U.S. patent application number 13/943897 was filed with the patent office on 2015-01-22 for re-time sheet buffering system for digital print finishers.
The applicant listed for this patent is Xerox Corporation. Invention is credited to Joseph J. Ferrara, Joseph M. Ferrara.
Application Number | 20150021843 13/943897 |
Document ID | / |
Family ID | 52301623 |
Filed Date | 2015-01-22 |
United States Patent
Application |
20150021843 |
Kind Code |
A1 |
Ferrara; Joseph M. ; et
al. |
January 22, 2015 |
RE-TIME SHEET BUFFERING SYSTEM FOR DIGITAL PRINT FINISHERS
Abstract
A re-time sheet buffering system is used in connection with a
finisher for a digital printing system and a plurality of media
sheets arranged in sets. A path loop between a sheet path entrance
and exit provides space for buffering. A registration nip
decelerates, registers and accelerates sheets 1 through N. A first
retime nip holds sheets 1 and 2 of the set at registration speed
for a longer time than remaining sheets, to gain time for
finishing, and then accelerates sheets 1 and 2. A second retime nip
accelerates sheets 1 and 2 of the set to compiling speed. Sheets
are transported, compiled, stapled, and ejected.
Inventors: |
Ferrara; Joseph M.;
(Webster, NY) ; Ferrara; Joseph J.; (Webster,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Xerox Corporation |
Norwalk |
CT |
US |
|
|
Family ID: |
52301623 |
Appl. No.: |
13/943897 |
Filed: |
July 17, 2013 |
Current U.S.
Class: |
270/1.01 |
Current CPC
Class: |
B65H 9/002 20130101;
B65H 2511/20 20130101; B65H 31/02 20130101; B65H 2701/1311
20130101; B65H 2553/822 20130101; B65H 29/125 20130101; B65H
2513/108 20130101; B65H 2513/108 20130101; B65H 2301/4452 20130101;
B65H 29/242 20130101; B65H 2555/26 20130101; B65H 29/68 20130101;
B65H 2301/4212 20130101; B65H 2301/4213 20130101; B65H 39/10
20130101; B65H 7/08 20130101; B65H 2220/01 20130101; B65H 2220/01
20130101; B65H 2220/02 20130101; B65H 29/6618 20130101; B65H
2301/3122 20130101; B65H 2301/44734 20130101; B65H 2511/20
20130101; B65H 2801/27 20130101; B65H 29/32 20130101; B65H 2406/323
20130101; B65H 2301/44734 20130101 |
Class at
Publication: |
270/1.01 |
International
Class: |
B65H 39/00 20060101
B65H039/00 |
Claims
1. A re-time sheet buffering system for use in connection with a
finisher for a digital printing system and a plurality of media
sheets arranged in sets, each set including sheets 1, 2, 3 through
N, the re-time sheet buffer comprising: a sheet path, having a
sheet path entrance to input the sheets at an input speed, a sheet
path exit to output the sheets, and a path loop between the sheet
path entrance and sheet path exit so as to provide space for
buffering; a compiler area between the path loop and the sheet path
exit; a compiler for compiling sheet sets at a compiler speed in
the compiler area; a registration nip disposed on the sheet path
for decelerating sheets 1 through N from the input speed to a
registration speed, for registration, and for accelerating selected
sheets; a first retime nip disposed on the sheet path downstream of
the registration nip for holding sheets 1 and 2 of the set at a
predetermined speed after registration, and for accelerating sheets
1 and 2 of the set; a second retime nip disposed on the sheet path
downstream of the first retime nip and before the compiler area,
for accelerating sheets 1 and 2 of the set to compiling speed; and
a plurality of sensors arrayed on the sheet path for sensing the
position and speed of the sheets; wherein sheets 1 and 2 of the set
are held at the predetermined speed for a longer time than
remaining sheets, so as to gain time for finishing.
2. The re-time sheet buffering system of claim 1, wherein: the
first retime nip further comprises an inboard nip having an idler
roller and a driven roller, an outboard nip having an idler roller
and a driven roller, a first drive shaft connecting the inboard and
outboard driven rollers, and a first stepper motor operatively
connected to the first drive shaft; the second retime nip further
comprises an inboard nip having an idler roller and a driven
roller, an outboard nip having an idler roller and a driven roller,
a second drive shaft connecting the inboard and outboard driven
rollers, and a second stepper motor operatively connected to the
second drive shaft; and the registration nip further comprises an
inboard nip having an idler roller and a driven roller, an outboard
nip having an idler roller and a driven roller, an inboard stepper
motor operatively connected to the inboard driven roller, an
outboard stepper motor operatively connected to the outboard driven
roller, the inboard and outboard driven rollers being collinear,
the inboard driven roller being unconnected to the outboard driven
roller.
3. The re-time sheet buffering system of claim 1, wherein: the
registration nip accelerates sheets 3 through N of the set to
compiling speed after registration; and the first and second retime
nips accelerate sheets 1 and 2 of the set to compiling speed after
registration; wherein sheets 1 and 2 of the set are held at
registration speed for a longer time than sheets 3 through N of the
set, so as to gain time for finishing.
4. The re-time sheet buffering system of claim 1, wherein: the
registration nip accelerates sheets 4 through N of the set to
compiling speed after registration; the first retime nip holds
sheets 1, 2, and 3 of the set at registration speed and accelerates
sheets 1, 2, and 3 of the set; and the second retime nip
accelerates sheets 1, 2, and 3 of the set to compiling speed;
wherein sheets 1, 2, and 3 of the set are held at registration
speed for a longer time than sheets 4 through N of the set, so as
to gain time for finishing.
5. The re-time sheet buffering system of claim 1, further
comprising: the input speed being approximately 1090 mm/s; the
registration speed being approximately 650 mm/s; the compiler speed
being approximately 1380 mm/s; and the predetermined speed being
between the registration speed and the compiler speed.
6. The re-time sheet buffering system of claim 1, further
comprising: a vacuum gripper transport adjacent the compiler area;
and a stapler between the compiler area and the sheet path exit for
stapling compiled sheet sets.
7. A re-time sheet buffering system for use in connection with a
finisher for a digital printing system and a plurality of media
sheets arranged in sets, each set including sheets 1, 2, 3 through
N, the re-time sheet buffer comprising: a sheet path, having a
sheet path entrance to input the sheets at an input speed, a sheet
path exit to output the sheets, and a path loop between the sheet
path entrance and sheet path exit so as to provide space for
buffering; a compiler area between the path loop and the sheet path
exit; a compiler for compiling sheet sets at a compiler speed in
the compiler area; a transport apparatus adjacent the compiler
area; a stapler between the compiler area and the sheet path exit
for stapling compiled sheet sets; a plurality of transport nips
arrayed along the path loop; a registration nip disposed on the
sheet path for decelerating sheets 1 through N from the input speed
to a registration speed, for registration, and for accelerating
selected sheets; a first retime nip disposed on the sheet path
downstream of the registration nip for holding sheets 1 and 2 of
the set at a predetermined speed after registration, after
registration and for accelerating sheets 1 and 2 of the set; a
second retime nip disposed on the sheet path downstream of the
first retime nip and before the compiler area, for accelerating
sheets 1 and 2 of the set to compiling speed; and a plurality of
sensors arrayed on the sheet path for sensing the position and
speed of the sheets; wherein sheets 1 and 2 of the set are held at
the predetermined speed for a longer time than remaining sheets, so
as to gain time for finishing.
8. The re-time sheet buffering system of claim 7, wherein: the
first retime nip further comprises an inboard nip having an idler
roller and a driven roller, an outboard nip having an idler roller
and a driven roller, a first drive shaft connecting the inboard and
outboard driven rollers, and a first stepper motor operatively
connected to the first drive shaft; the second retime nip further
comprises an inboard nip having an idler roller and a driven
roller, an outboard nip having an idler roller and a driven roller,
a second drive shaft connecting the inboard and outboard driven
rollers, and a second stepper motor operatively connected to the
second drive shaft; and the registration nip further comprises an
inboard nip having an idler roller and a driven roller, an outboard
nip having an idler roller and a driven roller, an inboard stepper
motor operatively connected to the inboard driven roller, an
outboard stepper motor operatively connected to the outboard driven
roller, the inboard and outboard driven rollers being collinear,
the inboard driven roller being unconnected to the outboard driven
roller.
9. The re-time sheet buffering system of claim 7, wherein: the
registration nip accelerates sheets 3 through N of the set to
compiling speed after registration; and the first and second retime
nips accelerate sheets 1 and 2 of the set to compiling speed after
registration; wherein sheets 1 and 2 of the set are held at
registration speed for a longer time than sheets 3 through N of the
set, so as to gain time for finishing.
10. The re-time sheet buffering system of claim 7, wherein: the
registration nip accelerates sheets 4 through N of the set to
compiling speed after registration; the first retime nip holds
sheets 1, 2, and 3 of the set at registration speed and accelerates
sheets 1, 2, and 3 of the set; and the second retime nip
accelerates sheets 1, 2, and 3 of the set to compiling speed;
wherein sheets 1, 2, and 3 of the set are held at registration
speed for a longer time than sheets 4 through N, so as to gain time
for finishing.
11. The re-time sheet buffering system of claim 7, further
comprising: the input speed being approximately 1090 mm/s; the
registration speed being approximately 650 mm/s; the compiler speed
being approximately 1380 mm/s; and the predetermined speed being
between the registration speed and the compiler speed.
12. The re-time sheet buffering system of claim 7, wherein the
transport apparatus further comprises a vacuum gripper
transport.
13. A method for re-time sheet buffering, for use in connection
with a finisher for a digital printing system and a plurality of
media sheets arranged in sets, each set including sheets 1, 2, 3
through N, the method comprising: inputting the sheets at an input
speed into a sheet path entrance of a sheet path; providing space
for buffering with a path loop between the sheet path entrance and
a sheet path exit; transporting the sheets along the path loop with
a plurality of transport nips; sensing the position and speed of
the sheets with a plurality of sensors arrayed on the sheet path;
decelerating sheets 1 through N from the input speed to a
registration speed with a registration nip on the sheet path;
registering the sheets 1 through N with the registration nip;
accelerating selected sheets to compiling speed with the
registration nip; holding sheets 1 and 2 of each set at a
predetermined speed with the registration nip and a first retime
nip disposed on the sheet path downstream of the registration nip;
accelerating sheets 1 and 2 of each set with the first retime nip;
accelerating sheets 1 and 2 of each set to compiling speed with a
second retime nip disposed on the sheet path downstream of the
first retime nip; holding sheets 1 and 2 of each set at
registration speed for a longer time than remaining sheets, so as
to gain time for finishing; compiling sheets of each set at a
compiler speed; and ejecting the set.
14. The method of claim 13, further comprising: accelerating sheets
3 through N of the set to compiling speed with the registration nip
after registration; accelerating sheets 1 and 2 of the set to
compiling speed with the first and second retime nips after
registration; and holding sheets 1 and 2 of each set at
registration speed for a longer time than sheets 3 through N, so as
to gain time for finishing.
15. The method of claim 13, further comprising: accelerating sheets
4 through N of the set to compiling speed with the registration nip
after registration; holding sheets 1, 2, and 3 of the set at
registration speed with the first retime nip accelerating sheets 1,
2, and 3 of the set with the first retime nip; accelerating sheets
1, 2, and 3 of the set to compiling speed with the second retime
nip; and holding sheets 1, 2, and 3 of the set at registration
speed for a longer time than sheets 4 through N, so as to gain time
for finishing.
16. The method of claim 13, further comprising: connecting inboard
and outboard driven rollers of the first retime nip together on a
common first drive shaft; driving the first drive shaft operatively
with a first stepper motor; connecting inboard and outboard driven
rollers of the second retime nip together on a common second drive
shaft; driving the second drive shaft operatively with a second
stepper motor; driving an inboard driven roller of the registration
nip operatively with an inboard stepper motor; driving an outboard
driven roller of the registration nip operatively with an outboard
stepper motor; and aligning the inboard driven roller collinear to
the outboard driven roller, the inboard driven roller being
unconnected to the outboard driven roller.
17. The method of claim 13, further comprising transporting the
sheets with a vacuum gripper transport before compiling.
18. The method of claim 13, further comprising stapling the set
with a stapler after compiling.
19. A method for re-time sheet buffering, for use in connection
with a finisher for a digital printing system and a plurality of
media sheets arranged in sets, each set including sheets 1, 2, 3
through N, the method comprising: inputting the sheets at an input
speed into a sheet path entrance of a sheet path; providing space
for buffering with a path loop between the sheet path entrance and
a sheet path exit; transporting the sheets along the path loop with
a plurality of transport nips; sensing the position and speed of
the sheets with a plurality of sensors arrayed on the sheet path;
decelerating sheets 1 through N from the input speed to a
registration speed with a registration nip on the sheet path;
driving an inboard driven roller of the registration nip
operatively with an inboard stepper motor; driving an outboard
driven roller of the registration nip operatively with an outboard
stepper motor; aligning the inboard driven roller collinear to the
outboard driven roller, the inboard driven roller being unconnected
to the outboard driven roller; registering the sheets 1 through N
with the registration nip; accelerating sheets 3 through N of the
set to compiling speed with the registration nip after
registration; holding sheets 1 and 2 of each set at the
registration speed with the registration nip and a first retime nip
disposed on the sheet path downstream of the registration nip;
connecting inboard and outboard driven rollers of the first retime
nip together on a common first drive shaft; driving the first drive
shaft operatively with a first stepper motor; holding sheets 1 and
2 of each set at the registration speed for a longer time than
sheets 3 through N of the set, so as to gain time for finishing;
accelerating sheets 1 and 2 of each set with the first retime nip;
accelerating sheets 1 and 2 of each set to compiling speed with a
second retime nip disposed on the sheet path downstream of the
first retime nip; connecting inboard and outboard driven rollers of
the second retime nip together on a common second drive shaft;
driving the second drive shaft operatively with a second stepper
motor; compiling sheets of each set at a compiler speed; and
ejecting the set.
20. The method of claim 19, further comprising: transporting the
sheets with a vacuum gripper transport before compiling; and
stapling the set with a stapler after compiling.
Description
INCORPORATION BY REFERENCE
[0001] U.S. Pat. No. 7,422,210, filed on Mar. 4, 2005, entitled,
"Sheet Deskewing System With Final Correction From Trail Edge
Sensing," and assigned to the assignee hereof is incorporated in
its entirety for the teachings therein.
TECHNICAL FIELD
[0002] This invention relates to buffering sheets in digital
printing machines, and, more particularly, to an apparatus, system,
and method for enabling increased productivity in a digital
printing machine by varying the time interval of selected sheets in
a finisher.
BACKGROUND
[0003] Digital printing machines can take on a variety of
configurations. One common process is that of electrostatographic
printing, which is carried out by exposing a light image of an
original document to a uniformly charged photoreceptive member to
discharge selected areas. A charged developing material is
deposited to develop a visible image. The developing material is
transferred to a medium sheet (paper) and heat fixed.
[0004] Another common process is that of direct to paper ink jet
printing systems. In ink jet printing, tiny droplets of ink are
sprayed onto the paper in a controlled manner to form the image.
Other processes are well known to those skilled in the art.
[0005] The primary output product for a typical digital printing
system is a printed copy substrate such as a sheet of paper bearing
printed information in a specified format. Quite often, customer
requirements necessitate that this output product be configured in
various specialized arrangements ranging from stacks of collated
loose printed sheets, to brief reports stapled together, to
tabulated and bound booklets. The sheets of media, usually paper,
are compiled, stapled, and ejected at the last stage of the job, in
a region called a finisher.
[0006] Various external output devices have been designed for
connection to a digital printing machine. The paper will exit the
printing system and be passed to an external finishing device,
wherein a critical parameter in such delivery is the capability to
operate at process speed so as to not inhibit the function of the
printing machine.
[0007] Finishing procedures, such as sorting, collating, stapling
and ejecting, require the movement of mechanical components. In
state-of-the-art digital printing machines, it is common to have a
quantity of sets in a job stream which require various sorts of
finishing activities. In order to accommodate multiple sets, each
set in the stream is typically held or delayed until the finishing
activity of the preceding set has been completed. Moreover, it is
often necessary to slow the output speed of the printing machine so
as not to exceed the rate at which the external device, or
finisher, can receive and process sets of output documents for
producing the final output product. These finishing delay times
detract from the overall productivity of the printing system.
[0008] Sheet buffering can be defined as holding sheets of paper
within a finisher paper path while functions like compiling,
stapling, and ejecting sets are accomplished. One type of finisher
will skip a sheet in between each set in order to free up time to
accomplish these functions. The problem with this method is that it
slows productivity. Another finisher uses a system that compiles
three sets at a time to buffer. A three tray set compiling unit
fills as sheets enter the finisher. They are unloaded by an
expensive clamping system that brings sets to the stapler. The
problem with this system is excessive hardware and associated cost.
Still another finisher uses buffering arms to temporarily hold
sheets and then drop them into a compiler. The apparatus is costly,
and further problems arise with registration issues and timing
constraints which limit the use of this system. Yet another
finisher uses a wait station to buffer a sheet. However, with
higher speed finishing devices, this type of buffering does not
work. An example of such a high speed finishing device is a newly
introduced production finisher which operates at 157 ppm production
rate.
[0009] An example of a sheet buffering system can be found in U.S.
Pat. No. 5,303,017, filed on May 7, 1993, entitled, "Print Skip
Avoidance For On-Line Compiling," and assigned to the assignee
hereof. An example of a sheet timing system can be found in U.S.
Pat. No. 7,706,704, filed on Jun. 12, 2006, entitled, "Digital
Printing Apparatus Having Substantially Equal Output Rates For
Various Sheet Sizes And Orientations," and assigned to the assignee
hereof. An example of a sheet registration system can be found in
U.S. Pat. No. 8,109,506, filed on May 29, 2009, entitled, "Sheet
Observer With A Limited Number Of Sheet Sensors," and assigned to
the assignee hereof.
[0010] Accordingly, there is a need to provide a sheet buffering
system that will vary the time interval of selected sheets in a
finisher to allow finishing of a set.
[0011] There is a further need to provide a sheet buffering system
of the type described and that not slow down the production rate of
the printer.
[0012] There is a yet further need to provide a sheet buffering
system of the type described and that is mechanically simple and
robust, thereby minimizing cost and avoiding the problems
associated with the prior art.
SUMMARY
[0013] In one aspect, a re-time sheet buffering system is used in
connection with a finisher for a digital printing system and a
plurality of media sheets arranged in sets. Each set includes
sheets 1, 2, 3 through N. The re-time sheet buffer comprises a
sheet path having a sheet path entrance to input the sheets at an
input speed. A sheet path exit outputs the sheets. A path loop
between the sheet path entrance and the sheet path exit provides
space for buffering. A compiler area is located between the path
loop and the sheet path exit. A compiler compiles sheet sets at a
compiler speed in the compiler area.
[0014] A registration nip is disposed on the sheet path for
decelerating sheets 1 through N from the input speed to a
registration speed. The registration nip also performs registering
and accelerating selected sheets.
[0015] A first retime nip is disposed on the sheet path downstream
of the registration nip. The first retime nip is for holding sheets
1 and 2 of the set at a predetermined speed and for accelerating
sheets 1 and 2 of the set.
[0016] A second retime nip is disposed on the sheet path downstream
of the first retime nip and before the compiler area. The second
retime nip is for accelerating sheets 1 and 2 of the set to
compiling speed.
[0017] A plurality of sensors is arrayed on the sheet path for
sensing the position and speed of the sheets, wherein sheets 1 and
2 of the set are held at registration speed for a longer time than
remaining sheets, so as to gain time for finishing.
[0018] In another aspect, a re-time sheet buffering system is used
in connection with a finisher for a digital printing system and a
plurality of media sheets arranged in sets. Each set includes
sheets 1, 2, 3 through N. The re-time sheet buffer comprises a
sheet path having a sheet path entrance to input the sheets at an
input speed. A sheet path exit outputs the sheets. A path loop
between the sheet path entrance and the sheet path exit provides
space for buffering. A compiler area is located between the path
loop and the sheet path exit. A compiler compiles sheet sets at a
compiler speed in the compiler area.
[0019] A transport apparatus is disposed adjacent the compiler
area. A stapler is located between the compiler area and the sheet
path exit for stapling compiled sheet sets. A plurality of
transport nips is arrayed along the path loop.
[0020] A registration nip is disposed on the sheet path for
decelerating sheets 1 through N from the input speed to a
registration speed. The registration nip is also performs
registering and accelerating selected sheets.
[0021] A first retime nip is disposed on the sheet path downstream
of the registration nip. The first retime nip is for holding sheets
1 and 2 of the set at a predetermined speed and for accelerating
sheets 1 and 2 of the set.
[0022] A second retime nip is disposed on the sheet path downstream
of the first retime nip and before the compiler area. The second
retime nip is for accelerating sheets 1 and 2 of the set to
compiling speed.
[0023] A plurality of sensors is arrayed on the sheet path for
sensing the position and speed of the sheets, wherein sheets 1 and
2 of the set are held at registration speed for a longer time than
remaining sheets, so as to gain time for finishing.
[0024] In yet another aspect, a method for re-time sheet buffering
is used in connection with a finisher for a digital printing system
and a plurality of media sheets arranged in sets. Each set includes
sheets 1, 2, 3 through N. The method comprises inputting the sheets
at an input speed into a sheet path entrance of a sheet path. Space
is provided for buffering by adding a path loop between the sheet
path entrance and a sheet path exit. The sheets are transported
along the path loop with a plurality of transport nips. The
position and speed of the sheets is sensed with a plurality of
sensors arrayed on the sheet path.
[0025] Sheets 1 through N are decelerated from the input speed to a
registration speed with a registration nip on the sheet path. The
sheets 1 through N are then registered with the registration nip.
Selected sheets are accelerated to compiling speed with the
registration nip.
[0026] Sheets 1 and 2 of each set are held at a predetermined speed
with the registration nip and a first retime nip which is disposed
on the sheet path downstream of the registration nip. Sheets 1 and
2 of each set are accelerated with the first retime nip.
[0027] Sheets 1 and 2 of each set are then accelerated to compiling
speed with a second retime nip disposed on the sheet path
downstream of the first retime nip. Sheets 1 and 2 of each set are
held at registration speed for a longer time than remaining sheets,
in order to gain time for finishing. Compiling the sheets of each
set is carried out at a compiler speed. The set is then
ejected.
[0028] In still another aspect, a method for re-time sheet
buffering is used in connection with a finisher for a digital
printing system and a plurality of media sheets arranged in sets.
Each set includes sheets 1, 2, 3 through N. The method comprises
inputting the sheets at an input speed into a sheet path entrance
of a sheet path. Space is provided for buffering by adding a path
loop between the sheet path entrance and a sheet path exit. The
sheets are transported along the path loop with a plurality of
transport nips. The position and speed of the sheets is sensed with
a plurality of sensors arrayed on the sheet path.
[0029] Sheets 1 through N are decelerated from the input speed to a
registration speed with a registration nip on the sheet path. An
inboard driven roller of the registration nip is driven operatively
with an inboard stepper motor. An outboard driven roller of the
registration nip is driven operatively with an outboard stepper
motor. The inboard driven roller is aligned collinear to the
outboard driven roller. The inboard driven roller is not connected
to the outboard driven roller. The sheets 1 through N are
registered with the registration nip. Sheets 3 through N of the set
are accelerated to compiling speed with the registration nip after
registration.
[0030] Sheets 1 and 2 of each set are held at the registration
speed with the registration nip and a first retime nip. The first
retime nip is disposed on the sheet path downstream of the
registration nip. Inboard and outboard driven rollers of the first
retime nip are connected together on a common first drive shaft.
The first drive shaft is driven operatively with a first stepper
motor. Sheets 1 and 2 of each set are held at the registration
speed for a longer time than sheets 3 through N of the set, so as
to gain time for finishing. Sheets 1 and 2 of each set are
accelerated with the first retime nip.
[0031] Sheets 1 and 2 of each set are accelerated to compiling
speed with a second retime nip disposed on the sheet path
downstream of the first retime nip. Inboard and outboard driven
rollers of the second retime nip are connected together on a common
second drive shaft. The second drive shaft is driven operatively
with a second stepper motor. The sheets of each set are compiled a
compiler speed. The set is then ejected.
[0032] These and other aspects, objectives, features, and
advantages of the disclosed technologies will become apparent from
the following detailed description of illustrative embodiments
thereof, which is to be read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a schematic side elevational, sectional view of an
exemplary production finisher showing a re-time sheet buffering
system constructed in accordance with the invention.
[0034] FIG. 2 is a schematic side elevational, sectional enlarged
view of the re-time sheet buffering system of FIG. 1, showing the
nips.
[0035] FIG. 3 is a schematic front elevational, sectional enlarged
view of the re-time sheet buffering system of FIG. 1, taken along
lines 3-3 of FIG. 2.
[0036] FIG. 4 is a schematic plan view of media sheets moving
through the re-time sheet buffering system of FIG. 1.
DETAILED DESCRIPTION
[0037] Describing now in further detail these exemplary embodiments
with reference to the Figures as described above, the re-time sheet
buffering system is typically used in a select location or
locations of the paper path or paths of various conventional media
handling assemblies. Thus, only a portion of an exemplary media
handling assembly path is illustrated herein. It should be noted
that the drawings herein are not to scale.
[0038] As used herein, a "printer," "printing assembly" or
"printing system" refers to one or more devices used to generate
"printouts" or a print outputting function, which refers to the
reproduction of information on "substrate media" or "media
substrate" or "media sheet" for any purpose. A "printer," "printing
assembly" or "printing system" as used herein encompasses any
apparatus, such as a digital copier, bookmaking machine, facsimile
machine, multi-function machine, etc. which performs a print
outputting function.
[0039] A printer, printing assembly or printing system can use an
"electrostatographic process" to generate printouts, which refers
to forming and using electrostatic charged patterns to record and
reproduce information, a "xerographic process", which refers to the
use of a resinous powder on an electrically charged plate to record
and reproduce information, or other suitable processes for
generating printouts, such as an ink jet process, a liquid ink
process, a solid ink process, and the like. Also, such a printing
system can print and/or handle either monochrome or color image
data.
[0040] As used herein, "media substrate" or "media sheet" refers
to, for example, paper, transparencies, parchment, film, fabric,
plastic, photo-finishing papers or other coated or non-coated
substrates on which information can be reproduced, preferably in
the form of a sheet or web. While specific reference herein is made
to a sheet or paper, it should be understood that any media
substrate in the form of a sheet amounts to a reasonable equivalent
thereto. Also, the "leading edge" or "lead edge" (LE) of a media
substrate refers to an edge of the sheet that is furthest
downstream in the process direction.
[0041] As used herein, a "media handling assembly" refers to one or
more devices used for handling and/or transporting media substrate,
including feeding, printing, finishing, registration and transport
systems.
[0042] As used herein, the terms "process" and "process direction"
refer to a procedure of moving, transporting and/or handling a
substrate media sheet. The process direction is a flow path the
sheet moves in during the process.
[0043] Referring to FIGS. 1, 2, and 3, the production finisher 10
uses a buffering system and method herein termed re-timing. The
re-time sheet buffering system 11 is used in connection with a
finisher for a digital printing system. The system uses a plurality
of media sheets 12 arranged in sets, with each set 14 including
sheets 1, 2, 3 through N. The finisher 10 typically has a media
sheet path entrance 16, and a sheet path 18 along which the sheet
12 moves. A compiler sorts the sheets at a compiler area 20. A
stapler 22 staples the sheets 12 in a set 14, and the set 14 is
ejected at a sheet path exit 24. The embodiment described herein
also has a vacuum gripper transport 26 or VGT adjacent the
compiler, and a compiler shelf 28 to receive finished sets of media
sheets. The VGT can be any conventional vacuum gripper transport.
An example is found in U.S. Pat. No. 7,628,396, filed on Mar. 21,
20076, entitled, "High Speed Shingled Sheet Compiler," and assigned
to the assignee hereof. The compiler area 20 may also include a
fine registration system to be implemented just prior to the
stapling process.
[0044] The process path or sheet path 18 will input the sheets 12
at an input speed at the sheet path entrance 16. The sheet path 18
has a path loop 30 between the sheet path entrance 16 and sheet
path exit 24 so as to provide space for buffering. In the
embodiment shown, the path loop 30 extends from the sheet path
entrance 16 to the compiler area 20. Media sheets 12 enter the
finisher sheet path entrance 16 at a nominal speed of about 1090
mm/s. The path loop 30 has a plurality of nips 32 and sensors 34 to
maintain about 1090 mm/s through the path loop 30.
[0045] At some point in the path loop 30 a registration nip 36 is
disposed on the sheet path 30 for decelerating sheets 1 through N
from the input speed to a registration speed. The registration nip
36 performs skew correction, cross-process registration, and speed
control. The lead edge (LE) of the sheet is sensed by two sensors
to determine the skew of the sheet. Sensors can also be employed
for edge detection. Reference is made to U.S. Pat. No. 7,422,210,
which is incorporated herein in its entirety. The registration nips
36 are driven at slight differential speeds such that the sheet
skew is corrected and eliminated. The registration nip 36 then
accelerates selected sheets to compiling speed. Selected sheets are
those sheets remaining after the first two or three sheets are
re-timed. Starting with sheets 1 through N in a set, if sheets 1
and 2 are re-timed, then sheets 3 through N are the selected
sheets. If sheets 1, 2, and 3 are re-timed, then sheets 4 through N
are the selected sheets.
[0046] The registration nip 36 includes an inboard nip 38 having an
idler roller 40 and a driven roller 42, and an outboard nip 44
having an idler roller 46 and a driven roller 48. The inboard 42
and outboard 48 driven nip rollers are on collinear rotation axes,
but driven separately. The inboard driven roller 42 is not
connected to the outboard driven roller 48. An inboard stepper
motor 50 is operatively connected to the inboard driven roller 42.
An outboard stepper motor 52 is operatively connected to the
outboard driven roller 48.
[0047] Upstream of the registration nip 36 are several transport
nips 32 having solenoids (arrows 54) that lift each idler nip
roller from the respective driven nip roller, so that registration
can proceed unhindered.
[0048] Downstream of the registration nip 36 on the sheet path 18
is a first retime nip 56. The first retime nip 56 holds sheets 1
and 2 of the set at a predetermined speed after registration, and
accelerates sheets 1 and 2 of the set. Predetermined speed is any
speed between registration speed and compiling speed. That is,
predetermined speed is equal to or greater than registration speed
and equal to or less than compiling speed. In the embodiment
described herein, the predetermined speed will typically be
registration speed. The first retime nip 56 includes an inboard nip
58 having an idler roller 60 and a driven roller 62, and an
outboard nip 64 having an idler roller 66 and a driven roller 68. A
first drive shaft 70 connects the inboard 62 and outboard 68 driven
rollers. A first stepper motor 72 is operatively connected to the
first drive shaft 70.
[0049] A second retime nip 74 is disposed on the sheet path 18
downstream of the first retime nip 56 and before the compiler area
20. The second retime nip 74 accelerates sheets 1 and 2 of the set
to compiling speed. The second retime nip 74 includes an inboard
nip 76 having an idler roller 78 and a driven roller 80, and an
outboard nip 82 having an idler roller 84 and a driven roller 86. A
second drive shaft 88 connects the inboard 80 and outboard 86
driven rollers. A second stepper motor 90 is operatively connected
to the second drive shaft 88.
[0050] Thus, sheets 1 and 2 of the set are held at the
predetermined speed for a longer time than remaining sheets, namely
sheets 3 through N. This opens up space between the last sheet of a
set and the first sheet of the next set to gain time for
finishing.
[0051] Downstream of the registration nip 36 is a first retime nip
56 and further downstream a second retime nip 74, as shown in FIG.
2. These three nips are specially controlled by a controller (not
shown) to allow synchronous acceleration, driving and deceleration
of the re-timed sheets. After the second retime nip 74 the sheet
path 18 is directed to the VGT 26 and the compiler and stapler 22.
At registration, all sheets are slowed to about 650 mm/s to allow
offsetting, whereupon registration is performed. In the case where
buffering is unnecessary, all sheets will speed up to compiling
speed of about 1380 mm/s before leaving the registration nips
36.
[0052] The sheets pass through both retime nips 56 & 74 at
about 1380 mm/s and enter the VGT 26 at that speed. The VGT 26 uses
pitched vacuum belts to acquire the LE of the sheet and to guide
the LE directly into the compiler area 20 and into the stapler 22
throat for the final fine registration. The VGT pitch system must
be carefully synchronized to the LE of the sheet for proper
function, especially at 1380 mm/s. That speed is needed to handle
sheets for the 157 prints per minute (PPM) production rate. The
sheet sets are stapled and stacked, or sometimes only stacked. The
sets are then ejected and exit the process path.
[0053] In the case where buffering is necessary in order to gain
time for compiling, stapling, and ejecting, the re-time sheet
buffering system is employed. The pitch time of sheets is defined
as the elapsed time from the LE of one sheet to the LE of the next
sheet in line. At the 157 ppm speed, the pitch time of sheets is
0.381 seconds (381 ms), as shown in FIG. 4. The nominal compiling
time requires about 0.260 seconds (260 ms). That leaves 0.121
seconds between sheets, which is insufficient for stapling and
ejecting. Stapling requires about 0.180 seconds and ejecting
requires another about 0.150 seconds. Stapling and ejecting thus
require about 0.330 seconds. These functions must be completed
before the next sheet (first sheet of the next set) enters the
compiler. The first few sheets of a set, typically two sheets and
optionally three sheets, are re-timed (buffered) such that they
remain at the slow speed, about 650 mm/s, through registration and
partly through the re-time transport. At some point the retime nips
56 & 74 will increase the sheet speed up to compiling speed of
about 1380 mm/s at the VGT. These sheets are buffered or delayed in
the paper path to free up some time, as the stapling and ejecting
functions of the previous set are accomplished. Buffering provides
about 0.110 seconds gain per sheet in the re-time transport. This
limit is based upon an allowable minimum distance between a sheet
trail edge and the next sheet lead edge. The limit is further
determined by the VGT speed and belt pitch length. Buffering 2
sheets by re-timing gains 0.220 seconds. Adding this to the 0.121
seconds after compiling yields 0.341 seconds of time gained.
Stapling and ejecting requires 0.330 seconds. Hence, these
functions can be completed just before the next sheet enters the
compiler.
[0054] The re-timing system is illustrated in FIG. 4. The first row
represents four sheets 12 as they travel through the sheet path 18
at a steady rate. Assume these are sheets as they reach the
compilers registration edge. The sheets are spaced apart with a
pitch time of 0.381 seconds, or 381 ms, as shown in the first row
of FIG. 4. When the last sheet of a set (sheet N) travels through
the path, the next sheet (Sheet 1 of set 2) is processed
differently than other sheets. It is specifically slowed down at
the registration nip 36 and remains at this slow speed. The
following sheet (Sheet 2 of set 2) is also slowed down when it gets
to the registration nip 36 and remains at the slow speed. The pitch
time is compressed to 0.271 seconds (271 ms) because of a limit
with the VGT. With two sheets being re-timed (buffered), the time
gained for stapling and ejecting is 0.220 seconds (220 ms). This is
graphically represented in the second row of FIG. 4. Sheets 1 and 2
then increase in speed up to the compiler speed just prior to
entering the VGT. Notice that in FIG. 4 the total pitch time
between sets of 1.143 seconds (1143 ms) does not change. Therefore,
the high production rate of 157 ppm is maintained, while the extra
time needed for stapling and ejecting has been achieved by the
re-time sheet buffering system.
[0055] It will be appreciated that variants of the above-disclosed
and other features and functions, or alternatives thereof, may be
desirably combined into many other different systems or
applications. Various presently unforeseen or unanticipated
alternatives, modifications, variations, or improvements therein
may be subsequently made by those skilled in the art which are also
intended to be encompassed by the following claims.
* * * * *