U.S. patent application number 12/635378 was filed with the patent office on 2010-06-17 for sheet feeding device and image forming apparatus provided with the sheet feeding device.
This patent application is currently assigned to Konica Minolta Business Technologies, Inc.. Invention is credited to Yutaka Otsuka, Yuta Tachibana, Yoshiyuki Toso, Shoichi Tsuge.
Application Number | 20100148431 12/635378 |
Document ID | / |
Family ID | 42026862 |
Filed Date | 2010-06-17 |
United States Patent
Application |
20100148431 |
Kind Code |
A1 |
Otsuka; Yutaka ; et
al. |
June 17, 2010 |
SHEET FEEDING DEVICE AND IMAGE FORMING APPARATUS PROVIDED WITH THE
SHEET FEEDING DEVICE
Abstract
A sheet feeding device that is suited to be employed in an image
forming apparatus having a printing section for printing an image
on a sheet. The sheet feeding device has feed rollers for feeding a
sheet at a speed "Va" and timing rollers for feeding a sheet fed by
the feed rollers to the printing section at a speed "Vb". Sensors
are provided between the feed rollers and the timing rollers, so
that the gap between a foregoing sheet and a following sheet can be
detected at a plurality of detection points while the foregoing
sheet is being fed by the timing rollers and the following sheet is
being fed by the feed rollers. When one of the sensors detects that
there is a gap between the sheets, a control unit controls the feed
rollers such that the speed "Va" will be higher than the speed
"Vb".
Inventors: |
Otsuka; Yutaka;
(Toyokawa-shi, JP) ; Tachibana; Yuta;
(Toyokawa-shi, JP) ; Toso; Yoshiyuki;
(Toyokawa-shi, JP) ; Tsuge; Shoichi; (Okazaki-shi,
JP) |
Correspondence
Address: |
MORRISON & FOERSTER LLP
1650 TYSONS BOULEVARD, SUITE 400
MCLEAN
VA
22102
US
|
Assignee: |
Konica Minolta Business
Technologies, Inc.
Tokyo
JP
|
Family ID: |
42026862 |
Appl. No.: |
12/635378 |
Filed: |
December 10, 2009 |
Current U.S.
Class: |
271/265.01 |
Current CPC
Class: |
B65H 2515/702 20130101;
B65H 2515/702 20130101; B65H 2701/1313 20130101; B65H 5/062
20130101; B65H 7/14 20130101; B65H 2701/1313 20130101; B65H
2301/4452 20130101; B65H 2701/1311 20130101; B65H 2511/514
20130101; B65H 2801/06 20130101; B65H 2301/4452 20130101; B65H
2701/1311 20130101; B65H 2513/104 20130101; B65H 2220/01 20130101;
B65H 2220/01 20130101; B65H 2220/03 20130101; B65H 2220/01
20130101; B65H 2220/03 20130101; B65H 2220/02 20130101; B65H
2220/02 20130101; B65H 2511/22 20130101; B65H 2513/104 20130101;
B65H 2511/22 20130101; B65H 2513/104 20130101; B65H 2220/03
20130101 |
Class at
Publication: |
271/265.01 |
International
Class: |
B65H 7/02 20060101
B65H007/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 12, 2008 |
JP |
2008-317144 |
Claims
1. A sheet feeding device that is suited to be used in an image
forming apparatus comprising a printing section for printing an
image on a sheet; a first feeder for feeding the sheet at a first
speed; a second feeder for feeding the sheet fed by the first
feeder to the printing section at a second speed; a detector, which
is located between the first feeder and the second feeder, for
detecting a gap between a first sheet and a second sheet at a
plurality of detection points while the first sheet is being fed by
the second feeder and the second sheet is being fed by the first
feeder; and a controller for controlling the first feeder or the
second feeder, wherein when the detector detects that there is a
gap between the first sheet and the second sheet, the controller
controls the first feeder or the second feeder such that the first
speed will be higher than the second speed.
2. A sheet feeding device according to claim 1, wherein the
controller controls the first feeder or the second feeder such that
the gap detected at a more downstream detection point of the
plurality of detection points will be smaller than the gap detected
at a more upstream detection point of the plurality of detection
points.
3. A sheet feeding device according to claim 1, wherein when the
detector detects that there is no gap between the first sheet and
the second sheet, the controller controls the first feeder or the
second feeder such that the first speed and the second speed will
be equal to each other.
4. A sheet feeding device according to claim 1, wherein when the
detector detects at the most upstream detection point that there is
no gap between the first sheet and the second sheet, the controller
controls the first feeder or the second feeder such that the first
speed will be lower than the second speed.
5. A sheet feeding device according to claim 1, wherein each of the
detection points has a specified length; wherein the controller
calculates the first speed, the second speed and a size of the gap
at each of the detection points as follows: the controller
calculates the second speed, based on a time necessary for a
trailing edge of the first sheet to complete passing by the
detection point and the specified length of the detection point;
the controller calculates the first speed, based on a time
necessary for a leading edge of the second sheet to complete
passing by the detection point and the specified length of the
detection point; and the controller calculates the size of the gap,
based on the specified length of the detection point, the second
speed and a time necessary for the gap to complete passing by the
detection point; and wherein the controller controls the first
feeder or the second feeder in accordance with the size of the gap
to adjust the first speed or the second speed.
6. A sheet feeding device according to claim 1, further comprising
a corrector for correcting an overlay of the first sheet and the
second sheet.
7. A sheet feeding device according to claim 1, wherein the first
speed is fixed.
8. An image forming apparatus comprising a printing section for
printing an image on a sheet, said image forming apparatus
comprising: a sheet feeding device comprising: a first feeder for
feeding the sheet at a first speed; a second feeder for feeding the
sheet fed by the first feeder to the printing section at a second
speed; a detector, which is located between the first feeder and
the second feeder, for detecting a gap between a first sheet and a
second sheet at a plurality of detection points while the first
sheet is being fed by the second feeder and the second sheet is
being fed by the first feeder; and a controller for controlling the
first feeder or the second feeder, wherein when the detector
detects that there is a gap between the first sheet and the second
sheet, the controller controls the first feeder or the second
feeder such that the first speed will be higher than the second
speed.
9. An image forming apparatus according to claim 8, wherein the
controller of the sheet feeding device controls the first feeder or
the second feeder such that the gap detected at a more downstream
detection point of the plurality of detection points will be
smaller than the gap detected at a more upstream detection point of
the plurality of detection points.
10. An image forming apparatus according to claim 8, wherein when
the detector of the sheet feeding device detects that there is no
gap between the first sheet and the second sheet, the controller of
the sheet feeding device controls the first feeder or the second
feeder such that the first speed and the second speed will be equal
to each other.
11. An image forming apparatus according to claim 8, wherein when
the detector of the sheet feeding device detects at the most
upstream detection point that there is no gap between the first
sheet and the second sheet, the controller controls the first
feeder or the second feeder such that the first speed will be lower
than the second speed.
12. An image forming apparatus according to claim 8, wherein each
of the detection points in the sheet feeding device has a specified
length; wherein the controller of the sheet feeding device
calculates the first speed, the second speed and a size of the gap
at each of the detection points as follows: the controller
calculates the first speed, based on a time necessary for a
trailing edge of the first sheet to complete passing by the
detection point and the specified length of the detection point:
the controller calculates the second speed, based on a time
necessary for a leading edge of the second sheet to complete
passing by the detection point and the specified length of the
detection point; and the controller calculates the size of the gap,
based on the specified length of the detection point, the second
speed and a time necessary for the gap to complete passing by the
detection point; and wherein the controller of the sheet feeding
device controls the first feeder or the second feeder in accordance
with the size of the gap to adjust the first speed or the second
speed.
13. An image forming apparatus according to claim 8, wherein the
sheet feeding device further comprises a corrector for correcting
an overlap of the first sheet and the second sheet.
14. An image forming apparatus according to claim 8, wherein the
first speed is fixed.
Description
[0001] This application is based on a Japanese patent application
No. 2008-317144 filed on Dec. 12, 2008, the content of which is
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a sheet feeding device and
an image forming apparatus provided with the sheet feeding device,
and more particularly to a sheet feeding device for feeding sheets
of printed medium successively and an image forming apparatus
provided with the sheet feeding device.
[0004] 2. Description of Related Art
[0005] When a sheet feeding device feeds a plurality of sheets
successively, it is preferred that the sheets are fed with no gaps
among the sheets for the reasons below. If there are gaps among
sheets, feed rollers and a transfer belt will rotate even while the
gaps are passing thereby. Therefore, in this case, the drive
distance of the feed rollers and the transfer belt is large,
compared with the case wherein there are no gaps among sheets.
Accordingly, when there are gaps among sheets, the feed rollers and
the transfer belt are abraded shortly. Also, when there are gaps
among sheets, the productivity becomes lower, compared with the
case wherein there are no gaps among sheets. For these reasons,
sheets are fed successively preferably with no gaps among the
sheets.
[0006] As a conventional sheet feeding device, for example, a sheet
feeding device as disclosed by Japanese Patent Laid-Open
Publication No. 2006-232475 (Reference 1) is well known. In this
sheet feeding device, when a detector detects that the gap between
two sheets (a foregoing sheet and a following sheet) that are
successively fed is lower than a specified value, a control unit
controls a feed-out means to slow down the speed of the following
sheet. With this control, it is possible to feed a plurality of
sheets successively while keeping constant gaps among the
sheets.
[0007] Thus, in the sheet feeding device disclosed by Reference 1,
the gaps among sheets are kept constant. However, Reference 1 is
silent about controlling the gaps closer to zero.
SUMMARY OF THE INVENTION
[0008] An object of the present invention is to provide a sheet
feeding device wherein the gaps among sheets successively fed can
be made closer to zero and an image forming apparatus provided with
the sheet feeding device.
[0009] An embodiment of the present invention is a sheet feeding
device that is suited to be used in an image forming apparatus
comprising a printing section for printing an image on a sheet, and
the sheet feeding device comprises: a first feeder for feeding the
sheet at a first speed; a second feeder for feeding the sheet fed
by the first feeder to the printing section at a second speed; a
detector, which is located between the first feeder and the second
feeder, for detecting a gap between a first sheet and a second
sheet at a plurality of detection points while the first sheet is
being fed by the second feeder and the second sheet is being fed by
the first feeder; and a controller for controlling the first feeder
or the second feeder, and when the detector detects that there is a
gap between the first sheet and the second sheet, the controller
controls the first feeder or the second feeder such that the first
speed will be higher than the second speed.
[0010] Another embodiment of the present invention is an image
forming apparatus, and the image forming apparatus comprises the
above-described sheet feeding device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] This and other objects and features of the present invention
will be apparent from the following description with reference to
the accompanying drawings, in which:
[0012] FIG. 1 is a schematic view showing the general structure of
an image forming apparatus according to an embodiment of the
present invention;
[0013] FIG. 2 is an enlarged view of a sheet feeding device
employed in the apparatus shown by FIG. 1;
[0014] FIGS. 3a-3c are illustrations showing operation of an
overlap correction mechanism;
[0015] FIG. 4 is a flowchart showing a procedure that is carried
out by a control unit while the sheet feeding device is feeding
sheets successively;
[0016] FIG. 5 is a graph showing waveforms of signals outputted
from sensors;
[0017] FIGS. 6a-6d are illustrations showing passing of two sheets
by a light receiving element;
[0018] FIGS. 7a-7d are illustrations showing passing of two sheets
by a light receiving element;
[0019] FIGS. 8a-8c are illustrations showing passing of two sheets
by a light receiving element;
[0020] FIGS. 9a-9c show modifications of the sensors provided for
the sheet feeding device; and
[0021] FIG. 10 shows a modification of the overlap correction
mechanism.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] A sheet feeding device and an image forming apparatus
according to an embodiment of the present invention are hereinafter
described.
Structure of Image Forming Apparatus
[0023] Referring to FIG. 1, an image forming apparatus 1 provided
with a sheet feeding device according to an embodiment of the
present invention is described.
[0024] The image forming apparatus 1 is an electrophotographic
color printer and forms a color image by combining four color (Y:
yellow, M: magenta, C: cyan and K: black) images in a tandem
method. The image forming apparatus 1 is to form an image on a
sheet of paper P in accordance with image data, and comprises a
printing section 2, a feeding section 15, a sheet feeding device
35, a fixing device 22 and a printed-sheet tray 23.
[0025] The feeding section 15 is to supply sheets P one by one, and
comprises a sheet tray 16, a feed-out roller 17 and separation
rollers 18. A plurality of sheets to be subjected to printing is
stacked in the sheet tray 16. The feed-out roller 17 is to pick the
sheets P out of the tray 16 one by one. The separation rollers 18
separate two or more sheets possibly picked out by the feed-out
roller 17 and feed surely one sheet P forward.
[0026] As FIG. 2 shows, the sheet feeding device 35 comprises feed
rollers 19, timing rollers 20, a control unit 30, a driver 31, a
storage 32, an overlap correction mechanism 40, a route R and
sensors Se1 to Se5. The feed rollers 19 are rotated by the driver
31 to feed the sheet P at a speed "Va". The driver 31 is, for
example, a motor. The feed rollers 19 and the driver 31 form a
feeder. The timing rollers 20 are rotated by another driver (not
shown) to feed the sheet P fed thereto by the feed rollers 19
further to a printing section 2 at a speed "Vb". The timing rollers
20 and the driver form another feeder. The route R is formed
between the feed rollers 19 and the timing rollers 20, and the
sheet P travels therein.
[0027] The sensors Se1 to Se5 are provided along the route R. When
two sheets P1 and P2 are fed successively as shown by FIG. 2, the
sensors Se1 to Se5 detect the gap between the sheets P1 and P2.
More specifically, while the sheet P1 is being fed by the timing
rollers 20 and while the sheet P2 is being fed by the feed rollers
19, the gap "g" between the trailing edge of the sheet P1 and the
leading edge of the sheet P2 (which is hereinafter referred to as
the gap "g" between the sheets P1 and P2) is detected by the plural
sensors Se1 to Se5 provided along the route R. Each of the sensors
Se1 to Se5 comprises a light source Se1-1 (Se2-1, Se3-1, Se4-1 or
Se5-1) and a light receiving element Se1-2 (Se2-2, Se3-2, Se4-2 or
Se5-2). The light source Se3-1 and the light receiving element
Se3-2 are shown in the magnified view in FIG. 2. The light sources
Se1-1 to Se5-1 emit light. The light receiving elements Se1-2 to
Se5-2 define detection points. The light receiving elements Se1-2
to Se5-2 receive the light emitted from the light sources Se1-1 to
Se5-1 and send the control unit 30 output signals Sig1 to Sig 5 in
accordance with the quantities of received light. Specifically,
when the light receiving elements Se1-2 to Se5-2 receive relatively
large quantities of light, the elements Se1-2 to Se5-2 send output
signals Sig1 to Sig5 of relatively high voltages, and when the
light receiving elements Se1-2 to Se5-2 receive relatively small
quantities of light, the elements Se1-2 to Se5-2 send output
signals Sig1 to Sig5 of relatively low voltages. As shown in the
magnified view in FIG. 2, the light receiving elements Se1-2 to
Se5-2 have a dimension (length) "l" in the sheet feeding direction.
In this embodiment, the sensors Se1 to Se5 are arranged at
intervals larger than the initial gap "g" between the sheets P1 and
P2, so that the gap "g" will never be detected by two or more
sensors concurrently.
[0028] The control unit 30 controls the driver 31 and the feed
rollers 19 in accordance with the detection results of the sensors
Se1 to Se5. The storage 32 is, for example, a hard disk or a
memory, and stores a table as shown by Table 1. The table shows the
relationship between the size "L" of the gap "g" and the speed
"Va".
TABLE-US-00001 TABLE 1 Size "L" of Gap "g" Speed "Va" 0 V1 0 < L
.ltoreq. L1 V2 L1 < L .ltoreq. L2 V3 L2 < L .ltoreq. L3 V4 L3
< L V5
[0029] The control unit 30 recognizes the size "L" of the gap "g"
based on the output signals Sig1 to Sig5 from the sensors Se1 to
Se5 and determines the speed "Va" with reference to the table. In
Table 1, the values meet the conditions L1<L2<L3,
V1<V2<V3<V4 and V1=Vb. That is, the speed "Va" is equal to
or greater than the speed "Vb" at all times. Thereby, when there is
a gap between the sheets P1 and P2 (L>0), the control unit 30
controls the driver 31 and the feed rollers 19 such that the gap
"g" detected by a more downstream sensor of the sensors Se1 to Se5
will be smaller than the gap "g" detected by a more upstream sensor
of the sensors Se1 to Se5. On the other hand, when one of the
sensors "Sen" detects no gap between the sheets P1 and P2 (L=0),
the control unit 30 controls the driver 31 and the feed rollers 19
such that the speed "Va" will be V1 that is equal to the speed
"Vb".
[0030] The overlap correction mechanism 40 is to correct an overlap
of the sheets P1 and P2. Specifically, as shown in FIGS. 1 and 2,
the overlap correction mechanism 40 is provided in a downstream
position in the route R (near the timing rollers 20), and is a
roller that has a cross section of a circle having a protrusion. If
the sheets P1 and P2 reach the overlap correction mechanism 40
while overlapping with each other, the leading edge of the sheet P2
is hooked by the protrusion of the overlap correction mechanism 40
as shown by FIG. 3a. Then, as shown by FIG. 3b, the sheet P2 is
pushed up by the force of the feed rollers 19, and accordingly, the
overlap correction mechanism 40 is rotated. When the overlap
correction mechanism 40 rotates by a specified amount, as shown by
FIG. 3c, the leading edge of the sheet P2 is released from the
protrusion of the overlap correction mechanism 40, and the sheet P2
is fed upward. Thereafter, the overlap correction mechanism 40
rotates further and returns to a state as shown by FIG. 3a. In this
way, the sheet P2 slows down. Meanwhile, during the period from
FIG. 3a to FIG. 3c, the sheet P1 is fed upward without slowing
down. Thereby, the overlap of the sheets P1 and P2 is
corrected.
[0031] The printing section 2 is to form a toner image on a sheet P
fed from the timing rollers 20. As shown in FIG. 1, the printing
section 2 comprises image forming units 24Y, 24M, 24C and 24K,
first transfer rollers 8Y, 8M, 8C and 8K, an intermediate transfer
belt 11, a driving roller 12, a driven roller 13, a second transfer
roller 14, and a cleaning device 21. The image forming units 24Y,
24M, 24C and 24K comprise photosensitive drums 4Y, 4M, 4C and 4K,
electric chargers 5Y, 5M, 5C and 5K, exposure devices 6Y, 6M, 6C
and 6K, developing devices 7Y, 7M, 7C and 7K, and cleaners 9Y, 9M,
9C and 9K, respectively. In the following description, when the
photosensitive drums, the electric chargers, the exposure devices,
the developing devices, the first transfer rollers, the cleaners
and the image forming units are discussed generally, they are
indicated as the photosensitive drum(s) 4, the electric charger(s)
5, the exposure device(s) 6, the developing device(s) 7, the first
transfer roller(s) 8, the cleaner(s) 9 and the image forming
unit(s) 24. When the photosensitive drums, the electric chargers,
the exposure devices, the developing devices, the first transfer
rollers, the cleaners and the image forming units are discussed
individually, they are indicated as the photosensitive drums 4Y,
4M, 4C and 4K, the electric chargers 5Y, 5M, 5C and 5K, the
exposure devices 6Y, 6M, 6C and 6K, the developing devices 7Y, 7M,
7C and 7K, the first transfer rollers 8Y, 8M 8C and 8K, the
cleaners 9Y, 9M, 9C and 9K, and the image forming units 24Y, 24M,
24C and 24K.
[0032] The electric chargers 5 charge the circumferential surfaces
of the photosensitive drums 4. The exposure devices 6 emit lasers
controlled by an exposure control unit (not shown in the drawings).
Thereby, electrostatic latent images are formed on the
circumferential surfaces of the photosensitive drums 4. Thus, the
electric chargers 5 and the exposure devices 6 serve as a unit for
forming electrostatic latent images on the circumferential surfaces
of the photosensitive drums 4.
[0033] The developing devices 7 are to supply toner to the
photosensitive drums 4 so as to form toner images on the
circumferential surfaces of the photosensitive drums 4. More
specifically, the developing devices 7 store toner therein and
charge the toner into the negative polarity by stirring the toner
or the like. Developing rollers provided in the respective
developing device 7 feed the toner toward the photosensitive drums
4. At this time, the negative charged toner moves from the
developing rollers to the photosensitive drums 4 influenced by the
electric fields of the electrostatic latent images on the
photosensitive drums 4. In this way, toner images are formed on the
circumferential surfaces of the photosensitive drums 4.
[0034] The intermediate transfer belt 11 is laid between the
driving roller 12 and the driven roller 13, and the toner images
formed on the photosensitive drums 4 are transferred onto the
intermediate transfer belt 1 such that the transferred images will
be laid on one another to be combined into a full-color image
(first transfer). The first transfer rollers 8 are located in
contact with the inner surface of the intermediate transfer belt
11. A first transfer voltage is applied from a voltage source (not
shown in the drawings) to the first transfer rollers 8, whereby the
toner images formed on the photosensitive drums 4 are transferred
onto the intermediate transfer belt 11. The cleaners 9 are to
collect residual toner remained on the photosensitive drums 4 after
the first transfer. The driving roller 12 is rotated by an
intermediate transfer belt driver (not shown in the drawings),
whereby the intermediate transfer belt 11 is driven. Then, the
intermediate transfer belt 11 carries the full-color toner image to
the second transfer roller 14.
[0035] The second transfer roller 14 is located opposite the
intermediate transfer belt 11, and a nip portion N is formed
between the second transfer roller 14 and the intermediate transfer
belt 11. While a sheet P fed from the timing rollers 20 is passing
through the nip portion N, the second transfer roller 14 transfers
the toner image carried by the intermediate transfer belt 11 onto
the sheet P (second transfer). After the second transfer, the
cleaning device 21 removes residual toner from the intermediate
transfer belt 11.
[0036] The sheet P that has been subjected to the second transfer
is fed to the fixing device 22. The fixing device 22 applies a
heating treatment and a pressing treatment to the sheet P so as to
fix the toner image on the sheet P. The printed sheet P is ejected
onto the printed-sheet tray 23.
Operation of Image Forming Apparatus
[0037] The operation of the image forming apparatus 1 provided with
the sheet feeding device 35 is hereinafter described with reference
to the drawings.
[0038] First, referring to FIGS. 5 to 8, the operation of the image
forming apparatus 1 is generally described. When the light
receiving elements Se1-2 to Se5-2 receive relatively large
quantities of light, the light receiving elements Se1-2 to Se5-2
output signals Sig1 to Sig5 of relatively high voltages. When the
light receiving elements Se1-2 to Se5-2 receive relatively small
quantities of light, the light receiving elements Se1-2 to Se5-2
output signals Sig1 to Sig5 of relatively low voltages. Therefore,
referring to FIG. 5, while the output signals Sig1 to Sig5 are high
(during the periods between time "0" to time "t3"), the gap "g"
between the sheets P1 and P2 are passing in front of the light
receiving elements Se1-2 to Se5-2, respectively. That is, the size
"L" of the gap "g" can be judged from the length of the period when
the voltage of the output signal Sig1 to Sig5 is high. The control
unit 30 times the period and calculates the size "L" of the gap "g"
between the sheets P1 and P2, and in accordance with the
calculation result, the control unit 30 controls the speed
"Va".
[0039] As shown in FIG. 5, the waveforms of the output signals Sig1
to Sig5 can be classified into three types. More specifically, the
waveforms of the output signals Sig1 and Sig2 are trapezoidal. The
waveform of the output signal Sig3 is four-cornered with the upper
side slanting. The waveform of the output signal Sig4 is triangle.
The output signal Sig5 is constant and flat, which indicates that
the gap "g" between the sheets P1 and P2 is zero.
[0040] The reason why the output signals Sig1 to Sig5 have
different waveforms is that the size "L" of the gap "g" is
changeable. Specifically, as shown by FIGS. 6a to 6d, when the size
"L" of the gap "g" is greater than the length "l" of the light
receiving element Sen-2, the output signal "Sign" has such a
waveform as those of the output signals Sig1 and Sig2. As shown by
FIGS. 7a to 7d, when the size "L" of the gap "g" is smaller than
the size of the light receiving element Sen-2, the output signal
"Sign" has such a waveform as that of the output signal Sig3. As
shown by FIGS. 8a to 8c, when the gap "g" becomes zero while
passing in front of the light receiving element Sen-2, the output
signal "Sign" has such a waveform as that of the output signal
Sig4. This is described in more details below.
[0041] Referring to FIGS. 6a to 6d, a case wherein the gap "g" is
larger than the length "l" of the light receiving element Sen-2 is
described. While the trailing edge of the sheet P1 is passing in
front the light receiving element Sen-2 (during the period from
FIG. 6a to FIG. 6b), the area of the light receiving element Sen-2
covered by the sheet P1 is decreasing. Accordingly, the voltage of
the output signal "Sign" is increasing like the output signals Sig1
and Sig 2 in the periods from "0" to "t1" shown in FIG. 5. Next,
when and after the trailing edge of the sheet P1 has completed
passing by the light receiving element Sen-2 (during the period
from FIG. 6b to FIG. 6c), the light receiving element Sen-2 is
covered neither by the sheet P1 nor by the sheet P2. Accordingly,
the voltage of the output signal "Sign" is fixed at a relatively
high level like the output signals Sig1 and Sig2 in the periods
from "t1" to "t2" shown in FIG. 5. Next, while the leading edge of
the sheet P2 is passing in front of the light receiving element
Sen-2 (during the period from FIG. 6c to FIG. 6d), the area of the
light receiving element Sen-2 covered by the sheet P2 is
increasing. Accordingly, the voltage of the output signal "Sign" is
decreasing like the output signals Sig1 and Sig2 in the periods
from "t2" to "t3" shown in FIG. 5. Finally, when and after the
leading edge of the sheet P2 has completed passing by the light
receiving element Sen-2 (after FIG. 6d), the light receiving
element Sen-2 is entirely covered by the sheet P2. Accordingly, the
voltage of the output signal "Sign" is fixed at a relatively low
level like the signals Sig1 and Sig2 after "t3" shown in FIG.
5.
[0042] Next, referring to FIGS. 7a to 7d, a case wherein the gap
"g" is smaller than the length "l" of the light receiving element
Sen-2 is described. In a first part of the period when the trailing
edge of the sheet P1 is passing in front of the light receiving
element Sen-2 (during the period from FIG. 7a to FIG. 7b), the area
of the light receiving element Sen-2 covered by the sheet P1 is
decreasing. Accordingly, the voltage of the output signal "Sign" is
increasing like the output signal Sig3 in the period from "0" to
"t1" shown in FIG. 5. Thereafter, as shown by FIG. 7b, the leading
edge of the sheet P2 comes to the light receiving element Sen-2
while the trailing edge of the sheet P1 is still passing in front
of the light receiving element "Sen-2". In this moment, because the
speed "Va" is higher than the speed "Vb", the covered area of the
light receiving element Sen-2 covered by the sheets P1 and P2 is
gradually increasing. Accordingly, the voltage of the output signal
"Sign" is gradually decreasing like the output signal Sig3 in the
period from "t1" to "t2" shown in FIG. 5. Next, when and after the
trailing edge of the sheet P1 has completed passing by the light
receiving element Sen-2 (after FIG. 7c), only the leading edge of
the sheet P2 passes in front of the light receiving element Sen-2,
and accordingly, the voltage of the output signal "Sign" is steeply
decreasing like the signal Sig3 in the period from "t2" to "t3"
shown in FIG. 5. Finally, when and after the leading edge of the
sheet P2 has completed passing by the light receiving element
"Sen-2" (after FIG. 7d), the light receiving element Sen-2 is
entirely covered by the sheet P2. Accordingly, the voltage of the
output signal "Sign" is fixed at a relatively low level like the
signal Sig3 after "t3" shown in FIG. 5. Thus, when the gap "g" is
smaller than the length "l" of the light receiving element "Sen-2",
the leading edge of the sheet P2 starts passing in front of the
light receiving element Sen-2 before the trailing edge of the sheet
P1 completes passing in front of the light receiving element Sen-2.
Therefore, during the period "t1" to "t2", the voltage of the
output signal "Sign" is not fixed but is gradually decreasing.
[0043] Next, referring to FIGS. 8a to 8c, a case wherein the gap
"g" becomes zero while the gap "g" is passing in front of the light
receiving element Sen-2 is described. In a first part of the period
when the trailing edge of the sheet P1 is passing in front of the
light receiving element Sen-2 (during the period from FIG. 8a to
FIG. 8b), the area of the light receiving element Sen-2 covered by
the sheet P1 is decreasing. Accordingly, the voltage of the output
signal "Sign" is increasing like the output signal Sig5 in the
period from "0" to "t1" shown in FIG. 5. Thereafter, as shown by
FIG. 8b, the leading edge of the sheet P2 comes to the light
receiving element Sen-2 while the trailing edge of the sheet P1 is
still passing in front of the light receiving element Sen-2. In
this moment, because the speed "Va" is higher than the speed "Vb",
the covered area of the light receiving element Sen-2 is gradually
increasing. Accordingly, the voltage of the output signal "Sign" is
gradually decreasing like the output signal Sig5 in the period from
"t1" to "t3" shown in FIG. 5. Next, the leading edge of the sheet
P2 catches up with the trailing edge of the sheet P1 as shown by
FIG. 8c, and thereafter, the light receiving element Sen-2 is
entirely covered by the sheets P1 and P2. Accordingly, the voltage
of the output signal "Sign" is fixed at a relatively low level like
the output signal Sig4 after "t3" shown in FIG. 5.
[0044] As described above, the timings of the passing of the
trailing edge of the sheet P1 and the passing of the leading edge
of the sheet P2 in front of the light receiving element Sen-2
depend on the size "L" of the gap "g". The control unit 30
recognizes the passing of the trailing edge of the sheet P1 and the
passing of the leading edge of the sheet P2, based on the waveform
of the output signal "Sign" from the light receiving element Sen-2.
Referring to FIG. 4, the operation of the image forming apparatus 1
is hereinafter described, focusing on this point.
[0045] The control unit 30 sets N to 1 at step S1. This step S1 is
carried out, for example, based on the time when the leading edge
of the sheet P1 is detected by the sensor Se5 located the most
downstream in the route R.
[0046] Next, in order to judge the presence or non-presence of a
gap "g" between the sheets P1 and P2, the control unit 30 judges
whether the sensor "Sen" (n: integer from 1 to 5) detects the
trailing edge of the sheet P1 during a period when the trailing
edge of the sheet P1 is expected to come thereto (step S2). While
the trailing edge of the sheet P1 is passing in front of the light
receiving element Sen-2, the covered area of the light receiving
element Sen-2 is decreasing, and the quantity of light received by
the light receiving element Sen-2 is increasing. Accordingly, the
voltage of the output signal "Sign" from the light receiving
element Sen-2 is increasing. Therefore, the control unit 30 judges
the up-edge of the output signal "Sign" as the time when the sensor
"Sen" starts detecting the trailing edge of the sheet P1.
Thereafter, the processing goes to step S4. On the other hand, when
the trailing edge of the sheet P1 is not detected, the control unit
30 judges that there is no gap between the sheets P1 and P2. Then,
the processing goes to step S3.
[0047] When the trailing edge of the sheet P1 is not detected, the
control unit 30 sets the speed "Va" to V1 at step S3. In this
procedure, when the control unit 30 judges that there is no gap
between the sheets P1 and P2, the control unit 30 judges that
adjustment of the speed "Va" is not necessary. Therefore, the
control unit 30 sets the speed "Va" to V1 that is equal to the
speed "Vb". Thereafter, the processing goes to step S18.
[0048] When the trailing edge of the sheet P1 is detected, the
control unit 30 starts a timer (step S4). As shown by FIG. 5, the
control unit 30 starts timing with the time of the up-edge of the
output signal "Sign" defined to be t=0. Next, the control unit 30
judges whether the increase in the voltage of the output signal
"Sign" has stopped (step S5). As shown by FIG. 6b, when the
trailing edge of the sheet P1 has completed passing by the light
receiving element "Sen-2, the sheet P1 stops covering the light
receiving element "Sen-2", and the quantity of light received by
the light receiving element "Sen-2" stops increasing. Accordingly,
the increase in the voltage of the output signal "Sign" stops. As
shown by FIGS. 7b and 8b, when the leading edge of the sheet P2 has
reached the light receiving element "Sen-2", the light receiving
element "Sen-2" starts to be covered by the sheet P2. Therefore, at
this time, also, the quantity of light received by the light
receiving element "Sen-2" stops increasing, and accordingly, the
increase in the voltage of the output signal "Sign" stops. At step
S5, however, the control unit 30 cannot judge whether the stop of
the increase in the voltage of the output signal "Sign" is due to
the completion of the passing of the trailing edge of the sheet P1
by the light receiving element "Sen-2" or due to the arrival of the
leading edge of the sheet P2 at the light receiving element
"Sen-2". This judgment is made at step S7 that will be described
later. When the increase in the voltage of the output signal "Sign"
stops, the processing goes to step S6. Unless the increase in the
voltage of the output signal "Sign" stops, the processing returns
to step S5. Until the increase in the voltage of the output signal
"Sign" stops, the process at step S5 is repeated.
[0049] At step S6, the control unit 30 takes in a value of the time
"t1" (see FIG. 5) when the increase in the voltage of the output
signal "Sign" stops.
[0050] Next, the control unit 30 judges whether the value "t1" is
equal to a value "ta" (step S7). The value "ta" is obtained by
dividing the length "l" of the light receiving element "Sen-2" by
the speed "Vb", and therefore, the value "ta" indicates the time
that is necessary for the trailing edge of the sheet P1 to complete
passing by the light receiving element "Sen-2". The speed "Vb" is a
fixed value known to the control unit 30. Thus, at step S7, by
judging whether the value "t1" is equal to the value "ta", the
control unit 30 judges whether the stop of the increase in the
voltage of the output signal "Sign" is due to the completion of the
passing of the trailing edge of the sheet P1 by the light receiving
element "Sen-2" as shown by FIG. 6b or due to the arrival of the
leading edge of the sheet P2 at the light receiving element "Sen-2"
as shown by FIGS. 7b and 8b. In other words, the control unit 30
judges which waveform of the output signals Sig1 to Sig4 shown in
FIG. 5 the output signal "Sign" has. When the value "t1" is equal
to the value "ta", the control unit 30 judges that the stop of the
increase in the voltage of the output signal "Sign" is due to the
completion of the passing of the trailing edge of the sheet P1 by
the light receiving element "Sen-2" (see the waveforms of the
signals Sig1 and Sig2 in FIG. 5). Thereafter, the processing goes
to step S8. On the other hand, when the value "t1" is not equal to
the value "ta", the control unit 30 judges that the stop of the
increase in the voltage of the output signal "Sign" is due to the
arrival of the leading edge of the sheet P2 at the light receiving
element "Sen-2" (see the waveforms of signals Sig3 and Sig4 in FIG.
5). Thereafter, the processing goes to step S10.
[0051] When it is judged that the time "t1" is equal to the time
"ta", the control unit 30 judges at step S8 whether the sensor
"Sen" has detected the leading edge of the sheet P2. As shown by
FIGS. 6c and 6d, while the leading edge of the sheet P2 is passing
by the light receiving element "Sen-2", the area of the light
receiving element "Sen-2" covered by the sheet P2 is increasing.
Accordingly, the quantity of light received by the light receiving
element "Sen-2" is decreasing, and the voltage of the output signal
"Sign" from the light receiving element "Sen-2" is decreasing like
the output signals Sig1 and Sig2 for the periods from "t2" to "t3".
The control unit 30 judges the down-edge of the output signal
"Sign" as the time when the leading edge of the sheet P2 has
reached the light receiving element "Sen-2". The process at step S8
is repeated until the sensor "Sen" starts detecting the leading
edge of the sheet P2. Then, when the control unit 30 judges that
the leading edge of the sheet P2 has reached the light receiving
element "Sen-2", the processing goes to step S9.
[0052] When it is judged at step S7 that the time "t1" is not equal
to "ta", the control unit 30 subsequently judges whether the time
"t1" is smaller than "ta" (step S10). The time "ta" is a time that
is necessary for the trailing edge of the sheet P1 to complete
passing by the light receiving element "Sen-2". Therefore, in the
normal state, the time "t1" is equal to or smaller than "ta", and
it never happens that the time "t1" is greater than "ta".
Accordingly, when it is judged that the time "t1" is greater than
"ta" ("NO" at step S10), the control unit 30 judges that an error
has occurred. Then, the processing is terminated. On the other
hand, when the time "t1" is smaller than "ta", the processing goes
to step S11.
[0053] At step S11, the control unit 30 judges whether the trailing
edge of the sheet P1 has completed passing by the light receiving
element "Sen-2". When and after the trailing edge of the sheet P1
has completed passing by the light receiving element "Sen-2", the
light receiving element "Sen-2" is covered by only the sheet P2 as
shown by FIG. 7c. Because the sheet P2 travels in such a direction
as to cover more part of the light receiving element "Sen-2", the
voltage of the output signal "Sign" is steeply decreasing like the
output signal Sig3 in the period from "t2" to "t3" shown in FIG. 5.
Thus, the control unit 30 judges whether the trailing edge of the
sheet P1 has completed passing by the light receiving element
"Sen-2" by judging whether the decreasing speed in the voltage of
the output signal "Sign" is accelerated. When the completion of the
passing of the trailing edge of the sheet P1 by the light receiving
element "Sen-2" is judged at step S11, the processing goes to step
S9. When the completion of the passing of the trailing edge of the
sheet P1 is not judged at step S11, the processing goes to step
S12.
[0054] At step S12, the control unit 30 judges whether the voltage
of the output signal "Sign" is zero. In other words, at step S12,
the control unit 30 judges whether the leading edge of the sheet P2
has caught up with the trailing edge of the sheet P1 while the
light receiving element "Sen-2" is detecting the trailing edge of
the sheet P1 and the leading edge of the sheet P2 as shown by the
output signal Sig4 in FIG. 5 and FIGS. 8a-8c. When the voltage of
the output signal "Sign" is zero at step S12, the control unit 30
judges that the leading edge of the sheet P2 has caught up with the
trailing edge of the sheet P1. Thereafter, the processing goes to
step S13. On the other hand, when the voltage of the output signal
"Sign" is not zero at step S12, the control unit 30 judges that the
leading edge of the sheet P2 has not caught up with the trailing
edge of the sheet P1. Thereafter, the processing returns to step
S11.
[0055] When the voltage of the output signal "Sign" is zero, the
size "L" of the gap "g" between the sheets P1 and P2 is judged to
be zero (step S13). Thereafter, the processing goes to step
S17.
[0056] At step S9, the control unit 30 takes in a value of the time
"t2" (see FIG. 5) when the voltage of the output signal "Sign"
starts decreasing due to the detection at step S8 or the detection
at step S11. Thereafter, at step S14, the control unit 30 judges
whether the leading edge of the sheet P2 has completed passing by
the light receiving element "Sen-2". When and after the leading
edge of the sheet P2 has completed passing by the light receiving
element "Sen-2", the light receiving element "Sen-2" is completely
covered by the sheet P2. Accordingly, the quantity of light
received by the light receiving element "Sen-2" becomes zero, and
the voltage of the output signal "Sign" becomes zero. Therefore,
the control unit 30 judges whether the leading edge of the sheet P2
has completed passing by the light receiving element "Sen-2" by
judging whether the voltage of the output signal "Sign" has become
zero. When the completion of the passing of the leading edge of the
sheet P2 by the light receiving element "Sen-2" is judged at step
S14, the processing goes to step S15. The process at step S14 is
repeated until it is judged that the leading edge of the sheet P2
has completed passing by the light receiving element "Sen-2".
[0057] At step S15, the control unit 30 takes in a value of the
time "t3" (see FIG. 5) when the leading edge of the sheet P2 has
completed passing by the light receiving element "Sen-2".
[0058] Then, the control unit 30 calculates the size "L" of the gap
"g" between the sheets P1 and P2 from the length "l" of the light
receiving element "Sen-2", the speed "Vb" and the time "t3".
Specifically, the control unit 30 figures out the size "L" of the
gap "g", based on the following expression (1).
L=t3.times.Vb-1 (1)
[0059] Next, at step S17, the control unit 30 controls the driver
31 and the feed rollers 19 to adjust the speed "Va" in accordance
with the size "L" of the gap "g". More specifically, the control
unit 30 specifies a value for the speed "Va", referring to Table 1,
and the control unit 30 controls the driver 31 and the feed rollers
19 so that the sheet P2 will be fed at the specified speed "Va".
Since the speeds V2, V3, V4 and V5 in Table 1 are larger than the
speed "Vb", the gap "g" between the sheets P1 and P2 will be
decreasing. Then, the processing goes to step S18.
[0060] At step S18, the control unit 30 judges whether N is equal
to five. Step S18 is a process to judge whether the processes from
step S2 to step S17 have been carried out with regard to all the
sensors Se1 to Se5. When N is equal to five, the procedure is
completed. When N is not equal to five, the processing goes to step
S19.
[0061] At step S19, the control unit 30 resets the timer.
Subsequently, the control unit 30 makes an increment of N at step
S20. Thereafter, the processing returns to step S2.
[0062] In this way, all the sensors Se1 to Se5 are subjected to the
same processing. Accordingly, as shown by FIG. 5, the gap "g"
detected by a more downstream sensor of the sensors Se1 to Se5 is
smaller than the gap "g" detected by a more upstream sensor.
Effects
[0063] In the sheet feeding device 35 or in the image forming
apparatus 1 provided with the sheet feeding device 35, the gap "g"
between two sheets P1 and P2 that are sequentially fed can be made
closer to zero. In the sheet feeding device 35, a plurality of
sensors Se1 to Se5 are provided in the sheet route R at a plurality
of locations, and the control unit 30 can adjust the speed "Va" of
the sheet P2 fed by the feed rollers 19 at a plural number of
times. Accordingly, the sheet feeding device 35 can control the
speed "Va" more precisely, compared with the sheet feeding device
disclosed by Reference 1 that detects the gap between sheets only
once. In the sheet feeding device 35 and the image forming
apparatus 1 provided with the sheet feeding device 35,
consequently, it is possible to make the gap "g" between sheets P1
and P2 closer to zero. Thereby, the lives of the feed rollers 19
and the intermediate transfer belt 11 are prolonged, and the
productivity is improved.
[0064] In the sheet feeding device 35 and in the image forming
apparatus 1 provided with the sheet feeding device 35, the gap "g"
between sheets P1 and P2 can be made closer to zero, and even if
the speeds "Va" and "Vb" are low, the productivity can be
maintained high. If the speeds "Va" and "Vb" are low, the speed of
a sheet traveling in the fixing device 22 is also low, which
permits the fixing temperature of the fixing device 22 to be set
low. Thereby, the power consumption of the image forming apparatus
1 can be lowered.
[0065] In the sheet feeding device 35 and in the image forming
apparatus 1 provided with the sheet feeding device 35, when the gap
"g" between sheets is relatively large, the speed "Va" is
accelerated, and when the gap "g" between sheets becomes relatively
small, the speed "Va" is decelerated. When the leading edge of the
sheet P2 is catching up with the trailing edge of the sheet P1, the
speed "Va" is decelerated so that the sheet P1 and the sheet P2 are
prevented from overlapping with each other.
[0066] Further, in the sheet feeding device 35 and the image
forming apparatus 1 provided with the sheet feeding device 35, an
overlap correction mechanism 40 is provided, and even if the sheets
P1 and P2 overlap with each other, the overlap can be corrected by
the overlap correction mechanism 40.
Modifications
[0067] The sheet feeding device 35 and the image forming apparatus
1 provided with the sheet feeding device 35 are not limited to the
embodiment above. Modifications are possible within the scope of
the invention. In the following, modifications of the sheet feeding
device 35 and the image forming apparatus 1 provided with the sheet
feeding device 35 is described.
[0068] FIGS. 9a-9c show modifications of the sensors Se1 to Se5 for
the sheet feeding device 35. As FIG. 9a shows, a light receiving
member Se1-2 may be provided for the light sources Se1-1 to Se5-1.
As FIG. 9b shows, a camera "C" may be provided instead of the
sensors Se1 to Se5. In this case, the camera "C" is preferably
located in a position suited to take pictures mainly around the
timing rollers 20 as shown by FIG. 9c. This is because the target
is that the gap "g" becomes zero before the gap "g" comes to the
timing rollers 20.
[0069] In the embodiment above, the control unit 30 adjusts the
speed "Va" while fixing the speed "Vb". However, the speed "Vb" may
be adjusted, while the speed "Va" may be fixed. In this case, when
there is a gap "g" between sheets P1 and P2, the control unit 30
controls the timing rollers 20 and a driver for the timing rollers
20 so that the speed "Vb" will be lower than the speed "Va".
[0070] Additionally, when the most upstream sensor Se1 detects no
gap between the sheets P1 and P2, the control unit 30 may control
the feed rollers 19 and the driver 31 or the timing rollers 20 and
the driver for the timing roller 20 so that the speed "Va" will be
lower than the speed "Vb". When the sensor Se1 detects no gap
between the sheets P1 and P2, there is a possibility that the
sheets P1 and P2 may overlap with each other. For this reason, the
control unit 30 makes a control so as to form a gap "g" between the
sheets P1 and P2 once and then to close the gap "g". Thereby, the
sheets P1 and P2 can be prevented from going out of the route R
while overlapping with each other. Further, when any other sensors
Set to Se5 than the sensor Se1 detect no gap between the sheets P1
and P2, the control unit 30 may control the feed rollers 19 and the
driver 31 or the timing rollers 20 and the driver for the timing
rollers 20 so that the speed "Va" will be lower than the speed
"Vb".
[0071] The overlap correction mechanism 40 is not limited to have
the structure shown by FIG. 2. FIG. 10 shows a modified overlap
correction mechanism 40'. The overlap correction mechanism 40' is
made by bending a guide plate that is a component of the route R.
The leading edge of the sheet P2 is hooked by the guide plate, and
thereby, an overlap of the sheets P1 and P2 is corrected.
[0072] Although the present invention has been described with
reference to the embodiments above, it is to be noted that various
changes and modifications are possible to those who are skilled in
the art. Such changes and modifications are to be understood as
being within the scope of the present invention.
* * * * *