Medium conveying device, control method, and control program

Abstract

To provide a medium conveyance device, a control method and a control program which can highly accurately determine whether double feed of a medium has occurred.SOLUTION: A medium conveyance device includes: a conveyance part for conveying a medium; a detection part for detecting permeation information on ultrasonic waves permeating through the medium or thickness information on the medium at a plurality of positions of the medium to be conveyed; a calculation part for calculating the size of an area where the permeation information or the thickness information in the medium to be conveyed is within a predetermined range; a determination part for comparing the value based on the permeation information or the thickness information with a threshold, and thereby determining whether double feed of the medium has occurred; and a control part for executing abnormality processing when it is determined that double feed of the medium has occurred. The determination part changes a threshold according to the size.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a medium transport device, and more particularly to a medium transport device that determines whether or not a multi-feed of media has occurred. [Background technology]

[0002] Generally, media transport devices such as scanners have the ability to detect whether a multi-feed, in which multiple media are transported together, has occurred and automatically stop transport of the media when a multi-feed occurs. However, when a medium with a photo attached, such as a resume, is transported, the media transport device may determine that a multi-feed has occurred and stop transport. Therefore, when scanning a medium with a photo attached, users must turn off the multi-feed detection function before transporting the medium, which reduces user convenience.

[0003] A multi-feed detection device has been disclosed that has a transport roller for transporting documents and a driven roller that is pressed against the transport roller with a predetermined biasing force and is displaceable according to the thickness of the documents (see Patent Document 1). This multi-feed detection device controls so as to prohibit multi-feed detection if the increase in the displacement of the driven roller detected while the documents pass between the two rollers is shorter than a predetermined time.

[0004] A method for receiving articles to be processed and detecting overlapping of the articles has been disclosed (see Patent Document 2). In this method, it is determined whether the overlapping position of the overlapping articles is within an acceptable range, and if the position is within a predetermined overlapping standard, the processing of the articles continues, and if the position is not within the predetermined overlapping standard, the processing of the articles is stopped. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 7-291485 [Patent Document 2] US Patent Application Publication No. 2005 / 0228535 Summary of the Invention [Problem to be solved by the invention]

[0006] It is desirable for a medium transport device to be able to determine with higher accuracy whether or not a double feed of media has occurred.

[0007] An object of the present invention is to provide a medium transport device, a control method, and a control program that can determine with higher accuracy whether or not a multi-feed of media has occurred. [Means for solving the problem]

[0008] A medium transport device according to one aspect of the present invention includes a transport unit that transports a medium. and a determination unit that determines whether or not a double feed of media has occurred by comparing a value based on measurement information measured for the transported media with a threshold value, and changes the threshold value depending on the length of an area where overlapping of media has occurred in the transported media. .

[0009] In addition, according to one aspect of the present invention Media transport The method is: The conveying section Transporting media and comparing a value based on measurement information measured for the transported medium with a threshold value to determine whether or not a double feed of media has occurred, and changing the threshold value according to the length of the area where the overlapping of media has occurred in the transported medium. .

[0010] A control program according to one aspect of the present invention is a control program for a medium transport device having a transport unit that transports a medium, the control program comprising: By comparing a value based on measurement information measured for the transported medium with a threshold value, it is determined whether or not a double feed of media has occurred, and the threshold value is changed depending on the length of the area where the overlapping of media has occurred in the transported medium. This is performed by the media transport device. Let . [Effects of the Invention]

[0011] According to the present invention, the medium conveying device, the control method, and the control program are capable of determining with higher accuracy whether or not a multi-feed of media has occurred. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a perspective view showing a medium conveying device 100 according to an embodiment. [Figure 2] 2 is a diagram for explaining a transport path inside the medium transport device 100. FIG. [Figure 3] 1 is a block diagram showing a schematic configuration of a medium conveying device 100. FIG. [Figure 4]FIG. 2 is a diagram showing a schematic configuration of a storage device 140 and a processing circuit 150. [Figure 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 the operation of a multifeed detection process. [Figure 7A] FIG. 10 is a schematic diagram for explaining the technical significance. [Figure 7B] FIG. 10 is a schematic diagram for explaining the technical significance. [Figure 7C] FIG. 10 is a schematic diagram for explaining the technical significance. [Figure 8] 10 is a flowchart illustrating an example of another operation of the multifeed detection process. [Figure 9] 10 is a diagram for explaining a transport path inside another medium transport device 200. FIG. [Figure 10A] FIG. 10 is a schematic diagram for explaining the technical significance. [Figure 10B] FIG. 10 is a schematic diagram for explaining the technical significance. [Figure 10C] FIG. 10 is a schematic diagram for explaining the technical significance. [Figure 11] FIG. 10 is a diagram showing a schematic configuration of a processing circuit 350 in another medium conveying device. DETAILED DESCRIPTION OF THE INVENTION

[0013] A medium conveying device, a control method, and a control program according to one aspect of the present invention will be described below with reference to the drawings. However, please note that the technical scope of the present invention is not limited to the embodiments, but extends to the inventions set forth in the claims and their equivalents.

[0014] FIG. 1 is a perspective view showing a medium conveying device 100 configured as an image scanner. The medium conveying device 100 conveys and captures an image of a medium, which is an original document. The medium is paper, cardboard, card, or the like. The medium also includes media with attached objects such as labels (stickers) or small pieces of paper (photographs, clippings, postage stamps, revenue stamps, etc.). The medium conveying device 100 may be a facsimile, a copier, a multifunction printer (MFP), or the like. Note that the medium being conveyed may not be an original document but may be a print target or the like, and the medium conveying device 100 may be a printer or the like.

[0015] The medium conveying device 100 includes a first housing 101, a second housing 102, a loading table 103, an ejection table 104, an operation device 105, a display device 106, and the like.

[0016] The first housing 101 is disposed above the medium conveying device 100 and is engaged with the second housing 102 by a hinge so that it can be opened and closed when a medium is jammed or when the inside of the medium conveying device 100 is to be cleaned.

[0017] The loading platform 103 engages with the second housing 102 so that the media to be transported can be placed on it. The loading platform 103 is provided on the side of the second housing 102 on the media supply side so that it can move in a substantially vertical direction (height direction) A1 by a motor (not shown). The loading platform 103 is located at the bottom end so that media can be easily loaded when not transporting media, and when transporting media, it rises to a position where the uppermost medium placed on it comes into contact with a pick roller (described later). The ejection platform 104 is formed on the first housing 101 so that it can hold ejected media, and it stacks the ejected media.

[0018] The operation device 105 has input devices such as buttons and an interface circuit for acquiring signals from the input devices, accepts input operations by a user, and outputs operation signals in response to the user's input operations. The display device 106 has a display such as a liquid crystal display, an organic EL (Electro-Luminescence) display, or the like, and an interface circuit for outputting image data to the display, and displays the image data on the display.

[0019] 1, arrow A2 indicates the medium transport direction, arrow A3 indicates the medium discharge direction, and arrow A4 indicates the width direction perpendicular to the medium transport direction. In the following, "upstream" refers to the upstream side of the medium transport direction A2 or the medium discharge direction A3, and "downstream" refers to the downstream side of the medium transport direction A2 or the medium discharge direction A3.

[0020] FIG. 2 is a diagram for explaining the transport path inside the medium transport device 100. As shown in FIG.

[0021] The transport path inside the media transport device 100 includes a first media sensor 111, a pick roller 112, a feed roller 113, a brake roller 114, a second media sensor 115, an ultrasonic transmitter 116a, an ultrasonic receiver 116b, first to eighth transport rollers 117a-h, first to eighth driven rollers 118a-h, a first imaging device 119a, and a second imaging device 119b.

[0022] The pick roller 112, the feed roller 113, the brake roller 114, the first to eighth conveyance rollers 117a-h, and the first to eighth driven rollers 118a-h are an example of a conveyance unit that conveys a medium. Note that the number of each of the pick roller 112, the feed roller 113, the brake roller 114, the first to eighth conveyance rollers 117a-h, and / or the first to eighth driven rollers 118a-h is not limited to one, and may be multiple. In this case, the multiple pick rollers 112, the feed roller 113, the brake roller 114, the first to eighth conveyance rollers 117a-h, and / or the first to eighth driven rollers 118a-h are arranged at intervals in the width direction A4. Hereinafter, the first imaging device 119a and the second imaging device 119b may be collectively referred to as the imaging device 119.

[0023] The surface of first housing 101 facing second housing 102 forms first guide 101a of the medium transport path, and the surface of second housing 102 facing first housing 101 forms second guide 102a of the medium transport path.

[0024] The first media sensor 111 is disposed on the mounting table 103, i.e., upstream of the feed roller 113 and the brake roller 114, and detects the state of the medium on the mounting table 103. The first media sensor 111 determines whether or not a medium is placed on the mounting table 103 by using a contact detection sensor that passes a predetermined current when the medium is in contact with the mounting table 103 or when the medium is not in contact with the mounting table 103. The first media sensor 111 generates and outputs a first media signal whose signal value changes depending on whether or not a medium is placed on the mounting table 103. Note that the first media sensor 111 is not limited to a contact detection sensor, and any other sensor capable of detecting the presence or absence of a medium, such as an optical detection sensor, may be used as the first media sensor 111.

[0025] Pick roller 112 is provided in first housing 101, and comes into contact with a medium placed on mounting table 103 raised to approximately the same height as the medium transport path, and feeds the medium downstream.

[0026] The feed roller 113 is provided inside the first housing 101 downstream of the pick roller 112, and feeds the media placed on the mounting table 103 and fed by the pick roller 112 further downstream. The brake roller 114 is provided inside the second housing 102 facing the feed roller 113. The feed roller 113 and the brake roller 114 perform a media separation operation, separating the media and feeding them one by one. The feed roller 113 is provided above the brake roller 114, and the medium conveying device 100 feeds the media using a so-called top-feed method.

[0027] The second medium sensor 115 is located downstream of the feed roller 113 and the brake roller 114 and upstream of the ultrasonic transmitter 116a and the ultrasonic receiver 116b. The second medium sensor 115 detects whether a medium is present at that position. The second medium sensor 115 includes a light emitter and a light receiver located on one side of the medium transport path, and a reflecting member such as a mirror located opposite the light emitter and the light receiver across the transport path. The light emitter emits light toward the transport path. The light receiver receives the light emitted by the light emitter and reflected by the reflecting member, and generates and outputs a second medium signal, which is an electrical signal corresponding to the intensity of the received light. When a medium is present at the second medium sensor 115, the light emitted by the light emitter is blocked by the medium, so the signal value of the second medium signal changes depending on whether a medium is present or not at the second medium sensor 115. The light emitter and the light receiver may be provided at positions facing each other across the transport path, and the reflecting member may be omitted.

[0028] The ultrasonic transmitter 116a and the ultrasonic receiver 116b are disposed downstream of the feed roller 113 and the brake roller 114 and upstream of the first to eighth conveyor rollers 117a-h and the first to eighth driven rollers 118a-h. The ultrasonic transmitter 116a and the ultrasonic receiver 116b are disposed near the medium conveyance path, facing each other across the conveyance path. The ultrasonic transmitter 116a emits ultrasonic waves. Meanwhile, the ultrasonic receiver 116b receives the ultrasonic waves emitted by the ultrasonic transmitter 116a that have passed through the medium, and generates and outputs an ultrasonic signal, which is an electrical signal corresponding to the received ultrasonic waves. The ultrasonic signal indicates transmission information of the ultrasonic waves that pass through the medium at multiple positions within the medium being conveyed by the conveyance unit. The transmission information indicates the magnitude of the ultrasonic waves received by the ultrasonic receiver 116b. Hereinafter, the ultrasonic transmitter 116a and the ultrasonic receiver 116b may be collectively referred to as the ultrasonic sensor 116. The number of ultrasonic sensors 116 is not limited to one, and may be more than one. In this case, the ultrasonic sensors 116 are arranged at intervals in the width direction A4.

[0029] The first to eighth conveying rollers 117a-h and the first to eighth driven rollers 118a-h are provided downstream of the feed roller 113 and the brake roller 114, and convey the medium fed by the feed roller 113 and the brake roller 114 downstream. The first to eighth conveying rollers 117a-h and the first to eighth driven rollers 118a-h are arranged opposite each other with the medium conveying path in between.

[0030] The first imaging device 119a is an example of an imaging unit and is located downstream of the first conveyor roller 117a and the first driven roller 118a in the medium conveying direction A2, i.e., downstream of the ultrasonic sensor 116. The first imaging device 119a has a line sensor based on a CIS (Contact Image Sensor) of a 1:1 optical system type having CMOS (Complementary Metal Oxide Semiconductor) imaging elements arranged linearly in the main scanning direction. The first imaging device 119a 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 first imaging device 119a captures an image of the surface of the medium being conveyed, generates an input image, and outputs it.

[0031] Similarly, the second imaging device 119b is an example of an imaging unit and is located downstream of the first conveyor roller 117a and the first driven roller 118a in the medium conveyance direction A2. The second imaging device 119b has a CIS line sensor with a 1:1 optical system having CMOS image sensors linearly arranged in the main scanning direction. The second imaging device 119b also has a lens that forms an image on the image sensor and an A / D converter that amplifies and A / D converts the electrical signal output from the image sensor. The second imaging device 119b captures an image of the back side of the medium being conveyed, generates an input image, and outputs it.

[0032] The medium conveying device 100 may be provided with only one of the first and second imaging devices 119a and 119b, and may read only one side of the medium. Also, instead of a CIS line sensor with an equal-magnification optical system and a CMOS imaging element, a CIS line sensor with an equal-magnification optical system and a CCD (Charge Coupled Device) imaging element may be used. Also, a reduction optical system type line sensor with a CMOS or CCD imaging element may be used.

[0033] The medium placed on the mounting table 103 is transported between the first guide 101a and the second guide 102a in the medium transport direction A2 by the rotation of the pick roller 112 and the feed roller 113 in the medium feed directions A5 and A6, respectively. Meanwhile, when multiple media are placed on the mounting table 103, the brake roller 114 rotates in the direction A7 opposite to the medium feed direction, so that only the media in contact with the feed roller 113 are separated from the media placed on the mounting table 103.

[0034] The medium is guided by the first guide 101a and the second guide 102a and fed to the imaging position of the imaging device 119 by the rotation of the first and second transport rollers 117a-b in the directions of arrows A8-A9, and is imaged by the imaging device 119. The medium is then ejected onto the ejection tray 104 by the rotation of the third to eighth transport rollers 117c-h in the directions of arrows A10-A15, respectively. The ejection tray 104 holds the media ejected by the eighth transport roller 117h.

[0035] FIG. 3 is a block diagram showing a schematic configuration of the medium conveying device 100. As shown in FIG.

[0036] In addition to the above-described components, the medium conveying device 100 further includes a motor 131, an interface device 132, a storage device 140, a processing circuit 150, and the like.

[0037] The motor 131 includes one or more motors, and rotates the pick roller 112, the feed roller 113, the brake roller 114, and the first to eighth transport rollers 117a-h to feed and transport the medium in response to a control signal from the processing circuit 150. The first to eighth driven rollers 118a-h may be configured to rotate by the driving force from the motor, rather than being driven to rotate in accordance with the rotation of the transport rollers.

[0038] The interface device 132 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 personal digital assistant, etc.) to transmit and receive scanned images and various information. Instead of the interface device 132, a communication unit having an antenna for transmitting and receiving wireless signals and a wireless communication interface circuit for transmitting and receiving signals via 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).

[0039] The storage device 140 includes a memory device such as a RAM (Random Access Memory) or a ROM (Read Only Memory), a fixed disk device such as a hard disk, or a portable storage device such as a flexible disk or optical disk. The storage device 140 also stores computer programs, databases, tables, and the like used for various processes of the medium conveying device 100. The computer programs may be installed into the storage device 140 from a computer-readable portable recording medium using a known setup program or the like. The portable recording medium is, for example, a CD-ROM (Compact Disc Read Only Memory), a DVD-ROM (Digital Versatile Disc Read Only Memory), or the like.

[0040] The processing circuit 150 operates based on a program stored in advance in the storage device 140. The processing circuit 150 is, for example, a CPU (Central Processing Unit). The processing circuit 150 may be a DSP (Digital Signal Processor), an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or the like.

[0041] The processing circuit 150 is connected to the operation device 105, the display device 106, the first medium sensor 111, the second medium sensor 115, the ultrasonic sensor 116, the image capture device 119, the motor 131, the interface device 132, the storage device 140, and the like, and controls each of these components. The processing circuit 150 controls the motor 131 to transport the medium, controls the image capture device 119 to capture an input image, and transmits the captured input image to the information processing device via the interface device 132. The processing circuit 150 also determines whether a multifeed of media has occurred based on the ultrasonic signal received from the ultrasonic sensor 116. In particular, the processing circuit 150 changes a multifeed threshold for comparing the magnitude of the ultrasonic waves depending on the size of an area where the magnitude of the ultrasonic waves is within a predetermined range. The multifeed threshold is an example of a threshold.

[0042] FIG. 4 is a diagram showing a schematic configuration of the storage device 140 and the processing circuit 150. As shown in FIG.

[0043] 4, the storage device 140 stores various programs, such as a control program 141, a detection program 142, a calculation program 143, a determination program 144, and a reception program 145. Each of these programs is a functional module implemented by software running on a processor. The processing circuit 150 reads each of the programs stored in the storage device 140 and operates in accordance with the read programs, thereby functioning as a control unit 151, a detection unit 152, a calculation unit 153, a determination unit 154, and a reception unit 155.

[0044] FIG. 5 is a flowchart showing an example of the operation of the medium reading process.

[0045] An example of the operation of the medium reading process of the medium conveying 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 processing circuit 150 in cooperation with each element of the medium conveying device 100 based on a program stored in advance in the storage device 140.

[0046] First, the control unit 151 waits until the user inputs an instruction to read a medium using the operation device 105 or the information processing device, and an operation signal instructing the reading of a medium is received from the operation device 105 or the interface device 132 (step S101).

[0047] Next, control unit 151 acquires a medium signal from first medium sensor 111 and determines, based on the acquired medium signal, whether or not a medium is placed on placement table 103 (step S102). If no medium is placed on placement table 103, control unit 151 returns the process to step S101 and waits until a new operation signal is received from operation device 105 or interface device 132.

[0048] On the other hand, if a medium is placed on the placement table 103, the control unit 151 drives a motor for moving the placement table 103, and moves the placement table 103 to a position where the medium can be fed. The control unit 151 drives the motor 131 to rotate the pick roller 112, the feed roller 113, the brake roller 114, and the first to eighth transport rollers 117a-h, and feeds and transports the medium placed on the placement table 103 (step S103).

[0049] Next, the control unit 151 determines whether or not a multi-feed of media has occurred in a multi-feed determination process executed in parallel with the medium reading process (step S104). In the multi-feed determination process, the determination unit 154 determines whether or not a multi-feed of media has occurred by comparing a value based on the ultrasonic signal with a multi-feed threshold. The determination unit 154 also changes the multi-feed threshold depending on whether or not the size of an area in the transported medium where the signal value of the ultrasonic signal is within a predetermined range is equal to or greater than the size threshold. The multi-feed determination process will be described in detail later.

[0050] If it is determined in the multifeed detection process that a multifeed of media has occurred, the control unit 151 executes abnormality processing (step S105). As the abnormality processing, the control unit 151 stops the motor 131 and stops the feeding and transport of the media by the transport unit. As the abnormality processing, the control unit 151 notifies the user by displaying information indicating that a multifeed of media has occurred on the display device 106 or by transmitting the information to the information processing device via the interface device 132. As the abnormality processing, the control unit 151 may eject the medium currently being transported and then stop the medium reading process. As the abnormality processing, the control unit 151 may drive the motor 131 and control the transport unit to reverse the medium, return it to the mounting table 103, and then re-feed it. This eliminates the need for the user to re-place the medium on the mounting table 103 and re-feed it, thereby enabling the control unit 151 to improve user convenience.

[0051] Next, the accepting unit 155 accepts from the user result information indicating whether the result of the determination of the multi-feed of media made by the determination unit 154 was correct or not (step S106). The accepting unit 155 receives the result information input by the user using the operation device 105 or the information processing device from the operation device 105 or the interface device 132. The accepting unit 155 stores the accepted result information in the storage device 140.

[0052] Next, the determination unit 154 corrects the determination sensitivity in the multifeed determination process based on the result information (step S107), and ends the series of steps.

[0053] The determination unit 154 lowers the determination sensitivity when the result information indicates that the determination result for multifeeding of media was incorrect. Note that the determination unit 154 may correct the determination sensitivity based on two or more pieces of result information received after the determination sensitivity was last updated. In this case, the determination unit 154 lowers the determination sensitivity when, among the most recent predetermined number of pieces of result information, the number or percentage of pieces of result information indicating that the determination result for multifeeding of media was incorrect exceeds a predetermined threshold. This allows the medium conveying device 100 to appropriately set the determination sensitivity for the type of media that it frequently conveys.

[0054] For example, the determination unit 154 corrects the multi-feed threshold as the determination sensitivity. In this case, when the result information indicates that the determination result of a multi-feed of media was incorrect, the determination unit 154 decreases the multi-feed threshold (first multi-feed threshold and / or second multi-feed threshold described below). The determination unit 154 may also correct the size threshold as the determination sensitivity. In this case, when the result information indicates that the determination result of a multi-feed of media was incorrect, the determination unit 154 increases the size threshold. This allows the medium conveying device 100 to prevent erroneous determination that a multi-feed of media has occurred.

[0055] If the result information indicates that the determination result of the multi-feed of media was correct, the determination unit 154 may correct the determination sensitivity to be higher. However, if the determination sensitivity is too high, there is a possibility that the determination unit 154 may frequently erroneously determine that multi-feed of media has occurred, so a settable range may be provided for each determination sensitivity.

[0056] The predetermined threshold may also be set by the user. This allows the medium conveying device 100 to change whether to prioritize reliably detecting the occurrence of a multi-feed or reducing the processing time of the medium reading process, depending on the user's application, thereby improving user convenience. Furthermore, the medium conveying device 100 may transmit the result information or the corrected judgment sensitivity to another medium conveying device, and the other medium conveying device may correct its own judgment sensitivity based on that information. This allows the medium conveying device 100 to share the multi-feed judgment result with the other medium conveying device, thereby further improving the accuracy of multi-feed judgment of media.

[0057] On the other hand, if it is determined in step S104 in the multifeed detection process that a multifeed of media has not occurred, the control unit 151 determines whether the entire medium has been imaged (step S108). The control unit 151 determines whether the trailing edge of the medium has passed the position of the second medium sensor 115, for example, based on the second medium signal received from the second medium sensor 115. The control unit 151 periodically acquires the second medium signal from the second medium sensor 115, and determines that the trailing edge of the medium has passed the position of the second medium sensor 115 when the signal value of the second medium signal changes from a value indicating the presence of the medium to a value indicating the absence of the medium. The control unit 151 determines that the trailing edge of the medium has passed the imaging position of the imaging device 119 and that the entire medium has been imaged when a predetermined time has elapsed since the trailing edge of the medium passed the position of the second medium sensor 115, and that the entire medium has been imaged. Note that the control unit 151 may also determine that the entire transported medium has been imaged when a predetermined time has elapsed since the start of feeding the medium.

[0058] If the entire conveyed medium has not yet been imaged, the control unit 151 returns the process to step S104 and repeats the processes of steps S104 to S108.

[0059] On the other hand, if the entire transported medium is imaged, the control unit 151 acquires an input image from the imaging device 119 and outputs the acquired input image by transmitting it to the information processing device via the interface device 132 (step S109).

[0060] Next, control unit 151 determines whether or not a medium remains on mounting table 103 based on the first medium signal received from first medium sensor 111 (step S110). If a medium remains on mounting table 103, control unit 151 returns the process to step S104 and repeats the processes of steps S104 to S110.

[0061] On the other hand, if there are no media remaining on the mounting table 103, the control unit 151 stops the motor 131, and stops the pick roller 112, the feed roller 113, the brake roller 114, and the first to eighth transport rollers 117a-h (step S111).

[0062] Next, similar to the process of step S106, the accepting unit 155 accepts from the user result information indicating whether the determination result of the determination unit 154 regarding the multi-feed of media was correct or not (step S112). The accepting unit 155 stores the accepted result information in the storage device 140.

[0063] Next, the determination unit 154 corrects the determination sensitivity at each position within the medium based on the result information (step S113), and ends the series of steps.

[0064] The determination unit 154 increases the determination sensitivity when the result information indicates that the determination result for multifeeding of media was incorrect. Note that the determination unit 154 may correct the determination sensitivity based on two or more pieces of result information received after the determination sensitivity was last updated. In this case, the determination unit 154 increases the determination sensitivity when, among the most recent predetermined number of pieces of result information, the number or percentage of pieces of result information indicating that the determination result for multifeeding of media was incorrect exceeds a predetermined threshold. This allows the medium conveying device 100 to appropriately set the determination sensitivity for the type of media that it frequently conveys.

[0065] For example, the determination unit 154 corrects the multi-feed threshold as the determination sensitivity. In this case, the determination unit 154 increases the multi-feed threshold when the result information indicates that the determination result of the multi-feed of media is incorrect. The determination unit 154 may also correct the size threshold as the determination sensitivity. In this case, the determination unit 154 decreases the size threshold when the result information indicates that the determination result of the multi-feed of media is incorrect. This prevents the medium conveying device 100 from determining that a multi-feed of media has not occurred when a multi-feed has actually occurred.

[0066] Note that either or both of steps S106 to S107 and steps S112 to S113 may be omitted.

[0067] FIG. 6 is a flowchart showing an example of the operation of the medium conveying device 100 in the process of determining whether or not a double feed occurs.

[0068] An example of the operation of the multifeed detection process of the medium conveying device 100 will be described below with reference to the flowchart shown in Fig. 6. The flow of the operation described below is executed mainly by the processing circuit 150 in cooperation with each element of the medium conveying device 100 based on a program stored in advance in the storage device 140. The flow of the operation shown in Fig. 6 is executed while the medium is being conveyed.

[0069] First, the detection unit 152 receives an ultrasonic signal from the ultrasonic sensor 116. The detection unit 152 detects the transmission information indicated in the received ultrasonic signal as transmission information of ultrasonic waves passing through the medium at multiple positions of the medium transported by the transport unit, and stores the information in the storage device 140 in association with the current time (step S201).

[0070] Next, the calculation unit 153 calculates the size of an area within the conveyed medium where the transmission information detected by the detection unit 152 is within a predetermined range as the overlap size where the media are overlapping (step S202). The calculation unit 153 considers that the media are overlapping at a position where the calculated value based on the transmission information is less than the first multifeed threshold. The calculation unit 153 calculates a statistical value (average, median, maximum, or minimum) of the transmission information detected within a predetermined period before and after the detection of each piece of transmission information as a calculated value. Note that the calculation unit 153 may use each piece of transmission information itself as a calculated value. The first multifeed threshold is set to a value between the transmission information detected when one piece of PPC (Plain Paper Copier) paper is conveyed and the transmission information detected when two pieces of PPC paper are conveyed. In particular, the first multifeed threshold is set to a value between the transmission information detected when one piece of PPC paper is conveyed and the transmission information detected when two pieces of thin paper are conveyed. If the calculated value based on the latest transmission information is equal to or greater than the first multifeed threshold, calculation unit 153 sets the overlap size to 0. On the other hand, if the calculated value based on the latest transmission information is less than the first multifeed threshold, calculation unit 153 references the transmission information stored in storage device 140, and calculates the overlap size as a value obtained by multiplying the most recent continuous time during which the calculated value has been less than the first multifeed threshold by the medium transport speed.

[0071] Note that when there are multiple ultrasonic sensors 116, the calculation unit 153 calculates the overlap size in the medium conveyance direction A2 for each ultrasonic sensor 116. Furthermore, the calculation unit 153 may calculate the size of the overlap of the medium in the width direction A4 as the overlap size in addition to or instead of the size of the overlap of the medium in the medium conveyance direction A2. In this case, the calculation unit 153 calculates the overlap size in the width direction A4 from the arrangement position of the ultrasonic sensor 116 that output transmission information that is less than the first multifeed threshold.

[0072] Next, the determination unit 154 determines whether the overlap size calculated by the calculation unit 153 is equal to or larger than a size threshold (step S203). The size threshold is set to, for example, the size of a photograph attached to a general resume, or the size of a postage stamp or a paper stamp plus a margin (for example, 50 mm).

[0073] If the overlap size is less than the size threshold, the determination unit 154 sets the multi-feed threshold to a second multi-feed threshold (step S204). The second multi-feed threshold is a value between the transparency information detected when one sheet of PPC paper is conveyed and the transparency information detected when two sheets of PPC paper are conveyed, and is set to a value smaller than the first multi-feed threshold. In particular, the second multi-feed threshold is set to a value between the transparency information detected when two sheets of thin paper are conveyed and the transparency information detected when two sheets of PPC paper are conveyed.

[0074] On the other hand, if the overlap size is equal to or greater than the size threshold, the determination unit 154 changes the multi-feed threshold from the second multi-feed threshold to the first multi-feed threshold (step S205).

[0075] In this way, the determination unit 154 changes the multi-feed threshold depending on the overlap size. In particular, the determination unit 154 changes the multi-feed threshold depending on whether the overlap size is equal to or greater than the size threshold. Note that the determination unit 154 may set the multi-feed threshold to one of three or more values. In this case, the determination unit 154 changes the multi-feed threshold so that the larger the overlap size, the larger the multi-feed threshold. This allows the determination unit 154 to change the multi-feed threshold more flexibly.

[0076] Next, the determination unit 154 calculates a calculation value based on the transmission information and determines whether the calculation value is equal to or greater than the multifeed threshold (step S206). The determination unit 154 reads out the transmission information detected by the detection unit 152 within the most recent predetermined period from the storage device 140, and calculates a statistical value (average value, median value, maximum value, or minimum value) of the read transmission information as the calculation value. Note that the determination unit 154 may use the most recent transmission information itself as the calculation value.

[0077] If the calculated value is equal to or greater than the multi-feed threshold, the determination unit 154 determines that a multi-feed of media has not occurred (step S207) and returns the process to step S201. In particular, even if the calculated value is less than the first multi-feed threshold, if the overlap size is less than the size threshold and the calculated value is equal to or greater than the multi-feed threshold (second multi-feed threshold), the determination unit 154 determines that a sticker has been affixed to the transported medium and determines that a multi-feed of media has not occurred. This prevents the determination unit 154 from erroneously determining that a multi-feed of media has occurred when a medium with a small-sized medium affixed is transported.

[0078] On the other hand, if the calculated value is less than the multifeed threshold, the determination unit 154 determines that a multifeed of media has occurred (step S208), and returns the process to step S201. In this case, it is determined that a multifeed has occurred in step S104 of FIG. 5, and abnormality processing is executed in step S105.

[0079] In this way, the determination unit 154 determines whether a multifeed of media has occurred by comparing a calculated value based on the transparency information detected by the detection unit 152 with the multifeed threshold. In particular, the calculation unit 153 updates the overlap size each time the detection unit 152 detects transparency information. Each time the detection unit 152 detects transparency information, the determination unit 154 compares the calculated value based on the transparency information with the multifeed threshold, and changes the multifeed threshold when the updated overlap size becomes equal to or greater than the size threshold. This allows the determination unit 154 to determine in real time whether a multifeed of media has occurred during media transport, and to immediately stop transport of media if a multifeed of media has occurred. Therefore, the medium transport device 100 can prevent damage to media.

[0080] Note that the transmission information may indicate the magnitude of the phase shift of the ultrasonic waves received by the ultrasonic receiver 116b relative to the phase of the ultrasonic waves emitted by the ultrasonic transmitter 116a, rather than the magnitude of the ultrasonic waves received by the ultrasonic receiver 116b. When media are overlapping, the phase shift of the ultrasonic waves passing through the media is greater than when the media are not overlapping. Therefore, when the magnitude of the phase shift of the ultrasonic waves is used as the transmission information, the medium conveying device 100 changes the multi-feed threshold so that the larger the overlap size, the smaller the multi-feed threshold becomes.

[0081] Furthermore, if the calculated value is less than the multi-feed threshold for a predetermined time or less, the determination unit 154 may consider this area to be caused by external noise or an air bubble in the adhesive, and may exclude this area from the multi-feed determination. This allows the determination unit 154 to reduce the influence of noise on the multi-feed determination.

[0082] 7A, 7B, and 7C are schematic diagrams for explaining the technical significance of changing the multi-feed threshold value according to the overlap size when determining whether or not a multi-feed of media has occurred based on transmission information.

[0083] 7A, 7B, and 7C are graphs 700, 710, and 720 showing the characteristics of transmission information (ultrasound amplitude). The horizontal axis of graphs 700, 710, and 720 represents time, and the vertical axis represents transmission information. In graphs 700, 710, and 720, values S1 and S2 represent the first and second multifeed thresholds, respectively, and length L represents the size threshold.

[0084] In graph 700, solid line 701 shows the characteristics of the transmission information when PPC sheet M1 and PPC sheet M2 are transported overlapping each other. PPC sheet M1 is a standard size such as A4, while PPC sheet M2 is a small sheet of paper about the size of a receipt or business card. The length of portion V1 where PPC sheet M1 and PPC sheet M2 overlap is smaller than size threshold L, but the transmission information in portion V1 where PPC sheet M1 and PPC sheet M2 overlap is smaller than second multifeed threshold S2. Therefore, it is correctly determined that a multifeed of media has occurred at time T1 when the leading edge of PPC sheet M2 overlaps with PPC sheet M1 and passes the position of ultrasonic sensor 116.

[0085] In graph 710, solid line 711 shows the characteristics of the transmission information when thin sheets M3 and M4 are transported overlapping each other. Thin sheets M3 and M4 are regular paper, such as A4 size. The attenuation of ultrasonic waves passing through thin sheets M3 and M4 is smaller than the attenuation of ultrasonic waves passing through PPC sheets M1 and M2. Therefore, the transmission information in portion V2 where thin sheets M3 and M4 overlap is larger than the transmission information in portion V1 where PPC sheets M1 and M2 overlap, and has a value between the first multi-feed threshold S1 and the second multi-feed threshold S2. Meanwhile, the length of portion V2 where thin sheets M3 and M4 overlap is greater than the size threshold L. Therefore, it is not determined that a multi-feed of media has occurred at time T2 when the leading edge of thin sheets M4 overlaps with thin sheets M3 and passes the ultrasonic sensor 116. However, at time T3 when the media have been transported by the size threshold L, the multi-feed threshold is changed to the first multi-feed threshold S1, and it is correctly determined that a multi-feed of media has occurred.

[0086] In graph 720, solid line 721 indicates the characteristics of the transmission information when PPC sheet M5 with sticker P affixed thereto is conveyed. PPC sheet M5 is a regular sheet of paper, such as A4 size, and sticker P is a small medium such as a stamp. When sticker P is affixed to PPC sheet M5, there is no air gap between PPC sheet M5 and sticker P, so the amount of ultrasonic attenuation is smaller than when sticker P is simply overlapping PPC sheet M5 without being affixed thereto. Therefore, the transmission information for portion V3 where sticker P is affixed to PPC sheet M5 is greater than the transmission information for portion V1 where PPC sheet M1 and PPC sheet M2 overlap, and has a value between first multifeed threshold S1 and second multifeed threshold S2. Therefore, at time T4 when the portion of PPC sheet M5 with sticker P affixed thereto passes the ultrasonic sensor 116, it is not determined that a multifeed of media has occurred. Furthermore, because the length of the portion V3 on the PPC sheet M5 to which the sticker P is attached is less than the size threshold L, the multi-feed threshold does not change from the second multi-feed threshold S2. Therefore, when a medium with a small medium attached is transported, it is not determined that a multi-feed of media has occurred.

[0087] As shown in FIGS. 7A to 7C, the difference in magnitude between the ultrasonic waves passing through two sheets of PPC paper and the ultrasonic waves passing through two sheets of thin paper or a portion of the PPC paper with a sticker attached is sufficiently large, so the second multi-feed threshold S2 is set appropriately. Similarly, the difference in magnitude between the ultrasonic waves passing through one sheet of PPC paper and the ultrasonic waves passing through two sheets of thin paper or a portion of the PPC paper with a sticker attached is sufficiently large, so the first multi-feed threshold S1 is set appropriately. However, as shown in FIGS. 7B and 7C, the difference in magnitude between the ultrasonic waves passing through two sheets of thin paper and the ultrasonic waves passing through a portion of the PPC paper with a sticker attached is similar, making it difficult to set an appropriate threshold between them. By using the overlap size, the determination unit 154 can appropriately distinguish between multi-feeding of thin paper and media with stickers attached.

[0088] As described above in detail, the medium conveying device 100 determines whether a double feed of media has occurred based on ultrasonic transmission information detected at multiple positions within the conveyed medium, and changes the determination threshold depending on the size of the overlapping area within the medium. This allows the medium conveying device 100 to more accurately determine whether a double feed of media has occurred.

[0089] In particular, when a medium with a sticker attached is being transported, medium transport device 100 can prevent the medium from being erroneously determined to be a multiple feed and stopping the transport of the medium. This allows medium transport device 100 to prevent an increase in the total time required for the medium reading process. Furthermore, the user no longer needs to re-place the medium on mounting table 103 and transport it again, so medium transport device 100 can improve user convenience.

[0090] Generally, the size of labels or small pieces of paper affixed to media is significantly smaller than the size of the media themselves, so by utilizing the overlap size, media conveying device 100 can appropriately distinguish between a thin paper double feed and a medium with an attached label.

[0091] Furthermore, when the overlap size is small, medium conveying device 100 does not omit (does not execute) the determination of whether or not a multi-feed of media has occurred, but changes the multi-feed threshold value according to the overlap size. Therefore, for example, when PPC paper or the like is conveyed, even if small media such as business cards or receipts are conveyed overlapping, medium conveying device 100 can detect the occurrence of a multi-feed of media.

[0092] FIG. 8 is a flowchart showing an example of the operation of the multifeed detection process according to another embodiment.

[0093] The flowchart shown in Fig. 8 is executed in place of the flowchart shown in Fig. 6. The flow of operations shown in Fig. 8 is executed every time a medium is transported.

[0094] First, similar to step S201 in FIG. 6, the detection unit 152 detects the transmission information indicated in the ultrasonic signal as transmission information at multiple positions of the medium, and stores it in the storage device 140 in association with the current time (step S301).

[0095] Next, detection unit 152 determines whether the trailing edge of the medium has passed the position of ultrasonic sensor 116 (step S302). Control unit 151 determines whether the trailing edge of the medium has passed the position of second medium sensor 115 in the same manner as step S108 in FIG. 5. Control unit 151 determines that the trailing edge of the medium has passed the position of ultrasonic sensor 116 when a predetermined time has elapsed since the trailing edge of the medium passed the position of second medium sensor 115. If the trailing edge of the medium has not yet passed the position of ultrasonic sensor 116, detection unit 152 returns to step S301 and repeats the processes of steps S301 and S302.

[0096] On the other hand, when the rear end of the medium has passed the position of the ultrasonic sensor 116, the calculation unit 153 calculates the size of the area within the transported medium where the transmission information detected by the detection unit 152 is within a predetermined range as the overlap size (step S303). The calculation unit 153 references the transmission information currently stored in the storage device 140, and calculates the overlap size as the value obtained by multiplying the maximum time during which the transmission information continues to be less than the first multifeed threshold by the transport speed of the medium.

[0097] Next, the determination unit 154 determines a multi-feed threshold based on the overlap size calculated by the calculation unit 153 (step S304). If the overlap size is less than the size threshold, the determination unit 154 sets the multi-feed threshold to a second multi-feed threshold, and if the overlap size is equal to or greater than the size threshold, the determination unit 154 sets the multi-feed threshold to a first multi-feed threshold. Note that the determination unit 154 may set the multi-feed threshold to one of three or more values. In this case, the determination unit 154 sets the multi-feed threshold so that the larger the overlap size, the larger the multi-feed threshold. This allows the determination unit 154 to set the multi-feed threshold more flexibly.

[0098] Next, the determination unit 154 refers to the transmission information stored in the storage device 140, calculates a calculated value based on each piece of transmission information detected by the detection unit 152 over a certain period of time, and determines whether each calculated value is equal to or greater than the multiple feed threshold (step S305).

[0099] If all the calculated values are equal to or greater than the multi-feed threshold, the determination unit 154 determines that a multi-feed of media has not occurred (step S306) and ends the series of steps. In particular, if any of the calculated values is less than the first multi-feed threshold, but the overlap size is less than the size threshold and the calculated value is equal to or greater than the multi-feed threshold (second multi-feed threshold), the determination unit 154 determines that a sticker has been affixed to the transported medium and determines that a multi-feed of media has not occurred. This prevents the determination unit 154 from erroneously determining that a multi-feed of media has occurred when a medium with a small-sized medium affixed is transported.

[0100] On the other hand, if either of the calculated values is less than the multifeed threshold, the determination unit 154 determines that a multifeed of media has occurred (step S307), and ends the series of steps. In this case, it is determined that a multifeed has occurred in step S104 of FIG. 5, and abnormality processing is executed in step S105.

[0101] In this way, calculation unit 153 calculates the overlap size after detection of the transparency information by detection unit 152 is completed. Determination unit 154 determines a multi-feed threshold based on the overlap size, and compares the determined multi-feed threshold with a calculated value based on the transparency information detected at multiple positions by detection unit 152. This allows determination unit 154 to reduce the amount of calculation during medium transport, reducing the processing load of the multi-feed determination process, while also being able to appropriately determine whether or not a multi-feed of media has occurred.

[0102] As described above in detail, the medium conveying device 100 is now able to more accurately determine whether a double feed of media has occurred, even when determining the double feed threshold after the trailing edge of the medium has passed the position of the ultrasonic sensor 116.

[0103] FIG. 9 is a diagram for explaining a transport path inside a medium transport device 200 according to another embodiment.

[0104] 9, medium conveying device 200 has the same components as medium conveying device 100. However, medium conveying device 200 has a thickness sensor 216 instead of ultrasonic sensor 116.

[0105] The thickness sensor 216 is disposed downstream of the feed roller 113 and the brake roller 114 and upstream of the first to eighth conveyor rollers 117a-h and the first to eighth driven rollers 118a-h. The thickness sensor 216 includes a light emitter 216a and a light receiver 216b. The light emitter 216a and the light receiver 216b are disposed near the medium conveyance path, facing each other across the conveyance path. The light emitter 216a emits light (infrared light or visible light) toward the light receiver 216b. The light receiver 216b receives the light emitted by the light emitter 216a and generates and outputs a thickness signal, which is an electrical signal corresponding to the intensity of the received light. When a medium is present at the thickness sensor 216, the light emitted by the light emitter 216a is attenuated by the medium, and the greater the thickness of the medium, the greater the amount of attenuation. For example, the thickness sensor 216 generates a thickness signal such that the signal value increases as the medium becomes thicker. The thickness signal indicates thickness information of the medium at multiple positions within the medium being transported by the transport unit. The number of thickness sensors 216 is not limited to one and may be multiple. In this case, the multiple thickness sensors 216 are arranged side by side at intervals in the width direction A4.

[0106] The thickness sensor 216 may be a reflective light sensor, a pressure sensor, or a mechanical sensor. The reflective light sensor includes a pair of a light emitter and a light receiver provided on one side of the media transport path and a pair of a light emitter and a light receiver provided on the other side. The reflective light sensor detects the distance between each pair and each side of the media based on the time between one pair irradiating one side of the media with light and receiving the reflected light, and the time between the other pair irradiating the other side of the media with light and receiving the reflected light. The reflective light sensor subtracts each detected distance from the distance between the two pairs to generate a thickness signal indicating thickness information. The pressure sensor detects pressure, which changes depending on the thickness of the media, and generates a thickness signal indicating the detected pressure as thickness information. The mechanical sensor detects the amount of movement of a contact member, such as a roller, that contacts the media and generates a thickness signal indicating the detected amount of movement as thickness information.

[0107] Like the medium conveying device 100, the medium conveying device 200 executes the medium reading process shown in FIG. 5 and the multifeed determination process shown in FIG.

[0108] 5, if the result information indicates that the determination result of the multi-feed of media is incorrect, the determination unit 154 increases the multi-feed threshold value. Also, if the result information indicates that the determination result of the multi-feed of media is incorrect, the determination unit 154 decreases the multi-feed threshold value.

[0109] 6, the detection unit 152 receives a thickness signal from the thickness sensor 216. The detection unit 152 detects the thickness information indicated in the received thickness signal as thickness information of the medium at multiple positions of the medium transported by the transport unit, and stores the information in the storage device 140 in association with the current time.

[0110] In step S202, the calculation unit 153 calculates the size of an area within the conveyed medium where the thickness information detected by the detection unit 152 is within a predetermined range as the overlap size. The calculation unit 153 considers that an overlap of media has occurred at a position where the thickness information is greater than the first multi-feed threshold. The first multi-feed threshold is set to a value between the thickness information detected when one sheet of PPC paper is conveyed and the thickness information detected when two sheets of PPC paper are conveyed. In particular, the first multi-feed threshold is set to a value between the thickness information detected when one sheet of PPC paper is conveyed and the thickness information detected when two sheets of thin paper are conveyed. Meanwhile, the second multi-feed threshold is set to a value between the thickness information detected when one sheet of PPC paper is conveyed and the thickness information detected when two sheets of PPC paper are conveyed, and is greater than the first multi-feed threshold. In particular, the second multi-feed threshold is set to a value between the thickness information detected when two sheets of thin paper are conveyed and the thickness information detected when two sheets of PPC paper are conveyed. If the latest thickness information is equal to or less than the first multi-feed threshold, calculation unit 153 sets the overlap size to 0. On the other hand, if the latest thickness information is greater than the first multi-feed threshold, calculation unit 153 references the thickness information stored in storage device 140 and calculates the overlap size as a value obtained by multiplying the most recent continuous time during which the thickness information has been greater than the first multi-feed threshold by the medium conveyance speed.

[0111] Note that when there are multiple thickness sensors 216, the calculation unit 153 calculates the overlap size in the medium transport direction A2 for each thickness sensor 216. Furthermore, the calculation unit 153 may calculate the size of overlapping of mediums in the width direction A4 as the overlap size in addition to or instead of the size of overlapping of mediums in the medium transport direction A2. In this case, the calculation unit 153 calculates the overlap size in the width direction A4 from the arrangement position of the thickness sensor 216 that output information greater than the first multifeed threshold.

[0112] In step S206, the determination unit 154 calculates a calculated value based on thickness information detected by the detection unit 152 within the most recent predetermined period and determines whether the calculated value is equal to or less than the multi-feed threshold. The determination unit 154 calculates a statistical value (average, median, maximum, or minimum) of the thickness information as the calculated value. Alternatively, the determination unit 154 may use the thickness information itself as the calculated value. If the calculated value is equal to or less than the multi-feed threshold, the determination unit 154 determines in step S207 that a multi-feed of media has not occurred. In particular, even if the calculated value is greater than the first multi-feed threshold, if the overlap size is less than the size threshold and the calculated value is equal to or less than the multi-feed threshold (second multi-feed threshold), the determination unit 154 determines that a sticker has been affixed to the transported media and determines that a multi-feed of media has not occurred. On the other hand, if the calculated value is greater than the multi-feed threshold, the determination unit 154 determines in step S208 that a multi-feed of media has occurred.

[0113] In this way, determination unit 154 determines whether a multi-feed of media has occurred by comparing the calculated value based on the thickness information detected by detection unit 152 with the multi-feed threshold. In particular, calculation unit 153 updates the overlap size every time detection unit 152 detects thickness information. Every time detection unit 152 detects thickness information, determination unit 154 compares the calculated value based on the thickness information with the multi-feed threshold, and changes the multi-feed threshold when the updated overlap size becomes equal to or greater than the size threshold.

[0114] 10A, 10B, and 10C are schematic diagrams for explaining the technical significance of changing the multi-feed threshold value according to the overlap size when determining whether or not a multi-feed of media has occurred based on thickness information.

[0115] 10A, 10B, and 10C are graphs 1000, 1010, and 1020 showing characteristics of thickness information (medium thickness). The horizontal axis of graphs 1000, 1010, and 1020 represents time, and the vertical axis represents thickness information values. In graphs 1000, 1010, and 1020, values S1 and S2 represent the first and second multi-feed thresholds, respectively, and length L represents the size threshold.

[0116] In graph 1000, solid line 1001 shows the characteristics of thickness information when PPC sheet M1 and PPC sheet M2 are transported overlapping each other. The length of portion V1 where PPC sheet M1 and PPC sheet M2 overlap is less than size threshold L, but the thickness information for portion V1 where PPC sheet M1 and PPC sheet M2 overlap is greater than second multifeed threshold S2. Therefore, it is correctly determined that a multifeed of media has occurred at time T1 when the leading edge of PPC sheet M2 overlaps with PPC sheet M1 and passes the position of ultrasonic sensor 116.

[0117] In graph 1010, solid line 1011 shows the characteristics of thickness information when thin sheets M3 and M4 are transported overlapping each other. The thicknesses of thin sheets M3 and M4 are smaller than the thicknesses of PPC sheets M1 and M2. Therefore, the thickness information for portion V2 where thin sheets M3 and M4 overlap is smaller than the thickness information for portion V1 where PPC sheets M1 and M2 overlap, and has a value between the first multi-feed threshold S1 and the second multi-feed threshold S2. Meanwhile, the length of portion V2 where thin sheets M3 and M4 overlap is equal to or greater than the size threshold L. Therefore, at time T2 when the leading edge of thin sheets M4 overlaps with thin sheets M3 and passes the position of thickness sensor 216, it is not determined that a multi-feed of media has occurred. However, at time T3 when the media have been transported by the size threshold L, the multi-feed threshold is changed to the first multi-feed threshold S1, and it is correctly determined that a multi-feed of media has occurred.

[0118] In graph 1020, solid line 1021 indicates the characteristics of thickness information when PPC sheet M5 with sticker P affixed thereto is conveyed. Sticker P is a small medium such as a stamp. When sticker P is affixed to PPC sheet M5, PPC sheet M5 and sticker P are in close contact with each other, and therefore the thickness of PPC sheet M5 and sticker P may be smaller than when sticker P is not affixed to PPC sheet M5 but overlaps it. Therefore, thickness information for portion V3 where sticker P is affixed to PPC sheet M5 is smaller than thickness information for portion V1 where PPC sheet M1 and PPC sheet M2 overlap, and has a value between first multifeed threshold S1 and second multifeed threshold S2. Therefore, it is not determined that a multifeed of media has occurred at time T4 when the portion of PPC sheet M5 with sticker P affixed thereto passes the position of thickness sensor 216. Furthermore, because the length of the portion V3 on the PPC sheet M5 to which the sticker P is attached is less than the size threshold L, the multi-feed threshold does not change from the second multi-feed threshold S2. Therefore, when a medium with a small medium attached is transported, it is not determined that a multi-feed of media has occurred.

[0119] Furthermore, similar to the medium conveying device 100, the medium conveying device 200 may execute the multi-feed determination process shown in FIG. 8 instead of the multi-feed determination process shown in FIG.

[0120] In this case, in step S301 of FIG. 8, the detection unit 152 detects the thickness information indicated in the thickness signal as thickness information at a plurality of positions on the medium, and stores it in the storage device 140 in association with the current time.

[0121] Furthermore, in step S302, the detection unit 152 determines whether the trailing edge of the medium has passed the position of the thickness sensor 216. If the trailing edge of the medium has passed the position of the thickness sensor 216, in step S303 the calculation unit 153 calculates, as the overlap size, the size of an area within the transported medium where the thickness information detected by the detection unit 152 is within a predetermined range.

[0122] In step S305, the determination unit 154 references the thickness information stored in the storage device 140, calculates a calculated value based on each piece of thickness information detected by the detection unit 152 over a certain period of time, and determines whether each calculated value is equal to or less than the multi-feed threshold. If all calculated values are equal to or less than the multi-feed threshold, the determination unit 154 determines in step S306 that a multi-feed of media has not occurred. In particular, if a calculated value is greater than the first multi-feed threshold but the overlap size is less than the size threshold and the calculated value is equal to or less than the multi-feed threshold (second multi-feed threshold), the determination unit 154 determines that a sticker has been affixed to the transported media and determines that a multi-feed of media has not occurred. On the other hand, if any calculated value is greater than the multi-feed threshold, the determination unit 154 determines in step S307 that a multi-feed of media has occurred.

[0123] In this way, calculation unit 153 calculates the overlap size after detection of thickness information is completed by detection unit 152. Determination unit 154 determines a multi-feed threshold based on the overlap size, and compares a value based on the thickness information detected by detection unit 152 at multiple positions with the determined multi-feed threshold.

[0124] As described above in detail, the medium conveying device 200 determines whether a double feed of media has occurred based on thickness information of the medium detected at multiple positions within the conveyed medium, and changes the determination threshold depending on the size of the overlapping area within the medium. This enables the medium conveying device 200 to more accurately determine whether a double feed of media has occurred.

[0125] FIG. 11 is a diagram showing a schematic configuration of a processing circuit 350 of a medium conveyance device according to another embodiment.

[0126] The processing circuit 350 is used in place of the processing circuit 150, and executes media reading processing and the like in place of the processing circuit 150. The processing circuit 350 has a control circuit 351, a detection circuit 352, a calculation circuit 353, a determination circuit 354, a reception circuit 355, and the like. Note that each of these components may be configured as an independent integrated circuit, microprocessor, firmware, or the like.

[0127] The control circuit 351 is an example of a control unit, and has the same functions as the control unit 151. The control circuit 351 receives an operation signal from the operation device 105 or the interface device 132, and a first medium signal from the first medium sensor 111, and controls the motor 131 to transport the medium based on the received signals. The control circuit 351 acquires an input image from the imaging device 119 and outputs it to the interface device 132. The control circuit 351 also reads the determination result of whether or not a multifeed has occurred from the storage device 140, and executes abnormality processing if it is determined that a multifeed of media has occurred.

[0128] The detection circuit 352 is an example of a detection unit, and has the same function as the detection unit 152. The detection circuit 352 receives an ultrasonic signal from the ultrasonic sensor 116 or a thickness signal from the thickness sensor 216, detects transmission information or thickness information at multiple positions within the medium based on the received signals, and stores the information in the storage device 140.

[0129] The calculation circuit 353 is an example of a calculation unit, and has the same function as the calculation unit 153. The calculation circuit 353 reads out the transmission information or thickness information from the storage device 140, calculates the overlap size based on the read information, and stores it in the storage device 140.

[0130] The determination circuit 354 is an example of a determination unit, and has the same function as the determination unit 154. The determination circuit 354 reads the overlap size from the storage device 140 and sets a multi-feed threshold based on the overlap size. The determination circuit 354 also reads the transparency information or thickness information from the storage device 140 and compares it with the set multi-feed threshold to determine whether a multi-feed of media has occurred, and stores the determination result in the storage device 140.

[0131] The reception circuit 355 is an example of a reception unit, and has the same function as the reception unit 155. The reception circuit 355 receives result information from the operation device 105 or the interface device 132, reads out the multifeed determination sensitivity from the storage device 140, corrects the multifeed determination sensitivity based on the received result information, and stores it in the storage device 140.

[0132] As described above in detail, the medium conveying device is now able to determine with higher accuracy whether or not a multifeed of media has occurred, even when the processing circuit 350 executes the medium reading process and the multifeed determination process. [Explanation of symbols]

[0133] 100, 200 medium conveying device, 112 pick roller, 113 feeding roller, 114 brake roller, 117a-h first to eighth conveying rollers, 118a-h first to eighth driven rollers, 151 control unit, 152 detection unit, 153 calculation unit, 154 determination unit, 155 reception unit

Claims

1. a transport unit that transports the medium; a determination unit that determines whether or not a double feed of media has occurred by comparing a value based on measurement information measured for the transported medium with a threshold value, and changes the threshold value depending on the length of an area where overlapping of media has occurred in the transported medium; A medium transport device comprising:

2. The medium transport device according to claim 1 , wherein the determination unit changes the threshold value while the medium is being transported.

3. The medium conveying device according to claim 1 , wherein the determining unit determines the threshold value after measurement of the measurement information for the conveyed medium is completed.

4. A medium transport device as described in any one of claims 1 to 3, wherein the determination unit determines that a sticker is attached to the medium being transported and that a double feed of the medium has not occurred if the length is less than a length threshold.

5. The device further includes a receiving unit that receives result information from a user, the result indicating whether or not the determination result of the determination unit regarding the multi-feed of media is correct, 5. The medium conveying device according to claim 1, wherein the determining unit corrects the threshold value based on the result information.

6. the determination unit changes the threshold depending on whether the length is equal to or greater than a length threshold; The device further includes a receiving unit that receives result information from a user, the result indicating whether or not the determination result of the determination unit regarding the multi-feed of media is correct, 5. The medium transport device according to claim 1, wherein the determining unit corrects the length threshold value based on the result information.

7. 7. The medium transport device according to claim 1, further comprising a control unit that executes abnormality processing when a double feed of media occurs.

8. 8. The medium transport device according to claim 1, further comprising a control unit that notifies a user when a double feed of media occurs.

9. The transport unit transports the medium. determining whether or not a double feed of media has occurred by comparing a value based on measurement information measured for the transported medium with a threshold value, and changing the threshold value according to the length of the area where the overlapping of media has occurred in the transported medium; A medium transport method comprising:

10. A control program for a medium conveying device having a conveying unit that conveys a medium, determining whether or not a double feed of media has occurred by comparing a value based on measurement information measured for the transported medium with a threshold value, and changing the threshold value according to the length of the area where the overlapping of media has occurred in the transported medium; a control program for causing the medium transport device to execute the above steps;

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