Document handler vacuum belt platen transport clamping system

A document handler 20 for presenting documents to the platen 23 of a copier 10 for copying with a vacuum belt platen transport system 32 having document transporting belts 35 movable under a substantially planar vacuum plenum backing and imaging background surface 33a overlying the platen, and a vacuum system 33 for applying a partial vacuum to a document sheet being transported by the movable belts over the platen; with a clamping and unclamping system for moving the vacuum plenum backing and imaging background surface 33a against the platen 23 to flatten the belts 35 and a document thereon against the platen for copying. During unclamping the surface 33a slightly fits away from the platen, while supplying the partial vacuum to lift a document away from the platen retained on the belts, by first lifting a first side 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 for assisting in retaining the documents to the belts, and moving the belts when the surface is lifted away from the platen. During clamping the first side of the surface 33a moves towards the platen beginning slightly before the opposite side to generate a controlled air flow expulsion of air.

Hereby cross-referenced, and incorporated by reference, is the copending 
application of the same assignee, U.S. Serial No. 029,027, now U.S. Pat. 
No. 4,794,42, entitled "Automatic Dual Mode Sheet and Web Document 
Transport For Copiers" Filed Mar. 23, 1987 by the same Thomas Acquaviva 
(sole) (Attorney Docket No.D/86036). 
The present invention relates to copier document handling, and, more 
particularly, to the improved transporting and positioning of documents 
for copying over the platen of a copier with a vacuum belt document 
transport system for an automatic document handling system. In particular 
there is disclosed herein an improved system for rapidly clamping 
documents from a vacuum transporting position to an imaging position 
(flattened against the platen) and unclamping the documents into a vacuum 
transporting position, which overcomes difficulties caused by the vacuum 
system and maintains control of the documents. There is also disclosed 
here an improved vacuum belt document transport system, with an improved 
manifolding system of applying vacuum document retention in a multibelt 
over-platen vacuum 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 compatibly combine with 
maintaining positional control over the document, especially when rapidly 
replacing the document with another document to be copied. 
The vacuum belt document transport system disclosed herein represents an 
improvement over the multibelt over-platen vacuum document transport and 
manifolding system of applying vacuum for document retention thereto of 
Xerox Corporation U.S. Pat. No. 4,618,138 issued Oct. 21, 1986 to Morton 
Silverberg. Also particularly noted thereon is Xerox Corporation U.S. Pat. 
No. 4,294,540 issued Oct. 13, 1981 to R. R. Thettu, although that is a 
single belt system. Other vacuum aperture/groove patterns in a document 
transport are disclosed in U.S. Pat. No. 4,544,265 issued Oct. 1, 1985 to 
E. A. Powers, and Eastman Kodak U.S. Pat. No. 4,412,738 issued Nov. 1, 
1983 to D. K. Ahern, et al. 
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 systems 
disclosed in prior patents, of which Xerox Corporation U.S. Pat. No. 
4,462,527 issued July 31, 1984 to T. N. Taylor et al 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 vacuum 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 Xerox Corporation 
U.S. Pat. No. 3,888,585 issued June 10, 1975 to T. R. Cross [see esp. 
FIGS. 6 & 7, and Col. 7, line 39 through Col. 8, line 21];U.S. Pat. 
No.4,335,954 issued June 22, 1982 to R. L. Phelps [see esp. FIG. 11 & 
Cols. 9-10]; U.S. Pat. No. 3,944,366 issued Mar. 16, 1976 to D. A. 
Robertson; and U.S. Pat. No. 3,623,806 issued J. M. Short. 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. 
The above U.S. Pat. No. 4,335,954 patent to R. L. Phelps is also of 
interest as noting at the top of Col. 10 the problem of the vacuum created 
when the clamp rises. This is addressed there by slots or grooves 190 in 
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-lifted unclamping. (The opposite of the present system.) 
Also noted is an assumed Japanese publication "Koukai Gihoh" No. 87-1432 
reportedly published by Fuji Xerox Corp. (their No. FX 19058) on Feb. 20, 
1987 in Japan. It discloses a solinoid lifted pressure plate pressing on 
the inside of a single unapertured document feeding belt over a platen 
when the belt is stopped. Noted as well is Fuji Xerox Corp. No. FX 16616 
Japanese application No. P 60-161752 by K. Yamazaki which was reportedly 
filed on July 24, 1985 and laid open on Feb. 5, 1987 as Laid Open No. 
62-27256. It 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 vacuum system, or non-uniform lifting or clamping. 
U.S. Pat. No. 4,592,652 issued June 3, 1986 to K. Henmi, et al, is noted 
for a movable copier platen clamp, noting especially FIG. 7 which 
discloses a vacuum and eccentric lifting cams. However, no document 
transport is provided. 
Other background references from other clamp applications include U.S. Pat. 
Nos. 4,029,404; 4,040,615; and 4,544,265. 
In the document clamping system disclosed here, in contrast, an entire 
vacuum manifold unit is movably mounted above, and carrying, a set of 
vacuum belts and also pushes them down to clamp a document. The disclosed 
system relates to clamping and unclamping a vacuum belt transport system. 
It teaches automatic clamping and unclamping of an entire vacuum 
manifold/belt unit for each document being fed by the platen transport. 
The disclosed system maintains the document on a vacuum transport and 
lifts it away from the platen during unclamping to do so. It has been 
known in the copier art for many years that a rapid opening of even a 
simple platen cover can lift a document off of the platen, but this has 
been considered undesirable, and likely to lose control of it, and the 
normal solution has been to try to keep the document down on the platen, 
as noted above, not lifted with the platen cover. 
Transporting documents over the platen spaced above the platen glass, 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. 
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, accurately 
register, 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. 
The art of original document sheet handling for copiers has been 
intensively pursued 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 alternatively allow 
the copier operator to conventionally manually place documents, including 
books, on the same copying 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 the edge of the document, 
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 automatically or semiautomatically rapidly feed, 
register and copy 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 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 single or plural transport belts or feed wheels, 
utilizing frictional and/or vacuum 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 of the platen before and after 
copying as well as registering the document. 
The cited art shows several approaches 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 proceeding 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 to also deskew the document, i.e., to properly 
rotate and align it 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 desirably be done without mechanical document 
stops on the platen, as disclosed for example in U.S. Pat. Nos. 4,043,665 
issued Aug. 23, 1977 to J. R. Caldwell; 4,132,401 issued Jan. 2, 1979 to 
J. F. Gauranski, et al; or 4,295,737 or 4,391,505 issued Oct. 20, 1981 and 
July 5, 1983 to Morton Silverberg,. 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 steppermotor 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 an RDH, is taught in U.S. Pat. No. 4,579,444 
issued Apr. 1, 1986 to T. S. Pinckney and H. J. Sanchez (D/84074), and 
references cited therein. 
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. U.S. Pat. No. 
4,411,418 or 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. U.S. Pat. Nos. 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, plastic, 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 
a recirculating document handling system or "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 Xerox Corporation RDH are U.S. Pat. Nos. 4,459,013 issued 
July 10, 1984 to T. J. Hamlin et al; 4,278,344 issued July 14, 1981 to R. 
B. Sahay; and 4,579,444, 325 or 326. Some other examples of recirculating 
document handlers are disclosed in U.S. Pat. Nos. 4,076,408; 4,176,945; 
4,428,667; 4,330,197; 4,466,733 and 4,544,148. A preferred vacuum 
corrugating feeder air knife, and a tray, for an RDH, are disclosed in 
U.S. Pat. Nos. 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 U.S. Pat. No. 
4,462,527. Various others of these patents, such as U.S. Pat. No. 
4,176,945 above, issued Dec. 4, 1979 to R. Holzhauser (Kodak) 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. 
A feature of the specific embodiment disclosed herein is to provide, a 
document handler for presenting documents to the platen of a copier for 
copying, comprising a vacuum belt platen transport system for feeding the 
documents over the platen and into an imaging position over the platen, 
wherein said vacuum belt platen transport system comprises plural document 
transporting belts movable under a substantially planar vacuum plenum 
backing and imaging background surface overlying said platen, and vacuum 
means for applying a partial vacuum to a document sheet being transported 
by said movable belts over said platen, and means for moving said belts, 
the improvement comprising clamping means for moving said vacuum plenum 
backing and imaging background surface against said platen to flatten said 
belts and a document thereon against said platen for copying said 
document, said clamping means including unclamping means for lifting said 
vacuum plenum backing and imaging background surface slightly away from 
said platen while supplying said partial vacuum with said vacuum means to 
lift a document away from said platen retained on said belts, for 
transporting a document with said belts, said unclamping means including 
means for lifting a first side of said vacuum plenum backing and imaging 
surface up away from said platen substantially before the opposite side 
thereof, and then subsequently lifting said opposite side, to generate a 
controlled air flow for assisting in retaining the document to said belts 
as said vacuum plenum backing and imaging surface is lifted away from said 
platen, said means for moving said belts being operable when said vacuum 
plenum backing and imaging surface is lifted away from said platen and 
while supplying said partial vacuum with said vacuum means to retain a 
document against said belts. 
Further features provided by the system disclosed herein, individually or 
in combination, include those wherein said clamping and unclamping means 
comprises plural cams with different cam rise times connected via cam 
lifters to lift said first side of said vacuum plenum backing and imaging 
surface with a different motion than said opposite side by said cams being 
rotatably driven for clamping and unclamping; wherein said clamping means 
moves down said first side of said vacuum plenum backing and imaging 
surface towards said platen beginning slightly before moving down said 
opposite side of said vacuum plenum backing and imaging surface towards 
said platen, to generate a controlled air flow expulsion of air out from 
under said vacuum plenum backing and imaging surface during clamping; 
wherein said clamping means moves down said first side of said vacuum 
plenum backing and imaging surface towards said platen beginning 
approximately 5 milliseconds before moving down said opposite side, with 
further rotation of said same cams, but beginning said movement of said 
first side before said opposite side with different said cam rise times 
configurations of said cams, to generate a controlled air flow expulsion 
of air out from under said vacuum plenum backing and imaging surface 
during clamping; wherein said unclamping means, with said rotation of said 
cams, first lifts said first side of said vacuum plenum backing and 
imaging surface about 2.5 mm away from said platen while said opposite 
side remains down in contact with the platen, and then lifts said opposite 
side about 0.8 mm, and then said vacuum plenum backing and imaging surface 
is leveled by lifting said opposite side from said about 0.8 mm to about 
1.75 mm, and, at approximately the same time, said first side is dropped 
from said about 2.5 mm to about 1.75 mm; wherein clamping and unclamping 
is accomplished by common rotation of said cams with different cam 
profiles providing said different cam rise times, and wherein after said 
unclamping is at least partially completed a document previously copied is 
ejected by said platen transport system and a next document is brought 
over the platen by said platen transport system, while maintaining said 
vacuum retention of the documents, and then before the copying of this 
next document it is clamped against the platen by moving down both said 
first side and said opposite side of said vacuum plenum backing and 
imaging surface with further rotation of the same cams but beginning the 
movement of said first side a fraction of a second before the movement of 
said opposite side to move said surface down at an angle towards said 
platen which squeeges out air from under the document before the final 
clamping, in which both said first and said opposite sides are flattened 
against said platen; and wherein additional vacuum retention means 
connecting with said vacuum means are provided along said first edge of 
said vacuum plenum backing and imaging surface to provide a substantially 
higher partial vacuum holding force to the edge area of a document 
overlying said first edge for resisting stripping of the document from 
said vacuum belt platen transport during said unclamping lifting movement. 
Further disclosed features include a copying method utilizing a document 
handler for presenting documents to the platen of a copier for copying, 
comprising a vacuum belt platen transport system for feeding the documents 
over the platen and into an imaging position over the platen, wherein said 
vacuum belt platen transport system comprises plural document transporting 
belts movable under a substantially planar vacuum plenum backing and 
imaging background surface overlying said platen, and vacuum means for 
applying a partial vacuum to a document sheet being transported by said 
movable belts over the platen, and means for moving said belts, comprising 
the steps of: 
clamping said vacuum plenum backing and imaging background surface against 
the platen to flatten said belts and a document thereon against the platen 
for copying said document by unevenly moving said vacuum plenum backing 
and imaging background surface and said belts down towards said platen, 
unclamping said vacuum plenum backing and imaging background surface and 
said belts and a document thereon from said platen by unevenly lifting 
said surface away from said platen while supplying a partial vacuum with 
said vacuum means to lift a document away from said platen retained on 
said belts, 
said unclamping including lifting a first side of said vacuum plenum 
backing and imaging surface up away from said platen substantially before 
the opposite side thereof, and then subsequently lifting said opposite 
side, to generate a controlled air flow for assisting in retaining the 
document to said belts as said vacuum plenum backing and imaging surface 
is lifted away from said platen, 
and transporting a document with movement of said belts and with said 
partial vacuum retaining a document against said belts after said 
unclamping is at least partially completed. 
Additional features, individually or in combination include those wherein 
said clamping moves down said first side of said vacuum plenum backing and 
imaging surface towards said platen beginning slightly before moving down 
said opposite side of said vacuum plenum backing and imaging surface 
towards said platen, to generate a controlled air flow expulsion of air 
out from under said vacuum plenum backing and imaging surface during 
clamping; wherein said unclamping first lifts said first side of said 
vacuum plenum backing and imaging surface about 2.5 mm away from said 
platen while said opposite side remains down in contact with said platen, 
and then lifts said opposite side about 0.8 mm, and then said vacuum 
plenum backing and imaging surface is leveled by lifting said opposite 
side from said about 0.8 mm to about 1.75 mm, and, at approximately the 
same time, said first side is dropped from said about 2.5 mm to about 1.75 
mm; wherein said clamping and unclamping is accomplished by rotation of 
cams with different cam profiles, and wherein after said unclamping is at 
least partially completed a document previously copied is ejected by said 
platen transport system and a next document is brought over the platen by 
said platen transport system, while maintaining said vacuum retention of 
the documents, and then before the copying of this next document it is 
clamped against the platen by moving down both said first side and said 
opposite side of said vacuum plenum backing and imaging surface with 
further rotation of the same cams but beginning the movement of said first 
side slightly before said opposite side to move said surface down at an 
angle towards said platen which squeegees out air from under the document 
before the final clamping, in which both said first and said opposite 
sides are flattened against said platen. 
Some examples of various other prior art copiers with document handlers, 
and especially with control systems therefor, including document sheet 
detecting switches, etc., are disclosed in U.S. Pat. Nos.: 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 descriptions 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. 
All references cited in this specification, and their references, are 
incorporated by reference herein where appropriate for appropriate 
teachings of additional or alternative details, features, and/or technical 
background.

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 DH 20 
illustrated here is similar to that shown in the above cross-referenced 
U.S. Ser. No. 029,027, or the generally comparable disclosures in U.S. 
Ser. No. 029,026, both filed Mar. 23, 1987. 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 previously known to 
have two separate document inputs, 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 vacuum belt platen transport system 
32 overlying the platen 23. Documents are inputted to one end of the 
platen transport 32 either from the RDH input provided by the restacking 
tray 21 on top of the unit, spaced above the platen, or from the separate 
document input 22 directly adjacent one side of the platen, shown at the 
right side here. 
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 drawing 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 U.S. Pat. No. 4,278,344 and others. The exemplary 
copier 10 may conventionally 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 in a known manner to provide duplex or simplex precollated or 
postcollated copy sets from either duplex or simplex original documents 
copied from the RHD 20. 
The control of all sheet feeding is, conventionally, by the machine 
controller 100. The controller 100 is preferably a known programmable 
microprocessor, exemplified by the previously cited art. 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 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 of the various configurations and operating 
mechanisms illustrated in various of the above-noted prior art references 
on registration gate systems. 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 in 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 U.S. Pat. No. 4,579,444, 
these provide side edge registration towards a rear edge guide at this 
input, 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 28 
into the input to the platen transport system 32. 
The platen transport system 32 here comprises a vacuum 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 
U.S. Pat. No. 4,618,138. The platen transport system 32 and the rollers 28 
may be incrementally servo motor driven by the controller 100 in a manner 
taught by various of the above-cited references. 
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 output including 
output rollers 38. If the decision gate 36 is down, as for RDH, and for 
job recovery here, 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 here also includes a variable position rear 
registration edge or backstop, illustrated here with several dashed lines, 
for initially accommodating and restacking various sizes of documents. The 
illustrated DH system 20 utilizes for its RDH feeding a known combined 
corrugated vacuum feeding and air knife separator system for feeding out 
sequentially the bottom-most sheet of the stack in the tray 21, as 
described in various of the above-cited references. 
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 platen vacuum 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 off" from one feeding nip to 
another along the document path with very restricted slippage to ensure 
positive and registered feeding. 
In the system illustrated here, 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 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 exemplary system disclosed herein, there is 
disclosed an improved platen transport system for copier, with features as 
previously described above in the introduction. The clamping and 
unclamping system disclosed here overcomes 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 platen exchange times. 
That is especially critical and difficult with vacuum 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 vacuum platen transport 32, and 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 
sheet is controlled. As this first edge lifts, inrushing air assists in 
lifting the rest of the sheet. Here, as the clamp closes, the clamping 
pushes 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, most of the above references teach 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 vacuum or a belt system. 
The moving clamp system here includes the external integral bottom surface 
33a of an entire moving vacuum manifold 33 above a set of belts 35, which 
surface 33a pushes the belts 35 down against the document for clamping. 
l.e. the entire vacuum 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 here because the clamp is lifting against the vacuum 
forces formed between the sheet and the platen glass. This vacuum 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 54, and apertured 53 into the manifold or plenum 33 interior, for 
vacuum application 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 further described in the above-cited U.S. 
Pat. No. 4,618,138 issued Oct. 21, 1986 to M. Silverberg. The clamping 
surface 33a also preferably has a preset, preformed, concave "bow", to 
assist or insure 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 the outer edges of surface 33a, to 
insure that this surface 33a presses flat against the platen. That is 
assisted by the illustrated 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 insure maximum document flattening at the document edges, where 
it is most optically sensitive. This "bow" or "belly" centerline is 
preferably approximately alligned with the centerline of the lens system 
where document spacing and distortion is 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 vacuum 
holddown forces. 
As shown in FIGS. 2 and 5, the unit 32 is lifted up against the spring 
force by lifting 4 cam followers 64 by rotation of 2 pairs of cams 60, 60a 
and 62, 62a, on two fixed camshafts 66, 67, which are servo driven, to 
provide the following unique movements to overcome the vacuum/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 redge 
edge) up by about 0.03 inch (0.8 mm). Then the belts 35 drive may be 
started, and the rear edge is dropped down by the rear cams from said 2.5 
mm to about 1.75 mm while raising the front edge from said 0.8 mm to said 
1.75 mm to level it. Note the document sheet feeding may be started during 
this special small but irregular 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 velocity 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 exemplary cams here. 
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. l.e., the cam rise and fall is very different for the front cams vs. 
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 vacuum grooves 58 and vacuum apertures 
59 along the rear registration edge of the surface 33a. Note particularly 
FIG. 6. These additional apertures 59 and grooves 58 increase the vacuum 
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 8 times 
deeper, so as to apply a much higher vacuum 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 vacuum 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 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 vacuum 
chamber is provided between the rear edge of the rearmost belt 35 and this 
rib 72, forming a substantially higher intensity vacuum under the outer 
edge of the document sheet. Note that the outer edge of the document is 
always overlying this high vacuum 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 here but may be provided by 
pre-registering 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, as described in the above cited patents. 
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 plural additional vacuum 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 33. 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 vacuum force 
as described above, is lifted first. The additional vacuum grooves 58 and 
vacuum apertures 59 along the registration edge vacuum 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 vacuum 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 squeegeeing 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 velocity 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 squeegeeing 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 
undersired 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 vacuum 
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 vacuum 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 squeegees out air from under the document before the final 
clamping in which both edges are against the platen. 
To summarize the exemplary 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 axies in normal 
operation (ie, unless the entire DH 20 is lifted up from the platen). The 
four conventional cam followers 64 are each positioned directly above the 
4 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 vacuum 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 4 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. 
Here, in a document feeder 20 for transporting document sheets over the 
platen of a copier with a vacuum belt platen transport system 32 with 
means for stopping the document sheet at an imaging position on the 
platen, the vacuum belt platen transport system 32 comprises plural white 
opaque belts 35 moving under a white vacuum plenum backing surface 
overlying the platen, and includes a conventional vacuum source for 
applying a partial vacuum to a document sheet being transported by the 
moving belts. The belts 35 are preferably thin, low-frictional, 
non-elastomeric, plastic belts as in said U.S. Pat. No. 4,618,138, but not 
translucent or transparent, because the belts 35 are optically masking 
vacuum holes 53 and 59 here. (Said U.S. Pat. No. 4,618,138 also disclosed 
white belts in Col. 9 lines 59-60.) The belts 35 are unapertured and the 
exposed area of the vacuum plenum clamping and backing surface 33a is 
unapertured in the imaging position, so that the vacuum belt 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 "sees" dark areas on the document 
transport through the document, particularly through a transparent or very 
thin or otherwise 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 of) one or 
more edges of the original. Both of these types of copy defects are 
particularly likely with vacuum platen transports and plural belt platen 
transports, because the belt edges and vacuum 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. 
Vacuum belt transports desirably provide a combination of non-critical 
frictional feeding by the belt(s) assisted by a partial vacuum applied 
through apertures in the belt or between the belts to retain or pull the 
document or portions thereof against the belt(s), as taught in the cited 
art. However, vacuum belt transports have introduced serious additional 
problems of "show-around" and "show-through" copy defects. Undesirable 
dark background markings on the copy sheets can occur from images of light 
absorbed in the vacuum apertures in or for the belt(s) or in the 
underlying vacuum manifold or plenum surface for the belt(s). 
The platen transport system 32 here includes a vacuum plenum or manifold 33 
having a novel 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, 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 commercially available polyester material. They are 
preferably much less than 1/2 mm thick, and a thickness of only 
approximately 0.2 mm has been found to be operative and desirable, as 
disclosed in the cited U.S. Pat. No. 4,618,138. 
The lower or outer (document transporting) surface of the belts should be 
sufficiently smooth so 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 for vaccum migration across the belt. 
Vacuum is applied to the document in the transport system 32 via the 
surface 33a in the gaps 35a between the belts. This vacuum holds a 
document sheet against the belts 35 with sufficient force that the low 
friction engagement of the moving belts 35 against such a vacuum-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 reliably transport the document 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 eject 
the document from the platen after it has been registered and copied. The 
applied vacuum 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 vacuum 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 axially deformable 
coil springs 70 or the like may be provided at the four corners of the 
upper surface of the vacuum 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 therefor maintains lateral registration 
of the transport and registration system. It allows the imaging surface of 
the platen transport and the belts thereon to closely conform to the plane 
of the upper surface of the platen during clamping. 
The bottom wall 33a of the vacuum plenum 33, providing the imaging surface, 
is formed with sufficient stiffness so 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 vacuum 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 vacuum system for the platen transport system 32, the 
vacuum source may be provided by a conventional but low pressure fan or 
blower. Preferably the vacuum source is pneumatically connected to one 
side (here the rear) of the manifold 33, as shown in FIG. 2. A very low 
level of partial vacuum may be applied, e.g. in the order of 20.+-.5 mm 
(approximately 1 inch) of water static vacuum in the manifold 33 plenum. 
To operatively communicate this vacuum 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 vacuum apertures 53 in the manifold surface 
33a. These vacuum apertures 53 here are located in opposite ends of a 
large number of small vacuum 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 vacuum channels 54. Thus, only 
a relatively small area of the belts 35 are subjected to any vacuum forces 
here, 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 vacuum 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 vacuum level along each channel under the area of the document 
between the belts 35. Different vacuum 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 partial 
vacuum from its 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 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. 
While the embodiment disclosed herein is preferred, it will be appreciated 
from this teaching that various alternatives, modifications, variations or 
improvments therein may be made by those skilled in the art, which are 
intended to be encompassed by the following claims: