JP2015231146A - Image reader, image forming apparatus and image reading method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a deviation between images when connecting read images.SOLUTION: An image reader includes: first carrying means (a pickup roller 1, a feed roller 2, a carriage roller 3, a carriage drum 4 and an eject roller 7) for carrying a document in a direction of carriage; second carrying means (carriage rollers 5 and 6) provided at an upstream or downstream side of the first carrying means for carrying the document in the direction of carriage; a CCD 16 employing a reduction optical system for reading an image on a front side of the document carried in the direction of carriage by the first carrying means; and a plurality of CIS 11 employing non-magnification optical systems arrayed in a staggered manner in a direction orthogonal with the direction of carriage for reading images on a rear side of the document carried in the direction of carriage by the second carrying means. A variation in a carrying speed of the document caused by the second carrying means is smaller than a variation in a carrying speed of the document caused by the first carrying means.

Description

  The present invention relates to an image reading apparatus, an image forming apparatus, and an image reading method.

  2. Description of the Related Art Conventionally, as an image reading apparatus, there is known an apparatus that includes a sensor that reads a front surface of a document (sheet-like medium) and a sensor that reads a back surface of the document, and reads both sides by one transport without inverting the document. (For example, refer to Patent Document 1).

  In such an image reading apparatus, the sensor that reads the surface (front surface) on the contact glass side is a sensor of a reduction optical system that also serves as a sensor that reads a document placed on the contact glass, and the opposite surface (back surface). In many cases, the sensor for reading the image is a sensor of an equal magnification optical system.

  As a sensor of the reduction optical system, for example, a CCD (Charge Coupled Device) that is superior in reading a cut and pasted document, a folded document, a book document, or the like can be cited. In addition, examples of the same-magnification optical sensor include a small and low-cost contact image sensor (CIS).

  Here, when reading both sides of a wide document, if a CIS longer than the width of the document is used, the cost increases. Therefore, a plurality of relatively low-cost small CISs may be arranged to read an image. In this case, for example, a plurality of CISs are arranged in a zigzag pattern in the document width direction (direction orthogonal to the document transport direction) to read an image. Then, one piece of image data is obtained by electrically connecting the image data read by a plurality of CISs.

  However, as described above, when a document image is read with a plurality of CISs, there is a problem that if the variation in the document conveyance speed is large, the images are shifted when the read images are joined. .

  The present invention has been made in view of the above, and in the case of reading an image of a document using a sensor of a reduction optical system and an equal magnification optical system, an image read by a plurality of sensors of the equal magnification optical system is used. An object of the present invention is to provide an image reading apparatus, an image forming apparatus, and an image reading method that reduce a shift between images at the time of joining.

  In order to solve the above-described problems and achieve the object, the present invention is provided with a first transport unit that transports a sheet-like medium in a predetermined direction, and provided upstream or downstream of the first transport unit. Second conveying means for conveying the sheet-like medium in the direction, and first reading means using a reduction optical system for reading an image on one surface of the sheet-like medium conveyed in the predetermined direction by the first conveying means; A plurality of staggered arrangements in a direction orthogonal to the predetermined direction, and a first-magnification optical system that reads an image on the other surface of the sheet-like medium conveyed in the predetermined direction by the second conveying means. 2, and a fluctuation in the conveyance speed of the sheet-like medium by the second conveyance means is smaller than a fluctuation in the conveyance speed of the sheet-like medium by the first conveyance means.

  According to the present invention, when an image of an original is read using a reduction optical system and an equal-magnification optical system sensor, a shift between images when the images read by the plural sensors of the equal-magnification optical system are joined is detected. There is an effect of reducing.

FIG. 1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment. FIG. 2 is a diagram illustrating a configuration of the image reading apparatus according to the embodiment. FIG. 3 is a diagram illustrating an arrangement of CISs installed in the image reading apparatus according to the embodiment. FIG. 4 is an explanatory diagram of slack formed in the image reading apparatus according to the embodiment. FIG. 5 is an explanatory diagram of slack formed in the image reading apparatus according to the embodiment. FIG. 6 is a diagram illustrating a configuration of the image reading apparatus when no discharge roller or the like is arranged. FIG. 7 is a diagram for explaining a shift in the joint between images due to a change in the document conveyance speed. FIG. 8 is a flowchart illustrating a flow when reading an image of a document in the image reading apparatus according to the embodiment.

  Hereinafter, embodiments of an image reading apparatus, an image forming apparatus, and an image reading method will be described in detail with reference to the accompanying drawings.

  An image forming apparatus equipped with an image reading apparatus according to an embodiment will be described below with reference to the accompanying drawings. FIG. 1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment. As shown in FIG. 1, an image forming apparatus 300 includes a sheet feeding unit 303 and an image forming apparatus main body 304, and an image reading apparatus 100 provided with an automatic document feeder (ADF) 200 on the top is mounted. Has been. In the image forming apparatus 300, the image reading apparatus 100 reads an image of a document, and forms an image read by an image forming unit (not shown) of the image forming apparatus main body 304 on a forming object such as paper.

  Next, the image reading apparatus 100 will be described. FIG. 2 is a diagram illustrating a configuration of the image reading apparatus according to the present embodiment. In the image reading apparatus 100 shown in FIG. 2, both sides of the original are read by one conveyance without inverting the original (sheet-like medium), and at that time, the ADF 200 is used to feed the original. The image reading apparatus 100 according to the present embodiment uses different reading methods for reading the front and back images.

  On the other hand, after the reflected light at an arbitrary position on the contact glass 13 is refracted by a plurality of mirrors arranged on the optical path 19, the light imaged on the image sensor (CCD 16) is received using a lens. This is called a reduction optical system reading method.

  The other is a method of receiving reflected light at a position close to the contact image sensor (CIS11), and this is called a reading method of an equal magnification optical system. FIG. 3 is a diagram showing an arrangement of CISs installed in the image reading apparatus according to the present embodiment. As shown in FIG. 3, in the equal-magnification optical system of the present embodiment, five (3a to 11e) CISs 11 having an A3 or A4 width are provided, and a direction perpendicular to the document transport direction d, that is, main scanning. It is arranged in two rows in a staggered manner in the direction. Here, in the image reading apparatus of the present embodiment, an example in which the CIS 11 of the equal-magnification optical system is arranged in a direction orthogonal to the document conveyance direction is shown. However, as long as the direction intersects the document conveyance direction. There may be some errors rather than orthogonal directions.

  Returning to FIG. 2, in the image reading apparatus 100 according to the present embodiment, the document placed on the document tray 18 is conveyed one by one by the pickup roller 1, the feed roller 2, and the conveyance roller 3. Then, the document is transported by the transport drum 4 (first transport roller), and the image on the surface (one surface) of the document is read by the CCD 16 in the reduction optical system reading unit 17.

  Next, when the document is conveyed by the conveyance roller 5 (second conveyance roller) and the conveyance roller 6 (third conveyance roller) provided downstream of the conveyance drum 4, it is provided to face the white reference roller 12. The image on the back side (the other side) of the document is read by the CIS 11 (11a to 11e). Then, the document is discharged by the discharge roller 7 (fourth transport roller).

  As shown in FIG. 3, in the image reading apparatus 100 according to the present embodiment, the image reading lines by the CIS 11 can be formed in two rows in the document conveyance direction. Is corrected to reduce image misalignment. Accordingly, when the document transport speed varies greatly, the gap between the joints of the image read by the CIS 11 becomes large, and it is necessary to transport the document with high accuracy so that the transport speed is as constant as possible. That is, it is preferable that the conveyance rollers 5 and 6 with the highest possible accuracy are installed before and after the CIS 11 and the conveyance rollers 5 and 6 are driven by the drive unit with the highest possible accuracy.

  As described above, in the case of the reading system using the equal-magnification optical system, if unevenness occurs in the conveyance speed between the leading edge, the middle edge, and the trailing edge of the document, a step is generated at the joint of the read image. However, in the case of a reduction optical system reading method, even if unevenness of the document conveyance speed occurs, an abnormal image such as a step difference does not occur. For this reason, the pick-up roller 1, the feed roller 2, the transport roller 3, the transport drum 4, the discharge roller 7 and their drive units are not required to have more precision than necessary.

  Therefore, in the image reading apparatus 100 according to the present embodiment, fluctuations in the document conveyance speed caused by the conveyance rollers 5 and 6 and the stepping motor 8 (second drive unit) serving as a driving unit are caused by the pickup roller 1, the feed roller 2, and the conveyance. It is smaller than the fluctuation of the document conveying speed by the roller 3, the conveying drum 4, the discharge roller 7, the DC motor 9 as the driving unit (first driving means) and the electromagnetic clutch 10. That is, the fluctuation of the surface speed when the transport rollers 5 and 6 are rotated at a predetermined speed is the surface when the pickup roller 1, the feed roller 2, the transport roller 3, the transport drum 4, and the discharge roller 7 are rotated at the predetermined speed. Less than speed fluctuation.

  Here, the above-described highly accurate transport roller refers to a transport roller having a small variation in the transport speed of the document. Specifically, for example, the thermal expansion coefficients of the transport rollers 5 and 6 in the image reading apparatus 100 of the present embodiment are the heat of the pickup roller 1, the feed roller 2, the transport roller 3, the transport drum 4, and the discharge roller 7. It is smaller than the expansion coefficient. When the thermal expansion coefficient is small, the deformation of the transport roller is small and the fluctuation of the document transport speed is also small.

  Further, for example, the dimensional accuracy of the outer diameters of the transport rollers 5 and 6 in the image reading apparatus 100 of the present embodiment is the outer diameter of the pickup roller 1, the feed roller 2, the transport roller 3, the transport drum 4, and the discharge roller 7. The dimensional accuracy is better. If the dimensional accuracy of the outer diameter is good, it becomes closer to a perfect circle, and fluctuations in the document conveyance speed are also reduced.

  Further, for example, the eccentric amounts of the transport rollers 5 and 6 in the image reading apparatus 100 of the present embodiment are smaller than the eccentric amounts of the pickup roller 1, the feed roller 2, the transport roller 3, the transport drum 4, and the discharge roller 7. ing. When the amount of eccentricity is small, the center of the roller is not biased, and the fluctuation in the document conveyance speed is also reduced.

  Thus, the smaller the coefficient of thermal expansion of the transport roller, the smaller the variation in the transport speed of the document even when the environment changes (for example, when the temperature increases or decreases). Further, the better the dimensional accuracy of the outer diameter of the conveying roller, the smaller the variation in the document conveying speed. Furthermore, the smaller the amount of eccentricity of the conveying roller, the smaller the fluctuation in the conveying speed of one rotation of the conveying roller.

  Although there are some conveyance rollers that do not perform outer diameter cutting while molding chloroprene rubber or the like, in the conveyance rollers 5 and 6 of the present embodiment, for example, a urethane or resin cut product with small thermal expansion is used as urethane. It is coated with rubber.

  Here, details of the drive unit will be described. The image reading apparatus according to the present embodiment includes, for example, a DC motor 9 as a drive unit and a electromagnetic clutch 10 as a drive unit of the discharge roller 7 in a reduction optical system reading method. On the other hand, a stepping motor 8 is mounted as a drive unit in the reading system of the equal magnification optical system to increase the accuracy of the document conveyance speed. That is, the fluctuations in the rotational speeds of the driving parts of the conveying rollers 5 and 6 are smaller than the fluctuations in the rotational speeds of the driving parts of the pickup roller 1, the feed roller 2, the conveying roller 3, the conveying drum 4 and the discharge roller 7. . Note that the stepping motor is an example of a motor with good document conveyance accuracy (small fluctuation in rotational speed), and another motor or the like may be used as the drive unit.

  As described above, the image reading apparatus 100 according to the present embodiment uses the reading system of the equal-magnification optical system and the reading system of the reduction optical system. In this embodiment, the conveyance unit (conveying rollers 5 and 6 and the stepping motor 8) in the reading system of the equal-magnification optical system and the other conveyance unit (the pickup roller 1, The feed roller 2, the conveyance roller 3, the conveyance drum 4, the discharge roller 7, the DC motor 9, and the electromagnetic clutch 10) are configured separately.

  The pickup roller 1, the feed roller 2, the transport roller 3, the transport drum 4, the discharge roller 7, the DC motor 9, and the electromagnetic clutch 10 correspond to the first transport unit. Further, the transport rollers 5 and 6 and the stepping motor 8 correspond to a second transport unit. Further, a CCD 16 or the like that reads an image of a document by a reduction optical system reading method corresponds to the first reading means. Further, the CIS 11 (11a to 11e) or the like that reads an image of a document by a reading method of an equal magnification optical system corresponds to the second reading unit.

  In addition, the image reading apparatus 100 according to the present embodiment forms a slack in a document after reading an image by a reduction optical system and before reading an image by an equal magnification optical system. FIG. 4 is an explanatory diagram of slack formed in the image reading apparatus of the present embodiment. As shown in FIG. 4, in the image reading apparatus 100, the pick-up roller 1, the feed roller 2, the transport roller 3, and the transport speed of the transport drum 4 and the transport roller 5 are adjusted. A slack S1 of the original is formed between the reduction optical system reading unit 17. As a result, even if unevenness occurs in the document conveyance speed in the reading method of the reduction optical system, the CIS 11 is not affected by the variation in the conveyance speed.

  Specifically, after the original is read by the reduction optical system, when the original reaches a predetermined position downstream of the conveying roller 5, the conveying roller 5 stops (or decelerates). At this time, since the transport rollers (pickup roller 1, feed roller 2, transport roller 3, transport drum 4) upstream of the transport roller 5 are driven, a slack S1 is formed on the upstream side of the transport roller 5.

  Furthermore, the image reading apparatus 100 according to the present embodiment forms a slack in the original after reading the image by the equal magnification optical system. FIG. 5 is an explanatory diagram of slack formed in the image reading apparatus of the present embodiment. As shown in FIG. 5, in the image reading apparatus 100, a document slack S <b> 2 is formed between the transport roller 6 and the discharge roller 7 by adjusting the transport speed of the transport roller 6 and the discharge roller 7. Thus, even if unevenness occurs in the conveyance speed of the document in the discharge roller 7, the CIS 11 is not affected by the variation in the conveyance speed.

  Specifically, after the original is read by the equal magnification optical system, when the original reaches a predetermined position downstream of the discharge roller 7, the discharge roller 7 stops (or decelerates). At this time, since the transport rollers 5 and 6 upstream of the discharge roller 7 are driven, a slack S2 is formed on the upstream side of the discharge roller 7.

  The discharge roller 7 normally has a shape that allows the trailing edge of the document to be kicked out in order to prevent the trailing edge of the document from remaining in the roller nip portion, and the document conveyance speed is not stable. Further, a plurality of rollers may be provided downstream of the discharge roller 7 in order to provide a reverse discharge function, an in-body discharge function, and the like. For this reason, even if unevenness in the conveyance speed of the document occurs in the plurality of rollers by forming the slack S2, the CIS 11 is not easily affected by the variation in the conveyance speed.

  In the image reading apparatus 100 of the present embodiment, two slacks, a slack S1 and a slack S2, are formed in order to obtain a sufficient effect. However, even if only the slack S1 or the slack S2 is formed, the influence due to the unevenness of the document transport speed can be partially removed, so that the effect is reduced, but the influence on the CIS 11 can be suppressed.

  As shown in FIG. 6, when the discharge roller 7 and other transport rollers (not shown) are not arranged on the downstream side of the transport roller 6, the transport section (the pickup roller 1, the feed roller 1 in the reading method of the reduction optical system). Only the unevenness of the conveying speed of the original of the roller 2, the conveying roller 3, and the conveying drum 4) is affected. Therefore, the influence on the CIS 11 can be suppressed only by forming the slack S1 in front of the transport roller 5.

  Next, a description will be given of misalignment of joints of images read by the reading method of the equal magnification optical system. FIG. 7 is a diagram for explaining a shift in the joint between images due to a change in the document conveyance speed. FIG. 7 shows an explanation of reading an image by two CISs and reading an image by one CIS. The former reading is the reading method of the back side of the document in the image reading apparatus of the present embodiment.

  A case where there is a change in the document conveyance speed (V) in both readings in FIG. 7 will be described. In the case of reading an image by two CISs, CIS-1 and CIS-2 are arranged so as to be shifted in the sub-scanning direction (original transport direction d). For this reason, the influence of the variation in the document conveying speed on the read image appears in different positions in the sub-scanning direction in CIS-1 and CIS-2 (see the CIS-1 passage speed and CIS-2 passage speed on the left in FIG. 7). ). As a result, the images of CIS-1 and CIS-2 do not mesh at the joint of the image, and the joint is emphasized (see A and B of the read image on the left in FIG. 7).

  On the other hand, in the case of reading an image with one CIS, the sub-scanning direction is slightly expanded and contracted, and the influence on the image due to fluctuations in the document conveyance speed is not as great as when the images read with two CIS are connected. (See the scanned image on the right in FIG. 7). In other words, when connecting images read by a plurality of CISs, it is easier to match the joints of images when the fluctuation in the document transport speed is smaller.

  Next, a flow when reading an image of a document will be described. FIG. 8 is a flowchart showing a flow when reading an image of a document in the image reading apparatus of the present embodiment.

  First, when the transport roller group (the pickup roller 1, the feed roller 2, the transport roller 3, the transport drum 4, the transport rollers 5, 6 and the discharge roller 7) is driven (step S1), the documents are fed one by one from the document tray 18. Sent out. Then, the image on the surface of the document is read by the CCD 16 in the reduction optical system reading unit 17, and the control unit (not shown) of the image reading apparatus 100 determines whether or not the leading edge of the document has reached a position 10 mm downstream of the conveying roller 5. Is determined (step S2). If not reached (step S2: No), the transport roller group is driven until it reaches.

  On the other hand, when it arrives (step S2: Yes), the conveyance rollers 5 and 6 are stopped (step S3). As a result, the conveyance roller 5 stops by pressing the leading edge of the document. At this time, since the pickup roller 1, the feed roller 2, the transport roller 3, and the transport drum 4 upstream of the transport roller 5 are driven, a slack S <b> 1 is formed on the upstream side of the transport roller 5.

  Next, a control part judges whether predetermined slack formation time passed (Step S4). If it has not elapsed (step S4: No), the transport rollers 5 and 6 are stopped until a predetermined slack formation time has elapsed. On the other hand, when the time has elapsed (step S4: Yes), the conveyance rollers 5 and 6 are driven, the entire document is conveyed while the slackness S1 is maintained, and the image on the back side of the document is read by the CIS 11 (step S5).

  Next, the control unit determines whether or not the leading edge of the document has reached a position 10 mm downstream of the discharge roller 7 (step S6). If not reached (step S6: No), the transport roller group is driven until it reaches.

  On the other hand, when it reaches | attains (step S6: Yes), the discharge roller 7 is stopped (step S7). As a result, the discharge roller 7 stops by pressing the leading edge of the document. At this time, since the pickup roller 1, the feed roller 2, the transport roller 3, the transport drum 4, and the transport rollers 5 and 6 upstream from the discharge roller 7 are driven, a slack S <b> 2 is formed on the upstream side of the discharge roller 7. It will be.

  And a control part judges whether predetermined slack formation time passed (Step S8). If it has not elapsed (step S8: No), the discharge roller 7 is stopped until a predetermined slack formation time has elapsed. On the other hand, when the time has elapsed (step S8: Yes), the discharge roller 7 is driven (step S9), and the entire original is conveyed while maintaining the slackness S1 and S2.

  Next, the control unit determines whether or not the document whose image has been read has been discharged (step S10). If the document is not discharged (step S10: No), the transport roller group is driven until it is discharged. On the other hand, when the document is discharged (step S10: Yes), the transport roller group is stopped (step S11), and the transport of the document is finished.

  The predetermined time for forming the slack is determined based on three factors: the length of the document, the dimensional accuracy of the outer diameter of the conveyance roller, and the rotation accuracy of the motor (drive unit).

  Further, in FIG. 8, the image reading in the case where the conveyance rollers 5, 6 or the discharge roller 7 are stopped to form the slack is described, but instead of stopping the conveyance rollers 5, 6 or the discharge roller 7, the image is decelerated. Even if it is a case, the same effect can be acquired.

  That is, FIG. 8 is replaced, and the conveyance rollers 5 and 6 are decelerated in step S3, and the conveyance rollers 5 and 6 are accelerated in step S5. In step S7, the discharge roller 7 is decelerated, and in step S9, the discharge roller 7 is accelerated.

  In the image reading apparatus of the present embodiment, after reading an image on the surface of a document by a reading method of a reduction optical system using a CCD or the like, an image on the back side of the document is read by a reading method of an equal magnification optical system using CIS or the like. However, the present invention is not limited to this. That is, an image on the front side of the document may be read by a reading method of the reduction optical system after the image on the back side of the document is read by the reading method of the equal magnification optical system.

  In the image reading apparatus of the present embodiment, as an example, a document such as paper is transported to read both sides. However, the present invention is not limited to this, and any medium other than paper can be used as long as it is a sheet-like medium. It may be. In addition, the image forming apparatus according to the present embodiment is an electrophotographic system, but is not limited thereto, and may be an inkjet system.

  As described above, in the image reading apparatus according to the present embodiment, the conveying unit (conveying rollers 5 and 6) in the reading system of the equal magnification optical system and the other conveying unit (pickup roller) including the reading method of the reduction optical system. 1, a feed roller 2, a transport roller 3, a transport drum 4, and a discharge roller 7), and the variation in the transport speed of the document by the transport section in the reading system of the equal magnification optical system is a reading system of the reduction optical system This is smaller than the fluctuation in the conveyance speed of the document by other conveyance sections including. For this reason, when images read by the CISs 11a to 11e arranged in a staggered manner in a direction (main scanning direction) orthogonal to the document conveyance direction are joined, it is possible to reduce the deviation between the images.

  The image forming apparatus according to the present invention includes an image reading apparatus such as a multifunction machine, a copier, a scanner apparatus, or a facsimile apparatus having at least two functions of a copy function, a printer function, a scanner function, and a facsimile function. It can be applied to both.

DESCRIPTION OF SYMBOLS 1 Pickup roller 2 Feed roller 3 Conveyance roller 4 Conveyance drum 5 Conveyance roller 6 Conveyance roller 7 Discharge roller 8 Stepping motor 9 DC motor 10 Electromagnetic clutch 11 CIS (11a-e)
12 White reference roller 13 Contact glass 17 Reduction optical system reading unit 18 Document tray 19 Optical path 100 Image reading device 200 Automatic document feeder (ADF)
300 Image forming apparatus 303 Paper feed unit 304 Image forming apparatus main body

JP 2004-282438 A

Claims (12)

First conveying means for conveying a sheet-like medium in a predetermined direction;
A second conveying means provided upstream or downstream of the first conveying means for conveying the sheet-like medium in the predetermined direction;
First reading means using a reduction optical system that reads an image on one surface of a sheet-like medium conveyed in the predetermined direction by the first conveying means;
A second optical system using an equal-magnification optical system that reads an image on the other surface of a sheet-like medium that is arranged in a zigzag manner in a direction orthogonal to the predetermined direction and is conveyed in the predetermined direction by the second conveying unit. Reading means,
An image reading apparatus characterized in that a fluctuation in the conveyance speed of the sheet-like medium by the second conveyance means is smaller than a fluctuation in the conveyance speed of the sheet-like medium by the first conveyance means. The first conveying unit includes a first conveying roller that conveys a sheet-like medium whose image is read by the first reading unit,
The second conveying unit includes a second conveying roller that is provided upstream of an image reading position by the second reading unit and conveys a sheet-like medium from which an image is read by the second reading unit,
By adjusting the conveyance speed of the first conveyance roller and the second conveyance roller, a first slack is formed in the sheet-like medium between the first conveyance roller and the second conveyance roller. The image reading apparatus according to claim 1. The second transport unit further includes a third transport roller that is provided downstream of the image reading position by the second reading unit and transports a sheet-like medium from which an image has been read by the second reading unit,
A fourth transport roller installed downstream of the third transport roller;
By adjusting the conveyance speed of the third conveyance roller and the fourth conveyance roller, a second slack is formed in the sheet-like medium between the third conveyance roller and the fourth conveyance roller. The image reading apparatus according to claim 1.   The fluctuation of the surface speed when the second conveying roller and the third conveying roller are rotated at a predetermined speed is the fluctuation of the surface speed when the first conveying roller and the fourth conveying roller are rotated at the predetermined speed. The image reading apparatus according to claim 3, wherein the image reading apparatus is smaller.   5. The image reading apparatus according to claim 3, wherein thermal expansion coefficients of the second conveyance roller and the third conveyance roller are smaller than thermal expansion coefficients of the first conveyance roller and the fourth conveyance roller. .   6. The dimensional accuracy of the outer diameters of the second transport roller and the third transport roller is better than the dimensional accuracy of the outer diameters of the first transport roller and the fourth transport roller. 6. The image reading apparatus according to claim 1.   The amount of eccentricity of the second conveying roller and the third conveying roller is smaller than the amount of eccentricity of the first conveying roller and the fourth conveying roller, according to any one of claims 3 to 6. Image reading device. The first conveying means further includes first driving means for driving the first conveying roller and the fourth conveying roller,
The second conveying means further includes second driving means for driving the second conveying roller and the third conveying roller,
8. The image reading apparatus according to claim 3, wherein a fluctuation in the rotation speed of the second driving unit is smaller than a fluctuation in the rotation speed of the first driving unit. 9.   The image reading apparatus according to claim 8, wherein the second driving unit is a stepping motor. An image reading apparatus according to claim 1;
An image forming unit that forms an image read by the image reading device on a member to be formed;
An image forming apparatus comprising: A first conveying step in which the first conveying means conveys the sheet-like medium in a predetermined direction;
A second conveying means provided upstream or downstream of the first conveying means, wherein the variation in the conveying speed of the sheet-like medium is smaller than the fluctuation in the conveying speed of the sheet-like medium by the first conveying means, the sheet in the predetermined direction A second transporting process for transporting the shaped medium;
A first reading step in which a first reading unit using a reduction optical system reads an image on one surface of a sheet-like medium conveyed in the predetermined direction by the first conveying unit;
The second surface of the sheet-like medium that is arranged in a zigzag manner in a direction orthogonal to the predetermined direction and is transported in the predetermined direction by the second transport unit by the second reading unit using the equal-magnification optical system. A second reading step of reading the image of
The first conveying unit includes a first conveying roller that conveys a sheet-like medium whose image is read by the first reading unit,
The second conveying unit includes a second conveying roller that is provided upstream of an image reading position by the second reading unit and conveys a sheet-like medium from which an image is read by the second reading unit,
A first slack forming step of forming a first slack in the sheet-like medium between the first transport roller and the second transport roller by adjusting a transport speed of the first transport roller and the second transport roller. An image reading method further comprising: The second transport unit further includes a third transport roller that is provided downstream of the image reading position by the second reading unit and transports a sheet-like medium from which an image has been read by the second reading unit,
The third conveying roller and the third conveying roller are arranged downstream of the third conveying roller and adjust the conveying speed of the fourth conveying roller that conveys the sheet-like medium from which the image has been read. The image reading method according to claim 11, further comprising a second slack forming step of forming a second slack in the sheet-like medium between the four transport rollers.

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