Lighting device and image reading device using the same

Abstract

To provide a lighting device and an image reading device to ensure a lighting area in a sub-scanning direction with a stable amount of light.SOLUTION: A lighting device includes: a light source unit in which a plurality of light-emitting elements are arranged in a main scanning direction and mounted on a substrate; an incident surface through which light is incident from the light source unit; and a light guide composed of an emission surface having a diffusion structure for emitting a light flux incident from the incident surface. In a sub-scanning cross-section, a diffusion angle in the sub-scanning direction varies depending on a region of the emission surface having the diffusion structure.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an illumination device for illuminating a document and an image reading device using the same.

Background Art

[0002] In recent years, illumination devices used in image reading devices such as copiers, image scanners, and multifunction printers (MFPs) that illuminate a document surface and sequentially perform linear image reading have been invented with many techniques of arranging LEDs (Light Emitting Diodes) in an array as a light source and further using a light guide to efficiently guide the light from the light source to the document surface to form a linear illumination device.

[0003] Particularly, in the case of an image reading device using a reduction optical system with a deep subject depth, the reading position may vary due to minute deviations in the attachment position and angle of a mirror or an imaging optical system arranged between the optical path lengths. Recently, due to the thermal influence caused by an increase in the number of sheets passed and the influence of the installation environment and transportation environment of the device, there are also cases where the reading position varies further. Therefore, it is required to secure an illumination area in the sub-scanning direction (the direction perpendicular to the direction in which the array direction of the light source is the main scanning direction) with more stable light quantity.

[0004] For this reason, the following illumination devices have been proposed for the above problems (see Patent Documents 1 and 2).

[0005] The illumination device described in Patent Document 1 has a diffusion structure provided on the light emitting surface of the light guide, and a light emitting device has been proposed in which the light emitted from the light guide is illuminated as diffused light toward the document surface.

[0006] The illumination device described in Patent Document 2 employs a non-circular arc-shaped surface in which the inclination of the tangent line in the sub-scanning cross-section continuously changes as an emission surface for emitting illumination light in a first direction (for direct illumination) and a second direction (for illumination via a reflector), and changes the refractive power of the region through which the light rays pass.

Prior Art Documents

Patent Document

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, in the method of Patent Document 1, the illuminance distribution in the main scanning direction can achieve an appropriate illuminance distribution by changing the diffusivity of the emission surface at the center and the ends in the main scanning direction. However, for the illuminance distribution in the sub-scanning direction, since the diffusivity of the emission surface is isotropically diffused in the sub-scanning direction, it is very difficult to achieve an appropriate illuminance distribution while maintaining the light amount and further expand the stable illumination area, and problems remain.

[0009] In the method of Patent Document 2, the effect is achieved by appropriately setting the refractive power of the region through which the luminous flux of the illumination light in the first direction (for direct illumination) and the second direction (for illumination through a reflector) passes. However, changing the refractive power in the region through which the illumination light directly illuminating the original document surface passes is not disclosed, and there are also problems in order to further expand the illumination area in the sub-scanning direction with a stable light amount.

[0010] The present invention has been made in view of the above problems, and an object thereof is to provide an illumination device and an image reading device capable of securing an illumination area in the sub-scanning direction with a stable light amount.

Means for Solving the Problems

[0011] In order to achieve the above object, the lighting device of the present invention is a lighting device including a light source unit arranged on a substrate with a plurality of light emitting elements arranged in the main scanning direction, an incident surface on which light is incident from the light source unit, and a light guide formed of an emission surface having a diffusion structure that emits a light beam incident from the incident surface, wherein in a sub-scanning cross section, the diffusion angle in the sub-scanning direction is different depending on the region of the emission surface having the diffusion structure.

Effect of the Invention

[0012] According to the present invention, it is possible to provide a lighting device and an image reading device capable of securing a lighting area in the sub-scanning direction with stable light quantity.

Brief Description of the Drawings

[0013]

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Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0015] [First Embodiment] FIG. 1 is a schematic main part diagram showing the basic configuration of an image reading apparatus equipped with an illumination device according to Embodiment 1 of the present invention. An integrated scanning optical system unit (hereinafter also referred to as a “carriage”) 7 in the figure has a reading means (line sensor or image sensor) 5 that reads a light beam from a document 1 illuminated by an illumination device 3 that illuminates the document 1 placed on a document table glass (document table) 2. Further, it has a plurality of folding mirrors 4a to 4d that guide the light beam from the document 1 to the reading means 5, an imaging optical system (imaging lens) 6 that forms an image of the light beam based on the image information from the document 1 on the surface of the reading means 5, and the like.

[0016] The integrated scanning optical system unit 7 configured as described above is scanned in the direction of arrow A (sub-scanning direction) shown in the figure by a drive motor (sub-scanning motor) 8 as a drive means.

[0017] Each element constituting the integrated scanning optical system unit 7 scans the document without changing the relative positional relationship of each element.

[0018] In the figure, the plurality of folding mirrors consist of a first folding mirror 4a, a second folding mirror 4b, a third folding mirror 4c, and a fourth folding mirror 4d. Each mirror is arranged such that the light beam from the document 1 is incident from the first folding mirror 4a to the second folding mirror 4b, from the second folding mirror 4b to the third folding mirror 4c, and from the third folding mirror 4c to the fourth folding mirror 4d. Then, the light beam incident on the fourth folding mirror 4d is imaged on the surface of the reading means 5 by the imaging optical system 6.

[0019] In such a configuration, the image information of the document read by the reading means 5 is sent as an electrical signal to a specific image processing unit (not shown), and after being subjected to specific signal processing, it is output. Further, the image reading apparatus 9 also has a power supply unit (not shown) for driving this apparatus.

[0020] (Illumination device) The illumination device according to this embodiment will be described in more detail. FIG. 2 is a sub-scanning cross-sectional view of the illumination device 3 according to Embodiment 1. The illumination device 3 is composed of an LED array in which a plurality of white LEDs 3a as light-emitting elements are arranged in the main scanning direction, a substrate 3b, and a light guide 10, and is arranged on both sides at positions substantially symmetric with respect to the reading optical axis.

[0021] A light source unit 3c is configured by arranging LED arrays formed by arranging a plurality of LEDs 3a in a row in the main scanning direction on the substrate 3b. Further, the light guide 10 is composed of a member made of an optically synthetic resin such as plastic.

[0022] (Light guide panorama) The light guide 10 constituting the illumination device 3 will also be described with reference to FIG. 2.

[0023] In a cross-section perpendicular to the arrangement direction of the light sources arranged in the main scanning direction, the light beam from the light source unit 3c is incident from the incident surface 11, guided between the total reflection side surfaces 13 and 14, and then emitted from the emission surface 12 in the direction of the document surface.

[0024] The light beam incident from the incident surface 11 of the light guide 10 is divided into the following light beams (described by arrows).

[0025] A light beam directly heading for the emission surface 12, a light beam heading for the emission surface 12 through total reflection at the total reflection side surface 13, and a light beam heading for the emission surface 12 through total reflection at the total reflection side surface 14.

[0026] In particular, the light beam traveling toward the emission surface 12 via total reflection at the total reflection side surface 13 mainly passes through the region of the emission surface 12a, and the light beam traveling toward the emission surface 12 via total reflection at the total reflection side surface 14 mainly passes through the region of the emission surface 12b.

[0027] (Light guide body emission surface) The emission surface of the light guide body according to this embodiment will be described in more detail. FIG. 3 is a perspective view of the light guide body of the lighting device according to the first embodiment.

[0028] The light guide body emission surface 12 is configured in an arc shape formed convex outward. By making it convex, it is possible to converge the light beam within an appropriate range of the original document surface while increasing the light collection efficiency. Furthermore, the emission surface 12 has a diffusion structure, and the diffusion angle varies depending on the region of the emission surface.

[0029] As shown in FIG. 13, the diffusion angle is defined as the full angle representing the position at which the illuminance of the diffused light obtained by diffusing the parallel light beam incident perpendicularly to the diffusion structure 101 becomes half of the illuminance.

[0030] As described above, the light beam traveling toward the emission surface 12 via total reflection at the total reflection side surface 13 mainly passes through the region of the emission surface 12a, and the light beam traveling toward the emission surface 12 via total reflection at the total reflection side surface 14 mainly passes through the region of the emission surface 12b, and the diffusion angles are made different in those regions 12a and 12b.

[0031] By making the diffusion angles different, it becomes possible to control the diffusion degree of each passing light beam and to control the illuminance profile of the original document surface. Therefore, it becomes possible to secure an illumination area in the sub-scanning direction with stable light quantity.

[0032] In particular, in the lighting device in which the light guide body 10 is arranged substantially symmetrically with respect to the reading optical axis as in the first embodiment, the diffusion angle of the region 12a farther from the region 12b near the reading optical axis is made smaller.

[0033] This is because the light beam passing through the total reflection side surface 13 becomes a light beam that irradiates the area on the document surface mainly from the reading optical axis to the area on the light guide body arrangement side. By reducing the divergence angle of this area 12a and increasing the light quantity, it becomes possible to secure an illumination area in the sub-scanning direction with a stable light quantity as an illumination device.

[0034] Fig. 4 shows the illuminance profiles of Embodiment 1 and a conventional example (when there is no change in the diffusion area). The upper part shows the illuminance profile of the illumination device, and the lower part shows the illuminance profile of only the light beam from the total reflection side surface 13. Also, the stable area (the illumination area with a stable light quantity) shown here indicates the area within 95% of the peak light quantity.

[0035] The illuminance profile of the light beam from the total reflection side surface 13 has increased the light quantity in the area from the reading optical axis to the light guide body arrangement side by passing through the area with a small divergence angle as described above. As a result, the light quantity in the area from the reading optical axis to the light guide body arrangement side also increases as an illumination device, the width of the stable area expands, and in the conventional example, the stable area is 3.0 mm wide, while in Embodiment 1, it is 4.8 mm, indicating that it is sufficiently secured.

[0036] Also, regarding the divergence angle of the emission surface 12, if the divergence angle of the area 12b closest to the reading optical axis is θn and the divergence angle of the area 12a farthest away is θf, it is configured to satisfy the following conditional expression. θf / θn ≦ 0.5 The above conditional expression is a conditional expression that defines the change ratio of the divergence angle. If it is equal to or greater than the conditional expression, the effective use of the different divergence angles cannot be achieved.

[0037] In Embodiment 1, specifically, θf = 10° and θn = 21° are adopted for each divergence angle, and θf / θn = 0.476, which is satisfied.

[0038] (Diffusion structure of the emission surface) The diffusion structure of the emission surface according to Embodiment 1 will be described in more detail. Fig. 5 is a shape diagram of the diffusion structure body provided on the light guide body emission surface according to this embodiment.

[0039] As shown in FIG. 5, the diffusion structures 51 and 52 have periodic fine structures in the main scanning direction and the sub-scanning direction.

[0040] In the main scanning direction (LED array direction), it is composed of a plurality of types of concavo-convex structures and is continuously connected. In the sub-scanning direction, the concavo-convex structures arranged in the main scanning direction are formed by shifting the concavo-convex structures with a uniform width. Thus, it is an anisotropic diffusion structure with different diffusion angles in the main scanning direction and the sub-scanning direction.

[0041] The diffusion in the main scanning direction is mainly used to improve the angular characteristics on the original document surface in the main scanning direction, that is, to improve the unevenness of illuminance in the main scanning direction. Therefore, a larger diffusion angle than that in the sub-scanning direction is required, so it is an anisotropic diffusion structure.

[0042] Also, the diffusion angles in the sub-scanning direction are made different in the regions 12a and 12b of the emission surface. This is achieved by making the intervals (pitches) in the sub-scanning direction of the concavo-convex structures different, as shown in the diffusion structures 51 and 52. By narrowing the interval (pitch) like 52 compared to 51 of the diffusion structure, the diffusion angle can be made smaller.

[0043] In this embodiment, specifically, the following numerical values are adopted.

[0044] The intervals (pitches) of the 14 types of concavo-convex structures in the main scanning direction are uniform at 42 μm, and the heights of the 14 types are in the range of 15 μm to 42 μm. The interval (pitch) in the sub-scanning direction of the emission surface 12a is 7 μm, and the interval (pitch) in the sub-scanning direction of the emission surface 12b is 3.5 μm.

[0045] Also, the diffusion structure of this embodiment is achieved by performing laser processing on an injection-moldable mold.

[0046] If it is such a periodic fine structure, it is possible to make the diffusion angles different even within the same plane, and it is possible to obtain the effects as in this embodiment.

[0047] In the following embodiments to be described later, the diffusion structure has a similar configuration, and the diffusion angle is changed by changing the interval (pitch) in the sub-scanning direction of the concavo-convex structure.

[0048] [Second Embodiment] FIG. 6 is a schematic diagram of a main part showing the basic configuration of an image reading apparatus equipped with the lighting device according to Embodiment 2 of the present invention. Since the image reading apparatus is only a change in the lighting system part shown in FIG. 7, the description thereof is omitted.

[0049] (Lighting Device) As shown in FIG. 7, the lighting device 23 is composed of a plurality of white LEDs 3a as light emitting elements arranged in a row in the main scanning direction, a substrate 3b, and a light guide 30, and is arranged on both sides at positions substantially symmetric with respect to the reading optical axis.

[0050] A light source unit 3c is configured by arranging a plurality of LED columns formed by arranging a plurality of LEDs 3a in a row in the main scanning direction on the substrate 3b. The light guide 30 is composed of a member made of an optically synthetic resin such as plastic.

[0051] (Light Guide Overview) The light guide 30 constituting the lighting device 23 will also be described with reference to FIG. 7.

[0052] In a cross section perpendicular to the arrangement direction of the light sources arranged in the main scanning direction, the light beam from the light source unit 3c is incident from the incident surface 31, and the light beam guided between the total reflection side surfaces 33 and 34 is deflected by the total reflection surface 35 and emitted from the emission surface 32 in the direction of the original document surface.

[0053] The light beam incident from the incident surface 31 of the light guide 30 is divided into the following light beams (described by arrows).

[0054] A light beam directly heading for the total reflection surface 35, a light beam heading for the total reflection surface 35 through total reflection at the total reflection side surface 33, and a light beam heading for the total reflection surface 35 through total reflection at the total reflection side surface 34.

[0055] In particular, the light beam that reaches the total reflection surface 35 through total reflection on the total reflection side surface 33 and heads toward the emission surface 32 mainly passes through the region of the emission surface 32a, and the light beam that reaches the total reflection surface 35 through total reflection on the total reflection side surface 14 and heads toward the emission surface 32 mainly passes through the region of the emission surface 32b.

[0056] (Light guide body emission surface) The emission surface of the light guide body according to the second embodiment will be described in more detail. FIG. 8 is a perspective view of the light guide body of the lighting device according to the second embodiment.

[0057] The light guide body emission surface 32 is configured in an arc shape that is convex outward as in the first embodiment. Further, the emission surface 32 has a diffusion structure, and the diffusion angle varies depending on the region of the emission surface.

[0058] As described above, the light beam that is deflected at the total reflection surface 35 through total reflection on the total reflection side surface 33 and heads toward the emission surface 32 mainly passes through the region of the emission surface 32a, and the light beam that is deflected at the total reflection surface 35 through total reflection on the total reflection side surface 34 and heads toward the emission surface 32 mainly passes through the region of the emission surface 32b. Similar to the first embodiment, the diffusion angles are made different in the regions 32a and 32b, and the diffusion angle in the region 32a is made smaller.

[0059] This has the same effect as in the first embodiment. The light beam passing through the total reflection side surface 33 becomes a light beam that mainly irradiates the region on the light guide body arrangement side from the reading optical axis on the original surface. By reducing the diffusion angle of this region 32a and increasing the light amount, it becomes possible to secure an illumination region in the sub-scanning direction with a stable light amount as a lighting device.

[0060] FIG. 9 shows the illuminance profiles of the second embodiment and a conventional example (when there is no change in the diffusion region). The upper part shows the illuminance profile of the lighting device, and the lower part shows the illuminance profile of only the light beam from the total reflection side surface 33.

[0061] The illuminance profile of the light beam from the total reflection side surface 33 increases the amount of light in the region on the light guide arrangement side from the reading optical axis by passing through the region with a small divergence angle as described above. As a result, as an illumination device, the amount of light in the region on the light guide arrangement side from the reading optical axis also increases, the width of the stable region widens, and in the conventional example, the stable region has a width of 3.4 mm, while in the first embodiment, it is 5.0 mm, indicating that it is sufficiently ensured.

[0062] In the second embodiment, specifically, since each divergence angle is the same as that in the first embodiment, θf = 10° and θn = 21° are adopted, and θf / θn = 0.476, which is satisfactory.

[0063] [Third Embodiment] FIG. 10 is a sub-scanning cross-sectional view of the illumination device according to the third embodiment of the present invention. Since the image reading device is the same as that in the second embodiment, the description thereof is omitted.

[0064] (Overall view of the light guide) The light guide 40 constituting the illumination device 23 will also be described with reference to FIG. 10.

[0065] In a cross-section perpendicular to the arrangement direction of the light sources arranged in the main scanning direction, the light beam from the light source unit 3c is incident from the incident surface 41, and the light beam guided between the total reflection side surfaces 43 and 44 is deflected by the total reflection surface 45 and emitted from the emission portion 42 in the direction of the original document surface.

[0066] The light beam incident from the incident surface 41 of the light guide 40 is divided into the following light beams (described with arrows).

[0067] The light beam directly heading for the total reflection surface 45, the light beam heading for the total reflection surface 45 via total reflection on the total reflection side surface 43, and the light beam heading for the total reflection surface 45 via total reflection on the total reflection side surface 44.

[0068] Particularly, the light beam that reaches the total reflection surface 45 through total reflection on the total reflection side surface 43 and heads toward the light emitting portion 42 mainly passes through the region of the emission plane 42a, and the light beam that reaches the total reflection surface 45 through total reflection on the total reflection side surface 44 and heads toward the light emitting portion 42 mainly passes through the region of the emission plane 42c.

[0069] (Light guide body light emitting portion) The light emitting surface of the light guide body according to Embodiment 3 will be described in more detail. FIG. 11 is a perspective view of the light guide body of the lighting device according to Embodiment 3.

[0070] The light guide body light emitting portion 42 is configured in a convex shape on the outside connected by three planes. Further, the light emitting portion 42 has a diffusion structure on each plane, and the diffusion angles of each plane are different.

[0071] As described above, the light beam that is deflected at the total reflection surface 45 and heads toward the light emitting portion 42 through total reflection on the total reflection side surface 43 mainly passes through the region of the emission plane 42a, and the light beam that is deflected at the total reflection surface 45 and heads toward the light emitting portion 42 through total reflection on the total reflection side surface 44 mainly passes through the region of the emission plane 42b. The diffusion angles are made different in the regions 42a, 42b, and 42c, and the diffusion angles are decreased in the order of the regions 42c, 42b, and 42a.

[0072] This is the same as the effect in Embodiment 1. The light beam passing through the total reflection side surface 43 becomes a light beam that irradiates mainly the region on the light guide body arrangement side from the reading optical axis on the original document surface. By decreasing the diffusion angle of this region 42a and increasing the light quantity, it becomes possible to secure an illumination region in the sub-scanning direction with a stable light quantity as a lighting device.

[0073] Also, an intermediate region is created in the region 42b so that the diffusion angle is gradually changed between the regions 42a and 42c, and it is adopted as an intermediate diffusion angle region.

[0074] FIG. 11 shows the illuminance profiles of Embodiment 3 and the conventional example (when there is no change in the diffusion region). The upper part shows the illuminance profile of the lighting device, and the lower part shows the illuminance profile of only the light beam from the total reflection side surface 43.

[0075] The illuminance profile of the light beam from the total reflection side surface 43 increases the amount of light in the area on the light guide body arrangement side from the reading optical axis by passing through the region with a small diffusion angle as described above. As a result, also as an illumination device, the amount of light in the area on the light guide body arrangement side from the reading optical axis increases, the width of the stable region expands, and in the conventional example, for a width of 3.4 mm, in the first embodiment, it is 5.4 mm, indicating that it is sufficiently ensured.

[0076] In the third embodiment, specifically, the respective diffusion angles are θf = 6° and θn = 24°, and θf / θn = 0.25, which is satisfactory.

Explanation of Signs

[0077] 1 Document 2 Document table glass 3, 23 Illumination device 4 Mirror 5 Reading means 6 Imaging optical system 7 Integrated scanning optical system unit 8 Driving motor 9 Image reading device 10, 30, 40 Light guide body 11, 31, 41 Incident surface 12, 32, 42 Exit surface (exit part) 13, 14, 33, 34, 43, 44 Total reflection side surface 35, 45 Total reflection surface 51, 52 Microfabricated shape

Claims

1. A lighting device comprising: a light source unit arranged on a substrate with a plurality of light emitting elements arranged in the main scanning direction; an incident surface on which light from the light source unit is incident; a light guide formed by an exit surface having a diffusion structure for emitting a light beam incident from the incident surface, wherein: In a sub-scanning cross section, the diffusion angle in the sub-scanning direction varies depending on the region of the exit surface having the diffusion structure.

2. The lighting device according to claim 1, wherein the light guide is configured to be arranged substantially symmetrically with respect to the reading optical axis.

3. The lighting device according to claim 1 or 2, wherein the diffusion angle in the sub-scanning direction of the light guide exit surface is smaller in a region farther from the reading optical axis than in a region closer to the reading optical axis.

4. When the diffusion angle in the sub-scanning direction of the light guide exit surface is θn for the region closest to the reading optical axis and θf for the region farthest from the reading optical axis, θf / θn ≤ 0.5 The lighting device according to any one of claims 1 to 3, characterized by satisfying the above condition.

5. The lighting device according to any one of claims 1 to 4, wherein the diffusion structure of the exit surface is an anisotropic diffusion structure that diffuses the light beam passing through the exit surface wider in the main scanning direction than in the sub-scanning direction.

6. The lighting device according to any one of claims 1 to 5, wherein the diffusion structure is a periodic fine structure.

7. The lighting device according to any one of claims 1 to 6, wherein the diffusion angle in the sub-scanning direction of the diffusion structure is varied by changing the interval of the pitch in the sub-scanning direction of the periodic fine structure.

8. The lighting device according to any one of claims 1 to 7, wherein the shape of the light guide includes first and second total reflection side surfaces that totally reflect a part of the light beam from the incident surface, a reflection surface that deflects a part of the light beam incident from the incident surface and a part of the light beam totally reflected by the total reflection side surfaces, and an exit surface from which the light beam from the reflection surface is emitted to the irradiated area.

9. In the light beam reaching the exit surface of the light guide, the light beam reaching the light beam passing region away from the reading optical axis is the light beam reflected through the first total reflection side surface immediately before reaching the reflection surface.

10. The lighting device according to any one of claims 1 to 9, wherein the periodic fine structure of the light guide is formed into a mold by laser processing and molded by injection molding.

11. An image reading apparatus, comprising: the lighting device according to any one of claims 1 to 10; a platen; reading means; and an imaging optical system that forms an image of a reading light beam reflected from the original surface on the reading means.

Images