Information
-
Patent Grant
-
6371479
-
Patent Number
6,371,479
-
Date Filed
Thursday, February 24, 200024 years ago
-
Date Issued
Tuesday, April 16, 200222 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 399 401
- 399 402
- 271 303
- 271 161
- 271 225
- 271 184
- 271 185
- 271 186
- 271 188
- 271 209
- 271 902
-
International Classifications
-
Abstract
A switchback device has an inverting tray for temporarily holding a sheet guided inside the switchback device thereon; a guide unit for guiding the sheet in pressing contact with the inverting tray when the sheet exits the switchback device in an exiting direction on the inverting tray, the exiting direction opposite to an entering direction of the sheet on the inverting tray; a guide switching unit for selectively changing the guide unit to a sheet guide allow state to allow the sheet to enter in the entering direction on the inverting tray and a sheet pressing state to make the sheet in pressing contact with the inverting; and a sheet transporting unit for transporting the sheet out of the switchback device in the exiting direction on the inverting tray.
Description
This application is based on patent application Nos. 11-47740 and 11-47741 filed in Japan, the contents of which are hereby incorporated by references.
BACKGROUND OF THE INVENTION
This invention relates to a switchback device for use in image forming apparatus such as copiers, laser printers, and facsimile machines, and particularly to a switchback device for use in image forming apparatus in the technical field of electrophotography.
FIG. 9
is a diagram of a switchback device of prior art for use in an image forming apparatus. Hereinafter, a conventional switchback device is described referring to FIG.
9
. The conventional switchback device
7
comprises: a tray
73
; a sheet transporting unit
74
including a switchback roller
741
, a switchback roller driver (not shown), a movable arm
742
, an arm shaft
743
, a solenoid
744
, an arm bias member
745
, and a spring
746
; and a sheet slapping unit
75
including a guide member
751
, a guide shaft
752
, a solenoid
753
, a guide bias member
754
, and a spring
755
.
An operation of the switchback device
7
is described. When the switchback device
7
is in a stand-by state, a rotation of the switchback roller
741
is suspended. In this state, the switchback roller
741
is set to a retracted state above the tray
73
, and the guide member
751
is also set to a retracted state (shown by the broken line in FIG.
9
).
When a sheet P is transported from an upstream-located path
24
with respect to a sheet transport direction of the image forming apparatus inside the switchback device
7
, an inlet guide roller pair
241
,
242
is driven to transport the sheet P in a sheet entering direction shown by the solid arrow → on the tray
73
. When the lead end of the sheet P in the entering direction is about to slide under the switchback roller
741
, the switchback roller
741
is pivoted downward to come into contact with the sheet P on the tray
73
and guides the sheet P on the tray
73
further in the entering direction (rightward direction in
FIG. 9
) by transmitting a counterclockwise rotational driving force of the switchback roller
741
in
FIG. 9
to the sheet P which is in contact with the switchback roller
741
. When the entirety of the sheet P is guided inside the switchback device
7
, the solenoid
753
is turned on, and the guide bias member
754
is changed from the broken-line state in
FIG. 9
to the solid-line state shown in
FIG. 9
against the spring force of the spring
755
. When the guide bias member
754
is set to the solid-line state, the guide member
751
is pivoted downward about the axis of the guide shaft
752
due to the weight thereof, thereby slapping a portion of the sheet P, which is certain distance away from a tail end thereof, while the sheet P is guided in the entering direction onto the tray
73
. In this way, the sheet P lands on the tray
73
. Then the guide member
751
is pivoted upward to resume its broken line state.
Subsequently, the switchback roller
741
is rotated in the reverse direction (clockwise direction in
FIG. 9
) to transport the sheet P in exiting direction on the tray
73
(shown by the arrow ← in
FIG. 9
) toward an outlet guide roller pair
251
,
252
disposed on a downstream-located path
25
with respect to the sheet transport direction of the image forming apparatus. Thus, the sheet P exits the switchback device
7
by the outlet guide roller pair
251
,
252
.
In the above conventional switchback device, the following problem is involved due to the fact that the image forming apparatus is loaded with a fixing unit. In the case where the tail end of the sheet P in the entering direction (namely, the lead end of the sheet P in the exiting direction) has a curled or warped portion, it is difficult to transport the sheet P having the curled portion properly into the downstream-located path
25
via the switchback device
7
. A sheet jam or a folded corner end of the sheet P may likely occur when the sheet P is transported in and out of the switchback device
7
.
Further, the sheet slapping operation in which the guide member
751
slaps the portion of the sheet P, which is certain distance away from the tail end thereof, against the tray
73
requires a fine adjustment of the timing to promptly transport the sheet P guided from the upstream-located path
24
toward the downstream-located path
25
. The sheet transporting unit
74
is an essential element in the conventional switchback device
7
in association with the driving mechanism of moving the switchback roller
741
toward and away from the tray
73
in order to guide the sheet P in and out of the switchback device
7
. The conventional switchback device
7
provided with these elements is required to have a complex structure and increases the production cost of the image forming apparatus due to the complex mechanism of accomplishing the sheet slapping operation in combination with driving the switchback roller
741
toward and away from the tray
73
.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a switchback device that enables to accurately transport a sheet downstream with respect to a sheet transport direction while carrying out a switchback operation without a possibility of causing a sheet jam or a folded corner end of the sheet even if the sheet has a curled or warped portion.
According to an aspect of this invention, the switchback device focusing an image forming apparatus comprises: an inverting tray for temporarily holding a sheet guided inside the switchback device thereon; a guide unit for guiding the sheet in pressing contact with the inverting tray when the sheet is transported in an exiting direction on the inverting tray, the exiting direction being opposite to an entering direction of the sheet on the inverting tray; a guide switching unit for selectively changing the guide unit to a sheet guide allow state to allow the sheet to enter the switchback device in the entering direction on the inverting tray and a sheet pressing state to make substantially an end of the sheet in the exiting direction in pressing contact with the inverting tray; and a sheet transporting unit for transporting the sheet out of the switchback device in the exiting direction on the inverting tray.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a schematic diagram of a switchback device incorporated in an image forming apparatus according to an embodiment of this invention,
FIG. 2
is a diagram illustrating a construction of the switchback device,
FIG. 3
is a perspective view of the switchback device,
FIGS. 4A
to
4
C are schematic diagrams showing a sequential operation of the switchback device,
FIGS. 5A and 5B
are diagrams illustrating an upper guide member and an inverting tray of the switchback device in which
FIG. 5A
shows a state that a sheet is in pressing contact with the upper guide member and the inverting tray, and
FIG. 5B
shows a positional relation between upper and lower ribs of the upper guide member and the inverting tray,
FIGS. 6 and 7
are schematic diagrams of a switchback device of an altered arrangement according to this invention,
FIGS. 8A
to
8
D are schematic diagrams showing a sequential operation of the switchback device of the altered arrangement, and
FIG. 9
is a schematic diagram of a switchback device according to prior art.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
FIG. 1
is a diagram illustrating an image forming apparatus incorporated with a switchback device embodying the present invention. An operation of the switchback device when the image forming apparatus implements a double-sided image formation is described referring to FIG.
1
.
Sheets accommodated in a sheet cassette
1
are dispensed one by one by a feed roller
11
, and the uppermost sheet P stacked in the sheet cassette
1
is transported into a transport path
21
, has its transport temporarily suspended when the lead end of the sheet P in a sheet transport direction reaches a registration roller pair
3
, and then is transported downstream in the sheet transport direction at a certain timing toward an image forming section
4
. When the sheet P is carried to the image forming section
4
, a toner image is transferred onto one surface (first surface) of the sheet P by a transfer unit
45
. The sheet P carrying the toner image is transported to a nip portion defined by a heater roller
51
and a presser roller
52
of a fixing unit
5
while transported along a transport path
23
. While the sheet P passes the nip portion, the toner image on the first surface of the sheet P is fixed by the fixing unit
5
. Then, the sheet P after the one side image formation is guided to a switchback device
7
via a transport path
24
by an operation of a switching device
6
for a switchback operation. After carried into the switchback device
7
, the sheet P has its transport direction reversed and is transported to a transport path
25
. In this way, the switchback operation is completed. Then, the sheet P after the one side image formation is transported to the registration roller pair
3
again via a transport path
26
. Upon the lead end of the sheet P reaching the registration roller pair
3
, the sheet P has its transport temporarily suspended thereat with the lead end of the sheet P nipped by the registration roller pair
3
, and then is transported to the image forming section
4
again at a certain timing for the opposite side image formation. When the sheet P is carried into the image forming section
4
again, a toner image is transferred onto the opposite side (second surface) of the sheet P by the transfer unit
45
. The sheet P carrying the toner image on the opposite side thereof is transported to the fixing unit
5
again via the transport path
23
where the toner image on the opposite side of the sheet P is fixed while the sheet P passes the nip portion of the heater roller
51
and the presser roller
52
of the fixing unit
5
. The sheet P thus completed with the double-sided image formation is discharged onto a discharge tray
9
via a discharge section by an operation of the switching device
6
.
FIG. 2
is a diagram showing a construction of the switchback device incorporated in the image forming apparatus in this embodiment.
FIG. 3
is a perspective view of the switchback device. The construction of the switchback device is described in detail referring to
FIGS. 2 and 3
.
The switchback device
7
includes a presser guide unit
71
(functioning as a guide unit), a presser guide switching unit
72
(functioning as a guide switching unit), an inverting tray
73
, and a sheet transporting unit
74
. The presser guide unit
71
has an upper guide member
711
, a guide shaft
712
, and a guide arm
713
(namely, a pair of guide arms
713
a
,
713
b
as shown in FIG.
3
). The presser guide switching unit
72
has a presser solenoid
721
and a presser spring
722
. The sheet transporting unit
74
has a switchback roller
741
, a switchback roller driver
78
, a pivotal arm
742
, an arm shaft
743
, a solenoid
744
, an arm bias member
745
, and a spring
746
.
Specifically, the upper guide member
711
of the presser guide unit
71
is switchingly set to a sheet guide allow state (shown by the broken line in
FIG. 1
) where the upper guide member
711
is rotated in a clockwise direction from a horizontal plane and a sheet pressing state (shown by the solid line in
FIGS. 1 & 2
) where the upper guide member
711
covers a left hand portion of a sheet transport plane
731
of the inverting tray
73
from above and maintains a certain clearance therebetween. The sheet pressing state of the upper guide member
711
is set by a downward pivotal movement of the upper guide member
711
about an axis of the guide shaft
712
which is driven by the presser guide switching unit
72
. The operation of the presser guide unit
71
is described below in detail.
The above clearance has such a height as to smoothly pass a sheet of a standardized size available on the market and to correct a curl or warp on the surface of the sheet properly, if any, by the time when the sheet is transported to a downstream-located path
25
disposed on a downstream side in the sheet transport direction out of the switchback device
7
. In view of the above, it is preferable to set the clearance between 1 mm to 5 mm.
As shown in
FIG. 3
, the lower surface of the upper guide member
711
which is brought into pressing contact with the sheet P when the upper guide member
711
is set to the sheet pressing state is formed with a series of downwardly projecting upper ribs
713
r
arrayed substantially in parallel to the sheet transport direction on the inverting tray
73
at a certain interval in the width direction of the upper guide member
711
(direction normal to the plane of FIGS.
1
and
2
). The upper ribs
713
r
are provided to smoothly transport the sheet P on the inverting tray
73
when the upper guide member
711
is set to the sheet pressing state.
Similar to the above arrangement, the sheet transport plane
731
of the inverting tray
73
is formed with a series of upwardly projecting lower ribs
733
r
arrayed substantially in parallel to the sheet transport direction at a certain interval in the width direction of the upper guide member
711
. The lower ribs
733
are provided to smoothly transport the sheet P on the inverting tray
73
in combination with the upper ribs
713
when the upper guide member
711
is set to the sheet pressing state.
FIGS. 5A and 5B
are schematic diagrams illustrating the construction of the upper guide member
711
and the inverting tray
73
.
FIG. 5A
shows a state that a sheet P is transported in the clearance defined by the upper guide member
711
and the inverting tray
73
when the upper guide member
711
is set to a sheet pressing state.
FIG. 5B
shows the construction of the upper and lower ribs
713
r
,
733
r
in
FIG. 5A
with the sheet P omitted to clarify the positional relation of the upper and lower ribs
713
r
,
733
r.
As shown in
FIG. 5B
, the width d
1
of the upper rib
713
and the width d
2
of the lower rib
733
are both set in the range of 0.5 mm to 4 mm. Preferably, the width d
1
(d
2
) is set in the range of 1.5 mm to 2.0 mm. The distal ends of the upper ribs
713
(lower ribs
733
) are shaped into a U-shape in section with the radius of curvature in the range of 0.25 mm to 2.0 mm. Preferably, the radius of curvature is in the range of 0.75 mm to 1.0 mm.
The upper ribs
713
r
(lower ribs
733
r
) are arrayed at an interval of 40 mm to 60 mm in the width direction of the upper guide member
711
(left and right directions in FIG.
5
). Preferably, the interval w
1
between the adjacent upper ribs
713
r
and the interval w
2
between the adjacent lower ribs
733
r
are both set at 50 mm. The upper and lower ribs
713
r
,
733
r
are alternately arrayed in the width direction of the upper guide member
711
.
The height h
1
of the upper ribs
713
r
and the height h
2
of the lower ribs
733
r
are both set at 5 mm. The vertical dimension h
3
overlapping the upper and lower ribs
713
r
,
733
r
is in the range of 1.5 mm to 4.5 mm. Preferably, the dimension h
3
is from 2.5 mm to 3.5 mm. Providing the upper and lower ribs
713
r
,
733
r
alternately with the certain height overlapping each other in the vertical direction enables to form a seemingly wavy surface on the sheet P when the sheet P is transported between the upper guide member
711
and the inverting tray
73
, as shown in FIG.
5
A. Thereby, a curl or warp of the sheet P is corrected while the sheet P passes through the clearance of the upper guide member
711
and the inverting tray
73
having the above configuration.
The presser guide switching unit
72
includes the presser solenoid
721
and the presser spring
722
. When the presser solenoid
721
is in an OFF-state, the presser spring
722
connected to a wall (not shown) of the image forming apparatus is urged in leftward direction in
FIG. 2
due to its spring force. In this state, the presser spring
722
urges the guide arm
713
in such a direction as to set the upper guide member
711
to the sheet guide allow state (shown by the broken line in
FIG. 1
) where the upper guide member
711
is pivotally rotated upward about an axis of the guide shaft
712
.
On the other hand, when the presser solenoid
721
is turned on, the presser solenoid
721
pulls the guide arm
713
against the spring force of the presser spring
722
. Thereby, the upper guide member
711
is set to the sheet pressing state (shown by the solid line in
FIG. 1
) where the upper guide member
711
is pivotally rotated downward about the axis of the guide shaft
712
with a sufficient clearance defined by the upper guide member
711
and the sheet transport plane
731
of the inverting tray
73
.
The inverting tray
73
includes the sheet transport plane
731
and a sheet regulating member
732
(see FIG.
2
). As mentioned above, the sheet transport plane
731
is formed with the series of lower ribs
733
r
to smoothly transport the sheet P. The sheet regulating member
732
is an optional item in the switchback device incorporated with the sheet transporting unit
74
according to this invention. In this embodiment, however, the sheet regulating member
732
is provided at a right end of the inverting tray
73
in
FIG. 2
to be slidably movable in the sheet transport direction (left and right directions in
FIG. 2
) in accordance with the size of the sheet in the sheet transport direction. The position of the sheet regulating member
732
is adjusted such that the distance from the sheet regulating member
732
to an access port
714
on the sheet transport plane
731
is set substantially equal to the length of the sheet P in the sheet transport direction (more precisely, slightly longer than the length of the sheet P in the sheet transport direction).
Through the access port
714
, the upstream-located path
24
(downstream-located path
25
) is connected to the interior of the switchback device
7
. The position of the sheet regulating member
732
is set by driving a rack and pinion gear unit
733
and a stepping motor
734
based on a detection signal indicating the size of the sheet P in the sheet transport direction or data concerning the sheet size designated by an operator.
The switchback roller
741
is made of a known material used for a feed roller and transport roller in a conventional image forming apparatus such as EPDM (ethylene-propylene-diene terpolymer), CR rubber (chloroprene rubber), urethane rubber, and natural rubber, and is controllably rotated in clockwise and counterclockwise directions in
FIG. 2
by a switchback roller driver
78
to transport the sheet P in and out of the switchback device
7
(left and right directions in
FIG. 1
, namely, sheet transport direction on the inverting tray
73
).
Next, a mechanism of the sheet transporting unit
74
to pivotally move the pivotal arm
742
toward and away from the inverting tray
73
is described. The switchback roller
741
is pivotally rotated about an axis of the arm shaft
743
while supported by the pivotal arm
742
. The switchback roller
741
is selectively set to a contact state (shown by the solid line in
FIG. 2
) where the switchback roller
741
makes contact with the inverting tray
73
and a retracted state (shown by the broken line in
FIG. 2
) where the switchback roller
741
is retracted above the inverting tray
73
.
When the solenoid
744
is in an OFF-state, the switchback roller
741
is set to the retracted state. In this state, the spring
746
connected to a wall (not shown) of the image forming apparatus urges the right end of the arm bias member
745
upward, causing the left end of the arm bias member
745
to press against the end of the pivot arm
742
so that the switchback roller
741
stays above the inverting tray
73
. When the sheet P is about to be guided on the inverting tray
73
, the solenoid
744
is turned on to set the switchback roller
741
to the contact state. When the solenoid
744
is turned on, a lead end
744
p
of a plunger of the solenoid
744
is retracted upward from the broken-line state to the solid-line state in
FIG. 2
, causing the arm bias member
745
to rotate about the pivot point
749
clockwise, overcoming the upwardly biased force generated in the spring
746
. As a result, the switchback roller
741
is pivotally rotated downward about the axis of the arm shaft
743
by its weight and is set to the contact state when the switchback roller
741
is brought into pressing contact with the sheet P which is being transported on the inverting tray
73
.
Now, an operation of the switchback device
7
is described with reference to
FIGS. 4A
to
4
C.
FIG. 4A
shows a state that the switchback device
7
is set to a stand-by state where the switchback device
7
waits for a sheet which is about to be guided into the switchback device
7
. In this state, the upper guide member
711
of the presser guide unit
71
is set to a sheet guide allow state.
FIG. 4B
shows a transitional stage of the switchback device
7
in which the upper guide member
711
is being changed from the sheet guide allow state shown in
FIG. 4A
to a sheet pressing state shown in FIG.
4
C.
In
FIG. 4A
, the switchback roller
741
is retracted above the inverting tray
73
with its rotation suspended, and the upper guide member
711
of the presser guide unit
71
is set to the sheet guide allow state. When a sheet P is about to be transported into the switchback device
7
in
FIG. 4A
from the upstream-located path
24
, the inlet guide roller pair
241
,
242
is driven in such a direction as to guide the sheet P into the switchback device
7
.
Next, when the lead end of the sheet P in entering direction on the inverting tray
73
is about to slide under the switchback roller
741
, the upper guide member
711
is changed from the sheet guide allow state to the sheet pressing state. Specifically, as shown in
FIG. 4B
, the switchback roller
741
is pivotally moved downward accompanied by a pivotal movement of the pivotal arm
742
about the axis of the arm shaft
743
and rendered in pressing contacts with the upper surface of the sheet P which is sliding over the inverting tray
73
. When the switchback roller
741
is brought into pressing contact with the sheet P, the rotational force of the switchback roller
741
(counterclockwise rotation in
FIG. 4B
) is transmitted to the sheet P, thereby guiding the sheet P further in the entering direction (rightward direction in FIG.
4
B). Upon the entirety of the sheet P coming into the switchback device
7
, the presser guide unit
71
is operated by the presser guide switching unit
72
in such a manner as to set the upper guide member
711
to the sheet pressing state where the upper guide member
711
opposes the sheet transport plane
731
of the inverting tray
73
with the certain clearance, as shown in FIG.
4
C. In this way, the upper guide member
711
of the presser guide unit
71
is changed from the state shown in
FIG. 4A
to the state shown in FIG.
4
C.
When the upper guide member
711
is set to the sheet pressing state shown in
FIG. 4C
, the rotation of the switchback roller
741
is reversed (clockwise rotation in
FIG. 4C
) to transport the sheet P into the downstream-located path
25
by the outlet guide rollers
251
,
252
, thereby finalizing the switchback operation of the sheet P.
FIG. 4C
shows a state that the sheet P is about to exit from the switchback device
7
after the switchback operation.
When the lead end of the sheet P in the exiting direction (tail end of the sheet P in the entering direction) is nipped by the outlet guide roller pair
251
,
252
, the presser solenoid
721
is turned off, and the upper guide member
711
is set to the sheet guide allow state shown in FIG.
4
A. Thereby, the switchback device
7
is rendered into a stand-by state to wait for a next sheet.
FIGS. 6 and 7
are schematic diagrams of a switchback device of an altered arrangement according to this invention.
FIGS. 8A
to
8
D are a diagrams showing a sequential operation of the switchback device of the altered arrangement. The, switchback device of the altered arrangement is described with reference to
FIGS. 6
to
8
D in detail. Note that the elements of the altered arrangement are denoted at the same reference numerals as those in the embodiment. In
FIGS. 6
to
8
D, P
1
denotes a first sheet entering a switchback device
7
for a switchback operation, and P
2
denotes a next sheet entering the switchback device
7
after the first sheet P
1
.
The switchback device
7
includes a sheet presser transporter unit
77
and an inverting tray
73
. The sheet presser transporter unit
77
includes a switchback roller driver
78
and a switchback roller driving mechanism
79
. The switchback roller driver
78
is adapted to rotate a switchback roller
761
in a certain direction. The switchback roller
761
, a presser arm
762
, an arm shaft
763
, a presser solenoid
774
, an arm bias member
775
, and a presser spring
776
constitute the switchback roller driving mechanism
79
.
The switchback roller
761
is made of a known material used for a feed roller and transport roller in a conventional image forming apparatus such as EPDM (ethylene-propylene-diene terpolymer), CR rubber (chloroprene rubber), urethane rubber, and natural rubber. The switchback roller driver
78
drivingly rotates the switchback roller
761
in clockwise direction in
FIGS. 6 and 7
to transport the sheet P in leftward or rightward direction in
FIGS. 6 and 7
or controllably suspends the rotation thereof.
The mechanism of the sheet presser transporter unit
77
, specifically, the construction of the switchback roller driving mechanism
79
(hereinafter also referred to as a switchback roller state change mechanism) is described.
The switchback roller
761
is pivotally supported by the presser arm
762
. The switchback roller
761
and the presser arm
762
are urged upward above on a left part of the inverting tray
73
in
FIGS. 6 and 7
in a stand-by state. The switchback roller
761
is pivotable about the arm shaft
763
to be selectively set to a sheet pressing state (contact state) where the switchback roller
761
is brought into pressing contact with a sheet guided on the inverting tray
73
and a sheet guide allow state (retracted state) where the switchback roller
761
is urged upward above the inverting tray
73
.
The switchback roller
761
is set to the sheet guide allow state in a stand-by state. When the switchback device
7
is in stand-by state, the presser solenoid
74
is turned off. In this state, the presser spring
776
pulls the right end of the arm bias member
775
upward due to its spring force to thereby pivotally lift the presser arm
762
upward in such a direction as to set the switchback roller
761
to the retracted state. Note that the arm bias member
775
is pivotable around a pivot point
779
. When the presser solenoid
774
is turned on, the upward lifting force of the arm bias member
775
to pivotally lift the presser arm
762
upward is released against the spring force of the presser spring
776
. Thereby, the switchback roller
761
is set to the contact state by the weight thereof to press the tail end of the sheet in the entering direction against a sheet transport plane
731
of the inverting tray
73
.
The inverting tray
73
includes the sheet transport plane
731
and a sheet regulating member
732
. The sheet transport plane
731
is formed with a series of ribs
733
arrayed at a certain interval in the width direction of the switchback device
7
(direction normal to the plane of
FIGS. 6 and 7
) to smoothly transport the sheet P on the inverting tray
73
. The sheet regulating member
732
is an optional item in the switchback device
7
provided with the sheet presser transporter unit
77
. In the altered arrangement, however, the sheet regulating member
732
is provided at a right end of the inverting tray
73
in
FIGS. 6 and 7
to be slidably movable in the sheet transport direction (left and right directions in
FIGS. 6 and 7
) in accordance with the size of the sheet in the sheet transport direction. The position of the sheet regulating member
732
is adjusted such that the distance from the sheet regulating member
732
to an access port
714
on the sheet transport plane
731
is set substantially equal to the length of the sheet P in the sheet transport direction. The position of the sheet regulating member
732
is set by driving a rack and pinion gear unit
733
and a stepping motor
734
based on a detection signal indicating the size of the sheet P in the sheet transport direction or data concerning the sheet size designated by an operator.
FIGS. 8A
to
8
D are diagrams showing a sequential operation of the switchback device
7
of the altered arrangement.
FIG. 8A
shows a state that the switchback device
7
is set to a stand-by state where the switchback device
7
waits for a sheet (in this case, the first sheet P
1
) which is about to be guided into the switchback device
7
.
FIG. 8B
shows a transitional stage of the switchback device
7
where the switchback device
7
is changed from the sheet guide allow state shown in
FIG. 8A
to a sheet pressing state shown in FIG.
8
C.
FIG. 8D
shows a state that the switchback device
7
is set to a stand-by state again after a switchback operation of the first sheet P
1
. In this state, the switchback device
7
is ready to guide a next sheet P
2
.
In
FIG. 8A
, the switchback roller
761
is set to a retracted state above the inverting tray
73
with a rotation thereof suspended. When the sheet P
1
is transported from an upstream-located path
24
, an inlet guide roller pair
241
,
242
is driven to guide the sheet P
1
inside the switchback device
7
.
Next, at a certain timing upon completion of transporting the entirety of the sheet P
1
on the inverting tray
73
, the switchback roller
761
is pivotally rotated downward about the axis of the arm shaft
763
accompanied by a downward pivotal movement of the presser arm
762
about the axis of the arm shaft
763
. In this way, the switchback roller
761
slaps down the tail end of the sheet P
1
in the entering direction and presses the sheet P
1
against the sheet transport plane
731
of the inverting tray
73
. As the switchback roller
761
is rotated in counterclockwise direction in pressing contact with the sheet P
1
, the sheet P
1
is guided further in the entering direction (rightward direction in FIG.
8
B).
The switchback roller
761
slaps down the sheet P
1
at a certain timing upon lapse of a certain time duration after a sheet sensor (not shown) such as a photo interrupter provided near the access port
714
detects passing of the tail end of the sheet P
1
.
Subsequently, upon rendering the sheet P
1
in pressing contact with the sheet transport plane
731
of the inverting tray
73
, the switchback roller
761
starts rotating in clockwise direction in
FIG. 8C
to transport the sheet P into a downstream-located path
25
by an outlet guide roller pair
251
,
252
. As shown in
FIG. 8C
, the sheet P
1
in an contact with the switchback roller
761
is transported toward the downstream-located path
25
on the inverting tray
73
.
The presser solenoid
744
is turned off at a certain timing after the lead end of the sheet P
1
in the exiting direction is securely nipped by the outlet guide roller pair
251
,
252
and before the lead end of the next sheet P
2
enters the switchback device
7
. When the presser solenoid
744
is turned off, the switchback roller
761
is set to a retracted state. Thus, as shown in
FIG. 8D
, the switchback device
7
is set to a sheet guide allow state to guide the next sheet P
2
inside the switchback device
7
with the first sheet P
1
exiting the switchback device
7
after the switchback operation.
In this way, the sheet presser transporter unit
77
is sequentially operated as shown in
FIGS. 8A
to
8
D to accomplish a sequential switchback operation of sheets which are guided into the switchback device
7
one after another.
As shown in
FIG. 7
, the switchback roller
761
in the altered arrangement is rotated in clockwise direction upon making contact with the sheet P
1
with such a rotation amount as to enable the lead end of the sheet P
1
in the exiting direction to reach the nip position of the outlet guide roller pair
251
,
252
. In this arrangement, the switchback roller
761
is promptly returned to the retracted state to wait for the next sheet P
2
coming into the switchback device
7
. This altered arrangement contributes to shortening the time required for an image formation as a whole.
Note that the term “sheet” throughout the description of this specification includes all kinds of sheets on which an image can be formed such as cut sheet used in image forming apparatus, transparent sheet for Over Head Projector (OHP), tracing paper, and sheet made of a material capable of color image formation.
In the above embodiment, the switchback device of this invention is described in the case where the switchback device is incorporated in the image forming apparatus capable of double-sided image formation. Alternatively, the switchback device of this invention may be incorporated in an image forming apparatus capable of composite image formation in which a plurality of sub-images are formed in combination on one side of a sheet.
In the above embodiment, when a sheet is guided in the entering direction on the inverting tray
73
, the switchback roller
741
(or
761
) is rotated in counterclockwise direction to cause the sheet to abut against the sheet regulating member
732
provided on the right end of the inverting tray
73
, and then is rotated in clockwise direction to transport the sheet in exiting direction toward the outlet guide roller pair
251
,
252
to finalize a switchback operation. Alternatively, when a sheet is guided in the entering direction on the inverting tray
73
, the rotation of the switchback roller
741
(or
761
) may be suspended for a certain time duration to allow the sheet to abut against the sheet regulating member
732
utilizing the inertia force of the sheet entering into the switchback device
7
.
In the above embodiment, as the sheet is being guided on the inverting tray
73
, the presser guide unit
71
is set to a sheet pressing state. As an altered form, the presser guide unit
71
may be set to a sheet pressing state at a certain timing when the lead end of a sheet in the entering direction is about to pass under the switchback roller
741
or the tail end of the sheet in the entering direction is about to pass between the inlet guide roller pair
241
,
242
.
In the embodiment, the presser guide unit
71
(guide unit) is kept in the sheet pressing state until the sheet is securely nipped by the outlet guide roller pair
251
,
252
after a switchback operation. Alternatively, it may be possible to set the presser guide unit
71
to a sheet pressing state at least once during a time period after the sheet is guided inside the switchback device
7
and before the lead end of the sheet in the exiting direction is securely nipped by the outlet guide roller pair
251
,
252
. This altered arrangement also makes it possible to correct a warp of a sheet in a vertical direction while the sheet is guided in the clearance defined by the sheet transport plane
731
of the inverting tray
73
and the upper guide member
711
of the presser guide unit
71
opposing each other even if the sheet has a curled or warped portion.
To sum up the above, according to an aspect of this invention, a switchback device for use in an image forming apparatus comprising: an inverting tray for temporarily holding a sheet guided inside the switchback device thereon; a guide unit for guiding the sheet in pressing contact with the inverting tray when the sheet is transported in an exiting direction on the inverting tray, the exiting direction being opposite to an entering direction of the sheet on the inverting tray; a guide switching unit for selectively changing the guide unit to a sheet guide allow state to allow the sheet to enter the switchback device in the entering direction on the inverting tray and a sheet pressing state to make substantially an end of the sheet in the exiting direction in pressing contact with the inverting tray; and a sheet transporting unit for transporting the sheet out of the switchback device in the exiting direction on the inverting tray.
In this arrangement, the guide unit pressingly guides the sheet against the inverting tray while the sheet is being transported on the inverting tray. In this state, the opposite sides of the sheet are securely guided by two planes (namely, guide unit and the inverting tray) respectively. Accordingly, even if the sheet has a curled or warped portion, the sheet transport is regulated in a vertical direction on the inverting tray, and the sheet is transported to the downstream-located path after correcting the warp or curl of the sheet in the vertical direction, if any. Also, this arrangement is effective in solving a problem such as sheet jam and folded corner end of the sheet which may likely to result from a sheet transport in and out of the switchback device of transporting the sheet having a curled portion.
According to another aspect of this invention, the guide unit is kept in the sheet pressing state after the sheet has entered the switchback device in the entering direction on the inverting tray until the sheet exits the switchback device in the exiting direction on the inverting tray.
In this arrangement, the guide unit keeps pressingly guiding the sheet against the inverting tray for the time period after the sheet is guided in the entering direction onto the inverting tray until the sheet exits the switchback device in the exiting direction on the inverting tray. The sheet is kept in pressing guide state between the guide unit and the inverting tray for the certain time period. This arrangement simplifies the operation of the guide unit and enhances the curl or warp correction effect due to the prolonged time of rendering the sheet in pressing contact with the guide unit and the inverting tray.
According to yet another aspect of this invention, the guide unit is set to the sheet pressing state after the sheet has entered the switchback device in the entering direction on the inverting tray, and is changed to the sheet guide allow state before a next sheet enters the switchback device in the entering direction on the inverting tray.
In this arrangement, the guide unit keeps pressingly guiding the sheet against the inverting tray for a certain time duration after the sheet is guided in the entering direction on the inverting tray. Thus, the opposite sides of the sheet are kept in pressing guide state by the planes of the guide unit and the inverting tray while the sheet is transported on the inverting tray. The guide unit is changed from the sheet pressing state to the sheet guide allow state before the next sheet enters the switchback device. In this way, keeping the guide unit in the sheet pressing state for the certain time duration after the first sheet is guided onto the inverting tray and before the next sheet comes into the switchback device simplifies the operation of the guide unit and enhances the curl correction effect of the sheet due to the prolonged time of rendering the sheet in pressing contact with the guide unit and the inverting tray.
According to still another aspect of this invention, a switchback device for use in an image forming apparatus comprising: an inverting tray for temporarily holding a sheet guided inside the switchback device thereon; and a sheet presser transporter unit including a switchback roller, a switchback roller state change mechanism for selectively changing the switchback roller to a sheet guide allow state to allow the sheet to enter the switchback device in the entering direction on the inverting tray and a sheet pressing state to make the sheet in pressing contact with the inverting tray, and a switchback roller driver for driving the switchback roller to transport the sheet in an exiting direction opposite to the entering direction on the inverting tray and the switchback roller state change mechanism sets the switchback roller to the sheet pressing state at a time when the sheet is guided into the switchback device and at a time when the sheet is guided out of the switchback device.
In this arrangement, the switchback roller presses the sheet against the inverting tray at a time when the sheet is guided into the switchback device and when the sheet is guided out of the switchback device. In this way, since the switchback roller directly presses the sheet against the inverting tray, the sheet is securely transported toward the downstream-located path. Also, this arrangement is effective in solving a problem such as sheet jam and folded corner end of the sheet which may likely to result from a sheet transport in and out of the switchback device of transporting the sheet having a curled portion.
According to a further aspect of this invention, the sheet pressing state of the switchback roller is set to begin upon completion of the sheet transport into the switchback device in the entering direction and the sheet pressing state is kept until the sheet exits the switchback device in the exiting direction.
In this arrangement, the switchback roller keeps pressingly guiding the sheet against the inverting tray for a certain time duration after completion of the sheet transport onto the inverting tray until the sheet is about to exit the switchback device. The opposite sides of the sheet are kept in pressing guide state by the switchback roller and the inverting tray for the certain time duration. Thus, driving the switchback roller to keep pressing the sheet directly against the inverting tray for the prolonged time securely transports the sheet toward the. downstream-located path and simplifies the operation of the switchback roller.
According to yet another aspect of this invention, the switchback roller is set to the sheet pressing state upon completion of the sheet transport into the switchback device in the entering direction on the inverting tray, and is changed to the sheet guide allow state before a next sheet enters the switchback device.
In this arrangement, the switchback roller keeps pressing the sheet against the inverting tray for a certain time duration after completion of the sheet transport onto the inverting tray until the sheet is about to exit the switchback device. The opposite sides of the sheet are kept in pressing guide state by the switchback roller and the inverting tray for the certain time duration. The switchback roller is changed from the sheet pressing state to the sheet guide allow state before the next sheet enters the switchback device. In this way, driving the switchback roller to keep pressing the sheet directly against the inverting tray for the prolonged time securely transports the sheet toward the downstream-located path and simplifies the operation of the switchback roller.
According to a still further aspect of this invention, the switchback roller comes into pressing contact with a tail end of the sheet in the entering direction on the inverting tray after the sheet has entered the switchback device
In this arrangement, the switchback roller presses the tail end of the sheet in the entering direction against the inverting tray when the sheet is guided in the entering direction on the inverting tray. The opposite sides of the sheet are guided by the switchback roller and the inverting tray, thereby eliminating a possibility of sheet jam and folded corner end of the sheet.
According to yet another aspect of this invention, a switchback device for use in an image forming apparatus comprising: an inverting tray for temporarily holding a sheet guided in a specified sheet transport direction thereon; a guide unit for guiding the sheet in pressing contact with the inverting tray when the sheet exits the switchback device in an exiting direction on the inverting tray, the exiting direction being opposite to an entering direction of the sheet on the inverting tray; a guide switching unit for selectively changing the guide unit to a sheet guide allow state to allow the sheet to enter the switchback device in the entering direction on the inverting tray and a sheet pressing state to make the sheet in pressing contact with the inverting tray; and a sheet transporting unit for transporting the sheet out of the switchback device in the exiting direction on the inverting tray, wherein a lower surface of the guide unit is formed with a plurality of ribs arrayed at a certain interval in a width direction of the guide unit, the width direction being substantially orthogonal to the sheet transport direction, an upper surface of the inverting tray is formed with a plurality of ribs arrayed at a certain interval in the width direction of the guide unit, and the guide switching unit selectively sets the guide unit to the sheet pressing state at least one time during a time period after the sheet has entered the switchback device in the entering direction on the inverting tray until the sheet exits the switchback device in the exiting direction on the inverting tray.
In this arrangement, the guide unit presses the sheet against the inverting tray at least once during a time duration after the sheet is guided in the entering direction on the inverting tray until the sheet is about to exit the switchback device in the exiting direction on the inverting tray. A warp or curl of the sheet in a vertical direction is corrected while the sheet is guided by the upper and lower ribs protruding in the vertical direction even if the sheet has such a curled or warped portion. Further, this arrangement is effective in solving a problem such as sheet jam and folded corner end of the sheet which may likely to result from a sheet transport in and out of the switchback device even if the sheet has such a curled or warped portion.
According to a further aspect of this invention, the guide unit is kept in the sheet pressing state after the sheet has entered the switchback device in the entering direction on the inverting tray until the sheet is about to exit the switchback device in the exiting direction on the inverting tray.
In this arrangement, the guide unit keeps pressingly guiding the sheet against the inverting tray for a certain time duration after the sheet is guided in the entering direction on the inverting tray until the sheet is about to exit the switchback device in the exiting direction on the inverting tray. A warp or curl of the sheet in the vertical direction is corrected while the sheet is guided in pressing contact With the guide unit and the inverting tray for the prolonged time even if the sheet has such a curled or warped portion. Keeping the guide unit in pressing contact state for the prolonged time simplifies the driving operation of the guide unit and enhances the curl correction effect of the sheet due to the prolonged time of rendering the sheet in pressing contact with the guide unit and the inverting tray.
According to a still further aspect of this invention, the guide unit is set to the sheet pressing state after the sheet has entered the switchback device in the entering direction on the inverting tray, and is changed to the sheet guide allow state before a next sheet enters the switchback device in the entering direction on the inverting tray.
In this arrangement, the guide unit keeps pressing the sheet against the inverting tray for a certain time duration after the sheet is guided into the switchback device in the entering direction on the inverting tray and before the next sheet enters the switchback device onto the inverting tray. A warp or curl of the sheet in the vertical direction is corrected while the sheet is guided in pressing contact with the guide unit and the inverting tray for the prolonged time even if the sheet has such a curled or warped portion. Keeping the guide unit in pressing contact state for the prolonged time simplifies the operation of the guide unit and enhances the curl correction effect of the sheet. Further, the guide unit is changed from the sheet pressing state to the sheet guide allow state before the next sheet is guided onto the inverting tray. This arrangement simplifies the driving operation of the guide unit.
According to yet another aspect of this invention, the ribs of the guide unit and the ribs of the inverting tray are alternately arrayed in the width direction of the guide unit.
In this arrangement, a warp or curl of the sheet in the vertical direction is corrected by the ribs of the guide unit and the ribs of the inverting tray while the sheet passes between the guide unit and the inverting tray. Thus, a warped or curled portion of the sheet is securely corrected.
According to still another aspect of this invention, the ribs of the guide unit and the ribs of the inverting tray overlap each other for a certain length in a vertical direction when said guide unit is set to said sheet pressing state.
In this arrangement, a warp or curl of the sheet in the vertical direction is corrected while the sheet passes between the ribs of the guide unit and the ribs of the inverting tray.
As this invention may be embodied in several forms without departing from the spirit of essential characteristics thereof, the present embodiment is therefore illustrative an not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds are therefore intended to embraced by the claims.
Claims
- 1. A switchback device for use in an image forming apparatus comprising:an inverting tray for temporarily holding a sheet guided inside the switchback device thereon; a guide unit for guiding the sheet in pressing contact with the inverting tray when the sheet is transported in an exiting direction on the inverting tray, the exiting direction being opposite to an entering direction of the sheet on the inverting tray; a guide switching unit for selectively changing the guide unit to a sheet guide allow state to allow the sheet to enter the switchback device in the entering direction on the inverting tray and a sheet pressing state to make substantially an end of the sheet in the exiting direction in pressing contact with the inverting tray; and a sheet transporting unit for transporting the sheet out of the switchback device in the exiting direction on the inverting tray.
- 2. The switchback device according to claim 1, wherein the guide unit is kept in the sheet pressing state after the sheet has entered the switchback device in the entering direction on the inverting tray until the sheet exits the switchback device in the exiting direction on the inverting tray.
- 3. The switchback device according to claim 1, wherein the guide unit is set to the sheet pressing state after the sheet has entered the switchback device in the entering direction on the inverting tray, and is changed to the sheet guide allow state before a next sheet enters the switchback device in the entering direction on the inverting tray.
- 4. The switchback device according to claim 1, wherein the guide unit includes an upper guide plate member which is placed above said inverting tray and is pivotable around an axis extending in a widthwise direction thereof to thereby make the guide plate member openable toward the sheet entering the switchback device when the guide unit is in the sheet guide allow state.
- 5. The switchback device according to claim 4, wherein said guide plate member has a lead end in the exiting direction and said inverting tray has a horizontal end in the exiting direction and said lead end and said horizontal end are substantially aligned when the guide unit is in the sheet pressing state.
- 6. A switchback device for use in an image forming apparatus, comprising:an inverting tray for temporarily holding a sheet guided inside the switchback device thereon; a guide unit for guiding the sheet in pressing contact with the inverting tray when the sheet is transported in an exiting direction on the inverting tray, the exiting direction being opposite to an entering direction of the sheet on the inverting tray, the guide unit including an upper guide plate member which is placed above said inverting tray and is pivotable around an axis extending in a widthwise direction thereof to thereby make the guide plate member openable toward the sheet entering the switchback device when the guide unit is in the sheet guide allow state, said guide plate member having a lead end in the exiting direction and said inverting tray having a horizontal end in the exiting direction, said lead end and said horizontal end being substantially aligned when the guide unit is in the sheet pressing state, said guide unit further including a pair of guide arms extending downward from opposite ends of said guide plate member in the widthwise direction and said guide arms each being pivotably attached to said axis that is provided underneath the inverting plate such that a span between said guide arm pair is wider than a width of the inverting tray in the widthwise direction; a guide switching unit for selectively changing the guide unit to a sheet guide allow state to allow the sheet to enter the switchback device in the entering direction on the inverting tray and a sheet pressing state to make substantially an end of the sheet in the exiting direction in pressing contact with the inverting tray; and a sheet transporting unit for transporting the sheet out of the switchback device in the exiting direction on the inverting tray.
- 7. A switchback device for use in an image forming apparatus comprising:an inverting tray for temporarily holding a sheet guided inside the switchback device thereon; and a sheet presser transporter unit including a switchback roller, a switchback roller state change mechanism for selectively changing the switchback roller to a sheet guide allow state to allow the sheet to enter the switchback device in the entering direction on the inverting tray and a sheet pressing state to make the sheet in pressing contact with the inverting tray, and a switchback roller driver for driving the switchback roller to transport the sheet in an exiting direction opposite to the entering direction on the inverting tray and the switchback roller state change mechanism sets the switchback roller to the sheet pressing state at a time when the sheet is guided into the switchback device and at a time when the sheet is guided out of the switchback device.
- 8. The switchback device according to claim 7, wherein the sheet pressing state of the switchback roller is set to begin upon completion of the sheet transport into the switchback device in the entering direction and the sheet pressing state is kept until the sheet exits the switchback device in the exiting direction.
- 9. The switchback device according to claim 7, wherein the switchback roller is set to the sheet pressing state upon completion of the sheet transport into the switchback device in the entering direction on the inverting tray, and is changed to the sheet guide allow state before a next sheet enters the switchback device.
- 10. The switchback device according to claim 7, wherein the switchback roller comes into pressing contact with a tail end of the sheet in the entering direction on the inverting tray after the sheet has entered the switchback device.
- 11. A switchback device for use in an image forming apparatus comprising:an inverting tray for temporarily holding a sheet guided in a specified sheet transport direction thereon; a guide unit for guiding the sheet in pressing contact with the inverting tray when the sheet exits the switchback device in an exiting direction on the inverting tray, the exiting direction being opposite to an entering direction of the sheet on the inverting tray; a guide switching unit for selectively changing the guide unit to a sheet guide allow state to allow the sheet to enter the switchback device in the entering direction on the inverting tray and a sheet pressing state to make the sheet in pressing contact with the inverting tray; and a sheet transporting unit for transporting the sheet out of the switchback device in the exiting direction on the inverting tray, wherein a lower surface of the guide unit is formed with a plurality of ribs arrayed at a certain interval in a width direction of the guide unit, the width direction being substantially orthogonal to the sheet transport direction, an upper surface of the inverting tray is formed with a plurality of ribs arrayed at a certain interval in the width direction of the guide unit, and the guide switching unit selectively sets the guide unit to the sheet pressing state at least one time during a time period after the sheet has entered the switchback device in the entering direction on the inverting tray until the sheet exits the switchback device in the exiting direction on the inverting tray.
- 12. The switchback device according to claim 11, wherein the guide unit is kept in the sheet pressing state after the sheet has entered the switchback device in the entering direction on the inverting tray until the sheet is about to exit the switchback device in the exiting direction on the inverting tray.
- 13. The switchback device according to claim 11, wherein the guide unit is set to the sheet pressing state after the sheet has entered the switchback device in the entering direction on the inverting tray, and is changed to the sheet guide allow state before a next sheet enters the switchback device in the entering direction on the inverting tray.
- 14. The switchback device according to claim 11, wherein the ribs of the guide unit and the ribs of the inverting tray are alternately arrayed in the width direction of the guide unit.
- 15. The switchback device according to claim 14, wherein the ribs of the guide unit and the ribs of the inverting tray overlap each other for a certain length in a vertical direction when said guide unit is set to said sheet pressing state.
- 16. The switchback device according to claim 11, wherein the guide unit includes an upper guide plate member having said lower surface formed with said plural ribs and said upper guide plate member is placed above said inverting tray and is pivotable around an axis extending in a widthwise direction thereof to thereby make the guide plate member openable toward the sheet entering the switchback device when the guide unit is in the sheet guide allow state.
- 17. The switchback device according to claim 16, wherein said guide plate member has a lead end in the exiting direction and said inverting tray has a horizontal end in the exiting direction and said lead end and said horizontal end are substantially aligned when the guide unit is in the sheet pressing state.
- 18. The switchback device according to claim 17, wherein said guide unit includes a pair of guide arms extending downward from opposite ends of said guide plate member in the widthwise direction and said guide arms each is pivotably attached to said axis that is provided underneath the inverting plate such that a span between said guide arm pair is wider than a width of the inverting tray in the widthwise direction.
Priority Claims (2)
Number |
Date |
Country |
Kind |
11-047740 |
Feb 1999 |
JP |
|
11-047741 |
Feb 1999 |
JP |
|
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Number |
Name |
Date |
Kind |
3900192 |
Gibson |
Aug 1975 |
A |
6244591 |
Paulat |
Jun 2001 |
B1 |
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Number |
Date |
Country |
2-75563 |
Mar 1990 |
JP |
2-225256 |
Sep 1990 |
JP |
4-246055 |
Sep 1992 |
JP |
5-246574 |
Sep 1993 |
JP |