sheet between its lead edge and trail edge, etc. The fuser roll nip velocity is preferably pre-set to always provide a somewhat slower speed (and therefore always provide a minimum buckle) suficient to compensate for any normal machine operating latitude or changes, including those which would increase the nip velocity. This allows a fixed and uncritical fuser roll drive which does not have to be adiusted relative to the photo-receptor surface drive.
A sheet sensor 40 of a suitable or conventîonal mechanical switch (or photo-optical~ type shown here provided in the path of the copy sheet 12 is an example of means providin~
an electrical si~nal indicative of the time at which the lead ~dge 22 of the copy sheet is first retained by the ~user roll nip 34. The switch 40 is sh~n in Fig. 1 positioned inside the vacuum manifold 28 with its switch actuating switch finger 41 extending through the bottom or guide surface 26. The finger ~ 103~73~ ~

41 is normally in the copy sheet path and is adapted to be moved from the illustrated dashed line position to the illustrated solid line position by the passage of the lead edge 22 of the copy sheet 12. A time cLelay circuit 42 can be utilized to provide an electrical output siynal after a time period corresponding to the time required for the lead edge 22 of the copy sheet to be driven from the position of switch finger 41 into the fuser nip. Various other switch locations along the copy sheet path may be utilized, of courseO
Alternatively, other available machine logic signals may be utilized instead, e.g., signals derived from a main cam bank or logic unit of the copier.
A controlled buckle is formed in the copy sheet without disturbing of the toner image and without exerting sufficient mechanlcal force on the copy sheet to cause slippage of the portion of the copy sheet on the photoreceptor surface 14. This is accomplished here by the novel construction and operation of the vacuum manifold unit 28. Referring initially to ~ig. 2, it may be seen that the vacuum manifold unit 28 may comprise an integral metal casting or the like with a top cover 44 which is shown removed in Fig. 2 for clarity. An internal divider or vertical wall 46 extends the full length of the interior of the manifold to divide the manifold into two separate plenum chambers 48 and 49. The wall 46 extends approximately, but slightly downstream of, the mid-point of the lower guide surface 26 of the vacuum manifold and transverse the paper path. Both plenum chambers 48 and 49 have copy sheet retalning vacuum apertures 30 therein, although the upstream plenum chamber 48 preerably has a laryer number and diametex of vacuum apertures than the downstream chamber 49~ particularly along the i~litiaI upstream edge of the guide surface 26 where the copy sheet is initially Z
held by the vacuum manifold unit. (Note Fig. 3).
As shown in Fig. 2, vacuum is applied to the vacuum manifold unit 28 from a single vacuum pump 50, which may be a simple axial fan or centrifugal blower motor unit. An appropriate vacuum level inside the vacuum manifold may be approximately one and one-half inches of water, or example, or approximately 3.8 grams per square centimeter. With the arrange-ment here the vacuum pump 50 may be located at any desired position within the machine and connected by a vacuum conduit 52 to the rear ~all of the vacuurn manifold unit, for example.
It is important to note, however, that the vacu~un connection here is only to the upstream plen~n chamber 48, The wall 46 is configured to isolate the vacuum input from the downstream plenum chamber 49. The only connection between the two plenum chambers, and therefore the only source of vacuum pressure for the upstream pIenum charnber 49 here is through an air flow restrictive slot 54 centrally of the wall 46, as may be seen from the arrows indicating air flow patterns in Fig. 1.
With this vacuum arrangement, it may be seen that vacuum is maintained in the upstream plenum char~ber 48 and, therefore, in the vacuum apertures 30 therein, at all times.
This prevents the copy sheet from falling away or buckling away from the guide surface 26 of the vacuum rnanifold in the region of the upstream plenum chamber 48 at all times. Thus, the toner image bearing side of the copy sheet is prevented ~rom contacting the stripper in~er 24 or the photoreceptor surface 14 at any time and the paper path from the photoxeceptor to the ~33'~3~3 vacuum manifold is consistent. That is~ after the initial lead edge stripping, the paper path between the area at which the body of the copy sheet strips from the photoreceptor and the vacuum manifold is constant and is maintained by the configura- T
tion and spacing of the upstream area of the vacuum manifold surface, since the copy sheet is mainkained thereagainst at all times. Thus, shifting or changing of the stripping point of the copy sheet from the photoreceptor sur~ace is prevented once the copy sheet lead edge has been captured by the vacuum manifold. This is important to prevent changes in the copy - d~ c ~ ~ h (~ ~ ~
sheet charge level at strippi~g, since stripping occurs duringl ~d~t the detacking corona emissions generator 20~
In contrast, the vacuum within the downstream plenum chamber 49 is cyclically fluctuated during the machine operation with each copy sheet, as will be described. Specifically, the vacuum pressure in the plenum chamber 49 acting on the copy sheet is effectively removed during the time period in which it is desired to form the speed compensating buckle or bridge 12' in the copy sheet 12. That is, the vacuum force is removed from the vacuum apertures 30 in the downstream half of the vacuum manifold to allow the buckle to freely form in a controlled manner in that r~gion, and downstream thereof, but not upstrea~ thereof, with no vacuum force acting upon the sheet in its desired buckle region 12' during the formation of the buc~le. Also, with this configuration the formation of the buckle is assisted by gravity, with the weight of the sheet in tha buckle area tendin~ to pull it downwardly away from the vacuum manifold 28 and any other guide 32. Thus, the formation o~ a buckle over a large area is pneumatically and .

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mechanically unimpeded, and in fact is assisted~ Yet the spxead of the buckle region upstream is prevented by the continued retention of the downstream portion of the copy sheet against the vacuum apertures 30 in the upstream plenum chamber 48. Thus, the formation of the buckle in the copy sheet will not cause substantial slippage force to be generated or transmitted through the copy sheet upstream to that portion o the copy sheet in contact with the photoreceptor.
Referring to FigO 1, the above-described cyclic removal of vacuum from the downstream plenum chamber 49 is accomplished here by a vent valve 56 rapidly operated by an electrical solenoid 58. Upon the receipt of an appropriately timed electrical signal, illustrated here by an electrical connection between the paper sensing switch 40 the time delay circuit 42 and the solenoid 58,the solenoid 58 operates to lift the vent valve 56 to its dashed illustrated position, thereby opening a vent opening 60 in the manifold top cover 44 to atmosphere (~ote Fig. 2). This allows, as shown by the dashed airflow arrows in Fig. 1, ambient air to ~reely enter the downstream plenum chamber 49 and quickly drop the vacuum pressure therein to effectively zero. The vacuum connecting slo-t 54 through ---w~ the wall 46 between the two plenum chambers continues to attempt to draw a vacuum therein, but this-restrictive slot 54 is much smaller than the vent opening 60, and thexefore is not capable of drawing a vacuum in the plenum chamber 49 when the vent opening 60 is opened by the vent 56 The relative proportions illustrated in the drawings are appropriate e~amples of th~se relative total areas, although the configuration~ location and spacing thereof may be varied as d~sired.

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Whe~ever the solenoid 58 is not actuated, i.e., as soon as the vent 56 is closed~ a vacuum is applied from the vacuum blower SO through the first ~lenum chamber 48 and the slot 54 in the wall 46 ko draw a vacuum pressure level in the plenum chamber 49 comparable to that in the plenum char~ber 48. The air flow path restriction provided by the slot 54, or other appropriate apertures between the two plenum chambers, is sufficiently restrictive in comparison to the total air flow provided by the vacuum pump 50 that the vacuum pressure in the plenum chamber 48 is not significantly affected by the sudden:
absence of vacuum in the plenum chamber 49 when the solenoid S8 is operated. How~ver, a higher initial vacuum can, if desired, be provided in the front plenum chamber 48 ~or the same size blower, for providing a vacuum stripping assistance effect, for example.
When the copy sheet 12 covers the ;nitial large vacuum holes 30 along the leading edge of the vacuum manifold, this reduces the air flow being drawn by the plenum chamber 48 through its vacuum holes 30. That allows an increase in the vacuum pressure available for the downstream plenum chamber ~9 as the copy sheet moves theretoward from the area of the up-stream plenum chamber 48, if so desired.
It is desirable to maintain full vacuum retention across the entire guide surace 26 of the vacuum manifold until the lead edge 22 o the copy sheet has been moved acxoss the entire vacuum manifold and has entered the nip 34 o the fuser roll. It is particularly desirable to maintain a full vacuurn holding force on the lead edye area of the sheet as it passes across the guide surface 26 of the downstream plenum chamber 49, . ~ .

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particularly if this lead edge has a pre-set tendency to curl away from the manifold guide surEace. Thus, the lead edge area of the copy sheet is fully supported from the photoreceptor until it is guided into the fuser. It is desired to remove the vacuum support from the copy sheet only after the lead edge of the copy sheet has been captured by, i.e., is supported in, the fuser nip 34. Also the speed mismatch problem does not begin to occur until the copy sheet reaches the fuser nip. The preferred planar configuration of the guide surface 26 here provides a smooth, unobstructed, linear path for the copy sheet 12 up to this point in its downstream movement, which is illustrated by the solid line position of the copy sheet 12 in Fig. 1.
When the lead edge 2~ of the copy sheet 12 reaches the fuser nip 34, the vent valve solenoid 58 is rapidly actuated, venting the plenum chamber 49 to atmosphere, and allowing the copy sheet to drop or bow away from the bottom sur~ace of that plenum chamber 49. Since the pre-set effective linear speed of the fuser rolls nip is slightly slower than that of the photo-receptor drum, the copy sheet therefor immediately begins to orm a buckle to begin to absorb and accommodate this speed mismatch. However, as noted, the vacuum in the upstream plenwn chamber 48 is maintained, so that the buckle forms only between the fuser roll nip and up to approximately the area of the vacuum separating wall 46.
This condition continues as the copy sheet feeds forward through the nip~ That is, the solenoid 58 retains the vent 56 open9 and the buckle 12 continues to expand until it reaches its maximum buc~le position, ~hich determined by the 13~

amount of speed mismatch which it must absorb and the length of the copy sheet being fed.
Then, as soon as the trail edge of the copy sheet 12 reaches its position 23', ti~e.~ as soon as the trail edge of the copy sheet has been removed from contact with the photo-receptor surface, and before the trail edge can pass beyond the supporting surface of the upstream plenum chamber 48) the solenoid 58 is deactivated to close the vent 56 and thereby restore vacuum pressure in the downstream plenum chamber 49.
This insures that the trail edge area of the copy sheet will be retained against the guide surface 26 under the downstream plenum chamber 49, and will not be allowed to flip, fall away or kick back upstream, which could cause disturbance of the loose toner image thereon, i.e., the trailing copy sheet area is retained in its passage over the entire vacuum manifold unit 28.
It may be seen that vacuum support for the copy sheet even under the downstream plenum chamber 49 is removed only for the intermediate portion of the copy sheet in which the desired buc~le is being formed, and not for either the leading or trailing portions of the copy sheet. If desired, the vacuum vent 56 may close even before the trail edge 23 of the copy sheet has completely left the photoreceptor surface, as long as the copy sheet has ~xited the transfer zone under the transfer corona generator 18. It may also be seen that this s~me cycle is repeated for every CGpy sheet.
The removal of the solenoid 58 signal to reclose the vent 56 in response to the stripping of the trail edge of the copy sheet from the photoreceptor can be controlled b~ d , ~
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copy sheet trail edge sensor in the paper path connected to appropriate circuitry such as a time delay circuit 42 here.
Alternatively, the tirne delay itself can be pre-set based on a machine setting signal responsive to the size of the copy sheets, in the paper path direction, being utilized.
A further feature disclosed herein relates to the different desired stripping positions of the lead edge of the copy sheet versus the main body of the copy sheet thereafter.
center line 62 is shown in ~ig. 1 connecting the actual corona emitting element (wire) 21 of the detacking corona generator 20 with the center line and tangent line of the photoreceptor 16.
As discussed above, the position of the lead area of the vacuum maniold unit and its angle xelative to the photoreceptor surface 14 determines the angle and position of the copy sheet 12 relative to the photoreceptor surface and, therefore, provides the control for the actual stripping point or line at which the copy sheet first lifts away from the photoreceptor.
It has been found desirable that this stripping position occurs at or closely adjacent to the center line 62, i.eO, at or directly adjacent the actual corona emitting element ~l~of the detack corona generator 20 so as to be centrally of the ion emission area of the detack corona generator 20~ The conductive shield 63 of the corona generator 20 provides an emission area onto the copy sheet for a substantial and approx-imately equal distance on either side of the corona emitting element 21. Of course, the output distribution is non-unifo~n, i.e., the actual ion current output is higher as the corona emitting element is approached, since the corona emitting element i9 closest to the photoreceptor and has a high~r field ~3~

acting on it in that region. With stripping occuring under the detacking corona element, the str;.ppiny is occuring while the detacking process is still proceeding, i.e., before the full charge neutralizing elfect has occurred, and while a substantial transfer charge still remains on the copy sheet from the upstream transfer corona generator 18.
However, it is important to note that this stripping point under the detacking corona generator electrode 21 is for the body o the sheet after the lead edge 22 has been stripped, not for the lead edge itself. As illustrated by the dashed line position 22a of the lead edge at the initial lead edge stripping point, this stripping point desirably occurs after the lead edge has passed the entire detacking corona generator 20 and has been subjected to the full detacking corona emis~n, so as to render the critical detacking of the lead edge easier by more fully removing the.transfer charge therefrom. The stripper finger 24 is positioned immediately downstream of the detacking corona generator 20, and closely under. the upstream llead) edge of the vacuum manifold unit 28, which defines the downstream end of the detacking zone~ The stripping edge is closely spaced from both the guide surface 26 and the d~wnstream edge of the detacXing corona generator 20, so that the smallest possible lead edge area of the copy sheet is subjected to the full detacking emissions. That is, the stripper rapidly moves the lead edge up to the manifold guide ~urface 26, and thereby moves the stripping point upstream to the desired location, bef~re a significant area of the copy : sheet has past beyond the detac]cing zone of the detacking corona generator 20.

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Considering now the embodiment of Figs. 4 6, it may be seen that there are a n~mber o~E elements in common which have been commonly nur~bered, However, there i5 a difference in the sp~ed mismatch structure and operation. With this system 100 the vacuum manifold unit 102 has a concave contour in its guide surface 104. Further, the roll fuser unit 36 is driven by a different drive interconnection lOS so that the : ~opy sheet pulling speed in the nip 34 is greater than that of the photoreceptor surface 14 at the transfer station, rather than slower as in the e~bodiment o Figs. 1 - 3.
Here the vacuum in the vacuum manifold 102 is also at least partially shut down to allow the copy sheet 106 to move away from the maniold guide surface 104. However, as shown in Fig. 4, the copy sheet 106 is initially buckled by the vacuum holding it against the concave guide surface 104~
and is pulled away from that guide surface 104 by the overdrive of the fuser roll nip 34 relative to the photoreceptor surface to partially straighten out the copy sheet 106 into the dashed line position 106'. That is, an initial curvature of the copy sheet 106 is pulled out, away from the vacuum shoe surface, by th~ arnount needed to.compensate for the speed mismatch between the fuser and the photoreceptor as lony as a portion of the copy sheet i5 still remaining on the photoreceptor. The vacuum can then be reapplied once the trail edge of the copy .
sheet leaves the photoreceptor to insure its support.
An elongated but shallow initial buckle formed by a vacuum manifold guide surface 10~ of that same coniguration may be provided as shown in Fig. 4 by forming a substaIltially uniform radius concave curvature over substantially the entixe 3~

lower surface of the vacuum manifold 102. The vacuum manifold 20 here is not divided into two separate plenl~ chambers with diferent vacuum levels during a part of the machine operation.
However, that could also be provided here, providing the upstream plenum chamber is sufficiently small to allow a large enou~h curvature in the guide surface 104 under the downstream plenum chamber.
Referring now to the illustrated vacuum system for this embodiment lO0 shown in Fig. 5, there is no atmospheric vent provided in the manifold itself. Rather, a butterfly valve 108 centrally rotated by a solenoid llO is provided in the vacuum conduit 52 to rapidly open or close this conduit connecting to the vacuum source. However, the atmospheric vent arrangement of Fig. l could also be provided here, providing sufficient air flow restriction were provided in the desired portion o the vacuum manifold 102. The timing of the operation of the valve 108 by the solenoid llO with relation to the leading and trailing edges of the copy sheet is similar to that described above for the embodiments of Figs. l - 3, That is, the vacuum is applied to the vacuum manifold 102, for the entire guide surface lO~, until the leading edge of the copy sheet is retained by the fuser roll nip 34. Then the vacuum is ~uickly removed or reduced. This allows the fuser roll nip 34 to advance the forward portion of the copy sheet 106 at a faster rate than the trailing area is being fed in from the photoreceptor surface 14 by pulling an extra length of the copy sheet out of the intermediate curved region thereof, with little mechanical or pneumatic resistance and, therefore, withou~
pulling the portion of thc copy sheet which is on the '~

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7;~3 photoreceptor, and thereby without smeariny the unfused toner image. As soon as the trail edge of the cop~ sheet 106 has left the photoreceptor the valve 108 is reopened to reapply vacuum support for the copy sheet against the guide surface 104.
The difference in velocity between the fuser roll nip drive and the pnotoreceptor surface drive is set so that normal machine variations or tolerances will not cause the fuser roll nip to be slower than the photoreceptor. On the other hand, the pre-set fuser roll nip velocity should not be so fast that, for the longest copy sheet to be utilized, all of the initial buckle is removed before the trail edge of the copy sheet leaves the photoreceptor. There is a maximum speed differential which can be accommodated for a given length of copy sheet here without removins all of the available initial buckle of the sheet. This is because if the sheet is pulled completely flat, then the hi~her velocity o the fusex roll nip would pull the entire sheet forward at that same velocity, including any portion thereof in contact with the photorecep-tor, and this would cause a significant trail edge toner smearing problem. However, it has been found that adequate speed compensation for normal machine tolerances can be provided by a buc~le in the sheet feeding direction of approximately 3 to 4 inches in length with only a relatively slight concave curvature displacement from a planar path. For ~xample 3 approximately only .02 inches displacement or a s~mi-cylindrical curvature with a large radius of, for example 7 1/2 inches. This curvature can be readily provided in the manufacture of the vacuum manifold 102.
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It is impor-tant to note in this system 100 utilizing an over-speed fuser roll, that the vacuum manifold surface 104 must initially preform the paper concavely, whereas with the embodiments of Figs. l - 3, the copy sheet configuration shou1d be initially planar or slightly convex, It is very difficult to change the direction of a sheet buckle once it has been initiated in the opposite direction.
With the change in the contour of the vacuum manifold 102 in the embodiment of Figs. 4 - 6 there may also be a change in the angle of approach of the copy sheet, as it comes off the guide surface 104, toward the fuser nip 34. Also, a longer guide surface 104 in the paper path may be desired so as to increase the available buckle space. If necessary, the uppermost o~ the two rolls of the fuser roll unik 36 can be re-oriented by shifting its axis further around the other roller in a downstream direction to provide additional space and a different orientation of the nip 34.
It is noted that the buckle in the copy sheet 106 provides an additional advantage in that it increases the beam strength of the copy sheet. This gives it added support from contacting hardware below the guide surface 104.
It will be appreciated that the actual buckle length area, i.e., the concave portion of the vacuum manifold guide surface 104, will be determined both by the amount of speed mismatch that can be expected and also by paper handling considerations. The buckle length is desirably as long as possible for maximum speed compensation, and also since a longer radius buckle will have less of a buckling or copy sheet -beam strength force tending to slip the trail edge of the copy sheet backward (upstream) on the photoreceptor as compared to a shorter buckle. However, since it is desired to have the copy sheet path length to the user relatively short, this provides a practical limitation of the length of the guide surace 104 in the copy sheet feeding direction, and therefore a practical limit on the available she~et buckle length.
The entire integral unit disclosed here in both embodiments of a vacuum manifold together with the transfer and detack corotron units mounted thereto, is preferably mounted in the xerographic apparatus such a way as to be pivota-ble at one end yet maintainable ln a fixed, pre-adjustable, spacing from the photoreceptor, as by a 3 point suspension system with conventional screw adjustable support pads on the machine framework. However, it will be appreciated that these three un.its may all be separately mounted if so desired.
I~ desired, one or both ends of the integral unit or indlvidual units may instead be directly supported from the photoreceptor surface by low friction drum sliding or riding shoes or rollers resting against the edges of the photoreceptor surface, outside of the image utilized area. Pnotoreceptor drum riding supports are known for other processor units in xerographlc copiers. For example, U. S. Patent 3,918,403~
issued November 11, 1975, to R. C. Vock, teaches a transfer corona generator with a plurality of rollers contacting the bac~ of the paper during transfer. U. S. ~atent 3,011,474, issued December 5, 1961, to H. 0. Ulrich teaches a photo-receptor roller mounted development electrode apparatus. A
photoreceptor drum riding mounting arrangement allows the corona generator units and/or the vacuum manifold to be - 2~ -3'7~

maintained at a pre-set constant spacing relative to the photoreceptor surface, irrespective of eccentricities or run-out variations in the photoreceptor or its supports.
However, the operating latitude of the present unit can accommodate normal such tolerances with a fixed mounting without requiring elimination of all xelative movement be~ween the unit and the photoreceptor.
As alternative embodiments to the external vacuum manifold valve or ~lappers illustrated, it will be appreciated that vacuum may be selectively removed from selected areas of the vacuum manifold in other ways. For example, a sliding shutter could be utilized inside the bottom of the manifold to cover selected areas of the vacuum apertures in the sheet guide surface. With appropriate flow design this could also cause a se-ected increase in the vacuum pressure at the uncovered apertures, e~g., at the lead or stripping edge area.
It will be appreciated that the present invention may be utiliæed in many transfer and fusing system configura-~ ~ .
tions other than those illustrated here. For example,additional sheet tensioning or movement dampening means may be provided as for example, those disclosed in U. S. Patent 3,893,760, issued July 8, 1975, to R. R. Thettu. The system may be one utilizing a bias transfer roller instead of a coxona generator, as shown hy example in U. S. Patent No.
3,781,105, issued December 25, 1973, to T. Meagher, or 3,895,793, issued July 22, 1975, to J. J. Bigenwald, where closer spacing between the fuser rolls and the transfer roller is desired. It may a]so be possible to generate the vacuum forces desirable herein by selectively activating different ~ ~5 -3~ ?!
pressure nozzles to provide a Bernoulli effect, as described in U. S. Patent 3,78~,190, issued January 8, 1~74, to R. P. Crawford.
Various alternative strippLng systems for the sheet lead edge may be utilized. For example, air pufEers, vacuum strippers, or electrostatic detack with curvature of the 5 photoreceptor for unassisted sheet beam strength stripping.
It will be noted with the embodiments disclosed herein that the copy sheet is supported by only stationary guide members between the transfer station and the fusing station. This is adv~ntageous in that rotating sheet transport members or belts with their additional mechanisms and expense are not required. However, the disclosed systems could also be applied to a copier in which the lead area of the unfused copy sheet is gripped by mechanical grippers, vacuum belts or rollers, or the like while a trail area of the same sheet is on the photo-receptor, (and the copy sheet is then subsequently fused in a radiant,flash or other type of fuser) by providing a similar buckle control interruptable vacuum guide surface for the non-unfused image side of the copy sheet. Also, while particularly applicable to preserving dry toner unfused images, the disclosed systems could also be utilized for liquid image systems in which wet ~yet undried) images on copy sheets are being removed from an initial support surface.
In conclusion, it may be seen that there is disclosed herein an improved image transfer system. While the apparatus and steps disclosed herein are preferred, it will be appreciated that numerous variations and improvements may be made without significantly departing from the scope of -the invention by those skilled in the art. The following claims are intended to cover all such vaxiations and improvements as fall within the spirit and scope of the invention.

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Claims (11)

WHAT IS CLAIMED IS:

1. In a copying system in which an unfused image of imaging material is transferred from a moving initial image support surface means onto one side of a copy sheet while said copy sheet overlies the initial image support surface and moves therewith, and in which a lead area of the transferred unfused image-bearing copy sheet is then engaged by a moving sheet transport means spaced from the initial image support surface while a trail area of the same copy sheet is still moving with the initial image support surface, with the copy sheet extending therebetween, the improvement comprising:
speed control means for moving said initial image support surface and said sheet transport means at a pre-set speed differential for moving the lead area and the trail area of the same copy sheet at different speeds when said lead area of the copy sheet is engaged by said sheet transport means, vacuum guide surface means for vacuum supporting the copy sheet against a vacuum guide surface from the side of the copy sheet opposite from the side bearing the transferred unfused image, said vacuum guide surface means being positioned between said initial image support surface and said sheet transport means for guiding the copy sheet therebetween, and vacuum control means cyclicly actuable for reducing the vacuum applied to said vacuum guide surface in coordination with the extension of the copy sheet between said initial image support surface and said sheet transport means for movement of the copy sheet away from said vacuum guide surface by said pre-set speed differential from said speed control means for speed variation compensation.

2. The copying system of Claim 1, wherein said sheet transport means is a rotatable roll fuser nip for fusing the unfused image on the copy sheet, and wherein said roll fuser nip is positioned closely adjacent said initial image support surface by a distance smaller than the dimensions of the copy sheet being fused in its direction of movement between the image support surface and the fuser roll nip.

3. The copying system of Claim 1, wherein said vacuum guide surface means has a vacuum applied thereto suffi-cient to conform the copy sheet to said vacuum guide surface thereof when said vacuum control means is not actuated to reduce said vacuum.

4. The copying system of Claim 1, wherein said copy sheet guide surface is stationary and is adapted for slidable movement of the copy sheet thereover.

5. The copying system of Claim 3, wherein said vacuum guide surface means has a large radius concave vacuum guide surface between said initial image support surface and said sheet transport means for initially forming a correspond-ing buckle in the copy sheet therebetween, and wherein said sheet transport means is driven at a faster speed than said initial support surface by said pre-set differential which is compensated for by the straightening of the buckle in the copy sheet away from said concave vacuum guide surface.

6. The copying system of Claim 1, wherein said vacuum guide surface means comprises a vacuum chamber pneumatically connecting with a pneumatic vacuum generating means, said vacuum chamber having an apertured side providing said vacuum guide surface, and wherein said vacuum control means comprises an automatically actuated pneumatic valve pneumatically connecting with said vacuum chamber for rapidly reducing the vacuum applied to said apertured side.

7. The copying system of Claim 1, wherein said vacuum guide surface has a first area adjacent said initial image support surface through which vacuum support is maintained for the copy sheet without substantial reduction by said vacuum control means and a second area further spaced from said image support surface against which the copy sheet is vacuum retained only when said vacuum control means is operative to maintain said vacuum support.

8. The copying system of Claim 1, wherein said vacuum guide surface means comprises at least two pneumatically discrete vacuum chambers with pneumatically separate vacuum guide surfaces, both of which vacuum chambers are provided with pneumatic vacuum from said pneumatic vacuum generating means and one of which vacuum chambers is controlled by said vacuum control means.

9. The copying system of Claim 1, wherein said vacuum control means is actuated to reduce the vacuum applied to said vacuum guide surface only while the trail area of the copy sheet is on the initial image support surface and the vacuum is reapplied to the vacuum guide surface upon the removal of the copy sheet from the initial image support surface.

10. The copying system of Claim 7, wherein said vacuum control means is actuated to reduce the vacuum applied to said vacuum guide surface only while the trail area of the copy sheet is on the initial image support surface and the vacuum is reapplied to the vacuum guide surface upon the removal of the copy sheet from the initial image support surface.

11. The copying system of Claim 1, wherein said sheet transport means is a rotatable roll fuser nip for fusing the unfused image on the copy sheet, and wherein said roll fuser nip is positioned closely adjacent said initial image support surface by a distance smaller than the dimensions of the copy sheet being fused in its direction of movement between the image support surface and the fuser roll nip;
wherein said vacuum guide surface means has a vacuum applied thereto sufficient to conform the copy sheet to said vacuum guide surface thereof when said vacuum control means is not actuated to reduce said vacuum;
wherein said vacuum guide surface is stationary and is adapted for slidable movement of the copy sheet thereover, and wherein said vacuum control means is actuated to reduce the vacuum applied to said vacuum guide surface only while the trail area of the copy sheet is on the initial image support surface and the vacuum is reapplied to the vacuum guide surface upon the removal of the copy sheet from the initial image support surface.