JP2011193205A - Illumination optical system and image reader - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an illumination optical system capable of suppressing generation of color unevenness in the illumination optical system using a white LED light source having an LED chip, and a first phosphor which emits light by being excited by light of the LED chip as a light source and an image reader using the same. <P>SOLUTION: The illumination optical system is constituted so that a curved mirror 22 is used, a dichroic coat layer 22D (first reflection part) is formed on the front surface 22b of the curved mirror 22, a reflection layer 22M (second reflection part) is formed on the rear surface 22c of the curved mirror 22, and the illumination optical system has long pass filter characteristics as the dichroic coat layer 22D. Furthermore, since curvature radius R2 of the rear surface 22c of the curved mirror 22 is considered as the one shorter than curvature radius R1 of the front surface 22b of the curved mirror 22, it becomes possible to irradiate an irradiated part 24 by making blue right and yellow light into approximately equivalent illuminance, and to appropriately suppress the generation of the color unevenness by the curved mirror 22. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an illumination optical system using a white LED (Light Emitting Diode) as a light source and an image reading apparatus using the illumination optical system.

  In recent years, LEDs have been actively developed, and the brightness of LED elements has been rapidly increasing. LEDs generally have advantages such as long life, high efficiency, and monochromatic light emission, and are expected to be applied in many lighting fields.

  The LED is used as an illumination optical system of an image reading apparatus such as a digital copying machine or an image scanner. As an illumination optical system for such an image reading apparatus, a method of illuminating light from a white LED in which a plurality of LEDs are arranged in parallel with the main scanning direction of the document in a line shape on the document surface is employed. As the white LED, a type called a so-called pseudo white LED, which is formed of a blue light emitting LED chip called a white LED package and a yellow phosphor, is currently used. The blue light-emitting LED chip is smaller than the phosphor, and is placed inward of the document surface than the phosphor, so the light that illuminates the document is distributed in the sub-scanning direction with blue light and yellow light. Therefore, color unevenness occurs in the sub-scanning direction.

  The occurrence of this color unevenness will be described with reference to FIG. FIG. 15 is a diagram for explaining an illuminance distribution (a) in an irradiated portion by a blue light emitting LED chip and an illuminance distribution (b) by a yellow phosphor in an illumination optical system using a conventional white LED light source.

  Since the blue light emitting LED chip 11B is a relatively small point light source as shown in FIG. 15A, the blue light emitted from the blue light emitting LED chip 11B is reflected by the curved mirror 12. The irradiated part 14 can be illuminated by the light 13B becoming parallel light. At this time, the blue light of the irradiated portion 14 shows an illuminance distribution 15B as shown in FIG. 15A, shows a large illuminance at the center of the irradiated portion 14 in the sub-scanning direction B, and the irradiated portion 14 A small illuminance is shown at the end in the sub-scanning direction B. On the other hand, the yellow light emitted from the yellow phosphor 11Y becomes a light beam excited by the blue light emitted from the blue light emitting LED chip, but becomes a surface light source 11Y having a larger light emitting area than the blue light emitting LED. As shown in FIG. 15B, reflected light 13Ya, 13Yb, and 13Yc whose reflected light travels in different directions depending on the position emitted from the surface light source 11Y become diffused in the sub-scanning direction B. As a result, the illuminance distribution of yellow light in the irradiated portion 14 is diffused in the sub-scanning direction B of the irradiated portion 14 as indicated by reference numeral 15Y, and yellow at the edge of the irradiated portion 14 in the sub-scanning direction. And color unevenness occurs in the sub-scanning direction B. Such a problem is that even in a high color rendering LED composed of a blue light emitting LED chip and a phosphor emitting green light and red light, the illuminance distribution of blue light is significantly different from the illuminance distribution of green light and red light. Color unevenness occurs in the direction. Note that the same color unevenness problem occurs in a surface mount type in which an LED chip is covered with a phosphor or a shell type to which a lens is added as an LED package for housing an LED.

  In order to cope with such a problem of color unevenness, a mask member having a window corresponding to the LED element is provided for the light source, and the light source unevenness is reduced by narrowing the illumination angle of the light source at the window of the mask member. It has been proposed to reduce color unevenness while suppressing color distortion (see, for example, Patent Document 1). However, in the thing of this patent document 1, since a part of light radiate | emitted from the light source will be shielded with a mask member, the problem that the utilization efficiency of light falls will be caused.

  In order to increase the light utilization efficiency, two reflecting mirrors having a concave curved inner surface in the cross section parallel to the longitudinal direction of the light source are provided on both sides of the reading optical axis in the vicinity of the light source. It has been proposed that the inner surfaces of the light sources are provided as desired, and the irradiation light from the light sources is concentratedly reflected on the reading surface of the read document (see, for example, Patent Document 2). However, in the thing of this patent document 2, using each LED which light-emits the light of the hue of red, green, and blue as a light source, the light radiate | emitted from these LED is made into a concave curve shape on the inner surface. When the white LED light source composed of blue light emitting LED chip and yellow phosphor is used instead of the light source of LED emitting light of red, green and blue hues because it is reflected by the formed reflecting mirror Cannot solve the problem of color unevenness.

  The present invention has been made in view of the above circumstances, and is an LED chip that emits light having a first wavelength λ1 as a peak wavelength, and is excited by the light of the LED chip and longer than the first wavelength. Illumination optical system capable of suppressing occurrence of color unevenness in an illumination optical system using a white LED light source having a first phosphor that emits light with the second wavelength λ2 as a peak as a light source, and an image using the same An object is to provide a reader.

In order to solve the above-mentioned problem, the invention according to claim 1 is directed to an LED chip that emits light having a peak wavelength of the first wavelength λ1 and longer than the first wavelength when excited by the light of the LED chip. Illumination optical system having a light source that uses one or more white LED light sources having a first phosphor that emits light with a second wavelength λ2 as a peak, and a curved mirror that deflects light from the light sources to an irradiated portion Because
The curved mirror includes a first reflecting portion and a second reflecting portion in order from an incident direction of light from the light source, and the first reflecting portion has the first wavelength λ1 and the second wavelength. It has a wavelength selectivity with respect to λ2.

The invention of claim 2 is the illumination optical system according to claim 1,
The wavelength selectivity is made by reflecting the light of the first wavelength λ1 with a reflectance of 0.5 or more and transmitting the light of the second wavelength λ2 with a reflectance of less than 0.5, The curved mirror includes the second reflecting portion having a second radius of curvature R2 shorter than the radius of curvature R1 of the first reflecting portion.

The invention of claim 3 is the illumination optical system according to claim 1,
The wavelength selectivity is made by reflecting the light of the second wavelength λ2 with a reflectance of 0.5 or more and transmitting the light of the first wavelength λ1 with a reflectance of less than 0.5, The curved mirror includes the second reflecting portion having a second radius of curvature R2 substantially the same as the radius of curvature R1 of the first reflecting portion.

According to a fourth aspect of the present invention, in the illumination optical system according to any one of the first to third aspects,
The wavelength selectivity is achieved by forming a dichroic coat layer on the first reflecting portion.

The invention according to claim 5 is the illumination optical system according to any one of claims 1 to 4,
The light having the first wavelength is blue light, and the first phosphor is a yellow phosphor.

  The invention according to claim 6 is the illumination optical system according to any one of claims 1 to 4, wherein the white LED light source is excited by light of the LED chip and has a third wavelength λ3 as a peak. It has the 2nd fluorescent substance which light-emits, and it is set as the said 2nd wavelength (lambda) 2 <3rd wavelength (lambda) 3.

  The invention according to claim 7 is the illumination optical system according to any one of claims 1 to 6, wherein the wavelength selectivity has a cutoff wavelength at which the reflectance is reduced by half as the first wavelength λ1. The first reflection unit is set between two wavelengths λ2.

The invention according to claim 8 is the illumination optical system according to claim 6,
The light of the first wavelength is blue light, the first phosphor is a green light-emitting phosphor, and the second phosphor is a red light-emitting phosphor.

Further, the invention of claim 9 is directed to an illumination optical system that irradiates light to the subject, a contact glass on which the subject is placed, and a plurality of mirrors that reflect light emitted from the illumination optical system. An image reading apparatus comprising: a lens that focuses the light reflected by the plurality of mirrors on an image sensor;
The illumination optical system is the illumination optical system according to any one of claims 1 to 8, wherein a plurality of the white LED light sources are arranged in a main scanning direction of image reading.

The invention of claim 10 is the image reading apparatus according to claim 9, wherein
A reflecting mirror for reflecting the light beam of the illumination optical system and irradiating the object to be photographed with the reading optical axis of the illumination optical system interposed therebetween is provided.

The invention according to claim 11 is the image reading apparatus according to claim 10,
The reflecting mirror includes a third reflecting portion and a fourth reflecting portion in order from the incident direction of light from the light source of the illumination optical system, and the third reflecting portion includes the first wavelength λ1 and the fourth reflecting portion. It has a wavelength selectivity with respect to the second wavelength λ2.

  According to a twelfth aspect of the present invention, in the image reading apparatus according to any one of the ninth to eleventh aspects, the illumination optical system is disposed so as to face the reading optical axis, and the respective illumination optics. Reflected light from a subject to be emitted from the system is reflected on the reading optical axis.

  According to the present invention, the curved mirror has a first reflecting portion and a second reflecting portion in order from an incident direction of light from the light source, and the first reflecting portion has the first wavelength λ1. And having the wavelength selectivity with respect to the second wavelength λ2, the LED chip that emits light having the first wavelength λ1 as a peak wavelength, and excited by the light of the LED chip, And an illumination optical system capable of suppressing the occurrence of color unevenness in an illumination optical system using a white LED light source having a first phosphor that emits light with a second wavelength λ2 having a long wavelength as a peak. The image reading apparatus can be provided.

It is a longitudinal cross-sectional view which shows schematic structure of the light source used with the illumination optical system which concerns on 1st Embodiment by this invention. It is sectional drawing which shows schematic structure of the illumination optical system which concerns on 1st Embodiment by this invention, (a) is a figure which shows the light ray locus from blue light emission LED, (b) is the light ray locus of yellow light. FIG. It is a graph which shows the relationship between the light emission spectrum of the light radiate | emitted with the light source shown in FIG. 1, and spectral intensity, and the relationship between the reflectance of the dichroic coat layer used in 1st Embodiment, and the wavelength of light. It is a longitudinal cross-sectional view which shows schematic structure of the light source used with the illumination optical system which concerns on 2nd Embodiment by this invention. It is a graph which shows the relationship between the light emission spectrum and spectral intensity of light radiate | emitted with a high color rendering type white LED light source, and the relationship between the reflectance of the dichroic coat layer used in 1st Embodiment, and the wavelength of light. It is sectional drawing which shows schematic structure of the illumination optical system which concerns on 3rd Embodiment by this invention, (a) is a figure which shows the light ray locus from blue light emission LED, (b) is the light ray locus of yellow light. FIG. It is a graph which shows the relationship between the light emission spectrum of the light radiate | emitted with the white LED light source shown in FIG. 1, and a spectral intensity, and the relationship between the reflectance of the dichroic coat layer used in 1st Embodiment, and the wavelength of light. 1 is a longitudinal sectional view illustrating a schematic configuration of an image reading apparatus according to a first embodiment of the present invention. FIG. 9 is a longitudinal sectional view showing a schematic configuration of a curved mirror used in the image reading apparatus according to the second embodiment of the present invention. FIG. 9A shows a translucent substrate having a dichroic coat layer formed on the surface thereof. The exploded sectional view of the curved mirror decomposed | disassembled into the board | substrate which formed the reflection layer on the surface, (b) is sectional drawing of the curved mirror which joined the translucent board | substrate shown to (a), and a board | substrate. It is a longitudinal cross-sectional view which shows schematic structure of the image reading apparatus which concerns on 2nd Embodiment by this invention. It is a longitudinal cross-sectional view which shows schematic structure of the image reader which concerns on 3rd Embodiment by this invention. It is a longitudinal cross-sectional view which shows schematic structure of the image reader which concerns on 4th Embodiment by this invention. It is a longitudinal cross-sectional view which shows schematic structure of the image reader which concerns on 5th Embodiment by this invention. It is a longitudinal cross-sectional view which shows schematic structure of the image reading apparatus which concerns on 6th Embodiment by this invention. It is a figure explaining the illumination intensity distribution (a) in the to-be-irradiated part by the blue light emission LED chip in the illumination optical system using the conventional white LED light source, and the illumination intensity distribution (b) by yellow fluorescent substance.

  Hereinafter, an illumination optical system according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a longitudinal sectional view showing a schematic configuration of a light source used in the illumination optical system according to the first embodiment of the present invention. FIG. 2 is a cross-sectional view showing a schematic configuration of the illumination optical system according to the first embodiment of the present invention. FIG. 2A is a view showing a ray trajectory from a blue light emitting LED, and FIG. FIG. FIG. 3 is a graph showing the relationship between the emission spectrum of the light emitted from the light source shown in FIG. 1 and the spectral intensity, and the relationship between the reflectance of the dichroic coat layer used in the first embodiment and the wavelength of the light. .

  As the white LED light source 21 used in the illumination optical system 20 according to the first embodiment of the present invention, as shown in FIG. 1, a blue light emitting LED chip 21B (for example, InGaN) that emits blue light to a resin package 21a is used. A blue light emitting LED chip) is included, and the blue light emitting LED chip 21B is covered with a yellow light emitting phosphor (for example, YAG: Ce) 21Y that emits yellow light in a yellow wavelength band. What is used is used. When a current is passed through the blue light emitting LED chip 21B, blue light having a peak wavelength of the first wavelength λ1 is emitted and emitted at a predetermined angle α. In this case, the chip diameter d1 of the blue light emitting LED chip 21B that emits blue light is 0.2 mm. The diameter d2 of the yellow light-emitting phosphor 21Y, which is the first phosphor that is excited by the blue light thus emitted and emits light with the second peak wavelength λ2 longer than the first wavelength λ1 as a peak. Yellow light is emitted from the (2 mm) light emitting surface, and white light including a wavelength in the visible light region having a wavelength of 400 nm to 700 nm is emitted from the light source 21.

  An illumination optical system of an image reading apparatus (described later) using such a light source 21 will be described with reference to FIGS. As shown in FIG. 2A, the illumination optical system 20 reflects the blue light emitted from the blue light emitting LED chip 21B that constitutes one of the white LED light sources, and reflects the reflected light 25 on the contact glass 23. A curved mirror 22 that irradiates the irradiated portion 24 is provided. The curved mirror 22 has a concave cylindrical surface 22b and a convex cylindrical lens rear surface 22c as shown in FIG. 2A, and the front surface 22b and the rear surface 22c are placed on the contact glass 23. A translucent substrate 22a made of glass having a thickness of 3.2 mm and extending in the main scanning direction of an object to be photographed such as a document to be placed is provided. The curved mirror 22 is formed with a dichroic coating layer 22D having a thickness of about 15 μm along the curved surface shape on the surface 22b of the translucent substrate 22a, and is coated with aluminum having an inner surface along the back surface shape on the back surface 22c. It has a light reflection layer 22M.

The dichroic coat layer 22D has the following characteristics. As shown in FIG. 3, the emission spectrum 111 of the white LED light source 21 used in this embodiment has a wavelength range of blue light having a first wavelength λ1 emitted from the blue light emitting LED chip 21B as a peak wavelength, A wavelength 111a having a minimum spectral intensity exists between the wavelength range of yellow light having the second wavelength λ2 emitted from the yellow light emitting phosphor 21Y. The dichroic coat layer 22D is set so as to have a wavelength characteristic 112 in the vicinity of the minimum wavelength 111a so as to have a cutoff wavelength 113 at which the reflectance 112 of the dichroic coat layer 22D is halved. That is, a characteristic that a light having a wavelength shorter than 490 nm has a high reflectance of 0.5 or more and a light having a wavelength longer than 490 nm has a high transmittance (a low reflectance having a reflectance of less than 0.5) (so-called long pass). Filter). Therefore, the dichroic coat layer 22D reflects blue light having the first peak wavelength λ1 and transmits yellow light having the second peak wavelength λ2, and the wavelength that can be selected for reflection and transmission according to the wavelength of the light. Selectivity. The dichroic coat layer 22D having such characteristics can be easily obtained by forming a multilayer body in which materials having different refractive indexes (for example, SiO ₂ and TiO ₂ ) are periodically laminated in units of several tens of nanometers. it can.

  The curvature radius R1 of the surface 22b of the curved mirror 22 is such that the blue light emitted from the blue light emitting LED chip 21B is formed on the surface 22b of the curved mirror 22 as shown in FIG. It is formed so as to have a radius of curvature that is reflected by the layer 22 </ b> D and that the reflected light 25 becomes substantially parallel light and irradiates the irradiated portion 24. For example, in this case, the radius of curvature R1 of the surface 22b of the curved mirror 22 is 17.8 mm. Accordingly, the irradiated portion 24 is irradiated with blue light with high efficiency.

  On the other hand, yellow light, which is another component of the white LED light source 21, is emitted as a surface light source having a predetermined diameter (2 mm in this example) as shown in FIG. Then, as shown in FIG. 3 described above, the yellow light is transmitted while being refracted by the dichroic coat layer 22D, reflected by the reflective layer 22M formed on the back surface 22b of the curved mirror, and transmitted through the dichroic coat layer 22D. The irradiated portion 24 is irradiated as reflected light 26. In this case, as shown in FIG. 2B, the radius of curvature R2 of the back surface 22c of the curved mirror 22 that forms the inner surface of the reflective layer 22M is set so that the reflected light 26 is condensed on the irradiated portion 24. ing. For example, in this example, it is 17.8 mm. Accordingly, the diffusion of yellow light irradiated to the irradiated portion 24 in the sub-scanning direction B is suppressed, and the illuminance of blue light is substantially equal, and the occurrence of color unevenness can be suppressed.

  In the same way as when manufacturing a cylindrical lens, the curved mirror 22 polishes one surface of the translucent substrate 22a to process the first cylindrical surface, and then polishes the opposite surface to polish the desired cylindrical surface. It can be easily manufactured by processing the surface. Further, a dichroic coat layer 22D made of a dielectric multilayer film capable of obtaining a desired long pass filter characteristic is formed on the front surface 22b of the translucent substrate 22a, and aluminum is deposited on the back surface 22c on the opposite side to reflect it. Layer 22M can be obtained.

  As described above, in the illumination optical system 20 according to the first embodiment, the curved mirror 22 is used, and the dichroic coat layer 22D (first reflecting portion) is formed on the surface 22b of the curved mirror 22, and the curved mirror A reflection layer 22M (second reflection portion) is formed on the back surface 22c of the film 22 so that the dichroic coat layer 22D has a long-pass filter characteristic. Further, since the curvature radius R2 of the back surface 22c of the curved mirror 22 is set to be shorter than the curvature radius R1 of the front surface 22b of the curved mirror 22, the curved mirror 22 can receive blue light and yellow light with substantially the same illuminance. It is possible to irradiate the irradiation unit 24, and it is possible to appropriately suppress the occurrence of color unevenness.

  In addition, as the white LED light source, there are a surface mount type including a blue light emitting LED and a bullet type equipped with a lens, and the function and effect of the dichroic coat layer 22D are achieved with either type. It is possible to reduce color unevenness in both types. Further, the cylindrical lens surface may be a free-form surface.

  Next, an illumination optical system according to a second embodiment of the present invention will be described with reference to FIGS. FIG. 4 is a longitudinal sectional view showing a schematic configuration of a light source used in the illumination optical system according to the second embodiment of the present invention. FIG. 5 is a graph showing the relationship between the emission spectrum and spectral intensity of light emitted from a high color rendering white LED light source, and the relationship between the reflectance of the dichroic coat layer used in the first embodiment and the wavelength of light. It is.

  The illumination optical system 201 according to the second embodiment is basically different from the illumination optical system 20 according to the first embodiment described above in the white LED light source. As shown in FIG. 4, in the white LED light source 202, a blue light emitting LED chip 202B that emits blue light is included in a resin package 202a, and the blue light emitting LED chip 202B has a green wavelength band around the blue light emitting LED chip 202B. A green light-emitting phosphor 202G that emits light and a red light-emitting phosphor 202R that emits red light in the red wavelength band are used. When a current is passed through the blue light emitting LED chip 202B, blue light having a peak wavelength of the first wavelength λ1 is emitted and emitted at a predetermined angle α. In this case, the chip diameter d1 of the blue light emitting LED chip 21B that emits blue light is 0.2 mm. A green light emitting phosphor 202G, which is a first phosphor that emits green light having a second peak wavelength λ2 longer than the first wavelength λ1 when excited by the blue light thus emitted, and Green light and red light are emitted from a light emitting surface 202b having a diameter d2 (2 mm) of a red light emitting phosphor 202R that is a second phosphor that emits red light having a peak at the third peak wavelength λ3. High-color-rendering type white light including wavelengths in the visible light region of 400 nm to 800 nm is emitted from the light source 202. In this case, as the green high-emitting phosphor 202G and the red light-emitting phosphor 202R, for example, a well-known phosphor that emits green light and red light when excited by blue light emitted from a blue light-emitting LED using InGaN, respectively. A phosphor can be used.

  Such a white LED light source 202 has a wavelength spectrum 121 as shown in FIG. 5, and a blue light wavelength region having a first wavelength λ1 emitted from the blue light emitting LED chip 202B as a peak wavelength, There is a wavelength 121a at which the spectral intensity is minimal between the wavelength range of yellow light having the second wavelength λ2 emitted from the green light emitting phosphor 202G and the third wavelength λ3 emitted from the red light emitting phosphor 202R. Exists. In the illumination optical system 201 according to the second embodiment, as in the illumination optical system 20 of the first embodiment described above, as shown in FIG. 2A, the blue color constituting one of the white LED light sources is formed. The blue light emitted from the light-emitting LED chip 201B (shown as 21B in FIG. 2A) is reflected to reflect the reflected light 25 (see FIG. 2A) of the contact glass 23 (see FIG. 2A). A curved mirror 22 (see FIG. 2A) that irradiates the irradiated portion 24 (see FIG. 2A) is provided. The curved mirror 22 has a concave cylindrical surface 22b (see FIG. 2A) and a convex cylindrical lens-shaped back surface 22c (see FIG. 2A), as shown in FIG. 2A. The front surface 22b and the back surface 22c have a translucent substrate 22a made of glass having a thickness of 3.2 mm and extending in the main scanning direction of an object to be photographed such as a document placed on the contact glass 23 (FIG. 2A). See). In the curved mirror 22, a dichroic coat layer 22D (see FIG. 2A) having a thickness of about 15 μm along the curved surface shape is formed on the front surface 22b of the translucent substrate 22a, and the back surface 22c follows the back surface shape. And an aluminum-coated light reflecting layer 22M (see FIG. 2A) having an inner surface.

  As shown in FIG. 5, the dichroic coat layer 22D (see FIG. 2) has a wavelength characteristic 122 such that the reflectance 112 of the dichroic coat layer 22D becomes a cut-off wavelength 123 in the vicinity of the minimum wavelength 121a. Is set. That is, a characteristic that a light having a wavelength shorter than 490 nm has a high reflectance of 0.5 or more and a light having a wavelength longer than 490 nm has a high transmittance (a low reflectance having a reflectance of less than 0.5) (so-called long pass). Filter). Therefore, as in the case of the first embodiment described above, blue light is reflected by the dichroic coat layer 22D, and green light and red light are transmitted through the dichroic coat layer 22D and reflected by the reflective layer 22M of the curved mirror 22. Will be.

  Further, similarly to the first embodiment described above, the curved mirror 22 irradiates the irradiated portion 24 (see FIG. 2A) with the reflected light 25 (see FIG. 2A) as parallel light. The back surface of the curved mirror 22 has the curvature radius R1 of the surface 22b of the curved mirror 22 and the reflected light 26 (see FIG. 2B) of green light and red light is condensed on the irradiated portion 24. It has a radius of curvature R2 of 22c. For example, R1 is 17.8 mm, and R2 has the same radius of curvature (17.8 mm) as R1. Therefore, the curved mirror 22 can irradiate the irradiated portion 24 with substantially the same illuminance of blue light, green light, and red light, and it is possible to appropriately suppress the occurrence of color unevenness.

  In addition, as the white LED light source, there are a surface mount type including a blue light emitting LED and a bullet type equipped with a lens, and the function and effect of the dichroic coat layer 22D are achieved with either type. It is possible to reduce color unevenness in both types. Further, the cylindrical lens surface may be a free-form surface.

  Next, an illumination optical system according to a third embodiment of the present invention will be described with reference to FIGS. FIG. 6 is a cross-sectional view showing a schematic configuration of an illumination optical system according to the third embodiment of the present invention. FIG. 6A is a view showing a ray locus from a blue light emitting LED, and FIG. FIG. FIG. 7 is a graph showing the relationship between the emission spectrum of the light emitted from the white LED light source shown in FIG. 1 and the spectral intensity, and the relationship between the reflectance of the dichroic coat layer used in the first embodiment and the wavelength of the light. It is. In addition, about the same structure as above-mentioned embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  The illumination optical system 30 according to the third embodiment uses the white LED light source 21 used in the first embodiment described above, but the configuration of the curved mirror is different from that of the first embodiment. As shown in FIG. 6A, the curved mirror 32 used in the illumination optical system 30 according to the third embodiment includes a surface 32b having a concave cylindrical shape and a back surface 32c having a convex cylindrical lens shape. The front surface 32b and the back surface 32c are provided with a translucent substrate 22a made of glass having a thickness of 3.2 mm and extending in the main scanning direction of an object to be imaged such as a document placed on the contact glass 23. The curved mirror 32 is formed by forming a dichroic coating layer 32D having a thickness of about 15 μm along the curved surface shape on the surface 32b of the translucent substrate 32a, and coating the back surface 32c with aluminum having an inner surface along the back surface shape. It has a light reflecting layer 32M.

  Then, as shown in FIG. 7, the dichroic coat layer 32D is set to have a wavelength characteristic 132 such that a cutoff wavelength 133 is obtained in which the reflectance of the dichroic coat layer 22D is halved in the vicinity of the minimum wavelength 111a. . That is, a characteristic that light having a wavelength shorter than 500 nm has high transmittance (low reflectance with a reflectance of less than 0.5) and light having a wavelength longer than 500 nm has high reflectance of 0.5 or more (so-called short circuit). Pass filter). Accordingly, the dichroic coat layer 32D transmits blue light having the first peak wavelength λ1 and reflects yellow light having the second peak wavelength λ2, and the wavelength that can be selected for reflection and transmission according to the wavelength of the light. Selectivity.

  Further, as shown in FIG. 6B, the curved mirror 32 is formed when the yellow light emitted from the yellow light emitting phosphor 21Y is reflected by the dichroic coat layer 32D on the surface 32b of the translucent substrate 32a. The surface 22b of the curved mirror 22 has a radius of curvature R11 so that the reflected light 36 is condensed on the irradiated portion 24. This R11 is, for example, 14.2 mm. On the other hand, as shown in FIG. 6A, the blue light emitted from the blue light emitting LED chip 21B is refracted and transmitted through the dichroic coat layer 32D, and is reflected on the back surface 32c of the translucent substrate 32a. Reflected by the layer 32M, the reflected light 35 irradiates the irradiated portion 24. In this case, the radius of curvature R12 of the back surface 32c of the translucent substrate 32a is set so that the reflected light 35 becomes substantially parallel light, as shown in FIG. 6A, for example, 19.6 mm. be able to. Thus, when the curvature radius of the front surface 32b and the back surface 32c of the translucent board | substrate 32a becomes the same, creation of a cylindrical lens surface becomes easy, and it is suitable. In this embodiment, the curvature radii of the front surface 32b and the back surface 32c of the translucent substrate 32a are set to the same value, but there is a difference of about ± 10% in these curvature radii. Even in this case, it has been confirmed that the same effect can be obtained.

  Thus, in the illumination optical system 30 according to the third embodiment, the curved mirror 32 is used, and the dichroic coat layer 32D (first reflecting portion) is formed on the surface 32b of the curved mirror 32, so that the curved mirror A reflective layer 32M (second reflective portion) is formed on the back surface 32c of 32, and the dichroic coat layer 32D has a short-pass filter characteristic. Further, the curvature radius R11 of the surface 32b of the curved mirror 32 is formed on the back surface 32c of the translucent substrate 32a by the blue light emitted from the blue light emitting LED chip 21B being refracted and transmitted through the dichroic coat layer 32D. Since the radius of curvature is such that the reflected light 35 reflected by the reflective layer 32M becomes parallel light, the irradiated portion 24 can be efficiently irradiated with blue light. By using such a curved mirror 32, it becomes possible to irradiate the irradiated portion 24 with substantially the same illuminance of blue light and yellow light, and it is possible to appropriately suppress the occurrence of color unevenness.

  In addition, as the white LED light source, there are a surface mount type including a blue light emitting LED and a bullet type equipped with a lens, and the function and effect of the dichroic coat layer 22D are achieved with either type. It is possible to reduce color unevenness in both types. Further, the cylindrical lens surface may be a free-form surface.

  In the illumination optical system 30 of the third embodiment, a blue light emitting LED chip 21B that emits blue light as a white LED light source and a yellow light emitting phosphor 21Y that emits yellow light when excited by the blue light are provided. Although used, the same action and effect can be obtained even when the high color rendering type white LED light source shown in FIG. 4 is used instead of the white LED light source.

  Next, the image reading apparatus according to the first embodiment of the present invention will be described with reference to FIG. FIG. 8 is a longitudinal sectional view showing a schematic configuration of the image reading apparatus according to the first embodiment of the present invention. In addition, about the same structure as above-mentioned embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  As shown in FIG. 8, the image reading apparatus according to the first embodiment emits white light to a contact glass 23 made of a transparent glass or the like on which an object to be imaged such as a document is placed, and an irradiated portion 24 of the object to be imaged. The illumination optical system 20 that irradiates, the first mirror 44a that reflects the reflected light (reading light) from the irradiated portion 24 (displayed as the reading optical axis 47), and the first light that reflects the reading light 47 reflected by the first mirror 44a. A second mirror 44b and a third mirror 44c that reflects the reading light 47 reflected by the second mirror 44b are provided. The image reading apparatus further includes a reduction system lens (imaging lens) 45 that forms an image of the reading light 47 reflected by the third mirror 44c on an image pickup element 46 such as a CCD (Charge Coupled Device).

  As the illumination optical system 20, the illumination optical system 20 according to the first embodiment described above is used, and a plurality of white LED light sources 21 are supported by a support member 27 in the main scanning direction and arranged. Further, as shown in FIG. 8, the curved mirror 22 has cylindrical reflection surfaces having curved shapes in the sub-scanning direction B on the front surface 22b and the back surface 22c of the translucent substrate 22a, respectively, and these front surface 22b and back surface 22c. Further, each has a dichroic coat layer 22D and a reflective layer 22M. The curved mirror 22 is held by the holding member 28 attached to the support member 27, and the white light emitted from the white LED light source 21 is covered as described with reference to FIGS. 2 (a) and 2 (b). The irradiation unit 24 is irradiated to form reflected light (reading light) having a reading optical axis 47 that is reflected substantially perpendicularly from the irradiated unit 24. In this case, the reading line of the object to be imaged (not shown) in the irradiated portion 24 is in the depth direction of the paper surface (referred to as the main scanning direction) in FIG. 8, and is collectively irradiated by the white LED light source 21 and image sensor. 46 is read in a batch. Then, the illumination optical system 20 is moved and scanned in the sub-scanning direction B as the first traveling body 48 displayed by a one-dot chain line together with the first mirror 44a, and reading is performed over the entire surface of the subject.

  In this case, the second mirror 44b and the third mirror 44c are moved in the sub-scanning direction B by moving the second traveling body 49 as a second traveling body 49 indicated by a one-dot chain line at half the moving speed of the first traveling body 48. The imaging element 46 is made to read (the subject to be photographed). This reading method is called a differential mirror method. While the document is being read, the positional relationship among the first traveling body 48, the second traveling body 49, the reduction system lens 45 and the image sensor 46 is slightly shifted, so that the same color as the color unevenness occurs in the reading light 41. However, there is a problem that image data of different colors is created depending on the read location even for a solid document. However, in the image reading apparatus according to the first embodiment, as described above, the curved mirror 22 has the dichroic coat layer 22D on the front surface 22b and the reflective layer 22M on the back surface 22c. Of the light emitted from the white LED light source 21, blue light is reflected by the dichroic coat layer 22 </ b> D on the surface of the curved mirror 22 and illuminates the irradiated portion 43. At this time, the reflected light 25 (see FIG. 2A) of the blue light is very close to the collimated light. On the other hand, the yellow light emitted from the yellow light-emitting phosphor 21Y (see FIG. 2B) is reflected by the reflective layer 22M on the back surface side of the curved mirror 22 and irradiates the irradiated portion 24. As shown in FIG. 2B, the illumination range of the reflected light 26 of the yellow light is condensed and almost equal to the blue light, and the ratio of the blue light and the yellow light approaches a constant in the irradiated range. . As a result, the occurrence of color unevenness is suppressed.

  In the image reading apparatus according to the first embodiment, the illumination optical system according to the first embodiment has been described as the illumination optical system. However, the illumination optical system according to another embodiment such as the second embodiment is also applicable. It can be used.

  Next, an image reading apparatus according to a second embodiment of the present invention will be described with reference to FIGS. FIG. 9 is a longitudinal sectional view showing a schematic configuration of a curved mirror used in the image reading apparatus according to the second embodiment of the present invention. FIG. 9A shows a translucent substrate having a dichroic coat layer formed on the surface thereof. The exploded sectional view of the curved mirror decomposed | disassembled into the board | substrate which formed the reflection layer on the surface, (b) is sectional drawing of the curved mirror which joined the translucent board | substrate shown to (a), and a board | substrate. FIG. 10 is a longitudinal sectional view showing a schematic configuration of an image reading apparatus according to the second embodiment of the present invention. In addition, about the same structure as above-mentioned embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  The image reading apparatus according to the second embodiment is different from the image reading apparatus according to the first embodiment described above in the method of processing the curved mirror. That is, as shown in FIG. 9A, the curved mirror 52 used in the image reading apparatus according to the second embodiment is the curved mirror 22 used in the image reading apparatus according to the first embodiment described above. The light transmitting substrate 50a has a cylindrical surface shape having the same curvature radii R1 and R2 as the curvature radii of the front surface 22a and the back surface 22b, the front surface 51b has a cylindrical surface having a curvature radius R2, and the back surface 51c is a flat surface. A substrate 51a is used. A dichroic coat layer 52D that is the same as the dichroic coat layer 22D used in the image reading apparatus according to the first embodiment is formed on the surface 50b of the translucent substrate 50a. On the other hand, a reflective layer 52M made of an aluminum vapor deposition film is formed on the surface 51b of the substrate 51a. As shown in FIG. 9B, the reflective layer 52M is formed on the back surface 50c of the translucent substrate 50a and the surface 51b of the substrate 51a. The curved mirror 52 is formed by joining the reflection layer 52M thus formed with a translucent adhesive having a refractive index close to that of the translucent substrate 50a. In this case, the substrate 51a may be a translucent substrate or a material that does not transmit light. However, it is desirable to use a translucent substrate made of the same material as the translucent substrate 50a in order to prevent internal stress from being generated as much as possible when the ambient temperature changes.

  As shown in FIG. 10, the image reading apparatus according to the second embodiment using such a curved mirror 52 and the image reading apparatus according to the first embodiment described above are attached to the support member 27 of the curved mirror. Without using the holding member 28, the back surface 51c of the substrate 51a can be directly bonded and fixed to the support member 27, and there is an advantage that the curved mirror can be easily attached to the support member 27.

  Although the image reading apparatus according to the second embodiment has been described as a modification of the curved mirror 22 in the illumination optical system 20 according to the first embodiment described above, such a curved mirror 52 includes the second and third curved mirrors 52. The curved mirror used in the illumination optical system according to the embodiment can be used similarly.

  Moreover, in the image reading apparatus according to the second embodiment, the white LED light source 21 using the blue light emitting LED and the yellow light emitting phosphor is used as the white LED light source. A white LED 202 can be used as well. The same applies to the image reading apparatus of each embodiment described below.

  Next, an image reading apparatus according to a third embodiment of the present invention will be described with reference to FIG. FIG. 11 is a longitudinal sectional view showing a schematic configuration of an image reading apparatus according to the third embodiment of the present invention. In addition, about the same structure as above-mentioned embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  The image reading apparatus according to the third embodiment is different from the image reading apparatus according to the second embodiment described above in reflecting means 71 that moves and scans the first traveling body 72 together with the illumination optical system 200 and the first mirror 44a. It is different in that it is attached. The reflecting means 71 includes a reflecting mirror 71b that reflects the visible light held by the second support member 71a having an L-shaped cross section facing the curved mirror 52 with the reading optical axis 47 interposed therebetween. The reflecting mirror 71b reflects the light emitted to the right side of the drawing without irradiating the curved mirror 52 out of the light emitted from the white LED light source 21, and irradiates the irradiated portion 24. ing. Therefore, in this image reading apparatus, a part of the light emitted from the white LED light source 21 is reflected by the curved mirror 52 with the blue light and the yellow light by the individual reflecting portions 22D and 22M, respectively. The light emitted to the right side of the figure without being irradiated is reflected by the reflecting mirror 71b of the reflecting means 71, and the irradiated portion 24 is illuminated from the two directions of the reflected light from the curved mirror 52 and the reflecting mirror 71b. It has become. The light distribution characteristic from the white LED light source 21 is a characteristic close to the Lambert distribution, and a region having a high light intensity can be efficiently guided to the irradiated portion 24 by the curved mirror 52. In addition, although the light intensity is low, the useless light beam in the second embodiment described above can be used, so that the light use efficiency is improved. In this case, since the amount of light applied to the reflecting mirror 71b is relatively small and the distance from the white LED light source 21 is longer than that of the curved mirror 52, the influence of color unevenness by the reflecting mirror 71b is small.

  Next, an image reading apparatus according to a fourth embodiment of the present invention will be described with reference to FIG. FIG. 12 is a longitudinal sectional view showing a schematic configuration of an image reading apparatus according to the fourth embodiment of the present invention. In addition, about the same structure as above-mentioned embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  The image reading apparatus according to the fourth embodiment uses a reflecting mirror 81 having a cylindrical concave surface on the reflecting surface 81a as a reflecting mirror with the image reading apparatus according to the third embodiment described above. Therefore, the reflected light reflected by the reflecting mirror 81 can be condensed on the irradiated portion 24, and compared with a reflecting mirror having a flat reflecting surface used in the image reading apparatus of the third embodiment described above. Thus, the light use efficiency can be further improved.

  Next, an image reading apparatus according to a fifth embodiment of the present invention will be described with reference to FIG. FIG. 13 is a longitudinal sectional view showing a schematic configuration of an image reading apparatus according to the fifth embodiment of the present invention. In addition, about the same structure as above-mentioned embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  As shown in FIG. 13, the image reading apparatus according to the fifth embodiment is different from the image reading apparatus according to the above-described fourth embodiment as a reflecting mirror in the curved mirror 52 used in the above-described second embodiment. Is different in that a curved mirror 91 having the same configuration is used. That is, as shown in FIG. 13, the curved mirror 91 is a mirror having a front-side reflecting surface (third reflecting portion) and an inner reflecting surface (fourth reflecting portion). The front-side reflective surface is formed by the dichroic coat layer 91D on which the above-described long-pass filter or dielectric multilayer film serving as a short-pass filter is formed, and the inner-surface reflective surface is formed by the reflective layer 91M made of an aluminum vapor deposition layer. Has been. Therefore, for example, if the surface is a surface reflecting surface composed of a dichroic coat layer 91D having a short-pass filter characteristic, the inner surface reflection includes a reflecting layer 91M that reflects blue light emitted from the white LED light source 21 and reflects yellow light. It is possible to reflect on the part. As a result, the reflected light that is reflected by the curved mirror 91 and irradiates the irradiated portion 24 becomes light that suppresses occurrence of color unevenness together with the curved mirror 52, and not only the light use efficiency is improved but also color unevenness. Is also suppressed.

  Next, an image reading apparatus according to a sixth embodiment of the present invention will be described with reference to FIG. FIG. 14 is a longitudinal sectional view showing a schematic configuration of an image reading apparatus according to the sixth embodiment of the present invention. In addition, about the same structure as above-mentioned embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  In the image reading apparatus according to the sixth embodiment, another illumination optical system 200B is arranged with the reading optical axis 47 interposed therebetween in place of the reflecting mirror in the image reading apparatus according to the fifth embodiment described above. Is different. That is, as shown in FIG. 14, the image reading apparatus according to the sixth embodiment includes a white LED light source 21A and a curved mirror 52A, and reflects the white light emitted from the white LED light source 21A by the curved mirror 52A. The first illumination optical system 200A that irradiates the irradiated portion 24 is used. At the same time, the white light emitted from the white LED light source 21B having the white LED light source 21B and the curved mirror 52B is reflected by the curved mirror 52B so as to face the first illumination optical system 200A across the reading optical axis 47. Thus, the second illumination optical system 200B that irradiates the irradiated portion 24 is used.

  As described above, in the image reading apparatus according to the sixth embodiment, the first and second illumination optical systems 200A and 200B are arranged to face each other with the reading optical axis 47 interposed therebetween, and irradiation is performed by the respective illumination optical systems 200A and 200B. Since the reflected read light of the irradiated portion 24 is formed on the reading optical axis, it is an illumination system that makes it easy to increase the illuminance of the irradiated portion 24 of the subject. Due to such a high illuminance illumination system, color unevenness tends to be noticeable. However, in the image reading apparatus of the sixth embodiment, in the illumination optical systems 200A and 200B, the dichroic coat layer 52D having the optical characteristics as described above is formed on the surface 50b having the radii of curvature R1 and R2 as described above. Therefore, the occurrence of color unevenness can be suppressed. By using such high-illuminance illumination, it is possible to provide a high-speed and high-quality image reading apparatus in which color unevenness is reduced.

  Further, the present invention is not limited to the above-described embodiment, and it is obvious that the above-described embodiment can be modified as appropriate within the scope of the technical idea of the present invention, other than suggested in the above-described embodiment. In addition, the number, position, shape, and the like of the constituent members are not limited to the above-described embodiment, and can be set to a suitable number, position, shape, and the like in carrying out the present invention.

11B, 21B Blue light emitting LED chip 11Y, 21Y Yellow light emitting phosphor 12, 22, 32, 52, 52A, 52B, 91 Curved mirror 13B, 25, 35 Blue reflected light 13Ya, 13Yb, 13Yc, 26, 36 Yellow reflection Light 14, 24 Irradiated part 15B Illuminance distribution of blue light 15Y Illuminance distribution of yellow light 20, 30, 200A, 200B Illumination optical system 21, 21A, 21B White LED light source 22a, 50a Translucent substrate 22b, 50b Surface 22c, 50c Back surface 22D, 32D, 52D, 91D Dichroic coat layer 22M, 32M, 52M, 91M Reflective layer 23 Contact glass 24 Irradiated part 25, 35 Blue reflected light 26, 36 Yellow reflected light 27 Support member 28 Holding member 44a First mirror 44b Second mirror 44c Third mirror 45 Reduction System lens 46 Image sensor 47 Reading optical axis 51a Substrate 51b Front surface 51c Back surface 71 Reflecting means 71a Support member 71b, 81 Reflective mirror 81a Reflecting surface 111, 112 Emission spectrum 111a, 112a Minimal wavelength 112, 122, 132 Wavelength characteristics 113, 123, 133 Cutoff wavelength 201 White LED light source 202a Resin package 202B Blue light emitting LED chip 202G Green light emitting phosphor 202R Red light emitting phosphor 202b Light emitting surface

JP 2009-175320 A JP 2002-142082 A

Claims (12)

An LED chip that emits light having a first wavelength λ1 as a peak wavelength, and a first phosphor that emits light having a peak at a second wavelength λ2 that is longer than the first wavelength when excited by the light of the LED chip. An illumination optical system having a light source that uses one or more white LED light sources having a curved surface mirror that deflects light from the light source to an irradiated portion,
The curved mirror includes a first reflecting portion and a second reflecting portion in order from an incident direction of light from the light source, and the first reflecting portion has the first wavelength λ1 and the second wavelength. An illumination optical system having wavelength selectivity with respect to λ2. The illumination optical system according to claim 1,
The wavelength selectivity is made by reflecting the light of the first wavelength λ1 with a reflectance of 0.5 or more and transmitting the light of the second wavelength λ2 with a reflectance of less than 0.5, In addition, the curved mirror includes the second reflecting portion having a second radius of curvature R2 shorter than the radius of curvature R1 of the first reflecting portion. The illumination optical system according to claim 1,
The wavelength selectivity is made by reflecting the light of the second wavelength λ2 with a reflectance of 0.5 or more and transmitting the light of the first wavelength λ1 with a reflectance of less than 0.5, In addition, the curved mirror includes the second reflecting part having a second radius of curvature R2 substantially the same as the radius of curvature R1 of the first reflecting part. The illumination optical system according to any one of claims 1 to 3,
The illumination optical system according to claim 1, wherein the wavelength selectivity is achieved by forming a dichroic coat layer on the first reflecting portion. In the illumination optical system according to any one of 1 to 4,
The illumination optical system, wherein the first wavelength light is blue light, and the first phosphor is a yellow phosphor. The illumination optical system according to any one of claims 1 to 4,
The white LED light source has a second phosphor that is excited by the light of the LED chip and emits light with a third wavelength λ3 as a peak, and the second wavelength λ2 <the third wavelength λ3. An illumination optical system. The illumination optical system according to any one of claims 1 to 6,
The illumination optical system according to claim 1, wherein the wavelength selectivity is made by the first reflecting section in which a cutoff wavelength at which the reflectance is halved is set between the first wavelength λ1 and the second wavelength λ2. The illumination optical system according to claim 6, wherein
The illumination optical system characterized in that the light of the first wavelength is blue light, the first phosphor is a green light-emitting phosphor, and the second phosphor is a red light-emitting phosphor. Reflected by the illumination optical system for irradiating the object to be photographed, a contact glass for placing the object to be photographed, a plurality of mirrors for reflecting light emitted from the illumination optical system, and the plurality of mirrors In an image reading apparatus including a lens that forms an image of light on an image sensor,
The illumination optical system according to any one of claims 1 to 8, wherein a plurality of the white LED light sources are arranged in a main scanning direction of image reading. . The image reading apparatus according to claim 9.
An image reading apparatus comprising: a reflecting mirror that reflects the light beam of the illumination optical system and irradiates the object to be photographed with the reading optical axis of the illumination optical system interposed therebetween. The image reading apparatus according to claim 10.
The reflecting mirror includes a third reflecting portion and a fourth reflecting portion in order from the incident direction of light from the light source of the illumination optical system, and the third reflecting portion includes the first wavelength λ1 and the fourth reflecting portion. An image reading apparatus having wavelength selectivity with respect to the second wavelength λ2. The image reading apparatus according to any one of claims 9 to 11,
The illumination optical system is disposed so as to face the reading optical axis, and reflected light from a subject to be emitted from each of the illumination optical systems is reflected on the reading optical axis. An image reading apparatus.