Method and apparatus for printing near page boundaries

A machine uses electrophotography to produce panels of images for transfer to a continuous web of image receiving media. The images are transferred to the media under control of signals synchronized with media movement under a transfer structure which has a width sufficient to accommodate image transfer immediately prior to stopping of the media as well as immediately after restart of the media movement. The media is stopped with boundaries between sheets within the transfer zone.

FIELD OF THE INVENTION 
This invention relates to apparatus and method for transferring images from 
a continuously moving member to a web type media wherein the media web is 
periodically stopped and started or at least slowed and accelerated. This 
invention particularly relates to methods and means for reducing the 
unprinted zone necessary for accommodating stop and start operations 
associated with laser printers, which are fed with fanfold or continuous 
form copy sheets, separated by perforations at their boundaries. 
BACKGROUND OF THE INVENTION 
High speed electrophotographic printers such as the IBM 3800 Printer, 
employ a large photoconductive surfaced drum or belt to sequentially 
deliver image panels to a transfer station. The images frequently are 
electronically generated with a laser, LED array or the like selectively 
discharging the previously charged photoconductor. Where continuous form 
or fanfold paper with perforations defining the boundaries between sheets 
are employed, the movement of the images on the drum and paper requires 
coordination and synchronization since the image panels are not normally 
placed on the photoconductor with abutting boundaries. 
Thus, it is necessary to periodically stop the image receiving media and 
separate it from the photoconductor until the next image approaches. The 
media is then again accelerated and brought into contact with the 
photoconductor. In the past, this has meant that a substantial guard band 
of no printing is required on either side of the perforation, or else some 
means of backing the paper up and resynchronizing its position with the 
photoconductor is needed. 
Printers like the IBM 3800 printer typically skip about one inch of paper 
during a paperline stop-start. Disclosed is a method for reducing the 
unprinted zone necessary for a stop start function of the large printer 
paperline. This method uses a wide transfer zone to give a greater 
distance for stopping and starting the paperline. 
Leaving minimal unprinted area above and below a forms perforation ("print 
to perf") is a requirement for many high speed printer users, particularly 
in Europe. Machines like the IBM 3800 printer typically leave about one 
half inch above and below each perforation during a normal stop/start 
operation at the paperline. It is particularly advantageous if it is 
possible to reduce this distance to one sixth inch above and below the 
perforation boundary between sheets. The prior art approach to solving 
this problem is by using a backhitch sequence at the transfer station. 
Consider the contemporary machine which accommodates paperlines by 
requiring one half inch for paperline stop and one half inch for paperline 
start. Several things happen during a paperline stop. First the corona is 
turned off and the paper is pulled from the drum after which it is 
decelerated and stopped. Three tenths of an inch is required to let all 
print leave the transfer zone before the paper is pulled from the drum. 
Another two tenths inch is required for deceleration. Acceleration of the 
paperline takes three tenths of an inch. Another two tenths inch are 
allowed for settling of transients and lowering the paper onto the drum. 
Thus the half inch guard band on either side of the perforation boundary. 
One method of printing to the perf, using the above described start stop 
profiles, is backing the paper up after deceleration and stop. Backing the 
paper up is called "backhitching". In order to accomplish the one sixth 
inch print from the perforation, it is necessary to back the paper up 
seven tenths of an inch. This backing up must take place in less than 30 
milliseconds and requires design of all other parts associated with the 
paperline accommodation to let the paper back up. This capability of 
backing up before restarting also requires a more complicated servo system 
along with specially designed elements and, at best, is not a cheap 
alternative. 
U.S. Pat. No. 3,914,047 by Hunt et al describes a technique for determining 
the location of the perforation in a media and timing control over machine 
stations in accordance with the location of the paper perforations. This 
patent relates to an electrophotographic copier wherein fanfold paper is 
sent through the transfer station. It does not suggest any method or means 
of printing close to the perforation (or copying close to the 
perforation), nor is there any discussion of restarting the paper line 
after a jam. Hunt et al maintain interframe spacing to eliminate image 
overlap and provide a space for a splice in the media web member. 
U.S. Pat. No. 4,110,027 to Sato et al in FIG. 3 shows feeding of fanfold 
paper through a transfer zone between two rollers, which press the fanfold 
paper against the photoconductor before and after the transfer corona. The 
two rollers are movable from the position in contact with the 
photoconductive drum to a position separated from the drum, and in that 
manner, a fanfold paper is separated from the drum. That is, a mechanism 
separates the transfer paper from the drum at the transfer station and 
then restores the transfer paper into contact with the drum. The patent 
contains no teachings relative to printing close to the perforations in 
the fanfold paper. 
U.S. Pat. No. 4,423,951 to Rightmyre relates to a copy machine for copying 
information onto fanfold paper and, in particular, relates to a roller 
transfer corona which physically holds the fanfold paper against the 
photoconductor drum, purporting to thereby overcome the problem of image 
voids that exist when using conventional xerographic copying systems with 
folded copy paper. There is no mention of a method of starting and 
stopping the paper within the machine, and maintaining transfer close to 
the perforated edge. 
U.S. Pat. No. 4,541,710 by McLeish shows another fanfold copier in which 
the system includes a break associated with the supply of the fanfold 
material in order to keep a constant tension on the fanfold paper as it 
moves through the machine. There is no mention of a method of starting and 
stopping the machine, and printing close to the perforation. 
DISCLOSURE OF THE INVENTION 
The present invention is especially useful for xerographic or 
electrophotographic machines which have a member, usually in the form of a 
photoconductor surfaced drum or a belt, for transporting one or more 
transferable images. Where the machine uses a media of a continuous stream 
of panels separated at a boundary as by a perforation. The panels are 
intended to receive images from the transporting member at an image 
transferring station. Since the images are sequential but spaced on the 
transport member, the machine includes a device for moving the media in 
the form of machine controls which periodically stop and restart the media 
so that an inter-panel boundary is at least briefly positioned at a stop 
position in proximity to the transfer station. 
The present invention includes a method and means for permitting image 
transfer to the media with minimal separation relative to the panel 
boundaries. It includes image transferring at the transferring station by 
use of an image transfer effecting area facing the media surface. This 
image transferring area extends a predetermined distance from both the 
upstream and downstream sides of the panel boundary stop position in the 
direction of the media movement. Image information is transferred to a 
first media panel in proximity to the trailing boundary of that panel as 
this trailing boundary initially encounters the upstream image 
transferring area. Immediately thereafter, the media panel is stopped with 
the boundary at the aforementioned stopping position. 
Movement of the media is reinitiated as the next image panel on the 
transferable image transporting member approaches the transfer station so 
that the transporting member and the media reach a common velocity. This 
makes it possible to transfer the next panel image to the media in the 
downstream portion of the image transfer area as the leading boundary of 
the next media panel is in proximity to the downstream edge of the image 
transfer area. 
Preferably, the image transferring is caused by a corona which has a wide 
mouth that defines a charge producing face for the image transfer 
effecting area. This cooperates with the media shifting structure or 
process that is responsive to controls for moving the media away from the 
transferable image transporting member immediately after the last image 
transfer to the panel and for moving the media into engagement with the 
image transporting member when the member and the media have attained a 
common velocity. 
Generally, the image receiving media is a continuous web which is divided 
into sheets by severable perforations with both the media and the moving 
member passing through a transfer station in a common general upstream to 
downstream direction. Image transfer is through an elongated image 
transfer area, which faces the transfer station with the length of the 
transfer area in the upstream to downstream direction divided into four 
zones that are consecutively encountered by the media as it moves through 
the transfer station. Image information is transferred to the portion of 
the media facing the first zone as the trailing perforation of the sheet 
enters that first zone. 
Next the web media is separated from the image transporting member and 
stopped so that the sheet perforation is in proximity with the end of the 
second zone. As the next image on the transporting member approaches the 
transfer station, the media is accelerated to the same velocity as the 
member as the inter-sheet perforation passes through the third zone. The 
next image is transferred to the next media sheet in at least one of the 
four zones as the leading edge of the perforation passes through the 
fourth zone. Thus, the ion charge transferring area can reside in all of 
the zones or only in those zones in which image transfer will occur.. 
Accordingly, this invention involves establishing at the transfer station 
an image transferring area extending predetermined distances from the 
upstream and downstream sides of the panel boundary stop position in the 
direction of the media movement. Image information is transferred to a 
media panel in proximity to the trailing boundary of that panel as the 
trailing boundary initially encounters the upstream image transferring 
means area. The media panel is stopped with the boundary at the stopping 
position. After detecting that the next transferable image on the 
transporting member is approaching the transfer station, movement of the 
media is initiated so that the transporting member and the media reach a 
common velocity. Then transfer of the next panel image to the media is 
enabled as the leading boundary of the next media panel is in proximity to 
the downstream edge of the image transfer area in the downstream portion 
of the image transfer area. 
Thus, this invention involves the provision of a wide transfer zone through 
provision of a wide transfer corona, or more than one transfer corona. The 
method and apparatus described herein when applied to a machine such as an 
IBM 3800 printer, can reduce the one inch guard band distance around the 
perforations to one third inch. Using a wide transfer zone in conjunction 
with image transfer controls makes it possible to avoid backhitching and 
allows a simpler servo system and paperline control than was possible with 
the prior art systems. 
Those having normal skill in the art will recognize the foregoing and other 
objects, features, advantages and applications of the present invention 
from the following more detailed description of the preferred embodiments 
as illustrated in the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A high speed printer 10 using an electrophotographic process is shown in 
FIG. 1. A supply bin 11 holds a stack of fanfold media 12 intended to 
receive the images developed by printer 10. Preferably media 12 is a 
stream of paper formed as a series of sheets having inter-sheet boundaries 
formed by perforations. It is guided along a path including the transfer 
station around image transfer assembly 15 where it is motivated by a 
tractor drive 16. 
The image originates at an electronic module 18 such as by a laser and 
rotating mirror device. Module 18 might also include an arrangement for 
concurrently applying whole image panels to the photoconductor ("PC") on 
the peripheral surface of drum 20. Essentially the PC acts as an image 
transporting member for delivering the image to the transfer station 26. A 
series of conventional elements are arrayed around the periphery of drum 
20 including an erase lamp 21, preclean corona 22, cleaner brush 23, a 
charge corona 24 and a developer 25. As is well known, these elements 
cooperate to charge the PC, selective discharge it to form the image, and 
apply toner to the image to render it visible. The image defining toner is 
transferred to media 12 in the transfer station 26. 
Web 12 is maintained in tension by pivotable arm 27 and passes through 
fuser 28 where the toner is melted onto the paper. The web is ten 
delivered to an output module such as bin 29. Bin 29 can include a 
burster/trimmer/stacker or such a unit can form an alternate output 
receptacle. 
The images applied to the PC of drum 20 are not in an abutting 
relationship. That is, there is a variable space between image panels. 
However, the web 12 is formed of abutting sheets. Therefore it is 
necessary to periodically stop and restart the movement of web 12 through 
the transfer station. The machine controls of contemporary such printers 
accommodate this velocity profiling in a well known manner. 
In accordance with the present invention, a relatively wide transfer zone 
is employed in conjunction with synchronized control of image transfer 
thereby making it possible to print closer to the sheet perforation 
boundaries than ever before. For simplicity, assume the transfer zone is 
one inch in width. Paperline stop occurs as follows. 
As indicated by arrow 41 in FIG. 2, the last line of print enters the 
transfer zone 26 just far enough to accomplish transfer, one quarter inch. 
After the last line has entered one quarter inch into the zone, the paper 
is pulled away from the drum and decelerated to a stop with the last line 
in the center of the transfer zone as shown by arrow 42 in FIG. 3. When 
the next image on the drum 20 is six tenths of an inch from the last line 
transferred as reflected by arrow 43 in FIG. 4, paper acceleration is 
started. The paper is accelerated such that it takes three tenths of an 
inch to reach drum speed. The drum will have traveled twice as far as the 
paper leaving one third inch between the print which was transferred to 
the paper and the print which is yet to be transferred. The paper is now 
brought down onto the drum with the first line of untransferred print in 
the last one quarter inch of the transfer zone as indicated by arrow 44 in 
FIG. 5. 
Image transfer now takes place and printing continues until the next stop. 
With the one third inch distance between the print transferred before the 
stop and the print transferred after the stop, the one sixth inch print to 
perf is accomplished. This print to perf method requires no relative 
motion between the drum and paper as the paper is pulled away and lowered 
onto the drum. With the sequence described, adequate transfer takes place 
within the first and last quarter of the transfer zone. 
Accordingly, the invention relates to a method of providing a short 
distance between the last line printed and the next line printed when a 
continuous form printer, such as the IBM 3800, is brought to a stop. The 
method enables a printer to print close to the perforation of fanfold 
paper on both the trailing and leading edges. Contemporary machines are 
not allowed to print to within 1/2-inch above and below each perforation 
which is an unacceptably large nonprint area for many applications. With 
the current invention, it is possible to print to within 1/6" of the 
perforation on both the trailing and leading edge side. 
In a practical application of this invention, the width of the transfer 
zone at the face of fixed transfer corona 36 was 1 inch in width. When the 
last line of print enters the transfer zone by 1/4-inch, transfer occurs. 
As seen in FIG. 3, the guide housing 35 surrounding fixed transfer corona 
35 is pulled away from the drum thereby removing paper 12 from the drum 
surface. Web paper 12 is then decelerated to a stop with the last line 
then in the center of the transfer zone (FIG. 3). 
Upon approach of the next information contained on image drum 20 to a point 
6/10th of an inch from the last line on the transferred paper, 
acceleration of the paper is started. This acceleration takes 3/10th of an 
inch to reach drum speed and as a consequence, the last line is then 
2/10ths of an inch from the end of the transfer zone. During that period 
of time, the drum will have traveled twice as far as the paper leaving 
1/3-inch between the last line on the paper and the first line yet to be 
transferred. At this point, the first line is in the center of the 
transfer zone. 
The paper is next brought down onto the drum such that the next image line 
will have practically a full 1/2 of the transfer zone in which transfer 
can occur. In this manner, only 1/3 exits between the last line on one 
sheet and the first line on the second sheet with the perforation between 
the two sheets 1/6th of an inch from each line. 
The transfer corona 36 remains fixed relative to the machine frame as the 
paper web guide 35 is moved. Varying of the width of the opening of the 
grid is possible by using an apertured scorotron for corona 36. Effective 
transfer occurs soon after the character enters the transfer zone. 
However, transfer efficiency may improve with more time in the transfer 
zone. 
During or prior to deceleration separation of paper 12 from drum 20 must 
occur without appreciable slippage to avoid character stretch. 
Additionally, acceleration and transient die out must have occurred before 
the paper contacts the photoconductive surface of drum 20 to avoid 
character stretch. 
As another example of a procedure at transfer to stop and start paper 
without backhitch, assume transfer zone 26 is 20mm wide extending 10mm on 
either side of scorotron 36 center line, and there is an allowable 
non-profit zone on either side of the perforations on continuous forms 
paper is 4mm. Assume further a photoconductor/paper speed between 
810mm/sec and 32mm/sec and the drum 20 has a seal 1-inch wide (25.4mm) 
which, at closest, is 2.6mm from the perf. 
On decelerate/stop, the perforation just enters transfer zone with the last 
character in the transfer zone for 4mm, 4.9m sec. Power is removed from 
corona 36 and housing 35 begins moving the paper guides away from the drum 
(2.08mm, 2.5 ms. Decelerate to bring the perforation to the center of the 
transfer zone involves 7.92mm photoconductor movement, 3.96mm of paper 
movement, and 9.7m sec. 
If effective transfer occurs shortly after entry into the transfer zone, 
then it is possible to stop the paper and pull it away from the drum 
before the character passes outside the transfer zone. 
Acceleration is begun and guides 35 are moved toward drum 20 with 
acceleration and transient alternation complete before paper contact with 
the drum PC. This takes 7mm. and 8.6m sec. Power is reapplied to corona 
(scorotron) 36 and the first character has 7mm, 8.6m sec. in the transfer 
zone to achieve effective transfer. Powering corona 36 just before contact 
may help tack paper 12 to drum 20 and reduce sensitivity to transients. 
During deceleration and acceleration, the paper moves 7.92 mm while the 
drum moves approximately 15.84 mm in 19.5m sec. The total gap with 
(7.times.) 11 in. sheets is 1.207in. =30.65mm. 
FIG. 6 is a paper positioning mechanism using a solenoid 46 with its 
extendable shaft 47 attached to the paper guide housing 35 of assembly 15. 
Springs 48 and 49 urge housing 35 away from the PC surface of drum 20. 
Actuation of solenoid 46 forces paper 12 into engagement with the drum 20. 
Paper tension force is essentially supplied by means not shown such as a 
clutched roller, a vacuum column or other means. 
Positioning of housing 35 is likewise obtained by the FIG. 7 mechanism. A 
stepper motor 52 drives its shaft 51 which in turn drives an eccentric 53. 
Stepper motor 52 can respond to a predetermined motion profile. Leaf 
spring 54 follows eccentric 53 and is attached to linkage 55 as is leaf 
spring 56. Linkage 55 rotates about the mid-point of spring 56 to push the 
movable guide 35 toward drum 20. Linkage 57 is pulled which causes the 
paper tension spring carrier 59 to pivot towards the guide housing 35 thus 
compensating for the change in paper length due to the guides 35 movement. 
Curved shield 58 applies tension to paper 12. Springs 54 and 56 produce 
the return force to move the guides 35 away from drum 20 and cause the 
paper tension spring carrier 59 to pivot away from guides 35. 
While the exemplary preferred embodiments of the present invention are 
described herein with particularity, those having normal skill in the art 
will recognize various changes, modifications, additions and applications 
other than those specifically mentioned herein without departing from the 
spirit of this invention.