Medium conveying apparatus for determining thickness of medium

A medium conveying apparatus includes a conveyance roller to convey a medium, a motor to drive the conveyance roller, a signal generator to output a pulse signal, a pulse width of which changes according to a rotation speed of the motor, and a processor to rotate the conveyance roller by controlling the motor, and detect a fluctuation of the pulse width caused by a load fluctuation when the conveyance roller conveys a medium to determine a thickness of the medium according to the pulse width.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of prior Japanese Patent Application No. 2019-053560 filed on Mar. 20, 2019, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments discussed in the present specification relate to medium conveyance.

BACKGROUND

Since a thickness of a sheet forming an image in a copying machine affects an image formation condition, there is a demand for finding out a thickness of a sheet before forming an image.

For example, a sheet conveying apparatus described in Japanese Patent Application Laid-Open No. 2013-136454 includes a conveyance roller provided on an internal circumference side of a part where a conveyance path of a sheet is crooked, a driving means driving rotation of the conveyance roller, and a drive control means controlling a rotation speed of the conveyance roller through the driving means. Then, the sheet conveying apparatus detects a thickness of a sheet on the basis of a conveyance speed of the sheet, a radius of the conveyance roller, and a rotation speed of the conveyance roller.

SUMMARY

According to some embodiments, a medium conveying apparatus includes a conveyance roller to convey a medium, a motor to drive the conveyance roller, a signal generator to output a pulse signal, a pulse width of which changes according to a rotation speed of the motor, and a processor to rotate the conveyance roller by controlling the motor, and detect a fluctuation of the pulse width caused by a load fluctuation when the conveyance roller conveys a medium to determine a thickness of the medium according to the pulse width.

According to some embodiments, a method for determining a thickness of a medium includes rotating a conveyance roller to convey a medium by controlling a motor to drive the conveyance roller, outputting a pulse signal, a pulse width of which changes according to a rotation speed of the motor, detecting a fluctuation of the pulse width caused by a load fluctuation when the conveyance roller conveys the medium, and determining a thickness of the medium according to the pulse width.

According to some embodiments, a computer program causes a medium conveying apparatus including a conveyance roller to convey a medium, a motor to drive the conveyance roller, a signal generator to output a pulse signal, a pulse width of which changes according to a rotation speed of the motor, to execute a process including rotating the conveyance roller by controlling the motor, detecting a fluctuation of the pulse width caused by a load fluctuation when the conveyance roller conveys the medium, and determining a thickness of the medium according to the pulse width.

DESCRIPTION OF EMBODIMENTS

Hereinafter, medium conveying apparatus, and method according to an embodiment, will be described with reference to the drawings. However, it should be noted that the technical scope of the invention is not limited to these embodiments, and extends to the inventions described in the claims and their equivalents.

FIG. 1is a configuration diagram of an example of an image processing system1according to an embodiment. The image processing system1includes a medium conveying apparatus100and an information processing apparatus200.

The medium conveying apparatus100is an image scanner or the like imaging an image of a medium while conveying the medium. A medium is paper, thick paper, a card, a brochure, a passport, or the like. The medium conveying apparatus100may be a facsimile, a copying machine, a multifunctional peripheral (MFP), or the like. A conveyed medium may be an object being printed on or the like rather than an original, and the medium conveying apparatus100may be a printer or the like. The information processing apparatus200is a server, a personal computer, a multifunctional mobile terminal, a mobile phone, or the like. The medium conveying apparatus100and the information processing apparatus200are connected to one another.

The medium conveying apparatus100includes a lower housing101, an upper housing102, a loading tray103, an output tray104, an operation device105, and a display device106.

The upper housing102is an example of an upper part of a housing, is located in a position covering a top surface of the medium conveying apparatus100, and is engaged with the lower housing101by a hinge in such a way as to be able to open and close in a case of a medium being stuck, cleaning inside the medium conveying apparatus100, or the like.

The loading tray103is formed by a resin member and is engaged with the lower housing101in such a way as to be able to place a medium to be conveyed. The loading tray103is provided in such a way that a placement surface of a medium is tilted against an installation surface of the medium conveying apparatus100. The output tray104is engaged with the lower housing101in such a way as to be able to hold an ejected medium.

The operation device105includes an input device, such as a button, and an interface circuit acquiring a signal from the input device, receives an input operation by a user, and outputs an operation signal based on the input operation by the user. The display device106includes a display including a liquid crystal or organic electro-luminescence (EL), and an interface circuit outputting image data to the display, and displays the image data on the display.

FIG. 2is a diagram for illustrating a conveyance path inside the medium conveying apparatus100.

The conveyance path inside the medium conveying apparatus100includes a first medium detection sensor111, a plurality of feed rollers112aandb, a plurality of brake rollers113aandb, a plurality of first conveyance rollers118aandb, a plurality of second conveyance rollers119aandb, a second medium detection sensor120, a first imaging device121a, a second imaging device121b, a plurality of third conveyance rollers122aandb, and a plurality of fourth conveyance rollers123aandb.

The feed rollers112aand112bmay be hereinafter collectively referred to as feed rollers112. Further, the brake rollers113aand113bmay be collectively referred to as brake rollers113. Further, the first conveyance rollers118aand118bmay be collectively referred to as first conveyance rollers118. Further, the second conveyance rollers119aand119bmay be collectively referred to as second conveyance rollers119. Further, the first imaging device121aand the second imaging device121bmay be collectively referred to as imaging devices121. Further, the third conveyance rollers122aand122bmay be collectively referred to as third conveyance rollers122. Further, the fourth conveyance rollers123aand123bmay be collectively referred to as fourth conveyance rollers123.

A top surface of the lower housing101forms a lower guide107aof a medium conveyance path, and a bottom surface of the upper housing102forms an upper guide107bof the medium conveyance path. An upper stream of the medium conveyance path hereinafter refers to an upper stream in a medium conveying direction A1, and a lower stream refers to a lower stream in the medium conveying direction A1.

The first medium detection sensor111is located on the upstream side of the feed rollers112and the brake rollers113. The first medium detection sensor111includes a contact detection sensor and detects whether or not a medium is placed on the loading tray103. The first medium detection sensor111generates and outputs a medium detection signal changing the signal value between a state in which a medium is placed on the loading tray103and a state in which a medium is not placed.

The feed rollers112are provided on the lower housing101and sequentially feed media placed on the loading tray103from the lower side. The brake rollers113are provided on the upper housing102and are located to face the feed rollers112.

The first imaging device121ais an example of an imaging device and includes a reduction optical system type line sensor including an imaging element based on charge coupled devices (CCDs) linearly located in a main scanning direction orthogonal to the medium conveying direction A1. Further, the first imaging device121aincludes a lens forming an image on the imaging element and an A/D converter amplifying and analog-digital (A/D) converting an imaging signal output from the imaging element. The first imaging device121agenerates and outputs an input image in which a back side of a conveyed medium is imaged, in accordance with control from a processing circuit to be described later.

Similarly, the second imaging device121bis an example of an imaging device and includes a reduction optical system type line sensor including an imaging element based on CCDs linearly located in the main scanning direction. Further, the second imaging device121bincludes a lens forming an image on the imaging element and an A/D converter amplifying and analog-digital (A/D) converting an imaging signal output from the imaging element. The second imaging device121bgenerates and outputs an input image in which a front side of a conveyed medium is imaged, in accordance with control from the processing circuit to be described later.

Only either of the first imaging device121aand the second imaging device121bmay be located in the medium conveying apparatus100, and only one side of a medium may be read. Further, a unity-magnification optical system type contact image sensor (CIS) including an imaging element based on a complementary metal oxide semiconductor (CMOS) may be used in place of the imaging element based on CCDs.

A medium placed on the loading tray103is conveyed between the lower guide107aand the upper guide107bin the medium conveying direction A1by the feed rollers112rotating in a direction A2inFIG. 2, that is, a medium feeding direction. When a medium is conveyed, the brake rollers113rotate in a direction A3, that is, a direction opposite to the medium feeding direction. By the workings of the feed rollers112and the brake rollers113, when a plurality of media are placed on the loading tray103, only a medium in contact with the feed rollers112, out of the media placed on the loading tray103, is separated. Consequently, the medium conveying apparatus100operates in such a way that conveyance of a medium other than the separated medium is restricted (prevention of multi feed).

A medium is fed between the first conveyance rollers118and the second conveyance rollers119while being guided by the lower guide107aand the upper guide107b. The medium is fed between the first imaging device121aand the second imaging device121bby the first conveyance rollers118and the second conveyance rollers119rotating in a direction A4and a direction A5, respectively. The medium read by the imaging devices121is ejected on the output tray104by the third conveyance rollers122and the fourth conveyance rollers123rotating in a direction A6and a direction A7, respectively. The first conveyance rollers118, the second conveyance rollers119, the third conveyance rollers122, and the fourth conveyance rollers123are examples of a conveyance roller that conveys a medium.

FIG. 3is a diagram schematically illustrating an example of a waveform of a pulse signal output from an encoder132for measuring a rotation speed of a motor131. The encoder132is an example of a signal generator.

The motor131performs a conveyance operation of a medium by rotating the first conveyance rollers118, the second conveyance rollers119, the third conveyance rollers122, and the fourth conveyance rollers123. The encoder132outputs a pulse signal P a pulse width T of which changes according to a rotation speed of the motor131. For example, an optical encoder includes a disk134on which a large number of slits133(light transmission holes) are formed, the disk134being provided to rotate according to rotation of the motor131, and a light emitter135and a light receiver136that are provided to face one another with the disk134in between.

For example, the encoder132schematically illustrated inFIG. 3outputs a relatively large signal value (High) while the light receiver136receives light emitted by the light emitter135from a slit133and outputs a relatively small signal value (Low) while light emitted by the light emitter135is blocked by the disk134. In other words, the pulse width T of the pulse signal P indicates a length of a period in which a slit133exists between the light emitter135and the light receiver136and changes according to a rotation speed of the motor131.FIG. 3illustrates a disk134including 12 slits133for convenience; however, an actual disk134includes several hundred slits133.

FIG. 4is a block diagram illustrating a schematic configuration of the medium conveying apparatus100.

The medium conveying apparatus100further includes a driving device130, an interface device142, a memory device150, and a processing circuit160in addition to the configuration described above.

The driving device130drives the motor131in accordance with a control signal from the processing circuit160and conveys a medium by rotating the feed rollers112, the first conveyance rollers118, the second conveyance rollers119, the third conveyance rollers122, and the fourth conveyance rollers123. The driving device130may cause separate motors to rotate the feed rollers112, the first conveyance rollers118, the second conveyance rollers119, the third conveyance rollers122, and the fourth conveyance rollers123, respectively.

For example, the interface device142includes an interface circuit conforming to a serial bus such as USB, is electrically connected to the information processing apparatus200, and transmits and receives an input image and various types of information. Further, a communication unit including an antenna transmitting and receiving wireless signals, and a wireless communication interface device for transmitting and receiving signals through a wireless communication line in conformance with a predetermined communication protocol may be used in place of the interface device142. For example, the predetermined communication protocol is a wireless local area network (LAN).

The memory device150includes 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. Further, the memory device150stores a computer program, a database, a table, and the like used for various types of processing in the medium conveying apparatus100. The computer program may be installed on the memory device150from a computer-readable portable recording medium by use of a known setup program or the like. For example, the portable recording medium is a compact disc read only memory (CD-ROM), a digital versatile disc read only memory (DVD-ROM), or the like.

For example, the processing circuit160is a processor, such as a central processing unit (CPU). The processing circuit160operates in accordance with a program previously stored in the memory device150. The processing circuit160may be a digital signal processor (DSP), a large scale integration (LSI), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), etc.

The processing circuit160is connected to the operation device105, the display device106, the first medium detection sensor111, the second medium detection sensor120, the imaging devices121, the encoder132, the driving device130, the interface device142, the memory device150, the processing circuit170, and the like through a bus180, and controls each of these units. The processing circuit160performs drive control of the driving device130, imaging control of the imaging devices121, and the like, acquires an input image, and transmits the input image to the information processing apparatus200through the interface device142.

The processing circuit160receives signals output from the first medium detection sensor111, the second medium detection sensor120, and the encoder132through the bus180. While each of the first medium detection sensor111, the second medium detection sensor120, and the encoder132includes an analog-digital conversion circuit, an analog-digital conversion circuit may be provided between the respective sensors and the processing circuit160.

The processing circuit170executes predetermined image processing on an image imaged by the imaging devices121and stores the image on which the image processing is executed into the memory device150. A DSP, an LSI, an ASIC, an FPGA, or the like may be used in place of the processing circuit170.

FIG. 5is a diagram illustrating schematic configurations of the memory device150and the processing circuit160.

As illustrated inFIG. 5, the memory device150stores a control program151, an image acquisition program152, a determination program153, an image correction program154, a segmentation program155, and the like. Each of these programs is a functional module implemented by software operating on a processor. The processing circuit160reads each program stored in the memory device150and operates in accordance with each read program. Consequently, the processing circuit160functions as a control module161, an image acquisition module162, a determination module163, an image correction module164, and a segmentation module165.

FIG. 6is a diagram for illustrating control processing of the motor131by the control module161. The control module161drives the motor131by controlling a motor driver137. The motor131is a DC motor. Further, for example, the motor driver137may be a motor driver circuit performing pulse width modulation (PWM) on a predetermined voltage providing a speed specified by the control module161and outputting the modulated voltage to the motor131. The motor driver137may be integrated into the motor131.

The control module161performs feedback control on the motor131in such a way that a rotation speed of the motor131follows a command value such as a previously set voltage value. The control module161acquires a cycle of a pulse signal output from the encoder132on a predetermined feedback control cycle (for example, at every 500 ns) and controls the motor driver137in such a way that a voltage value acquired by converting a frequency into voltage matches the command value. The encoder132is mounted on a rotation axis of the motor131and therefore outputs an encoder pulse related to a rotation speed of the motor131. While a DC motor is low-cost and also allows simple speed adjustment, a rotation speed changes due to an external cause such as a load fluctuation. However, by the feedback control described above, the motor can be controlled in such a way as to have a rotation speed based on the command value after a predetermined period.

FIG. 7(a)andFIG. 7(b)are diagrams illustrating a state in which a pulse width of a pulse signal output from the encoder132fluctuates due to a load fluctuation when a front edge part of a medium passes the conveyance rollers.

FIG. 7(a)illustrates a state in which a front edge part of a medium D1fed by the feed rollers112is about to be fed between the first conveyance rollers118and the second conveyance rollers119. At this time, the first conveyance rollers118rotate in the direction A4, and the second conveyance rollers119rotate in the direction A5; and a rotation speed of the motor131fluctuates by the load fluctuation when the first conveyance rollers118and the second conveyance rollers119pinch the front edge part of the medium D1.

FIG. 7(b)illustrates a state in which a pulse width of a pulse signal output from the encoder132fluctuates according to the rotation speed of the motor131. The horizontal axis inFIG. 7(b)indicates time, and the vertical axis inFIG. 7(b)indicates a magnitude of voltage of the pulse signal.

At a time t0before the medium D1is fed between the first conveyance rollers118and the second conveyance rollers119, the rotation speed of the motor131is kept constant by feedback control by the control module161, and therefore the pulse width of the pulse signal output from the encoder132is maintained at a mostly constant pulse width T0.

When the first conveyance rollers118and the second conveyance rollers119pinch the front edge part of the medium D1at a time t1, the rotation speed of the motor131slows down due to the load fluctuation, and the pulse width of the pulse signal P1becomes a pulse width T1, exceeding a predetermined threshold value Tt. Even when the pulse width of the pulse signal P1changes to the pulse width T1at the time t1, the feedback control is not immediately exerted, and therefore the rotation speed of the motor131does not return to the former speed for a certain while; and accordingly, the pulse width remains at the pulse width T1for a certain while.

In the example inFIG. 7(b), at a time t2after a predetermined feedback control cycle, the pulse width of the pulse signal output from the encoder132is returned to the former pulse width T0.

Thus, although the pulse width of the pulse signal output from the encoder132temporarily fluctuates due to the load fluctuation when the first conveyance rollers118and the second conveyance rollers119pinch the front edge part of the medium D1, the width returns to the pulse width before the fluctuation by the feedback control.

The second conveyance rollers119, the second imaging device121b, and the fourth conveyance rollers123located above the conveyance path are provided to be able to move upward and move upward according to a thickness of the conveyed medium D1. The medium D1fed under reading surfaces of the first imaging device121aand the second imaging device121bby the first conveyance rollers118and the second conveyance rollers119is read by the first imaging device121aand the second imaging device121b.

When the front edge part of the medium D1passes the third conveyance rollers122and the fourth conveyance rollers123while the first imaging device121aand the second imaging device121bread the medium D1, the pulse width of the pulse signal similarly fluctuates due to the load fluctuation. Further, when a rear edge part of the medium passes the first conveyance rollers118, the second conveyance rollers119, the third conveyance rollers122, and the fourth conveyance rollers123, the pulse width of the pulse signal similarly fluctuates due to the load fluctuation.

FIG. 8(a)andFIG. 8(b)are other diagrams illustrating a state in which a pulse width of a pulse signal output from the encoder132fluctuates due to a load fluctuation when a front edge part of a medium passes the conveyance rollers. A medium D2inFIG. 8(a)andFIG. 8(b)is thicker compared with the medium D1inFIG. 7(a)andFIG. 7(b).

As illustrated inFIG. 8(a), as a thickness of the medium D2increases, a load fluctuation when the first conveyance rollers118and the second conveyance rollers119pinch the medium D2increases. Consequently, as illustrated inFIG. 8(b), when the first conveyance rollers118and the second conveyance rollers119pinch the front edge part of the medium D2at a time t1, the rotation speed of the motor131becomes slower, and the pulse width of the pulse signal P2becomes a pulse width T2greater than the pulse width T1.

Thus, a magnitude of a fluctuation of the pulse width of the pulse signal when the medium passes the conveyance rollers varies depending on the thicknesses of the conveyed media D1and D2. Accordingly, the medium conveying apparatus100can determine the thicknesses of the media D1and D2on the basis of the fluctuation of the pulse width of the pulse signal due to the load fluctuation when each of the media D1and D2is conveyed.

FIG. 9(a)andFIG. 9(b)are yet other diagrams illustrating a state in which a pulse width of a pulse signal output from the encoder132fluctuates due to a load fluctuation when a medium passes the conveyance rollers.FIG. 9(a)andFIG. 9(b)differ fromFIG. 7(a)andFIG. 7(b)in that a medium D3includes a plurality of regions with different thicknesses such as a passport a page of which including a photograph is opened and read.

The medium D3illustrated inFIG. 9(a)is an example of a medium including regions with different thicknesses and includes a first region with a relatively small thickness (the left side in the diagram) and a second region with a relatively large thickness (the right side in the diagram).FIG. 9(a)illustrates a state in which the thick second region of the medium D3is about to be fed between the first conveyance rollers118and the second conveyance rollers119after the thin first region of the medium D3passes between the first conveyance rollers118and the second conveyance rollers119. In the state illustrated inFIG. 9(a), the first imaging device121aand the second imaging device121bare reading the thin first region of the medium D3.

A waveform of a pulse signal in a period from a time t0to a time t2during which the thin first region of the medium D3passes between the first conveyance rollers118and the second conveyance rollers119is the same asFIG. 7(b)except that a pulse width is a pulse width T3.

Subsequently, when the first conveyance rollers118and the second conveyance rollers119pinch the thick second region of the medium D3at a time t3, the rotation speed of the motor131slows down due to the load fluctuation, and the pulse width of the pulse signal P3becomes a pulse width T4greater than the pulse width T3. Subsequently the pulse width of the pulse signal is returned to the pulse width T0by the feedback control at a time t4.

Thus, even when the medium D3includes a plurality of regions with different thicknesses, the medium conveying apparatus100can detect that the thickness of the medium changes, on the basis of the fluctuation of the pulse width of the pulse signal output from the encoder132.

FIG. 10is a flowchart illustrating an operation example of medium reading processing by the medium conveying apparatus100. Referring to the flowchart illustrated inFIG. 10, the operation example of the medium reading processing in the medium conveying apparatus100will be described below. The operation flow described below is executed mainly by the processing circuit160in cooperation with each element in the medium conveying apparatus100in accordance with a program previously stored in the memory device150. The operation flow illustrated inFIG. 10is periodically executed.

First, the control module161rotates the feed rollers112by driving the driving device130and starts feeding a medium placed on the loading tray103(step S101).

Next, before the imaging devices121start imaging the medium, the control module161determines whether or not a pulse width of a pulse signal output from the encoder132fluctuates in such a way as to exceed a predetermined threshold value Tt (step S102). When the pulse width of the pulse signal fluctuates, the control module161executes pre-reading processing (step S103). The pre-reading processing will be described later (seeFIG. 11).

Next, the image acquisition module162determines that the front edge of the medium passes a position of the second medium detection sensor120when a signal value of a signal output from the second medium detection sensor120changes from a value indicating nonexistence of a medium to a value indicating existence of a medium. Then, the image acquisition module162causes the imaging devices121to start reading the medium (step S104).

Next, while the imaging devices121are reading the medium, the control module161determines whether or not the pulse width of the pulse signal output from the encoder132fluctuates in such a way as to exceed the predetermined threshold value Tt (step S105). When the pulse width of the pulse signal fluctuates, the control module161stores a position of an imaging signal on an input image, the imaging signal being imaged when the pulse width of the pulse signal fluctuates, into the memory device150(step S106).

Next, the control module161determines whether or not the medium passes reading surfaces of the imaging devices121(step S107). For example, the control module161determines that the medium passes the imaging devices121when a predetermined period elapses after the signal value of the signal output from the second medium detection sensor120changes from the value indicating nonexistence of a medium to the value indicating existence of a medium. The control module161repeats step S105to step S107until the medium passes the imaging devices121.

When the medium passes the imaging devices121, the image acquisition module162causes the imaging devices121to end the reading of the medium and acquires an input image (step S108).

Next, the image correction module164generates a corrected image by correcting the input image (step S109). Correction processing of the input image will be described later [seeFIG. 12(a)].

Next, the segmentation module165segments a region of the medium or a predetermined region on the medium from the corrected image generated by the image correction module164(step S110) and ends the series of processing. The processing of segmenting a predetermined region will be described later [seeFIG. 12(b)].

In the example inFIG. 10, the image correction processing and the processing of segmenting a predetermined region are performed on the medium conveying apparatus100side; however, the image correction processing and/or the processing of segmenting a predetermined region may be executed by the information processing apparatus200. In this case, the control module161transmits the input image and/or the corrected image, thickness information about the medium, to be described later, and information about a region where the load fluctuation has occurred to the information processing apparatus200through the interface device142. The medium conveying apparatus100may only generate an input image and may not perform the image correction processing and the processing of segmenting a predetermined region, that is, may omit steps S109and S110inFIG. 10.

FIG. 11is a flowchart illustrating an operation example of the pre-reading processing in step S103inFIG. 10.

The determination module163detects the fluctuation of the pulse width caused by the load fluctuation when the medium is conveyed, and determine a thickness of the medium according to the pulse width (step S201). For example, the determination module163may determine the thickness of the medium according to the pulse width T1of the pulse signal P1when the pulse width first exceeds the predetermined threshold value Tt as illustrated inFIG. 7(b). For that purpose, for example, the determination module163may previously store a table storing a pulse width and a thickness of a medium related to the pulse width in association with one another in the memory device150and determine the thickness of the medium by referring to the table. The table is prepared on the basis of actual measurements or the like of conveyance processing previously performed with varying medium thicknesses.

Next, the control module161estimates a type of the medium on the basis of the medium thickness determined by the determination module163(step S202). For example, the determination module163may previously store a table storing a medium thickness and a medium type related to the medium thickness in association with one another in the memory device150and estimate the medium type by referring to the table. The table is prepared on the basis of actual measurements or the like of conveyance processing previously performed with varying medium types.

Next, the control module161determines whether or not the medium type estimated by the determination module163is a type including a plurality of regions with different thicknesses such as a passport a page of which including a photograph is opened and read (step S203). The estimation of a medium type and the estimation of a type including regions with different thicknesses in steps S202and S203may be used in the image correction processing [seeFIG. 12(a)] and the processing of segmenting a predetermined region [seeFIG. 12(b)], to be described later.

When the medium type is determined not to be a type including a plurality of regions with different thicknesses in step S203, the control module161determines whether or not the medium thickness determined by the determination module163is greater than or equal to a predetermined thickness (step S204).

When the medium type is a type including a plurality of regions with different thicknesses or the medium thickness is greater than or equal to the predetermined thickness, the control module161controls the motor131in such a way that a medium conveyance speed becomes slower (step S205). Consequently, a load fluctuation when a boundary part of the medium where the thickness changes passes the first conveyance rollers118, the second conveyance rollers119, the third conveyance rollers122, and the fourth conveyance rollers123while the medium is being read, as illustrated inFIG. 9(a), is reduced. Further, a load fluctuation when a thick medium is conveyed by the first conveyance rollers118, the second conveyance rollers119, the third conveyance rollers122, and the fourth conveyance rollers123is reduced. The temporarily slowed down medium conveyance speed is controlled by the control module161in such a way as to be returned to the former conveyance speed at an appropriate timing such as a point in time when conveyance of the target medium is completed.

Next, the control module161changes a read timing of the medium in response to the slowdown of the conveyance speed (step S206). Specifically, the image acquisition module162performs control in such a way that an input image does not expand in the conveying direction even when the medium conveyance speed is slowed down, by changing a timing of acquiring a line image used for actual formation of an input image out of line images acquired by scanning the medium in a width direction on a predetermined cycle by the imaging devices121. For example, in a case of a regular conveyance speed, an input image is formed by using every line image acquired by the imaging devices121, whereas when the conveyance speed is slowed down, an input image is formed by use of (by thinning) only one out of three line images out of line images acquired by the imaging devices121.

When the medium type is not a type including a plurality of regions with different thicknesses and also the medium thickness is less than the predetermined thickness, the control module161ends the pre-reading processing.

FIG. 12(a)is a diagram for illustrating the correction processing of an input image301in step S109inFIG. 10.

When a medium conveyance speed fluctuates due to a load fluctuation when a medium passes the first conveyance rollers118, the second conveyance rollers119, the third conveyance rollers122, and the fourth conveyance rollers123, a distortion such as expansion and contraction occurs on the input image301.FIG. 12(a)illustrates an example of distortions311,312,321,322,331, and332occurring on the input image301due to the load fluctuation when the medium is conveyed.

Each of the distortions311and312occurs due to a load fluctuation when a front edge part of the medium is fed between the first conveyance rollers118and the second conveyance rollers119, and between the third conveyance rollers122and the fourth conveyance rollers123.

Further, each of the distortions321and322occurs due to a load fluctuation when a rear edge part of the medium comes out from a space between the first conveyance rollers118and the second conveyance rollers119, and a space between the third conveyance rollers122and the fourth conveyance rollers123.

Further, each of the distortions331and332occurs due to a load fluctuation when a boundary part of the medium where a thickness changes passes between the first conveyance rollers118and the second conveyance rollers119, and the third conveyance rollers122and the fourth conveyance rollers123.

The image correction module164corrects the distortions311,312,321,322,331, and332occurring on the input image301on the basis of, for example, a medium type estimated from a medium thickness in step S202inFIG. 11. For example, the image correction module164previously stores a table storing a medium type, a region where a distortion occurs on the input image301when the medium type is read, and an expansion ratio for correcting the region in association with one another in the memory device150. The table is prepared on the basis of actual measurements or the like of reading processing previously performed with varying medium types. Then, the image correction module164may refer to the table and correct the input image301by expanding or contracting a region where a distortion occurs on the input image301when the medium type is read, at an expansion ratio for correcting the region.

Further, the image correction module164may refer to information about a position of an imaging signal on the input image301, the imaging signal being imaged when a pulse width of a pulse signal fluctuates, the position being stored in step S106inFIG. 10, and may correct an input image related to a region where the thickness changes. Consequently, a distortion of an input image is more accurately corrected.

FIG. 12(b)is a diagram for illustrating the processing of segmenting a predetermined region in step S110inFIG. 10. An image illustrated inFIG. 12(b)is an example of a corrected image302corrected by the image correction module164. In the corrected image302illustrated inFIG. 12(b), a boundary of a medium region303and a boundary of a predetermined region304such as a photograph region of a passport are clarified by the distortions311,312,321,322,331, and332illustrated inFIG. 12(a)being corrected. Further, a boundary of a predetermined region305readable by optical character recognition (OCR) or the like, such as a machine readable zone (MRZ) provided on a passport, is also clarified. Consequently, the segmentation module165can accurately segment the clarified medium region303and the clarified predetermined regions304and305.

As described above, the medium conveying apparatus100includes the motor131driving the conveyance rollers conveying a medium, the control module161rotating the conveyance rollers by controlling the motor131, and a signal output device for outputting a pulse signal a pulse width of which changes according to a rotation speed of the motor131. Then, the determination module163detects the fluctuation of the pulse width based on the load fluctuation when the conveyance rollers convey the medium and determines a thickness of the medium conveyed by the conveyance rollers. Consequently, the medium conveying apparatus100can detect a thickness of a conveyed medium with a simple configuration.

Further, the determination module163determines a medium thickness on the basis of a pulse width of a pulse signal when the pulse width first exceeds a predetermined threshold value. Consequently, the medium conveying apparatus100can rapidly calculate a thickness of a conveyed medium with a small amount of computation.

Further, when a medium thickness determined by the determination module163is greater than or equal to a predetermined thickness, the control module161controls the motor131in such a way as to slow down rotation speeds of the conveyance rollers compared with a case of the medium thickness being less than the predetermined thickness. Consequently, a load fluctuation when a thick medium is conveyed by the first conveyance rollers118, the second conveyance rollers119, the third conveyance rollers122, and the fourth conveyance rollers123is reduced.

Further, when an estimated medium type is a type including a plurality of regions with different thicknesses, the control module161controls the motor131in such a way as to slow down the rotation speeds of the conveyance rollers compared with a case of the medium type not being a type including a plurality of regions with different thicknesses. Consequently, a load fluctuation when a boundary part where a medium thickness changes passes the first conveyance rollers118, the second conveyance rollers119, the third conveyance rollers122, and the fourth conveyance rollers123while the medium is being read is reduced.

Further, the control module161controls a rotation speed of a DC motor in such a way that a pulse width follows a command value. Consequently, a medium conveyance speed is stabilized by feedback control. Further, quietness is improved and power consumption is reduced, compared with a case of using a stepping motor.

Further, the determination module163detects a fluctuation of a pulse width before the imaging device starts reading a medium, and determines a thickness of the medium. Consequently, the medium conveying apparatus100can slow down a medium conveyance speed or change a read timing of the medium before the imaging devices121start imaging the medium.

Further, the imaging device changes a read timing of a medium according to a medium thickness determined by the determination module163. Consequently, the control module161suppresses expansion of an input image in a height direction due to a slowdown of a medium conveyance speed when the medium is thick.

Further, the determination module163detects a fluctuation of a pulse width while the imaging device is reading a medium and detects a region where a medium thickness changes; and the image correction module164corrects an input image related to the region where the thickness changes detected by the determination module163. Consequently, a distortion of an input image is more accurately corrected.

Further, the segmentation module165segments a predetermined region from an input image corrected by the image correction module164. Consequently, a medium region and a predetermined region clarified by the correction are accurately segmented.

Every embodiment described above merely represents a materialization example at implementation, and the technical scope shall not be interpreted in a limited manner. In other words, various forms may be implemented without departing from the technical concept or main features thereof.

FIG. 13is a diagram illustrating a schematic configuration of a processing circuit270in a medium conveying apparatus according to another embodiment. The processing circuit270is used in place of the processing circuit160in the medium conveying apparatus100and executes the medium reading processing, the determination processing, and the image correction processing in place of the processing circuit160. The processing circuit270includes a control circuit271, an image acquisition circuit272, a determination circuit273, and an image correction circuit274.

The control circuit271is an example of a control module and has a function similar to the control module161. The image acquisition circuit272is an example of an image acquisition module and has a function similar to the image acquisition module162. The determination circuit273is an example of a determination module and has a function similar to the determination module163. The image correction circuit274is an example of an image correction module and has a function similar to the image correction module164.

Each part included in the processing circuit may be independently configured with an integrated circuit, a microprocessor, firmware, etc. Further, some parts included in the processing circuit may be configured with a circuit, and other parts may be configured with a functional module implemented by software operating on a processor.

Further,FIG. 14is a block diagram illustrating a schematic configuration of an information processing apparatus200according to the other embodiment. In an image processing system1including the medium conveying apparatus100and the information processing apparatus200, the information processing apparatus200may have functions equivalent to the image correction module164and the segmentation module165in the medium conveying apparatus100. The information processing apparatus200includes an interface device242, a memory device250, and a processing circuit260.

For example, the interface device242includes an interface circuit conforming to a serial bus such as USB, is electrically connected to the medium conveying apparatus100, and transmits and receives an input image and various types of information. Further, a communication unit including an antenna transmitting and receiving wireless signals, and a wireless communication interface device for transmitting and receiving signals through a wireless communication line in conformance with a predetermined communication protocol may be used in place of the interface device242. For example, the predetermined communication protocol is a wireless LAN.

The memory device250includes a memory device such as a RAM or a ROM, a fixed disk device such as a hard disk, or a portable storage device such as a flexible disk or an optical disk. Further, the memory device250stores a computer program, a database, a table, and the like used for various types of processing in the information processing apparatus200. The computer program may be installed on the memory device250from a computer-readable portable recording medium by use of a known setup program or the like. For example, the portable recording medium is a CD-ROM, a DVD-ROM, or the like.

For example, the processing circuit260is a processor, such as a central processing unit (CPU). The processing circuit260operates in accordance with a program previously stored in the memory device250. The processing circuit260may be a DSP, an LSI, an ASIC, an FPGA, etc. The processing circuit260is connected to the interface device242, the memory device250, and the like, and controls each of these units. The processing circuit260receives an image from the medium conveying apparatus100through the interface device242, executes processing similarly to the image correction module164and the segmentation module165in the medium conveying apparatus100, and stores the processed image into the memory device250.

FIG. 15is a diagram illustrating a schematic configuration of the memory device250and the processing circuit260in the information processing apparatus200according to the other embodiment. According to the present embodiment, the information processing apparatus200executes the image correction processing in place of the medium conveying apparatus100.

As illustrated inFIG. 15, the memory device250stores programs such as a reception program251, an image correction program252, and a segmentation program253. Each of these programs is a functional module implemented by software operating on a processor. The processing circuit260reads each program stored in the memory device250and operates in accordance with each read program. Consequently, the processing circuit260functions as a reception module261, an image correction module262, and a segmentation module263.

The reception module261receives an input image from the medium conveying apparatus100through the interface device242. The image correction module262generates a corrected image by correcting the input image. The segmentation module165segments a medium region or a predetermined region on the medium from the corrected image.

The image processing system according to the present embodiment can also provide effects similar to the effects described above.

According to this embodiment, the medium conveying apparatus, the method, and the computer-readable, non-transitory medium storing the control program can detect a thickness of a conveyed medium with a simple configuration.