JP2019069773A - Head-up display - Google Patents

Abstract

To provide a head-up display with an optical element having a Fresnel structure, capable of forming an eye box appropriately without making a viewer feel oppressed or uncomfortable.SOLUTION: A head-up display includes: a light source unit for emitting light constituting a display image; and an optical element on which the light emitted from the light source unit is made incident from above and which is disposed in a direction the same as a tilt direction of a windshield of a moving body. By reflecting the light constituting the display image on the optical element, the display image is visually recognized as a virtual image. The optical element has a half-mirror having a Fresnel structure formed in one flat plate to reflect the light from the light source unit by the half-mirror. To the half-mirror, such the Fresnel structure that a center of a free-form surface constituting a base of the Fresnel structure is not located at a center of the half-mirror, is applied. In the head-up display, a relative position between the light source unit and the optical element is set so that the light reflected by the half-mirror is not totally reflected and is emitted to the outside of the optical element.SELECTED DRAWING: Figure 8

Description

  The present invention relates to the technical field of visualizing an image as a virtual image.

  2. Description of the Related Art Conventionally, a display device such as a head-up display for visually recognizing an image as a virtual image is known. Generally, in a head-up display, a half mirror called a combiner (combiner) is used to make a driver visually recognize a small screen (real image) such as a small liquid crystal display as an enlarged virtual image. For example, Patent Documents 1 and 2 propose a combiner using a Fresnel structure.

Patent No. 4776669 gazette JP, 2011-191715, A

  By the way, when a general concave half mirror is used as a combiner, if the position of a real image is fixed, a virtual image observable area (hereinafter referred to as an “eye box”) formed by the combiner is the driver's. The installation angle of the combiner required to form near the head is automatically determined. For example, in the case where light constituting a real image is made incident from above to a combiner installed in front of the driver, the installation angle of the combiner is inclined in the direction opposite to the inclination of the windshield. In this case, the eyebox is formed at an appropriate position (near the head of the driver), but the presence of the combiner is large, which may give the driver a sense of oppression or discomfort. Therefore, if the combiner is inclined in the same direction as the windshield, the sense of pressure and discomfort to the combiner will be reduced considerably, but the eyebox will not be formed at an appropriate position (eg an eyebox will be formed on the driver's abdomen) ), The driver can not see the virtual image.

  Here, when using a combiner in which the center of the Fresnel pattern is disposed at a position different from the center of the combiner as described in Patent Document 2 described above, the angle formed between the incident light and the reflected light is kept constant. It is considered possible to change the relative angle with the combiner while keeping the same. Therefore, it is considered that, by using such a combiner, an eyebox can be appropriately formed near the driver's head even if the combiner is inclined in the same direction as the windshield. However, the combiner which applied the Fresnel structure may not be emitted to the outside of the combiner by totally reflecting the light reflected by the reflective surface inside the substrate in the combiner because the reflective surface exists in the substrate instead of the surface. . Patent Literatures 1 and 2 do not consider such a defect.

  The problems to be solved by the present invention are as described above. An object of the present invention is to appropriately form an eye box in a head-up display having an optical element of a Fresnel structure without giving a sense of oppression or a sense of discomfort to a viewer.

  The invention according to claim 1 is a display device, which recognizes a display image as a virtual image by reflecting a light source unit emitting light forming a display image and a part of the light emitted by the light source unit. A mirror having a Fresnel structure, a substrate provided facing the mirror on the light incident surface side to the mirror, and light from the light source unit reflected by the mirror is totally reflected by the substrate The light source unit, the mirror, and an optical system including the substrate.

It is the figure which showed the general head up display roughly. The figure for demonstrating the relationship between the installation angle of a combiner, and the position of an eye box is shown. The figure for demonstrating the basic concept of a present Example is shown. The figure for demonstrating that a fault is solvable is shown by using the combiner to which the offset Fresnel structure was applied. The figure for demonstrating the subject 1 concretely is shown. The figure for demonstrating the subject 2 concretely is shown. The figure for demonstrating the conditions of the incident angle for making an injection angle less than a total reflection angle is shown. The figure for demonstrating the optimal example of arrangement | positioning of the combiner which concerns on 1st Example is shown. The figure for demonstrating the optimal example of arrangement | positioning of the combiner which concerns on 2nd Example is shown.

  In one aspect of the present invention, a light source unit for emitting light forming a display image, and an optical component from which light from the light source unit is incident from above and disposed in the same direction as the inclination direction of the windshield of the movable body A head-up display that includes an element and causes the light to constitute a display image to be reflected by the optical element to make the display image visible as a virtual image, wherein the optical element has a Fresnel structure in one flat plate A half mirror is formed, the light from the light source unit is reflected by the half mirror, and the half mirror is applied with a Fresnel structure in which the center of the free-form surface that is the origin of the Fresnel structure is not located at the center of the half mirror. And the relative position between the light source unit and the optical element is set so that the light reflected by the half mirror is emitted to the outside of the optical element without being totally reflected. It is.

  The above-mentioned head-up display is installed on a moving body, and is used to make the display image visible as a virtual image by reflecting the light constituting the display image emitted from the light source by an optical element (for example, a combiner). Ru. The light from the light source unit is incident from above on the optical element, and the optical element is disposed in the same direction as the tilt direction of the windshield of the movable body. Further, in the optical element, a half mirror of a Fresnel structure is formed in one flat plate, and the half mirror reflects light from the light source unit. The half mirror has a Fresnel structure in which the center (for example, the vertex) of the free-form surface that is the origin of the Fresnel structure is not located at the center of the half mirror. In the head-up display, the relative position between the light source unit and the optical element is set so that the light reflected by the half mirror is emitted to the outside of the optical element without being totally reflected inside the optical element. In other words, the light from the light source unit is incident on the optical element at an incident angle at which the light reflected by the half mirror is emitted to the outside without being totally reflected.

  According to the above head-up display, by using an optical element to which a Fresnel structure is applied in which the center of the free-form surface is not positioned at the center of the half mirror, the optical element on which light from the light source is incident from above The eye box can be properly formed near the head of the observer even if it is inclined in the same direction as in FIG. Therefore, the eye box can be formed at an appropriate position without giving a sense of oppression or a sense of discomfort to the observer. Further, according to the above-described head-up display, the relative position between the light source unit and the optical element is set so that the light reflected by the half mirror is emitted to the outside without being totally reflected. It is possible to properly emit light and to appropriately avoid such a problem that a part of the virtual image can not be viewed. Therefore, the entire surface of the optical element can be effectively used.

In one aspect of the above-described head-up display, an incident angle at which light from the light source unit is incident on the optical element is “θ _in ”, and a refractive index of a substrate provided outside the half mirror in the optical element is Assuming that "n", the focal length of the free-form surface is "f", and the distance between the position where the light from the light source portion is incident on the half mirror and the center of the free-form surface is "OFS" The relative position between the light source unit and the optical element is set such that θ _in satisfies the condition of the following expression.

θ _in > sin ⁻¹ [n · sin {2 tan ⁻¹ (OFS / 2 f) −sin ⁻¹ (1 / n)}]
In another aspect of the above-described head-up display, light from the light source unit is incident on the optical element such that the change in transmittance of the substrate provided outside the half mirror is equal to or less than a predetermined value. The relative position between the light source unit and the optical element is set such that the range of the incident angle is used.

  In this aspect, the relative position between the light source unit and the optical element is set such that a region having a small incident angle dependency of the transmittance of the substrate is used. This makes it possible to appropriately suppress the occurrence of luminance change (uneven luminance) in the plane of the optical element.

  In another aspect of the above-described head-up display, the light source unit emits P-polarized light. Thereby, the incident angle dependency of the transmittance (interface reflectance) of the substrate can be reduced as compared with the case of using S-polarization.

  In another aspect of the above-described head-up display, the light source unit includes an exit pupil enlarging element that enlarges an exit pupil of light emitted from the light source, and the light from the exit pupil expanding element is used as the optical element. I aim at and emit. When an LCD or CRT is used, light is diffused at a large angle, but in the configuration in which light from a projector or the like is expanded by the exit pupil expansion element, narrow control of the diffusion angle can be easily realized.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
<Basic concept>
First, before describing the contents of the present embodiment, the basic concept of the present embodiment will be described.
FIG. 1 is a view schematically showing a general head-up display. In the head-up display, the screen (real image RI) to be displayed is formed, and the light constituting the real image RI is reflected by the combiner 10 to make the driver visually recognize the virtual image VI corresponding to the real image RI. For example, the real image RI corresponds to a screen displayed by a small liquid crystal display or an image formed on a screen by a projector (in one example, an image formed by an exit-pupil expander (EPE)). . The small liquid crystal display, the projector, and the screen correspond to an example of the “light source unit” in the present invention.

  In order to visually recognize the virtual image VI brightly even in the daytime, it is sufficient to increase the light emission luminance of the real image RI. However, since the power consumption and the device cost increase, a method of increasing the light utilization efficiency is usually used. In a general head-up display, in order to increase the light utilization efficiency, the light emitting angle of the real image RI is limited and the concave half of the combiner 10 is used as the combiner 10 so that the light reflected by the combiner 10 is collected on the observer's head. The focal length of the concave half mirror is set to an appropriate value using a mirror. An area indicated by reference numeral EB in FIG. 1 is a virtual image observable area (eye box) formed in the vicinity of the head of the observer.

  FIG. 2 shows a diagram for explaining the relationship between the installation angle of the combiner 10 and the position of the eye box EB formed by the combiner 10. When a (concave) half mirror as shown in FIG. 1 is used as the combiner 10, the combiner necessary for forming the eye box EB near the driver's head when the position of the real image RI is fixed. The installation angle of 10 is decided automatically. For example, as shown in FIG. 2 (a), when light constituting the real image RI is made incident from above to the combiner 10 installed in front of the driver, the installation angle of the combiner 10 is opposite to the inclination of the windshield. It will lean in the direction. In this case, the eye box EB1 is formed at an appropriate position (near the head of the driver), but the presence of the combiner 10 is large, which may give the driver a sense of oppression or discomfort. Therefore, as shown in FIG. 2 (b), when the combiner 10 is inclined in the same direction as the front glass, the pressure and discomfort to the combiner 10 are considerably reduced, but the eyebox EB2 is formed on the driver's abdomen Therefore, the driver can not view the virtual image VI.

  In this embodiment, in order to solve the problems as described above, a combiner in which a half mirror of a Fresnel structure is formed inside a flat plate is used instead of the general combiner 10 as shown in FIG. Here, a combiner using a Fresnel structure is proposed, for example, in Patent Documents 1 and 2 described above. In particular, according to Patent Document 2, the optical axis of the first Fresnel lens in the first main surface provided with the first Fresnel lens is disposed at a position different from the center of the outline of the first main surface. By changing the angle between the light reflected by the surface of the main surface and the light reflected by the surface of the second main surface (surface reflected light), the double image (the light reflected by the surface of the first main surface) It has been proposed to suppress the occurrence of the phenomenon that occurs when the light reflected by the surface of the second main surface overlaps.

  FIG. 3 shows a diagram for explaining the basic concept of this embodiment. FIG. 3 shows an example of three combiners 10x1, 10x2, 10x3 (hereinafter referred to simply as "combiner 10x" when they are not distinguished from each other), and fronts of each of the combiners 10x1, 10x2, 10x3 The figure and sectional drawing (side view) are shown. In addition, the front view and the sectional view show an image schematically shown. The combiner 10x is applied to a head-up display in place of the combiner 10 shown in FIG. 1 (the same applies to combiners 10a and 10b described later).

  The combiner 10x has a half mirror of a Fresnel structure formed therein. Specifically, the combiner 10x is a half mirror by forming a plurality of minute reflecting surfaces (mirror surfaces) S2 corresponding to the curvature of the virtual paraboloid S1 that is the origin of the Fresnel structure (Fresnel pattern). Act as. The plurality of reflecting surfaces have, for example, a shape in which a lens having a virtual paraboloid S1 is divided and arrayed at equal intervals in the vertical direction in FIG. For example, the combiner 10x is two members having the same refractive index (hereinafter referred to as “substrate” as appropriate. The substrate is a cover layer, in other words, the substrate is a cover layer.) Between them, by sandwiching a reflective thin film having a certain degree of transparency. When light is vertically incident on the combiners 10x1, 10x2 and 10x3, all light incident on each of the combiners 10x1, 10x2 and 10x3 is the focal point P1 of the virtual parabolic surface S1 by the reflecting surface S2 formed inside (See arrows Ar11, Ar12 and Ar13).

  In the present specification, the “Fresnel structure” means a structure to which a shape similar to the surface shape of a known Fresnel lens is applied. That is, "half mirror of Fresnel structure" means a half mirror to which a shape similar to the surface shape of a known Fresnel lens is applied.

  Here, the vertex P2 of the virtual paraboloid S1 (in other words, the center of the virtual paraboloid S1; hereinafter the same) is located at the center (outer center) of the combiner 10x1. That is, the Fresnel structure based on the virtual paraboloid S1 in which the vertex P2 is located at the center point P3x1 on the surface of the half mirror is applied to the combiner 10x1. Therefore, in the combiner 10x1, the inclination of the reflective surface S2 formed inside is small. On the other hand, in the combiners 10x2 and 10x3, the vertex P2 of the virtual paraboloid S1 is not located at its center (outer center). That is, a Fresnel structure based on the virtual paraboloid S1 is applied to the combiners 10x2 and 10x3 based on the virtual paraboloid S1 in which the vertex P2 is located at a position deviated from the central points P3x2 and P3x3 on the surface of the half mirror. In other words, for the combiners 10x2 and 10x3, an area out of the center of the Fresnel pattern is applied. Therefore, in the combiners 10x2 and 10x3, the inclination of the reflective surface S2 formed inside is large (that is, the reflective surface S2 stands).

  Hereinafter, application of the virtual parabolic surface S1 in which the vertex P2 is located at a position deviated from the center points P3x2 and P3x3 of the half mirror, such as the combiners 10x2 and 10x3, is appropriately referred to as "offset". Also, the amount of offset from the vertex P2 of the virtual paraboloid S1 is called "offset amount". In one example, the “offset amount” is an amount by which the vertex P2 of the virtual paraboloid S1 is shifted from the center points P3x2 and P3x3 of the half mirror (in other words, the distance between the vertex P2 and the center points P3x2 and P3x3) expressed. In the example shown in FIG. 3, the combiner 10x2 has a Fresnel structure based on the virtual paraboloid S1 in which the vertex P2 is shifted by the offset amount OFSx2 from the center point P3x2 of the half mirror, and the combiner 10x3 is half A Fresnel structure based on a virtual paraboloid S1 in which the vertex P2 is shifted from the center point P3x3 of the mirror by the offset amount OFSx3 is applied.

  By using the combiners 10x2 and 10x3 to which the offset is applied in this way, as shown by arrows Ar12 and Ar13 in FIG. 3, the angle formed between the incident light and the reflected light in the half mirrors of the combiners 10x2 and 10x3 is changed. Can. On the other hand, since the angle of the surface reflected light (light reflected by the surface of the substrate) in the combiners 10x2 and 10x3 does not change, the double image as described above can be avoided. In addition, as shown by arrows Ar21, Ar22 and Ar23 in FIG. 3, with the combiners 10x1, 10x2 and 10x3 and with the angles formed by the incident light and the reflected light in the half mirrors of the combiners 10x1, 10x2 and 10x3 being kept constant. It is possible to change the relative angle of

  In addition, limitation is not carried out to using a paraboloid as a surface which becomes the origin of a Fresnel structure. A spherical shape may be used from the viewpoint of ease of fabrication, or an aspherical shape may be used to correct the aberration. That is, various free-form surfaces (e.g., curved surfaces for which focal points are defined) can be applied as the surface on which the Fresnel structure is derived. In one preferred example, the characteristics of the half mirror including the substrate (cover layer) covering the reflecting surface follow the paraboloid (that is, when light is vertically incident on the combiner, A non-parabolic surface can be applied as a surface on which the Fresnel structure originates, so that the light reflected by the reflective surface and transmitted through the substrate and directed to the focal point of the parabolic surface).

  FIG. 4 shows that the eyebox EB can be appropriately formed near the driver's head even if the combiner is inclined in the same direction as the windshield by using the combiner to which the offset Fresnel structure as described above is applied. Will be explained. FIG. 4 shows a state in which the combiners 10x1, 10x2, 10x3 shown in FIG. 3 are installed in the vehicle in a state of being rotated so that the angle of the reflected light becomes horizontal after making 90 ° clockwise. . From FIG. 4, for example, in the case of using the combiner 10 × 3 (the one to which the Fresnel structure having a relatively large offset amount is applied) is used, the eyebox EB is the head of the driver even if the combiner 10 × 3 is inclined in substantially the same direction It turns out that it can form appropriately near. That is, the problem as shown in FIG. 2B (the problem that the eye box EB2 of the real image RI installed near the ceiling in the combiner 10 inclined in the same direction as the front glass is formed in the abdomen) is solved It can be said that you can.

  Here, unlike the general combiner 10 as shown in FIG. 1, the combiner 10 x to which the above-described Fresnel structure is applied has several problems because its reflective surface S 2 exists in the substrate instead of the surface. (Problems 1 and 2) may occur. Problem 1 is a problem that the light reflected by the reflecting surface S2 inside the substrate in the combiner 10x is not totally emitted from the substrate (cover layer) by being totally reflected. The second problem is that the amount of light reaching the observer changes between the upper and lower portions of the combiner 10x. Such problems 1 and 2 will be specifically described with reference to FIGS. 5 and 6.

  FIG. 5 shows a diagram for specifically explaining Problem 1. As shown in FIG. FIGS. 5A and 5B illustrate the light reflected by the reflecting surface S2 inside the substrate in the combiner 10x (as shown, the light reflected by the reflecting surface S2 is incident on the substrate) It will be different from the angle). FIG. 5A shows a case where a Fresnel structure having a relatively small offset amount is applied. In this case, the light reflected by the reflecting surface S2 inside the substrate is emitted from the inside of the substrate to the outside. On the other hand, FIG. 5B shows a case where a Fresnel structure having a relatively large offset amount is applied. In this case, the light reflected by the reflecting surface S2 inside the substrate is totally reflected by the inner surface of the substrate surface, and is not emitted from the inside of the substrate to the outside (waveguides inside the substrate). From FIGS. 5A and 5B, it can be said that when the Fresnel structure having a relatively large offset amount is applied, the problem 1 is likely to occur.

FIG. 6 shows a diagram for specifically explaining the problem 2. FIG. 6 (a) shows a case where the real image RI is installed on the upper side with the combiner 10x inclined in the same direction as the windshield. In this case, the light from the real image RI is incident on the combiner 10x at a deep angle. Further, the incident angle theta ₁ which the light is incident on the lower portion of the combiner 10x, becomes larger than the incident angle theta ₂ which the light at the top of the combiner 10x is incident (θ _1> θ _2).

  FIG. 6B shows the relationship between the incident angle [°] and “incidence transmittance × emission transmittance” [%] in the combiner 10. The “incidence transmittance × emission transmittance” corresponds to the amount of light emitted from the combiner 10 x (that is, the amount of light reaching the observer). In FIG. 6B, a code GRp indicates a graph when P polarization is used, and a code GRs indicates a graph when S polarization is used. Such graphs GRp and GRs use the combiner 10x in which the refractive index n of the substrate (cover layer) is 1.59 and the focal distance f of the virtual paraboloid S1 is 300 [mm], and the offset amount is 250 This is the result obtained when light is incident on the position of [mm] (the reflectance of the reflective surface S2 is assumed to be 100%).

  It can be seen from FIG. 6 (b) that the value of “incidence transmittance × emission transmittance” changes in accordance with the incident angle to the combiner 10x. Specifically, it can be seen that in the region where the incident angle is large, the value of “incidence transmittance × emission transmittance” is significantly reduced. Also, in S-polarization, the value of “incidence transmittance × emission transmittance” is generally smaller than that of P-polarization, and the value of “incident transmittance × emission transmittance” starts to decrease. It can be seen that the incident angle is small. The reason that the value of “incidence transmittance × emission transmittance” is 0 [%] in a region where the incident angle is approximately 10 ° or less is that total reflection occurred.

From FIG. 6 (a) and (b), with the case of installing a real image RI on top of the combiner 10x with tilting the combiner 10x in the same direction as the front glass, the incident angle theta ₁ and theta ₂ is relatively large , since the greater the difference between the incident angle theta ₁ and the incident angle theta _2, it can be said that the value difference occurs a tendency of "incident upon transmittance × emission time transmittance" in the upper and lower parts of the combiner 10x. That is, it can be said that the amount of light reaching the observer at the top and bottom of the combiner 10x tends to change. That is, it can be said that task 2 is likely to occur.

  Hereinafter, specific examples (first and second examples) capable of solving the problems 1 and 2 will be described. The first embodiment mainly aims to solve the problem 1, and the second embodiment mainly aims to solve the problem 2.

First Embodiment
In the first embodiment, the combiner and the real image RI (substantially the light source are configured so that the light reflected by the reflecting surface in the combiner to which the Fresnel structure is applied is appropriately emitted to the outside of the combiner without total reflection. Set the relative position with the above. That is, in the first embodiment, the angle at which the light reflected by the internal reflection surface of the substrate in the combiner is incident on the inner surface of the substrate surface (hereinafter referred to as “emission angle” as appropriate) is less than the total reflection angle. The relative position between the combiner and the real image RI is set.

With reference to FIG. 7, the condition of the incident angle for making the emission angle less than the total reflection angle will be described. FIG. 7 shows a cross-sectional image view of the combiner 10a according to the first embodiment. As shown in FIG. 7, incident light enters the combiner 10a at an incident angle θ _in and is refracted by the substrate having a refractive index n to form an angle θ _in '. In this case, according to Snell's law, an expression such as “sin θ _in = n · sin θ _in ′” holds. Then, this incident light enters a point P10 on the reflecting surface S2 of the Fresnel structure inside the combiner 10a. The point P10 is located at a position separated by “OFS” in the x direction from the vertex P2 of the virtual paraboloid S1 (“OFS” corresponds to the offset amount). The virtual paraboloid S1 is expressed as “y = x ² / 4f” using the focal length f.

Here, an angle φ formed by a straight line parallel to the x-axis passing through the point P10 and a tangent of the virtual paraboloid S1 at the point P10 is “φ = tan ⁻¹ (OFS / 2f)”. When such an angle φ is used, the angle β at which the incident light of the angle θ _in ′ is incident on the reflecting surface S2 is “β = φ−θ _in ′”. Then, the light reflected at the point P10 on the reflective surface S2 is incident on the inner surface S3 of the substrate surface at an angle “θ _in '+ 2β”. The angle “θ _in '+ 2β” corresponds to the above-described emission angle. The condition for making the emission angle less than the total reflection angle “sin ⁻¹ (1 / n)” is expressed by the following equation (1).

θ _in '+ 2β <sin ⁻¹ (1 / n) Formula (1)
Further, the injection angle is rewritten as the following equation (2).

θ _in '+ 2β = 2φ-θ _in '
= 2 tan ⁻¹ (OFS / 2 f) −sin ⁻¹ (sin θ _in / n) Formula (2)
By substituting equation (2) like this into equation (1), a condition that the incident angle θ _in should satisfy _in order to make the emission angle less than the total reflection angle is obtained. The condition is expressed by the following equation (3).

θ _in > sin ⁻¹ [n · sin {2 tan ⁻¹ (OFS / 2 f) −sin ⁻¹ (1 / n)}] formula (3)
As shown in equation (3), the conditions that the incident angle θ _in should satisfy are represented by the refractive index n, the offset amount OFS, and the focal length f.

In the first embodiment, the relative position between the combiner 10a and the real image RI is set such that the incident angle θ _in satisfying the condition of the equation (3) is realized. That is, the relative position between the combiner 10a and the real image RI is set such that the light forming the real image RI enters the combiner 10a at the incident angle θ _in satisfying the condition of equation (3). As a result, the light reflected by the reflective surface S2 inside the substrate can be appropriately emitted to the outside, and a defect that a part of the virtual image can not be visually recognized can be appropriately avoided. Therefore, the entire surface of the combiner 10a can be effectively used.

  FIG. 8 is a view for explaining an example of the optimum arrangement of the combiner 10a according to the first embodiment. FIG. 8A shows a front image view of the combiner 10a according to the first embodiment. The combiner 10a according to the first embodiment has the same basic configuration as the above-described combiners 10x2 and 10x3. That is, in the combiner 10a according to the first embodiment, a half mirror to which the offset Fresnel structure is applied is formed inside.

  Here, the refractive index n of the substrate (cover layer) is 1.59 (polycarbonate is used as the substrate), and the focal length f of the virtual paraboloid that is the origin of the Fresnel structure is 300 [mm], The case of using the combiner 10a whose size in the longitudinal direction is 150 [mm] will be described as an example. In this combiner 10a, the offset amount (the distance between the focal point of the virtual paraboloid that is the origin of the Fresnel structure and the upper end portion of the combiner 10a) is 200 [mm] at the upper end, and the offset amount (Fresnel structure It is assumed that the distance between the focal point of the original virtual paraboloid and the lower end of the combiner 10a is 350 [mm]. In addition, the size of the real image RI (display screen) in the vertical direction is 50 mm, the distance between the real image RI and the combiner 10 a is 180 mm, and the combiner 10 a is inclined to the windshield by 20 °. Take the case of installation as an example.

  FIG. 8B shows a first arrangement example of the combiner 10a, and FIG. 8C shows a second arrangement example of the combiner 10a. FIGS. 8B and 8C show side image views of the combiner 10a and the real image RI. In the first arrangement example, the incident angle at which light is incident on the upper end portion of the combiner 10a is -3.3 [°], and the incident angle at which light is incident on the lower end portion of the combiner 10a is +26 [°]. In the second arrangement example, the incident angle at which light is incident on the upper end portion of the combiner 10a is +6 [°], and the incident angle at which light is incident on the lower end portion of the combiner 10a is +34.2 [°].

  In FIG. 8D, the horizontal axis indicates the offset amount [mm], the vertical axis indicates the incident angle [°], and the area satisfying the condition of the above-described equation (3) is filled and represented. It is assumed that the parameters (n, f) described in the description of FIG. 8A are substituted into the equation (3). According to FIG. 8D, in order to satisfy the condition of the equation (3), the incident angle needs to be -3.3 [°] or more at the upper end portion (offset amount = 200 [mm]) of the combiner 10a. In the lower end portion (offset amount = 350 [mm]) of the combiner 10a, it is understood that the incident angle needs to be +34.2 [°] or more.

  When the first arrangement example is applied, since the incident angle is -3.3 [°] at the upper end of the combiner 10a, the light reflected by the reflecting surface S2 inside the substrate is emitted only to the outside, Since the incident angle is +26 [°] at the lower end of the combiner 10a (that is, it is less than +34.2 [°]), the light reflected by the reflective surface S2 inside the substrate is totally reflected and not emitted to the outside . On the other hand, when the second arrangement example is applied, since the incident angle is +6 [°] at the upper end of the combiner 10a (that is, it is -3.3 [°] or more), the reflective surface inside the substrate The light reflected by S2 is emitted to the outside, and since the incident angle is +34.2 [°] at the lower end portion of the combiner 10a, the light reflected by the reflecting surface S2 inside the substrate is emitted only to the outside. Therefore, when the position of the real image RI with respect to the position of the combiner 10a is higher than the second arrangement example, the condition of the equation (3) is appropriately satisfied, and thus the light reflected by the reflective surface S2 inside the substrate is appropriately emitted. The Rukoto. Therefore, the entire surface of the combiner 10a can be effectively used.

Second Embodiment
Next, a second embodiment will be described. The second embodiment mainly aims to solve the problem 2. Specifically, in the second embodiment, the combiner and the combiner are used so that the range of the incident angle is used such that the variation of the transmittance of the substrate in the combiner is equal to or less than a predetermined value (a value determined in advance by adaptation). Set the relative position to the real image RI. That is, in the second embodiment, the relative position between the combiner and the real image RI is set such that a region having a small incident angle dependency of the transmittance of the substrate is used. According to such a second embodiment, it is possible to appropriately suppress the occurrence of luminance change (uneven luminance) in the plane of the combiner.

  FIG. 9 is a view for explaining an example of the optimum arrangement of the combiner 10b according to the second embodiment. FIG. 9A shows a front image view of the combiner 10b according to the second embodiment. The basic configuration of the combiner 10b according to the second embodiment is the same as that of the combiners 10x2 and 10x3 described above. That is, in the combiner 10b according to the second embodiment, a half mirror to which the offset Fresnel structure is applied is formed inside.

  Here, the refractive index n of the substrate (cover layer) is 1.59 (polycarbonate is used as the substrate), and the focal length f of the virtual paraboloid that is the origin of the Fresnel structure is 300 [mm], The case of using the combiner 10b whose size in the longitudinal direction is 100 [mm] will be described as an example. In this combiner 10b, the offset amount (the distance between the focal point of the virtual paraboloid that is the origin of the Fresnel structure and the point A) is 150 [mm] at the point A located at the upper end, and the offset at the point B located at the center The amount (the distance between the focal point of the virtual paraboloid that is the origin of the Fresnel structure and the point B) is 200 [mm], and the offset amount at the point C located at the lower end (the virtual paraboloid of the Fresnel structure It is assumed that the distance between the focal point and the point C is 250 [mm]. Also, an example in which the size in the vertical direction of the real image RI (display screen) is 36 [mm] and the distance between the real image RI and the combiner 10 b is 180 [mm] will be described as an example.

  9 (b) shows a first arrangement example of the combiner 10b, FIG. 9 (c) shows a second arrangement example of the combiner 10b, and FIG. 9 (d) shows a third arrangement of the combiner 10b. The example of arrangement is shown. FIG.9 (b)-(d) has shown the side image figure of the combiner 10b and real image RI. In the first arrangement example, the incident angle at point A of the combiner 10b is -10 [°], the incident angle at point B of the combiner 10b is 0 [°], and the incident angle at point C of the combiner 10b Is +10 [°]. In the second arrangement example, the incident angle at point A of the combiner 10b is +19 [°], the incident angle at point B of the combiner 10b is +30 [°], and the incident angle at point C of the combiner 10b is It is +37 [°]. In the third arrangement example, the incident angle at point A of the combiner 10b is + 52 °, the incident angle at point B of the combiner 10b is + 60 °, and the incident angle at point C of the combiner 10b is It is +64 [°].

  FIG. 9E is a diagram showing the relationship between the incident angle [°] on the substrate and the transmittance of the substrate (which means the transmittance of light reciprocated in the substrate). In FIG. 9E, graph GR1 shows the transmittance of the substrate for light incident on point A of combiner 10b, and graph GR2 shows the transmittance of the substrate for light incident on point B of combiner 10b. The graph GR3 shows the transmittance of the substrate for the light incident on the point C of the combiner 10b. The graphs GR <b> 1 to GR <b> 3 are obtained based on known interface reflectance (Fresnel reflectance) formulas. The graphs GR1 to GR3 assume the case where S polarized light is incident on the combiner 10b.

  When the first arrangement example is applied, the angles of incidence at points A, B and C of the combiner 10b are plotted on the graphs GR1, GR2 and GR3, respectively, to obtain points A1, B1 and C1, and these points A1 are obtained. , B1 and C1 are connected to obtain a broken line D1. It can be seen from the broken line D1 that when the first arrangement example is applied, the amount of change in transmittance with respect to the incident angle is large. Therefore, when the first arrangement example is applied, it can be said that the change in luminance (uneven luminance) in the plane of the combiner 10 b becomes large. Therefore, in the second embodiment, such a first arrangement example is not adopted.

  When the second arrangement example is applied, the angles of incidence at points A, B and C of the combiner 10b are plotted on the graphs GR1, GR2 and GR3, respectively, to obtain points A2, B2 and C2, and these points A2 , B2 and C2 are connected to obtain a broken line D2. From the broken line D2, it can be seen that when the second arrangement example is applied, the amount of change in transmittance with respect to the incident angle is small. Therefore, when the second arrangement example is applied, it can be said that the change in luminance (uneven luminance) in the plane of the combiner 10 b hardly occurs. Therefore, in the second embodiment, such a second arrangement example is adopted.

  When the third arrangement example is applied, the angles of incidence at points A, B and C of the combiner 10b are plotted on the graphs GR1, GR2 and GR3, respectively, to obtain points A3, B3 and C3, and these points A3 , B2 and C3 give the broken line D3. From the broken line D3, when the third arrangement example is applied, the change in transmittance is smaller than when the first arrangement example is applied, but the change in transmittance is more than when the second arrangement example is applied. I understand that it is big. In addition, in the region on the right side of the broken line D3, it can be seen that the amount of change in transmittance is large. Therefore, when the third arrangement example is applied, it can be said that a sharp change in brightness occurs just by slightly inclining the combiner 10b from the installation angle in the third arrangement example. Therefore, in the second embodiment, such a third arrangement example is not adopted.

  In addition, although the case where S polarization | polarized-light is used as light made to enter into the combiner 10b was illustrated in FIG. 9, you may use P polarization | polarized-light instead of S polarization | polarized-light. As shown in FIG. 6B, since P-polarization has smaller interface angle dependency of interface reflectance (transmittance) than S-polarization, it can be said that P-polarization is preferred to S-polarization.

  In the above, the second embodiment has been described to mainly solve the problem 2. However, according to the second embodiment, the problem 1 is also solved. If the problem 2 is solved, the problem 1 is also necessarily solved.

10, 10a, 10b, 10x Combiner P1 Focus P2 Vertex S1 Virtual Paraboloid S2 Reflective Surface RI Real Image VI Virtual Image

Claims (1)

A light source unit for emitting light constituting a display image;
A mirror having a Fresnel structure that causes the display image to be recognized as a virtual image by reflecting a part of the light emitted by the light source unit;
A substrate provided on the light incident surface side with respect to the mirror so as to face the mirror;
An optical system including the light source unit, the mirror, and the substrate, for guiding the light from the light source unit reflected by the mirror to the outside of the substrate without being totally reflected by the substrate;
A display device characterized by having.

Images