U.S. patent application number 10/546781 was filed with the patent office on 2006-07-06 for paper feeder.
Invention is credited to Katsutoshi Miyazaki, Yoshiyasu Tagawa, Tomomi Wakaura.
Application Number | 20060145412 10/546781 |
Document ID | / |
Family ID | 32984529 |
Filed Date | 2006-07-06 |
United States Patent
Application |
20060145412 |
Kind Code |
A1 |
Tagawa; Yoshiyasu ; et
al. |
July 6, 2006 |
Paper feeder
Abstract
A sheet feeding apparatus includes a sending element of an
ultrasonic sensor for outputting ultrasonic waves, a drive circuit
for supplying the sending element of the ultrasonic sensor with a
drive signal for driving the sending element, a receiving element
of the ultrasonic sensor disposed opposite the sending element of
the ultrasonic sensor across a sheet transfer path in the sheet
feeding apparatus, and for receiving the ultrasonic waves, a
setting unit for setting a threshold for the detection of transfer
of the plurality of paper sheets by using the output of the
receiving element of the ultrasonic sensor at the time of stopping
of the output of the sending element of the ultrasonic sensor as a
basic value, and a detection unit for detecting transfer of the
plurality of paper sheets by comparing the output of the receiving
element of the ultrasonic sensor with the threshold.
Inventors: |
Tagawa; Yoshiyasu;
(Ishikawa, JP) ; Wakaura; Tomomi; (Ishikawa,
JP) ; Miyazaki; Katsutoshi; (Ishikawa, JP) |
Correspondence
Address: |
STAAS & HALSEY LLP
SUITE 700
1201 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Family ID: |
32984529 |
Appl. No.: |
10/546781 |
Filed: |
March 10, 2004 |
PCT Filed: |
March 10, 2004 |
PCT NO: |
PCT/JP04/03132 |
371 Date: |
August 25, 2005 |
Current U.S.
Class: |
271/258.01 |
Current CPC
Class: |
B65H 7/125 20130101;
B65H 2553/30 20130101 |
Class at
Publication: |
271/258.01 |
International
Class: |
B65H 7/02 20060101
B65H007/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 12, 2003 |
JP |
2003-066277 |
Claims
1. A sheet feeding apparatus for detecting transfer of a plurality
of paper sheets by using ultrasonic waves, the apparatus
comprising: a sending element of an ultrasonic sensor for
outputting ultrasonic waves; a drive circuit for supplying the
sending element of the ultrasonic sensor with a drive signal for
driving the sending element; a receiving element of the ultrasonic
sensor disposed opposite the sending element of the ultrasonic
sensor across a sheet transfer path in the sheet feeding apparatus,
and for receiving the ultrasonic waves; a setting unit for setting
a threshold for the detection of transfer of the plurality of paper
sheets by using the output of the receiving element of the
ultrasonic sensor at the time of stopping of the output of the
sending element of the ultrasonic sensor as a basic value; and a
detection unit for detecting transfer of the plurality of paper
sheets by comparing the output of the receiving element of the
ultrasonic sensor with the threshold.
2. The sheet feeding apparatus according to claim 1, wherein the
threshold for detecting transfer of the plurality of paper sheets
is obtained by adding a fixed value to the output of the receiving
element of the ultrasonic sensor at the time of stopping the output
of the sending element of the ultrasonic sensor.
3. The sheet feeding apparatus according to claim 1, wherein the
threshold for detecting transfer of the plurality of paper sheets
is obtained by adding, to the output of the receiving element of
the ultrasonic sensor at the time of stopping of the output of the
sending element of the ultrasonic sensor, a value calculated,
correspondingly to the output of the receiving element of the
ultrasonic sensor at the time the sending element of the ultrasonic
sensor is driven stepwise by the drive circuit, according to the
correlation between the output and a correction value determined
based on the correlation between the sensitivity and the output of
the receiving element of the ultrasonic sensor and the correlation
between the fitting position and the output of the receiving
element of the ultrasonic sensor.
4. The sheet feeding apparatus according to claim 1, wherein the
output of the receiving element of the ultrasonic sensor at the
time of stopping of the output of the sending element of the
ultrasonic sensor is the average of a plurality of the outputs.
5. The sheet feeding apparatus according to claim 1, wherein the
output of the receiving element of the ultrasonic sensor is the
average of a plurality of the outputs.
6. The sheet feeding apparatus according to claim 1, wherein the
detection unit judges that, when the output of the receiving
element of the ultrasonic sensor is lower than the threshold a
prescribed number of times or more often, transfer of the plurality
of paper sheets is taking place.
7. The sheet feeding apparatus according to claim 1, wherein the
detection unit uses the threshold as a threshold for detecting
transfer of the plurality of paper sheets regarding a plurality of
types of paper sheets differing in ream weight.
8. The sheet feeding apparatus according to claim 1, further
comprising: a motor for transferring paper sheets, wherein the
detection unit, in the event of detecting transfer of the plurality
of paper sheets, drives the motor to stop the transfer of the paper
sheets.
9. The sheet feeding apparatus according to claim 1, further
comprising: feed rollers for transferring paper sheets to a reading
position, wherein the sending element of the ultrasonic sensor and
receiving element of the ultrasonic sensor are disposed upstream
from the reading position on the transfer path and in the vicinity
of downstream or upstream from the feed rollers.
10. The sheet feeding apparatus according to claim 1, further
comprising: a first amplifying circuit for amplifying the output of
the receiving element of the ultrasonic sensor; a filter for
removing noise from the output of the first amplifying circuit; a
second amplifying circuit for amplifying the signals cleared of
noise; a sample hold circuit for sampling and holding the peak
value of the output of the second amplifying circuit; and an AD
converter for converting the value held by the sample hold circuit
into a digital signal and inputting it to the setting unit.
11. A sheet feeding apparatus for detecting transfer of a plurality
of paper sheets by using ultrasonic waves, the apparatus
comprising: a sending element of an ultrasonic sensor for
outputting ultrasonic waves; a drive circuit for supplying the
sending element of the ultrasonic sensor with a drive signal for
driving the sending element; a receiving element of the ultrasonic
sensor disposed opposite the sending element of the ultrasonic
sensor across a sheet transfer path in the sheet feeding apparatus,
and for receiving the ultrasonic waves; an amplifier, comprising an
operational amplifier, for amplifying the output of the receiving
element of the ultrasonic sensor; and an adjusting unit provided in
the amplifier, and for forming a control signal for adjusting the
output of the amplifier, whereby the reference voltage of the
operational amplifier is adjusted.
12. A sheet feeding apparatus for detecting transfer of a plurality
of paper sheets by using ultrasonic waves, the apparatus
comprising: a sending element of an ultrasonic sensor for
outputting ultrasonic waves; a receiving element of the ultrasonic
sensor disposed opposite the sending element of the ultrasonic
sensor across a sheet transfer path in the sheet feeding apparatus,
and for receiving the ultrasonic waves; an amplifier for amplifying
the output of the receiving element of the ultrasonic sensor; an
adjusting unit for forming a control signal for adjusting the
output of the amplifier; and a drive circuit for supplying the
sending element of the ultrasonic sensor with a drive signal for
driving the sending element, the drive circuit varying the number
of waves or the duty ratio of clocks supplied to the sending
element of the ultrasonic sensor according to the control signal
from the adjusting unit which is provided in the drive circuit.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention generally relates to a sheet feeding
apparatus, and particularly to a sheet feeding apparatus which sets
a threshold that enables, in double feed detection using ultrasonic
waves, the double feed to be detected without fail even in a case
that the sensor output is varied by fluctuations in the sensitivity
or sound pressure of the ultrasonic sensor and the like.
[0003] 2. Description of the Related Art
[0004] For use in the front shield device of a sheet-fed press, for
example, an ultrasonic detector is known, which detects the
transfer or feeding of a plurality of (for example, two) paper
sheets (double feed or DF) by using ultrasonic waves. In this
ultrasonic detector, ultrasonic waves outputted from a sending
element of an ultrasonic sensor are received by a receiving element
of the ultrasonic sensor, and it is detected whether there is one
fed paper sheet or more according to the level (wave height) of the
received ultrasonic waves. That is, when the level of the received
ultrasonic waves is higher than a threshold, it is judged that
there is only one sheet. On the other hand, when the level is lower
than the threshold, it is judged that double feed has occurred
(see, for example, Patent Document Reference 1: Japanese Patent
Application Laid-Open No. 6-263288 (pp. 2-3)).
[0005] However, according to the above-mentioned prior art,
adjustment of every individual feeding apparatus is needed because,
when each feeding apparatus is shipped, the amplification rate is
adjusted with a variable resistance according to the
characteristics of its ultrasonic sensor in a state in which a
paper sheet is inserted in the device or a threshold for
determining double feed detection (hereinafter sometimes referred
to as a decision slice value) is determined and applied to the
feeding apparatus according to prior evaluation. Moreover,
readjustment is needed when ultrasonic sensor has run into trouble
and is to be replaced.
[0006] Further, in a case that the control is such as to determine
the decision slice value uniquely, it is difficult to secure a
sufficient margin of operation against variations in the ultrasonic
sensor output due to fluctuations in the sensitivity of the
ultrasonic sensor or its fitting to the feeding apparatus, ambience
or adherence of paper powder. Therefore, it may be impossible to
detect double feed when paper sheets of different thickness are
consecutively carried.
SUMMARY OF THE INVENTION
[0007] It is an object of the present invention to provide a sheet
feeding apparatus in which a threshold permitting secure detection
of double feed even when there are variations in the ultrasonic
sensor output due to fluctuations in the sensitivity or sound
pressure of the ultrasonic sensor.
[0008] A sheet feeding apparatus of the present invention is for
detecting transfer of a plurality of paper sheets by using
ultrasonic waves. The sheet feeding apparatus includes a sending
element of an ultrasonic sensor for outputting ultrasonic waves, a
drive circuit for supplying the sending element of the ultrasonic
sensor with a drive signal for driving the sending element, a
receiving element of the ultrasonic sensor disposed opposite the
sending element of the ultrasonic sensor across a sheet transfer
path in the sheet feeding apparatus, and for receiving the
ultrasonic waves, a setting unit for setting a threshold for the
detection of transfer of the plurality of paper sheets by using the
output of the receiving element of the ultrasonic sensor at the
time of stopping of the output of the sending element of the
ultrasonic sensor as a basic value, and a detection unit for
detecting transfer of the plurality of paper sheets by comparing
the output of the receiving element of the ultrasonic sensor with
the threshold.
[0009] According to the sheet feeding apparatus of the present
invention, since the threshold for detecting transfer of a
plurality of paper sheets is set by referencing the output of the
receiving element of the ultrasonic sensor at the time of stopping
of the output of the sending element of the ultrasonic sensor, the
threshold (decision slice value) so set is not fixed. Therefore, it
can follow variations in the environment of detection (for example,
variations in the sheet feeding apparatus) or in the ultrasonic
sensor's own characteristics (for example, aging) and, even after
shipment, double feed in the sheet feeding apparatus can be always
detected accurately. That is, even in a case that the sensor output
varies with fluctuations in the sensitivity, sound pressure or
fitting (accuracy) of the ultrasonic sensor, its ambience or
adhesion of paper powder, double feed can be detected without
fail.
[0010] A sheet feeding apparatus of the present invention is for
detecting transfer of a plurality of paper sheets by using
ultrasonic waves. The sheet feeding apparatus includes a sending
element of an ultrasonic sensor for outputting ultrasonic waves, a
drive circuit for supplying the sending element of the ultrasonic
sensor with a drive signal for driving the sending element, a
receiving element of the ultrasonic sensor disposed opposite the
sending element of the ultrasonic sensor across a sheet transfer
path in the sheet feeding apparatus, and for receiving the
ultrasonic waves, an amplifier, comprising an operational
amplifier, for amplifying the output of the receiving element of
the ultrasonic sensor, and an adjusting unit for forming a control
signal for adjusting the output of the amplifier, whereby the
reference voltage of the operational amplifier is adjusted.
[0011] Further, a sheet feeding apparatus of the present invention
is for detecting transfer of a plurality of paper sheets by using
ultrasonic waves. The sheet feeding apparatus includes a sending
element of an ultrasonic sensor for outputting ultrasonic waves, a
receiving element of the ultrasonic sensor disposed opposite the
sending element of the ultrasonic sensor across a sheet transfer
path in the sheet feeding apparatus, and for receiving the
ultrasonic waves, an amplifier for amplifying the output of the
receiving element of the ultrasonic sensor, an adjusting unit for
forming a control signal for adjusting the output of the amplifier,
and a drive circuit for supplying the sending element of the
ultrasonic sensor with a drive signal for driving the sending
element. The drive circuit varies the number of waves or the duty
ratio of clocks supplied to the sending element of the ultrasonic
sensor according to the control signal from the adjusting unit.
[0012] According to the sheet feeding apparatus of the present
invention, the output value of the receiving element of the
ultrasonic sensor is adjusted either by altering the reference
voltage of the operational amplifier or altering the frequency of
clocks supplied by the drive circuit or the duty ratio. Therefore,
at the time of shipping the sheet feeding apparatus, for example,
there is no need to adjust the amplification rate of the amplifier
of the ultrasonic receiving circuit with a variable resistance.
This is also true at the time of replacing the ultrasonic sensor,
for example. Even in a case that the ultrasonic receiving circuit
comprises a band pass filter, the output of the receiving element
of the ultrasonic sensor can be prevented from attenuating.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a structural diagram of a scanner, showing the
schematic structure of a scanner to which a sheet feeding apparatus
according to the present invention is applied.
[0014] FIG. 2 is a structural diagram of a scanner, showing the
schematic structure of a scanner to which a sheet feeding apparatus
according to the present invention is applied.
[0015] FIG. 3 is a diagram showing one example of structure of an
ultrasonic detector.
[0016] FIG. 4 is a diagram showing one example of structure of an
ultrasonic detector.
[0017] FIG. 5A and FIG. 5B are diagrams showing examples of
operation by a CPU.
[0018] FIG. 6 is a diagram showing one example of operation
processing flow at the time of adjustment to determine Vslice.
[0019] FIG. 7 is a diagram showing paper sheets and the output
transition of a receiving element of the ultrasonic sensor (US
sensor).
[0020] FIG. 8 is a diagram showing one example of operation
processing flow at the time of reading.
[0021] FIG. 9 is a diagram showing a sensor reception waveform
detected by the CPU.
[0022] FIG. 10 is a diagram showing one example of processing flow
to compute the correction value .alpha..
[0023] FIG. 11A, FIG. 11B and FIG. 11C are diagrams showing tables
to be used for determining the correction value .alpha..
[0024] FIG. 12A and FIG. 12B are diagrams showing examples of
device configuration for adjusting the input value of an ultrasonic
wave reception sensor.
[0025] FIG. 13 is a diagram showing a sequence of adjusting the
double feed output level.
[0026] FIG. 14 is a diagram showing a sequence of adjusting the
double feed output level.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] FIG. 1 and FIG. 2 are structural diagrams of a scanner,
showing the schematic structure of a scanner to which a sheet
feeding apparatus according to the present invention is applied.
Particularly, FIG. 1 shows an external view of the scanner, and
FIG. 2 shows a schematic section of a scanner.
[0028] This scanner is formed integrally with the sheet feeding
apparatus. The sheet feeding apparatus, as shown in FIG. 2,
comprises a paper sheet mounting table (shooter) 31, a pick roller
32, a pick arm 33, a separating pad 34, feed rollers 35 and 36, and
discharge rollers 37 and 38. And, the sheet feeding apparatus
further comprises the sending element of the ultrasonic sensor 17
and the receiving element of the ultrasonic sensor 18 of an
ultrasonic detector 1 to be described afterwards. In FIG. 2, the
two-dot chain line represents the transfer path of paper sheets 100
and the arrow R represents the reading position of the paper sheets
100.
[0029] The paper sheets 100 mounted on the paper sheet mounting
table (shooter) 31 are picked by the pick roller 32 in a state of
being subjected to an appropriate pressing force by the pick arm
33. Then, the paper sheets 100 are separated one by one
sequentially from the bottom by the pick roller 32 and the
separating pad 34. The picked paper sheets 100 are further
transferred by the pick roller 32 to the feed rollers 35 and 36,
transferred by the feed rollers 35 and 36 to their reading
position, and discharged by the discharge rollers 37 and 38.
[0030] In the transferring process of these paper sheets 100 along
the transfer path, a plurality of (usually two) paper sheets 100
which have failed to be separated one by one by the separating pad
34, namely double fed ones are detected by the sending element of
the ultrasonic sensor 17 and the receiving element of the
ultrasonic sensor 18. For this reason, the sending element of the
ultrasonic sensor 17 and the receiving element of the ultrasonic
sensor 18 are located upstream on the transfer path from the
reading position as shown in FIG. 2. Particularly, the sending
element of the ultrasonic sensor 17 and the receiving element of
the ultrasonic sensor 18 are positioned downstream or upstream from
the feed rollers 35 and 36 in the vicinity of the rollers 35 and
36. This enables double fed paper sheets 100 to be detected before
they reach the reading position, and to proceed necessary process
(for example, stopping of transfer).
[0031] Additionally, the scanner shown in FIG. 1 and FIG. 2 is one
example of image processing apparatus to which the sheet feeding
apparatus according to the present invention is applied. The
present invention can be applied sheet feeding apparatus for not
only scanners but also copying machines, facsimile machines and the
like.
[0032] FIG. 3 and FIG. 4 show one example of structure of
ultrasonic detector which is provided in the sheet feeding
apparatus according to the present invention. In FIG. 3, the
ultrasonic detector 1 detects the transfer of a plurality of paper
sheets 100 by using ultrasonic waves. The ultrasonic detector 1 of
the sheet feeding apparatus comprises the sending element of the
ultrasonic sensor 17, its drive circuit (sending circuit; the same
applies hereinafter) 41, the receiving element of the ultrasonic
sensor 18, a setting unit (26) for setting the threshold for the
transfer of a plurality of paper sheets 100 (double feed), and a
detection unit (26) for detecting the transfer of a plurality of
paper sheets 100.
[0033] The sending element of the ultrasonic sensor 17 outputs
ultrasonic waves. The drive circuit 41 supplies the sending element
of the ultrasonic sensor 17 with a drive signal to drive the sensor
17. The drive circuit 41 comprises a circuit (capable of ON/OFF
control) oscillating at a frequency near the resonance frequency of
the sending element of the ultrasonic sensor 17. The receiving
element of the ultrasonic sensor 18 is disposed opposite the
sending element of the ultrasonic sensor 17 across the sheet
transfer path in the sheet feeding apparatus, and receives the
ultrasonic waves. The setting unit uses the output of the receiving
element of the ultrasonic sensor 18 at the time of the stopping of
the output of the sending element of the ultrasonic sensor 17 by
the drive circuit 41 as a basic value, and sets a threshold for the
detection of the transfer of a plurality of paper sheets 100. The
detection unit compares the output of the receiving element of the
ultrasonic sensor 18 with the threshold, and detects the transfer
of a plurality of paper sheets 100.
[0034] The ultrasonic detector 1 further comprises an (first-stage)
amplifying circuit 21, a BPF (band pass filter) 22, an
(second-stage) amplifying circuit 23, a sample hold (S&H)
circuit 24, an AD converter 25, a CPU 26, a motor driver 27, a
motor 28, a ROM 29 and RAM 30. They make a receiving circuit 14
shown in FIG. 4. That is, the receiving element of the ultrasonic
sensor 18 outputs an electric signal corresponding to the
ultrasonic wave received from the sending element of the ultrasonic
sensor 17. And, the electric signal is amplified by the amplifying
circuit 21, and is cleared of noise by the BPF 22 after the
amplification. And, the signal cleared of noise is further
amplified by the amplifying circuit 23. Then, after the sample hold
circuit 24 samples and holds (SH) the peak value of the signal, the
AD converter 25 converts that value (analog signal) into a digital
value (digital signal). This digital signal (input signal) is
inputted to (the setting unit and detection unit of) the CPU 26 and
analyzed. In other words, the setting unit and the detection unit
(see FIG. 5) which are realized by setting and detection processing
programs set on the CPU 26 (and hardware) analyze the input signal.
The setting and detection processing programs are stored into, for
example, the ROM 29 and/or the RAM 30. The CPU 26 (namely the
detection unit), in double feed detection, for example, sends a
drive signal to the motor driver 27 to have the motor 28 driven and
to have the transfer of (a plurality of) paper sheets 100
stopped.
[0035] The ultrasonic detector 1 comprises a sending circuit (drive
circuit) 41. The sending circuit 41 comprises a drive IC 13, a
resistance frequency adjusting oscillator (OSC) 15 and a variable
resistor 16 shown in FIG. 4.
[0036] The drive IC 13 shown in FIG. 4 is a drive circuit which
supplies the sending element of the ultrasonic sensor 17 with a
drive signal to drive it. This causes the sending element of the
ultrasonic sensor 17 to output an ultrasonic wave. The receiving
element of the ultrasonic sensor 18 receives this ultrasonic wave,
and outputs a detection signal according to the intensity of the
received ultrasonic wave. For example, when no paper sheet 100 is
present between the sending element of the ultrasonic sensor 17 and
the receiving element of the ultrasonic sensor 18, the receiving
element of the ultrasonic sensor 18 detects a signal of a certain
level (referred to usual level). When one paper sheet 100 is
present between them, the receiving element of the ultrasonic
sensor 18 detects a signal of a level below the usual level but
higher than a prescribed threshold (referred to normal level). When
two (or more) paper sheets 100 are present between them, the
receiving element of the ultrasonic sensor 18 detects a signal of a
level below the usual level and the above-mentioned threshold
(referred to abnormal level).
[0037] For example, in advance of transferring paper sheets 100,
the drive IC 13 is so controlled that the receiving element of the
ultrasonic sensor 18 can receive a signal of the usual level
(actually a signal equal to or higher than the usual level). That
is, based on the ultrasonic wave received by the receiving element
of the ultrasonic sensor 18, the drive IC 13 is so controlled as to
match the drive frequency of the drive signal with the resonance
frequency of the sending element of the ultrasonic sensor 17, as
will be described afterwards (without using a variable
resistor).
[0038] FIG. 5A shows one example of setting unit and FIG. 6 shows a
flow of processing for setting at the time of setting the
threshold.
[0039] As described above, the setting unit sets (generates) the
threshold (decision slice value or Vslice) for the detection of
transfer of a plurality of paper sheets 100 by using the output of
the receiving element of the ultrasonic sensor 18 when the output
of the sending element of the ultrasonic sensor 17 is stopped by
the drive circuit 41, as the basic value. In this example, the
threshold is determined by adding a fixed value to the output of
the receiving element of the ultrasonic sensor at the time the
output of the sending element of the ultrasonic sensor is
stopped.
[0040] That is, as shown in FIG. 5A, in the CPU 26, sensor control
unit 101 sends a control signal to the sending circuit 41 to stop
the oscillation of the sending circuit 41. Also, the sensor control
unit 101 applies a prescribed bias voltage to (an operational
amplifier 106; see FIG. 12A of) the amplifying circuit 23. In this
state, a Vslice generating unit 102 of the CPU 26 repeatedly
receives from the AD converter 25 input signals iputted from the
receiving element of the ultrasonic sensor 18 tens of times, for
example, 32 times, computes their average, and uses it as a basic
value Vbase (step S11). That is, it is equal to measure signals at
32 points in one raster, for example. Then, the Vslice generating
unit 102 performs a correction to add a correction value .alpha. to
the basic value Vbase to generate a threshold Vslice
(Vslice=Vbase+.alpha.), and stores it into a register 103 (step
S12). The correction value .alpha. is empirically determined for
each device to be installed, with the influence of noise and other
factors being taken into consideration.
[0041] The correction value .alpha. may be determined in advance,
or correction value .alpha. may be determined as a variable value
for each apparatus on an ad hoc basis with the sensitivity of the
ultrasonic sensor, fluctuations in its sound pressure or fitting,
ambience, adhesion of paper powder and other factors being taken
into consideration.
[0042] FIG. 7 is a diagram showing paper sheets and the output
transition of the receiving element of the ultrasonic sensor (US
sensor), illustrating one example of threshold set by the
processing so far described. In FIG. 7, the vertical axis
represents the output (digital value) of the receiving element of
the ultrasonic (US) sensor, and the horizontal axis represents the
vertical scanning direction of paper sheets (raster).
[0043] The corrected threshold Vslice is set to a level relative to
the basic value Vbase as shown in FIG. 7, and used for detection of
double feed. For example, when the transferred paper sheets are two
sheets of 45K in ream weight (hereinafter referred to as 45K
sheets), the input signal level (Vin) is below the threshold
Vslice, and therefore it is judged that double feed has occurred
(abnormal feed). When only one of this 45K sheet is transferred,
though not shown, the input signal level (Vin) is even higher than
in a case of one 135K sheet or one 195K sheet which is heavier in
ream weight (or thicker), and surpass the threshold Vslice.
Therefore, the state is judged as normal feed. When two 135K or two
195K sheets are transferred, though not shown, the input signal
level is even lower than in a case of one 45K sheet, and does not
reach the threshold Vslice. Therefore, the state is judged as
double feed. When only one 135K or one 195K sheet is transferred,
the input signal level surpasses the threshold Vslice as shown in
FIG. 7. Therefore, the state is judged as normal feed.
[0044] Even in a case that the transferred sheets are 22K sheets,
which are very light in ream weight and thin, double feed can be
detected correctly. That is, when only one 22K sheet is
transferred, though not shown, the input signal level (Vin) is even
higher than in a case of one 135K sheet or the like, and surpasses
the threshold Vslice. Therefore, the state is judged as normal
feed. When two 22K sheets are transferred, the level of the input
signal Vin fluctuates as shown in FIG. 7. However, on the right
hand side of FIG. 7, the input signal Vin is lower and below the
threshold Vslice. Therefore, the state can be judged as double
feed. This is because the input signal becomes significantly low in
the vicinity of the position where paper sheets 100 are suppressed
by the feed rollers 35 through 38. That is, according to the
present invention, double feed can be correctly detected over a
broad range.
[0045] FIG. 5B shows an example of detection unit. FIG. 8 shows a
flow of processing for detection after the setting of the
threshold. FIG. 9 shows a drive pulse outputted by the sending
circuit 41 in detecting double feed.
[0046] As described above, the detection unit compares the output
of the receiving element of the ultrasonic sensor 18 with the
threshold, and detects transfer of a plurality of paper sheets 100.
That is, as shown in FIG. 5B, the sensor control unit 101 in the
CPU 26 sends a control signal to the sending circuit 41 etc. to
oscillate the sending circuit 41. Also, the sensor control unit 101
applies prescribed bias voltage to (the operational amplifier 106
of) the amplifying circuit 23. In this state, comparing unit 104 of
the CPU 26 repeatedly receives from the AD converter 25 input
signals (digital values) from the receiving element of the
ultrasonic sensor 18 tens of times, for example, 32 times, and
holds them (step S21).
[0047] Then, as shown in FIG. 9, after the oscillation of the
sending circuit 41 (the sending drive pulse) is stopped, signals in
a plurality of prescribed positions, for example, at 32 points, are
measured. The measuring positions are selected to be, for example,
once per the raster or once per a plurality of the rasters.
Further, when the output waveform of the receiving element of the
ultrasonic sensor 18 becomes gradually larger and reaches the
maximum level, that maximum level is sampled and held.
[0048] Next, the sensor control unit 101 or the comparing unit 104
sets the timer for an SH interrupt (step S22), and judges whether
or not the interrupt has occurred (step S23). In a case that 32
input signals are to be obtained, for example, as mentioned above,
32 times of the SH interrupt are set to occur. That is, using the
SH interrupt as a trigger, consecutive drive pulses on the sending
side shown in FIG. 9 are outputted. For example, 32 times of the SH
interrupt occur with the lapse of a prescribed length of time, at a
rate of one interrupt per the raster. When no interrupt occurs,
step S23 is repeated. When an interrupt does occur, the average,
for example, a moving average, of the 32 values earlier received
and held is computed, and this average is used as the value Vin of
the input signal for double feed (DF) detection (step S24).
[0049] After that, the comparing unit 104 compares the value Vin of
the input signal with the threshold Vslice of the register 103
(step S25), and when Vin<Vslice is not satisfied, the state is
judged as being normal feed. When Vin<Vslice is satisfied, the
comparing unit 104 further judges whether Vin<Vslice is
satisfied a prescribed number of times, for example, 10 times or
more (step S26). When Vin<Vslice is satisfied 10 times or more,
the comparing unit 104 judges that double feed occurs and outputs
an error signal. When Vin<Vslice is satisfied less than 10
times, the process of the step S22 and its subsequence is
repeated.
[0050] FIG. 10 and FIG. 11 illustrate an ultrasonic detector 1 in a
sheet feeding apparatus, which is another example of the present
invention in which the correction value .alpha. is a variable
value. That is, although a fixed value is used as the correction
value .alpha. in the foregoing example as indicated at the step S12
in FIG. 6, this correction value .alpha. may be a variable
value.
[0051] In this example, as shown in FIG. 11, the threshold Vslice
in the detection of transfer of a plurality of paper sheets is
calculated by adding a value .alpha. to an output Vbase. The output
Vbase is an output of the receiving element of the ultrasonic
sensor at the time the output of the sending element of the
ultrasonic sensor 17 is stopped. The value .alpha. is calculated,
correspondingly to the output Vt of the receiving element of the
ultrasonic sensor 18 at the time the sending element of the
ultrasonic sensor 17 is driven stepwise by the drive circuit 41,
according to a (third) correlation between the output of the
receiving element of the ultrasonic sensor 18 and the correction
value .alpha. (shown in FIG. 11C). The third correlation is
determined by a (first) correlation between the sensitivity and the
output Vt of the receiving element of the ultrasonic sensor 18
(shown in FIG. 11A) and a (second) correlation between the fitting
position and the output Vt of the receiving element of the
ultrasonic sensor 18 (shown in FIG. 11B).
[0052] In the same way as at the step S11, a bias voltage is
applied to measure the basic value Vbase (step S31). Next, in a
state without paper sheets, the sending element of the ultrasonic
sensor 17 is driven stepwise (step S32). That is, the drive circuit
41 applies a single drive pulse to the sending element of the
ultrasonic sensor 17. And the resultant output Vt of the receiving
element of the ultrasonic sensor 18 is measured (step S33), a
correction value .alpha. corresponding to the output Vt is
calculated by using the third correlation shown in FIG. 11C (step
S34), and the threshold Vslice=Vbase+.alpha. is determined by using
the correction value .alpha. (step S35).
[0053] For example, the correction value .alpha. is determined by
using the correlation diagrams shown in FIG. 11A to FIG. 11C as
described above. That is, the sensor sensitivity and the sensor
output Vt is in a proportional relationship as shown in FIG. 11A.
The sensor fitting position and the sensor output Vt have the
correlation shown in FIG. 11B. From the two correlations shown in
FIG. 11A and FIG. 11B, the third correlation is derived between the
sensor output Vt and the correction value .alpha. shown in FIG.
11C.
[0054] FIG. 12A, FIG. 13 and FIG. 14 show a structure of the
ultrasonic detector 1 in the other sheet feeding apparatus, which
is the other example of the present invention, in which the output
of the amplifying circuit 23 is adjusted not by varying an
amplification rate with variable resistance, but by using some
other units.
[0055] That is, the example shown in FIG. 12A and FIG. 13 comprises
the amplifying circuit 23, which is an amplifier for amplifying the
output of the receiving element of the ultrasonic sensor 18 and
comprises the operational amplifier 106, and first adjusting unit
which forms a control signal for adjusting the output of the
amplifying circuit 23. The first adjusting unit adjusts the
reference voltage Vref of the operational amplifier 106, so that
the level of output from the amplifying circuit 23 is adjusted.
More specifically, the offset of the operational amplifier 106 is
adjusted (optimized for the receiving circuit 14). This first
adjusting unit actually comprises the sensor control unit 101 and a
voltage adjuster 107. The amplifying circuit 23 is the second-stage
amplifier in FIG. 3. The amplifying circuit 23 comprises a fixed
resistor 105, the operational amplifier 106 and the voltage
adjuster 107 which may be a DA converter, for example. Numeral 108
denotes a fixed resistor. This example makes it possible to absorb
fluctuations in resistance and temperature characteristics of the
fixed resistors 105 and 108, to omit a manual adjustment at the
time of shipment or sensor replacement, and to adapt themselves to
status variations with the environment of use.
[0056] FIG. 13 shows a process of adjusting the double feed output
level. The sensor control unit 101 sets the central value of
conversion by the DA converter, which is the voltage adjuster 107,
to its intrinsic value (for example, x80 of 256 gradations), and
sets the number of burst waves to be applied to the sending element
of the ultrasonic sensor 17 to "0" (step S41). That is, the output
of the sending element of the ultrasonic sensor 17 is set to "0".
In this state, the sensor control unit 101 monitors (takes in) the
input value Vin from the receiving element of the ultrasonic sensor
18 (step S42), and judges, after the monitoring, whether or not
"the first slice upper limit">"the input value" is satisfied
(step S43). This first slice upper limit is an empirically
determined value. When "the first slice upper limit">"the input
value" is not satisfied, the sensor control unit 101 sets the
central value of conversion by the DA converter, which is the
voltage adjuster 107, to a value shifted by +x01 (step S44), and
the process of the step S42 and its subsequence is repeated. When
"the first slice upper limit">"the input value" is satisfied,
the sensor control unit 101 further judges whether or not "the
input value">"the first slice lower limit" is satisfied (step
S45). This first slice lower limit is an empirically determined
value. When "the input value">"the first slice lower limit" is
not satisfied, the sensor control unit 101 sets the central value
of conversion by the DA converter, which is the voltage adjuster
107, to a value shifted by -x01 (step S46), and the process of the
step S42 and its subsequence is repeated. When "the input
value">"the first slice lower limit" is satisfied, the process
is ended.
[0057] Further, the example shown in FIG. 12A and FIG. 14 comprises
second adjusting unit. The second adjusting unit forms a control
signal for adjusting the output of the amplifying circuit 23 which
amplifies the output of the receiving element of the ultrasonic
sensor 18. And, the number of waves (the number of pulses) or the
duty ratio of the drive pulses (burst waves) is varied which is
supplied by the drive circuit 41 according to a control signal from
the second adjusting unit to the sending element of the ultrasonic
sensor 17. The input value from the amplifying circuit 23 is
thereby adjusted. This second adjusting unit actually comprises the
sensor control unit 101 and the sending circuit (drive circuit) 41.
This example makes it possible to absorb fluctuations in the
sensitivity of the receiving element of the ultrasonic sensor 18,
and to prevent from attenuating the sensor output even in a case
that the receiving circuit 14 includes a band pass filter.
[0058] FIG. 14 shows a process of adjusting the output level. The
sensor control unit 101 sets the number of pulses (the number of
waves) of drive pulses (burst waves) to be applied to the sending
element of the ultrasonic sensor 17 to "1 wave" (step S51). The
duty ratio then is set to 50%. In this state, the sensor control
unit 101 monitors the input value Vin from the receiving element of
the ultrasonic sensor 18 (step S52), and judges, after the
monitoring, whether or not "the input value">"the second slice
upper limit" is satisfied (step S53). This second slice lower limit
is an empirically determined value, and differs from the first
slice lower limit. When "the input value">"the second slice
lower limit" is not satisfied, the sensor control unit 101 sets the
number of burst waves to +1 (step S54), and then the process of the
step S52 and its subsequence is repeated. When "the input
value">"the second slice lower limit" is satisfied, the sensor
control unit 101 monitors the input value Vin from the receiving
element of the ultrasonic sensor 18 (step S55), and further judges,
after the monitoring, whether or not "the second slice upper
limit">"the input value" is satisfied (step S56). This second
slice upper limit is an empirically determined value, and differs
from the first slice upper limit. When "the second slice upper
limit">"the input value" is not satisfied, the sensor control
unit 101 sets the value of the duty ratio (%) to a value shifted by
-1% (step S57), and the process of the step S55 and its subsequence
is repeated. When "the second slice upper limit">"the input
value" is satisfied, the process is ended.
[0059] Additionally, for comparison with FIG. 12A, one example of
adjustment of the input value from a receiving element of the
ultrasonic sensor 18 is shown in FIG. 12B. In FIG. 12B, numeral 42
denotes an amplifier circuit, 108 denotes a fixed resistor, 109
denotes a variable resistance, 110 denotes an operational
amplifier, and Vref denotes a reference voltage. As shown in FIG.
12B, according to the prior art, the input value from the receiving
element of the ultrasonic sensor 18 is adjusted by varying the gain
of the operational amplifier 110 with the variable resistance 109.
This method, however, requires manual adjustment at the time of
shipment or sensor replacement, and cannot adapt to status
variations with the environment of use.
[0060] As described above, according to the present invention, the
threshold (decision slice value) set in a sheet feeding apparatus,
since it is not fixed, can follow variations in the environment of
detection or in the ultrasonic sensor's own characteristics and,
even after shipment, double feed in the sheet feeding apparatus can
be always detected accurately. That is, even in a case that the
sensor output varies with fluctuations in the sensitivity, sound
pressure or fitting of the ultrasonic sensor, its ambience or
adhesion of paper powder, double feed can be detected without
fail.
[0061] Further, according to the present invention, the input value
from the receiving element of the ultrasonic sensor in the sheet
feeding apparatus is adjusted either by altering the reference
voltage of the operational amplifier or altering the frequency of
clocks supplied by the drive circuit or the duty ratio. Therefore,
at the time of shipping the sheet feeding apparatus, for example,
there is no need to adjust the amplification rate of the amplifier
of the ultrasonic receiving circuit with a variable resistance.
This is also true at the time of replacing the ultrasonic sensor,
for example. Even in a case that the ultrasonic receiving circuit
comprises a band pass filter, the output of the receiving element
of the ultrasonic sensor can be prevented from attenuating.
* * * * *