U.S. patent application number 11/225502 was filed with the patent office on 2006-04-06 for sheet processing apparatus and image forming apparatus having the same.
This patent application is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Tadashi Iwakawa, Daisaku Kamiya, Junichi Moteki, Yusuke Obuchi, Masaki Seto, Kenji Suzuki.
Application Number | 20060071411 11/225502 |
Document ID | / |
Family ID | 36124775 |
Filed Date | 2006-04-06 |
United States Patent
Application |
20060071411 |
Kind Code |
A1 |
Obuchi; Yusuke ; et
al. |
April 6, 2006 |
Sheet processing apparatus and image forming apparatus having the
same
Abstract
An adsorption standby unit is provided upstream in the sheet
conveying direction of a sheet stacking portion, which stacks
sheets to be processed thereon. During processing of sheets on the
sheet stacking portion, the next sheet to be processed is adsorbed
and put in a standby state by the adsorption standby unit, so that
the sheet can be retained and put in a standby state without
switching the sheet back.
Inventors: |
Obuchi; Yusuke; (Abiko-shi,
JP) ; Kamiya; Daisaku; (Abiko-shi, JP) ;
Moteki; Junichi; (Abiko-shi, JP) ; Iwakawa;
Tadashi; (Toride-shi, JP) ; Suzuki; Kenji;
(Abiko-shi, JP) ; Seto; Masaki; (Toride-shi,
JP) |
Correspondence
Address: |
Canon U.S.A. Inc.;Intellectual Property Division
15975 Alton Parkway
Irvine
CA
92618-3731
US
|
Assignee: |
Canon Kabushiki Kaisha
Ohta-ku
JP
|
Family ID: |
36124775 |
Appl. No.: |
11/225502 |
Filed: |
September 13, 2005 |
Current U.S.
Class: |
271/207 ;
271/306 |
Current CPC
Class: |
B65H 31/3027 20130101;
B65H 2301/42262 20130101; B65H 2301/4213 20130101; B42C 1/12
20130101; B65H 2406/31 20130101; B65H 2701/1313 20130101 |
Class at
Publication: |
271/207 ;
271/306 |
International
Class: |
B65H 31/00 20060101
B65H031/00; B65H 29/54 20060101 B65H029/54 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 15, 2004 |
JP |
2004-269018 |
Claims
1. A sheet processing apparatus operable to process sheets,
comprising: a sheet stacking portion configured to stack the sheets
to be processed thereon; a sheet conveying path facilitating
conveying a sheet to be processed to the sheet stacking portion; a
sheet conveying portion disposed in the sheet conveying path; and
an adsorption standby unit disposed in the sheet conveying path,
the adsorption standby unit configured to adsorb a next sheet to be
processed so as to be put in a standby state during processing of
the sheets on the sheet stacking portion, wherein the adsorption
standby unit adsorbs an end of the sheet conveyed to the sheet
conveying path by the sheet conveying portion.
2. The sheet processing apparatus according to claim 1, further
comprising: a step portion disposed upstream of the sheet conveying
path, wherein the adsorption standby unit is provided in the step
portion.
3. The sheet processing apparatus according to claim 2, wherein the
adsorption standby unit adsorbs the trailing end portion in the
sheet conveying direction of the next sheet to be processed along a
sheet stacking surface of the step portion.
4. The sheet processing apparatus according to claim 2, wherein the
step portion has a depth which prevents a sheet next to the
adsorbed sheet adsorbed by the adsorption standby unit from
abutting the trailing end in the sheet conveying direction of the
adsorbed sheet during proceeding towards the sheet conveying
path.
5. The sheet processing apparatus according to claim 1, further
comprising: a detection sensor configured to detect a sheet
conveyed to the sheet conveying path; and a controller controlling
driving of the sheet conveying portion so as to stop the trailing
end in the sheet conveying direction of the next sheet to be
processed at a position opposing the adsorption standby unit in
accordance with a signal from the detection sensor.
6. The sheet processing apparatus according to claim 1, wherein the
adsorption standby unit adsorbs the sheet by air adsorption.
7. The sheet processing apparatus according to claim 1, wherein the
adsorption standby unit adsorbs the sheet by electrostatic
adsorption.
8. The sheet processing apparatus according to claim 6, wherein the
adsorption standby unit adsorbs a plurality of sheets by shifting
the trailing ends in the sheet conveying direction of the
sheets.
9. The sheet processing apparatus according to claim 1, further
comprising a controller which controls a sheet adsorbing force of
the adsorption standby unit to correspond to at least one of the
material, size, and weight of the sheet.
10. An image forming apparatus comprising: an image forming portion
configured to form images on a sheet; a sheet processing apparatus
processing the sheet having images formed thereon by the image
forming portion, the sheet processing apparatus including: a sheet
stacking portion configured to stack the sheets to be processed
thereon; a sheet conveying path facilitating conveying a sheet to
be processed to the sheet stacking portion; a sheet conveying
portion disposed in the sheet conveying path; and an adsorption
standby unit disposed in the sheet conveying path, the adsorption
standby unit configured to adsorb a next sheet to be processed so
as to be put in a standby state during processing of the sheets on
the sheet stacking portion, wherein the adsorption standby unit
adsorbs an end of the sheet conveyed to the sheet conveying path by
the sheet conveying portion.
11. The image forming apparatus according to claim 10, wherein the
sheet processing apparatus further includes: a step portion
disposed upstream of the sheet conveying path, wherein the
adsorption standby unit is provided in the step portion.
12. The image forming apparatus according to claim 11, wherein the
adsorption standby unit adsorbs the trailing end portion in the
sheet conveying direction of the next sheet to be processed along a
sheet stacking surface of the step portion.
13. The image forming apparatus according to claim 11, wherein the
step portion has a depth which prevents a sheet next to the
adsorbed sheet adsorbed by the adsorption standby unit from
abutting the trailing end in the sheet conveying direction of the
adsorbed sheet during proceeding towards the sheet conveying
path.
14. The image forming apparatus according to claim 10, further
comprising: a detection sensor configured to detect a sheet
conveyed to the sheet conveying path; and a controller controlling
driving of the sheet conveying portion so as to stop the trailing
end in the sheet conveying direction of the next sheet to be
processed at a position opposing the adsorption standby unit in
accordance with a signal from the detection sensor.
15. The image forming apparatus according to claim 10, wherein the
adsorption standby unit adsorbs the sheet by air adsorption.
16. The image forming apparatus according to claim 10, wherein the
adsorption standby unit adsorbs the sheet by electrostatic
adsorption.
17. The image forming apparatus according to claim 15, wherein when
the adsorption standby unit adsorbs a plurality of sheets by
shifting the trailing ends in the sheet conveying direction of the
sheets.
18. The image forming apparatus according to claim 10, further
comprising a controller which controls a sheet adsorbing force of
the adsorption standby unit to correspond to at least one of the
material, size, and weight of the sheet.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to sheet processing
apparatuses, in which the next sheet is put in a standby state
while a sheet is processed, and an image forming apparatus having
the sheet processing apparatus, and in particular relates to a
sheet processing apparatus capable of holding a sheet in a standby
state without switching back the sheet and an image forming
apparatus having the sheet processing apparatus.
[0003] 2. Description of the Related Art
[0004] Recently, an image forming apparatus, such as an
electrophotographic copy machine and a laser beam printer, has been
provided with a sheet processing apparatus as an option, such as a
sorter for sorting sheets discharged from an image forming
apparatus body to have images formed thereon. By such a sheet
processing apparatus, not only the sorting, but also various kinds
of processing have been carried out, such as stacking of a
plurality of sheets, alignment, or binding sheets together with
staples by a stapler.
[0005] In the sheet processing apparatus having the stapler, when
binding sheets, sheets conveyed to the sheet processing apparatus
are stacked on a processing tray after passing them through a
conveying path within the body, and then bound. When a sheet bundle
is bound, by moving the stapler, the bundle is bound at one point
or plural points (two points generally).
[0006] During binding operation (binding processing), sheets for
the next job cannot be stacked on the processing tray, so that the
sheets have been generally spaced for the next job during the
binding. This results in reduced productivity.
[0007] Then, in order to prevent the deterioration of the
probability, during processing the sheets on the processing tray,
the next sheets to be processed are put in a standby state in the
upstream side of the processing tray without conveying them to the
processing tray (see Japanese Patent Laid-Open No.
2003-081517).
[0008] FIGS. 10A and 10B are drawings showing such a conventional
sheet processing apparatus, wherein FIG. 10A shows a sheet bundle
52 placed on a processing tray 51 going to be bound by a stapler
(not shown). In such a state, when a first sheet 53 for the next
job is conveyed to the inside of a finisher by an inlet roller 54,
the sheet 53 is first conveyed to the downstream of a buffer guide
55 by the rotation in arrow direction of a buffer roller 50
rotatable in normal and reverse directions.
[0009] Then, when the sheet 53 is conveyed downstream by a
predetermined distance X (switchback point) from the buffer guide
55, the buffer roller 50 is reversely rotated in arrow direction
shown in FIG. 10B, so that the sheet 53 is switched back (reversely
conveyed) so as to abut the buffer guide 55. Thereafter, the buffer
guide 55 is rotated in arrow direction by a solenoid (not shown) so
as to retain the trailing end of the sheet 53, thereby putting the
sheet 53 in a standby state at this position.
[0010] However, in the conventional sheet processing apparatus
structured as above, the conveyed sheet 53 is switched back after
being once stopped every time, so that the sheet 53 is liable to be
jammed as well as productivity is reduced because the number of
processed sheets per unit time decreases due to switching back
operation time.
[0011] Also, images on the sheet may deteriorate during switching
back by the buffer roller 50 because the sheet is rubbed with a
guide plate (not shown) arranged below the buffer roller 50 at
point A. Moreover, the switched back sheet may be damaged at an end
by being abutted by the buffer guide 55.
[0012] In addition, since the sheet 53 directly after having images
formed thereon generally is at high temperature, guides retaining
the sheet 53 are increased in temperature during putting the sheet
53 in a standby state. As a result, operability in jamming
treatment and durability of the buffer guide 55 may be reduced.
SUMMARY OF THE INVENTION
[0013] The present invention is directed to a sheet processing
apparatus capable of reserving sheets without switching them back
and an image forming apparatus having the sheet processing
apparatus.
[0014] In one aspect of the present invention, a sheet processing
apparatus operable to process sheets includes a sheet stacking
portion configured to stack the sheets to be processed thereon; a
sheet conveying path facilitating conveying a sheet to be processed
to the sheet stacking portion; a sheet conveying portion disposed
in the sheet conveying path; an adsorption standby unit disposed in
the sheet conveying path, and configured to adsorb a next sheet to
be processed so as to be put in a standby state during processing
of the sheets on the sheet stacking portion, wherein the adsorption
standby unit adsorbs an end of the sheet conveyed to the sheet
conveying path by the sheet conveying portion.
[0015] According to the present invention, during processing of the
sheets on the sheet stacking portion, the next sheet to be
processed is adsorbed so as to put it in a standby state by the
adsorption standby unit which is disposed upstream in the sheet
conveying direction of the sheet stacking portion, so that the
sheet can be retained and put in a standby state without switching
the sheet back.
[0016] Further features of the present invention will become
apparent from the following description of exemplary embodiments
with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic view of an image forming apparatus
having a sheet processing apparatus (finisher) according to an
embodiment of the present invention.
[0018] FIG. 2 is a first drawing illustrating the schematic
structure and buffer operation of the sheet processing
apparatus.
[0019] FIG. 3 is a second drawing illustrating the buffer operation
of the sheet processing apparatus.
[0020] FIG. 4 is a third drawing illustrating the buffer operation
of the sheet processing apparatus.
[0021] FIG. 5 is a fourth drawing illustrating the buffer operation
of the sheet processing apparatus.
[0022] FIG. 6 is a fifth drawing illustrating the buffer operation
of the sheet processing apparatus.
[0023] FIG. 7 is a sixth drawing illustrating the buffer operation
of the sheet processing apparatus.
[0024] FIG. 8 is a drawing showing the situation in that a
plurality of sheets are stacked like brick work in the sheet
processing apparatus.
[0025] FIG. 9 is a drawing illustrating another structure of the
sheet processing apparatus.
[0026] FIGS. 10A-B are drawings illustrating the buffer operation
of a conventional sheet processing apparatus.
DESCRIPTION OF THE EMBODIMENTS
[0027] Best mode for carrying out the invention will be described
below in detail with reference to the drawings.
[0028] FIG. 1 is a schematic view of an image forming apparatus
having a sheet processing apparatus according to an embodiment of
the present invention. Referring to FIG. 1, reference numeral 100
denotes an image forming apparatus; numeral 100A denotes an image
forming apparatus body (referred to as an apparatus body below);
and numeral 19 denotes a sheet processing apparatus for processing
sheets having images formed thereon and discharged from the
apparatus body 100A. According to the embodiment, the sheet
processing apparatus (referred to as a finisher below) 19 is
detachably mounted on the apparatus body 100A as an independent
optional apparatus. Alternatively, the sheet processing apparatus
19 of the present invention can be integrally incorporated to the
image forming apparatus 100 so as to be provided in the apparatus
body 100A.
[0029] The apparatus body 10A is provided with an image forming
portion 100B and a sheet feed portion 100C for supplying a sheet,
such as a plastic sheet accommodated in a cassette 115A, towards
the image forming portion 100B. On the apparatus body 100A, an
automatic document feeder 102 is provided.
[0030] In the image forming apparatus 100 structured as above, for
forming an image on a sheet, first, a document G placed on a
document tray 103 is corrected in skewing by a pair of register
rollers 105 after being sequentially separated one sheet at a time
by a feed portion 104. Then, the document G is passed through a
reading position 107 via a lead path 106. The reflection light
obtained by irradiating the document G passing through the reading
position 107 with light by an illuminating system 111 is led to an
optical element 113 (a CCD or other elements) with a mirror 112 so
that images formed on the surface of the document are read so as to
obtain image data.
[0031] The document with images being read out during passing
through the reading position 107 is discharged onto a discharge
tray 109 after passing through a discharge path 108. When both
sides of the document are read, after the top surface is read in
such a manner, the document G proceeds through the discharge path
108 so as to be reversed by a pair of reversing rollers 110 and to
be fed to the pair of register rollers 105 again in the inverted
state.
[0032] Furthermore, after being corrected in skewing by the pair of
register rollers 105 in the same way as that of the top surface
reading, the document G passes through the lead path 106 so that
images formed on the surface (bottom surface at this time) are read
at the reading position 107. Thereafter, the document G is
discharged to the discharge tray 109 via the discharge path
108.
[0033] In the image forming portion 100B, a photoconductor drum 114
is irradiated with laser light from an exposing unit (not shown)
based on the obtained image data so as to form latent images on the
surface of the photoconductor drum 114. In addition, the
photoconductor drum 114 may also be directly irradiated with
reflection light by the mirror 112.
[0034] Then, the latent images formed on the photoconductor drum
114 in such a manner are developed by toner supplied from a toner
supplying device (not shown), thereby forming toner images on the
photoconductor drum 114.
[0035] Along with such image forming operation, in the sheet feed
portion 100C, a sheet accommodated in the cassette 115A is fed to a
position opposing the photoconductor drum 114 in accordance with a
recording signal, and then, the toner images formed on the
photoconductor drum 114 are transferred onto the sheet by a
transfer device 116. Then, the sheet having the toner images
transferred thereon is fed to a fixing device 117 so that the
images are permanently fixed on the sheet by pressurizing and
heating them in the fixing device 117.
[0036] When images are formed on each side of a sheet, the sheet
having images fixed on one surface by the fixing device 117 in such
a manner is again conveyed to between the photoconductor drum 114
and the transfer device 116 via an each-side path 118 arranged
downstream to the fixing device 117. Thereby, toner images are also
formed on the bottom surface of the sheet. The sheet having images
on its one side or each side in such a manner is discharged outside
(to the finisher 19).
[0037] FIG. 2 is a drawing of the structure of the finisher 19.
Referring to FIG. 2, reference characters 1A and 1B denote a pair
of inlet rollers. A sensor 15 detects the leading end of a sheet
guided in a conveying path 2 arranged in the finisher 19. A buffer
roller 4 is rotated about a shaft B as a fulcrum in the horizontal
direction.
[0038] Reference character 5A denotes an upper discharge roller;
character 5B denotes a lower discharge roller; character 7A denotes
an upper bundle discharge roller; character 7B denotes a lower
bundle discharge roller; and numeral 6 denotes a holder movable in
the vertical direction for rotatably holding the upper discharge
roller 5A and the upper bundle discharge roller 7A. Reference
character 6A denotes a push-up member, and the holder 6 is moved
upward by the push-up member 6A. When the holder 6 is moved upward
in such a manner, the upper discharge roller 5A and the upper
bundle discharge roller 7A are separated from the lower discharge
roller 5B and the lower bundle discharge roller 7B,
respectively.
[0039] Reference numeral 13 denotes a step portion arranged
upstream of the conveying path 2 (downstream of the pair of inlet
rollers 1A and 1B). Under the step portion 13, an adsorption
standby unit such as an adsorption fan 3 is provided. As will be
described later, when the adsorption fan 3 is driven after the
trailing end of a sheet S1 arrives at above the step portion 13 so
as to stop, the trailing end of the sheet S1 is adsorbed while
being curved along an inclined surface 13a and the bottom surface
13b of the step portion 13.
[0040] Referring to FIG. 2, reference numeral 10 denotes a stack
tray rotatable in the normal and reverse directions for stacking
sheets discharged by the upper and lower pair of bundle discharge
rollers 7A and 7B; numeral 14 denotes a processing tray downward
inclined from the pair of bundle discharge rollers for stacking
sheets to be processed; and numeral 9 denotes a stapler for binding
the sheet bundle placed on the processing tray 14.
[0041] Reference numeral 12 denotes a rear end stopper disposed
adjacent to the inclined end of the processing tray 14 for abutting
a sheet dropping along the processing tray 14. The rear end stopper
12 is fixed to a belt 12a. The belt 12a is rotated by a driving
motor 11. The rear end stopper 12 is moved towards the stack tray
with the belt 12a rotated by the driving motor 11 after the binding
process of the sheet bundle placed on the processing tray 14 is
finished. By moving the rear end stopper 12 in such a manner, the
bound sheet bundle is discharged to the stack tray 10.
[0042] In addition, by the rotation of the pair of bundle discharge
rollers 7A and 7B in a direction reverse to arrow direction, a
sheet placed on the processing tray 14 is returned with a return
roller 8 towards the rear end stopper 12, so that the position of
the trailing end during stapling is restricted by the rear end
stopper 12.
[0043] After a predetermined number of sheets is abutted to the
rear end stopper 12 so as to form a sheet bundle with such normal
and reverse rotations of the pair of bundle discharge rollers 7A
and 7B and the return roller 8, the sheet bundle is bound by
driving the stapler 9. After completion of the binding operation,
by rotating the pair of bundle discharge rollers 7A and 7B in arrow
direction and by moving the rear end stopper 12, the bound sheet
bundle is discharged to the stack tray 10.
[0044] During the sheet processing in such a manner, when the first
sheet for the next job is discharged from the apparatus body 1, the
sheet S1, as shown in FIG. 2, is led to the conveying path 2 within
the finisher with the pair of inlet rollers 1A and 1B, and then the
end of the sheet S1 is detected by the sensor 15. Based on the
detection signal from the sensor 15, a controller (not shown)
drives the buffer roller 4 and the pair of discharge rollers 5A and
5B so as to convey the sheet S1 to a predetermined position
thereafter.
[0045] Then the sheet S1, as shown in FIG. 3, is conveyed to the
pair of bundle discharge rollers 7A and 7B, thereby being placed on
the stack tray 10 at its end. When the trailing end of the sheet S1
reaches on the step portion 13, the controller stops the buffer
roller 4, the pair of discharge rollers 5A and 5B, and the pair of
bundle discharge rollers 7A and 7B, and drives the adsorption fan 3
as well. The sheet S1, as shown in FIG. 4, is thereby adsorbed
along the inclined surface 13a and the bottom surface 13b of the
step portion 13 in a curved state.
[0046] According to the embodiment, the step portion 13 has a depth
so deep that the next sheet S2 proceeding toward the conveying path
2 cannot abut the trailing end of the adsorbed sheet S1.
Accordingly, when the sheet S1 is held at its rear end to such step
portion 13, the leading end of the sheet S2 entering freshly cannot
catch on the trailing end of the temporarily retained sheet S1, as
shown in FIG. 5. The sheet S1 discharged from the apparatus body 1
is generally in a high temperature because it has passed through
the fixing device 17. However, a conveying guide 2a of the
conveying path 2 cannot be in a high temperature since it is
effectively cooled by the adsorption fan 3.
[0047] Then, after the sheet S1 is adsorbed in such a manner, the
push-up member 6A, as shown in FIG. 5, is upward rotated about a
shaft C as a fulcrum with a driving unit (not shown). When the
push-up member 6A is rotated upward, the holder 6 is rotated upward
about a shaft D as a fulcrum so that the upper discharge roller 5A
and the upper bundle discharge roller 7A are separated from the
lower discharge roller 5B and the lower bundle discharge roller 7B,
respectively. As a result, the pair of discharge rollers 5A and 5B
and the pair of bundle discharge rollers 7A and 7B do not apply a
conveying force to the temporarily retained sheet S1.
[0048] Then, in this state, when a second sheet S2 is conveyed with
the pair of inlet rollers 1A and 1B from the apparatus body 1 as
shown in FIG. 5, the sensor 15 detects the leading end of the sheet
S2, and then the sheet S2 is conveyed with the buffer roller 4
after its trailing end has passed between the pair of inlet rollers
1A and 1B.
[0049] At this time, to the temporarily retained first sheet S1,
the conveying force obtained by multiplying the pressurizing force
of the buffer roller 4 by the friction coefficient between the two
sheets S1 and S2 is applied. However, since the adsorption force of
the adsorption fan 3 is established to be larger than this
conveying force, the first sheet S1 cannot be brought by the second
sheet S2. Only the second sheet S2 is thereby conveyed with the
buffer roller 4. Then, the sheet S2 is controlled by the controller
(not shown) to move until the trailing end of the sheet S2 reaches
above the trailing end of the adsorbed sheet S1.
[0050] Thus, when the trailing end of the second sheet S2 arrives
at the upper position of the trailing end of the first sheet S1,
the second sheet S2 is stopped by upwardly rotating the buffer
roller 4 about the fulcrum B with a driving unit such as a solenoid
(not shown). Thereafter, the push-up member 6A is downwardly
rotated about the shaft C and the holder 6 is downwardly rotated
about the shaft D.
[0051] Thereby, the two sheets S1 and S2 are pinched between the
upper and lower discharge rollers 5A and 5B and between the upper
and lower bundle discharge rollers 7A and 7B. Then, when the lower
discharge roller 5B and the lower bundle discharge roller 7B are
rotated, the temporarily retained first sheet S1 and the second
sheet S2 are conveyed. At this time, the first sheet bundle bound
on the processing tray 14 is already discharged on the stack tray
10.
[0052] When the two sheets S1 and S2 pass through between the pair
of discharge rollers 5A and 5B, and the pair of bundle discharge
rollers 7A and 7B are reversely rotated thereafter, the two sheets
S1 and S2 drop on the processing tray 14 so as to be abutted to the
rear end stopper 12 by the return roller 8, as shown in FIG. 7.
Thereafter, sheets are sequentially conveyed one by one from the
apparatus body 1 to the finisher 19. When the number of sheets
placed on the processing tray 14 becomes a predetermined number of
sheets, the stapler 9 binds sheet bundles within the processing
tray 14.
[0053] After the binding processing is finished in such a manner,
the rear end stopper 12 is moved toward the pair of bundle
discharge rollers with the belt 12a driven by the driving motor 11.
With the rear end stopper 12 and the pair of bundle discharge
rollers 7A and 7B, the bound sheet bundle is discharged on the
stack tray 10. In addition, while the second sheet bundle is bound,
the first sheet of the next job (third sheet bundle) is conveyed in
the conveying path 2, and is temporarily retained as shown in FIGS.
2 to 4.
[0054] While sheets on the stack tray are processed with the
adsorption fan 3 in such a manner, by putting at least one sheet to
be processed in the next in a standby state, the sheet can be
retained without switching it back, thereby achieving high
productivity and reducing jamming.
[0055] The rubbing and damage in images produced during switchback
operation are eliminated, thereby providing high quality sheets.
Using the adsorption fan 3 enables the buffer portion including the
step portion 13 for putting a high-temperature sheet in a standby
state to be cooled by air, preventing deterioration in durability
of the buffer portion and in jamming operability.
[0056] In the above description about controlling, after the
leading end of a sheet is detected by the sensor 15, the sheet is
stopped at a predetermined position. Alternatively, after the
trailing end of a sheet is detected by the sensor 15, the sheet may
be conveyed by a predetermined distance so as to have the same
effect.
[0057] In the above description, the number of sheets to be
temporarily retained is one. However, the number is not limited to
this. As shown in FIG. 8, by alternately shifting the first sheet
S1 and the second sheet S2 so as to have a phase difference of E
between the first and second sheets S1 and S2 at trailing ends, a
plurality of sheets can be temporarily retained even by adsorbing
with air. When a plurality of sheets are superimposed so as to
shift the trailing ends of sheets in the sheet conveying direction,
the second sheet S2 may be controlled to stop at a position
upstream remote from the first sheet S1 in the sheet conveying
direction. That is, since the trailing end of the sheet S2
protrudes from the trailing end of the sheet S1 by the phase
difference E upstream in the sheet conveying direction, the
trailing end portion of the sheet S2 can be directly and securely
adsorbed with the adsorption fan 3.
[0058] Furthermore, in the above description, the trailing end
portion of the sheet has been adsorbed with the adsorption fan 3
(adsorbing unit). However, the invention is by no means limited to
this, so that the leading end portion of a sheet or the entire
sheet may be adsorbed. In other words, the same effect can be
obtained as long as an adsorbing force is secured sufficiently
enough not to be conveyed by a frictional force of the other sheet
therebetween.
[0059] The adsorption method using air due to the adsorption fan 3
has been described. However, the invention is not limited to this,
and as shown in FIG. 9, an electrostatic adsorption unit 20 may be
used as an electrostatic adsorption standby unit so as to adsorb a
sheet with static electricity.
[0060] In the case of such electrostatic adsorption, an adsorption
force due to static electricity is exerted through the sheet, the
sheets S1 need not to be placed like brick work as shown FIG. 8,
and a plurality of sheets can be temporarily retained in a state
that sheet trailing ends are aligned. Since the electrostatic
adsorption may not adsorb the sheet at high speed unlike in the air
adsorption, when the finisher 19 is connected to a high productive
image forming apparatus with a short time interval between sheets,
the buffer operation should be assisted by ejecting air toward the
electrostatic adsorption unit 20 so as to urge the sheet toward the
electrostatic adsorption unit 20, as shown in FIG. 9.
[0061] In the adsorption methods using air and static electricity
described above, it is easily assumed that the required adsorption
force be different corresponding to the size, kind, and weight of
the sheet. Thus, the adsorption force may be established so as to
satisfy all the temporarily retained sheets. Alternatively, in
order to reduce electric power consumption and noise, the
adsorption force is controlled by the controller corresponding to
at least one of the size, kind, and weight of the sheet, for
example.
[0062] The adsorption unit is not limited to the air adsorption
unit and the electrostatic adsorption unit described above, and any
unit that can control the sheet adsorption of course has the same
effect. Moreover, in the above-description, the step portion 13 is
provided below the upstream of the conveying path 2. However, the
invention is not limited to this, so that the step portion 13 may
also be provided above the upstream of the conveying path 2 as long
as it does not prevent the next sheet from being conveyed while the
adsorption standby unit may be provided above the step portion
13.
[0063] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all modifications, equivalent
structures and functions.
[0064] This application claims the benefit of Japanese Application
No. 2004-269018 filed Sep. 15th, 2004, which is hereby incorporated
by reference herein in its entirety.
* * * * *