Optical device, illumination device, and image forming apparatus

Abstract

To provide an optical device capable of suppressing deterioration of optical performance.SOLUTION: According to an aspect of the present invention, there is provided an optical device including first and second light guides facing each other in a first direction, wherein the second light guide guides light from a light source to the first light guide and has a concave emission surface, and the first light guide includes a plurality of deflectors arranged in the first direction and each deflecting light from the second light guide.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical device and an illumination device, and more particularly to an optical device and an illumination device that are suitable for use in image forming devices such as laser beam printers (LBPs), digital copying machines, and multifunction printers. [Background technology]

[0002] 2. Description of the Related Art Conventionally, an image forming apparatus is provided with an optical device for guiding light from a light source so as to neutralize a photosensitive drum. Patent Document 1 discloses an optical device formed by a light guide having a diffusing portion that diffuses light from a light source. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-295093 Summary of the Invention [Problem to be solved by the invention]

[0004] On the other hand, in an optical device such as that disclosed in Patent Document 1, when the light guide is positioned far away from the light source depending on the structure, the efficiency with which the light guide captures light rays from the light source decreases, resulting in a decrease in optical performance. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an optical device that can suppress deterioration in optical performance. [Means for solving the problem]

[0005] In order to achieve the above object, one aspect of the present invention provides an optical device comprising first and second light guides facing each other in a first direction, wherein the second light guide guides light from a light source to the first light guide and has a concave exit surface, and the first light guide is arranged in the first direction and has a plurality of deflection portions each of which deflects light from the second light guide. Another aspect of the present invention is an optical device comprising first and second light guides facing each other in a first direction, wherein the second light guide guides light from a light source to the first light guide, and the first light guide is arranged in the first direction and has a plurality of deflection sections each of which deflects light from the second light guide. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide an optical device that can suppress deterioration in optical performance. [Brief explanation of the drawings]

[0007] [Figure 1] 1A and 1B are a cross-sectional view, a perspective view, and a partially enlarged perspective view of a lighting device according to a first embodiment. [Figure 2] 2A and 2B are cross-sectional views of an illumination device according to the first embodiment and a diagram showing a light amount distribution on a photosensitive drum by the illumination device according to the first embodiment. [Figure 3] 1 is a cross-sectional view of a lighting device according to a first embodiment. [Figure 4] 1A and 1B are cross-sectional views of an illumination device according to a first embodiment, and diagrams showing light quantity distributions on a photosensitive drum by the illumination device according to the first embodiment and a conventional illumination device, respectively. [Figure 5] FIG. 1 is a partial cross-sectional view of an illumination device according to a first embodiment. [Figure 6] FIG. 1 is a partial cross-sectional view of an illumination device according to a first embodiment. [Figure 7] 10A and 10B are cross-sectional views of an illumination device according to a second embodiment, and diagrams showing light quantity distributions on a photosensitive drum by the illumination device according to the second embodiment and a conventional illumination device, respectively. [Figure 8]10A and 10B are cross-sectional views of an illumination device according to a third embodiment, and diagrams showing light quantity distributions on a photosensitive drum by the illumination device according to the third embodiment and a conventional illumination device, respectively. [Figure 9] 10A and 10B are cross-sectional views of an illumination device according to a fourth embodiment, and diagrams showing light quantity distributions on a photosensitive drum by the illumination device according to the fourth embodiment and a conventional illumination device, respectively. [Figure 10] 10A and 10B are a cross-sectional view, a perspective view, and a partially enlarged perspective view of a lighting device according to a fifth embodiment. [Figure 11] 13A and 13B are cross-sectional views of a light source included in an illumination device according to a fifth embodiment, and views showing the light distribution of the light source. [Figure 12] FIG. 10 is a partial perspective view of a lighting device according to a fifth embodiment. [Figure 13] 13A and 13B are diagrams showing changes in the amount of light on the incident surface of a light guide in an illumination device according to a fifth embodiment. [Figure 14] FIG. 10 is a cross-sectional view of a lighting device according to a fifth embodiment. [Figure 15] 10A and 10B are a partially enlarged perspective view and a diagram showing how light rays are guided by a sub-light guide, a diagram showing the amount of light at each incident angle of light rays incident on the incident surface of the light guide, and a diagram showing the light amount distribution on a photosensitive drum, respectively. [Figure 16] 10A and 10B are a partial perspective view of an illumination device according to a sixth embodiment, a diagram showing the amount of light at each incident angle of a light ray incident on an incident surface of a light guide, and a diagram showing the light amount distribution on a photosensitive drum. [Figure 17] FIG. 13 is a partial perspective view of an illumination device according to a seventh embodiment. [Figure 18] FIG. 13 is a partial perspective view of an illumination device according to an eighth embodiment. [Figure 19] FIG. 13 is a partial cross-sectional view of an illumination device according to an eighth embodiment. [Figure 20] FIG. 2 is a sub-scanning cross-sectional view of a main part of the image forming apparatus according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] The lighting device according to the present embodiment will be described in detail below with reference to the accompanying drawings. Note that the drawings may be drawn at a scale different from the actual scale in order to facilitate understanding of the present embodiment. In the following, the direction in which the light guide 102 extends (the direction in which the multiple reflecting portions 201 are arranged) is defined as the Y direction (first direction), the direction in which the reflecting portions 201 extend is defined as the Z direction, and the direction perpendicular to the Y direction and the Z direction is defined as the X direction.

[0009] [First embodiment] BACKGROUND ART Conventionally, lighting devices formed by a light source such as a light emitting diode (LED) and a light guide (light conducting body) are known. In particular, image forming apparatuses such as copying machines and facsimiles are equipped with an illumination device that uses a light guide having a plurality of reflecting portions to uniformly illuminate a photosensitive drum.

[0010] In such lighting devices, the light source and the light guide are generally arranged close to each other in order to improve the efficiency of capturing the light rays emitted from the light source. On the other hand, in such lighting devices, it may be necessary to arrange the light source and the light guide at a distance from each other.

[0011] In such cases, in order to suppress the reduction in light intensity due to light rays emitted from the light source that do not enter the light guide, lighting devices have been proposed in which a lens or sub-light guide that focuses the light rays is provided between the light source and the light guide. However, in such lighting devices, if the light guide and lens are positioned without adjusting the optical axis in order to reduce assembly costs, and the optical axis is misaligned, light rays with a large angle of incidence will be reflected at the end of the lens and then enter the light guide.

[0012] In this case, if the light guide has multiple reflective portions that reflect light rays toward the photosensitive drum, the light rays that enter the light guide in this manner will travel in a concentrated manner toward the reflective portion that is located on the side of the light guide that is closer to the light source. As a result, the exposure area on the photosensitive drum that is closer to the light source is strongly illuminated, causing unevenness in the amount of light. Therefore, the present embodiment aims to provide an illumination device that can suppress an increase in unevenness in the amount of light on the photosensitive drum, even if the sub-light guide is misaligned when the sub-light guide and light guide are arranged, without the need for adjustment to reduce assembly costs.

[0013] 1(a), (b), and (c) are a schematic cross-sectional view, a perspective view, and a partially enlarged perspective view, respectively, of an illumination device 100 according to a first embodiment. The lighting device 100 of this embodiment includes a light source 101, a light guide 102 (first light guide), and a sub-light guide 103 (second light guide), and is used to eliminate static electricity by illuminating the surface of the photosensitive drum D, which is the illuminated surface, with a substantially uniform amount of light.

[0014] In other words, the illumination device 100 according to this embodiment includes a light source 101 and an optical device formed of a light guide 102 and a sub-light guide 103. In the illumination device 100 according to this embodiment, the light guide 102 and the sub-light guide 103 face each other in the Y direction, and the sub-light guide 103 is disposed between the light source 101 and the light guide 102 .

[0015] In the lighting device 100 according to this embodiment, the light source 101, the light guide 102, and the sub-light guide 103 are held by different holding members (holding portions) in a housing (not shown). The light guide 102 and the sub-light guide 103 are formed by injection molding polymethyl methacrylate (PMMA). This allows the light guide 102 and the sub-light guide 103 to be mass-produced easily and inexpensively.

[0016] As the light source 101, a light emitting diode (LED) is used, which includes a light emitting chip (not shown) and a sealing member made of a resin material for sealing the light emitting chip. Further, the light guide 102 is formed with a plurality of reflecting portions (deflecting portions) 201 for guiding (irradiating) the light beam emitted from the light source 101 toward the photosensitive drum D. Specifically, as shown in FIGS. 1(a) to 1(c), the plurality of reflecting portions 201 are arranged in the Y direction.

[0017] As shown in FIG. 1(c), the reflecting portion 201 forms a substantially isosceles triangle in the XY cross section and has a prism shape extending in the Z direction. In the light guide 102 provided in the lighting device 100 according to this embodiment, the length of each of the multiple reflecting portions 201 in the Z direction is adjusted so that the amount of light on the side farther from the light source 101 increases, taking into account fluctuations in the amount of light on the photosensitive drum D due to manufacturing errors.

[0018] Additionally, for the above-mentioned reasons, the light guide 102 provided in the lighting device 100 according to this embodiment is set so that the intervals between adjacent reflecting portions 201 become smaller as the distance from the light source 101 increases. The light guide 102 and the sub-light guide 103 have central axes Ax1 and Ax2, respectively.

[0019] The sub-light guide 103 guides the light from the light source 101 to the light guide 102, and the light guide 102 guides the light from the sub-light guide 103 onto the photosensitive drum D. That is, as shown in Figure 1(a), a light ray R1 that is emitted from the light source 101 and then enters the incident surface 104 of the sub-light guide 103 at a relatively small angle travels straight through the sub-light guide 103 and then exits from the exit surface 105, thereby entering the light guide 102. On the other hand, light ray R2 that is emitted from light source 101 and then enters incident surface 104 of sub-light guide 103 at a relatively large angle is totally reflected at least once by the side surface of sub-light guide 103 and then exits from exit surface 105, thereby entering light guide 102.

[0020] The light ray R1 is reflected by a reflecting portion 201 that is disposed in the light guide 102 at a position relatively far from the light source 101, and is guided to the photosensitive drum D. On the other hand, the light ray R2 is reflected by a reflecting portion 201 that is disposed in the light guide 102 at a position relatively close to the light source 101, and is guided to the photosensitive drum D.

[0021] FIG. 2(a) shows a schematic cross-sectional view of the lighting device 100 according to this embodiment. Specifically, Figure 2(a) shows a schematic cross-sectional view of the illumination device 100 according to this embodiment when the central axis Ax1 of the light guide 102 and the central axis Ax2 of the sub-light guide 103 are spaced apart from each other by a distance Δd in the X direction.

[0022] In the following description, a state in which the central axis Ax1 of the light guide 102 and the central axis Ax2 of the sub-light guide 103 are spaced apart from each other by a distance Δd in the X direction may be referred to as a state in which an axial misalignment occurs. In the following description, for convenience, it is assumed that the exit surface 105 of the sub-light guide 103 has a flat shape.

[0023] FIG. 2(b) shows the light amount distribution on the photosensitive drum D in the illumination device 100 according to this embodiment in a state where axial misalignment occurs and in a state where axial misalignment does not occur. Specifically, the horizontal axis in FIG. 2(b) indicates the position on the photosensitive drum D in the Y direction, and position 0 indicates the center of the exposure area of ​​the photosensitive drum D. On the photosensitive drum D, an exposure area of ​​±150 mm in the Y direction is illuminated by the illumination device 100 according to this embodiment.

[0024] The negative position on the horizontal axis of Figure 2(b) on the photosensitive drum D indicates the position on the light source 101 side relative to the center of the exposure area, and the positive position on the photosensitive drum D indicates the position on the opposite side of the light source 101 relative to the center of the exposure area. The vertical axis in FIG. 2(b) indicates the magnitude of the light amount at each position in the Y direction on the photosensitive drum D by the illumination device 100 according to this embodiment.

[0025] When an axial misalignment occurs in the illumination device 100 according to this embodiment, the amount of light incident on the light guide 102 decreases. Therefore, the overall amount of light on the photosensitive drum D is reduced compared to when no axial misalignment occurs, as shown in FIG. 2(b).

[0026] On the other hand, as shown in FIG. 2(b), the amount of light at each position on the photosensitive drum D, particularly at the side closer to the light source 101 from -150 mm to -130 mm, is increased compared to when no axial misalignment occurs. As a result, when an axial misalignment occurs in the illumination device 100 according to this embodiment, the difference between the maximum and minimum light amounts across the exposure area on the photosensitive drum D increases.

[0027] Here, we consider the maximum and minimum values ​​of the ratio of the difference between the light amount at position 0 on the photosensitive drum D (hereinafter referred to as the reference light amount) and the light amount at each position to the reference light amount. Then, we evaluate the difference between the maximum and minimum values ​​as the unevenness in the light amount. That is, in the illumination device 100 according to this embodiment, the occurrence of axial misalignment increases the unevenness in the amount of light on the photosensitive drum D.

[0028] FIG. 3 shows a schematic cross-sectional view of the lighting device 100 according to this embodiment. Specifically, FIG. 3 simply explains the principle by which the amount of light increases at a position on the photosensitive drum D on the light source 101 side when axial misalignment occurs in the illumination device 100 according to this embodiment.

[0029] In FIG. 3, the rectangle indicated by the dashed line represents the sub-light guide 103 when no axial misalignment occurs, and the rectangle indicated by the solid line represents the sub-light guide 103 when axial misalignment occurs. In addition, in FIG. 3, a light ray R3 is a light ray that does not enter the sub-light guide 103 when no axial misalignment occurs, and has a relatively large emission angle from the light source 101.

[0030] On the other hand, in FIG. 3, a light ray R4 is a light ray that does not enter the sub-light guide 103 when an axial misalignment occurs, and has a relatively small emission angle from the light source 101. As shown in FIG. 3, if the sub-light guide 103 has an axial misalignment, the angle of incidence of the light beam incident on the light guide 102 tends to be larger than when no axial misalignment occurs.

[0031] As shown in FIG. 3, when light ray R3 enters light guide 102 at a large angle of incidence, the number of times light ray R3 is reflected inside light guide 102 increases, and the probability that light ray R3 will be reflected by reflecting portion 201 also increases. Therefore, if an axial misalignment occurs in the sub-light guide 103, most of the light rays incident on the light guide 102 travel inside the light guide 102 toward the reflecting portion 201 on the light source 101 side. As a result, the exposure area on the photosensitive drum D on the side of the light source 101 is exposed in a concentrated manner, increasing the amount of light in that exposure area, and the maximum amount of light at each position on the photosensitive drum D increases compared to when no axial misalignment occurs in the sub-light guide 103.

[0032] On the other hand, when an axial misalignment occurs in the sub-light guide 103, the light ray R4, which has a relatively small emission angle from the light source 101, no longer enters the light guide 102, and the amount of light in the exposure area on the photosensitive drum D that is far from the light source 101 decreases. That is, the minimum value of the amount of light at each position on the photosensitive drum D is reduced compared to when no axial misalignment occurs in the sub-light guide 103. As described above, when axial misalignment occurs in the lighting device 100 according to this embodiment, the difference between the maximum and minimum light amounts at each position on the photosensitive drum D increases, thereby increasing the unevenness of the light amount on the photosensitive drum D.

[0033] FIG. 4(a) shows a schematic cross-sectional view of the lighting device 100 according to this embodiment. Specifically, FIG. 4(a) simply explains the principle of suppressing an increase in unevenness in the amount of light on the photosensitive drum D when axial misalignment occurs in the illumination device 100 according to this embodiment.

[0034] In FIG. 4(a), the dashed line indicates the exit surface 105 of a conventional sub-light guide having a planar shape. On the other hand, the curved line indicated by the solid line indicates the exit surface 105 of the sub-light guide 103 provided in the illumination device 100 according to this embodiment, which has a concave shape (recessed shape).

[0035] The sub-light guide 103 and the conventional sub-light guide have the same shape except that the shape of the exit surface 105 is different. In addition, an illumination device having the same configuration as the illumination device 100 according to this embodiment except for having the conventional sub-light guide instead of the sub-light guide 103 may be referred to as a conventional illumination device below.

[0036] In FIG. 4(a), the solid arrow indicates a light ray R5 guided in the lighting device 100 according to this embodiment, and the dashed arrow indicates a light ray R6 guided in the conventional lighting device. As shown in FIG. 4(a), a sub-light guide 103 provided in the lighting device 100 according to this embodiment is formed with an exit surface 105 having a concave shape.

[0037] This allows the angle of incidence of light rays incident on the light guide 102 to be reduced compared to the above-mentioned conventional illumination device. That is, in the lighting device 100 according to this embodiment, the exit surface 105 of the sub-light guide 103 has a concave shape, so that the light rays can travel farther from the light source 101 inside the light guide 102. As a result, in the illumination device 100 according to this embodiment, even if the sub-light guide 103 is misaligned, an increase in unevenness in the amount of light on the photosensitive drum D can be suppressed.

[0038] FIG. 4(b) shows the light amount distribution on the photosensitive drum D when axial misalignment occurs in the illumination device 100 according to this embodiment and in a conventional illumination device. The horizontal axis in Figure 4(b) indicates the position in the Y direction on the photosensitive drum D, with the negative side position indicating the position on the light source 101 side relative to the center of the exposure area on the photosensitive drum D, and the positive side position indicating the position on the opposite side of the light source 101 relative to the center. The vertical axis of Figure 4(b) shows the ratio (hereinafter referred to as the fluctuation ratio) of the difference between the light amount at position 0 on the photosensitive drum D (hereinafter referred to as the reference light amount) and the light amount at each position to the reference light amount.

[0039] As shown in FIG. 4(b), in a conventional lighting device equipped with a conventional sub-light guide having a flat exit surface 105, the amount of light in the exposure area on the light source 101 side of the photosensitive drum D is significantly increased. On the other hand, in the lighting device 100 of this embodiment, which is equipped with a sub-light guide 103 having an exit surface 105 with a concave shape, it can be seen that such an increase in the amount of light in the exposure area on the light source 101 side of the photosensitive drum D is suppressed. Specifically, the difference between the maximum and minimum values ​​of the above fluctuation ratio, i.e., the unevenness in light intensity, is 114% in the conventional lighting device, but is reduced to 84% in the lighting device 100 of this embodiment.

[0040] As described above, in the lighting device 100 according to this embodiment, the exit surface 105 of the sub-light guide 103 has a concave shape, so that the exit angle of the light beams exiting from the sub-light guide 103 can be reduced even if an axial misalignment occurs. This reduces the probability of reflection by the reflecting portion 201 on the light source 101 side inside the light guide 102, thereby suppressing an increase in the amount of light in the exposure area on the light source 101 side on the photosensitive drum D, and ultimately suppressing an increase in unevenness in the amount of light.

[0041] Next, a description will be given of a suitable arrangement and shape of each optical element in the illumination device 100 according to this embodiment. FIG. 5(a) is a partial schematic cross-sectional view illustrating each parameter of the lighting device 100 according to this embodiment.

[0042] First, let d be the diameter of the exit surface 105 of the sub-light guide 103 when projected onto the XZ cross section, and let point O, which is the center of the light-emitting surface of the light source 101, and central axis Ax2 of the sub-light guide 103 be spaced apart from each other by Δd in the X direction. Note that, hereinafter, point O is taken as the origin. A light ray emitted from point O at an emission angle θ enters sub-light guide 103 at point A on entrance surface 104, is reflected at point B on the side surface, and then exits from point D on exit surface 105.

[0043] The intersection of the line passing through point B and parallel to the central axis Ax2 with the exit surface 105 is defined as point C, and the intersection of the central axis Ax2 with the exit surface 105, ie, the vertex of the exit surface 105, is defined as point E. In this case, point D is required to be on the curve CE that passes through points C and E. In other words, the coordinate D in the X direction of point D is X is required to satisfy the following conditional expression (1).

number

[0044] Next, when the distance between point O in the Y direction and the incident surface 104 of the sub-light guide 103 is d1, the coordinate A of point A in the X direction is X is expressed as the following equation (2).

number

[0045] Next, let point B' be the intersection of a line passing through point A and parallel to the central axis Ax2 with a perpendicular line from point B to the central axis Ax2. The distance L between points B and B' is BB’ is expressed as the following equation (3) using equation (2).

number

number

[0046] Next, when the refractive index of the sub light guide 103 is n, the following equation (5) is obtained from Snell's law.

number

[0047] Then, by substituting equations (3) and (5) into equation (4), the following equation (6) is obtained.

number

[0048] Also, the coordinate B in the X direction of point B X is d / 2+Δd, and L BD’ =B X -D X Therefore, conditional expression (1) can be rewritten as the following conditional expression (7).

number

[0049] Here, the amount of axial misalignment Δd of the sub-light guide 103 in the X direction can be set to, for example, 1 mm based on the assembly precision of the holding member (not shown) that holds the sub-light guide 103 . Taking into consideration various types of light sources that can be used as the light source 101, it is preferable that the following conditional expressions (7) to (8) be satisfied for the light ray emitted from the light source 101 at an emission angle θ of 30°.

number

[0050] FIG. 5(b) is a schematic cross-sectional view of a portion of the lighting device 100 according to this embodiment. Specifically, FIG. 5(b) shows how the light rays are guided by the sub-light guide 103 so as to exceed the upper limit of conditional expression (7).

[0051] In Figure 5(b), the solid arrow indicates how light ray R7 emitted from light source 101 at emission angle θ is emitted from emission surface 105, which has a concave shape, of sub-light guide 103 provided in lighting device 100 of this embodiment. In addition, in Figure 5(b), the dashed arrow indicates how light ray R8 emitted from light source 101 at an emission angle θ is emitted from the flat emission surface of a conventional sub-light guide provided in a conventional lighting device.

[0052] As shown in FIG. 5(b), when the upper limit value of conditional expression (7) is exceeded, the light beam emitted from the light source 101 at an emission angle θ is no longer reflected inside the sub-light guide 103 as intended. Therefore, the light beam emitted from the sub-light guide 103 does not enter the light guide 102, and the amount of light on the photosensitive drum D is significantly reduced. Furthermore, in this case, since the exit surface 105 of the sub-light guide 103 has a concave shape, the exit angle of the light beam exiting from the exit surface 105 becomes larger than that of a conventional sub-light guide.

[0053] FIG. 5(c) is a schematic cross-sectional view of a portion of the illumination device 100 according to this embodiment. Specifically, FIG. 5C shows how the light rays are guided by the sub-light guide 103 so as to be below the lower limit of conditional expression (7).

[0054] In Figure 5(c), the solid arrow indicates how light ray R9 emitted from light source 101 at emission angle θ is emitted from emission surface 105, which has a concave shape, of sub-light guide 103 provided in lighting device 100 of this embodiment. In addition, in Figure 5(c), the dashed arrow indicates how light ray R10 emitted from light source 101 at an emission angle θ is emitted from the flat emission surface of a conventional sub-light guide provided in a conventional lighting device.

[0055] As shown in FIG. 5(c), when the lower limit of conditional expression (7) is not reached, a light ray emitted from the light source 101 to one side in the X direction at an emission angle θ is emitted to the other side in the X direction with respect to the central axis Ax2 at the emission surface 105 of the sub-light guide 103. In this case, the angle of incidence of the light beam when it enters the incident surface of the light guide 102 increases compared to when the light is guided by a conventional sub-light guide. In other words, if axial misalignment occurs in the sub-light guide 103 while the lower limit of conditional expression (7) is not met, the angle of incidence of the light rays entering the light guide 102 increases, thereby increasing the amount of light in the exposure range on the light source 101 side on the photosensitive drum D.

[0056] As described above, in the lighting device 100 according to this embodiment, the conditional expression (7) is satisfied, and therefore the angle of incidence of the light rays incident on the light guide 102 is reduced, thereby suppressing an increase in unevenness in the amount of light on the photosensitive drum D. In the lighting device 100 according to this embodiment, it is more preferable that the following conditional expression (8a) be fulfilled instead of the conditional expression (8).

number

[0057] By satisfying conditional expression (8a), the distance between the light source 101 and the sub-light guide 103 and the distance between the entrance surface 104 and the exit surface 105 of the sub-light guide 103 can be set more effectively. In the lighting device 100 according to this embodiment, the distance d1 and the distance d sub The refractive index n and diameter d are 2.1 mm, 7.0 mm, 1.48 mm and 4.0 mm, respectively. Therefore, the values ​​of the conditions (8) and (8a) are found to be 0.32 and are therefore satisfied.

[0058] Furthermore, it is preferable that the exit surface 105 formed on the sub-light guide 103 provided in the illumination device 100 according to this embodiment has a spherical shape. In the lighting device 100 according to this embodiment, the exit surface 105 formed on the sub-light guide 103 has a spherical shape, which makes it possible to continuously change the exit angle of each light ray exiting from the exit surface 105.

[0059] This makes it easier to control the unevenness in the amount of light on the photosensitive drum D at the design stage of the illumination device 100 according to this embodiment. When the radius of curvature in a predetermined cross section that includes the vertex of the exit surface 105 formed on the sub-light guide 103 provided in the illumination device 100 according to this embodiment and is parallel to the Y direction is defined as R, it is preferable that the following conditional expression (9) be satisfied:

number

[0060] In the lighting device 100 according to this embodiment, conditional expression (9) is satisfied, and as a result, it is possible to effectively suppress an increase in unevenness in the amount of light on the photosensitive drum D when axial misalignment occurs in the sub-light guide 103, as shown below. FIG. 6(a) is a schematic cross-sectional view of a portion of the lighting device 100 according to this embodiment. Specifically, FIG. 6(a) shows how the light rays are guided by the sub-light guide 103 so as to be below the lower limit of conditional expression (9).

[0061] In Figure 6(a), the solid arrow indicates how light ray R11 emitted from the light source 101 is emitted from the concave exit surface 105 of the sub-light guide 103 provided in the lighting device 100 of this embodiment. In addition, the dashed arrow in FIG. 6(a) shows how a light ray R12 emitted from the light source 101 is emitted from a planar emission surface of a conventional sub-light guide provided in a conventional lighting device.

[0062] As shown in FIG. 6(a), when the radius of curvature R of the exit surface 105 is reduced so as to fall below the lower limit of conditional expression (9), the angle of emergence of the light beam from the exit surface 105 becomes much smaller than in the past when an axial misalignment occurs in the sub-light guide 103. In this case, the amount of light in the exposure area on the light source 101 side of the photosensitive drum D decreases due to a decrease in the amount of light of light rays that enter the light guide 102 at a large angle. That is, the amount of light increases in the exposure area on the opposite side of the photosensitive drum D from the light source 101, which increases the unevenness in the amount of light.

[0063] FIG. 6(b) is a schematic cross-sectional view of a portion of the lighting device 100 according to this embodiment. Specifically, FIG. 6(b) shows how the light rays are guided by the sub-light guide 103 so as to exceed the upper limit of conditional expression (9).

[0064] In Figure 6(b), the solid arrow indicates how light ray R13 emitted from the light source 101 is emitted from the concave exit surface 105 of the sub-light guide 103 provided in the lighting device 100 of this embodiment. In addition, the dashed arrow in FIG. 6(b) shows how a light ray R14 emitted from the light source 101 is emitted from a flat emission surface of a conventional sub-light guide provided in a conventional lighting device.

[0065] As shown in FIG. 6(b), when the radius of curvature R of the exit surface 105 increases so as to exceed the upper limit of conditional expression (9), there is no significant difference between the shape of the exit surface 105 and the conventional planar shape. In this case, the illumination device 100 according to this embodiment does not convert the incident angle of the light beam incident on the light guide 102 to a smaller angle, making it difficult to achieve the above-described effect.

[0066] In particular, it is preferable that the absolute value of the incident angle of the light ray entering the light guide 102 is smaller than the absolute value of the exit angle of the light ray exiting from the light source 101 by 2.5° or more, and the upper limit value of conditional expression (9) is determined from this preferable condition. In the lighting device 100 according to this embodiment, it is more preferable that the following conditional expression (9a) be fulfilled instead of the conditional expression (9).

number

[0067] By setting the radius of curvature R of the exit surface 105 formed on the sub-light guide 103 so as to satisfy the conditional formula (9a), the angle of incidence of the light beam incident on the light guide 102 can be adjusted effectively. Furthermore, by satisfying conditional expression (9a), even if the sub-light guide 103 has manufacturing errors, the value of R / d will not be 0.55 or less.

[0068] In the lighting device 100 according to this embodiment, the radius of curvature R and the diameter d are 4.0 mm and 4.0 mm, respectively. Therefore, the values ​​of the conditions (9) and (9a) are found to be 1.00 and are therefore satisfied.

[0069] As described above, the lighting device 100 according to this embodiment is provided with a light source 101, a light guide 102, and a sub-light guide 103. The sub-light guide 103 guides light from the light source 101 to the light guide 102 and has a concave exit surface 105. As a result, even if the sub-light guide 103 is displaced, it is possible to suppress an increase in unevenness in the amount of light on the photosensitive drum D.

[0070] Although the lighting device 100 according to this embodiment uses a light emitting diode (LED) as the light source 101, the light source is not limited to this, and a white light bulb or a laser light source may also be used. Furthermore, the light guide 102 and the sub-light guide 103 provided in the lighting device 100 according to this embodiment are made of polymethyl methacrylate (PMMA), but are not limited to this and may be made of other resin materials or glass materials.

[0071] Furthermore, in the illumination device 100 according to this embodiment, the above-described effects do not change depending on the shape of the light guide 102, particularly the shape and arrangement of the reflecting portion 201. In addition, in the illumination device 100 according to this embodiment, the reflecting portion 201 formed on the light guide 102 is an approximately isosceles triangle in the XY cross section and has a prism shape extending in the Z direction, but is not limited to this and may have other shapes.

[0072] Furthermore, in the illumination device 100 according to this embodiment, the light source 101, the light guide 102, and the sub-light guide 103 are held by different holding members, but this is not limitative. That is, the light guide 102 and the sub-light guide 103 may be held by a single holding member, or the light source 101 and the sub-light guide 103 may be held by a single holding member. In other words, in the illumination device 100 according to this embodiment, a single holding member that holds all of the light source 101, the light guide 102, and the sub-light guide 103 is not provided.

[0073] Furthermore, in the illumination device 100 according to this embodiment, the exit surface 105 of the sub-light guide 103 has a circular shape in the XZ cross section, but this is not limiting and the exit surface 105 may have any other shape. In this case, instead of the diameter d of the exit surface 105 of the sub-light guide 103 when projected onto the XZ cross section, the maximum distance between two points on the circumference of the exit surface 105 of the sub-light guide 103 when projected onto the XZ cross section can be used.

[0074] [Second embodiment] FIG. 7(a) shows a schematic cross-sectional view of an illumination device 200 according to the second embodiment. The lighting device 200 according to this embodiment has the same configuration as the lighting device 100 according to the first embodiment except for different specification values, and therefore the same components are given the same reference numerals and their explanations are omitted.

[0075] Specifically, in the illumination device 200 according to this embodiment, the diameter d of the exit surface 105 of the sub-light guide 103 when projected onto the XZ cross section is larger than that of the illumination device 100 according to the first embodiment. In particular, the diameter d of the sub-light guide 103 is larger than the diameter of the light guide 102 when projected onto the XZ cross section of the incident surface.

[0076] In addition, in the illumination device 200 according to this embodiment, the radius of curvature R of the exit surface 105 formed on the sub-light guide 103 is larger than that of the illumination device 100 according to the first embodiment. Furthermore, in the illumination device 200 according to this embodiment, the distance d1 between the light source 101 and the incident surface 104 of the sub-light guide 103 is smaller than that of the illumination device 100 according to the first embodiment.

[0077] FIG. 7B shows the light amount distribution on the photosensitive drum D when axial misalignment occurs in the illumination device 200 according to this embodiment and in a conventional illumination device. The conventional lighting device has the same configuration as the lighting device 200 according to this embodiment, except that the exit surface 105 of the sub-light guide 103 has a flat shape.

[0078] The horizontal axis in Figure 7(b) indicates the position in the Y direction on the photosensitive drum D, with the negative side position indicating the position on the light source 101 side relative to the center of the exposure area on the photosensitive drum D, and the positive side position indicating the position on the opposite side of the light source 101 relative to the center. The vertical axis of Figure 7(b) shows the ratio (hereinafter referred to as the fluctuation ratio) of the difference between the light amount at position 0 on the photosensitive drum D (hereinafter referred to as the reference light amount) and the light amount at each position to the reference light amount.

[0079] As shown in Figure 7(b), in a conventional lighting device equipped with a conventional sub-light guide having a flat exit surface 105, the amount of light in the exposure area on the light source 101 side of the photosensitive drum D is significantly increased. On the other hand, in the illumination device 200 of this embodiment, which is equipped with a sub-light guide 103 having an exit surface 105 with a concave shape, it can be seen that such an increase in the amount of light in the exposure area on the light source 101 side of the photosensitive drum D is suppressed. Specifically, the difference between the maximum and minimum values ​​of the above fluctuation ratio, i.e., the unevenness in light intensity, is 108% in the conventional lighting device, but is reduced to 87% in the lighting device 200 according to this embodiment.

[0080] In the lighting device 200 according to this embodiment, the distance d1 and the distance d sub The refractive index n and diameter d are 1.1 mm, 9.5 mm, 1.48 mm and 6.0 mm, respectively. Therefore, the value of conditional expression (8) is found to be 0.49, and is therefore satisfied.

[0081] In the illumination device 200 according to this embodiment, the radius of curvature R and the diameter d are 14.9 mm and 6.0 mm, respectively. Therefore, the value of conditional expression (9) is found to be 2.48, which is satisfied.

[0082] As described above, the lighting device 200 according to this embodiment is provided with a light source 101, a light guide 102, and a sub-light guide 103. The sub-light guide 103 guides light from the light source 101 to the light guide 102 and has a concave exit surface 105. As a result, even if the sub-light guide 103 is displaced, it is possible to suppress an increase in unevenness in the amount of light on the photosensitive drum D.

[0083] [Third embodiment] FIG. 8(a) shows a schematic cross-sectional view of an illumination device 300 according to the third embodiment. The lighting device 300 according to this embodiment has the same configuration as the lighting device 100 according to the first embodiment except for different specification values, and therefore the same components are given the same reference numerals and their explanations are omitted.

[0084] Specifically, in the illumination device 300 according to this embodiment, the diameter d of the exit surface 105 of the sub-light guide 103 when projected onto the XZ cross section is smaller than that of the illumination device 100 according to the first embodiment. In particular, the diameter d of the sub-light guide 103 is smaller than the diameter of the light guide 102 when projected onto the XZ cross section of the incident surface.

[0085] Furthermore, in the illumination device 300 according to this embodiment, the radius of curvature R of the exit surface 105 formed on the sub-light guide 103 is smaller than that of the illumination device 100 according to the first embodiment. Furthermore, in the illumination device 300 according to this embodiment, the distance d1 between the light source 101 and the incident surface 104 of the sub-light guide 103 is greater than that of the illumination device 100 according to the first embodiment.

[0086] FIG. 8(b) shows the light amount distribution on the photosensitive drum D when axial misalignment occurs in the illumination device 300 according to this embodiment and in a conventional illumination device. The conventional lighting device has the same configuration as the lighting device 300 according to this embodiment, except that the exit surface 105 of the sub-light guide 103 has a flat shape.

[0087] The horizontal axis in Figure 8(b) indicates the position in the Y direction on the photosensitive drum D, with the negative side position indicating the position on the light source 101 side relative to the center of the exposure area on the photosensitive drum D, and the positive side position indicating the position on the opposite side of the light source 101 relative to the center. The vertical axis of Figure 8(b) shows the ratio (hereinafter referred to as the fluctuation ratio) of the difference between the light amount at position 0 on the photosensitive drum D (hereinafter referred to as the reference light amount) and the light amount at each position to the reference light amount.

[0088] As shown in Figure 8(b), in a conventional lighting device equipped with a conventional sub-light guide having a flat exit surface 105, the amount of light in the exposure area on the light source 101 side of the photosensitive drum D is significantly increased. On the other hand, in the illumination device 300 according to this embodiment, which is provided with a sub-light guide 103 having an exit surface 105 with a concave shape, it can be seen that such an increase in the amount of light in the exposure area on the light source 101 side of the photosensitive drum D is suppressed. Specifically, the difference between the maximum and minimum values ​​of the fluctuation ratio, i.e., the unevenness in the amount of light, is 81% in the conventional lighting device, but is reduced to 57% in the lighting device 300 according to this embodiment.

[0089] In the lighting device 300 according to this embodiment, the distance d1 and the distance d sub The refractive index n and diameter d are 3.0 mm, 7.0 mm, 1.48 mm and 3.5 mm, respectively. Therefore, the value of conditional expression (8) is found to be 0.07, and is therefore satisfied.

[0090] In the illumination device 300 according to this embodiment, the radius of curvature R and the diameter d are 2.0 mm and 3.5 mm, respectively. Therefore, the value of conditional expression (9) is found to be 0.57, and is therefore satisfied.

[0091] As described above, the lighting device 300 according to this embodiment is provided with a light source 101, a light guide 102, and a sub-light guide 103. The sub-light guide 103 guides light from the light source 101 to the light guide 102 and has a concave exit surface 105. As a result, even if the sub-light guide 103 is displaced, it is possible to suppress an increase in unevenness in the amount of light on the photosensitive drum D.

[0092] [Fourth embodiment] FIG. 9(a) shows a schematic cross-sectional view of an illumination device 400 according to the fourth embodiment. The illumination device 400 according to this embodiment has the same configuration as the illumination device 100 according to the first embodiment, except that a sub-light guide 403 is provided instead of the sub-light guide 103. Therefore, the same components are given the same reference numerals and their descriptions are omitted.

[0093] Specifically, the sub-light guide 403 provided in the lighting device 400 according to this embodiment is integrally formed with each other and has a flange portion 403a (held portion) and a cylindrical portion 403b which have different diameters in the XZ cross section. In other words, in the sub-light guide 403 provided in the illumination device 400 according to this embodiment, the flange portion 403a is integrally formed so as to protrude in a direction perpendicular to the Y direction. In the illumination device 400 according to this embodiment, the sub-light guide 403 has a flange 403a, which facilitates attachment for holding the sub-light guide 403 by a holding member (not shown) during assembly.

[0094] In the lighting device 400 according to this embodiment, the diameter of the flange portion 403a in the XZ cross section is set to 5.0 mm. In addition, in the illumination device 400 according to this embodiment, the diameter d of the sub-light guide 103 is determined by the diameter in the XZ cross section of the tubular portion 403b, which extends relatively farther in the Y direction than the flange portion 403a, and is specifically set to 4.0 mm.

[0095] In the illumination device 400 according to this embodiment, the flange 403a is preferably provided on the light source 101 side of the cylindrical portion 403b, that is, at the end of the sub-light guide 103 on the light source 101 side in the Y direction. This makes it possible to stabilize the amount of light guided through the light guide 102 and thus onto the photosensitive drum D.

[0096] FIG. 9B shows the light amount distribution on the photosensitive drum D when axial misalignment occurs in the illumination device 400 according to this embodiment and in a conventional illumination device. The conventional lighting device has the same configuration as the lighting device 400 according to this embodiment, except that the exit surface 405 of the sub-light guide 403 has a flat shape.

[0097] The horizontal axis in Figure 9(b) indicates the position in the Y direction on the photosensitive drum D, with the negative side position indicating the position on the light source 101 side relative to the center of the exposure area on the photosensitive drum D, and the positive side position indicating the position on the opposite side of the light source 101 relative to the center. The vertical axis of Figure 9(b) shows the ratio (hereinafter referred to as the fluctuation ratio) of the difference between the light amount at position 0 on the photosensitive drum D (hereinafter referred to as the reference light amount) and the light amount at each position to the reference light amount.

[0098] As shown in Figure 9(b), in a conventional lighting device equipped with a conventional sub-light guide in which an exit surface 405 having a flat shape is formed, the amount of light in the exposure area on the light source 101 side of the photosensitive drum D is greatly increased. On the other hand, in the illumination device 400 according to this embodiment, which is provided with a sub-light guide 403 having an exit surface 405 with a concave shape, it can be seen that such an increase in the amount of light in the exposure area on the light source 101 side of the photosensitive drum D is suppressed. Specifically, the difference between the maximum and minimum values ​​of the fluctuation ratio, i.e., the unevenness in the amount of light, is 114% in the conventional lighting device, whereas it is reduced to 99% in the lighting device 400 according to this embodiment.

[0099] In the lighting device 400 according to this embodiment, the distance d1 and the distance d sub The refractive index n and diameter d are 2.1 mm, 7.0 mm, 1.48 mm and 4.0 mm, respectively. Therefore, the values ​​of the conditions (8) and (8a) are found to be 0.32 and are therefore satisfied.

[0100] In the illumination device 400 according to this embodiment, the radius of curvature R and the diameter d are 6.0 mm and 4.0 mm, respectively. Therefore, the values ​​of the conditions (9) and (9a) are found to be 1.50 and are therefore satisfied.

[0101] As described above, the lighting device 400 according to this embodiment is provided with a light source 101, a light guide 102, and a sub-light guide 403. The sub-light guide 403 guides light from the light source 101 to the light guide 102 and has a concave exit surface 105. As a result, even if the sub light guide 403 is displaced, it is possible to suppress an increase in unevenness in the amount of light on the photosensitive drum D. Furthermore, since the sub-light guide 403 has the flange portion 403a, attachment for holding the sub-light guide 403 by a holding member (not shown) can be easily performed during assembly.

[0102] The values ​​of the conditional expressions and the optical characteristics of the illumination devices according to the first to fourth embodiments are shown in Table 1 below.

[0103] [Table 1]

[0104] [Fifth embodiment] As described above, conventionally, there has been proposed an illumination device in which a sub-light guide is provided between a light source and a light guide for guiding light rays emitted from the light source to the light guide. However, in such an illumination device, if the diameter of the exit surface of the sub-light guide is not sufficient compared to the diameter of the entrance surface of the light guide, there is a risk that the amount of light guided by the light guide will decrease.

[0105] In addition, in the past, lighting devices have been proposed in which the diameter of the exit surface of the sub-light guide is set larger than the diameter of the entrance surface of the light guide in order to increase the amount of light rays guided to the light guide by the sub-light guide. Additionally, in this lighting device, a lens for focusing the light beams guided by the sub-light guide to the light guide is provided between the sub-light guide and the light guide.

[0106] However, such an illumination device is large in size because the diameter of the exit surface of the sub-light guide is set large and a lens is provided. Therefore, an object of the present embodiment is to provide a lighting device that can improve light efficiency while suppressing an increase in size.

[0107] 10(a), (b), and (c) are a schematic cross-sectional view, a perspective view, and a partially enlarged perspective view, respectively, of an illumination device 500 according to a fifth embodiment. The lighting device 500 according to this embodiment has the same configuration as the lighting device 100 according to the first embodiment except for different specification values, so the same components are given the same reference numerals and their explanations are omitted.

[0108] The light guide 102 and the sub-light guide 103 provided in the illumination device 500 according to this embodiment each have a cylindrical shape. That is, the light guide 102 and the sub-light guide 103 have a circular shape in the XZ cross section.

[0109] The light guide 102 and the sub-light guide 103 have a common central axis Ax1. The exit surface 105 formed on the sub-light guide 103 has an infinite radius of curvature, that is, a flat surface.

[0110] As shown in Figure 10(a), a light ray R15 that is emitted from the light source 101 and then enters the incident surface 104 of the sub-light guide 103 at a relatively small angle travels straight through the sub-light guide 103 and then enters the light guide 102 by emitting from the exit surface 105. On the other hand, a light ray R16 that is emitted from the light source 101 and then enters the incident surface 104 of the sub-light guide 103 at a relatively large angle is totally reflected at least once by the side surface of the sub-light guide 103, and then exits from the exit surface 105 and enters the light guide 102.

[0111] The light ray R15 is reflected by a reflecting portion 201 that is disposed in the light guide 102 at a position relatively far from the light source 101, and is guided to the photosensitive drum D. On the other hand, the light ray R16 is reflected by the reflecting portion 201 that is disposed in the light guide 102 at a position relatively close to the light source 101, and is guided to the photosensitive drum D. In this way, the light quantity distribution on the photosensitive drum D is determined according to the quantity of light emitted from the light source 101 at each emission angle and the intensity of the light when it enters the light guide 102 at each incidence angle.

[0112] FIG. 11(a) shows a schematic cross-sectional view of a light source 101 provided in an illumination device 500 according to this embodiment. The light source 101 is a light emitting diode (LED) having a resin dome-shaped sealing member 101a formed of a dome portion 101ad and a plane portion 101ap that are integral with each other, and a light emitting chip 101b. The light source 101 has a peak wavelength of 600 nm.

[0113] Specifically, in the light source 101, the light emitting chip 101b is sealed inside the flat portion 101ap. In the lighting device 500 of this embodiment, by using such an LED as the light source 101, it is possible to concentrate the light rays emitted from the light-emitting chip 101b, thereby making it possible to make highly directional light rays enter the light guide 102. This makes it possible to make light rays enter the light guide 102 with higher efficiency than when a Lambertian LED is used as the light source 101, especially when the light source 101 and the light guide 102 are spaced apart from each other.

[0114] FIG. 11(b) is a graph showing, in polar coordinate format, the light distribution of the light source 101 provided in the lighting device 500 according to this embodiment. In FIG. 11(b), the light distribution P domeis shown by the solid line, while the luminous intensity distribution P Lam is shown by a dashed line.

[0115] As shown in FIG. 11(b), the light distribution P dome The full width at half maximum is approximately 35°, which shows that the directivity is higher than that of a Lambertian LED. In the lighting device 500 according to this embodiment, by using such a highly directional light source 101, the number of times total reflection occurs within the sub-light guide 103 can be reduced, thereby making it possible to shorten the sub-light guide 103. Furthermore, by reducing the number of times of total reflection within the sub-light guide 103, it is possible to suppress a decrease in the amount of light rays incident on the light guide 102.

[0116] FIG. 12 is a partial perspective view of an illumination device 500 according to this embodiment. As shown in Figure 12, the distance between the center of the light-emitting surface of the light-emitting chip 101b of the light source 101 and the incident surface 104 of the sub-light guide 103 on a straight line passing through the center of the light-emitting surface of the light-emitting chip 101b of the light source 101 and parallel to the Y direction is d1.

[0117] The distance between the incident surface 104 and the exit surface 105 of the sub-light guide 103, and the distance between the exit surface 105 of the sub-light guide 103 and the incident surface of the light guide 102 on a line passing through the center of the light source 101 and parallel to the Y direction are respectively defined as d sub and d2. In the lighting device 500 according to this embodiment, the distance d1 and the distance d2 are not zero.

[0118] The diameter of the exit surface 105 of the sub-light guide 103 and the diameter of the entrance surface of the light guide 102 when projected onto the XZ cross section are respectively defined as D sub and D LG Let's say. The radius of the exit surface 105 of the sub-light guide 103 when projected onto the XZ cross section is R LG Let's say.

[0119] Furthermore, the distance between the center of the light-emitting surface of the light-emitting chip 101b of the light source 101 and the incident surface of the light guide 102 on a line that passes through the center of the light-emitting surface of the light-emitting chip 101b of the light source 101 and is parallel to the Y direction is defined as L. That is, the distance L is expressed as d1+d sub Corresponds to +d2. In this case, in the illumination device 500 according to this embodiment, it is preferable that the light source 101 is arranged so that the following conditional expression (10) is satisfied.

number

[0120] That is, in the illumination device 500 according to this embodiment, the light source 101 is arranged so that the conditional expression (10) is satisfied, and therefore the advantage of using the sub-light guide 103 is increased. In the illumination device 500 according to this embodiment, it is more preferable that the following conditional expression (10a) be fulfilled instead of the conditional expression (10).

number

[0121] Specifically, in the illumination device 500 according to this embodiment, the radius R LG and the distance L is 2.00 mm and 14.50 mm, respectively, and R LG Since / L=0.14, the conditions (10) and (10a) are satisfied. In the illumination device 500 according to this embodiment, the diameter D of the exit surface 105 of the sub-light guide 103 is set so as to satisfy the following conditional expression (11): sub is preferably set.

number

[0122] In the illumination device 500 according to this embodiment, by satisfying conditional expression (11), it is possible to achieve a reduction in the size of the sub-light guide 103, and therefore a reduction in the size of the illumination device 500, while also achieving high efficiency. FIG. 13 shows the ratio D sub / D LG 10 shows the change in the amount of light on the incident surface of the light guide 102 when the temperature is changed. That is, the more the amount of light increases, the more the amount of light in the light guide 102 increases.

[0123] The vertical axis of Fig. 13 is the ratio D sub / D LG 1. The figure shows the ratio of each light amount to the light amount when the value of the light amount is 1 (hereinafter, this may be referred to as the light amount ratio). In FIG. 13, the solid line indicates the case where a dome-type LED is used as the light source 101, and the dotted line indicates the case where a Lambertian-type LED is used as the light source 101.

[0124] When a Lambertian LED with low directivity and a wide light distribution angle is used as the light source 101 , most of the light traveling inside the light guide 102 is generated by total reflection inside the sub-light guide 103 . Therefore, when a Lambertian LED is used as the light source 101, the amount of light is larger than the diameter D of the sub-light guide 103, as shown by the dotted line in FIG. sub increases in proportion to .

[0125] On the other hand, since the dome-shaped LED has high directivity, the amount of light due to total reflection inside the sub-light guide 103 is smaller than the ratio D sub / D LG The upper limit is reached when the value of is approximately 1. Therefore, the diameter D of the sub light guide 103 sub can be determined from the above results when a Lambertian LED or a dome-type LED is used as the light source 101.

[0126] Specifically, when a Lambertian LED is used as the light source 101, the ratio D sub / D LG The value of 0.60 was set as the lower limit of conditional expression (11). The upper limit of conditional expression (11) is set to 0.97, which is the value that can achieve the highest efficiency while miniaturizing the illumination device 500 according to this embodiment. In the illumination device 500 according to this embodiment, it is more preferable that the following conditional expression (11a) be fulfilled instead of the conditional expression (11).

number

[0127] The lower limit of the condition (11a) is the ratio D at which the light intensity ratio decreases to 90% when a Lambertian LED is used as the light source 101. sub / D LG The value was set to 0.85. The upper limit of the condition (11a) is determined by factors such as manufacturing errors. sub is the diameter D of the light guide 102 LG Taking into consideration the case where the upper limit of conditional expression (11) is larger than 0.97, the upper limit of conditional expression (11) is set to 0.96, which is 0.01 smaller than 0.97. In the illumination device 500 according to this embodiment, the diameter D sub and diameter D LG are 2.79 mm and 4.00 mm, respectively, and D sub / D LG =0.70, so conditional expression (11) is satisfied.

[0128] As described above, the lighting device 500 according to this embodiment satisfies conditional expression (11), and therefore can achieve both a smaller size and higher efficiency than conventional lighting devices. In the illumination device 500 according to this embodiment, the condition for the relative arrangement of the light source 101, the light guide 102, and the sub-light guide 103 can also be determined based on conditional expression (11) as follows:

[0129] FIG. 14 is a schematic cross-sectional view showing parameters regarding the relative arrangement of the light source 101, the light guide 102, and the sub-light guide 103 in the illumination device 500 according to this embodiment. Specifically, in the following, a predetermined radius R LG The light guide 102 has a minimum emission angle θ min The minimum radius R of the sub-light guide 103 when guiding the light beam emitted from sub has been decided.

[0130] First, the minimum emission angle θ from the light source 101 on the incident surface 104 of the sub-light guide 103 min The refraction angle of the emitted light is φ min Let's say. At this time, the following equation (12) is satisfied as shown in FIG.

number

[0131] Furthermore, consider a case where the illumination device 500 according to this embodiment is placed in air. In this case, when the refractive index of the sub-light guide 103 is n, the incident angle θ on the incident surface 104 of the sub-light guide 103 is min and the refraction angle φ min According to Snell's law, the following equation (13) is satisfied between

number

[0132] For the sake of simplicity, it is assumed that the approximations expressed by the following equations (14) and (14)′ hold true for the illumination device 500 according to this embodiment.

number

number

[0133] In this case, the above equation (12) can be rewritten as the following equation (15) using the above equations (13), (14) and (14)′.

number

[0134] Therefore, the minimum emission angle θ of the light ray emitted from the light source 101 is min From equation (15), the relationship expressed by the following equation (16) is satisfied.

number

[0135] The sub-light guide 103 has a minimum radius R sub When the sub-light guide 103 has the above-mentioned configuration, it is considered that the light beam emitted from the radial end of the exit surface of the sub-light guide 103 is incident on the radial end of the entrance surface of the light guide 102. At this time, the minimum radius R of the sub light guide 103 sub is expressed as the following equation (17).

number

[0136] Then, by substituting the above equation (16) into equation (17), R sub / R LG =D sub / D LG From this relationship, the following equation (18) can be obtained.

number

[0137] Then, by substituting the formula (18) into the above conditional formula (11), the following conditional formula (19) can be obtained.

number

[0138] Therefore, in the illumination device 500 according to this embodiment, the relative arrangement of the light source 101, the light guide 102, and the sub-light guide 103 is determined so as to satisfy the conditional expression (19). Specifically, in the illumination device 500 according to this embodiment, the value of conditional expression (19) is set to 0.26. This allows the sub-light guide 103 to be arranged so as to achieve both miniaturization and high efficiency.

[0139] If the upper limit of conditional expression (19) is exceeded, the efficiency of coupling light between the sub-light guide 103 and the light guide 102 will decrease. On the other hand, if the lower limit of conditional expression (19) is not reached, the light guide 102 and the sub-light guide 103 will be too close to each other, which may cause interference with each other during assembly or due to manufacturing errors.

[0140] In the illumination device 500 according to this embodiment, it is more preferable that the following conditional expression (19a) be fulfilled instead of the conditional expression (19):

number

[0141] In the illumination device 500 according to this embodiment, by arranging the light source 101, the light guide 102, and the sub-light guide 103 so as to satisfy the conditional formula (19a), interference between them is further suppressed, and assembly can be easily performed while achieving high efficiency. In the lighting device 500 according to this embodiment, the distances d1 and d sub and d2 are 5.00 mm, 7.00 mm, and 2.50 mm, respectively, and the refractive index n is 1.48, so the values ​​of conditional expressions (19) and (19a) are 0.26. Therefore, conditional expressions (19) and (19a) are satisfied.

[0142] Next, the shape of the sub-light guide 103 provided in the illumination device 500 according to this embodiment will be described. FIG. 15(a) shows a partially enlarged perspective view of the illumination device 500 according to this embodiment.

[0143] As shown in FIG. 15(a), the sub-light guide 103 provided in the illumination device 500 according to this embodiment has a tapered shape in a predetermined cross section parallel to the Y direction. Specifically, the angle α that the generatrix of the sub light guide 103 makes with respect to the central axis Ax1 is set to 2.5 degrees.

[0144] Further, sub-light guide 103 provided in illumination device 500 according to this embodiment is tapered so that the diameter of exit surface 105 is smaller than the diameter of entrance surface 104 in the XZ cross section. In the sub-light guide 103 provided in the illumination device 500 according to this embodiment, the centers of the entrance surface 104 and the exit surface 105 are positioned on the central axis Ax1.

[0145] In the illumination device 500 according to this embodiment, by providing the sub-light guide 103 having a tapered shape, it is possible to increase the amount of light on the photosensitive drum D on the light source 101 side as described below. FIG. 15(b) is a schematic diagram showing how light rays are guided by the sub-light guide 103. As shown in FIG.

[0146] Specifically, the solid line and the broken line in FIG. 15(b) respectively indicate the generatrix of the sub-light guide 103 having a tapered shape and the generatrix of a predetermined sub-light guide 903 having no tapered shape. In addition, the solid arrow and the dashed arrow in FIG. 15(b) indicate the light rays that are totally reflected inside the sub-light guide 103 and the light rays that are totally reflected inside the sub-light guide 903, respectively.

[0147] As shown in FIG. 15(b), it can be seen that the angle of incidence of light rays with respect to the exit surface 105 of the sub-light guide 103 is increased compared to the sub-light guide 903 due to the tapered shape. The light beam that is guided by the sub-light guide 103 and enters the inside of the light guide 102 is reflected by a reflecting portion 201 that is provided inside the light guide 102 on a side relatively closer to the light source 101 . This allows the amount of light on the photosensitive drum D from the light source 101 side to be increased.

[0148] It is preferable that the angle α (degrees) that the generatrix of the sub light guide 103 makes with respect to the central axis Ax1 satisfies the following conditional expression (20). 0.5≦α≦4.0 (20)

[0149] It is more preferable that the angle α (degrees) satisfies the following conditional expression (20a) instead of conditional expression (20). 1.0≦α≦3.0 (20a)

[0150] When conditional expression (20a) is satisfied, the above-mentioned effect can be further achieved. If the angle α is made too large, the diameter of the exit surface 105 of the sub-light guide 103 becomes too small, resulting in a decrease in light efficiency.

[0151] FIG. 15(c) shows the amount of light incident on the incident surface of the light guide 102 at each incident angle. In Figure 15(c), the solid line and dashed line respectively indicate the case where the light ray is guided by a sub-light guide 103 having a tapered shape with an angle α of 2.5 degrees, and the case where the light ray is guided by a sub-light guide 903 having no tapered shape. In addition, in FIG. 15(c), the light intensity is normalized by the light intensity when the incident angle is 0 degrees.

[0152] As shown in Figure 15(c), by guiding the light rays through the sub-light guide 103, the amount of light can be increased over a wide range of incident angles of 15 degrees or more compared to when the sub-light guide 903 is used. FIG. 15(d) shows the light amount distribution on the photosensitive drum D.

[0153] Specifically, the horizontal axis in FIG. 15(d) indicates the position on the photosensitive drum D in the Y direction, and position 0 indicates the center of the exposure area of ​​the photosensitive drum D. The vertical axis in FIG. 15(d) represents the ratio of the difference between the average value of the light amount and the light amount within the evaluation region of ±150 mm to the average value, that is, the unevenness of the light amount. The solid line and dotted line in FIG. 15(d) respectively show the case where a sub-light guide 103 having a tapered shape with an angle α of 2.5 degrees is used, and the case where a sub-light guide 903 having no tapered shape is used.

[0154] In the lighting device 500 according to this embodiment, the light source 101 and the light guide 102 are spaced apart by a predetermined distance, and therefore a dome-shaped LED is used as the light source 101. In this case, the light rays that enter the interior of the light guide 102 include many light rays with small angles of incidence.

[0155] Therefore, the amount of light (exposure amount) increases at a position on the photosensitive drum D far from the light source 101, that is, on the opposite side of the center from the light source 101 (hereinafter referred to as the anti-light source side). On the other hand, the amount of light (exposure amount) at a position on the photosensitive drum D close to the light source 101, that is, on the same side as the light source 101 with respect to the center (hereinafter referred to as the light source side), decreases.

[0156] Therefore, by using a dome-shaped LED as the light source 101 in the illumination device 500 according to this embodiment, the amount of light on the light source side on the photosensitive drum D decreases, and the unevenness in the amount of light increases. Specifically, as shown by the dotted line in Figure 15(d), when sub-light guide 903 is used instead of sub-light guide 103 in illumination device 500 of this embodiment, a light intensity unevenness of ±30% occurs within an evaluation area of ​​±150 mm.

[0157] Therefore, in the illumination device 500 according to this embodiment, by using the sub-light guide 103 having a tapered shape with an angle α of 2.5 degrees as described above, the unevenness in the amount of light within the evaluation area of ​​±150 mm is reduced to ±20%, as shown by the solid line in Figure 15(d). That is, in the illumination device 500 according to this embodiment, the use of the sub-light guide 103 having a tapered shape makes it possible to effectively reduce the unevenness in the amount of light on the photosensitive drum D.

[0158] As described above, the illumination device 500 according to this embodiment is provided with the light source 101, the light guide 102, and the sub-light guide 103, and satisfies the conditional expression (11). This makes it possible to reduce the size of the sub-light guide 103, and hence the size of the illumination device 500, while also achieving high efficiency.

[0159] Although a light emitting diode (LED) having a peak wavelength of 600 nm is used as the light source 101 provided in the lighting device 500 according to this embodiment, this is not limited thereto, and a light emitting diode (LED) having another peak wavelength may also be used. Furthermore, the light guide 102 and the sub-light guide 103 provided in the illumination device 500 according to this embodiment have a circular shape in the XZ cross section, but are not limited to this and may have other shapes.

[0160] [Sixth embodiment] FIG. 16(a) shows a partial perspective view of an illumination device 600 according to the sixth embodiment. The lighting device 600 according to this embodiment has the same configuration as the lighting device 500 according to the fifth embodiment except for different specification values, so the same components are given the same reference numerals and their explanations are omitted.

[0161] Specifically, in the illumination device 600 according to this embodiment, the distance between the light source 101 and the sub-light guide 103 is reduced compared to the illumination device 500 according to the fifth embodiment, thereby improving the illumination efficiency. FIG. 16(b) shows the amount of light at each incident angle of a light ray incident on the incident surface of the light guide 102 provided in the illumination device 600 according to this embodiment.

[0162] As shown in FIG. 16(b), in the lighting device 600 according to this embodiment, the amount of light is increased over the range of incident angles of 20 degrees or more, compared to the amount of light at each incident angle shown in FIG. 15(c) in the lighting device 500 according to the fifth embodiment. FIG. 16(c) shows the light amount distribution on the photosensitive drum D illuminated by the illumination device 600 according to this embodiment.

[0163] In the illumination device 600 according to this embodiment, the amount of light rays incident on the incident surface of the light guide 102 is increased over the range of incident angles of 20 degrees or more, as described above. This increases the amount of light on the photosensitive drum D from the light source 101 side, thereby reducing unevenness in the amount of light.

[0164] Specifically, in the illumination device 600 according to this embodiment, the angle α of the tapered shape of the sub-light guide 103 is set to 1.0 degrees so that the diameter of the incident surface 104 of the sub-light guide 103 does not become too large compared to the diameter of the exit surface 105. In the lighting device 600 according to this embodiment, the unevenness in the amount of light within the evaluation area of ​​±150 mm is ±17%, as shown in FIG. 16(c), and the unevenness in the amount of light on the photosensitive drum D is effectively reduced.

[0165] In the illumination device 600 according to this embodiment, the radius R LG and the distance L is 2.00 mm and 11.30 mm, respectively, and R LG Since / L=0.18, the conditions (10) and (10a) are satisfied. In addition, in the illumination device 600 according to this embodiment, the diameter D sub and diameter D LG are 3.40 mm and 4.00 mm, respectively, and D sub / D LG=0.85, the conditions (11) and (11a) are satisfied. In the lighting device 600 according to this embodiment, the distances d1 and d sub and d2 are 1.30 mm, 7.00 mm, and 3.00 mm, respectively, and the refractive index n is 1.48, so the values ​​of conditional expressions (19) and (19a) are 0.50. Therefore, conditional expressions (19) and (19a) are satisfied.

[0166] As described above, the illumination device 600 according to this embodiment is provided with the light source 101, the light guide 102, and the sub-light guide 103, and also satisfies conditional expression (11). This makes it possible to reduce the size of the sub-light guide 103, and hence the size of the illumination device 600, while also achieving high efficiency.

[0167] [Seventh embodiment] FIG. 17 is a partial perspective view of an illumination device 700 according to the seventh embodiment. The lighting device 700 according to this embodiment has the same configuration as the lighting device 500 according to the fifth embodiment except for different specification values, so the same components are given the same reference numerals and their explanations are omitted.

[0168] Specifically, in the illumination device 700 according to this embodiment, the sub-light guide 103 does not have a tapered shape. As a result, the entrance surface 104 and the exit surface 105 of the sub-light guide 103 have the same shape, which makes assembly easy.

[0169] In addition, in the illumination device 700 according to this embodiment, the radius R LG and the distance L is 2.00 mm and 12.00 mm, respectively, and R LG Since / L=0.17, the conditions (10) and (10a) are satisfied. In addition, in the illumination device 700 according to this embodiment, the diameter D sub and diameter D LG are 3.83 mm and 4.00 mm, respectively, and D sub / DLG =0.96, the conditions (11) and (11a) are satisfied. In the lighting device 700 according to this embodiment, the distances d1 and d sub and d2 are 2.60 mm, 7.00 mm, and 2.40 mm, respectively, and the refractive index n is 1.48, so the values ​​of conditional expressions (19) and (19a) are 0.33. Therefore, conditional expressions (19) and (19a) are satisfied.

[0170] As described above, the illumination device 700 according to this embodiment is provided with the light source 101, the light guide 102, and the sub-light guide 103, and satisfies conditional expression (11). This makes it possible to reduce the size of the sub-light guide 103, and hence the size of the illumination device 700, while also achieving high efficiency.

[0171] [Eighth embodiment] FIG. 18 shows a partial perspective view of an illumination device 800 according to the eighth embodiment. The illumination device 800 according to this embodiment has the same configuration as the illumination device 500 according to the fifth embodiment, except that a sub-light guide 803 is provided instead of the sub-light guide 103. Therefore, the same components are given the same reference numerals and their descriptions are omitted.

[0172] As shown in FIG. 18, the sub light guide 803 has a flange portion 803a and a cylindrical portion 803b that are integrally formed with each other. Moreover, the tubular portion 803b has a tapered shape similar to the sub-light guide 103, whereas the flange portion 803a does not have a tapered shape, that is, has a cylindrical shape. In addition, in order to achieve a compact size of the sub-light guide 803, the thickness of the flange portion 803a is set to be sufficiently smaller than the thickness of the cylindrical portion 803b.

[0173] In the sub-light guide 803 provided in the illumination device 800 according to this embodiment, the flange portion 803a is provided, so that the position in the Y direction parallel to the central axis Ax1 can be determined with high precision. That is, in the sub-light guide 803 provided in the lighting device 800 according to this embodiment, the surface perpendicular to the central axis Ax1 of the flange portion 803a is formed as a flat surface, and therefore, it is possible to position the sub-light guide 803 by abutting the surface against the holding member 810 as described below. This allows the relative position between the light source 101 and the sub-light guide 803 to be determined with high precision, thereby stabilizing the optical performance.

[0174] Furthermore, the sub-light guide 803 provided in the lighting device 800 according to this embodiment is provided with a flange portion 803a, which makes it easy to distinguish between the entrance surface and the exit surface, thereby reducing the risk of incorrect assembly. In particular, when the sub-light guide 803 has a tapered shape, it is effective to provide the flange portion 803a on the sub-light guide 803, since this reduces the risk of the sub-light guide 803 being assembled in an inverted state.

[0175] As described above, the sub-light guide 803 provided in the illumination device 800 according to this embodiment is positioned by bringing the flange portion 803 a into contact with the holding member 810 . Therefore, if the sub-light guide 803 is to be arranged in an inverted state, the sub-light guide 803 and the light guide 102 will interfere with each other. That is, the sub-light guide 803 provided in the lighting device 800 according to this embodiment is provided with a flange portion 803a, which makes it possible to assemble the sub-light guide 803 while easily distinguishing between the entrance surface and exit surface.

[0176] In other words, in the lighting device 800 according to this embodiment, in which it is difficult to secure sufficient assembly space due to the small distance between the sub-light guide 803 and the light guide 102, it is preferable that the flange portion 803a of the sub-light guide 803 is provided on the light source 101 side. FIG. 19(a) shows the state in which a sub-light guide 803 having a flange 803a formed on the light source 101 side is disposed in an illumination device 800 according to this embodiment. Specifically, in FIG. 19(a), the flange portion 803a abuts against a surface 810a of the holding member 810 on the light source 101 side, thereby disposing the sub-light guide 803.

[0177] On the other hand, FIG. 19(b) shows a state in which a sub-light guide 803 having a flange 803a formed on the opposite side to the light source 101 is disposed in an illumination device 800 according to this embodiment. Specifically, in FIG. 19(b), the flange portion 803a abuts against a surface 810b of the holding member 810 opposite to the light source 101, thereby disposing the sub-light guide 803.

[0178] As shown in Figure 19(b), if the flange portion 803a of the sub-light guide 803 is formed on the side opposite the light source 101, the flange portion 803a needs to be abutted against the holding member 810 while facing the light guide 102. In this case, if there is not enough assembly space between the sub-light guide 803 and the light guide 102, assembly becomes difficult.

[0179] If the distance between the sub-light guide 803 and the light guide 102 is increased for assembly purposes, the light efficiency will be significantly reduced. On the other hand, when the flange portion 803a of the sub-light guide 803 is formed on the light source 101 side as shown in Figure 19(a), the sub-light guide 803 can be easily positioned by abutting the flange portion 803a against the holding member 810. In view of the above, it is preferable that the flange portion 803a of the sub-light guide 803 provided in the illumination device 800 according to this embodiment is provided on the light source 101 side.

[0180] Furthermore, by providing flange portion 803a on sub-light guide 803, the tapered shape is preferably formed so that the area of ​​the incident surface is larger than the area of ​​the exit surface, in terms of injection molding sub-light guide 803. That is, when injection molding the sub-light guide 803, the boundary between the flange portion 803a and the tubular portion 803b is set at the boundary between the fixed side mold and the drive side mold, and the molded sub-light guide 803 is released by moving the drive side mold. In this case, when the fixed-side mold and the driving-side mold are in contact with each other and the driving-side mold is moved to separate them, the tapered shape of the sub-light guide 803 described above can prevent damage to the molded sub-light guide 803.

[0181] The sub-light guide 803 provided in the illumination device 800 according to this embodiment is a member formed by injection molding a resin material. Therefore, in order to maintain the optical performance of the sub-light guide 803, it is preferable that the gate portion be provided on the flange portion 803a, rather than on the cylindrical portion 803b that guides the light beam.

[0182] In the illumination device 800 according to this embodiment, the radius R LG and the distance L is 2.00 mm and 10.10 mm, respectively, and R LG Since / L=0.20, the conditions (10) and (10a) are satisfied. In addition, in the illumination device 800 according to this embodiment, the diameter D sub and diameter D LG are 3.83 mm and 4.00 mm, respectively, and D sub / D LG =0.96, the conditions (11) and (11a) are satisfied.

[0183] In the lighting device 800 according to this embodiment, the distances d1 and d sub and d2 are 2.60 mm, 5.00 mm, and 2.50 mm, respectively, and the refractive index n is 1.48, so the values ​​of conditional expressions (19) and (19a) are 0.42. Therefore, conditional expressions (19) and (19a) are satisfied. In the illumination device 800 according to this embodiment, the angle α of the tapered shape of the cylindrical portion 803b of the sub-light guide 803 is set to 1.5 degrees.

[0184] As described above, the illumination device 800 according to this embodiment is provided with the light source 101, the light guide 102, and the sub-light guide 103, and also satisfies the conditional expression (11). This makes it possible to reduce the size of the sub-light guide 103, and hence the size of the illumination device 800, while also achieving high efficiency. Furthermore, since the sub-light guide 803 has a flange portion 803a, the relative position between the light source 101 and the sub-light guide 803 can be determined with high precision, and the entrance surface and exit surface of the sub-light guide 803 can be easily distinguished during assembly.

[0185] The values ​​of the respective conditional expressions for the illumination devices according to the fifth to eighth embodiments are shown in Table 2 below.

[0186] [Table 2]

[0187] The configurations of the lighting devices according to the first to eighth embodiments described above can be combined as desired.

[0188] [Image forming device] FIG. 20 shows a sub-scanning cross-sectional view of a main part of an image forming apparatus 530 equipped with an illumination device 900 according to any one of the first to eighth embodiments.

[0189] As shown in FIG. 20, an image forming apparatus 530 receives code data Dc output from an external device 517 such as a personal computer. The input code data Dc is converted into image data (dot data) Di by a printer controller 511 provided inside the image forming apparatus 530.

[0190] Next, the converted image data Di is input to the optical scanning device 504, and the optical scanning device 504 emits a light beam 503 modulated according to the image data Di, and the photosensitive surface (scanned surface) of the photosensitive drum 501 is scanned in the main scanning direction by the light beam 503. A photosensitive drum 501, which is an electrostatic latent image carrier (photosensitive member), is rotated clockwise by a motor 515 as shown in FIG. As the photosensitive drum 501 rotates, the photosensitive surface of the photosensitive drum 501 moves in the sub-scanning direction perpendicular to the main scanning direction.

[0191] Above the photosensitive drum 501, an illumination device 900 according to any one of the first to eighth embodiments is provided to illuminate the surface of the photosensitive drum 501 to eliminate static electricity, i.e., electrically initialize (pre-expose) the surface. A charging roller 502 for uniformly charging the surface of the photosensitive drum 501 that has been neutralized in this way is provided above the photosensitive drum 501 on the downstream side in the direction of rotation so as to come into contact with the surface. The surface of the photosensitive drum 501 charged by the charging roller 502 is irradiated with a light beam 503 scanned by an optical scanning device 504 .

[0192] As described above, the light beam 503 is modulated based on the image data Di, and an electrostatic latent image is formed on the surface of the photosensitive drum 501 by irradiating the surface with the light beam 503 . The formed electrostatic latent image is developed into a toner image by a developing device 507 disposed so as to contact the photosensitive drum 501 further downstream in the rotation direction from the position on the photosensitive drum 501 where the light beam 503 is irradiated.

[0193] Next, the toner image developed by the developing device 507 is transferred onto a sheet of paper 512 as a transfer material by a transfer roller 508 (transfer device) disposed below the photosensitive drum 501 so as to face the photosensitive drum 501 . The paper 512 is stored in a paper cassette 509 in front of the photosensitive drum 501 (on the right side in FIG. 20), but can also be fed manually. A paper feed roller 510 is disposed at the end of the paper cassette 509, and feeds paper 512 in the paper cassette 509 into the transport path.

[0194] The paper 512 onto which the unfixed toner image has been transferred in this manner is transported to a fixing device 550 disposed behind the photosensitive drum 501 (on the left side in FIG. 20). The fixing unit 550 is composed of a fixing roller 513 having a fixing heater therein and a pressure roller 514 disposed so as to be in pressure contact with the fixing roller 513 .

[0195] Then, the paper 512 conveyed from the transfer roller 508 is heated and pressed by the pressure contact portion between the fixing roller 513 and the pressure roller 514, whereby the unfixed toner image on the paper 512 is fixed. Further, a paper discharge roller 516 is disposed behind the fixing unit 550 , and the paper 512 on which the toner image has been fixed is discharged to the outside of the image forming apparatus 530 .

[0196] As described above, the lighting device 900 according to any one of the first to eighth embodiments can illuminate the surface of the photosensitive drum 501 with a substantially uniform light intensity distribution, and therefore can reduce potential unevenness (charge unevenness) by uniformly discharging the surface of the photosensitive drum 501 during pre-exposure. Furthermore, in the illumination device 900 according to any one of the first to eighth embodiments mounted on the image forming apparatus 530 as described above, even if the sub-light guide is disposed at a position that is shifted due to a manufacturing error, it is possible to suppress an increase in unevenness in the amount of light on the photosensitive drum 501. This makes it possible to reduce unevenness in static elimination on the photosensitive drum 501.

[0197] Although not shown in FIG. 20, in addition to the above-described data conversion, the printer controller 511 also controls each member in the image forming apparatus 530 such as the motor 515 and the polygon motor in the optical scanning device 504. Although the preferred embodiments have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist.

[0198] The disclosure of the present embodiment includes the following configurations. (Configuration 1) An optical device including first and second light guides facing each other in a first direction, the second light guide guiding light from a light source to the first light guide and having a concave-shaped emission surface, the first light guide being arranged in the first direction and each having a plurality of deflection portions for deflecting light from the second light guide. (Configuration 2) The optical device according to Configuration 1, wherein the emission surface is a spherical surface. (Configuration 3) An optical device including first and second light guides facing each other in a first direction, the second light guide guiding light from a light source to the first light guide, the first light guide being arranged in the first direction and each having a plurality of deflection portions for deflecting light from the second light guide. (Configuration 4) When the diameters of the emission surface of the second light guide and the incident surface of the first light guide when projected onto a plane perpendicular to the first direction are D sub and D LG respectively, the optical device according to any one of Configurations 1 to 3, satisfying the condition of 0.60 ≦ D sub / D LG ≦ 0.97. (Configuration 5) When the maximum distance between two points on the circumference of the emission surface when projected onto a plane perpendicular to the first direction is d, and the radius of curvature of the emission surface in a predetermined plane parallel to the first direction including the apex of the emission surface is R, the optical device according to any one of Configurations 1 to 4, satisfying the condition of 0.55 < R / d < 2.50. (Configuration 6) The maximum distance between two points on the circumference of the light exit surface when projected onto a plane perpendicular to the first direction is d (mm), the distance between the center of the light emitting surface of the light source and the incident surface of the second light guide on a first line parallel to the first direction and passing through the center of the light emitting surface of the light source is d1 (mm), and the distance between the incident surface and the exit surface of the second light guide on the first line is d sub (mm), where n is the refractive index of the second light guide.

number

[0199] 101 Light source 102 light guide (first light guide) 103 Sub light guide (second light guide) 105 Exit surface 201 Reflection section (deflection section)

Claims

1. An optical device comprising first and second light guides facing each other in a first direction, the second light guide guides light from a light source to the first light guide and has a concave light exit surface; An optical device, characterized in that the first light guide has a plurality of deflection portions arranged in the first direction, each of which deflects light from the second light guide.

2. 2. The optical device according to claim 1, wherein the exit surface is a spherical surface.

3. When the maximum distance between two points on the circumference of the exit surface when projected onto a plane perpendicular to the first direction is d, and the radius of curvature of the exit surface in a predetermined plane that includes the vertex of the exit surface and is parallel to the first direction is R, 0.55<R / d<2.50 2. The optical device according to claim 1, wherein the following conditions are satisfied:

4. The maximum distance between two points on the circumference of the light exit surface when projected onto a plane perpendicular to the first direction is d (mm), and the distance between the center on a first line passing through the center of the light emitting surface of the light source and parallel to the first direction and the incident surface of the second light guide is d １ (mm), and the distance between the incident surface and the exit surface of the second light guide on the first straight line is d ｓｕｂ (mm), where n is the refractive index of the second light guide. [Equation 1] 2. The optical device according to claim 1, wherein the following conditions are satisfied:

5. The diameter of the exit surface of the second light guide and the diameter of the incident surface of the first light guide when projected onto a plane perpendicular to the first direction are respectively defined as D ｓｕｂ and D ＬＧ When 0.60≦D ｓｕｂ / D ＬＧ ≦0.97 2. The optical device according to claim 1, wherein the following conditions are satisfied:

6. 2. The optical device according to claim 1, wherein a holder for holding the first light guide and a holder for holding the second light guide are different from each other.

7. The distance between the center of the light emitting surface of the light source on a first line parallel to the first direction and the center of the light emitting surface of the light source is L, and the radius of the light emitting surface of the first light guiding body when projected onto a plane perpendicular to the first direction is R. ＬＧ When 0.05<R ＬＧ / L<0.40 2. The optical device according to claim 1, wherein the following conditions are satisfied:

8. On a first line passing through the center of the light emitting surface of the light source and parallel to the first direction, the distance between the center and the incident surface of the second light guide, the distance between the incident surface and the exit surface of the second light guide, and the distance between the exit surface of the second light guide and the incident surface of the first light guide are respectively defined as d １ , d ｓｕｂ and d ２ , where n is the refractive index of the second light guide, 0.03≦d ２ / (d １ +d ｓｕｂ / n)≦0.67 2. The optical device according to claim 1, wherein the following conditions are satisfied:

9. 2. The optical device according to claim 1, wherein the second light guide has a tapered shape in a predetermined plane parallel to the first direction.

10. 10. The optical device according to claim 9, wherein in a plane perpendicular to the first direction, the diameter of the exit surface of the second light guide is smaller than the diameter of the entrance surface of the second light guide.

11. When the angle between the direction parallel to the predetermined generatrix of the second light guide and the first direction is α (degrees), ０．５≦α≦４．０ 10. The optical device according to claim 9, wherein the following condition is satisfied:

12. 2. The optical device according to claim 1, wherein the second light guide has a held portion integrally formed so as to protrude in a direction perpendicular to the first direction.

13. 13. The optical device according to claim 12, wherein the held portion is provided at an end of the second light guide on the light source side in the first direction.

14. 13. The optical device according to claim 12, wherein the second light guide is a member formed by injection molding a resin material so that a gate portion is provided in the held portion.

15. An optical device comprising first and second light guides facing each other in a first direction, the second light guide guides light from a light source to the first light guide; An optical device, characterized in that the first light guide has a plurality of deflection portions arranged in the first direction, each of which deflects light from the second light guide.

16. The diameter of the exit surface of the second light guide and the diameter of the incident surface of the first light guide when projected onto a plane perpendicular to the first direction are respectively defined as D ｓｕｂ and D ＬＧ When 0.60≦D ｓｕｂ / D ＬＧ ≦0.97 16. The optical device according to claim 15, wherein the following condition is satisfied:

17. the light source; An illumination device comprising an optical device according to any one of claims 1 to 16.

18. 18. The lighting device according to claim 17, wherein the second light guide is disposed between the light source and the first light guide in the first direction.

19. 18. The lighting device according to claim 17, wherein a single holder for holding the light source, the first light guide, and the second light guide is not provided.

20. 18. An image forming apparatus comprising: an illumination device according to claim 17, which illuminates a surface to be scanned so as to eliminate static electricity; an optical scanning device which scans the surface to be scanned; a developing device which develops an electrostatic latent image formed on the surface to be scanned by the optical scanning device into a toner image; a transfer device which transfers the developed toner image to a transfer material; and a fixing device which fixes the transferred toner image to the transfer material.

Images