Light source apparatus and image formation apparatus

Abstract

To reduce light reflected by a non-light-emitting part of a light-emitting unit and entering a lens unit.SOLUTION: A light source apparatus 105 includes: a first light-emitting unit 209 and a second light-emitting unit 210 arranged at different positions in a first direction and a second direction perpendicular to the first direction on a first surface of a substrate 202; and a lens unit 212 for condensing light from the first and second light-emitting units. Each of the first and second light-emitting units includes: a second surface; and a plurality of light-emitting elements arranged in the first direction on the second surface. When viewed from the first direction, the second surface of at least one of the first and second light-emitting units is inclined with respect to the first surface.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a light source device used in an exposure head of an image forming apparatus. [Background technology]

[0002] Some electrophotographic printers form an electrostatic latent image by exposing a photosensitive drum, which serves as an irradiated surface, to light using an exposure head that uses LEDs, organic EL, etc. The exposure head includes multiple light-emitting units arranged in the longitudinal direction of the photosensitive drum, and a lens unit (lens array) that focuses light from the multiple light-emitting units onto the photosensitive drum.

[0003] Patent Document 1 discloses an exposure head that uses a light source in which a plurality of light-emitting units are arranged in two staggered rows, and a gradient index lens array. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-248803 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the exposure head of Patent Document 1 has a risk of reflected light occurring at the joints (non-light-emitting areas) between adjacent light-emitting units. This causes the amount of light on the photosensitive drum to be greater in the areas where reflected light from the joints is incident than in other areas. As a result, the density of the image formed in the areas where reflected light is incident becomes darker than the density of the image formed in other areas, appearing as streaks.

[0006] The present invention provides a light source device that can reduce light that is reflected by a light-emitting unit and enters a lens unit, and an image forming apparatus using the same. [Means for solving the problem]

[0007] A light source device according to one aspect of the present invention includes a first light-emitting unit and a second light-emitting unit arranged at different positions in a first direction and a second direction perpendicular to the first direction on a first surface of a substrate, and a lens unit that collects light from the first and second light-emitting units. Each of the first and second light-emitting units includes a second surface and a plurality of light-emitting elements arranged in the first direction on the second surface. When viewed from the first direction, the second surface of at least one of the first and second light-emitting units is inclined with respect to the first surface. Note that an image forming apparatus having the above light source device as an exposure head also constitutes another aspect of the present invention. [Effects of the Invention]

[0008] According to the present invention, it is possible to reduce the amount of light that is reflected by the light emitting unit in the light source device and enters the lens unit. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing the configuration of an image forming apparatus using an exposure head according to a first embodiment. [Figure 2] FIG. 2 is a diagram showing an exposure head and a photosensitive drum according to the first embodiment. [Figure 3] FIG. 2 is a diagram showing a light-emitting substrate in the exposure head of the first embodiment. [Figure 4] 3 is a diagram showing a light-emitting section and a gradient index lens array in the exposure head of the first embodiment. FIG. [Figure 5] FIG. 2 is a schematic diagram showing an exposure head and a photosensitive drum according to the first embodiment. [Figure 6] FIG. 3 is a diagram showing a light-emitting substrate, first and second light-emitting units, and a gradient index lens array in the exposure head of the first embodiment. [Figure 7] FIG. 2 is a cross-sectional view A showing the optical path of the exposure head of the first embodiment. [Figure 8] FIG. 3B is a cross-sectional view of the exposure head according to the first embodiment, showing the optical path of the exposure head; [Figure 9] FIG. 3 is a cross-sectional view taken along line C showing the optical path of the exposure head of the first embodiment. [Figure 10] FIG. 10 is a diagram showing a light emitting substrate, first and second light emitting units, and a gradient index lens array in an exposure head according to a second embodiment. [Figure 11] FIG. 10 is a cross-sectional view A showing the optical path of the exposure head of the second embodiment. [Figure 12] FIG. 10 is a cross-sectional view of the exposure head according to the second embodiment, showing the optical path of the exposure head; [Figure 13] FIG. 10 is a cross-sectional view taken along line C showing the optical path of the exposure head of the second embodiment. [Figure 14] FIG. 10 is a diagram showing a light emitting substrate, first and second light emitting units, and a gradient index lens array in Example 3. [Figure 15] FIG. 11 is a cross-sectional view A showing the optical path of the exposure head of the third embodiment. [Figure 16] FIG. 11 is a cross-sectional view of the exposure head according to the third embodiment, showing the optical path of the exposure head; [Figure 17] FIG. 11 is a cross-sectional view taken along line C showing the optical path of the exposure head of the third embodiment. [Figure 18] FIG. 10 is a diagram showing a light emitting substrate, first and second light emitting units, and a gradient index lens array in Example 4. [Figure 19] FIG. 10 is a cross-sectional view A showing the optical path of the exposure head of the fourth embodiment. [Figure 20] FIG. 10 is a cross-sectional view of the exposure head according to the fourth embodiment, showing the optical path of the exposure head; [Figure 21] FIG. 10 is a cross-sectional view taken along line C showing the optical path of the exposure head of the fourth embodiment. [Figure 22] FIG. 10 is a diagram showing a light emitting substrate and first and second light emitting units in an exposure head according to a modified example. [Figure 23] FIG. 10 is a cross-sectional view A showing the optical path of an exposure head of a comparative example. [Figure 24] FIG. 10B is a cross-sectional view showing the optical path of the exposure head of the comparative example. [Figure 25] FIG. 3 is a cross-sectional view taken along line C showing the optical path of an exposure head according to a comparative example. [Figure 26] FIG. 10 is a diagram showing the light distribution characteristics of a light-emitting element. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the drawings may be drawn to a scale different from the actual scale. In addition, the same reference numerals are used to designate the same components in the drawings, and redundant explanations will be omitted. [Example]

[0011] (Image forming device) FIG. 1 shows the configuration of an image forming apparatus 1 that uses an exposure head as a light source device of this embodiment. The image forming apparatus 1 is a color printer (MFP: Multi Function Printer) equipped with a reading device. However, the image forming apparatus may also be a copier that does not have a reading device. The image forming apparatus 1 is a so-called tandem type color image forming apparatus equipped with multiple photosensitive drums (irradiated surfaces) 103. However, the image forming apparatus may also be a color image forming apparatus equipped with a single photosensitive drum or an image forming apparatus that forms monochrome images.

[0012] The image forming apparatus 1 includes four image forming units 102Y, 102M, 102C, and 102K that form toner images of yellow (Y), magenta (M), cyan (C), and black (K). The Y, M, C, and K symbols indicate the corresponding toner colors. The image forming units 102Y, 102M, 102C, and 102K include photosensitive drums 103Y, 103M, 103C, and 103K, respectively. These photosensitive drums 103Y, 103M, 103C, and 103K are arranged at a distance from one another.

[0013] The image forming units 102Y, 102M, 102C, and 102K are also equipped with chargers 104Y, 104M, 104C, and 104K that charge the photosensitive drums 103Y, 103M, 103C, and 103K, respectively. The image forming units 102Y, 102M, 102C, and 102K are also equipped with LED exposure heads 105Y, 105M, 105C, and 105K that serve as light source devices that emit light to expose the photosensitive drums 103Y, 103M, 103C, and 103K, respectively. The image forming apparatus 1 is a so-called "bottom exposure type" image forming apparatus that exposes the photosensitive drums 103Y, 103M, 103C, and 103K from below.

[0014] The image forming units 102Y, 102M, 102C, and 102K are also equipped with developing units 106Y, 106M, 106C, and 106K that develop the electrostatic latent images on the photosensitive drums 103Y, 103M, 103C, and 103K with toner as a developer. The developing units 106Y, 106M, 106C, and 106K form toner images (developer images) of the respective colors on the photosensitive drums 103Y, 103M, 103C, and 103K.

[0015] The image forming apparatus 1 has an intermediate transfer belt 107 onto which toner images formed on the photosensitive drums 103Y, 103M, 103C, and 103K are transferred. The image forming apparatus 1 further includes primary transfer rollers 108Y, 108M, 108C, and 108K that sequentially transfer the toner images formed on the photosensitive drums 103Y, 103M, 103C, and 103K onto the intermediate transfer belt 107. The image forming apparatus 1 also includes a secondary transfer roller 109 that transfers the toner image on the intermediate transfer belt 107 onto recording paper P transported from the paper feed unit 101, and a fuser 110 that fuses the secondarily transferred image onto the recording paper P.

[0016] (Image formation process) Photosensitive drums 103Y, 103M, 103C, and 103K, which have been uniformly charged by chargers 104Y, 104M, 104C, and 104K, are exposed by LED exposure heads 105Y, 105M, 105C, and 105K to form electrostatic latent images. The electrostatic latent images are visualized as toner images of the respective colors by developers 106Y, 106M, 106C, and 106K, and transferred to intermediate transfer belt 107 at primary transfer stations Ty, Tm, Tc, and Tk.

[0017] The toner images of each color superimposed on the intermediate transfer belt 107 are transferred at once by a secondary transfer roller 109 at a secondary transfer section T2 onto a recording sheet P conveyed from a paper feed section 101. The recording sheet P onto which the toner images have been transferred is conveyed to a fixing device 110, where the toner images are fixed by heat and pressure, and then the recording sheet is discharged from a paper discharge section 111.

[0018] (Basic configuration of exposure head) The basic configuration of the exposure head 105 of the first embodiment will be described with reference to FIGS. 2(a), 2(b), 3(a) to 3(c), and 4. FIG.

[0019] Fig. 2(a) shows the arrangement of the exposure head 105 relative to the photosensitive drum 103. Fig. 2(b) shows a ZX cross section (short cross section, sub-scanning cross section), which is a plane perpendicular (orthogonal) to the Y direction when viewed from the Y direction, and shows how light emitted from the light-emitting element array 207 is collected on the photosensitive drum 103 by a gradient index lens array 212 serving as a lens unit. Note that in this embodiment, a gradient index lens array is used as the lens unit, but other lens arrays may also be used.

[0020] 3(a) shows a YZ cross section of a plurality of first light-emitting units 209 (-1 to -10) and a plurality of second light-emitting units 210 (-1 to -10) as light-emitting element array chips mounted on a mounting surface (first surface: hereinafter referred to as the substrate mounting surface) 203 of a light-emitting substrate 202. FIG. 3(b) shows an enlarged YZ cross section of a joint portion between one of the plurality of first light-emitting units 209 and one adjacent second light-emitting unit 210. The joint portion is a Y-direction portion where one of the first light-emitting units 209 and one adjacent second light-emitting unit 210 overlap in the Z direction, and is also referred to as a connection portion. Each light-emitting unit has a light-emitting element row 207 including a plurality of light-emitting elements 204(-1 to -n) arranged in a row in the Y direction as shown in Fig. 3(c). The light-emitting elements are light-emitting devices such as LEDs and organic ELs.

[0021] FIG. 4 shows the positional relationship between the light emitting element array 207 of the plurality of first light emitting units 209 and the plurality of second light emitting units 210 and the first refractive index distribution lens array 212-1 and the second refractive index distribution lens array 212-2 in the YZ cross section.

[0022] 2(b) and 3(a), the exposure head 105 has a plurality of first light-emitting units 209 (-1 to -10) and a plurality of second light-emitting units 210 (-1 to -10) mounted on a light-emitting substrate 202, a refractive index distribution lens array 212, and a housing 201. As described above, the plurality of first light-emitting units 209 and the plurality of second light-emitting units 210, each having a light-emitting element row 207, are mounted on the substrate mounting surface (first surface) 203 of the light-emitting substrate 202.

[0023] The plurality of first light-emitting units 209 (-1 to -10) are arranged in a row in the Y direction (first direction), which is the longitudinal direction of each light-emitting unit. The plurality of second light-emitting units 210 (-1 to -10) are arranged in a row in the Y direction at different positions from each other in the Z direction (second direction perpendicular to the first direction, sub-scanning direction), which is the short direction of each light-emitting unit, relative to the arrangement positions of the first light-emitting units 209. Furthermore, the plurality of first light-emitting units 209 and the plurality of second light-emitting units 210 are arranged at positions shifted from each other in the Y direction. More specifically, the first light-emitting units 209 and the second light-emitting units 210 are arranged so that a portion of each of the first light-emitting units 209 and the second light-emitting units 210 overlap in the Z direction, and the +Y direction end of the light-emitting element row 207 of the first light-emitting unit 209 and the -Y direction end of the light-emitting element row 207 of the second light-emitting unit 210 are aligned in the Y direction. In this way, the plurality of first light emitting units 209 and the plurality of second light emitting units 210 are arranged in two staggered rows.

[0024] As shown in FIGS. 3(b) and 4, in each of the first light-emitting unit 209 and the second light-emitting unit 210, which are semiconductor chips, a light-emitting element row 207 including a plurality of light-emitting elements 204 is mounted on a mounting surface (second surface: hereinafter referred to as the unit mounting surface) 205. The unit mounting surface 205 has the light-emitting element row 207 constituting a light-emitting portion and a non-light-emitting portion 208. In this embodiment, n=748 light-emitting elements 204 are arranged in the Y direction in the light-emitting element row 207 of each light-emitting unit at a predetermined image resolution pitch. The image resolution pitch is, for example, 1200 dpi (approximately 21.16 μm). The length from the -Y end to the +Y end of the light-emitting element row 207 including the 748 light-emitting elements 204 is approximately 15.8 mm.

[0025] Each of the plurality of first light-emitting units 209 and the plurality of second light-emitting units 210 includes 10 light-emitting units. That is, the total number of the first light-emitting units 209 and the second light-emitting units 210 is 20. This brings the total number of light-emitting elements 204 to 14,960, enabling image formation corresponding to an image width of approximately 316 mm.

[0026] Each light-emitting unit is configured by stacking a lower electrode layer, a light-emitting layer, and an upper electrode layer in this order on a Si substrate. The light-emitting layer forms multiple light-emitting elements 204, and the upper electrode layer that forms the surface of the unit mounting surface 205 increases the reflectivity of the non-light-emitting portion 208. For example, the reflectivity of the non-light-emitting portion 208 is 80%. Each light-emitting unit also has a built-in circuit (not shown) for controlling the multiple light-emitting elements 204.

[0027] 26 shows the light distribution characteristics of light emitted from the light-emitting element 204. In this embodiment, the light-emitting element 204 has Lambertian emission characteristics, but the emission characteristics of the light-emitting element are not limited to this. In addition, in this embodiment, the emission spectrum of the light-emitting element 204 peaks at 600 nm, but the emission spectrum is not limited to this, and a light-emitting element that emits near-infrared light with a peak at 780 nm, for example, may be used.

[0028] 4, the gradient index lens array 212 has a first gradient index lens array 212-1 extending in the Y direction and a second gradient index lens array 212-2 extending in the Y direction at a position shifted in the Z direction from the first gradient index lens array 212-1. Each of the first and second gradient index lens arrays 212-1 and 212-2 includes a plurality of gradient index lenses 211 arranged at a predetermined pitch in the Y direction. For example, the diameter of each cylindrical gradient index lens 211 is 290 μm.

[0029] 2(b), the gradient index lens array 212 is disposed so that the distance from the light-emitting element row 207 to each lens 211 is a first predetermined distance, and the distance from the light-emitting surface of each lens 211 to the surface of the photosensitive drum 103 is a second predetermined distance. The first predetermined distance and the second predetermined distance are substantially equal. The gradient index lens array 212 focuses the light emitted from the light-emitting element row 207 onto the photosensitive drum 103 so that an erect image of equal size is formed.

[0030] The refractive index distribution lens array 212 and the light emitting substrate 202 are fixed to the housing 201 with an adhesive.

[0031] The exposure head 105 having the above configuration is assembled individually in a factory, and is then completed by performing focus adjustment and light intensity adjustment to adjust the spot at the condensed position to a predetermined size. In focus adjustment, the mounting position of the refractive index gradient lens array 212 is adjusted so that the distance between the refractive index gradient lens array 212 and the light emitting element row 207 is a first predetermined distance. In light intensity adjustment, each of the multiple light emitting elements 204 in the light emitting element row 207 is sequentially made to emit light, and the drive current of each light emitting element is adjusted so that the light condensed on the photosensitive drum 103 via the refractive index gradient lens array 212 has a predetermined light intensity.

[0032] (Detailed configuration of exposure head) The detailed configuration of the exposure head 105 of the first embodiment will be described with reference to FIG. 5, FIGS. 6(a) to (c), FIGS. 7(a), (b), FIGS. 8(a), (b), and FIGS. 9(a), (b).

[0033] FIG. 5 shows a ZX cross section when viewed from the Y direction, and illustrates the arrangement of the exposure head 105 relative to the photosensitive drum 103. FIG. 6(a) shows an enlarged view of enlarged area 1 in FIG. 5 when viewed from the Y direction. FIG. 6(b) shows an enlarged view of area A in FIG. 6(a). FIG. 6(c) shows an enlarged view of area B in FIG. 6(a).

[0034] 7(a) shows an enlarged region 1 in FIG. 5 in cross section A in FIG. 3(b), illustrating how light emitted from the light-emitting element row 207 (light-emitting section) of the first light-emitting unit 209 enters the first and second gradient index lens arrays 212-1 and 212-2. FIG. 7(b) shows an enlarged region 2 in FIG. 5 in cross section A in FIG. 3(b), illustrating how light emitted from the light-emitting element row 207 of the first light-emitting unit 209 and then emitted from the first and second gradient index lens arrays 212-1 and 212-2 is condensed onto the photosensitive drum 103.

[0035] 8(a) shows an enlarged region 1 in FIG. 5 at cross section B in FIG. 3(b), illustrating how light emitted from the light-emitting element row 207 of the second light-emitting unit 210 is incident on the first and second gradient index lens arrays 212-1 and 212-2. FIG. 8(b) shows an enlarged region 2 in FIG. 5 at cross section B in FIG. 3(b), illustrating how light emitted from the light-emitting element row 207 of the second light-emitting unit 210 and then emitted from the first and second gradient index lens arrays 212-1 and 212-2 is condensed on the photosensitive drum 103.

[0036] 9(a) shows an enlarged region 1 in FIG. 5 in cross section C of FIG. 3(b), illustrating how light emitted from the light-emitting element row 207 of the first light-emitting unit 209 enters the first and second gradient index lens arrays 212-1 and 212-2. FIG. 9(b) shows an enlarged region 2 in FIG. 5 in cross section C of FIG. 3(b), illustrating how light emitted from the light-emitting element row 207 of the first light-emitting unit 209 and then emitted from the first and second gradient index lens arrays 212-1 and 212-2 is condensed onto the photosensitive drum 103.

[0037] When the exposure head 105 is attached to the image forming apparatus 1, it is desirable that the amount of light (ghost light) reflected by the non-light-emitting portion 208 at the joint between any one of the first light-emitting units 209 and the adjacent second light-emitting unit 210 is small. For this reason, in this embodiment, when the light-emitting substrate 202 and the first light-emitting unit 209 are viewed from the Y direction, the unit mounting surface (second surface) 205 of the first light-emitting unit 209 is inclined with respect to the substrate mounting surface (first surface) 203. Similarly, the unit mounting surface 205 of the second light-emitting unit 210 is inclined with respect to the substrate mounting surface 203 when viewed from the Y direction.

[0038] Here, the board mounting surface 203 is a flat surface that occupies most of the board, excluding the lands and pads. Similarly, the unit mounting surface 205 is also a flat surface that occupies most of the board. The inclination of the unit mounting surface 205 with respect to the board mounting surface 203 will be described in detail below.

[0039] As shown in FIG. 6(c), a line perpendicular to the unit mounting surface 205 of the first light-emitting unit 209 is defined as a first line, and a line perpendicular to the unit mounting surface 205 of the second light-emitting unit 210 is defined as a second line. The distance between the first line and the second line is defined as K. In this case, the unit mounting surfaces 205 of the first and second light-emitting units 209, 210 are inclined with respect to the board mounting surface 203 so that the distance K increases as the unit mounting surfaces 205 approach the refractive index gradient lens array 212. The distance K is the distance in a direction parallel to a third line, which will be described later.

[0040] In this embodiment, the direction in which the unit mounting surface 205 of the first light-emitting unit 209 is inclined relative to the board mounting surface 203 is different from the direction in which the unit mounting surface 205 of the second light-emitting unit 210 is inclined relative to the board mounting surface 203. That is, as shown in Fig. 6(c) , the unit mounting surface 205 of the first light-emitting unit 209 is inclined counterclockwise relative to the board mounting surface 203, while the unit mounting surface 205 of the second light-emitting unit 210 is inclined clockwise.

[0041] Next, the inclination angle of the unit mounting surface 205 with respect to the board mounting surface 203 will be described. As shown in Fig. 6(a), the distance between the center of the light-emitting portion (first light-emitting element) of the first light-emitting unit 209 and the center of the light-emitting portion (second light-emitting element) of the second light-emitting unit 210 when viewed from the Y direction is defined as T. Furthermore, the line connecting the centers of these light-emitting portions (first and second light-emitting elements) is defined as a third line.

[0042] The center of the incident surface of one of the gradient index lenses 211 in the gradient index lens array 212 is defined as the first point, and a line that includes the first point and is parallel to the third line is defined as the fourth line. The distance between the third line and the fourth line is defined as D, and the width of the gradient index lens array 212 (the first gradient index lens array 212-1 and the second gradient index lens array 212-2) on the fourth line is defined as W. Furthermore, as shown in FIG. 6(c), a line that is parallel to the unit mounting surface 205 of the first light-emitting unit 209 when viewed from the Y direction is defined as the fifth line, and a line that is parallel to the unit mounting surface 205 of the second light-emitting unit 210 is defined as the sixth line. The angles (inclination angles) θ1 and θ2 formed by the third line and the fifth line and the sixth line, respectively, are defined as θ. In this case, the condition of the following formula (1) is satisfied. The angle θ1 between the third and fifth lines and the angle θ2 between the third and sixth lines may be the same or different from each other.

[0043] 0.95<(W+T+4Dtanθ) / (2W)<18.50 (1) The condition of formula (1) indicates an appropriate range of the inclination angle θ of the unit mounting surface 205 relative to the board mounting surface 203. By setting the inclination angle θ within the range of formula (1), ghost light, which is reflected light generated at the joint between the adjacent first and second light-emitting units 209 and 210, can be reduced, resulting in a good image. The reason why reflected light occurs at the joint will be described later. If the inclination angle θ is equal to or less than the lower limit of formula (1), 0.95, the reflected light generated at the joint cannot be reduced, resulting in an image containing dark streaks. If the inclination angle θ is equal to or greater than the upper limit of formula (1), 18.50, the light emitted from the light-emitting element row 207 and incident on the gradient index lens array 212 is weakened, reducing the amount of light reaching the photosensitive drum 103, and reducing the light utilization efficiency of the exposure head 105.

[0044] The reason why the light incident on the refractive index distribution lens array 212 is weakened will be explained using FIG. 26. When the light emitting element has Lambertian emission characteristics, the half-maximum half-angle radiation angle is 60° because COS60°=0.5. In other words, when the inclination angle θ of the unit mounting surface 205 with respect to the board mounting surface 203 is greater than 60°, the amount of light incident on the refractive index distribution lens array 212 is less than 50% of that when the inclination angle is 0°. As such, since the light utilization efficiency decreases as the inclination angle θ of the unit mounting surface 205 increases, it is desirable to keep the inclination angle θ within the range of formula (1). Furthermore, it is preferable to set the numerical range of formula (1) as shown in the following formula (1a).

[0045] 1.00<(W+T+4Dtanθ) / (2W)<4.58 (1a) In Example 1, W = 0.539 mm, T = 0.40 mm, D = 2.74 mm, and θ (= θ1 = θ2) = 0.5°. Therefore, (W + T + 4D tan θ) / (2W) = 0.96, satisfying the condition of formula (1). In this case, the proportion of light reflected from the joints among the light reaching the area on the photosensitive drum 103 corresponding to the joints is 0.07%. Since the proportion of reflected light in the comparative example described below is 0.20%, the proportion of reflected light can be reduced by (1 - 0.07 / 0.20) × 100 = 65%. Furthermore, the proportion of light emitted from the light-emitting element array 207 that enters the gradient index lens array 212, i.e., the light utilization efficiency, is 100.0% based on a COS of 0.5°.

[0046] Although the above description illustrates a case where the reflectance of the non-light-emitting portion 208 is 80%, the reflectance of the non-light-emitting portion 208 need only be greater than 0%. When the reflectance is 50%, the proportion of reflected light from the joint is 0.07% × 50% / 80% = 0.04%. Similarly, in the comparative example, the proportion of reflected light from the joint is 0.20% × 50% / 80% = 0.13%. Therefore, the proportion of reflected light can be reduced by (1 - 0.04 / 0.13) × 100 = 69% compared to the comparative example. Note that the 69% reduction was achieved here because the third decimal point was omitted. However, if the third decimal point was not omitted, the reduction would be 65%, the same reduction rate as when the reflectance of the non-light-emitting portion 208 is 80%. It is desirable for the reflectance of the non-light-emitting portion 208 to be 50% or greater.

[0047] The condition of formula (1) is satisfied for all combinations of any one of the multiple first light-emitting units 209 (-1 to -10) and a second light-emitting unit adjacent to the one first light-emitting unit 209 among the multiple second light-emitting units 210 (-1 to -10).

[0048] FIGS. 23(a), 23(b), 24(a), 24(b), and 25(a), 25(b) show an exposure head as a comparative example. In this comparative example, the same reference numerals as those in Example 1 are used. FIG. 23(a) shows a region corresponding to the enlarged region 1 in FIG. 5 in a cross section corresponding to the cross section A in FIG. 3(b). This figure shows how light emitted from the light-emitting element array 707 of the first light-emitting unit 709 (light-emitting section) enters the first and second gradient index lens arrays 712-1 and 712-2. FIG. 23(b) shows a region corresponding to the enlarged region 2 in FIG. 5 in a cross section corresponding to the cross section A in FIG. 3(b). This figure shows how light emitted from the light-emitting element array 707 of the first light-emitting unit 709 and then emitted from the first and second gradient index lens arrays 712-1 and 712-2 is focused on the photosensitive drum 103.

[0049] 24(a) shows a region corresponding to the enlarged region 1 in FIG. 5 in a cross section corresponding to the cross section B in FIG. 3(b). This figure shows how light emitted from the light-emitting element row 707 of the second light-emitting unit 710 is incident on the first and second gradient index lens arrays 712-1 and 712-2. FIG. 24(b) shows a region corresponding to the enlarged region 2 in FIG. 5 in a cross section corresponding to the cross section B in FIG. 3(b). This figure shows how light emitted from the light-emitting element row 707 of the second light-emitting unit 710 and then emitted from the first and second gradient index lens arrays 712-1 and 712-2 is condensed on the photosensitive drum 103.

[0050] 25(a) shows a region corresponding to the enlarged region 1 in FIG. 5 in a cross section corresponding to the cross section C in FIG. 3(b). This figure shows how light emitted from the light-emitting element row 707 of the first light-emitting unit 709 is incident on the first and second gradient index lens arrays 712-1 and 712-2. FIG. 25(b) shows a region corresponding to the enlarged region 2 in FIG. 5 in a cross section corresponding to the cross section C in FIG. 3(b). This figure shows how light emitted from the light-emitting element row 707 of the first light-emitting unit 709 and then emitted from the first and second gradient index lens arrays 712-1 and 712-2 is condensed on the photosensitive drum 103.

[0051] The exposure head in the comparative example has the same configuration as exposure head 105 in Example 1, except that the inclination angle of unit mounting surface (second surface) 705 relative to board mounting surface (first surface) 703 is different from that of the exposure head in Example 1.

[0052] In the comparative example, W = 0.539 mm, T = 0.40 mm, D = 2.74 mm, and θ = 0°. Therefore, (W + T + 4D tan θ) / (2W) = 0.87, which does not satisfy the condition of formula (1). In this case, the proportion of reflected light (ghost light) from the joint portion of the first and second light-emitting units 709 and 710 among the light rays reaching the area on the photosensitive drum 103 corresponding to the joint portion is 0.20%. When such a large amount of reflected light occurs, an image including dark streaks is formed.

[0053] Here, the reason why reflected light occurs at the joint between the first and second light emitting units 709 and 710 will be explained.

[0054] As shown in Fig. 23(a), a light ray A1 emitted from the light emitting element row 707 of the first light emitting unit 709 is incident on the first and second gradient index lens arrays 712-1 and 712-2. The light ray A1 is a representative light ray among the light rays incident on the first and second gradient index lens arrays 712-1 and 712-2. As shown in Fig. 23(b), the light ray A1 emitted from the first and second gradient index lens arrays 712-1 and 712-2 is focused on the photosensitive drum 103.

[0055] From the viewpoint of cost, gradient index lenses are generally used with the lens surfaces uncoated. When the lens surface is uncoated, a portion of the light rays incident on it are reflected by Fresnel reflection. Of the light rays that are perpendicularly incident on the incident surface of a gradient index lens, the number of light rays that are Fresnel reflected is {(n-1) / (n+1)} 2As shown in FIG. 23(a), of the light ray A1, a light ray B1 that is Fresnel-reflected on the lens surfaces (incident surfaces) of the first and second gradient index lens arrays 712-1 and 712-2 reaches the board mounting surface 703 of the light-emitting board 702. Generally, the reflectance of the non-light-emitting portion of the board mounting surface 703 is low, and even if the light ray B1 is reflected on the board mounting surface (first surface) 703, the reflected light is weak, so the reflectance of the board mounting surface 703 can be approximated as 0%. As shown in FIG. 24(a), the light ray A2 emitted from the light-emitting element row 707 of the second light-emitting unit 710 is similar to the light ray A1, and the light ray B2 that is Fresnel-reflected on the incident surfaces of the first and second gradient index lens arrays 712-1 and 712-2 reaches the board mounting surface 703.

[0056] As shown in Figure 25(a), light ray A1 emitted from the light-emitting element row 707 of the first light-emitting unit 709 is incident on the first and second gradient index lens arrays 712-1 and 712-2. Light ray B1 of light ray A1 is Fresnel-reflected on the incident surfaces of the first and second gradient index lens arrays 712-1 and 712-2 and reaches the non-light-emitting portion 708 of the second light-emitting unit 710. The non-light-emitting portion 708 is formed of an electrode layer and has a high reflectance of 80%. Therefore, light ray C1 reflected by the non-light-emitting portion 708 becomes ghost light and is incident on the first and second gradient index lens arrays 712-1 and 712-2.

[0057] 25(b), the light rays A1 and C1 emitted from the first and second refractive index distribution lens arrays 712-1 and 712-2, respectively, are condensed onto the photosensitive drum 103. Since the light ray C1 is condensed onto the photosensitive drum 103 as ghost light, the proportion of ghost light from the joint portion among the light rays reaching the area on the photosensitive drum 103 corresponding to the position of the joint portion between the first and second light-emitting units 709 and 710 is 0.20%.

[0058] In this example, unlike the comparative example, powder 213 is disposed between the substrate mounting surface 203 and the back surface (third surface: hereinafter referred to as the unit back surface) 206 of the first and second light-emitting units 209 and 210, which is opposite the unit mounting surface 205, as shown in FIG. 6(b). The powder 213 is a component for imparting an inclination to the unit mounting surface 205 with respect to the substrate mounting surface 203. With the powder 213 sandwiched between the first and second light-emitting units 209 and 210 and the substrate mounting surface 203, the first and second light-emitting units 209 and 210 are bonded and fixed to the substrate mounting surface 203 with an adhesive (not shown). The inclination angle of the unit mounting surface 205 with respect to the substrate mounting surface 203 can be adjusted by selecting the height (thickness) of the powder 213. In this example, a 4 μm-high powder 213 is used to impart an inclination angle θ of 0.5° to the unit mounting surface 205. When viewed from the Y direction, the powder 213 is in contact with a portion (a portion near the end) of the unit rear surface 206 of each of the first and second light-emitting units 209 and 210.

[0059] In the cross section A shown in FIG. 7(a), as in the comparative example, even if a light ray B1 that is Fresnel-reflected at the incident surfaces of the first and second gradient index lens arrays 712-1 and 712-2 is reflected by the board mounting surface 203, the reflected light is weak. Therefore, the reflectance of the board mounting surface 203 can be approximated as 0%. In the cross section B shown in FIG. 8(a), even if a light ray B2 that is Fresnel-reflected is reflected by the board mounting surface 203, the reflected light is weak, so the reflectance of the board mounting surface 203 can be approximated as 0%. In the cross section C shown in FIG. 9(a), the Fresnel-reflected light ray B1 reaches the non-light-emitting portion 208 of the second light-emitting unit 210. Because the unit mounting surface 205 of the second light-emitting unit 210 is inclined, the light ray C1 that is reflected by the non-light-emitting portion 208 is less likely to enter the first and second gradient index lens arrays 212-1 and 212-2 than the light ray C1 in the comparative example shown by the dashed line. That is, the light beams C1 incident on the first and second gradient index lens arrays 212-1 and 212-2 can be reduced, thereby reducing the proportion of ghost light from the joints of the first and second light-emitting units 209 and 210 to 0.07% of the light beams reaching the areas on the photosensitive drum 103 corresponding to the positions of the joints.

[0060] In cross section C, the light rays that are emitted from the light-emitting element row 207 of the second light-emitting unit 210 and Fresnel-reflected on the incident surfaces of the first and second gradient index lens arrays 712-1 and 712-2 reach and are reflected on the non-light-emitting portions 208 of the first light-emitting unit 209. At this time, because the unit mounting surface 205 of the first light-emitting unit 209 is also inclined, it is possible to reduce the number of light rays that are reflected on the non-light-emitting portions 208 and enter the first and second gradient index lens arrays 212-1 and 212-2. This also applies to other embodiments described later.

[0061] In the exposure head 105 of Example 1 described above, the unit mounting surfaces 205 of the first and second light-emitting units 209, 210 are inclined with respect to the board mounting surface 203 of the light-emitting board 202. This inclination forms an angle of inclination such that light that is emitted from one of the light-emitting units, reflected by the gradient index lens array 212, reflected by the non-light-emitting portion 208 of the other light-emitting unit, and then again enters the lens array 212, is reduced compared to when there is no inclination with respect to the board mounting surface 203. This reduces the reflected light (ghost light) that is reflected by the non-light-emitting portion of the connecting portion of the first and second light-emitting units and enters the lens array, making it possible to form a good image with almost no unwanted streaks. [Example]

[0062] Next, a description will be given of Example 2. The configuration of an image forming apparatus using the exposure head of Example 2 is the same as that of the image forming apparatus 1 described in Example 1, and therefore a description thereof will be omitted.

[0063] The exposure head 105 of Example 2 is different from the exposure head 105 of Example 1 in the inclination angle θ of the unit mounting surface (second surface) 305 of the first and second light-emitting units 309, 310 relative to the board mounting surface (first surface) 303 of the light-emitting board 302. The configuration of the exposure head 105 of this example will be described using Figures 10(a) to (c), 11(a), (b), 12(a), (b), and 13(a), (b). The basic configuration of the exposure head 105 of this example is the same as that of the exposure head 105 of Example 1, and Figures 3(b) and 5 used in Example 1 will be used for the description.

[0064] Fig. 10(a) shows an enlarged region 1 in Fig. 5. Fig. 10(b) shows an enlarged region A in Fig. 10(a). Fig. 10(c) shows an enlarged region B in Fig. 10(a).

[0065] 11(a) shows an enlarged region 1 in FIG. 5 in cross section A of FIG. 3(b), illustrating how light emitted from the light-emitting element row 307 (light-emitting section) of the first light-emitting unit 309 enters the first and second gradient index lens arrays 312-1 and 312-2. FIG. 11(b) shows an enlarged region 2 in FIG. 5 in cross section A of FIG. 3(b), illustrating how light emitted from the light-emitting element row 307 of the first light-emitting unit 309 and then emitted from the first and second gradient index lens arrays 312-1 and 312-2 is condensed onto the photosensitive drum 103.

[0066] 12(a) shows an enlarged region 1 in FIG. 5 at cross section B in FIG. 3(b), illustrating how light emitted from light-emitting element row 307 of second light-emitting unit 310 is incident on first and second gradient index lens arrays 312-1 and 312-2. FIG. 12(b) shows an enlarged region 2 in FIG. 5 at cross section B in FIG. 3(b), illustrating how light emitted from light-emitting element row 307 of second light-emitting unit 310 and then emitted from first and second gradient index lens arrays 312-1 and 312-2 is condensed on photosensitive drum 103.

[0067] 13(a) shows an enlarged region 1 in FIG. 5 in cross section C of FIG. 3(b), illustrating how light emitted from the light-emitting element row 307 of the first light-emitting unit 309 enters the first and second gradient index lens arrays 312-1 and 312-2. FIG. 13(b) shows an enlarged region 2 in FIG. 5 in cross section C of FIG. 3(b), illustrating how light emitted from the light-emitting element row 307 of the first light-emitting unit 309 and then emitted from the first and second gradient index lens arrays 312-1 and 312-2 is collected on the photosensitive drum 103.

[0068] In Example 2, W = 0.539 mm, T = 0.40 mm, D = 2.74 mm, and θ (= θ1 = θ2) = 1.0°. Therefore, (W + T + 4D tan θ) / (2W) = 1.05, which satisfies the condition of formula (1). In this case, the proportion of reflected light (ghost light) from the joint portion of the first and second light-emitting units 309 and 310 among the light rays reaching the area on the photosensitive drum 103 corresponding to the joint portion is 0.00%. In contrast, the proportion of reflected light in the comparative example described above is 0.20%, so in this example, the proportion of reflected light can be reduced by (1 - 0.00 / 0.20) × 100 = 100%.

[0069] Furthermore, the proportion of light emitted from the light emitting element row 307 that is incident on the first and second refractive index gradient lens arrays 312-1 and 312-2 (light utilization efficiency) is 100.0% because of COS 1.0°.

[0070] In this embodiment, the condition of formula (1) is also satisfied in all combinations of any one of the multiple first light-emitting units 309 and a second light-emitting unit adjacent to the one first light-emitting unit 309 among the multiple second light-emitting units 310.

[0071] 10(b), in this embodiment, silk 313 is disposed between the board mounting surface 303 and the unit rear surface (third surface) 306. The silk 313 is a component for providing an inclination to the unit mounting surface 305 relative to the board mounting surface 303, and is provided by forming a single line by silk printing over the entire area (approximately 316 mm) in the Y direction on the board mounting surface 303. With the silk 313 sandwiched between the board mounting surface 303 in this manner, the first and second light-emitting units 309 and 310 are adhered and fixed to the board mounting surface 303 with an adhesive (not shown).

[0072] By selecting the height (thickness) of the silk 313, it is possible to adjust the inclination angle of the unit mounting surface 305 relative to the board mounting surface 303. In this embodiment, silk 313 with a height of 9 μm is used to give the unit mounting surface 305 an inclination angle θ = 1.0°. When viewed from the Y direction, the silk 313 is in contact with a portion (a portion near the end) of the unit back surface 306 of each of the first and second light-emitting units 309 and 310.

[0073] 11(a), as in the comparative example, the reflected light is weak even when the light ray B1 that is Fresnel-reflected on the incident surfaces of the first and second gradient index lens arrays 312-1 and 312-2 is reflected on the board mounting surface 303. Therefore, the reflectance of the board mounting surface 303 can be approximated to 0%.

[0074] Similarly, in the cross section B shown in FIG. 12(a), even if the Fresnel-reflected light ray B2 is reflected by the board mounting surface 303, the reflected light is weak, so the reflectance of the board mounting surface 303 can be approximated to 0%.

[0075] In the cross section C shown in FIG. 13(a), the Fresnel-reflected light ray B1 reaches the non-light-emitting portion 308 of the second light-emitting unit 310. Because the unit mounting surface 305 of the second light-emitting unit 310 is inclined, the light ray C1 reflected by the non-light-emitting portion 308 is less likely to enter the first and second gradient index lens arrays 312-1 and 312-2 than the light ray C1 in the comparative example shown by the dashed line. In other words, the light ray C1 incident on the first and second gradient index lens arrays 312-1 and 312-2 can be reduced. This makes it possible to reduce the proportion of ghost light to 0.00% of the light rays reaching the area on the photosensitive drum 103 corresponding to the joint between the first and second light-emitting units 309 and 310.

[0076] According to the exposure head 105 of the second embodiment described above, it is possible to reduce the reflected light (ghost light) that is reflected by the non-light-emitting parts of the connecting parts of the first and second light-emitting units and enters the lens array, thereby forming a good image with almost no unwanted streaks. [Example]

[0077] Next, a description will be given of Example 3. The configuration of an image forming apparatus using the exposure head of Example 3 is the same as that of the image forming apparatus 1 described in Example 1, and therefore a description thereof will be omitted.

[0078] The exposure head 105 of Example 3 is different from the exposure head 105 of Example 1 in the inclination angle θ of the unit mounting surface (second surface) 405 of the first and second light-emitting units 409, 410 relative to the board mounting surface (first surface) 403 of the light-emitting board 402. The configuration of the exposure head 105 of this example will be described using Figures 14, 15(a) and (b), 16(a) and (b), and 17(a) and (b). The basic configuration of the exposure head 105 of this example is the same as that of the exposure head 105 of Example 1, and Figures 3(b) and 5 used in Example 1 will be used for the description.

[0079] Fig. 14 shows an enlarged region 1 in Fig. 5. Fig. 15(a) shows an enlarged region 1 in Fig. 5 in the cross section A of Fig. 3(b), illustrating how light emitted from the light-emitting element row 407 (light-emitting section) of the first light-emitting unit 409 enters the first and second gradient index lens arrays 412-1 and 412-2. Fig. 15(b) shows an enlarged region 2 in Fig. 5 in the cross section A of Fig. 3(b), illustrating how light emitted from the light-emitting element row 407 of the first light-emitting unit 409 and then emitted from the first and second gradient index lens arrays 412-1 and 412-2 is condensed on the photosensitive drum 103.

[0080] 16(a) shows an enlarged region 1 in FIG. 5 at cross section B in FIG. 3(b), illustrating how light emitted from light-emitting element row 407 of second light-emitting unit 410 is incident on first and second gradient index lens arrays 412-1 and 412-2. FIG. 16(b) shows an enlarged region 2 in FIG. 5 at cross section B in FIG. 3(b), illustrating how light emitted from light-emitting element row 407 of second light-emitting unit 410 and then emitted from first and second gradient index lens arrays 412-1 and 412-2 is condensed on photosensitive drum 103.

[0081] 17(a) shows an enlarged region 1 in FIG. 5 in cross section C of FIG. 3(b), illustrating how light emitted from the light-emitting element row 407 of the first light-emitting unit 409 enters the first and second gradient index lens arrays 412-1 and 412-2. FIG. 17(b) shows an enlarged region 2 in FIG. 5 in cross section C of FIG. 3(b), illustrating how light emitted from the light-emitting element row 407 of the first light-emitting unit 409 and then emitted from the first and second gradient index lens arrays 412-1 and 412-2 is condensed on the photosensitive drum 103.

[0082] In this embodiment, W = 0.539 mm, T = 0.40 mm, D = 2.74 mm, and θ (= θ1 = θ2) = 20.0°. Therefore, (W + T + 4D tan θ) / (2W) = 4.57, which satisfies the condition of formula (1). In this case, the proportion of reflected light (ghost light) from the joint portion of the first and second light-emitting units 409 and 410 among the light rays reaching the area on the photosensitive drum 103 corresponding to the joint portion is 0.00%. Since the proportion of reflected light in the comparative example is 0.20%, the proportion of reflected light can be reduced by (1 - 0.00 / 0.20) × 100 = 100%.

[0083] Furthermore, the proportion of light emitted from the light emitting element row 407 that is incident on the first and second refractive index gradient lens arrays 412-1 and 412-2 (light utilization efficiency) is 94.0% based on COS 20.0°.

[0084] In this embodiment, the condition of formula (1) is also satisfied in all combinations of any one of the multiple first light-emitting units 409 and a second light-emitting unit adjacent to the one first light-emitting unit 409 among the multiple second light-emitting units 410.

[0085] 14 , in this embodiment, protrusions 413 are integrally formed on the unit rear surface (third surface) 406 of each of the first and second light-emitting units 409 and 410, and the protrusions 413 are in contact with the board mounting surface 403. The protrusions 413 are members for imparting an inclination to the unit mounting surface 405 relative to the board mounting surface 403. With the protrusions 413 in contact with the board mounting surface 403 in this manner, the first and second light-emitting units 409 and 410 are adhered and fixed to the board mounting surface 403 with an adhesive (not shown).

[0086] The inclination angle of the unit mounting surface 405 relative to the board mounting surface 403 can be adjusted by selecting the height of the protrusion 413. In this embodiment, the protrusion 413 has a height of 182 μm, giving the unit mounting surface 405 an inclination angle θ=20.0°. When viewed from the Y direction, the protrusion 413 is in contact with a portion (a portion near the end) of the unit back surface 406 of each of the first and second light-emitting units 409 and 410.

[0087] 15(a), as in the comparative example, the reflected light is weak even when the light ray B1 that is Fresnel-reflected on the incident surfaces of the first and second gradient index lens arrays 412-1 and 412-2 is reflected on the board mounting surface 403. For this reason, the reflectance of the board mounting surface 403 can be approximated to 0%.

[0088] Similarly, in the cross section B shown in FIG. 16(a), even if the Fresnel-reflected light ray B2 is reflected by the board mounting surface 403, the reflected light is weak, so the reflectance of the board mounting surface 403 can be approximated to 0%.

[0089] In the cross section C shown in FIG. 17(a), Fresnel-reflected light ray B1 reaches the non-light-emitting portion 408 of the second light-emitting unit 410. Because the unit mounting surface 405 of the second light-emitting unit 410 is inclined, light ray C1 reflected by the non-light-emitting portion 408 is less likely to enter the first and second gradient index lens arrays 412-1 and 412-2 than light ray C1 in the comparative example shown by the dashed line. In other words, it is possible to reduce the amount of light ray C1 incident on the first and second gradient index lens arrays 412-1 and 412-2. This makes it possible to reduce to 0.00% the proportion of ghost light from the joints of the first and second light-emitting units 409 and 410 among the light rays reaching the areas on the photosensitive drum 103 corresponding to the positions of the joints.

[0090] According to the exposure head 105 of the third embodiment described above, it is possible to reduce the reflected light (ghost light) that is reflected by the non-light-emitting portion of the connecting portion between the first and second light-emitting units and enters the lens array, thereby forming a good image with almost no unwanted streaks. [Example]

[0091] Next, a description will be given of Example 4. The configuration of an image forming apparatus using the exposure head of Example 4 is the same as that of the image forming apparatus 1 described in Example 1, and therefore a description thereof will be omitted.

[0092] The exposure head 105 of Example 4 is different from the exposure head 105 of Example 1 in the inclination angle θ of the unit mounting surface (second surface) 505 of the first and second light-emitting units 509, 510 relative to the board mounting surface (first surface) 503 of the light-emitting board 502. The configuration of the exposure head 105 of this example will be described using Figures 18, 19(a) and (b), 20(a) and (b), and 21(a) and (b). The basic configuration of the exposure head 105 of this example is the same as that of the exposure head 105 of Example 1, and Figures 3(b) and 5 used in Example 1 will be used for the description.

[0093] FIG. 18 shows the enlarged area 1 in FIG.

[0094] 19(a) shows an enlarged region 1 in FIG. 5 in cross section A of FIG. 3(b), illustrating how light emitted from light-emitting element row 507 of first light-emitting unit 509 (light-emitting section) is incident on first and second gradient index lens arrays 512-1 and 512-2. FIG. 19(b) shows an enlarged region 2 in FIG. 5 in cross section A of FIG. 3(b), illustrating how light emitted from light-emitting element row 507 of first light-emitting unit 509 and then emitted from first and second gradient index lens arrays 512-1 and 512-2 is focused on photosensitive drum 103.

[0095] 20(a) shows an enlarged region 1 in FIG. 5 at cross section B in FIG. 3(b), illustrating how light emitted from light-emitting element row 507 of second light-emitting unit 510 enters first and second gradient index lens arrays 512-1 and 512-2. FIG. 20(b) shows an enlarged region 2 in FIG. 5 at cross section B in FIG. 3(b), illustrating how light emitted from light-emitting element row 507 of second light-emitting unit 510 and then emitted from first and second gradient index lens arrays 512-1 and 512-2 is condensed on photosensitive drum 103.

[0096] 21(a) shows an enlarged region 1 in FIG. 5 in cross section C of FIG. 3(b), illustrating how light emitted from the light-emitting element row 507 of the first light-emitting unit 509 enters the first and second gradient index lens arrays 512-1 and 512-2. FIG. 21(b) shows an enlarged region 2 in FIG. 5 in cross section C of FIG. 3(b), illustrating how light emitted from the light-emitting element row 507 of the first light-emitting unit 509 and then emitted from the first and second gradient index lens arrays 512-1 and 512-2 is condensed on the photosensitive drum 103.

[0097] In this embodiment, W = 0.539 mm, T = 0.40 mm, D = 2.74 mm, and θ (= θ1 = θ2) = 45.0°. Therefore, (W + T + 4D tan θ) / (2W) = 11.04, which satisfies the condition of formula (1). In this case, the proportion of reflected light (ghost light) from the joint portion of the first and second light-emitting units 509 and 510 among the light rays reaching the area on the photosensitive drum 103 corresponding to the joint portion is 0.00%. Since the proportion of reflected light in the comparative example is 0.20%, the proportion of reflected light can be reduced by (1 - 0.00 / 0.20) × 100 = 100%.

[0098] Furthermore, the proportion of light emitted from the light emitting element row 507 that is incident on the first and second refractive index gradient lens arrays 512-1 and 512-2 (light utilization efficiency) is 70.7% based on a COS of 45.0°.

[0099] In this embodiment, the condition of formula (1) is also satisfied in all combinations of any one of the multiple first light-emitting units 509 and a second light-emitting unit adjacent to the one first light-emitting unit 509 among the multiple second light-emitting units 510.

[0100] 18 , protrusions 513 are integrally formed on substrate mounting surface 503, and protrusions 513 are in contact with unit rear surfaces (third surfaces) 506 of first and second light-emitting units 509 and 510. Protrusions 513 are members for imparting an inclination to unit mounting surface 505 relative to substrate mounting surface 503, and are provided over the entire Y-direction area (approximately 316 mm) of substrate mounting surface 503. With protrusions 513 in contact with unit rear surfaces 506 in this manner, first and second light-emitting units 509 and 510 are adhesively fixed to substrate mounting surface 503 with an adhesive (not shown).

[0101] The inclination angle of the unit mounting surface 505 relative to the board mounting surface 503 can be adjusted by selecting the height of the protrusions 513. In this embodiment, protrusions 513 having a height of 500 μm are provided to give the unit mounting surface 505 an inclination angle θ=45.0°. When viewed from the Y direction, the protrusions 513 are in contact with a portion (a portion near the end) of the unit back surfaces 506 of the first and second light-emitting units 509 and 510.

[0102] 19(a), as in the comparative example, the reflected light is weak even when the light ray B1 that is Fresnel-reflected on the incident surfaces of the first and second gradient index lens arrays 512-1 and 512-2 is reflected on the board mounting surface 503. For this reason, the reflectance of the board mounting surface 503 can be approximated to 0%.

[0103] Similarly, in the cross section B shown in FIG. 20(a), even if the Fresnel-reflected light ray B2 is reflected by the board mounting surface 503, the reflected light is weak, so the reflectance of the board mounting surface 503 can be approximated to 0%.

[0104] In the cross section C shown in FIG. 21(a), the Fresnel-reflected light ray B1 reaches the non-light-emitting portion 508 of the second light-emitting unit 510. Because the unit mounting surface 505 of the second light-emitting unit 510 is inclined, the light ray C1 reflected by the non-light-emitting portion 508 is less likely to enter the first and second gradient index lens arrays 512-1 and 512-2 than the light ray C1 in the comparative example shown by the dashed line. That is, the light ray C1 incident on the first and second gradient index lens arrays 512-1 and 512-2 can be reduced. This makes it possible to reduce to 0.00% the proportion of ghost light among the light rays reaching the area on the photosensitive drum 103 corresponding to the position of the joint between the first and second light-emitting units 509 and 510.

[0105] According to the exposure head 105 of Example 4 described above, it is possible to reduce the reflected light (ghost light) that is reflected by the non-light-emitting parts of the connecting parts of the first and second light-emitting units and enters the lens array, thereby forming a good image with almost no unwanted streaks.

[0106] In the above Examples 1 to 4, it is desirable that all of the plurality of first light-emitting units and the plurality of second light-emitting units satisfy the condition of formula (1), but it is not necessary that all of the plurality of first light-emitting units and the plurality of second light-emitting units satisfy the condition of formula (1). That is, when the total number of the plurality of first light-emitting units and the plurality of second light-emitting units is N, it is desirable that the number of first and second light-emitting units that satisfy the condition of formula (1) is 1.0×N, but it is sufficient that it is 0.7×N or more.

[0107] [Variations] Modifications of each embodiment will be described below. In Embodiments 1 to 4, the unit mounting surface of the first light-emitting unit is inclined counterclockwise with respect to the substrate mounting surface, and the unit mounting surface of the second light-emitting unit is inclined clockwise with respect to the substrate mounting surface, as viewed from the Y direction. However, the embodiments are not limited to this. For example, as shown in FIG. 22, the unit mounting surface 605 of the first light-emitting unit 609 may be inclined clockwise with respect to the substrate mounting surface 603 of the light-emitting substrate 602, and the unit mounting surface 605 of the second light-emitting unit 610 may be inclined counterclockwise with respect to the substrate mounting surface 603. In FIG. 22, two protrusions 613 are integrally formed on the substrate mounting surface 603, and the unit back surfaces 606 of the first and second light-emitting units 609 and 610 are brought into contact with the protrusions 613, thereby inclining the unit mounting surface 605 with respect to the substrate mounting surface 603. In this case, the optical paths of light from the light-emitting element arrays 607 of the first and second light-emitting units 609 and 610 are the same as those in Embodiments 1 to 4.

[0108] In addition, in Examples 1 to 4, the unit mounting surfaces of both the first and second light-emitting units are inclined with respect to the board mounting surface. However, it is not necessary that both the unit mounting surfaces of the first and second light-emitting units are inclined with respect to the board mounting surface, as long as the unit mounting surface of at least one of the first and second light-emitting units is inclined with respect to the board mounting surface.

[0109] The above embodiment includes the following configurations.

[0110] (Configuration 1) first and second light-emitting units arranged at different positions in a first direction on a first surface of the substrate and in a second direction perpendicular to the first direction; a lens unit that collects light from the first and second light-emitting units; Each of the first and second light emitting units includes a second surface and a plurality of light emitting elements arranged on the second surface in the first direction; The light source device, wherein the second surface of at least one of the first and second light emitting units is inclined with respect to the first surface when viewed from the first direction. (Configuration 2) The light source device described in configuration 1, characterized in that the amount of light that is emitted from a light-emitting unit including the second surface inclined with respect to the first surface, reflected by the lens unit, reflected by the second surface of the other light-emitting unit, and incident on the lens unit is less than when the second surface is not inclined. (Configuration 3) The light source device described in configuration 1 or 2, characterized in that when viewed from the first direction, the distance between the normals of the second surfaces of the first and second light-emitting units becomes longer as they are closer to the lens unit. (Configuration 4) 4. The light source device according to any one of configurations 1 to 3, wherein the second surfaces of the first and second light-emitting units are inclined with respect to the first surfaces. (Configuration 5) 5. The light source device according to configuration 4, wherein the second surfaces of the first and second light-emitting units are inclined in different directions relative to the first surface. (Configuration 6) The light source device described in any one of configurations 1 to 5, characterized in that the lens unit includes first and second lens arrays, each including a plurality of lenses arranged in the first direction, and the first and second lens arrays are arranged at different positions in the second direction. (Configuration 7) 7. The light source device according to any one of configurations 1 to 6, wherein the lens unit includes a gradient index lens. (Configuration 8) 8. The light source device according to any one of configurations 1 to 7, wherein the reflectance of the second surface is 50% or more. (Configuration 9) When viewed from the first direction, when the distance between the center of the first light-emitting element in the first light-emitting unit and the center of the second light-emitting element in the second light-emitting unit is T, a line connecting the centers of the first and second light-emitting units is a third line, a center of an incident surface of a lens included in the lens unit is a first point, a line including the first point and parallel to the third line is a fourth line, a distance between the third line and the fourth line is D, a width of the lens unit on the fourth line is W, a line parallel to the second surface of the first light-emitting unit is a fifth line, a line parallel to the second surface of the second light-emitting unit is a sixth line, and angles θ1 and θ2 formed by the third line, and the fifth line and the sixth line, respectively, are θ, 0.95<(W+T+4Dtanθ) / (2W)<18.50 5. The light source device according to configuration 4, which satisfies the following conditions: (Configuration 10) 1.00<(W+T+4Dtanθ) / (2W)<4.58 10. The light source device according to configuration 9, which satisfies the following conditions: (Configuration 11) The first and second light-emitting units are a third surface opposite the second surface; 11. The light source device according to any one of configurations 1 to 10, wherein a member for tilting the second surface relative to the first surface is disposed between the third surface and the first surface of the light-emitting unit whose second surface is tilted. (Configuration 12) the second surfaces of the first and second light-emitting units are inclined relative to the first surface, 12. The light source device according to claim 11, wherein the member is in contact with a portion of the third surface of each of the first and second light-emitting units. (Configuration 13) a plurality of the first and second light-emitting units are arranged in the first direction; The light source device described in configuration 9, characterized in that when the total number of the first light-emitting units and the second light-emitting units is N, the number of the first and second light-emitting units that satisfy the condition is 0.7×N or more. (Configuration 14) 14. The light source device according to configuration 13, wherein the number of the first and second light emitting units that satisfy the condition is 1.0×N. (Configuration 15) a light source device according to any one of configurations 1 to 14; and and a developing device for developing the electrostatic latent image formed on the surface to be irradiated by the light source device.

[0111] The embodiments described above are merely representative examples, and various modifications and alterations are possible to each embodiment when implementing the present invention. [Explanation of symbols]

[0112] 1. Image forming device 105 Exposure head 202,302,402,502,602 Light-emitting substrate 203, 303, 403, 503, 603 PCB mounting surface (first surface) 205, 305, 405, 505 Unit mounting surface (2nd surface) 206, 306, 406, 506 Unit back (third side) 207, 307, 407, 507, 607 Light emitting element row (light emitting part) 208,308,408,508 Non-luminous part 209, 309, 409, 509, 609 First light-emitting unit 210,310,410,510,610 Second light-emitting unit 212 Gradient index lens array 212-1, 312-1, 412-1, 512-1 First gradient index lens array 212-2, 312-2, 412-2, 512-2 Second gradient index lens array 213 Powder (component) 313 Silk (component) 413, 513, 613 Protrusions (components)

Claims

1. first and second light-emitting units disposed at different positions in a first direction on a first surface of the substrate and in a second direction perpendicular to the first direction; a lens unit that collects light from the first and second light-emitting units; Each of the first and second light emitting units includes a second surface and a plurality of light emitting elements arranged on the second surface in the first direction; The light source device, wherein the second surface of at least one of the first and second light emitting units is inclined with respect to the first surface when viewed from the first direction.

2. 2. The light source device according to claim 1, wherein the amount of light emitted from a light-emitting unit including the second surface inclined with respect to the first surface, reflected by the lens unit, and reflected by the second surface of the other light-emitting unit and incident on the lens unit is less than when the second surface is not inclined.

3. 2. The light source device according to claim 1, wherein when viewed from the first direction, the distance between normals of the second surfaces of the first and second light-emitting units becomes longer as they are closer to the lens unit.

4. 2. The light source device according to claim 1, wherein the second surfaces of the first and second light emitting units are inclined with respect to the first surface.

5. 5. The light source device according to claim 4, wherein the second surfaces of the first and second light emitting units are inclined in different directions relative to the first surface.

6. 2. The light source device according to claim 1, wherein the lens unit comprises first and second lens arrays each including a plurality of lenses arranged in the first direction, and the first and second lens arrays are arranged at different positions in the second direction.

7. 2. The light source device according to claim 1, wherein the lens unit includes a gradient index lens.

8. 2. The light source device according to claim 1, wherein the reflectance of the second surface is 50% or more.

9. When viewed from the first direction, when the distance between the center of the first light-emitting element in the first light-emitting unit and the center of the second light-emitting element in the second light-emitting unit is T, a line connecting the centers of the first and second light-emitting units is a third line, a center of an incident surface of a lens included in the lens unit is a first point, a line including the first point and parallel to the third line is a fourth line, a distance between the third line and the fourth line is D, a width of the lens unit on the fourth line is W, a line parallel to the second surface of the first light-emitting unit is a fifth line, a line parallel to the second surface of the second light-emitting unit is a sixth line, and angles θ1 and θ2 formed by the third line, and the fifth line and the sixth line, respectively, are θ, 0.95<(W+T+4Dtanθ) / (2W)<18.50 5. The light source device according to claim 4, wherein the following conditions are satisfied:

10. 1.00<(W+T+4Dtanθ) / (2W)<4.58 10. The light source device according to claim 9, wherein the following condition is satisfied:

11. The first and second light-emitting units are a third surface opposite the second surface; 2. The light source device according to claim 1, wherein a member for tilting the second surface relative to the first surface is disposed between the third surface and the first surface of the light-emitting unit in which the second surface is tilted.

12. the second surfaces of the first and second light-emitting units are inclined relative to the first surface, The light source device according to claim 11 , wherein the member is in contact with a portion of the third surface of each of the first and second light emitting units.

13. a plurality of the first light-emitting units and a plurality of the second light-emitting units are arranged in the first direction; 10. The light source device according to claim 9, wherein when the total number of the first light-emitting units and the second light-emitting units is N, the number of the first and second light-emitting units that satisfy the condition is 0.7×N or more.

14. 14. The light source device according to claim 13, wherein the number of the first and second light emitting units that satisfy the condition is 1.0×N.

15. The light source device according to any one of claims 1 to 14; and a developing device for developing the electrostatic latent image formed on the surface to be irradiated by the light source device.

Images