Suction-belt document handler

Abstract: A document handler (20) for presenting documents to the platen (23) of a copier (10) for copying with a document transport system (32) having document-transport belts (35) movable under a substantially-planar background surface (33a) overlying the platen, and a suction system (33) for applying a partial suction to a document sheet being transported by the movable belts over the platen; with a clamping and unclamping system for moving the background surface against the platen to flatten the belts and a document thereon against the platen for copying. During unclamping, the surface lifts slightly away from the platen, while the document is retained on the belts by suction, by first lifting one edge of the surface 33a up away from the platen substantially before the opposite side, and then subsequently lifting the opposite side, to generate a controlled air flow across the face of the document to retain it on the belts, and moving the belts when the surface is lifted away from the platen. During clamping the one side of the surface 33a moves towards the platen, beginning slightly before the opposite side, to generate a controlled expulsion of air. The disclosed system has two pairs of commonly rotatably driven cams (60, 60a, 62, 62a) with different cam rise times connected to lift the one side of the clamping surface with a motion different from that of the opposite side. The cams can first lift the one side about 2.5 mm, while the opposite side remains in contact with the platen, then lift the opposite side about 0.8 mm, and then the clamping surface can be leveled by lifting the opposite side to about 1.75 mm while the one side is dropped to about 1.75 mm.

Description: The present invention relates to copier document handling, and, more particularly, to the transporting and positioning of documents for copying over the platen of a copier with a Suction-belt document transport system. In particular there is disclosed herein a system for rapidly clamping documents in a transporting position to an imaging position (flattened against the platen), and unclamping the documents to revert to the transporting position, which overcomes difficulties caused by the suction system and maintains control of the documents. There is also disclosed a document transport system with a manifolding system of applying suction in a multi-belt over-platen document transport system. A particular problem with modern copiers with short conjugate optics is maintaining the document being copied sufficiently flat on the imaging platen to avoid optical distortion, and to maintain all of the document in focus. This is particularly difficult to combine with maintaining positional control over the document, especially when rapidly replacing the document with another document to be copied. The suction belt document transport system disclosed herein represents an improvement over the document transport system of Xerox Corporation's US-A-4,618,138. Also particularly noted is US-A-4,294,540, although that is a single-belt system. Other suction aperture/groove patterns in a document transport are disclosed in US-A-4,544,265 and US-A-4,412,738. The disclosed system of clamping documents from a transporting position to an imaging position against the platen, and unclamping the documents into a transporting position, is an improvement over various such known systems, of which Xerox Corporation US-A-4,462,527 is of particular interest as disclosing a non-uniform or variable spacing clamp lifting system, as particularly shown in Figs. 6-8 thereof and its description in Col. 12 lines 35-56, inter alia . As noted there and shown in Fig. 8, the clamp is lifted less near the rear of the platen (the rear document side path guide) by the two different cams of Figs. 6 and 7. Note also Col. 12, lines 10-14, Col. 13, lines 47-55, and Col. 15, lines 14-46. Tilted lifting of the platen clamp in this reference is described as for a different reason - to prevent a document from climbing over the rear registration edge by keeping that side of that clamp lower. Also, it does not show either belt transport or suction control of a document. It shows a frictional and feed-wheel document transport, with document slippage for registration. Other document clamping systems for document transports are disclosed in the following patents. They disclose other copier document platen transports in document handlers or feeders in which there is a clamping plate which automatically moves down to flatten the document against the platen for copying, and provide an imaging background surface, and then lifts away to allow document feeding. This art includes US-A-3,888,585 [see esp. Figs. 6&7, and Col. 7, line 39 through Col. 8, line 21]; 4,335,954 [see esp. Fig.11 & Cols.9-10]; 3,944,366, and US-A-3,623,806. They disclose various mechanisms for flattening a document original in relation to a platen. However, many of these also disclose clamps with large wheel apertures , through which feed wheels extend, not belts, and making undesirable holes in the imaging background surface, which can cause copy printout defects. US-A-4,335,954 is also of interest as noting at the top of Col. 10 the problem of the suction created when the clamp rises. This is addressed there by slots or grooves 190 in the clamp plate surface preventing all the air from being squeezed out from under the clamp to try to keep the copy on the platen surface after the cam-lifting unclamping. (The opposite of the present system.) Also noted is JP-A-87-1432. It discloses a solenoid-lifted pressure plate pressing on the inside of a single unapertured document feeding belt over a platen when the belt is stopped. JP-A-P 60-161752 (62 - 27256) discloses an eccentric cam driven mechanism for raising and lowering a plural belt document feeder copier platen transport, to press the document against the platen during copying. There is no apparent disclosure of any suction system, or non-uniform lifting or clamping. US-A-4, 592,652 discloses a movable copier platen clamp, noting especially Fig. 7 which discloses a suction system and eccentric lifting cams. However, no document transport is provided. Other background references include US-A-4,029,404; 4,040,615, and 4,544,265. In the present document-clamping system, an entire suction manifold unit is movably mounted above, and carries, a set of suction belts, and pushes them down to clamp a document. The disclosed system relates to clamping and unclamping a suction-belt document transport system. It teaches automatic clamping and unclamping of an entire suction manifold/belt unit for each document being fed by the platen transport. The disclosed system maintains the document on a suction transport, and lifts it away from the platen during unclamping. It has been known in the copier art for many years that a rapid opening of even a simple platen cover can lift an underlying document off the platen, but this has been considered undesirable, and likely to lose control of the position of the document, and the normal solution has been to try to keep the document down on the platen, as noted above, and not lifted with the platen cover by the influx of air. Transporting documents over the platen while spaced above it, as here, is desirable to avoid static generation and attraction to the glass. It also avoids abrasion of any anti-static conductive coatings on the platen glass. Our EP-A-0 284 305 is also relevant. As xerographic and other copiers increase in speed, and become more automatic, it is increasingly important to provide higher speed yet more reliable and more automatic handling of the document sheets being copied, i.e. the input to the copier. It is desirable to feed, register accurately, and copy document sheets of a variety or mixture of sizes, types, weights, materials, conditions and susceptibility to damage, yet with minimal document jamming, wear or damage by the document transporting and registration apparatus, even if the same documents are automatically fed and registered repeatedly, as for recirculating document set precollation copying. Document sheet handling for copiers has been intensively developed in recent years. Various systems have been provided for automatic or semiautomatic feeding of document sheets to and over the imaging station of the copier for copying. The documents are normally fed over the surface of an imaging station comprising a transparent platen, into a registered copying position on the platen, and then off the platen. Such automatic or semiautomatic document handlers eliminate the need for the operator to place and align each document on the platen by hand. This is a highly desirable feature for copiers. Document handlers can automatically feed documents as fast as they can be copied, which cannot be done manually with higher speed copiers, thus enabling the full utilization or productivity of higher speed copiers. A preferable document handling system is one that utilizes an existing or generally conventional copier optical imaging system, including the external transparent copying window (known as the platen or imaging station) of the copier. It is also desirable that the document handling system be readily removable, as by pivoting away, to allow the copier operator to place documents, including books, manually on the platen. Although faster, more accurate, and automatic feeding into and registration of each document at the correct position on the platen to be copied is highly desired, this is difficult to accomplish without document jams or skewing (rotating) the document and/or damaging its edge, particularly as it is being stopped. One problem is that documents can vary widely in sheet size, weight, thickness, material, condition, humidity, age, etc.. Documents may even have curls, wrinkles, tears, "dog-ears", cut-outs, overlays, tape, paste-ups, punched holes, staples, adhesive or slippery areas, or other irregularities. Unlike sets of copy sheets, which generally are all from the same new clean batches and therefore of almost exactly the same condition and size, documents often vary considerably even if they are all of the same "standard" size, (e.g. letter size, legal size, A4, B4, etc.). In contrast, documents even in the same set may have come from completely different paper batches or have variably changed size with different age or humidity conditions, etc.. Furthermore, the images on documents and their fusing can change the sheet-feeding characteristics, and these images may be subject to damage in feeding if not properly handled, e.g. smearing of fresh typewriting ink. Yet it is desirable to feed, register and copy automatically or semiautomatically even a mixture of sizes, types, and conditions of documents without document jams or document damage, and with each document correctly and accurately aligned to a desired registration position. One of the most difficult-to-achieve features for automatic document handling is the rapid, accurate, reliable, and safe registration of each document at the proper position for copying. Conventionally the document is desirably either center registered or corner registered (depending on the copier) by the document handler automatically at a preset registration position relative to the copier platen. At this registration position two orthogonal edges of the document are aligned with two physical or positional (imaginary) registration lines of the copier platen at which the original document is properly aligned with the copier optics and copy sheet/photoreceptor registration system for correct image transfer of the document image to the photoreceptor and then to the copy sheet. This registration accuracy is desirably consistently within approximately one millimeter. If the document is not properly registered, then undesirable dark borders and/or edge shadow images may appear on the ensuing copy sheet, or information near an edge of the document may be lost, i.e. not copied onto the copy sheet. Document misregistration, especially skewing, can also adversely affect further feeding and/or restacking of the documents. In preferred types of copying systems the document is registered for copying overlying a selected portion of a full-sized (full frame) platen which is at least as large as the largest document to be normally copied automatically. In such systems the document is preferably either scanned or flashed while it is held stationary on the platen in the desired registration position. That is, in these full-frame systems the document is preferably registered by being stopped and held during imaging at a preset position over the platen glass which is adjacent one side or edge thereof. As shown in the art, and further discussed below, document handling systems have been provided with various document transports to move the documents over the copier platen and into registration. Such document platen transports may comprise one or more transport belts or feed wheels, utilizing frictional and/or suction sheet-driving forces. Various combinations of such transports are known with various registration devices or systems. Preferably the same platen transport sheet feeder is used to drive a document onto and off the platen before and after copying as well as registering the document. Several approaches are known to registering a document for copying at an appropriate position relative to the transparent copying window. Typically the document is registered on one axis by driving it with a platen transport against a mechanical gate or stop positioned temporarily or permanently at or adjacent one edge of the platen. This is often at or closely adjacent the downstream edge of the platen. That allows unidirectional movement of the document across the platen, entering from the upstream side or edge closely following the preceding document, and ejecting after copying from the downstream side or edge of the platen. The registration gate or stop may comprise projecting aligned fingers, or roller nips, or a single vertical surface along one registration line, against which an edge of the sheet, preferably the leading edge, is driven into abutment to mechanically stop and thereby register the sheet on one axis, in its principal direction of movement. Another function of such mechanical registration is also to deskew the document, i.e., to rotate and align it properly with this registration line, as well as to determine and control its registration position. However, such a mechanical gate cannot be interposed in the path of a continuous web document and thus cannot be used for intermediate registration thereof. Also it can sometimes damage the lead edge of a document. Document registration can be done without mechanical document stops on the platen, as disclosed for example in US-A-4,043,665; 4,132,401; 4,295,737 or 4,391,505. This can be done by preregistering the document to a platen transport belt and then moving the document a known, preset, distance over the platen on the belt into registration, providing there is no slippage during this entire movement between the document and the belt. Alternatively, this can be done by sensing, on the platen or upstream of the platen, with a document edge sensor, an edge of a document being transported onto the platen. The document is fed over the platen with a non-slip transport driven by a servo-motor or stepper-motor which is stopped after a preset time period or movement to stop the document on the platen in the desired registration position. Such a measured-stop registration system, for a recirculation document hanlder (RDH), is taught in US-A-4,579,444. In some document handling systems, a system for also side registering (laterally positioning) the document on the platen is used, i.e. aligning the original on both axes while on the platen, e.g. US-A-4,411,418 and 4,335,954. However two axes on-platen registration is not required, and such lateral or second axis registration may be done upstream of the platen, as by confinement of the documents within the side guides in the document tray from which the documents are fed, or driving the sheet against a side guide, e.g. US-A-4,257,587; 4,266,762 or 4,381,893. In the description herein the term "document" or "sheet" refers to a usually-flimsy sheet of paper, plastics, or other such conventional individual image substrate, and not to microfilm or electronic images which are generally much easier to manipulate. It is important to distinguish electronic copying systems, such as the Xerox "9700" printer, which read and store images of documents electronically and create copies by writing on a photoreceptor with a laser beam, or the like, since they do not have the problems dealt with here. The "document" here is the sheet (original or previous copy) being copied in the copier onto the outputted "copy sheet", or "copy". Related plural sheets of documents or copies are referred to as a "set". A "simplex" document or copy sheet is one having an image and "page" on only one side or face of the sheet, whereas a "duplex" document or copy sheet has a "page", and normally an image, on both sides. The present invention is particularly suitable for precollation copying, i.e. automatically plurally recirculated document set copying provided by an RDH. However, it also has applicability to nonprecollation, or postcollation, copying, such as postcollation operation of an RDH, or semiautomatic document handling (SADH) as discussed above. Postcollation copying, or even manual document placement, is desirable in certain copying situations, even with an RDH, to minimize document handling, particularly for delicate, valuable, thick or irregular documents, or for a very large number of copy sets. Thus, it is desirable that a document handler for a precollation copying system be compatible with, and alternatively usable for, postcollation and manual copying as well. Some examples of RDH US patents are US-A-4,459,013; 4,278,344; and 4,579,444, 325 or 326. Some other examples of recirculating document handlers are disclosed in US-A-4,076,408; 4,176,945; 4,428,667; 4,330,197; 4,466,733 and 4,544,148. A preferred suction corrugating feeder air knife, and a tray, for an RDH, are disclosed in US-A-4,418,905 and 4,462,586. An integral semi-automatic and computer form feeder (SADH/CFF), which may be an integral part of an RDH, as noted in Col. 2, paragraph 2, therein, is disclosed in US-A-4,462,527. Various others of these patents, such as US-A-4,176,945 teach plural mode, e. g. RDH/SADH, document handlers. The present invention overcomes various of the above-discussed problems, and provides various of the above features and advantages. Accordingly the present invention provides a document handler for a copier, which is as claimed in the appended claims. Further features provided by the system disclosed herein, individually or in combination, include those wherein clamping and unclamping means comprises plural cams with different cam rise times connected via cam lifters to lift a first side of a suction plenum backing and imaging surface with a different motion from the opposite side, by the cams being rotatably driven for clamping and unclamping; wherein the clamping means moves down the first side of the suction plenum backing and imaging surface towards the platen, beginning slightly before moving down the opposite side of the surface towards the platen, to generate a controlled expulsion of air from under the surface during clamping; wherein the clamping means moves down the first side towards the platen beginning approximately 5 milliseconds before moving down the opposite side, with further rotation of the cams, but beginning the movement of the first side before the opposite side by means of different configurations of the cams, to generate the desired controlled expulsion of air; wherein the unclamping means, with rotation of the cams, first lifts the first side of the surface about 2.5 mm away from the platen while the opposite side remains in contact with, and then lifts the opposite side about 0.8 mm, and then the surface is leveled by lifting the opposite side from its height of 0.8 mm to about 1.75 mm, and, at approximately the same time, the first side is dropped from 2.5 mm to about 1.75 mm.; wherein clamping and unclamping is accomplished by common rotation of the cams with different cam profiles, providing the different cam rise times, and wherein after the unclamping is at east partially completed a document previously copied is ejected by the document transport system and a next document is brought over the platen, while maintaining suction retention of the documents, and then before the copying of this next document it is clamped against the platen by moving down both the first and opposite sides of the surface by further rotation of the cams, but beginning the movement of the first side a fraction of a second before the movement of the opposite side to move the non-parallel surface towards the platen, which squeezes out air from under the document before the final clamping, in which both the first and opposite sides are flattened against the platen; and wherein additional document retention means connecting with the suction means are provided along the first edge of the surface to provide a substantially higher holding force to the edge area of a document overlying the first edge, for resisting stripping of the document from the document transport during the unclamping and lifting movement. Further disclosed features include a copying method as claimed in the respective appended claims. Additional features are also claimed in the appended sub-claims. Some examples of various other known copiers with document handlers, and especially with control systems therefor, including document sheet detecting switches, etc., are disclosed in US-A-4,054,380; 4,062,061; 4,076,408; 4,078,787; 4,099,860; 4,125,325; 4,132,401; 4,144,550; 4,158,500; 4,176,945; 4,179,215; 4,229,101; 4,278,344; 4,284,270, and 4,475,156. It is well known in this art, and in general, how to program and execute document handler and copier control functions and logic with conventional or simple software instructions for conventional microprocessors. This is taught by the above and other patents and various commercial copiers. Such software may vary depending on the particular function and particular microprocessor or microcomputer system utilized, of course, but will be available to, or readily programmable by, those skilled in the applicable arts without experimentation from either description or prior knowledge of the desired functions, together with general knowledge in the general software and computer arts. It is also known that conventional or specified document-handling functions and controls may be alternatively conventionally provided utilizing various other known or suitable logic or switching systems. Various of the above-mentioned and further features and advantages will be apparent from the specific apparatus and its operation described in the example below. The present invention will be better understood by reference to this description of a specific embodiment thereof as shown in the accompanying drawings (approximately to scale), wherein: Fig. 1 is a side view of an exemplary recirculating but plural mode document handler for a copier, in which the document handler of the invention may be incorporated as shown in the other Figures; Fig. 2 is a partial side view of the document handler of Fig. 1, illustrating the clamping and unclamping system of the platen suction belt transport; Fig. 3 is a bottom view of the platen transport of the document handler of Figs. 1 and 2, with the belts shown partially broken away better to illustrate the underlying suction manifold surface grooves and mating aperture patterns with relation to the overlying document transport belts; Figs. 4 and 4A respectively show enlargements of the profiles of the front and rear lifting cams of the clamping and unclamping system illustrated in Figs. 2 and 5; Fig. 5 is a schematic partial top view of the clamping and unclamping system of Fig. 2, further illustrating the operation of the cams shown in Figs. 4 and 4A, and Fig. 6 is an enlarged partial cross sectional view of the rear registration edge area of the document transport surface and belts of Fig. 3. (Note that this Figure is "upside down" from the actual orientation, because Fig. 3 is a bottom view.) Describing now in further detail the example illustrated in the Figures, there is partially schematically shown in Fig. 1 an exemplary copier 10, with an exemplary document handling system 20 (preferably a plural mode RDH, to be described herein). The copier 10 may be of any known type, such as those disclosed in above-cited copier patents. The exemplary document handler (DH) 20 illustrated here is similar to that shown in EP-A-0 284 305. However the system disclosed herein is applicable to various other DH's, such as those shown in various above-cited patents thereon. As shown therein, it is known to have two separate document inlets, a recirculating or RDH input stacking tray 21, and a side entrance 22 for semiautomatic document handling (SADH), into which documents may be individually inserted by the operator, sequentially and/or in an operator-selected "job interrupt" mode. The RDH 20 provides for automatically transporting individual registered and spaced document sheets onto and over the conventional platen imaging station 23 of the copier 10, using a suction belt platen transport system 32 overlying the platen 23. Documents are inputt to one end of the platen transport 32 either from the RDH inlet provided by the restacking tray 21 on top of the unit, spaced above the platen, or from the separate document inlet 22 directly adjacent one side of the platen, shown at the right side as viewed. As is conventionally practiced, the entire document handler unit 20 pivotally mounts to the copier 10 so as to be liftable by the operator up away from the platen for manual document placement and copying or jam clearance of documents jammed in the platen area. The DH 20 has conventional external covers (not shown, for clarity). Other than the DH 20 system modifications and controls and other features to be described herein, the exemplary copier 10 may be, for example, the well-known "Xerox" "1075" or "1090" or any other xerographic or other copier, as illustrated and described in various patents cited above and otherwise, including US-A-4,278,344. The copier 10 may include a photoreceptor belt 12 and the conventional xerographic stations acting thereon for respectively charging, image exposing at 14, image developing, etc.. Documents on the platen 23 may be imaged onto the photoreceptor 12 at area 14 through a variable reduction ratio optical imaging system 16 to fit the document images to the selected size of copy sheets. The copier 10 is preferably adapted to provide duplex or simplex precollated or postcollated copy sets from either duplex or simplex original documents copied from the RDH 20. The control of all sheet feeding is, conventionally, by the machine controller 100. The controller 100 is preferably a known programmable microprocessor. The controller 100 conventionally controls all of the machine steps and functions described herein, including the operation of the document feeder 20, the document and copy sheet gates, the feeder drives, etc.. As further taught in those references, the controller 100 also conventionally provides for storage and comparison of the counts of the copy sheets, the number of documents recirculated in a document set, the desired number of copy sets and other selections by the operator through the panel of switches thereon, time delays, jam correction control, etc.. The controller 100 may be conventionally connected to receive jam and control signals from various conventional document sheet sensors mounted in the document recirculation path of the RDH, including those shown in the respective locations shown here in the Figure, including 39, 52, 55, 56, and 57. Referring further to the exemplary plural mode document handling system 20 illustrated in Fig. 1, documents may be fed to the same platen 23 and platen transport 32 input position from either the SADH input 22, or from the RDH tray 21. The latter input is through an RDH input path 24 between that tray 21 and the upstream end of the platen transport 32, preferably including, as shown, a known stack feeder/separator, a sensor 52, and a first set of turn baffles and feed rollers to invert the documents before copying. The SADH input 22 may conventionally include a tray and edge guide and sensors, and an SADH preregistration gate 30. This gate 30 may have any configuration . The gate 30 illustrated here is preferably retractable in and out of the SADH input path to the platen from the SADH input 22 by solenoid actuation controlled by the controller 100. The SADH input path feeds documents directly to the platen, without inversion, and bypassing, without interference, the RDH input path 24, so that the two inputs can automatically operate in a selected interleaved or interrupt feeding sequence. The SADH input 22 here preferably also includes slightly-skewed cross-rollers 26. As taught in the above-cited US-A-4,579,444, these provide side edge registration towards a rear edge guide at this inlet, as well as feeding of the document forward for registration and deskewing against the gate 30. Such cross-rollers may also be provided in the RDH input path 24. Just downstream of the gate 30 are take-away or on-platen rollers 28 providing a document sheet feeding nip for engaging and transporting any document sheet which is past the gate 30 or the RDH input path 24. The rollers 28 feed the documents directly past sensor 57 into the inlet to the platen transport system 32. The platen transport system 32 here comprises a suction manifold 33 for holding documents against plural belts 35 engaging and transporting the documents without slippage over the platen 23 into the desired registration position, of the general type disclosed in the above-cited US-A-4,618,138. The platen transport system 32 and the rollers 28 may be incrementally servo motor driven by the controller 100. After the documents are copied on the platen 23, they are, in this example, ejected by the platen transport system 32 into downstream or off-platen rollers 34 and fed past a gravity gate 37 and sensor 39 to a decision gate 36. If the gate 36 is up (it always is for CF or normal SADH copying) it deflects the documents directly to an SADH document outlet including output rollers 38. If the decision gate 36 is down, as for RDH, and for job recovery, sheet documents are deflected into an RDH return path 40, past sensor 55. However, this RDH return path 40 includes reversible rollers 42 to provide a choice of two return paths to the RDH tray 21; a simplex return path 44 with an inversion, or a duplex return path 46 without an inversion. For the duplex path 46 the rollers 42 are reversed to reverse feed the previous trail edge of the sheet back to the now-dropped gate 37 which now deflects that sheet into the path 46. The duplex return path 46 provides a desired circulation inversion of duplex documents, as returned to the tray 21, for copying their opposite sides in a subsequent circulation, or circulations, as described in the above-cited art. This is because a duplex document returned through the duplex return path 46 has only one inversion per circulation (in the RDH input path 24). In contrast, in the complete simplex circulation path there are two inversions per circulation, one in each of the paths 24 and 44, which equals no inversion per circulation. Thus, simplex documents are always returned to tray 21 in their original, face-up, orientation. As illustrated, the RDH tray 21 also includes a variable position rear registration edge or backstop, illustrated with several dashed lines, for initially accommodating and restacking various sizes of documents. The illustrated DH system 20 utilizes for its RDH feeding a combined corrugated suction feed and air knife separator system for feeding out sequentially the bottom-most sheet of the stack in the tray 21. For normal cut sheet SADH input 22 document feeding in the DH system 20, the documents are fed and controlled by, in order, the cross-rollers 26, the nips of the on-roll rollers 28, the document belt transport 32, the nips of the downstream or off-roll rollers 34, and then the nips of the output or exit roll rollers 38. For RDH circulation the sheets are additionally driven and controlled by the stack feeder/separator and the rollers and curved baffles in the paths 24 and 44 or 46, and the eject rollers at the restack entrance at the rear of the tray 21, as illustrated. Individual sheets are "handed on" from one feeding nip to another along the document path with very restricted slippage to ensure positive and registered feeding. In the system illustrated, the portions of all the roller pair units 26, 28, 34 and 38 which are below the document path are idler rollers mounted to the body of the copier. All the above-path rollers in each of these nip pairs are the driven rollers, and all of those are mounted to the pivotal platen cover unit of the DH system 20. Thus, these above-path rollers may all be lifted up, away from the platen 23, to expose it and to open all these roller nips and the platen transport 32. Turning now to details of the system disclosed herein, there is disclosed a document transport system for a copier. The clamping and unclamping system disclosed here overcomes a particularly-difficult document-handling problem in modern copiers with short conjugate optics providing a narrow depth of field calling for reliable document flattening against the platen with a very planar clamping surface, yet being compatible with high speed document handlers requiring rapid document exchange times. That is especially critical and difficult with suction transports, as discussed further herein. Here, as the clamp lifts, the inrush of air is controlled so as not to strip the sheet from the document transport 32, but preferably to help lift and hold the sheet against the transport 32 instead. This is provided by lifting the clamp first at the registration edge, where the position of the sheet is controlled. As this first edge lifts, inrushing air assists in lifting the rest of the sheet. As the clamp closes, the clamping translates the entire platen transport 32, and therefore the document held on it, towards the platen glass at an angle, pushing air aside. Clamping and unclamping can be achieved in 120 milliseconds or less with this system yet maintain document control. As noted, some prior art discloses clamps with apertures through which feed wheels extend, making undesirable holes in the imaging background surface which can show up as black areas on the copy sheets, and clearly being unsuitable either for a suction or a belt system. The moving clamp system includes the external integral bottom surface 33a of an entire suction manifold 33 above a set of belts 35, which surface 33a pushes the belts 35 down against the document for clamping. I.e. the entire suction belt feeder unit 32, including the manifold 33, its surface 33a, the belts 35 and their mounting frame and rollers, etc. moves up and down relative to the platen to provide automatic clamping and unclamping. The belts 35 press the document flat against the platen 23 because the surface 33a underlying them holds the belts flat. As will be described, the document-lifting movement required for the unclamping is difficult to achieve because the clamp is lifting against the suction forces formed between the sheet and the platen glass. This suction is formed as a result of greatly increasing the volume between them during lifting. The bottom or clamping surface 33a is generally planar, but channeled or grooved at 54, and apertured at 53 into the manifold or plenum 33 interior, for applying suction to the document in the gaps 35a between the belts 35, as will be described. The frame of the manifold unit 33 here also provides belt supports, such as those described in US-A-4,618,138. The clamping surface 33a also preferably has a preset, preformed, concave "bow", to assist or ensure flattening, of about 1 mm (millimeter) to 0.5 mm when not engaged. That is, the unstressed (unclamped) surface 33a preferably has a large radius concave "belly", with the center of surface 33a about 0.5 - 1.0 mm further away from the platen than are the outer edges of surface 33a, to ensure that this surface 33a presses flat against the platen. That is assisted by the springs 70 pressing down the outer corners of the frame holding the manifold 33 against the platen, except when the clamp is lifted. That is, the unit 32 is spring-loaded down. The "bow" also helps ensure maximum document flattening at the edges, where it is most optically sensitive. This "bow" or "belly" centerline is preferably approximately aligned with the centerline of the lens system, where document spacing and distortion are the least sensitive. Also, it helps provide for a small volume of air during clamping between the document sheet and the glass, to aid document unclamping by reducing suction holddown forces. As shown in Figs. 2 and 5, the unit 32 is lifted up against the spring force by lifting four cam followers 64 by rotation of two pairs of cams 60, 60a and 62, 62a, on two fixed camshafts 66, 67, which are servo driven, to provide the following movements to overcome the suction/air flow problems: First the rear or side registration edge of the clamp surface 33a is lifted by the rear cams 62, 62a by about 0.1 inch (2.5 mm), to allow air to get under the clamp there first. Then the front cams 60, 60a lift the front or operator side of the clamp (the side opposite the rear edge) up by about 0.03 inch (0.8 mm). Then the belt drive 35 may be started, and the rear edge is dropped down by the rear cams from 2.5 mm to about 1.75 mm, while the front edge is raised from 0.8 mm to 1.75 mm to level unit 32. Note the document sheet feeding may be started during this special small but sequential unclamping movement of the clamp. The configurations or profiles of the two identical front cams 60, 60a are shown in Fig. 4, and those of the two identical rear cams 62, 62a are shown in Fig. 4A. Figs. 2 and 5 show how these four cams move their cam followers 64, which directly translate the varying cam profiles into an equal movement of the entire platen transport unit 32. All the cams may be commonly rotated at the same speed and by the same rotation angle between two common (dashed-line) dwell angles for the final up and down (unclamped and clamped) positions. The clamping position is not critical for the cams because the springs 70 and gravity can do the actual or final clamping. The radii of all the cams at the two dwell points for the clamped and unclamped positions may be the same, but the intervening profiles of the rear cams differ substantially from those of the front cams, as shown in Fig. 4 vs. Fig. 4A. There may be less than approximately 2.6 mm between the largest and smallest radii of the cams. That represents the maximum possible difference between the raised and lowered positions of the lower surface 33a for these cams in this configuration. Note, however, that the angular positions at which the rear cams reach their maximum radius is very different from that of the front cams, i.e., the rise and fall of the front cams is very different from that of the rear cams. As the clamp lifts in this described manner, the surface 33a and the document sheet thereon "wave" upwardly from the rear or registration edge, rather than lifting straight up uniformly. This provides a desirable and controlled airflow pattern as the clamp is lifted. Cooperating therewith are additional grooves 58 and apertures 59 along the rear registration edge of the surface 33a. (See particularly Fig. 6). These additional apertures 59 and grooves 58 increase the retention of that edge of the document against the transport, resisting the airflow in that area as the clamp lifts. Note that the pattern or spacing of the apertures 59 and their communicating corresponding channels or grooves 58 is denser, i.e. they are both larger and closer together than the other apertures 53 and grooves 54 on the surface 33a. These rear edge grooves 58 are substantially deeper, e.g. approximately eight times deeper, so as to apply a much higher suction force to this rear registration edge of the document between the last belt 35 on that side and the registration edge. Because these rear edge apertures 59 are much larger in diameter and closely spaced, they are manufactured in the staggered pattern illustrated in Fig. 3 rather than arranged linearly as the other groups are. Further noting Fig. 6, additionally provided along the rear or registration edge of the surface 33a is a raised edge or rib seal 72 extending along the rear edge of the bottom plate 33a. The rib 72 height is approximately the same as the belt 35 thickness. This rib seal 72 is preferably approximately 0.25 mm high and 6 mm wide, and terminates and seals the outer ends of the edge grooves 58. Therefore a confined or defined suction chamber is provided between the rear edge of the rearmost belt 35 and this rib 72, forming a substantially higher intensity suction under the outer edge of the document sheet. Note that the outer edge of the document is always overlying this high-suction area and at least partially overlying the rib 72, because most documents fed by this document handler 20 are registered to the rear registration edge, which is directly over or immediately outside of the rib 72. That rear registration edge is not physically present in the platen area but may be provided by preregistering the rear edge of the document, to a line adjacent the outside edge of the rib 72, immediately upstream of the platen transport, by an edge registration guide provided in the document path there from both the RDH and SADH inputs, against which the rear edge of the document may be driven by crossed rollers. Thus, the rear edge of most sizes of documents are always lying on and sealing this rib seal 72, not inside thereof, and not extending substantially beyond this rib 72. The rib 72 also reduces document distortion at the top edge area where that is most sensitive. Alternatively to the additional vaccum grooves 58, a single shallow flat-bottomed channel (e.g., 4 mm wide by 0.5 mm deep, below the rib 72) can be provided extending along and parallel to and just inside the rib 72, i.e. extending in the direction of document motion, so as to be closed by an overlying document. In Fig. 6 it could appear substantially the same as present Fig. 6 except that at reference 58 the solid line would be where the lower dashed line is now. It will also be noted that an additional groove or channel pattern 74 may be provided at the front edge of the surface 33a. However these grooves 74 are only functionally utilized in the case of very large (very long) documents which would extend out over these grooves 74. As the clamp lifts in the manner described, the surface 33a and the document sheet thereon "wave" upwardly, starting from the rear registration edge, rather than lifting straight up uniformly. The rear registration edge of the document, which is held with extra suction force as described above, is lifted first. The additional grooves 58 and apertures 59 along the registration edge retain the document edge against any peeling or separating tendency caused by the airflow entering there as the clamp lifts. Note that it would be undesirable to apply such a large suction retention force for the entire document. That would have several disadvantages, including increased drag forces of the belt and document against the surface 33a, and possible wrinkling of thin documents. Turning now to the clamping operation and movement, this differs considerably from the above-described unclamping movement, even though here it is accomplished by further movement of the same cams. For clamping, the extent and direction of motion of the front and rear edges of the surface 33a may be the same, but preferably the rear or registration edge starts to drop about 5 milliseconds before the front edge. Thus an air squeezing action occurs during clamping, in which air is squeezed out from under the clamp toward the front during clamping. Thus the rear or registration edge will contact the platen first, although the movement of both the front and rear edges of the surface 33a is decelerated before the platen is engaged. Both front and rear ends of the clamp can be moved down at about the same speed until this deceleration occurs, shortly before the contact of the rear edge. Then after the rear edge contacts, the continued rotation of the cams flattens both the front and rear edges of the surface 33a with equal force against the platen. This wave or squeezing of the document down during the clamping movement helps to keep lightweight documents from being wrinkled by the belt transport by overpressure by trapped air pockets under the document against which the thin document would be forced, i.e., localized undesired air pressure against the document which could cause buckling or wrinkling of a thin document. To summarize the motions during unclamping, the rear edge is first lifted about 2.5 mm while the front edge remains down in contact with the platen. Then the front edge is lifted to about 0.8 mm. Then the belts may be started, since there is enough air available to provide adequate suction retention and therefore nonslip transport. Then the clamp is leveled by lifting the front edge from 0.8 mm to 1.75 mm and, at the same time, the rear edge is dropped from 2.5 mm to 1.75 mm. The document previously copied is ejected by the platen transport and the next document is brought over the platen by this platen transport, maintaining suction retention at all times. Then before the copying of this next document, it is clamped against the platen by moving down both front and rear edges of surface 33a with further movement of the same cams but beginning the movement of the rear about 5 milliseconds before the front to move the clamp down at an angle which squeezes out air from under the document before the final clamping in which both edges are against the platen. To summarize the motion drive disclosed herein, as shown in Figs. 2 and 5, the four cams are on two driven shafts mounted to the frame of the entire DH unit 20 and therefore rotating about fixed axes in normal operation (i.e., unless the entire DH 20 is lifted up from the platen). The four conventional cam followers. 64 are each positioned directly above the four cams, to be lifted in proportion to the cam profile or radii and angle of rotation. The cam followers 64 are fastened to a rigid support frame fastened to and holding the suction plenum, and preferably the belts. This movement from the cam profiles is thereby transmitted directly to the platen transport unit 32, including surface 33a. In addition to gravity, the four springs 70 between the DH 20 frame and the frame of the platen transport unit 32 act to press the latter down, and also hold the cam followers 64 down against the cams and assist rapid downward (clamping) acceleration. Note that this clamping and unclamping must occur at the document exchange rate, which is equal to, or one-half of, the full copying rate of the copier. To hold the platen transport in position horizontally yet allow vertical unclamping movement relative to the cams and the cam shafts, there are illustrated here in Fig. 5 additional cylindrical bearings on the cam shafts 66, 67, and mating confining bearing retainers on the unit 32 allowing vertical movement but not horizontal movement. Mating pins, guides, slide plates or other retainers could be used. In a document feeder 20 for transporting document sheets over the platen of a copier with a suction belt platen transport system 32, with means for stopping the document sheet at an imaging position on the platen, the document transport system 32 comprises several white belts 35 moving under a white backing surface overlying the platen, and includes a conventional pump for applying a partial suction to a document sheet being transported by the moving belts. The belts 35 are preferably thin, low-frictional, non-elastomeric, plastics belts as in US-A-4,618,138, but not translucent or transparent, because the belts 35 are optically masking suction holes 53 and 59. The belts 35 are unapertured and the exposed area of the backing surface 33a is unapertured in the imaging position, so that the document transport system is effectively invisible to the copier. That is, the apertures 53 here extend in rows over most of the surface 33a, but only underlying the edges of belts 35. As observed in various references, multiple belt transports have often had very serious "printout" or copy defect problems with "show-around" and "show-through". "Show-through" is the printing out of dark areas on the copy sheet because the copier optics "see" dark areas on the document transport through the document, particularly through a transparent or very thin translucent document. Show-around" can occur when the document is mis-registered, or a reduction copy is being made, which directly exposes areas of the platen transport beyond (outside) one or more edges of the original. Both of these types of copy defects are particularly likely with suction platen transports and plural belt platen transports, because the belt edges and suction apertures tend to have both printable edge shadows and dirt contamination (visible darkening), particularly if such belts are of a relatively thick or high friction elastomeric material. This can produce very undesirable dark areas on the copy sheets. Suction belt transports desirably provide a combination of non-critical frictional feeding by the belt(s), assisted by a partial suction applied through apertures in the belt or between the belts, to retain or pull the document or portions thereof against the belt(s). However, belt transports have introduced serious additional problems of "show-around" and "show-through" copy defects. The document transport system 32 here includes a suction plenum or manifold 33 having a white backing or imaging surface 33a closely overlying the platen 23, as will be further described. This plenum backing surface 33a is closely overlayed with a plurality of driven transport belts 35, spaced apart by relatively narrower defined gaps 35a. The belts 35 are each relatively narrow endless loops. These belts 35 may be, for example, uniformly made from a single layer of polyester material. They are preferably much less than 0.5 mm thick, and a thickness of only approximately 0.2 mm has been found to be operative and desirable. The lower or outer (document transporting) surface of the belts should be sufficiently smooth as to resist the accumulation of contaminants such as paper lint thereon, and so as to maintain the preferred invisibility of the belts to the copier. If desired, some belt surface texturing may be provided across the belt. Suction is applied to the document in the transport system 32 via the surface 33a in the gaps 35a between the belts. This suction holds a document sheet against the belts 35 with sufficient force that the low friction engagement of the moving belts 35 against such a suction-retained document provides an adequate transporting force. That is, sufficient normal force between the sheet and the belts 35 such that, even with the low coefficient of friction of the belts, there is sufficient forward transporting force to transport the document reliably with minimal slippage from the initial engagement of the document upstream (off) of the platen, then across the platen towards the downstream edge thereof, i.e., towards and into the forward edge registration position, and then to elect the document from the platen after it has been registered and copied. The applied suction also helps to retain or lift up the document sheet thereon out of substantial engagement with the platen during feeding (while unclamped), thereby reducing frictional resistance to feeding and static electricity generation between the document and the platen. (Conventional conductive brush or pin coronode or other electrostatic discharge means may be provided for the documents, the belts and/or the platen, if desired). The conformable mounting of the platen transport system 32 over the platen may be variously provided. As previously described, preferably the entire platen transport system 32, comprising the plenum 33, its imaging surface 33a, the belts and their supports, and all of the components directly attached thereto, are mounted for a slight but controlled independent movement relative to the rest of the document handling system 20, i.e., relative to the cover and the frames of the DH system 20 which support the platen transport system 32. It is mounted so as to be able to conform to the platen surface when clamping. Limited axiallydeformable coil springs 70 or the like may be provided at the four corners of the upper surface of the plenum or its mounting frame. The mounting of the platen transport system 32 to the frame of the document handling system 20 allows independent vertical movement of the platen transport but prevents its lateral movement and therefore maintains lateral registration of the transport and registration system. It allows the imaging surface of the platen transport and the belts thereon to conform closely to the plane of the upper surface of the platen during clamping. The bottom wall 33a of the suction plenum 33, providing the imaging surface, is formed with sufficient stiffness as to maintain the flatness of that surface. This may be assisted by stiffening ribs or corrugations on the interior surface thereof. It may also have a preset bow as described. The inside surfaces of the lower flights of the belts are supported by, and slide over, especially-designed portions or areas of the backing surface 33a of the plenum 33. Here it is important to note from Fig. 3 that these areas are largely ungrooved, to avoid applying suction under the belts and thereby substantially reduce belt friction with surface 33a. The opposite ends of each belt loop are mounted on rollers at opposite ends of the platen transport system 32. Turning now to the suction system for the platen transport system 32, the suction source may be provided by a conventional low-pressure fan or blower. Preferably it is pneumatically connected to one side (here the rear) of the manifold 33, as shown in Fig. 2. A very low level of partial suction may be applied, e.g. in the order of 20 ± 5 mm (approximately 1 inch) of water, in the manifold 33 plenum. For this suction to work for document transporting, it must be provided between the document and the backing or imaging surface 33a. With the present system, as shown in Figs. 3 and 6, this is accomplished with a large number of small apertures 53 in the manifold surface 33a. These apertures 53 are located in opposite ends of a large number of small channels 54. The channels 54 and their apertures 53 extend in rows across the surface 33a as shown. These concave hemicylindrical channels 54 extend transversely across the surface 33a in between adjacent belts 35, across the interbelt gaps 35a, but do not extend substantially under the belts, i.e., each channel 54 extends between an aperture 53 under one belt edge only to another aperture 53 under the adjacent edge of the next adjacent belt, but not passing under a belt. The pattern of channels 54 extends across and widely covers the areas of the belt gaps 35a. The apertures 53 are fully covered by the edges of the lower flights of the belts, as shown in Fig. 3. The apertures 53 are not in the interbelt gaps 35a. All but the outer edges of the belts 35 ride on smooth, ungrooved, unapertured, areas of the surface 33a. Only the belt edges are over (end) areas of the air flow channels 54. Thus, only a relatively small area of the belts 35 are subjected to any suction forces, and consequently there is low frictional drag between the belts and their (predominantly smooth) underlying surface 33a. Yet, when a document sheet is present, the partial suction applied to the document from between the belts by the channels 54 is more than sufficient to lift the document up against the belts, and thereby normally hold both up away from the platen surface, and to maintain sufficient normal force between the document and the belts for non-slip feeding by the belts. Although the channels 54 are relatively shallow, they have sufficient cross-sectional area to conduct the requisite relatively low air flow therealong with relatively low resistance, and thereby to relatively uniformly apply the same suction level along each channel under the area of the document between the belts 35. Different suction levels might be provided in different channels 54, but that is not necessary in the central area of the surface 33a. However a wider interbelt gap 35a may be provided there than elsewhere. Each row of channels 54 is for pneumatically communicating the apertures 52 at each end thereof into one gap 35a between the belts with as little surface 33a perturbation as possible in the gaps 35a, since these gaps 35a are directly exposed to the copier optics. The channels 54 have gently sloping side walls so as to be substantially as highly reflective as the rest of the surface 33a and therefore effectively optically invisible. The depth of the channels 54 may be approximately 2 mm, or less. As noted previously, there are provided additional, deeper, rear side channels 58, also transverse to the direction of movement of the belts 35, at the rear edge of the surface 33a. They may be angled to reduce paper edge catching if desired.

Claims: A document handler for presenting documents to the platen of a copier for copying, comprising a multi-belt transport system for feeding the documents over the platen and into an imaging position over the platen, wherein the transport system comprises several document-transport belts (35) movable under a substantially-planar backing surface (33a) overlying the platen (23), and suction means (33) for applying a partial suction to a document sheet being transported by the belts over the platen, the document handler including clamping means (64,66) for moving the backing surface against the platen to flatten the belts, and any document thereon, for copying the document, characterized in that: the clamping means includes unclamping means (64) for lifting the backing surface and the belts slightly away from the platen while keeping the document retained on the belts, the unclamping means including means (60,62) for lifting one side of the backing surface up from the platen substantially before the opposite side thereof moves, and then subsequently lifting the opposite side, to generate a controlled air flow across the face of the document for assisting in retaining the document on the belts as the backing surface is lifted, and in that means is provided for moving the belts when the backing surface is lifted from the platen with the document retained by suction in contact with the belts. A document handler as claimed in claim 1, wherein the clamping and unclamping means comprises two or more cams (60, 62) with different cam rise times connected via cam lifters (64) to lift the one side of the backing surface with a motion different from that of the opposite side as the cams are driven. A document handler as claimed in claim 2, wherein the clamping means (60,62,64,70) is arranged to move the one side of the backing surface towards the platen slightly before the opposite side, to generate a controlled expulsion of air across the face of a captured document from under the backing surface as it moves towards the platen. A document handler as claimed in claim 3, wherein the clamping means is arranged to move the one side of the backing surface towards the platen approximately 5 milliseconds before it moves the opposite side, with simultaneous rotation of the cams. A document handler as claimed in any any one of claims 2 to 4, wherein the unclamping means is arranged, by rotation of the cams, first to lift the one side of the backing surface about 2.5 mm away from the platen while the opposite side remains in contact with the platen, then to lift the opposite side about 0.8 mm, and finally to level the backing surface by lifting the said opposite side to a distance of about 1.75 mm, and, at approximately the same time, dropping the one said side to the same final distance. A document handler as claimed in any one of claims 2 to 5, wherein the document transport system is operable, when unclamping of the backing surface is at least partially completed, to eject a document previously copied and to bring the next document over the platen while maintaining suction retention of the documents; and wherein the clamping means is arranged, by rotation of the cams, to clamp the said next document against the platen by moving down both the one side and the opposite side of the backing surface, but beginning the movement of the one side shortly before the movement of the opposite side to move the surface towards the platen while it is held at an angle thereto which squeezes out air across the face of the document before reaching the clamped position, in which position both sides of the backing surface are flattened against the platen. A document handler as claimed in any preceding claim, wherein additional suction means (58,59) are provided along the one side of the backing surface to provide a substantially higher partial suction holding force to the respective end area of a document overlying the one side, for resisting detachment of the document from the belts during the unclamping movement. A copying method utilizing a document handler (20) for presenting documents to the platen (23) of a copier for copying, comprising a multi-belt document transport system for feeding the documents seriatim over the platen and into an imaging position over the platen, wherein the transport system comprises several document transport belts (35) movable under a substantially-planar backing surface (33a) overlying the platen, and suction means (33) for applying a partial suction to a document sheet to be transported by the belts over the platen, the method including moving the backing surface against the platen to flatten the belts, and any document held thereon, for copying the document, characterized by the steps of: unclamping the backing surface and the belts and the document thereon from the platen by unevenly lifting the surface away from the platen while supplying a partial suction with the suction means to lift the captured document away from the platen with the belts, the unclamping step including lifting one edge of the backing surface up from the platen substantially before the opposite edge is lifted, and then subsequently lifting the opposite side, to generate a controlled flow of air across the face of the document for assisting in retaining the document in position on the belts as the backing surface is lifted from the platen, and transporting the document by movement of the belts, with the partial suction retaining the document against the belts, after the unclamping is at least partially completed. A method as claimed in claim 8, further including the step of clamping the backing surface against the platen, wherein the one edge of the backing surface is moved towards the platen beginning slightly before the opposite edge is moved in the same direction, to generate a controlled expulsion of air across the document face and from between the backing surface and platen during clamping. A method as claimed in claim 8 or 9, wherein, for unclamping, the one edge of the backing surface is lifted about 2.5 mm from the platen while the opposite edge remains in contact with it, then the said opposite edge is lifted about 0.8 mm, and then the backing surface is leveled by lifting the said opposite edge to a distance of about 1.75 mm, and, at approximately the same time, the said one edge is dropped to about the same distance. A method as claimed in any one of claims 8 to 10, wherein unclamping is accomplished by rotation of cams with different cam profiles, and wherein after unclamping is at least partially completed a document previously copied is ejected by the document transport system, and the next document is brought over the platen by it, while maintaining both documents in contact with the belts by suction, and then before the copying of this next document it is clamped against the platen by moving down first the one edge and then the opposite edge of the backing surface by rotation of the cams so as to move the surface towards the platen while held at an angle, to squeeze out air from under the document before the final clamping, in which both edges of the surface are against the platen.

Inventors: HERLEY JAMES A, IAIA THOMAS C JR, MALE ROGER C, MCKEOWN DOUGLAS A, MCLAUGHLIN WILLIAM J, SCHAFFER ROBERT R, SIEGEL ROBERT P, SPEHRLEY CHARLES W JR, HERLEY, JAMES A., IAIA, THOMAS C., JR., MALE, ROGER C., MCKEOWN, DOUGLAS A., MCLAUGHLIN, WILLIAM J., SCHAFFER, ROBERT R., SIEGEL, ROBERT P., SPEHRLEY, CHARLES W., JR.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1989
Main classification: G03B27
IPC codes: B65H5, G03G15, G03B27