JPH10181950A - Overlap feed detector for paper sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an overlap feed detector improving detection accuracy of an overlap feed of paper sheets. SOLUTION: This overlap feed detector is provided with a displacement means 2; 3 displaced in accordance with thickness of a paper sheet P during conveyance and a displacement amount detection means 11; 12 detecting a displacement amount of the displacement means to output a displacement amount data. Over a total region of length in a conveying direction of the paper sheet P, the displacement amount data is sampled, also based on this sampled displacement amount data, an obtained averaged displacement amount is compared with a reference displacement amount corresponding to a displacement amount of the displacement means when the paper sheet is a single sheet, whether an overlap feed is provided or not of the paper sheet is decided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double feed detecting device for detecting a double feed in which two or more sheets are conveyed while being overlapped.

[0002]

2. Description of the Related Art Conventionally, in a medium processing apparatus such as a printer for feeding single sheets of paper in a hopper, a magazine or the like, one sheet at a time, and transporting the sheets to a printing section for printing, etc. Paper sheets must be completely separated one by one. If a double feed occurs in which two or more sheets are conveyed while being overlapped, this must be detected and the conveyance must be temporarily stopped to remove the overlapped sheets. . For this reason, conventionally, a double feed detecting device for paper sheets as described below has been used.

FIGS. 5A and 5B are principle diagrams of a conventional double feed detecting device. The paper sheet P is nipped by the transport roller 1 and the press roller 2 and transported in the F direction. The pressing roller 2 is rotatably supported at one end by an intermediate portion of a displacement detecting lever 3 rotatably supported by a support shaft 3a, and is constantly moved in a direction approaching the transport roller 1 by urging means (not shown). Being energized. Further, a transmission type optical sensor 4 is provided so as to detect the detected portion 3b of the displacement detection lever 3. That is, the amount of change of the pressing roller 2 in the thickness direction of the sheet is mechanically enlarged in the detected portion 3b of the displacement detection lever 3.

[0004] As shown in FIG.
In the case where there is no paper sheet P or one paper sheet P is sandwiched between them, the pressing roller 2 and the displacement detection lever 3 are in the positions shown by solid lines, and FIG. As shown,
Detected portion 3b provided at end of displacement detection lever 3
Are set so that the detection light L of the optical sensor 4 is shielded and the optical sensor 4 is turned off. The detected part 3
b may be provided at a portion other than the end of the displacement detection lever 3. When two or more sheets P are double-fed and sandwiched between the rollers 1 and 2, the pressing roller 2 and the displacement detection lever 3 are displaced to positions shown by a two-dot chain line, The detection portion 3b of the displacement detection lever 3 is set so as to deviate from the detection light L and the optical sensor 4 is turned on. That is, when the output of the optical sensor 4 is turned on, double feeding of paper sheets can be detected.

[0005]

In the above-described conventional apparatus, the amount of change in the thickness of a sheet is mechanically enlarged by the displacement detection lever 3, but the detection is made by the presence or absence of the sheet. The movement amount of the part 3b is only small.
For this reason, the transmission type optical sensor 4 turns on / off the output in response to the slight movement of the detected portion 3b, so that the output state has to be unstable. That is, although the number of paper sheets is one, the optical sensor 4 is turned on, or the number of paper sheets is two,
Since the optical sensor 4 may not be turned on, the detection accuracy when detecting the double feed must be low. Further, it is necessary to manually adjust the relative position between the displacement detection lever 3 and the optical sensor 4 according to the thickness of the paper sheet, but such a delicate adjustment operation is troublesome and time-consuming. For this reason, when dealing with paper sheets having different thicknesses, the displacement detection lever 3 and the optical sensor 4 must be positioned one by one in accordance with the thickness of the paper sheets. It is difficult to respond flexibly to leaves. The present invention has been made in view of such circumstances, and an object of the present invention is to improve the detection accuracy of multi-feeding of paper sheets, eliminate the need for troublesome mechanical positioning work, and provide a sheet having a different thickness. An object of the present invention is to provide a paper sheet multifeed detecting device capable of flexibly responding to leaves.

[0006]

According to the first aspect of the present invention,
A displacement unit that is displaced in accordance with the thickness of the sheet being conveyed, a displacement amount detection unit that detects a displacement amount of the displacement unit and outputs displacement amount data, and a case where the number of the sheets is one. Reference displacement amount setting means for setting a reference displacement amount corresponding to the displacement amount of the displacement means, and sampling the displacement amount data over the entire length of the sheet in the transport direction, and the sampled displacement amount The average displacement amount calculating means for calculating the average displacement amount based on the data, and the average displacement amount output from the average displacement amount calculating means during the conveyance of the sheet are supplied from the reference amount setting means. Determining means for determining the presence or absence of double feeding of the sheets by comparing with the reference displacement amount. According to the above configuration, the displacement amount of the displacement unit that changes in accordance with the thickness of the paper sheet being conveyed is detected by the displacement amount detection unit, and the detected displacement amount data is sampled, and the sampled displacement amount is sampled. The average displacement amount obtained based on the data is compared with a reference displacement amount corresponding to the displacement amount of the displacement means when the number of sheets is one, and the double feed of sheets is detected.

According to a second aspect of the present invention, in the first aspect, the reference displacement setting means outputs the average displacement output from the mean displacement calculating means during conveyance of the sheet in the reference value setting mode. The amount is set as a reference displacement amount, and in the normal transport mode, the reference displacement amount set in the reference value setting mode is supplied to a determination unit. According to the above configuration, in the reference value setting mode, the average displacement obtained based on the actual sheet is set as the reference displacement, and in the normal transport mode, the average displacement is set to the reference displacement. The double feed is detected by comparing.

According to a third aspect of the present invention, in the first or the second aspect of the present invention, the reference displacement amount setting means includes a plurality of reference displacement amounts set corresponding to the type of the paper sheet. And selecting the reference displacement amount corresponding to the type of the designated paper sheet from the list, and supplying the selected reference displacement amount to the determination means. According to the above configuration, the reference displacement amount corresponding to the type of the sheet is selected, and the double feed is detected based on the selected reference displacement amount.

According to a fourth aspect of the present invention, in the invention of any one of the first to third aspects, the sheet length detecting means for detecting a length of the sheet in the conveying direction; Reference sheet length setting means for setting a sheet reference length, which is a length in the transport direction of the sheet, wherein the determination means is configured to determine the length of the sheet detected by the sheet length detection means. The sheet length is compared with the reference sheet length supplied from the reference sheet length setting means to determine the presence / absence of multifeed of sheets. According to the above configuration, the sheet length obtained by detecting the length of the sheet being conveyed is compared with the reference sheet length to detect double feeding of the sheet.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, the reference sheet length setting means outputs the sheet length detecting means while the sheet is being conveyed in the reference value setting mode. The reference sheet length is set as a reference sheet length, and the reference sheet length set in the reference value setting mode is supplied to a determination unit in a normal transport mode. It is characterized by. According to the above configuration, the sheet length obtained by measuring the actual sheet length is set as the reference sheet length, and the double feed is detected based on the reference sheet length.

According to a sixth aspect of the present invention, in accordance with the fourth or fifth aspect, the reference sheet length setting means includes a plurality of reference sheet lengths set in accordance with the type of sheet. Selecting the reference sheet length corresponding to the type of designated sheet from among the sheet lengths, and supplying the selected reference sheet length to a determination unit. I have. According to the above configuration, the reference sheet length corresponding to the type of the sheet is selected, and the double feed is detected based on the selected reference displacement amount.

[0012]

Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a multi-feed detecting apparatus for paper sheets according to the present invention, and FIG.
FIG. 3 and FIG. 4 are operation flowcharts according to the first embodiment. In FIG. 1, members that are the same as or correspond to those in FIG.

The configuration will be described with reference to FIG. 1
Numeral 0 denotes a transmission type optical sensor for detecting the length of the paper sheet in the transport direction, which is off (dark) when the paper sheet is present in the detection area of the optical sensor 10 and when the paper sheet is present. Turns on (bright) when not present. A displacement sensor 11 is provided near the detected part 3b of the displacement detection lever 3. The displacement sensor 11 irradiates the detection target 3b of the displacement detection lever 3 as an object with the detection light and detects the amount of displacement between the object and the object based on the position of the reflected light beam that returns. Alternatively, a sensor that outputs a detection signal according to the displacement amount can be used. Also, the displacement sensor 1
1 is a detected part 3 of the displacement lever 3 according to the thickness of the paper sheet.
It is necessary to have a resolution enough to reliably detect the fluctuation of b. Note that the displacement sensor 11 is not limited to the above-described type, and may be of any type as long as it can output a detection signal corresponding to the amount of displacement of the displacement detection lever 3.

Reference numeral 12 denotes an A / D converter for A / D converting a detection signal output from the displacement sensor and outputting displacement data. That is, when the press roller 2 is displaced in accordance with the presence or absence of the sheet and the thickness of the sheet, the displacement amount is enlarged by the displacement detection lever 3 and detected by the displacement sensor 11, and the detected amount is used as a detection signal as A / D conversion unit 1
2 is input. The A / D converter 12 outputs displacement data according to the detection signal.

Reference numeral 13 denotes a transport motor for driving the transport rollers 1 and the like for transporting paper sheets, and is constituted by a step motor or the like. Reference numeral 14 denotes a motor control unit for controlling the drive of the transport motor 13, and a control unit 15
The driving of the transport motor 13 is performed in units of steps based on the instruction from the controller. That is, the control unit 15
Can manage the feed amount of paper sheets based on the number of steps of the transport motor 13.

The control unit 15 includes a CPU, an I / O port, and the like.
The displacement amount data from the conversion unit is input, and the motor control unit 14 is controlled. Reference numeral 16 denotes a ROM that stores a control program of the control unit 15, various setting data, and the like.
Reference numeral 17 denotes a RAM for providing a working area, having a value and a counter used in each arithmetic processing and the like, as shown in FIG. Reference numeral 18 denotes an operation unit for inputting predetermined operation information to the control unit 15. The operation unit 18 inputs the type of paper sheet to be conveyed, as described later.

FIG. 2 is an explanatory diagram showing a main part of the contents of the RAM 17. The RAM 17 stores an origin displacement amount Dz, a reference displacement amount Dr, and a reference sheet length Lr, all described later.
And the actually measured displacement amount Dm and the actually measured paper sheet length Lm actually measured by the processing described later. The reference displacement Dr is a value corresponding to the displacement of the displacement detection lever 3 when one sheet is present between the transport roller 1 and the pressing roller 2. The RAM 17 stores a sheet length counter C1 for counting step data of the transport motor 13 which is a value indicating the sheet length, and a displacement amount data output from the A / D converter 12 as appropriate. A displacement counter C2 for counting the total of sampling data obtained by sampling at a sampling cycle and a sampling number counter C3 for counting the number of samplings of the sampling data are provided. The RAM 17 is backed up by a battery in order to hold the above numerical data even when the power of the apparatus is turned off.

Next, specific operations will be described with reference to FIGS. 1 and 2 and the flowcharts shown in FIGS.

First, as shown in FIG. 3, the operator operates the operation unit 18 to set the operation mode to one of the reference value setting mode and the normal transport mode (step ST1). The normal transport mode is a mode in which a sheet processing apparatus such as a printer provided with the double feed detection device of the present embodiment performs a normal operation, for example, a printing operation.

The control unit 15 determines whether the operation mode set based on the setting operation performed on the operation unit 18 is the reference value setting mode or the normal transport mode (step ST).
2). Here, the description will be given on the assumption that the reference values (reference sheet length and reference displacement amount) have not been set, and the operation mode has been set to the reference value setting mode. Therefore, step S
Proceed to T3 or later. If the normal transport mode is set by the setting operation in step ST1, FIG.
It proceeds to the flowchart of.

The control unit 15 determines whether or not a sheet to be conveyed is set in a sheet processing apparatus having a double feed detecting device for the sheet by means of a sheet detecting means (not shown). A determination is made (step ST3). At this time, only one sheet is set so that the sheets are not double fed.
If sheets are set ("Y" in step ST3), the control unit 15 gives a command to the motor control unit 14 to start driving the transport motor 13 (step ST3).
4).

Next, a sheet length detecting process A consisting of steps ST5 to ST7 and a displacement amount detecting process B consisting of steps ST9 to ST12 are executed in parallel. The sheet length detecting process A will be described. The control unit 15 monitors whether the output of the optical sensor 10 is off (step S).
T5) If step ST5 is "Y", it is determined that the sheet P has passed the sensor 10, and the sheet length counter C1 is set to an appropriate count signal (for example, the motor driving step of the motor control unit 14). Signal (step ST6). Next, it is monitored whether or not the optical sensor 10 is turned on (step ST7). As long as step ST7 is “N”, that is, as long as the paper sheet is detected by the optical sensor 10, the process returns to step ST6. The counting operation of the paper sheet length counter C1 is continued. When step ST7 becomes "Y", the process proceeds to step ST8, and the counter value counted by the sheet length counter C1 is stored in the RAM 17 as the reference sheet length Lr (step ST7).
8). Step ST8 is not included in the sheet detection process A.

The displacement detection processing B will be described. The control unit 15 outputs from the A / D conversion unit 17 corresponding to the amount of displacement of the lever 3 when there are no sheets between the transport roller 1 and the pressing roller 2, that is, when both rollers 1 and 2 are in close contact with each other. The displacement amount data is stored in the RAM 17 as a predetermined origin displacement amount Dz (see FIG. 2). Control unit 15
Monitors whether the sheet P exists between the rollers 1 and 2 by comparing the displacement amount data output from the A / D converter 17 based on the origin displacement amount Dz. (Step ST9). Then, step ST9 returns "Y".
If so, the displacement data output from the A / D converter 17 is sampled at an appropriate sampling interval to obtain sampling data (step ST10). Then, the sampling data is added to the displacement counter C2 (step ST11), and the number of added sampling data is counted by the sampling number counter C3 (step ST12).

The control unit 15 controls the A / D converter 12
By comparing the displacement amount data output from the printer based on the origin displacement amount Dz, it is monitored whether or not the sheet P exists between the transport roller 1 and the pressing roller 2 (step ST).
13) If step ST13 is "N", that is, if a sheet is present between the rollers 1 and 2, the process proceeds to step ST10 and the above-described steps ST10 to ST1.
Step 2 is repeated. If step ST13 is "Y", that is, if the sheet P passes between the rollers 1 and 2, the count value of the displacement counter C2 is divided by the count value of the sampling number counter C3 at that time. , Calculate the average displacement amount, which is the average value of the displacement amounts (step ST
14). Then, the average displacement is stored in the RAM 17 as the reference displacement Dr (step ST15).

The above steps ST8 and ST15
Is completed, the control unit 15 determines whether or not the sheet conveyance operation is completed by a sheet detection unit (not shown) (step ST16). A command is given to the controller 14 to stop driving the transport motor 13 (step ST17).

The reference sheet length Lr and the reference displacement Dr of the sheet are set in the RAM 17 by the operations of steps ST3 to ST17 described above. As mentioned above,
The reference displacement amount Dr is a plurality of sampling data (displacement amount data) in the conveying direction of the actually used paper sheet.
Is a stable value that is not affected by a partial change in the thickness of one sheet. The sampling number of the displacement amount data for one sheet is not particularly limited, but a stable reference displacement amount can be set with, for example, about 50 to 200 sampling numbers. .

Next, in FIG. 3, the operation in the case where the determination in step ST2 is "N", that is, the operation in the normal transport mode will be described with reference to FIG. First, the control unit 15 determines whether or not a sheet is set in the sheet processing apparatus based on an output of a sheet detecting unit (not shown) (step ST20). If “Y”, a command is given to the motor control unit 14 to drive the transport motor 13 (step ST21). Then, the two processes already described in FIG. 3, that is, the sheet length detection process A and the displacement amount detection process B are executed in parallel.

The count value of the sheet length counter C1 obtained by executing the sheet length detection process A is stored in the RAM 17 as the actually measured sheet length Lm (step ST2).
2). The average displacement obtained by executing the displacement detection processing B is stored in the RAM 17 as the actually measured displacement Dm (step ST23). The measured displacement amount obtained at this time is also a plurality of sampling data (displacement amount data) in the transport direction of the sheet, similarly to the above-described reference displacement amount.
Is a stable value that is not affected by a partial change in thickness of one sheet. Further, the sampling number of the displacement amount data in one sheet is not particularly limited as in the case of the reference change amount.

When steps ST22 and ST23 are completed, the measured sheet length Lm is compared with the reference sheet length Lr to determine whether the sheet length is normal (step ST24). If this is "N", at least two or more sheets are conveyed in a state of being shifted and overlapping with respect to the conveyance direction, and double feeding has occurred. Therefore, the control unit 15
A command is given to the motor control unit 14 to stop driving the transport motor 13 (step ST27), and a notification operation indicating that multifeed has occurred is executed (step ST28), and the operation is stopped.

On the other hand, if step ST24 is "Y", the measured displacement Dm is compared with the reference displacement Dr to determine whether or not the displacement is normal (step ST25). If step ST25 is "N", steps ST27 and ST28 are executed because two or more sheets overlap. If "Y" in step ST25, since there is no double feed, normal processing, for example, conveyance to the printing unit or the like is executed (step ST26), and the operation ends.

According to the above-described embodiment, the presence or absence of double feeding is determined by comparing the actually measured sheet length with the reference sheet length (FIG. 4: step ST24), and the actually measured displacement amount is determined by the reference displacement amount. (Step ST25 in FIG. 4). That is, it is determined that there is a double feed unless both of the two determination results indicate that there is no double feed. Therefore, the order of steps ST24 and ST25 may be reversed.

In the above-described embodiment, when two or more sheets are conveyed with only a very small portion overlapping each other, the average value of the displacement data is taken as the actually measured displacement. There may be a case where the measured displacement changes only a small amount compared to the reference displacement. In such a case, although the determination of the displacement amount (step ST25) may be “Y”, the determination of the sheet length (step S25)
Since T24) surely becomes "N", the double feed can be detected without fail. However, if it is not necessary to assume the above-described inconvenience, it is not necessary to detect the double feed based on the length of the paper sheet, so that the presence or absence of the double feed may be determined based only on the displacement amount.

As described above, according to the present embodiment,
Since a plurality of displacement data can be sampled and averaged in the transport direction of the paper sheet and a stable measured displacement can be measured, double feed can be detected with high accuracy, unlike the related art. Further, since the presence or absence of the double feed is determined based on the two values of the paper sheet length and the displacement amount, the double feed of the paper sheets can be reliably detected. Since both the reference sheet length and the reference displacement amount can be measured and set based on the actual sheet, the reference value is set correctly according to the thickness and length of the sheet actually used. can do.
When the thickness or the length of the paper sheet changes, the reference value may be set again in accordance with the paper sheet, and troublesome mechanical positioning work is unnecessary unlike the related art.

Here, the correspondence between the description of the embodiment and the description of the claims will be described. The pressing roller 2 and the displacement detection lever 3 shown in FIG. 1 constitute "displacement means" that is displaced according to the thickness of the paper sheet being conveyed. Also,
The displacement sensor 11 and the A / D converter 12 constitute a "displacement amount detecting means" that detects the amount of displacement of the displacement means and outputs displacement amount data.

In FIG. 4, the control unit 15 for performing the operation of the displacement amount detection processing B samples the displacement amount data over the entire length of the sheet in the transport direction, and based on the sampled displacement amount data. This corresponds to “average displacement amount calculating means” for obtaining the average displacement amount.

In FIG. 4, the control unit 15 performing the operation of step ST25 calculates the average displacement amount output from the average displacement amount calculating means when a sheet is conveyed.
This corresponds to “determining means” for determining whether or not double-feeding of sheets is performed by comparing with a reference displacement amount corresponding to the displacement amount of the displacement means when there is one sheet.

In FIG. 3, the control unit 15 performing the operation of step ST15 operates in the reference value setting mode.
While setting the average displacement amount output from the average displacement amount calculating means during the conveyance of the paper sheet as the reference displacement amount, and
In the normal transport mode, it corresponds to "reference displacement amount setting means" for supplying the reference displacement amount to the determination means.

Further, the optical sensor 10 shown in FIG. 1 and the control unit 15 for performing the sheet length detecting process A shown in FIG. Is composed.

In the reference value setting mode, the control unit 15, which performs step ST15 in FIG. 3, sets the sheet length output from the sheet length detecting means as the reference sheet length, and performs normal conveyance. In the mode, it corresponds to "reference sheet length setting means" for supplying the reference sheet length to the determination means.

In FIG. 4, the controller 15 performing the operation of step ST24 determines the length of the sheet detected by the sheet length detecting means when the sheet is conveyed, as a reference. This corresponds to “determination means” for determining whether or not double-feeding of paper sheets has occurred by comparing with the paper sheet length.

In the above-described embodiment, the reference sheet length and the reference displacement amount obtained by measuring actual sheets are set in the RAM 17, but the operation unit 1 is manually operated.
The values may be set in the RAM 17 by directly inputting a predetermined reference sheet length and a reference displacement amount from 8. Also in this case, as described above, if it is not necessary to detect the double feed based on the length of the paper sheet, input and set only the reference displacement amount and perform the double feed based on only the displacement amount. You may make it detect.

In the above-described embodiment, a case has been described in which double feed is detected for one type of paper sheet.
However, it is also possible to adopt a configuration for detecting a double feed corresponding to a plurality of types of paper sheets. For example, the reference sheet length and the reference displacement amount corresponding to a plurality of types of sheets are previously stored in a ROM.
The reference sheet length and the reference displacement amount may be appropriately selected and used according to the type of the sheet to be conveyed. In this case as well, if it is not necessary to detect the double feed based on the length of the paper sheet, it is possible to set only the reference displacement amount and detect the double feed based on only the displacement amount. In the reference value setting mode,
The reference sheet length and the reference displacement amount corresponding to a plurality of types of sheets are actually measured and stored in the RAM 17, and the reference sheet length is determined according to the type of the conveyed sheet. And the reference displacement amount may be appropriately selected and used. In this case as well, if it is not necessary to detect the double feed based on the length of the sheet, the reference displacement is measured and set, and the double feed is detected based only on the displacement. Is also good.

[0043]

According to the first aspect of the present invention, the displacement amount corresponding to the thickness of the paper sheet being conveyed is sampled to obtain the displacement amount data, and the average displacement obtained based on the displacement amount data is obtained. The amount is compared with a reference displacement amount corresponding to the displacement amount when the number of sheets is one, and the presence / absence of multifeed of the sheets is determined. Therefore, unlike the conventional apparatus, the multi-feed can be detected with high accuracy, and the troublesome mechanical positioning operation performed according to the thickness of the paper sheet is not required.

According to the second aspect of the present invention, the double feed can be detected based on the reference displacement amount corresponding to the thickness of the sheet actually used.

According to the third aspect of the present invention, it is possible to determine the presence or absence of double feeding based on the reference displacement amount corresponding to the type of paper sheet. There is no need to do this, and it is possible to respond flexibly to different types of paper sheets.

According to the fourth aspect of the present invention, the sheet length obtained by detecting the length of the sheet being conveyed is compared with the reference sheet length to determine whether or not the sheet is multi-fed. Is determined. Therefore, double feed detection can be performed more reliably than when double feed is detected based only on the amount of displacement of paper sheets.

According to the fifth aspect of the invention, in addition to the effect of the fourth aspect, the double feed can be detected based on the reference sheet length according to the length of the sheet actually used.

According to the sixth aspect of the invention, in addition to the effects of the fourth or fifth aspect, the presence or absence of double feed can be determined based on the reference sheet length corresponding to the type of sheet. Unlike conventional devices, there is no need for complicated positioning work,
Flexible handling of different types of paper sheets.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an embodiment of a sheet multi-feed detecting device according to the present invention.

FIG. 2 is an explanatory diagram showing storage contents of a RAM.

FIG. 3 is an operation flowchart in the embodiment.

FIG. 4 is an operation flowchart in the embodiment.

FIG. 5 is a block diagram showing a conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Conveyance roller 2 Holding roller 3 Displacement detection lever 10 Optical sensor 11 Displacement sensor 12 A / D conversion part 13 Conveyance motor 14 Motor control part 15 Control part 17 RAMP Sheet Dz Origin displacement amount Dr Reference displacement amount Dm Actual displacement amount Lr Standard sheet length Lm Actual sheet length

Claims (6)

[Claims] 1. A displacement means for displacing according to the thickness of a paper sheet being conveyed, a displacement amount detection means for detecting a displacement amount of the displacement means and outputting displacement data, Reference displacement amount setting means for setting a reference displacement amount corresponding to the displacement amount of the displacement means when the sheet is a sheet, while sampling the displacement amount data over the entire length of the sheet in the transport direction, Means for calculating an average amount of displacement based on the sampled amount of displacement data; anda means for setting the average amount of displacement output from the means for calculating average displacement during the transport of the paper sheet to the reference amount. Determining means for comparing the reference displacement amount supplied from the means with respect to the presence or absence of multifeed of the paper sheets, and a multifeed detection device for paper sheets. 2. The reference displacement amount setting means sets an average displacement amount output from the average displacement amount calculation means during conveyance of a sheet as a reference displacement amount in a reference value setting mode, and 2. The multi-feed detecting device for paper sheets according to claim 1, wherein in the normal transport mode, the reference displacement amount set in the reference value setting mode is supplied to a determination unit. 3. 3. The reference displacement amount setting means selects the reference displacement amount corresponding to a designated sheet type from a plurality of reference displacement amounts set corresponding to the sheet type. 3. The multi-feed detecting device for paper sheets according to claim 1, wherein the selected reference displacement amount is supplied to a determination unit. 4. 4. A sheet length detecting means for detecting a length of the sheet in the conveying direction, and a reference sheet length for setting a sheet reference length which is the length in the conveying direction of the sheet. Setting means, the determining means, the length of the sheets detected by the sheet length detecting means, the reference sheet length supplied from the reference sheet length setting means, The multi-feed detecting device for paper sheets according to any one of claims 1 to 3, wherein the presence / absence of multi-feed of paper sheets is determined by comparison. 5. A reference sheet length setting unit, in a reference value setting mode, sets a sheet length output from a sheet length detection unit during conveyance of a sheet as a reference sheet length. And supplying the reference sheet length set in the reference value setting mode to a determination means in a normal transport mode, wherein: Double feed detection device. 6. The reference sheet length setting means, wherein the reference sheet length corresponding to a designated sheet type is selected from a plurality of reference sheet lengths set corresponding to the sheet type. The multi-feed detection of paper sheets according to claim 4 or 5, wherein a reference paper sheet length is selected, and the selected reference paper sheet length is supplied to a determination unit. apparatus.