Automatic restacking registration in a recirculating document handler

In a system of plurally recirculating a set of document sheets for precollated copying wherein the document sheets are repeatedly individually fed seriatim from the bottom of an overlying stack thereof for copying with registration and returned to the top of the stack for restacking in a tray having a support surface, a rear guide and two edge guides, an improvement is disclosed that includes a straight ramp attached to one of the edge guides so that document sheets returned to the support surface will lie flat against the edge guide and thereby provide a positive registration position along the junction between the ramp and the rear guide thereby reducing the possibility of mis-registration due to bending of the document sheets during feeding and recirculation.

BACKGROUND OF THE INVENTION 
The present invention relates to a document handling system and more 
particularly relates to an apparatus that automatically registers 
documents in a tray against a rear and a side registration surface of the 
tray. This apparatus is particularly suited for a recirculatory document 
(precollation copying) system in which documents are fed from the bottom 
of a stack. 
It has become desirable to provide for automatic and accurate feeding and 
registration of individual original document sheets being copied, in order 
to utilize the higher speed copying capabilities of new copiers. However, 
one of the most important, and difficult to achieve, requirements for 
automatic handling is the accurate and reliable, but safe, registration of 
the original document at the proper position for copying. Conventionally, 
the document is desirably automatically either center registered or corner 
registered (depending on the copier) by the document handler at a pre-set 
registration position relative to the copier platen, with two orthogonal 
edges of the document aligned with two registration lines of the copier 
platen, i.e. with the original document aligned with the copier optics and 
copy sheet registration system. This registration accuracy is desirably 
consistently within less than 1 millimeter. If the document is not 
properly registered, then undesirable dark borders and/or edge shadow 
images may appear on the ensueing copy, or information near an edge of the 
document may be lost, i.e. not copied onto the copy sheets. 
Document handling system in the past have been equipped with various 
document transports to move the original document sheets over the copier 
platen and into and out of registration. It is known in the art to 
register the original document for copying at the appropriate position 
relative to the transparent copying window in various ways. Typically, the 
document sheet is registered by driving it against a gate or stop at one 
edge of the platen. This may comprise projecting aligned fingers, or 
roller nips, or a single vertical surface, against which an edge of the 
sheet is driven into abutment. An important function of such registration 
is to also de-skew the moving original document, i.e., to properly align 
it with the registration lines as well as to determine and control its 
registration position. 
However, many such known recirculating document handlers drive a document 
onto the platen and register only the lead or trail edge of the document, 
without precisely side (laterally) registering the document. Any side 
registration of the document that occurs in such systems is performed 
prior to moving the document onto the platen, and is generally merely that 
provided by the edge side guides of the document tray, which must be set 
to accommodate the maximum lateral dimensions of the largest document 
systems, a system for also side registering or positioning the document 
after it is on the platen is used, i.e., positioning of the original on 
two axis with respect to the desired imaging position on the platen. 
The use of top restacking and bottom feeding document recirculation 
aggravates the above-discussed problem of accurate registration of the 
document being fed. For example, with bottom sheet feeders, since the 
stack height and weight is variable, the normal force on the bottom sheet, 
(pressing the stack against the bottom sheet and pressing the bottom sheet 
against the stack tray) is also variable. Further, even if a document 
sheet is laterally re-registered as it is being restacked, the agitation 
of the stack by the bottom feeder, particularly if an air sheet separation 
system is used, may disturb the initial alignment of the sheet as the 
sheet works its way down from the top of the stack to the bottom before it 
is fed out again. 
Because of variations in the sizes of documents of even the same standard 
size, it is often not possible to maintain lateral alignment by edge 
guides or even with edge joggers or tampers. Those sheets in the stack 
which are undersized can still vary in position by the difference in size 
between those smaller sheets and the larger sheets in the stack, since the 
edge guides and/or conventional side joggers are limited in setting by the 
widest sheets in the stack. Obviously, if edge guides were to be moved in, 
i.e., set for the smaller sheets, this would not allow flat stacking or 
settling or unobstructed feeding out of the larger sheets from between 
these edge guides. Thus, the side guides may have to be set apart by up to 
a several millimeters greater width than the width of the narrowest sheet 
in the stack, allowing a corresponding lateral misregistration of such 
narrower sheets. [As used herein, width or narrowness refers to the sheet 
dimension transverse its circulative feeding direction, regardless of 
whether the sheet is fed edgewise (long edge first) or lengthwise (short 
edge first). The former is more conventional]. 
Binding of the sheets between edge guides which are too close together, or 
even forcibly dragging the sheet against one edge guide, can cause wear or 
damage to the document edges, particularly for the multiple circulations 
used in precollation copying. Frictional rubbing of documents against only 
one edge guide, especially over the platen, can also cause skewing of the 
document as it is being fed. An edge guide on the platen itself has other 
disadvantages, e.g. potential "show around" printout of a line or shadow 
on the sides of the copy sheets, or loss of an edge image. Thus, platen 
edge guides are not generally used, or are withdrawn, in an automatic 
document feeder. Constant edge tampering or jogging is even worse, because 
it typically requires repeatedly forceably striking the edges of the 
stack, usually in only a small and constant area thereof, which can deform 
or otherwise damage these document edge areas, particularly over the 
extended time of repeated document recirculations. Older, and/or more 
brittle documents and extending oversize documents in a set are 
particularly vulnerable to this damage. In any case, as noted, such edge 
jogging cannot positively register all of the undersized documents in a 
set. 
In contrast, with the disclosed system herein, each bottom sheet in the 
stack is individually, and gently, aligned directly against a defined 
reference lateral edge guide regardless of variations in size of the 
sheets in the stack, i.e. for a wide range of sheet widths, and without 
any interference of feeding or larger sheets. The sheets are not aligned 
by hitting their edges. Rather, they are allowed to fall due to gravity 
against an inclined registration edge. By using a recirculating document 
handler (RDH) which minimizes document sheet skewing in the feeding system 
from the document set stack to the registration position on the platen no 
other lateral registration system is needed for the entire RDH system. 
Thus, there is no significant edge guide drag on the documents. 
Further details of an exemplary recirculating document handler with which 
the present invention may be utilized, including relevant teachings of 
such features as disclosed in FIG. 1 herein, are disclosed in U.S. Pat. 
No. 4,418,905 which is incorporated herein by reference to the extent 
necessary to practice the present invention. 
A preferred specific feature of the present invention is to provide a 
recirculating document handling apparatus that includes the combination of 
less rear corner restriction and straight ramp tray configuration that 
automatically registers documents against a rear registration surface, 
especially during restack, bends documents in only one direction during 
feeder acquisition, and feeds documents in a straight line. In 
combination, this system eliminates side registration over the platen and 
side stack jogging during restack of documents. 
Further features and advantages of the invention will be better understood 
by reference to the following description, and to the drawings forming a 
part thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring particularly to FIG. 1, there is illustrated an exemplary 
automatic sheet separator feeder incorporating the present invention for 
installation over the exposure platen 3 of a conventional xerographic 
reproduction machine. This is merely one example of a document handler 
with which the automatic registration system of the present invention may 
be combined. The document handler 1 is provided with a document tray 5 
adapted for supporting a stacked set of documents 7. A vacuum belt 
corrugating feeder mechanism 9 is located below the front or forward area 
of the document tray for acquiring and corrugating the bottom document 
sheet in the stack and for feeding out that document sheet to take-away 
roll pair 11 through document guides 13 to a feed-roll pair 15 and under 
platen roll 17 onto the platen of the copy machine for reproduction. A 
rectractable registration edge 18 is provided here to register the lead 
edge of the document fed onto the platen. Following exposure of the 
document, the edge 18 is retracted by suitable means such as a solenoid 
and the document is fed off the platen by roll 17 onto guide 19 and 
feed-roll pair 21 and returned back to the top of the document stack 7 
through a feed-roll pair 23. Restacking lateral realignment is provided by 
an edge guide 62 (see FIG. 2) spaced from an opposing fixed edge guide 64. 
Inclined surfaces 63 and 65 in conjunction with flat surface 67 help 
settle incoming (restacking) sheets between the two guides 62 and 64. A 
resettable edge guide could be provided adjacent side guide 64 if desired 
in order to adjust tray 60 to handle any size documents if desired. 
In the event it is desired to present the opposite side of a document for 
exposure, the document is fed from the stack 7 through guides 13 until the 
trail edge passes document diverter 24. Document diverter 24 is then 
rotated counterclockwise, i.e. into the document sheet path. The document 
direction is reversed and the document is diverted by diverter 24 through 
guides 26 and feed-roll pair 28 onto the platen 3. 
The document handler 1 is also provided with a sheet separator finger 35, 
as is well known in the art, to sense and indicate the documents to be fed 
versus those documents returned to the document handler, i.e. to count 
each set circulated. Upon removal (feed out) of the last document from 
beneath sheet separator finger 35, the finger 35 drops through a slot 
provided in the tray 5 to actuate a suitable sensor indicating that the 
last document in the set has been removed from the tray. The finger 35 is 
then automatically rotated in a clockwise direction or otherwise lifted to 
again come to rest on top of all the documents in the stack 7, for the 
start of the next circulation of document set 7. 
Referring more particularly to FIGS. 1, 2 and 3 and the document sheet 
separator-feeder 9, disclosed is a feed belt 37 supported for movement on 
feed belt rolls 39 and 40. Spaced within the run of the belt 37 there is 
provided a vacuum plenum 41 having openings 43 therein adapted for 
cooperation with perforations 45 in the belt 37 to provide a vacuum for 
pulling the bottom document in the document stack onto the belt 37. The 
plenum 41 is provided with a raised portion 49, beneath the center belt 37 
so that upon capture of the bottom document in the stack against belt 37, 
a center corrugation will be produced in the bottom sheet. This raised 
portion may project above the plane of the remainder of the belt by 
approximately 2 millimeters. Thus the document is corrugated into a double 
valley configuration parallel to the direction in which it is fed. The 
flat surfaces of the vacuum belt 37 on each side of the raised center of 
the belt generates a region of stress on the document which varies with 
the document beam strength. In the unlikely event that more than one 
document is pulled down into contact with the vacuum feed belt, the beam 
strength of the second (overlying) document resists this corrugating 
action. Thus, gaps are opened between the first and second sheets, which 
gaps extend to the sheet lead edges. These gaps or channels reduce the 
vacuum pressure levels between these sheets due to porosity in the first 
(bottom) sheet and provide for entry of the separating air flow from the 
air knife 12. Air knife 12 is preferably of the type employing a laterally 
converging stream as disclosed in U.S. Pat. No. 4,418,905 which has been 
incorporated herein by reference. 
In operation, the air knife injects air between the bottommost document 
pulled down against the feed belt and the documents in the stack 
thereabove to provide an air cushion or bearing between the stack and the 
bottom document to minimize the force needed for removing the bottom 
document from the stack. With the use of this air knife in conjunction 
with the above described bottom sheet corrugator, even if two documents 
are pulled down toward the belt 37, since the top sheet would not be 
corrugated, the air knife would inject air into the space between the two 
documents and force the second document off from the raised belt back 
toward the document stack. 
As can be seen by reference to FIG. 1, the stack tray is designed such that 
the lead edge of the documents in the stack are spaced a slight distance 
from the front edge of the tray. Further, the air knife is canted such 
that the air from knife 12 is discharged at an angle to the plane of the 
surface of the belt 37. With this disclosed interrelationship between the 
vacuum feed belt, the lead edge of the stack of documents, and the air 
knife location and angular orientation, the document feeder is capable of 
reliably separating and feeding individual document sheets even if the 
documents have some up-curl. 
By suitable valving and controls, it is also desirable to provide a delay 
between the time the vacuum is applied to pull the document onto the feed 
belts and the start up of the feed belts, to assure that the bottom 
document is captured on the belts before belt movement commences and to 
allow time for the air knife to separate the bottom sheet from any sheets 
that were pulled down with it. 
To further increase the efficiency of the system, the stack tray is 
provided with a rearward tilt as shown in FIG. 1. When flotation air is 
provided under the stack or between the first and second sheets, gravity 
will allow the sheets to settle or float back against rear tray wall 61. 
Thus, the sheet being removed is pulled uphill while gravity helps hold 
the remainder of the sheets back, helping to prevent multifeeds, and 
providing alignment or initial end registration of the stack 7 on one axis 
(in the feeding direction). 
In particular reference to FIG. 2, and in accordance with the present 
invention improvements for automatically edge registering documents in 
tray 60 is shown that insures non-skewed feeding of documents in the high 
performance recirculating document handler 1. The improvements among other 
things include straight ramps 63 and 65 attached to side wall or guide 62 
and raised support surface 68 respectively. The ramps are slightly 
inclined to an appropriate degree. Also, corner restrictions from a 
portion of end wall 61 are removed to allow free flow of air in a 
non-concentric manner which favors the rear corner of the tray. With these 
features in the tray, documents are aligned along the side of side guide 
62 by airflow from air knife 12 only, i.e., no additional lateral 
registration means is necessary. As shown in FIG. 5, straight ramp 63 and 
side guide 62 could be separate and individual members attached to each 
other by conventional means if desired. 
Airflow from the air knife 12 automatically moves the documents toward the 
registration corner 61, 62 for alignment. The straight ramp 63 as shown in 
FIG. 3 allows the document 7 to lie flat against side guide 62 and 
provides a positive registration position along the junction between the 
ramp and the rear guide or wall surface 61 thus reducing the possibility 
of misregistration due to bending of the documents if curved ramps were 
used. With curved rails, document registration varies depending upon the 
stiffness of the document. Additional airflow can be made available if 
required by removing material 69 from the rear portion of side guide 62 as 
shown. Raised support surface 68 together with slanted ramp 65 and lower 
support surface 67 serve to force documents into registration corner 
junction 61, 62 and against side guide 62 and slanted ramp 63, and thereby 
provide a further position influence on document lateral registration in a 
straight line along side guide 62. 
With the lateral and side registration system disclosed herein, no separate 
lateral registration means is required. That is, with a low skew document 
feeder, as disclosed herein, no lateral re-registration is required over 
the platen or anywhere else in the entire document recirculation system. 
As an alternative, a vacuum plenum and feed belt configuration shown as 42 
and 38 respectively in FIG. 4 could be employed as the vacuum belt 
corrugation feeder mechanism 9 if desired to provide corrugation in 
documents 7 as they are fed. Belt 38 and vacuum plenum 42 have holes 
therein that facilitate the attachment of documents to the belt. A 
centerline raised surface or ridge is positioned on belt 38 in order for 
corrugation of the documents to be accomplished. 
It should now be apparent that a recirculating document handler has been 
disclosed having an airflow assisted document restack tray which includes 
bottom, side and rear confining surfaces and wherein the bottom surface 
comprises a substantially horizontal surface spaced between two inclined 
surfaces at least one of which abuts a side surface to which the documents 
are to be registered and wherein the rear surface comprises a rear dam 
which defines an airflow exit path that enhances a corner registration of 
the documents. 
While the recirculative document sheet lateral edge registration and 
feeding system disclosed herein is preferred, it will be appreciated that 
various other alternatives, modifications, variations or improvements 
thereon may be made by those skilled in the art, and the following claims 
are intended to encompass all of those falling within the true spirit and 
scope of the invention.