JP2021002050A - 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 a technical field in which an image is visually recognized as a virtual image.

Conventionally, display devices such as head-up displays that allow images to be visually recognized as virtual images have been known. Generally, in a head-up display, a half mirror called a combiner is used in order to make a driver visually recognize a small screen (real image) such as a small liquid crystal display as a magnified virtual image. For example, Patent Documents 1 and 2 propose a combiner using a Fresnel structure.

Japanese Patent No. 4776669 Japanese Unexamined Patent Publication No. 2011-191715

By the way, when a general concave half mirror is used as a combiner, when the position of the real image is fixed, the virtual image observable area (hereinafter referred to as "eye box") formed by the combiner is defined as the driver's eye box. The installation angle of the combiner required to form 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 oppression or discomfort. Therefore, if the combiner is tilted in the same direction as the windshield, the feeling of pressure and discomfort on the combiner is considerably reduced, but the eyebox is not formed in an appropriate position (for example, an eyebox is formed on the driver's abdomen). ), 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 is used, the angle formed by the incident light and the reflected light is kept constant. It is thought that the relative angle with the combiner can be changed as it is. Therefore, by using such a combiner, it is considered that the eye box can be appropriately formed near the driver's head even if the combiner is tilted in the same direction as the windshield. However, since the reflecting surface of the combiner to which the Fresnel structure is applied exists inside the substrate instead of the surface, the light reflected by the reflecting surface inside the substrate in the combiner may not be emitted to the outside of the combiner due to total internal reflection. .. Patent Documents 1 and 2 do not consider such a defect.

Examples of 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 having a Fresnel structure without giving an observer a feeling of oppression or discomfort.

The invention according to claim 1 is a display device, which recognizes the display image as a virtual image by reflecting a light source unit that emits light constituting the display image and a part of the light emitted by the light source unit. The light from the mirror having the Frenel structure, the substrate provided facing the mirror on the incident surface side of the light with respect to the mirror, and the light source portion reflected by the mirror is totally reflected by the substrate. It is characterized by having the light source unit, the mirror, and an optical system including the substrate, which can be led out to the outside of the substrate without any trouble.

It is a figure which showed schematic | general head-up display. 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 this Example is shown. The figure for demonstrating that a defect can be solved by using a combiner to which an offset Fresnel structure is applied is shown. A diagram for specifically explaining Problem 1 is shown. A diagram for specifically explaining Problem 2 is shown. The figure for demonstrating the condition of the incident angle for making the injection angle less than the total reflection angle is shown. The figure for demonstrating the optimum arrangement example of the combiner which concerns on 1st Example is shown. The figure for demonstrating the optimum arrangement example of the combiner which concerns on 2nd Example is shown.

From one aspect of the present invention, the light source unit that emits the light constituting the display image and the optics that the light from the light source unit is incident from above and arranged in the same direction as the tilt direction of the front glass of the moving body. A head-up display including an element and reflecting the light constituting the display image by the optical element so that the display image can be visually recognized as a virtual image. The optical element has a Frenel structure in one flat plate. A half mirror is formed, and the light from the light source unit is reflected by the half mirror, and the half mirror has a Frenel structure in which the center of the free curved surface which is the basis of the Frenel 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 to the outside of the optical element without being completely reflected.

The above-mentioned head-up display is installed on a moving body and is used to visually recognize the display image as a virtual image by reflecting the light constituting the display image emitted from the light source unit by an optical element (for example, a combiner). To. 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. Further, in the optical element, a Fresnel-structured half mirror is formed in one flat plate, and the light from the light source portion is reflected by the half mirror. A Fresnel structure is applied to the half mirror in which the center (for example, apex) of the free-form 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 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 such that 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 in which the center of the free-form surface is not located at the center of the half mirror is applied, the optical element in which the light from the light source portion is incident from above is windshielded. Even if it is tilted in the same direction as the above, the eye box can be appropriately formed near the observer's head. Therefore, the eye box can be formed at an appropriate position without giving the observer a feeling of oppression or discomfort. Further, according to the above-mentioned head-up display, since 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, the light is reflected by the half mirror. It is possible to appropriately emit light and appropriately avoid problems such as the inability to see a part of the virtual image. Therefore, the entire surface of the optical element can be effectively used.

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

θ _in > sin ^-1 [n · sin {2tan ^-1 (OFS / 2f) -sin ^-1 (1 / n)}]
In another aspect of the head-up display described above, light from the light source unit is incident on the optical element so that the amount of change in the 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 so that the range of the incident angle is used.

In this embodiment, the relative positions of the light source unit and the optical element are set so that a region in which the transmittance of the substrate is less dependent on the incident angle is used. As a result, it is possible to appropriately suppress the occurrence of luminance change (luminance unevenness) in the plane of the optical element.

In another aspect of the head-up display described above, the light source unit emits P-polarized light. As a result, the incident angle dependence of the transmittance (interfacial reflectance) of the substrate can be reduced as compared with the case of using S-polarized light.

In another aspect of the head-up display, the light source unit has an exit pupil enlargement element that enlarges the exit pupil of the light emitted from the light source, and the light from the exit pupil enlargement element is sent to the optical element. It emits toward. When an LCD or CRT is used, the light is diffused at a large angle, but in a configuration in which the light from a projector or the like is spread by an exit pupil enlargement element, it is possible to easily control the diffusion angle to be narrow.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
<Basic concept>
First, before explaining the contents of this embodiment, the basic concept of this embodiment will be described.
FIG. 1 is a diagram schematically showing 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, so that the driver can 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 the 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 make the virtual image VI bright and visible even in the daytime, it is sufficient to increase the emission brightness of the real image RI, but since the power consumption and the device price increase, a method of increasing the light utilization efficiency is usually used. In order to improve the efficiency of light utilization, in a general head-up display, the emission angle of the real image RI is limited, and the concave half is used as the combiner 10 so that the light reflected by the combiner 10 is collected on the observer's head. A mirror is used and the focal length of the concave half mirror is set to an appropriate value. The region represented by the reference numeral EB in FIG. 1 is a virtual image observable region (eye box) formed near the observer's head.

FIG. 2 shows a diagram for explaining the relationship between the installation angle of the combiner 10 and the position of the eyebox EB formed by the combiner 10. When the (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 eyebox EB near the driver's head. The installation angle of 10 is 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. It will tilt in the direction. In this case, the eyebox EB1 is formed at an appropriate position (near the driver's head), but the combiner 10 has a large presence and may give the driver a feeling of oppression or discomfort. Therefore, when the combiner 10 is tilted in the same direction as the windshield as shown in FIG. 2B, the feeling of pressure and discomfort on the combiner 10 is considerably reduced, but the eyebox EB2 is formed on the driver's abdomen. Therefore, the driver cannot visually recognize the virtual image VI.

In this embodiment, in order to solve the above-mentioned problems, a combiner in which a Fresnel-structured 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, for example, in Patent Documents 1 and 2 described above. In particular, in Patent Document 2, 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), the double image (light reflected on the surface of the first main surface) and It has been proposed to suppress the occurrence of (a phenomenon caused by overlapping with the light reflected on the surface of the second main surface).

FIG. 3 shows a diagram for explaining the basic concept of this embodiment. FIG. 3 shows an example of three combiners 10x1, 10x2, and 10x3 (hereinafter, they are simply referred to as "combiner 10x" when they are not distinguished), and the front of each of the combiners 10x1, 10x2, and 10x3 is shown. The figure and the cross-sectional view (side view) are shown. The front view and the cross-sectional view are schematic image views. The combiner 10x is applied to the 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-structured half mirror formed inside. Specifically, the combiner 10x is a half mirror by forming a plurality of minute reflective surfaces (mirror surfaces) S2 corresponding to the curvature of the virtual paraboloid S1 which is the basis of the Fresnel structure (Fresnel pattern). Functions as. The plurality of reflecting surfaces have a shape such that, for example, a lens having a virtual paraboloid S1 is vertically divided and arranged at equal intervals in FIG. For example, the combiner 10x is two members having the same refractive index, in which irregularities corresponding to the curvature of the virtual paraboloid S1 are formed (hereinafter, appropriately referred to as a “substrate”. In other words, the substrate is a cover layer). It is created by sandwiching a reflective thin film having a certain degree of transparency between the two. When light is vertically incident on the combiners 10x1, 10x2, and 10x3, all the light incident on each of the combiners 10x1, 10x2, and 10x3 is the focal point P1 of the virtual paraboloid S1 due to the reflecting surface S2 formed inside. Is reflected in the direction of (see 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, the "half mirror having a Fresnel structure" means a half mirror to which a shape similar to the surface shape of a known Fresnel lens is applied.

Here, the apex P2 of the virtual paraboloid S1 (in other words, the center of the virtual paraboloid S1 and the same applies hereinafter) is located at the center (outer shape center) of the combiner 10x1. That is, the combiner 10x1 has a Fresnel structure based on the virtual paraboloid S1 in which the apex 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, in the combiners 10x2 and 10x3, the apex P2 of the virtual paraboloid S1 is not located at the center (outer shape center). That is, the combiners 10x2 and 10x3 have a Fresnel structure based on the virtual paraboloid S1 in which the apex P2 is located at a position deviated from the center points P3x2 and P3x3 on the surface of the half mirror. In other words, the combiners 10x2 and 10x3 are applied with regions off the center of the Fresnel pattern. Therefore, in the combiners 10x2 and 10x3, the inclination of the reflecting surface S2 formed inside is large (that is, the reflecting surface S2 stands).

In the following, applying the virtual paraboloid S1 in which the apex P2 is located outside 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". Further, the amount of offset from the apex P2 of the virtual paraboloid S1 is called an "offset amount". In one example, the "offset amount" is the amount by which the apex P2 of the virtual paraboloid S1 is deviated from the center points P3x2 and P3x3 of the half mirror (in other words, the distance between the apex 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 apex 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 apex P2 is shifted by an offset amount OFSx3 from the center point P3x3 of the mirror is applied.

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

The surface used as the base surface of the Fresnel structure is not limited to the paraboloid. A spherical shape may be used from the viewpoint of ease of production, or an aspherical shape may be used to correct aberrations. That is, various free-form surfaces (for example, curved surfaces whose focal points are defined) can be applied as the surface on which the Fresnel structure is based. In one preferred example, the characteristics of the half mirror with the substrate (cover layer) covering the reflective surface follow the paraboloid (ie, when light is incident perpendicularly to the combiner). A non-paraboloid can be applied as the underlying surface of the Fresnel structure (so that the light reflected by the reflecting surface and transmitted through the substrate and emitted towards the focal point of the paraboloid).

In FIG. 4, by using a 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 combiners 10x1, 10x2, and 10x3 shown in FIG. 3 are rotated 90 ° clockwise and then rotated so that the angle of the reflected light becomes horizontal and installed in the vehicle. .. From FIG. 4, for example, when a combiner 10x3 (a Fresnel structure having a relatively large offset amount is applied) is used, even if the combiner 10x3 is tilted in substantially the same direction as the windshield, the eyebox EB is placed on the driver's head. It can be seen that it can be formed appropriately in the vicinity. That is, the problem as shown in FIG. 2B (the problem that the eyebox EB2 of the real image RI installed near the ceiling is formed in the abdomen in the combiner 10 inclined in the same direction as the windshield) is solved. It can be said that it can be done.

Here, unlike the general combiner 10 as shown in FIG. 1, the combiner 10x to which the Fresnel structure as described above is applied has some problems because its reflecting surface S2 exists in the substrate instead of the surface. (Problems 1 and 2) can occur. The first problem is that the light reflected by the reflecting surface S2 inside the substrate in the combiner 10x may not be emitted from the substrate (cover layer) due to total internal reflection. The second problem is that the amount of light reaching the observer changes 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 shows a diagram for specifically explaining the problem 1. 5 (a) and 5 (b) exemplify the light reflected by the reflecting surface S2 inside the substrate in the combiner 10x (as shown in the figure, 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 on the surface of the substrate and is not emitted from the inside of the substrate to the outside (guided inside the substrate). From FIGS. 5A and 5B, it can be said that the problem 1 is likely to occur when the Fresnel structure having a relatively large offset amount is applied.

FIG. 6 shows a diagram for specifically explaining the problem 2. FIG. 6A shows a case where the real image RI is installed on the combiner 10x in a state of being tilted 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 θ ₁ where the light is incident on the lower part of the combiner 10x is larger than the incident angle θ ₂ where the light is incident on the upper part of the combiner 10x (θ ₁ > θ ₂ ).

FIG. 6B shows the relationship between the incident angle [°] and the “transmittance at incident × transmittance at exit” [%] in the combiner 10. The “transmittance at the time of incidence × transmittance at the time of emission” corresponds to the amount of light emitted from the combiner 10x (that is, the amount of light reaching the observer). In FIG. 6B, the reference numeral GRp shows a graph when P-polarized light is used, and the reference numeral GRs shows 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 the result obtained when light is incident on the position of [mm] (the reflectance of the reflecting surface S2 is assumed to be 100%).

From FIG. 6B, it can be seen that the value of “transmittance at the time of incidence × transmittance at the time of emission” changes according to the angle of incidence on the combiner 10x. Specifically, it can be seen that the value of "transmittance at the time of incidence x transmittance at the time of emission" is significantly reduced in the region where the incident angle is large. Further, in S-polarized light, the magnitude of the value of "transmittance at incident x transmittance at exit" is smaller overall than that of P-polarized light, and the value of "transmittance at incident x transmittance at exit" begins to decrease. It can be seen that the incident angle is small. The value of "transmittance at incident x transmittance at exit" is 0 [%] in a region where the incident angle is approximately 10 [°] or less because total reflection has occurred.

From FIGS. 6A and 6B, when the combiner 10x is tilted in the same direction as the windshield and the real image RI is installed above the combiner 10x, the incident angles θ ₁ and θ ₂ become relatively large. Since the difference between the incident angle θ ₁ and the incident angle θ ₂ is also large, it can be said that there is a tendency for a difference in the value of “incident transmittance × emission transmittance” 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 embodiments) that can solve the problems 1 and 2 will be described. The first embodiment has the main purpose of solving the problem 1, and the second embodiment has the main purpose of solving the problem 2.

<First Example>
In the first embodiment, the combiner and the real image RI (substantially a light source) 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 internal reflection. It is a part. The same shall apply hereinafter.) Set the relative position. That is, in the first embodiment, the angle at which the light reflected by the reflection surface inside the substrate in the combiner is incident on the inner surface of the substrate surface (hereinafter, appropriately referred to as “injection angle”) is less than the total reflection angle. The relative position between the combiner and the real image RI is set in.

With reference to FIG. 7, the conditions of the incident angle for making the injection angle less than the total reflection angle will be described. FIG. 7 shows a cross-sectional image of the combiner 10a according to the first embodiment. As shown in FIG. 7, the 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 obtain an angle θ _in '. In this case, according to Snell's law, an equation such as "sinθ _in = n · sineθ _in '" holds. Then, this incident light is incident on the 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 apex P2 of the virtual paraboloid S1 ("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, the angle φ formed by the straight line passing through the point P10 and parallel to the x-axis and the tangent line 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 at the angle θ _in'is incident on the reflection 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-mentioned injection angle. The condition for setting the injection angle to be less than the total reflection angle "sin ^-1 (1 / n)" is expressed by the following equation (1).

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

θ _in '+ 2β = 2φ-θ _in '
= 2 tan ^-1 (OFS / 2f) -sin ^-1 (sin θ _in / n) Equation (2)
By substituting such an equation (2) into the equation (1), a condition that the incident angle θ _in must be satisfied _in order to make the injection angle less than the total reflection angle can be obtained. The condition is expressed by the following equation (3).

θ _in > sin ^-1 [n · sin {2tan ^-1 (OFS / 2f) -sin ^-1 (1 / n)}] Equation (3)
As shown in the equation (3), the conditions to be satisfied by the incident angle θ _in are expressed by the refractive index n, the offset amount OFS, and the focal length f.

In the first embodiment, the relative positions of the combiner 10a and the real image RI are set so 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 so that the light constituting the real image RI is incident on the combiner 10a at an incident angle θ _in satisfying the condition of the equation (3). As a result, 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 effectively used.

FIG. 8 shows a diagram for explaining an optimum arrangement example 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 combiners 10x2 and 10x3 described above. That is, in the combiner 10a according to the first embodiment, a half mirror to which an 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 basis of the Fresnel structure is 300 [mm]. An example is given when a combiner 10a having a vertical size of 150 [mm] is used. In this combiner 10a, the offset amount (distance between the focal point of the virtual paraboloid that is the basis of the Fresnel structure and the upper end portion of the combiner 10a) is 200 [mm] at the upper end portion, and the offset amount (the Fresnel structure) at the lower end portion. The distance between the focal point of the original virtual paraboloid and the lower end of the combiner 10a) is 350 [mm]. Further, 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 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. 8 (b) and 8 (c) 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 of the combiner 10a is -3.3 [°], and the incident angle at which light is incident on the lower end 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 offset amount [mm] is shown on the horizontal axis, the incident angle [°] is shown on the vertical axis, and the region satisfying the above-mentioned equation (3) is filled in. It is assumed that the parameters (n, f) described in the description of FIG. 8 (a) are substituted into the equation (3). According to FIG. 8 (d), in order to satisfy the condition of the equation (3), the incident angle must be -3.3 [°] or more at the upper end portion (offset amount = 200 [mm]) of the combiner 10a. It can be seen that the incident angle must be +34.2 [°] or more 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 of the combiner 10a, the light reflected by the reflection surface S2 inside the substrate is emitted to the outside as much as possible. 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, since the incident angle is +6 [°] at the upper end of the combiner 10a (that is, because 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 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 higher than that of the second arrangement example, the condition of the equation (3) is appropriately satisfied, and the light reflected by the reflecting surface S2 inside the substrate is appropriately emitted. The Rukoto. Therefore, the entire surface of the combiner 10a can be effectively used.

<Second Example>
Next, the second embodiment will be described. The second embodiment has the main purpose of solving the problem 2. Specifically, in the second embodiment, the combiner is used so that the range of the incident angle is used so that the amount of change in the transmittance of the substrate in the combiner is equal to or less than a predetermined value (a value predetermined by conformity or the like). Set the relative position with the real image RI. That is, in the second embodiment, the relative position between the combiner and the real image RI is set so that the region where the transmittance of the substrate is less dependent on the incident angle is used. According to such a second embodiment, it is possible to appropriately suppress the occurrence of luminance change (luminance unevenness) in the plane of the combiner.

FIG. 9 shows a diagram for explaining an optimum arrangement example of the combiner 10b according to the second embodiment. FIG. 9A shows a front image of the combiner 10b according to the second embodiment. The combiner 10b according to the second embodiment has the same basic configuration as the combiners 10x2 and 10x3 described above. That is, in the combiner 10b according to the second embodiment, a half mirror to which an 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 basis of the Fresnel structure is 300 [mm]. An example is given when a combiner 10b having a vertical size of 100 [mm] is used. In this combiner 10b, the offset amount (distance between the focal point of the virtual parabolic surface that is the basis 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 (distance between the focal point of the virtual parabolic surface that is the source of the Fresnel structure and the point B) is 200 [mm], and at the point C located at the lower end, the offset amount (the distance of the virtual parabolic surface that is the source of the Fresnel structure) It is assumed that the distance between the focal point and the point C) is 250 [mm]. Further, a case where the size of the real image RI (display screen) in the vertical direction is 36 [mm] and the distance between the real image RI and the combiner 10b is 180 [mm] will be taken 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 example of the combiner 10b. An arrangement example is shown. 9 (b) to 9 (d) show side image views of the combiner 10b and the real image RI. In the first arrangement example, the incident angle of the combiner 10b at the point A is -10 [°], the incident angle of the combiner 10b at the point B is 0 [°], and the incident angle of the combiner 10b at the point C. Is +10 [°]. In the second arrangement example, the incident angle of the combiner 10b at the point A is +19 [°], the incident angle of the combiner 10b at the point B is +30 [°], and the incident angle of the combiner 10b at the point C is. It is +37 [°]. In the third arrangement example, the incident angle of the combiner 10b at the point A is +52 [°], the incident angle of the combiner 10b at the point B is +60 [°], and the incident angle of the combiner 10b at the point C is. It is +64 [°].

FIG. 9E is a diagram showing the relationship between the angle of incidence [°] on the substrate and the transmittance of the substrate (which means the transmittance of light reciprocating in the substrate). In FIG. 9E, graph GR1 shows the transmittance of the substrate with respect to the light incident on the point A of the combiner 10b, and graph GR2 shows the transmittance of the substrate with respect to the light incident on the point B of the combiner 10b. Graph GR3 shows the transmittance of the substrate with respect to the light incident on the point C of the combiner 10b. Graphs GR1 to GR3 are obtained based on a known formula for calculating interfacial reflectance (Fresnel reflectance). Further, the 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, respectively, to obtain points A1, B1, and C1, and these points A1. , B1 and C1 are connected to obtain a broken line D1. From the broken line D1, it can be seen that the amount of change in the transmittance with respect to the incident angle is large when the first arrangement example is applied. Therefore, when the first arrangement example is applied, it can be said that the change in brightness (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, 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 the amount of change in the transmittance with respect to the incident angle is small when the second arrangement example is applied. Therefore, when the second arrangement example is applied, it can be said that the in-plane luminance change (luminance unevenness) of the combiner 10b hardly occurs. Therefore, in the second embodiment, such a second arrangement example will be 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, respectively, to obtain points A3, B3, and C3, and 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 amount of change in transmittance is smaller than when the first arrangement example is applied, but the amount of change in transmittance is smaller than when the second arrangement example is applied. You can see that it is big. Further, it can be seen that the amount of change in the transmittance becomes large 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 sudden change in brightness occurs even if the combiner 10b is slightly tilted from the installation angle in the third arrangement example. Therefore, in the second embodiment, such a third arrangement example is not adopted.

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

In the above, it was stated that the second embodiment was mainly intended to solve the problem 2, but the problem 1 is also solved according to the second embodiment. 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 Reflective surface RI Real image VI Virtual image

Claims (1)

A light source unit that emits light that constitutes the display image,
A mirror having a Fresnel structure that recognizes the displayed image as a virtual image by reflecting a part of the light emitted by the light source unit.
A substrate provided on the incident surface side of the light with respect to the mirror so as to face the mirror.
An optical system including the light source unit, the mirror, and the substrate that guides the light reflected by the mirror to the outside of the substrate without being totally reflected by the substrate.
A display device characterized by having.

Images