Media transport device

Abstract

To provide a medium conveying device capable of favorably conveying a medium.SOLUTION: The medium conveying device includes: a first conveying roller pair; a first pressing portion for pressing one of the rollers included in the first conveying roller pair toward the other roller side; a second conveying roller pair; and a second pressing portion for pressing one of the rollers included in the second conveying roller pair toward the other roller side. A pressing force by the second pressing portion is set to be smaller than a pressing force by the first pressing portion, at least one of the rollers included in the first conveying roller pair and at least one of the rollers included in the second conveying roller pair are driven by the same motor. A roller diameter of at least one of the rollers included in the second conveying roller pair is set to be larger than a roller diameter of at least one of the rollers included in the first conveying roller pair.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a media transport device, and more particularly to a media transport device having two pairs of transport rollers. [Background technology]

[0002] In general, a medium transport device such as a scanner captures an image of a medium transported by a pair of transport rollers to generate an image. In such a medium transport device, if the medium is not transported properly, distortion may occur in the image captured of the medium.

[0003] A sheet material conveying device consisting of two or more pairs of conveying rollers for conveying a sheet material has been disclosed (see Patent Document 1). In this sheet material conveying device, when transferring a sheet material among two pairs of conveying rollers, the peripheral speed of a first pair of conveying rollers on the upstream side in the conveying direction is made slower than the peripheral speed of a second pair of conveying rollers on the downstream side in the conveying direction. In this sheet material conveying device, the conveying force of the first pair of conveying rollers is made greater than the conveying force of the second pair of conveying rollers, and the roller material of the second pair of conveying rollers is made of a material that has elasticity and a low coefficient of friction. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-321384 Summary of the Invention

[0005] A medium transport device is required to transport a medium in an excellent manner.

[0006] The purpose of the media transport device is to enable good transport of the media.

[0007] A medium transport device according to one aspect of an embodiment includes a medium separating section including a feeding member and a separating member, a first pair of transport rollers arranged downstream of the medium separating section in a medium transport direction, a second pair of transport rollers arranged downstream of the first pair of transport rollers in the medium transport direction, a separating member pressing section that presses the separating member toward the feeding member, and a first transport roller pair pressing section that presses one of the rollers included in the first transport roller pair toward the other roller, wherein a roller hardness of at least one of the rollers included in the second transport roller pair is set to be smaller than a roller hardness of at least one of the rollers included in the first transport roller pair, and the pressing force by the first transport roller pair pressing section is smaller than the pressing force by the separating member pressing section. is more than three times .

[0008] In the media transport device, the first transport roller pair includes a first roller and a second roller arranged above the first roller, and the second transport roller pair includes a third roller and a fourth roller arranged above the third roller, and it is preferable that the roller hardness of the third roller is set to be less than the roller hardness of the second roller, or the roller hardness of the fourth roller is set to be less than the roller hardness of the first roller. In the media transport device, the first transport roller pair includes a first roller provided in a first housing and a second roller provided in a second housing different from the first housing, and the second transport roller pair includes a third roller provided in the first housing and a fourth roller provided in the second housing, and it is preferable that the roller hardness of the third roller is set to be smaller than the roller hardness of the second roller, or the roller hardness of the fourth roller is set to be smaller than the roller hardness of the first roller. In the media transport device, it is preferable that the first transport roller pair includes a first transport roller and a first driven roller, and the second transport roller pair includes a second transport roller and a second driven roller, and that the roller hardness of the second transport roller is set to be smaller than the roller hardness of the first driven roller, or that the roller hardness of the second driven roller is set to be smaller than the roller hardness of the first transport roller. In the medium transport device, it is preferable that the roller diameter of at least one of the rollers included in the second transport roller pair is set to be larger than the roller diameter of at least one of the rollers included in the first transport roller pair. It is preferable that the media conveying device further has a processing unit arranged downstream of the first conveying roller pair in the media conveying direction and performing a predetermined process on the media conveyed by the first conveying roller pair, and that the second conveying roller pair is capable of conveying the media while the predetermined process is being performed by the processing unit. In the medium transport device, at least one of the rollers included in the first transport roller pair and at least one of the rollers included in the second transport roller pair are preferably driven by the same motor. It is preferable that the medium conveying device further has a second conveying roller pair pressing section that presses one of the rollers included in the second conveying roller pair toward the other roller, and that the pressing force by the second conveying roller pair pressing section is set to be smaller than the pressing force by the first conveying roller pair pressing section. In the medium conveying device, it is preferable that the pressing force W1 by the first conveying roller pair pressing portion and the pressing force W2 by the second conveying roller pair pressing portion are set so as to satisfy W1 / W2≧1.3. 。 medium In the body conveying device, it is preferable that the roller diameters of the two rollers included in the second conveying roller pair are set to the same size, and the roller diameters of the two rollers included in the first conveying roller pair are set to the same size.

[0009] According to this embodiment, the medium transport device is able to transport the medium well.

[0010] The objects and advantages of the invention will be realized and obtained by means of the elements and combinations particularly pointed out in the claims. Both the foregoing general description and the following detailed description are exemplary and explanatory but are not restrictive of the invention as claimed. [Brief description of the drawings]

[0011] [Figure 1] 1 is a perspective view showing a medium conveying device 100 according to an embodiment. [Diagram 2] 2 is a diagram for explaining a transport path inside the medium transport device 100. FIG. [Diagram 3] 5A and 5B are schematic diagrams for explaining forces applied to each roller. [Figure 4] 11 is a schematic diagram showing a state in which the leading edge of the medium M has reached the nip position. [Diagram 5] 1A and 1B are schematic diagrams for explaining a pressing force. [Figure 6] 11 is a schematic diagram for explaining the relationship between a pressing force and a conveying distance. FIG. [Figure 7] 13 is a graph showing the relationship between pressing force and overfeed rate. [Figure 8] 13 is a graph showing the relationship between pressing force and overfeed rate. [Figure 9] 1 is a block diagram showing a schematic configuration of a medium conveying device 100. FIG. [Figure 10] FIG. 2 is a diagram showing a schematic configuration of a storage device 140 and a processing circuit 150. [Figure 11] 10 is a flowchart illustrating an example of the operation of a medium reading process. [Figure 12] FIG. 13 is a diagram showing a schematic configuration of another processing circuit 250. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, a medium conveying device, a control method, and a control program according to one aspect of the present disclosure will be described with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to the embodiments, but extends to the inventions described in the claims and their equivalents.

[0013] 1 is a perspective view showing a medium conveying device 100 configured as an image scanner. The medium conveying device 100 conveys a medium, which is an original document, and captures an image of the medium. The medium is paper, thin paper, thick paper, a card, an envelope, or the like. The medium conveying device 100 may be a facsimile, a copier, a multifunction printer (MFP, Multifunction Peripheral), or the like. Note that the medium being conveyed may not be an original document, but may be a print target, or the like, and the medium conveying device 100 may be a printer, or the like.

[0014] The medium conveying device 100 includes a lower housing 101, an upper housing 102, a loading stand 103, an ejection stand 104, an operation device 105, and a display device 106. In Fig. 1, an arrow A1 indicates the medium conveying direction, an arrow A2 indicates the width direction perpendicular to the medium conveying direction, and an arrow A3 indicates the height direction perpendicular to the medium conveying surface. In the following, upstream refers to the upstream side of the medium conveying direction A1, and downstream refers to the downstream side of the medium conveying direction A1.

[0015] The upper housing 102 is positioned to cover the top surface of the medium conveying device 100, and is rotatably engaged with the lower housing 101 by a hinge so that it can be opened and closed when a medium is jammed, when the inside of the medium conveying device 100 is cleaned, etc.

[0016] The placement stage 103 engages with the lower housing 101 and places thereon the media to be fed and transported. The ejection stage 104 engages with the upper housing 102 and places thereon the ejected media. Note that the ejection stage 104 may also engage with the lower housing 101.

[0017] The operation device 105 has an input device such as a button and an interface circuit for acquiring a signal from the input device, accepts an input operation by a user, and outputs an operation signal according to the input operation by the user. The display device 106 has a display including a liquid crystal, an organic EL (Electro-Luminescence), or the like, and an interface circuit for outputting image data to the display, and displays the image data on the display.

[0018] FIG. 2 is a diagram for explaining a transport path inside the medium transport device 100. As shown in FIG.

[0019] The transport path inside the medium transport device 100 includes a medium sensor 111, a feed roller 112, a separation roller 113, a first transport roller 114, a first driven roller 115, an imaging device 116, a second transport roller 117, and a second driven roller 118. The medium transport device 100 also includes a first motor 121, a first transmission mechanism 122, a second motor 123, and a second transmission mechanism 124.

[0020] The number of each of the feed roller 112, separation roller 113, first conveyor roller 114, first driven roller 115, second conveyor roller 117, and / or second driven roller 118 is not limited to one, and may be more than one. In this case, the multiple feed rollers 112, separation rollers 113, first conveyor roller 114, first driven roller 115, second conveyor roller 117, and / or second driven roller 118 are arranged at intervals in the width direction A2.

[0021] The top surface of the lower housing 101 forms a lower guide 101a of the medium transport path, and the bottom surface of the upper housing 102 forms an upper guide 102a of the medium transport path. The lower guide 101a forms a medium transport surface.

[0022] The media sensor 111 is disposed upstream of the feed roller 112 and the separation roller 113. The media sensor 111 has a contact detection sensor, and detects whether or not a medium is placed on the placement table 103. The media sensor 111 generates and outputs a media signal whose signal value changes depending on whether or not a medium is placed on the placement table 103. Note that the media sensor 111 is not limited to a contact detection sensor, and any other sensor capable of detecting the presence or absence of a medium, such as a light detection sensor, may be used as the media sensor 111.

[0023] The feed roller 112 is provided in the lower housing 101, and separates and feeds the media placed on the placement table 103 in order from the bottom. The separation roller 113 is a so-called brake roller or retard roller, and is provided in the upper housing 102, and is arranged opposite to the feed roller 112. The separation roller 113 is provided so as to be rotatable or stoppable in the opposite direction to the medium feeding direction. The medium conveying device 100 has, as its feeding modes, a separation mode in which the medium is separated while being fed, and a non-separation mode in which the medium is fed without being separated. The feeding mode is set by the user using the operation device 105 or an information processing device that is communicatively connected to the medium conveying device 100. When the feeding mode is set to the separation mode, the separation roller 113 rotates or stops in the opposite direction to the medium feeding direction to separate the medium. On the other hand, when the feeding mode is set to the non-separation mode, the separation roller 113 rotates in the medium feeding direction. Alternatively, the feed roller 112 may be provided in the upper housing 102 and the separation roller 113 may be provided in the lower housing 101, and the feed roller 112 may feed the media placed on the placement table 103 in order from the top.

[0024] The first conveying roller 114 and the first driven roller 115 are an example of a first conveying roller pair, and are disposed downstream of the feeding roller 112 and the separation roller 113 so as to face each other. The first conveying roller 114 is provided in the upper housing 102, and conveys the medium fed by the feeding roller 112 and the separation roller 113 to the imaging device 116. The first driven roller 115 is provided in the lower housing 101 below the first conveying roller 114, and rotates following the first conveying roller 114. That is, the first conveying roller 114 and the first driven roller 115 are provided so as to be able to convey the medium fed by the feeding roller 112 in a state in which the separation roller 113 rotates in the opposite direction to the medium feeding direction or is stopped in the separation mode. Note that the first conveying roller 114 may be provided in the lower housing 101, and the first driven roller 115 may be provided in the upper housing 102.

[0025] The imaging device 116 is an example of a processing unit, and is disposed downstream of the first conveying roller 114 and the first driven roller 115 in the medium conveying direction A1, and performs imaging processing on the medium conveyed by the first conveying roller 114 and the first driven roller 115. The imaging processing is an example of a predetermined processing. The imaging device 116 includes a first imaging device 116a and a second imaging device 116b disposed opposite each other across the medium conveying path.

[0026] The first imaging device 116a has a line sensor using a CIS (Contact Image Sensor) of a life-size optical system type having imaging elements using CMOS (Complementary Metal Oxide Semiconductor) linearly arranged in the main scanning direction. The first imaging device 116a also has a lens that forms an image on the imaging elements, and an A / D converter that amplifies and analog-to-digital (A / D) converts the electrical signal output from the imaging elements. The first imaging device 116a captures the surface of the medium being conveyed under the control of a processing circuit described later, generates an input image, and outputs it.

[0027] Similarly, the second imaging device 116b has a line sensor using a CIS of a life-size optical system type having CMOS imaging elements arranged in a line in the main scanning direction. The second imaging device 116b also has a lens that forms an image on the imaging element, and an A / D converter that amplifies and analog-to-digital (A / D) converts the electrical signal output from the imaging element. The second imaging device 116b captures the back side of the medium being conveyed under the control of a processing circuit described later, generates an input image, and outputs it.

[0028] The medium conveying device 100 may have only one of the first imaging device 116a and the second imaging device 116b arranged to read only one side of the medium. Also, instead of a CIS line sensor of an equal magnification optical system type having a CMOS imaging element, a CIS line sensor of an equal magnification optical system type having a CCD (Charge Coupled Device) imaging element may be used. Also, a reduction optical system type line sensor having a CMOS or CCD imaging element may be used.

[0029] The second conveying roller 117 and the second driven roller 118 are an example of a second conveying roller pair, and are disposed facing each other downstream of the imaging device 116. The second conveying roller 117 is provided in the upper housing 102, and conveys the medium conveyed by the first conveying roller 114 and the first driven roller 115 and imaged by the imaging device 116 further downstream and discharges it to the discharge tray 104. The second driven roller 118 is provided in the lower housing 101 below the second conveying roller 117, and rotates following the second conveying roller 117. That is, the second conveying roller 117 and the second driven roller 118 are provided so as to be able to convey the medium during the imaging process being performed by the imaging device 116. Note that the second conveying roller 117 may be provided in the lower housing 101, and the second driven roller 118 may be provided in the upper housing 102.

[0030] The first motor 121 is provided in the lower housing 101, and is connected to the feed roller 112 via a first transmission mechanism 122. The first motor 121 generates a first driving force for rotating the feed roller 112 in response to a control signal from a processing circuit, which will be described later.

[0031] The first transmission mechanism 122 includes one or more pulleys, belts, gears, etc., provided between the first motor 121 and a shaft that is a rotation axis of the feed roller 112. The first transmission mechanism 122 transmits a first driving force generated by the first motor 121 to the feed roller 112.

[0032] The second motor 123 is an example of a motor, is provided in the upper housing 102, and is connected to the first conveyor roller 114, the second conveyor roller 117, and the separation roller 113 via a second transmission mechanism 124. The second motor 123 generates a second driving force for rotating the first conveyor roller 114, the second conveyor roller 117, and the separation roller 113 in response to a control signal from the processing circuit.

[0033] The second transmission mechanism 124 includes one or more pulleys, belts, gears, etc. provided between the second motor 123 and each shaft which is a rotation axis of the separation roller 113, the first conveyor roller 114, and the second conveyor roller 117. In particular, one or more gears are provided between the shaft of the first conveyor roller 114 and the shaft of the separation roller 113 to vary the rotation direction and rotation speed of the separation roller 113. The second transmission mechanism 124 transmits the second driving force generated by the second motor 123 to the separation roller 113, the first conveyor roller 114, and the second conveyor roller 117.

[0034] The first driven roller 115 and / or the second driven roller 118 may be transport rollers that rotate by a second driving force from the second motor 123. This increases the medium transport force of each roller, and allows the medium transport device 100 to transport the medium well even if the pressing force between the first transport roller 114 and the first driven roller 115 and / or the pressing force between the second transport roller 117 and the second driven roller 118 is small.

[0035] Furthermore, separation roller 113 may be connected to first motor 121 via first transmission mechanism 122, instead of being connected to second motor 123 via second transmission mechanism 124, and may be provided so as to be rotated by a first driving force generated by first motor 121. Furthermore, first motor 121 may be disposed in upper housing 102, instead of lower housing 101. Furthermore, second motor 123 may be disposed in lower housing 101, instead of upper housing 102.

[0036] In this way, at least one of the rollers included in the first conveying roller pair and at least one of the rollers included in the second conveying roller pair are driven by the same second motor 123. This allows the medium conveying device 100 to share a motor among multiple rollers, making it possible to reduce the size and cost of the device.

[0037] The rotation of the first motor 121 causes the feed roller 112 to rotate in the direction of the arrow A4. When the feed mode is set to the separation mode, the rotation of the second motor 123 causes the separation roller 113 to rotate in the direction of the arrow A5 or to stop, and the first conveyor roller 114 and the second conveyor roller 117 to rotate in the directions of the arrows A6 and A7, respectively.

[0038] The medium placed on the mounting table 103 is transported between the lower guide 101a and the upper guide 102a in the medium transport direction A1 by the rotation of the feed roller 112 in the direction of the arrow A4, i.e., the medium feed direction. When the feed mode is set to the separation mode, the separation roller 113 rotates or stops in the direction of the arrow A5, i.e., the opposite direction to the medium feed direction. When multiple media are placed on the mounting table 103, the feed roller 112 and the separation roller 113 function to separate only the media placed on the mounting table 103 that are in contact with the feed roller 112. This limits the transport of media other than the separated media (preventing double feeding).

[0039] The medium is fed between first conveyor roller 114 and first driven roller 115 while being guided by lower guide 101a and upper guide 102a. The medium is fed between first imaging device 116a and second imaging device 116b as first conveyor roller 114 rotates in the direction of arrow A6. The medium read by imaging device 116 is discharged onto discharge tray 104 as second conveyor roller 117 rotates in the direction of arrow A7.

[0040] FIG. 3 is a schematic diagram for explaining forces applied to the separation roller 113, the first driven roller 115, and the second driven roller 118. As shown in FIG.

[0041] As shown in FIG. 3, the medium conveying device 100 further includes a separation roller pressing member 113a, a first pressing member 115a, and a second pressing member 118a.

[0042] The separation roller pressing member 113a has one end attached to the upper housing 102 and the other end attached to a shaft that is the rotation axis of the separation roller 113, and presses the separation roller 113 toward the feed roller 112. The separation roller pressing member 113a includes an elastic member such as a torsion coil spring, and generates a pressing force W0 that presses the separation roller 113 toward the feed roller 112. Note that the separation roller pressing member 113a may include other spring members such as a leaf spring, or a rubber member, etc.

[0043] The first pressing member 115a is an example of a first pressing portion, and is provided with one end on the lower housing 101 and the other end on a shaft that is a rotation axis of the first driven roller 115, and presses the first driven roller 115 toward the first conveyor roller 114. The first pressing member 115a includes an elastic member such as a torsion coil spring, and generates a pressing force W1 that presses the first driven roller 115 toward the first conveyor roller 114. The first pressing member 115a may include other spring members such as a leaf spring, or a rubber member. The first pressing member 115a may be provided so as to press the first conveyor roller 114 toward the first driven roller 115. In this way, the first pressing member 115a presses one of the rollers included in the first conveyor roller pair toward the other roller.

[0044] The second pressing member 118a is an example of a second pressing portion, and is provided with one end on the lower housing 101 and the other end on a shaft that is a rotation axis of the second driven roller 118, and presses the second driven roller 118 toward the second conveyor roller 117. The second pressing member 118a includes an elastic member such as a torsion coil spring, and generates a pressing force W2 that presses the second driven roller 118 toward the second conveyor roller 117. The second pressing member 118a may include other spring members such as a leaf spring, or a rubber member. The second pressing member 118a may be provided so as to press the second conveyor roller 117 toward the second driven roller 118. In this way, the second pressing member 118a presses one of the rollers included in the second conveyor roller pair toward the other roller.

[0045] The pressing force W2 applied by the second pressing member 118a is set to be smaller than the pressing force W1 applied by the first pressing member 115a.

[0046] Further, the roller diameter R3 of the second conveyor roller 117 is set to be larger than the roller diameter R1 of the first conveyor roller 114. The roller diameter R4 of the second driven roller 118 is also set to be larger than the roller diameter R2 of the first driven roller 115. Note that the roller diameter R4 of the second driven roller 118 may be set to be the same as the roller diameter R2 of the first driven roller 115 or smaller than the roller diameter R2 of the first driven roller 115.

[0047] When the first driven roller 115 is a transport roller rotated by the second driving force from the second motor 123, it is preferable that the roller diameter R1 of the first transport roller 114 and the roller diameter R2 of the first driven roller 115 are set to the same size. Similarly, when the second driven roller 118 is a transport roller rotated by the second driving force from the second motor 123, it is preferable that the roller diameter R3 of the second transport roller 117 and the roller diameter R4 of the second driven roller 118 are set to the same size. As a result, the transport force by the roller arranged on the upper side and the transport force by the roller arranged on the lower side become the same, and the medium transport device 100 can suppress the application of a peeling (shearing) force to the transported medium, and can transport the medium well.

[0048] In this case, the roller diameter R3 of the second conveyor roller 117 and the roller diameter R4 of the second driven roller 118 are set to be larger than the roller diameter R1 of the first conveyor roller 114 and the roller diameter R2 of the first driven roller 115, respectively. Note that the roller diameter R1 of the first conveyor roller 114 and the roller diameter R2 of the first driven roller 115 may be set to different sizes. Also, the roller diameter R3 of the second conveyor roller 117 and the roller diameter R4 of the second driven roller 118 may be set to different sizes.

[0049] In this manner, the roller diameter of at least one of the rollers included in the second conveyor roller pair is set to be larger than the roller diameter of at least one of the rollers included in the first conveyor roller pair.

[0050] The technical significance of making the pressing force W2 applied by the second pressing member 118a to the downstream second driven roller 118 smaller than the pressing force W1 applied by the first pressing member 115a to the upstream first driven roller 115 will be described below.

[0051] 3, after the leading edge of the medium M being transported passes through the nip position between the first transport roller 114 and the first driven roller 115, the medium M is pulled by the first transport roller 114 and the first driven roller 115. At this time, the medium M receives a force in the direction A5 opposite the medium feeding direction by the separation roller 113 at the nip position between the feed roller 112 and the separation roller 113. Therefore, the pressing force W1 by the first pressing member 115a needs to be made large to a certain extent so as not to be defeated by the force in the direction A5 opposite the medium feeding direction by the separation roller 113.

[0052] FIG. 4 is a schematic diagram showing a state in which the leading edge of the medium M has reached the nip position between the second conveyor roller 117 and the second driven roller 118. As shown in FIG.

[0053] 4, when the leading edge of the medium M being conveyed reaches the nip position between the second conveyor roller 117 and the second driven roller 118, the imaging device 116 is performing an imaging process on the medium M. At this time, if the pressing force W2 by the second pressing member 118a is too large, the leading edge of the medium M may not smoothly enter the nip position between the second conveyor roller 117 and the second driven roller 118 and may collide with the nip position, causing the medium M to bend. In that case, the input image generated by the imaging device 116 may contain distortion in the main scanning direction and / or the sub-scanning direction. Therefore, the pressing force W2 by the second pressing member 118a needs to be made small to some extent so that the leading edge of the medium M can enter the nip position between the second conveyor roller 117 and the second driven roller 118.

[0054] 5(A) and (B) are schematic diagrams for explaining the force pushing the leading edge of medium M into the nip position. Fig. 5(A) is a schematic diagram of second conveyor roller 117 and second driven roller 118 as viewed from the side, and Fig. 5(B) is a schematic diagram showing the relationship of forces at position C where second driven roller 118 and medium M come into contact with each other.

[0055] As shown in Fig. 5(A), the second conveying roller 117 and the second driven roller 118 form a nip and the medium M has a certain thickness, so that the leading edge of the medium M abuts against the second driven roller 118 at a predetermined position C upstream of the nip position before entering the nip position. As shown in Fig. 5(B), at the predetermined position C, the leading edge of the medium M is subjected to a pushing force P toward the nip position along the medium conveying direction A1 and a reaction force W of a pressing force W2 by the second pressing member 118a along a height direction A3 perpendicular to the medium conveying direction. In Fig. 5(B), a straight line L indicates a straight line inclined with respect to the medium conveying direction A1 by an angle θ formed by a straight line passing through the center position of the second conveying roller 117 and the center position of the second driven roller 118 and a straight line passing through the center position of the second conveying roller 117 and the predetermined position C.

[0056] On the straight line L, a force (Pcosθ) due to the pushing force P, a frictional force (μPsinθ) between the medium M and the second driven roller 118 due to the pushing force P, and a frictional force (μWcosθ) between the medium M and the second driven roller 118 due to the reaction force W are generated toward the upstream side. Here, μ is the coefficient of friction between the medium M and the second driven roller 118. On the other hand, on the straight line L, a force (Wsinθ) due to the reaction force W is generated toward the downstream side. In order for the medium M to properly enter the nip position, the force toward the upstream side on the straight line L needs to be greater than the force toward the downstream side, and therefore the following formula (1) needs to be established. Pcosθ+μPsinθ+μWcosθ>Wsinθ (1) From equation (1), the following equation (2) must hold. P>W(sinθ-μcosθ) / (cosθ+μsinθ) (2)

[0057] In order to establish formula (2), the smaller the reaction force W of the pressing force W2 by the second pressing member 118a, the more preferable, and the smaller the pressing force W2 by the second pressing member 118a, the more preferable. In particular, by reducing the pressing force W2 by the second pressing member 118a, the medium conveying device 100 can satisfactorily convey a medium having a thickness such as a card.

[0058] Furthermore, the pressing force W2 of the second conveying roller 117 and the second driven roller 118 only needs to have the minimum force necessary to eject the medium, and the medium conveying device 100 is able to reduce power consumption by reducing the pressing force W2.

[0059] As described above, in medium conveying device 100, pressing force W2 by second pressing member 118a is set to be smaller than pressing force W1 by first pressing member 115a. This allows medium conveying device 100 to properly convey the medium against the separation force applied to the medium by separation roller 113, while allowing imaging device 116 to properly image the medium, thereby enabling a good input image to be obtained.

[0060] The relationship between the pressing force W1 by the first pressing member 115a, the pressing force W2 by the second pressing member 118a, and the pressing force W0 by the separation roller pressing member 113a will be described below.

[0061] As a result of an experiment in which an A3 size paper was transported and imaged while changing the pressing force W2 applied by the second pressing member 118a, it was found that in order to smoothly eject the A3 size paper and obtain an input image without distortion, it was necessary to set the pressing force W2 to approximately 1.5 kgf.

[0062] On the other hand, the force required for the separation roller to return the medium to the upstream side is generally in the range of 500 gf to 900 gf (4.9 N to 8.8 N). If the total widthwise size (roller width) of one or more transport rollers provided downstream of the separation roller is 40 mm, the load tension on the transport roller will be 0.12 N / mm to 0.22 N / mm.

[0063] Figure 15 in "Okamoto Noriaki: Contact Mechanics of Friction Driven by Rubber Rollers, Journal of the Japan Rubber Association, Vol. 74, 8 (2001) 300" shows a graph showing the paper transport speed characteristics of rollers. This graph shows the relationship between the pressing force [N / mm] between opposing rollers and the speed ratio of the media transport speed (value obtained by dividing the media transport speed by the roller peripheral speed) for multiple rollers with different load tensions. From this graph, it can be seen that for a roller with a load tension of 0.11 [N / mm], in order to keep the speed ratio within a range close to 1 (0.99 or more and 1.01 or less), the pressing force needs to be set to 0.4 [N / mm] or more. In other words, if the pressing force is 3.6 times the load tension (= 0.4 [N / mm] / 0.11 [N / mm]) or more, the speed ratio will be kept within a range close to 1. Also, for a roller with a load tension of 0.216 [N / mm], it is found that in order to keep the speed ratio within a range close to 1 (0.99 or more and 1.01 or less), the pressing force needs to be set to 0.8 [N / mm] or more. In other words, if the pressing force is 3.7 times the load tension (= 0.8 [N / mm] / 0.216 [N / mm]) or more, the speed ratio will be kept within a range close to 1.

[0064] Therefore, if the pressing force is about four times the load tension, the speed ratio of the medium transport speed is kept within a range close to 1, the medium transport speed is approximately equal to the peripheral speed of the roller, and the occurrence of medium slippage due to the roller is suppressed. As described above, a force in the range of 500 gf or more and 900 gf or less is generally required as the force by the separation roller to return the medium to the upstream side. Therefore, if the pressing force W1 by the first pressing member 115a is 2.0 kgf or more and 3.6 kgf or less, the speed ratio of the medium transport speed is kept within a range close to 1, and the occurrence of medium slippage due to the roller is suppressed.

[0065] As described above, in order to smoothly eject A3 size paper and obtain an input image without distortion, it is necessary to set the pressing force W2 by the second pressing member 118a to about 1.5 [kgf]. Therefore, it is desirable to set the pressing force W1 by the first pressing member 115a and the pressing force W2 by the second pressing member 118a so as to satisfy the following formula (3). W1 / W2≧2[kgf] / 1.5[kgf]≒1.3 (3) As a result, the medium conveying device 100 can smoothly discharge A3 size paper using the second conveying rollers 117 to obtain an input image without distortion, while preventing the first conveying rollers 114 from causing the medium to slip.

[0066] In addition, an experiment was conducted in which various types of media were conveyed while changing the pressing force W0 by the separation roller pressing member 113a, and as a result, in order to prevent the occurrence of media jams or double feeding, the pressing force W0 needed to be 300 [gf] or more and 600 [gf] or less. Therefore, it is desirable to set the pressing force W1 by the first pressing member 115a and the pressing force W0 by the separation roller pressing member 113a so as to satisfy the following formula (4) based on the relationship between the minimum value of W1 (2.0 [kgf]) and the maximum value of W0 (0.6 [kgf]). W1 / W0≧2.0[kgf] / 0.6[kgf]≒3 (4) This allows the medium conveying device 100 to prevent the first conveying roller 114 from causing a medium slip while preventing the separation roller 113 from causing a jam or multiple feeding of the medium.

[0067] If the pressing force W1 by the first pressing member 115a is too large, a reaction force is generated in the lower housing 101 supporting the first pressing member 115a, and the lower housing 101 is deflected. In that case, the positions of the components provided in the lower housing 101 may vary, and the medium conveying device 100 may not be able to convey the medium well. If the pressing force W1 by the first pressing member 115a is too large, the first pressing member 115a pushes up the shaft of the first driven roller 115 significantly. In the case where the first pressing member 115a is disposed at the center of the shaft of the first driven roller 115 in the width direction A2 and the first driven roller 115 is disposed outside the first pressing member 115a, the center of the shaft is pushed up, and the first driven roller 115 is disposed downward. As a result, the amount of protrusion of the first driven roller 115 relative to the lower guide 101a becomes smaller, making it difficult for the leading edge of the medium being transported to enter the nip between the first transport roller 114 and the first driven roller 115, which may cause the medium to jam.

[0068] The medium conveying device 100 is able to suppress bending of the lower housing 101 and the shaft of the first driven roller 115 by setting an upper limit value of the pressing force W1 by the first pressing member 115a while taking into account variations in design and processing of components.

[0069] By setting the pressing force W2 by the second pressing member 118a to a small value, the conveying force by the second conveying roller 117 and the second driven roller 118 is reduced, and the medium may not be pulled effectively downstream by the second conveying roller 117 and the second driven roller 118. This may cause bending of the medium M between the second conveying roller 117 and the second driven roller 118 and the first conveying roller 114 and the first driven roller 115, and may cause distortion in the input image generated by the imaging device 116.

[0070] Fig. 6 is a schematic diagram for explaining the relationship between the pressing force applied to the rollers and the distance the medium is transported by the rollers. Fig. 6 is a schematic diagram of two rollers D1 and D2 facing each other, as viewed from the side.

[0071] In the example shown in Fig. 6, the upper roller D1 is made of a material with high hardness such as iron, and the lower roller D2 is made of a material with low hardness such as rubber. In this case, the upper part of the lower roller D2 is pressed by the upper roller D1, and the lower roller D2 is deformed. The apparent radius R of the lower roller D2 is calculated by the following formula (5) (see "Kawauchi Masataka, Paper Feeding Device and Rubber Materials, Journal of the Society of Rubber Science and Technology of Japan, 62, 11, pp. 683-694 (1989)").

number

[0072] As shown in formula (5), the apparent radius R of roller D2, which is made of a low-hardness material, depends on the area ΔV of the nip portion between rollers D1 and D2; the larger the area ΔV, the larger the apparent radius R of roller D2. The area ΔV of the nip portion between rollers D1 and D2 depends on the pressing force generated between rollers D1 and D2; the larger the pressing force, the larger the area ΔV. Therefore, the greater the pressing force generated between rollers D1 and D2, the larger the apparent radius R of roller D2 becomes, and the greater the transport distance of the medium when roller D2 makes one revolution.

[0073] That is, by setting the pressing force W2 by the second pressing member 118a to be smaller than the pressing force W1 by the first pressing member 115a, the transport distance of the medium when the second transport roller 117 makes one revolution is smaller than the transport distance of the medium when the first transport roller 114 makes one revolution. Therefore, bending of the medium M occurs between the second transport roller 117 and the second driven roller 118 and the first transport roller 114 and the first driven roller 115, and there is a possibility that the input image generated by the imaging device 116 contains distortion.

[0074] For example, by providing a motor for driving the second conveyor roller 117 and a motor for driving the first conveyor roller 114 separately and rotating the second conveyor roller 117 faster than the first conveyor roller 114, the occurrence of bending of the medium M can be suppressed. However, in that case, the device size and device cost of the medium conveying device will increase.

[0075] As described above, in the medium conveying device 100, the first conveying roller 114 included in the first conveying roller pair and the second conveying roller 117 included in the second conveying roller pair are driven by the same second motor 123. Also, in the medium conveying device 100, the roller diameter of the second conveying roller 117 included in the second conveying roller pair is set to be larger than the roller diameter of the first conveying roller 114 included in the first conveying roller pair.

[0076] As a result, the medium conveying device 100 can make the medium conveying speed by the second conveying roller 117 higher than the medium conveying speed by the first conveying roller 114, while sharing one second motor 123 between the first conveying roller 114 and the second conveying roller 117. Furthermore, the medium conveying device 100 can make the medium conveying speed by the second conveying roller 117 higher than the medium conveying speed by the first conveying roller 114, while simplifying the structure of the second transmission mechanism 124 without using a special structure such as a reduction gear. Therefore, the medium conveying device 100 can suppress bending of the medium at the imaging position and suppress distortion in the input image, while suppressing increases in device size and device costs.

[0077] FIG. 7 is a graph 700 showing the relationship between the pressing force applied between two opposing rollers and the overfeed rate caused by the two rollers.

[0078] The horizontal axis of the graph in Fig. 7 indicates the pressing force [kgf] applied between the two opposing rollers, and the vertical axis indicates the overfeed rate caused by the two rollers. The overfeed rate is calculated by the following formula (6) using the actual radius r and the apparent radius R of the deforming roller. (Overfeed rate)=(Rr) / r (6)

[0079] As shown in the graph 700, the greater the pressing force between the two opposing rollers, the greater the overfeed rate of the two rollers. For example, when the pressing force W1 of the first conveying roller 114 and the first driven roller 115 is 3 kgf, the overfeed rate of the first conveying roller 114 and the first driven roller 115 is about 0.012. On the other hand, when the pressing force W2 of the second conveying roller 117 and the second driven roller 118 is 1.5 kgf, the overfeed rate of the second conveying roller 117 and the second driven roller 118 is about 0.006. Therefore, by setting the roller diameter d1 of the first conveying roller 114 and the roller diameter d2 of the second conveying roller 117 to satisfy the following formula (7), the medium conveying device 100 can suppress the occurrence of bending of the medium. (d2-d1) / d1≒0.012-0.006 (7)

[0080] In the medium conveying device 100, instead of making the roller diameter of the upstream roller different from that of the downstream roller, the roller hardness of the upstream roller may be made different from that of the downstream roller. In this case, the roller hardness of the second conveying roller 117 is set to be smaller than that of the first conveying roller 114. The roller hardness of the second driven roller 118 is also set to be smaller than that of the first driven roller 115. The roller hardness of the second driven roller 118 may be set to be the same as that of the first driven roller 115 or to be larger than that of the first driven roller 115.

[0081] When the first driven roller 115 is a transport roller rotated by the second driving force from the second motor 123, it is preferable that the roller hardness of the first transport roller 114 and the roller hardness of the first driven roller 115 are set to the same magnitude. Similarly, when the second driven roller 118 is a transport roller rotated by the second driving force from the second motor 123, it is preferable that the roller hardness of the second transport roller 117 and the roller hardness of the second driven roller 118 are set to the same magnitude. As a result, the transport force by the roller arranged on the upper side and the transport force by the roller arranged on the lower side become the same, and the medium transport device 100 can suppress the application of a peeling (shearing) force to the transported medium, and can transport the medium well.

[0082] In this case, the roller hardness of the second conveyor roller 117 and the roller hardness of the second driven roller 118 are set to be smaller than the roller hardness of the first conveyor roller 114 and the roller hardness of the first driven roller 115, respectively. The roller hardness of the first conveyor roller 114 and the roller hardness of the first driven roller 115 may be set to different values. The roller hardness of the second conveyor roller 117 and the roller hardness of the second driven roller 118 may be set to different values.

[0083] In this manner, the roller hardness of at least one of the rollers included in the second transport roller pair is set to be smaller than the roller hardness of at least one of the rollers included in the first transport roller pair.

[0084] FIG. 8 is a graph showing the relationship between the pressing force applied between two opposing rollers and the overfeed rate caused by the two rollers.

[0085] The horizontal axis of the graph shown in Fig. 8 indicates the pressing force [kgf] applied between two opposing rollers, and the vertical axis indicates the overfeed rate by the two rollers. Graph 800 shown in Fig. 8 indicates the overfeed rate when one of the two opposing rollers, a conveying roller, has a rubber hardness of 45° as specified by JIS-A. On the other hand, graph 801 shown in Fig. 8 indicates the overfeed rate when one of the two opposing rollers, a conveying roller, has a rubber hardness of 60° as specified by JIS-A.

[0086] 8, the lower the hardness (softer) of the transport roller, the greater the overfeed rate caused by that transport roller. By setting the roller hardness of the second transport roller 117 to be lower than the roller hardness of the first transport roller 114, the medium transport device 100 can make the medium transport speed by the second transport roller 117 higher than the medium transport speed by the first transport roller 114. Therefore, the medium transport device 100 can suppress bending of the medium at the imaging position and suppress distortion in the input image while reducing the device size and device costs.

[0087] When a roller with a hardness of 60° (graph 801) is used as the first conveying roller 114 and the pressing force W1 applied to the first conveying roller 114 is 2 [kgf], the overfeed rate of the first conveying roller 114 and the first driven roller 115 is about 0.005. On the other hand, when a roller with a hardness of 45° (graph 800) is used as the second conveying roller 117 and the pressing force W2 applied to the second conveying roller 117 is 1.1 [kgf], the overfeed rate of the second conveying roller 117 and the second driven roller 118 is also about 0.005. That is, by making the roller hardness of the first conveying roller 114 and the second conveying roller 117 different, the medium conveying device 100 can eliminate the influence of the speed difference due to the pressing force applied to the first conveying roller 114 and the second conveying roller 117. Therefore, in the medium conveying device 100, by making the roller hardness of the first conveying roller 114 and the second conveying roller 117 different, it is possible to suppress the occurrence of bending of the medium.

[0088] When the roller hardness of the upstream roller is made different from that of the downstream roller, the roller diameter of the upstream roller may be set to the same value. Conversely, when the roller diameter of the upstream roller is made different from that of the downstream roller, the roller hardness of the upstream roller may be set to the same value.

[0089] In the medium conveying device 100, the roller diameter of the second conveying roller 117 may be set to be larger than the roller diameter of the first conveying roller 114, and the roller hardness of the second conveying roller 117 may be set to be smaller than that of the first conveying roller 114.

[0090] As described above, for example, when the pressing force W1 of the first conveying roller 114 and the first driven roller 115 is 3 kgf, the overfeed rate of the first conveying roller 114 and the first driven roller 115 is about 0.012. On the other hand, when the pressing force W2 of the second conveying roller 117 and the second driven roller 118 is 1.5 kgf, the overfeed rate of the second conveying roller 117 and the second driven roller 118 is about 0.006. As shown in FIG. 8, when the pressing force between the two rollers is 1.5 kgf and the rubber hardness of the rollers is 45°, the overfeed rate of the two rollers is about 0.004. On the other hand, when the pressing force between the two rollers is 1.5 kgf and the rubber hardness of the rollers is 60°, the overfeed rate of the two rollers is about 0.007. Therefore, by using a roller with a hardness of 60° as the first conveyor roller 114 and a roller with a hardness of 45° as the second conveyor roller 117, the difference in the overfeed rate of the two rollers can be approximately 0.003. In this case, by setting the roller diameter d1 of the first conveyor roller 114 and the roller diameter d2 of the second conveyor roller 117 to satisfy the following formula (8), the medium conveying device 100 can suppress the occurrence of bending of the medium. (d2-d1) / d1≒0.003 (8)

[0091] FIG. 9 is a block diagram showing a schematic configuration of the medium conveying device 100. As shown in FIG.

[0092] In addition to the components described above, the medium conveying device 100 further includes an interface device 131, a storage device 140, a processing circuit 150, and the like.

[0093] The interface device 131 has an interface circuit conforming to a serial bus such as USB, and is electrically connected to an information processing device (not shown, for example, a personal computer, a mobile information terminal, etc.) to transmit and receive input images and various information. Also, instead of the interface device 131, a communication unit having an antenna for transmitting and receiving wireless signals and a wireless communication interface device for transmitting and receiving signals through a wireless communication line in accordance with a predetermined communication protocol may be used. The predetermined communication protocol is, for example, a wireless LAN (Local Area Network). The communication unit may have a wired communication interface device for transmitting and receiving signals through a wired communication line in accordance with a communication protocol such as a wired LAN.

[0094] The storage device 140 includes a memory device such as a random access memory (RAM) or a read only memory (ROM), a fixed disk device such as a hard disk, or a portable storage device such as a flexible disk or an optical disk. The storage device 140 also stores computer programs, databases, tables, and the like used for various processes of the medium conveying device 100. The computer programs may be installed in the storage device 140 from a computer-readable portable recording medium using a known setup program or the like. The portable recording medium is, for example, a compact disc read only memory (CD-ROM), a digital versatile disc read only memory (DVD-ROM), or the like.

[0095] The processing circuit 150 operates based on a program previously stored in the storage device 140. The processing circuit is, for example, a CPU (Central Processing Unit). The processing circuit 150 may be, for example, a DSP (digital signal processor), an LSI (large scale integration), an ASIC (Application Specific Integrated Circuit), or an FPGA (Field-Programmable Gate Array).

[0096] The processing circuit 150 is connected to the operation device 105, the display device 106, the medium sensor 111, the imaging device 116, the first motor 121, the second motor 123, the interface device 131, the storage device 140, etc., and controls each of these components. The processing circuit 150 performs drive control of the first motor 121 and the second motor 123, imaging control of the imaging device 116, etc., based on the medium signal received from the medium sensor 111. The processing circuit 150 acquires an input image from the imaging device 116, and transmits it to the information processing device via the interface device 131.

[0097] FIG. 10 is a diagram showing a schematic configuration of the storage device 140 and the processing circuit 150. As shown in FIG.

[0098] 11, the storage device 140 stores a control program 141, an image acquisition program 142, and the like. Each of these programs is a functional module implemented by software that runs on a processor. The processing circuitry 150 reads each program stored in the storage device 140 and operates according to the read program. In this way, the processing circuitry 150 functions as a control unit 151 and an image acquisition unit 152.

[0099] FIG. 11 is a flowchart showing an example of the operation of the medium reading process of the medium conveying device 100.

[0100] An example of the operation of the medium reading process of the medium conveying device 100 will be described below with reference to the flowchart shown in Fig. 11. Note that the flow of the operation described below is executed mainly by the processing circuit 150 in cooperation with each element of the medium conveying device 100 based on a program stored in advance in the storage device 140.

[0101] First, the control unit 151 waits until a user inputs an instruction to read a medium using the operation device 105 or an information processing device, and an operation signal instructing the user to read a medium is received from the operation device 105 or the interface device 131 (step S101).

[0102] Next, control unit 151 acquires a medium signal from medium sensor 111, and determines whether or not a medium is placed on mounting table 103 based on the acquired medium signal (step S102). If no medium is placed on mounting table 103, control unit 151 ends the series of steps.

[0103] On the other hand, when a medium is placed on the placement table 103, the control unit 151 drives the first motor 121 and the second motor 123 to rotate the feed roller 112, the separation roller 113, the first conveyor roller 114 and / or the second conveyor roller 117 (step S103). In this way, the control unit 151 causes each roller to feed and convey the medium.

[0104] Next, the control unit 151 causes the imaging device 116 to capture an image of the medium, acquires an input image from the imaging device 116, and outputs the acquired input image by transmitting it to the information processing device via the interface device 131 (step S104).

[0105] Next, control unit 151 determines whether or not a medium remains on mounting table 103 based on the medium signal received from medium sensor 111 (step S105). If a medium remains on mounting table 103, control unit 151 returns the process to step S104, and repeats the processes of steps S104 to S105.

[0106] On the other hand, if there are no media remaining on the placement table 103, the control unit 151 controls the first motor 121 and the second motor 123 to stop the feed roller 112, the separation roller 113, the first conveyor roller 114 and / or the second conveyor roller 117 (step S106). Then, the control unit 151 ends the series of steps.

[0107] As described above in detail, the medium conveying device 100 makes the pressing force of the downstream conveying roller pair smaller than that of the upstream conveying roller pair, while making the roller diameter of the downstream conveying roller pair larger than that of the upstream conveying roller pair. Alternatively, the medium conveying device 100 makes the pressing force of the downstream conveying roller pair smaller than that of the upstream conveying roller pair, while making the roller hardness of the downstream conveying roller pair smaller than that of the upstream conveying roller pair. This makes it possible for the medium conveying device 100 to convey the medium well while suppressing increases in device size and device costs by sharing the second motor 123 among multiple conveying rollers.

[0108] 12 is a diagram showing a schematic configuration of a processing circuit 250 in a medium conveying device according to yet another embodiment. The processing circuit 250 is used in place of the processing circuit 150 of the medium conveying device 100, and executes medium reading processing and the like in place of the processing circuit 150. The processing circuit 250 has a control circuit 251, an image acquisition circuit 252, and the like. Each of these components may be formed of an independent integrated circuit, microprocessor, firmware, and the like.

[0109] The control circuit 251 is an example of a control unit, and has the same functions as the control unit 151. The control circuit 251 receives an operation signal from the operation device 105 or the interface device 131, and a medium signal from the medium sensor 111. The control circuit 251 controls the first motor 121 and the second motor 123 based on each piece of received information.

[0110] The image acquisition circuit 252 is an example of an image acquisition unit, and has the same function as the image acquisition unit 152. The image acquisition circuit 252 acquires an input image from the imaging device 116, and outputs it to the interface device 131.

[0111] As described above in detail, the medium conveying device is able to convey the medium satisfactorily even when the processing circuit 250 is used.

[0112] Although preferred embodiments have been described above, the embodiments are not limited to these. For example, the medium transport device may be a printer that transports a print target or the like as a medium. In this case, the medium transport device has a printing device instead of the imaging device 116. The printing device is disposed at a position where the imaging device 116 is disposed, and executes a printing process on the medium transported by the first transport roller 114 and the first driven roller 115. The printing process is an example of a predetermined process. The medium transport device can suppress the occurrence of bending in the transported medium (print target), making it possible to perform good printing on the print target. [Explanation of symbols]

[0113] 100 medium conveying device, 112 feeding roller, 113 separation roller, 114 first conveying roller, 115 first driven roller, 115a first pressing member, 116 imaging device, 117 second conveying roller, 118 second driven roller, 118a second pressing member

Claims

1. a media separation unit including a feeding member and a separating member; a first conveying roller pair disposed downstream of the medium separating unit in a medium conveying direction; a second conveying roller pair disposed downstream of the first conveying roller pair in a medium conveying direction; a separating member pressing portion that presses the separating member toward the feeding member; a first conveying roller pair pressing portion that presses one of the rollers included in the first conveying roller pair toward the other roller, a roller hardness of at least one of the rollers included in the second conveying roller pair is set to be smaller than a roller hardness of at least one of the rollers included in the first conveying roller pair; the pressing force of the first conveying roller pair pressing portion is three times or more the pressing force of the separating member pressing portion; A medium transport device comprising:

2. the first conveying roller pair includes a first roller and a second roller disposed above the first roller, the second conveying roller pair includes a third roller and a fourth roller disposed above the third roller, The medium transport device according to claim 1 , wherein a roller hardness of the third roller is set to be smaller than a roller hardness of the second roller, or a roller hardness of the fourth roller is set to be smaller than a roller hardness of the first roller.

3. the first conveying roller pair includes a first roller provided in a first housing and a second roller provided in a second housing different from the first housing, the second conveying roller pair includes a third roller provided in the first housing and a fourth roller provided in the second housing, The medium transport device according to claim 1 , wherein a roller hardness of the third roller is set to be smaller than a roller hardness of the second roller, or a roller hardness of the fourth roller is set to be smaller than a roller hardness of the first roller.

4. the first conveying roller pair includes a first conveying roller and a first driven roller, the second conveying roller pair includes a second conveying roller and a second driven roller, 2. The medium transport device of claim 1, wherein the roller hardness of the second transport roller is set to be less than the roller hardness of the first driven roller, or the roller hardness of the second driven roller is set to be less than the roller hardness of the first transport roller.

5. A medium transport device as described in any one of claims 1 to 4, wherein a roller diameter of at least one of the rollers included in the second transport roller pair is set to be larger than a roller diameter of at least one of the rollers included in the first transport roller pair.

6. a processing unit that is disposed downstream of the first conveying roller pair in a medium conveying direction and that performs a predetermined process on the medium conveyed by the first conveying roller pair; 5. The medium transport device according to claim 1, wherein the second transport roller pair is capable of transporting the medium while the processing section is executing the predetermined process.

7. A medium transport device as described in any one of claims 1 to 4, wherein at least one of the rollers included in the first transport roller pair and at least one of the rollers included in the second transport roller pair are driven by the same motor.

8. a second conveying roller pair pressing portion that presses one of the rollers included in the second conveying roller pair toward the other roller, 5. The medium transport device according to claim 1, wherein a pressing force applied by the second transport roller pair pressing portion is set to be smaller than a pressing force applied by the first transport roller pair pressing portion.

9. The pressing force W1 by the first conveying roller pair pressing portion and the pressing force W2 by the second conveying roller pair pressing portion are W1 / W2≧1.3 The medium transport device according to claim 8 , wherein the medium transport device is configured to satisfy the following expression.

10. The roller diameters of the two rollers included in the second conveying roller pair are set to the same size, 10. The medium transport device according to claim 1, wherein the roller diameters of the two rollers included in the first transport roller pair are set to the same value.

Images