Patent Publication Number: US-2022234856-A1

Title: Medium conveying apparatus to correct skew of medium using second roller while moving first roller to be spaced apart from medium

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority of prior Japanese Patent Application No. 2021-008739, filed on Jan. 22, 2021, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     Embodiments discussed in the present specification relate to medium conveyance. 
     BACKGROUND 
     In a medium conveying apparatus such as a scanner, a skew (oblique motion) in which a medium is conveyed in an inclined manner may occur. When the skew (oblique motion) of the medium occurs, the medium conveying apparatus is required to appropriately correct the skew of the medium since the medium may abut a side wall of a conveyance path and a jam (paper jam) of the medium may occur. 
     A sheet conveying apparatus having a conveying roller located along a width direction of a sheet conveyance path, and a pressing member to press a sheet to the conveying roller, is disclosed (Japanese Unexamined Patent Publication (Kokai) No. 2013-147300). The sheet conveying apparatus has a pair of resist rollers to correct the skew by forming a loop in the sheet by a front end of the conveyed sheet abutting on the resist rollers, and controls to release the pressing member from being pressed to the conveying roller when a predetermined time elapses after the sheet starts forming the loop. 
     SUMMARY 
     According to some embodiments, a medium conveying apparatus includes a first roller to convey a medium, a movement mechanism to move the first roller between a first position in contact with the medium and a second position spaced apart from the medium, a second roller located on a downstream side of the first roller in a medium conveying direction to convey the medium, and a processor to detect a skew of the conveyed medium, and control the movement mechanism to move the first roller to the second position, and correct the skew of the medium using the second roller when the skew of the medium is detected. 
     According to some embodiments, a method for correcting a skew of a medium, includes, conveying the medium, by a first roller, moving the first roller between a first position in contact with the medium and a second position spaced apart from the medium, by a movement mechanism, conveying the medium, by a second roller located on a downstream side of the first roller in a medium conveying direction, detecting the skew of the conveyed medium, and controlling the movement mechanism to move the first roller to the second position, and correcting the skew of the medium using the second roller when the skew of the medium is detected. 
     According to some embodiments, a computer-readable, non-transitory medium stores a computer program. The computer program causes a medium conveying apparatus including a first roller to convey a medium, a movement mechanism to move the first roller between a first position in contact with the medium and a second position spaced apart from the medium, a second roller located on a downstream side of the first roller in a medium conveying direction to convey the medium, to execute a process including detecting the skew of the conveyed medium, and controlling the movement mechanism to move the first roller to the second position, and correcting the skew of the medium using the second roller when the skew of the medium is detected. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view illustrating a medium conveying apparatus  100 . 
         FIG. 2  is a diagram for illustrating a conveyance path inside the medium conveying apparatus  100 . 
         FIG. 3A  is a schematic view for illustrating a movement mechanism  113 . 
         FIG. 3B  is a schematic view for illustrating the movement mechanism  113 . 
         FIG. 4  is a schematic view for illustrating arrangement positions of each roller and each sensor. 
         FIG. 5  is a block diagram illustrating a schematic configuration of the medium conveying apparatus  100 . 
         FIG. 6  is a diagram illustrating schematic configurations of a storage device  140  and a processing circuit  150 . 
         FIG. 7  is a flowchart illustrating an operation example of the medium reading processing. 
         FIG. 8  is a schematic view for illustrating a skew of a medium. 
         FIG. 9  is a flowchart illustrating an operation example of the correction processing. 
         FIG. 10  is a schematic view for illustrating movement timing. 
         FIG. 11  is a schematic view illustrating a state in which a correction of the skew of the medium is completed. 
         FIG. 12  is a schematic view illustrating a state in which a front end of the medium has passed through a position of a sixth sensor. 
         FIG. 13  is a schematic view illustrating a state in which a rear end of the medium has passed through a position of the pick roller. 
         FIG. 14A  is a diagram for illustrating another movement mechanism  213 . 
         FIG. 14B  is a diagram for illustrating the other movement mechanism  213 . 
         FIG. 15  is a diagram illustrating a schematic configuration of a processing circuit  350  according to another embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory, and are not restrictive of the invention, as claimed. 
     Hereinafter, a medium conveying apparatus, a method for correcting a skew of a medium, and a computer-readable, non-transitory medium storing a computer program 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. 1  is a perspective view illustrating a medium conveying apparatus  100  configured as an image scanner. The medium conveying apparatus  100  conveys and images a medium being a document. The medium is a paper, a thick paper, a card, etc. The medium conveying apparatus  100  may be a fax machine, a copying machine, a multifunctional peripheral (MFP), etc. A conveyed medium may not be a document but may be an object being printed on etc., and the medium conveying apparatus  100  may be a printer etc. 
     The media conveying device  100  includes a first housing  101 , a second housing  102 , a medium tray  103 , an ejection tray  104 , an operation device  105  and a display device  106 , etc. 
     The first housing  101  is located on an upper side of the medium conveying apparatus  100  and is engaged with the second housing  102  by hinges so as to be opened and closed at a time of medium jam, during cleaning the inside of the medium conveying apparatus  100 , etc. 
     The medium tray  103  is engaged with the second housing  102  in such a way as to be able to place a medium to be conveyed. The medium tray  103  is provided on a side surface of the second housing  102  on a medium supply side to be movable in a substantially vertical direction (height direction) A 1 . The ejection tray  104  is a tray formed on the first housing  101  capable of holding the ejected medium, to load the ejected medium. 
     The operation device  105  includes 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 device  106  includes a display including a liquid crystal or organic electro-luminescence (EL), and an interface circuit for outputting image data to the display, and displays the image data on the display. 
     In  FIG. 1 , an arrow A 2  indicates a medium conveying direction, and an arrow A 3  indicates a width direction perpendicular to the medium conveying direction. Hereinafter, an upstream refers to an upstream in the medium conveying direction A 2 , and a downstream refers to a downstream in the medium conveying direction A 2 . 
       FIG. 2  is a diagram for illustrating a conveyance path inside the medium conveying apparatus  100 . 
     A conveyance path inside the medium conveying apparatus  100  includes a first sensor  111 , a pick roller  112 , a movement mechanism  113 , an encoder  114 , a feed roller  115 , a brake roller  116 , a second sensor  117 , a third sensor  118 , a fourth sensor  119 , a fifth sensor  120 , a first to eighth conveying rollers  121   a  to  121   h , a first to eighth driven rollers  122   a  to  122   h , a sixth sensor  123 , a first imaging device  124   a  and a second imaging device  124   b , etc. 
     The number of each of the pick roller  112 , the feed roller  115 , the brake roller  116 , the first to eighth conveying rollers  121   a  to  121   h , and/or the first to eighth driven rollers  122   a  to  122   h  is not limited to one, and may be plural. In that case, a plurality of feed rollers  115 , brake rollers  116 , first to eighth conveying rollers  121   a  to  121   h , and/or first to eighth driven rollers  122   a  to  122   h  are located apart from each other along in the width direction A 3  perpendicular to the medium conveying direction, respectively. 
     The surface of the first housing  101  facing the second housing  102  forms a first guide  101   a  of the medium conveyance path, and the surface of the second housing  102  facing the first housing  101  forms a second guide  102   a  of the medium conveyance path. 
     The first sensor  111  is located on the medium tray  103 , i.e., on the upstream side of the feed roller  115  and the brake roller  116 , to detect a mounting state of the medium in the medium tray  103 . The first sensor  111  determines whether or not the medium is placed on the medium tray  103 , by a contact detection sensor to pass a predetermined current when a medium is in contact or a medium is not in contact. The first sensor  111  generates and outputs a first medium signal whose signal value changes between a state in which a medium is placed on the medium tray  103  and a state in which a medium is not placed. The first sensor  111  is not limited to the contact detection sensor, any other sensor, such as a light detection sensor, capable of detecting the presence or absence of the medium may be used as the first sensor  111 . 
     The pick roller  112  is an example of a first roller. The pick roller  112  is provided in the first housing  101 , and comes into contact with the medium placed on the medium tray  103  lifted to a height substantially equal to that of the medium conveyance path to feed and convey the medium to the downstream side. 
     The encoder  114  is located in such a way that at least a part of the encoder  114  is overlapped with the pick roller  112  in the medium conveying direction A 2 , i.e., at least a part of the encoder  114  is overlapped with the pick roller  112  when viewed from the width direction A 3 , to detect a conveyance of the medium at an arrangement position of the pick roller  112 . The encoder  114  includes a disk on which a large number of slits (light transmission holes) are formed, the disk being provided to rotate according to the medium fed by the pick roller  113 , and a light emitter and a light receiver provided to face one another with the disk in between. The light emitter is an LED (Light Emitting Diode), etc., and emits light toward the disk (light receiver). The light receiver receives the light emitted by the light emitter through the disk. The light receiver detects the number of times of changes from a state in which a slit exists between the light emitter and the light receiver to a state in which the slit is not present and the light is blocked by the disk, within a predetermined period. The light receiver detects a movement distance of the medium conveyed by the pick roller  112  by multiplying the detected number of times of changes by a distance by which an outer peripheral surface of the encoder  114  moves when the disk rotates by a distance between two slits adjacent to each other. The encoder  114  generates and outputs a distance signal indicating the detected movement distance. 
     The feed roller  115  is an example of a second roller. The feed roller  115  is located in the first housing  101 , and on the downstream side of the pick roller  112  in the medium conveying direction A 2 , to feed and convey the medium placed on the medium tray  103  and fed and conveyed by the pick roller  112  further toward the downstream side. The brake roller  116  is located in the second housing  102 , to face the feed roller  115 . The feed roller  115  and the brake roller  116  perform a medium separation operation to separate the media and feed them one by one. 
     The first to eighth conveying rollers  121   a  to  121   h  and the first to eighth driven rollers  122   a  to  122   h  are provided on the downstream side of the feed roller  115  and the brake roller  116 , to convey the medium fed by the feed roller  115  and the brake roller  116  toward the downstream side. 
     The first imaging device  124   a  and the second imaging device  124   b  are examples of an Imaging device, and are located on the downstream side of the first to second conveying rollers  121   a  to  121   b , i.e., on the downstream side of the second to sixth sensors  117 ,  118 ,  119 ,  120  and  123 , in the medium conveying direction A 2 . 
     The first imaging device  124   a  includes a line sensor based on a unity-magnification optical system type contact image sensor (CIS) including an imaging element based on a complementary metal oxide semiconductor (CMOS) linearly located in a main scanning direction. Further, the first imaging device  124   a  includes a lens for forming an image on the imaging element, and an A/D converter for amplifying and analog-digital (A/D) converting an electric signal output from the imaging element. The first imaging device  124   a  generates and outputs an input image by imaging a front side of the conveyed medium. 
     Similarly, the second imaging device  124   b  includes a line sensor based on a unity-magnification optical system type CIS including an imaging element based on a CMOS linearly located in a main scanning direction. Further, the second imaging device  124   b  includes a lens for forming an image on the image element, and an A/D converter for amplifying and analog-digital (A/D) converting an electric signal output from the imaging element. The second imaging device  124   b  generates and outputs an input image by imaging a back side of the conveyed medium. 
     Only either of the first imaging device  124   a  and the second imaging device  124   b  may be located in the medium conveying apparatus  100  and only one side of a medium may be read. Further, a line sensor based on a unity-magnification optical system type CIS including an imaging element based on charge coupled devices (CCDs) may be used in place of the line sensor based on a unity-magnification optical system type CIS including an imaging element based on a CMOS. Further, a line sensor based on a reduction optical system type line sensor including an imaging element based on CMOS or CCDs may be used. Hereinafter, the first imaging device  124   a  and the second imaging device  124   b  may be collectively referred to as imaging devices  124 . 
     A medium placed on the medium tray  103  is conveyed in the medium conveying direction A 2  between the first guide  101   a  and the second guide  102   a  by the pick roller  112  rotating in a medium feeding direction A 11  and the feed roller  115  rotating in a medium feeding direction A 12 . On the other hand, when a plurality of media are placed on the medium tray  103 , only a medium in contact with the feed roller  115 , out of the media placed on the medium tray  103  is separated, by the brake roller  116  rotating in a direction A 13  opposite to the medium feeding direction. 
     The medium is fed to an imaging position of the imaging device  124  while being guided by the first guide  101   a  and the second guide  102   a , by the first to second conveyance rollers  121   a  to  121   b  rotating in directions of arrows A 14  to A 15 , respectively, and is imaged by the imaging device  124 . The medium is ejected on the ejection tray  104  by the third to eighth conveyance rollers  121   c  to  121   h  rotating in directions of arrows A 16  to A 21 , respectively. 
       FIGS. 3A and 3B  are schematic views for illustrating the movement mechanism  113 .  FIGS. 3A and 3B  are schematic views of the pick roller  112  and the movement mechanism  113 , as viewed from the side of the medium conveying apparatus  100 . 
     As illustrated in the  FIGS. 3A and 3B , the movement mechanisms  113  include a cam member  113   a  and a solenoid  113   b , etc. 
     The cam member  113   a  has a U-shape, and supports the pick roller  112 . One end  113   c  of the cam member  113   a  is rotatably supported by the first housing  101 , and a shaft  112   a  being a rotation shaft of the pick roller  112 , is attached to the other end of the cam member  113   a . The front end of the movable magnetic pole  113   e  of the solenoid  113   b  is attached to the central portion  113   d  of the cam member  113   a.    
     The solenoid  113   b  is located inside the first housing  101  so as to be inclined with respect to the cam member  113   a . The solenoid  113   b  slides the movable magnetic pole  113   e  in accordance with a control signal from a processing circuit to be described later. 
     As shown in  FIG. 3A , in an initial state, the movable magnetic pole  113   e  is pushed out, and the pick roller  112  attached to the cam member  113   a  is located at a first position in contact with the medium placed on the medium tray  103 . On the other hand, as shown in the  FIG. 3B , when the movable magnetic pole  113   e  is pulled in a direction of an arrow A 31 , the cam member  113   a  rotates about the one end  113   c  in a direction of an arrow A 32  according to the sliding motion of the movable magnetic pole  113   e . The pick roller  112  moves upward in the height direction A 1  according to the rotation of the cam member  113   a , and is located at a second position spaced apart from the medium placed on the medium tray  103 . Thus, the movement mechanism  113  moves the pick roller  112  between the first position in contact with the conveyed medium and the second position spaced apart from the conveyed medium. 
       FIG. 4  is a schematic view for illustrating the arrangement positions of each roller and each sensor.  FIG. 4  is a schematic view of a part of the first housing  101  in an open state, as viewed from the conveyance path side. 
     In an example shown in  FIG. 4 , The number of the pick roller  112 , the feed roller  115  and the first to eighth conveying rollers  121   a  to  121   h  included in the medium conveying apparatus  100  is two, respectively. 
     A plurality of feed rollers  115  are located apart from each other along in the width direction A 3  perpendicular to the medium conveying direction. The feed rollers  115  are provided in such a way as to independently rotate, and feed the medium by separate motors, respectively. The feed rollers  115  may be provided in such a way as to rotate by a common motor. 
     The second sensor  117  is an example of a second medium sensor. The second sensor  117  is located on the downstream side of the feed roller  115  and the brake roller  116  and on the upstream side of the first conveying roller  121   a  and the first driven roller  122   a , particularly on the upstream side of the third to fifth sensors  118  to  120 , in the medium conveying direction A 2 . The second sensor  117  is located at a central portion, particularly between the feed rollers  115 , in the width direction A 3  perpendicular to the medium conveying direction. The second sensor  117  includes a light emitter and a light receiver provided on one side with respect to the conveyance path of the medium, and a reflection member such as a mirror provided at a position facing the light emitter and the light receiver with the conveyance path in between. The light emitter is an LED, etc., and emits light toward the medium conveyance path. On the other hand, the light receiver receives light projected by the light emitter and reflected by the reflection member, and generates and outputs a second medium signal being an electric signal based on intensity of the received light. 
     The light emitted by the light emitter is shielded by the medium when the medium is present at the position of the second sensor  117 . Therefore, the signal value of the second medium signal is changed in a state where the medium is present at the position of the second sensor  117  and a state where the medium is not present. Consequently, the second sensor  117  detects whether or not a medium exists at the position and detects a fed medium. The light emitter and the light receiver of the second sensor  117  may be provided at positions facing one another with the conveyance path in between, and the reflection member may be omitted. The second sensor  117  may detect the presence of the medium by a contact detection sensor, etc., to pass a predetermined current when a medium is in contact or a medium is not in contact. 
     The third to fifth sensors  118  to  120  are examples of a plurality of medium sensors. The third to fifth sensors  118  to  120  are located on the downstream side of the feed roller  115  and the brake roller  116 , particularly on the downstream side of the second sensor  117 , and on the upstream side of the first conveying roller  121   a  and the first driven roller  122   a , in the medium conveying direction A 2 . The third to fifth sensors  118  to  120  are located apart from each other along in the width direction A 3  perpendicular to the medium conveying direction. The third sensor  118  is located in the central portion, in particular between the feed rollers  115 , in the width direction A 3 . The fourth and fifth sensors  119  and  120  are located outside the third sensor  118 , particularly outside the feed rollers  115 . The fourth and fifth sensors  119  and  120  are located on opposite sides to each other with respect to the third sensor  118 . 
     The third to fifth sensors  118  to  120  have the same configuration as the second sensor  117 , respectively. The third sensor  118  generates and outputs a third medium signal being an electrical signal corresponding to intensity of the received light emitted by the light emitter and reflected by the reflecting member. The fourth sensor  119  generates and outputs a fourth medium signal being an electrical signal corresponding to intensity of the received light emitted by the light emitter and reflected by the reflecting member. The fifth sensor  120  generates and outputs a fifth medium signal being an electrical signal corresponding to intensity of the received light emitted by the light emitter and reflected by the reflecting member. 
     The sixth sensor  123  is an example of a third medium sensor. The sixth sensor  123  is located on the downstream side of the first conveying roller  121   a  and the first driven roller  122   a  and on the upstream side of the second conveying roller  121   b  and the second driven roller  122   b , i.e., between the third to fifth sensors  118  to  120  and the imaging device  124 , in the medium conveying direction A 2 . The third sensor  118  is located in the central portion in the width direction A 3 , particularly between the first conveying rollers  121   a.    
     The sixth sensor  123  has the same configuration as the second sensor  117 . The sixth sensor  123  generates and outputs a sixth medium signal being an electrical signal corresponding to intensity of the received light emitted by the light emitter and reflected by the reflecting member. 
       FIG. 5  is a block diagram illustrating a schematic configuration of a medium conveying apparatus  100 . 
     The medium conveying apparatus  100  further includes a motor  131 , an interface device  132 , a storage device  140 , and a processing circuit  150 , etc., in addition to the configuration described above. 
     The motor  131  includes one or more motors, and rotatably drives the pick roller  112 , the feed roller  115 , the brake roller  116 , and the first to eighth conveying rollers  121   a  to  121   h  by a control signal from the processing circuit  150  to feed and convey the medium. In particular, the motor  131  has separate motors to rotate the feed rollers  115  independently, respectively. The first to eighth driven rollers  122   a  to  122   h  may be provided to rotate by the driving force from the motor  131  rather than to be driven to rotate according to the rotation of the first to eighth conveying rollers  121   a  to  121   h.    
     The interface device  132  includes, for example, an interface circuit conforming to a serial bus such as universal serial bus (USB), is electrically connected to an unillustrated information processing device (for example, a personal computer or a mobile information terminal), and transmits and receives an input image and various types of information. Further, a communication device including an antenna transmitting and receiving wireless signals, and a wireless communication interface circuit 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 device  132 . For example, the predetermined communication protocol is a wireless local area network (LAN). 
     The storage device  140  is an example of a storage module. The storage device  140  includes a memory device such as a random access memory (RAM) or a read only memory (ROM), a fixed disk device such as a hard disk, or a portable storage device such as a flexible disk or an optical disk. Further, the storage device  140  stores a computer program, a database, a table, etc., used for various types of processing in the medium conveying apparatus  100 . The computer program may be installed on the storage device  140  from a computer-readable, non-transitory medium such as a compact disc read only memory (CD-ROM), a digital versatile disc read only memory (DVD-ROM), etc., by using a well-known setup program, etc. 
     The processing circuit  150  operates in accordance with a program previously stored in the storage device  140 . The processing circuit  150  is, for example, a CPU (Central Processing Unit). The processing circuit  150  may 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 circuit  150  is connected to the operation device  105 , the display device  106 , the first sensor  111 , the solenoid  113   b , the encoder  114 , the second sensor  117 , the third sensor  118 , the fourth sensor  119 , the fifth sensor  120 , the sixth sensor  123 , the imaging device  124 , the motor  131 , the interface device  132  and the storage device  140 , etc., to control these respective units. The processing circuit  150  controls the motor  131  to feed and convey the medium, and controls the imaging device  124  to acquire an input image, and transmits the acquired input image to the information processing apparatus via the interface device  132 . The processing circuit  150  detects a skew of the medium based on each medium signal output from each sensor, controls the solenoid  113   b  to move the pick roller  112 , and controls the motor  131  to correct the skew of the medium. 
       FIG. 6  is a diagram illustrating schematic configurations of the storage device  140  and the processing circuit  150 . 
     As shown in  FIG. 6 , each program such as a control program  141  and a detection program  142 , etc., is stored in the storage device  140 . Each of these programs is a functional module implemented by software operating on a processor. The processing circuit  150  reads each program stored in the storage device  140  and operates in accordance with each read program, to function as a control module  151  and the detection module  152 . 
       FIG. 7  is a flowchart illustrating an operation example of the medium reading processing. 
     Hereinafter, the operation example of the medium reading processing in the medium conveying apparatus  100  will be described with referring to the flowchart shown in  FIG. 7 . The operation flow described below is executed mainly by the processing circuit  150  in cooperation with each element in the medium conveying apparatus  100 , in accordance with a program previously stored in the storage device  140 . Before the flow shown in  FIG. 7  is performed, the pick roller  112  is located in the first position in contact with the medium placed on the medium tray  103 . 
     First, the control module  151  stands by until an instruction to read a medium is input by the user by use of the operation device  105  or the information processing device, and an operation signal instructing to read the medium is received from the operation device  105  or the interface device  132  (step S 101 ). 
     Next, the control module  151  acquires the first medium signal from the first sensor  111  and determines whether or not a medium is placed on the medium tray  103  based on the acquired first medium signal (step S 102 ). When a medium is not placed on the medium tray  103 , the control module  151  returns the processing to step S 101  and stands by until newly receiving an operation signal from the operation device  105  or the interface device  132 . 
     On the other hand, when the medium is placed on the medium tray  103 , the control module  151  drives the motor  131  and rotates the pick roller  112 , the feed roller  115 , the brake roller  116 , and the first to eighth conveying rollers  121   a  to  121   h  (step S 103 ). Thus, the control module  151  feeds and conveys the medium placed on the medium tray  103 . At this time, the control module  151  rotates the feed rollers  115  so that the respective circumferential speeds of the feed rollers  115  are the same reference speed. 
     Next, the detection module  152  determines whether or not the skew of the conveyed medium has occurred (step S 104 ). The detection module  152  periodically acquires a second medium signal from the second sensor  117 , a third medium signal from the third sensor  118 , a fourth medium signal from the fourth sensor  119 , and a fifth medium signal from the fifth sensor  120 , respectively. The detection module  152  determines whether or not the skew of the conveyed medium has occurred based on the acquired second medium signal, the third medium signal, the fourth medium signal and the fifth medium signal. 
     The detection module  152  determines that the front end of the medium has passed through a position of each sensor that generated each medium signal when a signal value of each medium signal changes from a value indicating that there is no medium to a value indicating that a medium exists. For example, the detection module  152  determines that the skew of the medium has occurred when the front end of the medium passes through the position of the fourth sensor  119  or the fifth sensor  120 , before the front end of the medium passes through the position of the second sensor  117 . Further, the detection module  152  determines that the skew of the medium has occurred when the front end of the medium does not pass through the position of the third sensor  118  in a first predetermined time after the front end of the medium passes through the position of the fourth sensor  119  or the fifth sensor  120 , after the front end of the medium passes through the position of the second sensor  117 . The first predetermined time, for example, is set to the minimum value of a difference between the time when the front end of the medium conveyed with an inclination that causes a jam of the medium passes through the position of the fourth sensor  119  or the fifth sensor  120 , and the time when it passes through the position of the third sensor  118 . 
       FIG. 8  is a schematic view for illustrating the skew of the medium. 
     As shown in  FIG. 8 , when the front end of the conveyed medium M passes through the position of the fourth sensor  119  or the fifth sensor  120  located on the downstream side of the second sensor  117  and outside of the second sensor  117  before it passes through the position of the second sensor  117 , the medium M is likely to be inclined. Further, even when the front end of the medium M passes through the position of the fourth sensor  119  or the fifth sensor  120  located downstream of the second sensor  117 , after the front end of the medium M passes through the position of the second sensor  117 , the medium M may be inclined. For example, when the time from when the front end of the medium M passes through the position of the fourth sensor  119  or the fifth sensor  120  located on the outside to when it passes through the position of the third sensor  118  located in the central portion is large, the medium M is likely to be inclined. 
     Therefore, the detection module  152  determines whether or not the medium is conveyed with an inclination, to detect the skew of the fed and conveyed medium, based on the output signals from the second sensor  117 , the third sensor  118 , the fourth sensor  119  and the fifth sensor  120 . 
     Incidentally, the detection module  152  may determine whether or not the skew of the medium has occurred, based on the image generated by the imaging device  124 . In that case, the detection module  152  acquires a medium image including at least the front end of the conveyed medium from the imaging device  124 . The detection module  152  calculates an absolute value (hereinafter, referred to as an adjacent difference value) of the difference between the gradation values of both adjacent pixels in the vertical direction of each pixel in each vertical line, in order from the upper side, for each vertical line extending in the vertical direction (the sub-scanning direction) in the acquired medium image. The detection module  152  detects a pixel whose adjacent difference value exceeds a gradation threshold value in each vertical line as an edge pixel, and detects an edge pixel initially detected in each vertical line, i.e., an edge pixel located at the uppermost side as an upper edge pixel. The gradation value is a luminance value or a color value (R value, G value or B value). For example, the gradation threshold value may be set to a difference in brightness value (for example,  20 ) according to which a person may determine a difference in brightness on an image by visual observation. 
     The detection module  152  may calculate the absolute value of the difference between the gradation values of the two pixels separated each other by a predetermined distance in the vertical direction in the medium image as the adjacent difference value. Further, the detection module  152  may detect the edge pixel by comparing the gradation value of each pixel in the medium image with the threshold value. For example, the detection module  152  detects a specific pixel as the edge pixel when the gradation value of the specific pixel is less than the threshold value and the gradation value of the pixel adjacent to the specific pixel in the vertical direction or the pixel separated by a predetermined distance in the vertical direction is equal to or more than the threshold value. 
     Next, the detection module  152  detects a straight line passing through each upper edge pixel using the least squares method or the Huff transform. The detection module  152  calculates an inclination angle of the detected straight line with respect to the horizontal direction (the main scanning direction), and determines that the skew of the medium has occurred when the absolute value of the calculated inclination angle is equal to or more than the angle threshold value. 
     The control module  151  proceeds the process to step S 106  when the detection module  152  determines that the skew of the medium has not yet occurred, i.e., when the skew of the medium is not detected. 
     On the other hand, the control module  151  starts a correction processing (step S 105 ) when the detection module  152  determines that the skew of the medium has occurred, i.e., when the skew of the medium is detected. Thereafter, the correction processing is performed in parallel with the medium reading processing. The control module  151  controls the solenoid  113   b  to move the pick roller  112  to the second position spaced apart from the medium in the correction processing, and corrects the skew of the medium using the feed roller  115 . Details of the correction processing will be described later. 
     Next, the control module  151  determines whether or not the rear end of the medium has passed through the imaging position of the imaging device  124  (step S 106 ). The control module  151  periodically acquires the sixth medium signal from the sixth sensor  123 , and determines that the rear end of the medium has passed through the position of the sixth sensor  123  when the signal value of the sixth medium signal changes from a value indicating that the medium is present to a value indicating that there is no medium. The control module  151  determines that the rear end of the medium has passed through the imaging position when a second predetermined time has elapsed after the rear end of the medium passes through the position of the sixth sensor  123 . The second predetermined time is set to a value acquired by adding a margin to a division value acquired by dividing a distance between the position of the sixth sensor  123  and the imaging position, by a conveyance speed of the medium. When the rear end of the medium has not yet passed through the imaging position, the control module  151  returns the process to step S 104 , and repeats the processes in steps S 104  to S 106 . 
     On the other hand, when the rear end of the medium has passed through the imaging position, the control module  151  acquires the input image from the imaging device  124 , and outputs the acquired input image by transmitting it to the information processing apparatus via the interface device  132  (step S 107 ). 
     Next, the control module  151  determines whether or not a medium remains on the medium tray  103 , based on the first medium signal received from the first sensor  111  (step S 108 ). When a medium remains on the medium tray  103 , the control module  151  returns the process to step S 104  and repeats the processes in steps S 104  to S 108 . 
     On the other hand, when the medium does not remain on the medium tray  103 , the control module  151  stops the motor  131  to stop the rotation of the respective rollers (step S 109 ), and ends the series of steps. 
       FIG. 9  is a flowchart illustrating an operation example of the correction processing of the medium conveying apparatus  100 . 
     Hereinafter, the operation example of the correction processing in the medium conveying apparatus  100  will be described with referring to the flowchart shown in  FIG. 9 . The operation flow described below is executed mainly by the processing circuit  150  in cooperation with each element in the medium conveying apparatus  100 , in accordance with a program previously stored in the storage device  140 . The flow of the operation shown in  FIG. 9  starts in step S 105  of the medium reading processing shown in  FIG. 7 . 
     First, the control module  151  waits until the front end of the medium passes through the position of the second sensor  117  (step S 201 ). The control module  151  proceeds the process to step S 202  when the detection module  152  determines that the front end of the medium has already passed through the position of the second sensor  117  in step S 104 . On the other hand, the control module  151  determines whether or not the front end of the medium has passed through the position of the second sensor  117 , in the same manner as the process of step S 104 , when the detection module  152  has not yet determined that the front end of the medium has passed through the position of the second sensor  117  in step S 104 . 
     When the front end of the medium passes through the position of the second sensor  117 , the control module  151  controls the solenoid  113   b  to move the pick roller  112  to the second position spaced apart from the medium placed on the medium tray  103  (step S 202 ). Thus, the control module  151  controls the solenoid  113   b  so as to move the pick roller  112  to the second position when the front end of the fed and conveyed medium passes through the position of the second sensor  117 . 
       FIG. 10  is a schematic view for illustrating the movement timing of the pick roller  112 .  FIG. 10  shows a state in which the medium M shown in  FIG. 8  is further conveyed to the downstream side. 
     As shown in  FIG. 10 , the second sensor  117  is located on the downstream side of the feed rollers  115  in the medium conveying direction A 2  and between the feed rollers  115  in the width direction A 3 . Therefore, even when the medium M is conveyed with an inclination, the front end of the medium M is likely to have passed through a nip position of the feed roller  115  and the brake roller  116  when the front end of the medium M has passed through the position of the second sensor  117 . In particular, even when the medium M is conveyed in a state being placed in the central portion of the medium tray  103  in the width direction A 3 , or even when the medium M is conveyed in a state being placed closer to one end of the medium tray  103 , the front end of the medium M is likely to have passed through the nip position when the front end of the medium M has passed through the position of the second sensor  117 . Therefore, even when the pick roller  112  moves to the second position and is spaced apart from the medium M, the medium M is likely to be stably fed by the feed roller  115  and the brake roller  116 . 
     Thus, the control module  151  can more reliably feed the medium, by moving the pick roller  112  to the second position when the front end of the medium passes through the position of the second sensor  117 . 
     Incidentally, the process of step S 201  may be omitted, and the control module  151  may move the pick roller  112  to the second position, regardless of whether the front end of the medium has passed through the position of the second sensor  117 . In other words, the control module  151  may control the solenoid  113   b  to move the pick roller  112  to the second position when the front end of the fed and conveyed medium passes through the position of the fourth sensor  119  or the fifth sensor  120 . In other words, the control module  151  may control the solenoid  113   b  to move the pick roller  112  to the second position when the fed and conveyed medium first passes a position of any of a plurality of medium sensors. Thus, the control module  151  can start the correction of the medium earlier, and thereby, reduce the conveyance time of the medium. 
     Next, the control module  151  corrects the skew of the medium using the feed roller  115  (step S 203 ). The control module  151 , for example, corrects the skew of the medium by making the circumferential speeds of the feed rollers  115  vary from each other. 
     The control module  151  changes a circumferential speed of each feed roller  115  in such a way that a circumferential speed of a feed roller  115  located on the side where progression of the medium is delayed in the width direction A 3  is faster (higher) than a circumferential speed of a feed roller  115  located on the preceding side. The control module  151  accelerates (increases) the circumferential speed of the feed roller  115  located on the side where progression of the medium is delayed and/or decelerates (decreases) the circumferential speed of the feed roller  115  located on the preceding side. For example, the control module  151  sets each circumferential speed in such a way that the circumferential speed of the feed roller  115  located on the side where progression of the medium is delayed is faster than the circumferential speed of the feed roller  115  located on the preceding side by a factor greater than or equal to 3 and less than or equal to  10 . In the example shown in  FIG. 10 , each circumferential speed is set so that the circumferential speed of the right feed roller  115  is faster than the circumferential speed of the left feed roller  115 . 
     Thus, since the medium rotates about the feed roller  115  located on the preceding side, the skew of the medium is eliminated. Further, at this time, the pick roller  112  is located at the second position, and is not in contact with the fed medium. Therefore, the medium conveying apparatus  100  can efficiently rotate the medium to efficiently eliminate the skew of the medium. Further, since the medium is not pressed by the pick roller  112  while being rotated by the feed roller  115 , the medium conveying apparatus  100  can suppress that the damage of the medium occurs. 
     Further, the control module  151  returns the circumferential speed of the feed rollers  115  to the reference speed, and ends the skew correction of the medium, after a third predetermined time has elapsed after the skew correction of the medium is started. The third predetermined time may be changed according to the magnitude of the inclination of the medium. For example, the third predetermined time when the front end of the medium passes through the position of the fourth sensor  119  or the fifth sensor  120  before it passes through the position of the second sensor  117 , may be set to a value more than the third predetermined time otherwise. 
     Incidentally, the control module  151  may correct the skew of the medium, by controlling a stopper (not shown). In this case, the stopper is located on the downstream side of the feed roller  115  and on the upstream side of the first conveying roller  121   a  in the medium conveying direction A 2 . The stopper is movably provided between an opposed position facing the fed medium and the non-opposed position not facing the fed medium according to the driving force from the motor  131 . The control module  151  controls the motor to drive the stopper to place the stopper in the opposed position by the third predetermined time, to correct the skew of the medium, when the skew of the medium occurs. Although the fed medium is pushed to the downstream side by the feed roller  115 , the front end of the medium is stopped by the stopper and does not proceed to the downstream side of the stopper. Therefore, when the front end of the medium is inclined, the front end of the medium rotates so as to be substantially parallel to the width direction A 3  at the arrangement position of the stopper by the force pushed out by the feed roller  115 . 
     Next, the control module  151  waits until the restoration condition for returning the pick roller  112  to the first position in contact with the medium is satisfied (step S 204 ). 
     For example, the control module  151  determines that the restoration condition is satisfied when the correction of the skew of the medium is completed, i.e., when the third predetermined time elapses after the skew correction of the medium is started. Further, the control module  151  may determine that the restoration condition is satisfied when the front end of the medium passes through the position of the third sensor  118  located in the central portion of the width direction A 3 . 
     Further, the control module  151  may determine that the restoration condition is satisfied when the front end of the conveyed medium passes through the position of the sixth sensor  123  located on the downstream side of the third to fifth sensors  118  to  120 . In that case, the control module  151  periodically acquires the sixth medium signal from the sixth sensor  123 , and determines that the front end of the medium has passed through the position of the sixth sensor  123  when the signal value of the sixth medium signal changes from a value indicating that there is no medium to a value indicating that a medium is present. 
     Further, the control module  151  may determine that the restoration condition is satisfied when the conveyance of the medium at the arrangement position of the pick roller  112  stops. In that case, the control module  151  periodically acquires the distance signal from the encoder  114 , and determines that the conveyance of the medium at the arrangement position of the pick roller  112  stops when the movement distance indicated in the distance signal becomes  0 . That is, in this case, the rear end of the currently conveyed medium has passed through the arrangement position of the pick roller  112 , a medium to be fed next or a placing surface of placing table  103  is opposed to the pick roller  112 . 
     Next, when the restoration condition is satisfied, the control module  151  controls the solenoid  113   b  to return the pick roller  112  to the first position (step S 205 ), and ends the series of steps. 
       FIG. 11  is a schematic view illustrating a state in which the correction of the skew of the medium M shown illustrated in  FIG. 8 . 
     For example, the control module  151  returns the pick roller  112  to the first position when the correction of the skew of the medium M is completed and the skew of the medium M is eliminated, as shown in  FIG. 11 . Since the medium M in which the skew is eliminated is fed while being pressed by the pick roller  112  thereafter, it is suppressed that the medium M rotates too much, and thereby is inclined in the reverse direction. Therefore, the medium conveying apparatus  100  can suppress overcorrection of the skew of the medium M. 
       FIG. 12  is a schematic view showing a state in which the front end of the medium M shown in  FIG. 8  has passed through the position of the sixth sensor  123 . 
     For example, the control module  151  returns the pick roller  112  to the first position when the correction of the skew of the medium M is completed, and further the front end of the medium M passes through the position of the sixth sensor  123 , as shown in  FIG. 12 . Since the medium M in which the skew is eliminated is fed while being pressed by the pick roller  112  thereafter, it is suppressed that the medium M rotates too much, and thereby is inclined in the reverse direction. Therefore, the medium conveying apparatus  100  can suppress overcorrection of the skew of the medium M. In general, a fixed time is required from when the motor  131  is controlled to return the circumferential speed of each feed roller  115  to the reference speed until the circumferential speed of each feed roller  115  is actually changed. The control module  151  can return the pick roller  112  to the medium M at a timing when the correction of the skew of the medium M is more reliably completed, by returning the pick roller  112  when the medium M passes through the position of the sixth sensor  123 . Therefore, the control module  151  can prevent that the damage of the medium occurs. 
       FIG. 13  is a schematic view illustrating a state in which the rear end of the medium M shown in  FIG. 8  has passed through the position of the pick roller  112 . 
     For example, the control module  151  returns the pick roller  112  to the first position when the correction of the skew of the medium M is completed and further the rear end of the medium M passes through the position of the pick roller  112 , as shown in  FIG. 13 . Since the pick roller  112  does not contact the fed medium M, it is suppressed that the feed speed of the medium to be fed next suddenly changes, in particular, that the feed speed is increased, by the load applied to the medium to be fed next through the fed medium M. Therefore, the medium conveying apparatus  100  can suppress the occurrence of the jam of the medium, and a deviation (noise) of the medium in the input image, etc. 
     As described in detail above, the medium conveying apparatus  100  moves the pick roller  112  which is not used for the correction of the skew of the medium, to be spaced apart from the medium, while correcting the skew of the medium by the feed roller  115 , when the skew of the medium is detected. Thus, the medium conveying apparatus  100  can suppress that the load is applied to the medium by the pick roller  112  while the medium is rotated by the feed roller  115 , and thereby can satisfactorily correct the skew of the medium. 
     Further, since the medium conveying apparatus  100  can satisfactorily correct the skew of the medium, the user does not need to align the front end of the medium when setting the medium to the medium tray  103 . Therefore, the medium conveying apparatus  100  can improve the convenience of the user. 
       FIGS. 14A and 14B  are diagrams for illustrating a movement mechanism  213  of a medium conveying apparatus according to another embodiment.  FIGS. 14A and 14B  are a schematic views of the pick roller  112  and the movement mechanism  213 , as viewed from the side of the medium conveying apparatus. 
     As illustrated in  FIG. 14A  and  FIG. 14B , the movement mechanism  213  is used in place of the movement mechanism  113 . The movement mechanism  213  includes a cam member  213   a  and a second motor  213   b , etc. 
     The cam member  213   a  is rotatably provided inside the first housing  101  and supports the pick roller  112 . The shaft  112   a  being a rotation shaft of the pick roller  112 , is attached to one end of the cam member  213   a . A rack  213   c  is formed on a side portion of the cam member  213   a  so as to extend in an arc shape. 
     A pinion  213   d  is provided on a rotation shaft of the second motor  213   b  so as to be engaged with and combined with the rack  213   c . The second motor  213   b  rotates in accordance with a control signal from the processing circuit  150  to rotate the pinion  213   d.    
     As illustrated in  FIG. 14A , in the initialization, the pick roller  112  attached to the cam member  213   a  is located at the first position in contact with the medium placed on the medium tray  103 . On the other hand, as shown in  FIG. 14B , when the rotation shaft of the second motor  213   b  rotates in a direction of an arrow A 41 , the pinion  213   d  rotates in the direction of the arrow A 41 , the rack  213   c  moves according to the rotation of the pinion  213   d , and the cam member  213   a  rotates in a direction of an arrow A 42 . The pick roller  112  moves upward in the height direction A 1  according to the rotation of the cam member  213   a , and is located at a second position spaced apart from the medium placed on the medium tray  103 . Thus, the movement mechanism  213  moves the pick roller  112  between the first position in contact with the medium and the second position spaced apart from the medium. 
     As described in detail above, the medium conveying apparatus  100  can satisfactorily correct the skew of the medium even when using the second motor  213   b  as the movement mechanism. 
     The medium conveying apparatus may move the feed roller  115  to be spaced apart from the medium while correcting the skew of the medium using the first conveying roller  121   a  when the skew of the medium is detected. 
     In this case, the feed roller  115  is an example of the first roller, and the first conveying roller  121   a  is an example of the second roller. The movement mechanism  113  or  213  is provided to move the feed roller  115  between the first position in contact with the medium and the second position spaced apart from the medium. The first conveying rollers  121   a  are located apart from each other in the width direction A 3  perpendicular to the medium conveying direction, and are provided so as to independently rotate and convey the medium, respectively. The motor  131  includes separate motors to independently rotate the first conveying rollers  121   a , respectively. The controller  151  corrects the skew of the medium by making the circumferential speeds of the feed rollers  115  vary from each other. The third to fifth sensors  118  to  120  are located on the downstream side of the first conveying roller  121   a  and the upstream side of the sixth sensor  123  in the medium conveying direction A 2 . The second sensor  117  is located on the downstream side of the first conveying roller  121   a  and on the upstream side of the third to fifth sensors  118  to  120  in the medium conveying direction A 2  and between the first conveying rollers  121   a  in the width direction A 3 . The encoder  114  is located in such a way that at least a part of the encoder  114  is overlapped with the feed roller  115  in the medium conveying direction A 2 , i.e., at least a part of the encoder  114  is overlapped with the feed roller  115  when viewed from the width direction A 3 , to detect the conveyance of the medium at the arrangement position of the feed roller  115 . 
     As described in detail above, the medium conveying apparatus can satisfactorily correct the skew of the medium even when the feed roller  115  is moved to be spaced apart from the medium while correcting the skew of the medium using the first conveying roller  121   a.    
       FIG. 15  is a diagram illustrating a schematic configuration of a processing circuit  350  of a medium conveying apparatus according to another embodiment. 
     The processing circuit  350  is used in place of the processing circuit  150  of the medium conveying apparatus  100  and executes the medium read processing and the correction processing, etc., in place of the processing circuit  150 . The processing circuit  350  includes a control circuit  351  and a detection circuit  352 , etc. Note that each unit may be configured by an independent integrated circuit, a microprocessor, firmware, etc. 
     The control circuit  351  is an example of a control module, and has a function similar to the control module  151 . The control circuit  351  receives the operation signal from the operation device  105  and the first medium signal from the first sensor  111  and controls the motor  131  to control each roller based on the received signal. The control circuit  351  receives a detection result of the state of the medium including the skew of the medium from the detection circuit  352 . The control circuit  351  controls the motor  131  to correct the skew of the medium based on the received detection result, and controls the solenoid  113   b  or the second motor  213   b  to move the pick roller  112  or feed roller  115 . Further, the control circuit  351  acquires an input image from the imaging device  124 , and outputs it to the interface device  132 . 
     The detection circuit  352  is an example of a detection module, and has a function similar to the detection module  152 . The detection circuit  352  receives the distance signal from the encoder  114  and the second to sixth medium signals from the second to sixth sensors  117  to  120 ,  123 , detects the state of the medium including the skew of the medium based on the received signal, and outputs the detection result to the control circuit  351 . 
     As described in detail above, the medium conveying apparatus can satisfactorily correct the skew of the medium even when the medium reading processing and the correction processing are executed by the processing circuit  350 . 
     According to some embodiments, the medium conveying apparatus, the control method, and the computer-readable, non-transitory medium storing the control program, can satisfactorily correct the skew of the medium. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiment(s) of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.