JP2000134419A - Image sensor, image reader, image forming device, image read method and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reader by which occurrence of set-off is avoided without making the size of the reader large so as to obtain an image with high quality in the case of reading an image at a same position on the front and rear sides of an original sheet. SOLUTION: Close contact type image sensors 1, 2 where a peak frequency of a light source and a peak frequency of spectral sensitivity of a sensor array are close to each other are placed on both sides with an original sheet carrying face inbetween. The respective close contact type image sensors 1, 2 have the characteristic as above, but the peak frequency of each light source and the peak frequency of the spectral sensitivity of each sensor array are respectively different from each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image sensor for photoelectrically converting reflected light from a document sheet surface, an image reading device such as a scanner provided with the image sensor, an image reading method, and the image reading device. And an image forming method such as a copying machine.

[0002]

2. Description of the Related Art Conventionally, as an image reading apparatus for reading an image of a document, for example, (1) a flow reading type image reading apparatus for reading a running document image by a fixed reading section; There has been proposed a scanning-type image reading device that reads an image by scanning a surface of a document with a reading unit.

[0003] Among them, the image reading apparatus of the flow reading system is capable of processing a large number of original sheets in a short time in combination with an automatic original feeder and the like, and has been widely used in recent years. In recent years, in order to diversify information, save sheets, and the like, double-sided manuscripts in which image information is described on the front and back of a sheet have been frequently used.

In the case of reading a double-sided original, the original sheet is guided to one reading section to read an image on one side, then the original sheet is inverted, and the original sheet is guided again to the reading section to read the other side. A method of reading an image (hereinafter, referred to as a switchback double-sided reading method) is generally adopted.

However, this switchback double-sided reading method has the following disadvantages. (1) When reading an image on both sides, it takes at least twice as long as when reading an image on one side.
(2) When a document sheet is reversed, sheet conveyance is not stable, and a paper jam tends to occur.

In view of such a drawback, a reading unit is disposed on each side of a document sheet in a document sheet conveyance path to read image information on both sides of the document sheet without inverting the document sheet (hereinafter referred to as a through both-side reading method). Has been proposed. In particular, in a through-only read-only machine as a peripheral device of a computer, a device using a contact type image sensor on both sides of a document sheet conveyance path has been put to practical use.

[0007]

However, the conventional image reading apparatus using the through-both-side reading method has the following problems.

When a contact image sensor having a conventional configuration is disposed on both sides of a document sheet and two sensors attempt to read images on the same reading line on the front and back surfaces of the document sheet, the document image on one side is changed to the other side. (So-called show-through), and the image quality is significantly reduced. In order to avoid show-through, it is possible to dispose the two close contact image sensors in the original sheet conveyance direction, but this may lead to an increase in the size of the apparatus.

In view of the above-mentioned conventional problems, the present invention provides a method for reading images at the same position on the front and back surfaces of an original sheet.
Avoiding show-through without increasing the size of the device,
It is an object of the present invention to provide an image sensor, an image reading device, an image reading method, an image forming device, and an image forming method capable of obtaining a high-quality image.

[0010]

According to an aspect of the present invention, there is provided an image sensor, comprising: a light source for emitting light to a sheet surface; and a light source for receiving light from the sheet surface. In an image sensor having a sensor array, a peak frequency of spectral sensitivity of the sensor array is set near a peak frequency of an emission spectrum of the light source.

According to a second aspect of the present invention, in the image sensor according to the first aspect, the emission spectrum of the light source has a single peak frequency.

According to a third aspect of the present invention, in the image sensor according to the first or second aspect, the sensor array includes a color filter passing light from the sheet surface, and the color filter. And a photoelectric conversion unit that photoelectrically converts light that has passed therethrough.

According to a fourth aspect of the present invention, in the image sensor according to the third aspect, the color filter is a blue or red filter.

According to a fifth aspect of the present invention, in the image sensor according to any one of the first to fourth aspects, the light source has a constant inclination with respect to a normal direction of a sheet surface located on a reading line. The light source is installed so as to emit light.

According to a sixth aspect of the present invention, in the image sensor according to the fifth aspect, a cover glass for guiding the light from the light source to the reading line and supporting a sheet is provided. And

According to a seventh aspect of the present invention, in the image reading apparatus having first and second image sensors for individually reading the images on each of the front and back surfaces of the sheet, the first and second image sensors are provided. Wherein each of the image sensors according to claim 1 is configured such that the peak frequency of the emission spectrum of each light source and the peak frequency of the spectral sensitivity of each sensor array are equal to those of the first and second image sensors. Are characterized by different configurations.

According to the image reading apparatus of the present invention, in the image reading apparatus of the present invention,
The reading position of the first image sensor and the reading position of the second image sensor are at the same position on each of the front and back surfaces of the sheet.

According to a ninth aspect of the present invention, in the image reading apparatus according to the seventh or eighth aspect, the first and second image sensors are arranged as follows.
It is a contact type image sensor.

According to a tenth aspect of the present invention, there is provided an image forming apparatus comprising the image reading apparatus according to the seventh aspect, wherein the image forming apparatus performs a predetermined image forming process on the image data read by the image reading apparatus. Features.

According to an eleventh aspect of the present invention, there is provided an image reading method comprising the steps of: providing first and second image sensors each including the image sensor according to the first aspect; The image on the back side of the sheet is read by the second image sensor while reading the image on the front side.

According to a twelfth aspect of the present invention, in the image reading method according to the eleventh aspect, the reading position of the first image sensor and the reading position of the second image sensor are different from each other. It is characterized in that it is located at the same location on each of the front and back surfaces of the sheet.

According to a thirteenth aspect of the present invention, there is provided an image forming method, comprising the steps of: providing the image reading device of the seventh aspect and performing a predetermined image forming process on image data read by the image reading device. Features.

[0023]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a main part of an image reading apparatus according to an embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a first contact-type image sensor, and a second contact-type image sensor 2 composed of substantially the same components is disposed at a position facing the first contact-type image sensor 1. ing.

The first contact type image sensor 1 includes a first frame 5 in which a first LED array 3 as a light source, a cover glass 6, a first lens array 7, and a first sensor array 10 are provided. It has. The first LED array 3 has the first
And a plurality of LED elements 4 are arranged corresponding to the width of the document, and are arranged on the slope of the elongated space in the first frame 5. Thereby, the first LED array 3
Light is emitted with a certain inclination with respect to the normal line direction of the S1 surface of the document sheet positioned on the reading line. The cover glass 6 guides the light from the first LED array 3 to a reading line on the S1 surface of the document sheet S,
It functions to support the document sheet S.

The first sensor array 10 includes a first optical filter 8 and a first photoelectric conversion element 9, and a plurality of the first photoelectric conversion elements 9 are arranged corresponding to the document width. I have. The graph P10 indicated by the solid line in FIG.
Is the spectral sensitivity characteristic of the sensor array 10 of FIG.
(Nm), the sensitivity reaches a peak, and near 600 (nm), the sensitivity becomes almost zero. The same characteristics can be created by using the optical filter 8 as a blue color filter, for example.

Light L emitted from the first LED array 3
Reference numeral 1 illuminates an original image on the S1 surface of the original sheet S through a cover glass 6 extending over a length substantially equal to the original width. The light reflected on the S1 surface sequentially passes through the first lens array 7 and the first optical filter 8, enters the first photoelectric conversion element 9, where it is converted into an electric signal.

Further, the second contact type image sensor 2 comprises:
In the second frame 13, a second LED array 11, a cover glass 14, a second lens array 15, and a second sensor array 18 are provided. Second LED array 11
Is configured by arranging a plurality of second LED elements 12 corresponding to the width of the document, and is disposed on the slope of the elongated space in the second frame 13. This allows the second LED
The array 11 emits light with a constant inclination with respect to the normal direction of the sheet surface located on the reading line. The cover glass 14 functions to guide the light from the second LED array 11 to a reading line on the S2 surface of the document sheet S and to support the document sheet S.

The second sensor array 18 includes a second optical filter 16 and a second photoelectric conversion element 17, and a plurality of the second photoelectric conversion elements 17 are arranged corresponding to the document width. I have. Graph P1 indicated by a dashed line in FIG.
Reference numeral 8 denotes a spectral sensitivity characteristic of the second sensor array 18, and the sensitivity is zero and 500 up to a wavelength around 500 (nm).
(Nm), the sensitivity increases, and near 650 (nm), the sensitivity reaches a peak. The same characteristics are obtained with the optical filter 1 described above.
6 can be produced, for example, by using a red color filter.

The light L2 emitted from the second LED array 11 passes through a cover glass 14 extending over a length substantially equal to the width of the original, and irradiates the original image on the S2 surface of the original sheet S. I do. The light reflected on the S2 surface sequentially passes through the first lens array 15 and the second optical filter 16, enters the second photoelectric conversion element 17, where it is converted into an electric signal.

As shown in FIG. 1, light emitted from the first and second LED arrays 3 and 11 disposed on the first and second contact image sensors 1 and 2, respectively, is transmitted to a document sheet. Since substantially the same position is illuminated on the front and back sides of S, the optical axes incident on the corresponding photoelectric conversion elements 9 and 17 are substantially on the same straight line.

On the other hand, the original sheet S passes between the pair of conveying rollers 20 and 21 and between the conveying guides 22 and 23, and the cover glasses 6 and 14 of the first and second contact type image sensors 1 and 2 face each other. Conveyed to the gap. Further, the document sheet S passes between the conveyance guides 24 and 25 and is conveyed by conveyance rollers 26 and 27 in a direction V indicated by an arrow in the figure.

FIG. 3 is a graph showing an emission spectrum of the LED element.

The first LED element 4 in FIG. 1 has a blue LED of GaN having a peak wavelength of 490 (nm) in FIG.
D is used as the second LED element 12 in FIG. 1 and a GaP red LE having a peak wavelength at 700 (nm) in FIG.
D is used.

With this configuration, 490
The original image on the S1 surface illuminated by the first LED element 4 (blue) having a peak wavelength (nm) has a wavelength of 450 nm.
The first sensor array 10 having a sensitivity peak near (nm) can receive light with high sensitivity. At this time, it is expected that the document image on the S1 side is simultaneously shown off and enters the second sensor array 18. However, in this case, the second sensor array 18 has a spectral sensitivity characteristic as shown by a dashed line P18 in FIG. 2 (the sensitivity is zero up to a wavelength around 500 nm and the sensitivity reaches a peak around 650 (nm)). Therefore, the show-through image of the S1 surface by the first LED element 4 can be almost cut.

Similarly, the original image on the S2 surface illuminated by the second LED element 12 (red) having a peak wavelength at 700 (nm) has a second sensor having a sensitivity peak near a wavelength of 650 (nm). Although the array 18 can receive light with high sensitivity, the show-through image of the S2 surface is indicated by a solid line P10 in FIG.
The spectral sensitivity characteristic of the first sensor array 10 as shown by (the sensitivity reaches a peak near a wavelength of 450 nm,
m becomes almost zero).

As described above, in the present embodiment, the contact type image sensors 1 and 2 in which the peak frequency of the light source and the peak frequency of the spectral sensitivity of the sensor array are close to each other are arranged on both sides of the original sheet conveying surface. . Each of the contact-type image sensors 1 and 2 has the above-described characteristics. However, regarding the characteristics of the contact-type image sensors 1 and 2, the peak frequency of each light source and the peak frequency of the spectral sensitivity in each sensor array are different. Thereby, the sensor arrays 10, 1 for reading the original images on the front and back of the original sheet S, respectively.
Reference numeral 8 makes it possible to cut off the show-through image on the other side and to faithfully read only the original image on each side.

The present invention is not limited to the illustrated embodiment, but can be variously modified. For example, there are the following modifications.

(1) In the above embodiment, an LED array is used as a light source. However, as long as the light source has the above characteristics, the light source may be another light source such as a fluorescent tube, a xenon tube, a halogen tube, and an EL light source. May be used.

(2) The spectral sensitivity characteristic may not be created by the optical filter, and the sensor itself may have the same spectral sensitivity characteristic.

(3) In the above embodiment, the first light source
The blue color LED array 4 and the red color LED array 12 are used, and correspondingly the same color filters are used for the optical filters 8 and 16. However, the peak of the emission spectrum of the first light source is obtained. Near the frequency, the first paired with it
The first sensor array has a characteristic that the spectral sensitivity is low with respect to the peak frequency of the emission spectrum of the second light source facing the second sensor array. The array also has a second pair
The frequency characteristics of each light source and sensor array are not particularly limited to blue and red as long as the light source and the first light source facing each other have the same configuration.

(4) The positional relationship between the blue and red light sources is as follows:
It may be opposite to the above embodiment with the document sheet interposed.

(5) The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of one device.

[0045]

As described in detail above, the image sensor according to the first to sixth aspects of the present invention, the image reading apparatus according to the seventh to ninth aspects of the invention, and the eleventh or tenth aspect of the present invention. According to the image reading method of the invention described in Item 12, it is possible to read the same portion on each of the front and back surfaces of the sheet without increasing the size of the apparatus, and to achieve a high-quality image with no show-through with a simple configuration. A read image can be obtained. This makes it possible to reduce the size of the device that employs the through-side reading method.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram of a main part of an image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a graph showing spectral sensitivity characteristics of a sensor array.

FIG. 3 is a graph showing an emission spectrum of the LED element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st contact image sensor 2 2nd contact image sensor 3 1st LED array 4 1st LED element 5 1st frame 6 cover glass 7 1st lens array 8 1st optical filter 9 1st photoelectric conversion element 10 1st sensor array 11 2nd LED array 12 2nd LED element 13 2nd frame 14 cover glass 15 2nd lens array 16 2nd optical filter 17 2nd photoelectric Conversion element 18 Second sensor array 20, 21 Transport roller 22, 23 Transport guide S Document sheet

Claims (13)

[Claims] A light source for emitting light to a sheet surface;
An image sensor comprising: a sensor array that receives light from the sheet surface; and a peak frequency of a spectral sensitivity of the sensor array is set near a peak frequency of an emission spectrum of the light source. . 2. The image sensor according to claim 1, wherein an emission spectrum of the light source has a single peak frequency. 3. The sensor array according to claim 1, wherein the sensor array includes a color filter that transmits light from the sheet surface, and a photoelectric conversion unit that performs photoelectric conversion of the light that has passed through the color filter. The image sensor according to claim 2. 4. The image sensor according to claim 3, wherein the color filter is a blue or red filter. 5. The light source according to claim 1, wherein the light source is installed so as to emit light with a constant inclination with respect to a normal direction of a sheet surface located on a reading line. Image sensor. 6. The image sensor according to claim 5, further comprising a cover glass that guides light from the light source to the reading line and supports a sheet. 7. An image reading apparatus having first and second image sensors for individually reading images on both sides of a sheet, wherein the first and second image sensors are arranged as described in claim 1. Each of the first and second image sensors is constituted by an image sensor, and a peak frequency of an emission spectrum of each light source and a peak frequency of a spectral sensitivity of each sensor array are different between the first and second image sensors. Image reading device. 8. The sheet according to claim 7, wherein the reading position of the first image sensor and the reading position of the second image sensor are at the same position on each of the front and back surfaces of the sheet. Image reading device. 9. The first and second image sensors,
8. The image sensor according to claim 7, wherein the image sensor is a contact image sensor.
Alternatively, the image reading device according to claim 8. 10. An image forming apparatus, comprising: the image reading apparatus according to claim 7; and performing predetermined image forming processing on image data read by the image reading apparatus. 11. A first image sensor and a second image sensor each comprising the image sensor according to claim 1, wherein an image on a front side of a sheet is read by the first image sensor, 2. An image reading method, wherein an image on the back side of the sheet is read by the image sensor. 12. A read position of the first image sensor and a read position of the second image sensor,
The image reading method according to claim 11, wherein the sheet is located at the same position on each of the front and back surfaces of the sheet. 13. An image forming method comprising: preparing the image reading device according to claim 7; and performing predetermined image forming processing on image data read by the image reading device.