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 multi-feed detection device, and more particularly to a multi-feed detection device that detects multi-feeding of media using ultrasonic waves. [Background technology]

[0002] Devices such as scanners that transport media such as documents and read images on the transported media have a function for detecting whether a multi-feed has occurred, in which multiple media are transported overlapping each other. Generally, multi-feed detection devices such as scanners include an ultrasonic transmitter that transmits ultrasonic waves and an ultrasonic receiver that outputs a signal corresponding to the received ultrasonic waves, and detect multi-feed based on the signal output by the ultrasonic receiver when the media is transported.

[0003] However, the ultrasonic reception level when a plastic card is transported as the medium is close to the ultrasonic reception level when a paper double feed occurs, and if such a card is transported, it may be erroneously determined that a double feed has occurred.

[0004] A medium transport device is disclosed that detects whether or not a double feed of media transported on a transport path based on the output of an ultrasonic sensor having an ultrasonic transmitter and an ultrasonic receiver arranged to face each other across the transport path of the media (see Patent Document 1). This medium transport device distinguishes between a first medium and a second medium transported on the transport path based on the difference in the length of the sides between the first medium and the second medium, and further detects whether or not a double feed of media has occurred based on the discrimination result.

[0005] An image reading device that detects double feeding of documents based on image data obtained by reading documents transported on a transport path has been disclosed (see Patent Document 2). This image reading device estimates the length of the document from the image data, and determines that double feeding of documents has occurred when an edge is detected at a position that is a document length away from the leading edge of the document, and another edge is detected within a range closer than the transport interval of the document from the position that is the document length away. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2013-63843 A [Patent Document 2] JP 2012-253414 A Summary of the Invention [Problem to be solved by the invention]

[0007] It is desirable to prevent false detection of multi-feeds of media.

[0008] It is desirable to prevent false detection of multi-feeds of media. [Means for solving the problem]

[0009] A double-feed detection device according to one aspect of the present invention has a transport section for transporting media, an ultrasonic sensor including an ultrasonic transmitter section for emitting ultrasonic waves and an ultrasonic receiver section arranged opposite the ultrasonic transmitter section and generating a signal in response to the received ultrasonic waves, a double-feed detection section for detecting double-feed of media by comparing the signal with a threshold value, and an operation section for setting the shape of the media at which detection of double-feed will be stopped, and when the shape of the media being transported by the transport section corresponds to the shape of the media set by the operation section, the double-feed detection section stops detecting double-feed of media by comparing the signal with the threshold value.

[0010] Furthermore, a control method according to one aspect of the present invention is a control method for a multi-feed detection device having a transport section for transporting a medium, an ultrasonic sensor including an ultrasonic transmitter section for emitting ultrasonic waves and an ultrasonic receiver section arranged opposite the ultrasonic transmitter section and generating a signal in response to the received ultrasonic waves, and a multi-feed detection section for detecting multi-feed of media by comparing the signal with a threshold value, in which a user's operation is used to set a shape of the medium for which detection of multi-feed will be stopped, and the multi-feed detection device is caused to stop detection of multi-feed, and when the shape of the medium being transported by the transport section corresponds to the shape of the medium set by the user's operation, the multi-feed detection section stops detecting multi-feed of media by comparing the signal with the threshold value.

[0011] Furthermore, a control program according to one aspect of the present invention is a control program for a multi-feed detection device having a transport section for transporting a medium, an ultrasonic sensor including an ultrasonic transmitter section for emitting ultrasonic waves and an ultrasonic receiver section arranged opposite the ultrasonic transmitter section and generating a signal in response to the received ultrasonic waves, and a multi-feed detection section for detecting multi-feed of media by comparing the signal with a threshold value, wherein a user's operation allows the shape of the medium for which detection of multi-feed will be stopped to be set, and the multi-feed detection device is caused to stop detection of multi-feed, and when the shape of the medium being transported by the transport section corresponds to the shape of the medium set by the user's operation, the multi-feed detection section stops detecting multi-feed of media by comparing the signal with the threshold value. Effect of the Invention

[0012] According to the present invention, it is possible to prevent erroneous detection of multiple media feed. [Brief description of the drawings]

[0013] [Figure 1] 1 is a perspective view showing a multifeed detection device 100 according to an embodiment. [Diagram 2] 2 is a diagram for explaining a transport path inside the double feed detection device 100. FIG. [Diagram 3] 1 is a block diagram showing a schematic configuration of a double feed detection device 100. FIG. [Figure 4]FIG. 1 shows a schematic configuration of a storage device 130 and a CPU 140. [Diagram 5] 10 is a flowchart illustrating an example of the operation of a medium reading process. [Figure 6] 10 is a flowchart illustrating an example of an operation of a multifeed detection process. [Figure 7] 10 is a flowchart illustrating an example of an operation of a multifeed detection process. [Figure 8] 10 is a flowchart illustrating an example of an operation of a multifeed detection process. [Figure 9A] 11A and 11B are schematic diagrams for explaining the relationship between the change in medium width and the number of vertices. [Figure 9B] 11A and 11B are schematic diagrams for explaining the relationship between the change in medium width and the number of vertices. [Figure 9C] 11A and 11B are schematic diagrams for explaining the relationship between the change in medium width and the number of vertices. [Figure 9D] 11A and 11B are schematic diagrams for explaining the relationship between the change in medium width and the number of vertices. [Figure 9E] 11A and 11B are schematic diagrams for explaining the relationship between the change in medium width and the number of vertices. [Figure 9F] 11A and 11B are schematic diagrams for explaining the relationship between the change in medium width and the number of vertices. [Figure 10] 11A and 11B are schematic diagrams for explaining the relationship between the change in medium width and the number of vertices. [Figure 11A] FIG. 4 is a schematic diagram for explaining a first threshold value. [Figure 11B] FIG. 11 is a schematic diagram for explaining a second threshold value. [Figure 11C] FIG. 11 is a schematic diagram for explaining a third threshold value. [Figure 11D] FIG. 13 is a schematic diagram for explaining a fourth threshold value. [Figure 12] 10 is a flowchart illustrating an example of an operation of an ultrasonic signal determination process. [Figure 13] 3A and 3B are schematic diagrams for explaining characteristics of an ultrasonic signal. [Figure 14] 10 is a flowchart illustrating an example of a portion of the operation of another multifeed detection process. [Figure 15] 13 is a flowchart illustrating an example of a portion of the operation of another ultrasonic signal determination process. [Figure 16] FIG. 13 is a diagram showing a schematic configuration of a processing circuit 250 in another double feed detection device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, a multi-feed detection device according to one aspect of the present invention will be described with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to the embodiment, but extends to the inventions described in the claims and their equivalents.

[0015] FIG. 1 is a perspective view showing a multi-feed detection device 100 configured as an image scanner. The multi-feed detection device 100 conveys a medium, which is an original, and captures an image. The medium is paper, cardboard, a card, a passport, or the like. The card is, for example, a resin card made of plastic. In particular, the card is an ID (Identification) card defined by ISO (International Organization for Standardization) / IEC (International Electrotechnical Commission) 7810. Note that the card may be other types of cards. The multi-feed detection device 100 may be a facsimile, a copier, a printer / multifunction peripheral (MFP), or the like.

[0016] The double feed detection device 100 includes a lower housing 101, an upper housing 102, a placement table 103, a discharge table 104, an operation device 105, a display device 106, and the like.

[0017] The upper housing 102 is disposed in a position covering the top surface of the double feed detection device 100, and engages with the lower housing 101. The loading platform 103 engages with the lower housing 101 so that the medium to be transported can be loaded thereon. The ejection platform 104 engages with the lower housing 101 so that the ejected medium can be held thereon.

[0018] The operation device 105 has an input device such as a button and an interface circuit for acquiring a signal from the input device, accepts an input operation by a user, and outputs an operation signal according to the input operation by the user. The display device 106 has a display including a liquid crystal, an organic EL (Electro-Luminescence), or the like, and an interface circuit for outputting image data to the display, and displays the image data on the display.

[0019] FIG. 2 is a diagram for explaining the transport path inside the double feed detection device 100. As shown in FIG.

[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. The number of each roller is not limited to one, and each roller may be provided in multiple numbers.

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

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

[0023] The ultrasonic transmitter 114a and the ultrasonic receiver 114b are examples of an ultrasonic transmitter and an ultrasonic receiver, respectively. The ultrasonic transmitter 114a and the ultrasonic receiver 114b are provided downstream of the feed roller 112 and the brake roller 113 and upstream of the first conveyor roller 115 and the second conveyor roller 116, that is, upstream of the first image pickup device 117a and the second image pickup device 117b. The ultrasonic transmitter 114a and the ultrasonic receiver 114b are disposed in the vicinity of the medium conveyance path, facing each other across the conveyance 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 the ultrasonic receiver 114b may be collectively referred to as the ultrasonic sensor 114.

[0024] The first imaging device 117a has a line sensor of a reduction optical system type equipped with imaging elements using CCDs (Charge Coupled Devices) linearly arranged in the main scanning direction. The first imaging device 117a also has a lens that forms an image on the imaging elements, and an A / D converter that amplifies and analog-to-digital (A / D) converts the electrical signal output from the imaging elements. The first imaging device 117a images the back surface of the medium being transported by the feed roller 112, the brake roller 113, the first transport roller 115, and the second transport roller 116. The first imaging device 117a sequentially generates and outputs line images that capture an area of ​​the transported medium facing the line sensor at regular intervals. That is, the number of pixels in the vertical direction (sub-scanning direction) of the line image is one, 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 imaging elements using CCDs linearly arranged in the main scanning direction. The second imaging device 117b also has a lens that forms an image on the imaging element, and an A / D converter that amplifies and analog-to-digital (A / D) converts the electrical signal output from the imaging element. The second imaging device 117b images the surface of the medium being transported by the feed roller 112, the brake roller 113, the first transport roller 115, and the second transport roller 116. The second imaging device 117b sequentially generates and outputs line images obtained by capturing an image of an area of ​​the transported medium facing the line sensor at regular intervals.

[0026] The multifeed detection device 100 may be configured with only one of the first imaging device 117a and the second imaging device 117b, and may read only one side of the medium. Also, a CIS (Contact Image Sensor) of a life-size optical system type having an imaging element based on a CMOS (Complementary Metal Oxide Semiconductor) instead of a CCD may be used. Hereinafter, the first imaging device 117a and the second imaging device 117b may be collectively referred to as the imaging device 117. The imaging device 117 is an example of an imaging section.

[0027] The medium placed on the mounting table 103 is transported between the lower guide 107a and the upper guide 107b in the medium transport direction A1 by the rotation of the feed roller 112 in the direction of the arrow A2 in Fig. 2. The brake roller 113 rotates in the direction of the arrow A3 when transporting the medium. When multiple media are placed on the mounting table 103, the feed roller 112 and the brake roller 113 function to separate only the media placed on the mounting table 103 that is in contact with the feed roller 112. This operates to restrict the transport of media other than the separated media (preventing double feeding).

[0028] The medium is fed between the first conveyor roller 115 and the second conveyor roller 116 while being 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 by the first conveyor roller 115 and the second conveyor roller 116 rotating in the directions of the arrows A4 and A5, respectively. The medium read by the imaging device 117 is discharged onto the discharge table 104 by the third conveyor roller 118 and the fourth conveyor roller 119 rotating in the directions of the arrows A6 and A7, respectively. The feed roller 112, the brake roller 113, the first conveyor roller 115, and the second conveyor roller 116 are an example of a conveying unit that conveys the medium.

[0029] FIG. 3 is a block diagram showing a schematic configuration of the double feed detection device 100. As shown in FIG.

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

[0031] The drive device 121 includes one or more motors, and rotates the feed roller 112, the brake roller 113, the first conveyor roller 115, the second conveyor roller 116, the third conveyor roller 118, and the fourth conveyor roller 119 in response to a control signal from the CPU 140 to convey the medium.

[0032] The interface device 122 has an interface circuit conforming to a serial bus such as USB, and is electrically connected to an information processing device (not shown, for example, a personal computer, a mobile information terminal, etc.) to transmit and receive input images and various information. Also, instead of the interface device 122, a communication unit having an antenna for transmitting and receiving wireless signals and a wireless communication interface device for transmitting and receiving signals through a wireless communication line in accordance with a predetermined communication protocol may be used. The predetermined communication protocol is, for example, a wireless LAN (Local Area Network).

[0033] The storage device 130 includes a memory device such as a random access memory (RAM) or a read only memory (ROM), a fixed disk device such as a hard disk, or a portable storage device such as a flexible disk or an optical disk. The storage device 130 also stores computer programs, databases, tables, and the like used for various processes of the multifeed detection device 100. The computer programs may be installed in the storage device 130 from a computer-readable portable recording medium using a known setup program or the like. The portable recording medium is, for example, a compact disk read only memory (CD-ROM), a digital versatile disk read only memory (DVD-ROM), or the like.

[0034] The CPU 140 operates based on a program previously stored in the storage device 130. Instead of the CPU 140, a digital signal processor (DSP), a large scale integration (LSI), or the like may be used. Instead of the CPU 140, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or the like may be used.

[0035] The CPU 140 is connected to the operation device 105, the display device 106, the medium detection sensor 111, the ultrasonic sensor 114, the imaging device 117, the drive device 121, the interface device 122, the storage device 130, etc., and controls each of these components. The CPU 140 performs drive control of the drive device 121, image capture control of the imaging device 117, etc., acquires images, and transmits them to an information processing device (not shown) via the interface device 122. The CPU 140 also detects multiple feeds of the 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 image after the image processing in the storage device 130. Note that instead of the processing circuit 150, a DSP, an LSI, an ASIC, an FPGA, or the like may be used.

[0037] FIG. 4 is a diagram showing a schematic configuration of the storage device 130 and the CPU 140. As shown in FIG.

[0038] 4, the storage device 130 stores a control program 131, an image acquisition program 132, a medium width detection program 133, a vertex number detection program 134, a medium length detection program 135, a shape estimation program 136, and a multi-feed detection program 137. Each of these programs is a functional module implemented by software that runs on a processor. The CPU 140 reads each program stored in the storage device 130 and operates according to the read program. As a result, the CPU 140 functions as a control unit 141, an image acquisition unit 142, a medium width detection unit 143, a vertex number detection unit 144, a medium length detection unit 145, a shape estimation unit 146, and a multi-feed detection unit 147.

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

[0040] An example of the operation of the medium reading process of the multi-feed detection device 100 will be described below with reference to the flowchart shown in Fig. 5. The flow of the operation described below is executed mainly by the CPU 140 in cooperation with each element of the multi-feed detection device 100 based on a program previously stored in the storage device 130. The flow of the operation shown in Fig. 5 is executed periodically.

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

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

[0043] If no medium is placed on the placement table 103, the control unit 141 returns the process to step S101 and waits until a new operation signal is received from the operation device 105.

[0044] On the other hand, if a medium is placed on the placement table 103, the control unit 141 drives the drive device 121 to rotate the feed roller 112, the 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 imaging device 117 to capture an image of the transported medium, and acquires a line image (step S104).

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

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

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

[0049] On the other hand, if no double feed is 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 whether the rear end of the medium has passed the imaging device 117, for example, based on a medium detection signal output from a medium detection sensor (not shown) provided downstream of the imaging device 117. Note that the image acquisition unit 142 may determine that the entire transported medium has been imaged when it acquires a predetermined number of line images from the imaging device 117.

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

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

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

[0053] Next, control unit 141 determines whether or not a medium remains on mounting table 103 based on a medium detection signal received from medium detection sensor 111 (step S111). If a medium remains on mounting table 103, control unit 141 returns the process to step S104, and repeats the processes of steps S104 to S111.

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

[0055] 6 to 8 are flowcharts showing an example of the operation of the double feed detection process.

[0056] The operational flow shown in FIGS. 6 to 8 is executed in step S105 of the flowchart shown in FIG.

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

[0058] The medium width detection unit 143 may calculate the absolute value of the difference between the luminance values ​​of two pixels that are a predetermined distance away from each pixel in the line image as the adjacent difference value. The medium width detection unit 143 may also 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. The medium width detection unit 143 may extract edge pixels by comparing the luminance value or color value of the line image with a threshold value. For example, when the luminance value or color value of a specific pixel is less than the threshold value and the luminance value or color value of a pixel adjacent to the specific pixel or a pixel that is a predetermined distance away from the specific pixel is equal to or greater than the threshold value, the medium width detection unit 143 determines that the specific pixel is an edge pixel.

[0059] Next, the medium width detection unit 143 detects the medium width in 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 medium width detection unit 143 detects the medium width in each line image for each line image generated sequentially. The medium width detection unit 143 identifies the edge pixel located on the leftmost side and the edge pixel located on the rightmost side among the edge pixels extracted from the line image, and detects the distance (number of pixels) between the identified edge pixels as the medium width.

[0060] Next, the shape estimation unit 146 judges whether the detected medium width exceeds a predetermined length (step S203). The predetermined length is set based on the size of an ID card defined by, for example, ISO / IEC 7810. The ID card defined by ISO / IEC 7810 has a substantially rectangular shape with a long side of 85.60 mm and a short side of 53.98 mm. The angles of the four vertices of the ID card may not be right angles and may be rounded. The predetermined length is set to the number of pixels equivalent to the value (for example, 102 mm) obtained by adding a margin to the diagonal length (101.20 mm) of the ID card, for example. No matter how inclined the ID card is conveyed, the width of the ID card captured in the imaging line of the imaging device 117 does not exceed the defined diagonal length.

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

[0062] On the other hand, if the detected medium width does not exceed the predetermined length, the vertex number detection unit 144 determines whether or not a predetermined number of line images have been newly acquired for which the detection process for the number of vertices of the medium has not been performed (step S204). The predetermined number is set to a pixel number (e.g., 3) that allows a change in the medium width in the sub-scanning direction to be detected satisfactorily. The predetermined number may also be 1. If the predetermined number of line images has not been newly acquired, the vertex number detection unit 144 ends the series of steps. That is, the processes of the following steps S205 to S406 are executed each time a predetermined number of line images are newly generated.

[0063] On the other hand, when a predetermined number of line images are newly acquired, the vertex number detection unit 144 judges whether or not a medium width equal to or greater than the 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, one pixel. The predetermined width may be set to a value of two pixels or more so that the influence of noise is eliminated.

[0064] If a medium width equal to or greater than the predetermined width has not yet been detected, the vertex number detection unit 144 determines that the number of vertices of the medium included in the line image acquired so far is 0 (step S206), and ends the series of steps.

[0065] On the other hand, if a medium width equal to or greater than the predetermined width is detected, the vertex number detection unit 144 detects a change in the medium width in each line image. The vertex number detection unit 144 specifies the latest line image among the predetermined number of newly acquired line images as the target image, and specifies the line image acquired immediately before acquiring the predetermined number of line images as the reference image. Note that the vertex number detection unit 144 may use an image in which the average or median value of corresponding pixels in the multiple line images acquired immediately before is used as the gradation value of each pixel as the reference image. This allows the vertex number detection unit 144 to improve the reliability of the reference image.

[0066] The vertex number detection unit 144 determines whether the medium width in the target image is larger than the medium width in the reference image (step S207). Note that the vertex number detection unit 144 may determine that the medium width in the target image is larger than the medium width in the reference image only when the medium width in the target image is larger than the medium width in the reference image and the difference between the medium width in the target image and the medium width in the reference image is a predetermined difference (e.g., 3 pixels) or more.

[0067] If the medium width in the target image is larger than the medium width in the reference image, the vertex number detection unit 144 determines that the number of vertices of the medium contained in the line image acquired so far is 1 (step S208) and transitions to step S301.

[0068] 9A to 9F and 10 are schematic diagrams for explaining the relationship between the change in medium width and the number of vertices.

[0069] 9A to 9F show a rectangular medium M being transported at an angle. As shown in FIGS. 9A to 9F, the medium M may be transported at an angle, and when the medium M is transported at an angle, each of the vertices V1 to V4 of the medium M passes through the imaging position of the imaging device 117 at different times. FIG. 10 shows a plurality of line images P0 to P9 captured while the medium M is being transported. Note that for ease of explanation, only a plurality of line images P0 to P9 are shown in FIG. 10, but many line images are captured while each line image is captured.

[0070] FIG. 9A shows the medium M in a state where none of the vertices have yet reached the imaging position, and the line image P0 in FIG. 10 is imaged at this timing. FIG. 9B shows the medium M immediately after the first vertex V1 has passed the imaging position, and the line image P1 in FIG. 10 is imaged at this timing. FIG. 9C shows the medium M in a state where the second vertex V2 has reached the imaging position, and the line image P3 in FIG. 10 is imaged at this timing. FIG. 9D shows the medium M in a state where the third vertex V3 has reached the imaging position, and the line image P6 in FIG. 10 is imaged at this timing. FIG. 9E shows the medium M just before the fourth vertex V4 reaches the imaging position, and the line image P8 in FIG. 10 is imaged at this timing. FIG. 9F shows the medium M in a state where all of the vertices have passed the imaging position, and the line image P9 in FIG. 10 is imaged at this timing.

[0071] 10, the line images from the line image captured immediately before line image P1 to the line image captured immediately before line image P3 each include only one vertex V1. In these line images, the distance D between the edge pixels L and R at both ends increases with each new line image captured. In other words, when the medium width in the target image is greater than the medium width in the reference image, the vertex number detection unit 144 can determine that the number of vertices of the medium included in the line images acquired up to now is one.

[0072] On the other hand, if the medium width in the target image is not larger than the medium width in the reference image, the vertex number detection unit 144 determines whether the medium width in the target image is the same as the medium width in the reference image (step S209). Note that, if the difference between the medium width in the target image and the medium width in the reference image is equal to or smaller than a predetermined difference, the vertex number detection unit 144 may determine that the medium width in the target image is the same as the medium width in the reference image.

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

[0074] 10, the line images from the line image captured immediately before line image P1 to the line image captured immediately before line image P6 include two vertices V1 and V2. The distance D between the edge pixels L and R at both ends is the same in each line image from the line image captured immediately after line image P3 to the line image captured immediately before line image P6. In other words, when the medium width in the target image is the same as the medium width in the reference image, the vertex number detection unit 144 can determine that the number of vertices of the medium included in the line images acquired so far is two.

[0075] Note that, since the medium width in line image P3 is greater than that of the line image captured immediately before, the number of vertices of the medium included in the line image acquired up to that point is determined to be 1. However, the medium width of the line image captured next is the same as that of the line image P3 captured immediately before, and the number of vertices of the medium included in the line image acquired up to that point is determined to be 2. Therefore, although the timing at which the number of vertices is correctly detected is delayed by one line pixel, the interval at which each line image is captured is sufficiently short, so that the vertex number detection unit 144 can detect the number of vertices with sufficiently high accuracy.

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

[0077] If the medium width in the target image is greater than 0, i.e., if a medium is present in the target image, the vertex number detection unit 144 determines that the number of vertices of the medium contained in the line image acquired so far is 3 (step S212), and transitions to step S301.

[0078] 10, the line images from the line image captured immediately before line image P1 to line image P8 include three vertices V1, V2, and V3. In addition, in each of the line images from the line image captured immediately after line image P6 to line image P8, the distance D between the edge pixels L and R at both ends decreases with each line image captured more recently, and a medium is present. In other words, when the medium width in the target image is smaller than the medium width in the reference image and a medium is present in the target image, the vertex number detection unit 144 can determine that the number of vertices of the medium included in the line images acquired up to now is three.

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

[0080] On the other hand, if the medium width in the target image is 0, i.e., if no medium is present in the target image, the vertex number detection unit 144 determines that the number of vertices of the medium contained in the line image acquired so far is 4 (step S213), and transitions to step S301.

[0081] 10, the line images from the line image captured immediately before the line image P1 to the line image captured after the line image P8 include four vertices V1, V2, V3, and V4. The line image captured after the line image P8 does not include the medium M. That is, when no medium exists in the target image, the vertex number detection unit 144 can determine that the number of vertices of the medium included in the line images acquired up to now is four.

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

[0083] Next, the medium length detection unit 145 detects the medium length in the vertical direction (sub-scanning direction) of the medium contained in the line images acquired so far, i.e., in the direction perpendicular to the medium width (step S301). As described above, the number of pixels in the vertical direction (sub-scanning direction) of the line image is 1. The medium length detection unit 145 detects the number of images from the line image in which a medium width equal to or greater than a predetermined width was first detected for the medium to the most recent line image or the line image in which the medium width first became 0 as the medium length (number of pixels in the vertical direction) of the medium contained in the line image. In this way, the medium length detection unit 145 detects the medium length in the direction perpendicular to the medium width of the medium contained in the line images generated sequentially.

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

[0085] FIG. 11A is a schematic diagram for explaining the first threshold value.

[0086] 11A, the first threshold is set to the number of pixels equivalent to a value (e.g., 46 mm) that includes a margin added to the distance T1 (45.66 mm) between the diagonal X of the ID card C defined by, for example, ISO / IEC 7810 and a vertex that is not included in the diagonal X. Note that the distance T1 is calculated by solving the following relational expressions (1) and (2) with the long side of the ID card C being W (85.60 mm) and the short side being H (53.98 mm). H 2 +W 2 =X 2 (1) H×W=X×T1 (2)

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

[0088] When the ID card C is transported, no matter how tilted the ID card C is, when the ID card C is transported a distance T1 after the vertex V1 has passed the imaging position, at least one of the vertex V2 and the vertex V3, which share an edge with the vertex V1, always passes the imaging position. Therefore, when the medium length detected by the medium length detection unit 145 is equal to or greater than the first threshold value and the number of vertices detected by the vertex number detection unit 144 is less than 2, the shape estimation unit 146 can determine that the medium is larger than a card.

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

[0090] FIG. 11B is a schematic diagram for explaining the second threshold value.

[0091] As shown in FIG. 11B, the second threshold is set to the number of pixels equivalent to a value (eg, 86 mm) adding a margin to the length T2 (85.60 mm) of the long side W of the ID card C defined by ISO / IEC7810, for example.

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

[0093] When the ID card C is transported, no matter how the ID card C is transported, when the ID card C is transported a further distance T2 after the vertex V1 has passed the imaging position, both the vertex V2 and the vertex V3, which share an edge with the vertex V1, always pass the imaging position. Therefore, when the medium length detected by the medium length detection unit 145 is equal to or greater than the second threshold value and the number of vertices detected by the vertex number detection unit 144 is less than 3, the shape estimation unit 146 can determine that the medium is larger than a card.

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

[0095] FIG. 11C is a schematic diagram for explaining the third threshold value.

[0096] As shown in FIG. 11C, the third threshold is set to the number of pixels equivalent to a value (eg, 102 mm) obtained by adding a margin to the length T3 (101.20 mm) of the diagonal X of the ID card C defined by ISO / IEC7810, for example.

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

[0098] When the ID card C is transported, no matter how inclined the ID card C is, after the vertex V1 passes the imaging position, all of the other vertices V2 to V4 pass the imaging position before the ID card C is transported a distance T3. Therefore, when the medium length detected by the medium length detection unit 145 is equal to or greater than the third threshold value and the number of vertices detected by the vertex number detection unit 144 is not four, the shape estimation unit 146 can determine that the medium is larger than a card.

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

[0100] FIG. 11D is a schematic diagram for explaining the fourth threshold value.

[0101] As shown in FIG. 11D, the fourth threshold is set to the number of pixels equivalent to a value (eg, 53 mm) obtained by subtracting a margin from the length T4 (53.98 mm) of the short side H of an ID card C defined by ISO / IEC7810, for example.

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

[0103] When the ID card C is transported, no matter how the ID card C is transported, all of the other vertices V2 to V4 will not pass the imaging position before the vertex V1 has passed the imaging position and been transported a distance T4. Therefore, when 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, the shape estimation unit 146 can determine that the medium is smaller than a card.

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

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

[0106] 11D, when ID card C is transported, no matter how ID card C is transported, when vertex V1 passes the imaging position and is transported a distance T2, both vertices V2 and V3, which share an edge with vertex V1, always pass the imaging position. Therefore, when the detected medium length is equal to or less than the second threshold and the detected number of vertices is three or more, the shape estimation unit 146 can determine that the medium is a medium having a size equivalent to that of a card or a medium smaller than a card. In general, it is unlikely that a medium smaller than a card is transported, so the medium is estimated to be a card.

[0107] On the other hand, if the medium length is less than the second threshold or the number of vertices is less than three, the shape estimation unit 146 determines whether the number of vertices is four (Step S307).

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

[0109] If all the vertices pass the imaging position without satisfying the conditions in steps S302 to S307, shape estimation unit 146 can determine that the medium is a medium having a size similar to that of a card or a medium smaller than a card. In general, since it is unlikely that a medium smaller than a card is transported, the medium is estimated to be a card.

[0110] On the other hand, if the number of vertices is less than four, shape estimation unit 146 determines that the shape of the medium cannot yet be estimated, and ends the series of steps.

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

[0112] Furthermore, the shape estimation unit 146 estimates the shape of the medium in real time for each of the sequentially generated line images each time a predetermined number of line images are generated, and therefore can estimate the shape of the medium before the entire medium is imaged. In particular, the shape estimation unit 146 can estimate the shape of the medium early when a medium other than a card is transported, and therefore the multi-feed detection unit 147 can quickly execute the multi-feed detection process described below for media other than cards. Meanwhile, the shape estimation unit 146 does not estimate that the shape of the medium is that of a card until a characteristic specific to a card is detected, and therefore can prevent the medium from being erroneously estimated as a card even when a long document such as a receipt is transported in the longitudinal direction.

[0113] When the shape estimation unit 146 estimates that the shape of the medium is not the shape of a card (step S401), the multi-feed detection unit 147 determines whether the multi-feed flag is ON (step S403). The multi-feed flag is set to OFF when reading of each medium starts, and is set to ON when it is determined in the ultrasonic signal determination process described later that the signal value of the ultrasonic signal is equal to or less than the determination threshold.

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

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

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

[0117] An example of the operation of the ultrasonic signal determination process of the multi-feed detection device 100 will be described below with reference to the flowchart shown in Fig. 12. Note that the flow of the operation described below is executed mainly by the CPU 140 in cooperation with each element of the multi-feed detection device 100 based on a program previously stored in the storage device 130. The flow of the operation shown in Fig. 12 is executed periodically during medium 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 or not the signal value of the acquired ultrasonic signal is less than the determination threshold value (step S502).

[0120] FIG. 13 is a schematic diagram for explaining the characteristics of an ultrasonic signal.

[0121] In graph 1300 of Fig. 13, solid line 1301 indicates the characteristics of the ultrasonic signal when a single sheet of paper is being transported as a medium, and dotted line 1302 indicates the characteristics of the ultrasonic signal when a double feed of paper occurs. The horizontal axis of graph 1300 indicates time, and the vertical axis indicates the signal value of the ultrasonic signal. Due to the occurrence of a double feed, the signal value of the ultrasonic signal of dotted line 1302 drops in section 1303. The determination 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. This allows the double feed detection unit 147 to determine whether a double feed of media has occurred by determining whether the signal value of the ultrasonic signal is less than the determination threshold.

[0122] On the other hand, dashed line 1304 indicates the characteristics of the ultrasonic signal when only one card, which is thicker than paper, is being transported. When a card is being transported, the signal value of the ultrasonic signal is smaller than the judgment threshold, and so the multi-feed detection unit 147 erroneously judges that a multi-feed of media has occurred. In particular, the signal value of the ultrasonic signal when a multi-feed of thin paper has occurred is close to the signal value of the ultrasonic signal when a card is being transported, and it is difficult to set the judgment threshold to a value between these two signal values. However, when the multi-feed detection unit 147 estimates that the shape of the medium is the shape of a card, it stops detecting the multi-feed, and therefore it is possible to prevent erroneous detection of a multi-feed of media.

[0123] If the signal value of the ultrasonic signal is less than the judgment threshold, the multi-feed detection unit 147 sets the multi-feed flag to ON (step S503) and ends the series of steps. On the other hand, if the signal value of the ultrasonic signal is equal to or greater than the judgment threshold, the multi-feed detection unit 147 does not execute any particular process and ends the series of steps. In this way, the multi-feed detection unit 147 detects multi-feed of media by comparing the ultrasonic signal with the judgment threshold.

[0124] As described above in detail, the multi-feed detection device 100 stops detection of multi-feeding based on the shape of the medium by operating according to the flowcharts shown in Figs. 5 to 8 and 12. This allows the multi-feed detection device 100 to prevent errors in detecting multi-feeding of media. The multi-feed detection device 100 also estimates the shape of the medium based on the medium length and the number of vertices of the medium included in the line images generated sequentially. This allows the multi-feed detection device 100 to estimate the shape of the medium before the entire medium is imaged, making it possible to estimate the shape of the medium at an early stage. Therefore, the multi-feed detection device 100 is able to detect multi-feeding of media at an earlier stage while preventing errors in detecting multi-feeding of media.

[0125] In addition, when the user has the multi-feed detection device 100 transport card media, the user no longer needs to set the multi-feed detection function to OFF in order to prevent the multi-feed detection device 100 from mistakenly detecting that a multi-feed of media has occurred, making it possible for the multi-feed detection device 100 to improve user convenience.

[0126] Furthermore, the double feed detection device 100 can detect whether or not the medium is a card without using a special sensor such as a thickness sensor, making it possible to suppress increases in device costs.

[0127] FIG. 14 is a flowchart showing an example of part of the operation of a multifeed detection process according to another embodiment.

[0128] The process shown in Fig. 14 is executed in place of the process shown in Fig. 8. Note that the process shown in Fig. 14 is executed following the processes shown in Figs. 6 to 7, similar to the process shown in Fig. 8.

[0129] When the shape estimation unit 146 estimates that the shape of the medium is not that of a card (step S601), the multifeed detection unit 147 determines whether or not a first multifeed flag is ON (step S603). The first multifeed flag is set to OFF when reading of each medium starts, and is set to ON when it is determined in the ultrasonic signal determination process described below that the signal value of the ultrasonic signal is equal to or less than a first determination threshold.

[0130] If the first multifeed flag is ON, the multifeed detection unit 147 determines that a multifeed has occurred (step S604), sets the first multifeed flag to OFF, and ends the series of steps. On the other hand, if the first multifeed flag is OFF, the multifeed detection unit 147 determines that a multifeed has not occurred (step S605), and ends the series of steps.

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

[0132] If the second multifeed flag is ON, the multifeed detection unit 147 determines that a multifeed has occurred (step S607), sets the second multifeed flag to OFF, and ends the series of steps. On the other hand, if the second multifeed flag is OFF, the multifeed detection unit 147 determines that a multifeed has not occurred (step S608), and ends the series of steps. In this manner, the multifeed detection unit 147 changes the determination threshold for multifeed based on the estimated shape of the medium. In particular, if the shape of the medium is estimated to be the shape of a card, the multifeed detection unit 147 changes the determination threshold to a value smaller than the determination threshold when the shape of the medium is estimated to be not the shape of a card.

[0133] FIG. 15 is a flowchart showing an example of a part of the operation of the ultrasound signal determination process according to another embodiment.

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

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

[0136] Next, the multi-feed detection unit 147 judges whether the signal value of the acquired ultrasonic signal is less than a first judgment threshold (step S702). The first judgment threshold is set to a value between the signal value S1 of the ultrasonic signal when one sheet of paper is being conveyed and the signal value S2 of the ultrasonic signal when a multi-feed of paper occurs, as in the judgment threshold used in the ultrasonic signal judgment process of FIG. 12. In order to prevent an error in detecting a multi-feed, it is preferable that the first judgment threshold is set to a value sufficiently larger than the signal value S2 of the ultrasonic signal when a multi-feed of paper occurs. Therefore, the first judgment threshold is set to a value larger than the signal value S3 of the ultrasonic signal when a card is being conveyed.

[0137] If the signal value of the ultrasonic signal is less than the first determination threshold, the multifeed detection unit 147 sets the first multifeed flag to ON (step S703). On the other hand, if the signal value of the ultrasonic signal is equal to or greater than the first determination threshold, the multifeed detection unit 147 does not execute any particular process and shifts the process to step S704.

[0138] Next, the multifeed detection unit 147 determines whether the signal value of the acquired ultrasonic signal is less than a second determination threshold (step S704). The second determination threshold is set to a value between the signal value S3 of the ultrasonic signal when a card is being conveyed and the signal value S2 of the ultrasonic signal when a multifeed of paper is occurring, as shown in FIG. 13, so that it is possible to determine whether a card is being conveyed or a multifeed of paper is occurring.

[0139] If the signal value of the ultrasonic signal is less than the second determination threshold, the multifeed detection unit 147 sets the second multifeed flag to ON (step S705) and ends the series of steps. On the other hand, if the signal value of the ultrasonic signal is equal to or greater than the second determination threshold, the multifeed detection unit 147 does not execute any particular process and ends the series of steps.

[0140] In this way, when it is estimated that a medium other than a card is being transported, the multi-feed detection unit 147 detects the multi-feed using the first determination threshold set to a value greater than the signal value S3 of the ultrasonic signal when a card is being transported. This allows the multi-feed detection unit 147 to prevent the occurrence of an erroneous detection of the multi-feed. On the other hand, when it is estimated that a card is being transported, the multi-feed detection unit 147 detects the multi-feed using the second determination threshold 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 multi-feed of paper occurs. This allows the multi-feed detection unit 147 to correctly detect the occurrence of the multi-feed even when a multi-feed of media having a size similar to that of a card, such as a business card, occurs. Therefore, the multi-feed detection unit 147 can more accurately determine whether a card is being transported or a multi-feed of paper occurs.

[0141] As described above in detail, the multi-feed detection device 100 changes the multi-feed determination threshold based on the shape of the medium by operating according to the flowcharts shown in Figures 5-6 and 14-15. This allows the multi-feed detection device 100 to determine with high accuracy whether a card is being transported or a multi-feed of paper has occurred while preventing erroneous detection of multi-feed of media. Therefore, the multi-feed detection device 100 can detect multi-feed of media at an earlier stage while preventing erroneous detection of multi-feed of media.

[0142] 16 is a diagram showing a schematic configuration of a processing circuit 250 in a multi-feed detection device according to yet another embodiment. The processing circuit 250 is used in place of the processing circuit 150 of the medium conveying device 100, and executes the medium reading process, the multi-feed detection process, and the ultrasonic signal determination process in place of the CPU 160. The processing circuit 250 has a control circuit 251, an image acquisition circuit 252, a medium width detection circuit 253, a vertex number detection circuit 254, a medium length detection circuit 255, a shape estimation circuit 256, a multi-feed detection circuit 257, and the like. Each of these components may be formed of an independent integrated circuit, microprocessor, firmware, and the like.

[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 an operation signal from the operation device 105 and a medium detection signal from the medium detection sensor 111, drives the drive device 121 in response to each of the received signals, and stops transport of the media when a double feed of media is detected.

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

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

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

[0147] The medium length detection circuit 255 is an example of a medium length detection unit, and has the same function as the medium length detection unit 145. The medium length detection circuit 255 reads the line image from the storage device 130, detects the medium length of the medium 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 function as the shape estimation unit 146. The shape estimation circuit 256 reads out the detection results of the number of vertices and the detection results of the medium length 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 multi-feed detection circuit 257 is an example of a multi-feed detection section, and has the same function as the multi-feed detection section 147. The multi-feed detection circuit 257 receives an ultrasonic signal from the ultrasonic sensor 114, detects multi-feeding of media, and outputs the detection result to the control circuit 251. The multi-feed detection circuit 257 also reads out the estimated result of the shape of the media from the storage device 130, and changes the determination threshold for multi-feeding or stops detection of multi-feeding based on the shape of the media.

[0150] As described above in detail, even when the processing circuit 250 is used, the multi-feed detection device is able to detect multi-feed of media at an earlier stage while preventing erroneous detection of multi-feed of media.

[0151] Although the 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 defined in ISO / IEC 7810, but is another shape.

[0152] For example, the shape estimation unit 146 accepts the shape of the medium for which the double feed determination threshold is changed (for example, the length of the long side and the length of the short side of a rectangle) or the shape of the medium for which detection of double feed is stopped, which is specified by the user using the operation device 105. The shape estimation unit 146 calculates the distance between the diagonal line of the medium and the vertex not included in the diagonal line based on the accepted length of the long side and the short side, and sets the first threshold value based on the calculated distance. The shape estimation unit 146 also sets the second threshold value and the fourth threshold value based on the accepted length of the long side and the short side, calculates the length of the diagonal line, and sets the third threshold value based on the calculated length of the diagonal line. This allows the user to set the shape of the medium for which the double feed determination threshold is changed or the shape of the medium for which detection of double feed is stopped, and the double feed detection device can improve 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 detector 144 Vertex Count Detection Unit 145 Media length detector 146 Shape estimation part 147 Double feed detector

Claims

1. A transport unit that transports the medium; an ultrasonic sensor including an ultrasonic transmitter that transmits ultrasonic waves, and an ultrasonic receiver that is disposed opposite the ultrasonic transmitter and generates a signal in response to the received ultrasonic waves; a multi-feed detection unit that detects multi-feeding of media by comparing the signal with a threshold; an operation unit for setting a shape of a medium for which detection of a double feed is to be stopped; the double feed detection unit stops detecting double feed of media by comparing the signal with the threshold value when the shape of the medium being transported by the transport unit corresponds to the shape of the medium set by the operation unit. A double feed detection device comprising:

2. An imaging unit that captures an image of the medium and generates an image, The multi-feed detection device according to claim 1 , wherein the multi-feed detection unit stops detecting the multi-feed based on a shape of the medium set by the operation unit and a shape of the medium included in the image generated by the imaging unit.

3. The multi-feed detection device according to claim 2 , wherein the multi-feed detection unit stops detecting the multi-feed when a shape of the medium included in the image generated by the imaging unit corresponds to a shape of the medium set by the operation unit.

4. A method for controlling a multi-feed detection device having a transport section for transporting a medium, an ultrasonic sensor including an ultrasonic transmitter section for transmitting ultrasonic waves, and an ultrasonic receiver section disposed opposite the ultrasonic transmitter section and for generating a signal in response to the received ultrasonic waves, and a multi-feed detection section for detecting multi-feeding of media by comparing the signal with a threshold value, comprising: A user sets a shape of a medium for which detection of double feed is to be stopped, and causes the double feed detection device to stop detecting double feed; the double feed detection unit stops detecting the double feed of the medium by comparing the signal with the threshold value when the shape of the medium being transported by the transport unit corresponds to the shape of the medium set by a user operation. A control method comprising:

5. A control program for a multi-feed detection device having an ultrasonic sensor including a transport unit for transporting a medium, an ultrasonic transmitter for transmitting ultrasonic waves, and an ultrasonic receiver arranged opposite the ultrasonic transmitter and for generating a signal in response to the received ultrasonic waves, and a multi-feed detection unit for detecting multi-feeding of media by comparing the signal with a threshold value, A user sets a shape of a medium for which detection of double feed is to be stopped, and causes the double feed detection device to stop detecting double feed; the double feed detection unit stops detecting the double feed of the medium by comparing the signal with the threshold value when the shape of the medium being transported by the transport unit corresponds to the shape of the medium set by a user operation. A control program comprising:

Images