JPH02290363A - Original reading device - Google Patents

Abstract

PURPOSE:To adjust the position of a backup roller to the thickness of an original automatically with respect to an original guide means by allowing the backup roller of an original reader to apply original reading and electronic shading continuously without being moved and supported contactless to the original guide means. CONSTITUTION:When an original 1 is loaded to an original reader, it is detected by a 1st sensor 7 provided to an upper unit case 3 and its detection signal is used to drive carrier rollers 5-7 and drive a backup roller 14 thereby lighting a lighting lamp 13. The tip of a carried original 1 is sensed by a 2nd sensor 18 and the carrying speed is varied in response to the magnification selected in advance and the paper is fed by a roller 6 and sensed by a resist sensor 19. Then a reflected light from the roller 14 at the read position 12 is read by a CCD 16 through a lens 15 and the surface of the roller 14 is coated in white color and the reflected density is selected to a prescribed value and the read position 12 of the roller 14 is adjusted automatically.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention conveys a document supported on a document guiding means made of a transparent body to a reading position by means of a document conveying means, and performs electronic shading correction at the reading position. The present invention relates to a document reading device that reads a document together with a reference member.

[Prior Art] An example of a digital or analog document reading device installed in various devices such as a cofacsimile machine or a copying machine is the device described in Japanese Patent Application Laid-open No. 183258/1983. In this device, a transparent reading guide plate having a reference member for electronic shading correction is moved up and down during correction and document reading, so that electronic shading is performed for each document, and the reading roller By pressing the original against the reading guide plate, the position of the original is regulated in the depth direction of the lens, thereby preventing image distortion.

[Problems to be Solved by the Invention] However, the above-mentioned conventional device has the following problems. First, the reading guide plate is moved up and down and the reading roller is separated from the reading guide plate, so it is necessary to provide a reciprocating mechanism that includes a special vibration source, making the mechanism complicated. It turns into Furthermore, in order to perform electronic shading for each document, the movement of the reading guide, guide plate, and reading roller is repeated before reading the document, which increases the time required from the start of inserting the document to the start of reading.

Furthermore, a correction reference member and a protection plate are provided on the side of the document travel path of the transparent member, which forces the document travel path to take a curved shape, making it unsuitable for running and reading thick documents. It is.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a document reading device that has a simple configuration and can read even thick documents in a short time.

Further, the above-mentioned conventional device also has the following problems. Since the document is read near the contact point between the transparent reading guide plate and the reading roller, contact between the transparent reading guide plate and the reading roller or contact between them and the original may cause the transparent reading guide plate and the reading roller to It can hurt,
For this reason, the quality of the read image may be significantly degraded. For this reason, some proposals have been made in which a predetermined distance is provided between the transparent reading guide plate and the reading roller.
It is unavoidable that hard originals or foreign objects other than originals will damage or stain them.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a document reading device that does not cause deterioration in read image quality even if scratches or stains occur.

Furthermore, conventional devices are configured to read documents at the point in the transport path where the gap between the transparent reading guide plate and the reading roller is the narrowest, making it difficult for the leading edge of the document to enter this narrow document reading area. Disturbances may occur at the leading edge of the read image.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a document reading device that can smoothly enter a document into a reading position and prevent disturbances at the leading edge of a read image.

Furthermore, in conventional devices, if the document that has passed through the reading section is curled significantly toward the back side, there is a problem in that the document tends to get wrapped around the reading roller, and dirt adhering to the document side also Since it adheres to the reference member for electronic shading correction and causes a deterioration in the quality of the read image, it is necessary to frequently clean the roller.

Furthermore, the reading roller tends to become electrically charged due to sliding contact and friction with the original, which makes it easier for dirt and dust to adhere to the roller, resulting in a reduction in the quality of the scanned image and the problem of accelerating the wrapping of the original. There is.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a document reading device that can prevent a document from being wrapped around the document and also prevent deterioration in read image quality due to adhesion of dirt or dust or charging.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the invention described in claim 1 conveys a document supported on a document guiding means made of a transparent body to a reading position by a document conveying means. , in a document reading device configured to read a document together with a reference member for electronic shading correction at a reading position, the device is arranged facing the document guiding means at a predetermined interval so as not to be in contact with the document guiding means; The image forming apparatus includes a backup roller extending in the main scanning direction so as to be able to be separated from each other as described above, and the backup roller is configured to be provided as a reference member for electronic shading correction.

In addition, the invention described in claim 2 conveys the original supported on the original guiding means made of a transparent body to the reading position by the original transporting means, and at the reading position, the original is conveyed together with the reference member for electronic shading correction. In the document reading device configured to read the document, the document guide means is arranged facing the document guide means at a predetermined distance so as not to be in contact with the document guide means, and extends in the main scanning direction so as to be able to be separated by a distance greater than the predetermined distance. The backup roller is provided as a reference member for electronic shading correction, and the reading position is a position slightly away from a position where the document guide means and the backup roller are opposed to each other. It has a configuration that can be installed in

Furthermore, the invention described in claim 3 conveys the original supported on the original guiding means made of a transparent body to the reading position by the original transporting means, and the original together with the reference member for electronic shading correction at the reading position. In the document reading device configured to read the document, the document guide means is arranged facing the document guide means at a predetermined distance so as not to be in contact with the document guide means, and extends in the main scanning direction so as to be able to be separated by a distance greater than the predetermined distance. The back anoprowler is provided as a reference member for electronic shading correction, and the reading position is downstream in the document conveyance direction from a position where the document guide means and the backup roller are opposed to each other. It has a configuration that allows it to be installed at a location that is separate from the side.

Furthermore, the invention described in claim 4 conveys the original supported on the original guiding means made of a transparent body to a reading position by the original transporting means, and at the reading position, the original is conveyed together with a reference member for electronic shading correction. In the document reading device configured to read the documents, the document guide means is arranged facing the document guide means at a predetermined distance so as not to be in contact with the document guide means, and extends in the main scanning direction so as to be able to be separated by more than the predetermined distance. The backup roller is provided as a reference member for electronic shading correction, and the reading position is from a position where the document guide means and the hike-up roller are opposed to each other. A configuration in which the optical axis of the document reading means is provided at a slightly distant position and passes through the reading position, and is arranged so that the optical axis of the document reading means passes near the center of the rotation axis of the backup roller and is substantially perpendicular to the surface of the backup roller. It is equipped with

According to the invention described in claim 5, a document supported on a document guiding means made of a transparent body is conveyed to a reading position by a document conveying means, and the document is read together with an electronic shading correction reference member at the reading position. In the document reading device, the M document guide means is arranged opposite to the M document guide means at a predetermined interval so as not to be in contact with the M document guide means, and extends in the main scanning direction so as to be able to be separated by more than the predetermined interval. A backup roller is provided, and a document wrapping prevention member is provided in contact with the circumferential surface of the backup roller.

In addition, the invention described in claim 6 conveys the original supported on the original guiding means made of a transparent body to the reading position by the original transporting means, and at the reading position, the original is transferred together with the reference member for electronic shading correction. In the document reading device configured to read the document, the document guide device is arranged opposite to the document guide means with a predetermined gap so as not to be in contact with the document guide means, and extends in the main scanning direction so as to be able to be separated by more than the predetermined distance. A backup roller having a diameter of 9 is provided, and a document wrapping prevention member is provided in contact with the peripheral surface of the backup roller, and the document wrapping prevention member is provided in contact with the M document wrapping prevention member over a maximum document reading width. At the same time, it is configured to be provided as a cleaning member for the circumferential surface of the Vanoquano propeller.

[Function] In the means recited in claim 1 having such a configuration, the backup roller is maintained in a non-contact state with respect to the document guide means and can read and electronically read the document without being moved. While shading is performed continuously, the position of the backup roller relative to the document guide means is automatically adjusted in accordance with the thickness of the document.

Furthermore, in the means recited in claim 2 having the above structure, in addition to the effect of the means recited in claim 1, in the event that the document guide means is damaged by the backup roller or the document, The read image quality is not degraded even in the case of

Furthermore, in the means recited in claim 3 having the above configuration, in addition to the effect of the means recited in claim 1, the leading end portion of the document is smoothly entered into the reading position. The leading edge of the read image is not disturbed.

Furthermore, in the means recited in claim 4 having the above configuration, in addition to the effect of the means recited in claim 1, the amount of reflected light from the backup roller is maximized to achieve optimal shading. Correction data is now available.

In the means recited in claim 5 having the above configuration, in addition to the effect of the means recited in claim 1, the document is separated from the pack associator by the document wrapping prevention member. It has become.

In the means recited in claim 6 having the above configuration, in addition to the effect of the means recited in claim 1, the document is separated from the backup roller by the document wrapping prevention member, and the document is Dirt and electrical charges attached to the rollers are automatically removed at all times.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

As shown in FIG. 1, on a document table 2 on which a document 1 is placed, an upper unit case 3 is supported by a support shaft 4 so as to be vertically swingable. Conveyance rollers 5, 6, and 7 are arranged on the document table 2, and these rollers are rotated by a drive motor and a drive system (not shown). Presser rollers 8,9,10 are arranged so as to be in pressure contact with the conveyance rollers 5,6,7, respectively, and each presser roller 8,9,10 is rotatably supported by the upper unit case 3. There is.

A contact glass 11 is provided as a transparent document guiding means between the transport rollers 6 and 7 so as to be flush with the document table 2. That is, each conveyance roller 5
．． The upper surface of the contact glass 11 and the upper surface of the document table 2 are located on the tangent at the contact point between the contact roller 6.7 and the presser rollers 8, 9, and 10. Also contact glass 1
1 predetermined position 12 is set as a reading position,
The document 1 above the reading position 12 is illuminated by an illumination device 13, such as an illumination lamp such as a fluorescent lamp. At the reading position 12, the contact glass 11
A backup roller 14 is provided to face the contact glass 11, and the backup roller 14 and the contact glass 11 are spaced apart from each other at a predetermined distance. They are arranged so that the original 1 is placed between them at minute intervals of 0.1 to 0.2 mm. The backup roller 14 is supported by the upper unit case 3, and is rotationally driven by a motor and drive system (not shown).

The reflected light from the document 1 illuminated by the illumination device 13 passes through a lens 15 installed in the lower part of the contact glass 11, and is imaged and read by a CCD 16 as a light receiving member.

The insertion operation of the original 1 is detected by the first sensor 17 provided in the upper unit case 3, and based on the detection signal, the transport rollers 5, 6, 7 are driven, and the backup roller 14 is rotated. Furthermore, the illumination lamp 13 is turned on.

When the leading edge of the document 1 being conveyed is detected by the second sensor 18, the conveying speed is changed to correspond to the preselected magnification ratio, and the document 1 is further fed by the conveying roller 6 and the leading edge of the document 1 is detected by the registration sensor 19. is detected, the bathok aso prowler 1 at the reading position 12
The reflected light from 4 begins to be read by CCD 16 through lens 15. At this time, Hack Ano Roller 1
The surface of 4 is painted white, and its reflection density is 0.
03-0.08 (reflectance 93-83%). The reflected light data of the backup roller 12 thus read is A/D converted and stored in the shading RAM as shading correction data.

Such operations are repeated until just before the leading edge of the M document reaches the exposure position 12. During this time, the data stored in the RAM and the A/D conversion output are constantly compared.
Control is such that if the A/D conversion output has a higher value than the stored data, they are replaced. Therefore, even if there is unevenness in the amount of light when the fluorescent lamp starts up during this period, it is not affected. Furthermore, even if the surface of the backup roller 14 is partially dirty, if there is even a small white part, the A/D conversion output will be included in the stored data, and the influence of dirt on the surface of the puncture roller 14 will be almost negligible. Never. An example of such a shading correction device is represented by block lines in FIG.

Thereafter, when the original 1 reaches the contact glass 11 and is transported through the gap between the contact glass 11 and the backup roller 14, exposure by the illumination lamp 13 is performed at the reading position 12, that is, the scanning position, and the light is reflected. The light is reduced to form an image on the CCD 16 by the lens 15 and then read. Scanned manuscript 1
The image data of is corrected by the shading correction data, and the unevenness of the light amount of the illumination lamp l3 and the c of the lens 15 are corrected by the shading correction data.
Decrease in light intensity due to the os'θ law, uneven sensitivity of each image of the CCD 16, etc. are corrected as appropriate.

After reading and scanning, the original 1 is ejected to a paper ejection tray 20 by a conveyance roller 7 and a presser roller 10.

The upper unit case 3 is pivoted upward around a support shaft 4 by a predetermined angle to open the surfaces of the original table 2 and the contact glass 11, and this opening action causes each roller, Maintenance work such as cleaning the guide plate, sensor, and contact glass, processing of transported l-rubble originals, and replacing the lamp 13 can be easily performed. A cover 21 is also provided to protect the illumination lamp l3, lens 15, and CCD l6 from dust from the outside.

On the other hand, in FIG. 2 showing a cross section of the lens 15 on a plane passing through the optical axis, a plurality of sets, for example, two sets of optical systems including two sets of lenses 15 are arranged in parallel in the main scanning direction of the original 1.
In each of these optical systems, the image information of the document 1 is individually received and read by the CCD 16. In FIG. 2, a lens 15 and a CCD 16 are arranged along two optical axes 22, respectively. contact glass 11
Since the backup roller 14 is rotationally driven when the document 1 is transferred between the contact glass 1 and the back associative roller 14, the backup roller 14
1 will damage the contact glass 11. Therefore, the backup roller 14 is supported in such a manner that the necessary minimum gap is maintained. For this purpose, in FIG. 2, guide rollers 23 are rotatably supported at both ends of the shaft of the backup roller 14.

The guide roller 23 is placed on the contact glass 11, and its diameter is set to be larger than the diameter of the backup roller 14 by an amount corresponding to the amount of clearance for the backup roller 14. A pulley 25 for movement is attached to the shaft of the backup roller 14 via a one-way clutch 26.

The original 1 is pressed against the surface of the contact glass 11 by the contact glass 11 and the backup roller 14 and is flattened, so even if the original 1 has curls or creases, the distance between the original surface and the lens 15 remains the same. Therefore, the original 1 will not be lifted up from the contact glass 11, and defocusing of the joint between images of adjacent optical systems at the illumination position of the original 1 and loss of images will be prevented. It has become.

The axis of the backup roller 14 is set to the optical axis 22, that is, the reading position 12, so that the read image quality will not be degraded even if the contact glass 11 is touched by the backup roller 14 or the original 1 for some reason. On the other hand, it can also be arranged slightly shifted in the document feeding direction, for example, in the right direction in FIG. The amount of positional shift of the backup roller 14 in this case is set to an amount that does not cause any inconvenience to the shading correction data obtained from the light reflected from the surface of the backup roller 14. In this way, the contact glass 11
and the backup roller 14 are disposed facing each other with a minimum interval between them, and the reading position 12 is provided at a position on the downstream side in the document conveyance direction with respect to this minimum interval position.
Reading is not performed in a state where the leading edge of the document 1 is difficult to enter at the minimum interval position, and the leading edge of the read image is not disturbed.

In FIGS. 3 and 4, the backup roller 1
A timing belt 27 is applied to a pulley 25 supported by a one-way clutch 26 on the shaft of the presser roller 9 provided on the upstream side of the backup roller 14 in the document conveyance direction. A drive pulley 29 is fixed to the drive pulley 30, and the timing belt 27 is placed around the drive pulley 29, thereby drivingly connecting the pulley 25 and the drive pulley 29. The presser roller 9 is brought into pressure contact with the conveyance roller 6 and is frictionally driven by the conveyance roller 6.
The rotational force of the presser roller 9 is transmitted to the backup roller 14 via the flute pulley 29, the timing belt 27, and the pulley 25. The shaft 3o of the presser roller 9 is supported by a bearing 32 that is vertically movably mounted in a long hole 31 in the side plate of the upper unit case 3, and is installed parallel to the rotational axis of the backup roller 14. Also, the shaft 30 of this presser roller 9
An arm 33 is rotatably supported via a bearing, and a backup roller 1 is attached to the arm 33.
4 is rotatably supported by a bearing 34. That is, the presser roller 9 is moved up and down according to the thickness of the document 1, and the document 1 is pressed against the conveyance roller 6 in an optimal state to feed the document 1. The timing belt 27 that moves the backup roller 14 is tensioned to a predetermined tension by a tension adjustment pulley 35. As a result, the backup roller 14 is rotated at a speed that is substantially synchronized with the conveyance speed of the document 1.

Since the backup roller 14 is supported by the arm 33, when the document 1 that is thicker than the gap created by the difference in diameter with the guide roller 23 is transported, it is swung around the axis 3o, and the document 1 is moved against the contact glass 11. It is designed to escape so that it will not be forced into contact. In this case, the backup roller 14 uses its own weight to press the original 1 onto the contact glass 11 to prevent the original 1 from floating.

The original 1 that has passed the reading position 12 is conveyed without being wrapped around the backup roller 14 by a blade-shaped original wrapping prevention member 41 . The document wrapping prevention member 41 has a proximal edge portion supported by the guide member 40, and a distal edge portion slidingly contacted on the pack associative roller 14. The document wrapping prevention member 41 is made of an elastic member, and is in contact with the circumferential surface of the backup roller over the maximum document reading cap. Therefore, it also has the function of scraping off dirt adhering to the backup roller 14. In addition, the document wrapping prevention member 41 is made of a conductive material and is grounded, thereby eliminating static electricity from the surface of the backup roller 14 that is charged due to friction with the document 1 . It is possible to prevent dust and the like from adhering, and also to prevent the original l from being wrapped around due to electrostatic force.

The position of the backup roller 14 when taking shading correction data from a thick original is 0.
．． Since the position is the same as that for originals with a thickness of 1 to 0.2 nm or less, the a-light level of the read image remains unchanged regardless of the thickness of the original.

Further, the backup roller 14 is rotated at a speed substantially synchronized with the conveyance speed of the conveyance roller 6, and in the case of a thick document, the bank amplifier roller 14 is pressed against the document 1, so that it can be used as a means for conveying the document 1. The function is maintained regardless of the thickness of the document. Further, since the backup roller 14 is supported by an arm 33 that can swing around the shaft 30, when it is rotated, it is biased with a force in the direction of moving away from the contact glass 11, and the document 1 is moved away from the contact glass 11. The action of being caught and locked between the contact glass 11 does not occur. Therefore, the document 1 is locked between the backup roller 14 and the contact glass 1.
1 is scratched to prevent image quality from being degraded due to this deviation.

Furthermore, even if a curled original, a folded original, or a wrinkled original is received, since the Hanoku anno-prowler 14 is pressed against the contact glass 11 side, a good read image can be obtained, which has been a problem in the past. High-quality reading is also possible for leading edge curls, trailing edge curls, and creases.

Further, in the embodiment shown in FIGS. 6 and 7, the optical axis 22 of the document reading means 15, 16 passing through the reading position ]-2 is installed slightly obliquely from the vertical direction in the drawing. At the same time, it is set to pass near the center of the rotation axis of the handle up roller 14 and to be substantially perpendicular to the surface of the handle up roller 14. In this way, the amount of light reflected from the Hasokuanoproler 14 becomes the maximum value, and optimal shading correction data can be obtained, accurate reading can be performed without causing ghosts in the read image, and moreover, space can be secured. It is advantageous.

[Effects of the Invention] As described above, the invention described in claim 1 is such that the document guiding means is arranged facing the document guide means at a predetermined distance so as not to be in contact with it, and is spaced apart from the document guide means by more than the predetermined distance. In order to make this possible, a backup roller is provided which extends in the main scanning direction, and the backup roller is provided as a reference member for electronic shading correction. Reading and electronic shading of the original are performed continuously while remaining in a non-contact state with the means and without being moved, and the position of the backup roller relative to the document guiding means is adjusted to correspond to the thickness of the original. It is automatically adjusted, has a simple configuration, and can read even thick originals in a short time.

In addition to the configuration of the means described in claim 1, the invention described in claim 2 is such that the reading position is slightly separated from the position where the document guide means and the back anopler are arranged facing each other. In addition to the effect of the means recited in claim 1, even if the document guide means is jammed by the backup roller or the document, the read image quality will not deteriorate. can be prevented.

Furthermore, in addition to the configuration of the means described in claim 1, the invention as set forth in claim 3 is arranged so that the reading position is positioned downstream in the document conveyance direction from the facing position of the document guide means and the banoquano propeller. Since the structure is provided at a position separated from the side, in addition to the effect of the means described in claim 1 above, the leading edge of the document can be smoothly entered into the reading position, and the reading position is It is possible to prevent the front end of the image from being disturbed and to prevent the quality of the read image from deteriorating.

Furthermore, the invention stated in claim 4 is based on claim 1.
In addition to the configuration of the means described in , a reading position is provided at a position slightly away from a position where the document guide means and the bank amplifier roller are opposed to each other, and the optical axis of the document reading means passing through the reading position is Since it is arranged so as to pass near the center of the rotational axis of the 8-inch amplifier roller and be almost perpendicular to the surface of the backup roller,
In addition to the effects of the means described in claim 1 above,
By maximizing the amount of light reflected from the backup roller, you can obtain optimal shading correction data.

The invention set forth in claim 5 has, in addition to the structure of the means set forth in claim 1, a structure in which a document wrapping prevention member is provided in contact with the circumferential surface of the backup roller. In addition to the effects of the means described in claim 1, the document can be separated and guided from the banoquano propeller by the document wrapping prevention member, and the document can be conveyed smoothly.

In addition to the structure of the means described in claim 1, the invention as set forth in claim 6 provides the following: a document wrapping prevention member is provided so as to come into contact with the circumferential surface of the back anoprowler;
In addition, since the document wrapping prevention member is brought into contact with the document over the maximum document reading width and is provided as a cleaning member for the peripheral surface of the bathoqua knob roller, the effect of the means described in claim 1 can be achieved. In addition, the original wrapping prevention member allows the original to be smoothly separated from the backup roller, and it constantly automatically removes dirt and electrical charges adhering to the bank amplifier roller, reducing the quality of the scanned image due to adhesion of dust and charging. It is possible to prevent a decrease in

[Brief explanation of drawings]

FIGS. 1 and 2 are a front view and a front view showing the configuration of a document reading device according to an embodiment of the present invention,
3 and 4 are side and front views showing an enlarged view of the document reading section of the document reading device shown in FIGS. 1 and 2, and FIG. 5 is an example of a shading correction device. FIGS. 6 and 7 are a side view and a front view showing the configuration of a document reading device according to another embodiment of the present invention. 5, 6.7... Conveyance roller, 8, 9.10...
・Press roller 11...Contact glass, 12
...Reading position, 13...Illumination lamp, 14...
... Backup roller, 15 ... Lens, 16
...CCD, (1 other person)

Claims (1)

[Scope of Claims] 1. An original document supported on an original guide means made of a transparent body is conveyed to a reading position by an original conveying means, and the original document is read together with an electronic shading correction reference member at the reading position. In the reading device, a backup roller is arranged opposite to the document guide means at a predetermined interval so as not to be in contact with the document guiding means, and extends in the main scanning direction so as to be able to be separated by more than the predetermined interval. A document reading device comprising: The backup roller is provided as a reference member for electronic shading correction. 2. In a document reading device in which a document supported on a document guiding means made of a transparent body is conveyed to a reading position by a document conveying means, and the document is read together with an electronic shading correction reference member at the reading position, the document as described above is provided. A backup roller is provided facing the guide means at a predetermined interval so as not to be in contact with the guide means, and extends in the main scanning direction so as to be able to be separated by more than the predetermined interval, The backup roller is provided as a reference member for electronic shading correction, and the reading position is provided at a position slightly away from a position where the document guide means and the backup roller are opposed to each other. reading device. 3. In a document reading device in which a document supported on a document guiding means made of a transparent body is conveyed to a reading position by a document conveying means, and the document is read together with a reference member for electronic shading correction at the reading position, the document as described above. A backup roller is provided facing the guide means at a predetermined interval so as not to be in contact with the guide means, and extends in the main scanning direction so as to be able to be separated by more than the predetermined interval, The backup roller is provided as a reference member for electronic shading correction, and the reading position is provided at a position downstream in the document transport direction from a position where the document guide means and the backup roller are opposed to each other. Characteristic document reading device. 4. In a document reading device in which a document supported on a document guiding means made of a transparent body is conveyed to a reading position by a document conveying means, and the document is read together with an electronic shading correction reference member at the reading position, the document as described above. A backup roller is provided facing the guide means at a predetermined interval so as not to be in contact with the guide means, and extends in the main scanning direction so as to be able to be separated by more than the predetermined interval, The backup roller is provided as a reference member for electronic shading correction, and the reading position is provided at a position slightly apart from a position where the document guiding means and the backup roller are opposed to each other, and the document passing through the reading position A document reading device characterized in that the optical axis of the reading means is disposed so as to pass near the center of the rotation axis of the backup roller and to be substantially perpendicular to the surface of the backup roller. 5. In a document reading device in which a document supported on a document guiding means made of a transparent body is conveyed to a reading position by a document conveying means, and the document is read together with an electronic shading correction reference member at the reading position, the document as described above. A backup roller is provided facing the guide means at a predetermined interval so as not to be in contact with the guide means, and extends in the main scanning direction so as to be able to be separated by more than the predetermined interval, A document reading device characterized in that a document wrapping prevention member is provided in contact with a circumferential surface of the backup roller. 6. In a document reading device in which a document supported on a document guiding means made of a transparent body is conveyed to a reading position by a document conveying means, and the document is read together with an electronic shading correction reference member at the reading position, the document as described above. A backup roller is provided facing the guide means at a predetermined interval so as not to be in contact with the guide means, and extends in the main scanning direction so as to be able to be separated by more than the predetermined interval, A document wrapping prevention member is provided so as to be in contact with the peripheral surface of the backup roller, and the document wrapping prevention member is provided in contact with the maximum document reading width and is provided as a cleaning member for the peripheral surface of the backup roller. A document reading device characterized in that: