Patent Application
20160282617
1. Technical Field
The present invention relates to a head-up display which allows a viewer positioned within an eyebox to visually recognize a virtual image.
2. Description of the Related Art
Conventionally, a head-up display has been proposed in which light emitted from a back light of a liquid crystal panel is made uniform and is then transmitted through the liquid crystal panel to illuminate the panel (see Japanese Patent Unexamined Publication No. 2007-108429, for example). The head-up display is equipped with a light source, a first condensing lens, a diffusing plate, and a second condensing lens. This configuration allows a reduced unevenness in luminance of the illumination light, with a decrease in luminance of the light being suppressed when it passes through the display.
The present disclosure provides a head-up display which features only a small difference in luminance between the central and corner portions of a virtual image being displayed on the display.
A head-up display according to the present disclosure includes an illuminating device and an optical reflection unit for reflecting light from the illuminating device. The illuminating device includes a plurality of light sources arranged in a first direction and a plurality of first lenses disposed corresponding to the plurality of light sources in an emitting direction of the plurality of light sources. Each of the plurality of first lenses has a first incidence plane and a first emitting plane. At least one of the first incidence plane and the first emitting plane is convex. The illuminating device also includes a second lens disposed in an emitting direction of the plurality of first lenses and a diffusing plate disposed in an emitting direction of the second lens. The second lens has a second incidence plane and a second emitting plane. At least one of the second incidence plane and the second emitting plane has a concave cross-section in the first direction.
The head-up display according to the present disclosure is capable of reducing a difference in luminance between the central and peripheral portions of a virtual image being displayed on the display.
Hereinafter, detailed descriptions of embodiments will be made with reference to the accompanying drawings as deemed appropriate. However, descriptions in more detail than necessary will sometimes be omitted. For example, detailed descriptions of well-known items and duplicate descriptions of substantially the same configuration will sometimes be omitted, for the sake of brevity and easy understanding by those skilled in the art.
Note that the accompanying drawings and the following descriptions are presented to facilitate full understanding of the present disclosure by those skilled in the art and, therefore, are not intended to impose any limitations on the subject matter described in the claims.
Moreover, an XYZ rectangular coordinate system is defined in each of the drawings to be referred to. That is, an X-axis and Y-axis are respectively defined along two sides of either an upper or a lower surface of a liquid crystal panel, while a Z-axis is defined in the direction of the normal line of the emitting surface of the panel. Furthermore, the X-axis direction is referred to as a first direction, while the Y-axis direction orthogonal to the X-axis direction is referred to as a second direction.
Hereinafter, a first embodiment will be described with reference to
In head-up display 100, illuminating device 110 illuminates liquid crystal panel 121 (see
Optical reflection unit 130 is configured with first mirror 131 and second mirror 132. First mirror 131 reflects light, which has been emitted from liquid crystal panel 121, toward second mirror 132. Second mirror 132 reflects the light from first mirror 131 toward windshield 230. The reflecting face of second mirror 132 has a concave shape. Optical reflection unit 130 may not be configured with two mirrors, but with one mirror, or three or more mirrors. Moreover, optical reflection unit 130 may adopt a dioptric system such as a lens.
Housing 140 has opening 141. Opening 141 may be equipped with a transparent cover.
In the case where liquid crystal panel 121 is disposed parallel to illuminating device 110 (see
Moreover, eyebox 600 is commonly larger in the X-axis direction than in the Y-axis direction; therefore, light distribution angle 131 in the X-axis direction is larger than light distribution angle 62 in the Y-axis direction.
As shown in
Each of light sources 111, e.g. a chip-type light-emitting diode (LED), is a light-emitting body to supply the illumination light to liquid crystal panel 121. In the embodiment, the plurality of light sources 111 is disposed in a line in the direction of a long side (the X-axis direction in
First lenses 112 each have a function of receiving light via first incidence plane 112a, with the light having been emitted from corresponding one of light sources 111, and a function of deflecting the thus-received light to emit it as a substantially parallel light. Moreover, first lenses 112 are disposed in an array in one-to-one correspondence with the plurality of light sources 111. Note that, both first incidence plane 112a and first emitting plane 112b of each of first lenses 112 shown in
In the embodiment, the center of light sources 111 and the center of corresponding first lenses 112 are identical to each other; however, it is not always necessary for these centers to be identical.
Second lens 113 has a function of deflecting the emission light from first lenses 112 toward a desired direction. That is, the emission light from each of the plurality of first lenses 112 is deflected by second lens 113 such that the light enters a corresponding region of diffusing plate 114.
Second incidence plane 113a of second lens 113 has a planar shape. Second emitting plane 113b of second lens 113 has a concave shape in the X-axis direction. In the embodiment, second lens 113 has a so-called toroidal shape which is concave in the X-axis direction, i.e. the first direction, and is convex in the Y-axis direction, i.e. the second direction. It is only required for second lens 113 to deflect the emission light from first lenses 112, thereby allowing the light to enter the corresponding region of diffusing plate 114. Therefore, at least one of second incidence plane 113a and second emitting plane 113b is only required to have a concave shape in the X-axis direction.
First lenses 112 and second lens 113 are configured with a transparent material having a predetermined refractive index. The refractive index of the transparent material is about 1.4 to about 1.6, for example. The transparent material may be a resin such as an epoxy resin, a silicon resin, an acryl resin, or a polycarbonate. In the embodiment, a polycarbonate is used in view of heat resistance properties.
Diffusing plate 114 is disposed on the emitting plane side of second lens 113 and on the incidence plane side of liquid crystal panel 121. Moreover, diffusing plate 114 diffuses the light, which has come from second lens 113 and entered every region of diffusing plate 114, and emits the light toward liquid crystal panel 121. This configuration causes the light from the plurality of light sources 111 to be equivalent to light from a surface light source, thereby reducing unevenness in luminance at the inside of eyebox 600. It is only required for diffusing plate 114 to be an optical sheet having a function of diffusing the light. For example, the diffusing plate may be configured with a surface having a bead member or a fine asperity structure, or with a rough surface. Moreover, the diffusing plate may also be a dotted sheet, a translucent milk-white sheet, or the like.
In the embodiment, first lenses 112 are such that the plurality of the lenses is disposed in an array in the X-axis direction. However, it is only required for first lenses 112 to be disposed to correspond to light sources 111;
therefore, the first lenses may be disposed such that the lenses are either separated at intervals from each other or in contact with each other. Moreover, the plurality of first lenses 112 may be integrally formed as a single body.
The emission light from light sources 111 is received by first lenses 112 including first incidence planes 112a and first emitting planes 112b, and is then deflected by second lens 113 including second incidence plane 113a and second emitting plane 113b to the extent to which the light becomes outward-extending rays. Diffusing plate 114 extends the light to the extent to which the light can correspond to the width of eyebox 600, thereby allowing the desired characteristics of light distribution.
Note that, in the case where the length of eyebox 600 in the up-and-down direction is different from that in the right-and-left direction, the required angle of light distribution in the direction of the long side is different from that in the direction of the short side. In such a case, diffusing plate 114 is preferably a member that offers different diffusivity (diffusion angle) in each of the X-axis direction i.e. the first direction and the Y-axis direction i.e. the second direction. Such a member is an anisotropic one. In diffusing plate 114 according to the embodiment, the diffusivity in the Y-axis direction is restricted compared to that in the X-axis direction, which corresponds respectively to the directions of the shorter and longer sides of eyebox 600.
As described above, in the embodiment, head-up display 100 includes illuminating device 110, liquid crystal panel 121, optical reflection unit 130, and housing 140. Illuminating device 110 includes the plurality of light sources 111 disposed in the first direction (X-axis direction in
At least one of first incidence plane 112a and first emitting plane 112b has a convex shape. In addition, illuminating device 110 includes second lens 113 disposed in the emitting direction of first lenses 112, and diffusing plate 114 disposed in the emitting direction of second lens 113. The second lens includes second incidence plane 113a and second emitting plane 113b. In the first direction, the cross-section of at least one of second incidence plane 113a and second emitting plane 113b has a concave shape.
The plurality of first lenses 112 is disposed corresponding respectively to the plurality of light sources 111; at least one of first incidence plane 112a and first emitting plane 112b has the convex shape. Accordingly, the light emitted from first lenses 112 is condensed. Second lens 113 includes second incidence plane 113a and second emitting plane 113b; the cross-section of at least one of second incidence plane 113a and second emitting plane 113b has the concave shape in the first direction. Accordingly, the light emitted from second lens 113 is deflected such that the light has a larger outward emitting angle at a closer position to an end portion of the lens. The light emitted from second lens 113 is extended over the whole region of eyebox 600 via diffusing plate 114 serving as the diffusing member, liquid crystal panel 121, and virtual-image optical system 500. Therefore, at any position within eyebox 600, it is possible to visually recognize virtual image 400 with reduced unevenness in luminance.
Here,
Hereinafter, a second embodiment will be described with reference to
Since head-up display 100 according to the second embodiment has the same basic configuration as that according to the first embodiment, descriptions to be made below will focus on their differences.
In the first embodiment, light sources 111 are disposed such that the center line of each of the light sources is located at the apex of corresponding one of first lenses 112. On the other hand, in the second embodiment, light sources 111 are disposed such that the center line of each of the light sources is located out of position in the X-axis direction from the apex of corresponding one of first lenses 112.
In the second embodiment, light sources 111 are disposed at smaller pitches of arrangement than the pitches of arrangement of the apexes of first lenses 112. That is, the arrangement position of each of light sources 111 is more greatly out of position toward the center with respect to the corresponding one of first lenses 112, at a greater distance away from the center in the X-axis direction. In this configuration, each of light sources 111 is preferably shifted out of position to the extent to which, regarding the emission light from the light source concerned, the amount of the light incident on the corresponding one of first lenses 112 is not smaller than the amount of the light incident on an adjacent one of the first lenses.
As described above, light sources 111 and first lenses 112 are disposed with their respective centers being out of position from each other, which causes the principal ray of the light emitted from each of first lenses 112 to make a larger outward angle at a larger distance from their center to an end portion of them. This configuration can reduce the refracting power of the concave surface of second lens 113, allowing a smaller curvature of the concave surface. Such a smaller curvature results in a reduction in thickness of the second lens. In addition, this makes it possible to reduce costs of formation and materials of second lens 113.
As described above, the first and second embodiments have been described to exemplify the technology disclosed in the present application.
However, the technology is not limited to these embodiments, and is also applicable to embodiments that are subjected, as appropriate, to various changes and modifications, replacements, additions, omissions, and the like. Moreover, the technology disclosed herein also allows another embodiment which is configured by combining the appropriate constituent elements in the first and second embodiments described above.
Thus, other embodiments will be exemplified hereinafter.
In the first and second embodiments, it is only required for liquid crystal panel 121 to be a transmission-type display device which serves as a video display apparatus.
Moreover, the descriptions have been made using the example where the liquid crystal panel is disposed orthogonal to the principal ray of the light source; however, the panel may be disposed and inclined relative to the ray.
A Fresnel shape, which is a discontinuous surface structure, may be used in first incidence planes 112a and first emitting planes 112b of first lenses 112, and second incidence plane 113a and second emitting plane 113b of second lens 113. Such a Fresnel shape allows a reduction in size of display unit 120. In this case, the Fresnel shape may be such that it has different curvatures in different directions, that is, the X-axis direction and the Y-axis direction. Alternatively, the Fresnel shape may be formed only in one axial direction.
Although first lenses 112 have been exemplified by convex lenses, total internal reflection (TIR) lenses may be used for them. This configuration allows the light from light sources 111 to be efficiently emitted toward second lens 113, resulting in improved light utilization efficiency.
Illuminating device 110 may be such that a plurality of rows of light sources 111 and a plurality of rows of first lenses 112 are disposed when viewed from the Y-axis direction, i.e. the direction of the short sides. In this case, the emitting plane of second lens 113 is formed in a concave shape in the Y-axis direction, in the same manner as that in the X-axis direction, i.e. the direction of the long sides. This configuration allows a reduction in the difference in luminance between the center and the periphery of virtual image 400 in head-up display 100 in which virtual image 400 is visually recognized, with the virtual image being extended to a size larger than liquid crystal panel 121.
Although the member for reflecting the emission light from head-up display 100 has been exemplified by windshield 230, the reflecting member is not limited to this. A combiner may also be used as the reflecting member. The light sources have been exemplified by LEDs; however, laser diodes, organic light-emitting diodes, or the like may also be used instead of them.
The technology according to the present disclosure is applicable to projectors with which virtual images are visually recognized. Specifically, the technology is applicable to head-up displays and the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-247614 | Dec 2014 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2015/005163 | Oct 2015 | US |
| Child | 15179230 | US |
