MEDIUM FEEDING APPARATUS, MEDIUM FEEDING METHOD, AND NON-TRANSITORY RECORDING MEDIUM

Abstract

A medium feeding apparatus includes a media tray, a feed roller to sequentially feed a plurality of media placed on the media tray, a separation roller located facing the feed roller, and circuitry. The circuitry detects a leading end position of each of a plurality of media in a nip between the feed roller and the separation roller, determines a distance between a leading end position of a preceding medium, which is of the plurality of media in the nip, and a leading end position of a medium following the preceding medium, and sets a characteristic value of the separation roller based on the distance.

Description

BACKGROUND

The present disclosure relates to a medium feeding apparatus, a medium feeding method, and a non-transitory recording medium.

A medium conveying apparatus such as a scanner that sequentially feeds multiple media while separating the media and captures images of the media is required to prevent or reduce the occurrence of multi-feed in which two or more media are fed together.

A sheet feeding apparatus that includes a sensor that detects the number of sheets at a nip between a conveyance roller and a separation roller or downstream of the nip and a sheet position sensor that detects the position of a sheet projected downstream from the nip is known. When the sensor detects two sheets, the sheet feeding apparatus controls the pressure-contact load or the separation torque of the separation roller so that the position of the second sheet detected by the sheet position sensor matches a target value.

A sheet conveying apparatus that separates sheets multi-fed from a sheet bundle at a separation nip between a feed roller and a separation roller and conveys the sheets one by one is known. The sheet conveying apparatus images the next sheet separated by the separation roller by an area sensor, and detects a leading edge from the image data, thus acquiring a projection amount of the leading end of the next sheet from the separation nip. The sheet conveying apparatus determines the deterioration state of the separation roller based on the projection amount of the next sheet, and displays a warning according to the determination result.

A sheet feeding apparatus including a feeding rotator that feeds sheets stacked on a tray, size detection means that detects the size of a sheet in a width direction, and leading end detection means that detects a leading end of a sheet passing through a nip between a first member and a second member is known. When the sheet fed by the feeding rotator passes through a detection area of the leading end detection means, the sheet feeding apparatus moves the feeding rotator to a retracted position based on the detection according to the sheet size detected by the size detection means. When the fed sheet does not pass through the detection area, the sheet feeding apparatus moves the feeding rotator to the retracted position after a predetermined time period elapses since the feeding rotator starts to feed the sheet.

SUMMARY

In one aspect, a medium feeding apparatus includes a media tray, a feed roller to sequentially feed a plurality of media placed on the media tray, a separation roller located facing the feed roller, and circuitry. The circuitry detects a leading end position of each of a plurality of media in a nip between the feed roller and the separation roller, determines a distance between a leading end position of a preceding medium, which is one of the plurality of media in the nip, and a leading end position of a medium following the preceding medium, and sets a characteristic value of the separation roller based on the distance.

In another aspect, a medium feeding method includes sequentially feeding a plurality of media placed on a media tray by a feed roller, detecting a leading end position of each of a plurality of media in a nip between the feed roller and a separation roller located facing the feed roller, determining a distance between a leading end position of a preceding medium, which is one of the plurality of media in the nip, and a leading end position of a medium following the preceding medium, and setting a characteristic value of the separation roller based on the distance.

In another aspect, a non-transitory recording medium stores a plurality of instructions which, when executed by one or more processors of a medium feeding apparatus, causes the one or more processors to perform a method. The method includes sequentially feeding a plurality of media placed on a media tray by a feed roller, detecting a leading end position of each of a plurality of media in a nip between the feed roller and a separation roller located facing the feed roller, determining a distance between a leading end position of a preceding medium, which is one of the plurality of media in the nip, and a leading end position of a medium following the preceding medium, and setting a characteristic value of the separation roller based on the distance.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of embodiments of the present disclosure and many of the attendant advantages and features thereof can be readily obtained and understood from the following detailed description with reference to the accompanying drawings, wherein:

FIG. 1 is a perspective view of a medium feeding apparatus according to an embodiment;

FIG. 2 is a diagram illustrating a conveying path in the medium feeding apparatus of FIG. 1;

FIG. 3 is a schematic diagram for describing a first imaging device, etc. of the medium feeding apparatus of FIG. 1;

FIG. 4 is a schematic diagram for describing a driving mechanism of the medium feeding apparatus of FIG. 1;

FIG. 5 is a block diagram schematically illustrating a configuration of the medium feeding apparatus of FIG. 1;

FIG. 6 is a block diagram schematically illustrating a configuration of a storage device and a processing circuit of the medium feeding apparatus of FIG. 1;

FIG. 7 is a flowchart illustrating an example of a media reading process;

FIG. 8 is a flowchart illustrating an example of a setting process;

FIG. 9A and FIG. 9B are schematic diagrams each illustrating an example of an input image;

FIG. 10A and FIG. 10B are schematic diagrams each illustrating an example of an input image;

FIG. 11 is a flowchart illustrating another example of the setting process;

FIG. 12 is a flowchart illustrating another example of the setting process;

FIG. 13A and FIG. 13B are schematic diagrams each illustrating an example of a second input image; and

FIG. 14 is a block diagram schematically illustrating a configuration of a processing circuit according to another embodiment.

The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. Also, identical or similar reference numerals designate identical or similar components throughout the several views.

DETAILED DESCRIPTION

In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have a similar function, operate in a similar manner, and achieve a similar result.

Referring now to the drawings, embodiments of the present disclosure are described below. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

The objects and advantages of the present invention are recognized and achieved by the elements particularly pointed out in the appended claims and the combinations thereof. It is to be understood that both the above-described general description and the detailed description described below are exemplary and explanatory only and are not intended to restrict the claimed invention.

A medium feeding apparatus, a media feeding method, and a control program according to an aspect of the present disclosure are described below with reference to the drawings. However, the technical scope of the present disclosure is not limited to the embodiments described below but includes the scope of the appended claims and the equivalents thereof.

FIG. 1 is a perspective view of a medium feeding apparatus 100 as an image scanner. The medium feeding apparatus 100 feeds and conveys a medium, which is an original document, and images the medium. The medium is, for example, a sheet of plain paper, a sheet of thin paper, a sheet of thick paper, a card, or a booklet. The medium feeding apparatus 100 may be, for example, a facsimile machine, a copier, or a multifunction peripheral (MFP). The medium to be conveyed may be, for example, an object to be printed instead of an original document, and the medium feeding apparatus 100 may be, for example, a printer.

The medium feeding apparatus 100 includes a lower housing 101, an upper housing 102, a media tray 103, an ejection tray 104, an operation device 105, and a display device 106. In FIG. 1, Arrow A1 indicates the direction in which media are conveyed (may be referred to as a “medium conveying direction A1” in the following description). Arrow A2 indicates the width direction of the medium feeding apparatus 100 (may be referred to as a “width direction A2” in the following description) perpendicular to the medium conveying direction A1. Arrow A3 indicates the height direction perpendicular to a medium conveying path. In the following description, the term “upstream” refers to upstream in the medium conveying direction A1, and the term “downstream” refers to downstream in the medium conveying direction A1.

The upper housing 102 is located at a position covering the upper face of the medium feeding apparatus 100, and is engaged with the lower housing 101 via a hinge such that the upper housing 102 can be opened and closed to, for example, remove a jammed medium or clean the inside of the medium feeding apparatus 100.

The media tray 103 is engaged with the lower housing 101. Media to be fed and conveyed are placed on the media tray 103. The ejection tray 104 is engaged with the upper housing 102 and stacks ejected media. The ejection tray 104 may be engaged with the lower housing 101.

The operation device 105 includes an input device such as keys and an interface circuit that acquires signals from the input device. The operation device 105 receives an input operation performed by a user and outputs an operation signal corresponding to the input operation. The display device 106 includes a display and an interface circuit that outputs image data to the display, and displays image data on the display. Examples of the display include a liquid crystal display and an organic electroluminescent (EL) display.

FIG. 2 is a diagram illustrating a conveying path inside the medium feeding apparatus 100.

The medium feeding apparatus 100 includes a first media sensor 111, a feed roller 112, a separation roller 113, a light source device 114, a first imaging device 115, a pressing mechanism 116, a second media sensor 117, a first conveyance roller 118, a first driven roller 119, a third media sensor 120, a second imaging device 121, a second conveyance roller 122, and a second driven roller 123 along the conveying path.

The number of each of the feed roller 112, the separation roller 113, the first conveyance roller 118, the first driven roller 119, the second conveyance roller 122, and/or the second driven roller 123 is not limited to one but may be two or more. In this configuration, the two or more rollers of the feed rollers 112, the separation rollers 113, the first conveyance rollers 118, the first driven rollers 119, the second conveyance rollers 122, and/or the second driven rollers 123 are aligned and spaced apart in the width direction A2 perpendicular to the medium conveying direction.

The upper face of the lower housing 101 forms a lower guide 101a for the medium conveying path. The lower face of the upper housing 102 forms an upper guide 102a for the medium conveying path. The medium feeding apparatus 100 has a so-called straight path, feeds and conveys media placed on the media tray 103 sequentially from the bottom, and ejects the media to the ejection tray 104.

The first media sensor 111 is located upstream from the feed roller 112 and the separation roller 113. The first media sensor 111 includes a contact detection sensor and detects whether a medium is placed on the media tray 103. The first media sensor 111 generates a first media signal of which the signal value changes depending on whether a medium is placed on the media tray 103 and outputs the generated first media signal. The first media sensor 111 is not limited to the contact sensor. The first media sensor 111 may be any other sensor that can detect the presence of a medium such as an optical sensor.

The feed roller 112 is located in the lower housing 101. The feed roller 112 is rotatable in a medium feeding direction A4 and sequentially separates and feeds the media on the media tray 103 from the bottom. The separation roller 113 is a so-called brake roller or retard roller. The separation roller 113 is located in the upper housing 102 and faces the feed roller 112. The separation roller 113 is stoppable or rotatable in a direction A5 opposite to the medium feeding direction.

The pressing mechanism 116 is an example of a pressing device and presses the separation roller 113 toward the feed roller 112. The pressing mechanism 116 is designed to be able to adjust a pressing force to press the separation roller 113 toward the feed roller 112. The pressing mechanism 116 includes an elastic member 116a, a supporting member 116b, and a driving source 116c.

The elastic member 116a is, for example, a spring member such as a torsion coil spring. The clastic member 116a may be a rubber member or another spring member such as a compression coil spring. One end of the elastic member 116a is attached to the supporting member 116b, and the other end is attached to a shaft 113a of the separation roller 113. The elastic member 116a presses the separation roller 113 toward the feed roller 112.

The supporting member 116b supports the elastic member 116a. The supporting member 116b is designed to be movable according to a driving force generated by the driving source 116c.

Examples of the driving source 116c include a solenoid. The driving source 116c may be a motor or the like. The driving source 116c generates a driving force for adjusting a pressing force with which the elastic member 116a presses the separation roller 113 toward the feed roller 112 according to a control signal from a processing circuit described later. When the driving source 116c is a solenoid, the supporting member 116b slides in accordance with the linear movement of the movable magnetic pole of the solenoid and adjusts the pressing force applied by the elastic member 116a. When the driving source 116c is a motor, the supporting member 116b swings in accordance with the rotation of the motor and adjusts the pressing force applied by the elastic member 116a. When the driving source 116c is a motor, a rack and a pinion may be provided between the driving source 116c and the supporting member 116b. In this configuration, the supporting member 116b may slide in accordance with the rotation of the motor and adjusts the pressing force applied by the elastic member 116a.

The second media sensor 117 is located downstream from the feed roller 112 and upstream from the first conveyance roller 118 and detects a medium conveyed to the position where the second media sensor 117 is located. The second media sensor 117 includes a light emitter, a light receiver, and a light guide. The light emitter and the light receiver are located on one side of the medium conveying path. The light guide faces the light emitter and the light receiver across the medium conveying path. The light emitter is, for example, a light-emitting diode (LED), and emits light toward the medium conveying path. The light receiver is, for example, a photodiode and receives light that is emitted by the light emitter and guided by the light guide. When a medium is present at a position facing the second media sensor 117, the light emitted from the light emitter is blocked by the medium, and therefore the light receiver does not detect the light emitted from the light emitter. Based on the intensity of the light received by the light receiver, the second media sensor 117 generates and outputs a second media signal of which the signal value changes between when a medium is present at the position of the second media sensor 117 and when a medium is absent at the position of the second media sensor 117.

A reflector such as a mirror may be used instead of the light guide. The light emitter and the light receiver may be located facing each other with the medium conveying path. Further, the second media sensor 117 may detect the presence of the medium with, for example, a contact sensor that causes a predetermined current to flow when a medium is in contact with the contact sensor or when no medium is in contact with the contact sensor.

The first conveyance roller 118 and the first driven roller 119 are located downstream from the feed roller 112 and the separation roller 113 in the medium conveying direction A1 and face each other. The first conveyance roller 118 is located in the upper housing 102 and conveys the medium fed by the feed roller 112 and the separation roller 113 to the second imaging device 121. Alternatively, the first conveyance roller 118 may be located in the lower housing 101 and the first driven roller 119 may be located in the upper housing 102.

The third media sensor 120 is located downstream from the first conveyance rollers 118 and upstream from the second imaging device 121 and detects the medium conveyed to the position where the third media sensor 120 is located. The third media sensor 120 includes a light emitter, a light receiver, and a light guide. The light emitter and the light receiver are located on one side of the medium conveying path. The light guide faces the light emitter and the light receiver across the medium conveying path. The light emitter is, for example, an LED and emits light toward the medium conveying path. The light receiver is, for example, a photodiode and receives light that is emitted by the light emitter and guided by the light guide. Based on the intensity of the light received by the light receiver, the third media sensor 120 generates and outputs a third media signal of which the signal value changes between when a medium is present at the position of the third media sensor 120 and when a medium is absent at the position of the third media sensor 120.

A reflector such as a mirror may be used instead of the light guide. The light emitter and the light receiver may be located facing each other with the medium conveying path therebetween. Further, the third media sensor 120 may detect the presence of the medium with, for example, a contact sensor that causes a predetermined current to flow when a medium is in contact with the contact sensor or when no medium is in contact with the contact sensor.

The second conveyance rollers 122 is located downstream from the first conveyance roller 118 and upstream from the second conveyance roller 122 in the medium conveying direction A1. The second imaging device 121 images the medium conveyed by the first conveyance roller 118 and the first driven roller 119. The second imaging device 121 includes a front-side imaging device 121a and a back-side imaging device 121b facing each other with the medium conveying path therebetween.

The front-side imaging device 121a includes a line sensor based on a unity-magnification optical system type contact image sensor (CIS) including complementary metal oxide semiconductor—(CMOS-) based imaging elements linearly arranged in a main scanning direction. The front-side imaging device 121a further includes a lens that forms an image on the imaging elements and an analog-to-digital (A/D) converter that amplifies electrical signals output from the imaging elements and performs A/D conversion. The front-side imaging device 121a generates a medium image by imaging the front side of a conveyed medium under control of a processing circuit described later and outputs the generated medium image.

Similarly, the back-side imaging device 121b includes a line sensor based on a unity-magnification optical system type CIS including CMOS-based imaging elements linearly arranged in the main scanning direction. The back-side imaging device 121b further includes a lens that forms an image on the imaging elements and an A/D converter that amplifies electrical signals output from the imaging elements and performs A/D conversion. The back-side imaging device 121b generates a medium image by imaging the back side of a conveyed medium under control of the processing circuit described later and outputs the generated medium image.

The second imaging device 121 may include either the front-side imaging device 121a or the back-side imaging device 121b and read only one side of the medium. Instead of the line sensor based on a unity-magnification optical system type CIS including CMOS-based imaging elements, a line sensor based on a unity-magnification optical system type CIS including charge-coupled device—(CCD-) based imaging elements may be used. A reduction optical system type line sensor including CMOS-based or CCD-based imaging elements may be used.

The second conveyance roller 122 and the second driven roller 123 are located downstream from the second imaging device 121, that is, from the first conveyance roller 118 and the first driven roller 119 in the medium conveying direction A1 and face each other. The second conveyance roller 122 is located in the upper housing 102. The second conveyance roller 122 conveys the medium conveyed by the first conveyance roller 118 and the first driven roller 119 further downstream and ejects the medium to the ejection tray 104. Alternatively, the second conveyance roller 122 may be located in the lower housing 101 and the second driven roller 123 may be located in the upper housing 102.

As the feed roller 112 rotates in the medium feeding direction A4, the medium is conveyed from the media tray 103 in the medium conveying direction A1 between the lower guide 101a and the upper guide 102a. The medium feeding apparatus 100 has two feeding modes: a separation mode in which media are fed while being separated and a non-separation mode in which media are fed without being separated. The feeding mode is set by a user using the operation device 105 or an information processing apparatus connected to the medium feeding apparatus 100 for communication. When the feeding mode is set to the separation mode, the separation roller 113 rotates in the direction A5 opposite to the medium feeding direction or stops. Due to the action of the feed roller 112 and the separation roller 113, when a plurality of media is placed on the media tray 103, only a medium in contact with the feed roller 112 among the media placed on the media tray 103 is separated. This prevents the feeding of a medium other than the separated medium. In other words, the multi-feed is prevented. When the feeding mode is set to the non-separation mode, the separation roller 113 rotates in the medium feeding direction opposite to the direction A5.

The medium is fed between the first conveyance roller 118 and the first driven roller 119 while being guided by the lower guide 101a and the upper guide 102a. As the first conveyance roller 118 and the first driven roller 119 rotate in the forward directions A6 and A7, respectively, the medium is fed between the front-side imaging device 121a and the back-side imaging device 121b. After the second imaging device 121 reads the medium, the medium is ejected to the ejection tray 104 as the second conveyance roller 122 and the second driven roller 123 rotate in the directions A8 and A9, respectively.

FIG. 3 is a schematic diagram of the light source device 114 and the first imaging device 115. Specifically, FIG. 3 is a schematic view of an area around the medium conveying path viewed from the upper housing 102 side.

In the example illustrated in FIG. 3, two feed rollers 112, two separation rollers 113, two first conveyance rollers 118, two first driven rollers 119, two second conveyance rollers 122, and two second driven rollers 123 are located.

The light source device 114 includes a first light source device 114a and a second light source device 114b.

The first light source device 114a is an example of a light emitter. The first light source device 114a is located in the upper housing 102 upstream from a nip N between each pair of the feed roller 112 and the separation roller 113 in the medium conveying direction A1 and between the nips N between one pair of the feed roller 112 and the separation roller 113 in the width direction A2 and the nip N between the other pair of the feed roller 112 and the separation roller 113. The first light source device 114a is, for example, an LED and emits light downward and downstream. The first light source device 114a irradiates an area overlapping with the nip N when viewed from the width direction A2 perpendicular to the medium conveying direction, that is, an area overlapping with the nip N in the medium conveying direction A1. The first light source device 114a irradiates an area between the two nips N in the width direction A2.

The second light source device 114b is an example of a second light emitter. The second light source device 114b is located in the upper housing 102 upstream from the nip N between each pair of the feed roller 112 and the separation roller 113 in the medium conveying direction A1 and between the nip N between one pair of the feed roller 112 and the separation roller 113 and the nip N between the other pair of the feed roller 112 and the separation roller 113 in the width direction A2. The second light source device 114b is, for example, an LED and emits light downward and downstream. The second light source device 114b irradiates the area overlapping with the nip N when viewed from the width direction A2 perpendicular to the medium conveying direction, that is, the area overlapping with the nip N in the medium conveying direction A1 from a direction different from a direction in which the first light source device 114a irradiates the area. The second light source device 114b irradiates the area between the two nips N in the width direction A2 in the same or substantially the same manner as the first light source device 114a.

The second light source device 114b is located upstream from the first light source device 114a in the medium conveying direction A1. In other words, an angle between the direction of the light emitted from the second light source device 114b and the medium conveying path is smaller than an angle between the direction of the light emitted from the first light source device 114a and the medium conveying path. For example, the first light source device 114a is located so that the angle between the direction of the light emitted from the first light source device 114a and the medium conveying path is equal to or greater than 45° and less than 90°. The second light source device 114b is set so that the angle between the direction of the light emitted from the second light source device 114b and the medium conveying path is less than 45° and greater than 0°.

The first imaging device 115 is an example of an imager. The first imaging device 115 is located in the upper housing 102 downstream from the nip N between each pair of the feed roller 112 and the separation roller 113 in the medium conveying direction A1. The first imaging device 115 is located between the nip N between one pair of the feed roller 112 and the separation roller 113 and the nip N between the other pair of the feed roller 112 and the separation roller 113 in the width direction A2. The first imaging device 115 includes a reduction optical system type imaging sensor including CCD-based imaging elements arranged two-dimensionally. The first imaging device 115 further includes a lens that forms an image on the imaging elements and an A/D converter that amplifies electrical signals output from the imaging elements and performs A/D conversion. The first imaging device 115 generates an input image by imaging the leading end position of the fed medium in an area overlapping with the nip N when viewed from the width direction A2 perpendicular to the medium conveying direction and between the two nips N in the width direction A2.

Instead of the reduction optical system type imaging sensor including the CCD-based imaging elements, a reduction optical system type imaging sensor including a CMOS-based imaging elements may be used. Alternatively, a unity-magnification optical system type imaging sensor including CCD-based or CMOS-based imaging elements may be used. Still alternatively, instead of the imaging sensor including the imaging elements arranged two dimensionally, an imaging sensor (line sensor) including imaging elements arranged one dimensionally along the width direction A2 may be used. In this configuration, the first imaging device 115 generates line images by imaging a predetermined position of a fed medium at regular intervals and generates an input image by combining the line images.

The input image generated by the first imaging device 115 is used to detect the state of the leading end of a medium placed on the media tray 103. By using the two-dimensional input image including the area between the two nips N, the medium feeding apparatus 100 can properly detect the state of the leading end of the medium regardless of the position of the leading end of the medium within the imaging range of the first imaging device 115. By detecting the state of the leading end of the medium using one input image generated at a predetermined timing, the medium feeding apparatus 100 can detect the state of the leading end of the medium with less load than when the leading end of the medium is continuously monitored at a predetermined position (point). Further, since the medium feeding apparatus 100 can detect the state of the leading end of the medium using only one first imaging device 115 without using a plurality of sensors, an increase in the cost and size of the apparatus is prevented or reduced.

The first imaging device 115 can generate an input image in which the leading end of the medium is imaged more suitably by imaging from the downstream side toward the upstream side. However, the medium to be fed is likely to be a white medium such as a plain paper copier (PPC). Accordingly, it may be difficult to identify the leading end of the medium in the input image. To cope with this, the first light source device 114a emits light from the upstream side toward the downstream side, thereby forming the shadow of the leading end of the medium favorably when viewed from the first imaging device 115. Thus, the leading end of the medium is clearly included in the input image. Further, the second light source device 114b emits light from a direction different from the first light source device 114a, thereby forming a shadow of the leading end of the medium that is different in thickness from the shadow formed by the first light source device 114a. Thus, the medium feeding apparatus 100 can detect the state of the leading end of the medium with high accuracy by using the difference in thickness between the shadows of the leading end of the medium formed by the first light source device 114a and the second light source device 114b.

FIG. 4 is a schematic diagram illustrating the driving mechanism 130 of the separation roller 113. Specifically, FIG. 4 is a schematic top view of an area around the separation roller 113 in the upper housing 102.

As illustrated in FIG. 4, the driving mechanism 130 includes a first motor 131, first to sixth gears 132a to 132f, first to fourth electromagnetic clutches 133a to 133d, and first to fourth torque limiters 134a to 134d.

The first motor 131 is coupled to the separation roller 113 via the first to sixth gears 132a to 132f and the shaft 113a and drives the separation roller 113. The first motor 131 generates a driving force for rotating the separation roller 113 according to a control signal from the processing circuit such that the separation roller 113 separates and feeds a medium. Examples of the first motor 131 include a direct current (DC) motor such as a brushed DC motor. Alternatively, the first motor 131 may be another type of DC motor such as a brushless DC motor, or a stepping motor. The first motor 131 is designed such that the motor torque of the first motor 131 can be changed according to supplied electric power.

The greater the amount of current supplied to the DC motor or the stepping motor, that is, the greater the amount of electric power supplied to the DC motor or the stepping motor, the greater the motor torque of the DC motor or the stepping motor. Conversely, the smaller the amount of current supplied to the DC motor or the stepping motor, that is, the smaller the amount of electric power supplied to the DC motor or the stepping motor, the smaller the motor torque of the DC motor or the stepping motor. Accordingly, the medium feeding apparatus 100 can change the motor torque of the first motor 131 by changing the amount of electric power supplied to the first motor 131. The medium feeding apparatus 100 can increase the motor torque of the first motor 131 by increasing the amount of electric power supplied to the first motor 131, and thus can increase the torque applied to the separation roller 113 (i.e., a load component applied to a medium by the separation roller 113). On the other hand, the medium feeding apparatus 100 can reduce the motor torque of the first motor 131 by reducing the amount of electric power supplied to the first motor 131, and thus can reduce the torque applied to the separation roller 113 (i.e., a load component applied to a medium by the separation roller 113).

The first gear 132a is attached to the rotation shaft of the first motor 131. The first gear 132a is engaged with the second gear 132b, the second gear 132b is engaged with the third gear 132c, the third gear 132c is engaged with the fourth gear 132d, the fourth gear 132d is engaged with the fifth gear 132e, and the fifth gear 132e is engaged with the sixth gear 132f. The sixth gear 132f is attached to one end of the shaft 113a which is the rotation shaft of the separation roller 113.

The first electromagnetic clutch 133a is attached to a shaft which is the rotation shaft of the second gear 132b. The first torque limiter 134a is attached to the shaft which is the rotation shaft of the second gear 132b via the first electromagnetic clutch 133a. The first torque limiter 134a defines a limit value of the torque applied to the separation rollers 113 by defining a limit value of the torque applied to the second gear 132b. The limit value of the first torque limiter 134a is set so that the limit value of the torque applied to the separation roller 113 is a first limit value when only the first torque limiter 134a is coupled to the separation roller 113. In other words, the limit value of the first torque limiter 134a is set so that the sum of the limit value of the first torque limiter 134a and the motor torque of the first motor 131 is the first limit value. The first electromagnetic clutch 133a is, for example, a micro powder clutch, and connects or disconnects power between the second gear 132b and the first torque limiter 134a according to a control signal from the processing circuit.

The second electromagnetic clutch 133b is attached to a shaft which is the rotation shaft of the third gear 132c. The second torque limiter 134b is attached to the shaft which is the rotation shaft of the third gear 132c via the second electromagnetic clutch 133b. The second torque limiter 134b defines a limit value of the torque applied to the separation rollers 113 by defining a limit value of the torque applied to the third gear 132c. The limit value of the second torque limiter 134b is set so that the limit value of the torque applied to the separation roller 113 is a second limit value when only the second torque limiter 134b is coupled to the separation roller 113. In other words, the limit value of the second torque limiter 134b is set so that the sum of the limit value of the second torque limiter 134b and the motor torque of the first motor 131 is the second limit value. The second electromagnetic clutch 133b is, for example, a micro powder clutch, and connects or disconnects power between the third gear 132c and the second torque limiter 134b according to a control signal from the processing circuit.

The third electromagnetic clutch 133c is attached to a shaft which is the rotation shaft of the fourth gear 132d. The third torque limiter 134c is attached to the shaft which is the rotation shaft of the fourth gear 132d via the third electromagnetic clutch 133c. The third torque limiter 134c defines a limit value of the torque applied to the separation rollers 113 by defining a limit value of the torque applied to the fourth gear 132d. The limit value of the third torque limiter 134c is set so that the limit value of the torque applied to the separation roller 113 is a third limit value when only the third torque limiter 134c is coupled to the separation roller 113. In other words, the limit value of the third torque limiter 134c is set so that the sum of the limit value of the third torque limiter 134c and the motor torque of the first motor 131 is the third limit value. The third electromagnetic clutch 133c is, for example, a micro powder clutch, and connects or disconnects power between the fourth gear 132d and the third torque limiter 134c according to a control signal from the processing circuit.

The fourth electromagnetic clutch 133d is attached to a shaft which is the rotation shaft of the fifth gear 132e. The fourth torque limiter 134d is attached to the shaft which is the rotation shaft of the fifth gear 132e via the fourth electromagnetic clutch 133d. The fourth torque limiter 134d defines a limit value of the torque applied to the separation rollers 113 by defining a limit value of the torque applied to the fifth gear 132e. The limit value of the fourth torque limiter 134d is set so that the limit value of the torque applied to the separation roller 113 is a fourth limit value when only the fourth torque limiter 134d is coupled to the separation roller 113. In other words, the limit value of the fourth torque limiter 134d is set so that the sum of the limit value of the fourth torque limiter 134d and the motor torque of the first motor 131 is the fourth limit value. The fourth electromagnetic clutch 133d is, for example, a micro powder clutch, and connects or disconnects power between the fifth gear 132e and the fourth torque limiter 134d according to a control signal from the processing circuit.

When the first to fourth electromagnetic clutches 133a to 133d connect power, the torques applied to the second to fifth gears 132b to 132e are limited by the first to fourth torque limiters 134a to 134d, respectively. On the other hand, when the first to fourth electromagnetic clutches 133a to 133d disconnect power, the torques applied to the second to fifth gears 132b to 132e are not limited by the first to fourth torque limiters 134a to 134d, respectively.

The limit value of the torque applied to the separation roller 113 is an example of a torque value of the separation roller 113 and an example of a characteristic value of the separation roller 113. The first limit value, the second limit value, the third limit value, and the fourth limit value are examples of a first torque value, a second torque value, a third torque value, and a fourth torque value, respectively.

The first limit value, the second limit value, the third limit value, and the fourth limit value are set to values at which the transmission of a first driving force from the first motor 131 is cut off when one medium is fed and the first driving force from the first motor 131 is transmitted when multiple media are fed. As a result, when one medium is fed, the separation roller 113 is rotated by the rotation of the feed roller 112, without being rotated by the driving force from the first motor 131. In other words, the separation roller 113 is set to rotate in the same direction as the feed roller 112 when a torque equal to or greater than the limit value is applied to the separation roller 113. When multiple media are fed, the separation roller 113 rotates in the direction A5 opposite to the medium feeding direction and separates the medium in contact with the feed roller 112 from the other media to prevent the occurrence of multi-feed. At this time, instead of rotating in the direction A5 opposite to the medium feeding direction, the separation roller 113 may be kept stationary such that the outer circumferential surface of the separation roller 113 applies a force in the direction A5 opposite to the medium feeding direction to the media.

The limit value of the second torque limiter 134b is set to a value greater than the limit value of the first torque limiter 134a. The limit value of the third torque limiter 134c is set to a value greater than the limit value of the first torque limiter 134a and smaller than the limit value of the second torque limiter 134b. The limit value of the fourth torque limiter 134d is set to a value equal to or greater than the limit value of the second torque limiter 134b. The limit values of the first to fourth torque limiters 134a to 134d are set to values smaller than the motor torque of the first motor 131. In other words, the second limit value is set to a value greater than the first limit value. The third limit value is set to a value greater than the first limit value and smaller than the second limit value. The fourth limit value is set to a value equal to or greater than the second limit value. The medium feeding apparatus 100 can change the limit value of the torque applied to the separation roller 113 by controlling the first to fourth electromagnetic clutches 133a to 133d.

In the following description, the first to fourth electromagnetic clutches 133a to 133d may be collectively referred to as “electromagnetic clutches 133,” each of which may be referred to as an “electromagnetic clutch 133.” The electromagnetic clutch 133 may be another type of clutch such as a hysteresis clutch. Alternatively, an electromagnetic brake such as a micro powder brake or a hysteresis brake may be used instead of the electromagnetic clutch 133.

FIG. 5 is a block diagram schematically illustrating a configuration of the medium feeding apparatus 100.

The medium feeding apparatus 100 further includes a second motor 141, a third motor 142, an interface device 143, a storage device 150, and a processing circuit 160, in addition to the above-described configuration.

The second motor 141 rotates the feed roller 112 according to a control signal from the processing circuit 160 and feeds a medium.

The third motor 142 rotates the first conveyance roller 118 and the second conveyance roller according to a control signal from the processing circuit 160 and conveys a medium. Alternatively, the first driven roller 119 and/or the second driven roller 123 may be driven by the driving force from the third motor 142.

The interface device 143 includes an interface circuit compatible with a serial bus such as a universal serial bus (USB) and is electrically connected to an information processing apparatus (e.g., a personal computer or a mobile information processing terminal) to transmit and receive an input image and various kinds of information to and from the information processing apparatus. The interface device 143 may be substituted by a communication unit including an antenna to transmit and receive wireless signals and a wireless communication interface device to transmit and receive the signals through a wireless communication line according to a predetermined communication protocol. The predetermined communication protocol is, for example, a wireless local area network (LAN) communication protocol. The communication unit may include a wired communication interface device to transmit and receive signals through a wired communication line according to, for example, a wired LAN communication protocol.

The storage device 150 includes memories such as a random-access memory (RAM) and a read-only memory (ROM), a fixed disk device such as a hard disk, or a portable memory such as a flexible disk or an optical disc. The storage device 150 stores, for example, computer programs, databases, and tables used for various processes performed by the medium feeding apparatus 100. The computer programs may be installed in the storage device 150 from a computer-readable portable recording medium using, for example, a known setup program. The portable recording medium is, for example, a compact disc read-only memory (CD-ROM) or a digital versatile disc read-only memory (DVD-ROM).

The processing circuit 160 operates according to a program prestored in the storage device 150. The processing circuit 160 is, for example, a central processing unit (CPU). Alternatively, a digital signal processor (DSP), a large-scale integration (LSI), an application-specific integrated circuit (ASIC), or a field-programmable gate array (FPGA) may be used as the processing circuit 160.

The processing circuit 160 is connected to the operation device 105, the display device 106, the first media sensor 111, the light source device 114, the first imaging device 115, the second media sensor 117, the third media sensor 120, the second imaging device 121, the driving source 116c, the first motor 131, the electromagnetic clutches 133, the second motor 141, the third motor 142, the interface device 143, and the storage device 150, and controls these components. The processing circuit 160 controls the driving of the motors described above and the imaging by the second imaging device 121 according to the media signals received from the media sensors described above. The processing circuit 160 acquires the medium image from the second imaging device 121 and transmits the medium image to the information processing apparatus via the interface device 143. Further, the processing circuit 160 detects the leading end position of the medium in the nip N based on the input image acquired from the first imaging device 115, and sets the characteristic value of the separation roller 113 based on the detection result.

FIG. 6 is a block diagram schematically illustrating a configuration of the storage device 150 and the processing circuit 160.

As illustrated in FIG. 6, the storage device 150 stores a control program 151, a detection program 152, and a setting program 153. These programs are functional modules implemented by software operating on a processor. The processing circuit 160 reads the programs from the storage device 150 and operates according to the read programs. Thus, the processing circuit 160 functions as a control unit 161, a detection unit 162, and a setting unit 163.

FIG. 7 is a flowchart illustrating an example of a media reading process performed by the medium feeding apparatus 100.

A description is given below of the media reading process performed by the medium feeding apparatus 100, with reference to the flowchart of FIG. 7. The operation process described below is executed, for example, by the processing circuit 160 in cooperation with the components of the medium feeding apparatus 100 according to the programs prestored in the storage device 150.

The control unit 161 waits until the control unit 161 receives an operation signal instructing the reading of media from the operation device 105 or the interface device 143 (step S101). The operation signal is output when the user inputs an instruction to read media using the operation device 105 or the information processing apparatus.

Subsequently, the control unit 161 acquires the first media signal from the first media sensor 111 and determines whether a medium is placed on the media tray 103 based on the acquired first media signal (step S102). When no medium is present on the media tray 103, the control unit 161 ends the series of steps.

By contrast, when a medium is placed on the media tray 103, the processing circuit 160 performs a setting process (step S103). In the setting process, the processing circuit 160 detects the leading end positions of media in the nip N and sets the characteristic value of the separation roller 113 based on the detection result. A detailed description is given later of the setting process.

Subsequently, the control unit 161 drives the second motor 141 to rotate the feed roller 112 to feed media and drives the first motor 131 to rotate the separation roller 113 to separate the media. Further, the control unit 161 drives the third motor 142 to rotate the first conveyance rollers 118, the first driven roller 119, the second conveyance roller 122, and/or the second driven roller 123 to convey the medium (step S104). At this time, as the separation roller 113 is rotating according to the characteristic value being set in the setting process of step S103, the medium feeding apparatus 100 can appropriately control the separation roller 113 depending on the leading end positions of the media placed on the media tray 103 and appropriately separate the media.

Subsequently, the control unit 161 waits until the leading end of the fed medium passes through a nip between the first conveyance roller 118 and the first driven rollers 119 (step S105). In the following description, the nip between the first conveyance roller 118 and the first driven roller 119 may be referred to as a “conveyance area.” The control unit 161 periodically acquires the third media signal from the third media sensor 120 and determines that the leading end of the medium has passed through the position of the third media sensor 120 when the signal value of the third media signal changes from a value indicating the absence of a medium to a value indicating the presence of a medium. The control unit 161 determines that the leading end of the medium has passed through the conveyance area when the leading end of the medium has passed through the position of the third media sensor 120. Alternatively, the control unit 161 may determine that the leading end of the medium has passed through the conveyance area when a preset time has elapsed since the start of the feeding of the medium.

Subsequently, the control unit 161 controls the second imaging device 121 to start imaging the medium (step S106).

Subsequently, the control unit 161 controls the second motor 141 to stop the feed roller 112 (step S107). As a result, the medium is thereafter conveyed by the first conveyance roller 118 and the second conveyance roller 122, whereas the feed roller 112 is rotated by the medium being conveyed. By stopping the feed roller 112, the control unit 161 can prevent the medium from being jammed due to the medium being pushed by the feed roller 112 and bent between the feed roller 112 and the first conveyance roller 118.

Subsequently, the control unit 161 determines whether a medium remains on the media tray 103 based on the first media signal received from the first media sensor 111 (step S108).

When a medium remains on the media tray 103, the control unit 161 waits until the trailing end of the fed media passes through the nip N between the feed roller 112 and the separation roller 113 (step S109). In the following description, the nip N between the feed roller 112 and the separation roller 113 may be referred to as a “separation area.” The control unit 161 periodically acquires the second media signal from the second media sensor 117 and determines that the trailing end of the medium has passed through the position of the second media sensor 117 when the signal value of the second media signal changes from a value indicating the presence of a medium to a value indicating the absence of a medium. The control unit 161 determines that the trailing end of the medium has passed through the separation area when the trailing end of the medium has passed through the position of the second media sensor 117. Alternatively, the control unit 161 may determine that the trailing end of the medium has passed through the separation area when a preset time has elapsed since the start of the feeding of the medium.

Subsequently, the processing circuit 160 performs the setting process in the same or substantially the same manner as the process of step S103 (step S110).

Subsequently, the control unit 161 drives the second motor 141 to re-rotate the feed roller 112 to feed the following medium (step S111). In other words, when the trailing end of the preceding medium has passed through the separation area, the control unit 161 re-rotates the feed roller 112 to start feeding of the following medium. At this time, as the separation roller 113 is rotating according to the characteristic value being set in the setting process of step S110, the medium feeding apparatus 100 can appropriately control the separation roller 113 depending on the leading end positions of the media placed on the media tray 103 and appropriately separate the media.

Subsequently, the control unit 161 waits until the trailing end of the conveyed medium passes through the imaging position of the second imaging device 121 (step S112). Similarly, the control unit 161 periodically acquires the third media signal from the third media sensor 120 and determines that the trailing end of the medium has passed through the position of the third media sensor 120 when the signal value of the third media signal changes from a value indicating the presence of a medium to a value indicating the absence of a medium. The control unit 161 determines that the trailing end of the medium has passed through the imaging position when a first predetermined time period has elapsed since the trailing end of the medium has passed through the position of the third media sensor 120. The first predetermined time period is set to a time taken for a medium to move from the third media sensor 120 to the imaging position. Alternatively, the control unit 161 may determine that the trailing end of the medium has passed through the imaging position when a preset time has elapsed since the start of the feeding of the medium.

Subsequently, the control unit 161 acquires a medium image from the second imaging device 121 and transmits (i.e., outputs) the acquired medium image to the information processing apparatus via the interface device 143 (step S113).

The control unit 161 then returns to step S105 and repeats the operations of the step S105 and subsequent steps for the following medium.

By contrast, when no medium remains on the media tray 103 in step S108, the control unit 161 waits until the trailing end of the conveyed medium passes through the imaging position of the second imaging device 121 in the same or substantially the same manner as the operation of step S112 (step S114).

Subsequently, the control unit 161 acquires a medium image from the second imaging device 121 and transmits (i.e., outputs) the acquired medium image to the information processing apparatus via the interface device 143 (step S115).

Subsequently, the control unit 161 waits until the trailing end of the conveyed medium passes through the nip between the second conveyance roller 122 and the second driven roller 123 (step S116). In the following description, the nip between the second conveyance roller 122 and the second driven roller 123 may be referred to as an “ejection area.” The control unit 161 determines that the trailing end of the medium has passed through the ejection area when a second predetermined time period has elapsed since the trailing end of the medium has passed through the position of the third media sensor 120. The second predetermined time period is set to a time taken for a medium to move from the third media sensor 120 to the downstream end of the ejection area. Alternatively, the control unit 161 may determine that the trailing end of the medium has passed through the ejection area when a preset time has elapsed since the start of the feeding of the medium.

Subsequently, the control unit 161 controls the second motor 141 and the third motor 142 to stop the separation roller 113, the first conveyance roller 118, the first driven roller 119, the second conveyance roller 122, and/or the second driven roller 123 (step S117). Then, the control unit 161 ends the series of steps.

FIG. 8 is a flowchart illustrating an example of the setting process.

The setting process is performed in step S103 and step S110 of the media reading process of FIG. 7.

First, the detection unit 162 acquires an input image from the first imaging device 115 (step S201). The detection unit 162 controls the first imaging device 115 to image a medium to generate the input image with the first light source device 114a turned on and the second light source device 114b turned off. Alternatively, the detection unit 162 may control the first imaging device 115 to image a medium to generate the input image with both the first light source device 114a and the second light source device 114b turned on.

FIG. 9A, FIG. 9B, FIG. 10A, and FIG. 10B are diagrams schematically illustrating examples of input images P1, P2, P3, and P4, respectively.

Each of the input images P1 to P4 includes two nips N formed by two sets of the feed rollers 112 and the separation rollers 113, and an area between the two nips N. In the input images, the medium conveying direction A1 corresponds to the horizontal direction and the width direction A2 corresponds to the vertical direction. Each of the input images P1 to P4 includes a medium M1, a medium M2, and a medium M3 placed on the media tray 103. The medium M1, medium M2, and medium M3 are placed in the order of the medium M1, medium M2, and medium M3 from the bottom. In each of the input images P1 to P4, a position C is the center position of the nip N in the medium conveying direction A1, a position F1 is the leading end (downstream end) position of the medium M1, and a position F2 is the leading end (downstream end) position of the medium M2.

As described above, the setting process is performed before the start of feeding of media (step S103 in FIG. 7), or when the trailing end of the preceding medium passes through the separation area after the leading end of the preceding medium passes through the conveyance area and the feed roller 112 is stopped (step S110 in FIG. 7). When a user places multiple media on the media tray 103 before the start of feeding of media, the user may push the media into the separation area (nip N). Due to such an operation by the user, the leading ends of media may enter the separation area (nip N). Also after the start of feeding media, when the trailing end of the preceding medium passes through the separation area, the leading end of the following medium may enter the separation area (nip N) due to dragged by the preceding medium.

In the input image P1, the leading end position F1 of the medium M1 is located upstream from the center position C, and a distance L between the leading end position F1 of the medium M1 and the leading end position F2 of the medium M2 is sufficiently long. In this configuration, a time period during which the separation force by the separation roller 113 is applied to the medium M1 and the medium M2 is sufficiently long, and the separation force by the separation roller 113 is applied separately to the leading end of the medium M1 and the leading end of the medium M2. Accordingly, the medium M1 and the medium M2 are highly likely to be separated appropriately.

In the input image P2, the leading end position F1 of the medium M1 is located upstream from the center position C, and the distance L between the leading end position F1 of the medium M1 and the leading end position F2 of the medium M2 is short. In this configuration, although a time period during which the separation force by the separation roller 113 is applied to the medium M1 and the medium M2 is sufficiently long, the separation force by the separation roller 113 is applied collectively to the leading end of the medium M1 and the leading end of the medium M2. Accordingly, compared to the state indicated by the input image P1, the medium M1 and the medium M2 are less likely to be separated from each other.

In the input image P3, the leading end position F1 of the medium M1 is located downstream from the center position C, and the distance L between the leading end position F1 of the medium M1 and the leading end position F2 of the medium M2 is sufficiently long. In this configuration, although the separation force by separation roller 113 is applied separately to the leading end of the medium M1 and the leading end of medium M2, a time period during which the separation force by the separation roller 113 is applied to medium M1 and the medium M2 is short. Accordingly, compared to the state indicated by the input image P1, the medium M1 and the medium M2 are less likely to be separated from each other. However, in this configuration, compared to the state indicated by the input image P2, the medium M1 and the medium M2 are more likely to be separated from each other.

In the input image P4, the leading end position F1 of the medium M1 is located downstream from the center position C, and the distance L between the leading end position F1 of the medium M1 and the leading end position F2 of the medium M2 is short. In this configuration, a time period during which the separation force by the separation roller 113 is applied to the medium M1 and the medium M2 is short, and the separation force by the separation roller 113 is applied integrally to the leading end of the medium M1 and the leading end of the medium M2. Accordingly, compared to the states indicated by the input images P1 to P3, the medium M1 and the medium M2 are less likely to be separated from each other.

Subsequently, the detection unit 162 detects the leading end positions of media in the nip N between the feed roller 112 and the separation roller 113 (step S202). The detection unit 162 detects the leading end position of a preceding medium (medium to be fed next) and the leading end position of a medium following the preceding medium (medium to be fed second) in the nip N based on the acquired input image.

The medium feeding apparatus 100 stores in advance in the storage device 150 the positions of the two sets of the feed roller 112, the separation roller 113, and the nip N in the input image and a predetermined position in each of the nips N in the medium conveying direction A1. The predetermined position is, for example, the center position C of the nip N in the medium conveying direction A1. The predetermined position may be any other position in the nip N.

The detection unit 162 calculates, for each pixel at a specific position in the width direction A2 (vertical direction) between the two nips N in the input image, a difference obtained by subtracting a gradation value of a pixel adjacent to the left of each pixel in the medium conveying direction A1 (horizontal direction) from a gradation value of a pixel adjacent to the right, starting from the downstream end (left end). In the following description, the difference may be referred to as an “adjacent difference value.” The detection unit 162 detects a pixel of which the adjacent difference value exceeds a gradation threshold value as an edge pixel. The gradation value is, for example, a brightness value or a color value such as an R value, a G value, or a B value. The gradation threshold value is set to, for example, a difference in the brightness value (e.g., 20) at which a person can visually distinguish a difference in brightness on an image. In other words, starting from the downstream end, the detection unit 162 detects a pixel of which the brightness value changes from a high value (a color close to white) to a low value (a color close to black) as the edge pixel. The detection unit 162 detects the position of the edge pixel detected first, i.e., the position of the edge pixel located on the most downstream side in the medium conveying direction A1 as the leading end position of the preceding medium. Further, the detection unit 162 detects the position of the edge pixel detected second, i.e., the position of the edge pixel located second from the most downstream side in the medium conveying direction A1 as the leading end position of the medium following the preceding medium.

Alternatively, the detection unit 162 may calculate the difference between the gradation values of two pixels that are apart from each pixel by a predetermined distance in the input image in the medium conveying direction A1 as the adjacent difference value. The detection unit 162 may detect an edge pixel by comparing the gradation value of each pixel in the input image with a threshold value. For example, when the gradation value of a particular pixel is equal to or greater than the threshold value and the gradation value of an adjacent pixel upstream of the particular pixel or a pixel apart from the particular pixel by a predetermined distance is less than the threshold value, the detection unit 162 detects the particular pixel as the edge pixel.

Subsequently, the detection unit 162 determines the distance between the leading end position of the preceding medium and the leading end position of the medium following the preceding medium detected by the detection unit 162 in the nip N (step S203). The detection unit 162 calculates the number of pixels between the leading end position of the preceding medium and the leading end position of the medium following the preceding medium detected in the input image. The medium feeding apparatus 100 sets in advance in the storage device 150 a table indicating a relation between the number of pixels in an image and an actual distance for each resolution of the input image. The detection unit 162 refers to the table set in advance in the storage device 150 and determines the actual distance between the leading end position of the preceding medium and the leading end position of the medium following the preceding medium corresponding to the calculated number of pixels based on the resolution of the input image.

Subsequently, the detection unit 162 determines whether the leading end position of the preceding medium is located downstream in the medium conveying direction A1 from the predetermined position in the nip N (step S204).

When the leading end of the preceding medium is not located downstream from the predetermined position, that is, when the leading end of the preceding medium is located upstream from the predetermined position, the detection unit 162 determines whether the distance between the leading end of the preceding medium and the leading end of the medium following the preceding medium is equal to or greater than a threshold value (step S205). The threshold value is set in advance to, for example, a maximum value or an average value of the distance when the multi-feed of media occurs in a preliminary experiment in which various types of media are fed.

When the distance between the leading end of the preceding medium and the leading end of the medium following the preceding medium is equal to or greater than the threshold value, the setting unit 163 sets the limit value of the torque applied to the separation roller 113 to the first limit value (step S206), and ends the series of steps. The setting unit 163 sets the first electromagnetic clutch 133a to connect the power between the second gear 132b and the first torque limiter 134a, and sets the other electromagnetic clutches to disconnect the power between the other gears and the other torque limiters. Thus, the setting unit 163 sets the limit value of the torque applied to the separation roller 113 to the first limit value, and limits the load component applied to the medium by the separation roller 113 to the first limit value.

When the leading end position F1 of the preceding medium is located upstream from the predetermined position in the medium conveying direction A1 and the distance L is equal to or greater than the threshold value as indicated by the input image P1, the setting unit 163 sets the limit value of the torque applied to the separation roller 113 to the first limit value. When the medium M1 and the medium M2 are highly likely to be separated appropriately, the setting unit 163 sets the limit value of the torque applied to separation roller 113 to the first limit value which is sufficiently small. Accordingly, the medium feeding apparatus 100 can prevent the force with which a medium is nipped by the feed roller 112 and the separation roller 113 from being too large, thereby preventing media from jamming.

By contrast, when the distance between the leading end of the preceding medium and the leading end of the medium following the preceding medium is less than the threshold value, the setting unit 163 sets the limit value of the torque applied to the separation roller 113 to the second limit value (step S207), and ends the series of steps. The setting unit 163 sets the second electromagnetic clutch 133b to connect the power between the third gear 132c and the second torque limiter 134b, and sets the other electromagnetic clutches to disconnect the power between the other gears and the other torque limiters. Thus, the setting unit 163 sets the limit value of the torque applied to the separation roller 113 to the second limit value.

When the leading end position F1 of the preceding medium is located upstream from the predetermined position in the medium conveying direction A1 and the distance L is less than the threshold value as indicated by the input image P2, the setting unit 163 sets the limit value of the torque applied to the separation roller 113 to the second limit value. When the medium M1 and the medium M2 are difficult to separate, the setting unit 163 sets the limit value of the torque applied to separation roller 113 to the second limit value which is greater than the first limit value. Accordingly, the medium feeding apparatus 100 can increase the separation force by the feed roller 112 and the separation roller 113 and prevent or reduce the occurrence of multi-feed of media.

When the detection unit 162 determines that the leading end of the preceding medium is located downstream from the predetermined position in step S204, the detection unit 162 determines whether the distance between the leading end of the preceding medium and the leading end of the medium following the preceding medium is equal to or greater than a threshold value (step S208).

When the distance between the leading end of the preceding medium and the leading end of the medium following the preceding medium is equal to or greater than the threshold value, the setting unit 163 sets the limit value of the torque applied to the separation roller 113 to the third limit value (step S209), and ends the series of steps. The setting unit 163 sets the third electromagnetic clutch 133c to connect the power between the fourth gear 132d and the third torque limiter 134c, and sets the other electromagnetic clutches to disconnect the power between the other gears and the other torque limiters. Thus, the setting unit 163 sets the limit value of the torque applied to the separation roller 113 to the third limit value.

When the leading end position F1 of the preceding medium is located downstream from the predetermined position in the medium conveying direction A1 and the distance L is equal to or greater than the threshold value as indicated by the input image P3, the setting unit 163 sets the limit value of the torque applied to the separation roller 113 to the third limit value. When the medium M1 and the medium M2 are slightly difficult to separate, the setting unit 163 sets the limit value of the torque applied to separation roller 113 to the third limit value which is greater than the first torque value and smaller than the second torque value. Accordingly, the medium feeding apparatus 100 can slightly increase the separation force by the feed roller 112 and the separation roller 113, thereby preventing media from jamming and preventing or reducing the occurrence of multi-feed of media.

When the distance between the leading end of the preceding medium and the leading end of the medium following the preceding medium is less than the threshold value, the setting unit 163 sets the limit value of the torque applied to the separation roller 113 to the fourth limit value (step S210), and ends the series of steps. The setting unit 163 sets the fourth electromagnetic clutch 133d to connect the power between the fifth gear 132e and the fourth torque limiter 134d, and sets the other electromagnetic clutches to disconnect the power between the other gears and the other torque limiters. Thus, the setting unit 163 sets the limit value of the torque applied to the separation roller 113 to the fourth limit value.

When the leading end position F1 of the preceding medium is located downstream from the predetermined position in the medium conveying direction A1 and the distance L is less than the threshold value as indicated by the input image P4, the setting unit 163 sets the limit value of the torque applied to the separation roller 113 to the fourth limit value. When the medium M1 and the medium M2 are extremely difficult to separate, the setting unit 163 sets the limit value of the torque applied to separation roller 113 to the fourth limit value which is greater than the first limit value, the second limit value, and the third limit value. Accordingly, the medium feeding apparatus 100 can extremely increase the separation force by the feed roller 112 and the separation roller 113 and prevent or reduce the occurrence of multi-feed of media.

As described above, the setting unit 163 changes the limit value of the torque applied to the separation roller 113 based on the distance between the leading end position of the preceding medium and the leading end position of the medium following the preceding medium, which are detected by the detection unit 162 in the nip N. Further, the setting unit 163 changes the limit value of the torque applied to the separation roller 113 depending on whether the leading end position F1 of the preceding medium detected by the detection unit 162 is located downstream from the predetermined position in the medium conveying direction A1. Accordingly, the medium feeding apparatus 100 can prevent media from jamming and prevent or reduce the occurrence of multi-feed of media.

The setting process is performed immediately before the feed roller 112 starts to rotate (steps S105 and S111 of FIG. 7). In other words, the detection unit 162 detects the leading end position of the medium immediately before the feed roller 112 starts to rotate, and the setting unit 163 sets the characteristics of the separation roller 113 based on the detection result. Accordingly, the medium feeding apparatus 100 can appropriately change the characteristics of the separation roller 113 based on the state of media on the media tray 103 immediately before the start of feeding, thereby appropriately separating the media.

The processes of steps S204 and S208 to S210 may be omitted. In this operation, the setting unit 163 may change the limit value of the torque applied to the separation roller 113 based on only the distance, regardless of the leading end position F1 of the preceding medium. Further, the processes of steps S205, S207, S208, and S210 may be omitted. In this operation, the setting unit 163 may change the limit value of the torque applied to the separation roller 113 only based on the leading end position F1 of the preceding medium, regardless of the distance.

The detection unit 162 may detect the leading end position of each medium in the nip N using information other than the input image. In this configuration, the medium feeding apparatus 100 includes multiple overlap sensors that detect the overlap of media, instead of the light source device 114 and the first imaging device 115. The overlap sensors are located between the nips N of the two pairs of the feed roller 112 and the separation roller 113 in the width direction A2. The overlap sensors are located at intervals at positions overlapping the nip N when viewed from the width direction A2, that is, at positions overlapping the nip N in the medium conveying direction A1.

The overlap sensors are, for example, ultrasonic sensors. Each ultrasonic sensor includes an ultrasonic transmitter and an ultrasonic receiver. Each ultrasonic transmitter and ultrasonic receiver are located near the medium conveying path to face each other across the medium conveying path. The ultrasonic transmitter transmits ultrasonic waves. The ultrasonic receiver receives the ultrasonic waves transmitted by the ultrasonic transmitter and passed through a medium, and generates and outputs an ultrasonic signal which is an electrical signal corresponding to the received ultrasonic waves. At the position where a medium is present, the ultrasonic waves transmitted by the ultrasonic sensor are attenuated by the medium, and thus the signal value of the ultrasonic signal decreases. At the position where media overlap each other, the ultrasonic waves transmitted by the ultrasonic sensor are attenuated by an air layer between media, and thus the signal value of the ultrasonic signal further decreases.

In this operation, in step S201, the detection unit 162 acquires the ultrasonic signal from each of the ultrasonic sensors. In step S202, the detection unit 162 determines whether the signal value of the ultrasonic signal output from each ultrasonic sensor is equal to or less than a first ultrasonic threshold value and whether the signal value is equal to or less than a second ultrasonic threshold value which is smaller than the first ultrasonic threshold value. The first ultrasonic wave threshold value is set to, for example, a value between the signal value of the ultrasonic wave signal detected when a medium is not present and the signal value of the ultrasonic wave signal detected when one PPC sheet is present. The second ultrasonic threshold value is set to a value between the signal value of the ultrasonic signal detected when one PPC sheet is present and pass-through information detected when two PPC sheets are conveyed.

The detection unit 162 detects the position of the ultrasonic sensor located on the most downstream side among the ultrasonic sensors that output ultrasonic signals of which the signal values are equal to or less than the first ultrasonic threshold value as the leading end position of the preceding medium. Further, the detection unit 162 detects the position of the ultrasonic sensor located on the most downstream side among the ultrasonic sensors that output ultrasonic signals of which the signal values are equal to or less than the second ultrasonic threshold value as the leading end position of the medium following the preceding medium.

Alternatively, the overlap sensors may be thickness sensors. Each thickness sensor includes a light emitter and a light receiver. Each light emitter and each light receiver are located near the medium conveying path to face each other across the medium conveying path. The light emitter emits light (infrared light or visible light) toward the light receiver. The light receiver receives the light from the light emitter, generates a thickness signal which is an electrical signal corresponding to the intensity of the received light, and outputs the thickness signal. When a medium is present at the position of the thickness sensor, the light emitted by the light emitter is attenuated by the medium. The greater the thickness of the medium, the greater the attenuation. For example, the thickness sensor generates the thickness signal such that the signal value increases as the thickness of the medium increases.

Still alternatively, the thickness sensor may be a reflected light sensor, a pressure sensor, or a mechanical sensor. The reflected light sensor includes one set of a light emitter and a light receiver (referred to as an “emitter-receiver set” in the following description) located on one side of the medium conveying path and another emitter-receiver set located on the other side of the medium conveying path. The reflected light sensor detects the distance between one emitter-receiver set and one side of the medium based on the time from when the one emitter-receiver set emits light to the one side of the medium to when the one emitter-receiver set receives the reflected light and the distance between another emitter-receiver set and the other side of the medium based on the time from when the other emitter-receiver set emits light to the other side of the medium to when the other emitter-receiver set receives the reflected light. The reflected light sensor generates a thickness signal indicating a value obtained by subtracting each detected distance from the distance between the two emitter-receiver sets. The pressure sensor detects a pressure that changes according to the thickness of the medium, and generates a thickness signal indicating the detected pressure. The mechanical sensor detects the amount of movement of a roller in contact with the medium and generates a thickness signal indicating the detected amount of movement.

In this operation, in step S201, the detection unit 162 acquires the thickness signal from each thickness sensor. In step S202, the detection unit 162 determines whether the signal value of the thickness signal output by each thickness sensor is equal to or greater than a first thickness threshold value and whether the signal value is equal to or less than a second thickness threshold value which is greater than the first thickness threshold value. The first thickness threshold value is set to, for example, a value between the signal value of the thickness signal detected when a medium is not present and the signal value of the thickness signal detected when one PPC sheet is present. The second thickness threshold value is set to a value between the signal value of the thickness signal detected when one PPC sheet is present and pass-through information detected when two PPC sheets are conveyed.

The detection unit 162 detects the position of the thickness sensor located on the most downstream side among the thickness sensors that output thickness signals of which the signal values are equal to or greater than the first thickness threshold value as the leading end position of the preceding medium. Further, the detection unit 162 detects the position of the thickness sensor located on the most downstream side among the thickness sensors that output thickness signals of which the signal values are equal to or less than the second thickness threshold value as the leading end position of the medium following the preceding medium.

In steps S206, S207, S209, and S210, the setting unit 163 may change the torque applied to the separation roller 113 by changing the motor torque of the first motor 131 instead of changing the torque limiter.

In this operation, in steps S206, S207, S209, and S210, the setting unit 163 changes the limit value of the torque applied to the separation roller 113 by changing the motor torque of the first motor 131 instead of changing the first electromagnetic clutch 133a to the fourth electromagnetic clutch 133d. In step S206, the setting unit 163 sets the motor torque of the first motor 131 so that the limit value of the torque applied to the separation roller 113 is the first torque value, that is, the sum of the limit value of the torque limiter coupled to the separation roller 113 and the motor torque of the first motor 131 is the first limit value. In step S207, the setting unit 163 sets the motor torque of the first motor 131 so that the limit value of the torque applied to the separation roller 113 is the second torque value, that is, the sum of the limit value of the torque limiter coupled to the separation roller 113 and the motor torque of the first motor 131 is the second limit value. In step S209, the setting unit 163 sets the motor torque of the first motor 131 so that the limit value of the torque applied to the separation roller 113 is the third torque value, that is, the sum of the limit value of the torque limiter coupled to the separation roller 113 and the motor torque of the first motor 131 is the third limit value. In step S210, the setting unit 163 sets the motor torque of the first motor 131 so that the limit value of the torque applied to the separation roller 113 is the fourth torque value, that is, the sum of the limit value of the torque limiter coupled to the separation roller 113 and the motor torque of the first motor 131 is the fourth limit value.

The setting unit 163 changes the motor torque of the first motor 131 by setting the amount of electric power (current) supplied to the first motor 131 to the amount of electric power (current) corresponding to each of the torque values.

As described above in detail, the medium feeding apparatus 100 changes the torque value, which is the characteristic value of the separation roller 113, based on the distance between the leading end position of the preceding medium and the leading end position of the medium following the preceding medium in the nip N between the feed roller 112 and the separation roller 113. Accordingly, the medium feeding apparatus 100 can appropriately change the separation force of the separation roller 113 depending on the feeding state (separation state) of media placed on the media tray 103, thereby preventing media from being jammed and also preventing or reducing the occurrence of multi-feed of media. Thus, the medium feeding apparatus 100 can appropriately prevent or reduce the occurrence of multi-feed of media.

FIG. 11 is a flowchart illustrating another example of the setting process.

The operation of the flowchart illustrated in FIG. 11 is performed instead of the operation of the flowchart illustrated in FIG. 8. Since the processes of steps S301 to S305 and S308 of FIG. 11 are respectively the same or substantially the same as the processes of steps S201 to S205 and S208 of FIG. 8, redundant descriptions thereof will be omitted. A description is given below of steps S306 to S307 and S309 to S310.

In step S306, the setting unit 163 sets the pressing force with which the pressing mechanism 116 presses the separation roller 113 toward the feed roller 112 to a first pressing force (step S306), and ends the series of steps. The first pressing force is set to a sufficiently large value. The setting unit 163 controls the driving source 116c of the pressing mechanism 116 so that the pressing force by the pressing mechanism 116 is the first pressing force. The pressing force with which the pressing mechanism 116 presses the separation roller 113 toward the feed roller 112 is an example of the characteristic value of the separation roller 113.

As described above, the setting unit 163 sets the pressing force by the pressing mechanism 116 to the first pressing force when the leading end position of the preceding medium is located upstream from the predetermined position in the nip N and the distance between the leading end position of the preceding medium and the leading end position of the medium following the preceding medium is equal to or greater than the threshold value. When multiple media are highly likely to be separated appropriately, the setting unit 163 sets the pressing force with which the separation roller 113 is pressed toward the feed roller 112 to the first pressing force, which is sufficiently large. Accordingly, the medium feeding apparatus 100 can firmly nip a medium between the feed roller 112 and the separation roller 113, thereby preventing a medium from being jammed.

In step S307, the setting unit 163 sets the pressing force with which the pressing mechanism 116 presses the separation roller 113 toward the feed roller 112 to a second pressing force (step S307), and ends the series of steps. The second pressing force is set to a value smaller than the first pressing force. The setting unit 163 controls the driving source 116c of the pressing mechanism 116 so that the pressing force by the pressing mechanism 116 is the second pressing force.

As described above, the setting unit 163 sets the pressing force by the pressing mechanism 116 to the second pressing force when the leading end position of the preceding medium is located upstream from the predetermined position in the nip N and the distance between the leading end position of the preceding medium and the leading end position of the medium following the preceding medium is less than the threshold value. When multiple media are difficult to be separated, the setting unit 163 sets the pressing force with which the separation roller 113 is pressed toward the feed roller 112 to the second pressing force, which is smaller than the first pressing force. Accordingly, the medium feeding apparatus 100 can make it easy for the separation roller 113 to return a medium toward the media tray 103, thereby preventing or reducing the occurrence of multi-feed of media.

In step S309, the setting unit 163 sets the pressing force with which the pressing mechanism 116 presses the separation roller 113 toward the feed roller 112 to a third pressing force (step S309), and ends the series of steps. The third pressing force is set to a value smaller than the first pressing force and greater than the second pressing force. The setting unit 163 controls the driving source 116c of the pressing mechanism 116 so that the pressing force by the pressing mechanism 116 is the third pressing force.

As described above, the setting unit 163 sets the pressing force by the pressing mechanism 116 to the third pressing force when the leading end position of the preceding medium is located downstream from the predetermined position in the nip N and the distance between the leading end position of the preceding medium and the leading end position of the medium following the preceding medium is equal to or greater than the threshold value. When multiple media are slightly difficult to be separated, the setting unit 163 sets the pressing force with which the separation roller 113 is pressed toward the feed roller 112 to the third pressing force, which is smaller than the first pressing force and greater than the second pressing force. Accordingly, the medium feeding apparatus 100 can make it easy for the separation roller 113 to return a medium slightly toward the media tray 103, thereby preventing media from being jammed and preventing or reducing the occurrence of multi-feed of media.

In step S310, the setting unit 163 sets the pressing force with which the pressing mechanism 116 presses the separation roller 113 toward the feed roller 112 to a fourth pressing force (step S310), and ends the series of steps. The fourth pressing force is set to a value smaller than the second pressing force. The setting unit 163 controls the driving source 116c of the pressing mechanism 116 so that the pressing force by the pressing mechanism 116 is the fourth pressing force.

As described above, the setting unit 163 sets the pressing force by the pressing mechanism 116 to the fourth pressing force when the leading end position of the preceding medium is located downstream from the predetermined position in the nip N and the distance between the leading end position of the preceding medium and the leading end position of the medium following the preceding medium is less than the threshold value. When multiple media are extremely difficult to be separated, the setting unit 163 sets the pressing force with which the separation roller 113 is pressed toward the feed roller 112 to the fourth pressing force, which is smaller than the first pressing force, the second pressing force, and the third pressing force. Accordingly, the medium feeding apparatus 100 can make it easy for the separation roller 113 to return a medium largely toward the media tray 103, thereby preventing or reducing the occurrence of multi-feed of media.

In the same or substantially the same manner as the setting process described with reference to FIG. 8, the processes of steps S304 and S308 to S310 or steps S305, S307, S308, and S310 may be omitted. The detection unit 162 may detect the leading end position of each medium in the nip N using the overlap sensor.

As described above in detail, the medium feeding apparatus 100 can appropriately prevent or reduce the occurrence of multi-feed of media also by changing the pressing force with which the pressing mechanism 116 presses the separation roller 113 toward the feed roller 112 based on the distance between the leading end of the preceding medium and the leading end of the medium following the preceding medium.

FIG. 12 is a flowchart illustrating still another example of the setting process.

The operation of the flowchart illustrated in FIG. 12 is performed instead of the operation of the flowchart illustrated in FIG. 8. Since the processes of steps S401, S408 to S409 and S411 to S412 of FIG. 12 are respectively the same or substantially the same as the processes of steps S201, S206 to S207, and S209 to S210 of FIG. 8, redundant descriptions thereof will be omitted. A description is given below of steps S402 to S407 and S410.

In step S402, the detection unit 162 controls the first light source device 114a to be turned off and controls the second light source device 114b to be turned on (step S402).

Subsequently, the detection unit 162 acquires a second input image from the first imaging device 115 (step S403). In other words, the detection unit 162 controls the first imaging device 115 to image a medium to generate an input image with the first light source device 114a turned off and the second light source device 114b turned on.

FIG. 13A and FIG. 13B are diagrams schematically illustrating examples of second input images P5 and P6, respectively.

In the same or substantially the same manner as the input images P1 to P4, each of the second input images P5 and P6 includes two sets of the feed rollers 112 and the separation rollers 113, two nips N, an area between the two nips N, and the media M1, M2, and M3 placed on the media tray 103. In the second input image P5, the leading end position F1 of the medium M1 is located upstream from the center position C, and the distance between the leading end position F1 of the medium M1 and the leading end position F2 of the medium M2 is sufficiently long. On the other hand, in the second input image P6, the leading end position F1 of the medium M1 is located upstream from the center position C, and the distance between the leading end position F1 of the medium M1 and the leading end position F2 of the medium M2 is short.

As described above, an angle between the direction of the light emitted from the second light source device 114b and the medium conveying path is smaller than an angle between the direction of the light emitted from the first light source device 114a and the medium conveying path. Accordingly, the length T of the shadow of the leading end of each of the medium M1 and the medium M2 in the medium conveying direction A1 in the second input image captured with light emitted only by the second light source device 114b is longer than the length T in the media conveyance direction of the shadow of the leading end of each of the medium M1 and the medium M2 in the medium conveying direction A1 in the input image. As a result, as indicated by the second input image P6, when the distance between the leading end position F1 of the medium M1 and the leading end position F2 of the medium M2 is short, the shadow of the leading end of the medium M1 and the shadow of the leading end of the medium M2 connect with each other.

Subsequently, the detection unit 162 detects the leading end positions of media in the nip N between the feed roller 112 and the separation roller 113 (step S404). In the same or substantially the same manner as the process of step S202 of FIG. 8, the detection unit 162 detects the leading end position of the preceding medium and the leading end position of the medium following the preceding medium in the nip N from each of the input image and the second input image.

Subsequently, the detection unit 162 detects the distance between the leading end position of the preceding medium and the leading end position of the medium following the preceding medium detected by the detection unit 162 in the nip N (step S405). The detection unit 162 determines the distance between the leading end position of the preceding medium and the leading end position of the medium following the preceding medium based on the input image in the same or substantially the same manner as the process of step S202 of FIG. 8. The detection unit 162 further determines the distance between the leading end position of the preceding medium and the leading end position of the medium following the preceding medium based on the second input image.

The detection unit 162 detects an edge pixel in the second input image in the same or substantially the same manner as the process of step S202 of FIG. 8. Further, the detection unit 162 calculates, for each pixel at a specific position between the two nips N in the width direction A2 (vertical direction) in the second input image, a difference obtained by subtracting a gradation value of a pixel adjacent to the right of each pixel from a gradation value of a pixel adjacent to the left of each pixel in the medium conveying direction A1 (horizontal direction), starting from the downstream end (left end). In the following description, the difference may be referred to as a “second adjacent difference value.” The detection unit 162 detects a pixel of which the adjacent difference value exceeds a gradation threshold value as a second edge pixel. In other words, starting from the downstream end, the detection unit 162 detects a pixel of which the brightness value changes from a low value (a color close to black) to a high value (a color close to white) as the second edge pixel. The detection unit 162 calculates the number of pixels between the edge pixel detected first and the second edge pixel.

The detection unit 162 refers to a table indicating a relation between the number of pixels in an image and the actual distance and determines a distance corresponding to the calculated number of pixels as the length of the shadow of the preceding medium. The table is set in the storage device 150 in advance. When the determined length of the shadow of the preceding medium is less than the threshold value, the detection unit 162 determines that the shadow of the preceding medium and the shadow of the medium following the preceding medium are not connected to each other and the distance between the leading end position of the preceding medium and the leading end position of the medium following the preceding medium is equal to or greater than the threshold value. By contrast, when the determined length of the shadow of the preceding medium is equal to or greater than the threshold value, the detection unit 162 determines that the shadow of the preceding medium and the shadow of the medium following the preceding medium are connected to each other and the distance between the leading end position of the preceding medium and the leading end position of the medium following the preceding medium is less than the threshold value.

The greater the thickness of a medium being fed, the longer the length of the shadow of the leading end of the medium in the input image. In view of this, the detection unit 162 may change the threshold value depending on the thickness of the medium being fed. Since media stacked on the media tray 103 are highly likely to be of the same type (i.e., have the same thickness), the detection unit 162 estimates the thickness of a medium based on the length of the shadow of the leading end of a medium fed after the preceding medium. The detection unit 162 detects an area between the second edge pixel and the edge pixel detected second (or third or later) as a shadow of the leading end of the medium fed after the preceding medium. The detection unit 162 sets a distance corresponding to the number of pixels of the area as the threshold value to be compared with the length of the shadow of the preceding medium. Thus, the detection unit 162 can detect the distance between the leading end position of the preceding medium and the leading end position of the medium following the preceding medium with high accuracy regardless of the thickness of the media being fed.

Subsequently, the detection unit 162 determines whether the leading end position of the preceding medium is located downstream in the medium conveying direction A1 from the predetermined position in the nip N (step S406).

When both the leading end position of the preceding medium detected from the input image and the leading end position of the preceding medium detected from the second input image are located downstream from the predetermined position, the detection unit 162 determines that the leading end position of the preceding medium is located downstream from the predetermined position. By contrast, when at least one of the leading end position of the preceding medium detected from the input image and the leading end position of the preceding medium detected from the second input image is located upstream from the predetermined position, the detection unit 162 determines that the leading end position of the preceding medium is located upstream from the predetermined position. Alternatively, when at least one of the leading end position of the preceding medium detected from the input image and the leading end position of the preceding medium detected from the second input image is located downstream from the predetermined position, the detection unit 162 may determine that the leading end position of the preceding medium is located downstream from the predetermined position. In this operation, when both the leading end position of the preceding medium detected from the input image and the leading end position of the preceding medium detected from the second input image are located upstream from the predetermined position, the detection unit 162 determines that the leading end position of the preceding medium is located upstream from the predetermined position.

In steps S407 and S410, the detection unit 162 determines whether the distance between the leading end of the preceding medium and the leading end of the medium following the preceding medium is equal to or greater than the threshold value (steps S407 and S410).

When both the distance detected from the input image and the distance detected from the second input image are equal to or greater than the threshold value, the detection unit 162 determines that the distance between the leading end position of the preceding medium and the leading end position of the medium following the preceding medium is equal to or greater than the threshold value. By contrast, when at least one of the distance detected from the input image and the distance detected from the second input image is less than the threshold value, the detection unit 162 determines that the distance between the leading end position of the preceding medium and the leading end position of the medium following the preceding medium is less than the threshold value. Alternatively, when at least one of the distance detected from the input image and the distance detected from the second input image is equal to or greater than the threshold value, the detection unit 162 may determine that the distance between the leading end position of the preceding medium and the leading end position of the medium following the preceding medium is equal to or greater than the threshold value. In this configuration, when both the distance detected from the input image and the distance detected from the second input image are less than the threshold value, the detection unit 162 determines that the distance between the leading end position of the preceding medium and the leading end position of the medium following the preceding medium is less than the threshold value.

As described above, the detection unit 162 detects the leading end positions of the media and the distance between the leading end position of the preceding medium and the leading end position of the medium following the preceding medium using two input images captured with lights emitted from different directions. Accordingly, the detection unit 162 can detect the leading end positions of the media and the distance with higher accuracy. Alternatively, the detection unit 162 may detect the leading end positions of the media and the distance using only the second input image without using the input image.

In the same or substantially the same manner as the setting process described with reference to FIG. 8, the processes of steps S406 and S410 to S412 or steps S407, S409, S410, and S412 may be omitted. In steps S408 to S409 and S411 to S412, the setting unit 163 may set the pressing force by the pressing mechanism 116 in the same or substantially the same manner as in steps S306 to S307 and S309 to S310 of FIG. 11.

As described above in detail, the medium feeding apparatus 100 can appropriately prevent or reduce the occurrence of multi-feed of media also when the leading end positions of the media and the distance are detected using two input images generated with lights emitted from different directions.

FIG. 14 is a block diagram schematically illustrating a configuration of a processing circuit 260 of a medium feeding apparatus according to another embodiment. The processing circuit 260 substitutes for the processing circuit 160 and performs the media reading process instead of the processing circuit 160. The processing circuit 260 includes a control circuit 261, a detection circuit 262, and a setting circuit 263. These circuits may be implemented by, for example, independent integrated circuits, microprocessors, or firmware.

The control circuit 261 is an example of a control unit and functions in the same or substantially the same manner as the control unit 161. The control circuit 261 receives the operation signal from the operation device 105 or the interface device 143. Further, the control circuit 261 receives the first media signal, the second media signal, and the third media signal from the first media sensor 111, the second media sensor 117, and the third media sensor 120, respectively. The control circuit 261 controls the first motor 131, the second motor 141, and the third motor 142 based on the received signals, acquires a medium image from the second imaging device 121, and outputs the medium image to the interface device 143.

The detection circuit 262 is an example of a detection unit and functions in the same or substantially the same manner as the detection unit 162. The detection circuit 262 receives an input image from the first imaging device 115 while controlling the light source device 114. The detection circuit 262 detects the leading end positions of the media and the distance based on the received input image, and outputs the detection result to the setting circuit 263.

The setting circuit 263 is an example of a setting unit and functions in the same or substantially the same manner as the setting unit 163. The setting circuit 263 receives the detection results of the leading end positions of the media and the distance from the detection circuit 262, and controls the electromagnetic clutch 133, the first motor 131, or the driving source 116c based on the received detection results.

As described above in detail, the medium feeding apparatus can appropriately prevent or reduce the occurrence of multi-feed of media also when the processing circuit 260 is used.

Although the preferred embodiments have been described above, the embodiments are not limited thereto. For example, in the medium feeding apparatus, instead of the first to fourth electromagnetic clutches 133a to 133d and the first to fourth torque limiters 134a to 134d, one electromagnetic clutch for defining the limit value of the torque applied to the separation roller 113 may be used. The setting unit 163 changes the limit value of the torque applied to the separation roller 113 by controlling the electromagnetic clutch instead of switching the first to fourth torque limiters 134a to 134d. In this configuration as well, the medium feeding apparatus can appropriately prevent or reduce the occurrence of multi-feed of media.

The medium feeding apparatus may also have a so-called U-turn path, feed and convey media placed on the media tray sequentially from the top, and eject the media to the ejection tray. In this configuration, the separation roller is located below the feed roller and faces the feed roller. The first light source device and the second light source device are located below the medium conveying path and emit light upward (toward the medium conveying path). The first imaging device is located below the medium conveying path and images an upper side. In this configuration as well, the medium feeding apparatus can appropriately prevent or reduce the occurrence of multi-feed of media.

For a medium feeding apparatus, there is a demand for preventing or reducing the occurrence of multi-feed of media appropriately.

According to one or more embodiments, the medium feeding apparatus, the medium feeding method, and the control program can appropriately prevent or reduce the occurrence of multi-feed of media.

The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present invention. Any one of the above-described operations may be performed in various other ways, for example, in an order different from the one described above.

The functionality of the elements disclosed herein may be implemented using circuitry or processing circuitry which includes general purpose processors, special purpose processors, integrated circuits, application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), and/or combinations thereof which are configured or programmed, using one or more programs stored in one or more memories, to perform the disclosed functionality. Processors are considered processing circuitry or circuitry as they include transistors and other circuitry therein. In the disclosure, the circuitry, units, or means are hardware that carry out or are programmed to perform the recited functionality. The hardware may be any hardware disclosed herein which is programmed or configured to carry out the recited functionality.

There is a memory that stores a computer program which includes computer instructions. These computer instructions provide the logic and routines that enable the hardware (e.g., processing circuitry or circuitry) to perform the method disclosed herein. This computer program can be implemented in known formats as a computer-readable storage medium, a computer program product, a memory device, a record medium such as a CD-ROM or DVD, and/or the memory of an FPGA or ASIC.

Claims

1. A medium feeding apparatus, comprising: a media tray;a feed roller to sequentially feed a plurality of media placed on the media tray;a separation roller located facing the feed roller; andcircuitry configured to: detect a leading end position of each of a plurality of media in a nip between the feed roller and the separation roller;determine a distance between a leading end position of a preceding medium, which is one of the plurality of media in the nip, and a leading end position of a medium following the preceding medium; andset a characteristic value of the separation roller based on the distance.

2. The medium feeding apparatus according to claim 1, wherein the characteristic value is a torque value,the separation roller is set to rotate in the same direction as the feed roller when a torque equal to or greater than the torque value is applied to the separation roller, andthe circuitry sets the torque value to a first torque value when the distance is equal to or greater than a threshold value, and sets the torque value to a second torque value greater than the first torque value when the distance is less than the threshold value.

3. The medium feeding apparatus according to claim 2, wherein the circuitry sets the torque value to a third torque value, which is greater than the first torque value and less than the second torque value, when the detected leading end position of the preceding medium is downstream from a predetermined position in the nip in a medium conveying direction and the distance is equal to or greater than the threshold value.

4. The medium feeding apparatus according to claim 2, wherein the circuitry sets the torque value to the second torque value or a fourth torque value greater than the second torque value when the detected leading end position of the preceding medium is downstream from the predetermined position in the nip in the medium conveying direction and the distance is less than the threshold value.

5. The medium feeding apparatus according to claim 1, further comprising a pressing device to press the separation roller toward the feed roller, wherein the characteristic value is a pressing force with which the pressing device presses the separation roller toward the feed roller, andthe circuitry sets the pressing force to a first pressing force when the distance is equal to or greater than a threshold value, and sets the pressing force to a second pressing force less than the first pressing force when the distance is less than the threshold value.

6. The medium feeding apparatus according to claim 1, wherein the circuitry detects the leading end position immediately before the feed roller starts to rotate.

7. The medium feeding apparatus according to claim 1, further comprising an imager to image the leading end position of the medium in an area overlapping the nip when viewed from a direction perpendicular to a medium conveying direction and generate an input image, wherein the circuitry detects the leading end position of the medium in the nip based on the input image.

8. The medium feeding apparatus according to claim 7, wherein the imager is located downstream from the nip in the medium conveying direction.

9. The medium feeding apparatus according to claim 8, further comprising a light emitter that is located upstream from the nip in the medium conveying direction and irradiates the area overlapping the nip when viewed from the direction perpendicular to the medium conveying direction.

10. The medium feeding apparatus according to claim 9, further comprising a second light emitter that is located upstream from the nip in the medium conveying direction and irradiates the area overlapping the nip when viewed from the direction perpendicular to the medium conveying direction from a direction different from the light emitter.

11. A medium feeding method, comprising: sequentially feeding a plurality of media placed on a media tray by a feed roller;detecting a leading end position of each of a plurality of media in a nip between the feed roller and a separation roller located facing the feed roller;determining a distance between a leading end position of a preceding medium, which is one of the plurality of media in the nip, and a leading end position of a medium following the preceding medium; andsetting a characteristic value based on the distance.

12. A non-transitory recording medium storing a plurality of instructions which, when executed by one or more processors of a medium feeding apparatus, causes the one or more processors to perform a method, the method comprising: sequentially feeding a plurality of media placed on a media tray by a feed roller;detecting a leading end position of each of a plurality of media in a nip between the feed roller and a separation roller located facing the feed roller;determining a distance between a leading end position of a preceding medium, which is one of the plurality of media in the nip, and a leading end position of a medium following the preceding medium; andsetting a characteristic value of the separation roller based on the distance.