JP2006085975A - Bar shape light guide, lighting unit, and image reading device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rod-shape light guide in which the illuminance of light emitted from an emitting face formed along the longitudinal direction is uniform. <P>SOLUTION: The rod-shape light guide 12 exposes the emitting face 12a from a white case 11 and has a pattern 14 for diffusing and reflecting light at the bottom face opposed to the emitting face. The pattern 14 is formed of white paint or a fine concavo-convex. Further, the end face 15 on the opposite side to the incident side of the rod-shape light guide 12 is made into a cube corner reflector shape. That is, the end face 15 is made into a mountain shape by mirror-finished flat surfaces 15a, 15b, and the flat surfaces 15a, 15b are inclined to an angle in which the incident angle θ of the light which has advanced in parallel with the longitudinal direction of the rod-shape light guide 12 in the light guide 12 becomes smaller than a critical angle. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a rod-shaped light guide that emits light incident from one end face from an emission surface provided along the longitudinal direction, an illumination unit that combines the light guide and a light source, and an image reading unit incorporating the illumination unit. Relates to the device.

  Many rod-shaped light guides used in a part of an image reading apparatus such as a facsimile, a copying machine, and a scanner device have a light emitting unit such as an LED arranged only on one end side of the rod-shaped light guide. In this way, when the light emitting units are arranged only on one end side, the number of the light emitting units is reduced, which is advantageous in terms of heat generation and cost. Ingenuity is required.

  Therefore, in Patent Document 1, the end surface opposite to the incident end surface is used as a mirror surface, and a member having high reflection efficiency is disposed outside the opposite end surface, so that the light is incident from one end surface side and the inside of the light guide is inside. It is disclosed that the light that has reached the end surface on the opposite side is reflected toward the incident side, and by repeating this, all incident light is consumed as irradiation light from the light scattering pattern.

  In Patent Document 2, the end face opposite to the incident end face is a rough face using the cut face as it is, and the manufacturing cost is reduced. On the other hand, the light scattering pattern near the end face is widened to increase the incident light. It is disclosed that the portion is consumed as scattered light before reaching the opposite end face.

Patent Document 3 discloses that light reaching the end surface is scattered by applying a white paint on the end surface opposite to the incident end surface. Further, although it is a technical field unrelated to the rod-shaped light guide, Patent Document 4 discloses a corner cube type reflecting mirror for retroreflection.
JP-A-8-163320 Japanese Patent Laid-Open No. 10-126581 Japanese Patent Laid-Open No. 11-84544 Japanese Patent No. 2954709

  The above-described light guide is housed in a white case so that the exit surface is exposed and set in the image reading apparatus. A highly transparent acrylic resin is used as the material of the light guide, and a low-cost resin is used as the material of the case.

  In addition, since image reading apparatuses such as facsimiles, copying machines, and scanners may become hot during transportation and storage, it is necessary to consider the difference in thermal expansion when placing the light guide in the case. However, when the line illumination device is cooled after being left at a high temperature, the shrinkage rate of the light guide is larger due to the difference in the above materials, and the end surface of the light guide, particularly the end surface opposite to the side where the light emitting unit is provided, A gap is formed between the inner surface of the case. In addition to the difference in thermal expansion coefficient, gaps are likely to occur due to manufacturing errors.

  When the gap is formed in this way, the light that has been reflected and returned to the one end side is transmitted without being reflected by the opposite end face and scattered by the inner surface of the case, and the scattered light is opposite. The light is emitted from the vicinity of the end face on the side. For this reason, the illuminance is abnormally higher in the vicinity of the opposite end face than in other locations. This tendency is remarkable when the end surface opposite to the light emitting unit as disclosed in Patent Document 1 is a mirror surface.

  In addition, the configurations disclosed in Patent Document 2 and Patent Document 3 have poor illumination efficiency.

  In order to solve the above problems, a rod-shaped light guide according to a first aspect of the present invention is a rod-shaped light guide that reflects light incident from one end surface on the inner surface and emits the light from an exit surface provided along the longitudinal direction. The end surface of the light body opposite to the incident surface has a corner cube shape in which the light beam that has traveled in the light guide parallel to the longitudinal direction is totally reflected toward the one end surface.

  Here, the corner cube shape is a shape capable of retroreflecting incident light rays toward the light emitting source as shown in Patent Document 4, and specifically, a mountain shape, a pyramid shape, or a cone shape can be considered. . In the case of the present invention, the surfaces constituting the corner cube shape must be mirror-finished.

  The rod-shaped light guide according to the second aspect of the invention is a rod-shaped light guide that reflects light incident from one end surface on the inner surface and emits the light from an emission surface provided along the longitudinal direction. A cap that covers the end surface opposite to the incident surface is attached as a separate body from the case so that the exit surface is exposed except for the end opposite to the surface.

  As a specific configuration of the second invention, the end portion of the light guide body with the cap attached protrudes from the case, or the entire light guide body with the cap attached is housed in the case. A configuration is mentioned.

  Furthermore, the illumination unit according to the present invention has a light source attached to one end side of the rod-shaped light guide, and the image reading apparatus according to the present invention includes the illumination unit, a line image sensor including a photoelectric conversion element, And an erecting equal-magnification imaging system for condensing the reflected light from the original of the irradiation light from the illumination unit toward the line image sensor.

  According to the rod-shaped light guide according to the first invention, the illuminance from the exit surface provided along the longitudinal direction can be made uniform. In particular, in a conventional light guide in which a light emitting unit is arranged only at one end, the illuminance at the end opposite to the end where the light emitting unit is provided tends to be abnormally high due to shrinkage due to temperature change. However, according to the present invention, the irradiation light that has traveled to the opposite end portion returns to the one end side again without being scattered there, so that the light scattering pattern provided on the bottom surface of the light guide and the like is long. Scatters uniformly in the direction.

  Further, according to the rod-shaped light guide according to the second invention, no gap is formed between the end surface of the rod-shaped light guide and the case even if the temperature changes, so that the illuminance at the end surface opposite to the light emitting unit Can be prevented from becoming extremely high.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of an image reading apparatus incorporating a rod-shaped light guide according to the present invention. In the image reading apparatus, a linear illumination unit 10 is disposed in a recess 1a formed in a frame 1, and photoelectric conversion is performed at the bottom. A sensor substrate 3 having an element (line image sensor) 2 is attached, and the reflected light from the document out of the light emitted from the illumination unit 10 is condensed toward the photoelectric conversion element 2 at the center of the frame 1. A lens array 4 for double imaging is attached, the illumination light emitted from the illumination unit 10 is irradiated onto the document through the document table, and the reflected light is detected by the line image sensor 2 through the lens array 4, thereby the document. Read. In the illustrated example, only one lighting unit 10 is provided, but a pair may be provided.

  A rod-shaped lens array is used as the lens array 4, but a plurality of lens plates are stacked to form an erecting equal-magnification lens, and each lens plate has a large number of minute lenses regularly 2 at a predetermined pitch. A lens array arranged in a dimension may be used.

  2 is an overall view of the illumination unit 10, and FIG. 3 is an exploded perspective view of the illumination unit 10. The illumination unit 10 is a rod-shaped guide obtained by injection molding a transparent resin such as acrylic resin in a white case 11. The light body 12 is accommodated, and a light emitting unit 13 is attached to one end. The light emitting unit 13 holds LEDs of three primary colors on a resin plate, and each of the three primary color LEDs is located on the normal line of the bottom surface of the rod-shaped light guide 12.

  The rod-shaped light guide 12 is provided with a pattern 14 that exposes the emission surface 12a from the white case 11 and scatters / reflects light on the bottom surface facing the emission surface. The pattern 14 is formed from a white paint or fine unevenness.

  Furthermore, the end face 15 on the opposite side to the incident side of the rod-shaped light guide 12 has a corner cube shape. That is, as shown in FIG. 4, the end face 15 is formed into a mountain shape with mirror-finished planes 15 a and 15 b, and the inclination angle of the planes 15 a and 15 b is the longitudinal direction of the rod-shaped light guide 12 in the rod-shaped light guide 12. The incident angle θ of the light beam that has traveled parallel to the angle is inclined to an angle that is smaller than the critical angle. For example, it shape | molds so that the plane 15a and the plane 15b may make 90 degrees.

  FIGS. 5A to 5C are diagrams showing the end face shape of the light guide according to another embodiment. In the embodiment shown in FIG. 5A, the end face 15 has a quadrangular pyramid shape. In the embodiment shown in b), the end face 15 has a conical shape, and in the embodiment shown in (c), the end face 15 has a large number of chevron shapes. As described above, various shapes of the end face 15 are conceivable, but any end face 15 may be mirror-finished so long as the light reaching the end face 15 is totally reflected and returns to the one end side again.

  FIG. 6 is a view showing an end portion of an illumination unit incorporating a light guide according to the second invention. In this second invention, a locking portion is provided at the end of the rod-shaped light guide 12 opposite to the incident side. 16 is formed, and a cap 17 is locked to the locking portion 16 and the end surface 15 is covered with the cap 17. The cap 17 is made of white resin or provided with a reflection layer 18 on the inner surface, and the reflection layer 18 is in close contact with the mirror-finished end surface 15.

  Further, a gap 19 is formed between the end of the case 11 housing the rod-shaped light guide 12 and the cap 17. This gap is for preventing the cap 17 from being strongly pressed against the case 11 when the lighting unit 10 is cooled after being exposed to a high temperature and when the contraction rate of the rod-shaped light guide 12 is larger than that of the case 11. is there.

  FIG. 7 is a view showing another embodiment of the second invention. In this embodiment, the cap 17 is also housed in the case 11. In this case, even if the length of the rod-shaped light guide 12 is shortened by cooling, the cap 17 is fixed to the end portion of the rod-shaped light guide 12. It is possible to prevent a disadvantage that a gap is formed between the inner surface and light is diffusely reflected in the gap and the illuminance at the end is abnormally high.

  The rod-shaped light guide according to the present invention is effectively used as an image reading apparatus such as a copying machine or a facsimile.

Sectional drawing of the image reading apparatus incorporating the rod-shaped light guide which concerns on this invention Overall view of an illumination unit incorporating a rod-shaped light guide according to the first invention Exploded perspective view of the lighting unit Enlarged view of the corner cube-shaped end of the rod-shaped light guide (A)-(c) is a figure which shows the edge part of the rod-shaped light guide which concerns on another Example. The figure which shows the edge part of the illumination unit incorporating the light guide which concerns on 2nd invention. The figure which shows another Example of 2nd invention

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Frame, 1a ... Concave part, 2 ... Photoelectric conversion element (line image sensor), 3 ... Sensor substrate, 4 ... Lens array, 10 ... Illumination unit, 11 ... White case, 12 ... Bar-shaped light guide, 12a ... Output surface , 13 ... light emitting unit, 14 ... light scattering pattern, 15 ... end face, 15a, 15b ... plane constituting the end face, 16 ... locking portion, 17 ... cap, 18 ... reflective layer, 19 ... gap.

Claims (6)

In the rod-shaped light guide that reflects the light incident from one end surface on the inner surface and emits the light from the exit surface provided along the longitudinal direction, the end surface opposite to the entrance surface of the light guide is inside the light guide. A rod-shaped light guide having a corner cube shape in which a light beam traveling parallel to the longitudinal direction is totally reflected toward the one end face. 2. The rod-shaped light guide according to claim 1, wherein the corner cube shape has a mirror-finished mountain shape, a pyramid shape, or a cone shape. In a rod-shaped light guide that reflects light incident from one end surface on the inner surface and emits the light from an exit surface provided along the longitudinal direction, the light guide has an exit surface except for an end opposite to the entrance surface. A rod-shaped light guide, wherein the cap is housed in the case so as to be exposed, and a cap that covers the end surface opposite to the incident surface is attached separately from the case. The rod-shaped light guide according to claim 3, wherein the end of the light guide attached with the cap protrudes from the case, or the entire light guide with the cap attached is accommodated in the case. A rod-shaped light guide characterized by that. An illumination unit comprising a light source attached to one end of the rod-shaped light guide according to claim 1. An illumination unit according to claim 5, a line image sensor comprising a photoelectric conversion element, and an erecting equal magnification for condensing reflected light from a document out of irradiation light from the illumination unit toward the line image sensor. An image reading apparatus comprising an image system.