Light guide body, illumination device, and close-contact image sensor

Abstract

The light guide body (22) propagates the light incident from the end surface (22a) in the longitudinal direction while reflecting the light on the inner surface, and emits the light from the light emission surface (22b). The light guide (22) includes: a light reflecting surface (22c) substantially facing the light emitting surface (22b); and a plurality of diffusion structures (26) for diffusing and reflecting light, the diffusion structures (26) being provided on the light reflecting surface (22c). When the length of the diffusion structure (26) in the direction perpendicular to the longitudinal direction is Wr and the length of the light reflecting surface (22c) in the direction perpendicular to the longitudinal direction is Wp, Wr < Wp.

Description

Technical Field

[0001] The present invention relates to a light guide for guiding and emitting light from a light source, and an illumination device and a contact type image sensor using the light guide. Background Art

[0002] For devices such as fax machines, copiers, and handheld scanners, image reading devices such as image sensors are used as devices for reading manuscripts. In addition, as a type of image reading device, a contact image sensor (CIS) is used, which has a short optical path length and is easy to assemble into the device. In the case of this contact image sensor, reading is performed in a state where the illumination intensity is higher than that of the portion to be read of the manuscript that can be read by the lighting device, but the range of illumination is a strip that is long in the main scanning direction (length direction) and narrow in the sub-scanning direction orthogonal thereto. Therefore, the lighting device used for the contact image sensor is sometimes called a "linear lighting device."

[0003] Patent document 1 describes an invention related to a 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 performing multiple reflections inside the light guide, and has a light incident surface for incident light from a light source such as an LED, a light exit surface for emitting light in a ray-like shape, and a light reflecting surface roughly opposite to the light exit surface at the end. In the light guide described in Patent document 1, a concave-convex shape or a concave portion with a roughly circular cross-section is formed on a portion of the light reflecting surface, thereby seeking to suppress uneven illumination.

[0004] [Prior art literature]

[0005] [Patent Document]

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 10-133026 Summary of the invention

[0007] [Problems to be solved by the invention]

[0008] In the lighting device having the light guide described in Patent Document 1, it is taught that unevenness in the irradiated surface can be suppressed without having the existing light reflecting coating on the light reflecting surface. However, for example, there is no mention of the reduction of the radiant flux and irradiance in the case where a part of the original placed on the original table (sometimes also called contact glass, original table glass) floats (a part of the original leaves the original table surface that should be in close contact). In actual operation, there are many cases where it is necessary to read the image of the floating original, so whether it is the surface in contact with the contact glass or the surface at the position away from the contact glass, it is strongly desired to make the radiation amount such as radiant flux and irradiance uniform.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to achieve uniformity of radiation amounts such as radiation flux and radiation illuminance on a transparent manuscript table.

[0010] [Technical solutions for solving technical problems]

[0011] In order to solve the above-mentioned problem, a light guide according to one solution of the present invention is a light guide that propagates light incident from an end face along a length direction while reflecting it on an inner surface and emits it from a light exit surface, and includes a light reflecting surface substantially opposite to the light exit surface, and a plurality of diffusion structures disposed on the light reflecting surface for diffusing and reflecting light. When the length in a direction perpendicular to the length direction of the diffusion structure is denoted as Wr, and the length in a direction perpendicular to the length direction of the light reflecting surface is denoted as Wp, Wr<Wp.

[0012] Another embodiment of the present invention is a lighting device, which includes the above-mentioned light guide and a light source, wherein the light source is arranged at or near the end face so that light is incident from the end face of the light guide.

[0013] Another embodiment of the present invention is a close contact image sensor, which includes: a manuscript table; the above-mentioned lighting device, which is used to illuminate the manuscript placed on the manuscript table; a lens array, which collects reflected light from a part of the manuscript illuminated by the lighting device; and a light receiving element array, which receives the light collected by the lens array.

[0014] In addition, any combination of the above-mentioned constituent elements, or changes between the expression methods and devices of the present invention, etc., may also be effective as aspects of the present invention.

[0015] Effects of the Invention

[0016] According to the present invention, it is possible to achieve uniformity of radiation amounts such as radiation flux and radiation illuminance on a transparent manuscript stage. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic perspective view of a contact-type image sensor according to an embodiment of the present invention.

[0018] Figure 2 This is a schematic cross-sectional view perpendicular to the longitudinal direction of the contact type image sensor according to the embodiment of the present invention.

[0019] Figure 3 This is a schematic stereogram of an example of an erect equal-magnification lens array.

[0020] Figure 4 This is a schematic perspective view of an example of an illumination device used for a contact-type image sensor.

[0021] Figure 5 (a) and Figure 5 (b) is a schematic diagram showing an LED package on which a plurality of LED chips are mounted.

[0022] Figure 6 (a)~ Figure 6 (c) is a schematic three-view diagram showing an example of a light guide having a diffusion structure composed of a plurality of divided cylindrical side surfaces on a light reflecting surface.

[0023] Figure 7 This is an enlarged schematic top view of a light reflecting surface provided with a diffusion structure formed by dividing the side surface of a cylinder.

[0024] Figure 8 This is a diagram showing a diffusion structure formed by dividing the side surfaces of a cylinder.

[0025] Fig. 9 This is an enlarged schematic plan view of a light reflecting surface provided with a diffusion structure composed of spherical recesses.

[0026] Fig.10 It is a diagram showing a diffusion structure composed of spherical recesses.

[0027] Fig.11 This is a diagram qualitatively showing the z-direction dependency of the radiant illuminance on the document stage.

[0028] Fig.12 It is a cross-sectional view of a light guide according to another embodiment.

[0029] Fig.13 (a)~ Fig.13 (c) is a schematic three-view diagram of the light guide of the first embodiment.

[0030] Fig.14 This is a schematic enlarged view of a portion of a groove-shaped diffusion structure group.

[0031] Fig.15It is a diagram showing a lighting device according to a second embodiment.

[0032] Fig.16 This is a schematic cross-sectional view perpendicular to the longitudinal direction of the contact-type image sensor according to the third embodiment.

[0033] Fig.17 It is a diagram showing the relationship between the y and z dependencies of the irradiance in the vicinity of the reading position.

[0034] Fig.18 (a)~ Fig.18 (c) is a schematic three-view diagram of the light guide of the fourth embodiment.

[0035] Fig.19 It is a diagram showing the relationship between the y and z dependencies of the irradiance in the vicinity of the reading position.

[0036] Fig. 20 (a)~ Fig. 20 (c) is a schematic three-view diagram of the light guide of the first comparative example.

[0037] Fig.21 It is a diagram showing the relationship between the y and z dependencies of the irradiance in the vicinity of the reading position. DETAILED DESCRIPTION

[0038] The following is a description of the embodiments of the present invention. The same or equivalent components, members, and processes shown in the drawings are marked with the same reference numerals, and repeated descriptions are appropriately omitted. In addition, the embodiments do not limit the invention, but are only examples, and all the features and combinations described in the embodiments are not the substantive contents of the invention.

[0039] Figure 1 FIG. 1 is a schematic perspective view of a contact type image sensor 10 according to an embodiment of the present invention. Figure 1 As shown, the contact image sensor 10 may have a length in the longitudinal direction corresponding to the width or length of the document or workpiece to be read. For example, when the document to be read is A4 size, the contact image sensor 10 may have a length corresponding to the width of A4 paper.

[0040] Figure 2 FIG. 1 is a schematic cross-sectional view perpendicular to the longitudinal direction of the contact type image sensor 10 according to the embodiment of the present invention. Figure 2As shown, the close contact image sensor 10 includes: a transparent parallel flat plate-shaped manuscript table 12, which is used to place the image reading object, that is, the manuscript 11; an illumination device 13, which is used to illuminate a part of the manuscript 11 placed on the manuscript table 12; an erecting equal-magnification lens array 14, which focuses a part of the image of the manuscript 11 illuminated by the illumination device 13 into an erecting equal-magnification image; and a light receiving element array 15, which is used to read the image focused by the erecting equal-magnification lens array 14. Furthermore, Figure 1 The contact type image sensor 10 shown in FIG. 1 includes a housing 16 for integrating these components in an appropriate arrangement.

[0041] The manuscript table 12 is formed as a transparent parallel flat plate. The manuscript table 12 needs to be highly transparent, so it can be formed of glass or a transparent resin with high light transmittance such as cycloolefin, propylene, or polycarbonate. Alternatively, in the case where the mechanical strength is significantly higher and high light transmittance is required, tempered glass may be used. When the manuscript table 12 is formed of glass, it may also be referred to as manuscript table glass, contact glass, manuscript table glass, etc. The manuscript table 12 is formed of glass. Figure 1 As shown, it may be long in one direction, or it may be a rectangular shape having long sides in a certain direction when viewed from above.

[0042] In the upright equal-magnification lens array 14, a plurality of single lenses having an object-image relationship of an upright equal-magnification system are arranged in a manner such that the optical axes of the lenses are parallel to each other at least along the length direction (main scanning direction). Here, a lens array as an upright equal-magnification system is adopted, but a lens array of an imaging system that is not upright or an imaging system that is not equal-magnification can also be adopted. From the perspective of the compactness requirement of the close-contact image sensor 10 and the robustness related to the tolerance to the positional deviation of each component, it is preferred to adopt an upright equal-magnification lens array.

[0043] As the lens array, SELFOC lens array (SELFOC is a registered trademark) manufactured by Nippon Sheet Glass Co., Ltd., or plastic lens array manufactured by Mitsubishi Chemical Corporation, or Linear Micro Lens Array of two lenses of Pixon Corporation can be used. Each single lens constituting the first two is a refractive index distribution type rod lens having a refractive index distribution in which the refractive index decreases from the center to the periphery inside a transparent cylindrical dielectric, and can have the function of refracting light without setting the interface with the air as a curved surface.

[0044] Figure 3 It is a schematic perspective view of an example of the erecting equal-magnification lens array 14 . Figure 3In the upright equal-magnification lens array 14 shown in FIG. 1 , the refractive index distribution type rod lenses 17 are arranged in one or more rows along the main scanning direction in such a manner that the central axes thereof are substantially parallel to each other, and a plurality of ( Figure 3 The lens array shown in FIG. 1 is configured as a row). The upright equal-magnification lens array 14 is as shown in FIG. Figure 3 As shown, it is sandwiched between two plate-like base materials 18 and 19, and is integrated with spacers (plates) 20 and 21 arranged at both ends.

[0045] As described above, this upright equal-magnification lens array 14 is characterized by not needing to set the end face corresponding to the light output and incident face as a curved surface, etc., and has extremely efficient processability, the lens diameter can be reduced, the resolution and contrast are high, and an upright equal-magnification image can be easily obtained.

[0046] In the light receiving element array 15, light receiving elements such as PD (photodiode) or APD (avalanche photodiode) are arranged at least long in the main scanning direction. The light receiving element array 15 receives light reflected from a part of the image of the original 11 on the original table 12 and collected by the upright 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 storage device, an image engine, and other devices.

[0047] Alternatively, the light receiving element array 15 may be arranged in three rows along the sub-scanning direction, for example, and the light receiving elements in each row may have color filters corresponding to R (red), G (green), and B (blue) on the light receiving surface. Alternatively, the light of the image of the original document emitted from the upright equal-magnification lens array 14 may be split by a diffraction grating or a beam splitter prism, and the split light may be received by the light receiving element array 15 arranged in three rows along the sub-scanning direction, thereby obtaining a color image of the original document.

[0048] Figure 4 1 is a schematic perspective view of an example of an illumination device 13 used in the contact type 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 configured to allow light to enter from at least one end surface 22a of the light guide 22; and a light guide cover 24 that is used to accommodate the light guide 22.

[0049] Figure 2 This is a cross-sectional view of the contact type image sensor 10 perpendicular to the main scanning direction (longitudinal direction), so the light source 23 arranged on the end surface 22a of the light guide 22 or in the vicinity thereof cannot be shown. Figure 2 In, but in Figure 2 In FIG. 1 , a light source axis is assumed to pass through the center of the light source 23 and be perpendicular to the paper surface, and the light source 23 is represented at a position corresponding to the axis.

[0050] exist Figure 2 In the contact type image sensor 10 shown in FIG, the position of the light source 23 is taken as the origin, and an orthogonal coordinate system is set, which includes an x-axis (light source axis) passing through the origin and perpendicular to the paper surface, a z-axis passing through the origin and perpendicular to the x-axis and parallel to the surface of the manuscript table, and a y-axis passing through the origin and perpendicular to the x-axis and the z-axis. From the viewpoint of the scanning performance of the contact type image sensor 10, the direction (x-direction) which is the longitudinal direction of each component and perpendicular to the paper surface is referred to as the main scanning direction, and the direction (z-direction) which is perpendicular to the main scanning direction is referred to as the sub-scanning direction.

[0051] The function of the lighting device 13 is described below. Figure 4 In the embodiment, light emitted from a light source 23 disposed at an end face 22a of the light guide 22 or in the vicinity thereof is incident on the inside of the light guide 22 from the end face 22a. The light incident on the light guide 22 propagates along the length direction inside the light guide 22. The light guide 22 has: a light emitting surface 22b that emits light linearly along the length direction; and side surfaces other than the light emitting surface 22b. The light emitting surface 22b and the side surfaces are longer in one direction. One side surface of the light guide 22 may be a light reflecting surface that directs the traveling direction of a part of the light toward the light emitting surface 22b. The light reflecting surface may include a surface opposite to the light emitting surface 22b.

[0052] The light source 23 may be, for example, an LED. The LED may emit white light. The light source 23 may contain a plurality of LED chips that emit light of red, green, and blue wavelengths, respectively, in one package. In this case, the three-color LED chips are sequentially illuminated, and the light intensity is sequentially detected together with the timing of their illumination, so that even if it is a row of the light receiving element array 15, a color image of the original document can be obtained through image processing in a post-process, etc. In addition, for example, it is also possible to use the LED contained in one package after dipping those LED chips and the LED chips that emit light of red and blue wavelengths in a transparent resin to which a fluorescent agent is added. It is also possible to use the LED as a color display LED that indicates white from the light emitting surface of the package by emitting fluorescence of light of green wavelengths from the fluorescent agent excited by a part of the light of blue wavelength. On the other hand, the LED chips that emit light of red, green, and blue wavelengths can be respectively arranged on the end surface 22a of the light guide 22 to constitute the lighting device 13. At this time, the three-color LED chips are sequentially lit, and the color and light intensity are detected by the light receiving element array 15 together with the timing of the light emission, and mixed by the image processing device, etc., so that a color image of the original document can be obtained. If the dependence of the radiant illumination of the light emitted from the lighting device 13 on the end surface position of the LED is known in advance, the radiant illumination and the radiant flux can be reflected on the specific position of the end surface 22a of the light guide 22 where a relatively large radiation intensity is obtained, and the uniformity of the radiant illumination of each color in the original document and its vicinity can be sought.

[0053] Figure 5 (a) and Figure 5 (b) is a schematic diagram showing an LED package 25 in which LED chips 25a, 25b, and 25c radiating monochromatic light of R (red), G (green), and B (blue) are mounted in one package. Figure 5 (a) is a top view of the LED package 25, Figure 5 (b) is a cross-sectional view of the LED package 25 .

[0054] The LED package 25 may have a horizontal length wL1 of 0.7 mm to 3 mm and a vertical length wL2 of 0.7 mm to 3 mm in a plan view, or wL1 = wL2. The LED package 25 may have a height hL of 0.3 mm to 5 mm.

[0055] Alternatively, the light guide 22 may be made of a transparent dielectric so that light can be efficiently transmitted. At least in the wavelength range of the light to be used, the absorption of the light guide 22 is as small as possible, and it is preferably made of a material with a high internal transmittance. As such a material, for example, glass can be exemplified. In addition, as a material constituting the light guide 22, from the perspective of its formability, a transparent resin (plastic) can be exemplified. The resin is not limited thereto, but examples thereof include polymethyl methacrylate (acrylic resin), polycarbonate, polystyrene, AS resin, epoxy resin, silicone resin, or cycloolefin resin.

[0056] Regarding the light guide 22, a cross section perpendicular to the x direction (length direction) (hereinafter referred to as "cross section of the light guide") may be substantially rectangular. In addition to being substantially rectangular, the cross section of the light guide 22 may be in any shape consisting of straight lines and curves. In particular, when the curve includes a portion of an ellipse, the light is enclosed in the light guide because of a focal effect, and sometimes it can be expected that the efficiency of extracting light from the light guide 22 will be improved.

[0057] When the cross-sectional shape of the light guide 22 is substantially rectangular, a portion of the corners may be formed by the C surface and the R surface. In the portion of the light guide 22 that is relatively far from the light source 23, there is a tendency for the radiant illumination and radiant intensity of the light to decrease. Therefore, in order to compensate for this, the cross-sectional shape of the light guide 22 may also be changed according to the position in the longitudinal direction thereof.

[0058] The light guide 22 has a light exit surface 22b extending in the longitudinal direction. The light exit surface 22b has a function of taking out light for illumination from the light guide 22. The light exit surface 22b is configured to effectively illuminate the image reading position of the original 11 on the original table 12. The light exit surface 22b may be directed in the direction of the image reading position.

[0059] Regarding the light emitting surface 22b, its surface can be either a flat surface or a surface including a curved surface. In the case where the light emitting surface 22b includes a curved surface, since it has the function of converging light, the radiation intensity and radiation illumination of the light in a specific place will be increased, and it can be controlled inversely. The surface roughness of the light emitting surface 22b is not determined, and it can be a so-called mirror surface or have concavities and convexities. When the mirror surface or the concavities and convexities on the surface are very small, it is easy to control the directivity of the light taken out from the light emitting surface 22b. When the concavities and convexities on the surface are of a size that causes scattering or diffusion of light, the illumination light can be uniformed by the scattering or diffusion, and other diffuse reflection effects.

[0060] The light guide 22 has side surfaces extending in the length direction other than the light emitting surface 22b. Alternatively, each side surface may function as a reflective surface for propagating light inside the light guide 22 along the length direction of the light guide 22. Inside the light guide 22, light is repeatedly reflected in a manner of being reflected toward a portion of the side surface, thereby propagating along the length direction of the light guide 22. When the angle of light propagating in the light guide 22 when reaching the side surface is large enough, it propagates while being reflected in a manner of total reflection or close to total reflection. In the case where the light reaches the side surface of the light guide 22 under the condition that total reflection cannot be achieved, a portion of the light may sometimes be emitted from the side surface. The side surface of the light guide 22 may be either a flat surface or a surface including a curved surface. In the case where the light emitting surface 22b includes a curved surface, it can have the effect of converging light. The surface roughness of the side surface of the light guide 22 is not determined. When the surface unevenness is small, it is easy to control the directionality of the light emitted from the light emitting surface 22b. When the surface unevenness is large enough to cause scattering or diffusion of light, the radiant illumination and radiation intensity of the light in the light guide 22 can be uniformed through the scattering or diffusion effect.

[0061] At least a portion of the side surface of the light guide 22 may have a function such as directing a portion of the reflected light toward the light emitting surface 22b. The portion having such a function is referred to as a "light reflecting portion". In the case where the cross-sectional shape of the light guide 22 is a rectangle, the side surface has a plurality of side surfaces divided by edges. On the other hand, the cross-sectional shape of the light guide 22 is sometimes not divided by clear edges such as a roughly circular or elliptical shape. In the case where the cross-sectional shape of the light guide 22 is a rectangle, at least one surface of the light guide 22 may be a surface having the function of a light reflecting portion. The side surface having a portion of the function of a light reflecting portion is referred to as a "light reflecting surface". The light reflecting surface may also be a surface opposite to the light emitting surface or a portion of such a surface.

[0062] Alternatively, the light reflecting surface may have a structure such that a portion of the light reaching the surface or portion is directed toward the light emitting surface 22b. The structure of the light reflecting surface used to exert or improve its function is not limited. For example, in order to improve the reflection efficiency of light, the light reflecting surface may also have a colored portion such as silver or white on a portion thereof. Alternatively, such silver or white may be formed by coating or printing. By such coloring with high light reflectivity, the radiation of light reflected in a manner that reaches a portion of the light reflecting surface and is directed toward the light emitting surface will become larger. In addition, the surface of the colored portion such as silver or white, which is provided on the surface of the light guide by coating or printing, etc., may or may not be a mirror surface. In the case where the surface of such a colored portion is not a mirror surface, diffuse reflection of light will be promoted, directed toward the light emitting surface, and the radiation intensity of the light will be helped to be uniform.

[0063] In addition, regarding the colored portion such as silver or white provided on a part of the light reflecting surface by printing or coating, the pattern thereof may be changed along the length direction of the light guide 22. Since the radiation amount such as the radiation illumination and the radiation intensity decreases as the distance from the light source 23 is inside the light guide 22, the radiation amount of the light reflected from the light reflecting surface and emitted to the light emitting surface 22b also decreases accordingly. Therefore, it is also possible to set the pattern as follows: as the distance from the light source 23 is increased, for example, the area of ​​the portion such as white or silver that improves the light reflection ability increases, and the area of ​​the portion that reflects is decreased at the portion on the side close to the light source 23.

[0064] In the case where the light reflecting surface does not include a colored portion such as silver or white provided by printing or coating, the radiation amount of the light reaching the light reflecting surface and directed to the light emitting surface 22b sometimes becomes smaller. In this case, the light extraction efficiency from the light emitting surface 22b will be reduced, so it is not preferred. Alternatively, in order to partially improve or control its diffuse reflectivity and scattering, the light reflecting surface may have a structure having a concave or convex portion. For example, consider a case where the light reflecting surface has a concave portion that includes a portion of the side surface of a cylinder. When light reaches the light reflecting surface at a predetermined incident angle, the diffuse reflectivity of the light reflected by the surface of the concave portion becomes higher than that of the flat surface. The so-called diffuse reflectivity refers to a state in which when multiple light rays reach a predetermined surface and are reflected, they are not reflected at a constant reflection angle, but at multiple reflection angles, so that the light rays are reflected dilatatively (diffusely) as a whole. In the case where the light reflecting surface does not include such a structure or a colored portion, it strongly promotes the propagation of light inside the light guide 22, so the radiation amount of light directed to the light exit surface 22b cannot be increased, and the light extraction efficiency will become relatively poor. The structure that diffuses and reflects part of the light on the light reflecting surface is called a "diffusion structure".

[0065] Regarding the scheme of the diffusion structure in the light reflecting surface, as long as it is a structure that diffuses and reflects a part of the light reaching the surface, it will not be determined. For example, the invention disclosed in Japanese Patent Publication No. 2006-120932 and Japanese Patent Publication No. 2003-197016 discloses a light guide, which has a spherical recess and a triangular groove ("V" shaped groove), and a divided cylindrical groove ("U" shaped groove) in the surface opposite to the light emitting surface (called the light scattering surface). The scheme of the diffusion structure of the present embodiment can be set to any one of them, or a scheme obtained by appropriately combining them. According to the patent document, structures similar to these diffusion structures are formed for the following purpose: to reduce the deviation of the radiation amount of uneven color and uneven brightness.

[0066] The diffusion structure having these conditions may be provided on the entire light reflecting surface, or may be a light reflecting surface including a portion of the light reflecting surface of the diffusion structure having such conditions. In addition, the diffusion structure having these conditions may also be provided in appropriate combination. Alternatively, the light guide 22 in this embodiment may partially have a diffusion structure on the light reflecting surface.

[0067] Figure 6 (a)~ Figure 6 (c) is a schematic three-view diagram showing 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 the light reflecting surface. Figure 6 (a) is a view of the light guide 22 as viewed from the end face 22a side. Figure 6 (b) is a side view showing a portion of the light guide 22. Figure 6 (c) is a view obtained by observing from the light reflecting surface side of the light guide 22. Figure 6 (a)~ Figure 6 In (c), an x'y'z' orthogonal coordinate system is shown. Figure 6 (a)~ Figure 6 The light guide 22 shown in (c) has a light emitting surface 22b that is at right angles to the end surface 22a, and has a light reflecting surface 22c on the surface opposite to the light emitting surface 22b. In the light guide 22, the light emitting surface 22b and the light reflecting surface 22c are parallel, but the light emitting surface 22b and the light reflecting surface 22c may be in a relationship where the interval between them decreases in a tapered manner along the length direction, for example.

[0068] exist Figure 6 (a)~ Figure 6 In the light guide 22 shown in (c), the direction parallel to the end face 22a is denoted as the y' direction, and the length direction of the light guide 22 (in Figure 6The direction perpendicular to the paper surface in (a) is recorded as the x' direction, and the direction perpendicular to the x' direction and the y' direction and parallel to the light reflecting surface 22c is recorded as the z' direction. The intersection of the edge connecting the end surface 22a and the light reflecting surface 22c and the bisector parallel to the x' direction that bisects the light reflecting surface 22c in the z' direction is taken as the origin.

[0069] exist Figure 6 In (c), a dashed line L1 parallel to the x' direction that divides the light reflecting surface 22c into two is described (there is no such line in the actual light guide 22, but it is described for the sake of explanation). Figure 6 In the light reflecting surface 22c shown in (c), the upper side of the one-dot chain line L1 is the first reflecting surface 22c1, and the lower side is the second reflecting surface 22c2.

[0070] like Figure 6 (a)~ Figure 6 As shown in (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 length direction of the light guide 22. Starting from the origin close to the x'y'z' orthogonal coordinate system, they are sequentially represented as diffusion structures 26(1), 26(2), ... 26(n). In addition, when the diffusion structures are collectively referred to below, they are simply referred to as diffusion structures 26.

[0071] exist Figure 6 (a)~ Figure 6 In the light guide 22 shown in (c), the length Wr(k) of each diffusion structure 26(k) parallel to the z' direction (perpendicular to the main scanning direction) is Wr(k)<Wp. Here, Wp is the width of the light reflecting surface 22c (the length in the z' direction). The length Wr(k) of a part of the diffusion structure 26(k) is shorter than 1 / 2×Wp, and the length Wr(k) of a part of the diffusion structure 26(k) is approximately equal to 1 / 2×Wp, which is Wr(k)≤1 / 2×Wp. In addition, the length Wr(k) of a part of the diffusion structure 26(k) is longer than 1 / 2×Wp. In addition, the end of a part of the diffusion structure 26(k) in the z' direction does not reach the end (edge) of the light reflecting surface 22c in the z' direction.

[0072] Figure 7 This is an enlarged schematic top view of a light reflecting surface 22c provided with a diffusion structure composed of split cylindrical side surfaces. Figure 7 , four diffusion structures 26(k) to 26(k+3) are shown. Some of the diffusion structures 26(k) and 26(k+1) are provided across the first reflection surface 22c1 and the second reflection surface 22c2. In addition, some of the diffusion structures 26(k+2) and 26(k+3) are provided only on the first reflection surface 22c1. Figure 7 In this way, when the diffusion structure 26 disposed on the light reflecting surface is viewed from above, the center line that divides the diffusion structure 26 into two along the x' direction is assumed, and the length on the center line of the diffusion structure 26 can be used as the length of the diffusion structure 26, or the maximum length of the diffusion structure 26 in the z' direction can be used as the length of the diffusion structure 26. Alternatively, the width of the light reflecting surface 22c on the extension of the center line of the diffusion structure 26 can be recorded as Wp, and when the light reflecting surface is a substantially rectangular shape when viewed from above, it can be equal to the length of the side in the z' direction and the width of the central part of the light reflecting surface. The length of the diffusion structure 26 and Wp can be measured by a measuring microscope, a projector with a measuring device, a vernier caliper, a micrometer, etc.

[0073] The volume of one diffusion structure 26 belonging to the first reflection surface 22c1 is represented by Vp1, and the volume of the diffusion structure 26 belonging to the second reflection surface 22c2 is represented by Vp2. Figure 8 The diffusion structure 26 provided across the first reflecting surface 22c1 and the second reflecting surface 22c2 is divided into a region of volume Vp1 belonging to the first reflecting surface 22c1 and a region of volume Vp2 belonging to the second reflecting surface 22c2.

[0074] In this embodiment, Figure 6 (c) Figure 7 Some of the diffusion structures 26 shown in φ have Vp2<Vp1, and also include diffusion structures 26 with Vp2<0.5×Vp1 and diffusion structures 26 with Vp2=0.

[0075] The relationship between Vp1 and Vp2 in the diffusion structure 26 is Vp2≤Vp1, preferably Vp2≤0.5×Vp1, more preferably Vp2≤0.25×Vp1, and particularly preferably Vp2≤0.1×Vp1. In addition, Vp2=0 may be satisfied.

[0076] Here, a concave diffusion structure 26 including the side of a cylinder (or a column) is described, but it is not limited to a strict cylinder, and may also include a side of a roughly cylindrical cross-section such as an ellipse or an ellipse. When the light reaching the diffusion structure 26 is reflected (diffused) in multiple directions, its shape is not limited. The diffusion structure 26 can have a depth of 0.05mm to 2mm, or it can be parallel to the light reflecting surface 22c and have a width of 0.2mm to 10mm in the x' direction. In addition, the diffusion structure 26 can also be the following scheme: when viewed from above from the light reflecting surface on which they are provided, its width and depth taper down in the z' direction.

[0077] Fig. 9FIG. 2 is an enlarged schematic top view of a light reflecting surface 22c provided with a diffusion structure composed of spherical recesses. Fig. 9 In, with Figure 7 Likewise, a dashed line L1 is shown dividing the light reflecting surface 22c into two. Fig. 9 , four diffusion structures 26(k) to 26(k+3) are shown. Some of the diffusion structures 26(k) and 26(k+1) are provided across the first reflection surface 22c1 and the second reflection surface 22c2. In addition, some of the diffusion structures 26(k+2) and 26(k+3) are provided only on the first reflection surface 22c1.

[0078] exist Fig. 9 In the diffusion structures 26 shown in FIG. , Wr(k) < Wp, in some diffusion structures 26, Wr(k) ≤ 1 / 2×Wp, and in other diffusion structures 26, 1 / 2×Wp < Wr(k) < 3 / 5×Wp. In addition, Fig. 9 In this way, when the diffusion structure 26 disposed on the light reflecting surface is viewed from above, the center line that divides the diffusion structure 26 into two along the x' direction is assumed, and the length on the center line of the diffusion structure 26 can be used as the length of the diffusion structure 26, or the maximum length of the diffusion structure 26 in the z' direction can be used as the length of the diffusion structure 26. Alternatively, the width of the light reflecting surface 22c on the extension of the center line of the diffusion structure 26 can be recorded as Wp, and when the light reflecting surface is a substantially rectangular shape when viewed from above, it can be equal to the length of the side in the z' direction and the width of the central part of the light reflecting surface. The length of the diffusion structure 26 and Wp can be measured by a measuring microscope, a projector with a measuring device, a vernier caliper, a micrometer, etc.

[0079] Fig.10 The diffuser structure 26 provided across the first reflecting surface 22c1 and the second reflecting surface 22c2 is divided into a region of volume Vp1 belonging to the first reflecting surface 22c1 and a region of volume Vp2 belonging to the second reflecting surface 22c2. In the present embodiment, some of the diffuser structures 26 satisfy Vp2<Vp1, and further, Vp2<0.5×Vp1, Vp2=0.

[0080] Alternatively, the diffusion structure 26 formed of the spherical concave portion is provided only on the first reflecting surface 22c1. The diffusion structure 26 formed of the spherical concave portion may be circular, elliptical or oval in plan view. The curved surface portion of the spherical concave portion may be a portion of a non-spherical shape such as a portion of a rotating ellipsoid, in addition to being a portion of a spherical surface.

[0081] The diffusion structure 26 composed of the aforementioned "U"-shaped groove and spherical concave portion is not limited thereto. In addition, both the groove-shaped diffusion structure 26 and the spherical concave-shaped diffusion structure 26 can be included in the light reflecting surface 22c. When the diffusion structure 26 that satisfies the above conditions is used to form the lighting device 13 with the light guide 22 included in the light reflecting surface 22c, the line width of the linear illumination light emitted from the lighting device 13 will become smaller, and the radiation amount such as the central radiant illumination will become larger. As mentioned above, in the absence of printing or coating such as white for reflecting or diffusing light, the light reflecting surface and the side surfaces containing the diffusion structure have a stronger effect of propagating the light reaching them along the length direction of the light guide. Therefore, the diffusion structure 26 is provided for the purpose of increasing the radiation amount of the light directed to the light exit surface 22b, but by limiting the length of the light reflection surface 22c of the diffusion structure 26 in the width direction (smaller than the width of the light reflection surface 22c), the concentration of the distribution of the radiation illuminance directed to the light exit surface 22b is increased, and the line width of the illumination light emitted linearly is reduced. For example, it can be said that the first reflection surface 22c1 in the light reflection surface 22c has the function of increasing the radiation amount of the light directed to the light exit surface 22b, and the second reflection surface 22c2 has the function of increasing the radiation amount of the light propagating in the length direction of the light guide 22. The line width of the linear light emitted from the lighting device 13 is reduced, which has the advantage that the radiation illuminance irradiated to the original 11 on the original table 12 is increased.

[0082] In the close-contact image sensor 10, when the reading object portion of the original 11 on the original table 12 is displaced in the y direction (sometimes also manifested as when it leaves the original table 12 and the original becomes "floating"), there is a requirement to make the radiation illumination received by the reading object portion of the original 11 constant.

[0083] Fig.11 This is a diagram that qualitatively shows the z-direction dependency of the irradiance on the document table 12 in the contact type image sensor 10, using the conditions of y=0 (document table surface) and y=y1 (position after displacement y1 in the y direction). It can be seen from this that there is a singular point: when z=z0, the irradiance does not change even with displacement in the y direction, or the difference in irradiance is minimal. The contact type image sensor 10 is designed by rotating the lighting device 13 around the x direction, and taking into account the predetermined y length and z0 as the singular point at this time.

[0084] In the present embodiment, light having a radiant illumination distribution with a small dispersion and a high concentration of radiant illumination in the center portion is emitted from the illumination device 13, and reaches the vicinity of the original document 11. This teaches that, in the relationship representing the z-direction dependency of the radiant illumination on the original document stage 12, the difference between the value of z (zM) corresponding to the portion with high radiant illumination and the value of z0 corresponding to the singular point becomes small, and the radiation amount such as radiant illumination in the singular point becomes high.

[0085] Fig.12 FIG. 2 is a cross-sectional view showing another embodiment of the light guide 22. Fig.12 As shown, in its cross section, a part of the corner 22e of the side 22d roughly opposite to the diffusion structure 26 is chamfered. By doing so, a new side 22f roughly opposite to the diffusion structure 26 is generated in the cross section of the light guide 22. Since the new side 22f roughly opposite to the diffusion structure 26 is provided, a part of the light diffused and reflected from the diffusion structure 26 reaches the new side 22f and is further reflected into the light guide 22, thereby the light confinement effect is exerted and the light utilization efficiency is improved. In addition, in the case where there is no chamfering of the corner 22e, when the lighting device 13 is configured so that the light emitting surface 22b of the light guide 22 is opposite to the part of the original 11 of the reading object part, there is the possibility that a part of the light is emitted in a direction that is greatly different from the reading object part of the original 11. By chamfering the corner 22e, such a situation can be suppressed, and the light utilization efficiency can be expected to be improved.

[0086] The scheme of the roughly opposite chamfered portions of the diffusion structure 26 can be expected to improve the light confinement effect, and is not limited as long as the line width of the linear illumination light emitted from the light emitting surface 22b becomes smaller and the radiant illuminance of the central part of the irradiation illuminance distribution becomes larger. The scheme of the new side 22f generated by the chamfer can be either an R surface (curved surface) or a C surface (flat surface), or a scheme obtained by combining them. In other words, the new side 22f can be roughly opposite to the diffusion structure 26 in the cross section of the light guide 22, contact with the light emitting surface 22b, and have an angle with the light emitting surface 22b that exceeds 90°. Alternatively, this new side 22f may be called an "expanded side".

[0087] In the cross section of the light guide 22, the removed length cL in the light emitting surface 22b (the length of the expanded side surface 22f in the direction parallel to the light emitting surface 22b) can be 0.1×W0'≤cL≤0.3×W0' (W0' represents the width of the light emitting surface 22b removed by chamfering, or the width of the light emitting surface 22b when the expanded side surface 22f is present). In addition, the angle αc formed by the expanded side surface 22f and the light emitting surface 22b can also be 100° to 160°.

[0088] Furthermore, the expanded side surface 22f produced by chamfering may be colored with a color having a high light reflectivity such as white or silver in order to improve the reflection efficiency of the light that reaches the expanded side surface 22f. The coloring of white or silver may also be provided by printing or painting.

[0089] Alternatively, the lighting device 13 includes a structure covering the light guide 22. Light incident on the light guide 22 from the light source 23 propagates in the length direction inside the light guide 22. The propagation of the light is performed while repeating reflection based on the side surface of the light guide 22, as described above. When the light reaching the side surface of the light guide 22 satisfies the condition of total reflection in the relationship with the incident angle of the side surface, approximately 100% of the light will be reflected, but when this is not the case, a portion of the light will be emitted from the side surface of the light guide 22. Therefore, in order to seek to improve the efficiency of light utilization, the lighting device 13 of the present embodiment may also include a light guide cover 24 covering at least a portion of the side surface of the light guide 22. Since the lighting device 13 includes the light guide cover 24 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 can be reflected on the inner surface of the light guide cover 24 and then incident on the light guide 22. Regarding the light guide cover 24, it may be, for example Figure 2 As shown in the cross-sectional view of , the cross section perpendicular to the longitudinal direction (x direction) is roughly "U"-shaped, and the inner surface of the light guide cover 24 may be set to be in close contact with a part of the side surface of the light guide 22. In addition, in order to improve the reflectivity of light, the inner surface of the light guide cover 24 may be colored with a high light reflectivity such as white or silver. This coloring method may also be printing or painting. From the viewpoint of its moldability and the requirement for low price, the light guide cover 24 may be composed of plastic as a material. Examples of plastics that become the material of the light guide cover 24 include polyamide, polycarbonate, polyacetal, modified polyphenylene ether, polybutylene terephthalate, polyphenylene sulfide, polyether sulfone, polyarylate, polyetherimide, liquid crystal polymer, etc. In addition, from the viewpoint that the light guide cover 24 preferably has a color with a high light reflectivity, it may be formed from white plastic (sometimes also containing white or silver pigment or dye) from the beginning.

[0090] The operation and effects of the embodiments of the light guide 22, the lighting device 13, and the contact image sensor 10 having various configurations and conditions will be described through simulation.

[0091] (First embodiment)

[0092] Fig.13 (a)~ Fig.13 (c) is a schematic three-dimensional view of the light guide 22 of the first embodiment. Fig.13 (a)~ Fig.13 As shown in (c), the cross section perpendicular to the longitudinal direction (x' direction) is a roughly rectangular rod (rod-shaped). Regarding the light guide 22 of the first embodiment, in its interior, within the wavelength range of the light used, the absorption coefficient α is set to 0.0011 [mm-1] (internal transmittance = 98.9% / 10mm), and at the boundary with air, etc., Snell's law is followed. The refractive index of the light guide 22 is set to 1.48816. The light guide 22 of the first embodiment is a roughly rectangular column with an end face having a shape roughly the same as the cross section perpendicular to the longitudinal direction, a size of 3.9 mm × 2.5 mm, and a length of 226 mm.

[0093] The light guide 22 of the first embodiment functionally includes a light emitting surface 22b, a side surface, and a light incident surface 22a. The light incident surface 22a is an end surface of the light guide 22, and is perpendicular to the light emitting surface 22b and the side surface. Furthermore, the light guide 22 has a light reflecting surface 22c on the side surface opposite to the light emitting surface 22b. The light emitting surface 22b is a rectangle of 2.5mm×226mm, and the light reflecting surface 22c is a rectangle of 1.9mm×226mm. The light reflecting surface 22c is parallel to the light emitting surface 22b, and the distance between them is 3.9mm.

[0094] The light guide 22 of the first embodiment has a surface state that does not cause scattering or diffuse reflection unless otherwise specified. Fig.13 (a)~ Fig.13 The x'y'z' orthogonal coordinate system represented in (c) is set. The length 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, and the y' axis passes through the origin and is perpendicular to the light reflecting surface 22c. The z' axis passing through the origin and being perpendicular to the x' axis and the y' axis must be determined. In addition, these axis marks or center lines are only used for explanation and are not recorded on the actual light guide.

[0095] Regarding the light emitting surface 22b, 0≤x'≤226, -2.5 / 2≤z'≤2.5 / 2, y'=3.9, the light reflecting surface 22c is a surface determined by 0≤x'≤226, -1.9 / 2≤z'≤1.9 / 2, y'=0 (all units are mm).

[0096] The light reflecting surface 22c of the light guide 22 of the first embodiment includes a plurality of groove-shaped diffusion structures 26. The diffusion structures 26 are arranged along the x' direction while changing their arrangement intervals. The arrangement intervals and sizes thereof are optimized in terms of calculation so as to emit uniform light in the longitudinal direction of the light exiting surface of the light guide.

[0097] Fig.14 This is a schematic enlarged view of a portion of the groove-shaped diffusion structure group viewed from the z' direction. Fig.14 In FIG. 1 , a part of the trajectory of light that advances toward the diffusion structure 26 and is scheduled to reach the diffusion structure 26 is indicated by a dotted arrow 30 . Fig.14 The schematic diagram shows that light is greatly 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 called a "diffusion structure", "diffusion structure", or "diffusion surface" because it makes the light reflective surface 22c have a large diffusion area. Fig.14 In this embodiment, a diffusion structure 26 having a groove shape on a part of the curved surface of the cylindrical side is shown, but it is taught that the shape of the diffusion structure 26 is not determined as long as it has an inclined concave shape in a part that diffuses the incident light, at least when observed from the cross section and side of the light guide 22.

[0098] The diffusion structure 26 possessed by the light reflecting surface 22c of the light guide 22 of the first embodiment is a concave structure in a "U" shape and forms a part of the side surface of a cylinder with a radius r=0.40mm. The width w of the diffusion structure 26 in the x' direction is 0.71mm. The depth d of the diffusion structure 26 in the y' direction is 0.22mm. The diffusion structure 26 is arranged parallel to the z' direction within the range of 0mm≤z'≤1.9 / 2mm. In the light reflecting surface 22c, when the range of 0mm≤z'≤1.9 / 2mm is set as the first reflecting surface 22c1 and the range of -1.9 / 2mm≤z'≤0mm is set as the second reflecting surface 22c2 with the x' axis dividing the light reflecting surface 22c into two as the boundary, the diffusion structure 26 is formed only on the first reflecting surface 22c1. In other words, the light guide 22 of the first embodiment includes a diffusion structure 26 in its light reflecting surface 22c, and the diffusion structure 26 has a length of 1 / 2 of the width of the light reflecting surface 22c from one end in the width direction of the light reflecting surface 22c. In addition, with respect to the arrangement of the diffusion structures 26 throughout the x' direction (arrangement interval of the diffusion structures 26), the radiation illuminance distribution of the linear light emitted from the light emitting surface 22b is arranged to be uniform in the x' direction (length direction). Generally speaking, the intervals of the diffusion structures 26 are arranged to be relatively large in the portion close to the light source 23, and the intervals of the diffusion structures 26 are arranged to be relatively small in the portion far from the light source 23.

[0099] (Second embodiment)

[0100] Fig.15The lighting device 13 of the second embodiment is shown. The lighting device 13 of the second embodiment includes the light guide 22 of the first embodiment. For the description of the lighting device 13, the x'y'z' orthogonal coordinate system used in the description of the light guide 22 is used.

[0101] In the lighting device 13 of the second embodiment, a light source 23 is arranged on one end surface 22a of the light guide 22. The light source 23 has a light emitting surface of a rectangular shape of 0.25 mm×0.25 mm, and its orientation property is Lambertian light distribution. The so-called Lambertian light distribution refers to a light distribution pattern in which the light intensity in the direction of an angle θ° can be expressed as cosθ times the light intensity Io on the optical axis (θ=0°) (the angle that becomes the half value of the light intensity Io on the optical axis can be calculated as θ=60° based on cosθ=0.5). As the light source 23, an LED is assumed. The center of the light emitting surface of the light source 23 is arranged at (-0.4, 1.9, 0) (all units are mm) in the x'y'z' orthogonal coordinate system. In the simulation for clarifying the function of the lighting device 13, 5×106 light rays are emitted from the light source, and all the light rays are incident on the light guide 22 from the light incident surface 22a. The interval between the light source 23 and the light incident surface 22a of the light guide 22 is set to 0.4 mm, and Fresnel reflection based on the light incident surface 22a is not considered. In addition, in the simulation, the wavelength of the light source 23 is set to 550 nm, and the effect of the refractive index dispersion of the light guide 22 and other media is not considered, and all non-polarized light is emitted. In order to drive the LED, a circuit such as a driver and a power supply are originally required, and a printed wiring substrate for electrical connection to the LED chip is necessary, but it will be omitted in the calculation and description of this second embodiment.

[0102] The lighting device 13 of the second embodiment has a light guide cover 24 covering the side surface of the light guide 22. The light guide cover 24 is made of white plastic, assuming that it also includes the inner surface opposite to the side surface of the light guide 22. The inner surface of the light guide cover 24 is a Lambertian reflection surface, and the radiation intensity follows the Lambert cosine law. The reflectivity of the inner surface of the light guide cover 24 is set to 87% (absorption rate 13%). Fig.15 , an end face perpendicular to the x' direction of the light guide cover 24 is shown. The light guide cover 24 has a substantially U-shaped cross section.

[0103] (Third embodiment)

[0104] Fig.16 1 is a schematic cross-sectional view perpendicular to the longitudinal direction of the contact type image sensor 10 of the third embodiment. The contact type image sensor 10 of the third embodiment includes the lighting device 13 of the second embodiment. In the third embodiment, the diffusion structure 26 on the light reflecting surface of the light guide 22 is arranged so as to be close to the document reading position.

[0105] The contact type image sensor 10 of the third embodiment includes: a document table 12 for placing a document including an image reading target portion; a light receiving element array 15 arranged in the longitudinal direction; and an erecting equal-magnification lens array 14 for focusing an image of the reading target portion on the light receiving element array 15. Furthermore, with respect to the contact type image sensor 10 of the third embodiment, the lighting device 13 of the second embodiment for illuminating the image reading target portion is arranged such that the light emitting surface 22b is substantially opposite to the image reading target portion.

[0106] Here, consider an orthogonal coordinate system for explaining the operation of the contact type image sensor 10. The center of the light source 23 included in the lighting device 13 of the second embodiment is taken as the origin, and 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 and is parallel to the document placement surface 12a of the document table 12 and perpendicular to the x-axis, and the y-axis passes through the origin and is perpendicular to the x-axis and the z-axis. In addition, in the cross section of the contact type image sensor 10, the angle between the normal line of the light emitting surface 22b and the z-axis or the x-z plane is set to 40°.

[0107] The radiation amount such as the radiant illumination at the image reading target portion (hereinafter referred to as the "reading position") and the vicinity of the reading position when the lighting device 13 of the second embodiment is driven under the above conditions is obtained by simulation. Fig.16 , the irradiance is calculated while increasing z from the reading position (y, z) = (6.4, 0) on the manuscript table 12, then the irradiance is calculated while increasing z from the reading position (y, z) = (6.4 + 1, 0) on the manuscript table 12, then the irradiance is calculated while increasing z from the reading position (y, z) = (6.4 + 2, 0) on the manuscript table 12, then the irradiance is calculated while increasing z from the reading position (y, z) = (6.4 + 3, 0) on the manuscript table (all units are mm). The value of the irradiance is obtained by averaging the irradiance in the range of x = 100 mm to 150 mm in the length 226 mm of the light guide 22. In this way, the y, z dependence of the irradiance at the reading position and its vicinity is obtained by simulation.

[0108] Fig.17 The relationship between the y and z dependencies of the irradiance at the reading position and its vicinity is shown in Fig.17It can be seen that there is a singular point of z where the change in radiant illumination is minimal even when the change is Δy = 0 to 3 mm. When the singular point of z is recorded as z0, in the contact type image sensor 10 of the third embodiment, z0 = 4.9 mm. The change to Δy = 0 to 3 mm means that the read object is separated from the manuscript table 12 by this distance, that is, "the manuscript floats up". By setting the distance in the z direction between the lighting device 13 and the reading position to z0 (4.9 mm), even when the manuscript floats up from the manuscript table 12, the change in radiant illumination of the illumination light that illuminates the image of the read object can be said to be small. In addition, there is also a case where the z singular point z0 is the position where DOI becomes the smallest. The so-called DOI is defined as Depth Of Illumination (illumination depth) or Depth Of Irradiance (radiation depth), etc., and it can be said that it is very necessary in the process of designing a contact type image sensor with a predetermined lighting device.

[0109] In addition, according to Fig.17 In the contact image sensor 10 of the third embodiment, the average value of the radiant illumination at the z singular point z0 of each characteristic with Δy=0 to 3 mm is 9.95×10-6.

[0110] (Fourth embodiment)

[0111] Fig.18 (a)~ Fig.18 (c) is a schematic three-dimensional view of the light guide 22 of the fourth embodiment. Fig.18 As shown in (a), compared with the light guide 22 of the first embodiment, a C-chamfer is performed on the corner roughly opposite to the diffusion structure 26, and one more side surface is added. Regarding the light guide 22 of the fourth embodiment, in its cross section, the length cL corresponding to the removed light exit surface 22b is 0.4mm, and the angle αc formed by the new side surface 22f and the light exit surface 22b is 150°. The new side surface 22f set by the C-chamfer is a rectangle of 0.81mm×226mm, and the properties of the surface are set to be the same as the other side surfaces of the light guide 22. Regarding the light guide 22 of the fourth embodiment, except that the corner roughly opposite to the diffusion structure 26 in its cross section is C-chamfered in the length direction, its structure, characteristics, and parameters are set to be the same as those of the light guide 22 of the first embodiment.

[0112] (Fifth embodiment)

[0113] The lighting device 13 of the fifth embodiment includes the light guide 22 of the fourth embodiment. The lighting device 13 of the fifth embodiment has the same structure, characteristics, parameters, etc. as the lighting device 13 of the second embodiment, except that the light guide 22 of the fourth embodiment is used instead of the light guide 22 of the first embodiment. The lighting device 13 of the fifth embodiment is not shown in the figure, but is similar in appearance to the lighting device 13 of the second embodiment. Fig.15 The lighting devices represented in are substantially the same.

[0114] (Sixth embodiment)

[0115] The contact type image sensor of the sixth embodiment includes the light guide 22 of the fourth embodiment and the lighting device of the fifth embodiment. In the sixth embodiment, the lighting device 13 is arranged so that the diffusion structure 26 of the light reflecting surface 22c is on the side close to the document reading position and the expanded side surface 22f substantially opposite to the diffusion structure 26 is on the side far from the document reading position. Except that the light guide 22 of the fourth embodiment is used instead of the light guide 22 of the first embodiment, the structure, characteristics, parameters, etc. are the same as those of the contact type image sensor 10 of the third embodiment.

[0116] In the contact image sensor 10 of the sixth embodiment, similarly to the contact image sensor 10 of the third embodiment, an xyz orthogonal coordinate system is set up, and the y,z dependence of the radiation illuminance at the reading position and its vicinity is calculated through simulation.

[0117] Fig.19 The relationship between the y and z dependencies of the irradiance at the reading position and its vicinity is shown in Fig.19 In the embodiment, regarding the z singular point z0 where the change in irradiance is the smallest even when the change is Δy = 0 to 3 mm, in the contact type image sensor 10 of the sixth embodiment, z0 = 5.0 mm. Fig.19 In the contact image sensor 10 of the sixth embodiment, the average value of the radiant illumination at the z singular point z0 of each characteristic with Δy=0 to 3 mm is 11.9×10-6.

[0118] (Comparative Example 1)

[0119] Fig. 20 (a)~ Fig. 20(c) is a schematic three-view diagram of the light guide 122 of the first comparative example. The light guide 122 of the first comparative example has the same structure as the light guide 22 of the first embodiment, except that the groove-shaped diffusion structure 126 including the shape of the cylindrical side surface is provided over the entire width of the light reflecting surface 122c in the z' direction, the radius of the cylinder constituting the diffusion structure 126 is set to 0.203 mm, and the arrangement of the groove-shaped diffusion structure 126 over the x' direction is determined with the goal of making the radiation illuminance on the light emitting surface approximately uniform.

[0120] (Comparative Example 2)

[0121] 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 the light guide 122 of the first comparative example is provided instead of the light guide 22 of the first example.

[0122] (Comparative Example 3)

[0123] The contact image sensor of the third comparative example has the same structure, characteristics, parameters, etc. as the contact image sensor 10 of the third comparative example, except that the illumination device 13 of the second comparative example is replaced with the illumination device of the second comparative example.

[0124] In the contact image sensor of the third comparative example, similarly to the contact image sensor 10 of the third embodiment, an xyz orthogonal coordinate system was set up, and the y and z dependencies of the irradiance at the reading position and its vicinity were obtained by simulation.

[0125] Fig.21 The relationship between the y and z dependencies of the irradiance at the reading position and its vicinity is shown in Fig.21 In the z singular point z0 where the change in irradiance is the smallest even when the change is Δy = 0 to 3 mm, in the contact type image sensor of the third comparative example, z0 = 6.0 mm. Fig.21 In the contact type image sensor of the third comparative example, the average value of the radiant illuminance at the z singular point z0 of each characteristic with Δy=0 to 3 mm is 6.62×10-6.

[0126] Reference Fig.17 , Fig.19 and Fig.21 , the contact type image sensor 10 of the third embodiment and the sixth embodiment is compared with the contact type image sensor of the third comparative example. As described above, Fig.17 , Fig.19 and Fig.21The following are graphs showing the y and z dependencies of the irradiance near the reading position in the contact type image sensors of the third embodiment, the sixth embodiment and the third comparative example. In the relationship shown in each graph, the maximum value of the irradiance at the position where Δy=0 mm, i.e., the position in contact with the surface of the document table 12 (no lifting of the document), is 1.60×10-6 (zM=2.45 mm, zM is the z value corresponding to the maximum irradiance), 1.80×10-6 (zM=2.95 mm) and 1.30×10-6 (zM=2.95 mm) in the order of the contact type image sensors of the third embodiment, the sixth embodiment and the third comparative example, and their ratio is 1.23:1.38:1.

[0127] In addition, the absolute value Δz=|zM-z0| of the difference between the z value zM corresponding to the maximum value of the radiant illuminance and the z singular point z0 is Δz=2.45mm, 2.05mm and 3.05mm in the order of the contact image sensors of the third embodiment, the sixth embodiment and the third comparative example.

[0128] From these results, it can be seen that, regarding the contact type image sensor, the maximum value of the radiant illumination increases in the order of the third comparative example, the third embodiment, and the sixth embodiment, and the value of Δz decreases. Therefore, in the contact type image sensors of the third and sixth embodiments, even when Δy=0 to 4 mm (when there is floating of the original), the radiation amount such as the radiant illumination for illuminating the original can be made relatively large.

[0129] In a close-contact image sensor, the direction parallel to the surface of the manuscript table and perpendicular to the longitudinal direction is referred to as the z direction, the direction perpendicular to the z direction and the surface of the manuscript table is referred to as the y direction, the position in the z direction where the change in radiation illuminance within the range of 0 to 4 mm in the y direction from the surface of the manuscript table becomes the smallest is referred to as z0, and the position in the z direction where the radiation illuminance becomes the largest on the surface of the manuscript table is referred to as zM, preferably, Δz=|z0-zM|≤2.5[mm].

[0130] The present invention has been described above based on the embodiments. It should be understood by those skilled in the art that the embodiments are merely illustrative and that various modifications may exist in the combination of their constituent elements or processing procedures, and such modifications are also within the scope of the present invention.

[0131] [Industrial Applicability]

[0132] The present invention can be used in a contact type image sensor.

[0133] [Explanation of Reference Numerals]

[0134] 10. Close-contact image sensor, 12. Original document table, 13. Illumination device, 14. Upright equal-magnification lens array, 15. Light receiving element array, 16. Housing, 17. Refractive index distribution type 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 that allows light incident from an end face to propagate in a longitudinal direction while being reflected on an inner surface and to be emitted from a light emitting surface; The light guide is characterized by comprising: a light reflecting surface, which is substantially opposite to the light emitting surface, and A plurality of diffusion structures, which are arranged on the light reflecting surface and are used to diffuse and reflect light; When the length of the diffusion structure in a direction perpendicular to the longitudinal direction is represented by Wr, and the length of the light reflecting surface in a direction perpendicular to the longitudinal direction is represented by Wp, Wr<Wp.

2. The light guide according to claim 1, wherein: When the light reflecting surface is divided into two and one area is used as the first reflecting surface and the other area is used as the second reflecting surface, Vp2<Vp1, wherein 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.

3. The light guide according to claim 1 or 2, characterized in that: The diffusion structure includes a shape of a side surface of a cylinder or a part of a spherical surface on the surface of the recessed portion.

4. The light guide according to claim 2, wherein: Vp2=0.

5. The light guide according to any one of claims 1 to 4, characterized in that: In a cross section perpendicular to the longitudinal direction, a side surface connected to the light emitting surface and substantially opposite to the diffusion structure is included.

6. The light guide according to claim 5, wherein: In a cross section perpendicular to the longitudinal direction, an angle αc formed by the side surface and the light emitting surface is αc=100-160°.

7. A lighting device, characterized in that: include: The light guide according to any one of claims 1 to 6, and The light source is arranged on the end surface or in the vicinity of the end surface so that light is incident from the end surface of the light guide.

8. A close contact image sensor, characterized in that: include: original table, The lighting device according to claim 7, which is used to illuminate the original placed on the original table, a lens array that condenses reflected light from a portion of the original illuminated by the illumination device, and The light receiving element array receives the light collected by the lens array.

9. The contact type image sensor according to claim 8, characterized in that: In the cross section perpendicular to the longitudinal direction of the contact image sensor, the lighting device is arranged so that the diffusion structure is on a side close to a reading position of the document.

10. The contact type image sensor according to claim 8 or 9, characterized in that: When the direction parallel to the surface of the manuscript 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 manuscript table is defined as the y direction, the position in the z direction where the change in irradiance in the range of 0 to 4 mm from the surface of the manuscript table in the y direction becomes the smallest is defined as z0, and the position in the z direction where the irradiance in the surface of the manuscript table becomes the largest is defined as zM, |zM―z0|≤2.5mm.

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