Lighting device and image sensor

Abstract

To achieve equalization of the radiational illuminance in a line-formed lighting device.SOLUTION: A lighting device 10 includes: a transparent material 12 having a first end surface 12a, a second end surface 12b facing the first end surface 12a, and a light emission surface 12c; a light emitting source which emits light toward the first end surface 12a of the transparent material 12; and a transparent material case 14 which has at least a wall 14b including a facing surface 14a facing the second end surface 12b of the transparent material 12 and houses the transparent material 12. When the lighting device 10 is viewed from the second end surface side of the transparent material 12, a part of the second end surface 12b of the transparent material 12 is exposed.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an illumination device that provides line-shaped illumination and an image sensor incorporating such an illumination device. [Background technology]

[0002] Contact type image sensors are used as devices for reading originals in facsimile machines, copying machines, image scanners, etc. This contact type image sensor is equipped with a line illumination device that linearly illuminates the original surface over the main scanning range.

[0003] As a line lighting device, one using a rod-shaped light guide is known. For example, Patent Document 1 describes a line lighting device including a transparent rectangular columnar light guide for guiding light, a light source that emits light from one end (incident surface) of the light guide toward the inside of the light guide, and a light guide case that houses the light guide inside.

[0004] The light guide has an exit surface for emitting light in a line shape on at least one surface in the longitudinal direction, and a surface on which a light scattering pattern is formed for scattering (diffuse reflection) or reflecting the light that reaches the light guide inside the light guide.

[0005] In addition, the light guide case that houses the light guide has the aim of improving the efficiency of light utilization by reflecting the light propagating through the light guide back into the light guide by the internal surface of the light guide case facing the light guide when the light is emitted to the outside from a surface other than the light guide's exit surface.

[0006] Therefore, all surfaces of the light guide are considered to be covered by the light guide case, except for the exit surface of the light guide and the entrance surface for making the light from the light source enter the light guide. Many lighting devices with similar functions that are actually available on the market also have such a relationship between the light guide and the light guide case. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2002-135529 A Summary of the Invention [Problem to be solved by the invention]

[0008] The light guide and the light guide case are long in one direction (the longitudinal direction or main scanning direction), and their length, for example in an image sensor for acquiring information on the surface of an A4 sheet of paper, is at least as long as the length of the short side of the A4 sheet of paper, and also takes into account the size of the document or work to be read.

[0009] Since light guides and light guide cases are often made of plastic and are industrially produced by injection molding, shrinkage occurs during molding, which can lead to dimensional mismatches between the light guide and the light guide case it is housed in. To compensate for unexpected dimensional gaps, there is a tendency to make the inside dimensions of the light guide case, which correspond to the length of the light guide, larger than the length of the light guide.

[0010] Furthermore, even after being incorporated into an image sensor, plastic light guides and light guide cases undergo thermal expansion and contraction depending on the ambient temperature. Therefore, to avoid unnecessary interference between the light guide and the light guide case, there is a tendency to make the inner dimensions of the light guide case larger than the length of the light guide.

[0011] As a result, when assembling the image sensor or when using the image sensor, the gap between the second end face of the light guide, which faces the first end face on which a light source for making light incident on the rectangular columnar light guide is disposed, and the inner surface of the light guide case, which faces the second end face, may become large. It can also be understood that the occurrence of an unexpected gap between the light guide and the inner dimensions of the light guide case that covers it is noticeable in the longitudinal direction, where the actual dimensions are large, due to the nature of thermal expansion and contraction.

[0012] When the distance between the second end face of the light guide and the surface of the light guide case facing the second end face becomes larger than a certain value, a phenomenon may occur in the lighting device where the intensity of the light emitted from the vicinity of the second end face of the light guide becomes locally higher than other areas. This phenomenon is not a good property when the lighting device is used in a scanning image sensor because the irradiance of the target or work to be read becomes locally higher.

[0013] 1(a) to 1(c) are diagrams for explaining a phenomenon in which the intensity of light emitted from the vicinity of the second end face of the light guide in a lighting device is locally increased. FIG. 1(a) is a schematic cross-sectional view showing an example of a conventional lighting device. The lighting device 1 shown in FIG. 1(a) includes a rod-shaped transparent light guide 2, a light source 3 that emits light toward a first end face 2a of the light guide 2, and a light guide case 4 that houses the light guide 2 therein. The lighting device 1 shown in FIG. 1(a) is long in the left-right direction on the paper. As shown in FIG. 1(a), the distance between the second end face 2b of the light guide 2 facing the first end face 2a and the inner surface 4a of the light guide case 4 facing the second end face 2b is d. In the lighting device 1, the surface of the light guide 2 on the upper side of the paper becomes the light emission surface 2c.

[0014] 1(b) and 1(c) are enlarged cross-sectional views of the vicinity of the second end face 2b of the light guide 2 in the lighting device 1 shown in FIG. 1(a). In both of FIG. 1(b) and FIG. 1(c), the second end face 2b of the light guide 2 is entirely covered by the inner surface 4a of the light guide case 4. At least the length of the second end face 2b of the light guide 2 in a direction perpendicular to the light exit surface 2c and the length of the inner surface 4a of the light guide case 4 in the same direction are set to be approximately equal. FIG. 1(b) shows a case where the distance d between the second end face 2b of the light guide 2 and the inner surface 4a of the light guide case 4 facing the second end face 2b is small. FIG. 1(c) shows a case where the distance d between the second end face 2b of the light guide 2 and the inner surface 4a of the light guide case 4 facing the second end face 2b is large. In this embodiment, the light flux L2 emitted to the upper side of the paper (the light exit surface side) when the distance d is large is relatively larger than the light flux L1 emitted to the light exit surface side when the distance d is small.

[0015] The reason why the magnitude of the light beam changes when the distance d changes is considered as follows. When the distance d is small, the light emitted from the second end face 2b of the light guide 2 reaches and is reflected by the inner surface 4a of the light guide case 4 opposite the second end face 2b, and most of the light beam re-enters the light guide 2. On the other hand, when the distance d is large, the light emitted from the second end face 2b of the light guide 2 reaches and is reflected by the inner surface 4a of the light guide case 4 opposite the second end face 2b, but because the distance d is large, most of the light beam is emitted to the light exit surface before reaching the second end face 2b of the light guide 2.

[0016] The present invention has been made in view of the above circumstances, and has an object to provide an illumination device capable of achieving uniform irradiance, and an image sensor including the illumination device. [Means for solving the problem]

[0017] In order to solve the above problems, an illumination device according to an embodiment of the present invention includes a rod-shaped light guide having a first end face, a second end face opposite to the first end face, and a light exit surface formed on at least a part of a side surface along a longitudinal direction of the light guide, a light emission source that emits light toward the first end face of the light guide, and a light guide case that houses the light guide and has at least a wall including an opposing surface that faces the second end face of the light guide. When the illumination device is viewed from the second end face side of the light guide, a part of the second end face of the light guide is exposed.

[0018] Another aspect of the present invention is an image sensor including the above-mentioned lighting device for illuminating an object, a lens array for collecting light reflected from the object, and a light receiving element for receiving the light collected by the lens array.

[0019] Any combination of the above components and any conversion of the present invention into a method, device, system, etc. are also valid aspects of the present invention. Effect of the Invention

[0020] According to the present invention, it is possible to provide an illumination device capable of achieving uniform irradiance and an image sensor including the illumination device. [Brief description of the drawings]

[0021] [Figure 1] 1(a) to 1(c) are diagrams illustrating a phenomenon in which the intensity of light emitted from the vicinity of a second end face of a light guide in an illumination device is locally increased. [Diagram 2] 1 is a schematic cross-sectional view of an image sensor according to an embodiment; [Diagram 3] 1 is a schematic perspective view of a lighting device according to an embodiment; [Figure 4] 1 is a schematic exploded perspective view of a lighting device according to an embodiment; [Diagram 5] 5(a) and 5(b) are schematic diagrams showing a light guide. [Figure 6] 6(a) to 6(c) are schematic diagrams illustrating the configuration of an illumination device according to an embodiment. [Figure 7] 7(a) and 7(b) are schematic diagrams showing a lighting device according to a comparative example. [Figure 8] 8(a) to 8(d) are diagrams each showing a schematic view of the illumination device as viewed from the second end face side of the light guide. [Figure 9] 9(a) and 9(b) are diagrams showing a model of an image sensor used for the simulation. [Figure 10] FIG. 13 is a diagram showing the irradiance distribution when the offset amount Lc=0 mm. [Figure 11] FIG. 13 is a diagram showing the irradiance distribution when the offset amount Lc is 0.7 mm. [Figure 12] FIG. 13 is a diagram showing the irradiance distribution when the offset amount Lc is 1.2 mm. [Figure 13] FIG. 13 is a graph showing the dependency of the PRNU value on the interval d and the offset amount Lc. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The following describes the embodiments of the present invention. The same or equivalent components, parts, and processes shown in each drawing are given the same reference numerals, and duplicated descriptions are omitted as appropriate. In addition, the embodiments are illustrative and do not limit the invention, and all the features and combinations thereof described in the embodiments are not necessarily essential to the invention.

[0023] Fig. 2 is a schematic cross-sectional view of an image sensor 100 according to an embodiment. As shown in Fig. 2, the image sensor 100 includes a housing 102, a glass plate 104 for placing an original G thereon, an illumination device 10 for irradiating light onto the original G, a rod lens array 106 for collecting reflected light from the original G, and a line image sensor (light receiving element) 108 for receiving the light collected by the rod lens array 106. Fig. 2 shows only parts necessary for explaining the image sensor 100 according to the embodiment, and omits, for example, details of a drive system, a driver, an electronic board, a structure and associated parts for fixing each part, and a structure and associated parts for mounting the image sensor to another device.

[0024] As shown in FIG. 2, a first recess 102a is formed above the housing 102, and a second recess 102b is formed below the housing 102. The upper surface of the first recess 102a is covered with a transparent parallel plate made of glass, resin, or the like. In addition, an illumination device 10 is fixed obliquely in the first recess 102a. The illumination device 10 is fixed so as to properly illuminate the intersection of the optical axis Ax of the rod lens array 106 and the upper surface of the glass plate 104 and its vicinity. Since it is necessary to illuminate the original G obliquely in order to set the optical axis Ax of the rod lens array 106 for reading substantially perpendicular to the original G, the illumination device 10 is provided obliquely with respect to the optical axis Ax. A support such as a substrate having a line image sensor 108 is attached to the second recess 102b. Furthermore, the rod lens array 106 is held between the first recess 102a and the second recess 102b of the housing 102. The rod lens array 106 may constitute an erect life-size system in relation to the document G and the line image sensor 108 .

[0025] In the image sensor 100, light emitted from the illumination device 10 is directed through a glass plate 104 to an original G, and light reflected from the original G is detected by a line image sensor 108 via a rod lens array 106, thereby reading the original G. A desired area of ​​the original G can be read by scanning the housing 102 with respect to the original G in the sub-scanning direction (the direction of the arrow shown in FIG. 2).

[0026] Image sensor 100 has a cross section shown in Fig. 2 and is long in a direction perpendicular to the paper, and accordingly, illumination device 10, rod lens array 106, line image sensor 108, and housing 102 containing them are also long in a direction perpendicular to the paper. When reading information on the surface of a document or work having a certain area, image information contained in the certain area can be read by scanning image sensor 100 as shown in Fig. 2 in a certain direction. In image sensor 100 or parts contained therein, the direction perpendicular to the paper in Fig. 2 is defined as the "main scanning direction", and the direction perpendicular to the main scanning direction (the direction of the arrow shown in Fig. 2) is defined as the "sub-scanning direction".

[0027] Fig. 3 is a schematic perspective view of the lighting device 10 according to the embodiment. Fig. 4 is a schematic exploded perspective view of the lighting device 10 according to the embodiment. As shown in Figs. 3 and 4, in the lighting device 10, a rod-shaped light guide 12 is housed in a white light guide case 14, and a light-emitting unit 16 is provided at one end. Figs. 3 and 4 show only parts necessary for explaining the lighting device 10 according to the embodiment, and omit a drive system, an electronic board, a driver, and other structures for fixing.

[0028] 4, the light emitting unit 16 may include at least three light emitting elements (LEDs) 18. The three LEDs 18 may be LEDs that emit R (red), G (green), and B (blue) colors.

[0029] The light guide case 14 of the lighting device 10 has a U-shaped cross section. The light guide 12 is obtained by injection molding a transparent resin such as acrylic, and has a substantially rectangular cross section. The light guide case 14 accommodates the light guide 12 therein so as to cover all surfaces of the light guide 12 except for the light entrance surface and the light exit surface.

[0030] As shown in Fig. 3 and Fig. 4, in this embodiment, the light emitting unit 16 is disposed on one end face (first end face) side of the rod-shaped light guide 12. In Fig. 3, the light emitting unit 16 is hidden behind the light guide 12 and the light guide case 14. The light emitted from each LED 18 of the light emitting unit 16 enters the inside of the light guide 12 from the first end face 12a of the light guide 12, and a part of the light is reflected by the side face of the light guide 12 or the inner face of the light guide case 14 covering the side face, and travels inside the light guide. At least one side face of the light guide 12 functions as a light exit surface 12c for illuminating an object such as a document or a workpiece when incorporated into the image sensor 100. The light exit surface 12c is exposed from the light guide case 14.

[0031] 5(a) and 5(b) are schematic diagrams showing the light guide 12. FIG. 5(a) is a side view of the light guide 12, and FIG. 5(b) is a bottom view of the light guide 12. In the light guide 12, a side surface opposite to one side surface constituting the light exit surface 12c is conveniently referred to as a bottom surface 12d. The bottom surface 12d of the light guide 12 is also covered by the inner surface of the light guide case 14. A light scattering pattern 20 that scatters or diffusely reflects the light that reaches the bottom surface 12d of the light guide 12 is formed. An example of a light scattering pattern is shown in FIG. 5(a) and FIG. 5(b) as a schematic diagram.

[0032] As shown in Fig. 5(a) and Fig. 5(b), the light scattering pattern 20 is formed by forming a plurality of concave structures extending in a direction perpendicular to the main scanning direction (longitudinal direction of the light guide 12) on the bottom surface 12d of the light guide 12. The concave shape includes a cylindrical side surface extending perpendicular to the longitudinal direction of the light guide 12, and the light scattering pattern 20 is formed so that its density increases with increasing distance from the light emitting unit 16. In the illustrated example, the light scattering pattern 20 may be formed so that its width increases in the short direction (sub-scanning direction) with increasing distance from the light emitting unit 16. By increasing the density of the light scattering pattern with increasing distance from the incident surface 12a, the light emitted from the light emitting surface 12c can be made uniform over the entire length in the longitudinal direction (main scanning direction when provided in the image sensor 100).

[0033] In this embodiment, the surface constituting the light exit surface 12c of the light guide 12 may include a rectangular flat surface which is one of the side surfaces of the light guide 12. In this embodiment, the illumination device 10 is attached to the housing 102 of the image sensor 100 such that the surface constituting the light exit surface 12c is located on the document G side, as shown in FIG.

[0034] Here, orthogonal coordinate axes are defined for the explanation. In Fig. 3 and Fig. 4, the x-direction corresponds to the main scanning direction of the image sensor 100, the longitudinal direction of the illumination device 10 and the light guide 12 is the x-direction, the direction perpendicular to the x-direction and perpendicular to the surface constituting the light exit surface 12c is the z-direction, and the direction perpendicular to the x-direction and the z-direction is the y-direction.

[0035] When manufacturing an image sensor 100 capable of reading an A4-sized document or workpiece, an illumination device 10 is required that is at least as long as or longer than one side (or the short side), and the length of the light guide 12 (length in the x direction) and the length of the light guide case 14 (length in the x direction) are necessarily required to be accordingly long. When it is planned to house the light guide 12 in the light guide case 14, ensuring the accuracy of the dimensional difference between the light guide 12 and the light guide case 14 becomes an issue. Specifically, it is necessary to control the dimensional difference that occurs in the design value of each part, the mold dimensions, the actual dimensions of the finished product, and the like, and further to control the dimensional fluctuation of each part due to the difference in thermal expansion during use. In particular, since the actual dimensions of the light guide 12 and the light guide case 14 in the longitudinal direction are large (approximately 300 mm), it becomes more important to control the dimensional difference and dimensional fluctuation in this direction.

[0036] A simpler method is to ensure that the inner dimensions of the light guide case 14 are somewhat larger than the outer dimensions of the light guide 12, and in this case, it is possible to compensate for dimensional differences and dimensional variations that occur during the manufacture of each part. In the light guide 12, the end face on the side where the light emitting unit 16 is arranged is defined as the first end face 12a, and the opposite end face is defined as the second end face 12b. When the distance between the second end face 12b of the light guide 12 and the inner face 14a of the light guide case 14 facing the second end face 12b (hereinafter, the opposite face of the second end face) is d [mm], the distance d is typically and preferably 0.1 mm to 1.0 mm in view of the balance of cost, manufacture, and assembly accuracy. If the distance d is less than 0.05 mm, the design tolerance of each part becomes strict, and the margin of manufacturing conditions during injection molding becomes significantly smaller. On the other hand, if the distance d exceeds 1.0 mm, it becomes easier to set tolerances during design and manufacturing conditions tend to be more relaxed, but the irradiance of the light emitted from the second end face 12b and the light emitting face 12c in the vicinity of the second end face 12b becomes biased, making it difficult to achieve a uniform irradiance. The distance d between the second end face 12b of the light guide 12 and the opposing face 14a of the second end face may more preferably be 0.3 mm to 0.7 mm.

[0037] Furthermore, in the lighting device 10 according to the present embodiment, when the lighting device 10 is viewed in a direction parallel to the x direction from the second end face side, the second end face 12b of the light guide 12 is partially exposed. In other words, when the lighting device 10 is viewed in a direction parallel to the x direction from the second end face side, a partial area of ​​the second end face 12b of the light guide 12 is covered by the light guide case 14 (i.e., the entire area is not completely covered).

[0038] 6(a) to 6(c) are schematic diagrams for explaining the configuration of a lighting device 10 according to an embodiment. Fig. 6(a) is a schematic diagram of the lighting device 10 when viewed parallel to the x direction from the second end face side. Fig. 6(b) is a partial cross-sectional view of the lighting device 10 when viewed parallel to the y direction. Fig. 6(c) is a side view showing the second end face 12b of the light guide 12.

[0039] Before describing the configuration of the lighting device 10 according to the present embodiment, a comparative example will be shown. Figs. 7(a) and 7(b) are schematic diagrams showing a lighting device according to a comparative example. This lighting device according to the comparative example corresponds to the lighting device 1 shown in Figs. 1(a) to 1(c), and therefore the same reference numerals are used. Fig. 7(a) is a schematic diagram of the lighting device 1 as viewed parallel to the x direction from the second end face side. Fig. 7(b) is a partial cross-sectional view of the lighting device 1 as viewed parallel to the y direction.

[0040] As shown in Fig. 7(a) and Fig. 7(b), in the lighting device 1 according to the comparative example, the entire area of ​​the second end face 2b of the light guide 2 is covered by the inner surface 4a of the light guide case 4. In this case, as described with reference to Figs. 1(a) to 1(c), when the distance d between the second end face 2b of the light guide 2 and the inner surface 4a of the light guide case 4 is equal to or greater than a certain value, most of the light that is emitted from the second end face 2b of the light guide 2 and reflected by the inner surface 4a of the light guide case 4 is emitted toward the light exit surface of the lighting device 1. As a result, the irradiance of the lighting device 1 in the area corresponding to the second end face 2b of the light guide 2 and its vicinity becomes large, which may cause the irradiance to become non-uniform.

[0041] As shown in Figures 6(a) and 6(b), in the lighting device 10 of this embodiment, the area where the opposing surface 14a of the second end surface of the light guide case 14 covers the second end surface 12b of the light guide 12 is limited (a part of the second end surface 12b is exposed), so that the light flux reflected from the opposing surface 14a of the second end surface and emitted toward the light emission surface is reduced. As a result, the increase in irradiance in the area corresponding to or near the second end surface 12b is suppressed, thereby making it possible to uniform the radiation intensity.

[0042] The area of ​​the second end surface 12b of the light guide 12 is S 0 [mm 2 ], and the area of ​​the exposed region of the second end surface 12b of the light guide 12 when the lighting device 10 is viewed in the x direction (longitudinal direction) from the second end surface side is S 1 [mm 2 ], then S 0 S for 1 Ratio of S 1 / S 0 The ratio S is preferably 0.12 to 0.25. 1 / S 0 When the ratio S is smaller than 0.1, the uniformity of the irradiance of the light guide is not sufficient when the interval d is in the above range (d=0.1 mm to 1.0 mm). 1 / S 0 When the ratio S is greater than 0.26, the light emitted from the second end face 12b of the light guide 12 becomes a large luminous flux that exits the light guide case 14, reducing the light utilization efficiency, or the irradiance near the second end face 12b of the light guide 12 becomes relatively small, resulting in insufficient uniformity of the irradiance. 1 / S 0 More preferably, it may be 0.13 to 0.24.

[0043] As shown in FIG. 6(a) and FIG. 6(b), in the lighting device 10 according to the present embodiment, a surface 14c on the light exit surface side of the wall 14b of the light guide case 14, including the opposing surface 14a of the second end surface (hereinafter referred to as the top surface on the second end surface side of the light guide case 14) is offset from the surface constituting the light exit surface 12c of the light guide 12, thereby exposing a part of the second end surface area of ​​the light guide 12. The wall 14b of the light guide case 14 separates the inside and outside of the light guide case 14. Furthermore, the light exit surface 12c and the top surface 14c on the second end surface side of the light guide case 14 are approximately parallel to each other. As shown in FIG. 6(a) and FIG. 6(b), an offset amount Lc [mm] of the top surface 14c on the second end surface side of the light guide case 14 is specified and used to specify the exposed area of ​​the second end surface 12b of the light guide 12. The offset amount Lc is preferably Lc=0.4 mm to 1.0 mm, and more preferably Lc=0.5 mm to 0.9 mm. When the lighting device 10 is viewed parallel to the x direction from the second end face side of the light guide 12, the second end face 12b of the light guide 12 should be exposed so as to satisfy the above condition. In Fig. 6(a) and Fig. 6(b), the light exit surface 12c and the top face 14c on the second end face side of the light guide case 14 are approximately parallel to each other, but are not limited thereto.

[0044] 8(a) to 8(d) are schematic diagrams showing the illumination device 10 as viewed in the x direction from the second end face side of the light guide 12. Fig. 8(a) to 8(d) show several examples of the manner in which the second end face 12b of the light guide 12 is exposed. In the figures, the hatched highlighted area indicates the exposed area E of the second end face 12b of the light guide 12. The manner in which the second end face 12b of the light guide 12 is exposed is not limited to these.

[0045] In the lighting device 10 shown in FIG. 8(a), the top surface 14c of the second end surface side of the light guide case 14 is inclined with respect to the light exit surface 12c of the light guide 12. In the lighting device 10 shown in FIG. 8(b), the top surface 14c of the second end surface side of the light guide case 14 is formed of a plurality of bent surfaces. In the lighting device 10 shown in FIG. 8(c), the top surface 14c of the second end surface side of the light guide case 14 includes a curved surface. In the lighting device 10 shown in FIG. 8(d), one or more through holes are provided in the wall 14b of the light guide case 14 including the surface facing the second end surface, to expose a part of the second end surface 12b. All of the exposure modes of the second end surface 12b of the light guide 12 shown in FIG. 8(a) to FIG. 8(d) are examples, and modes in which a part of the second end surface 12b is exposed so as to satisfy certain conditions by combining some or all of these elements with each other are within the scope of the disclosure of this specification.

[0046] The effect of the lighting device according to this embodiment was verified by simulation together with a comparative example. The lighting device used in the simulation corresponds to the lighting device 10 shown in Figs. 3 and 4. The light guide 12 is a substantially rectangular column having a length of 226 mm in the longitudinal direction (x direction). The shape of the second end face 12b of the light guide 12 is the same as that of the first end face 12a, the length in the y direction is about 2.8 mm, and the length in the z direction is about 3.9 mm. The areas of the first end face 12a and the second end face 12b are each 8.85 mm. 2 It is.

[0047] The light exit surface 12c of the light guide 12 is a rectangular flat surface in plan view, with a length in the y direction of about 2.1 mm and a length in the x direction of 226 mm.

[0048] It is also assumed that the refraction and reflection of light at the interface of the light guide 12 follows Snell's law, and that the absorption inside the light guide 12 is 40% per 20 cm length.

[0049] On the surface substantially opposite to light exit surface 12c, a plurality of light scattering patterns 20 are provided, each of which is made up of recesses including a side surface shape of a cylinder having a generatrix parallel to the yz plane as shown in FIG.

[0050] The light guide case 14 covers the side surfaces other than the light exit surface 12c. The second end surface 12b of the light guide 12 is exposed by offsetting the top surface 14c of the wall 14b, including the surface facing the second end surface 12b of the light guide 12, from the light exit surface 12c, as shown in Figures 6(a) and 6(b). Conditions were set so that the light that reaches the inner surface 14a of the light guide case 14 exhibits "light behavior such as reflection."

[0051] The light source is assumed to be a minute surface close to a point, and a light beam with a wavelength of 550 nm is emitted from approximately the center of the first end face 12a of the light guide 12 into the light guide at a wavelength of 2.5×10 6 The book was positioned so that the light beam was incident on it.

[0052] 9(a) and 9(b) show a model of the image sensor 100 used for the simulation. Fig. 9(a) is a cross section perpendicular to the longitudinal direction of the image sensor 100 as viewed from the first end face side of the light guide 12, and Fig. 9(b) is a cross section perpendicular to the longitudinal direction of the image sensor 100 as viewed from the second end face side of the light guide 12.

[0053] With the arrangement shown in Fig. 9(a) and Fig. 9(b), the irradiance (arbitrary unit) by the illumination device 10 was calculated by counting the light flux that reaches per unit area near a specific line segment Li. Note that Fig. 9(a) and Fig. 9(b) show a cross section perpendicular to the longitudinal direction, and therefore the line segment Li for counting the light flux is shown as a point. In Fig. 9(a) and Fig. 9(b), a parallel plate H with a refractive index of 1.46 and a thickness of 2.9 mm is provided on the upper side of the illumination device 10 in place of a manuscript table, and a line segment Li including the portion for counting the light flux is disposed on the surface of the parallel plate H opposite to the illumination device side.

[0054] In FIG. 9(a), the position of the light source arranged at the approximate center of the light guide 12 is the origin, the direction perpendicular to the paper is the x' direction corresponding to the x direction of the lighting device, the direction perpendicular to the x' direction and parallel to the surface of the parallel plate H is the z' direction, and the direction perpendicular to the x' direction and the z' direction is the y' direction. The coordinates of the line segment Li are (x1', 6.45, 4.70) (where x1'=0 to 225). The angle between the normal to the light exit surface 12c of the light guide 12 and the y' direction is 50°. With regard to the light scattering pattern 20 provided on the light guide 12, a plurality of recesses are arranged so that the irradiance distribution is approximately uniform in the x' direction, except for the region corresponding to the light exit surface 12c near the first end surface 12a and the second end surface 12b.

[0055] The distance d between the second end face 12b of the light guide 12 and the face of the light guide case 14 facing the second end face 12b of the light guide 12 was appropriately changed from 0.05 mm to 1.25 mm, and the offset amount Lc of the top face 14c of the light guide case 14 on the second end face side from the light exit face 12c of the light guide 12 was set as a parameter: 0 mm, 0.3 mm, 0.5 mm, 0.7 mm, 0.9 mm, and 1.2 mm. The irradiance was obtained while changing each parameter. The total area S of the second end face 12b at these offset amounts was 0 The area S of the exposed region of the second end surface 12b 1 Ratio of S 1 / S 0 are shown in Table 1 below. [Table 1]

[0056] Fig. 10 shows the irradiance distribution when the offset amount Lc = 0 mm. Fig. 11 shows the irradiance distribution when the offset amount Lc = 0.7 mm. Fig. 12 shows the irradiance distribution when the offset amount Lc = 1.2 mm. In Figs. 10 to 12, the horizontal axis represents the distance in the x' direction from the origin in the x'y'z' coordinate system shown in Fig. 9(a), and the vertical axis represents the irradiance (arbitrary units) per unit area including the line segment Li.

[0057] Furthermore, the irradiance distribution was obtained by varying the distance d and the offset amount Lc, and the PRNU value (Photoresponse Nonuniformity value) for evaluating the uniformity of the irradiance distribution was obtained from the following formula. PRNU = (maximum illuminance - minimum illuminance) / (maximum illuminance + minimum illuminance) x 100 [%]

[0058] Fig. 13 shows a graph showing the dependency of the PRNU value on the distance d and the offset amount Lc. The PRNU value was calculated in the range of 200 mm≦x'≦218 mm shown in Fig. 10 to Fig. 12. In Fig. 13, it is assumed that the calculated values ​​of each parameter set can be connected by a virtual line between each offset amount set.

[0059] From Figure 13, the offset amount Lc = 0 mm (S 1 / S 0 = 0, i.e., the exposed area of ​​second end face 12b is zero), the PRNU value increases monotonically as the distance d between second end face 12b of light guide 12 and inner surface 14a of light guide case 14 facing second end face 12b increases. In addition, when offset amount Lc = 0 mm, if distance d is greater than 0.3 mm, the PRNU value exceeds 10%.

[0060] Also, from Figure 13, the offset amount Lc = 0.5 mm (S 1 / S 0 = 0.08), it is estimated that the minimum value is near the distance d = 0.5 mm, suggesting that the PRNU value is 10% or less when the distance d is in the range of 0.2 mm to 0.7 mm.

[0061] Also, from Figure 13, the offset amount Lc = 0.7 mm (S 1 / S 0 = 0.18), it is estimated that the minimum value is within the range of distance d = 0.3 mm to 0.7 mm, suggesting that the PRNU value is 10% or less at least within the range of distance d = 0.5 mm to 0.8 mm.

[0062] Also, from Figure 13, the offset amount Lc = 0.9 mm (S 1 / S 0 = 0.23), it is estimated that the minimum value is within the range of distance d = 0.3 mm to 0.7 mm, suggesting that the PRNU value is 10% or less at least within the range of distance d = 0.5 mm to 0.8 mm.

[0063] Also, from Figure 13, the offset amount Lc = 1.2 mm (S 1 / S 0 = 0.32), it cannot be confirmed that the PRNU value is 10% or less, at least within the range of spacing d = 0.3 mm to 0.7 mm.

[0064] In the general usage of the image sensor and the required specifications, the PRNU value is required to be at least 12% or less, and preferably 10% or less. Therefore, taking into account the case where the interval d can vary within the range of 0.3 mm to 0.7 mm, S 1 / S 0 The value of is preferably 0.12 to 0.25, and more preferably 0.13 to 0.23. When a top surface 14c of a wall 14b including an inner surface 14a of the light guide case 14 facing the second end surface 12b of the light guide 12 is approximately parallel to the light exit surface 12c of the light guide 12, an offset amount Lc representing the distance between the light exit surface 12c and the top surface 14c is preferably Lc = 0.4 mm to 1.0 mm, and more preferably Lc = 0.5 mm to 0.9 mm.

[0065] The present invention has been described above based on the embodiment. This embodiment is merely an example, and it will be understood by those skilled in the art that various modifications are possible in the combination of each component and each treatment process, and that such modifications are also within the scope of the present invention. [Explanation of symbols]

[0066] 10 lighting device, 12 light guide, 14 light guide case, 16 light emitting unit, 18 LED, 20 light scattering pattern, 100 image sensor, 102 housing, 104 glass plate, 106 rod lens array, 108 line image sensor

Claims

1. a rod-shaped light guide having a first end face, a second end face opposite to the first end face, and a light exit surface formed on at least a part of a side face along a longitudinal direction of the light guide; a light source that emits light toward the first end surface of the light guide; a light guide case that accommodates the light guide, the light guide case having at least a wall including an opposing surface that faces the second end surface of the light guide; A lighting device comprising: A lighting device, characterized in that, when the lighting device is viewed from the second end face side of the light guide, a part of the second end face of the light guide is exposed.

2. 2 . The lighting device according to claim 1 , wherein a top surface of the wall of the light guide case is offset from the light exit surface, thereby exposing a partial area of ​​the second end surface of the light guide.

3. 3. The lighting device according to claim 2, wherein the top surface of the wall is substantially parallel to the light exit surface of the light guide.

4. 3. The lighting device according to claim 2, wherein the top surface of the wall is configured to be oblique with respect to the light exit surface of the light guide.

5. 3. The lighting device according to claim 2, wherein the top surface of the wall is formed of a curved surface.

6. The lighting device of claim 2 , wherein the top surface of the wall includes a curved surface.

7. The lighting device according to claim 1 , wherein the wall has a through hole, and a partial area of ​​the second end surface of the light guide is exposed through the through hole.

8. 2. The lighting device according to claim 1, wherein a distance between the second end surface of the light guide and the opposing surface of the light guide case is 0.1 mm to 1.0 mm.

9. The area of ​​the second end surface of the light guide is S ０ When the lighting device is viewed from the second end face side of the light guide, the area of ​​the exposed region of the second end face of the light guide is S １ Then, S ０ S for １ The ratio S １ / S ０ 9. The lighting device according to claim 8, wherein is 0.12 to 0.

25.

10. a distance between the second end surface of the light guide and the opposing surface of the light guide case is 0.1 mm to 1.0 mm; 3. The illumination device according to claim 2, wherein the offset of the top surface from the light exit surface is between 0.4 mm and 1.0 mm.

11. The lighting device according to claim 1 , which illuminates an object; a lens array for collecting reflected light from the object; a light receiving element that receives the light collected by the lens array; An image sensor comprising:

Images