U.S. patent application number 11/118386 was filed with the patent office on 2005-12-08 for sheet feeding apparatus and method of detecting double feed.
This patent application is currently assigned to NISCA CORPORATION. Invention is credited to Hirose, Syunichi, Sano, Kazuhide, Yamashita, Masashi.
Application Number | 20050269759 11/118386 |
Document ID | / |
Family ID | 35446818 |
Filed Date | 2005-12-08 |
United States Patent
Application |
20050269759 |
Kind Code |
A1 |
Sano, Kazuhide ; et
al. |
December 8, 2005 |
Sheet feeding apparatus and method of detecting double feed
Abstract
A sheet feeding apparatus includes a stacker for stacking a
sheet; a feeding device for feeding the sheet on the stacker to a
predetermined processing position; a drive device for driving the
feeding device; a double feed detection device having a sending
element and a receiving element arranged at a downstream side of
the feeding device for detecting a double feed of the sheet; a
sensitivity adjustment device for comparing a detected value of the
receiving element with a predetermined reference value for
adjusting an output of the sending element; and a control device
for controlling a transport speed of the feeding device. The
sensitivity adjustment device adjusts the output of the sending
element when the control device controls the drive device to stop
the sheet or to decelerate the sheet at a predetermined speed.
Inventors: |
Sano, Kazuhide;
(Yamanashi-ken, JP) ; Hirose, Syunichi;
(Minami-alps-shi, JP) ; Yamashita, Masashi;
(Kofu-shi, JP) |
Correspondence
Address: |
KANESAKA BERNER AND PARTNERS LLP
SUITE 300, 1700 DIAGONAL RD
ALEXANDRIA
VA
22314-2848
US
|
Assignee: |
NISCA CORPORATION
Minamikoma-gun
JP
|
Family ID: |
35446818 |
Appl. No.: |
11/118386 |
Filed: |
May 2, 2005 |
Current U.S.
Class: |
271/3.01 ;
343/700MS |
Current CPC
Class: |
B65H 7/125 20130101;
B65H 2557/61 20130101; B65H 2553/30 20130101 |
Class at
Publication: |
271/003.01 ;
343/700.0MS |
International
Class: |
B65H 083/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 8, 2004 |
JP |
2004-170395 |
Claims
What is claimed is:
1. A sheet feeding apparatus comprising: a stacker for stacking
sheets; a feeding device for feeding the sheets on the stacker to a
predetermined processing position; a drive device for driving the
feeding device; a double feed detection device arranged at a
downstream side of the feeding device for detecting a double feed
of the sheets and having a sending element and a receiving element;
a control device for controlling a transport speed of the feeding
device; and a sensitivity adjustment device for comparing a
detected value of the receiving element with a predetermined
reference value for adjusting an output of the sending element,
said sensitivity adjustment device adjusting the output of the
sending element in a condition such that the control device
controls the drive device to stop the sheet or to decelerate the
sheet at a predetermined speed.
2. A sheet feeding apparatus according to claim 1, wherein said
sending element includes an ultrasonic wave sending element and
said receiving element includes an ultrasonic wave receiving
element, said sensitivity adjustment device having an amplifier
device for increasing or decreasing amplitude of the ultrasonic
wave sending element.
3. A sheet feeding apparatus, comprising: a stacker for stacking
sheets; a feeding device for separating the sheets on the stacker
into a single sheet and feeding the sheet to a predetermined
processing position; first and second transport devices arranged
between the stacker and the sheet processing position with a
predetermined distance therebetween; a double feed detection device
arranged between the first and the second transport devices for
detecting a double feed of the sheets, and having a sending element
and a receiving element disposed oppositely; a control device for
controlling transport speeds of the first and second transport
devices; a sheet sensor for detecting that the sheet fed from the
stacker reaches a downstream side of the first and second transport
devices; and a sensitivity adjustment device for comparing a
detected value of the sending element with a predetermined
reference value for adjusting an output of the sending element so
that the sensitivity adjustment device increases or decreases the
output of the sending element according to a sheet leading edge
detection signal from the sheet sensor.
4. A sheet feeding apparatus according to claim 3, wherein said
control device stops the drive device according to the sheet
leading edge detection signal from the sheet sensor, and restarts
the drive device after the sensitivity adjustment device increases
or decreases the output of the sending element.
5. A sheet feeding apparatus according to claim 3, wherein said
control device drives the drive device at a predetermined speed
according to the sheet leading edge detection signal from the sheet
sensor, and drives the drive device at a speed higher than before
after the sensitivity adjustment device increases or decreases the
output of the sending element.
6. A sheet feeding apparatus according to claim 3, wherein said
first and said second transport devices have a first operation mode
to transport the sheet to the sheet processing position at a first
speed to perform a specific process, and a second operating mode to
transport the sheet to the sheet processing position at a second
speed without performing the specific process, said first speed
being higher than the second speed.
7. A method of detecting a double feed of sheets transported from a
stacker, comprising: a transport step for transporting the sheet on
the stacker to a predetermined processing position; a double feed
detection step arranged between the stacker and the sheet
processing position for detecting the double feed of the sheets
with an ultrasonic wave sensor having a sending element and a
receiving element; a sensor sensitivity adjustment step for
changing an output of the sending element while the sheet is
stopped or is decelerated at a predetermined speed between the
stacker and the sheet processing position; and a discharging step
for discharging the sheet by restarting the sheet or moving the
sheet at a speed higher than the predetermined speed after the
sensor sensitivity adjustment step.
8. A method according to claim 7, wherein said sensor sensitivity
adjustment step is executed when the sheet is nipped by at least
two transport devices arranged at an upstream side and a downstream
side in a direction that the sheet is transported.
Description
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
[0001] The present invention relates to a sheet feeding apparatus
for sequentially separating sheets such as originals on a stacker
into a single sheet and feeding the sheet to a processing platen
for reading in other processes. More particularly, the present
invention relates to a sheet feeding apparatus provided with a
double feed detection function for detecting a double feed of
sheets in a path from the stacker to a processing platen.
[0002] A conventional sheet feeding apparatus feeds sheets such as
originals to a processing platen. A reading apparatus for reading
images on the sheets at the processing platen is widely known as a
scanner, copier, or a facsimile machine. An apparatus for printing
at a processing platen is widely used as a printer.
[0003] It is necessary to accurately separate the sheets into a
single sheet and to feed the sheet to the processing platen with
proper positioning. Particularly, when sequentially reading a
series of originals, it is possible that the sheet is not fed to
the platen, i.e., a non-feed, or two or more sheets are fed to the
platen, i.e., a double feed, thereby causing an improper process at
the processing platen. When printing a series of originals at the
processing platen, an incorrect process may occur at the platen due
to the non-feed or double feed.
[0004] Accordingly, it is necessary to stop a process when the
double feed or non-feed is detected while feeding the sheet from
the stacker to the processing platen. For example, a sensor is
provided for detecting the sheet prior before the processing platen
(at an upstream side). When the sheet does not reach a
predetermined position for a predetermined amount of time after the
sheet is fed from the stacker, it is determined that the non-feed
occurs and the process at the platen stops.
[0005] It is difficult to accurately detect the double feed of the
sheets, and a detection element and a judgment circuit are
expensive. In a system in which scanners or copiers are linked
through a network, the double feed of the sheets can cause a
serious system error. Accordingly, it is necessary to accurately
detect the double feed with low cost.
[0006] Japanese Utility Model (Kokoku) No. 06-49567, and Japanese
Patent Publications (Kokai) No. 2000-95390 and No. 2003-176063
disclose devices for detecting the double feed using a pair of
ultrasonic wave sensors. In the devices, a pair of ultrasonic wave
sensors is arranged at opposing positions to sandwich a sheet in a
sheet transport path. A sensor on a wave receiving side (wave
receiving element) detects ultrasonic waves emitted from a wave
sending side (wave sending element) to detect the double fed
through attenuation of the ultrasonic waves permeating the
sheet.
[0007] FIG. 2 shows an example of a widely known ultrasonic wave
sensor for detecting the sheet. A piezoelectric diaphragm is
embedded in a metal case covering the sensor. A high-frequency
voltage is applied to an electrode formed on the piezoelectric
diaphragm, thereby generating ultrasonic waves from a surface of
the case. The case is filled with a plastic 13. A wave receiving
element has a structure same as that of the wave sending element
and receives the ultrasonic waves to oscillate a surface of the
case. As a result, the piezoelectric diaphragm fixed to the case
also oscillates to output electrical energy to an external
source.
[0008] The piezoelectric diaphragm may have a variance in a
dimension and a shape thereof, and the metal case may have a
variance in a characteristic frequency. Accordingly, in a
manufacturing process, it is necessary to combine the wave sending
and wave receiving elements within a tolerable range to achieve
accurate detection. Therefore, conventionally, characteristics of
each of the elements are measured in the manufacturing process, so
that only the elements within a tolerance level are used to produce
the ultrasonic wave sensor.
[0009] The elements of the conventional ultrasonic wave sensor for
detecting the double-feed of the sheets are measured in the
manufacturing process as described above, thereby increasing cost
of the elements. When an ambient temperature fluctuates or the
sensor is deformed upon receiving an impact, it is possible to
cause an erroneous detection. Accordingly, it is necessary to
select the detection elements with similar characteristics within a
specific range for the wave sending side and the wave receiving
side, so that the sensors detect the sheets without an influence of
a temperature or deformation. Accordingly, the apparatus tends to
be expensive and durability may be compromised.
[0010] In view of the problems described above, an object of the
present invention is to provide a sheet handling apparatus capable
of accurately detecting a double feed of sheets fed from a stacker
to a processing platen, thereby eliminating an erroneous process at
the processing platen. In the sheet feeding apparatus, detection
elements for detecting the double feed of the sheets are adjusted
in a state that the detection elements are disposed in a transport
path, so that a variance in characteristics between the detection
elements at sending and receiving sides is adjusted.
[0011] Further objects and advantages of the invention will be
apparent from the following description of the invention.
SUMMARY OF THE INVENTION
[0012] In order to attain the objects described above, according to
the invention, a sheet feeding apparatus includes a stacker for
holding sheets; a feeding device for kicking a sheet from the
stacker to a predetermined processing position; and a sending
element and a receiving element disposed at a downstream side of
the feeding device for detecting a double feed of the sheets. The
sending and receiving elements are composed of a wave sending
element and a wave receiving element of an ultrasonic wave sensor,
and are arranged to face each other on opposite sides of the sheet.
A sensitivity adjustment device is provided for comparing a
detected value of the wave receiving element with a predetermined
reference value to adjust an output of the wave sending element. A
control device of a drive device is provided for driving the
feeding device.
[0013] The sensitivity adjustment device adjusts the output of the
wave sending element when the drive device is stopped or
decelerated at a predetermined speed. The sensitivity adjustment
device compares the output value of the wave receiving element with
the predetermined reference value. According to a result of the
comparison, the sensitivity adjustment device increases or
decreases, for example, amplitude of high frequency power in a case
of the ultrasonic sensor to change electrical energy supplied to
the wave sending element. Accordingly, it is possible to obtain a
predetermined output from the wave receiving element. It is
possible to stably detect the double feed of the sheets even if
detection sensitivity of the wave sending element and the wave
receiving element is degraded due to a temperature change or
aging.
[0014] According to the present invention, first and second
transport devices may be arranged between the stacker and the
predetermined processing position with a gap therebetween. The
double feed detection device having the sending element and the
receiving element is arranged between the first and second
transport devices. The sensitivity adjustment device is disposed
for comparing the detected value of the sending element to a
predetermined reference value and adjusting the output of the
sending element. A sheet sensor is disposed for detecting that the
sheet from the stacker reaches a downstream side of the first and
second transport devices to send a sheet leading-edge detection
signal. According to the sheet leading-edge detection signal, the
sensitivity adjustment device adjusts the output of the sending
element. Also, according to the sheet leading-edge detection signal
from the sheet sensor, the first and second transport devices stop.
After the sensitivity adjustment device completes the sensitivity
adjustment, the first and second transport devices restart to
discharge the sheet at a high speed.
[0015] According to the present invention, a method of detecting a
double feed includes a transport step for transporting a sheet from
a stacker to a predetermined sheet processing position; a double
feed detection step for detecting the double feed of the sheets
with an ultrasonic wave sensor comprising a sending element and a
receiving element and arranged between the stacker and the sheet
processing position; a sensor sensitivity adjustment step for
changing an output of the sending element by stopping the sheet
traveling between the stacker and the sheet processing position or
decelerating the sheet at a predetermined speed; and a discharge
step for moving the sheet after the sensor sensitivity adjustment
step or discharging the sheet at a speed higher than the
predetermined speed. In the sensor sensitivity adjustment step, the
sheet is nipped by at least two transport devices arranged at
upstream and downstream sides in a transport direction of the
sheet.
[0016] In the invention, the sending element and the receiving
element of the ultrasonic wave sensor are arranged in a path for
transporting the sheets. When detecting the double feed of the
sheets, the sensitivity adjustment device compares the output of
the receiving element with the predetermined reference value for
adjusting the output of the sending element. Accordingly, it is
possible to accurately detect the double feed through the
adjustment of the output of the sending element even if a
fluctuation occurs due to a variance in characteristics of the
sending and receiving side elements, mounting positions of the
elements, or an ambient temperature.
[0017] Accordingly, even when the ultrasonic wave sensor has
characteristics changing easily, a tolerable range of
characteristics is widened, thereby reducing manufacturing cost.
Further, the output of the wave sending side is adjusted when
transport of the sheet such as a test sheet is stopped or the sheet
is decelerated to a predetermined speed. Accordingly, it is
possible to accurately obtain the output of the wave sending
element without an influence of a variance in a sheet transport
speed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a schematic view showing a sheet feeding apparatus
according to the present invention;
[0019] FIG. 2 is a schematic view showing a double feed detection
device composed of an ultrasonic wave sensor;
[0020] FIGS. 3(a) and 3(b) are block diagrams showing a control
circuit of the sheet feeding apparatus shown in FIG. 1, wherein
FIG. 3(a) shows a control circuit for double-feed detection, and
FIG. 3(b) shows a sensitivity adjustment circuit;
[0021] FIGS. 4(a) and 4(b) are graphs showing waveforms of output
signals from the ultrasonic wave sensor shown in FIG. 2, wherein
FIG. 4(a) shows a single feed and FIG. 4(b) shows a double
feed;
[0022] FIG. 5 shows a block diagram showing the control circuit of
the sheet feeding apparatus shown in FIG. 1;
[0023] FIG. 6 is a flow chart showing an operation of adjusting
sensitivity of the sheet feeding apparatus shown in FIG. 1;
[0024] FIG. 7 is a flow chart showing an operation of detecting the
double feed of sheets in the sheet feeding apparatus shown in FIG.
1;
[0025] FIG. 8 is a schematic view of an image reading apparatus and
an image forming apparatus with the image reading apparatus as a
unit according to the present invention;
[0026] FIG. 9 is a view showing a sheet feeding unit of the image
reading apparatus shown in FIG. 8;
[0027] FIG. 10 is a perspective view showing a paper feed stacker
of the image reading apparatus shown in FIG. 9;
[0028] FIGS. 11(a) and 11(b) are views showing a drive mechanism of
the image reading apparatus shown in FIG. 9, wherein FIG. 11(a)
shows a sheet feeding unit, and FIG. 11(b) shows a transport unit;
and
[0029] FIGS. 12(a) to 12(e) are views showing an operation of
feeding a sheet in the image reading apparatus shown in FIG. 8.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0030] Hereunder, preferred embodiments of the present invention
will be explained with reference to the accompanied drawings. The
invention applies to an apparatus and a method for detecting a
double feed of two or more overlapped sheets before reaching a
processing position when the sheets stacked on a stacker in a sheet
feeding unit of an image reading apparatus such as a copier, or
printer are separated and transported one by one to the processing
position such as an image reading platen, or printing platen.
[0031] FIG. 1 is a schematic view of a sheet feeding mechanism
according to an embodiment of the present invention. FIG. 2 is a
schematic view of a double feed detection device composed of an
ultrasonic wave sensor. FIGS. 3(a) and 3(b) are circuit diagrams of
a control circuit.
[0032] As shown in FIG. 1, the sheet feeding apparatus is equipped
with a stacker 1 for storing sheets; a sheet guide 3 for guiding
the sheets from the stacker 1 to the processing platen 2; at least
two transport devices, i.e. first and second transport devices 4
and 5, arranged on the sheet guide 3; and a double feed detection
device 6 arranged between the first transport device 4 and the
second transport device 5 for detecting a double feed of the
sheets. A separating device separates the sheets stacked on the
stacker 1 into a single sheet, and the first and second transport
devices 4 and 5 feed the sheet to a processing position (platen 2).
Predetermined processes such as reading images, printing, stamping
or stapling are performed at the processing position. Then, the
sheet is discharged to a discharge stacker 9.
[0033] The stacker 1 is composed of a tray for stacking the sheets.
An empty sensor S1 for detecting the presence of sheets, and a size
sensor S2 for detecting a length of the sheets can be mounted
according to specifications required by the apparatus. The
separating device for sequentially separating the uppermost or the
lowermost sheets for feeding is disposed at the leading end of the
stacker 1.
[0034] A combination of a first transport roller 4a and a friction
pad 4b as shown in the drawing, or a combination of a forward drive
roller and a reverse drive roller, or the combination of a feed
roller and separating claw (corner separator) are widely known and
used as the separating device. Depending on the apparatus, even a
vacuum separation can be used. The present invention allows for the
use of either of these methods for separating sheets into single
sheets. The drawing provided shows a configuration for the
separating device that employs a first transport roller 4a
(although a belt is also perfectly acceptable) for rotating in a
direction to feed the sheet, and a friction pad 4b that prevents a
double feed of sheets. The transport device 4 transports the
separated sheet toward the platen 2. A resist roller 5a for
temporarily idling a sheet in the transport path between the
separating device and the platen 2, and a transport roller 8a are
disposed for continuing to transport a sheet from the first
transport roller 4a to the platen 2.
[0035] At least two transport devices of the first and second
transport device between the stacker 1 and the processing platen 2
are provided. As shown in the drawing, the first transport roller
4a is set as the first transport device; and the resist roller 5a
is set as the second transport device. The first and second
transport devices 4a and 5a are disposed with a spacing that is
shorter than the shortest size sheet length. Note that the resist
rollers 5 employ a known configuration. A pair of rollers 5a and 5b
in mutual contact forms a curve in sheets fed from the transport
roller 4a to correct any skewing in the sheet. Then, at a
predetermined timing, the rollers 5a and 5b feed the sheet to the
platen 2.
[0036] A double feed detection sensor 6 and the sheet sensor 7 for
detecting a leading edge of a sheet are arranged between the first
and the second transport rollers 4 and 5. The double feed detection
sensor 6 is configured by arranging a pair of a wave sending
element 6a and a wave receiving element 6b at opposite positions
with the sheet moving therebetween along the sheet guide 3. The
sheet sensor 7 is configured by arranging a pair of a light
emitting element 7a and a light receiving element 7b to oppose each
other. The double feed detection sensor 6 shown in the drawing is
an ultrasonic wave sensor. The wave sending element 6a and the wave
receiving element 6b have a same structure of a piezoelectric
diaphragm. Note that the symbol 8a in the drawing represents a
transport roller and is disposed at the sheet guide 3 for
controlling the feeding of the sheet to the platen at a
predetermined speed.
[0037] The double feed detection sensor 6 is composed of an
ultrasonic wave sensor. The wave sending element 6a and the wave
receiving element 6b are disposed at opposite positions. Both the
wave sending element 6a and the wave receiving element 6b are
composed of a piezoelectric diaphragm having a same structure, as
shown in the example of FIG. 2. In each of the ultrasonic wave
sensors, a piezoelectric diaphragm 11 such as a piezoelectric
diaphragm ceramic plate is embedded in and connected to cylindrical
external frame cases 10 made of a metallic material such as an
aluminum alloy. The case 10 is filled with a resilient plastic 13.
Electrodes are formed on the front and back surfaces of the
piezoelectric diaphragms 11. One of the lead wires 12 is connected
to the piezoelectric diaphragm 11 and the other is connected to the
case to provide electrical grounding. When the high-frequency power
is applied to the lead wire 12, the piezoelectric diaphragm 11
oscillates at a predetermined frequency. Then, electromotive force
generated by the excited piezoelectric diaphragm 11 on one side is
transmitted outside along the lead wire 12.
[0038] The wave sending element 6a is electrically connected to a
high frequency power source. The following will describe the
electrical connection in reference to FIG. 3(a). The power 14 is
connected to the high frequency oscillating circuit 15. The
oscillating circuit generates high frequency voltages of between 30
KHz and 40 KHz. An amplifier circuit 16 amplifies and supplies that
to the wave sending element 6a. When this occurs, the piezoelectric
diaphragm 11, whose inherent oscillating frequency is set to a
predetermined frequency, generates ultrasonic waves from the case
10 at that frequency. Note that the amplifier rate of the amplifier
circuit 16 is set by the control CPU. Instruction signals from the
CPU undergo D/A conversion and are then relayed to the amplifier
circuit 16.
[0039] The ultrasonic waves generated from the wave sending element
6a are transmitted to the wave receiving element 6b passing through
the sheet S on the sheet guide 3. The ultrasonic waves that travel
through the sheet cause the case 10 to oscillate in the wave
receiving element 6b, thereby causing the piezoelectric diaphragm
11 that is mounted to the case 10 also to oscillate. The
electromotive force generated by the oscillation of the
piezoelectric diaphragm 11 is led to the lead wire 12 from the
electrode. The current is output as a detected value proportional
to the amplitude of the piezoelectric diaphragm 11.
[0040] The wave receiving element 6b is connected to an amplifier
circuit 18 for amplifying the detecting current. The amplifier
circuit 18 amplifies the detected current generated by the
piezoelectric diaphragm 11. The amplifier circuit 18 is connected
to a smoothing circuit 19 composed of an integrated circuit. The
detected current of the amplified wave is averaged by the smoothing
circuit 19 and sent to the comparator circuit 20. At the comparator
circuit 20, the current from the smoothing the circuit 19 is
compared to a preset reference value. The reference value is
determined in the following way.
[0041] FIGS. 4(a) and 4(b) show the output values (analog voltage)
of the smoothing circuit 19. FIG. 4(a) shows the output value when
a single sheet is fed through the transport path. FIG. 4(b) shows
the output value when two sheets are fed. A sheet kicked from the
stacker 1 is transported from the first transport roller 4a to the
second transport roller 5a. In FIG. 4(a), the symbol A represents
the output value when the leading edge of the sheet is moving from
the first transport roller 4a toward the second transport roller
5a. In that span of time, the waveform is unstable. In the same
drawing, the symbol B represents the output value when the sheet is
nipped and held by the first transport roller 4a and the second
transport roller 5a. During the span of time, the waveform is
stable. In the same drawing, the symbol C is the output value when
the trailing edge of the sheet, still held by the second transport
roller 5a, is released from the first transport roller 4a. At this
time, the waveform becomes unstable again.
[0042] It is clear that the levels of the output values are
different in the region B representing the stable waveforms in the
drawing when there is a single sheet or two sheets. Specifically,
when the ultrasonic waves pass through the sheet, the degree of
attenuation is smaller when there is one sheet, which means there
is a higher detected electrical current. Conversely, when there are
two or more sheets, the degree of attenuation of the ultrasonic
waves increases, thereby reducing the amount of detected electrical
current. In other words, the detected current output from the
smoothing circuit is higher than the detected current when there is
one sheet between the pair of transport rollers 4a and 5a, and it
is lower than the detected current when there are two or more
sheets when compared to the stable reference value. Note that the
thicknesses of paper or the quality of paper used can differ.
Therefore, it is necessary to experiment using a variety of
different paper types to find the appropriate reference value for
of the machine specifications.
[0043] Comparison data received from the comparator circuit 20 is
then transferred to the control CPU (control circuit) 21. Size
sensors S2 and S3 arranged on the stacker 1, a sheet sensor 7, and
a discharge sensor, not shown, arranged on the sheet guide 3 are
connected to the control CPU21. The sheet sensor 7 is arranged
between the first transport roller 4a and second transport roller
5a for transmitting the timing for the arrival of the leading edge
of a sheet to the control CPU21.
[0044] The control CPU is connected for transmitting instruction
signals to the motor driver circuit 22 of the drive motor M for
driving the first and second transport rollers 4a and 5a. Power 25
is connected to a pulse generator 23 for supplying pulse currents
to the motor driver circuit 22. The drive motor M, which receives
energy from the power 25, is composed of a stepping motor. The
pulse generator 23 is connected to a counter 24. The counter 24
calls the number of pulse currents that are supplied to the drive
motor M, and is connected to the control CPU 21.
[0045] An operation for detecting a double feed of sheets on the
apparatus having the configuration of FIG. 1 will be explained with
reference to the flowchart in FIG. 7. The control programs on the
CPU 21 are configured as described below for the transport control
unit 28. When the power 14 to the apparatus is turned on, the CPU
21 judges whether there is a sheet on the stacker 1 according to
the status signals received from the empty sensor S1 (F1). If a
sheet is present, the CPU 21 issues a start signal to the motor
drive circuit 22. Receiving the signal, the motor driver circuit 22
begins supplying pulse power from the power 25 to the drive motor M
via the pulse generator 23. At the start up of the drive motor M
(F2), the first transport roller 4a that is connected to the drive
motor M rotates in the clockwise direction of FIG. 1 to kick a
sheet from the top of the stacker 1.
[0046] The friction pad 4b separates the sheets into a single sheet
when the first transport roller 4a kicks several sheets from the
stacker 1. The single sheet advances along the sheet guide 3, and
the leading edge of the sheet arrives at the second transport
device 5 passing between the double feed detection sensor 6, then
the sheet sensor 7. The second transport device 5 is in a stopped
state at this time. Therefore, when the leading edge of the sheet
enters a nipping point (where the rollers are in contact with each
other) between the second transport rollers 5a and 5b, the sheet
forms a corrective loop shape. When the leading edge of the sheet
arrives at the sheet sensor 7, the transport control unit 28 starts
the timer (F3) by receiving the detection signal from this sheet
sensor 7. The drive motor M stops after the time T1 (F4).
[0047] Next, the CPU 21 receives processing start signal from the
main apparatus such as an image reading device or printer as a
paper feed signal (F5), then restarts the drive motor M with that
signal. The drawing shows a transmission mechanism configured of a
one-way clutch, so that the forward drive of the drive motor M
rotates the first transport roller 4a and the reverse drive rotates
the second transport roller 5a (selectively).
[0048] Therefore, when the drive motor M restarts, it rotates the
second transport roller 5a, and the first transport roller 4a
remains in a stopped status. The second transport roller 5a then
feeds the sheet toward the transport roller 8a (F6). Simultaneous
to this, the transport control unit 28 of the CPU 21 restarts a
timer T2 (F7). The timer T2 is set to a value where T1<T2, so
that the loop in the sheet (curved in a registration loop) can be
released. When a predetermined amount of time passes for the timer
T2, the CPU 21 issues a double feed detection instruction signal
(F8). Upon receiving the signal, the detection signal/reference
value comparator 29 inside the CPU 21 receives the double feed
comparison data (see FIG. 3(a)) and judges whether there is a
double feed of sheets (F9). To detect a double feed (or judge the
double feed), values detected from the wave receiving element 6a
are compared with predetermined reference values (LVO in FIG. 2) at
the comparator circuit 20. If the detected value is lower than the
reference value, the system judges that there has been a double
feed of two or more sheets. [0037]
[0049] Changes in the ambient environment or other conditions can
cause erroneous detections to occur in the detection
signal/reference value comparator unit 29 of the configuration
shown in the drawings. To prevent erroneous detections in the
detected value of the wave receiving element 6b, the sheet is
formed into a registration loop by the second transport device 5,
and an air layer is formed between the two or more sheets. Then,
the double feed detection is performed when the registration loop
is released. Also, the sheet is detected while nipped by both the
first transport roller 4a and the second transport roller 5a. As
the sheet is being transported, the system judges with the average
value detected for a predetermined distance (length).
[0050] The detection signal/reference value comparison unit 29
executes a double feed process (F10) when a double feed of sheets
has been judged. In the double feed process, the apparatus stops
and the operation panel displays that there has been a double feed
in the system. In this case, an operator may either take a sheet
out of the sheet guide 3 and reset it on the stacker 1, or
discharge the sheet to a discharge stacker 9 without any processing
at the processing platen 2. When the detection signal/reference
value comparison unit 29 has determined that the feeding of a sheet
is normal (that there has not been a double feed), the second
transport roller 5a and the transport roller 8a feed the sheet to
the processing platen where a predetermined process is applied to
the sheet (F12). When the trailing edge of the sheet passes over
the sheet sensor 7, the CPU 21 detects the status signal to drive
the drive motor M (F2) to cause a next sheet to be kicked from the
stacker 1 in the same way.
[0051] Note that the transport roller 8a is linked to a drive motor
that is different from the drive motor M mentioned above. However,
it feeds the sheet to the processing platen 2 at a predetermined
speed. The sheet having undergone the predetermined process at the
processing platen 2 is sequentially fed and stored in the discharge
stacker 9. A discharge sensor disposed on the edge of the sheet
exit on the discharge stacker 9 detects that a sheet has been
stored (F13). At the status signal from the empty sensor S1 for
detecting whether there are sheets on the stacker 1, the CPU 21
determines whether to continue the series in the job or to end the
series (Fl4). When the empty sensor S1 detects a next original on
the stacker 1, the CPU 21 issues a paper feed instruction signal
(F5) to feed the next sheet to the processing platen 2.
[0052] The operation described above relates to conventional sheet
feeding steps. If the apparatus is a scanner device for reading
images sequentially on a sheet at the processing platen 2, the
transport control unit 28 which is executed in the CPU 21,
described above, controls the speed of the drive motor M in the
following way.
[0053] The transport control unit 28 sets the transport speed of
the first transport device 4 and the transport roller 8a according
to the sheet processing conditions at the signals from the scanner
device. The transport speed is determined according to the reading
conditions of images by the scanner device. The conditions include
color, or black-and-white, high or low reading resolutions.
Therefore, the transport speed can vary according to the
conditions. Generally, color and high resolution readings are
performed at a low speed, whereas black-and-white and low
resolution readings are set to a high speed. Therefore, the
transport speed is set to a variety of high or low speeds according
to the reading conditions.
[0054] FIG. 3(b) shows a sensitivity adjustment circuit (means) 35
embedded in the CPU 21. The detective value from the wave receiving
element 6b is amplified by the amplifier circuit 18. The smoothing
circuit 19 smoothes this value, and the comparator circuit 20
compares it to the reference value. In this circuit configuration,
first the amplifier rate is transmitted as an analog voltage value
from the sensitivity adjustment circuit 35 of the CPU 21 to the
amplifier circuit 16, which supplies high-frequency power to the
wave sending element 6a, via the D/A converter 17. The amplifier
circuit 16 supplies high-frequency voltage to the wave sending
element 6a at the amplitude of the amplifier rate that was set. On
the other hand, detected currents from the wave sending element 6a
passes through the amplifier circuit 18, and the output value
(detected value) from the smoothness circuit 19 is converted into
digital values by the A/D converter 36. The values are then sent to
the sensitivity adjustment circuit 35.
[0055] The sensitivity adjustment circuit 35 compares the output
value of the wave receiving element 6b to the predetermined
reference value (at the output value/reference value comparator
unit 37) and judges the output value according to the complete
results of the comparison (output value judgment unit 39). The
amplifier rate is set (amplifier rate setting unit 38) according to
the results of the judgment of the output value judgment unit 39. A
gain is used to set the amplifier circuit 16 via the D/A converter
17.
[0056] A preset amplifier rate reference value 41 is read, for
example, from ROM to set the amplifier circuit 16 gain to generate
the ultrasonic waves from the wave sending element 6a. The wave
receiving element 6b detects ultrasonic waves passing through a
test sheet (reference sheet) and outputs that to the A/D converter
36 from the smoothing circuit 19 via the amplifier circuit 18. The
output value (an analog voltage value) is compared to the reference
value. If the output value matches the reference value (in a
constant range), the amplifier rate is stored in an amplifier rate
memory 40. If the output voltage does not meet the reference value,
the output value judgment unit 39 sets the amplifier rate, so that
the output value (the analog voltage) rises to predetermined amount
such as 0.1 V. (the amplifier rate setting unit 38)
[0057] The amplifier rate is increased by a predetermined amount,
and the output value/reference value comparison unit 37 compares
that again with the output value of the wave receiving element 6b.
If they match, the amplifier rate is stored in the amplifier rate
memory 40. If the output value does not meet the reference value,
the amplifier rate is increased further by the predetermined
amount. The same adjustments are repeated. If the amplifier rate
setting reaches a maximum value 42 for the preset amplifier rate,
the CPU judges that there has been a system error in the double
feed detection of the wave sending element 6a and the wave
receiving element 6b. It may display an error message on the
control panel for example to prompt an operator to repair or to
continue the sheet processing on the system without using the
double feed detection function.
[0058] Note that according to the embodiment of the present
invention, if the output value from the smoothness circuit 19 is
within a range of 3.5V to 4.0V, a correct (normal) amplifier rate
is judged. Also, the reference value for adjusting the amplifier
rate in the invention is set to a value wherein the output value
(an analog voltage value) after smoothing does not exceed a maximum
of the minimum increment (for example 0.1 V) of an amp rte even
when the element (or device) in use is combined with a highly
sensitive component.
[0059] The following will explain adjusting the sensitivity of the
amplifier rate on the apparatus of FIG. 1 while referring to the
flow chart of FIG. 6.
[0060] First, the sensitivity adjustment mode is entered (F20). The
mode can be entered either by an operator using a switch on the
control panels, or the main apparatus such as an image reader or
printer can automatically enter the mode at the same time as it is
initializing the system. When entered, the CPU 21 judges whether
there is a sheet on the stacker 1 according to the status signals
received from the empty sensor S1. In this case, the CPU 21 judges
whether there is a test sheet placed on the stacker 1. If there is
a test sheet, it starts the drive motor M.
[0061] The drive speed of the drive motor M is set to the same
speed as when processing a sheet, as described above. The sheet on
the stacker 1 is kicked by the drive of the drive motor M. The
leading edge of the sheet passes through (F22) the ultrasonic wave
sensor (double feed detection device) to start the feeding of the
test sheet (F23). When the leading edge of the sheet arrives at the
sheet sensor 7 (F24), the timer T1 starts with a signal from the
sheet sensor 7 (F25). After a predetermined amount of time has
passed on the timer T1 (F26), the drive motor M stops, thereby
stopping the first transport roller 4a (F27).
[0062] Next, the drive motor M drives in the reverse direction,
thereby starting a drive of the second transport roller 5a (F28).
At the same time that the drive motor M starts, the counter 24
connected to the pulse generator 23 counts the number of pulses.
The CPU 21 uses this to judge whether a predetermined length of the
sheet has been transported by the second transport roller 5a. The
predetermined amount for the sheet to be transported is set so that
the sheet will be straightened from the registration loop by the
second transport roller 5a.
[0063] Just about the time that the registration loop is released,
the transport control unit 28 of the CPU 21 stops the drive motor M
or decelerates it to a predetermined speed. The drive motor is
stopped to prevent the variations in the ultrasonic sensor
detection value caused by the movement of the sheet for the
sensitivity adjustment that follows thereafter. The deceleration to
a predetermined speed is set to an optimum speed for the amount of
time for the sensor adjustment that follows to be completed when
changing the detection value according to the transport speed and
in the transport of the sheet. Normally, the speed for sensitivity
adjustment is set to a speed slower than the minimum speed for the
predetermined process that occurs on a sheet at the processing
platen 2.
[0064] Sensitivity adjustments are conducted as described below
while the sheet is traveling at a low speed or decelerating. First,
the sensitivity adjustment circuit 35 supplies high frequency power
to the wave sending element 6a at the gain set by the amplifier
rate reference value 41 (F36). The output value (an analog voltage)
from the wave receiving element 6b passes through the A/D converter
36 and is compared. If the results match, the amp value is stored
in the amplifier rate memory 40 to complete the sensitivity
adjustment. If the comparison results do not matched, the output
value judgment unit 39 increases the amplifier rate by the
predetermined amount. When the amplifier rate setting unit 38 does
not exceed a maximum value (which is set to a range wherein the
gain of the amplifier circuit is not saturated) of the amplifier
rate, power is supplied from the amplifier circuit 60 to the wave
sending element 6a.
[0065] If the amplifier rate from the output value judgments unit
39 exceeds the maximum value, the CPU 21 issues a failure signal to
the main apparatus (F38). The transport control unit 28 drives the
transport roller 8a at high speed to discharge the test sheet to
the discharge stacker 9 (F39). Having been notified of the failure
signal at the main apparatus, the operator can then select whether
to process the sheet without using the double feed detection
function (the non-detection operating mode) (F40), or to repair the
double feed detection device (F42) (by stopping machine
operations). If the operator selects the non-detection operating
mode, a message indicating that it is possible to feed the sheet
but not to perform the double feed detection is displayed on the
control panel. Then, the sheet can be processed as described above
(F41).
[0066] After adjustments are completed for the appropriate
sensitivity from the wave receiving element 6b (F32), the transport
roller 8a drives at a high speed to discharge the sheet on the
sheet guide 3 into the discharge stacker 9 (F33) The control panel
of the main apparatus displays a message indicating that the
adjustments are completed (F34). The adjustment mode is exited and
the system is prepared for processing a next sheet (F35). Then, the
appropriately adjusted amplifier rate is stored in the amplifier
rate memory 40 and is used at the gain setting up of the amplifier
circuit 16 when feeding a sheet.
[0067] An image reading apparatus according to an embodiment of the
present invention will be explained next. FIG. 8 shows an image
reading apparatus A and an image forming apparatus B mounted with
the image reading apparatus A as a unit. FIG. 9 shows a sheet
feeding unit in the image forming apparatus B.
[0068] The image forming apparatus B mounted with the image reading
apparatus A is embedded with a print drum 102 inside the casing
100; a paper feed cassette 101 that feeds paper to the print drum
102; a developer 108 that forms images using toner on the print
drum 102; and a fixer 104. A print head 103 such as a laser forms
latent images on the print drum 102. Paper fed from the paper feed
cassette 101 is sent by the transport rollers 105 to the print drum
102, and the images formed by the print head 103 are transferred to
the sheet and then fixed thereupon by the fixer 104. The sheet with
images is stored in the discharge stacker 121 from the discharge
roller 107.
[0069] The image forming apparatus B is widely known as a printer,
and is composed of a paper feed unit, a printing unit, and a
discharge storage unit. Their functions are various and are not
limited to the structure described above. For example, it is
perfectly acceptable to employ an inkjet printer, or a silkscreen
printer.
[0070] A data control circuit 109 is electrically interlocked to
the print head 103 to sequentially transfer image data that is
accumulated by the memory apparatus 122 such as a hard disk for
accumulating image data to the print head. On the upper portion of
the image forming apparatus B, the image reading apparatus A is
mounted as a unit. The image reading apparatus A is mounted with
the platen 112 on the casing 110. An optical mechanism 114 and a
photoelectric converting element 113 are arranged to read the
original through the platen. A CCD is widely known and used for the
photoelectric converting element 113.
[0071] As shown in FIG. 9, the sheet feeding apparatus C is
installed on the platen 112. Above the platen 112 are arranged a
paper feed stacker 115 and a discharge stacker 116 above each other
on the sheet feeding apparatus C. The sheets from the paper feed
stacker 115 are guided to the discharge stacker 116 via the
U-shaped transport path 134 traveling over the platen 112.
[0072] Arranged on the paper feed stacker 115 are an empty sensor
117 for detecting the sheets on the stacker, and a size sensor 132.
As shown in the drawing, a side guide 133 aligns the side edges of
the sheets. The size sensor 132 and the side guide 133 are
described in further detail below with reference to FIG. 10.
[0073] Arranged at a downstream side of the paper feed stacker 115
are a separating roller 119 and a stationary roller 120 in contact
with the roller. A kick roller 118 is mounted on the bracket 119b
mounted on the rotating shaft 119a of the separating roller 119.
When the rotating shaft 119a rotates in the clockwise direction,
the kick roller 118 lowers to above the paper feed stacker 115.
Conversely, when the rotating shaft 119a rotates in a
counterclockwise direction, the kick roller 118 rises to a state
shown in the drawing. The mechanism is described in further detail
below.
[0074] At a downstream side of the separating roller 119 are the
double feed detection sensor 123 that detects the double feed of
the sheets, and a sheet edge detection device 124 that detect the
leading edge and the trailing edge of the sheet. These are arranged
in the transport path 134. Also, equipped in order on the transport
guide 134 are the resist rollers 125a and 125b; feed rollers 127a
and 127b; a transport roller 129; and a pair of discharge rollers
130a and 130b. These are sequentially arranged to transport the
sheets from the paper feed stacker 115 to the discharge stacker
116.
[0075] As shown in the drawing, a lead sensor 126 detects the
leading edge of the sheet. A guide 128 supports the sheets at the
platen 112 position. A circulating path 131 circulates the sheets
from the platen 112 to the resist rollers 125a and 125b through a
path switching gate 131a.
[0076] Next, the side guide 133 and the size sensor 132 will be
explained. A pair of side guides 133 (133a and 133b) is disposed on
the left and right of the paper feed stacker 115 to control the
side edges of the sheets. The side guides are movably mounted in
the width direction of the sheets. The racks 135 and 136 are
integrally mounted to the left and right guides 133a and 133b.
These mate with the pinion rotatably fixed to the paper feed
stacker 115.
[0077] The left and right guides 133a and 133b are moved in the
opposite directions for the same amount by a pinion 137. The
detection piece 139 composed of a protrusion at a position that
corresponds to the size of the sheets is disposed on one of the
racks 136. The position of the detection piece 139 is detected by
the position sensor 138 mounted to the bottom of the stacker 115.
The position sensor is composed of a slidac volume and can detect
the position of the side guide 133 by detecting the variation in
the resistance value varying with the length of engagement with the
detection piece 139. Furthermore, size sensors 132 are disposed in
plurality on the stacker 115 to detect the trailing edge of the
sheet.
[0078] The position sensor 138 detects the width direction of
sheets on the stacker 115, and with the judgment by the size sensor
132 for sheets having the same width, the size of the sheet on the
stacker 115 is detected.
[0079] FIGS. 11(a) and 11(b) show a drive mechanism for the
separating roller 19 and the resist rollers 125. The paper feed
drive motor 140 capable of both forward and reverse rotations
drives the kick roller 118, the separating roller 119, and the
resist rollers 125. The transport drive motor 141 drives the paper
feed roller 127, the transport out roller 129, and the discharge
roller 130. With the forward rotation, the paper feed drive motor
140 drives the kick roller 118 and the separating roller 119. With
its reverse drive, it drives the resist roller 125. Simultaneously,
the paper feed drive motor 140 controls the rising and lowering of
the kick roller 118. Force from the paper feed drive motor 140 is
transmitted to the resist rollers by a one-way clutch 142 via the
belts B1 and B2 only in one direction of rotation. At the same
time, the paper feed drive motor is connected to a rotating shaft
of the separating roller 119 by the one-way clutch 143 to transmit
drive relatively with the one-way clutches 142 and 143.
[0080] The bracket 119b is supported on the rotating shaft of the
separating roller 119 via the spring clutch 144. Drive is
transmitted to the kick roller 118 mounted on the bracket 119b by
the transmission belt B3. When the paper feed drive motor 140
rotates in the forward direction, rotating drive is transmitted to
the separating roller 119 and the kick roller 118. Simultaneously,
the spring clutch 144 is released so that the bracket 119b becomes
free and lowers from an idled and raised position shown in FIG. 9
and the kick roller 118 touches the sheet on the stacker. Rotating
the paper feed drive motor 140 in the reverse direction transmits
drive to the resist rollers 125. Simultaneously, the spring clutch
144 contracts, thereby raising the bracket 119b to return to the
idled position shown in FIG. 9.
[0081] The transport unit drive motor 141 is connected to the feed
rollers 127, transport rollers 129, and discharge rollers 130 via
the belts B5, B6 and B7. The feed rollers 127 and transport rollers
129 always rotate in one direction with the forward and reverse
rotations of the motor with the one-way clutch. The discharge
rollers 130 rotate forward and reverse with the forward and reverse
rotations of the motor.
[0082] Sensors for detecting the leading edge of the sheets are
arranged in the transport path 134. Their functions will be
explained. The size sensors 132 that detect the size of the sheets
set on the paper feed stacker 115 are arranged in plurality. These
detect the size of the sheets to control sheet transport. The empty
sensor 117 is disposed on the leading edge of the paper feed
stacker 115 to detect the sheets on the stacker. This detects the
transport of the final sheet and sends a signal to the processing
apparatus, such as the image reading apparatus A. At a downstream
side of the separating roller 119 are disposed the double feed
detection sensor 123 described above and the sheet edge detection
sensor 124.
[0083] A lead sensor 126 is disposed in front of the paper feed
roller 127. This relays the leading edge of the sheet to the image
reading apparatus for reading images and calculates the starting
line for printing. Simultaneously, if the sheet is not detected
after a predetermined amount of time from the paper feed
instruction signal from the resist roller 125, the drive motor
stops because of a jam and issues a warning signal. At a downstream
side of the transport rollers 129 is disposed the discharge sensor
145 to judge jams by detecting the leading-edge and the
trailing-edge of the sheets.
[0084] The following will outline an operation of the apparatus
described above. The power to the apparatus is turned on, and
sheets are placed in the paper feed stacker 115. By setting the
sheets, the empty sensor 117 detects the sheets and starts the
paper feed drive motor 140. With the rotation of the paper feed
drive more 140, the kick roller 118 and separating roller 119
separate the sheets and kick them out. They are fed to the
transport guide 128 between the separating roller 119 and the
transport rollers 125. The sheet edge detection means 124
(hereinafter referred to as sensor 124) detects the leading edge of
the sheets (ST101). The timer T1 activates after the detection
signal of the leading edge of the sheet (see FIGS. 4(a) and 4(b))
to stop the motor 140 after a predetermined amount of time
(ST102).
[0085] According to the operations as shown in FIG. 12(a), the
sensor 124 detects the leading edge of the sheet and activates the
timer T1. Next, in FIG. 12(b), the leading edge of the sheet
strikes the resist rollers 125 and a loop is formed in the sheet.
In this state, a set amount of time for the timer T1 ends and the
motor 140 stops.
[0086] When the paper feed instruction signal is generated from the
control unit of the image reading apparatus A, the motor 140 starts
rotating again in the reverse direction. Also, with the paper feed
instruction signal, the timer T2 is activated. With the timer T2,
the registration loop is removed and the sheet is supported between
the separating roller 119 and the resist rollers 125 for transport
in a straight line as shown in FIG. 11(c).
[0087] Next, as shown in FIG. 11(d), until the trailing edge of the
sheet is released from the separating roller 19, the double feed
detection sensor 123 detects the double feeding of the sheets. The
trailing edge of the sheet transported in that way is detected by
the sensor 124. Approximately about the time when the trailing edge
of the sheet is detected, the lead sensor 126 detects the leading
edge of the sheet and the feed roller 127 feeds the sheet toward
the platen 112.
[0088] When the leading edge of the sheet is detected by the lead
sensor 126 and the sheet reaches the platen 112, the reading
process is executed as electrical signals by the optical mechanism
114 and the photoelectric converting element 113. After the sheet
has been read, it is discharged to the discharge stacker 116 by the
transport rollers 129 and the discharge rollers 130. The discharge
of the sheet is detected by the discharge sensor 145.
[0089] The double feed detection device is composed of the
ultrasonic wave sensor arranged in a path leading to the resist
rollers 125 at a downstream side of the separating roller 119
(feeding device). The sensitivity adjustment circuit 35 explained
with reference to FIG. 3(a) is disposed on the wave sending element
of the ultrasonic wave sensor. A smoothed output value (analog
voltage) is compared to a reference value. If a test sheet is
placed on the stacker 115 and the sensor sensitivity adjustment
mode is selected using the control panel of the apparatus, the
output of the wave sending elements is adjusted to the appropriate
conditions as described in the operation flowchart shown in FIG.
7.
[0090] The disclosure of Japanese Patent Application No.
2004-170395, filed on Jun. 8, 2004, is incorporated in the
application.
[0091] While the invention has been explained with reference to the
specific embodiments of the invention, the explanation is
illustrative and the invention is limited only by the appended
claims.
* * * * *