U.S. patent application number 12/629291 was filed with the patent office on 2010-06-10 for printer.
This patent application is currently assigned to SONY CORPORATION. Invention is credited to Shigeyoshi Hirashima, Shunji Yamaguchi.
Application Number | 20100140862 12/629291 |
Document ID | / |
Family ID | 42230200 |
Filed Date | 2010-06-10 |
United States Patent
Application |
20100140862 |
Kind Code |
A1 |
Yamaguchi; Shunji ; et
al. |
June 10, 2010 |
PRINTER
Abstract
A second driven roller that is rotated by following a second
driving roller has a larger outer diameter than a first driven
roller. A front edge of a recording sheet being lifted up from a
first nip contacts the second driven roller, and hence the front
edge does not directly hit the first driven roller. The second
driven roller rotates at a higher rotational speed than a
rotational speed of the first driven roller. The second driven
roller gently flips the front edge of the recording sheet which has
contacted the second driven roller, and leads the front edge
quickly to the first nip. The front edge of the recording sheet is
smoothly led to the nip.
Inventors: |
Yamaguchi; Shunji;
(Kanagawa, JP) ; Hirashima; Shigeyoshi; (Kanagawa,
JP) |
Correspondence
Address: |
SONNENSCHEIN NATH & ROSENTHAL LLP
P.O. BOX 061080, WACKER DRIVE STATION, WILLIS TOWER
CHICAGO
IL
60606-1080
US
|
Assignee: |
SONY CORPORATION
Tokyo
JP
|
Family ID: |
42230200 |
Appl. No.: |
12/629291 |
Filed: |
December 2, 2009 |
Current U.S.
Class: |
271/10.11 |
Current CPC
Class: |
B65H 5/062 20130101;
B65H 2404/1416 20130101; B41J 13/03 20130101; G03G 2215/00409
20130101; G03G 15/657 20130101; B41J 13/076 20130101; B65H 2513/104
20130101; B65H 2401/11 20130101; G03G 2215/00413 20130101; G03G
2215/00679 20130101; B65H 2801/06 20130101; B65H 29/125 20130101;
B65H 2404/531 20130101; B65H 2801/12 20130101; B65H 2404/1115
20130101 |
Class at
Publication: |
271/10.11 |
International
Class: |
B65H 5/06 20060101
B65H005/06 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 5, 2008 |
JP |
2008-310503 |
Claims
1. A printer comprising: a driving roller conveyance mechanism and
a driven roller conveyance mechanism both arranged downstream of a
print section in a conveying direction of a sheet with a conveyance
path interposed between the driving roller conveyance mechanism and
the driven roller conveyance mechanism, wherein the driving roller
conveyance mechanism includes a first driving roller having an
outer circumferential surface made of a material having a large
friction coefficient, the first driving roller having a shaft
center extending in a direction orthogonal to the conveying
direction, a second driving roller having an outer circumferential
surface made of a material having a smaller friction coefficient
than the outer circumferential surface of the first driving roller,
the second driving roller being coaxial with the first driving
roller, a first driving mechanism configured to rotate the first
driving roller so that the sheet is conveyed toward a downstream
side in the conveying direction, and a second driving mechanism
configured to rotate the second driving roller at a higher
rotational speed than a rotational speed of the first driving
roller so that the sheet is conveyed toward the downstream side in
the conveying direction, wherein the driven roller conveyance
mechanism includes a rotatable first driven roller being in contact
with the first driving roller, the first driven roller having a
shaft center extending in the direction orthogonal to the conveying
direction, a rotatable second driven roller being in contact with
the second driving roller, the second driven roller having a shaft
center extending in the direction orthogonal to the conveying
direction, the second driven roller having a larger outer diameter
than the first driven roller, a first urging mechanism urging the
first driven roller in a direction in which the first driven roller
contacts the first driving roller, and a second urging mechanism
urging the second driven roller in a direction in which the second
driven roller contacts the second driving roller, and wherein the
second driven roller is formed of a spur roller having a toothed
part on an outer circumferential part of the second driven
roller.
2. The printer according to claim 1, wherein the first driving
mechanism includes a first drive shaft having a shaft center
extending in the direction orthogonal to the conveying direction,
wherein the first driving roller is attached to the first drive
shaft so that the first driving roller rotates with the first drive
shaft, wherein the second driving roller is rotatably supported by
the first drive shaft, wherein the second driving mechanism
includes a second drive shaft extending in parallel to the first
drive shaft, a first power transmission mechanism linking the first
drive shaft with the second drive shaft, and a second power
transmission mechanism linking the second drive shaft with the
second driving roller, and wherein at least one of the first power
transmission mechanism and the second power transmission mechanism
rotates the second driving roller at a higher rotational speed than
a rotational speed of the first drive shaft.
3. The printer according to claim 2, wherein the second driving
roller includes a plurality of second driving rollers provided at
an interval in a longitudinal direction of the first drive shaft,
and wherein the second driven roller includes a plurality of second
driven rollers corresponding to the plurality of second driving
rollers.
4. The printer according to claim 2, wherein the first driving
roller includes a plurality of first driving rollers provided at an
interval in a longitudinal direction of the first drive shaft,
wherein the second driving roller includes a plurality of second
driving rollers provided at a plurality of positions on the first
drive shaft not occupied by the first driving rollers, the second
driving rollers rotatably supported by the first drive shaft,
wherein the first driven roller includes a plurality of first
driven rollers corresponding to the plurality of first driving
rollers, and wherein the second driven roller includes a plurality
of second driven rollers corresponding to the plurality of second
driving rollers.
5. The printer according to claim 2, wherein the conveyance path
has a width orthogonal to the conveying direction, wherein the
second driving roller includes three second driving rollers
disposed at the center and both ends in a width direction of the
conveyance path, wherein the first driving roller includes two
first driving rollers disposed among the three second driving
rollers, at both sides of the center of the conveyance path,
wherein the first driven roller includes a plurality of first
driven rollers corresponding to the plurality of first driving
rollers, and wherein the second driven roller includes a plurality
of second driven rollers corresponding to the plurality of second
driving rollers.
6. The printer according to any of claims 1 to 5, wherein the
second urging mechanism provides a smaller urging force for urging
the second driven roller in the direction in which the second
driven roller contacts the second driving roller than an urging
force of the first urging mechanism for urging the first driven
roller in the direction in which the first driven roller contacts
the first driving roller.
7. The printer according to any of claims 1-5, wherein the outer
circumferential surface of the first driving roller is made of
rubber, and wherein the outer circumferential surface of the second
driving roller is made of synthetic resin having a smaller friction
coefficient than the rubber.
8. The printer according to any of claims 1-5, wherein the first
driven roller is formed of a spur roller having a toothed part on
an outer circumferential part of the first driven roller.
9. The printer according to any of claims 1-5, wherein the first
driving roller has an outer diameter equivalent to the second
driving roller.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a printer.
[0003] 2. Description of the Related Art
[0004] A recording sheet has to be conveyed at a constant speed
during printing in either of an inkjet printer or a thermal printer
that conveys a recording sheet to the position of a print head and
performs printing.
[0005] A recording sheet is typically conveyed by rotating a
plurality of pairs of conveying rollers provided in a recording
area.
[0006] Each pair of conveying rollers includes a driving roller
that is connected to a motor and rotates by itself, and a driven
roller that is pressed to the driving roller and rotates by
following the driving roller. When a recording sheet is pinched by
the driving roller and the driven roller, the recording sheet can
be conveyed. The rotational speed of the pair of conveying rollers
is controlled, so that the recording sheet is conveyed with high
precision.
[0007] However, when the front edge of the sheet enters a nip of
the pair of conveying rollers, the conveying speed of the recording
sheet may be temporarily decreased, and hence, the quality of an
image printed on the recording sheet may be degraded.
[0008] To prevent the conveying speed of the recording sheet from
being decreased, the following techniques have been suggested.
[0009] In the technique described in Japanese Unexamined Patent
Application Publication No. 2006-248670, the linear speed of a
registration roller is increased by rotation controlling means
immediately before the front edge of a sheet enters a fixing
section.
[0010] In the technique described in Japanese Unexamined Patent
Application Publication No. 7-271126, a conveyance guide plate is
provided. The conveyance guide plate is curved to cause a sheet to
form a smooth loop and arranged between upstream and downstream
pairs of conveying rollers. In addition, a pair of auxiliary
conveying rollers is provided in the middle of the conveyance guide
plate. The pair of auxiliary conveying rollers moves up and down in
accordance with the loosened and tensed states of the sheet.
[0011] In the technique described in Japanese Unexamined Patent
Application Publication No. 2003-306260, second conveying means is
provided downstream of first conveying means in a sheet conveying
direction. The second conveying means includes a plurality of
driven rollers at a plurality of positions different from one
another in the sheet conveying direction. The urging force applied
by a driven roller of the first conveying means to a sheet is
smaller than the urging force applied by the other driven
rollers.
SUMMARY OF THE INVENTION
[0012] Meanwhile, a recording sheet may warp due to the
manufacturing process or storage state of the recording sheet.
[0013] When the front edge of the warping sheet hits the
circumferential surfaces of the pair of conveying rollers, the
conveying speed of the recording sheet is temporarily decreased,
and an image printed on the recording sheet may have defects such
that lines appear and unevenness in printing frequently occurs.
[0014] Any of the techniques described above of the related art
does not consider about warping of a sheet. Thus, the techniques of
the related art are not sufficient for addressing the defects.
[0015] It is desirable to provide a printer that is advantageously
assure the quality of a printed image even when a warping sheet is
used.
[0016] A printer according to an embodiment of the present
invention includes a driving roller conveyance mechanism and a
driven roller conveyance mechanism both arranged downstream of a
print section in a conveying direction of a sheet with a conveyance
path interposed between the driving roller conveyance mechanism and
the driven roller conveyance mechanism. The driving roller
conveyance mechanism includes a first driving roller, a second
driving roller, a first driving mechanism, and a second driving
mechanism. The first driving roller has an outer circumferential
surface made of a material having a large friction coefficient. The
first driving roller has a shaft center extending in a direction
orthogonal to the conveying direction. The second driving roller
has an outer circumferential surface made of a material having a
smaller friction coefficient than the outer circumferential surface
of the first driving roller. The second driving roller is coaxial
with the first driving roller. The first driving mechanism is
configured to rotate the first driving roller so that the sheet is
conveyed toward a downstream side in the conveying direction. The
second driving mechanism is configured to rotate the second driving
roller at a higher rotational speed than a rotational speed of the
first driving roller so that the sheet is conveyed toward the
downstream side in the conveying direction. The driven roller
conveyance mechanism includes a rotatable first driven roller, a
rotatable second driven roller, a first urging mechanism, and a
second urging mechanism. The first driven roller is in contact with
the first driving roller. The first driven roller has a shaft
center extending in the direction orthogonal to the conveying
direction. The rotatable second driven roller is in contact with
the second driving roller. The second driven roller has a shaft
center extending in the direction orthogonal to the conveying
direction. The second driven roller has a larger outer diameter
than the first driven roller. The first urging mechanism urges the
first driven roller in a direction in which the first driven roller
contacts the first driving roller. The second urging mechanism
urges the second driven roller in a direction in which the second
driven roller contacts the second driving roller. The second driven
roller is formed of a spur roller having a toothed part on an outer
circumferential part of the second driven roller.
[0017] In the embodiment, the second driven roller and the second
driving roller can lead the front edge of the recording sheet to
the position at which the first driven roller and the first driving
roller pinch the recording sheet.
[0018] With this leading, the recording sheet receives
substantially no shock in the conveying direction. Accordingly, a
highly qualified printed result without lines or unevenness in
printing can be obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a cross-sectional view of a printer according to
an embodiment;
[0020] FIG. 2 is a perspective view of the printer without a print
head;
[0021] FIG. 3 is a perspective view of a primary portion of the
printer;
[0022] FIG. 4 is a cross-sectional view of a driving roller
conveyance mechanism;
[0023] FIG. 5 is an explanatory diagram illustrating the print head
and a sheet ejection section;
[0024] FIG. 6 is an enlarged view of the sheet ejection
section;
[0025] FIG. 7 illustrates rotation loci of spur rollers of first
and second driven rollers;
[0026] FIG. 8 illustrates the state in which the front edge of a
recording sheet is near the sheet ejection section;
[0027] FIG. 9 illustrates the state in which the front edge of the
recording sheet is in contact with a spur;
[0028] FIG. 10 illustrates the state in which the front edge of the
recording sheet is being led to a nip by the second driven
roller;
[0029] FIG. 11 illustrates the state in which the front edge of the
recording sheet is being pinched at the nip; and
[0030] FIG. 12 illustrates the state in which the front edge of the
recording sheet has passed through the nip.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] An embodiment of the present invention will be described
below with reference to the attached drawings.
[0032] First, the basic structure of a printer 10 according to this
embodiment will be described.
[0033] FIG. 1 is a cross-sectional view of the printer 10 according
to this embodiment.
[0034] FIG. 2 is a perspective view of the printer 10 without a
print head 20. FIG. 3 is a perspective view of a primary portion of
the printer 10.
[0035] Referring to FIG. 1, the printer 10 of this embodiment is an
inkjet printer. The printer 10 performs printing by discharging ink
from a fixed print head 20 onto a recording sheet 2A that is fed
from a recording sheet roll 2.
[0036] The printer 10 does not have to be an inkjet printer, and
may be, for example, a sublimation printer or the like in related
art. The printer 10 does not have to use a recording sheet roll,
and may use previously cut recording sheets having a predetermined
size.
[0037] Referring to FIG. 1, the printer 10 includes a case 12. The
printer 10 also includes a recording sheet roll container 14, a
sheet feed section 16, a sheet ejection section 18, a print section
19, a cutter device 24, and a motor 26 (FIG. 2), these components
being arranged in the case 12.
[0038] In FIG. 1, a conveyance path 4 extends in a horizontal
plane. The recording sheet 2A pulled from the recording sheet roll
2 is conveyed through the conveyance path 4.
[0039] Guide plates 4A and 4B are arranged upstream of the print
head 20 in a conveying direction A of the recording sheet 2A. The
guide plates 4A and 4B respectively guide the upper surface
(surface to be printed) and the lower surface (back surface) of the
recording sheet 2A.
[0040] The sheet feed section 16 conveys the recording sheet 2A
pulled from the recording sheet roll 2 to the print section 19. The
print section 19 performs printing on the recording sheet 2A. Then,
the sheet ejection section 18 conveys the printed recording sheet
2A to the cutter device 24. The cutter device 24 cuts the recording
sheet 2A into a sheet having a predetermined size. The cut
recording sheet 2A is ejected through an ejection port 1202 that is
provided in the case 12, and the recording sheet 2A is ejected onto
a sheet ejection tray or the like disposed outside the case 12.
[0041] In FIG. 1, guide plates 4C and 4D are arranged upstream of
the cutter device 24 in the conveying direction A. The guide plates
4C and 4D respectively guide the upper surface (surface to be
printed) and the lower surface (back surface) of the recording
sheet 2A.
[0042] The recording sheet roll container 14 contains and holds the
recording sheet roll 2 so that the recording sheet roll 2 is
rotatable, by using a recording sheet roll supporting device of
related art.
[0043] The sheet feed section 16 feeds the recording sheet 2A to
the print section 19. The recording sheet 2A is pulled from the
recording sheet roll 2 contained in the recording sheet roll
container 14.
[0044] Referring to FIG. 2, the sheet feed section 16 includes a
sheet feed roller 32 and a pinch roller 34 arranged with the
conveyance path 4 interposed therebetween. The sheet feed roller 32
and the pinch roller 34 convey the recording sheet 2A toward the
downstream side in the conveying direction A along the conveyance
path 4.
[0045] The sheet feed section 16 includes a drive shaft 30 linked
to the motor 26 through a belt pulley mechanism 36. The drive shaft
30 extends in a direction orthogonal to the conveying direction A.
The sheet feed roller 32 is attached to the drive shaft 30 so that
the sheet feed roller 32 rotates with the drive shaft 30.
[0046] The pinch roller 34 is opposite to the sheet feed roller 32
with respect to the conveyance path 4. The pinch roller 34 includes
a plurality of pinch rollers 34 provided at an interval in the
direction orthogonal to the conveying direction A of the recording
sheet 2A.
[0047] That is, the sheet feed roller 32 is disposed below the
conveyance path 4. The pinch rollers 34 are disposed above the
conveyance path 4.
[0048] The pinch rollers 34 are respectively supported by one ends
of arms 38 to be rotatable around an axis parallel to the drive
shaft 30.
[0049] An intermediate portion of each of the arms 38 is supported
swingably around a spindle 40. An urging member 42, such as an
extension spring, is stretched between the case 12 and another end
of each arm 38. The urging member 42 urges the outer
circumferential surface of the corresponding pinch roller 34 in a
direction in which the outer circumferential surface of the pinch
roller 34 contacts the outer circumferential surface of the sheet
feed roller 32.
[0050] Thus, the power of the motor 26 rotates the drive shaft 30
and the sheet feed roller 32. The pinch rollers 34 are rotated by
following the conveyance of the recording sheet 2A while the pinch
rollers 34 and the sheet feed roller 32 pinch the recording sheet
2A.
[0051] Referring to FIG. 1, the print section 19 includes the print
head 20 and a table 22 for printing.
[0052] The print head 20 is arranged downstream of the sheet feed
section 16 in the conveying direction A. The print head 20 is
disposed above the conveyance path 4.
[0053] The print head 20 includes ink discharge nozzles 20Y, 20M,
20C, and 20K that respectively discharge inks of yellow, magenta,
cyan, and black on a surface to be printed of the recording sheet
2A.
[0054] The ink discharge nozzles 20Y, 20M, 20C, and 20K are
arranged in order from the upstream side toward the downstream side
in the conveying direction A of the recording sheet 2A.
[0055] The print head 20 is a line head. The ink discharge nozzles
20Y, 20M, 20C, and 20K linearly extend in the direction orthogonal
to the conveying direction A of the recording sheet 2A. That is,
the ink discharge nozzles 20Y, 20M, 20C, and 20K linearly extend
over the entire length in the width direction of a recording sheet
2A having a maximum printable size. In other words, the ink
discharge nozzles 20Y, 20M, 20C, and 20K linearly extend over the
entire length in the width direction of the conveyance path 4.
[0056] Referring to FIG. 1, the table 22 for printing is opposite
to the print head 20 with respect to the conveyance path 4. In
other words, the table 22 for printing is arranged below the
conveyance path 4.
[0057] Referring to FIGS. 2 and 3, the table 22 for printing
includes an ink absorber 44 and a plurality of guide ribs 46.
[0058] The ink absorber 44 is a rectangular plate extending in the
conveying direction A of the recording sheet 2A and in the width
direction. The ink absorber 44 is made of a material that absorbs
ink. An upper surface 4402 of the ink absorber 44 is a flat
plane.
[0059] The ink absorber 44 absorbs ink dropped from the print head
20, ink discharged from the print head 20 when the recording sheet
2A is not provided below the print head 20, suspended ink mist,
etc., to prevent the recording sheet 2A from being contaminated
with ink.
[0060] The plurality of guide ribs 46 guide the back surface of the
recording sheet 2A in the conveying direction A.
[0061] The plurality of guide ribs 46 protrude upward from the
upper surface 4402 of the ink absorber 44 through a plurality of
openings formed in the ink absorber 44. The tops of the guide ribs
46 are located in a common flat plane parallel to the horizontal
plane.
[0062] The plurality of guide ribs 46 provide a gap between the
back surface of the recording sheet 2A and the ink absorber 44.
Thus, ink absorbed by the ink absorber 44 can be prevented from
adhering on the back surface of the recording sheet 2A.
[0063] Referring to FIG. 1, the cutter device 24 cuts in the width
direction the recording sheet 2A conveyed by the sheet ejection
section 18 after the print section 19 performs printing.
[0064] The cutter device 24 may use a structure of related art,
such as a roller-type cutter or a slide-type cutter.
[0065] Next, the sheet ejection section 18, which is a feature of
the present invention, will be described below in detail.
[0066] FIG. 4 is a cross-sectional view of a driving roller
conveyance mechanism 50. FIG. 5 is an explanatory diagram
illustrating the print head 20 and the sheet ejection section 18.
FIG. 6 is an enlarged view of the sheet ejection section 18.
[0067] Referring to FIGS. 2 and 3, the sheet ejection section 18
includes a driving roller conveyance mechanism 50 and a driven
roller conveyance mechanism 52 both arranged downstream of the
print section 19 in the conveying direction A of the recording
sheet 2A with the conveyance path 4 interposed therebetween.
[0068] Referring to FIG. 3, the driving roller conveyance mechanism
50 is arranged below the conveyance path 4. The driven roller
conveyance mechanism 52 is arranged above the conveyance path
4.
[0069] The driving roller conveyance mechanism 50 includes a first
driving roller 54, a second driving roller 56, a first driving
mechanism 58, and a second driving mechanism 60.
[0070] The outer circumferential surface of the first driving
roller 54 is made of a material having a large friction
coefficient. The first driving roller 54 has the shaft center
extending in the direction orthogonal to the conveying direction
A.
[0071] The outer circumferential surface of the first driving
roller 54 is made of, for example, rubber.
[0072] The first driving mechanism 58 rotates the first driving
roller 54 so that the recording sheet 2A is conveyed toward the
downstream side in the conveying direction A.
[0073] Referring to FIGS. 3 and 4, the first driving mechanism 58
includes a first drive shaft 62 having the shaft center extending
in the direction orthogonal to the conveying direction A. The first
driving roller 54 is attached to the first drive shaft 62 so that
the first driving roller 54 rotates with the first drive shaft
62.
[0074] Referring to FIG. 2, the first drive shaft 62 is linked to
the drive shaft 30 through a belt pulley mechanism 64, and hence
rotated by the motor 26.
[0075] In this embodiment, referring to FIGS. 3 and 4, the first
driving roller 54 includes a plurality of first driving rollers 54
provided at an interval in the longitudinal direction of the first
drive shaft 62.
[0076] The outer circumferential surface of the second driving
roller 56 is made of a material having a smaller friction
coefficient than the outer circumferential surfaces of the first
driving rollers 54. The second driving roller 56 is coaxial with
the first driving rollers 54.
[0077] The outer circumferential surface of the second driving
roller 56 is made of, for example, synthetic resin such as
polyacetal resin (POM).
[0078] In this embodiment, referring to FIGS. 3 and 4, the second
driving roller 54 includes a plurality of second driving rollers 56
provided at a plurality of positions on the first drive shaft 62
not occupied by the first driving rollers 54. The second driving
rollers 56 are rotatably supported by the first drive shaft 62.
[0079] To be more specific, three second driving rollers 56 are
provided at the center and both ends in the width direction of the
conveyance path 4. Two first driving rollers 54 are provided among
the three second driving rollers 56, at both sides of the center of
the conveyance path 4.
[0080] The outer diameter of the first driving rollers 54 and the
outer diameter of the second driving rollers 56 may be equivalent
to one another or may be different from one another. The equivalent
diameters of the first and second driving rollers 54 and 56 are
advantageous to smoothly convey the recording sheet 2A.
[0081] The second driving mechanism 60 rotates the second driving
rollers 56 at a higher rotational speed than the rotational speed
of the first driving rollers 54 so that the recording sheet 2A is
conveyed toward the downstream side in the conveying direction
A.
[0082] Referring to FIG. 3, the second driving mechanism 60
includes a second drive shaft 66, a first power transmission
mechanism 68, and a second power transmission mechanism 70.
[0083] The second drive shaft 66 extends in parallel to the first
drive shaft 62.
[0084] The first power transmission mechanism 68 links the first
drive shaft 62 with the second drive shaft 66.
[0085] In this embodiment, the first power transmission mechanism
68 is formed of a belt pulley mechanism 6808 including a pulley
6802 attached to the first drive shaft 62, a pulley 6804 attached
to the second drive shaft 66, and a belt 6806 hung over the pulleys
6802 and 6804.
[0086] The second power transmission mechanism 70 links the second
drive shaft 66 with the corresponding second driving roller 56.
[0087] In this embodiment, referring to FIGS. 3 and 4, a
small-diameter part 5602 is formed at an end in the longitudinal
direction of each second driving roller 56. A pulley 7002 is
attached to the second drive shaft 66 at a position corresponding
to the small-diameter part 5602.
[0088] Also, a belt 7004 is hung over the small diameter part 5602
of the second driving roller 56 and the pulley 7002. Thus, the
second power transmission mechanism 70 includes the small-diameter
part 5602, the pulley 7002, and the belt 7004.
[0089] At least one of the first power transmission mechanism 68
and the second power transmission mechanism 70 rotates the second
driving rollers 56 at a higher rotational speed than the rotational
speed of the first drive shaft 62.
[0090] In this embodiment, the pulley 7002 has a larger outer
diameter than the small-diameter part 5602. Thus, the second
driving rollers 56 rotate at a higher rotational speed than the
rotational speed of the first drive shaft 62.
[0091] Accordingly, a second driven roller 74 rotates at a higher
rotational speed than the rotational speed of a first driven roller
72 (described below in detail). In this embodiment, when the second
driven roller 74 directly contacts the corresponding second driving
roller 56 and hence the second driven roller 74 is rotated, the
rotational speed of the second driven roller 74 is about 1.2 to 1.5
times the rotational speed of the first driven roller 72.
[0092] Referring to FIGS. 3, 5, and 6, the driven roller conveyance
mechanism 52 includes the first driven roller 72, the second driven
roller 74, a first urging mechanism, and a second urging
mechanism.
[0093] The first driven roller 72 is in contact with the first
driving roller 54, has the shaft center in the direction orthogonal
to the conveying direction A, and is rotatable.
[0094] In this embodiment, the first driven roller 72 is a spur
roller having a toothed part on an outer circumferential part of
the first driven roller 72.
[0095] The first driven roller 72 includes a plurality of first
driven rollers 72 corresponding to the plurality of first driving
rollers 54.
[0096] In this embodiment, two first driven rollers 72 are provided
for every first driving roller 54.
[0097] Each second driven roller 74 is in contact with the
corresponding second driving roller 56, has the shaft center
extending in the direction orthogonal to the conveying direction A,
has a larger outer diameter than the first driven roller 72, and is
rotatable.
[0098] In this embodiment, the second driven roller 74 is a spur
roller having a toothed part on an outer circumferential part of
the second driven roller 74.
[0099] The second driven roller 74 includes a plurality of second
driven rollers 74 corresponding to the plurality of second driving
rollers 56.
[0100] In this embodiment, the second driven rollers 74 are
respectively provided for the three second driving rollers 56 one
by one.
[0101] The first urging mechanism urges each first driven roller 72
in a direction in which the first driven roller 72 contacts the
corresponding first driving roller 54.
[0102] The second urging mechanism urges each second driven roller
74 in a direction in which the second driven roller 74 contacts the
corresponding second driving roller 56.
[0103] The second driving roller 56 and the second driven roller 74
lead a front edge 2B of the recording sheet 2A being in contact
with the second driven roller 74 to a first nip 80, which will be
described below.
[0104] The urging force for urging the second driven roller 74 to
the second driving roller 56 is smaller than the urging force for
urging the first driven roller 72 to the first driving roller 54.
Thus, the conveyance of the recording sheet 2A by the first driving
roller 54 and the first driven roller 72 is stabilized.
[0105] The first and second urging members may use any of various
structures of related art, such as the arms 38, the spindle 40, and
the urging members 42, which have been described above in the
description for the pinch rollers 34.
[0106] Now, the operation of the printer 10 will be described.
[0107] Referring to FIGS. 1 and 5, assume that the recording sheet
2A pulled from the recording sheet roll container 14 is pinched
between the sheet feed roller 32 and the pinch rollers 34 in
advance.
[0108] In this state, when the motor 26 rotates the sheet feed
roller 32 with the drive shaft 30, the sheet feed section 16
conveys the recording sheet 2A to the print section 19 at a
constant conveying speed.
[0109] When the recording sheet 2A reaches the print section 19,
the ink discharge nozzles 20Y, 20M, 20C, and 20K eject inks on the
surface to be printed of the recording sheet 2A and thus an image
is printed on the surface of the recording sheet 2A.
[0110] Referring to FIG. 5, when the front edge 2B of the recording
sheet 2A reaches the sheet ejection section 18, the recording sheet
2A is conveyed by the sheet feed section 16 and the sheet ejection
section 18 continuously at the constant conveying speed, and in
this conveying state, the print section 19 performs printing.
[0111] Referring to FIG. 1, the sheet ejection section 18 ejects
the recording sheet 2A after printing through the ejection port
1202. The cutter device 24 cuts the recording sheet 2A into a
predetermined size. The cut recording sheet 2A is ejected onto a
sheet ejection tray.
[0112] Next, the operation of the sheet ejection section 18 will be
described below in detail.
[0113] FIG. 7 illustrates rotation loci of the spur rollers of the
first and second driven rollers 72 and 74. FIG. 8 illustrates the
state in which the front edge 2B of the recording sheet 2A is near
the sheet ejecting section 18. FIG. 9 illustrates the state in
which the front edge 2B of the recording sheet 2A is in contact
with a spur. FIG. 10 illustrates the state in which the front edge
2B of the recording sheet 2A is being led to the nip 80 by the
second driven roller 74. FIG. 11 illustrates the state in which the
front edge 2B of the recording sheet 2A is being pinched at the nip
80. FIG. 12 illustrates the state in which the front edge 2B of the
recording sheet 2A has passed through the nip 80.
[0114] In FIGS. 7 to 11, reference numeral 80 denotes a first nip
at which the first driven roller 72 and the first driving roller 54
pinch the recording sheet 2A, and reference numeral 82 denotes a
second nip at which the second driven roller 74 and the second
driving roller 56 pinch the recording sheet 2A.
[0115] Referring to FIGS. 5, 6, and 8, a case will be described in
which the recording sheet 2A with the entire front edge 2B in the
width direction warping upward enters the sheet ejection section
18.
[0116] Referring to FIG. 9, the front edge 2B of the recording
sheet 2A contacts the second driven roller 74.
[0117] The second driven roller 74 has a larger outer diameter than
the first driven roller 72, as indicated by the rotation locus of
the addendum (tip part) of the gear of each spur roller defining
the second driven roller 74 in FIG. 7.
[0118] Thus, the front edge 2B of the recording sheet 2A lifted up
from the first nip 80 contacts the second driven roller 74. Hence,
the front edge 2B does not directly hit the first driven roller
72.
[0119] In addition, the rotational speed of the second driven
roller 74 is higher than the rotational speed of the first driven
roller 72. Thus, the circumferential speed of the second driven
roller 74 is higher than the circumferential speed of the first
driven roller 72.
[0120] The second driven roller 74 gently flips the front edge 2B
of the recording sheet 2A which has contacted the second driven
roller 74, and leads the front edge 2B quickly to the first nip
80.
[0121] The recording sheet 2A receives substantially no shock. The
front edge 2B is smoothly led to the first nip 80.
[0122] As the second driven roller 74 has a larger diameter, a
direction of a force acting on the front edge 2B when the front
edge 2B has contacted the second driven roller 74 can be closer to
the conveying direction A of the recording sheet 2A. This
arrangement is advantageous to smoothly lead the front edge 2B.
[0123] In this embodiment, the urging force for urging the second
driven roller 74 to the second driving roller 56 is smaller than
the urging force for urging the first driven roller 72 to the first
driving roller 54.
[0124] Hence, the second driven roller 74 has a small moment of
inertia. Thus, the force applied to the front edge 2B of the
recording sheet 2A which has contacted the second driven roller 74
becomes smaller than the force applied by the first driven roller
72 to cause the recording sheet 2A to be conveyed in the conveying
direction A. Therefore, this arrangement is advantageous to
stabilize the conveyance of the recording sheet 2A by the first
driving roller 54 and the first driven roller 72.
[0125] Then, referring to FIG. 10, the front edge 2B of the
recording sheet 2A reaches the first nip 80 because of leading with
the second driven roller 74.
[0126] In this embodiment, the first driving roller 54 has the
outer diameter equivalent to the outer diameter of the second
driving roller 56.
[0127] The first nip 80 and the second nip 82 are located along a
line in the width direction of the recording sheet 2A.
[0128] Thus, theoretically, the front edge 2B of the recording
sheet 2A does not contact the teeth of the first driven roller 72
until the front edge 2B reaches the first nip 80 by leading with
the second driven roller 74.
[0129] Referring to FIG. 11, the recording sheet 2A attains a
designed sheet passage state at the first nip 80. The first driving
roller 54 and the first driven roller 72 bite the front edge 2B of
the recording sheet 2A.
[0130] The recording sheet 2A is pinched by the first driving
roller 54 and the first driven roller 72 with a sufficient nip
pressure and further conveyed toward the downstream side.
[0131] In particular, the recording sheet 2A is pinched by the
first driving roller 54 and the first driven roller 72 at the first
nip 80, and at the same time, the recording sheet 2A is pinched by
the second driving roller 56 and the second driven roller 74 at the
second nip 82.
[0132] The outer circumferential surface of the second driving
roller 56 is made of a material having a smaller friction
coefficient than the outer circumferential surface of the first
driving roller 54. Thus, the second driving roller 56 is idly
rotated even when the second driving roller 56 contacts the
recording sheet 2A. The second driven roller 74 is rotated by
following the conveyance of the recording sheet 2A.
[0133] Hence, the conveying force applied by the second driving
roller 56 and the second driven roller 74 to the recording sheet 2A
is substantially negligible. Therefore, this arrangement is
advantageous to maintain the conveying speed to be constant without
an adverse effect for the conveying operation of the recording
sheet 2A applied by the first driving roller 54 and the first
driven roller 72.
[0134] With this embodiment, the second driven roller 74 and the
second driving roller 56 lead the front edge 2B of the recording
sheet 2A to the first nip 80 at which the first driven roller 72
and the first driving roller 54 pinch the recording sheet 2A. Thus,
the recording sheet 2A receives substantially no shock in the
conveying direction A.
[0135] The conveying speed of the recording sheet 2A can be
prevented from being temporarily decreased. The unstable conveyance
can be prevented during printing. Accordingly, this embodiment is
advantageous to obtain a highly qualified printed result without
lines or unevenness in printing.
[0136] Also, the recording sheet 2A can be prevented from being
stacked. Malfunction of the printer 10 can be prevented, and the
recording sheet 2A is not wasted. This embodiment is advantageous
to increase the commercial value of the printer 10.
[0137] Further, in this embodiment, since the first driven roller
72 and the second driven roller 74 are formed of the spur rollers
having the toothed parts on the outer circumferential parts
thereof, ink does not adhere onto the recording sheet 2A although
the first driven roller 72 and the second driven roller 74 contact
the surface to be printed of the recording sheet 2A.
[0138] Thus, the situation, in which the ink adhering on the first
driven roller 72 and the second driven roller 74 is transferred
onto the surface to be printed of the recording sheet 2A and the
surface to be printed is contaminated because of the transferred
ink, can be prevented. In particular, this embodiment is
advantageous when the print head 20 is an inkjet print head.
[0139] The present application contains subject matter related to
that disclosed in Japanese Priority Patent Application JP
2008-310503 filed in the Japan Patent Office on Dec. 5, 2008, the
entire content of which is hereby incorporated by reference.
[0140] It should be understood by those skilled in the art that
various modifications, combinations, sub-combinations and
alterations may occur depending on design requirements and other
factors insofar as they are within the scope of the appended claims
or the equivalents thereof.
* * * * *