Double feed detection device, control method, and control program

Abstract

To provide a double feed detection device capable of early detecting double-feeding of a medium while preventing the double-feeding of the medium from being detected erroneously.SOLUTION: A double feed detection device 100 comprises: an ultrasonic sensor 114; an imaging part 117 for sequentially generating line images by imaging a medium; a medium width detection part 143 for detecting a medium width inside each line image for every sequentially generated line image; an apex number detection part 144 for detecting the apex number of the medium included in the sequentially generated line image, based on the medium width inside each line image; a medium length detection part 145 for detecting the medium length in a direction orthogonal to the medium width of the medium included in the sequentially generated line image; a shape estimation part 146 for estimating a medium shape, based on the apex number and the medium length; and a double feed detection part 147 for detecting double-feeding of the medium by comparing an ultrasonic signal with a threshold value. The double feed detection part changes the threshold value, or stops detecting the double-feeding, based on the medium shape.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a double-feed detection device, and more particularly to a double-feed detection device that detects double-feed of a medium using ultrasonic waves.

Background Art

[0002] Devices such as scanners that convey a medium such as a document and read an image of the conveyed medium have a function of detecting whether double-feed, in which a plurality of media are conveyed overlapping each other, has occurred. Generally, a double-feed detection device such as a scanner includes an ultrasonic wave transmitting unit that transmits ultrasonic waves and an ultrasonic wave receiving unit that outputs a signal corresponding to the received ultrasonic waves, and detects double-feed based on the signal output by the ultrasonic wave receiving unit when the medium is conveyed.

[0003] However, the reception level of ultrasonic waves when a plastic card is conveyed as a medium is close to the reception level of ultrasonic waves when double-feed of paper has occurred. When such a card is conveyed, there is a possibility that it may be erroneously determined that double-feed has occurred.

[0004] A medium conveyance device is disclosed that detects the presence or absence of double-feed of a medium conveyed on a conveyance path based on the output of an ultrasonic sensor having an ultrasonic transmitter and an ultrasonic receiver arranged to face each other across the medium conveyance path (see Patent Document 1). This medium conveyance device discriminates between a first medium and a second medium based on the difference in the side length between the first medium and the second medium conveyed on the conveyance path, and further detects the presence or absence of double-feed of the medium based on the discrimination result.

[0005] An image reading device is disclosed that detects double-feed of a document based on image data obtained by reading a document conveyed on a conveyance path (see Patent Document 2). This image reading device estimates the document length from the image data, and determines that there is double-feed of the document when an edge is detected at a position away from the document length from the document leading edge and another edge is detected within a range closer to the conveyance interval of the document than the document length from the position away from the document length.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2013-63843 [Patent Document 2] Japanese Patent Publication No. 2012-253414 [Overview of the project] [Problems that the invention aims to solve]

[0007] It is desirable to prevent errors in detecting double feeding of media.

[0008] It is desirable to prevent errors in detecting double feeding of media. [Means for solving the problem]

[0009] A double-feed detection device according to one aspect of the present invention includes a transport unit for transporting a medium, an ultrasonic sensor including an ultrasonic transmitting unit for emitting ultrasonic waves and an ultrasonic receiving unit positioned opposite the ultrasonic transmitting unit and generating a signal corresponding to the received ultrasonic waves, a double-feed detection unit for detecting a double-feed of a medium based on the signal, and an operation unit for setting the shape of the medium for stopping the detection of a double-feed. A detection unit that detects the shape of the medium transported by the transport unit, The double-feed detection unit has, Detected by the detection unit The shape of the medium, Control panel If the format matches the configured media shape, the detection of double feeds will be stopped.

[0010] Furthermore, a control method relating to one aspect of the present invention is a control method for a double-feed detection device having a transport unit for transporting a medium, an ultrasonic transmitting unit for emitting ultrasonic waves, an ultrasonic sensor including an ultrasonic receiving unit arranged opposite the ultrasonic transmitting unit and generating a signal corresponding to the received ultrasonic waves, and a double-feed detection unit for detecting double-feeding of a medium based on the signal, wherein the user can set the shape of the medium for which double-feed detection will be stopped by operating the device, The transport unit detects the shape of the transported medium, and the detected The shape of the medium, By user operation When the shape matches the set configuration, the double-feed detection device is instructed to stop detecting double feeds.

[0011] Also, a control program according to one aspect of the present invention is a control program for a double-feed detection device having a conveyance unit that conveys a medium, an ultrasonic wave transmission unit that transmits ultrasonic waves, and an ultrasonic sensor including an ultrasonic wave reception unit that is disposed opposite to the ultrasonic wave transmission unit and generates a signal corresponding to the received ultrasonic wave, and a double-feed detection unit that detects double-feed of the medium based on the signal, and causes the shape of the medium whose double-feed detection is stopped by a user operation to be set, The transport unit detects the shape of the transported medium, and the detected where the shape of the medium is By user operation when corresponding to the set shape, causes the double-feed detection device to stop detecting double-feed.

Advantages of the Invention

[0012] According to the present invention, it becomes possible to prevent detection errors of double-feed of the medium.

Brief Description of the Drawings

[0013] [Figure 1] It is a perspective view showing a double-feed detection device 100 according to an embodiment. [Figure 2] It is a diagram for explaining a conveyance path inside the double-feed detection device 100. [Figure 3] It is a block diagram showing a schematic configuration of the double-feed detection device 100. [Figure 4] It is a diagram showing a schematic configuration of a storage device 130 and a CPU 140. [Figure 5] It is a flowchart showing an example of an operation of a medium reading process. [Figure 6] It is a flowchart showing an example of an operation of a double-feed detection process. [Figure 7] It is a flowchart showing an example of an operation of a double-feed detection process. [Figure 8] It is a flowchart showing an example of an operation of a double-feed detection process. [Figure 9A] It is a schematic diagram for explaining the relationship between a change in the medium width and the number of vertices. [Figure 9B] It is a schematic diagram for explaining the relationship between a change in the medium width and the number of vertices. [Figure 9C]It is a schematic diagram for explaining the relationship between the change in the medium width and the number of apexes. [Figure 9D] It is a schematic diagram for explaining the relationship between the change in the medium width and the number of apexes. [Figure 9E] It is a schematic diagram for explaining the relationship between the change in the medium width and the number of apexes. [Figure 9F] It is a schematic diagram for explaining the relationship between the change in the medium width and the number of apexes. [Figure 10] It is a schematic diagram for explaining the relationship between the change in the medium width and the number of apexes. [Figure 11A] It is a schematic diagram for explaining the first threshold value. [Figure 11B] It is a schematic diagram for explaining the second threshold value. [Figure 11C] It is a schematic diagram for explaining the third threshold value. [Figure 11D] It is a schematic diagram for explaining the fourth threshold value. [Figure 12] It is a flowchart showing an example of the operation of the ultrasonic signal determination process. [Figure 13] It is a schematic diagram for explaining the characteristics of the ultrasonic signal. [Figure 14] It is a flowchart showing an example of the operation of a part of another retransmission detection process. [Figure 15] It is a flowchart showing an example of the operation of a part of another ultrasonic signal determination process. [Figure 16] It is a diagram showing the schematic configuration of the processing circuit 250 in another retransmission detection device.

Mode for Carrying Out the Invention

[0014] Hereinafter, a retransmission detection device according to one aspect of the present invention will be described with reference to the drawings. However, note that the technical scope of the present invention is not limited to those embodiments, and extends to the invention described in the claims and its equivalents.

[0015] Figure 1 is a perspective view showing a double-feed detection device 100 configured as an image scanner. The double-feed detection device 100 transports and images the medium, which is the original document. The medium can be paper, cardboard, a card, or a passport, etc. The card is, for example, a plastic resin card. In particular, the card is an ID (Identification) card as defined by ISO (International Organization for Standardization) / IEC (International Electrotechnical Commission) 7810. Note that other types of cards may also be used. The double-feed detection device 100 may also be a facsimile machine, copier, printer / multifunction device (MFP, Multifunction Peripheral), etc.

[0016] The double-feed detection device 100 includes a lower housing 101, an upper housing 102, a mounting table 103, a discharge table 104, an operating device 105, and a display device 106, etc.

[0017] The upper housing 102 is positioned to cover the upper surface of the double-feed detection device 100 and engages with the lower housing 101. The mounting table 103 engages with the lower housing 101 so that the transported medium can be placed on it. The discharge table 104 engages with the lower housing 101 so that the discharged medium can be held.

[0018] The operating device 105 has input devices such as buttons and an interface circuit that acquires signals from the input devices, accepts input operations from the user, and outputs an operation signal corresponding to the user's input operation. The display device 106 has a display including liquid crystal, organic EL (Electro-Luminescence), etc. and an interface circuit that outputs image data to the display, and displays the image data on the display.

[0019] Figure 2 is a diagram illustrating the transport path inside the double-feed detection device 100.

[0020] The transport path inside the double-feed detection device 100 includes a medium detection sensor 111, a feed roller 112, a brake roller 113, an ultrasonic transmitter 114a, an ultrasonic receiver 114b, a first transport roller 115, a second transport roller 116, a first imaging device 117a, a second imaging device 117b, a third transport roller 118, and a fourth transport roller 119, etc. Note that the number of each roller is not limited to one, and there may be multiple rollers for each type.

[0021] The upper surface of the lower housing 101 forms the lower guide 107a of the medium transport path, and the lower surface of the upper housing 102 forms the upper guide 107b of the medium transport path. In Figure 2, arrow A1 indicates the transport direction of the medium. Hereafter, "upstream" refers to the upstream direction of the medium transport direction A1, and "downstream" refers to the downstream direction of the medium transport direction A1.

[0022] The media detection sensor 111 has a contact detection sensor and detects whether or not a medium is placed on the mounting table 103. The media detection sensor 111 generates and outputs a media detection signal whose signal value changes depending on whether or not a medium is placed on the mounting table 103.

[0023] The ultrasonic transmitter 114a and ultrasonic receiver 114b are examples of an ultrasonic transmitting unit and an ultrasonic receiving unit, respectively. The ultrasonic transmitter 114a and ultrasonic receiver 114b are installed downstream of the feed roller 112 and brake roller 113 and upstream of the first transport roller 115 and second transport roller 116, that is, upstream of the first imaging device 117a and second imaging device 117b. The ultrasonic transmitter 114a and ultrasonic receiver 114b are arranged near the transport path of the medium, facing each other across the transport path. The ultrasonic transmitter 114a outputs ultrasonic waves. On the other hand, the ultrasonic receiver 114b receives ultrasonic waves transmitted by the ultrasonic transmitter 114a and passing through the medium, and generates and outputs an ultrasonic signal, which is an electrical signal corresponding to the received ultrasonic waves. Hereinafter, the ultrasonic transmitter 114a and ultrasonic receiver 114b may be collectively referred to as the ultrasonic sensor 114.

[0024] The first imaging device 117a has a reduction optical system type line sensor equipped with CCD (Charge Coupled Device) image sensors arranged linearly in the main scanning direction. The first imaging device 117a also has a lens that forms an image on the image sensor and an A / D converter that amplifies the electrical signal output from the image sensor and performs analog-to-digital (A / D) conversion. The first imaging device 117a images the back surface of the medium being transported by the feed roller 112, brake roller 113, first transport roller 115, and second transport roller 116. At regular intervals, the first imaging device 117a sequentially generates and outputs line images of the area of ​​the transported medium facing the line sensor. That is, the number of pixels in the vertical direction (sub-scanning direction) of the line image is 1, and the number of pixels in the horizontal direction (main scanning direction) is multiple.

[0025] Similarly, the second imaging device 117b has a reduction optical system type imaging sensor equipped with CCD image sensors arranged linearly in the main scanning direction. The second imaging device 117b also has a lens that forms an image on the image sensor and an A / D converter that amplifies the electrical signal output from the image sensor and performs analog-to-digital (A / D) conversion. The second imaging device 117b images the surface of the medium being transported by the feed roller 112, brake roller 113, first transport roller 115, and second transport roller 116. At regular intervals, the second imaging device 117b sequentially generates and outputs line images of the region of the transported medium facing the line sensor.

[0026] The double-feed detection device 100 may also consist of only one of the first imaging device 117a and the second imaging device 117b, and read only one side of the medium. Alternatively, a 1:1 optical system type CIS (Contact Image Sensor) equipped with a CMOS (Complementary Metal Oxide Semiconductor) image sensor can be used instead of a CCD. Hereinafter, the first imaging device 117a and the second imaging device 117b may be collectively referred to as imaging device 117. Imaging device 117 is an example of an imaging unit.

[0027] The medium placed on the loading platform 103 is transported between the lower guide 107a and the upper guide 107b in the transport direction A1 by the rotation of the feed roller 112 in the direction of arrow A2 in Figure 2. The brake roller 113 rotates in the direction of arrow A3 during medium transport. Due to the action of the feed roller 112 and the brake roller 113, when multiple media are placed on the loading platform 103, only the media in contact with the feed roller 112 are separated. This restricts the transport of media other than the separated media (preventing double feeding).

[0028] The medium is fed between the first transport roller 115 and the second transport roller 116, guided by the lower guide 107a and the upper guide 107b. The medium is fed between the first imaging device 117a and the second imaging device 117b as the first transport roller 115 and the second transport roller 116 rotate in the directions of arrows A4 and A5, respectively. The medium read by the imaging device 117 is discharged onto the discharge platform 104 as the third transport roller 118 and the fourth transport roller 119 rotate in the directions of arrows A6 and A7, respectively. The feed roller 112, brake roller 113, first transport roller 115, and second transport roller 116 are examples of transport units that transport the medium.

[0029] Figure 3 is a block diagram showing the schematic configuration of the double-feed detection device 100.

[0030] In addition to the configuration described above, the double-feed detection device 100 further includes a drive unit 121, an interface device 122, a storage device 130, a CPU (Central Processing Unit) 140, a processing circuit 150, and the like.

[0031] The drive unit 121 includes one or more motors and, based on control signals from the CPU 140, rotates the feed roller 112, brake roller 113, first transport roller 115, second transport roller 116, third transport roller 118, and fourth transport roller 119 to transport the medium.

[0032] The interface device 122 has an interface circuit similar to a serial bus such as USB, and electrically connects to an information processing device (not shown) (e.g., a personal computer, a portable information terminal, etc.) to transmit and receive input images and various types of information. Alternatively, instead of the interface device 122, a communication unit may be used that has an antenna for transmitting and receiving wireless signals and a wireless communication interface device for transmitting and receiving signals via a wireless communication line according to a predetermined communication protocol. The predetermined communication protocol is, for example, a wireless LAN (Local Area Network).

[0033] The storage device 130 includes memory devices such as RAM (Random Access Memory) and ROM (Read Only Memory), fixed disk devices such as hard disks, or portable storage devices such as flexible disks and optical disks. The storage device 130 also stores computer programs, databases, tables, etc., used for various processes of the double-feed detection device 100. The computer programs may be installed into the storage device 130 from a computer-readable portable recording medium using a known setup program. Examples of portable recording media include CD-ROMs (compact disk read-only memory) and DVD-ROMs (digital versatile disk read-only memory).

[0034] The CPU 140 operates based on a program pre-stored in the memory device 130. Alternatively, a DSP (digital signal processor), LSI (large-scale integration), etc., may be used instead of the CPU 140. Furthermore, an ASIC (Application Specific Integrated Circuit), FPGA (Field-Programmable Gate Array), etc., may be used instead of the CPU 140.

[0035] The CPU 140 is connected to the operating device 105, display device 106, medium detection sensor 111, ultrasonic sensor 114, imaging device 117, drive device 121, interface device 122, and storage device 130, and controls each of these components. The CPU 140 controls the drive of the drive device 121, controls the imaging of the imaging device 117, acquires images, and transmits them to an information processing device (not shown) via the interface device 122. The CPU 140 also detects double feeding of transported media based on the ultrasonic signal generated by the ultrasonic sensor 114 and the line image captured by the imaging device 117.

[0036] The processing circuit 150 performs predetermined image processing on the image captured by the imaging device 117 and stores the processed image in the storage device 130. A DSP, LSI, ASIC, FPGA, etc., may be used instead of the processing circuit 150.

[0037] Figure 4 shows a schematic configuration of the storage device 130 and the CPU 140.

[0038] As shown in Figure 4, the storage device 130 stores the control program 131, the image acquisition program 132, the media width detection program 133, the vertex count detection program 134, the media length detection program 135, the shape estimation program 136, and the double feed detection program 137, among others. Each of these programs is a functional module implemented by software running on the processor. The CPU 140 reads each program stored in the storage device 130 and operates according to each program it has read. As a result, the CPU 140 functions as the control unit 141, the image acquisition unit 142, the media width detection unit 143, the vertex count detection unit 144, the media length detection unit 145, the shape estimation unit 146, and the double feed detection unit 147.

[0039] Figure 5 is a flowchart showing an example of the operation of the media reading process of the double-feed detection device 100.

[0040] The following describes an example of the operation of the media reading process of the double-feed detection device 100, referring to the flowchart shown in Figure 5. The operation flow described below is executed primarily by the CPU 140 in cooperation with each element of the double-feed detection device 100, based on a program pre-stored in the storage device 130. The operation flow shown in Figure 5 is executed periodically.

[0041] First, the control unit 141 waits until the user inputs an instruction to read the medium using the operating device 105 and receives an operation signal from the operating device 105 instructing the reading of the medium (step S101).

[0042] Next, the control unit 141 determines whether or not a medium is placed on the mounting table 103 based on the medium detection signal received from the medium detection sensor 111 (step S102).

[0043] If no media is placed on the mounting table 103, the control unit 141 returns to step S101 and waits until it receives a new operation signal from the operating device 105.

[0044] On the other hand, when a medium is placed on the mounting table 103, the control unit 141 drives the drive unit 121 to rotate the feed roller 112, brake roller 113, and the first to fourth transport rollers 115, 116, 118, and 119 to transport the medium (step S103).

[0045] Next, the image acquisition unit 142 causes the transported medium to be imaged by the imaging device 117 to acquire a line image (step S104).

[0046] Next, the CPU 140 executes the double-feed detection process (step S105). In the double-feed detection process, the double-feed detection unit 147 detects a double feed of the medium by comparing the ultrasonic signal generated by the ultrasonic sensor 114 with a determination threshold. The shape estimation unit 146 estimates the shape of the medium based on the line image, and the double-feed detection unit 147 changes the determination threshold or stops detecting the double feed based on the shape of the medium. Details of the double-feed detection process will be described later.

[0047] Next, the control unit 141 determines whether or not a double feed has been detected in the double feed detection process, that is, whether or not it has been determined that a double feed has occurred (step S106).

[0048] If double feeding is detected, the control unit 141, as an abnormality handling measure, stops the drive unit 121 to stop the transport of the medium, and notifies the user that an abnormality has occurred via a speaker, LED, etc. (not shown) (step S107), and ends the series of steps.

[0049] On the other hand, if double feeding is not detected, the image acquisition unit 142 determines whether the entire transported medium has been imaged (step S108). The image acquisition unit 142 determines whether the entire medium has been imaged by determining, for example, whether the rear end of the medium has passed the imaging device 117, based on a medium detection signal output from a medium detection sensor (not shown) located downstream of the imaging device 117. The image acquisition unit 142 may also determine that the entire transported medium has been imaged when it has acquired a predetermined number of line images from the imaging device 117.

[0050] If the entire transported medium has not yet been imaged, the image acquisition unit 142 returns to step S104 and repeats the processes in steps S104 to S108.

[0051] On the other hand, if the entire transported medium is imaged, the image acquisition unit 142 generates an input image by combining all the acquired line images (step S109).

[0052] Next, the image acquisition unit 142 transmits the input image to an information processing device (not shown) via the interface device 122 (step S110). If the image acquisition unit 142 is not connected to an information processing device, it stores the input image in the storage device 130.

[0053] Next, the control unit 141 determines whether or not there is any medium remaining on the mounting tray 103 based on the medium detection signal received from the medium detection sensor 111 (step S111). If there is any medium remaining on the mounting tray 103, the control unit 141 returns to step S104 and repeats the process from steps S104 to S111.

[0054] On the other hand, if there is no media remaining on the mounting table 103, the control unit 141 stops the drive unit 121 (step S112) and ends the series of steps.

[0055] Figures 6 to 8 are flowcharts illustrating examples of the operation of the double-feed detection process.

[0056] The operation flow shown in Figures 6 to 8 is executed in step S105 of the flowchart shown in Figure 5.

[0057] First, the media width detection unit 143 extracts edge pixels from the line image acquired by the image acquisition unit 142 (step S201). That is, the media width detection unit 143 extracts edge pixels for each line image that is generated sequentially. The media width detection unit 143 calculates the absolute value of the difference in brightness values ​​between each pixel in the line image and the pixels adjacent to it in the horizontal direction (hereinafter referred to as the adjacent difference value), and if the adjacent difference value exceeds the threshold Th1, it extracts that pixel as an edge pixel. This threshold Th1 can be set, for example, to a difference in brightness values ​​that a person can visually distinguish from the difference in brightness on the image (for example, 20).

[0058] The media width detection unit 143 may calculate the adjacent difference value as the absolute value of the difference in luminance values ​​between two pixels that are a predetermined distance apart from each pixel in the line image. Alternatively, the media width detection unit 143 may calculate the adjacent difference value using the color value (R value, G value, or B value) of each pixel instead of the luminance value of each pixel. Furthermore, the media width detection unit 143 may extract edge pixels by comparing the luminance value or color value of the line image with a threshold. For example, the media width detection unit 143 may identify a specific pixel as an edge pixel if the luminance value or color value of that specific pixel is less than the threshold, and the luminance value or color value of a pixel adjacent to that specific pixel or a pixel that is a predetermined distance apart from that specific pixel is greater than or equal to the threshold.

[0059] Next, the media width detection unit 143 detects the media width within the line image acquired by the image acquisition unit 142 based on the extracted edge pixels and stores it in the storage device 130 (step S202). That is, the media width detection unit 143 detects the media width within each line image for each line image that is generated sequentially. The media width detection unit 143 identifies the leftmost edge pixel and the rightmost edge pixel among the edge pixels extracted from the line image, and detects the distance (number of pixels) between the identified edge pixels as the media width.

[0060] Next, the shape estimation unit 146 determines whether the detected media width exceeds a predetermined length (step S203). The predetermined length is set, for example, based on the size of an ID card as defined in ISO / IEC 7810. An ID card as defined in ISO / IEC 7810 has a roughly rectangular shape with a long side of 85.60 mm and a short side of 53.98 mm. Note that the angles of the four vertices of the ID card do not have to be right angles, but may be rounded. The predetermined length is set to the number of pixels corresponding to the length of the diagonal of this ID card (101.20 mm) plus a margin (for example, 102 mm). No matter how the ID card is tilted during transport, the width of the ID card captured on the imaging line of the imaging device 117 will not exceed the defined diagonal length.

[0061] Therefore, if the detected media width exceeds a predetermined length, that is, if the media width detection unit 143 detects a media width exceeding a predetermined length from the line image, the shape estimation unit 146 estimates that the shape of the transported media is not that of a card (step S401). In this case, in the processing described later, the vertex count detection unit 144 does not detect the number of vertices of the media included in the sequentially generated line images. Therefore, the shape estimation unit 146 can estimate the shape of the media in a shorter time, and the processing load of the double-feed detection process can be reduced.

[0062] On the other hand, if the detected media width does not exceed a predetermined length, the vertex count detection unit 144 determines whether a predetermined number of line images have been newly acquired for which the detection process for the number of vertices of the media has not been performed (step S204). The predetermined number is set to a number of pixels (for example, 3) for which changes in the sub-scanning direction of the media width can be detected well. The predetermined number may also be 1. If a predetermined number of line images have not been newly acquired, the vertex count detection unit 144 terminates the series of steps. That is, the processing in the subsequent steps S205 to S406 is executed each time a predetermined number of line images are newly generated.

[0063] On the other hand, if a predetermined number of line images are newly acquired, the vertex detection unit 144 determines whether a media width greater than or equal to a predetermined width has been detected in any of the line images acquired so far for that medium (step S205). The predetermined width is set to, for example, 1 pixel. The predetermined width may be set to a value of 2 pixels or more in order to remove the effects of noise.

[0064] If no media width greater than or equal to a predetermined width has been detected yet, the vertex count detection unit 144 determines that the number of vertices of the media included in the line images acquired so far is 0 (step S206), and terminates the series of steps.

[0065] On the other hand, if a media width greater than a predetermined width is detected, the vertex count detection unit 144 detects a change in the media width within each line image. The vertex count detection unit 144 identifies the latest line image from the newly acquired predetermined number of line images as the target image, and identifies the line image acquired immediately before acquiring that predetermined number of line images as the reference image. The vertex count detection unit 144 may also use an image as the reference image in which the grayscale value of each pixel is the average or median value of the corresponding pixels in the multiple line images acquired up to that point. This allows the vertex count detection unit 144 to improve the reliability of the reference image.

[0066] The vertex count detection unit 144 determines whether the media width in the target image is greater than the media width in the reference image (step S207). The vertex count detection unit 144 may determine that the media width in the target image is greater than the media width in the reference image only if the media width in the target image is greater than the media width in the reference image and the difference between the media width in the target image and the media width in the reference image is greater than or equal to a predetermined difference (e.g., 3 pixels).

[0067] If the media width in the target image is greater than the media width in the reference image, the vertex count detection unit 144 determines that the number of vertices in the media included in the line images acquired so far is 1 (step S208), and proceeds to step S301.

[0068] Figures 9A to 9F and Figure 10 are schematic diagrams illustrating the relationship between changes in media width and the number of vertices.

[0069] Figures 9A to 9F show a rectangular medium M being transported at an angle. As shown in Figures 9A to 9F, the medium M may be transported at an angle, and when the medium M is transported at an angle, each vertex V1 to V4 of the medium M passes the imaging position of the imaging device 117 at a different timing. Figure 10 shows multiple line images P0 to P9 captured while the medium M is being transported. For the sake of simplicity, only multiple line images P0 to P9 are shown in Figure 10, but many line images are captured between each line image.

[0070] Figure 9A shows the medium M before any vertices have reached the imaging position, and the line image P0 in Figure 10 was captured at this time. Figure 9B shows the medium M immediately after the first vertex V1 has passed the imaging position, and the line image P1 in Figure 10 was captured at this time. Figure 9C shows the medium M after the second vertex V2 has reached the imaging position, and the line image P3 in Figure 10 was captured at this time. Figure 9D shows the medium M after the third vertex V3 has reached the imaging position, and the line image P6 in Figure 10 was captured at this time. Figure 9E shows the medium M just before the fourth vertex V4 reaches the imaging position, and the line image P8 in Figure 10 was captured at this time. Figure 9F shows the medium M after all vertices have passed the imaging position, and the line image P9 in Figure 10 was captured at this time.

[0071] As shown in Figure 10, the line images from the line image captured immediately before line image P1 to the line image captured immediately before line image P3 contain only one vertex V1. In these line images, the distance D between the edge pixels L and R at both ends increases with each newly captured line image. That is, the vertex count detection unit 144 can determine that the number of vertices of the medium included in the line images acquired so far is 1 if the medium width in the target image is greater than the medium width in the reference image.

[0072] On the other hand, if the media width in the target image is not greater than the media width in the reference image, the vertex count detection unit 144 determines whether the media width in the target image is the same as the media width in the reference image (step S209). The vertex count detection unit 144 may also determine that the media width in the target image is the same as the media width in the reference image if the difference between the media width in the target image and the media width in the reference image is less than or equal to a predetermined difference.

[0073] If the media width in the target image is the same as the media width in the reference image, the vertex count detection unit 144 determines that the number of vertices in the media included in the line images acquired so far is 2 (step S210), and proceeds to step S301.

[0074] As shown in Figure 10, the line images from the line image captured immediately before line image P1 to the line image captured immediately before line image P6 contain two vertices V1 and V2. Furthermore, in each line image from the line image captured immediately after line image P3 to the line image captured immediately before line image P6, the distance D between the edge pixels L and R at both ends is the same. That is, the vertex count detection unit 144 can determine that the number of vertices of the medium included in the line images acquired so far is 2, given that the medium width in the target image is the same as the medium width in the reference image.

[0075] In line image P3, the media width increases compared to the immediately preceding line image, so the number of vertices of the media included in the line images acquired up to that point is determined to be 1. However, in the next line image acquired, the media width becomes the same as the immediately preceding line image P3, so the number of vertices of the media included in the line images acquired up to that point is determined to be 2. Therefore, the timing at which the number of vertices is correctly detected is delayed by one line pixel, but since the interval between acquisitions of each line image is sufficiently short, the vertex detection unit 144 can detect the number of vertices with sufficiently high accuracy.

[0076] On the other hand, if the media width in the target image is not the same as the media width in the reference image, that is, if the media width in the target image is less than the media width in the reference image, the vertex detection unit 144 determines whether the media width in the target image is greater than 0 (step S211).

[0077] If the media width within the target image is greater than 0, that is, if media exists within the target image, the vertex count detection unit 144 determines that the number of vertices of the media included in the line images acquired so far is 3 (step S212), and proceeds to step S301.

[0078] As shown in Figure 10, the line images from the line image immediately preceding line image P1 to line image P8 contain three vertices V1, V2, and V3. Furthermore, in each line image from the line image immediately following line image P6 to line image P8, the distance D between the edge pixels L and R at both ends decreases with each newly captured line image, and a medium is present. In other words, the vertex count detection unit 144 can determine that the number of vertices of the medium included in the line images acquired so far is 3 if the medium width in the target image is less than the medium width in the reference image and a medium is present in the target image.

[0079] In line image P6, the media width is the same as the line image captured immediately before, so the number of vertices of the media included in the line images acquired up to that point is determined to be 2. However, in the next line image captured, the media width is smaller than that of the line image P6 captured immediately before, so the number of vertices of the media included in the line images acquired up to that point is determined to be 3. In other words, the timing at which the number of vertices is correctly detected is delayed by one line pixel, but since the interval between the capture of each line image is sufficiently short, the vertex detection unit 144 can detect the number of vertices with sufficiently high accuracy.

[0080] On the other hand, if the media width within the target image is 0, that is, if no media exists within the target image, the vertex count detection unit 144 determines that the number of vertices of media included in the line images acquired so far is 4 (step S213), and proceeds to step S301.

[0081] As shown in Figure 10, the line images from the line image captured immediately before line image P1 to the line image captured after line image P8 contain four vertices V1, V2, V3, and V4. The line image captured after line image P8 does not contain the medium M. In other words, the vertex count detection unit 144 can determine that if the medium is not present in the target image, the number of vertices of the medium included in the line images acquired so far is 4.

[0082] In this way, the vertex count detection unit 144 detects the number of vertices of the media included in the sequentially generated line images based on the media width within each line image.

[0083] Next, the media length detection unit 145 detects the media length in the vertical direction (sub-scanning direction), i.e., the direction perpendicular to the media width, of the media included in the line images acquired so far for that media (step S301). As described above, the number of pixels in the vertical direction (sub-scanning direction) of the line image is 1. The media length detection unit 145 detects the number of images from the first line image in which a media width of a predetermined width or more is detected for that media, up to the latest line image or the line image in which the media width first becomes 0, as the media length (number of pixels in the vertical direction) of the media included in the line images. In this way, the media length detection unit 145 detects the media length in the direction perpendicular to the media width of the media included in the sequentially generated line images.

[0084] Next, the shape estimation unit 146 determines whether the media length detected by the media length detection unit 145 is greater than or equal to the first threshold and whether the number of vertices detected by the vertex number detection unit 144 is less than 2 (step S302).

[0085] Figure 11A is a schematic diagram illustrating the first threshold.

[0086] As shown in Figure 11A, the first threshold is set to the number of pixels corresponding to the value (e.g., 46 mm) obtained by adding a margin to the distance T1 (45.66 mm) between the diagonal X of ID card C as defined in ISO / IEC 7810 and a vertex not included in that diagonal X. The distance T1 is calculated by solving the following relational equations (1) and (2), where the long side of ID card C is W (85.60 mm) and the short side is H (53.98 mm). H 2 +W 2 =X 2 (1) H × W = X × T1 (2)

[0087] Next, the shape estimation unit 146 estimates that the shape of the medium is not that of a card if the medium length is greater than or equal to the first threshold and the number of vertices is less than 2 (step S401).

[0088] When ID card C is transported, regardless of how tilted ID card C is, if vertex V1 has passed the imaging position and has been transported a further distance T1, at least one of vertex V2 or vertex V3, which shares an edge with vertex V1, will always pass the imaging position. Therefore, the shape estimation unit 146 can determine that the medium is larger than the card if the medium length detected by the medium length detection unit 145 is greater than or equal to the first threshold and the number of vertices detected by the vertex number detection unit 144 is less than 2.

[0089] On the other hand, the shape estimation unit 146 determines whether the medium length is equal to or greater than the second threshold and the number of vertices is less than three if the medium length is less than the first threshold or the number of vertices is two or more (step S303).

[0090] Figure 11B is a schematic diagram illustrating the second threshold.

[0091] As shown in Figure 11B, the second threshold is set to a number of pixels that corresponds to the length T2 (85.60 mm) of the long side W of ID card C as defined in ISO / IEC 7810, plus a margin (e.g., 86 mm).

[0092] Next, the shape estimation unit 146 estimates that the shape of the medium is not that of a card if the medium length is greater than or equal to the second threshold and the number of vertices is less than 3 (step S401).

[0093] When ID card C is transported, regardless of how ID card C is transported, when vertex V1 has passed the imaging position and has been transported a further distance T2, both vertices V2 and V3, which share an edge with vertex V1, will inevitably pass the imaging position. Therefore, the shape estimation unit 146 can determine that the medium is larger than the card if the medium length detected by the medium length detection unit 145 is greater than or equal to the second threshold and the number of vertices detected by the vertex number detection unit 144 is less than 3.

[0094] On the other hand, the shape estimation unit 146 determines whether the medium length is equal to or greater than the third threshold and the number of vertices is less than four, if the medium length is less than the second threshold or the number of vertices is three or more (step S304).

[0095] Figure 11C is a schematic diagram illustrating the third threshold.

[0096] As shown in Figure 11C, the third threshold is set to a number of pixels that corresponds to the length T3 (101.20 mm) of the diagonal X of ID card C as defined in ISO / IEC 7810, plus a margin (e.g., 102 mm).

[0097] Next, the shape estimation unit 146 estimates that the shape of the medium is not that of a card if the medium length is greater than or equal to the third threshold and the number of vertices is less than 4 (step S401).

[0098] When ID card C is transported, regardless of how tilted ID card C is, all other vertices V2 to V4 pass the imaging position before vertex V1 passes the imaging position and is transported a distance T3. Therefore, the shape estimation unit 146 can determine that the medium is larger than the card if the medium length detected by the medium length detection unit 145 is greater than or equal to the third threshold and the number of vertices detected by the vertex number detection unit 144 is not 4.

[0099] On the other hand, the shape estimation unit 146 determines whether the medium length is less than the third threshold or the number of vertices is 4, and whether the medium length is less than the fourth threshold and the number of vertices is 4 (step S305).

[0100] Figure 11D is a schematic diagram illustrating the fourth threshold.

[0101] As shown in Figure 11D, the fourth threshold is set to a number of pixels corresponding to the value obtained by subtracting a margin (e.g., 53 mm) from the length T4 (53.98 mm) of the short side H of ID card C as defined in ISO / IEC 7810.

[0102] Next, the shape estimation unit 146 estimates that the shape of the medium is not that of a card if the medium length is less than the fourth threshold and the number of vertices is 4 (step S401).

[0103] When ID card C is transported, regardless of how ID card C is transported, all other vertices V2 to V4 will not pass the imaging position before vertex V1 has passed the imaging position and traveled a distance T4. Therefore, the shape estimation unit 146 can determine that the medium is smaller than a card if the medium length detected by the medium length detection unit 145 is less than the fourth threshold and the number of vertices detected by the vertex number detection unit 144 is 4.

[0104] On the other hand, the shape estimation unit 146 determines whether the medium length is less than or equal to the second threshold and the number of vertices is 3 or greater if the medium length is greater than or equal to the fourth threshold or if the number of vertices is less than 4 (step S306).

[0105] Next, the shape estimation unit 146 estimates that the shape of the medium is that of a card if the medium length is less than or equal to the second threshold and the number of vertices is 3 or more (step S402).

[0106] As shown in Figure 11D, when ID card C is transported, regardless of how ID card C is transported, when vertex V1 has passed the imaging position and has been transported a further distance T2, both vertices V2 and V3, which share an edge with vertex V1, will always pass the imaging position. Therefore, the shape estimation unit 146 can determine that the medium is either the same size as a card or smaller than a card if the detected medium length is less than or equal to the second threshold and the number of detected vertices is 3 or more. Generally, the possibility of transporting a medium smaller than a card is low, so the medium is estimated to be a card.

[0107] On the other hand, the shape estimation unit 146 determines whether the number of vertices is 4 if the media length is less than the second threshold or if the number of vertices is less than 3 (step S307).

[0108] Next, the shape estimation unit 146 estimates that the shape of the medium is that of a card if the number of vertices is 4 (step S402).

[0109] If all vertices pass through the imaging position without satisfying any of the conditions in steps S302 to S307 described above, the shape estimation unit 146 can determine that the medium is either the same size as a card or smaller than a card. Generally, the possibility of a medium smaller than a card being transported is low, so the medium is estimated to be a card.

[0110] On the other hand, if the number of vertices is less than 4, the shape estimation unit 146 determines that it cannot yet estimate the shape of the medium and terminates the series of steps.

[0111] In this way, the shape estimation unit 146 estimates the shape of the medium based on the number of vertices detected by the vertex detection unit 144 and the length of the medium in the medium transport direction detected by the medium length detection unit 145. By estimating the shape of the medium based on the number of vertices and the length of the medium in the medium transport direction, the shape estimation unit 146 can accurately estimate whether or not the medium is a card, even when the medium is transported at an angle. Furthermore, the shape estimation unit 146 can estimate the shape of the medium without performing complex image processing, thereby suppressing an increase in the processing load of the double-feed detection process.

[0112] Furthermore, the shape estimation unit 146 estimates the shape of the medium in real time each time a predetermined number of line images are generated for the sequentially generated line images, so it can estimate the shape of the medium before the entire medium is imaged. In particular, since the shape estimation unit 146 can estimate the shape of the medium early when a medium other than a card is transported, the double-feed detection unit 147 can execute the double-feed detection process described later for medium other than cards at an early stage. On the other hand, since the shape estimation unit 146 does not estimate the shape of the medium to be that of a card until card-specific features are detected, it is possible to prevent the medium from being mistakenly estimated as a card even when a long document such as a receipt is transported in the longitudinal direction.

[0113] If the shape estimation unit 146 estimates that the shape of the medium is not that of a card (step S401), the double feed detection unit 147 determines whether the double feed flag is ON or OFF (step S403). The double feed flag is set to OFF at the start of reading for each medium, and is set to ON when the ultrasonic signal determination process described later determines that the signal value of the ultrasonic signal is below the determination threshold.

[0114] If the double feed flag is ON, the double feed detection unit 147 determines that a double feed has occurred (step S404), sets the double feed flag to OFF, and terminates the series of steps. On the other hand, if the double feed flag is OFF, the double feed detection unit 147 determines that a double feed has not occurred (step S405), and terminates the series of steps. In this way, the double feed detection unit 147 detects double feeds of the transported media.

[0115] On the other hand, if the shape estimation unit 146 estimates that the shape of the medium is that of a card (step S402), the double feed detection unit 147 stops detecting double feeds (step S406) and terminates the series of steps. In this way, the double feed detection unit 147 stops detecting double feeds based on the estimated shape of the medium.

[0116] Figure 12 is a flowchart showing an example of the operation of the ultrasonic signal determination process.

[0117] The following describes an example of the operation of the ultrasonic signal determination process of the double-feed detection device 100, referring to the flowchart shown in Figure 12. The operation flow described below is mainly executed by the CPU 140 in cooperation with each element of the double-feed detection device 100, based on a program pre-stored in the storage device 130. The operation flow shown in Figure 12 is executed periodically during media transport.

[0118] First, the double-feed detection unit 147 acquires an ultrasonic signal from the ultrasonic sensor 114 (step S501).

[0119] Next, the double-feed detection unit 147 determines whether the signal value of the acquired ultrasonic signal is less than the judgment threshold (step S502).

[0120] Figure 13 is a schematic diagram illustrating the characteristics of ultrasonic signals.

[0121] In Graph 1300 of Figure 13, the solid line 1301 shows the characteristics of the ultrasonic signal when a single sheet of paper is being transported as the medium, and the dotted line 1302 shows the characteristics of the ultrasonic signal when a double feed of paper occurs. The horizontal axis of Graph 1300 represents time, and the vertical axis represents the signal value of the ultrasonic signal. Due to the occurrence of a double feed, the signal value of the ultrasonic signal shown by the dotted line 1302 decreases in section 1303. The judgment threshold is set to a value between the signal value S1 of the ultrasonic signal when a single sheet of paper is being transported and the signal value S2 of the ultrasonic signal when a double feed of paper occurs. As a result, the double feed detection unit 147 can determine whether or not a double feed of the medium has occurred by determining whether or not the signal value of the ultrasonic signal is less than the judgment threshold.

[0122] On the other hand, the dashed line 1304 shows the characteristics of the ultrasonic signal when only one card thicker than paper is being transported. When a card is being transported, the signal value of the ultrasonic signal becomes smaller than the judgment threshold, causing the double-feed detection unit 147 to incorrectly determine that a double feed of the medium has occurred. In particular, the signal value of the ultrasonic signal when thin paper is being double-fed is close to the signal value of the ultrasonic signal when a card is being transported, making it difficult to set the judgment threshold to a value between these two signal values. However, the double-feed detection unit 147 stops detecting a double feed when it estimates that the shape of the medium is that of a card, thus preventing errors in detecting a double feed of the medium.

[0123] The double-feed detection unit 147 sets the double-feed flag to ON (step S503) if the ultrasonic signal value is less than the judgment threshold, and terminates the series of steps. On the other hand, if the ultrasonic signal value is greater than or equal to the judgment threshold, the double-feed detection unit 147 terminates the series of steps without performing any special processing. In this way, the double-feed detection unit 147 detects double-feeding of the medium by comparing the ultrasonic signal with the judgment threshold.

[0124] As detailed above, the double-feed detection device 100 stops detecting double feeds based on the shape of the medium by operating according to the flowcharts shown in Figures 5 to 8 and Figure 12. This makes it possible for the double-feed detection device 100 to prevent errors in detecting double feeds of the medium. In addition, the double-feed detection device 100 estimates the shape of the medium based on the medium length and number of vertices of the medium included in the sequentially generated line images. This makes it possible for the double-feed detection device 100 to estimate the shape of the medium before the entire medium is imaged, enabling early estimation of the medium's shape. Therefore, the double-feed detection device 100 can detect double feeds of the medium earlier while preventing errors in detecting double feeds of the medium.

[0125] Furthermore, when users transport the card medium to the double-feed detection device 100, they no longer need to set the double-feed detection function to OFF to prevent the device from mistakenly detecting a double-feed, thus improving user convenience for the double-feed detection device 100.

[0126] Furthermore, since the double-feed detection device 100 can detect whether or not the medium is a card without using special sensors such as thickness sensors, it is possible to suppress an increase in equipment costs.

[0127] Figure 14 is a flowchart showing an example of some of the operations of the double feed detection process according to another embodiment.

[0128] The process shown in Figure 14 is executed instead of the process shown in Figure 8. Note that the process shown in Figure 14 is executed immediately following the processes shown in Figures 6 and 7, similar to the process shown in Figure 8.

[0129] If the shape estimation unit 146 estimates that the shape of the medium is not that of a card (step S601), the double feed detection unit 147 determines whether the first double feed flag is ON or OFF (step S603). The first double feed flag is set to OFF at the start of reading for each medium, and is set to ON when the ultrasonic signal determination process described later determines that the signal value of the ultrasonic signal is less than or equal to the first determination threshold.

[0130] If the first double feed flag is ON, the double feed detection unit 147 determines that a double feed has occurred (step S604), sets the first double feed flag to OFF, and terminates the series of steps. On the other hand, if the first double feed flag is OFF, the double feed detection unit 147 determines that no double feed has occurred (step S605), and terminates the series of steps.

[0131] On the other hand, if the shape estimation unit 146 estimates that the shape of the medium is that of a card (step S602), the double feed detection unit 147 determines whether the second double feed flag is ON or OFF (step S606). The second double feed flag is set to OFF at the start of reading for each medium, and is set to ON when the ultrasonic signal determination process described later determines that the signal value of the ultrasonic signal is less than or equal to the second determination threshold, which is smaller than the first determination threshold.

[0132] If the second double feed flag is ON, the double feed detection unit 147 determines that a double feed has occurred (step S607), sets the second double feed flag to OFF, and terminates the series of steps. On the other hand, if the second double feed flag is OFF, the double feed detection unit 147 determines that no double feed has occurred (step S608), and terminates the series of steps. In this way, the double feed detection unit 147 changes the double feed determination threshold based on the estimated shape of the medium. In particular, if the double feed detection unit 147 determines that the shape of the medium is a card, it changes the determination threshold to a value smaller than the determination threshold when the shape of the medium is not estimated to be a card.

[0133] Figure 15 is a flowchart showing an example of some of the operations of the ultrasonic signal determination process according to another embodiment.

[0134] The process shown in Figure 15 is executed in place of the process shown in Figure 12 when the process shown in Figure 14 is executed instead of the process shown in Figure 8.

[0135] First, the double-feed detection unit 147 acquires an ultrasonic signal from the ultrasonic sensor 114 (step S701).

[0136] Next, the double-feed detection unit 147 determines whether the signal value of the acquired ultrasonic signal is less than the first judgment threshold (step S702). The first judgment threshold is set to a value between the signal value S1 of the ultrasonic signal when a single sheet of paper is being transported and the signal value S2 of the ultrasonic signal when a double-feed of paper occurs, similar to the judgment threshold used in the ultrasonic signal judgment process in Figure 12. In order to prevent double-feed detection errors, it is preferable to set the first judgment threshold to a value sufficiently larger than the signal value S2 of the ultrasonic signal when a double-feed of paper occurs. For this reason, the first judgment threshold is set to a value greater than the signal value S3 of the ultrasonic signal when a card is being transported.

[0137] The double-feed detection unit 147 sets the first double-feed flag to ON if the signal value of the ultrasonic signal is less than the first judgment threshold (step S703). On the other hand, if the signal value of the ultrasonic signal is equal to or greater than the first judgment threshold, the double-feed detection unit 147 does not perform any special processing and proceeds to step S704.

[0138] Next, the double-feed detection unit 147 determines whether the signal value of the acquired ultrasonic signal is less than the second judgment threshold (step S704). The second judgment threshold is set to a value between the signal value S3 of the ultrasonic signal when a card is being transported and the signal value S2 of the ultrasonic signal when a paper double-feed occurs, as shown in Figure 13, so that it is possible to determine whether a card is being transported or a paper double-feed has occurred.

[0139] If the signal value of the ultrasonic signal is less than the second judgment threshold, the double feed detection unit 147 sets the second double feed flag to ON (step S705) and terminates the series of steps. On the other hand, if the signal value of the ultrasonic signal is equal to or greater than the second judgment threshold, the double feed detection unit 147 does not perform any special processing and terminates the series of steps.

[0140] Thus, when the double feed detection unit 147 estimates that a medium other than a card is being transported, it detects a double feed using a first determination threshold set to a value greater than the ultrasonic signal value S3 when a card is being transported. This prevents the double feed detection unit 147 from making errors in detecting double feeds. On the other hand, when the double feed detection unit 147 estimates that a card is being transported, it detects a double feed using a second determination threshold set to a value between the ultrasonic signal value S3 when a card is being transported and the ultrasonic signal value S2 when a paper double feed occurs. This allows the double feed detection unit 147 to correctly detect a double feed even when a double feed occurs of a medium similar in size to a card, such as a business card. Therefore, the double feed detection unit 147 can determine with higher accuracy whether a card is being transported or a paper double feed is occurring.

[0141] As detailed above, the double-feed detection device 100 changes the double-feed detection threshold based on the shape of the media by operating according to the flowcharts shown in Figures 5-6 and 14-15. This makes it possible for the double-feed detection device 100 to determine with high accuracy whether a card is being transported or a paper double-feed has occurred, while preventing errors in detecting double-feeds of media. Therefore, the double-feed detection device 100 can detect double-feeds of media at an earlier stage while preventing errors in detecting double-feeds of media.

[0142] Figure 16 shows a schematic configuration of the processing circuit 250 in a double-feed detection device according to yet another embodiment. The processing circuit 250 is used in place of the processing circuit 150 of the media transport device 100 and performs media reading processing, double-feed detection processing, and ultrasonic signal determination processing in place of the CPU 160. The processing circuit 250 includes a control circuit 251, an image acquisition circuit 252, a media width detection circuit 253, a vertex count detection circuit 254, a media length detection circuit 255, a shape estimation circuit 256, and a double-feed detection circuit 257, etc. Each of these parts may be composed of an independent integrated circuit, microprocessor, firmware, etc.

[0143] The control circuit 251 is an example of a control unit and has the same functions as the control unit 141. The control circuit 251 receives operation signals from the operating device 105 and medium detection signals from the medium detection sensor 111, and drives the drive unit 121 according to each received signal. If a double feed of medium is detected, the control circuit 251 stops the transport of the medium.

[0144] The image acquisition circuit 252 is an example of an image acquisition unit and has the same functions as the image acquisition unit 142. The image acquisition circuit 252 receives line images from the imaging device 117, stores them in the storage device 130, generates an input image from the line images, and transmits it to an information processing device (not shown) via the interface device 122.

[0145] The media width detection circuit 253 is an example of a media width detection unit and has the same function as the media width detection unit 143. The media width detection circuit 253 reads a line image from the storage device 130, detects the media width within the line image, and stores the detection result in the storage device 130.

[0146] The vertex count detection circuit 254 is an example of a vertex count detection unit and has the same function as the vertex count detection unit 144. The vertex count detection circuit 254 reads the detection result of the media width from the storage device 130, detects the number of vertices of the media included in the line image, and stores the detection result in the storage device 130.

[0147] The media length detection circuit 255 is an example of a media length detection unit and has the same function as the media length detection unit 145. The media length detection circuit 255 reads a line image from the storage device 130, detects the media length of the media included in the line image, and stores the detection result in the storage device 130.

[0148] The shape estimation circuit 256 is an example of a shape estimation unit and has the same functions as the shape estimation unit 146. The shape estimation circuit 256 reads the vertex count detection result and the medium length detection result from the storage device 130, estimates the shape of the medium based on each detection result, and stores the estimation result in the storage device 130.

[0149] The double-feed detection circuit 257 is an example of a double-feed detection unit and has the same function as the double-feed detection unit 147. The double-feed detection circuit 257 receives an ultrasonic signal from the ultrasonic sensor 114, detects a double-feed of the medium, and outputs the detection result to the control circuit 251. The double-feed detection circuit 257 also reads the estimated shape of the medium from the storage device 130 and changes the double-feed determination threshold or stops double-feed detection based on the shape of the medium.

[0150] As detailed above, even when using the processing circuit 250, the double-feed detection device can detect double-feeds of media earlier while preventing errors in detection.

[0151] While preferred embodiments have been described above, the embodiments are not limited to these. For example, the shape estimation unit 146 may estimate whether the shape of the medium is not the shape of an ID card as defined in ISO / IEC 7810, but rather another shape.

[0152] For example, the shape estimation unit 146 receives the shape of a medium to change the double-feed detection threshold (e.g., the length of the long side and the short side of a rectangle) or the shape of a medium to stop detecting double feeds, as specified by the user using the operating device 105. Based on the received length of the long side and the short side, the shape estimation unit 146 calculates the distance between the diagonal of the medium and the vertices not included in the diagonal, and sets a first threshold based on the calculated distance. The shape estimation unit 146 also sets a second threshold and a fourth threshold based on the received length of the long side and the short side, calculates the length of the diagonal, and sets a third threshold based on the calculated length of the diagonal. This makes it possible for the user to set the shape of a medium to change the double-feed detection threshold or the shape of a medium to stop detecting double feeds, thereby improving the convenience of the user. [Explanation of symbols]

[0153] 100 Double Feed Detection Device 112 Feeding roller 113 Brake Roller 114 Ultrasonic Sensor 115 First conveyor roller 116 Second conveyor roller 117 Imaging device 143 Media width detection unit 144 Vertex count detection unit 145 Medium length detection unit 146 Shape estimation part 147 Double Feed Detection Unit

Claims

1. A transport unit that transports the media, An ultrasonic sensor including an ultrasonic transmitting unit that emits ultrasonic waves, and an ultrasonic receiving unit that is positioned opposite the ultrasonic transmitting unit and generates a signal corresponding to the received ultrasonic waves, A double-feed detection unit that detects double-feeding of the medium based on the aforementioned signal, An operating unit for setting the shape of the medium that will stop double feeding detection, It includes a detection unit for detecting the shape of the medium conveyed by the conveying unit, The double-feed detection unit stops detecting a double feed if the shape of the medium detected by the detection unit corresponds to the shape of the medium set by the operation unit. A double-feed detection device characterized by the following features.

2. The double-feed detection device according to claim 1, wherein the shape of the medium includes the size of the medium.

3. It further includes an imaging unit that captures images of a medium and generates an image, The double feed detection device according to claim 1 or 2, wherein the double feed detection unit stops detecting a double feed based on the shape of the medium set by the operation unit and the shape of the medium included in the image generated by the imaging unit.

4. The double feed detection device according to claim 3, wherein the double feed detection unit stops detecting a double feed when the shape of the medium included in the image generated by the imaging unit corresponds to the shape of the medium set by the operation unit.

5. A control method for a double-feed detection device having a transport unit for transporting a medium, an ultrasonic transmitting unit for emitting ultrasonic waves, an ultrasonic sensor including an ultrasonic receiving unit positioned opposite the ultrasonic transmitting unit and generating a signal corresponding to the received ultrasonic waves, and a double-feed detection unit for detecting double-feeding of the medium based on the signal, The user can set the shape of the medium that will stop double feeding detection. The shape of the medium conveyed by the conveying unit is detected. When the shape of the detected medium corresponds to the shape set by the user's operation, the double-feed detection device is instructed to stop detecting double feeding. A control method characterized by the following:

6. The control method according to claim 5, wherein the shape of the medium includes the size of the medium.

7. A control program for a double-feed detection device having a transport unit for transporting a medium, an ultrasonic transmitting unit for emitting ultrasonic waves, an ultrasonic sensor including an ultrasonic receiving unit positioned opposite the ultrasonic transmitting unit and generating a signal corresponding to the received ultrasonic waves, and a double-feed detection unit for detecting double-feeding of the medium based on the signal, The user can set the shape of the medium that will stop double feeding detection. The shape of the medium conveyed by the conveying unit is detected. When the shape of the detected medium corresponds to the shape set by the user's operation, the double-feed detection device is instructed to stop detecting double feeding. A control program characterized by the following features.

8. The control program according to claim 7, wherein the shape of the medium includes the size of the medium.

Images