JP2002320075A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reader that attains excellent image reading similarly to the case with a platen scan system by preventing image quality deterioration due to the effect of a foreign material and image quality deterioration caused by deviation in a focal position even in the case of image reading by the CVT(Constant Velocity Transfer) system. SOLUTION: The image reader is configured such that an optical path length between a solid-state image pickup element array 16 and an original placing position on the upper face of a 1st platen glass plate 11 on which an original is placed is almost equal to an optical path length between the solid-state image pickup element array 16 and the original moving position floated by a prescribed interval from the upper face of a 2nd platen glass plate 16 provided in addition to the 1st platen glass 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus for optically reading an image drawn on a document to be read, such as a copying machine or a scanner.

[0002]

2. Description of the Related Art Generally, an image reading apparatus reads an image from a document placed on a platen glass,
A so-called platen scan type is widely known. In this platen scan type image reading apparatus, when an original is placed on the platen glass, the original on the platen glass is scanned by an optical scanning system movable along the platen glass, and the original is scanned via the optical scanning system. The image drawn on the original by CCD (Charge Coupled Device)
e) Reading is performed by a solid-state image sensor array such as a sensor.

In recent years, in addition to the platen scanning method, a so-called C
Some of them can also support the VT (Constant Velocity Transfer) method. When the image reading is performed by the CVT method, the image reading apparatus sets the optical scanning system at a predetermined position below the platen glass for CVT provided separately from the platen glass on which the original is placed in the platen scanning method. While still, the automatic document feeder (A
By moving the original to be read on the platen glass for CVT using DF (Automatic Document Feeder) etc., the image drawn on the original is read by the CCD.
The image is read by a solid-state image sensor array such as a sensor.

[0004]

SUMMARY OF THE INVENTION However, CVT
At the time of image reading by the method, the optical scanning system is stopped at a predetermined position below the platen glass for CVT. Therefore, if there is a foreign matter on the platen glass for CVT, etc., black stripes in the sub-scanning direction appear on the read image. Etc. may occur, and as a result, the image quality of the read image may be degraded.

On the other hand, the original is moved while being floated on the platen glass for CVT so that the original does not slide directly on the platen glass for CVT. CV
It is also conceivable to avoid adhesion on the T platen glass. However, in this case, since the original is moved while being floated on the platen glass for CVT, the optical focal position is shifted accordingly. Accordingly, there is a possibility that the resolution of the reading result is reduced, the MTF (Modulation Transfer Function) is deteriorated, or the like due to the deviation of the focal position. Further, for example, Japanese Patent Application Laid-Open No. 2000-2
As disclosed in Japanese Patent Publication No. 36422, it is conceivable to provide a means for changing the focal position to prevent image quality deterioration due to the deviation of the focal position, but the means complicates the device configuration. This leads to an increase in the size and cost of the apparatus.

Accordingly, the present invention can prevent both image quality deterioration due to the influence of foreign matter and image quality deterioration due to the shift of the focal position even when reading an image by the CVT method. An object of the present invention is to provide an image reading apparatus capable of performing good image reading as in the case.

[0007]

According to the present invention, there is provided an image reading apparatus devised to achieve the above object, wherein a first platen glass on which a document is placed and a first platen glass are provided. A second platen glass provided separately, a document conveying means for moving a document at a position floating a predetermined distance from an upper surface of the second platen glass, and a first platen glass under the first platen glass. Optical scanning means that can move along the platen glass and be located at a predetermined position below the second platen glass, and a document placed on the first platen glass via the optical scanning means or A solid-state image sensor array for optically reading an image from a document conveyed by the document conveying means on the second platen glass; The optical path length between the original mounting position and the solid-state image sensor row and the optical path length between the original moving position floating from the upper surface of the second platen glass by a predetermined distance and the solid-state image sensor row are substantially the same. It is characterized by comprising.

[0008] According to the image reading apparatus having the above-mentioned configuration, the original image on the first platen glass is moved by the solid-state imaging device array via the first platen glass and the optical scanning means moving along the first platen glass. Image reading. On the other hand, with respect to the document conveyed by the document conveying means, the solid-state image sensor array optically reads an image via the second platen glass and the optical scanning means located at a predetermined position below the second platen glass. At this time, since the document conveyed by the document conveying means moves at a position floating a predetermined distance from the upper surface of the second platen glass, it does not slide directly on the upper surface of the second platen glass.
Therefore, it is possible to suppress foreign substances such as dust and toner residue from adhering to the upper surface of the second platen glass as much as possible.
In addition, the optical path length between the original moving position and the solid-state image sensor row at that time is substantially the same as the optical path length between the upper surface of the first platen glass and the solid-state image sensor row. Is floating only a predetermined distance from the upper surface of the second platen glass, the optical focus position does not shift by that much.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image reading apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a configuration example of a main part of an image reading apparatus according to the present invention, and FIG. 2 is a side sectional view showing an example of a schematic configuration of the image reading apparatus according to the present invention.

First, a schematic configuration of the image reading apparatus will be described. The image reading device described here is for optically reading an image drawn on a document from a sheet-shaped document, and furthermore, can be compatible with both a platen scan method and a CVT method. Is what it is. Therefore, as shown in FIG. 2, the image reading apparatus includes a scanner unit 10 and a CVT original feeding unit 20.
And

The scanner unit 10 includes a platen glass 11 on which a document is placed when reading an image by a platen scan method, and a full-rate carriage (scanning) for scanning a reading surface of the document placed on the platen glass 11. Hereinafter, abbreviated as “F / R-CRG”) 12 and F / R
A half-rate carriage (hereinafter abbreviated as “H / R-CRG”) that moves in a half area at half the speed of CRG12
13 are provided. The F / R-CRG 12 has a lamp 12a for irradiating the original on the platen glass 11, and a first mirror 12 for changing the optical axis direction of the light reflected from the original.
b. Further, the H / R-CRG 13 is equipped with a second mirror 13a and a third mirror 13b that convert the direction of the optical axis of the light reflected from the first mirror 12b. These F / R-CRG12 and H / R-CR
Each of G13 is driven by a carriage driving motor such as a pulse motor (not shown). The difference in the moving speed and the moving area between the F / R-CRG 12 and the H / R-CRG 13 is because the optical path length between the F / R-CRG 12 and the solid-state image sensor array described later is always kept constant.

The scanner unit 10 includes a platen glass 11, an F / R-CRG12 and an H / R-CRG1.
3, these F / R-CRG12 and H / RC
A lens 14 for condensing the reflected light from the document obtained via the RG 13 and a CCD for receiving the condensed reflected light
A solid-state image sensor array 15 including sensors and the like is provided. Among them, the solid-state imaging element array 15 has a three-line configuration corresponding to the spectral sensitivity characteristics of each of R (red), G (green), and B (blue) in order to read a color image. May have a one-line configuration corresponding to the reading of a black-and-white image, or may be a combination of these.

When a document is placed on the platen glass 11, the carriage driving motor drives the document.
The F / R-CRG 12 and the H / R-CRG 13 scan the original on the platen glass 11. As a result of this scanning, the solid-state image sensing device array 15 has the platen glass 11, F /
Image information is read from a document on the platen glass 11 via the mirrors 12a, 13a, 13b mounted on the R-CRG 12 and the H / R-CRG 13 and the lens 14. That is, the image reading apparatus reads an image corresponding to the platen scan method.

On the other hand, the scanner unit 10 having such a configuration
A CVT document feeder 20 is provided above the document feeder.
The CVT document feeder 20 is composed of a so-called Automatic Document Feeder (ADF), and is a feed tray 2 on which documents to be read are stacked.
1 and a discharge tray 22 from which the read original is discharged
And a document conveying means 23 for sequentially feeding out the documents set on the paper feed tray 21 and discharging the same to the paper discharge tray 22. The document conveying means 23 may have a document reversing mechanism for reading images from both sides of the document.

By the way, such a CVT document feeder 2
In the case of 0, a CVT document reading position is provided at a predetermined position on the document conveying path between the paper feed tray 21 and the paper discharge tray 22. Correspondingly, in the scanner unit 10, a platen glass 16 for CVT is provided separately from the platen glass 11, and the F / R-CRG1 is located at a predetermined position below the platen glass 16 for CVT.
2 can be located.

In the CVT document feeder 20, the F / R-CRG 12 and the H / R-CR 12 of the scanner 10 are used.
While the G13 is stationary at a predetermined position corresponding to the CVT document reading position, the document to be read is conveyed so as to pass at a constant speed over the CVT document reading position. Thus, the image reading device performs image reading corresponding to the CVT method.

As described above, the image reading apparatus can selectively cope with both the image reading by the platen scanning method and the image reading by the CVT method. However, in any case, the image reading is performed by the F / R-CRG12 and the H / R-CRG.
13 is performed using the solid-state imaging device array 15.
F / R between platen scan mode and CVT mode
Whether the CRG 12 is located below the platen glass 11 or the CVT platen glass 16, that is, the reflected light from the original to be read is the platen glass 1
1 and the CVT platen glass 16 are different.

Here, the platen glass 11 and the CVT platen glass 16 will be described in more detail. As shown in FIG. 1A, the platen glass 11 and the CVT platen glass 16 are arranged such that their upper surfaces are substantially flush.

Between the platen glass 11 and the CVT platen glass 16, that is, downstream of the CVT document reading position A in the document transport direction, a document that has passed the CVT document reading position A is guided so as to be directed upward. A wedge-shaped downstream guide member 17 is provided. Thereby, C
The document that has passed the VT document reading position A is directed upward by the downstream guide member 17 so that the document is conveyed.
The document is reliably collected by the document conveying means 23, and
2 will be transported. The downstream guide member 1
The vertical end face on the downstream side in the document conveyance direction at 7 is the abutting surface (reference surface) of the document placed on the platen glass 11.
It is designed to work as well.

On the upper surface of the CVT platen glass 16 on the upstream side of the CVT document reading position A in the document transport direction,
A flat upstream guide member 18 for guiding the original is provided. As a result, the original conveyed by the original conveying means 23 is guided by sliding on the upper surface of the upstream guide member 18, so that the original is conveyed by a predetermined distance (thickness of the upstream guide member 18) from the upper surface of the CVT platen glass 16. It will move at the position where it floats by (minute).

The downstream guide member 17 and the upstream guide member 18 may be formed of the same material as the platen glass 16 for CVT, or may be formed of a resin member different from the platen glass 16 for CVT. Is also good.

By the downstream guide member 17 and the upstream guide member 18, the platen glass 16 for CVT is provided.
The height of the original conveyed above, that is, the height of the original moving position at the CVT original reading position A is the platen glass 1
1 is higher than the original placement position. The fact that the original moving position is higher than the original placing position is determined by the CVT
This is suitable for simplifying the configuration of the document feeder 20.
This is because the higher the document movement position is compared to the document placement position, the more mechanical limitations in configuring the CVT document feeder 20 (problems such as routing of the transport path, securing space for the transport rollers, etc.). ) Is reduced. Therefore, if the original moving position is higher than the original placing position, the CVT original feeding unit 20 is compared with the case where there is no difference between the positions.
Since the configuration can be simplified, it is easy to improve the operation reliability and reduce the device cost due to the simplification.

In addition, the presence of the upstream guide member 18 causes the document to move at a position floating a predetermined distance (the thickness of the upstream guide member 18) from the upper surface of the CVT platen glass 16. , Does not slide directly on the upper surface of the CVT platen glass 16. Therefore, it is possible to minimize the attachment of foreign matter such as dust and toner residue to the upper surface of the CVT platen glass 16 during the document conveyance, and to reduce the image quality deterioration such as black streaks in the sub-scanning direction on the read image. This can be avoided.

By the way, as described above, the original is
The height of the document placement position on the platen glass 11 and the CV
If the height of the document moving position on the T platen glass 16 is made different from each other, there is a possibility that the optical focal position when reading an image is shifted accordingly.
Such a shift of the focal position may cause a reduction in the resolution of the reading result, a deterioration in the MTF, or the like.

Therefore, in the image reading apparatus of this embodiment, the height of the original placing position and the height of the original moving position are different from each other by making the thickness of the platen glass 11 and the thickness of the CVT platen glass 16 different. However, the optical path length between each of these positions and the solid-state image sensor row 15 is set to be substantially the same.

More specifically, as shown in FIG. 1B, the original is moved at the original movement position (see A in the figure) by the amount by which the original is lifted from the upper surface of the CVT platen glass 16 (see h in the figure). Since it is higher than the placement position (see B in the figure), the thickness of the CVT platen glass 16 (see t2 in the figure) is larger than the thickness of the platen glass 11 (see t1 in the figure).

This is because, when the thickness of the transmitted glass is different, the mode of refraction of the light when passing through the glass is also different. Therefore, even if the actual optical path length considering the refraction of light is the same, Apparent optical path length without considering the refraction of light,
That is, there is a difference in the position of the light imaging point. From this, it can be said that the apparent optical path length is greatly affected by the thickness of the glass through which light passes and the refractive index thereof.

Now, as shown in the figure, the light transmitted through the platen glass 11 having the thickness t1 is refracted on the lower surface of the platen glass 11, and is converged at the original placing position B on the upper surface of the platen glass 11. Consider a case where an optical path length between the solid-state imaging device array 15 and the solid-state imaging device array 15 is set so as to form an image. At this time, the light is refracted below the lower surface of the platen glass 11 by the dimension t3, and the thickness t1 + t3 (= t3
If the light is transmitted through the glass by the amount of 2), the refraction point changes, so that the light does not form an image at the original placing position B (see the dashed line in the figure). Will move further upward. That is, by increasing the thickness of the glass through which light passes, the apparent optical path length can be increased.

Therefore, the thickness t of the platen glass 11
1. If the thickness t2 of the platen glass 16 for CVT, the difference t3 between them, and the floating amount h of the document (thickness of the upstream guide member 18) h at the time of CVT reading are appropriately set, the CVT for CVT can be obtained. The image forming point when light passes through the platen glass 16 can be made to coincide with the document moving position A that is floated by the floating amount h from the upper surface of the CVT platen glass 16. In other words, the height of the original moving position A and the height of the original placing position B are different, and even if the apparent optical path length between each of these positions and the solid-state image sensor array 15 is different, The actual optical path lengths taking into account the refraction effect of the above are substantially the same.

As described above, by making the actual optical path lengths between the original placing position B and the solid-state image sensor array 15 and between the original moving position A and the solid-state image sensor array 15 substantially the same, In the image reading apparatus according to the present embodiment, even if the height of the original moving position A and the height of the original placing position B are different, the optical focal position when reading an image by the CVT method is shifted. There is no such thing. Therefore, it is possible to avoid a decrease in the resolution of the reading result, a deterioration in the MTF, and the like due to the shift of the focal position.

Further, since there is no deviation in the focal position when reading an image by the CVT method, the original can be read while being floated from the upper surface of the CVT platen glass 16 and the focus at that time can be changed. The document can be surely adjusted to the original surface. That is, the upper surface of the CVT platen glass 16 is in a defocused state. Therefore, if the platen glass for CVT 1
Even if foreign matter such as dust adheres to the upper surface of 6, the foreign matter is read in a defocused state.
Since it is difficult to appear as a black streak in the sub-scanning direction, it can be said that this point is also effective in avoiding deterioration of the image quality of the read image.

Moreover, in the image reading apparatus of the present embodiment, the thickness t1 of the platen glass 11 is made different from the thickness t2 of the platen glass 16 for CVT, and more specifically, t2 is made thicker than t1. ,
Since the actual optical path lengths are substantially the same, there is no need to provide a complicated mechanism such as a means for changing the focal position, and the original moving position A can be higher than the original placing position B. . Therefore, the optical path lengths can be made substantially the same with a simple configuration such as simply making the thickness of the glass different, and the configuration of the CVT document feeder 20 can be simplified. Even if it is realized, it does not cause an increase in size and cost of the apparatus.

Further, in the image reading apparatus of the present embodiment, the original moving position A is changed to the original placing position B for the above-described reason.
Higher than the upper surface of the platen glass 11 and C
By making the upper surface of the VT platen glass 16 substantially flush with the upper surface, the difference between the positions A and B is minimized. In other words, the difference between the original moving position A and the original placing position B is reduced while minimizing the adhesion of foreign matter to the upper surface of the CVT platen glass 16 and simplifying the configuration of the CVT original feeder 20. By minimizing the size of the image reading apparatus, miniaturization of the entire image reading apparatus is facilitated.

In this embodiment, the platen glass 1
1 and the thickness t2 of the CVT platen glass 16
In this example, the actual optical path lengths between the document placement position B and the solid-state image sensor array 15 and between the document movement position A and the solid-state image sensor array 15 are substantially the same. However, the present invention is not limited to this. For example, platen glass 11 and CV
If the T platen glass 16 and the T platen glass 16 are formed of glass members having different light refractive indices, the actual optical path lengths can be made substantially the same even if there is no difference in their thicknesses.

Even if the platen glass 11 and the CVT platen glass 16 have exactly the same thickness and the same optical refractive index, if they are arranged so that a step is formed between them,
Since the height of the document moving position A and the document placing position B can be set to be substantially the same, it is possible to suppress the adhesion of foreign matter on the upper surface of the CVT platen glass 16 and to shift the focal position when reading an image by the CVT method. Can be avoided.

[0036]

As described above, the image reading apparatus according to the present invention is capable of reading an image on the upper surface of the first platen glass used for reading an image on the platen scan system and reading the image on the CVT system. Since the optical path length between the solid-state image sensor row and each of the document moving positions floating at a predetermined distance from the upper surface of the second platen glass used at the time are substantially the same, CVT is used.
Even when reading an image by the method, it is possible to prevent both the deterioration of the image quality due to the influence of the foreign matter and the deterioration of the image quality due to the shift of the focal position, and perform the good image reading similarly to the case of the platen scan method. be able to.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration example of a main part of an image reading apparatus according to the present invention, wherein FIG. 1 (a) illustrates a document placing position and a document moving position in the image reading apparatus, and FIG. FIG. 3 is a diagram illustrating a mode of refraction of light in the image reading device.

FIG. 2 is a side sectional view showing an example of a schematic configuration of an image reading apparatus according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Scanner part, 11 ... Platen glass, 12 ... Full rate carriage (F / R-CRG), 13 ... Half rate carriage (H / R-CRG), 15 ... Solid-state image sensor row, 16 ... Platen glass for CVT, 17 ... a downstream guide member, 18 ... an upstream guide member, 20 ... a CVT document feeder, 23 ... document transport means

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H04N 1/04 H04N 1/10 105 1/12 Z 1/107 F term (Reference) 2H076 AA02 AA06 AA17 AA58 BA02 BA15 BA24 BA47 BA95 2H108 AA19 BA01 DA01 5B047 BA02 BB02 BC05 5C051 AA01 BA03 DB22 DC04 DC07 FA01 5C072 AA01 BA17 DA02 XA01

Claims (4)

[Claims] A first platen glass on which an original is placed; a second platen glass provided separately from the first platen glass; and a predetermined distance from an upper surface of the second platen glass. A document conveying means for moving a document at a position where the document is moved, a position below the first platen glass can be moved along the first platen glass, and a document can be located at a predetermined position below the second platen glass. Optical scanning means, and optically converting an image from a document placed on the first platen glass or a document conveyed by the document conveying means on the second platen glass via the optical scanning means. A solid-state image sensor row for reading, an optical path length between a document placement position on the top surface of the first platen glass and the solid-state image sensor row, and the second platen Image reading apparatus characterized by optical path length is configured to be substantially the same between the scan top a predetermined distance floated moving original position and the solid-state imaging device array. 2. Due to the difference between the thickness of the first platen glass and the thickness of the second platen glass, even if the height of the original placing position and the height of the original moving position are different from each other, 2. The image reading device according to claim 1, wherein an optical path length between a position and the solid-state image sensor row is substantially the same. 3. An image reading apparatus according to claim 2, wherein said second platen glass is thicker than said first platen glass, and said document moving position is higher than said document placing position. . 4. A height of the original placing position and the height of the original moving position are different from each other due to a difference between a refractive index of light on the first platen glass and a refractive index of light on the second platen glass. 2. The image reading apparatus according to claim 1, wherein an optical path length between each of these positions and the solid-state imaging element row is substantially the same.