JP2016139152A - Head-up display - Google Patents

Abstract

PROBLEM TO BE SOLVED: 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 a technical field in which an image is visually recognized as a virtual image.

  Conventionally, a display device such as a head-up display for visually recognizing an image as a virtual image is known. In general, in a head-up display, a half mirror called a combiner (synthesizer) 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.

Japanese Patent No. 4776669 JP 2011-191715 A

  By the way, when a general concave half mirror is used as a combiner, if the position of the real image is fixed, a virtual image observable region (hereinafter referred to as an “eye box”) formed by the combiner. The installation angle of the combiner necessary for forming near the head is automatically determined. For example, when the light constituting the real image is incident on the combiner installed in front of the driver from above, 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 driver's head), but the presence of the combiner is large, which may give the driver a feeling of pressure or discomfort. Therefore, if the combiner is tilted in the same direction as the windshield, the feeling of pressure and discomfort to the combiner is considerably reduced, but the eyebox is not formed at an appropriate position (for example, an eyebox is formed on the abdomen of the driver). ), The driver will not be able to see the virtual image.

  Here, when a combiner in which the center of the Fresnel pattern is arranged at a position different from the center of the combiner as described in Patent Document 2 described above, the angle between the incident light and the reflected light is kept constant. The relative angle with the combiner can be changed. Therefore, it is considered that by using such a combiner, the eyebox can be appropriately formed in the vicinity of the driver's head even if the combiner is inclined in the same direction as the windshield. However, in a combiner using a Fresnel structure, since the reflection surface is not in the surface but in the substrate, the light reflected by the reflection surface inside the substrate in the combiner may not be emitted to the outside of the combiner due to total reflection. . Patent Documents 1 and 2 do not consider such a problem.

  Examples of the problem 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 having a Fresnel structure without giving a viewer a feeling of pressure or discomfort.

  The invention according to claim 1 is a head-up display, which is disposed along the inclination direction of the windshield of the moving body, and includes an optical element including a Fresnel structure mirror that reflects a part of incident light; A light source unit that emits light constituting a display image from above toward the optical element, and the optical element reflects the light to cause the display image to be viewed as a virtual image, and the light source unit The light reflected by the mirror is arranged so as to be emitted to the outside of the optical element without being totally reflected at the interface with air.

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 eyebox is shown. The figure for demonstrating the basic concept of a present Example is shown. The figure for demonstrating that a malfunction can be solved by using the combiner to which the offset Fresnel structure was applied is shown. 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 emission angle less than a total reflection angle is shown. The figure for demonstrating the optimal arrangement | positioning example of the combiner which concerns on 1st Example is shown. The figure for demonstrating the optimal arrangement | positioning example of the combiner which concerns on 2nd Example is shown.

  In one aspect of the present invention, a light source unit that emits light constituting a display image, and an optical device in which light from the light source unit is incident from above and arranged in the same direction as the tilt direction of the windshield of the moving body A head-up display that visually recognizes the display image as a virtual image by reflecting light constituting the display image with the optical element, the optical element having 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 curved surface that is the basis of the Fresnel structure is not located at the center of the half mirror 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 outside the optical element without being totally reflected. It is.

  The head-up display is installed on a moving body and is used to visually recognize the display image as a virtual image by reflecting light constituting the display image emitted from the light source unit with an optical element (for example, a combiner). The The optical element receives light from the light source unit from above and is arranged in the same direction as the inclination direction of the windshield of the moving body. In the optical element, a Fresnel half mirror is formed in one flat plate, and the light from the light source unit is reflected by the half mirror. The half mirror employs a Fresnel structure in which the center (for example, the vertex) of the free curved surface that is the basis 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 outside the optical element without being totally reflected inside the optical element. In other words, the light from the light source unit enters the optical element at an incident angle such that the light reflected by the half mirror is emitted outside without being totally reflected.

  According to the above head-up display, by using an optical element to which a Fresnel structure in which the center of the free curved surface is not located at the center of the half mirror is used, the optical element on which light from the light source unit is incident from above is windshielded. The eye box can be appropriately formed in the vicinity of the observer's head. Therefore, the eyebox can be formed at an appropriate position without giving the observer a feeling of pressure or discomfort. In addition, according to the above 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 appropriately emit light, and it is possible to appropriately avoid a problem that a part of the virtual image cannot be visually recognized. Therefore, the entire surface of the optical element can be used effectively.

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

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

  In this aspect, the relative position between the light source unit and the optical element is set so that a region where the transmittance of the substrate is less dependent on the incident angle is used. Thereby, generation | occurrence | production of the luminance change (luminance nonuniformity) within the surface of an optical element can be suppressed appropriately.

  In another aspect of the head-up display described above, the light source unit emits P-polarized light. Thereby, the incident angle dependence of the transmittance | permeability (interface reflectance) of a board | substrate can be made small compared with the case where S polarized light is used.

  In another aspect of the head-up display, the light source unit includes an exit pupil enlarging element that expands an exit pupil of light emitted from the light source, and uses the light from the exit pupil enlarging element as the optical element. Exit toward. In the case of using an LCD or CRT, light diffuses at a large angle. However, in a configuration in which light from a projector or the like is spread by an exit pupil enlarging element, it is possible to easily realize a narrow control of the diffusion angle.

  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 diagram schematically illustrating a general head-up display. In the head-up display, a screen to be displayed (real image RI) is formed, and the light constituting the real image RI is reflected by the combiner 10, thereby allowing the driver to 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)). . A small liquid crystal display, a projector, and a screen correspond to an example of a “light source unit” in the present invention.

  In order to make the virtual image VI bright and visible 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 price increase, a method of increasing the light use efficiency is usually used. In order to increase the light use efficiency, in a general head-up display, the emission angle of the real image RI is limited, and the concave half-half 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. In FIG. 1, a region indicated by reference numeral EB is a virtual image observable region (eye box) formed near the observer's head.

  FIG. 2 is 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, when the position of the real image RI is fixed, the combiner required to form the eye box EB near the driver's head. Ten installation angles are automatically determined. For example, as shown in FIG. 2A, when the light constituting the real image RI is incident on the combiner 10 installed in front of the driver from above, the installation angle of the combiner 10 is opposite to the inclination of the windshield. Will tilt in the direction. In this case, the eye box EB1 is formed at an appropriate position (near the driver's head), but the presence of the combiner 10 is large, which may give the driver a feeling of pressure or discomfort. Therefore, as shown in FIG. 2B, when the combiner 10 is tilted in the same direction as the windshield, the feeling of pressure and discomfort to the combiner 10 is considerably reduced, but the eye box EB2 is formed on the abdomen of the driver. Therefore, the driver cannot visually recognize the virtual image VI.

  In this embodiment, in order to solve the above-described problems, a combiner in which a Fresnel half mirror 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 in Patent Documents 1 and 2 described above, for example. In particular, Patent Document 2 discloses that the optical axis of the first Fresnel lens on the first main surface provided with the first Fresnel lens is arranged at a position different from the center of the outer shape of the first main surface. By changing the angle between the light reflected on the surface of the main surface and the light reflected on the surface of the second main surface (surface reflected light), a double image (light reflected on the surface of the first main surface and It has been proposed to suppress the occurrence of a phenomenon that occurs when light reflected by the surface of the second main surface overlaps.

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

  The combiner 10x has a Fresnel half mirror inside. Specifically, the combiner 10x has a plurality of minute reflecting surfaces (mirror surfaces) S2 corresponding to the curvature of the virtual paraboloid S1 that is the basis of the Fresnel structure (Fresnel pattern). Function as. The plurality of reflecting surfaces have a shape in which, for example, lenses having a virtual paraboloidal surface S1 are divided and arranged at equal intervals in the vertical direction in FIG. For example, the combiner 10x has two members having the same refractive index on which irregularities corresponding to the curvature of the virtual paraboloid S1 are formed (hereinafter referred to as “substrate” as appropriate. The substrate is a cover layer in other words). It is created by sandwiching a reflective thin film having a certain degree of transparency in between. When light is incident vertically on the combiners 10x1, 10x2, and 10x3, all the light incident on the combiners 10x1, 10x2, and 10x3 is focused on the virtual paraboloid S1 by the reflecting surface S2 formed inside. (Refer to arrows Ar11, Ar12, 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, “Fresnel half mirror” means a half mirror to which a shape similar to the surface shape of a known Fresnel lens is applied.

  Here, the combiner 10x1 has a vertex P2 of the virtual paraboloid S1 (in other words, the center of the virtual paraboloid S1, and the same shall apply hereinafter) at the center (outline center). That is, the combiner 10x1 has a 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. Therefore, in the combiner 10x1, the inclination of the reflecting surface S2 formed inside is small. On the other hand, the vertexes P2 of the virtual paraboloid S1 are not located at the centers (outer shape centers) of the combiners 10x2 and 10x3. That is, the combiner 10x2, 10x3 has a Fresnel structure based on the virtual paraboloid S1 in which the vertex P2 is located at a location deviating from the center points P3x2, P3x3 on the surface of the half mirror. In other words, the combiner 10x2, 10x3 is applied with a region off the center of the Fresnel pattern. Therefore, in combiner 10x2, 10x3, the inclination of reflective surface S2 formed inside is large (that is, reflective surface S2 stands).

  Hereinafter, applying the virtual paraboloid S1 in which the vertex P2 is located at a location deviating from the center points P3x2 and P3x3 of the half mirror, such as the combiners 10x2 and 10x3, to the Fresnel structure is appropriately referred to as "offset". The amount of offset from the vertex P2 of the virtual paraboloid S1 is referred to as “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 a virtual paraboloid S1 in which the vertex P2 is shifted from the center point P3x2 of the half mirror by an offset amount OFSx2, and the combiner 10x3 is a half A Fresnel structure based on a virtual paraboloid S1 in which the vertex P2 is shifted by the offset amount OFSx3 from the mirror center point P3x3 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 by the incident light and the reflected light in the half mirrors of the combiners 10x2 and 10x3 is changed. Can do. On the other hand, the angle of the surface reflected light (light reflected by the surface of the substrate) in the combiners 10x2 and 10x3 does not change, so that the double image as described above can be avoided. Further, as indicated by arrows Ar21, Ar22, Ar23 in FIG. 3, combiners 10x1, 10x2, 10x3 and 10x1, 10x2, 10x3 with the angle formed by the incident light and the reflected light in the half mirrors of combiners 10x1, 10x2, 10x3 kept constant. The relative angle of can be changed.

  In addition, it is not limited to using a paraboloid as a surface from which the Fresnel structure is based. From the viewpoint of ease of production, a spherical shape may be used, or an aspherical shape may be used to correct aberration. In other words, various free-form surfaces (for example, curved surfaces with a focal point defined) can be applied as the basis of the Fresnel structure. In one suitable example, the characteristics of the half mirror including the substrate (cover layer) covering the reflecting surface are in accordance with the paraboloid (that is, when light is incident on the combiner vertically) A non-parabolic surface can be applied as the basis of the Fresnel structure (so that light reflected from the reflecting surface and transmitted through the substrate is emitted toward the focal point of the parabolic surface).

  FIG. 4 shows that by using the combiner to which the offset Fresnel structure as described above is applied, the eyebox EB can be appropriately formed near the driver's head even if the combiner is tilted in the same direction as the windshield. Will be described. FIG. 4 shows a state in which the combiner 10x1, 10x2, 10x3 shown in FIG. 3 is installed in the vehicle in a state where the angle of the reflected light is rotated horizontally after being rotated 90 ° clockwise. . From FIG. 4, for example, when a combiner 10x3 (applying a Fresnel structure with a relatively large offset amount) is used, the eyebox EB can be attached to the driver's head even if the combiner 10x3 is inclined in the same direction as the windshield. It can be seen that it can be properly formed in the vicinity. That is, the problem as shown in FIG. 2B (the problem that the combiner 10 tilted in the same direction as the windshield causes the eye box EB2 of the real image RI installed near the ceiling to be formed in the abdomen) is solved. I can say that.

  Here, the combiner 10x to which the Fresnel structure as described above is applied differs from the general combiner 10 as shown in FIG. 1 in that the reflecting surface S2 is not in the surface but in the substrate, so there are some problems. (Problems 1 and 2) may occur. The problem 1 is a problem that the light reflected by the reflection surface S2 inside the substrate in the combiner 10x may not be emitted from the substrate (cover layer) due to total reflection. The problem 2 is a problem that the amount of light reaching the observer is changed between the upper part and the lower part of the combiner 10x. Such problems 1 and 2 will be specifically described with reference to FIGS. 5 and 6.

  FIG. 5 is a diagram for specifically explaining the first problem. FIGS. 5A and 5B illustrate light reflected by the reflecting surface S2 inside the substrate in the combiner 10x (as illustrated, the light reflected by the reflecting surface S2 is incident on the substrate). Will be different from the angle). FIG. 5A shows a case where a Fresnel structure with 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 (waveguided inside the substrate). 5 (a) and 5 (b), it can be said that Problem 1 is likely to occur when a Fresnel structure with a relatively large offset amount is applied.

FIG. 6 is a diagram for specifically explaining the problem 2. FIG. 6A shows a case where the real image RI is installed on the upper part of the combiner 10x in a state where the combiner 10x is inclined in the same direction as the windshield. In this case, light from the real image RI is incident on the combiner 10x at a deep angle. Further, the incident angle θ _{1 at} which light enters the lower part of the combiner 10 x is larger than the incident angle θ _{2 at} which light enters the upper part of the combiner 10 x (θ ₁ > θ ₂ ).

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

  FIG. 6B shows that the value of “transmittance upon incidence × transmittance upon exit” varies depending on 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 “transmittance upon incidence × transmittance upon exit” is greatly reduced. In addition, the value of “transmittance at incidence × transmittance at output” is generally smaller for S-polarized light than that for P-polarized light, and the value of “transmittance at incident × transmittance at output” starts to decrease. It can be seen that the incident angle is small. The reason why the value of “transmittance upon incidence × transmittance upon exit” is 0 [%] in the region where the incident angle is approximately 10 ° or less is that total reflection has 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 difference between the incident angle θ ₁ and the incident angle θ ₂ also becomes large, it can be said that there is a tendency that a difference in “incidence transmittance × transmission transmittance” occurs between the upper part and the lower part of the combiner 10x. That is, it can be said that the amount of light reaching the observer tends to change between the upper part and the lower part of the combiner 10x. That is, it can be said that the problem 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 is mainly intended to solve the problem 1, and the second embodiment is mainly intended to solve the problem 2.

<First embodiment>
In the first embodiment, the combiner and the real image RI (substantially a light source) are arranged so that the light reflected by the reflecting surface in the combiner to which the Fresnel structure is applied is appropriately emitted outside the combiner without being totally reflected. The relative position is set. That is, in the first embodiment, the angle at which the light reflected by the reflecting surface inside 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. Then, 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 is incident on the combiner 10a at an incident angle θ _in and is refracted by a substrate having a refractive index n to become an angle θ _in ′. In this case, an expression such as “sin θ _in = n · sin θ _in ′” holds according to Snell's law. And this incident light injects into the point P10 on the reflective surface S2 of the Fresnel structure inside the combiner 10a. The point P10 is located at a location separated from the vertex P2 of the virtual paraboloid S1 by “OFS” in the x direction (“OFS” corresponds to an offset amount). The virtual paraboloid S1 is expressed as “y = x ² / 4f” when the focal length f is used.

Here, an angle φ formed by a straight line passing through the point P10 and parallel to the x-axis and the tangent to 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 ′ enters the reflecting surface S2 is “β = φ−θ _in ′”. Then, the light reflected at the point P10 on the reflecting surface S2 is incident on the inner surface S3 of the substrate surface at an angle “θ _in '+ 2β”. This angle “θ _in '+ 2β” corresponds to the above-described emission angle. The condition for setting the emission angle to be less than the total reflection angle “sin ⁻¹ (1 / n)” is expressed by the following formula (1).

θ _in '+ 2β <sin ⁻¹ (1 / n) Equation (1)
Further, the exit angle can be rewritten as the following formula (2).

θ _in '+ 2β = 2φ-θ _in '
= 2 tan ⁻¹ (OFS / 2f) −sin ⁻¹ (sin θ _in / n) Equation (2)
By substituting such an expression (2) into the expression (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 represented by the following formula (3).

θ _in > sin ⁻¹ [n · sin {2 tan ⁻¹ (OFS / 2f) −sin ⁻¹ (1 / n)}] Equation (3)
As shown in Expression (3), the condition that the incident angle θ _in should satisfy is expressed by a refractive index n, an offset amount OFS, and a focal length f.

In the first embodiment, the relative position between the combiner 10a and the real image RI is set so that the incident angle θ _in that satisfies the condition of Expression (3) is realized. That is, the relative position between the combiner 10a and the real image RI is set so that the light constituting the real image RI is incident on the combiner 10a at an incident angle θ _{in that} satisfies the condition of the expression (3). Thereby, the light reflected by the reflecting surface S2 inside the substrate can be appropriately emitted to the outside, and it is possible to appropriately avoid the problem that a part of the virtual image cannot be visually recognized. Therefore, the entire surface of the combiner 10a can be used effectively.

  FIG. 8 is a diagram for explaining an optimal arrangement example of the combiner 10a according to the first embodiment. Fig.8 (a) has shown the front image figure of the combiner 10a which concerns on 1st Example. The combiner 10a according to the first embodiment has the same basic configuration as the combiners 10x2, 10x3 described above. 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 underlying the Fresnel structure is 300 [mm], The case where the combiner 10a whose vertical size is 150 [mm] is used is given as an example. In this combiner 10a, the offset amount (distance between the focal point of the virtual paraboloid on which the Fresnel structure is based and the upper end portion of the combiner 10a) is 200 [mm] at the upper end, and the offset amount (of the Fresnel structure) at the lower end. 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 vertical size of the real image RI (display screen) is 50 [mm], the distance between the real image RI and the combiner 10a is 180 [mm], and the combiner 10a is placed on the windshield side at an inclination angle of 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. 8B and 8C are side image diagrams 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 enters the upper end portion of the combiner 10a is +6 [°], and the incident angle at which light enters the lower end portion of the combiner 10a is +34.2 [°].

  FIG. 8D shows the offset amount [mm] on the horizontal axis, the incident angle [°] on the vertical axis, and a region that satisfies the condition of the above equation (3) is filled. It is assumed that the parameters (n, f) described in the description of FIG. According to FIG.8 (d), in order to satisfy | fill the conditions of Formula (3), an incident angle needs to be more than -3.3 [degrees] in the upper end part (offset amount = 200 [mm]) of the combiner 10a. It can be seen that the incident angle needs to be not less than +34.2 [°] at the lower end of the combiner 10a (offset amount = 350 [mm]).

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

<Second embodiment>
Next, a second embodiment will be described. The second embodiment is mainly intended to solve the second problem. Specifically, in the second embodiment, the combiner is used so that an incident angle range in which the amount of change in transmittance of the substrate in the combiner is equal to or less than a predetermined value (a value determined in advance by adaptation or the like) is used. A relative position with respect to the real image RI is set. That is, in the second embodiment, the relative position between the combiner and the real image RI is set so that a region where the transmittance of the substrate is less dependent on the incident angle is used. According to the second embodiment as described above, it is possible to appropriately suppress the occurrence of a luminance change (luminance unevenness) in the plane of the combiner.

  FIG. 9 is a diagram for explaining an optimal arrangement example of the combiner 10b according to the second embodiment. Fig.9 (a) has shown the front image figure of the combiner 10b which concerns on 2nd Example. The basic structure of the combiner 10b according to the second embodiment is the same as that of the combiners 10x2, 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 underlying the Fresnel structure is 300 [mm], The case where the combiner 10b whose vertical size is 100 [mm] is used is taken as an example. In this combiner 10b, the offset amount (the distance between the focal point of the virtual paraboloid on which the Fresnel structure is based and the point A) is 150 [mm] at the point A positioned at the upper end, and the offset is set at the point B positioned at the center. The amount (the distance between the focal point of the virtual paraboloid that is the basis of the Fresnel structure and the point B) is 200 [mm], and the offset amount (of the virtual paraboloid that is the basis of the Fresnel structure) at the point C located at the lower end. It is assumed that the distance between the focal point and the point C) is 250 [mm]. Further, a case where the vertical size of the real image RI (display screen) is 36 [mm] and the distance between the real image RI and the combiner 10b is 180 [mm] will be described as an example.

  FIG. 9B shows a first arrangement example of the combiner 10b, FIG. 9C shows a second arrangement example of the combiner 10b, and FIG. 9D shows a third arrangement of the combiner 10b. An arrangement example is shown. FIGS. 9B to 9D are side image diagrams of the combiner 10b and the real image RI. In the first arrangement example, the incident angle at the point A of the combiner 10b is −10 [°], the incident angle at the point B of the combiner 10b is 0 [°], and the incident angle at the point C of the combiner 10b. Is +10 [°]. In the second arrangement example, the incident angle at the point A of the combiner 10b is +19 [°], the incident angle at the point B of the combiner 10b is +30 [°], and the incident angle at the point C of the combiner 10b is +37 [°]. In the third arrangement example, the incident angle at the point A of the combiner 10b is +52 [°], the incident angle at the point B of the combiner 10b is +60 [°], and the incident angle at the point C of the combiner 10b is +64 [°].

  FIG. 9E is a diagram showing the relationship between the incident angle [°] to the substrate and the transmittance of the substrate (meaning the transmittance of light reciprocating in the substrate). In FIG. 9 (e), the graph GR1 shows the transmittance of the substrate for light incident on the point A of the combiner 10b, and the graph GR2 shows the transmittance of the substrate for light incident on the point B of the 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 GR1 to GR3 are obtained based on a known formula for calculating the interface reflectance (Fresnel reflectance). Graphs GR1 to GR3 assume a case where S-polarized light is incident on the combiner 10b.

  When the first arrangement example is applied, the incident angles at points A, B, and C of the combiner 10b are plotted on the graphs GR1, GR2, and GR3 to obtain points A1, B1, and C1, and these points A1. , 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 luminance change (luminance unevenness) in the plane of the combiner 10b becomes large. Therefore, in the second embodiment, such a first arrangement example is not adopted.

  When the second arrangement example is applied, the incident angles at points A, B, and C of the combiner 10b are plotted on the graphs GR1, GR2, and GR3 to obtain points A2, B2, and C2, and these points A2 , B2, and C2 are connected to obtain a broken line D2. It can be seen from the broken line D2 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 there is almost no luminance change (luminance unevenness) in the plane of the combiner 10b. Therefore, in the second embodiment, such a second arrangement example is adopted.

  When the third arrangement example is applied, the incident angles at points A, B, and C of the combiner 10b are plotted on the graphs GR1, GR2, and GR3 to obtain points A3, B3, and C3. These points A3 , B2 and C3 are connected to obtain a broken line D3. From the broken line D3, when the third arrangement example is applied, the transmittance change amount is smaller than when the first arrangement example is applied, but the transmittance change amount is smaller than when the second arrangement example is applied. You can see that it ’s big. Also, it can be seen that the amount of change in transmittance increases in the region on the right side of the broken line D3. Therefore, when the third arrangement example is applied, it can be said that a sharp change in brightness occurs just by slightly tilting 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.

  9 illustrates the case where S-polarized light is used as the light incident on the combiner 10b, but P-polarized light may be used instead of S-polarized light. As shown in FIG. 6B, it can be said that it is preferable to use P-polarized light rather than S-polarized light because P-polarized light has a smaller incident angle dependency of interface reflectance (transmittance) than S-polarized light.

  In the above description, the second embodiment is described as the main purpose of solving the problem 2. However, according to the second embodiment, the problem 1 is also solved. This is because if the problem 2 is solved, the problem 1 is inevitably solved.

10, 10a, 10b, 10x combiner P1 focus P2 vertex S1 virtual paraboloid S2 reflecting surface RI real image VI virtual image

Claims (5)

An optical element including a Fresnel structure mirror that is disposed along the inclination direction of the windshield of the moving body and reflects a part of incident light;
A light source unit that emits light constituting a display image from above toward the optical element;
With
The optical element causes the display image to be visually recognized as a virtual image by reflecting the light,
The head-up display, wherein the light source unit is arranged so that light reflected by the mirror is emitted outside the optical element without being totally reflected at an interface with air. An incident angle at which light from the light source unit enters the optical element is “θ _in ”, a refractive index of a substrate provided outside the mirror in the optical element is “n”, and the origin of the Fresnel structure is The focal length of the free-form surface is “f”, and the distance between the position where the light from the light source unit enters the mirror and the center of the free-form surface is “OFS”.
In order for the incident angle θ _in to satisfy the following equation:
θ _in > sin ⁻¹ [n · sin {2 tan ⁻¹ (OFS / 2f) −sin ⁻¹ (1 / n)}]
The head-up display according to claim 1, wherein the light source unit is arranged.   The light source unit is used such that an incident angle range in which light from the light source unit is incident on the optical element so that a change amount of transmittance of a substrate provided outside the mirror is equal to or less than a predetermined value. The head-up display according to claim 1, wherein the head-up display is arranged.   The head-up display according to any one of claims 1 to 3, wherein the light source unit emits P-polarized light with respect to an incident surface of the optical element.   The light source unit includes an exit pupil enlarging element that expands an exit pupil of light emitted from the light source, and emits light from the exit pupil enlarging element toward the optical element. The head up display as described in any one of thru | or 4.

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