Head-up display

Abstract

To provide a head-up display that effectively inhibits stray light caused by external light and can be reduced in size.SOLUTION: A head-up display comprises a device that emits light in a predetermined region corresponding to an original image and a projection optical system that projects a projection image. The projection optical system includes: a first mirror that reflects the light in the predetermined region emitted from the device in a shape of a reflection surface; a first lens that condenses the light reflected by the first mirror; a second mirror that reflects the light and forms an intermediate image; and a third mirror that reflects the light forming the intermediate image to a reflection member. The first mirror, the first lens, the second mirror, and the third mirror are arranged in order along an optical path to the reflection member.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a head-up display.

Background Art

[0002] Patent Document 1 discloses a head-up display that projects a display image onto a windshield. This head-up display includes a display device having a display surface for displaying an image on the display surface, a concave mirror, and a lens having a condensing action disposed between the concave mirror and the display surface. Further, this head-up display includes a first optical system that forms an intermediate image in which the image is enlarged by imaging the light rays emitted from the display surface via the lens and the concave mirror. Furthermore, this head-up display includes a second optical system that projects the intermediate image onto the windshield. The intermediate image formed by imaging by the first optical system is larger than the display image displayed by the display device on the display surface. Thereby, miniaturization of the first optical system and the second optical system is achieved.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] The present disclosure provides a head-up display that is effective in suppressing stray light caused by external light and can be miniaturized.

[0005] The head-up display of the present disclosure is a head-up display that projects a projected image formed from an original image onto a transmissive reflective member to allow an observer to visually recognize a virtual image, and includes a device that emits light in a predetermined region corresponding to the original image, and a projection optical system that projects the projected image. The projection optical system includes a first mirror that reflects the light in the predetermined region emitted from the device in the shape of a reflection surface, a first lens that condenses the light reflected by the first mirror, a second mirror that reflects light to form an intermediate image, and a third mirror that reflects the light that has formed the intermediate image to the reflective member. The first mirror, the first lens, the second mirror, and the third mirror are arranged in the order of the optical path to the reflective member.

[0006] The head-up display according to the present disclosure presents a virtual image with little distortion, is effective in suppressing stray light due to external light, and can be miniaturized.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0008] (Knowledge underlying the present disclosure) The head-up display of Patent Document 1 aims to reduce the size of the head-up display device by using an optical system that forms an intermediate image. However, in a head-up display device, with the three-dimensionalization of virtual images and the like, there is a strong demand for further size reduction.

[0009] The present disclosure provides a head-up display that can be made smaller than conventional ones by using a lens having a condensing action between an optical element having a condensing action and an optical element having a diverging action.

[0010] (Embodiment 1) Hereinafter, Embodiment 1 will be described with reference to FIGS. 1 to 4.

[0011] [1-1. Configuration] [1-1-1. Overall configuration of the head-up display] Specific embodiments and examples of the head-up display 100 of the present disclosure will be described below with reference to the drawings.

[0012] FIG. 1 is a cross-sectional view of a vehicle 200 equipped with the head-up display 100 according to the present disclosure. As shown in FIG. 1, the head-up display 100 is disposed inside a dashboard 210 below a windshield 220 of the vehicle 200. An observer D recognizes an image projected from the head-up display 100 as a virtual image I.

[0013] FIG. 2 is a schematic diagram showing the configuration of the head-up display 100 according to the present embodiment. FIG. 3 is a schematic diagram for explaining the configuration of the head-up display 100 according to the present embodiment.

[0014] As shown in FIG. 2, the head-up display 100 includes a display device 110 and a projection optical system 140. The head-up display 100 projects an image displayed by the display device 110 onto the windshield 220. The projected light is reflected by the windshield 220 and guided to the viewing area 300 of the observer D. Thereby, the head-up display 100 allows the observer D to visually recognize the virtual image I. Here, the viewing point is the principal point when considering the eyes of the observer D as lenses. Further, the viewing area 300 is an area where the virtual image I can be visually recognized without omission, and is the area where the viewing point of the observer D is located.

[0015] Here, in the present disclosure, the front is the direction in which the windshield 220 of the vehicle 200 is located as seen from the observer D. The rear is the direction opposite to the front. Also, the downward direction is the direction of the ground on which the vehicle 200 travels. The upward direction is the direction opposite to the downward direction. The inner side is the passenger seat side as seen from the observer D in the driver's seat. The outer side is the direction opposite to the inner side. Also, the viewing area 300 is an area where the observer D can visually recognize the virtual image I without omission.

[0016] Here, as shown in FIG. 2, among the light rays emitted from the display device 110, the light ray that reaches the viewing area 300 is defined as the light ray L. Also, among the light rays emitted from the display device 110, the light ray that passes through the center of the virtual image I and reaches the center of the viewing area 300 is defined as the reference light ray Lc. That is, when viewed from the observer D, the reference light ray Lc corresponds to the optical path from the center of the virtual image I to the viewing point of the observer D. The reference light ray Lc visually recognized by the observer D is actually the one that has reached the observer D from the display device 110 through the optical system. Therefore, the light ray from the display device 110 to the observer D corresponding to the reference light ray Lc emitted from the center of the virtual image I is also expressed as the reference light ray Lc, and the optical path corresponding to these light rays is also expressed as the reference light ray Lc. However, it is assumed that the viewing point of the observer D is at the center of the viewing area 300.

[0017] The display device 110 displays a display image on a diffusing surface or the like based on control by a control unit such as a CPU (not shown). As the display device 110, for example, a liquid crystal display (LCD) with a backlight, an organic light-emitting diode (OLED), a plasma display, or the like can be used. Further, as the display device 110, a screen that diffuses or reflects light and a projector or a scanning laser may be used to generate an image. The display device 110 can display various types of information such as road navigation display, the distance to the vehicle ahead, the remaining battery level of the vehicle, and the current vehicle speed. Further, the display device 110 may electronically distort the image in advance according to the distortion generated in the projection optical system 130 or the windshield 220 and the position of the observer D obtained by a camera (not shown). Thereby, a good virtual image I can be visually recognized by the observer D. Further, the display device 110 may display display pixels of a plurality of wavelengths shifted for each display position in advance according to the chromatic aberration generated in the projection optical system 130. Thereby, a good virtual image I can be visually recognized by the observer D.

[0018] The projection optical system 140 includes a relay optical system 120 and a projection optical system 130. The relay optical system 120 includes a second lens 121, a first mirror 122 as a first optical element, a first lens 123, and a second mirror 124 as a second optical element. The relay optical system 120 forms an intermediate image M that magnifies the display image by imaging the light beam emitted from the display device 110. The intermediate image M is formed to be larger than the display image displayed on the screen of the display device 110. That is, even if the display image displayed on the screen of the display device 110 is small, a large intermediate image M can be obtained. Thereby, the size of the screen of the display device 110 can be reduced. Further, since the intermediate image M is large, the magnification in the projection optical system 130 can be lowered. Thereby, the positive power of the third mirror 125 of the projection optical system 130 can be weakened, and screen distortion can be suppressed.

[0019] The intermediate image M does not need to be imaged at a good point at the intermediate image position. Spherical aberration, coma aberration, field curvature, and astigmatism may occur.

[0020] The projection optical system 130 includes a third mirror 125. The projection optical system 130 reflects the intermediate image M formed by the relay optical system 120 via the third mirror 125. Thereby, the projection optical system 130 projects the intermediate image M onto the windshield 220. Note that the intermediate image M is an aerial image formed in the air and does not form an image on a projection surface that diffusely reflects. The third mirror 125 is disposed on the optical path from the intermediate image M to the windshield 220.

[0021] [1-1-2. Arrangement Configuration of Projection Optical System, Relay Optical System, and Display Device] As shown in FIG. 2, the second lens 121 is located in front of the vehicle 200 in the forward direction with respect to the display device 110. As shown in FIG. 2, the second lens 121 is arranged to be inclined counterclockwise with respect to the reference ray Lc in a view from the XZ plane of FIG. 2. Thereby, it is possible to prevent stray light caused by external light entering the housing and reflecting on the display surface of the display device 110.

[0022] Further, the second lens 121 is a free-form surface lens having different curvatures in the X-axis direction and the Y-axis direction. The surface (incident surface) of the second lens 121 on the display device 110 side has a shape in which the X-axis direction and the Y-axis direction face the display device 110 side in a plane. Also, the surface (exit surface) of the second lens 121 on the first mirror 122 side has a convex shape in which the X-axis direction and the Y-axis direction are convex toward the first mirror 122 side.

[0023] The first mirror 122 is located in front of the second lens 121 in the forward direction of the vehicle 200. The first mirror 122 condenses the light rays emitted from the second lens 121 and reflects them toward the first lens 123. The reflecting surface of the first mirror 122 is eccentrically arranged so as to reflect the display image displayed on the display device 110 in the direction of the second mirror 124. Here, the reflecting surface of the first mirror 122 is concave. That is, the first mirror 122 enlarges the light incident from the second lens 121 and projects it onto the first lens 123. Also, the first mirror 122 has a free-form surface shape. This is to correct the distortion of the virtual image caused by reflection.

[0024] The first lens 123 is located behind the first mirror 122 in the rearward direction of the vehicle 200 as shown in FIG. 2. The first lens 123 is arranged to be inclined downward with respect to the reference light ray Lc as shown in FIG. 2. Thereby, it is possible to prevent stray light caused by external light entering the housing and reflecting on the display surface of the display device 110.

[0025] Also, the first lens 123 is a free-form surface lens having different curvatures in the X-axis direction and the Y-axis direction. The incident surface, which is the surface of the first lens 123 on the first mirror 122 side, has a convex surface shape that is convex in the X-axis direction and the Y-axis direction on the first mirror 122 side. Also, the exit surface, which is the surface of the first lens 123 on the second mirror 124 side, has a shape in which the X-axis direction and the Y-axis direction face the display device 110 side with a flat surface.

[0026] The second mirror 124 is located behind the first lens 123 in the rearward direction of the vehicle 200. The second mirror 124 diverges the light rays emitted from the first lens 123 and forms an intermediate image M in which the display image is enlarged in the optical path between the second mirror 124 and the third mirror 125. The reflecting surface of the second mirror 124 is eccentrically arranged so as to enlarge the display image projected by the first lens 123 and form the intermediate image M in the optical path between the second mirror 124 and the third mirror 125. Here, the reflecting surface of the second mirror 124 is convex. The second mirror 124 has a free-form surface shape. This is to correct the distortion of the virtual image caused by reflection.

[0027] The projection optical system 130 includes a third mirror 125 as a third optical element. The third mirror 125 is located in front of the vehicle 200 in the forward direction compared to the second mirror 124. The third mirror 125 condenses the light rays diverged by the second mirror 124 and projects an intermediate image M onto the windshield 220. The reflecting surface of the third mirror 125 is eccentrically arranged so as to project the intermediate image M onto the windshield 220. Here, the reflecting surface of the third mirror 125 has a concave shape. The third mirror 125 has a free-form surface shape. This is to correct the distortion of the virtual image caused by reflection.

[0028] In the projection optical system 140 in the present embodiment, in the order of the optical path from the display device 110, a first mirror 122 as a first optical element having a condensing action and a third mirror 125 as a third optical element projecting the intermediate image M are arranged. Further, a first lens 123 having a condensing action is arranged between the first mirror 122 and the third mirror 125. In this way, by arranging the first lens 123 between the first mirror 122 that forms the intermediate image M and the third mirror 125 that projects the intermediate image M, the intermediate image M can be formed at a position close to the exit side of the first lens 123. That is, the first lens 123 itself can be miniaturized. As a result, the head-up display 100 can be miniaturized.

[0029] Also, in the relay optical system 120 in the present embodiment, a first lens 123 having a positive power and a second mirror 124 having a negative power are arranged from the display device 110 toward the intermediate image M. That is, in the relay optical system 120, a so-called telephoto arrangement is adopted. By adopting such a telephoto arrangement, the first lens 123 increases the negative power of the second mirror 124, and the second mirror 124 increases the positive power of the first lens 123. That is, the first lens 123 and the second mirror 124 enhance the power of each other. As a result, the overall length of the relay optical system 120 can be shortened, and the head-up display 100 can be miniaturized.

[0030] FIG. 3 is a diagram for explaining the effect of the telephoto arrangement. In FIG. 3, for ease of understanding, the relay optical system 120 and the projection optical system 130 are arranged on a straight line. As can be seen from FIG. 3, compared with the comparative example without the first lens 123 shown in FIG. 3(A), in the present embodiment in which the first lens 123 and the second mirror 124 shown in FIG. 3(B) are in a telephoto arrangement, the overall length of the relay optical system 120 is shorter.

[0031] Also, in the vicinity of the second mirror 124 having a negative power for forming the intermediate image M, the light rays for forming the intermediate image M are converging. By arranging the first lens 123 having a positive power in the vicinity of the second mirror 124 having such a negative power to realize a telephoto arrangement, the first lens 123 itself can be miniaturized.

[0032] As described above, in the present embodiment, a first lens 123 having a positive power is arranged between the first mirror 122 as the first optical element and the third mirror 125 as the third optical element for projecting the intermediate image M. In particular, in the order of the optical path from the display device 110, the first lens 123 having a positive power is arranged in front of the second mirror 124 having a negative power and forming the intermediate image M. Thereby, by shortening the overall length of the relay optical system 120 and miniaturizing the first lens 123 itself, the head-up display 100 can be miniaturized.

[0033] Also, in the present embodiment, as shown in FIG. 4, the incident surface and the exit surface of the second lens 121 are inclined counterclockwise with respect to the reference ray Lc in the XZ plane view of FIG. 4. Further, the incident surface and the exit surface of the first lens 123 are inclined clockwise with respect to the reference ray Lc in the XZ plane view of FIG. 4. Thereby, the reflected light due to external light in the first lens 123 is reflected upward from the first mirror 122, and the reflected light due to external light in the second lens 121 is reflected downward from the first mirror 122. That is, it is possible to prevent external light from entering the viewpoint region 300. Here, the inclination of the second lens 121 and the first lens 123 with respect to the reference ray Lc is desirably set to an angle such that when external light incident along the reference ray Lc is reflected at the incident surface or the exit surface, the reflected light does not enter the first mirror 122. More desirably, the above inclination is set to an angle such that when external light incident from the first mirror 122 to the second lens 121 or the first lens 123 is reflected at the incident surface or the exit surface of the second lens 121 or the first lens 123, the reflected light does not enter the first mirror 122. Note that the fact that the second lens 121 and the first lens 123 are inclined with respect to the reference ray Lc means that the location where the optical refracting surface of the second lens 121 and the first lens 123 intersects the reference ray Lc is not horizontal with respect to the plane perpendicular to the reference ray Lc.

[0034] In the present embodiment, the second lens 121 has a wedge shape in which the lens thickness becomes thinner toward the lower side with respect to the reference ray Lc. The first lens 123 has a wedge shape in which the lens thickness becomes thinner toward the upper side with respect to the reference ray Lc. When the exit surface of the second lens 121 has a convex surface shape symmetric in the vertical direction with respect to the reference ray Lc, when the second lens 121 is inclined with respect to the reference ray Lc, the optical path length of the light ray passing through the upper side of the second lens 121 with respect to the reference ray Lc is different from the optical path length of the light ray passing through the lower side. Similarly, when the incident surface of the first lens 123 has a convex surface shape symmetric with respect to the reference ray Lc, when the first lens 123 is inclined with respect to the reference ray Lc, the optical path length of the light ray passing through the upper side of the first lens 123 with respect to the reference ray Lc is different from the optical path length of the light ray passing through the lower side.

[0035] Therefore, in the present embodiment, the second lens 121 has a wedge shape in which the lens thickness becomes thinner toward the lower side with respect to the reference ray Lc. Further, the first lens 123 has a wedge shape in which the lens thickness becomes thinner toward the upper side with respect to the reference ray Lc. By configuring in this way, the light ray emitted from the display device 110 and transmitted through the upper side (i.e., the thick portion of the lens thickness of the second lens 121) with respect to the reference ray Lc of the second lens 121 is reflected by the first mirror 122. Then, the reflected light ray passes through the upper side (i.e., the thin portion of the lens thickness of the first lens 123) with respect to the reference ray Lc of the first lens 123. Also, the light ray emitted from the display device 110 and transmitted through the lower side (i.e., the thin portion of the lens thickness of the second lens 121) with respect to the reference ray Lc of the second lens 121 is reflected by the first mirror 122. Then, the reflected light ray passes through the lower side (i.e., the thick portion of the lens thickness of the first lens 123) with respect to the reference ray Lc of the first lens 123. In this way, the optical path length of the light ray passing through the second lens 121 and the first lens 123 is adjusted, and the optical path length of the light ray can be made uniform regardless of the location passing through the second lens 121 and the first lens 123.

[0036] In the present embodiment, the exit surface of the second lens 121 is provided downward with respect to the entrance surface. That is, the shape of the second lens 121 in the Y-axis direction is a wedge shape. By making the cross-sectional shape along the Y-axis direction of the second lens 121 a wedge shape, the optical path length of the light passing through the upper side of the second lens 121 becomes longer than the optical path length of the light passing through the lower side of the second lens 121. That is, the optical path length until the video light emitted from the display device 110 reaches the first mirror 122 can be changed according to the position in the Y-axis direction. Thereby, the decentered image plane curvature generated in the first mirror 122 can be corrected favorably.

[0037] [1-2. Effects, etc.] A head-up display 100, which is an example of the head-up display according to Embodiment 1, is a head-up display that projects an image onto a windshield 220 (an example of a transmissive reflective member) so that an observer D can visually recognize a virtual image I. The head-up display 100 includes a display device 110, which is an example of a display device, and a projection optical system 140. The display device 110 displays an image. The projection optical system 140 has a function of forming an image of the image displayed by the display device 110 as an intermediate image M. The projection optical system 140 includes, in order of the optical path from the display device 110, a first mirror 122, which is an example of a first optical element having a condensing action, a first lens 123 having a condensing action, and a third mirror 125, which is an example of a third optical element that projects the intermediate image M. Thus, in the head-up display 100 according to Embodiment 1, a first lens 123 is disposed between the first mirror 122 that creates the intermediate image M and the third mirror 125 that projects the intermediate image M. Therefore, the intermediate image M can be formed at a position close to the exit side of the first lens 123. As a result, the first lens 123 itself can be miniaturized, and the head-up display 100 can be miniaturized.

[0038] The head-up display 100 according to Embodiment 1 uses a first mirror 122 as an example of a first optical element and a third mirror 125 as an example of a third optical element. Therefore, it is possible to enlarge the image displayed on the small display device 110 to create the intermediate image M, and further enlarge the intermediate image M and project it onto the observer D.

[0039] The projection optical system 140 according to Embodiment 1 includes a second mirror 124, which is an example of a second optical element having a diverging action, between the first lens 123 and a third mirror 125, which is an example of a third optical element. Then, in the order of the optical path from the display device 110, the first lens 123 having a positive power is disposed in front of the second mirror 124 having a negative power and forming the intermediate image M to form a telephoto arrangement. Therefore, the overall length of the relay optical system 120 can be shortened, and the first lens 123 itself can be miniaturized, so that the head-up display 100 can be miniaturized.

[0040] In the head-up display 100 according to Embodiment 1, as an example of the second optical element, a second mirror 124 having a negative power is used near the intermediate image M. Thereby, the second mirror 124 functions as a so-called field lens. Therefore, the first lens 123, the first mirror 122, and the second lens 121 can be miniaturized.

[0041] In the head-up display 100 according to Embodiment 1, at least one surface of the first lens 123 has a free-form surface shape. Therefore, in an imaging optical system such as the head-up display 100, good optical characteristics can be realized while suppressing reflection of external light.

[0042] In the head-up display 100 according to Embodiment 1, the first lens 123 has a wedge shape. Therefore, even when the first lens 123 is tilted with respect to the reference light beam Lc, the optical path length of the light beam passing through the first lens 123 can be adjusted.

[0043] The head-up display 100 according to Embodiment 1 includes a second lens 121 between the display device 110 and a first mirror 122 which is an example of the first optical element. The second lens 121 has a wedge shape and at least one surface has a free-form surface shape. Further, the first lens 123 and the second lens 121 are arranged such that the light beam passing through the portion where one lens thickness is thin passes through the portion where the other lens thickness is thick, and the light beam passing through the portion where one lens thickness is thick passes through the portion where the other lens thickness is thin. Therefore, even when the first lens 123 and the second lens 121 are tilted with respect to the reference light beam Lc, the optical path lengths of the light beams passing through the first lens 123 and the second lens 121 can be made uniform.

[0044] In the head-up display 100 according to Embodiment 1, the intermediate image M is an aerial image formed in the air on the optical path from the display device 110 to the virtual image I. Therefore, without adding a member for forming the intermediate image M, the image displayed on the small display device 110 can be enlarged to form the intermediate image M, and the intermediate image M can be further enlarged and projected onto the observer D.

[0045] In the head-up display 100 according to Embodiment 1, the first mirror 122, the first lens 123, and the second mirror 124 are arranged in the order of the optical path from the display device 110. As a result, the first lens 123 and the second mirror 124 enhance each other's power. As a result, the overall length of the relay optical system 120 can be shortened, and the head-up display 100 can be miniaturized.

[0046] A vehicle 200, which is an example of a moving body according to Embodiment 1, includes a head-up display 100 and a windshield 220 as a transmissive reflective member. As a result, the observer D driving the vehicle 200 can visually recognize the image projected on the windshield 220 as the virtual image I.

[0047] (Embodiment 2) Next, Embodiment 2 will be described with reference to FIG. 5.

[0048] [2-1. Configuration] FIG. 5 is a schematic diagram for explaining the optical path for explaining the head-up display 100 according to Embodiment 2. As shown in FIG. 5, the head-up display 100 of the present embodiment includes a third lens 126 in which a first lens portion 126a and a second lens portion 126b corresponding to the first lens and the second lens in Embodiment 1 are integrally formed.

[0049] As shown in FIG. 5, the third lens 126 is located in front of the display device 110 and the second mirror 124 in the forward direction of the vehicle 200. In the third lens 126, as shown in FIG. 5, the surface on the side facing the first mirror 122 has a convex shape convex toward the first mirror 122 in the X-axis direction and the Y-axis direction. Also, in the third lens 126, as shown in FIG. 5, the surface on the side facing the display device 110 and the second mirror 124 has a planar shape facing the display device 110 and the second mirror 124. The third lens 126 is a free-form surface lens in which the curvature of the convex surface is different in the X-axis direction and the Y-axis direction.

[0050] In the optical path from the display device 110 to the first mirror 122, the planar surface of the second lens portion 126b is the incident surface, and the convex surface is the exit surface. In the second lens portion 126b, the incident surface and the exit surface are arranged to be inclined in the counterclockwise direction in the XZ plane view shown in FIG. 5 with respect to the reference light beam Lc. Thereby, it is possible to prevent stray light caused by external light entering the housing and reflecting off the display surface of the display device 110 and the first mirror 122.

[0051] In the optical path from the first mirror 122 to the second mirror 124, the planar surface of the first lens portion 126a is the exit surface, and the convex surface is the incident surface. The first lens portion 126a is arranged to be inclined in the clockwise direction in the XZ plane view shown in FIG. 5 with respect to the reference light beam Lc. Thereby, it is possible to prevent stray light caused by external light entering the housing and reflecting off the display surface of the display device 110 and the first mirror 122.

[0052] In the relay optical system 120 according to the present embodiment, a first lens unit 126a having a positive power and a second mirror 124 having a negative power are arranged from the display device 110 toward the intermediate image M. That is, in the relay optical system 120, a so-called telephoto arrangement is adopted. By adopting such a telephoto arrangement, the first lens unit 126a enhances the negative power of the second mirror 124, and the second mirror 124 enhances the positive power of the first lens unit 126a. That is, the first lens unit 126a and the second mirror 124 enhance the power of each other. As a result, the overall length of the relay optical system 120 can be shortened, and the head-up display 100 can be miniaturized.

[0053] As described above, in the present embodiment, the first lens unit 126a is arranged between the first mirror 122 as the first optical element and the third mirror 125 as the third optical element that projects the intermediate image M. In particular, in the order of the optical path from the display device 110, the first lens unit 126a having a positive power is arranged in front of the second mirror 124 that has a negative power and forms the intermediate image M. As a result, the overall length of the relay optical system 120 is shortened, and the head-up display 100 can be miniaturized by miniaturizing the first lens unit 126a itself.

[0054] In the present embodiment, the third lens 126 is a lens in which a first lens unit 126a and a second lens unit 126b corresponding to the second lens 121 and the first lens 123 in the first embodiment are integrally formed. The first lens unit 126a and the second lens unit 126b have a wedge shape in which the lens thickness becomes thinner toward the end side with respect to the central portion of the third lens 126. When the third lens 126 is tilted with respect to the reference light beam Lc as described above, in the optical path from the display device 110 to the first mirror 122, the optical path length of the light beam passing through the upper side of the second lens unit 126b with respect to the reference light beam Lc is different from the optical path length of the light beam passing through the lower side. Similarly, in the optical path from the first mirror 122 to the second mirror 124, the optical path length of the light beam passing through the upper side of the first lens unit 126a with respect to the reference light beam Lc is different from the optical path length of the light beam passing through the lower side.

[0055] Therefore, in the present embodiment, the second lens unit 126b has a wedge shape in which the lens thickness becomes thinner toward the lower side with respect to the reference light beam Lc, and the first lens unit 126a has a wedge shape in which the lens thickness becomes thinner toward the upper side with respect to the reference light beam Lc. By configuring in this way, the light beam emitted from the display device 110 and transmitted through the upper side with respect to the reference light beam Lc of the second lens unit 126b (that is, the portion where the lens thickness of the second lens unit 126b is thick) is reflected by the first mirror 122. Then, the reflected light beam passes through the upper side with respect to the reference light beam Lc of the first lens unit 126a (that is, the portion where the lens thickness of the first lens unit 126a is thin).

[0056] Also, the light beam emitted from the display device 110 and transmitted through the lower side with respect to the reference light beam Lc of the second lens unit 126b (that is, the portion where the lens thickness of the second lens unit 126b is thin) is reflected by the first mirror 122. Then, the reflected light beam passes through the lower side with respect to the reference light beam Lc of the first lens unit 126a (that is, the portion where the lens thickness of the first lens unit 126a is thick).

[0057] In the present embodiment, in this way, the optical path lengths of the light beams passing through the second lens unit 126b and the first lens unit 126a of the third lens 126 are adjusted, and the optical path lengths of the light beams can be made uniform regardless of the portions passing through the third lens 126.

[0058] Here, the inclination of the third lens 126 with respect to the reference light beam Lc is preferably set to an angle such that the external light incident along the reference light beam Lc is not reflected by the incident surface or the exit surface of the third lens 126 and the reflected light does not enter the first mirror 122. Note that the fact that the third lens 126 is inclined with respect to the reference light beam Lc means that the portion where the optical refracting surface of the third lens 126 intersects the reference light beam Lc is not horizontal with respect to the plane perpendicular to the reference light beam Lc.

[0059] Furthermore, in the optical path from the display device 110 to the first mirror 122, the exit surface of the second lens unit 126b is provided downward relative to the entrance surface. The shape of the second lens unit 126b in the Y-axis direction is wedge-shaped. By making the cross-sectional shape along the Y-axis direction of the second lens unit 126b wedge-shaped, in the optical path from the display device 110 to the first mirror 122, the optical path length of the light passing above the second lens unit 126b becomes longer than the optical path length of the light passing below the second lens unit 126b. That is, the optical path length from when the video light emitted from the display device 110 reaches the first mirror 122 can be changed according to the position in the Y-axis direction. Thereby, the decentered image plane curvature generated in the first mirror 122 can be corrected favorably.

[0060] In the present embodiment, as described above, a third lens 126 is provided in which the first lens unit 126a and the second lens unit 126b corresponding to the second lens 121 and the first lens 123 in Embodiment 1 are integrated. Thereby, the number of components can be reduced, and the manufacturing cost of the head-up display 100 can be reduced.

[0061] [2-2. Effects, etc.] As an example of the head-up display according to Embodiment 2, the head-up display 100 is a head-up display that allows an observer D to visually recognize a virtual image I. The head-up display 100 includes a display device 110 as an example of a display device and a projection optical system 140. The display device 110 displays an image. The projection optical system 140 has a function of forming an image of the image displayed by the display device 110 as an intermediate image M. The projection optical system 140 includes, in the order of the optical path from the display device 110, a first mirror 122 as an example of a first optical element having a condensing action, and a third lens 126 having a condensing action. The third lens 126 is a lens in which a first lens portion 126a and a second lens portion 126b corresponding to the first lens 123 and the second lens 121 in Embodiment 1 are integrally formed. Further, the projection optical system 140 includes a third mirror 125 as an example of a third optical element that projects the intermediate image M. Thus, in the head-up display 100 according to Embodiment 2, the first lens portion 126a is disposed between the first mirror 122 that forms the intermediate image M and the third mirror 125 that projects the intermediate image M. Therefore, the intermediate image M can be formed at a position close to the exit side of the first lens portion 126a, and the first lens portion 126a itself can be miniaturized. As a result, the head-up display 100 can be miniaturized. Also, in the third lens 126, the second lens 121 and the first lens 123 in Embodiment 1 are integrally formed. Therefore, the number of parts can be reduced, and the manufacturing cost of the head-up display 100 can be reduced.

[0062] The projection optical system 140 according to Embodiment 2 includes a second mirror 124 as an example of a second optical element having a diverging action between the first lens portion 126a and the third mirror 125 as an example of a third optical element. Then, in the order of the optical path from the display device 110, the first lens portion 126a having a positive power is disposed in front of the second mirror 124 having a negative power and forming the intermediate image M to form a telephoto arrangement. Therefore, by shortening the overall length of the relay optical system 120 and miniaturizing the first lens portion 126a itself, the head-up display 100 can be miniaturized.

[0063] In this embodiment, the light beam emitted from the display device 110 passes through the third lens 126 twice in the optical path from the display device 110 to the first mirror 122 and in the optical path from the first mirror 122 to the second mirror 124. Also in this case, the projection optical system 140 includes, in the order of the optical path from the display device 110, the first mirror 122 having a condensing action, the third lens 126 having a condensing action, the second mirror 124 having a diverging action, and the third mirror 125 for projecting the intermediate image M, which remains unchanged. Further, the light beam emitted from the display device 110 travels in the order of the first mirror 122, the third lens 126, the second mirror 124, and the third mirror 125, and there is no change in allowing the observer D to visually recognize the virtual image I.

[0064] In the head-up display 100 according to the second embodiment, at least one surface of the third lens 126 has a free-form surface shape. Therefore, in an imaging optical system such as the head-up display 100, good optical characteristics can be realized while suppressing reflection of external light.

[0065] In the head-up display 100 according to the second embodiment, the first lens portion 126a and the second lens portion 126b of the third lens 126 have a wedge shape. Therefore, even when the third lens 126 is tilted with respect to the reference light beam Lc, the optical path length of the light beam passing through the third lens 126 can be adjusted.

[0066] In the head-up display 100 according to the second embodiment, the first lens portion 126a and the second lens portion 126b of the third lens 126 have a wedge shape. Therefore, in the optical path from the display device 110 to the first mirror 122, the light rays passing through the portion where the lens thickness of the second lens portion 126b is thin pass through the portion where the lens thickness of the first lens portion 126a is thick in the optical path from the first mirror 122 to the second mirror 124. Similarly, in the optical path from the display device 110 to the first mirror 122, the light rays passing through the portion where the lens thickness of the second lens portion 126b is thick pass through the portion where the lens thickness of the first lens portion 126a is thin in the optical path from the first mirror 122 to the second mirror 124. Therefore, even when the third lens 126 is tilted with respect to the reference light ray Lc, the optical path lengths of the light rays passing through the third lens 126 can be made uniform.

[0067] In the head-up display 100 according to the second embodiment, the intermediate image M is an aerial image formed in the air on the optical path from the display device 110 to the virtual image I. Therefore, without adding a member for forming the intermediate image M, it is possible to enlarge the image displayed on the small display device 110 to form the intermediate image M, and further enlarge the intermediate image M and project it onto the observer D.

[0068] (Embodiment 3) Next, Embodiment 3 will be described with reference to FIG. 6.

[0069] [3-1. Configuration] FIG. 6 is a schematic diagram for explaining the optical path for explaining the head-up display 100 according to the third embodiment. As shown in FIG. 6, the head-up display 100 of the present embodiment includes a fourth lens 127 as another example of the first optical element.

[0070] The display device 110 and the second lens 121 of the present embodiment have the same configuration as the display device 110 and the second lens 121 in each of the above-described embodiments. However, the arrangement positions are different from those in each of the above-described embodiments. In the present embodiment, as shown in FIG. 6, the display device 110 and the second lens 121 are located in front of the vehicle 200 rather than the fourth lens 127 as the first optical element.

[0071] As shown in FIG. 6, both the incident surface on the side facing the second lens 121 and the exit surface on the side facing the first lens 123 of the fourth lens 127 have a convex surface shape convex to the respective sides of the second lens 121 and the first lens 123 in the X-axis direction and the Y-axis direction. The fourth lens 127 is a free-form surface lens in which the curvature of the convex surface shape is different in the X-axis direction and the Y-axis direction.

[0072] In the present embodiment, the second lens 121, the fourth lens 127, and the first lens 123 are arranged to be inclined in the clockwise direction in the XZ plane view shown in FIG. 6 with respect to the reference light beam Lc. Thereby, it is possible to prevent stray light caused by external light entering the housing and being reflected by the second lens 121, the fourth lens 127, or the first lens 123.

[0073] As described above, in the present embodiment, the fourth lens 127 as the first optical element is used. A first lens 123 having a positive power is disposed between the third mirror 125 as the third optical element that projects the intermediate image M and the fourth lens 127. In particular, in the order of the optical path from the display device 110, the first lens 123 having a positive power is disposed in front of the second mirror 124 having a negative power and forming the intermediate image M. Therefore, the overall length of the relay optical system 120 can be shortened, and the head-up display 100 can be miniaturized by miniaturizing the first lens 123 itself.

[0074] In this embodiment, although the positional relationship between the first lens 123 and the second lens 121 is different from that in the first embodiment, the positions of the thick and thin portions of the lens thickness with respect to the reference ray Lc are arranged to be opposite to each other. Therefore, similar to the first embodiment, the optical path length of the ray passing through the second lens 121 and the first lens 123 can be adjusted so that the optical path length of the ray is uniform regardless of the portion passing through the second lens 121 and the first lens 123.

[0075] [3-2. Effects, etc.] A head-up display 100 as an example of a head-up display according to the third embodiment is a head-up display that allows an observer D to visually recognize a virtual image I. The head-up display 100 includes a display device 110 as an example of a display device and a projection optical system 140. The display device 110 displays an image. The projection optical system 140 has a function of forming an image of the image displayed by the display device 110 as an intermediate image M. The projection optical system 140 includes, in order of the optical path from the display device 110, a fourth lens 127 as an example of a first optical element having a condensing action, a first lens 123 having a condensing action, and a third mirror 125 as an example of a third optical element that projects the intermediate image M. Thus, in the head-up display 100 according to the third embodiment, the first lens 123 is disposed between the fourth lens 127 that forms the intermediate image M and the third mirror 125 that projects the intermediate image M. Therefore, the intermediate image M can be formed at a position close to the emission side of the first lens 123, and the first lens 123 itself can be miniaturized. As a result, the head-up display 100 can be miniaturized.

[0076] The head-up display 100 according to Embodiment 3 includes, as a projection optical system 140, a second mirror 124 as an example of a second optical element having a diverging action between a first lens 123 and a third mirror 125 as an example of a third optical element. Then, in the order of the optical path from the display device 110, the first lens 123 having a positive power is arranged in front of the second mirror 124 having a negative power and forming an intermediate image M to form a telephoto arrangement. As a result, the overall length of the relay optical system 120 can be shortened, and the head-up display 100 can be downsized by downsizing the first lens 123 itself.

[0077] In the head-up display 100 according to Embodiment 3, at least one surface of the first lens 123, the second lens 121, and the fourth lens 127 has a free-form surface shape. Therefore, in an imaging optical system such as the head-up display 100, good optical characteristics can be realized while suppressing reflection of external light.

[0078] In the head-up display 100 according to Embodiment 3, the first lens 123 and the second lens 121 have a wedge shape. Therefore, even when the first lens 123 and the second lens 121 are tilted with respect to the reference light beam Lc, the optical path length of the light beam passing through the first lens 123 and the second lens 121 can be adjusted.

[0079] In the head-up display 100 according to Embodiment 3, the positions of the thick and thin portions of the lens thickness in the first lens 123 and the second lens 121 with respect to the reference light beam Lc are arranged to be opposite to each other. Therefore, similar to Embodiment 1, the optical path length of the light beam passing through the second lens 121 and the first lens 123 can be adjusted to make the optical path length of the light beam uniform regardless of the portions passing through the second lens 121 and the first lens 123.

[0080] In the head-up display 100 according to Embodiment 3, the intermediate image M is an aerial image formed in the air on the optical path from the display device 110 to the virtual image I. Therefore, without adding a member for forming the intermediate image M, the image displayed on the small display device 110 can be enlarged to form the intermediate image M, and the intermediate image M can be further enlarged and projected onto the observer D.

[0081] (Embodiment 4) Next, Embodiment 4 will be described with reference to FIG. 7.

[0082] [4-1. Configuration] FIG. 7 is a schematic diagram for explaining the optical path for explaining the head-up display 100 according to Embodiment 4. As shown in FIG. 7, the head-up display 100 of the present embodiment includes a fifth lens 128 as another example of the second optical element.

[0083] The first mirror 122 of the present embodiment has the same configuration as the first mirror 122 in Embodiment 1 and Embodiment 2. However, the arrangement position is different from that in each of the above-described embodiments. The first mirror 122 in the present embodiment is arranged at the rearmost position of the vehicle 200 in the head-up display 100 as shown in FIG. 7. Also, the display device 110 and the second lens 121 in the present embodiment have the same configuration as the display device 110 and the second lens 121 in each of the above-described embodiments. However, the arrangement position is different from that in each of the above-described embodiments. In the present embodiment, the display device 110 and the second lens 121 are located in the forward direction of the vehicle 200 rather than the first mirror 122 as shown in FIG. 7.

[0084] The first lens 123 of the present embodiment has the same configuration as the first lens 123 in Embodiment 1 and Embodiment 3. However, the first lens 123 of the present embodiment is different in arrangement position from Embodiment 1 and Embodiment 3. The first lens 123 in the present embodiment is located in the rearward direction of the vehicle 200 rather than the fifth lens 128 as the second optical element.

[0085] The fifth lens 128 is a free-form surface lens with different curvatures in the X-axis direction and the Y-axis direction. In the fifth lens 128, the surface on the first lens 123 side is a flat incident surface, and the surface on the third mirror 125 side is an exit surface with a concave shape that is concave on the third mirror 125 side in the X-axis direction. The curvature of the exit surface of the fifth lens 128 in the Y-axis direction is smaller than the curvature in the X-axis direction. That is, the shape of the fifth lens 128 in the Y-axis direction is a concave shape, a convex shape, or a flat shape with a curvature smaller than that in the X-axis direction.

[0086] In the present embodiment, as shown in FIG. 7, the incident surface and the exit surface of the fifth lens 128 are inclined counterclockwise with respect to the reference light beam Lc in the XZ plane view in FIG. 7. Thereby, the reflected light can be reflected downward from the fifth lens 128 so as not to enter the viewpoint region 300. Here, the inclination of the fifth lens 128 with respect to the reference light beam Lc is desirably set to an angle such that when external light incident along the reference light beam Lc is reflected at the incident surface or the exit surface, the reflected light does not enter the first mirror 122 and the third mirror 125. More desirably, the above inclination is set to an angle such that when external light incident from the first mirror 122 to the fifth lens 128 is reflected at the incident surface or the exit surface of the fifth lens 128, the reflected light does not enter the first mirror 122. Note that the fact that the fifth lens 128 is inclined with respect to the reference light beam Lc means that the portion where the optical refracting surface of the fifth lens 128 intersects the reference light beam Lc is not horizontal with respect to the plane perpendicular to the reference light beam Lc.

[0087] Furthermore, the exit surface of the fifth lens 128 has a wedge shape in the XZ plane view of FIG. 7. By making the cross-sectional shape along the Y-axis direction of the fifth lens 128 into a wedge shape, the optical path length of the light passing above the fifth lens 128 becomes longer than the optical path length of the light passing below the second lens 121. That is, the optical path length until the image light emitted from the display device 110 forms an intermediate image M can be changed according to the position in the Y-axis direction. Thereby, the decentered image plane curvature generated in the first mirror 122 can be corrected favorably.

[0088] In the projection optical system 140 according to the present embodiment, in the order of the optical path from the display device 110, a first mirror 122 as a first optical element having a condensing action and a third mirror 125 as a third optical element for projecting an intermediate image M are arranged. Further, a first lens 123 having a condensing action is arranged between the first mirror 122 and the third mirror 125. Thus, in the present embodiment, the first lens 123 is arranged between the first mirror 122 that forms the intermediate image M and the third mirror 125 that projects the intermediate image M. As a result, the intermediate image M can be formed at a position close to the exit side of the first lens 123, and the first lens 123 itself can be miniaturized. As a result, the head-up display 100 can be miniaturized.

[0089] Further, in the relay optical system 120 according to the present embodiment, a first lens 123 having a positive power and a fifth lens 128 having a negative power are arranged from the display device 110 toward the intermediate image M. That is, the relay optical system 120 has a so-called telephoto arrangement. By adopting such a telephoto arrangement, the first lens 123 enhances the negative power of the fifth lens 128, and the fifth lens 128 enhances the positive power of the first lens 123. That is, the first lens 123 and the fifth lens 128 enhance each other's power. As a result, the overall length of the relay optical system 120 can be shortened, and the head-up display 100 can be miniaturized.

[0090] Also, in the present embodiment, as shown in FIG. 7, the incident surface and the exit surface of the second lens 121 are inclined in the clockwise direction with respect to the reference ray Lc in the XZ plane view of FIG. 7. Further, the incident surface and the exit surface of the first lens 123 are inclined in the counterclockwise direction with respect to the reference ray Lc in the XZ plane view of FIG. 7. Thereby, the reflected light due to external light in the first lens 123 is reflected upward from the first mirror 122, and the reflected light due to external light in the second lens 121 is reflected downward from the first mirror 122. That is, it is possible to prevent external light from entering the viewpoint region 300. Here, the inclination of the second lens 121 and the first lens 123 with respect to the reference ray Lc is desirably set to an angle such that when external light incident along the reference ray Lc is reflected at the incident surface or the exit surface, the reflected light does not enter the first mirror 122. More desirably, the above inclination is set to an angle such that when external light incident from the first mirror 122 to the second lens 121 or the first lens 123 is reflected at the incident surface or the exit surface of the second lens 121 or the first lens 123, the reflected light does not enter the first mirror 122. Note that the fact that the second lens 121 and the first lens 123 are inclined with respect to the reference ray Lc means that the portion where the optical refracting surface of the second lens 121 and the first lens 123 intersects the reference ray Lc is not horizontal with respect to the plane perpendicular to the reference ray Lc.

[0091] In the present embodiment, similar to the first embodiment, the positions of the thick portions and the thin portions of the lens thickness in the first lens 123 and the second lens 121 with respect to the reference ray Lc are arranged to be opposite to each other. Therefore, similar to the first embodiment, the optical path length of the light rays passing through the second lens 121 and the first lens 123 can be adjusted to make the optical path length of the light rays uniform regardless of the portions passing through the second lens 121 and the first lens 123.

[0092] [4-2. Effects, etc.] As an example of the head-up display according to Embodiment 4, the head-up display 100 is a head-up display that allows an observer D to visually recognize a virtual image I. The head-up display 100 includes a display device 110 as an example of a display device and a projection optical system 140. The display device 110 displays an image. The projection optical system 140 has a function of forming an image of the image displayed by the display device 110 as an intermediate image M. The projection optical system 140 includes, in the order of the optical path from the display device 110, a first mirror 122 as an example of a first optical element having a condensing action, a first lens 123 having a condensing action, and a third mirror 125 as an example of a third optical element that projects the intermediate image M. Thus, in the head-up display 100 according to Embodiment 4, the first lens 123 is disposed between the first mirror 122 that creates the intermediate image M and the third mirror 125 that projects the intermediate image M. Therefore, the intermediate image M can be formed at a position close to the exit side of the first lens 123, and the first lens 123 itself can be miniaturized. As a result, the head-up display 100 can be miniaturized.

[0093] The first mirror 122 is used as an example of the first optical element according to Embodiment 4, and the third mirror 125 is used as an example of the third optical element. As a result, it is possible to sufficiently enlarge the image displayed on the small display device 110 to create the intermediate image M, and further enlarge the intermediate image M and project it onto the observer D.

[0094] The projection optical system 140 according to Embodiment 4 includes a fifth lens 128 as an example of a second optical element having a diverging action between the first lens 123 and the third mirror 125 as an example of the third optical element. Then, in the order of the optical path from the display device 110, the first lens 123 having a positive power is disposed in front of the fifth lens 128 having a negative power and forming the intermediate image M to form a telephoto arrangement. As a result, the overall length of the relay optical system 120 can be shortened, and the head-up display 100 can be miniaturized by miniaturizing the first lens 123 itself.

[0095] In the head-up display 100 according to Embodiment 4, a fifth lens 128 having a negative power is used as an example of the second optical element. Therefore, an intermediate image M can be formed near the fifth lens 128, and the first lens 123 itself can be miniaturized.

[0096] In the head-up display 100 according to Embodiment 4, at least one surface of the first lens 123 has a free-form surface shape. Therefore, in an imaging optical system such as the head-up display 100, good optical characteristics can be realized while suppressing reflection of external light.

[0097] In the head-up display 100 according to Embodiment 4, the first lens 123 has a wedge shape. Therefore, even when the first lens 123 is tilted with respect to the reference light beam Lc, the optical path length of the light beam passing through the first lens 123 can be adjusted.

[0098] The head-up display 100 according to Embodiment 4 includes a second lens 121 between the display device 110 and the first mirror 122 as an example of the first optical element. The second lens 121 has a wedge shape and at least one surface has a free-form surface shape. Also, in the head-up display 100 according to Embodiment 4, the first lens 123 and the second lens 121 are arranged such that the light beam passing through the portion where the lens thickness of one lens is thin passes through the portion where the lens thickness of the other lens is thick. Also, the first lens 123 and the second lens 121 are arranged such that the light beam passing through the portion where the lens thickness of one lens is thick passes through the portion where the lens thickness of the other lens is thin. Therefore, even when the first lens 123 and the second lens 121 are tilted with respect to the reference light beam Lc, the optical path lengths of the light beams passing through the first lens 123 and the second lens 121 can be made uniform.

[0099] In the head-up display 100 according to Embodiment 4, the intermediate image M is an aerial image formed in the air on the optical path from the display device 110 to the virtual image I. Therefore, without adding a member for forming the intermediate image M, the image displayed on the small display device 110 can be enlarged to form the intermediate image M, and the intermediate image M can be further enlarged and projected onto the observer D.

[0100] (Other Embodiments) As described above, as examples of the technology disclosed in the present application, Embodiments 1 to 4 have been described. However, the technology in the present disclosure is not limited to this, and can also be applied to embodiments in which changes, replacements, additions, omissions, etc. are made. Further, it is also possible to combine the components described in the above Embodiments 1 to 4 to form a new embodiment.

[0101] In Embodiments 1 to 4, the second lens 121 is shown as an example of the refractive optical system provided between the display device 110 and the first mirror 122. However, the refractive optical system is not limited to the second lens 121 which is a single lens element. For example, the refractive optical system may be one in which a plurality of lens elements are arranged between the display device 110 and the first mirror 122. When there are a plurality of lens elements, it is desirable that the lens element on which the light emitted from the display device first enters has a positive power.

[0102] In Embodiments 1 to 4, one third mirror 125 is arranged as the projection optical system 140, but two or more mirrors may be arranged. Further, the additional mirror may be arranged in front of the vehicle with respect to the third mirror 125, or may be arranged in the inner or outer direction of the vehicle, that is, in the direction perpendicular to the paper surface in FIGS. 1, 2, and 4 to 7.

[0103] In Embodiments 1 to 4, lens elements are used in the relay optical system 120. However, the configuration of the head-up display 100 is not limited to this. For example, a lens element may be additionally arranged between the third mirror 125 and the windshield 220.

[0104] In the head-up displays 100 of Embodiments 1 to 4, the first mirror 122, the second mirror 124, and the third mirror 125 have been described using rotationally asymmetric mirrors, but the present invention is not limited to this. For example, these mirrors may have a so-called saddle-shaped surface shape in which the signs of the curvature are different in the X-axis direction and the Y-axis direction.

[0105] In Embodiments 1 to 4, the surface shape of the lens element used is not limited to a free-form surface shape. The surface shape of the lens element may be, for example, a toroidal shape, an anamorphic shape, or a cylindrical shape. Further, lenses having these shapes may be arranged eccentrically with respect to the reference light beam Lc.

[0106] In Embodiment 4, the entire X-axis direction of the exit surface of the fifth lens 128 does not need to be a concave surface, and it may locally have a convex surface shape.

[0107] In Embodiments 1 to 4, the plane shape surface of the lens element used may be a convex surface or a concave surface, or may locally have a curved surface shape.

[0108] In Embodiments 1 to 4, the shape of the reflection surface of the first mirror 122, the second mirror 124, and the third mirror 125 is not limited to a free-form surface shape. The reflection surfaces of these mirrors may be a spherical shape, an aspherical shape, a toroidal shape, or an anamorphic shape. Further, mirrors having these shapes may be arranged eccentrically with respect to the reference light beam Lc.

[0109] In Embodiments 1 to 4, the head-up display 100 is arranged below the dashboard 210, but it may also be arranged above the dashboard 210.

[0110] As described above, embodiments have been described as examples of the technology in the present disclosure. For this purpose, the accompanying drawings and detailed descriptions have been provided. Therefore, among the components described in the accompanying drawings and detailed descriptions, there may be not only components essential for solving the problems, but also components not essential for solving the problems for exemplifying the above technology. Therefore, just because those non-essential components are described in the accompanying drawings or detailed descriptions, it should not be immediately recognized that those non-essential components are essential.

[0111] Also, since the above-described embodiments are for exemplifying the technology in the present disclosure, various changes, replacements, additions, omissions, etc. can be made within the scope of the claims or their equivalents.

[0112] (Summary of Embodiment) (1) The head-up display of the present disclosure is a head-up display that projects an image onto a transmissive reflective member and allows an observer to visually recognize a virtual image, and includes a display device that displays the image, and a projection optical system that projects the image displayed on the display device as a virtual image onto the observer. The projection optical system has a function of forming an intermediate image of the image, and includes a first optical element having a condensing action, a first lens having a condensing action, and a second optical element having a diverging action. The first optical element, the first lens, and the second optical element are arranged in the order of the optical path from the display device.

[0113] In this way, since the first lens having a condensing action is arranged between the first optical element having a condensing action and the second optical element having a diverging action, the first optical element and the first lens can enhance their powers with each other. As a result, the lens itself can be miniaturized, and the head-up display can be miniaturized.

[0114] (2) In the head-up display of (1), the first optical element is a mirror. Therefore, it is possible to sufficiently enlarge the image displayed on the small display device to create an intermediate image, and further enlarge the intermediate image and project it onto the observer.

[0115] (3) In the head-up display of (1) or (2), the first lens is disposed between the first optical element and the second optical element. Therefore, a telephoto arrangement can be achieved, the overall length of the relay optical system can be shortened, and the first lens itself can be miniaturized, thereby miniaturizing the head-up display.

[0116] (4) In the head-up display of (1) to (3), the second optical element is a mirror. Therefore, the intermediate image M can be formed near the lens, and the first lens itself can be miniaturized.

[0117] (5) In any one of the head-up displays of (1) to (4), at least one surface of the first lens has a free-form surface shape. Therefore, in an imaging optical system such as a head-up display, good optical characteristics can be realized while suppressing the reflection of external light.

[0118] (6) In any one of the head-up displays of (1) to (5), the first lens has a wedge shape. Therefore, even when the first lens is tilted with respect to the reference light beam, the optical path length of the light beam passing through the first lens can be adjusted.

[0119] (7) In any one of the head-up displays according to (1) to (6), the projection optical system is disposed between the display device and the first optical element, and includes a second lens having a condensing action. The second lens has a wedge shape. At least one surface of the second lens has a free-form surface shape. The first lens and the second lens are arranged such that light rays passing through a thin portion of the lens thickness of the first lens pass through a thick portion of the lens thickness of the second lens, and light rays passing through a thick portion of the lens thickness of the first lens pass through a thin portion of the lens thickness of the second lens. Therefore, even when the first lens and the second lens are tilted with respect to the reference light ray, the optical path lengths of the light rays passing through the first lens and the second lens can be made uniform.

[0120] (8) In any one of the head-up displays according to (1) to (7), the first lens and the second lens are integrally formed. Therefore, the number of parts can be reduced, and the manufacturing cost of the head-up display can be reduced.

[0121] (9) In any one of the head-up displays according to (1) to (8), the intermediate image is an aerial image formed in the air on the optical path. Therefore, it is possible to enlarge the image displayed on the small display device as an intermediate image without adding a member for forming the intermediate image, and further enlarge the intermediate image and project it onto the observer.

Industrial Applicability

[0122] The present disclosure is applicable to a head-up display using a refractive optical system such as a lens. Specifically, the present disclosure is applicable to a head-up display for vehicles and the like.

Explanation of Reference Numerals

[0123] 100 Head-up display 110 Display device 120 Relay optical system 121 Second lens 122 First mirror 123 First lens 124 Second mirror 125 Third mirror 126 Third lens 127 Fourth lens 128 Fifth lens 130 Projection optical system 140 Projection optical system 200 Vehicle 210 Dashboard 220 Windshield 300 Viewpoint area D Observer I Virtual image M Intermediate image L Light ray Lc Reference light ray

Claims

1. A head-up display that projects a projection image formed from an original image onto a transparent reflecting member to allow an observer to view a virtual image, a device for emitting light of a predetermined area corresponding to the original image; a projection optical system that projects the projection image, The projection optical system includes: a first mirror that reflects the light in the predetermined region emitted from the device in the shape of a reflective surface; a first lens that collects light reflected by the first mirror; a second mirror that reflects light to form an intermediate image; a third mirror that reflects the light that formed the intermediate image to the reflecting member, the first mirror, the first lens, the second mirror, and the third mirror are arranged in this order on an optical path to the reflecting member; Head-up display.

2. the intermediate image is an aerial image formed in the air on the optical path between the second mirror and the third mirror. The head-up display according to claim 1 .

3. the intermediate image is formed at a position closer to the second mirror than to the third mirror; The head-up display according to claim 2 .

4. the third mirror is a concave mirror; The head-up display according to claim 1 .

5. the third mirror has a free-form surface shape; The head-up display according to claim 4.

6. the second mirror has a free-form surface shape; The head-up display according to claim 1 .

7. The projection optical system includes: a second lens disposed between the device and the first mirror and configured to collect light emitted from the device; The head-up display according to claim 1 .

8. When a light ray that reaches the center of the viewpoint area of the observer and corresponds to the center of the virtual image is defined as a reference light ray, the first mirror changes the direction of the reference light ray that is reflected toward the first lens with respect to the reference light ray incident on the first mirror. The head-up display according to claim 1 .

9. an optical path between the first mirror and the first lens is in air; the first lens directly receives the light reflected by the first mirror; The head-up display according to claim 8.

10. the second mirror changes the direction of the reference light beam reflected toward the third mirror relative to the direction of the reference light beam reflected by the first mirror; The head-up display according to claim 8.

Images