Light guide, illumination device, and contact-type image sensor

Abstract

This light guide (22) reflects at an inner surface thereof incident light from an end surface (22a) thereof while transmitting the light in a longitudinal direction and emits the light from a light emission surface (22b) thereof. The light guide (22) comprises: a light reflection surface (22c) that substantially faces the light emission surface (22b); and a plurality of diffusion structures (26) that are provided to the light reflection surface (22c) and that are for diffusing and reflecting the light. When the length of each diffusion structure (26) in a direction perpendicular to the longitudinal direction is defined as Wr and the length of the light reflection surface (22c) in the direction perpendicular to the longitudinal direction is defined as Wp, Wr < Wp.

Description

Light guide, lighting device and contact image sensor

[0001] The present invention relates to a light guide that guides light from a light source and emits it, and to an illumination device and a contact image sensor that use the light guide.

[0002] Devices such as facsimiles, copiers, and hand scanners use image reading devices, such as image sensors, to read documents. Contact image sensors (CISs) are commonly used as image reading devices because they have a short optical path and are easily incorporated into devices. Contact image sensors read documents by illuminating the document to be read with an illumination device at an illuminance sufficient to read the document. The illuminated area is long in the main scanning direction (longitudinal direction) and narrow in the sub-scanning direction, which is perpendicular to the main scanning direction. For this reason, illumination devices used with contact image sensors are sometimes referred to as "linear illumination devices."

[0003] Patent Document 1 describes an invention related to a light guide (light guide) used in a lighting device. The light guide described in Patent Document 1 is a rod-shaped body that propagates light in the longitudinal direction while undergoing multiple reflections therein, and has a light incident surface at one end for receiving light from a light source such as an LED, a light exit surface for emitting the light in a line, and a light reflecting surface substantially opposite the light exit surface. In the light guide described in Patent Document 1, unevenness in illumination is suppressed by forming an uneven shape or a recess with a substantially circular cross section on part of the light reflecting surface.

[0004] Japanese Patent Application Publication No. 10-133026

[0005] In the lighting device equipped with the light guide described in Patent Document 1, it is suggested that unevenness on the illuminated surface can be suppressed without providing a conventional light-reflecting coating on the light-reflecting surface. However, there is no mention of reducing the radiant flux or irradiance in a situation where, for example, a part of a document placed on a document table (also called a contact glass or platen glass) floats (a part of the document is separated from the document table surface where it should be in close contact). In actual work, there are many cases where it is necessary to read the image of a floating document, so it is highly desirable to uniformize the amount of radiation, such as the radiant flux and irradiance, whether on the surface in contact with the contact glass or on the surface away from the contact glass.

[0006] The present invention has been made in view of the above circumstances, and its object is to make uniform the amount of radiation, such as the radiant flux and irradiance, on a transparent document table.

[0007] In order to solve the above problems, a light guide according to one embodiment of the present invention is a light guide that transmits light incident from an end face in a longitudinal direction while being reflected by an internal surface and that emits the light from a light exit surface, the light guide comprising: a light reflecting surface substantially opposite the light exit surface; and a plurality of diffusion structures provided on the light reflecting surface for diffusing and reflecting the light. When the length of the diffusion structures in a direction perpendicular to the longitudinal direction is Wr and the length of the light reflecting surface in a direction perpendicular to the longitudinal direction is Wp, Wr<Wp.

[0008] Another aspect of the present invention is a lighting device, which includes the above-described light guide and a light source disposed on or near the end surface of the light guide so that light is incident from the end surface.

[0009] Yet another aspect of the present invention is a contact-type image sensor that includes a document table, the above-described illumination device for illuminating a document placed on the document table, a lens array for collecting light reflected from a portion of the document illuminated by the illumination device, and a light-receiving element array for receiving the light collected by the lens array.

[0010] Any combination of the above components, and any modifications between the expression methods and devices of the present invention are also valid aspects of the present invention.

[0011] According to the present invention, it is possible to make uniform the amount of radiation, such as the radiant flux and irradiance, on the transparent document table.

[0012] 1 is a schematic perspective view of a contact-type image sensor according to an embodiment of the present invention; FIG. 2 is a schematic cross-sectional view perpendicular to the longitudinal direction of the contact-type image sensor according to an embodiment of the present invention; FIG. 3 is a schematic cross-sectional view of an example of an erecting equal-magnification lens array; FIG. 4 is a schematic perspective view of an example of an illumination device used in a contact-type image sensor; FIGS. 5(a) and 5(b) are schematic views showing an LED package in which a plurality of LED chips are mounted; FIGS. 6(a) to 6(c) are schematic three-view diagrams showing an example of a light guide provided on its light-reflecting surface with a diffusing structure made of a plurality of divided cylindrical side surfaces; FIG. 6(a) to FIG. 6(c) are schematic three-view diagrams showing an example of a light guide provided on its light-reflecting surface with a diffusing structure made of a divided cylindrical side surface; FIG. 6(c) is a diagram showing a diffusing structure made of a divided cylindrical side surface; FIG. 6(c) is a schematic enlarged plan view of a light-reflecting surface provided with a diffusing structure made of a spherical recess; FIG. 6(c) is a diagram showing a diffusing structure made of a spherical recess; FIG. 6(c) is a graph qualitatively showing the z-direction dependency of irradiance on a document table; FIG. 7 is a cross-sectional view of a light guide according to another embodiment; FIGS. 13(a) to 13(c) are schematic three-view diagrams of a light guide according to a first example; FIG. 7(c) is a schematic enlarged view of a portion of a group of groove-shaped diffusing structures; and FIG. 7(c) is a diagram showing an illumination device according to a second example. 18(a) to 18(c) are schematic three-view diagrams of a light guide according to a fourth embodiment; and FIG. 20(a) to FIG. 20(c) are schematic three-view diagrams of a light guide according to a first comparative example ....

[0013] Hereinafter, embodiments of the present invention will be described. The same or equivalent components, parts, and processes shown in each drawing will be given the same reference numerals, and redundant explanations will be omitted where appropriate. Furthermore, the embodiments are illustrative and do not limit the invention, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

[0014] 1 is a schematic perspective view of a contact image sensor 10 according to an embodiment of the present invention. As shown in FIG. 1, the contact image sensor 10 may have a longitudinal length corresponding to the width or length of a document or workpiece to be read. For example, if the document to be read is A4 size, the contact image sensor 10 may have a length corresponding to the width of an A4 sheet of paper.

[0015] 2 is a schematic cross-sectional view perpendicular to the longitudinal direction of a contact image sensor 10 according to an embodiment of the present invention. As shown in Fig. 2, the contact image sensor 10 includes a transparent plate-like document table 12 on which a document 11 to be read is placed, an illumination device 13 for illuminating a portion of the document 11 placed on the document table 12, an erecting equal-magnification lens array 14 for condensing the image of the portion of the document 11 illuminated by the illumination device 13 as an erect equal-magnification image, and a light-receiving element array 15 for reading the image condensed by the erecting equal-magnification lens array 14. The contact image sensor 10 shown in Fig. 1 further includes a housing 16 for integrating these parts in an appropriate arrangement.

[0016] The document table 12 is configured as a transparent parallel plate. Since the document table 12 is required to have high transparency, it may be made of glass or a transparent resin with high light transmittance, such as cycloolefin, acrylic, or polycarbonate. If extremely high mechanical strength and high light transmittance are required, tempered glass may be used. When the document table 12 is made of glass, it may be called a platen glass, contact glass, document table glass, etc. As shown in FIG. 1 , the document table 12 may be elongated in one direction, or may be rectangular in plan view with a long side in a certain direction.

[0017] The erect life-size lens array 14 is configured by arranging a large number of single lenses having an erect life-size object-image relationship so that the optical axes of the lenses are parallel to one another at least in the longitudinal direction (main scanning direction). While an erect life-size lens array is used here, a non-erect life-size lens array or a non-life-size lens array can also be used. From the viewpoints of the need for compactness of the contact image sensor 10 and robustness in terms of tolerance to misalignment of each part, it is preferable to use an erect life-size lens array.

[0018] Examples of lens arrays that can be used include the Selfoc Lens Array (Selfoc is a registered trademark) manufactured by Nippon Sheet Glass Co., Ltd., a plastic lens array manufactured by Mitsubishi Chemical Corporation, and the Linear Micro Lens Array, a two-lens system, manufactured by Pixon Corp. Each single lens in the former two is a gradient index rod lens that has a refractive index distribution inside a transparent cylindrical dielectric material, where the refractive index decreases from the center to the periphery, and enables the lens to refract light without the need for a curved interface with air.

[0019] Fig. 3 is a schematic perspective view of an example of an erecting equal-magnification lens array 14. The erecting equal-magnification lens array 14 shown in Fig. 3 is configured by arranging a plurality of gradient index rod lenses 17 in one or more rows in the main scanning direction so that the central axes of the lenses are approximately parallel to each other (the lens array shown in Fig. 3 is arranged in one row). As shown in Fig. 3, the erecting equal-magnification lens array 14 is sandwiched between two plate-like substrates 18 and 19 and integrated with spacers (plates) 20 and 21 arranged on both ends.

[0020] As mentioned above, such an erect life-size lens array 14 does not require the end faces corresponding to the light exit and entrance surfaces to be curved, and is characterized by extremely efficient processability, allowing the lens diameter to be small, and enabling high resolution and contrast to be achieved, making it possible to easily obtain an erect life-size image.

[0021] The light receiving element array 15 is a long array of light receiving elements such as PDs (photodiodes) and APDs (avalanche photodiodes) arranged at least in the main scanning direction. The light receiving element array 15 receives light that is reflected from a portion of the image of the original 11 on the platen 12 and then condensed by an erecting equal-magnification lens array. The light received by the light receiving element array 15 is converted into an electrical signal according to its light intensity and transmitted to a device such as a storage device or an image engine.

[0022] The light receiving element array 15 may be arranged in, for example, three rows in the sub-scanning direction, and the light receiving elements in each row may be provided with color filters corresponding to R (red), G (green), and B (blue) on their light receiving surfaces. Alternatively, the light of the document image emitted from the erecting equal-magnification lens array 14 may be split by a diffraction grating or a spectroscopic prism, and each split light may be received by the light receiving element array 15 arranged in three rows in the sub-scanning direction, thereby obtaining a color image of the document.

[0023] 4 is a schematic perspective view of an example of the illumination device 13 used in the contact image sensor 10. The illumination device 13 includes a rod-shaped light guide 22 that is long in the main scanning direction, a light source 23 that is arranged to emit light from at least one end surface 22 a of the light guide 22, and a light guide cover 24 that houses the light guide 22.

[0024] Since Figure 2 is a cross-sectional view perpendicular to the main scanning direction (longitudinal direction) of the contact image sensor 10, the light source 23 arranged at or near the end face 22a of the light guide 22 cannot be shown in Figure 2. However, in Figure 2, a light source axis is assumed to pass through the center of the light source 23 and to be perpendicular to the paper surface, and the light source 23 is shown at a position corresponding to that axis.

[0025] 2, an orthogonal coordinate system is set up with the position of the light source 23 as the origin, the x-axis (light source axis) passing through the origin and perpendicular to the paper surface, the z-axis passing through the origin and perpendicular to the x-axis and parallel to the surface of the document table, and the y-axis passing through the origin and perpendicular to the x-axis and z-axis. From the viewpoint of the scannability of the contact image sensor 10, the longitudinal direction of each part and perpendicular to the paper surface (x-direction) is called the main scanning direction, and the direction perpendicular to the main scanning direction (z-direction) is called the sub-scanning direction.

[0026] The function of the lighting device 13 will now be described. For example, in FIG. 4, light emitted from a light source 23 disposed on or near an end face 22a of a light guide 22 enters the interior of the light guide 22 from the end face 22a. The light incident on the light guide 22 propagates longitudinally within the light guide 22. The light guide 22 has a light exit surface 22b that emits light in a line in the longitudinal direction, and side surfaces other than the light exit surface 22b. The light exit surface 22b and the side surfaces are elongated in one direction. One side surface of the light guide 22 can be a light reflecting surface that directs the traveling direction of a portion of the light toward the light exit surface 22b. The light reflecting surface may include a surface facing the light exit surface 22b.

[0027] The light source 23 may be, for example, an LED. The LED may emit white light. The light source 23 may be a package containing multiple LED chips emitting light of red, green, and blue wavelengths. By sequentially emitting light from the three color LED chips and sequentially detecting the light intensity along with the timing of their emission, a color image of the document can be obtained through subsequent image processing, even with a single row of the light-receiving element array 15. Alternatively, an LED may be used in which LED chips emitting light of red and blue wavelengths are impregnated with a transparent resin containing a fluorescent agent and packaged together. The fluorescent agent may be excited by a portion of blue wavelength light, causing the LED to emit fluorescent light of green wavelengths, thereby producing a white color from the light-emitting surface of the package. Alternatively, the lighting device 13 may be configured by arranging LED chips emitting light of red, green, and blue wavelengths on the end surface 22a of the light guide 22, respectively. At this time, the three color LED chips are caused to emit light sequentially, and the color and light intensity are detected by the light receiving element array 15 along with the timing of the light emission, and processing such as mixing is performed by the function of an image processing device, etc., thereby making it possible to obtain a color image of the original. If the dependency of the irradiance of the light emitted from the lighting device 13 on the end face position of the LED is known in advance, it is possible to reflect characteristics such as irradiance and radiant flux at a specific position on the end face 22a of the light guide 22 where a relatively high radiant intensity is obtained, and thereby achieve uniformity of the irradiance of each color on the original and its vicinity.

[0028] 5(a) and 5(b) are schematic diagrams showing an LED package 25 in which LED chips 25a, 25b, and 25c that emit light of the single colors R (red), G (green), and B (blue) are mounted in one package. Fig. 5(a) is a plan view of the LED package 25, and Fig. 5(b) is a cross-sectional view of the LED package 25.

[0029] The LED package 25 may have a horizontal length wL1 of, for example, 0.7 mm to 3 mm when viewed from above, and a vertical length wL2 of, for example, 0.7 mm to 3 mm, or may have a relationship of wL1=wL2. The LED package 25 may also have a height hL of, for example, 0.3 mm to 5 mm.

[0030] The light guide 22 may be made of a transparent dielectric to allow light to propagate effectively. Preferably, the light guide 22 is made of a material that has low absorption and high internal transmittance, at least in the wavelength range of the light used. An example of such a material is glass. Furthermore, a transparent resin (plastic) can be used as the material for the light guide 22 from the viewpoint of formability. Examples of resins include, but are not limited to, polymethyl methacrylate (acrylic resin), polycarbonate, polystyrene, AS resin, epoxy resin, silicone resin, and cycloolefin resin.

[0031] The light guide 22 may have a substantially rectangular cross section perpendicular to the x direction (longitudinal direction) (hereinafter simply referred to as the "cross section of the light guide"). The cross section of the light guide 22 may be substantially rectangular or may have any shape formed by straight lines and curves. In particular, when the curves include a part of an ellipse, the effect of having a focal point can be expected to exert an effect of confining light within the light guide, or to improve the efficiency of extracting light from the light guide 22.

[0032] When the cross-sectional shape of the light guide 22 is substantially rectangular, some corners may be formed as C-faces or R-faces. Since the irradiance and radiant intensity of light tend to decrease in portions of the light guide 22 that are relatively far from the light source 23, the cross-sectional shape of the light guide 22 may vary depending on the position in the longitudinal direction in order to compensate for this.

[0033] The light guide 22 has a light exit surface 22b extending in the longitudinal direction. The light exit surface 22b functions as a surface that extracts light used for illumination from the light guide 22. The light exit surface 22b is positioned so as to effectively illuminate an image reading position of the original 11 on the platen 12. The light exit surface 22b may be oriented toward the image reading position.

[0034] The light exit surface 22b may have a flat surface or a curved surface. When the light exit surface 22b has a curved surface, it can be given the effect of converging light, thereby increasing the radiation intensity or irradiance of light at a specific location, or conversely, controlling it. The surface roughness of the light exit surface 22b is not specified, and it may be a so-called mirror surface or may have irregularities. When the mirror surface or surface irregularities are very small, it is easy to control the directionality of the light rays extracted from the light exit surface 22b. When the surface irregularities are large enough to cause light scattering or diffusion, it is possible to achieve uniform illumination light due to the effects of the scattering, diffusion, and other effects such as diffuse reflection.

[0035] The light guide 22 has side surfaces extending in the longitudinal direction, other than the light exit surface 22b. Each side surface may function as a reflective surface for propagating light in the longitudinal direction of the light guide 22 within the light guide 22. Inside the light guide 22, light propagates in the longitudinal direction of the light guide 22 by repeatedly reflecting off parts of the side surfaces. If the angle at which light propagates within the light guide 22 reaches the side surface is sufficiently large, the light propagates while being reflected by total reflection or near-total reflection. If the light reaches the side surface of the light guide 22 under conditions that do not result in total reflection, some of the light may exit from the side surface. The side surface of the light guide 22 may be flat or may include a curved surface. If the light exit surface 22b includes a curved surface, it can have the effect of focusing light. The surface roughness of the side surface of the light guide 22 is not specified. When the surface unevenness is small, it is easy to control the directionality of the light rays extracted from the light emitting surface 22b, and when the surface unevenness is large enough to cause scattering or diffusion of light, the scattering and diffusion effect can make it possible to uniform the irradiance and radiation intensity of light within the light guide 22.

[0036] At least a portion of the side surface of the light guide 22 may have a function of directing a portion of reflected or other light toward the light exit surface 22b. A portion having such a function is referred to as a "light reflecting portion." When the cross-sectional shape of the light guide 22 is rectangular, the side surface has multiple side surfaces defined by sides. On the other hand, the cross-sectional shape of the light guide 22 may be substantially circular or elliptical, and may not be defined by clear sides. When the cross-sectional shape of the light guide 22 is rectangular, at least one surface of the light guide 22 may function as a light reflecting portion. A side surface partially functioning as a light reflecting portion is referred to as a "light reflecting surface." The light reflecting surface may be a surface facing the light exit surface or a part of that surface.

[0037] The light-reflecting surface may be configured to direct a portion of light reaching that surface or portion toward the light-emitting surface 22b. The configuration of the light-reflecting surface for achieving or improving its function is not specified. The light-reflecting surface may have a colored portion, such as silver or white, in order to improve light reflection efficiency. Such silver or white coloring may be achieved by painting or printing. Such highly light-reflective coloring increases the radiation of light that reaches a portion of the light-reflecting surface and is reflected toward the light-emitting surface. Furthermore, the surface of a colored portion, such as silver or white, provided on the surface of the light guide by painting or printing may or may not be a mirrored surface. If the surface of such a colored portion is not a mirrored surface, it promotes diffuse reflection of light, directing it toward the light-emitting surface, and helps to uniform the radiation amount, such as the irradiance and radiant intensity of the light.

[0038] Furthermore, a colored portion such as silver or white provided by printing or painting on a part of the light reflecting surface may have a pattern that changes along the longitudinal direction of the light guide 22. Inside the light guide 22, the amount of radiation such as irradiance and radiation intensity decreases as the distance from the light source 23 increases, and accordingly the amount of light that is reflected by the light reflecting surface and directed toward the light exit surface 22b also decreases. Therefore, a pattern may be adopted in which the area of ​​the portion that improves the light reflecting ability, such as white or silver, increases with increasing distance from the light source 23, and the area of ​​the reflective portion decreases in the portion closer to the light source 23.

[0039] If the light-reflecting surface does not include a colored portion, such as silver or white, provided by printing or painting, the amount of radiation of light reaching the light-reflecting surface directed toward the light-exiting surface 22b may be reduced. This undesirably reduces the efficiency of light extraction from the light-exiting surface 22b. The light-reflecting surface may have recessed or protruding structures to partially improve or control its diffuse reflectivity and scattering properties. For example, consider a light-reflecting surface having a recessed portion that includes a portion of the side surface of a cylinder. When light reaches the light-reflecting surface at a certain incident angle, the diffuse reflectivity of the light is higher when it is reflected by the recessed surface than by a flat surface. Diffuse reflectivity refers to the state in which multiple light rays reach a certain surface and are reflected at multiple reflection angles rather than a constant reflection angle, resulting in a broadened (diffused) reflection of the light rays as a whole. If the light-reflecting surface does not include such structures or colored portions, it has a strong effect of promoting light propagation within the light guide 22, thereby preventing a large amount of light radiation directed toward the light-exiting surface 22b and resulting in relatively poor light extraction efficiency. A structure that diffuses and reflects part of light on a light reflecting surface is called a "diffusing structure."

[0040] The form of the diffusion structure on the light-reflecting surface is not limited as long as it diffuses and reflects a portion of the light that reaches the surface. For example, the inventions disclosed in JP-A-2006-120932 and JP-A-2003-197016 disclose light guides having spherical recesses, triangular grooves (V-shaped grooves), and divided cylindrical grooves (U-shaped grooves) on the surface facing the light-emitting surface (referred to as the light-scattering surface). The diffusion structure of this embodiment can be any of these forms, or an appropriate combination thereof. According to the above-mentioned patent documents, structures similar to these diffusion structures are formed for the purpose of reducing radiation bias, such as color unevenness and brightness unevenness.

[0041] The diffusing structure satisfying these conditions may be provided on the entire light-reflecting surface, or the light-reflecting surface may include a portion of the light-reflecting surface having a diffusing structure satisfying these conditions. Furthermore, diffusing structures satisfying these conditions may be provided in an appropriate combination. The light guide 22 in this embodiment may be provided with a diffusing structure only partially on the light-reflecting surface.

[0042] 6(a) to 6(c) are schematic three-view diagrams illustrating an example of a substantially rectangular columnar light guide having a diffusion structure composed of a plurality of divided cylindrical side surfaces (U-shaped grooves) on its light-reflecting surface. Fig. 6(a) is a view of the light guide 22 from the end surface 22a, Fig. 6(b) is a view of a partial side surface of the light guide 22, and Fig. 6(c) is a view of the light guide 22 from the light-reflecting surface side. Figs. 6(a) to 6(c) illustrate an x'y'z' Cartesian coordinate system. The light guide 22 shown in Figs. 6(a) to 6(c) has a light-emitting surface 22b perpendicular to the end surface 22a and a light-reflecting surface 22c opposite the light-emitting surface 22b. In this light guide 22, the light emitting surface 22b and the light reflecting surface 22c are parallel to each other, but the light emitting surface 22b and the light reflecting surface 22c may have a relationship in which the distance between them tapers along the longitudinal direction, for example.

[0043] 6(a) to 6(c), the direction parallel to the end face 22a is the y' direction, the longitudinal direction of the light guide 22 that is perpendicular to the y' direction (the direction perpendicular to the paper surface in FIG. 6(a)) is the x' direction, and the direction perpendicular to the x' and y' directions and parallel to the light reflecting surface 22c is the z' direction. The origin is the intersection of the edge connecting the end face 22a and the light reflecting surface 22c with the bisector that is parallel to the x' direction and bisects the light reflecting surface 22c in the z' direction.

[0044] 6(c) shows a dashed-dotted line L1 parallel to the x' direction that divides light-reflecting surface 22c into two halves (such a line does not exist on the actual light guide 22, but is shown for the sake of explanation). In light-reflecting surface 22c shown in FIG. 6(c), the upper side of dashed-dotted line L1 is first reflecting surface 22c1, and the lower side is second reflecting surface 22c2.

[0045] 6(a) to 6(c), a plurality of diffusion structures 26(k) (k=1, 2, ..., n) are formed on the light reflecting surface 22c of the light guide 22 along the longitudinal direction of the light guide 22. The diffusion structures are denoted as 26(1), 26(2), ..., 26(n) in order from the one closest to the origin in the x'y'z' Cartesian coordinate system. Note that, hereinafter, when the diffusion structures are referred to collectively, they will be simply referred to as the diffusion structure 26.

[0046] In the light guide 22 shown in FIGS. 6( a) to 6(c), the length Wr(k) of each diffusion structure 26(k) parallel to the z' direction (perpendicular to the main scanning direction) satisfies Wr(k) < Wp. Here, Wp is the width (length in the z' direction) of the light reflecting surface 22c. The length Wr(k) of some diffusion structures 26(k) is shorter than ½ × Wp, while the length Wr(k) of some diffusion structures 26(k) is approximately equal to ½ × Wp, i.e., Wr(k) ≦ ½ × Wp. Furthermore, the length Wr(k) of some diffusion structures 26(k) is longer than ½ × Wp. Furthermore, the ends in the z' direction of some diffusion structures 26(k) do not reach the ends (sides) in the z' direction of the light reflecting surface 22c.

[0047] FIG. 7 is an enlarged schematic plan view of the light-reflecting surface 22c on which a diffusing structure composed of a divided cylindrical side surface is provided. Four diffusing structures 26(k) to 26(k+3) are illustrated in FIG. Some diffusing structures 26(k) and 26(k+1) are provided across the first reflective surface 22c1 and the second reflective surface 22c2. Some diffusing structures 26(k+2) and 26(k+3) are provided only on the first reflective surface 22c1. In a plan view of the diffusing structure 26 provided on the light-reflecting surface as shown in FIG. 7 , a center line is assumed to divide the diffusing structure 26 into two in the x' direction, and the length of the diffusing structure 26 may be the length of the diffusing structure 26 along the center line, or the maximum length of the diffusing structure 26 in the z' direction. The width Wp of the light reflecting surface 22c on an extension of the center line of the diffusion structure 26 may be defined as Wp, and when the light reflecting surface is substantially rectangular in plan view, it may be equal to the length of the side in the z' direction or the width of the central part of the light reflecting surface. The length and Wp of the diffusion structure 26 can be measured using a measuring microscope, a projector with a measuring device, vernier calipers, a micrometer, or the like.

[0048] The volume of one diffusing structure 26 belonging to first reflecting surface 22c1 is denoted by Vp1, and the volume of one diffusing structure 26 belonging to second reflecting surface 22c2 is denoted by Vp2. Fig. 8 shows how diffusing structure 26 provided across first reflecting surface 22c1 and second reflecting surface 22c2 is divided into an area of ​​volume Vp1 belonging to first reflecting surface 22c1 and an area of ​​volume Vp2 belonging to second reflecting surface 22c2.

[0049] In this embodiment, some of the diffusion structures 26 shown in Figures 6(c) and 7 have Vp2<Vp1, and further include diffusion structures 26 with Vp2<0.5 x Vp1, and also include diffusion structures 26 with Vp2=0.

[0050] The relationship between Vp1 and Vp2 in the diffusion structure 26 may be Vp2≦Vp1, preferably Vp2≦0.5×Vp1, more preferably Vp2≦0.25×Vp1, and particularly preferably Vp2≦0.1×Vp1. Alternatively, Vp2=0 may be satisfied.

[0051] Here, the diffusing structure 26 is described as being concave and including a cylindrical (or columnar) side surface. However, the shape is not limited to a strict cylinder, and may include a substantially cylindrical side surface, such as an elliptical or oval cross section. The shape is not limited as long as light reaching the diffusing structure 26 is reflected (diffused) in various directions. The diffusing structure 26 may have a depth of 0.05 mm to 2 mm and a width of 0.2 mm to 10 mm in the x' direction, which is parallel to the light-reflecting surface 22c. Furthermore, the diffusing structure 26 may have a tapered width or depth in the z' direction when viewed in plan from the light-reflecting surface on which it is provided.

[0052] Fig. 9 is an enlarged schematic plan view of the light-reflecting surface 22c provided with diffusing structures each composed of a spherical recess. Similar to Fig. 7, Fig. 9 also shows a dashed-dotted line L1 dividing the light-reflecting surface 22c into two. Fig. 9 also shows four diffusing structures 26(k) to 26(k+3). Some of the diffusing structures 26(k) and 26(k+1) are provided across the first reflective surface 22c1 and the second reflective surface 22c2. Some of the diffusing structures 26(k+2) and 26(k+3) are provided only on the first reflective surface 22c1.

[0053] In the diffusing structure 26 shown in FIG. 9 , Wr(k) < Wp, and in some diffusing structures 26, Wr(k) ≦ ½ × Wp, and in some further diffusing structures 26, ½ × Wp < Wr(k) < 3 / 5 × Wp. In a planar view of the diffusing structure 26 provided on the light-reflecting surface as shown in FIG. 9 , a center line is assumed to divide the diffusing structure 26 into two halves in the x′ direction. The length of the diffusing structure 26 may be the length of the diffusing structure 26 along the center line, or the maximum length of the diffusing structure 26 in the z′ direction. The width of the light-reflecting surface 22c on an extension of the center line of the diffusing structure 26 may be Wp. When the light-reflecting surface is substantially rectangular in planar view, Wp may be equal to the length of the side in the z′ direction or the width of the central portion of the light-reflecting surface. The length and Wp of the diffusing structure 26 can be measured using a measuring microscope, a projector with a measuring device, a vernier caliper, a micrometer, or the like.

[0054] 10 shows how diffusing structure 26, which is provided across first reflecting surface 22c1 and second reflecting surface 22c2, is divided into a region with a volume Vp1 belonging to first reflecting surface 22c1 and a region with a volume Vp2 belonging to second reflecting surface 22c2. In this embodiment, some of diffusing structures 26 satisfy Vp2<Vp1, and further satisfy Vp2<0.5×Vp1, and Vp2=0.

[0055] The diffusion structure 26 composed of a spherical recess may be provided only on the first reflecting surface 22c1. The diffusion structure 26 composed of a spherical recess may have a circular, elliptical, or oval shape in plan view. The curved surface portion of the spherical recess may be a part of a spherical surface or a part of an aspherical shape such as a part of a spheroid.

[0056] The diffusion structures 26 formed from the aforementioned U-shaped grooves or spherical recesses are not limited to these. Furthermore, both groove-shaped diffusion structures 26 and spherical recess-shaped diffusion structures 26 may be included in the light-reflecting surface 22c. When the lighting device 13 is configured using a light guide 22 whose light-reflecting surface 22c includes a diffusion structure 26 satisfying the above conditions, the line width of the linear illumination light emitted from the lighting device 13 becomes smaller, and the radiation amount, such as the central irradiance, becomes larger. As described above, when there is no white print or paint for reflecting or diffusing light, the light-reflecting surface without a diffusion structure and the side surface including such a surface have a strong effect of propagating light rays that reach them in the longitudinal direction of the light guide. Therefore, the diffusing structure 26 is provided for the purpose of increasing the amount of light radiation directed toward the light exit surface 22b. However, by limiting the width of the light reflecting surface 22c of the diffusing structure 26 (making it smaller than the width of the light reflecting surface 22c), the concentration of the irradiance distribution directed toward the light exit surface 22b increases, and the line width of the linearly emitted illumination light decreases. For example, it can be said that the first reflecting surface 22c1 of the light reflecting surface 22c increases the amount of light radiation directed toward the light exit surface 22b, and the second reflecting surface 22c2 increases the amount of light radiation propagating in the longitudinal direction of the light guide 22. Reducing the line width of the linear light emitted from the illumination device 13 has the advantage of increasing the irradiance irradiated onto the document 11 on the document table 12.

[0057] In a contact-type image sensor 10, when the reading target portion of the document 11 on the document table 12 shifts in the y direction (when it is separated from the document table 12, which may also be expressed as the document being in a "floating" state), there is a demand to keep the irradiance received by the reading target portion of the document 11 constant.

[0058] FIG. 11 shows the z-direction dependency of the irradiance on the platen 12 in the contact image sensor 10, with respect to y=0 (platen surface) and y=y １ (a position shifted by y1 in the y direction) is a graph qualitatively showing the relationship between the two conditions. ０It can be seen that there is a singular point where the irradiance does not change or the difference in irradiance is minimum even when shifted in the y direction. The contact image sensor 10 rotates the illumination device 13 (around the x-axis) and finds the length related to a certain y and the singular point z at that time. ０ It is designed taking into consideration the following.

[0059] In this embodiment, the illumination device 13 emits linear illumination with a small line width, and light with a small dispersion and a high concentration of irradiance in the center reaches the vicinity of the document 11. As a result, in the relationship representing the z-direction dependency of irradiance on the document table 12, the value of z (z Ｍ ) and z corresponding to the singular point ０ This suggests that the difference between the values ​​of the two becomes smaller, and the amount of radiation, such as irradiance, at the singular point becomes higher.

[0060] FIG. 12 shows a cross-sectional view of a light guide 22 according to another embodiment. As shown in FIG. 12 , the light guide 22 may have a corner 22e of a side surface 22d that generally faces the diffusion structure 26 chamfered in its cross section. This creates a new side surface 22f that generally faces the diffusion structure 26 in the cross section of the light guide 22. By providing the new side surface 22f that generally faces the diffusion structure 26, a portion of the light diffused and reflected from the diffusion structure 26 reaches the new side surface 22f and is further reflected back into the light guide 22, thereby confining the light and improving light utilization efficiency. Furthermore, if the corner 22e is not chamfered, when the illumination device 13 is positioned so that the light exit surface 22b of the light guide 22 faces the portion of the document 11 to be read, some of the light may be emitted in a direction significantly different from the portion of the document 11 to be read. Chamfering the corner 22e can prevent this phenomenon, which in turn can be expected to improve light utilization efficiency.

[0061] The shape of the approximately opposing chamfered portions of the diffusion structure 26 is not limited as long as it is expected to improve the light confinement effect, reduce the line width of the linear illumination light emitted from the light exit surface 22b, and increase the irradiance at the center of the irradiation irradiance distribution. The shape of the new side surface 22f created by the chamfer may be an R-surface (curved surface), a C-surface (flat surface), or a combination of these. In other words, the new side surface 22f may be approximately opposite the diffusion structure 26 in the cross section of the light guide 22, be tangent to the light exit surface 22b, and have an angle with the light exit surface 22b that exceeds 90°. Such a new side surface 22f may be referred to as an "extended side surface."

[0062] In the cross section of the light guide 22, the removed length c at the light exit surface 22b Ｌ (the length of the extended side surface 22f in the direction parallel to the light exit surface 22b) is 0.1×W ０ '≦c Ｌ ≦0.3×W ０ ' (W ０ ' represents the width of the light emitting surface 22b removed by chamfering or the width of the light emitting surface 22b when the extended side surface 22f is provided.) Also, the angle α between the extended side surface 22f and the light emitting surface 22b ｃ may be between 100° and 160°.

[0063] The extended side surface 22f formed by the chamfering may be colored with a color having high light reflectance, such as white or silver, in order to improve the reflection efficiency of the light that reaches the extended side surface 22f. The white or silver coloring may be applied by printing or painting.

[0064] The lighting device 13 may include a structure that covers the light guide 22. Light incident on the light guide 22 from the light source 23 propagates longitudinally within the light guide 22. As described above, this light propagates while repeatedly being reflected by the side surfaces of the light guide 22. When the light reaches the side surface of the light guide 22, nearly 100% of the light is reflected if the angle of incidence with the side surface satisfies the condition for total reflection. However, if this is not the case, a portion of the light is emitted from the side surface of the light guide 22. Therefore, in order to improve light utilization efficiency, the lighting device 13 according to this embodiment may include a light guide cover 24 that covers at least a portion of the side surface of the light guide 22. By including the light guide cover 24 in the lighting device 13 corresponding to the side surface of the light guide 22, a portion of the light emitted from the side surface of the light guide 22 is reflected by the inner surface of the light guide cover 24 and can be re-entered into the light guide 22. The light guide cover 24 may have a substantially U-shaped cross section perpendicular to the longitudinal direction (x direction), as shown in the cross-sectional view of FIG. 2 , and may be provided so that the inner surface of the light guide cover 24 and a portion of the side surface of the light guide 22 are in close contact with each other. Furthermore, to increase light reflectance, the inner surface of the light guide cover 24 may be colored with a highly reflective color, such as white or silver. Such coloring may be achieved by printing or painting. The light guide cover 24 may be made of a plastic material, considering moldability and low cost. Examples of plastic materials that can be used for the light guide cover 24 include polyamide, polycarbonate, polyacetal, modified polyphenylene ether, polybutylene terephthalate, polyphenylene sulfide, polyethersulfone, polyarylate, polyetherimide, and liquid crystal polymer. Furthermore, the light guide cover 24 may be molded from a naturally white plastic (which may contain a white or silver pigment or dye) because a highly reflective color is desirable.

[0065] The functions and effects of examples of the light guide 22, the illumination device 13, and the contact image sensor 10 having various configurations and conditions will be explained by simulation.

[0066] (First Example) Figures 13(a) to 13(c) are schematic three-view diagrams of a light guide 22 according to a first example. As shown in Figures 13(a) to 13(c), the light guide 22 according to the first example is rod-shaped with a substantially rectangular cross section perpendicular to the longitudinal direction (x' direction). The light guide 22 according to the first example has an absorption coefficient α of 0.0011 [mm] within the wavelength range of light used. －１ ] (internal transmittance = 98.9% / 10 mm), and Snell's law was obeyed at the interface with air or the like. The refractive index of the light guide 22 was set to 1.48816. The light guide 22 according to the first example is a substantially rectangular pillar having dimensions of 3.9 mm x 2.5 mm at the end faces having substantially the same shape as the cross section perpendicular to the longitudinal direction, and a length of 226 mm.

[0067] The light guide 22 according to the first embodiment functionally includes a light exit surface 22b, a side surface, and a light incident surface 22a. The light incident surface 22a is one end surface of the light guide 22 and is perpendicular to the light exit surface 22b and the side surface. Furthermore, the light guide 22 has a light reflecting surface 22c on the side surface opposite the light exit surface 22b. The light exit surface 22b is a rectangle measuring 2.5 mm x 226 mm, and the light reflecting surface 22c is a rectangle measuring 1.9 mm x 226 mm. The light reflecting surface 22c and the light exit surface 22b are parallel to each other with a distance of 3.9 mm between them.

[0068] Unless otherwise specified, the light guide 22 according to the first embodiment has a surface state that does not cause scattering or diffuse reflection. For the purpose of describing the light guide 22, an x'y'z' Cartesian coordinate system is established as shown in Figures 13(a) to 13(c). The longitudinal direction of the light guide 22 is defined as the x' direction, and the x' axis is parallel to the x' direction and divides the light reflecting surface 22c into two on the light reflecting surface 22c. The origin is the intersection of the x' axis and the end surface 22a. The y' axis passes through the origin and is perpendicular to the light reflecting surface 22c. A z' axis passes through the origin and is perpendicular to the x' and y' axes. Note that these axis notations and center lines are used for explanatory purposes and are not actually depicted on the light guide.

[0069] The light emitting surface 22b is a surface specified by 0≦x'≦226, -2.5 / 2≦z'≦2.5 / 2, y'=3.9, and the light reflecting surface 22c is a surface specified by 0≦x'≦226, -1.9 / 2≦z'≦1.9 / 2, y'=0 (both units are mm).

[0070] The light reflecting surface 22c of the light guide 22 according to the first embodiment includes a plurality of groove-shaped diffusion structures 26. The diffusion structures 26 are arranged at varying intervals in the x' direction. The arrangement intervals and sizes of the diffusion structures 26 are mathematically optimized so that light is emitted uniformly along the longitudinal direction of the light exit surface of the light guide.

[0071] FIG. 14 is a schematic enlarged view of a portion of the groove-shaped diffusion structure group as viewed from the z′ direction. In FIG. 14 , the trajectory of a portion of light traveling toward and destined to reach the diffusion structure 26 is indicated by a dashed arrow 30. FIG. 14 also schematically illustrates how light is largely diffused and reflected in accordance with the inclination of the curved surface of the diffusion structure 26. The structure 26 provided on the light-reflecting surface 22c is referred to as a “diffusion structure,” “diffusion structure,” or “diffusion surface” because it generates diffuse reflection as shown in FIG. 14 . In this example, a groove-shaped diffusion structure 26 on a curved surface of a cylindrical side surface is shown. However, this suggests that the shape of the diffusion structure 26 is not limited as long as it is a recessed shape with a slope that diffuses incident light, at least when viewed from the cross section or side of the light guide 22.

[0072] The diffusing structure 26 on the light reflecting surface 22c of the light guide 22 according to the first embodiment is a U-shaped concave structure that forms part of the side surface of a cylinder with a radius r = 0.40 mm. The width w of the diffusing structure 26 in the x' direction is 0.71 mm. The depth d of the diffusing structure 26 in the y' direction is 0.22 mm. The diffusing structure 26 is provided parallel to the z' direction within the range of 0 mm ≦ z' ≦ 1.9 / 2 mm. On the light reflecting surface 22c, when the range of 0 mm ≦ z' ≦ 1.9 / 2 mm is defined as the first reflecting surface 22c1 and the range of -1.9 / 2 mm ≦ z' ≦ 0 mm is defined as the second reflecting surface 22c2, with the x' axis dividing the light reflecting surface 22c into two, the diffusing structure 26 is formed only on the first reflecting surface 22c1. In other words, the light guide 22 according to the first embodiment includes, on its light reflecting surface 22c, diffusing structures 26 each having a length extending from an end of the light reflecting surface 22c in the width direction to half the width of the light reflecting surface 22c. The diffusing structures 26 are arranged in the x' direction (the spacing between the diffusing structures 26) with the goal of achieving a uniform irradiance distribution of the linear light beams emitted from the light emitting surface 22b in the x' direction (the longitudinal direction). Generally, the spacing between the diffusing structures 26 is relatively large in the portion closer to the light source 23, and relatively small in the portion farther from the light source 23.

[0073] 15 shows an illumination device 13 according to a second embodiment. The illumination device 13 according to the second embodiment includes the light guide 22 according to the first embodiment. To explain the illumination device 13, the x'y'z' Cartesian coordinate system used in the explanation of the light guide 22 will be used.

[0074] In the lighting device 13 according to the second embodiment, a light source 23 is disposed on one end surface 22a of a light guide 22. The light source 23 has a rectangular light-emitting surface measuring 0.25 mm x 0.25 mm, and its orientation attribute is a Lambertian light distribution. A Lambertian light distribution is a light distribution pattern in which the luminous intensity in the direction of an angle θ° can be expressed as cosθ times the luminous intensity Io on the optical axis (θ = 0°). (The angle at which the luminous intensity Io on the optical axis is half-value can be calculated as cosθ = 0.5 to θ = 60°.) An LED was assumed as the light source 23. The center of the light-emitting surface of the light source 23 is located at (-0.4, 1.9, 0) in the x'y'z' Cartesian coordinate system (all units are mm). In a simulation to clarify the function of the lighting device 13, a 5x10 ６ The light source 23 emits four light rays, all of which enter the light guide 22 through the light incident surface 22a. The distance between the light source 23 and the light incident surface 22a of the light guide 22 is 0.4 mm, and Fresnel reflection by the light incident surface 22a is not taken into account. Furthermore, in the simulation, the wavelength of the light source 23 is set to 550 nm, and the effects of refractive index dispersion of the light guide 22 and other media are not taken into account, and all light is assumed to be unpolarized. Driving an LED normally requires an electrical circuit such as a driver and a power supply, and a printed wiring board or the like is essential for electrically connecting the LED chip, but these will not be discussed in the calculations and explanation of this second embodiment.

[0075] The lighting device 13 according to the second example has a light guide cover 24 that covers the side surface of the light guide 22. The light guide cover 24, including the inner surface facing the side surface of the light guide 22, was assumed to be made of white plastic. The inner surface of the light guide cover 24 was assumed to be a Lambertian reflecting surface whose radiant intensity follows Lambert's cosine law. The reflectance of the inner surface of the light guide cover 24 was set to 87% (absorption rate 13%). Figure 15 shows the end surface of the light guide cover 24 perpendicular to the x' direction. The cross section of the light guide cover 24 is approximately U-shaped.

[0076] 16 is a schematic cross-sectional view perpendicular to the longitudinal direction of a contact image sensor 10 according to a third embodiment. The contact image sensor 10 according to the third embodiment includes the illumination device 13 according to the second embodiment. In the third embodiment, the diffusion structure 26 on the light reflecting surface of the light guide 22 is disposed on the side closer to the document reading position.

[0077] The contact image sensor 10 according to the third embodiment includes a document table 12 for placing a document including an area to be image-read, a light receiving element array 15 arranged in the longitudinal direction, and an erect equal-magnification lens array 14 for focusing the image of the object to be read onto the light receiving element array 15. Furthermore, the contact image sensor 10 according to the third embodiment includes the illumination device 13 according to the second embodiment for illuminating the area to be image-read, which is disposed so that the light exit surface 22b is substantially opposite the area to be image-read.

[0078] Consider a Cartesian coordinate system for explaining the function of the contact image sensor 10. The origin is the center of the light source 23 included in the illumination device 13 according to the second embodiment. The x-axis passes through the origin and is parallel to the longitudinal direction (the direction perpendicular to the paper surface), the z-axis passes through the origin, is parallel to the document placement surface 12a of the document table 12, and is perpendicular to the x-axis, and the y-axis passes through the origin and is perpendicular to the x-axis and z-axis. Furthermore, in the cross section of the contact image sensor 10, the angle between the normal to the light exit surface 22b and the z-axis or the x-z plane is set to 40°.

[0079] The illumination device 13 according to the second embodiment was driven under the above conditions to determine the radiation amount, such as irradiance, at the image reading target (hereinafter referred to as the "reading position") and near the reading position through simulation. In FIG. 16 , the irradiance was calculated by increasing z from the reading position (y,z)=(6.4,0) on the platen 12, then by increasing z from the reading position (y,z)=(6.4+1,0), then by increasing z from the reading position (y,z)=(6.4+2,0), and then by increasing z from the reading position (y,z)=(6.4+3,0) on the platen (all values ​​are in mm). The irradiance value was calculated by averaging the irradiance over the range x=100 mm to 150 mm within the 226 mm length of the light guide 22. In this way, the y and z dependencies of the irradiance at the reading position and its vicinity were obtained by simulation.

[0080] FIG. 17 shows the relationship between the y and z dependency of the irradiance at the reading position and its vicinity. In FIG. 17, it can be seen that there is a singular point of z where the change in irradiance is smallest even when Δy is changed from 0 to 3 mm. This singular point of z is called z ０ In the contact image sensor 10 according to the third embodiment, z ０ Varying Δy from 0 to 3 mm means that the reading object is moved away from the platen 12 by that amount, that is, "the document floats." The distance in the z direction between the illumination device 13 and the reading position is changed by z ０ By setting the z singular point z (4.9 mm), even if the document is lifted from the document table 12, the change in the irradiance of the illumination light illuminating the image to be read is small. ０ The DOI is sometimes referred to as the position that minimizes the DOI. DOI is defined as Depth Of Illumination or Depth Of Irradiance, and is a very important factor in the process of designing a contact image sensor using a specific illumination device.

[0081] 17, in the contact image sensor 10 according to the third embodiment, the z singular points z ０ The average irradiance at ―６ It was.

[0082] 18(a) to 18(c) are schematic three-view diagrams of a light guide 22 according to a fourth embodiment. As shown in FIG. 18(a), the light guide 22 according to the fourth embodiment has a configuration in which, compared to the light guide 22 according to the first embodiment, a corner portion substantially facing the diffusion structure 26 is chamfered and one side surface is added. In the cross section of the light guide 22 according to the fourth embodiment, a length c corresponding to the removed light exit surface 22b is Ｌ is 0.4 mm, and the angle α between the new side surface 22f and the light exit surface 22b is ｃ is 150°. The new side surface 22f provided by C-chamfering is a rectangle of 0.81 mm x 226 mm, and the surface attributes are the same as those of the other side surfaces of the light guide 22. The light guide 22 according to the fourth example has the same structure, characteristics, and parameters as the light guide 22 according to the first example, except that the corners substantially facing the diffusion structure 26 in the cross section are C-chamfered in the longitudinal direction.

[0083] Fifth Example The lighting device 13 according to the fifth example includes the light guide 22 according to the fourth example. The lighting device 13 according to the fifth example has the same structure, characteristics, parameters, etc. as the lighting device 13 according to the second example, except that the light guide 22 according to the fourth example is used instead of the light guide 22 according to the first example. Although the lighting device 13 according to the fifth example is not shown, its appearance is substantially the same as the lighting device shown in FIG.

[0084] Sixth Embodiment A contact-type image sensor according to the sixth embodiment includes the light guide 22 of the fourth embodiment and the illumination device of the fifth embodiment. In the sixth embodiment, the illumination device 13 is disposed so that the diffusion structure 26 of the light-reflecting surface 22c is closer to the document reading position, and the extended side surface 22f substantially opposing the diffusion structure 26 is farther from the document reading position. Except for the use of the light guide 22 of the fourth embodiment instead of the light guide 22 of the first embodiment, the structure, characteristics, parameters, etc. of the contact-type image sensor 10 according to the third embodiment are the same as those of the contact-type image sensor 10 according to the third embodiment.

[0085] In the contact-type image sensor 10 of the sixth embodiment, as in the contact-type image sensor 10 of the third embodiment, an xyz Cartesian coordinate system was set up, and the y and z dependencies of the irradiance at the reading position and its vicinity were determined by simulation.

[0086] Figure 19 shows the relationship between the y and z dependencies of the irradiance at the reading position and its vicinity. In Figure 19, the z singular point z where the change in irradiance is smallest even when Δy changes from 0 to 3 mm is ０ In the contact image sensor 10 according to the sixth embodiment, z ０ 19, in the contact image sensor 10 according to the sixth embodiment, the z singular points z ０ The average irradiance at ―６ It was.

[0087] 20(a) to 20(c) are schematic three-view diagrams of a light guide 122 according to a first comparative example. The light guide 122 according to the first comparative example has the same structure as the light guide 22 according to the first example, except that groove-shaped diffusion structures 126 including the shape of a cylindrical side surface are provided across the entire width of the light reflecting surface 122c in the z' direction, the radius of the cylinders constituting the diffusion structures 126 is set to 0.203 mm, and the arrangement of the groove-shaped diffusion structures 126 across the x' direction is determined with the goal of making the irradiance on the light exit surface approximately uniform.

[0088] (Second Comparative Example) The lighting device of the second comparative example has the same structure, characteristics, and parameters as the lighting device 13 of the second example, except that it has the light guide 122 of the first comparative example instead of the light guide 22 of the first example.

[0089] (Third Comparative Example) The contact-type image sensor of the third comparative example has the same structure, characteristics, parameters, etc. as the contact-type image sensor 10 of the third example, except that it is equipped with the illumination device of the second comparative example instead of the illumination device 13 of the second example.

[0090] In the contact-type image sensor of the third comparative example, similar to the contact-type image sensor 10 of the third embodiment, an xyz Cartesian coordinate system was established, and the y and z dependencies of the irradiance at the reading position and its vicinity were determined by simulation.

[0091] Figure 21 shows the relationship between the y and z dependencies of the irradiance at the reading position and its vicinity. In Figure 21, the z singular point z where the amount of change in irradiance is smallest even when Δy changes from 0 to 3 mm is ０ In the contact image sensor according to the third comparative example, z ０ 21, in the contact image sensor according to the third comparative example, the z singular points z ０ The average irradiance at ―６ It was.

[0092] 17, 19, and 21, the contact-type image sensors 10 according to the third and sixth examples will be compared with the contact-type image sensor according to the third comparative example. As mentioned above, FIGS. 17, 19, and 21 are graphs showing the y- and z-dependencies of irradiance near the reading position for the contact-type image sensors according to the third example, the sixth example, and the third comparative example, respectively. In the relationships shown in each graph, the maximum value of irradiance at Δy=0 mm, i.e., at a position in contact with the surface of the platen 12 (where the document is not floating), is 1.60×10 for the contact-type image sensors according to the third example, the sixth example, and the third comparative example, in that order. －６ (z Ｍ = 2.45 mm, z Ｍis the z value corresponding to the maximum irradiance), 1.80 x 10 ―６ (z Ｍ = 2.95 mm) and 1.30 × 10 －６ (z Ｍ = 2.95 mm), and the ratio thereof was 1.23:1.38:1.

[0093] Also, z is the z value corresponding to the maximum irradiance. Ｍ and z singular point z ０ The absolute value of the difference Δz = |z Ｍ -z ０ | was Δz=2.45 mm, 2.05 mm, and 3.05 mm for the contact image sensors according to the third example, the sixth example, and the third comparative example, respectively.

[0094] These results show that the maximum value of irradiance increases and the value of Δz decreases in the contact image sensors in the order of the third comparative example, the third example, and the sixth example. This shows that the contact image sensors according to the third and sixth examples can make the amount of radiation, such as the irradiance, that illuminates the original relatively large, even when Δy varies from 0 to 4 mm (when the original is floating).

[0095] In a contact-type image sensor, the direction parallel to the surface of the document table and perpendicular to the longitudinal direction is defined as the z direction, and the direction perpendicular to the z direction and the surface of the document table is defined as the y direction. The position in the z direction where the change in irradiance is smallest within the range of 0 to 4 mm from the surface of the document table in the y direction is defined as the z axis. ０ When the position in the z direction where the irradiance is maximum on the surface of the document table is zM, Δz=|z ０ -z Ｍ It is preferable that |≦2.5 [mm].

[0096] The present invention has been described above based on the embodiments. These embodiments are merely examples, and it will be understood by those skilled in the art that various modifications are possible in the combination of the components and treatment processes, and that such modifications are also within the scope of the present invention.

[0097] The present invention can be used in a contact type image sensor.

[0098] 10 Contact type image sensor, 12 Document table, 13 Illumination device, 14 Erect equal-magnification lens array, 15 Light receiving element array, 16 Housing, 17 Refractive index distribution rod lens, 18 Plate-shaped substrate, 22 Light guide, 23 Light source, 24 Light guide cover, 25 LED package, 26 Diffusion structure.

Claims

1. A light guide body in which light incident from an end face is reflected on an inner surface while propagating in a longitudinal direction and is emitted from a light exit surface, a light reflecting surface substantially opposite the light emitting surface; A plurality of diffusion structures provided on the light reflecting surface for diffusing and reflecting light; Equipped with A light guide characterized in that, when the light reflecting surface is divided into two regions, one of which is a first reflecting surface and the other is a second reflecting surface, Vp2≦Vp1 (Vp1 is the volume of the diffusion structure belonging to the first reflecting surface, and Vp2 is the volume of the diffusion structure belonging to the second reflecting surface).

2. 10. The light guide of claim 1, wherein the diffusing structure comprises the shape of a side of a cylinder or a portion of a sphere.

3. 3. The light guide according to claim 1, wherein Vp2=0.

4. 3. The light guide according to claim 1, further comprising a chamfered surface connected to the light exit surface in a cross section perpendicular to the longitudinal direction.

5. In a cross section perpendicular to the longitudinal direction, the angle α between the chamfered surface and the light exit surface ｃ is α ｃ 5. The light guide according to claim 4, wherein: = 100° to 160°.

6. The light guide according to claim 1 ; a light source disposed on or near the end surface of the light guide such that light is incident from the end surface; A lighting device comprising:

7. A light guide according to claim 4, a light source disposed on or near the end surface of the light guide such that light is incident from the end surface; A lighting device comprising:

8. A manuscript stand, an illumination device according to claim 6 or 7 for illuminating a document placed on the document table; a lens array that collects reflected light from a portion of the document illuminated by the illumination device; a light receiving element array that receives the light collected by the lens array; A contact type image sensor comprising:

9. 9. The contact image sensor according to claim 8, wherein the illumination device is disposed so that the diffusion structure is closer to a reading position of the document in a cross section perpendicular to the longitudinal direction of the contact image sensor.

10. The direction parallel to the surface of the document table and perpendicular to the longitudinal direction is defined as the z direction, the direction perpendicular to the z direction and the surface of the document table is defined as the y direction, and the position in the z direction at which the change in irradiance is smallest within a range of 0 to 4 mm from the surface of the document table in the y direction is defined as the z direction. ０ The position in the z direction where the irradiance is maximum on the surface of the document table is defined as z Ｍ When |z Ｍ -z ０ 9. The contact type image sensor according to claim 8, wherein |≦2.5 mm.