Image reading device and image forming apparatus

Abstract

To provide an image reading device and an image forming apparatus that can prevent a situation where the quantity of visible light and infrared light incident on imaging means falls below the quantity of light necessary for reading performed by the imaging means.SOLUTION: An image reading device comprises: a visible light source that irradiates a document with visible light; an infrared light source that irradiates the document with infrared light; and a plurality of mirrors that are installed on optical paths of the visible light and the infrared light from the document up to imaging means. At least one of the plurality of mirrors is a mirror having a reflectance of light in a wavelength region of 450 nm or more and 900 nm or less of 93% or more at an angle of reflection of 45°.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to an image reading apparatus and an image forming apparatus.

Background Art

[0002] Conventionally, there has been known an image reading apparatus having a visible light source that irradiates a document with visible light, an infrared light source that irradiates the document with infrared light, and a plurality of mirrors installed on an optical path from the visible light and infrared light reflected from the document to an imaging means.

[0003] Patent Document 1 describes an apparatus that includes a visible light source and an infrared light source, and enables reading of an invisible copy prohibition pattern on a document by lighting the infrared light source, and stops a copying operation when the copy prohibition pattern is read.

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, there has been a risk that the light amount of at least one of the visible light and the infrared light incident on the imaging means is less than the light amount necessary for reading by the imaging means.

Means for Solving the Problems

[0005] In order to solve the above-described problems, the present invention provides an image reading apparatus including a visible light source that irradiates a document with visible light, an infrared light source that irradiates the document with infrared light, and a plurality of mirrors installed on an optical path from the document to an imaging means, wherein at least one of the plurality of mirrors is a mirror having a reflectance of 93% or more at a reflection angle of 45° for light in a wavelength range of 450 nm or more and 900 nm or less.

Effects of the Invention

[0006] According to the present invention, it is possible to suppress the light amount of the visible light and the infrared light incident on the imaging means from being less than the light amount necessary for reading by the imaging means.

Brief Description of the Drawings

[0007]

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Best Mode for Carrying Out the Invention

[0008] Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. It should be noted that those skilled in the art can easily make changes and modifications to the present invention within the scope of the claims to form other embodiments, and these changes and modifications are included in the scope of the claims. The following description is an example of the best mode in this invention and does not limit the scope of the claims.

[0009] Hereinafter, an embodiment in which the present invention is applied to an image forming apparatus including an image reading apparatus will be described. FIG. 1 is a perspective view showing an image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 shown in FIG. 1 has functions of a copier, a printer, a facsimile apparatus, a scanner, etc., and can record and output a full-color image or a monochrome image on a recording paper or output it in a predetermined data format based on input data such as read image data.

[0010] Above the paper feed unit, the scanner unit 10, and the image forming unit 100 of the image forming apparatus 1, there is provided an ADF 120 which is an automatic document feeder. The scanner unit 10 constitutes the main body of the image reading apparatus, and together with the ADF 120, it constitutes the image reading apparatus 130.

[0011] The paper feed unit of the image forming unit 100 includes, for example, a plurality of paper feed cassettes for storing cut recording paper respectively, and a plurality of sets of paper feed rollers for picking up and feeding the recording paper from any of these paper feed cassettes. Further, the paper feed unit has a paper feed path including various rollers and the like for transporting the recording paper fed from any of the paper feed rollers to a predetermined image forming position of the image forming unit 100.

[0012] The image forming unit 100 includes, for example, an exposure unit, a plurality of photosensitive drums, a developing device using four colors of toner of cyan (C), magenta (M), yellow (Y), and black (K), a transfer belt, a secondary transfer unit, a fixing unit, and the like.

[0013] The image forming unit 100 forms an electrostatic latent image on each photosensitive drum by exposing the photosensitive drums of respective colors with an exposure unit, for example, based on the read image read by the image reading device 130, and develops the latent image on each photosensitive drum by supplying toner thereto with the developing units of respective colors of the developing device. Further, the image forming unit 100 primarily transfers the toner image on each photosensitive drum to the transfer belt, secondarily transfers the toner image on the recording paper after superposing it on the recording paper by the secondary transfer unit, and then heats and presses the toner image on the recording paper by the fixing unit to fix it, so that a color image can be formed. Furthermore, the image forming unit 100 can form an external output image such as an image file or data that can be output to the outside based on the read image by the scanner unit 10. Instead of the electrophotographic image forming unit 100 as described above, an image forming unit employing another recording method such as an inkjet method may be used.

[0014] FIG. 2 is a perspective view showing the scanner unit 10. An ADF 120 is mounted on the scanner unit 10 and is swingably supported by a hinge, so that the upper surface of the scanner unit 10 can be opened and closed. The upper surface of the scanner unit 10 is provided with a contact glass 57 and a slit glass 58 as transparent members.

[0015] FIG. 3 is a perspective view showing the inside of the scanner unit 10. As shown in FIG. 3, the scanner unit 10 has a housing portion 10a of a substantially rectangular parallelepiped box-shaped member that houses an integrated scanning unit 200 and the like, and a scanner cover 10b attached to the housing portion 10a so as to close the upper surface of the housing portion 10a. The integrated scanning unit 200 is movably supported in the direction of arrow G in the figure by a guide rod 52 and a guide rail 51 attached to the housing portion 10a in the left-right direction in the figure.

[0016] FIG. 4 is a schematic configuration diagram showing the integrated scanning unit 200. As shown in FIG. 4, an illumination device 401 is stored in the frame 408 of the integrated scanning unit 200. Also stored are five reflecting mirrors 402a, 402b, 402c, 402d, 402e that refract the reflected light from the document 414 as the imaging object, a first lens group 403 for forming an image of the reflected light from these reflecting mirrors, and a second lens group 404. Also stored are an image sensor 405 as an imaging means for photoelectrically converting the light imaged by the first lens group 403 and the second lens group 404, a drive circuit board 406, and the like. The drive circuit board 406 outputs an image signal based on the electrical signal output from the image sensor 405.

[0017] The first lens group 403 disposed on the side of the reflecting mirror 402e is fixed to the lens receiving base 409 by a lens band 407. The second lens group 404 disposed on the side of the image sensor 405 is attached to the lens receiving base 409 via a lens fixing bracket 413.

[0018] The first lens group 403 is a lens having a positive power, and the second lens group 404 is a lens having a negative power. In the present embodiment, by configuring with the first lens group 403 having a positive power and the second lens group 404 having a negative power, chromatic aberration is corrected, and an image with high resolution can be formed on the image sensor 405. Also, the focal length can be shortened, and the integrated scanning unit 200 can be made more compact. Furthermore, the so-called back focus, which is the distance from the second lens group 404 to the image sensor 405, can also be shortened, and the integrated scanning unit 200 can be made more compact.

[0019] The drive circuit board 406 on which the image sensor 405 is mounted is attached to the lens receiving base 409 via a fixing bracket 410. As the image sensor 405, a CCD (charge-coupled device), a CMOS (Complementary Metal Oxide Semiconductor), or the like can be used. Note that the image sensor 405 of the present embodiment is capable of imaging in the visible light region and the infrared region.

[0020] The lighting device 401 has a substrate 502 on which a plurality of white point light sources 501 for irradiating light and an infrared point light source 701 are arranged in an array on a mounting surface 502a. Further, the lighting device 401 has a light guide 503 that guides the light emitted from these point light sources 501, 701 to the illumination area of the document. The light guide 503 is formed of a resin or the like with a high transmittance such as acrylic, and a diffusing agent as a diffusing means is applied to the emission surface 503a. When the light from the point light sources 501, 701 is emitted from the emission surface 503a of the light guide 503, the light is diffused, and variations in illuminance and chromaticity in the main scanning direction (the width direction of the document) irradiated on the document surface due to variations in chromaticity and illuminance of each point light source can be suppressed.

[0021] White light and infrared light are irradiated from the lighting device 401 toward the document surface of the document 414, which is the object to be irradiated, placed on the contact glass 57. The reflected light reflected from the document surface is reflected by five reflecting mirrors 402a, 402b, 402c, 402d, 402e. The reflected light that is reflected and guided enters the image sensor 405 through the first lens group 403 and the second lens group 404, is received by the image sensor 405, and the image of the document surface is read.

[0022] When the integrated scanning unit 200 moves in the direction of arrow G in the figure, the image of the document surface placed on the contact glass 57 is sequentially read by the image sensor 405, and the image of the entire document surface is read.

[0023] Also, when reading the image of the document surface of the conveyed document conveyed by the document automatic feeding device (ADF) 120, the integrated scanning unit 200 is positioned at the home position shown in FIG. 3. When positioned at this home position, the light from the lighting device 401 is irradiated toward the slit glass 58. Thereby, the image of the document surface of the conveyed document conveyed by the document automatic feeding device (ADF) 120 passing over the slit glass 58 is read by the image sensor 405.

[0024] FIG. 5 is a perspective view of a substrate 502 on which a white point light source 501 and an infrared point light source 701 are arranged in an array on a mounting surface 502a. The plurality of white point light sources 501 are arranged in an array in the main scanning direction (the width direction of the document). The plurality of white point light sources 501 are side view type LEDs, and the light irradiation surface S1 is perpendicular to the mounting surface 502a and is arranged in the same plane as the end face of the end portion of the substrate 502. The emission wavelength of the white point light source is about 450 to 780 nm.

[0025] Also, an infrared point light source 701 is arranged between the white point light sources 501. The infrared point light source 701 is also a side view type LED, and is mounted on the substrate 502 so that the light irradiation surface is perpendicular to the mounting surface 502a. The emission wavelength of the infrared point light source is 850 to 900 nm.

[0026] By arranging the infrared point light source 701 between the white point light sources 501, it is possible to read a document image with white light and read a document image with infrared light. For example, when performing character recognition (OCR (Optical Character Recognition / Reader) optical character recognition) of a document image, the document image is read by irradiating infrared light. By irradiating infrared light, the color of the document image can be invalidated, and the accuracy of character recognition can be improved.

[0027] Also, by irradiating infrared light, it is possible to read an IR image (an image visualized by irradiating infrared light). For example, an IR image formed for forgery prevention printed on various certificates, confidential documents, etc. is read by irradiating infrared light. If there is an IR image, copying is prohibited. Thereby, forgery can be prevented. Further, forgery prevention may be achieved by printing an IR image read by irradiating infrared light with a visible toner such as black toner to indicate that it is a copy.

[0028] As shown in FIG. 4, five reflecting mirrors 402a, 402b, 402c, 402d, and 402e are used in the integrated scanning unit 200. The reflected light reflected on the original document surface is reflected by the reflecting mirrors many times and finally reaches the image sensor 405. The amount of light reaching the image sensor 405 decreases according to the reflectance and the number of reflections of the reflecting mirror. As a result, there is a possibility that an IR image or a visible image of a desired quality cannot be read by the image sensor 405.

[0029] In order to make the amount of white light and infrared light reaching the image sensor 405 the desired amount of light, it is conceivable to increase the irradiation light amount of the white point light source 501 and the infrared point light source 701. However, there may be a case where it is not possible to secure the irradiation light amount necessary to make the amount of white light and infrared light reaching the image sensor 405 the desired amount of light due to the layout constraints of the lighting device.

[0030] In particular, since the integrated scanning unit 200 needs to use many reflecting mirrors in order to obtain an imaging distance within the frame 408 with limited layout, the number of reflections is large and the influence of the light amount reduction by the reflecting mirror is significant.

[0031] Also, in the integrated scanning unit 200, the angle of view of the first lens group 403 is wide. Therefore, in the case of a reflecting mirror having a high dependence of the reflectance on the reflection angle (the reflectance varies greatly depending on the reflection angle), the amount of light incident on the image sensor 405 will vary greatly in the main scanning direction.

[0032] FIG. 6 is a diagram for explaining the reflection angle in the main scanning direction of the reflecting mirror. When the half field angle of the first lens group 403 is θ, the reflection angles in the main scanning direction at both ends in the main scanning direction are the same as θ, which is the half field angle of the first lens group 403. The reflection angle in the main scanning direction at the center O1 in the main scanning direction is 0°, and the reflection angle in the main scanning direction at an intermediate position between the center O1 in the main scanning direction and the end in the main scanning direction indicated by the broken line in the figure is (θ / 2). Thus, in the range from 0° to the half field angle θ of the first lens group 403, as going towards the end in the main scanning direction, the reflection angle of the reflection mirror in the main scanning direction gradually increases. The larger the half field angle of the first lens group 403 is, the larger the difference in the reflection angles in the main scanning direction between the center in the main scanning direction and the end in the main scanning direction becomes.

[0033] As described above, in the integrated scanning unit 200, since the field angle of the first lens group 403 is wide, the difference in the reflection angles in the main scanning direction between the center in the main scanning direction and the end in the main scanning direction becomes large. As a result, when using a reflection mirror with a high angle dependence of reflectivity as the reflection mirror, the difference in the amount of light incident on the image sensor 405 at the center in the main scanning direction and the amount of light at the end in the main scanning direction becomes large, and there is a possibility that an image cannot be read well.

[0034] Therefore, in the present embodiment, at least one of the five reflection mirrors 402a, 402b, 402c, 402d, 402e is a surface reflection mirror (hereinafter referred to as a silver mirror) with a metal reflection film material being silver.

[0035] FIG. 7 is a diagram showing the reflectivities at each wavelength of a reflection angle of 5° and a reflection angle of 45° of an aluminum mirror with a protective film. The reflectivities at each wavelength were measured using a spectrophotometer. The maximum reflectivity rmax(5°) in the wavelength range of 450 nm to 900 nm at a reflection angle of 5° of the aluminum mirror with a protective film was approximately 90%, the minimum reflectivity rmin(5°) was approximately 82%, and the flatness ((minimum reflectivity / maximum reflectivity)×100%) was approximately 91%, which was less than 96%.

[0036] The maximum reflectance rmax(45°) in the wavelength range of 450 nm to 900 nm at a reflection angle of 45° for the aluminum mirror with a protective film is about 90%, and the minimum reflectance rmin(45°) is about 81%. The flatness ((minimum reflectance / maximum reflectance) × 100%) in the wavelength range of 450 nm to 900 nm at a reflection angle of 45° is about 90%, which is less than 96%.

[0037] As shown in FIG. 7, the aluminum mirror with a protective film had a maximum reflectance of about 90% in the wavelength range of 450 nm to 900 nm. Therefore, in the case of the aluminum mirror with a protective film, the amount of light decreases by 10% or more with one reflection. As a result, in the integrated scanning unit 200 of the present embodiment in which five reflecting mirrors 402a, 402b, 402c, 402d, and 402e are used, the amount of white light and infrared light reaching the image sensor 405 significantly decreases. Therefore, there is a possibility that the visible light image and the infrared light image cannot be read well.

[0038] In addition, the aluminum mirror with a protective film also has a flatness below 96%, which is poor, and has a poor reflectance for light in the wavelength range near 450 nm and for near-infrared light near 850 nm. Therefore, the amount of blue light and the amount of near-infrared light incident on the image sensor may be less than the desired amount of light, and there is a possibility that the blue image and the infrared image cannot be read well.

[0039] Also, the aluminum mirror with a protective film has a large difference in reflectance between when the reflection angle is 5° and when the reflection angle is 45° in the vicinity of a wavelength of 450 nm, and the reflectance characteristics are different between when the reflection angle is 5° and when the reflection angle is 45°. As a result, in the aluminum mirror with a protective film, in the vicinity of a wavelength of 450 nm, the lower the reflection angle, the higher the reflectance, so the blue image at the end of the main scanning direction becomes darker than at the center of the main scanning direction. As a result, the color tone of the read visible light image varies greatly between the center and the end of the main scanning direction, and the read quality of the visible light image is poor.

[0040] FIG. 8 is a diagram showing the reflectance at each wavelength of the reflection angles of 5° and 45° of the enhanced reflection aluminum mirror. The enhanced reflection aluminum mirror is obtained by applying a dielectric multilayer film to the surface of aluminum. As can be seen from the comparison between FIGS. 7 and 8, its reflectance is higher than that of the aluminum mirror with a protective film. However, for the enhanced reflection aluminum mirror as well, in the wavelength range of 450 nm to 900 nm, the reflectance of wavelengths near 450 nm and the reflectance of near-infrared light near 850 nm are less than 93%. Therefore, there is also a possibility that the aluminum mirror with a protective film cannot read blue images and infrared images well.

[0041] Also, the flatness of the enhanced reflection aluminum mirror at a reflection angle of 5° in the wavelength range of 450 nm to 900 nm is about 82%, and the flatness at a reflection angle of 45° is about 95%, which is also less than 96%.

[0042] Also, the enhanced reflection aluminum mirror has a high angle dependence near a wavelength of 450 nm, and the reflectance characteristics are different between when the reflection angle is 5° and when the reflection angle is 45°. In the enhanced reflection aluminum mirror, near a wavelength of 450 nm, the higher the reflection angle, the higher the reflectance. As a result, the blue image at the center of the main scanning direction becomes darker than that at the end of the main scanning direction. As a result, for the enhanced reflection aluminum mirror as well, the color tone of the visible light image varies greatly between the center and the end of the main scanning direction, and the reading quality of the visible light image is poor.

[0043] FIG. 9 is a diagram showing the reflectance at each wavelength of the silver mirror at a reflection angle of 5° and a reflection angle of 45°. As shown in FIG. 9, the silver mirror has a high reflectance of 93% or more at both reflection angles of 5° and 45° for all wavelengths in the range of 450 nm to 900 nm. Also, the flatness ((minimum reflectance / maximum reflectance) × 100%) in the wavelength range of 450 nm to 900 nm at both reflection angles of 5° and 45° is about 97%, and the flatness is also 96% or more. Thereby, a certain reflectance can be obtained from visible light to near-infrared light, and both visible light images and infrared light images can be read well.

[0044] Also, when the reflection angle is 5° and when the reflection angle is 45°, it has similar reflectance characteristics and low angular dependence. As a result, for all wavelengths from 450 nm to 900 nm, the amount of light incident on the image sensor 405 can be made uniform in the main scanning direction. Thereby, it is possible to suppress the occurrence of dark portions in the read image in the main scanning direction. Also, it is possible to suppress the difference in color tone between the end and the center of the read visible light image in the main scanning direction, and the difference in brightness between the end and the center of the infrared light image in the main scanning direction. Therefore, the visible light image and the infrared light image can be read well. Note that the above-mentioned similar reflectance characteristics mean that the difference between the reflectance at a reflection angle of 5° and the reflectance at a reflection angle of 45° for each wavelength in the range of 450 nm to 900 nm is 7% or less.

[0045] FIG. 10 is a diagram showing the reflectance of another silver mirror at each wavelength. This silver mirror also has a high reflectance of 93% or more, and the flatness ((minimum reflectance / maximum reflectance) × 100%) is 98% or more, and a constant reflectance can be obtained from visible light to near-infrared light.

[0046] FIG. 11 is a graph showing the output of the image sensor at each position in the main scanning direction when all the reflection mirrors are aluminum mirrors and when half of these aluminum mirrors are replaced with silver mirrors. As can be seen from FIG. 11, by using a silver mirror, the sensor output of the image sensor 405 can be increased compared to the case where all the reflection mirrors are aluminum mirrors, and the original image can be read well. Thus, by making at least one of the five reflection mirrors 402a, 402b, 402c, 402d, 402e a silver mirror, it is possible to suppress a decrease in the amount of visible light and near-infrared light reaching the image sensor 405. Thereby, the amount of light incident on the image sensor 405 can be made more than desired. Also, by having high flatness, the amount of light does not decrease at a specific wavelength. Thereby, the visible light image and the infrared light image can be read well.

[0047] Since the silver mirror is more expensive than the aluminum mirror and the enhanced reflection aluminum mirror, it is preferable that among the reflecting mirrors 402a, 402b, 402c, 402d, 402e, the reflecting mirror with a smaller reflection area is a silver mirror. In the present embodiment, the reflecting mirror 402e arranged at the most downstream in the light traveling direction is the shortest in the main scanning direction and has the smallest reflection area. Therefore, it is preferable that this reflecting mirror 402e is a silver mirror. In this way, by making at least the reflecting mirror with the smallest reflection area among the plurality of reflecting mirrors a silver mirror, an increase in the cost of the apparatus can be suppressed.

[0048] FIG. 12 is a schematic view showing a scanner unit 110 of an image reading unit of a differential mirror system. As shown in FIG. 12, a first carriage 201 and a second carriage 202 are provided in a scanner unit 110 of an image reading unit of a differential mirror system. The first carriage 201 includes an illumination device 401 and a first reflecting mirror 201a. The second carriage 202 includes a second reflecting mirror 202a and a third reflecting mirror 202b.

[0049] When image reading starts, the illumination device 401 irradiates a document placed on the contact glass with white light and infrared light, and moves the first carriage 201 from the left side to the right side in the figure. Further, the second carriage 202 is moved to the right side in the figure at a speed half that of the first carriage 201. In this way, the second carriage 202 moves in the same direction as the first carriage 201 at half the speed of the first carriage 201 so that the optical path length of the light beam from the document surface to the imaging lens 203 does not change.

[0050] In the process of moving the first and second carriages 201, 202 from the left side to the right side in the figure at a speed ratio of 2:1, the light emitted from the illumination device 401 is reflected by the document placed on the contact glass 57. The reflected light from the document is guided to the imaging lens 203 via the first reflecting mirror 201a, the second reflecting mirror 202a, and the third reflecting mirror 202b, forms an image on the image sensor 405, and the document image is read.

[0051] In this differential mirror type image reading unit as well, at least one of the three reflecting mirrors is a silver mirror. As a result, at least one of the three reflecting mirrors can be a mirror having a high reflectance of 93% or more for all wavelengths in the wavelength range of 450 nm to 900 nm, at both reflection angles of 5° and 45°. Further, at least one of the three reflecting mirrors can be a mirror having flatness ((minimum reflectance / maximum reflectance) × 100%) of 96% or more in the wavelength range of 450 nm to 900 nm.

[0052] As a result, a decrease in the amount of light incident on the image sensor 405 can be suppressed, and a visible light image and an infrared light image of the document can be read well. Also, since the dependency on the reflection angle is low, it is possible to suppress the occurrence of dark portions in the main scanning direction in the read image, and a visible light image and an infrared light image of the document can be read well.

[0053] As described above, the preferred embodiments of the present invention have been described. However, the present invention is not limited to such specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims, unless otherwise particularly limited in the above description.

[0054] In the present embodiment, at least one of the plurality of reflecting mirrors is a silver mirror. However, the present invention is not limited to a silver mirror, and at least one mirror having the following reflection characteristics may be arranged. That is, it is a mirror having a reflection characteristic in which the reflectance at a reflection angle of 45° of light in the wavelength range of 450 nm or more and 900 nm or less is 93% or more, or a reflection characteristic in which the flatness of the reflectance of light in the wavelength range of 450 nm or more and 900 nm or less is 96% or more.

[0055] What has been described above is an example, and specific effects are exhibited for each of the following aspects. (Aspect 1) An image reading apparatus such as a scanner unit 10 including a visible light source such as a white point light source 501 that irradiates a document with visible light, an infrared light source such as an infrared point light source 701 that irradiates the document with infrared light, and a plurality of mirrors installed on the optical paths of the visible light and the infrared light from the document to an imaging means such as an image sensor 405. At least one of the plurality of mirrors is a mirror having a reflectance of 93% or more at a reflection angle of 45° for light in a wavelength range of 450 nm or more and 900 nm or less. Visible light in the range of 450 nm to 780 nm and infrared light (near-infrared light) in the range of 800 to 900 nm reflected from the document are reflected by the plurality of mirrors multiple times before reaching the imaging means. The amount of visible light and infrared light decreases according to the reflectance and the number of reflections of the mirror, and there was a possibility that the amount of at least one of the visible light and the infrared light incident on the imaging means would be less than the amount of light required for the imaging means to read. In contrast, in Embodiment 1, by making at least one of the plurality of mirrors a mirror having a reflectance of 93% or more at a reflection angle of 45° for light in a wavelength range of 450 nm or more and 900 nm or less, it is possible to suppress the decrease in the amount of visible light and infrared light due to the reflection of the mirror. As a result, it is possible to suppress the amount of visible light and infrared light incident on the imaging means from falling below the amount of light required for the imaging means to read, and the imaging means can read the visible light image and the infrared light image of the document well.

[0056] (Embodiment 2) An image reading apparatus such as a scanner unit 10 including a visible light source such as a white point light source 501 that irradiates a document with visible light, an infrared light source such as an infrared point light source 701 that irradiates the document with infrared light, and a plurality of mirrors installed on the optical paths of the visible light and the infrared light from the document to an imaging means such as an image sensor 405. At least one of the plurality of mirrors is a mirror having a flatness of reflectance ((minimum reflectance / maximum reflectance) × 100%) of 96% or more at a reflection angle of 45° for light in a wavelength range of 450 nm or more and 900 nm or less. According to this, as described in the embodiment, the amount of light in the wavelength range of 450 nm or more and 900 nm or less incident on the imaging means such as the image sensor 405 can be made uniform, and a visible image and an infrared image of a good document can be read.

[0057] (Aspect 3) In Aspect 1, the flatness of the reflectance ((minimum reflectance / maximum reflectance) × 100%) of the mirror with a reflectance of 93% or more at a reflection angle of 45° for light in the wavelength range of 450 nm or more and 900 nm or less is 96% or more. According to this, as described in the embodiment, the amount of light in the wavelength range of 450 nm or more and 900 nm or less incident on the imaging means such as the image sensor 405 can be made uniform, and a visible image and an infrared image of a good document can be read.

[0058] (Aspect 4) In any one of Aspects 1 to 3, the reflectance characteristics at a reflection angle of 5° and the reflectance characteristics at a reflection angle of 45° in the wavelength range of 450 nm or more and 900 nm or less of the mirror with a reflectance of 93% or more or the mirror with a flatness of 96% or more are the same. According to this, as described in the embodiment, the dependence on the reflection angle of the mirror can be suppressed to a low level. Thereby, even if a wide-angle lens is used and the difference between the reflection angle (0°) in the main scanning direction at the center in the main scanning direction of the mirror and the reflection angle (half angle of the lens) in the main scanning direction at the end in the main scanning direction is large, the difference between the amount of light after reflection at the center in the main scanning direction and the amount of light after reflection at the end in the main scanning direction can be reduced. Thereby, the amount of light in the wavelength range of 450 nm or more and 900 nm or less incident on the imaging means such as the image sensor can be made uniform in the main scanning direction, and the brightness in the main scanning direction of the read image can be made uniform. Also, in the visible light image, the color tone between the center and the end in the main scanning direction can be made uniform.

[0059] (Aspect 5) In any one of Aspects 1 to 4, the mirror with a reflectance of 93% or more or the mirror with a flatness of 96% or more is a surface reflection mirror of a metal reflection film material of silver. According to this, as described in the embodiment, the reflectance of light in the wavelength range of 450 nm or more and 900 nm or less can be made 93% or more, and the flatness of the reflectance in the above wavelength range can be made 93% or more. Furthermore, the reflectance at a reflection angle of 5° can be made the same as the reflectance at a reflection angle of 45°.

[0060] (Aspect 6) In any of Aspects 1 to 5, among the plurality of mirrors, the mirror with a reflectance of 93% or more or the mirror with a flatness of 93% or more has the smallest mirror area. According to this, as described in the embodiment, a mirror with a reflectance of 93% or more such as a silver mirror or a mirror with a flatness of 93% or more is expensive. Therefore, by making the mirror with the smallest mirror area among the plurality of mirrors a mirror with a reflectance of 93% or more or a mirror with a flatness of 96% or more, an increase in the cost of the apparatus can be suppressed.

[0061] (Aspect 7) In any of Claims 1 to 6, a visible light source such as a white point light source 501, an infrared light source such as an infrared point light source 701, a plurality of mirrors, imaging means such as an image sensor 405, and a lens for forming an image of the original image on the light receiving surface of the imaging means are arranged on a frame 408 movable along the original surface. According to this, as described in the embodiment, in the limited space of the frame 408, in order to obtain an imaging distance, the number of mirrors is larger than that in the differential mirror method shown in FIG. 12. Therefore, the influence of the light amount reduction by the mirrors is larger than that in the differential mirror method. In addition, it is necessary to arrange the lens in the limited space of the housing, and the lens cannot be enlarged, and the half angle of view of the lens becomes larger than that in the differential mirror method. As a result, the difference in the reflection angle in the main scanning direction between the center and the end in the main scanning direction becomes large. Therefore, by making one of the plurality of mirrors a mirror with a reflectance of 93% or more or a mirror with a flatness of 96% or more, the light amount reduction by the mirrors can be effectively suppressed, and the light amount incident on the imaging means in the main scanning direction can be made uniform.

[0062] (Aspect 8) An image reading apparatus such as a scanner unit 10 includes a visible light source such as a white point light source 501 that irradiates an original with visible light, an infrared light source such as an infrared point light source 701 that irradiates the original with infrared light, and a plurality of mirrors installed on the optical paths of visible light and infrared light from the original to imaging means such as an image sensor 405. At least one of the plurality of mirrors is a metal reflective film material such as a silver mirror, which is a surface reflection mirror of silver. According to this, as described in the embodiment, one of the plurality of mirrors is a highly reflective mirror having a reflectivity of 93% or more for light in a wavelength region of 450 nm or more and 900 nm or less, a flatness of the reflectivity in the wavelength region of 93% or more, and the same reflectivity at a reflection angle of 5° and a reflection angle of 45°. Thereby, the visible light image and the infrared light image of the original can be read well.

[0063] (Aspect 9) In an image forming apparatus including image reading means such as an image reading apparatus 130 that reads an image of an original and image forming means that forms an image on a sheet, any one of the image reading apparatuses according to Aspects 1 to 8 is used as the image reading means. According to this, a high-quality image can be copied.

Explanation of Signs

[0064] 1: Image forming apparatus 10: Scanner unit 10a: Housing unit 10b: Scanner cover 51: Guide rail 52: Guide rod 57: Contact glass 58: Slit glass 100: Image forming section 110: Scanner unit 120: ADF 130: Image reading apparatus 200: Integrated scanning unit 401: Lighting device 402a: Reflective mirror 402b: Reflective mirror 402c: Reflective mirror 402d: Reflective mirror 402e: Reflective mirror 403: First lens group 404: Second lens group 405: Image sensor 406: Drive circuit board 407: Lens band 408: Frame 409: Lens pedestal 410: Fixed bracket 413: Lens fixing bracket 414: Document 501: White point light source 502: Substrate 502a: Mounting surface 503: Light guide 503a: Emission surface 701: Infrared point light source O1: Center in the main scanning direction rmax: Maximum reflectance rmin: Minimum reflectance θ: Half angle of view

Prior art documents

Patent documents

[0065]

Patent Document 1

Claims

1. A visible light source that irradiates a document with visible light, An infrared light source that irradiates the document with infrared light, In an image reading apparatus comprising a plurality of mirrors installed on the optical paths of visible light and infrared light from the document to the imaging means, An image reading apparatus, characterized in that at least one of the plurality of mirrors is a mirror having a reflectance of 93% or more at a reflection angle of 45° for light in a wavelength range of 450 nm or more and 900 nm or less.

2. A visible light source that irradiates a document with visible light, An infrared light source that irradiates the document with infrared light, In an image reading apparatus comprising a plurality of mirrors installed on the optical paths of visible light and infrared light from the document to the imaging means, An image reading apparatus, characterized in that at least one of the plurality of mirrors is a mirror having a flatness ((minimum reflectance / maximum reflectance) × 100%) of 96% or more for light in a wavelength range of 450 nm or more and 900 nm or less at a reflection angle of 45°.

3. In the image reading apparatus according to Claim 1, An image reading apparatus, characterized in that the flatness ((minimum reflectance / maximum reflectance) × 100%) of the reflectance at a reflection angle of 45° for light in a wavelength range of 450 nm or more and 900 nm or less of the mirror having a reflectance of 93% or more is 96% or more.

4. In the image reading apparatus according to Claim 1 or 2, An image reading apparatus, characterized in that the reflectance characteristics at a reflection angle of 5° and the reflectance characteristics at a reflection angle of 45° in a wavelength range of 450 nm or more and 900 nm or less of the mirror having a reflectance of 93% or more or the mirror having a flatness of 96% or more are the same.

5. In the image reading apparatus according to Claim 1 or 2, An image reading apparatus, characterized in that the mirror having a reflectance of 93% or more or the mirror having a flatness of 96% or more is a surface reflection mirror of a metal reflection film material of silver.

6. In the image reading apparatus according to Claim 1 or 2, An image reading apparatus, characterized in that the mirror having a reflectance of 93% or more or the mirror having a flatness of 96% or more has the smallest mirror area among the plurality of mirrors.

7. In the image reading apparatus according to Claim 1 or 2, An image reading apparatus, characterized in that the visible light source, the infrared light source, the plurality of mirrors, the imaging means, and a lens that forms an image of the document image on the light receiving surface of the imaging means are arranged on a frame movable along the document surface.

8. A visible light source that irradiates a document with visible light, An infrared light source that irradiates the original document with infrared light, In an image reading apparatus including a plurality of mirrors installed on the optical path of visible light and infrared light from the original document to the imaging means, An image reading apparatus, wherein at least one of the plurality of mirrors is a surface reflection mirror whose metal reflection film material is silver.

9. An image forming apparatus including image reading means for reading an image of an original document, And image forming means for forming an image on a sheet, The image forming apparatus, wherein the image reading apparatus according to claim 1, 2 or 8 is used as the image reading means.

Images