JPH11301885A - Lapping feed sensor and feeder using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a feeder suitable for sheets to be fed, if easy to damage in application of frictional force. SOLUTION: A feeder using a pickup roller 11 for picking one sheet 20a to be fed out of a plurality of stacked sheets 20 includes a lapping feed sensor 19 formed by a circuit containing a parallel plane electrode capacitor provided on the side of feedout of the sheets of the pickup roller 11 for detecting the lapping feed of the sheets 20 in no contact and an arithmetic circuit 9 for indexing the number of sheets passing between the parallel plane electrodes from the output of the lapping feed sensor 19, the lapping feed sensor 19 causing the pickup roller 11 to be stopped immediately when the lapping feed of the sheets is detected by the lapping feed sensor 19.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double feed sensor and a paper feeder provided with the same, and more particularly to a paper feeder which can be suitably used even when paper to be fed is easily damaged by friction.

[0002]

2. Description of the Related Art Conventionally, as this kind of sheet feeding apparatus, for example, a sheet feeding apparatus employing a method called a separation pad system as shown in FIG. 5 and a retard roller as shown in FIG. It is known that a system called a system is adopted. First, in a method called a separation pad method shown in FIG. 5, usually, only the uppermost sheet 20a of the stacked sheets 20 is picked up by the pickup roller 1a.
1 and the transport roller 12 and the separation pad 1
3 is sent. However, when the pickup roller 11 removes not only the uppermost sheet 20a but also the lower sheet 20b of the sheet 20a, the plurality of sheets are transported by the transport roller 12a.
And the separation pad 13. The above-mentioned separation pad 13 is made of a rubber-based material having a large friction coefficient. The separation pad 13 is also in contact with the transport roller 12 also made of a rubber-based material having a large friction coefficient because of a contact area with the paper 20a. , As paper transport force due to friction,
The configuration is such that "the paper transport force by the transport roller 12 is greater than the paper transport force by the separation pad 13". Therefore, when only the uppermost sheet 20a is taken out by the pickup roller 11 and sent between the conveyance roller 12 and the separation pad 13, the sheet 20a smoothly moves between the conveyance roller 12 and the separation pad 13. After passing, it is sent to the next process. Pickup roller 1
When the sheet 20a of the lowermost layer is accompanied by not only the sheet 20a of the uppermost layer but also the sheet 20b of the lower layer at the time of the take-out operation by No. 1, of the two sheets fed between the transport roller 12 and the separation pad 13, The paper 20a in contact with the transport roller 12 is separated from the transport roller 12 and the separation pad 1 in the same manner as above.
3 and is sent to the next process.
0b indicates that the frictional force between the paper 20a and the paper 20b is
0b and the separation pad 13, the slippage occurs between the paper 20a and the separation pad 13 in contact with the separation pad 13, and further conveyance in the state of contact with the separation pad 13 is prevented. Will be. This is the separation operation of the separation pad 13.

On the other hand, in a system called a retard roller system shown in FIGS. 6A and 6B, the uppermost sheet 20a of the stacked sheets 20 is usually taken out by a pickup roller 11 and conveyed. It is fed between the roller 12 and the retard roller 14. When the pickup roller 11 removes not only the uppermost sheet 20a but also the lower sheet 20b of the sheet 20a, the plurality of sheets are transported by the transport roller 1a.
2 and the retard roller 14. A torque limiter 15 is provided between the retard roller 14 and its shaft.
Is set, and the retard roller 14 itself is
It always rotates counterclockwise in the figure with a small torque. In addition, the retard roller 14 is rotated clockwise (that is,
When a large force equal to or greater than the set value of the torque limiter 15 is applied to the paper feed direction), the retard roller 14 follows the transport roller 12 and rotates clockwise. Also in this paper feeder, the uppermost sheet 20a of the paper 20 is taken out by the pickup roller 11 and sent to the transport roller 12 and the retard roller 14 (FIG. 6A).
reference). In this case, the paper 20a smoothly passes between the transport roller 12 and the retard roller 14 and is sent to the next process. Further, at the time of the take-out operation by the pickup roller 11, not only the uppermost sheet 20a but also the sheet 2a
0a, the paper 20b in contact with the transport roller 12 of the two sheets fed between the transport roller 12 and the retard roller 14
a passes through the space between the transport roller 12 and the retard roller 14 and is sent to the next process, as in the case of the upper sheet 20b.
Indicates that the frictional force between the paper 20a and the paper 20b is smaller than the frictional force between the paper 20b and the retard roller 14, and that the retard roller 14 is rotating in the counterclockwise direction in FIG. 14, a slip occurs between the retard roller 1 and the sheet 20 a in a state where the retard roller 1 contacts the sheet 20 a.
4 is prevented from being further transported in a state of being in contact with 4 (see FIG. 6B). This is the separating operation by the retard roller 14.

[0004]

However, the above-described prior art apparatus has the following problems. In other words, when this device is used as a paper feeding device that is easily damaged when a frictional force is applied, when the second paper 20b is accompanied, the conveyance is prevented by the separation pad 13. The second sheet 20b and the uppermost sheet 20a, or the retard roller 14 rotating in the direction opposite to the conveying direction of the sheet 20a, and the sheet 20a are continuously rubbed. However, there is a problem that the surface of the paper 20a is damaged. The object of the present invention is to solve the above-mentioned problems in the prior art,
An object of the present invention is to provide a sheet feeding device that can be suitably used even when a sheet that is easily damaged when a frictional force is applied becomes a sheet to be fed.

[0005]

In order to achieve the above object, according to the present invention, the number of sheets of paper entering by using the capacitance of a parallel plate electrode capacitor through which the entering paper passes is described. Is characterized by According to a second aspect of the present invention, in the paper multi-feed sensor according to the first aspect, the double feed sensor utilizes a change in capacitance. Further, according to a third aspect of the present invention, in the paper multi-feed sensor according to the first or second aspect, the capacitance value handled by the double-feed sensor uses an average value of a plurality of capacitance values. . According to a fourth aspect of the present invention, in the paper multi-feed sensor according to the first or second aspect, the capacitance value handled by the double-feed sensor uses an integrated value of the capacitance value in a predetermined period. I have. According to a fifth aspect of the present invention, there is provided a sheet feeding device including a sheet sending unit that sends one sheet to be fed from a plurality of stacked sheets, wherein a sheet sending side of the sheet sending unit is provided with a sheet sending unit. A double feed sensor according to any one of Items 1 to 4, is provided. Further, according to a sixth aspect of the present invention, in the paper feeder of the fifth aspect, the double feed sensor continuously performs a detecting operation even while the sheet is passing. According to a seventh aspect of the present invention, in the paper feeder according to the fifth or sixth aspect, when the double feed sensor detects a double feed of the paper, the paper feeding means is stopped. . According to an eighth aspect of the present invention, in the paper feeder according to the fifth or sixth aspect, a conveying roller for feeding the sheet sent by the sheet sending means to a next step and a double feed preventing roller pressed against the feeding roller are provided. And a multi-feed sensor configured to reverse the multi-feed prevention roller for a predetermined time when the multi-feed sensor detects multi-feed. Further, the invention according to claim 9 is the paper feeder according to claim 7 or 8,
When a double feed of paper is detected by the double feed sensor,
An error display output device for displaying or outputting a paper feeding error is provided.

[0006] With the above-described configuration, it is possible to immediately and non-contactly detect when a double feed of paper occurs. In addition, when a double feed of paper is detected, it is possible to immediately stop taking out the paper or to rotate the retard roller for a predetermined time to discharge the paper from the retard roller. It is possible to realize a sheet feeding device that can be suitably used when the sheet is easily damaged by frictional force. Further, when the double feed prevention device stops the sheet feeding means or when the double feed prevention roller rotates in reverse, an error is displayed on the error display output device, so that the operator can quickly remove the cause of the double feed.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described.
A specific description will be given based on the drawings. FIG. 1 is a diagram illustrating a main part of a sheet feeding device according to an embodiment of the present invention. As for the symbols in the figure, the same symbols are used for the same components as those in FIGS. 5 and 6 described above. That is, 11
Is a pickup roller, 12 and 12 ′ are transport rollers,
Reference numeral 20 denotes laminated paper, 20a denotes one sheet of the uppermost layer, 2
0b indicates the sheet immediately below. A double feed detection sensor 19 includes a parallel plate electrode capacitor, a CR oscillation circuit including the same, a CPU, and the like. Reference numeral 17 denotes a motor that drives the pickup roller 11 and the transport rollers 12 and 12 ′, and 9 denotes a control unit that controls the motor 17 based on the output of the double feed sensor 19. The double feed sensor 19 performs the discrimination of the number of sheets by utilizing the capacitance between the electrodes or a change in the capacitance, based on the thickness of the sheet 20 existing between the two parallel plate electrodes. It is necessary to set the characteristics in advance according to the type and thickness of the paper to be used. In the paper feeder according to the present embodiment, the pickup roller 11 is controlled by the control unit 9 based on the output of the double feed sensor 19 as described below.
And the operation of the transport roller 12 is controlled. The control unit 9
Includes a CPU, based on the output of the double feed sensor 19 and the like.
The operation of the motor 17 is controlled.

FIG. 2 is an operation flowchart showing an example of the operation control program of the control unit 9. When the paper 20 is fed, the pickup roller 11 and the transport roller 12 are rotated counterclockwise in the figure by the motor 17 (step 31). With this operation, the uppermost sheet 20 a of the sheet 20 is sent out by the frictional force with the pickup roller 11. At this time, the next second sheet 20b may be sent out along with one sheet 20a of the uppermost layer of the sheet 20. Hereinafter, the operation of the sheet feeding device according to the present embodiment will be described in detail for the case where only the uppermost sheet 20a is taken out and the case where the second sheet 20b is accompanied. The common operation includes the sheet 20 a (or 20 sheet) taken out by the pickup roller 11.
a and 20b) are supplied to the double feed sensor 19, where the sheet thickness is checked (step 32). Then, based on the result of the sheet thickness check, a characteristic operation of the sheet feeding apparatus according to the present embodiment is performed as follows.

First, when only one sheet of paper 20a is taken out of the uppermost layer, the fact is recognized by the check by the double feed sensor 19 (NO in step 32), and the result is sent to the control unit 9, The control unit 9 includes a pickup roller 11
Is rotated as it is, and the paper 20a is sent out to the next stage by the transport roller 12.

On the other hand, when not only the uppermost sheet 20a but also the second sheet 20b is accompanied, the double feed sensor 1
9 recognizes that fact (YES in step 32), and sends the result to the control unit 9. Control unit 9
Immediately stops the pickup roller 11 and the transport roller 12 based on the above information (step 3).
3). As a result, the two sheets are not sent to the next stage in a state in which the sheets are multi-fed. Also, at this time, it is preferable to notify the operator by displaying a notice or an error message using a well-known warning sound (not shown) (step 34). According to the above-described embodiment, double feed of the paper 20 can be reliably detected.
Since the feeding of 0 is immediately interrupted, a sheet feeding device that can be suitably used, for example, even when the sheet 20 to be fed is a sheet that is easily damaged when a frictional force is applied, is realized. There is an effect that can be.

FIG. 3 is a diagram showing a main part of a sheet feeding apparatus according to another embodiment of the present invention. The symbols in the figure are the same as those in FIGS. 1, 5 and 6 shown earlier,
The same symbols are used. That is, 9 is a control unit, 11 is a pickup roller, 12 is a conveyance roller, 14 is a retard roller, 17 is a motor for driving the pickup roller 11 and the conveyance roller 12, and 19 is a double feed sensor. Further, reference numeral 18 denotes a motor for forcibly driving the retard roller 14 in a counterclockwise direction in the figure, 20 denotes a stacked paper,
"a" indicates one sheet of the uppermost layer, and "20b" indicates a sheet immediately below.

FIG. 4 is an operation flowchart showing an example of an operation control program of the control unit 9 according to the present embodiment. Hereinafter, the operation of the device configured as described above will be described. When the paper 20 is fed, the pickup roller 11 and the transport roller 12 are rotated counterclockwise in the figure by the motor 17 (step 31). By this operation, the uppermost sheet 20 a of the sheet 20 is moved to the pickup roller 11.
Is sent out by the frictional force with Below, one sheet of the top layer 2
The operation of the paper feeding device according to the present embodiment will be described for the case where only 0a is taken out and the case where the second sheet 20b is accompanied. As a common operation, the sheet 20a (or 20a and 20b) taken out by the pickup roller 11 is supplied to the double feed sensor 19, where the sheet thickness is checked (step 3).
2). Then, based on the result of the sheet thickness check, a characteristic operation of the sheet feeding apparatus according to the present embodiment is performed as follows.

First, when only one sheet 20a of the uppermost layer is taken out, it is recognized by the check by the sheet thickness sensor 19 (NO in step 32), and the result is sent to the control unit 9, The control unit 9 includes the pickup roller 1
1 is rotated forward as it is, and the paper 20a is sent to the next stage. This operation is the same as in the above-described embodiment.

On the other hand, if not only the uppermost sheet 20a but also the second sheet 20b is accompanied, the double feed sensor 19
Is recognized by the check by
ES), and the result is sent to the control unit 9. The control unit 9
Based on this information, while the drive of the pickup roller 11 and the transport roller 12 is continued as it is, the motor 18 is driven to forcibly drive (reversely rotate) the retard roller 14 counterclockwise in the figure for a certain period of time (step). 41-4
3). As a result, the two sheets are separated according to the magnitude relationship of the frictional force described above, the sheet 20a is conveyed as it is and sent to the next stage, and the sheet 20b is reversely fed by the reverse rotation of the retard roller 14 for a predetermined time. Will be discharged. After a certain period of time, the reverse rotation of the retard roller 14 stops. During the period of the suppression, the retard roller 14 and the paper 20a are continuously rubbed, but there is no problem because the sliding contact is only at the end of the paper 20a and is a part other than the printing area. As described above, the conventional retard roller uses the torque limiter, and thus continuously rubs the photosensitive material surface of the sheet 20a during the multi-feed. However, according to the present invention, the non-contact multi-feed sensor electrically controls the retard roller. ,
In addition, since the reverse rotation is stopped before the retard roller contacts the printing area of the paper 20a, the photosensitive material surface of the paper 20a is not rubbed. If the retard roller 14 is forcibly driven in the counterclockwise direction in the figure for a certain period of time, a warning sound or an error message is displayed (step 34), and the operator is notified of that. Is good. According to the above-described embodiment, double feed of the paper 20 can be reliably detected.
0, the feeding of the first sheet 20a is continued, and the feeding of the second sheet 20b is refrained. Even in the case where the sheet is easily damaged when a force is applied, there is an effect that a sheet feeding device that can be suitably used can be realized. It should be noted that various known methods other than the above can be used for the treatment at the time of the above-described abnormality. Examples of paper that is easily damaged when the above-described frictional force is applied include various types of transfer paper in addition to thermal transfer paper. Further, the above-described embodiment shows an example of the present invention, and it is needless to say that the present invention is not limited to this.
For example, it goes without saying that various changes can be made to the control program used for the control unit 9.

Next, a detailed circuit configuration example of the above-described double feed sensor 19 will be described. FIG. 7 is based on a system called a V / F (voltage-frequency) conversion system, where C is a capacitor composed of the above-mentioned parallel plate electrodes, R is a charging resistor, and V0
Is a charging power supply voltage, the power supply voltage V0 is applied to the capacitor C via the charging resistor R, and the capacitor C is charged with a time constant composed of CR. OP is an operational amplifier whose negative terminal is grounded and whose positive terminal is a charging resistor R and a capacitor C.
Is connected, and the other end of the capacitor C is connected to the output side of the operational amplifier OP to form an integral circuit as a whole. A switching element is connected in parallel to the capacitor C, and a control terminal of the switching element is connected to an output side of a one-shot multi-described later. CMP is a comparison circuit. The reference voltage Vr is applied to its negative terminal and the charging voltage of the capacitor C is applied to its positive terminal. When the charging voltage of the capacitor C exceeds the reference voltage Vr, an output signal from the comparison circuit CMP is output. It is sent out to the next one-shot multi. With this output signal, the one-shot multi outputs one pulse to the next-stage switching element and counter. The switching element connected in parallel to the capacitor C is turned on by the pulse from the reset circuit, and the electric charge stored in the capacitor C is discharged. The next-stage counter counts the pulses from the one-shot multi, and outputs the pulse to the next-stage CPU. The operation is performed in the CPU. That is, according to this method, the value of the capacitor C is different between the case where one sheet is present and the case where two sheets are present between the above-mentioned parallel plate electrodes, and the value of the capacitor C becomes In the case of double feeding, the dielectric constant of the paper increases, and the value of the capacitor C increases. Therefore, the charging time constant of the capacitor changes, and the charging voltage of the capacitor C quickly reaches the reference voltage Vr in the case of normal single-sheet feeding, whereas the charging voltage of the capacitor C in the case of multi-feeding increases the reference voltage Vr.
r slower to reach. Therefore, the frequency F output from the one-shot multi is different. FIG. 8 illustrates this state, in which (a) shows a case where two sheets are fed and (b) shows a case where one sheet is fed. If the frequency F is obtained by the counter, the following equation is calculated by the CPU at the next stage, and C is obtained from F = 1 / (V0.RCC / Vr). C = Vr / (V0 · R · F)

FIG. 9 is an explanatory diagram of a system based on the same principle as above. C is a capacitor composed of the above-mentioned parallel plate electrodes, R is a charging resistor, and V0 is a charging power supply voltage.
A CR integration circuit having a series connection circuit composed of a charging resistor R and a capacitor C is configured, and a power supply voltage V0 is applied to the CR integration circuit. CMP is a comparison circuit. The reference voltage Vr is applied to its negative terminal and the charging voltage of the capacitor C is applied to its positive terminal. When the charging voltage of the capacitor C exceeds the reference voltage Vr, an output signal from the comparison circuit CMP is output. It is output to the next stage reset circuit. With this output signal, the reset circuit
One reset pulse is output to the R integration circuit, and a pulse is output to the next-stage counter. The CR integrator is turned on by the pulse from the reset circuit, and the electric charge stored in the capacitor C is discharged and reset. The next-stage counter counts the input pulses, and the next-stage CP
Output to U. The operation is performed in the CPU. If the frequency F is obtained by the counter, the following equation is calculated by the CPU of the next stage from F = 1 / (V0.RCC / Vr), and C is obtained. C = Vr / (V0 · R · F)

FIG. 10 shows the calculation of the capacitance C by obtaining the period T due to the change in the capacitance, instead of observing the change in the capacitance at the frequency F as shown in FIGS. 7 and 9. Things. The period T is obtained by counting clock pulses entering the counter between the F made in FIGS. 7 and 9 and the next F. When the frequency T is obtained by the counter, the following CPU calculates the following equation by the next CPU, and C
Is found. C = Vr · T / V0 · R

FIG. 11 shows a system called a CR oscillator system. C is a capacitor composed of the above-mentioned parallel plate electrodes, R is a charging resistor, V 'is a charging voltage for charging the capacitor, and OP is an operational amplifier. CMP is a comparison circuit, and VF is an output voltage of the comparison circuit CMP. In this method, the frequency of V ′ changes due to a change in the capacitance C, and one cycle T is obtained from the frequency.
In this case, V 'and VF have waveforms as shown in FIG. The capacitor charging voltage V ′ becomes a triangular wave, and VF takes a positive value when the triangular wave decreases and a negative value when the triangular wave increases. From this, the period T is obtained, so that from T = RC,
C is determined by C = T / R

FIG. 13 shows a system in which an AC power supply is directly applied to the capacitor C. When a known v = Vmsinωt is applied to the circuit of the capacitor C, i = ωCVmsin (ωt + π / 2), and the current maximum value Im and the effective value | I | are obtained by measuring the current i. On the other hand, since Vm and ω are known, C can be obtained from the following equation. Im = ωCVm C = Im / ωVm Alternatively, if the effective values | I | and | V | of the current and the voltage are calculated, | I | = ωC | V |

FIG. 14 is an explanatory diagram of an AC power supply system based on the same principle as that of FIG. Here, the output v of the comparison circuit
Since 0 is v0 = RF · i, C is obtained by measuring i in the same manner as above. The above is a specific circuit configuration example of the double feed sensor 19 described above.

Next, a description will be given of compensation for variations among devices, temperature dependency, and changes over time in double feed detection considered in the present invention. Usually, in detecting the presence or absence of multifeed, a predetermined threshold value is set in order to discriminate between the case of one sheet and the case of two or more sheets. Of the paper and the variation of the dielectric constant of the paper. For example, if a sheet having a dielectric constant twice as large as that of a normal sheet is used, the conventional detection method will cause C to have a value of a plurality of sheets. It was decided.
However, it is actually very troublesome to reset the threshold value in response to such variations, and it takes time and expertise. This problem is solved in the present invention as follows. That is, the threshold value is not determined by an absolute value, but is determined by a relative value, that is, a value corresponding to a difference between one sheet and two or more sheets.

FIG. 15 illustrates this principle. The vertical axis represents the period T obtained by one of the above-described methods, and the horizontal axis represents the time t.
It is. First, the cycle T is T0 until time t0 when the sheet does not reach between the electrodes (when there are no sheets), the cycle T becomes T1 when one sheet is inserted, and the cycle T is when two sheets are inserted. Is T2. Therefore, in the absolute value method in which the threshold value is provided between the periods T1 and T2, if a sheet having a dielectric constant twice that of a normal sheet arrives, the threshold value is set to one sheet. It will be exceeded and will be judged as double feed. However, here, one cycle T1
The CPU learns in advance the difference ΔT1 (that is, the change in the capacitance) between the cycle T0 and the cycle T0 of zero sheets, and judges double feeding based on this. Therefore, when double feed occurs, 2
The difference between the cycle T2 of the sheet and the cycle T0 of the sheet is ΔT
2 and greatly exceeds the reference value ΔT1, so that it is determined that double feeding has occurred. With such a relative value method, even when a sheet having a dielectric constant twice as large as that of a normal sheet arrives, the reference value ΔT1 only becomes a large value. Since the transmission is determined, no erroneous determination is made. Since the paper is transported by the CPU, the capacitance can be detected at the timing when the paper completely enters between the electrodes, so that the gradual change in the capacitance when the paper enters between the electrodes can be measured. This can prevent erroneous detection.

Further, once the determination when using the CPU is made, it is preferable that the determination is not always made again for the paper, but is always made sequentially. The reason is shown in FIG.
This will be described with reference to the drawings shown in FIGS. FIG.
(A) is a normal state in which one sheet enters between the parallel plate electrodes, and the change of the capacitance C (and thus the period T) also changes with time on the horizontal axis as shown in the figure. As described above, the capacitance is detected by detecting the timing when the paper completely enters between the electrodes. Therefore, a gradual change in the capacitance when the paper enters between the electrodes (the dotted line in the figure) ) Is disregarded and the measurement is made at ta when the paper completely enters between the electrodes. Here, in order to make the change of the period T easier to see,
It is schematically depicted so that the paper changes from T0 to Ta in a step-like manner when the paper enters halfway between the parallel plate electrodes.
Then, the difference ΔTa between the periods Ta and T0 at this time is compared with the comparison reference ΔT1 for the learning so far, and it is determined that the learning is normal. FIG. 16B shows the capacitance C (and thus the period T) in the case of an abnormal state where two sheets enter between the electrodes at the same time.
Of FIG. The measurement is performed at the time tb when the paper completely enters between the electrodes, and the difference ΔTb between the period Tb and T0 is compared with the comparison reference ΔT1 for the learning so far, so that it is determined that the sheet is abnormal because it is greatly different. Again, the change in capacitance during transition when the paper enters between the electrodes is indicated by the dotted line in the figure,
In order to make it easy to see the change, it is schematically depicted so that the paper changes stepwise from T0 to Tb when the paper enters halfway between the parallel plate electrodes. FIG. 16C shows an abnormal state in which two sheets of paper are temporally shifted between the electrodes, and the change of the capacitance C changes as shown in the figure with the time change on the horizontal axis. Here, a gradual change in the capacitance during the transition when the paper enters between the electrodes is omitted to make it easier to see by omitting the steps from T0 to Tc1.
It is schematically depicted as changing from Tc1 to Tc2.
The measurement is performed at time tc1 when the paper completely enters between the electrodes, and the difference ΔTc1 between the periods Tc1 and T0 is compared with the learning ΔT1, but it is determined to be normal at this time. If detection is performed only once for one sheet of paper, such an abnormal state in which two sheets are shifted in time cannot be detected. However, by performing double feed detection continuously and sequentially, the next time tc2 is detected. Measured and its period T
When the difference ΔTc2 between c2 and T0 is compared with ΔT1 of learning, it is determined that there is an abnormality.

Further, since it is conceivable that the above various reference values are compensated according to changes in the environment, for example, changes in humidity, the type of paper to be detected and the measurement environment (humidity, temperature, etc.) In addition, it is effective to select a reference value that matches the current environment from past data stored in the CPU as the reference value in accordance with the size (size, thickness, etc.). Further, in order to improve the accuracy of detection, it is preferable to increase the number of extracted data and obtain an average value thereof in order to suppress the influence of noise during one measurement. FIG.
(A) illustrates this principle. FIG. 17 (a),
(B) shows a temporal transition of the capacitance before the paper enters between the electrodes → the capacitance during the transition period → the capacitance after the carry-in. FIG. 17A shows not only the detection of the capacitance C1 alone, but also the capacitances C2, C3,.
And n times. By taking the average, even if dust or the like at the measuring location of the capacitance C1 accidentally adheres, an erroneous detection of the abnormally large capacitance C1 due to the adhesion can be prevented.

In addition to the above-described data averaging method shown in FIG. 17A, noise prevention by integrating data can be considered. FIG. 17B illustrates this principle. If an integrating circuit is used, as shown in the figure, even if there is some noise in the capacitance C, the noise is absorbed by the integration effect, and the period T may be measured. The above embodiments are merely examples of the present invention, and the present invention should not be limited to these.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific embodiment of the double feed detection performed according to the present invention will be described below. 1. First, the measurement of the thickness dp and the calculation of the relative dielectric constant .epsilon.p of the image receiving paper for a thermal transfer printer used for the double feed detection were performed in advance. a) Measurement of thickness dp: When the thickness dp of the image receiving paper for a thermal transfer printer was measured, it was found that dp = 160 × 10 ⁻⁶ (m). b) The relative permittivity εp was calculated as follows: LC
The capacitance of the image receiving paper was measured with an R meter under the following conditions. (1) Measurement conditions: ・ Applied voltage V = 1 (Vrms) ・ Frequency f = 1 (kHz) ・ Electrode area S = 1.96 × 10 ^-5 (m ² ) (2) The capacitance Cp of the image receiving paper The measurement results are as follows: Capacitance Cp = 2.2 × 10 when there is only one image receiving paper
^-12 (F).・ Capacitance Cp = 1.1 × 10 when there are two image receiving papers
^-12 (F). (3) From the above measurement results, the relative permittivity εp of the image receiving paper was calculated by the following equation. .epsilon.p = (Cp.times.n.times.dp) / (. epsilon.0.times.S) where Cp is the capacitance, n is the number of inserted image receiving papers, dp
Is the thickness of the receiving paper, ε0 is the vacuum permittivity, and S is the electrode area. (4) Calculation results: • The relative permittivity εp (calculated value) of the image receiving paper when one image receiving paper is used
= 2.025 ・ Relative permittivity εp (calculated value) of the image receiving paper when there are two image receiving papers
= 2.025 From the above, the relative dielectric constant εp of the image receiving paper was set to 2.025. 2. Now, the thickness dp of the image receiving paper obtained as described above
Using the relative permittivity .epsilon.p of the image receiving paper and each of the known constants, double feed detection was performed according to the principle of double feed detection as shown in FIG. That is, the electrode area Se (Se = 2 cm × 2 cm = 4 × 1
0 ^-4 (m ² )) parallel plate electrodes made of an aluminum plate are separated by a distance de (m), and n sheets of the image receiving paper having the measured thickness dp and relative permittivity εp are inserted between the electrodes. Then, the capacitance Ce (n) between the parallel plate electrodes is obtained. In this case, the capacitance Ce (n) between the parallel plate electrodes
Is as follows:

[0027]

(Equation 1)

That is, the vacuum permittivity ε0 (ε0 = 8.8)
54 × 10 ⁻¹² ) and the electrode area Se (Se) of the parallel plate electrode
= 4 × 10 ⁻⁴ (m ² )) is known and the thickness d of the image receiving paper is known.
p from ^{(dp = 160 × 10 -6 (} m)) and the image receiving sheet of the dielectric constant εp (εp = 2.025) is also known, between the parallel plate electrodes the capacitance Ce (n) and the image receiving paper The relationship with the number n of insertions is as shown in FIG. 19, using the distance de (m) between the parallel plate electrodes as a parameter. That is, when the distance de of the parallel plate electrode is 1.2 (mm), the capacitance Ce = 3.0 (p
F), where n = 1 and the capacitance Ce = 3.2 (pF)
Where n = 2 and the capacitance Ce = 3.4 (pF). The capacitance Ce is 3.7 (pF) for n = 3 sheets.
When the distance de of the parallel plate electrodes is 1.0 (mm), the capacitance Ce is 3.5 (pF) when n = 0 sheets, and
The capacitance Ce = 3.8 (pF) for n = 1 sheet, and n =
The capacitance Ce of the two sheets is 4.2 (pF). The capacitance Ce is 4.6 (pF) for n = 3 sheets. When the distance de of the parallel plate electrodes is 0.8 (mm), the capacitance Ce = 4.5 (pF) when n = 0 sheets, and the capacitance Ce = 5.0 when n = 1 sheet. (PF), and the capacitance Ce = 5.5 (pF) for n = 2 sheets. Capacitance C for n = 3 sheets
e = 6.3 (pF). As can be seen from FIG. 19, the capacitance Ce between the parallel plate electrodes changes substantially linearly depending on the number n of inserted image receiving papers. Therefore, the image reception is performed by detecting the capacitance Ce between the parallel plate electrodes. The number n of inserted papers can be determined. In practice, the shorter the distance de between the parallel plate electrodes is, the larger the value of the capacitance Ce between the parallel plate electrodes is, and the greater the dependence on the number of image receiving papers, the easier the discrimination becomes. Thus, it is preferable to make the distance de between the parallel plate electrodes as short as possible.

[0029]

As described above in detail, according to the present invention, the paper feeding apparatus can be used suitably even when the paper to be fed is easily damaged by a frictional force or the like. Can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a main part of a sheet feeding device according to an embodiment of the present invention.

FIG. 2 is an operation flowchart illustrating a characteristic operation of the sheet feeding apparatus according to the embodiment;

FIG. 3 is a diagram illustrating a main part of a sheet feeding device according to another embodiment.

FIG. 4 is an operation flowchart illustrating a characteristic operation of the sheet feeding apparatus according to the embodiment;

FIG. 5 is a diagram (part 1) illustrating a main part of a conventional sheet feeding device.

FIG. 6 is a diagram (part 2) illustrating a main part of a conventional sheet feeding device.

FIG. 7 is a diagram (part 1) illustrating a specific circuit configuration of the double feed sensor 19 including a parallel plate capacitor.

FIG. 8 is a diagram for explaining the operation of the configuration shown in FIG. 7;

FIG. 9 is a diagram (part 2) illustrating another circuit configuration of the double feed sensor 19 including a parallel plate capacitor.

FIG. 10 is a diagram (part 3) illustrating another circuit configuration example of the double feed sensor 19;

FIG. 11 is a diagram (part 4) illustrating another example of the circuit configuration of the double feed sensor 19;

FIG. 12 is a diagram illustrating the operation of the configuration shown in FIG. 11;

FIG. 13 is a diagram (part 5) illustrating another circuit configuration example of the double feed sensor 19;

FIG. 14 is a diagram (part 6) illustrating another example of the circuit configuration of the double feed sensor 19;

FIG. 15 shows a relative value (change in capacitance) employed by the present invention.
FIG. 4 is a diagram showing the principle of double feed determination based on the above.

FIG. 16 is a diagram illustrating a principle that an abnormal state in which two sheets of paper are shifted in time can be detected by sequential detection employed in the present invention.

FIG. 17 is a diagram showing a principle adopted by the present invention as a measure against a partial noise of a sheet.

FIG. 18 is a diagram illustrating the principle of double feed detection using parallel parallel plate electrodes.

FIG. 19 is a graph showing the relationship between the capacitance Ce (n) between the parallel plate electrodes and the number n of receiving paper sheets when the distance de (m) between the parallel plate electrodes is used as a parameter.

[Explanation of symbols]

Reference Signs List 9 control unit 11 pickup roller 12, 12 'transport roller 14 retard roller 17 motor for driving pickup roller 11, transport roller 12 18 motor for driving retard roller 14 19 double feed sensor 20 composed of a circuit including a parallel plate capacitor 20 Paper

Claims (9)

[Claims] 1. A multi-feed sensor, wherein the number of incoming sheets is determined using the capacitance of a parallel plate electrode capacitor through which the incoming sheets pass. 2. The multi-feed sensor according to claim 1, wherein the multi-feed sensor utilizes a change in capacitance. 3. The multi-feed sensor according to claim 1, wherein the capacitance value handled by the multi-feed sensor uses an average value of a plurality of capacitance values. 4. The multi-feed sensor according to claim 1, wherein the capacitance value handled by the multi-feed sensor uses an integral value of the capacitance value during a predetermined period. 5. A paper feeder comprising a paper feeding means for feeding one sheet to be fed from a plurality of stacked sheets, wherein a paper feeding side of said paper feeding means is provided.
A sheet feeding device provided with the double feed sensor according to any one of claims 4 to 7. 6. The paper feeding device according to claim 5, wherein the multi-feed sensor continuously performs a detecting operation even while the paper is passing. 7. The sheet feeding device according to claim 5, wherein when the double feed sensor detects double feed of the sheet,
A sheet feeding device, wherein the sheet feeding means is stopped. 8. The sheet feeding device according to claim 5, wherein the sheet feeding unit feeds the sheet sent out by the sheet sending unit to a next process, and a double feed prevention roller pressed against the feeding roller. A sheet feeding device provided with conveying means, wherein the double feed preventing roller is reversely rotated for a predetermined time when the double feed of the sheet is detected by the double feed sensor. 9. The paper feeding device according to claim 7, wherein when the double feed sensor detects double feed of the sheet,
A sheet feeding device provided with an error display output device for displaying or outputting a sheet feeding error.