JP2000349965A - Original reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress occurrence a skew and jam of an original with a simple structure. SOLUTION: An original read face 11 made of a glass plate of a close contact type image sensor 10 is opposed to a rear face sheet 21 with a very small gap 23. The position of the rear face sheet 21 is restricted to a lower end face 22a of a rear face plate 22. The original read face 11 forms a smooth projected curved face 11a close to the rear face sheet 21 from the middle in the main scanning direction X toward both ends. A lower end face 22a of the rear face plate 22 forms a smooth recessed curved face 22a close to the close contact image sensor 10 from the middle in the main scanning direction X toward both ends, the position of the rear face sheer 21 is restricted by the recessed curved face 22a, and the rear face sheet 21 itself forms a smooth recessed curved face 21a. The original is formed into a curved face to provide so-called high 'stiffness', in contact with the projected curved face 11a in the middle and both ends of the original are in contact with the rear face sheer 21 having small friction coefficient to suppress a couple of forces from being produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a document reading apparatus mounted on a facsimile apparatus, a copying machine, an image scanner, or the like for reading an image of a document, and particularly suppresses skew (skew) in document conveyance. More specifically, the present invention relates to a technique for suppressing skew when a back-sheet-type contact image sensor is used as an image sensor.

[0002]

2. Description of the Related Art When reading a document with an image sensor, it is important to read the document as close as possible to the document reading surface. Particularly, in a contact type image sensor that reads a document while sliding the document, the depth of focus is considerably shallow, so that the adhesion of the document to the document reading surface poses a problem.

[0003] A utility model registration as a first prior art second
In the document reading apparatus disclosed in Japanese Patent Application Laid-Open No. 527654 (Japanese Utility Model Laid-Open Publication No. Hei 2-13354), a document pressing member slidably supported in the up and down direction is disposed opposite the document reading surface of the contact image sensor. The document pressing member is pressed and urged toward the document reading surface by a spring. In this case, since both the original reading surface and the original pressing member have a flat planar shape over the entire surface and are pressed by a spring, it is assumed that the adhesion between the original pressed by the original pressing member and the original reading surface is good. Conceivable.

Japanese Patent Laid-Open No. 8-192 as a second prior art
In the document reading apparatus disclosed in Japanese Unexamined Patent Publication No. 935/1993, the document feed roller is brought into close contact with the document reading surface of the contact type image sensor, and the contact type image sensor is pressed against the document feed roller by being urged by a spring. To do,
Based on the assumption that the document is fed by driving and rotating the document transport roller, the central portion of the document transport roller is a large-diameter portion and almost all of the both sides are small-diameter portions according to the arrangement and width of the separation roller. In this configuration, annular spacer portions are formed at both ends outside the maximum original reading width.
The ring-shaped spacer portion does not press the document, and is located outside both ends of the document so as to directly contact the document reading surface. The diameter of the annular spacer portion is smaller than the large diameter portion and larger than the small diameter portion. The elasticity of the ring-shaped spacer is smaller than that of the large-diameter portion. That is, the hardness is higher. By forcibly contacting the document reading surface at both ends with the annular spacer portion having a diameter smaller than the large diameter portion, the large diameter portion can be strongly pressed against the document at the center, and the small diameter portion smaller than the annular spacer portion can be pressed. It can be raised from the manuscript. The entire document transport roller is forcibly bent, and the large-diameter portion has greater elasticity with respect to the ring-shaped spacer, so that the large-diameter portion is bent until the ring-shaped spacer comes into contact with the document reading surface. The portion is elastically deformed, and the adhesion to the document is enhanced. Since the close contact with the document is high in the large-diameter portion where the position matches the separation roller, and since the small-diameter portions on both sides do not contact the document, the oblique tension from the separation roller does not act on the document. In addition, it is described that since the nip (biting) on both sides of the document is eliminated, the skew of the document (skew; the document is inclined obliquely with respect to the transport direction) is suppressed.

Japanese Patent Laid-Open No. 11-27 as a third prior art
The document reading apparatus disclosed in Japanese Patent No. 455 uses a back-sheet-type contact image sensor. The back sheet (film sheet) contacts the original reading surface of the contact type image sensor, and an elastic member such as a sponge is disposed on the back surface of the back sheet for the contact.
And the shape of the elastic member is devised. The width of the elastic member in the document conveying direction is made larger in the central portion which is a fixed width range at the center, and the width is made smaller in the outer portions on both sides. Alternatively, the thickness of the elastic member is made larger at the central portion and smaller at the outer portion. Alternatively, the thickness is continuously changed. By devising the shape of the elastic member, the force by which the elastic member presses the original to the original reading surface via the back sheet is changed in the main scanning direction. That is, the pressing force is increased on the center side in the main scanning direction, and the pressing force is reduced on both sides. As a result, especially for a wide original, generation of couples (two forces which are parallel to each other and have the same magnitude in opposite directions) is suppressed from occurring, and the skew of the original is suppressed.

[0006]

However, each of the above three prior arts has the following problems. In the case of the first prior art, both the original reading surface and the original pressing member are flat surfaces, but actually,
The friction force acting between the document reading surface and the document and the friction force acting between the document pressing member and the document may fluctuate in the main scanning direction, causing skew (skew) of the document,
There is a problem that jam (paper jam) occurs due to skew.

Further, in the case of the second prior art, the original transport roller serves both for transporting the original and for pressing the original against the original reading surface, and the structure is considerably complicated including a large number of parts. . In addition, the effect of suppressing skew and jam is considered to be insufficient.

Further, in the case of the third prior art, the use of an elastic member for pressing the back sheet against the original reading surface and the use of a special shape for the elastic member also result in the following problem. The structure is quite complicated including the large number of parts. Also, as in the above, it is considered that the effect of suppressing skew and jam is not sufficient.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems. In a back sheet type original reading apparatus using an image sensor of a type in which an original is read close to an original reading surface, a skew of original conveyance is provided. In order to suppress the skew, an object is to realize skew suppression with a simple structure.

[0010]

According to a first aspect of the present invention, there is provided a document reading apparatus for solving the above-mentioned problems, wherein the document reading surface of the image sensor is separated from a document reading surface by a minute gap for document passage. It is assumed that the image reading surface of the image sensor is formed in a convex curved surface approaching the back sheet side from the center to both ends in the main scanning direction. According to this configuration, the following operation is provided. That is, the original is deformed along the shape of the convex curved surface protruding from the center of the original reading surface, and the original itself becomes a curved surface, so that the original has a so-called stiffness. In addition, the curved original is more strongly contacted at its center with the original reading surface having the centrally projecting convex curved surface, and the contact pressure on the original reading surface at both ends of the original tends to be weaker. Becomes As a result of these synergies, the frictional force applied to the document being conveyed is smaller at both ends than at the center, thereby suppressing the generation of couples.

According to a second aspect of the present invention, in the document reading apparatus according to the first aspect, the shape of the back sheet is adjusted from the center in the main scanning direction to both ends in accordance with the convex curved surface of the document reading surface. It is formed on a concave curved surface approaching the image sensor side.
According to this configuration, the following operation is provided. That is,
The minute gap between the convex curved surface of the document reading surface and the concave curved surface of the back sheet is in a curved state, and the document passing through the minute gap is forcibly deformed into a curved surface shape. The original deformed into the curved surface shape attempts to restore the original flat planar shape, but this restoring action is different between the center and both ends of the original. At the center of the document, the document tends to contact the convex curved surface of the document reading surface more strongly than the back sheet. The coefficient of friction of the original reading surface is relatively large. On the other hand, at both ends of the document, the document tends to contact the concave curved surface of the back sheet more strongly than the document reading surface. The coefficient of friction of the back sheet is very small. As described above, in the main scanning direction, the frictional force received at the center of the document from the document reading surface having the convex curved surface is large, while the frictional force received at both ends of the document from the back sheet is small. This, combined with the fact that so-called stiffness is generated in the curved document, reliably suppresses the generation of couples in the document and suppresses the occurrence of skew.

According to a third aspect of the present invention, in the original reading apparatus according to the second aspect, the position of the back sheet is regulated to an end surface of the back plate, and the shape of the end surface of the back plate is read by the original reading device. A concave curved surface approaching the image sensor side from the center to both ends in the main scanning direction in accordance with the convex curved surface of the surface, and the back sheet is arranged along the concave curved surface of the end surface of the back plate. And According to this configuration, the following operation is provided. That is, since the back sheet itself is flexible and highly flexible, it is difficult to maintain the back sheet itself in the concave curve as described above. However, when the end surface of the back plate behind it is a concave curved surface and the back sheet is made to follow this concave curved surface, it becomes possible to keep the back sheet in a desired concave curved surface.

According to a fourth aspect of the present invention, in the document reading apparatus according to the first to third aspects, the image sensor is a contact image sensor. Although the contact type image sensor has a considerably small depth of focus, the present invention is most suitably applied to a document reading apparatus having such a contact type image sensor.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a document reading apparatus according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a front view of the configuration of a main part of the document reading apparatus viewed from the main scanning direction. FIG. 2 is a vertical sectional end view showing the internal structure of the contact type image sensor and its external shape. FIG. 3 is a perspective view showing a form of the back plate, and FIG. 4 is a perspective view showing a positional relationship and a shape relationship between the contact type image sensor and the back plate and the back sheet.

A back sheet 21 is disposed above the original reading surface 11 of the contact type image sensor 10 generally called a CIS (Contact Image Sensor). Specifically, an angle-shaped back plate 22 is attached to an operation panel bottom frame 30 which is a part of the bottom of an operation panel (not shown), and the back sheet 21 is attached to a step portion 30 a on the bottom surface of the operation panel bottom frame 30. The base side is arranged and attached, and the free end side of the back sheet 21 is restricted in position by the lower end surface 22 a of the back plate 22. Y indicates the document transport direction. The base side of the back sheet 21 is located on the upper side in the document transport direction Y, and the free end side is located on the lower side. The document transport direction Y is also a sub-scanning direction in document reading. The step portion 30a of the operation panel bottom frame 30 has a shape that is smoothly and slightly curved higher toward the upper side of the document conveying direction Y, and the base side of the back sheet 21 is also smoothly and slightly curved along this shape. I have. The back sheet 21 is made of a flexible and flexible white or nearly white polyester film or the like. The reason why the color is white is to prevent the contact-type image sensor 10 from interfering with the operation of identifying and reading a white portion and a black portion of the document.

The original reading surface 11 of the contact type image sensor 10 and the back sheet 21 face each other vertically with a small gap 23 therebetween. The minute gap 23 is a passage for the document. A document tray (not shown) is arranged on the upper side of the document conveying direction Y with respect to the minute gap 23, and a separation roller and a separation plate (not shown) are arranged slightly below the document tray. A part 41 is provided. On the slightly lower side of the paper feeding unit 41, transport rollers 42 and 43 that are in contact with each other in the upper and lower directions are provided. These transport rollers 4
One of the rollers 2 and 43 is a driving roller, and the other is a driven roller. The document reading surface 11 of the contact type image sensor 10 is located near the lower side of the contact portion between the transport rollers 42 and 43.
A document guide 44 on the paper feed side is arranged to the upper end of the document feeder. On the other hand, on the lower side of the document conveying direction Y with respect to the minute gap 23 between the original reading surface 11 of the contact type image sensor 10 and the back sheet 21, a discharge side original guide which is vertically opposed to the minute gap 23 in a continuous state. 45, 46 are provided, and further, discharge rollers 47, 48 which are vertically opposed to each other are provided on the lower side. These discharge rollers 47,
One of the 48 is a driving roller and the other is a driven roller. A stacker (not shown) is provided below the discharge rollers 47 and 48.

As shown in FIG. 2, the contact type image sensor 10 includes a light emitting element array 13 and a rod lens array 1 in a housing 12 elongated in the main scanning direction X.
4 and a sensor array 15, and a glass plate 16 forming the document reading surface 11 is fitted on the upper surface. The light emitting element array 13 is, for example, a light emitting diode array or an EL.
It is composed of an element array (EL: Electro Luminescent) and is arranged along the main scanning direction X. The rod lens array 14 is formed by arranging a number of rod lenses in parallel in the main scanning direction X using the lens function of an optical fiber. The sensor array 15 includes a CCD (charge coupled device) array, a photoelectric conversion array made of amorphous silicon, and the like.
They are arranged along the main scanning direction X.

Next, a characteristic configuration according to the present invention will be described. As shown in FIG. 2, the contact type image sensor 1
The zero document reading surface 11 is formed as a convexly curved surface 11a which has both ends in the main scanning direction X at a low level, gradually becomes higher as it approaches the center, and becomes the highest at the center. That is, the front and rear side walls 1 of the housing 12
2A and 12B are formed such that their upper end surfaces 12a and 12b are smooth convex curved surfaces with a high center at the center as described above and front and rear side walls 12A and 1B.
The glass plate support portions 12c, 12d of the ridges integrally formed to support the glass plate 16 on the inner surface of 2B are also formed so as to have a smooth convex curved surface with a high center at the center as described above. The glass plate 16 is supported by the glass plate supporting portions 12c and 12d having such a convex curved surface,
By fixing the glass plate 16 to the housing 12 with the upper surface of the glass plate 16 along the convex curved surfaces 12a, 12b of the front and rear side walls 12A, 12B, the original reading surface 11, which is the upper surface of the glass plate 16, As shown in the above, it is formed on a smooth convex curved surface 11a having a high center and protruding from the center.
Original reading surface 1 of such a contact type image sensor 10
The state of the convex curved surface 11a is exaggerated in FIGS. 2 and 4 for the sake of simplicity. However, the upward projection H1 with respect to both ends at the center is determined by the maximum original reading width W. If the document size is equivalent to A4 to A3, 0.
A range of about 3 to 3.0 mm is preferable. There is no particular limitation on the shape of each convex curved surface, and any shape may be adopted as long as it is a smooth convex curved surface as described above. Alternatively, a part of an ellipse having an appropriate curvature is preferable.

On the other hand, as shown in FIG.
Is also the convex curved surface 11a of the original reading surface 11 facing this.
It is concavely curved according to the shape of. That is, FIG.
As shown in FIG. 2, the lower end surface 22a of the rear plate 22 is formed by forming a central concave portion having a central high position in which both ends in the main scanning direction X are at a low level, gradually become higher as approaching the center, and become the highest at the center. The rear sheet 21 is formed along the concave curved surface 22a by regulating the position of the back sheet 21 on the concave curved surface 22a. The both ends in the main scanning direction X are at a low level in accordance with the shape of the convex curved surface 11a, and gradually become higher as approaching the center, and become the highest at the center. 21a. For convenience of explanation, the common reference numeral 22a is used for the lower end surface of the back plate 22 and the concave curved surface thereof. Further, the reference numeral 21a is used for the lower surface of the back sheet 21 in more detail than the concave curved surface of the back sheet 21.

Since the back sheet 21 itself is flexible and highly flexible, it is difficult to maintain the back sheet 21 itself on the concave curved surface 21a as described above, but the lower end face of the back plate 22 behind the back sheet 21 is difficult. When the back sheet 21 is made to follow the concave curved surface 22a as a concave curved surface 22a, the back sheet 21 can be kept in a desired concave curved surface 21a. 3 shows the state of the concave curved surface 22a which is the lower end surface of the back plate 22, and FIG. 4 shows the state of the concave curved surface 21a of the back sheet 21 in an exaggerated manner for easy understanding. However, the amount of indentation H2 upward from both ends at the center is 0.3 to 3.0, where the maximum original reading width W is equivalent to the original sizes A4 to A3.
mm is preferable, and in practice, the original reading surface 1
It is preferable to match the protrusion amount H1. Concave curved surface 21a,
The specific shape of the convex curved surface 11a of the document reading surface 11 can be said to be the same as the specific shape of the convex curved surface 11a. However, it is preferable that the concave curved surfaces 21a and 22a have the same shape as the convex curved surface 11a. Concave curved surface 22 which is the lower end surface of back plate 22
a and the center point which is the deepest recessed portion of the concave curved surface 21a of the back sheet 21 is located at a position different from the center point which is the highest projected portion of the convex curved surface 11a which is the document reading surface 11 of the contact type image sensor 10. In the main scanning direction X,
The lowest end points of the concave curved surfaces 21a and 22a coincide in the main scanning direction X with the lowest end points of the convex curved surface 11a. Therefore, the vertical dimension of the minute gap 23 which is a passage of the document between the convex curved surface 11a which is the document reading surface 11 and the concave curved surface 21a of the back sheet 21 is all the same in any point in the main scanning direction X. It is the same. In FIG. 4, a double-headed arrow W indicated by a curved broken line is shown.
Indicates the maximum original reading width, and the maximum original reading width W
Are uniform over the entire range of. Although the vertical dimension of the minute gap 23 is exaggerated in FIGS. 1 and 4, the dimension is set to be equal to or smaller than the focal depth of the contact image sensor 10.

Next, the operation of the document reading apparatus according to the embodiment configured as described above will be described. A plurality of originals to be read are stacked on an original tray (not shown). When an operation for instructing document feeding is performed on the operation panel, documents on the document tray are separated one by one and fed to the paper feeding unit 41 by cooperation of a separating roller (not shown) and a separating plate. The document that has reached the paper feeding unit 41 is conveyed while being nipped by conveying rollers 42 and 43 that are in contact with each other at the top and bottom, and the document is guided by a document guide 44 on the paper feeding side and the document reading surface 11 of the contact image sensor 10 The sheet is fed into a passage, which is a minute gap 23 between the sheet and the back sheet 21. Then, the paper passes between the upper and lower discharge side document guides 45 and 46, is nipped by discharge rollers 47 and 48 which are in contact with each other at the upper and lower sides, and is discharged to a stacker (not shown).

When a document passes through the minute gap 23, the contact image sensor 10 reads the document image. That is, the light emitting element array 13 is driven to emit light, and the light is transmitted through the glass plate 16 and illuminates the lower surface of the original that passes through the original reading surface 11 that is the upper surface of the glass plate 16. I do. Then, an image image represented by a black portion and a white portion in the document is captured based on the presence or absence of light reflection. The reflected light again passes through the glass plate 16 and enters the sensor array 15 via the rod lens array 14, where the optical signal is converted into an electric signal by photoelectric conversion. That is, the image on the document is read. In this reading, one line is simultaneously read over the maximum document reading width W along the main scanning direction X. The image data obtained by the sensor array 15 is sent to the next-stage image processing unit as a grayscale image signal. In the case of a document reading apparatus that can read a color image, R (red),
Assume that a combination of light emitting elements of three primary colors of G (green) and B (blue) or a color filter of three primary colors is used, and the light of the three primary colors is sequentially switched cyclically and emitted, and reflected light is emitted. It is assumed that the incident sensor array 15 is common to the three primary colors and is sent to the next stage image processing unit as a grayscale image signal for identifying R, G and B.

For a document passing between the document reading surface 11 and the back sheet 21 which are extremely close within the depth of focus of the contact image sensor 10, the document reading surface 11 has a convex curved surface 11.
a, and the back sheet 21 has a concave curved surface 21a in accordance with this, so that the original document also undergoes forcible deformation along this curved surface shape, and the original document itself has a smooth curved surface shape. Becomes An original having a curved surface shape has a so-called waist strength. In other words, the second moment of area is increased, and the flexibility can be reduced to have a slight but rigid element.

In addition, while the central portion of the document in the main scanning direction X receives a large frictional force from the document reading surface 11 of the convex curved surface 11a, both ends of the document have concave curved surfaces 21a.
The frictional force received from the back sheet 21 is small. The original is originally a flat plane along one plane. This is forcibly deformed into a curved surface shape as described above. The original deformed into a curved surface shape attempts to restore the original flat planar shape, but this restoring action is performed at the center and both ends of the original.
Also, the lower surface and the upper surface of the document are different. At the center of the document, the lower surface of the document comes into stronger contact with the convex curved surface 11 a of the document reading surface 11. The document reading surface 11 is made of glass and has a relatively large coefficient of friction. The upper surface of the central portion of the document tends to be separated from the back sheet 21. On the contrary,
At both ends of the document, the upper surface of the document comes into stronger contact with the concave curved surface 21 a of the back sheet 21. The back sheet 21 is made of a polyester film or the like, and has a very small coefficient of friction. The lower surface of both ends of the document is the convex curved surface 1 of the document reading surface 11.
1a tends to be separated.

The biggest cause of skew (skew) and jam (paper jam) is mainly due to frictional couples at both sides of the document at both ends in the main scanning direction X. One force occurs. That is, the document is rotated due to the couple moment N = F × L, which causes skew.
The moment N of the couple increases as the frictional force F on both sides of the document increases, and increases as the lateral width L of the document increases.

In the above-described embodiment of the present invention, as described above, the so-called stiffness is generated in a document having a curved surface, and the frictional force at both ends is caused by the curved surface. In combination with the reduction of skew, the occurrence of couples can be suppressed, the occurrence of skew can be suppressed, and the occurrence of jams due to skew can also be suppressed. Can be performed well. As a result, the reading of the original can be performed well. Moreover, when suppressing skew,
It has a simple configuration in which the shapes of the document reading surface 11, the back sheet 21, and the back plate 22 of the contact type image sensor 10 are simply devised, and the structure is simple without increasing the number of parts as compared with the conventional technology. Yes, skew and jam prevention are achieved without increasing cost burden.

The present invention can be suitably implemented as a back sheet type document reading apparatus in a facsimile machine, a copying machine, especially a digital copying machine, and an image scanner.

Although one embodiment has been described in detail above, the present invention can include the following configuration.

(1) In the above embodiment, the convex curved surface 11a of the document reading surface 11 and the concave curved surface 2 of the back sheet 21 are used.
Although 1a is a congruent shape, it is not always necessary to do so, and both may have slightly different shapes.

(2) In the above embodiment, the concave curved surface 21a of the back sheet 21 and the concave curved surface 22a of the back plate 22 are combined, but it is not always necessary to do so, and both are slightly The shape may be different.

(3) In the above embodiment, the back sheet 21 is formed to have the concave curved surface 21a in conformity with the convex curved surface 11a of the document reading surface 11, but it is not always necessary to do so. The sensor 10 is lower and the back sheet 21 is higher, and the document reading surface 11 is a convex curved surface 11.
If it is a, the back sheet 21 may have a flat planar shape. Although inferior to the embodiment, the effect of suppressing skew is expected to be expected to some extent.

(4) In the above embodiment, the contact type image sensor 10 is placed at the lower position and the back sheet 21 is placed at the upper position. However, it is not always necessary to do so, and a configuration in which the image sensor 10 is turned upside down may be used. Make it not exist. Further, the facing direction of the contact type image sensor 10 and the back sheet 21 does not always need to be the up and down direction, and may be facing in the left and right direction and other directions.

(5) In the above embodiment, the back plate 22
Is attached to the operation panel bottom frame 30 and the back sheet 21 is also attached to the operation panel bottom frame 30, but it is not always necessary to do so.
May be attached to any member, and the back sheet 21
May be attached to any member.

(6) In the above embodiment, the contact type image sensor 10 is used as the image sensor, but it is not always necessary to use such a type, and an image sensor of another type may be used. Shall be.

(7) In the above embodiment, the back sheet 21 is made of a polyester film or the like, but it is not always necessary to do so, and any material may be used.

(8) In the above embodiment, the back sheet 21 and the back plate 22 are formed separately, but it is not always necessary to do so.
May be integrated. In that case, the whole shall be molded with the same material.

(9) This is a deformation mode. However, if it is only expected that the original has a curved surface so as to have a so-called stiffness and suppress skew, the original reading surface 11 may be changed. In forming a curved surface shape, it is not always necessary to use a convex curved surface, and it can be considered that an inverted concave curved surface may be used.

The above items (1) to (9) are independent of each other, and any of these items may be appropriately combined in any number.

Finally, notes on the description of the specification relating to the present case will be described. In the specification (especially, the detailed description of the invention and the claims) or the drawings relating to the present case, regarding any given matter (including any element or a connection relation / combination relation of any element), Reserve the possibility of omission. Furthermore, the possibility of adding any matter not described in the claims but described in the detailed description of the invention or in the drawings to the claims and the possibility of changing the description accompanying the additions is described. Reserve

[0041]

According to the first aspect of the document reading apparatus, the document is also deformed into a curved shape along the convex curved surface protruding from the center of the document reading surface, thereby generating a so-called waist strength in the document. At the same time, since the contact frictional force between the original and the original reading surface having the convex curved surface is made weaker at both ends than at the center, it is possible to suppress generation of couple in the original. As a result, the occurrence of skew can be suppressed, and the occurrence of jams due to the skew can be suppressed. As a result, the document can be transported satisfactorily, and the document can be read satisfactorily. be able to. However, it has a simple structure that only requires a shape change, and has a simple structure without any increase in the number of parts compared to the conventional technology, and can prevent skew and jam without increasing the cost burden. It has become.

According to the second aspect of the invention, when the original deformed into the curved surface shape attempts to restore the original flat planar shape, the central portion of the original has a convex curved surface of the original reading surface. The frictional force applied to the original in the main scanning direction is made different in the main scanning direction, thereby reducing the frictional force at both ends of the original. Therefore, the occurrence of couples can be suppressed reliably, so that the occurrence of skew can be suppressed, and the occurrence of jams due to the skew can also be suppressed. it can. The reading of the original can be performed well.
However, it has a simple structure that only requires a shape change, and has a simple structure without any increase in the number of parts compared to the conventional technology, and can prevent skew and jam without increasing the cost burden. It has become.

According to the third aspect of the present invention, the shape of the end face of the back plate is a concave curved surface, and the back sheet is made to conform to the end surface shape. Even if it is a back sheet, this can be kept in a desired concave curved surface. The structure for this purpose is only the shape of the end face of the back plate, and does not require an increase in the number of parts or a complicated structure.

According to the fourth aspect, this is most effective in a document reading apparatus having a contact type image sensor having a considerably small depth of focus.

[Brief description of the drawings]

FIG. 1 is a front view of a configuration of a main part of a document reading apparatus according to an embodiment of the present invention, viewed from a main scanning direction.

FIG. 2 is a combined view of a vertical cut end view showing an internal structure of a contact image sensor according to an embodiment and a perspective view showing an external shape.

FIG. 3 is a perspective view showing a form of a back plate according to the embodiment.

FIG. 4 is a perspective view showing a positional relationship and a shape relationship between a contact image sensor, a back plate, and a back sheet according to the embodiment.

[Explanation of symbols]

10 Contact image sensor (CIS: Contact Image)
Sensor), 11: original reading surface, 11a: convex curved surface, 1
2 ... housing, 12A, 12B ... front and rear side walls, 12
a, 12b: upper end surface, 12c, 12d: glass plate support, 13: light emitting element array, 14: rod lens array, 15: sensor array, 16: glass plate, 21: back sheet, 21a: concave curved surface, 22 .., Rear plate, 22a ... concave curved surface (lower end surface), 23 ... minute gap, 30 ... operation panel bottom frame, 30a ... stepped portion, 41 ... paper feed unit, 42,
43: conveyance roller, 44: paper guide on paper feed side, 45, 4
6: discharge side original guide, 47, 48: discharge roller, X:
Main scanning direction, Y: Document transport direction, W: Maximum document reading width, H1: Projection amount, H2: Recess amount

Claims (4)

[Claims] 1. An image sensor, comprising: a back sheet facing a document reading surface of the image sensor with a small gap through which a document passes, wherein the shape of the document reading surface is set from the center in the main scanning direction. A document reading device, wherein the document reading device is formed on a convex curved surface approaching the back sheet side at both ends. 2. The method according to claim 1, wherein the shape of the back sheet is formed in a concave curved surface approaching the image sensor from the center to both ends in the main scanning direction in accordance with the convex curved surface of the document reading surface. Item 2. The document reading device according to Item 1. 3. The position of the back sheet is restricted to the end face of the back plate, and the shape of the end face of the back plate is adjusted from the center in the main scanning direction to both ends in accordance with the convex curved surface of the document reading surface. 3. The document reading apparatus according to claim 2, wherein the back sheet is formed along a concave curved surface approaching the image sensor side, and the rear sheet is arranged along a concave curved surface at an end surface of the rear plate. 4. The document reading apparatus according to claim 1, wherein said image sensor is a contact type image sensor.