JP2014218373A - Double feeding detection device, sheet conveyance control device, double feeding detection method and double feeding detection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect double feeding of sheets with high accuracy while suppressing increase in device cost.SOLUTION: A double feeding detection device for detecting a double feeding state in which sheets conveyed by a roller rotationally driven by using feedback control are conveyed overlapped in a plurality of pieces includes: a variation amount calculation unit 501 for acquiring a signal outputted for each predetermined period from the feedback control of the roller, and for allowing a storage medium to store a variation amount of rotation speed of the roller in time sequence; a sheet inrush determination unit 502 for detecting the start of sheet conveyance by the roller based on the variation amount stored in time sequence; and a double feeding detection unit 503 for detecting the double feeding state based on the change of the variation amount after the start of the sheet conveyance by the roller is detected.

Description

  The present invention relates to a double feed detection device, a paper transport control device, a double feed detection method, and a double feed detection system, and more particularly to detection of double feed by feedback of a transport mechanism.

  In recent years, there has been a tendency to digitize information, and image processing apparatuses such as printers and facsimiles used for outputting digitized information and scanners used for digitizing documents have become indispensable devices. Such an image processing apparatus is often configured as a multifunction machine that can be used as a printer, a facsimile, a scanner, or a copier by providing an imaging function, an image forming function, a communication function, and the like.

  Among such image processing apparatuses, in an image forming apparatus used for image formation output of digitized information, double feeding in which two sheets for image formation output are conveyed in some cases may occur. In order to eliminate the double feed state by shifting the paper when such double feed occurs, a shift roller that rotates in a direction opposite to the paper transport direction is opposed to the transport roller. Is provided. Further, a method for detecting a double feed state based on the rotational speed of the above-described shifting roller has been proposed (see, for example, Patent Document 1).

  Further, as a related technique, when the trailing edge of the sheet is not detected at the timing at which the trailing edge of the sheet is detected with reference to a sensor signal for detecting the conveyance state of the sheet, There has been proposed a method for determining that a carry that is conveyed in an overlapping manner occurs (see, for example, Patent Document 2).

  In determining the double feed of paper, methods such as detecting the light transmittance of the paper being transported and detecting the thickness of the paper being transported are also used. In order to do this, a highly accurate sensor is required, which leads to an increase in device cost.

  The rotation of the conveyance roller for conveying the paper is performed using a feedback PWM (Pulse Width Modulation) motor or the like in order to control the paper conveyance speed with high accuracy. On the other hand, in the case of the technique disclosed in Patent Document 1, a feedback mechanism is also required for the shift roller, leading to an increase in apparatus cost.

  Such a problem is not limited to an image forming apparatus that forms an image on a sheet, but also occurs in the sheet conveyance in a scanner having a sheet conveyance mechanism such as an ADF (Auto Document Feeder). obtain.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to detect an increase in apparatus cost and detect double feeding of sheets with high accuracy.

  In order to solve the above-described problem, one aspect of the present invention is a double feed detection device that detects a double feed state in which a plurality of sheets conveyed by a roller that is rotationally driven using feedback control is conveyed. A rotation speed information storage processing unit that acquires a signal output every predetermined period from the feedback control of the roller and stores rotation speed information related to the rotation speed of the roller in a storage medium in time series; and the rotation Based on speed information, based on a change in the rotation speed information after detecting that the paper has started to be transported by the roller, and a paper transport detector that detects that the paper has started to be transported by the roller. And a double feed detector for detecting a double feed state.

  According to another aspect of the present invention, there is provided a sheet conveyance control device that controls conveyance of a sheet conveyed by a roller that is rotationally driven using feedback control, and the rotation speed is constant based on an input target value. A feedback control unit that rotationally drives the roller to obtain a signal output from the feedback control unit every predetermined period, and rotational speed information related to the rotational speed of the roller is stored in a storage medium in time series A rotational speed information storage processing section to be stored, a paper transport detection section for detecting that the paper has started to be transported by the roller based on the rotational speed information, and a detection that the paper has started to be transported by the roller And a double feed detection unit that detects a double feed state based on a change in the rotation speed information after being performed.

  According to still another aspect of the present invention, there is provided a multi-feed detection method for detecting a multi-feed state in which a plurality of sheets conveyed by a roller that is rotationally driven using feedback control is conveyed, and the roller A signal output every predetermined period from the feedback control is acquired, and based on the acquired signal, rotational speed information related to the rotational speed of the roller is stored in a storage medium in time series, and stored in the storage medium The rotational speed information stored in the storage medium after detecting that the paper has started to be conveyed by the roller based on the rotational speed information thus detected and detecting that the paper has been conveyed by the roller It is characterized in that a double feed state is detected on the basis of the change in.

  According to still another aspect of the present invention, there is provided a multifeed detection system that detects a multifeed state in which a plurality of sheets conveyed by a roller that is rotationally driven by using feedback control is conveyed, and the roller A rotation speed information storage processing unit that obtains a signal output every predetermined period from the feedback control and stores rotation speed information related to the rotation speed of the roller in a storage medium in time series, and based on the rotation speed information A paper transport detection unit that detects that the paper has started to be transported by the roller, and a multi-feed state based on a change in the rotation speed information after it has been detected that the paper has started to be transported by the roller And a double feed detection unit for detecting

  According to the present invention, it is possible to detect the double feeding of paper with high accuracy while suppressing an increase in apparatus cost.

1 is a block diagram showing an overall configuration of an apparatus or system according to an embodiment of the present invention. It is a block diagram which shows the structure of the information processing apparatus which concerns on embodiment of this invention. It is a figure showing composition of an engine concerning an embodiment of the present invention. It is a figure which shows the function structure of the conveyance roller drive part which concerns on embodiment of this invention. It is a block diagram which shows the function structure of the double feed detection apparatus which concerns on embodiment of this invention. It is a figure which shows the example of the waveform produced at the time of the paper conveyance which concerns on embodiment of this invention. It is a figure which shows the example of the waveform produced at the time of the double feed detection which concerns on embodiment of this invention. It is a figure which shows the example of the waveform produced at the time of the double feed detection which concerns on embodiment of this invention. It is a figure which shows the example of the waveform produced at the time of the double feed detection which concerns on embodiment of this invention. 6 is a flowchart illustrating a sheet conveying operation according to the embodiment of the present invention. It is a flowchart which shows the double feed detection operation | movement which concerns on embodiment of this invention. It is a flowchart which shows the peak determination operation | movement which concerns on embodiment of this invention. It is a figure which shows the aspect of the frequency analysis which concerns on embodiment of this invention. It is a figure which shows the other example of the waveform produced at the time of the paper conveyance which concerns on embodiment of this invention. It is a figure which shows the other example of the waveform produced at the time of the double feed detection which concerns on embodiment of this invention. It is a figure which shows the other example of the waveform produced at the time of the double feed detection which concerns on embodiment of this invention. 6 is a flowchart illustrating a sheet conveying operation in an image forming output for one page according to the embodiment of the present invention. It is a figure which shows the example of the profile selection table which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present embodiment, a multi-feed detection device that detects multi-feed of paper in a transport mechanism that transports the paper on which an image is to be formed by the image forming apparatus will be described as a feature.

  FIGS. 1A and 1B are block diagrams illustrating the overall configuration of an image forming apparatus and an image forming system including a double feed detection device according to the present embodiment. FIG. 1A is a diagram illustrating a configuration of an image forming apparatus, and includes a display panel 1, a main body controller 2, an engine controller 3, an engine 4, and a multifeed detection device 5 as illustrated in FIG.

  The display panel 1 functions as an operation unit for a user to operate the apparatus in the image forming apparatus, and also functions as a display unit for obtaining information from the apparatus. The main body controller 2 is a control unit that controls the operation of the entire image forming apparatus, and performs exchange of information via the network, control of received print jobs, image processing, and the like.

  The engine controller 3 is a control unit that controls the engine 4 that actually executes the image forming output, and performs drive control of each unit included in the engine 4. The engine 4 is a mechanism portion that actually executes image formation output, and includes a conveyance mechanism that conveys a sheet, an image formation mechanism that forms an image on a sheet, and the like. The double feed detection device 5 detects double feed of the paper conveyed in the engine 4 based on a signal output from the engine 4.

  FIG. 1B is a diagram illustrating a configuration of an image forming system used for PP (Product Printing), and includes a display 6, a DFE (Digital Front End) 7, a PP engine controller 8, a PP engine 9, and a multifeed detection device. 5 is included. The display 6 is a display device used for displaying information of the DFE 7 that controls the entire system.

  The DFE 7 is a control device that controls the entire system, and exchanges information via the network, controls received print jobs, performs image processing, and the like, similar to the main body controller 2 described above. The PP engine controller 8 is a control unit that controls the PP engine 9, and performs drive control of each unit included in the PP engine 9. The PP engine 9 is an image forming mechanism that is larger than the engine 4, and includes a transport mechanism that transports a sheet, an image forming mechanism that forms an image on a sheet, and the like.

  In the case of the system shown in FIG. 1B, the double feed detection device 5 detects double feed of paper conveyed by the PP engine 9 based on a signal output from the PP engine 9. As described above, the multi-feed detection device 5 according to the present embodiment detects multi-feed of the transported paper based on the signal output from the component including the transport mechanism that transports the paper.

  Next, referring to FIG. 2, the hardware configuration that forms the functional blocks of the information processing apparatus such as the main body controller 2, the engine controller 3, the double feed detection device 5, the DFE 7, and the PP engine controller 8 according to the present embodiment will be described. explain. FIG. 2 is a block diagram illustrating a hardware configuration of the double feed detection device 5 according to the present embodiment. FIG. 2 shows the hardware configuration of the multifeed detection device 5, but the same applies to other information processing devices.

  As shown in FIG. 2, the multifeed detection device 5 according to the present embodiment has the same configuration as an information processing device such as a general PC (Personal Computer) or a server. That is, the multi-feed detection device 5 according to the present embodiment includes a CPU (Central Processing Unit) 10, a RAM (Random Access Memory) 20, a ROM (Read Only Memory) 30, an HDD (Hard Disk Drive) 40, and an I / F 50. They are connected via a bus 60.

  The CPU 10 is a calculation means and controls the operation of the entire multifeed detection device 5. The RAM 20 is a volatile storage medium capable of reading and writing information at high speed, and is used as a work area when the CPU 10 processes information. The ROM 30 is a read-only nonvolatile storage medium and stores a program such as firmware. The HDD 40 is a non-volatile storage medium that can read and write information, and stores an OS (Operating System), various control programs, application programs, and the like. The I / F 50 connects and controls the bus 60 and various hardware and networks.

  In such a hardware configuration, a program stored in a recording medium such as the ROM 30, the HDD 40, or an optical disk (not shown) is read into the RAM 20, and the CPU 10 performs calculations according to those programs, thereby configuring a software control unit. The A functional block that realizes the functions of the information processing apparatus such as the multifeed detection apparatus 5 according to the present embodiment is configured by a combination of the software control unit configured as described above and hardware.

  Next, the mechanical configuration of the engine 4 and the sheet conveyance path will be described with reference to FIG. As shown in FIG. 3, the engine 4 according to this embodiment includes photosensitive drums 102 </ b> Y, 102 </ b> M, 102 </ b> C, and 102 </ b> K for the respective colors along the conveyance belt 101 that is an endless moving unit (hereinafter, generally referred to as the photosensitive drum 102. ) Are arranged, so-called tandem type. That is, along the conveyance belt 101 which is an intermediate transfer belt on which an intermediate transfer image to be transferred to a sheet (an example of a recording medium) fed from the sheet feed tray 103 is formed, A plurality of photosensitive drums 102Y, 102M, 102C, and 102K are arranged in order from the upstream side.

  Each color image developed with toner on the surface of the photosensitive drum 102 of each color is superimposed on the conveyor belt 101 and transferred to form a full color image. The full-color image formed on the conveyance belt 101 in this manner is the surface of the sheet conveyed on the path by the function of the transfer roller 104 at a position closest to the sheet conveyance path indicated by a broken line in the drawing. Transcribed above.

  The paper on which the image is formed on the paper surface is further conveyed, the image is fixed by the fixing roller 105, and then discharged to the paper discharge tray 107. In the case of duplex printing, the sheet on which an image is formed and fixed on one side is conveyed to the reversing path 106, reversed, and conveyed again to the transfer position of the transfer roller 104.

  The PP engine 9 generally has a larger configuration than the engine 4, but the basic configuration is the same as the configuration shown in FIG. In such an engine 4 and PP engine 9, the paper fed from the paper feed tray 103 is transported by the transport roller 108 and sent to the image transfer position by the transfer roller 104.

  The transport roller 108 is rotationally driven by a PWM (Pulse Width Modulation) motor with feedback in order to transport the sheet at a predetermined transport speed. The gist of the present embodiment is to detect double feeding of paper based on a signal obtained in the configuration for rotationally driving the transport roller 108. The sheet conveyed by the conveyance roller 108 is adjusted in conveyance timing by the registration roller 109 before being sent to the image transfer position by the transfer roller 104.

  FIG. 4 is a diagram illustrating a functional configuration of the transport roller driving unit 200 that rotationally drives the transport roller 108. As shown in FIG. 4, the transport roller driving unit 200 according to the present embodiment includes a drive control unit 201, a rotation driving unit 202, a rotation unit 203, a rotation detection unit 204, an FB (FeedBack) acquisition unit 205, and a state output unit 206. including. With such a configuration, the transport roller driving unit 200 according to the present embodiment functions as a feedback control unit that feedback-controls the rotation of the transport roller 108.

  The drive control unit 201 rotates the rotation unit 203 based on the target value of the rotation speed of the transport roller 108 input from the engine controller 3 and the PP engine controller 8 and the feedback signal input from the FB acquisition unit 205. The control value of is output. The rotation drive unit 202 generates and outputs a PWM signal for rotating the rotation unit 203 based on the control value input from the drive control unit 201.

  The rotating unit 203 is a motor that rotates in accordance with the PWM signal input from the rotation driving unit 202. The conveyance roller 108 is rotated by the rotation of the rotating unit 203. In addition, by using a mechanism that switches the transmission state of the rotational force such as a clutch, one motor may be configured to drive different rollers for forward rotation and reverse rotation. The unit 203 drives only the conveyance roller 108 to rotate. That is, the conveyance roller 108 and the registration roller 109 are driven by different driving sources. A marker for detecting the rotation speed is added to the conveyance roller 108, and the rotation detection unit 204 detects the rotation speed of the conveyance roller 108 by optically reading the marker added to the conveyance roller 108. .

  Specifically, when the conveyance roller 108 rotates, the marker added to the conveyance roller 108 passes through a reading position where the rotation detection unit 204 optically reads. Thereby, the optical reading state by the rotation detection unit 204 changes, and the rotation detection unit 204 detects the marker and outputs a detection signal. The FB acquisition unit 205 acquires the detection signal of the rotation detection unit 204, calculates the rotation speed of the transport roller 108 based on the number of times the marker is detected per unit time, and inputs the rotation speed to the drive control unit 201 as a feedback value. To do.

  Accordingly, the drive control unit 201 controls the rotation unit 203 to rotate based on the difference between the target value input from the engine controller 3 and the PP engine controller 8 and the feedback value input from the FB acquisition unit 205. Output the value.

  The state output unit 206 acquires and outputs a value indicating the rotation state of the transport roller 108 (hereinafter referred to as “transport roller state value”) in the feedback control cycle by the transport roller driving unit 200 as described above. As indicated by a broken line in FIG. 4, the value indicating the rotation state of the conveyance roller 108 includes the detection signal of the rotation detection unit 204 acquired by the FB acquisition unit 205 and the value of the conveyance roller 108 calculated by the FB acquisition unit 205. Rotational speed can be used.

  Further, a control value input by the drive control unit 201 to the rotation drive unit 202 can be used. Furthermore, a PWM signal output from the rotation drive unit 202 can be used. Furthermore, a rotation speed detection signal output from the rotation detection unit 204, that is, a signal indicating a driving speed before feedback control is applied can be used. The conveyance roller state value output by the state output unit 206 is input to the double feed detection device 5.

  In this embodiment, as described above, a PWM motor with feedback is used as the rotation unit 203, and the rotation drive unit 202 generates and outputs a PWM signal based on the control value input from the drive control unit 201. Take the case as an example. Therefore, when the output of the rotation driving unit 202 is used as the above-described conveyance roller state value, a PWM signal is used.

  In addition, for example, when a voltage-driven motor is used as the rotation unit 203, the output signal of the rotation drive unit 202 is a voltage value signal corresponding to the control value input from the drive control unit 201. When a current-driven motor is used as the rotation unit 203, the output signal of the rotation drive unit 202 is a signal having a current value corresponding to the control value input from the drive control unit 201. These signals may be used as the transport roller state value described above.

  In the feedback control according to the present embodiment, the drive control unit 201 outputs a control value based on the target value of the rotation speed of the transport roller 108 and the feedback value. That is, control based on the rotation speed (hereinafter referred to as “speed control”) is performed. In addition, for example, control based on the rotational position of the transport roller 108 (hereinafter referred to as “position control”) may be performed. In particular, position control may be performed to match the image forming position on the paper.

  When performing position control, the FB acquisition unit 205 calculates the rotational position of the transport roller 108 based on the number of times the marker has been detected, and inputs it to the drive control unit 201 as a feedback value. In addition, the target value of the rotational position is input to the drive control unit 201. Accordingly, the drive control unit 201 generates and outputs a control value for controlling the rotation of the transport roller 108 based on the difference between the target value and the feedback value.

  One of the speed control and the position control described above may be selected, or both controls may be used in combination. When both controls are used together, a gain is set for each control, and the difference value calculated in the speed control and the difference value calculated in the position control are multiplied by the gain, and then the final difference value is calculated. Then, a control value is generated based on the final difference value.

  Next, a functional configuration of the multifeed detection device 5 according to the present embodiment will be described with reference to FIG. In the following description, the case of the image forming apparatus shown in FIG. 1A will be described as an example. As shown in FIG. 5, the double feed detection device 5 according to the present embodiment includes a fluctuation amount calculation unit 501, a paper entry determination unit 502, a double feed detection unit 503, an initial setting unit 504, a fluctuation amount storage unit 505, a shock time. A storage unit 506 and a profile storage unit 507 are included.

  The fluctuation amount calculation unit 501 calculates the fluctuation amount of the rotation speed of the conveyance roller 108 based on the conveyance roller state value output from the state output unit 206 of the conveyance roller driving unit 200. The state output unit 206 outputs the conveyance roller state value at a predetermined sampling rate. Therefore, the fluctuation amount calculation unit 501 calculates the fluctuation amount in time series at a predetermined sampling rate and stores the fluctuation amount in the fluctuation amount storage unit 505. Thereby, the fluctuation amount storage unit 505 stores the fluctuation amount of the rotation speed of the transport roller 108 within a predetermined period in time series.

  That is, the fluctuation amount calculation unit 501 according to the present embodiment acquires a signal output every predetermined period from the feedback control of the conveying roller 108, and sets the rotation speed information that is information related to the rotation speed of the roller in time series. It functions as a rotation speed information storage processing unit that is generated and stored in the fluctuation amount storage unit 505. In the present embodiment, as an example, the amount of change from the target value of the rotation speed of the transport roller 108 is used as the rotation speed information.

  The paper entry determination unit 502 determines the entry of the paper into the conveyance roller 108 based on the fluctuation amount of the rotation speed of the conveyance roller 108 stored in time series in the fluctuation amount storage unit 505. As described above, the conveyance roller driving unit 200 controls the conveyance roller 108 based on the target value input from the engine controller 3. When inputting the target value to the transport roller driving unit 200, the engine controller 3 inputs a signal indicating the start of paper transport (hereinafter referred to as “paper transport start signal”) to the paper intrusion determining unit 502.

  As a result, the paper entry determination unit 502 determines the paper entry based on the fluctuation amount sequentially stored in the fluctuation amount storage unit 505. When the paper entry determination unit 502 determines paper entry based on the fluctuation amount stored in the fluctuation amount storage unit 505, a signal indicating the paper entry determination to the double feed detection unit 503 (hereinafter referred to as “paper entry determination signal”). ).

  That is, the paper entry determination unit 502 according to the present embodiment detects that the paper has started to be conveyed by the conveyance roller 108 based on the fluctuation amount stored in the fluctuation amount storage unit 505 in time series, that is, rotation speed information. Functions as a paper conveyance detection unit.

  The double feed detection unit 503 determines the double feed of the paper based on the fluctuation amount sequentially stored in the fluctuation amount storage unit 505 based on the paper entry determination signal. The double feed detection unit 503 acquires a profile for each paper input from the initial setting unit 504 and stores the profile in the shock time storage unit 506 when determining double feed of paper. As a result, the shock time storage unit 506 stores profile information corresponding to the type of paper being conveyed in the engine 4. The double feed detection unit 503 determines paper double feed based on the fluctuation amount sequentially stored in the fluctuation amount storage unit 505 based on the profile for each paper stored in the shock time storage unit 506.

  When the double feed detection unit 503 determines the double feed of the paper, it outputs a signal indicating the double feed of the paper (hereinafter referred to as “double feed detection signal”) to the main body controller 2 and the engine controller 3. As a result, the main body controller 2 can control the display panel 1 to notify the user that paper double feeding has occurred. Further, the engine controller 3 can control each part of the engine 4 such as the conveyance roller driving unit 200 to control the discharge of the paper, the stop of the image forming output, and the like.

  Based on information input from the main body controller 2, the initial setting unit 504 acquires profile information corresponding to the type of paper to be conveyed from the profile storage unit 507 and inputs the profile information to the double feed detection unit 503. Therefore, when the main body controller 2 receives a print job via the network, performs image processing, and inputs image information to the engine controller 3, information indicating the type of paper that is the target of image formation output by the print job. Is input to the double feed detection device 5.

  The profile storage unit 507 stores paper profile information for a plurality of types of paper that may be transported by the engine 4. Here, an example of profile information stored in the profile storage unit 507 will be described.

  FIG. 6 is a diagram showing the variation amount stored in the variation amount storage unit 505 by the variation amount calculation unit 501, that is, the speed of the conveyance roller 108 in time series when one sheet is conveyed by the conveyance roller 108. It is. As shown in FIG. 6, when the sheet S enters the conveyance roller 108, the rotation speed of the conveyance roller 108 is disturbed due to the influence of the entry of the sheet.

  Specifically, when the sheet enters the conveying roller 108, the conveying roller 108 is required to have a torque for conveying the sheet. On the other hand, as described with reference to FIG. 4, the conveyance roller 108 is driven to rotate at the rotational speed of the target value by feedback control. Therefore, the moment the sheet enters the conveyance roller 108, the friction between the sheet and the roller The rotational speed of the roller is temporarily reduced by the force. The absolute value of the fluctuation amount exceeds a threshold value a for paper entry determination set in advance according to the type of paper.

  When the rotation speed of the transport roller 108 becomes slow, a decrease in the rotation speed is detected by the rotation detection unit 204 and transmitted to the drive control unit 201 via the FB acquisition unit 205. As a result, the drive control unit 201 changes the control value input to the rotation drive unit 202. As a result, the rotation drive unit 202 generates and outputs a PWM signal for rotating the rotation unit 203 with a stronger torque than before the sheet enters the conveyance roller 108.

By such feedback control, the rotation speed of the conveying roller 108 converges to the speed before the paper enters, but a predetermined period is required depending on the gain of the feedback control until the rotation speed converges. In the present embodiment, as shown in FIG. 6, a threshold value c for determining convergence of the fluctuation amount before timing t ₁ until the period T ₁ elapses from timing t ₀ when the fluctuation amount exceeds a. It converges as follows.

Further, if the paper rushes in a normal state where no double feed occurs, the fluctuation amount due to the disturbance of the rotational speed caused by the paper rush is less than the threshold value b for determining that the fluctuation amount is too large. It is. Then, after the timing t ₂ when the period T ₂ elapses from the timing t ₀ , the trailing edge of the sheet exits the conveyance roller 108. As a result, as shown in FIG. 6, the conveyance speed is less disturbed than when the sheet is rushed.

The values of threshold values a, b, c and periods T ₁ , T ₂ shown in FIG. 6 are stored in the profile storage unit 507 as profile information for each of a plurality of types of sheets that may be transported by the engine 4. Yes.

Next, an aspect of double feed detection by the double feed detection unit 503 will be described. FIG. 7 is a diagram illustrating an aspect of double feed detection by the double feed detection unit 503 according to the present embodiment. As shown in FIG. 7, when the paper S ₁ and the paper S ₂ are transported with the leading edges aligned, the transport speed generated by the paper entry due to the overlap of the paper and the doubled thickness. It is conceivable that the disturbance will increase.

As a result, the absolute value of the fluctuation amount exceeds the threshold value b for determining that the fluctuation amount is too large. The amount of change at this time is P _1. Double feed detection unit 503, if the value of the variation amount is sequentially stored in the shift amount storage unit 505 is a value P ₁ exceeds the threshold value b, as shown in FIG. 6, the double feed occurs in the paper Judge that

FIG. 8 is a diagram illustrating an aspect of double feed detection by the double feed detection unit 503 according to the present embodiment, which is different from FIG. 7. As shown in FIG. 7, when the paper S ₁ and the paper S ₂ are transported in a state where the leading ends are shifted, the rush occurs twice according to the shift amount of the paper. As a result, as shown by the values P ₂ and P ₃ in FIG. 8, the absolute value of the extreme value of the fluctuation amount that should gradually converge increases during the period T ₁ .

Thus, the double feed detection unit 503 during the period T _1, when exceeded extremum obtains an extreme value of the variation amount in the order, extrema acquired later is already acquired, the paper Judge that double feed is occurring. In other words, when the absolute value of the extreme value of the variation amount sequentially acquired increases in time series after the timing t ₀ and until the period T ₁ elapses, the double feed detection unit 503 performs the overlap detection. Detect feed.

Also, depending on how the fluctuation amount converges, the extreme value may not increase due to the second entry. However, since the disturbance of the rotational speed due to the rush occurs surely twice, the period until the fluctuation amount converges becomes longer. As a result, as shown in the variation of the value P ₄ in FIG. 8, not even not converge fluctuation amount exceeds the period T _1, exceeds the threshold value c for determining the convergence of variation.

Thus, the double feed detection unit 503, when the absolute value of the variation amount after a lapse of period T ₁ from the time t ₀ exceeds the threshold value c, it is determined that double feeding of the paper has occurred. In other words, the double feed detection unit 503 detects double feed when the fluctuation amount exceeds the threshold value c after the period T ₁ has elapsed after the timing t ₀ .

FIG. 9 is a diagram showing an aspect of double feed detection by the double feed detection unit 503 according to the present embodiment, which is different from FIGS. 7 and 8. As shown in FIG. 9, when the paper S ₁ and the paper S ₂ are transported in a state where the leading ends are further shifted than those in FIG. 8, rushing occurs twice according to the amount of paper misalignment. The rush of the second sheet, the amount of change during the period T ₁ is generated after the convergence.

As a result, as shown in the values P ₅ in FIG. 9, after the period T ₁ from the time t ₀ has elapsed, before the period T ₂ has elapsed, so that the variation amount exceeds the threshold value a. Accordingly, the double feed detection unit 503 generates a double feed when the absolute value of the fluctuation amount exceeds the threshold value a after the period T1 has elapsed from the timing t0 and before the period T2 has elapsed. Judge. In other words, the double feed detection unit 503, after the rush of the sheet to the conveying roller 108 at the timing t ₀ is detected, detects a double feed when the re-entry sheet before the period T ₂ has elapsed is detected To do.

When the fluctuation amount exceeds the threshold value c after the period T ₁ has elapsed and before the period T ₂ has elapsed, double feeding is detected in the manner described in FIG. Therefore, the double feed detection process shown in FIG. 9 can be omitted.

  As described above, in the double feed detection device 5 according to the present embodiment, when the paper is carried by the carry roller 108, the double feed of the paper is determined based on the rotation speed of the carry roller 108 that changes in time series. To do. In other words, the multifeed detection device 5 according to the present embodiment assumes that the transport roller 108 is rotationally driven by feedback control, and based on a feedback response when the paper starts to be transported by the transport roller 108. Judgment of double feed.

  As a conventional technique for detecting double feeding of paper, for example, there is a method of referring to an output signal of a sensor for detecting that paper is being transported in a paper transport path. In this method, after the leading edge of the paper has passed the detection position of the sensor, if the trailing edge of the paper is not detected at a timing at which the trailing edge of the paper should pass the detection position of the sensor, It is detected that they are transported in a state where they overlap.

  When such a conventional technique is used, the timing at which the double feed is detected is the timing at which the trailing edge of the preceding paper reaches the detection position of the sensor. As a result, depending on the control of the entire image forming apparatus, development of the electrostatic latent image already formed on the photosensitive drum has been started, thereby causing wasteful toner consumption. That is, it is required to detect double feeding as early as possible.

  On the other hand, according to the double feed detection method according to the present embodiment, it is possible to detect double feed of paper at the stage where the leading edge of the subsequent paper enters the transport roller 108. Therefore, in any of FIGS. 7 to 9, it is possible to detect double feeding at a timing earlier than the timing at which the trailing edge of the sheet should pass the detection position of the sensor.

  Next, the double feed detection operation by the double feed detection device 5 according to the present embodiment will be described. FIG. 10 is a flowchart showing the operation of the double feed detection device 5 according to this embodiment. As a premise of the operation shown in FIG. 10, the main body controller 2 receives a print job and starts image processing and control of the engine controller 3. Further, only when the paper is passed through the conveyance roller 108, the rotation unit 203 which is a conveyance motor is driven to rotate. At this time, the initial setting unit 504 acquires information indicating the paper type from the main body controller 2, thereby performing initial setting processing such as acquisition of profile information from the profile storage unit 507 and input to the double feed detection unit 503. (S1001).

  Thereafter, by acquiring a sheet conveyance start signal from the engine controller 3, the sheet entry determination unit 502 recognizes the start of sheet conveyance (S1002), and starts sheet entry determination (S1003). When the conveyance of the paper is started and the conveyance roller driving unit 200 starts to rotate the conveyance roller 108, the fluctuation amount calculation unit 501 changes the fluctuation amount storage unit 505 based on the conveyance roller state value output from the state output unit 206. The variation is stored in time series.

  The paper entry determination unit 502 that has started the paper entry determination acquires the variation amount stored in time series in the variation amount storage unit 505 and determines whether or not the threshold value a has been exceeded as described with reference to FIG. S1005). When the fluctuation amount stored in the fluctuation amount storage unit 505 exceeds the threshold value a (S1005 / YES), the paper entry determination unit 502 detects that the paper has entered the conveyance roller 108, and sends it to the double feed detection unit 503. Input a paper entry judgment signal. Thereby, the double feed detection unit 503 starts the double feed detection process (S1006).

Double feed detection unit 503 that started the double feed detection process, timing began double-feed detection, that is, by counting an elapsed time period from the timing t ₀ shown in FIG. 6, in the count value is within the period T ₂ It is determined whether or not there is (S1007). If it is within the period T2, the double feed detection unit 503 performs double feed detection processing (S1008).

As a result, it repeated if double feed is detected (S1009 / NO) lapse determining the period _{T 2.} If double feed is detected, double feed error processing for outputting a detection signal to the main body controller 2 and the engine controller 3 is performed (S1010), and the processing ends. On the other hand, while double feed is not detected, if the period _{T 2} has elapsed (S1007 / NO), the double feed detection unit 503 terminates the process.

  Next, details of the double feed determination process in S1008 of FIG. 10 will be described with reference to FIG. As shown in FIG. 11, the double feed detection unit 503 determines the peak value of the fluctuation amount, that is, the extreme value in the double feed determination process, and sequentially stores the values determined as extreme values in the storage medium ( S1101).

  Here, the peak value acquisition operation according to the present embodiment will be described with reference to FIG. When the double feed detection unit 503 acquires the latest fluctuation amount from the fluctuation amount storage unit 505 (S1201), it determines whether or not the difference from the fluctuation amount already acquired is equal to or less than a predetermined threshold (S1202). ). The determination in S1201 is a determination as to whether or not the variation of the variation in time series is small enough to be regarded as zero. Therefore, the difference between the latest fluctuation amount and the previous fluctuation amount may be determined, or the difference between the latest predetermined fluctuation amount maximum value and the re-small value may be determined.

  The extreme value is a value at which the temporal fluctuation amount becomes zero, and also the point where the positive and negative of the temporal fluctuation amount is reversed. Therefore, in S1202, in addition to determining whether or not the variation amount is small enough to be regarded as zero, it may be determined whether the temporal variation amount is positive or negative.

  As a result of the determination in S1202, when it is determined that the fluctuation amount is equal to or less than a predetermined threshold and is small enough to be regarded as zero (S1202 / YES), the double feed detection unit 503 performs peak determination (S1203) and is acquired in S1201. The latest variation value is saved as a peak value. By repeating such processing, the peak value acquisition processing in the flow of FIG. 11 is realized.

  The double feed detection unit 503 determines the value of the fluctuation amount separately from the determination of the peak value, and when the absolute value of the fluctuation amount exceeds the threshold value b (S1102 / YES), the aspect described in FIG. Double feed detection is performed (S1106). When the absolute value of the fluctuation amount does not exceed the threshold value b (S1102 / NO), in the peak values sequentially acquired after S1101, a peak value exceeding the already acquired peak value is acquired (S1103 / YES), the double feed detection unit 503 performs the double feed detection of the mode described in FIG. 8 (S1106).

Double feed detection unit 503 during the shock time is determined by the duration _{T 1} described in FIG. 6, S1102, S1103 repeated processing of (S1104 / NO), the shock time elapses (S1104 / YES), the variation Is determined to have converged (S1105). In S1105, the double feed detection unit 503, as described in FIG. 8, the absolute value of the fluctuation amount after period T ₁ is passed it is determined whether exceeds the threshold value c. Further, as described with reference to FIG. 9, after the convergence variation amount within the period T _1, it is determined whether the absolute value of the variation amount with inrush paper leading edge again exceeds the threshold value a.

  If the variation amount has not converged as a result of the determination in S1105 (S1105 / YES), the double feed detection unit 503 performs the double feed detection in the mode described in FIG. 8 or FIG. 9 (S1106). On the other hand, if the fluctuation amount has converged (S1105 / NO), the double feed detection unit 503 ends the process as it is.

  As described above, according to the image forming apparatus and the image forming system including the double feed detection device 5 according to the present embodiment, the function of the transport roller driving unit 200 for driving the transport roller 108 is used. It is possible to detect double feeding of paper. Therefore, it is not necessary to provide a dedicated sensor, and it is possible to detect an increase in apparatus cost and detect double feeding of paper with high accuracy.

  In the above embodiment, as illustrated in FIGS. 7 to 9, the state in which two sheets overlap each other has been described as an example. However, the double feeding of sheets is not limited to two sheets, and there may be three or more sheets. Even in such a case, it is possible to detect double feeding by the detection mode described with reference to FIGS.

  Further, in the above-described embodiment, the double feed detection in the case where the paper is conveyed at the time of image formation output has been described as an example. However, the present invention is not limited to paper conveyance at the time of image formation output, and can be similarly applied to paper conveyance. For example, the present invention can be similarly applied to the conveyance of paper in a scanner having a paper conveyance mechanism such as ADF (Auto Document Feeder).

  Moreover, in the said embodiment, as demonstrated in FIGS. 7-8, the case where it determined by setting various conditions with respect to the variation | change_quantity which changes in time series was demonstrated as an example. However, as described with reference to FIG. 6, if the same type of paper is being transported, the change waveform of the amount of variation that occurs when the paper enters the transport roller 108 and when the paper exits the transport roller 108. Should have a similar waveform.

  Accordingly, the waveform pattern for each sheet is stored as profile information in the profile storage unit 507 as a normal pattern, and matching with the variation pattern of the variation amount sequentially stored in the variation amount storage unit 505 when the sheet is conveyed is performed. By doing so, it is possible to determine whether or not the sheet conveyance is normal. For this pattern matching, a known method can be used.

  In other words, the double feed detection unit 503 is based on the difference between the information indicating the time-series change of the fluctuation amount when the paper is normally conveyed and the fluctuation amount stored in the fluctuation amount storage unit 505 in real time. Can detect double feed.

  Also, FFT (Fast Fourier Transform) can be used to determine the analogy of waveform patterns. Such an example will be described with reference to FIGS. FIG. 13A is a diagram illustrating an example of the FFT result of the change pattern of the fluctuation amount when the paper conveyance is performed normally described with reference to FIG.

  On the other hand, as described with reference to FIG. 7, in the double feed state in which the sheets are overlapped with the leading edges aligned, the shock due to the entry of the sheet increases, so the FFT result of the change pattern of the variation amount is, for example, As shown in FIG. The example of FIG. 13B is an example in which the peak value of the frequency band in which the waveform appears in FIG.

  Further, as described with reference to FIGS. 8 and 9, in the double feed state in which the sheets are shifted and overlapped, the fluctuation amount fluctuation due to the entry of the paper is irregular, so the FFT result of the fluctuation amount change pattern For example, as shown in FIG. The example of FIG. 13C is an example in which a peak appears in a frequency band that did not appear in a normal state.

  As described above, it is possible to determine whether or not the variation amount change pattern stored in the variation amount storage unit 505 in time series is normal also by pattern matching on the result of the frequency analysis by FFT. . Further, in the case of pattern matching using frequency analysis based on the FFT result, it is only necessary to determine the peak value for each predetermined frequency range. Therefore, the amount of calculation is less than when the change patterns as shown in FIGS. It is feasible.

  Further, in the above embodiment, the case where the feedback response of the rotation speed of the conveyance roller 108 when the sheet enters the conveyance roller 108 vibrates while converging as described in FIG. 6 has been described as an example. However, the feedback response of the rotation speed of the conveying roller 108 changes according to the feedback gain. If the feedback response is different, different judgment modes are required for judgment of double feed detection. Such an embodiment will be described below.

  FIG. 14 is a diagram illustrating an example of a case where the feedback gain is lower than that of the mode illustrated in FIG. 6 when the paper conveyance state is normal. When the feedback gain is low, as shown in FIG. 14, the rotation speed of the conveying roller 108 that has decreased due to the entry of the sheet gradually returns to the original state without vibration.

  Even in this case, the amount of decrease in the rotation speed due to the entry of the sheet is almost the same as that of the embodiment shown in FIGS. It is. Further, it is possible to detect double feeding in a state where the leading ends are aligned by determining the threshold value b.

FIG. 15 is a diagram illustrating a time-series change in the fluctuation amount when the feedback gain is low in the double feed state in which the leading edge of the sheet is slightly shifted as described in FIG. In this case, since the fluctuation amount does not vibrate, it cannot be determined that the absolute value of the extreme value has increased as in the determination of the values P ₂ and P ₃ in FIG. However, after the leading edge of the paper enters the conveying roller 108, the leading edge of the paper that is shifted and overlaps enters the conveying roller 108, thereby generating extreme values as indicated by P ₂ and P ₃ in FIG. It becomes.

Thus, the double feed detection unit 503, after the first extreme value occurring after the timing t _0, it is possible to detect a double feed of the sheets when the extreme value occurs again. Further, double feed may be detected when the extreme value is generated twice after the first extreme value, as in P ₂ and P ₃ in FIG.

On the other hand, in the double feed state in which the leading edge of the paper is shifted, the period required for the rotation speed of the transport roller 108 to return to the original state is the same as in the case of FIG. Accordingly, as shown in the values P ₄ in FIG. 15, at the timing t ₁ to time T ₁ from the time t ₀ has elapsed, the determination by the absolute value of the variation amount exceeds the threshold value c equally to FIG. 8 It is.

  FIG. 16 is a diagram illustrating a time-series change in the amount of fluctuation when the feedback gain is low in the double feed state in which the leading edge of the paper is largely displaced as described in FIG. In this case, similarly to FIG. 9, after the rotational speed of the transport roller 108 returns to the original value, the rotational speed fluctuates again due to the entry of the paper. In this case, it is possible to detect the double feed of the paper in the same manner as in FIG.

  Moreover, in the said embodiment, as demonstrated in Fig.1 (a), (b), when the multifeed detection apparatus 5 is provided separately from the main body controller 2, the engine controller 3, DFE7, and PP engine controller 8. Was described as an example. However, this is only an example, and for example, it may be configured as a part of the main body controller 2, the engine controller 3, the DFE 7, the PP engine controller 8, and the like.

  For example, by combining the transport roller driving unit 200 and the double feed detection device 5 described in FIG. 4, it is possible to configure a paper transport control device that controls the transport of paper. In any case, an interface for obtaining a signal indicating a control state of the rotation speed of the transport roller 108 output from the transport roller driving unit 200, and processing and accumulating such signals are shown in FIGS. If there is an arithmetic function for making such a determination, a function similar to that of the double feed detection device 5 according to the present embodiment can be realized.

  Further, a part of the function of the multifeed detection device 5 described in FIG. For example, FIG. 5 illustrates an example in which the fluctuation amount calculation unit 501 calculates the fluctuation amount based on a signal output from the conveyance roller driving unit 200, but the function of the fluctuation amount calculation unit 501 is driven by the conveyance roller. In the double feed detection device 5 included in the unit 200, the information output from the transport roller driving unit 200 may be stored only in the storage medium.

  In the above embodiment, the profile storage unit 507 is provided in the double feed detection device 5 as an example, but the storage medium provided in the main body controller 2, the engine controller 3, the DFE 7, the PP engine controller 8, and the like. It may be realized by.

  In the above embodiment, the profile information as described in FIGS. 6 to 9 and FIGS. 14 to 16 is stored in the profile storage unit 507, and the initial setting unit 504 stores the corresponding profile information in S1001. The case of obtaining and setting has been described as an example. Here, when the apparatus is continuously used, it is conceivable that the physical state of the transport roller 108 and the electrical state of the transport roller driving unit 200 change over time.

  The change in the physical state of the conveying roller 108 is, for example, a change in the roller diameter due to wear or a change in the rotation state due to wear of a gear to which power is transmitted from the crab rolling unit 203. The change in the electrical state of the transport roller driving unit 200 is, for example, a change in the amount of electric power necessary for applying a specific torque to the rotating unit 203.

  When such a change occurs, the waveform of the conveyance roller state output from the state output unit 206 changes over time, and it is erroneously detected as a double feed even though a double feed has not occurred. It is possible that a double feed cannot be detected despite the occurrence. On the other hand, such a problem can be solved by changing the profile information in accordance with the travel distance of the transport roller 108. Hereinafter, an aspect in which the profile information is changed according to the travel distance will be described.

  FIG. 17 is a flowchart showing an operation until a sheet is conveyed to a transfer position when image formation output for one page is executed. Based on FIG. 17, the update of the travel distance of the conveyance roller 108 will be described. As shown in FIG. 17, when image formation output is started based on a print job, the engine controller 3 starts driving the transport roller 108 (S1701), and waits until the rotation of the transport roller 108 is stabilized (S1702). ).

  Subsequently, the sheet is fed out from the sheet feed tray 103 and the conveyance of the sheet by the conveyance roller 108 is started (S1703). As a result, the double feed detection process described with reference to FIG. As a result, if the double feed is not detected and is normally conveyed (S1705 / YES), the engine controller 108 stops the driving of the conveyance roller 108 (S1706). Then, the engine controller 108 updates the travel distance of the transport roller 108 according to the rotation from S1701 to S1706 (S1707).

  Thereafter, the engine controller 3 waits for the transfer image to be formed on the conveyor belt 101 (S1708), and drives the registration roller 109 in accordance with the transfer of the transfer image formed on the conveyor belt 101. Is started (S1709). Thereby, image formation output is executed.

  On the other hand, if double feed is detected as a result of the double feed detection process (S1705 / NO), the engine controller 3 stops the operation of the apparatus according to the print job (S1710), and avoids useless apparatus operation. Then, the travel distance of the transport roller 108 is updated according to the rotation between S1701 and S1710 (S1711). As described above, each time the rotation driving of the transport roller 108 is stopped, the travel distance is updated, so that information on the cumulative travel distance of the transport roller 108 can be obtained in real time.

FIG. 18 is a view showing a table of profile information (hereinafter referred to as “profile selection table”) corresponding to the travel distance of the transport roller 108 according to the present embodiment. As described above, the profile information is information including threshold values a, b, and c and periods T ₁ and T ₂ shown in FIG. 6, for example. In the above-described embodiment, an example has been described in which profile information that is different for each paper type is stored in the profile storage unit 507.

In the case of changing the profile information in accordance with the travel distance of the transport roller 108, as shown in FIG. 18, the profile selection table includes a paper type such as “paper type A”, “paper type B”. Each time, a profile is set according to the range of travel distance. For example, when the travel distance is equal to or less than “Th ₁ ” and “paper type A”, “profile A ₁ ” is selected.

Each profile information such as “profile A ₁ ”, “profile A ₂ ”, “profile A ₃ ”,... Is the transport roller 108 as the values of the above-described threshold values a, b, c and periods T ₁ , T _2. A value corresponding to a change with time determined based on the travel distance is included. Such setting of the profile information according to the travel distance is executed in the initial setting process in S1001 of FIG.

  That is, in the process of S1001, the initial setting unit 504 acquires information indicating the paper type from the main body controller 2, and acquires information indicating the travel distance of the transport roller 108 from the engine controller 3, and stores the information in the table illustrated in FIG. The corresponding profile information is acquired based on the initial setting. As a result, it is possible to set appropriate profile information corresponding to changes with time of the transport roller 108 and the transport roller driving unit 200.

DESCRIPTION OF SYMBOLS 1 Display panel 2 Main body controller 3 Engine controller 4 Engine 5 Double feed detector 6 Display 7 DFE
8 PP engine controller 9 PP engine 10 CPU
20 RAM
30 ROM
40 HDD
50 I / F
60 Bus 101 Conveying belt 102, 102Y, 102M, 102C, 102K Photosensitive drum 103 Feed tray 104 Transfer roller 105 Fixing roller 106 Reverse path 107 Discharge tray 108 Conveying roller 109 Registration roller 200 Conveying roller driving unit 201 Driving control unit 202 Rotation drive unit 203 Rotation unit 204 Rotation detection unit 205 FB acquisition unit 206 Status output unit 501 Fluctuation amount calculation unit 502 Paper entry determination unit 503 Double feed detection unit 504 Initial setting unit 505 Fluctuation amount storage unit 506 Shock time storage unit 507 Profile storage Part

Special Table 2004-359462 JP 2009-18945 A

Claims (10)

A multi-feed detection device that detects a multi-feed state in which a plurality of sheets conveyed by a roller that is rotationally driven using feedback control is conveyed,
A rotational speed information storage processing unit that acquires a signal output every predetermined period from the feedback control of the roller and stores rotational speed information related to the rotational speed of the roller in a storage medium in time series;
A paper transport detection unit that detects that the paper starts to be transported by the roller based on the rotation speed information;
A double feed detection device comprising: a double feed detection unit that detects a double feed state based on a change in the rotation speed information after it is detected that the paper has started to be conveyed by the roller.   The multi-feed detection unit detects a multi-feed state when the rotation speed information exceeds a predetermined threshold after detecting that the sheet starts to be conveyed by the roller. The double feed detection device according to 1.   The multi-feed detection unit detects a multi-feed state when the rotation speed information exceeds a predetermined threshold after a predetermined period has elapsed after detecting that the sheet has started to be conveyed by the roller. The multifeed detection device according to claim 2.   The double feed detection unit acquires an extreme value of the rotation speed information that changes in time series, and after detecting that the paper has started to be conveyed by the roller, the double feed detection unit detects the extreme value over time within a predetermined period. The double feed detection device according to claim 1, wherein the double feed state is detected when the absolute value of the value increases.   The multi-feed detection unit detects that the sheet starts to be conveyed again by the roller after a predetermined period has elapsed after it is detected that the sheet has been conveyed by the roller. The double feed detection device according to claim 1, wherein the double feed state is detected.   The multi-feed detection unit is configured to perform multi-feed based on a difference between time-series information of the rotation speed information when the paper is normally conveyed and the rotation speed information stored in the storage medium. The double feed detection device according to claim 1, wherein the state is detected.   The multifeed according to claim 6, wherein the multifeed detection unit detects a multifeed state based on a result of frequency analysis of a time-series change in the rotation speed information stored in the storage medium. Detection device. A paper transport control device for controlling transport of paper transported by a roller that is rotationally driven using feedback control,
A feedback control unit that rotationally drives the roller so that the rotational speed is constant based on the input target value;
A rotational speed information storage processing unit that acquires a signal output from the feedback control unit every predetermined period and stores rotational speed information related to the rotational speed of the roller in a storage medium in time series;
A paper transport detection unit that detects that the paper starts to be transported by the roller based on the rotation speed information;
And a double feed detection unit that detects a double feed state based on a change in the rotation speed information after it is detected that the paper has started to be conveyed by the roller. A multi-feed detection method for detecting a multi-feed state in which a plurality of sheets conveyed by a roller that is rotationally driven using feedback control is conveyed,
Acquire a signal output every predetermined period from the feedback control of the roller,
Based on the acquired signal, rotational speed information related to the rotational speed of the roller is stored in a storage medium in time series,
Based on the rotational speed information stored in the storage medium, it is detected that the paper has started to be conveyed by the roller,
A multi-feed detection method, wherein a multi-feed state is detected based on a change in the rotation speed information stored in the storage medium after it is detected that the sheet starts to be conveyed by the roller. A double feed detection system that detects a double feed state in which a plurality of sheets conveyed by a roller that is rotationally driven using feedback control is conveyed,
A rotational speed information storage processing unit that acquires a signal output every predetermined period from the feedback control of the roller and stores rotational speed information related to the rotational speed of the roller in a storage medium in time series;
A paper transport detection unit that detects that the paper starts to be transported by the roller based on the rotation speed information;
A double feed detection system, comprising: a double feed detection unit that detects a double feed state based on a change in the rotation speed information after it is detected that the paper has started to be conveyed by the roller.