Head-up display

Abstract

To provide a head-up display capable of downsizing.SOLUTION: The head-up display includes: a device for emitting light beams for converting an original image into a projected image; and a projection optical system that forms the projected image from the original image and projects the projected image to an observer as a virtual image. The projection optical system includes: a first lens that has a refractive surface that receives the light beam emitted from the device; a second mirror that reflects the light downwards; and a third mirror that reflects the light reflected by the second mirror onto a reflective member as the projected image.The first lens, the second mirror, and the third mirror are arranged in that order in an optical path to the reflective member. The projection optical system has a function that uses the light beams emitted from the device to form an intermediate image from the original image below the second mirror, and forms the projected image from the intermediate image.SELECTED DRAWING: Figure 7

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 effect disposed between the concave mirror and the display surface. Further, this head-up display includes a first optical system that forms an intermediate image by imaging light rays emitted from the display surface through the lens and the concave mirror, and enlarging the image. 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 can be miniaturized.

[0005] The head-up display of this disclosure is a head-up display that projects a projected image formed from an original image onto a transparent reflective member to allow an observer to see a virtual image, and comprises a device that emits light rays to make the original image a projected image, and a projection optical system that forms a projected image from the original image and projects the projected image as a virtual image to the observer. The projection optical system comprises a first lens having a refractive surface into which light rays emitted from the device are incident, a second mirror that reflects the light rays downward, and a third mirror that reflects the light reflected by the second mirror as a projected image to a reflective member. The first lens, the second mirror, and the third mirror are arranged in the order of the optical path to the reflective member. The projection optical system has the function of forming an intermediate image of the original image below the second mirror by light rays emitted from the device, and forming a projected image from the intermediate image.

[0006] The head-up display in this disclosure presents a virtual image with minimal distortion and can be miniaturized. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic diagram illustrating a vehicle equipped with a head-up display in Embodiment 1. [Figure 2] Figure 2 is a schematic diagram showing the configuration of the head-up display in Embodiment 1. [Figure 3] Figure 3 is a schematic diagram illustrating the telephoto arrangement in Embodiment 1. [Figure 4] Figure 4 is a schematic diagram showing the configuration of the relay optical system in Embodiment 1. [Figure 5] Figure 5 is a schematic diagram showing the configuration of the head-up display of Embodiment 2. [Figure 6] Figure 6 is a schematic diagram showing the configuration of the head-up display according to Embodiment 3. [Figure 7] Figure 7 shows the operation of the head-up display in Embodiment 4. [Figure 8] Figure 8 is a schematic diagram showing the configuration of the head-up display according to Embodiment 5. [Figure 9] Figure 9 shows the operation of the head-up display in Embodiment 6. [Modes for carrying out the invention]

[0008] The embodiments will be described in detail below, with reference to the drawings as appropriate. However, unnecessarily detailed explanations may be omitted. For example, detailed explanations of already well-known matters and redundant explanations of substantially identical configurations may be omitted. This is to avoid the following explanation becoming unnecessarily verbose and to facilitate understanding for those skilled in the art.

[0009] The inventors provide the accompanying drawings and the following description so that those skilled in the art may fully understand the disclosure, and not to limit the subject matter described in the claims.

[0010] (Embodiment 1) Embodiment 1 will be described below with reference to Figures 1 to 4.

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

[0012] Figure 1 is a diagram showing a cross-section of a vehicle 200 equipped with a head-up display 100 according to this disclosure. As shown in Figure 1, the head-up display 100 is located inside the dashboard 210 at the bottom of the windshield 220 of the vehicle 200. Observer D recognizes the image projected from the head-up display 100 as a virtual image I.

[0013] Figure 2 is a schematic diagram showing the configuration of the head-up display 100 according to this embodiment. Figure 3 is a schematic diagram illustrating the configuration of the head-up display 100 according to this embodiment.

[0014] As shown in Figure 2, the head-up display 100 comprises a display device 110 and a projection optical system 140. The head-up display 100 projects the image displayed by the display device 110 onto the windshield 220. The projected light is reflected by the windshield 220 and guided to the observer D's viewpoint area 300. In this way, the head-up display 100 allows the observer D to see a virtual image I. Here, the viewpoint is the principal point when the observer D's eye is considered as a lens. The viewpoint area 300 is the area where the observer D's viewpoint is located, from which the virtual image I can be seen without any loss.

[0015] In this disclosure, "forward" refers to the direction of the windshield 220 of the vehicle 200 as seen from observer D. "Rearward" refers to the opposite direction from forward. "Downward" refers to the direction of the ground on which the vehicle 200 is traveling. "Upward" refers to the opposite direction from downward. "Inward" refers to the passenger side as seen from observer D in the driver's seat. "Outward" refers to the opposite direction from inward. The viewpoint area 300 is the area in which observer D can see the virtual image I without any loss of detail.

[0016] Here, as shown in Figure 2, among the light rays emitted from the display device 110, the ray that reaches the viewpoint region 300 is defined as ray L. Furthermore, among the light rays emitted from the display device 110, the ray that passes through the center of the virtual image I and reaches the center of the viewpoint region 300 is defined as the reference ray Lc. That is, from the perspective of observer D, the reference ray Lc corresponds to the optical path from the center of the virtual image I to observer D's viewpoint. The reference ray Lc seen by observer D is actually the ray that traveled from the display device 110 through the optical system to observer D. Therefore, the ray from the display device 110 to observer D, corresponding to the reference ray Lc emitted from the center of the virtual image I, is also expressed as the reference ray Lc. Similarly, the optical paths corresponding to these rays are also expressed as the reference ray Lc. However, it is assumed that observer D's viewpoint is at the center of the viewpoint region 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. Also, 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 displays, the distance to the vehicle ahead, the remaining battery level of the vehicle, and the current vehicle speed. Also, 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. Also, 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 second optical element, a first lens 123, and a second mirror 124 as a first optical element. The relay optical system 120 forms an intermediate image M that magnifies the display image by imaging the light rays emitted from the display device 110. The intermediate image M is formed to be magnified compared to 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. Also, because 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 as 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 that is imaged 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 along 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 or the first mirror 122.

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

[0023] The first mirror 122 is positioned in the forward direction of the vehicle 200, relative to the second lens 121. The first mirror 122 focuses the light rays emitted from the second lens 121 and reflects them toward the first lens 123. The reflective surface of the first mirror 122 is eccentrically positioned to reflect the display image shown on the display device 110 toward the second mirror 124. Here, the reflective surface of the first mirror 122 is concave. That is, the first mirror 122 magnifies the light incident from the second lens 121 and projects it toward the first lens 123. Furthermore, the first mirror 122 has a freeform surface shape. This is to correct for distortion of the virtual image caused by reflection.

[0024] As shown in Figure 2, the first lens 123 is positioned further rearward from the first mirror 122 of the vehicle 200. As shown in Figure 2, the first lens 123 is positioned at a clockwise inclination with respect to the reference ray Lc in the XZ plan view of Figure 2. The inclination of the first lens 123 with respect to the reference ray Lc is, for example, an angle between 15 and 30 degrees. This prevents stray light caused by ambient light entering the housing and being reflected by the first mirror 122 or the second mirror 124.

[0025] Furthermore, the first lens 123 is a free-form surface lens with different curvatures in the X-axis and Y-axis directions. The surface of the first lens 123 on the first mirror 122 side (incident surface) has a convex shape that is convex toward the first mirror 122 in both the X-axis and Y-axis directions. The surface of the first lens 123 on the second mirror 124 side (exit surface) has a shape where the plane faces toward the display device 110 in both the X-axis and Y-axis directions.

[0026] The second mirror 124 is positioned further rearward from the vehicle 200 than the first lens 123. The second mirror 124 diverges the light rays emitted from the first lens 123 and forms an enlarged intermediate image M of the displayed image in the optical path between the second mirror 124 and the third mirror 125. The reflective surface of the second mirror 124 is eccentrically positioned to enlarge the displayed image projected by the first lens 123 and form an intermediate image M in the optical path between the second mirror 124 and the third mirror 125. Here, the reflective surface of the second mirror 124 is convex in shape. The second mirror 124 has a freeform 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 positioned further forward of the vehicle 200 than the second mirror 124. The third mirror 125 focuses the light rays diverged by the second mirror 124 and projects an intermediate image M onto the windshield 220. The reflective surface of the third mirror 125 is eccentrically positioned to project the intermediate image M onto the windshield 220. Here, the reflective 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 of this embodiment, a first mirror 122, a first lens 123 having a light-gathering effect, and a second mirror 124 having a diverging effect and acting as a first optical element for forming an intermediate image M are arranged in the order of the optical path from the display device 110. By arranging the first lens 123 and the second mirror 124 for forming the intermediate image M in this order of the optical path, the intermediate image M can be formed closer to the output 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.

[0029] Furthermore, in the relay optical system 120 of this embodiment, a first lens 123 having positive power and a second mirror 124 having negative power are arranged from the display device 110 toward the intermediate image M. In other words, the relay optical system 120 has a so-called telephoto arrangement. By using this 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 mutually 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.

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

[0031] Furthermore, near the second mirror 124, which has negative power to form the intermediate image M, the light rays that form the intermediate image M are narrowed. By placing the first lens 123, which has positive power, near the second mirror 124, which has negative power, a telephoto arrangement can be achieved, making the first lens 123 itself smaller.

[0032] Furthermore, in this embodiment, as shown in Figure 4, the incident and exit surfaces of the second lens 121 are tilted counterclockwise with respect to the reference ray Lc in the XZ plan view of Figure 4. In addition, the incident and exit surfaces of the first lens 123 are tilted clockwise with respect to the reference ray Lc in the XZ plan view of Figure 4. As a result, the light reflected from ambient light by the first lens 123 is reflected upward from the first mirror 122, and the light reflected from ambient light by the second lens 121 is reflected downward from the first mirror 122. In other words, ambient light can be prevented from entering the viewpoint area 300. Here, it is desirable that the inclination of the second lens 121 and the first lens 123 with respect to the reference ray Lc be such that when ambient light incident along the reference ray Lc is reflected at the incident or exit surface, the reflected light does not enter the first mirror 122. More preferably, the above inclination is such that when ambient light incident from the first mirror 122 to the second lens 121 or the first lens 123 is reflected at the incident or exit surface of the second lens 121 or the first lens 123, the reflected light does not incident on the first mirror 122. Note that when the second lens 121 and the first lens 123 are inclined with respect to the reference ray Lc, it means that the points where the optical refractive surfaces of the second lens 121 and the first lens 123 intersect with the reference ray Lc are not horizontal with respect to a plane perpendicular to the reference ray Lc.

[0033] In this embodiment, the second lens 121 has a wedge shape in which the lens thickness decreases towards the lower side with respect to the reference ray Lc. The first lens 123 has a wedge shape in which the lens thickness decreases towards the upper side with respect to the reference ray Lc. As described above, when the second lens 121 is tilted with respect to the reference ray Lc, if the exit surface of the second lens 121 is a convex shape symmetrical with respect to the reference ray Lc, the optical path length of the light ray passing above the second lens 121 relative to the reference ray Lc will be different from the optical path length of the light ray passing below it. Similarly, when the first lens 123 is tilted with respect to the reference ray Lc, if the incident surface of the first lens 123 is a convex shape symmetrical with respect to the reference ray Lc, the optical path length of the light ray passing above the first lens 123 relative to the reference ray Lc will be different from the optical path length of the light ray passing below it.

[0034] Therefore, in this embodiment, the second lens 121 has a wedge shape in which the lens thickness decreases towards the lower side relative to the reference ray Lc. Similarly, the first lens 123 has a wedge shape in which the lens thickness decreases towards the upper side relative to the reference ray Lc. With this configuration, light rays emitted from the display device 110 that pass through the upper side of the second lens 121 relative to the reference ray Lc (i.e., the thicker part of the second lens 121) are reflected by the first mirror 122. The reflected light rays then pass through the upper side of the first lens 123 relative to the reference ray Lc (i.e., the thinner part of the first lens 123). Also, light rays emitted from the display device 110 that pass through the lower side of the second lens 121 relative to the reference ray Lc (i.e., the thinner part of the second lens 121) are reflected by the first mirror 122. The reflected light rays then pass through the lower side of the reference light ray Lc of the first lens 123 (i.e., the thicker part of the first lens 123). In this way, 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 point in which they pass through the second lens 121 and the first lens 123.

[0035] In this embodiment, the emission surface of the second lens 121 is positioned downward from the incidence surface. That is, the shape of the second lens 121 in the Y-axis direction is wedge-shaped. By making the cross-sectional shape of the second lens 121 along the Y-axis direction wedge-shaped, the optical path length of light passing above the second lens 121 becomes longer than the optical path length of light passing below the second lens 121. In other words, the optical path length from the image light emitted from the display device 110 to the first mirror 122 can be changed according to the position in the Y-axis direction. This makes it possible to effectively correct the eccentric image plane curvature that occurs in the first mirror 122.

[0036] [1-2. Effects, etc.] The head-up display 100, as an example of a head-up display according to Embodiment 1, is a head-up display that projects an image onto a windshield 220 (an example of a transparent reflective member) to allow an observer D to view a virtual image I. The head-up display 100 comprises 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 the function of forming an image as an intermediate image M of the image displayed by the display device 110. The first lens 123 included in the projection optical system 140 is arranged at an angle with respect to a reference ray Lc. Therefore, even when ambient light is incident into the projection optical system 140, stray light due to reflection of ambient light by the first lens 123, etc., can be suppressed. The projection optical system 140 also comprises, in the order of the optical path from the display device 110, a first lens 123 having a light-gathering effect and a second mirror 124 as an example of a first optical element having a diverging effect. Thus, in the head-up display 100 according to Embodiment 1, the first lens 123, which has positive power, is placed before the second mirror 124, which has negative power and forms an intermediate image M, in the optical path from the display device 110, thus creating 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, thereby making the head-up display 100 smaller.

[0037] As an example of the first optical element according to Embodiment 1, a second mirror 124 was used. Therefore, it is possible to enlarge the image displayed on the small display device 110 to create an intermediate image M, and then further enlarge the intermediate image M and project it onto the observer D.

[0038] In the head-up display 100 according to Embodiment 1, at least one surface of the first lens 123 is a free-form surface. Therefore, in an imaging optical system such as the head-up display 100, good optical characteristics can be achieved while suppressing reflection of ambient light.

[0039] 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 ray Lc, the optical path length of the light ray passing through the first lens 123 can be adjusted.

[0040] The head-up display 100 according to Embodiment 1 includes a first mirror 122 as an example of a second optical element and a second lens 121. The first mirror 122 is positioned between the display device 110 and the first lens 123. The second lens 121 is also positioned between the display device 110 and the first mirror 122. The second lens 121 has a wedge shape, and at least one face is a free-form surface. Furthermore, in the head-up display 100 according to Embodiment 1, the first lens 123 and the second lens 121 are positioned such that light rays passing through the thinner part of one lens pass through the thicker part of the other lens, and light rays passing through the thicker part of one lens pass through the thinner part of the other lens. Therefore, even when the first lens 123 and the second lens 121 are tilted with respect to the reference light ray Lc, the optical path length of the light rays passing through the first lens 123 and the second lens 121 can be made uniform.

[0041] In the head-up display 100 according to Embodiment 1, the intermediate image M is an aerial image formed in the air along the optical path from the display device 110 to the virtual image I. Therefore, without adding a member to form 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 then further enlarge the intermediate image M and project it onto the observer D.

[0042] A vehicle 200, which is an example of a mobile body according to Embodiment 1, is equipped with a head-up display 100 and a windshield 220 as a transparent reflective material. As a result, an observer D driving the vehicle 200 can view the image projected onto the windshield 220 as a virtual image I.

[0043] (Embodiment 2) Next, Embodiment 2 will be described using Figure 5.

[0044] [2-1. Structure] Figure 5 is a schematic diagram illustrating the optical path for explaining the head-up display 100 according to Embodiment 2. As shown in Figure 5, the head-up display 100 of this 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 second lens in Embodiment 1, are integrally formed.

[0045] As shown in Figure 5, the third lens 126 is positioned in the forward direction of the vehicle 200, relative to the display device 110 and the second mirror 124. In the third lens 126, as shown in Figure 5, the surface facing the first mirror 122 has a convex shape that is convex toward the first mirror 122 in the X-axis and Y-axis directions. Also, as shown in Figure 5, the surface facing the display device 110 and the second mirror 124 has a planar shape with its plane 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 differs in the X-axis and Y-axis directions.

[0046] 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 positioned at an angle to the reference ray Lc in a counterclockwise direction on the XZ plane view shown in Figure 5. This prevents stray light caused by ambient light entering the housing and reflecting off the display surface of the display device 110 and the first mirror 122.

[0047] 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 positioned at an angle to the reference ray Lc in a clockwise direction on the XZ plane view shown in Figure 5. This prevents stray light caused by ambient light entering the housing and reflecting off the display surface of the display device 110 and the first mirror 122.

[0048] Furthermore, in the relay optical system 120 of this embodiment, a first lens section 126a having positive power and a second mirror 124 having negative power are arranged from the display device 110 toward the intermediate image M. In other words, the relay optical system 120 has a so-called telephoto arrangement. By using this telephoto arrangement, the first lens section 126a increases the negative power of the second mirror 124, and the second mirror 124 increases the positive power of the first lens section 126a. That is, the first lens section 126a and the second mirror 124 mutually 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.

[0049] As described above, in this embodiment, the first lens section 126a is positioned between the first mirror 122, which is a second optical element, and the third mirror 125, which projects the intermediate image M. In particular, in the optical path from the display device 110, the third lens 126, which has positive power, is positioned before the second mirror 124, which has negative power and forms the intermediate image M, which is a first optical element. Therefore, the overall length of the relay optical system 120 can be shortened and the first lens section 126a itself can be miniaturized, thereby making the head-up display 100 smaller.

[0050] In this embodiment, the third lens 126 is a lens in which a first lens portion 126a and a second lens portion 126b, corresponding to the second lens 121 and first lens 123 in Embodiment 1, are integrally formed. The first lens portion 126a and the second lens portion 126b have a wedge shape in which the lens thickness becomes thinner towards the ends relative to the center of the third lens 126. As described above, when the third lens 126 is tilted with respect to the reference ray Lc, in the optical path from the display device 110 to the first mirror 122, the optical path length of the ray passing above the second lens portion 126b and the optical path length of the ray passing below the reference ray Lc are different. Similarly, in the optical path from the first mirror 122 to the second mirror 124, the optical path length of the ray passing above the second lens portion 126b and the optical path length of the ray passing below the reference ray Lc are different.

[0051] Therefore, in this embodiment, the second lens portion 126b has a wedge shape in which the lens thickness decreases towards the lower side with respect to the reference ray Lc, and the first lens portion 126a has a wedge shape in which the lens thickness decreases towards the upper side with respect to the reference ray Lc. With this configuration, light rays emitted from the display device 110 that pass through the upper side of the second lens portion 126b with respect to the reference ray Lc (i.e., the thicker part of the second lens portion 126b) are reflected by the first mirror 122. The reflected light rays then pass through the upper side of the first lens portion 126a with respect to the reference ray Lc (i.e., the thinner part of the first lens portion 126a).

[0052] Furthermore, light rays emitted from the display device 110 that pass through the lower side of the reference light ray Lc of the second lens section 126b (i.e., the thinner part of the lens of the second lens section 126b) are reflected by the first mirror 122. The reflected light rays then pass through the lower side of the reference light ray Lc of the first lens section 126a (i.e., the thicker part of the lens of the first lens section 126a).

[0053] In this embodiment, the optical path length of the light rays passing through the second lens portion 126b and the first lens portion 126a of the third lens 126 can be adjusted to make the optical path length of the light rays uniform regardless of where they pass through the third lens 126.

[0054] Here, the inclination of the third lens 126 with respect to the reference ray Lc is preferably such that when ambient light incident along the reference ray Lc is reflected at the incident or exit surface of the third lens 126, the reflected light does not incident on the first mirror 122. Note that the inclination of the third lens 126 with respect to the reference ray Lc means that the point where the optical refractive surface of the third lens 126 intersects with the reference ray Lc is not horizontal with respect to a plane perpendicular to the reference ray Lc.

[0055] Furthermore, in the optical path from the display device 110 to the first mirror 122, the emission surface of the second lens portion 126b is positioned downwards from the incidence surface. The shape of the second lens portion 126b in the Y-axis direction is wedge-shaped. By making the cross-sectional shape of the second lens portion 126b along the Y-axis direction wedge-shaped, the optical path length of light passing above the second lens portion 126b in the optical path from the display device 110 to the first mirror 122 becomes longer than the optical path length of light passing below the second lens portion 126b. In other words, the optical path length from the image light emitted from the display device 110 to the first mirror 122 can be changed according to the position in the Y-axis direction. This makes it possible to effectively correct the eccentric image plane curvature that occurs in the first mirror 122.

[0056] In this embodiment, as described above, a third lens 126 is provided, which is an integrated unit of the first lens portion 126a and the second lens portion 126b, corresponding to the second lens 121 and first lens 123 in Embodiment 1. This reduces the number of parts and lowers the manufacturing cost of the head-up display 100.

[0057] [2-2. Effects, etc.] The head-up display 100, as an example of a head-up display according to Embodiment 2, is a head-up display that allows an observer D to view a virtual image I. The head-up display 100 comprises 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 the function of forming an intermediate image M of the image displayed by the display device 110. The third lens 126 included in the projection optical system 140 is arranged at an angle with respect to the reference ray Lc. Therefore, even when ambient light is incident into the projection optical system 140, stray light due to reflection of ambient light by the third lens 126, etc., can be suppressed. The projection optical system 140 also comprises, in the order of the optical path from the display device 110, a third lens 126 with a light-gathering effect and a second mirror 124 as an example of a first optical element with a diverging effect. The third lens 126 is a lens formed by integrally integrating the first lens portion 126a and the second lens portion 126b, which correspond to the first lens 123 and the second lens 121 in Embodiment 1. Thus, in the head-up display 100 according to Embodiment 2, the third lens 126 and the second mirror 124 are arranged in the order of the optical path from the display device 110. Therefore, the intermediate image M can be formed at a position close to the output 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. Furthermore, 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.

[0058] In the projection optical system 140 according to Embodiment 2, the third lens 126 and the second mirror 124 having a divergent effect are arranged in the order of the optical path from the display device 110. Therefore, in the order of the optical path from the display device 110, the first lens section 126a having positive power is placed before the second mirror 124 which has negative power and forms an intermediate image M, thereby realizing a telephoto arrangement. As a result, the overall length of the relay optical system 120 can be shortened and the first lens section 126a can be miniaturized, making it possible to miniaturize the head-up display 100.

[0059] In this embodiment, the light rays emitted from the display device 110 pass 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. In this case as well, the projection optical system 140 still comprises the first mirror 122 with a focusing effect, the third lens 126 with a focusing effect, the second mirror 124 with a diverging effect, and the third mirror 125 that projects the intermediate image M, in the order of the optical path from the display device 110. Furthermore, the light rays emitted from the display device 110 still proceed in the order of the first mirror 122, the third lens 126, the second mirror 124, and the third mirror 125, allowing the observer D to see the virtual image I.

[0060] In the head-up display 100 according to Embodiment 2, at least one surface of the third lens 126 is a free-form surface. Therefore, in an imaging optical system such as the head-up display 100, good optical characteristics can be achieved while suppressing reflection of ambient light.

[0061] In the head-up display 100 according to Embodiment 2, 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 ray Lc, the optical path length of the light ray passing through the third lens 126 can be adjusted.

[0062] In the head-up display 100 according to Embodiment 2, the third lens 126, which is formed by integrally integrating a first lens portion 126a and a second lens portion 126b corresponding to the first lens 123 and second lens 121 in Embodiment 1, has a wedge shape. Therefore, in the optical path from the display device 110 to the first mirror 122, light rays passing through the thin lens portion of the second lens portion 126b pass through the thick lens portion of the first lens portion 126a 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, light rays passing through the thick lens portion of the second lens portion 126b pass through the thin lens portion of the first lens portion 126a 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 ray Lc, the optical path length of the light rays passing through the third lens 126 can be made uniform.

[0063] In the head-up display 100 according to Embodiment 2, the intermediate image M is an aerial image formed in the air along the optical path from the display device 110 to the virtual image I. Therefore, without adding a member to form 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 then further enlarge the intermediate image M and project it onto the observer D.

[0064] (Embodiment 3) Next, Embodiment 3 will be described using Figure 6.

[0065] [3-1. Structure] Figure 6 is a schematic diagram illustrating the optical path for explaining the head-up display 100 according to Embodiment 3. As shown in Figure 6, the head-up display 100 of this embodiment includes a fourth lens 127 as another example of the second optical element.

[0066] The display device 110 and the second lens 121 in this embodiment have the same configuration as the display device 110 and the second lens 121 in the embodiments described above. However, their arrangement differs from the embodiments described above. In this embodiment, as shown in Figure 6, the display device 110 and the second lens 121 are positioned in the forward direction of the vehicle 200, relative to the fourth lens 127, which acts as a second optical element.

[0067] As shown in Figure 6, the fourth lens 127 has a convex shape on both its incident surface facing the second lens 121 and its exit surface facing the first lens 123, with the convex shape extending towards the second lens 121 and the first lens 123 in the X-axis and Y-axis directions, respectively. The fourth lens 127 is a free-form lens in which the curvature of the convex surface differs in the X-axis and Y-axis directions.

[0068] In this embodiment, the second lens 121, the fourth lens 127, and the first lens 123 are positioned at an angle clockwise with respect to the reference ray Lc in the XZ plane view shown in Figure 6. This prevents stray light from entering the housing and being reflected by the second lens 121, the fourth lens 127, or the first lens 123.

[0069] As described above, this embodiment uses a fourth lens 127 as a second optical element. A first lens 123 is positioned between the fourth lens 127 and the third mirror 125 that projects the intermediate image M. In particular, in the optical path from the display device 110, the first lens 123, which has positive power, is positioned before the second mirror 124, which has negative power and forms the intermediate image M as a first optical element. Therefore, the overall length of the relay optical system 120 can be shortened and the first lens 123 itself can be miniaturized, thereby making the head-up display 100 smaller.

[0070] In this embodiment, the positional relationship between the first lens 123 and the second lens 121 differs from that of Embodiment 1, but the positions of the thicker and thinner parts of the lens relative to the reference ray Lc are arranged to be opposite to each other. Therefore, similar to Embodiment 1, 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 point in which they pass through the second lens 121 and the first lens 123.

[0071] [3-2. Effects, etc.] The head-up display 100, as an example of a head-up display according to Embodiment 3, is a head-up display that allows an observer D to view a virtual image I. The head-up display 100 comprises 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 the function of forming an intermediate image M of the image displayed by the display device 110. The first lens 123 included in the projection optical system 140 is arranged at an angle with respect to a reference ray Lc. Therefore, even when ambient light is incident into the projection optical system 140, stray light due to reflection of the ambient light by the first lens 123, the second lens 121, or the fourth lens 127 can be suppressed. The projection optical system 140 also comprises, in the order of the optical path from the display device 110, a fourth lens 127 as an example of a second optical element, a first lens 123 having a light-gathering effect, and a second mirror 124 as an example of a first optical element having a diverging effect. Thus, in the head-up display 100 according to Embodiment 3, a telephoto arrangement is achieved by placing the first lens 123, which has positive power, before the second mirror 124, which has negative power and forms an intermediate image M, in the optical path from the display device 110. Therefore, the head-up display 100 can be miniaturized by shortening the overall length of the relay optical system 120 and miniaturizing the first lens 123 itself.

[0072] The head-up display 100 according to Embodiment 3 has at least one surface of the first lens 123, the second lens 121, and the fourth lens 127 as a free-form surface. Therefore, in an imaging optical system such as the head-up display 100, good optical characteristics can be achieved while suppressing reflection of ambient light.

[0073] 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 ray Lc, the optical path length of the light ray passing through the first lens 123 and the second lens 121 can be adjusted.

[0074] In the head-up display 100 according to Embodiment 3, the positions of the thick and thin portions of 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 Embodiment 1, 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 portion of the light rays passing through the second lens 121 and the first lens 123.

[0075] In the head-up display 100 according to Embodiment 3, the intermediate image M is an aerial image formed in the air along the optical path from the display device 110 to the virtual image I. Therefore, without adding a member to form 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 then further enlarge the intermediate image M and project it onto the observer D.

[0076] (Embodiment 4) Next, Embodiment 4 will be described using Figure 7.

[0077] [4-1. Structure] Figure 7 is a schematic diagram illustrating the optical path for explaining the head-up display 100 according to Embodiment 4. As shown in Figure 7, the head-up display 100 of this embodiment includes a fifth lens 128 in front of the first lens 123 in the optical path from the first mirror 122 to the second mirror 124.

[0078] The fifth lens 128 is a free-form surface lens with different curvatures in the X-axis and Y-axis directions. In the fifth lens 128, the surface on the first mirror 122 side is a planar incident surface, and the surface on the first lens 123 side is a concave exit surface that is concave towards the first lens 123 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, convex, or planar shape with a curvature smaller than that in the X-axis direction.

[0079] In this embodiment, as shown in Figure 7, the incident and exit surfaces of the fifth lens 128 are tilted clockwise with respect to the reference ray Lc in the XZ plane view in Figure 7. As a result, reflected light is reflected upward from the fifth lens 128. Therefore, reflected light can be prevented from entering the viewpoint area 300. Here, it is desirable that the tilt of the fifth lens 128 with respect to the reference ray Lc be such that when ambient light incident along the reference ray Lc is reflected at the incident or exit surface, the reflected light does not enter the first mirror 122 and the second mirror 124. More preferably, the tilt is such that when ambient light incident from the first mirror 122 to the fifth lens 128 is reflected at the incident or exit surface of the fifth lens 128, the reflected light does not enter the first mirror 122. Furthermore, when we say that the fifth lens 128 is tilted with respect to the reference ray Lc, it means that the point where the optical refractive surface of the fifth lens 128 intersects with the reference ray Lc is not horizontal with respect to a plane perpendicular to the reference ray Lc.

[0080] The fifth lens 128 is a lens element with negative refractive power. By placing such a fifth lens 128 in front of the first lens 123 in the optical path from the first mirror 122 to the second mirror 124, chromatic aberration occurring in the first lens 123 can be suppressed.

[0081] In the projection optical system 140 of this embodiment, the fifth lens 128, the first mirror 122 as a second optical element having a light-gathering effect, and the second mirror 124 as a first optical element that forms an intermediate image M are arranged in the order of the optical path from the display device 110. By arranging the first lens 123 in front of the second mirror 124 that forms the intermediate image M in the order of the optical path from the display device 110, the intermediate image M can be formed closer to the output side of the first lens 123. As a result, the first lens 123 itself can be miniaturized. Consequently, the head-up display 100 can be miniaturized. In addition, the negative refractive power of the fifth lens 128 can suppress chromatic aberration that occurs in the first lens 123.

[0082] Furthermore, in the relay optical system 120 of this embodiment, a first lens 123 having positive power and a second mirror 124 having negative power are arranged from the display device 110 toward the intermediate image M. In other words, the relay optical system 120 has a so-called telephoto arrangement. By using this 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 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.

[0083] Furthermore, in this embodiment, as shown in Figure 7, the incident and exit surfaces of the second lens 121 are tilted counterclockwise with respect to the reference ray Lc in the XZ plan view of Figure 7. Also, the incident and exit surfaces of the first lens 123 are tilted clockwise with respect to the reference ray Lc in the XZ plan view of Figure 7. As a result, the reflected light from ambient light at the first lens 123 is reflected downward from the second mirror 124, and the reflected light from ambient light at the second lens 121 is reflected downward from the first mirror 122. Therefore, reflected light can be prevented from entering the viewpoint area 300. Here, it is desirable that the inclination of the second lens 121 and the first lens 123 with respect to the reference ray Lc be such that when ambient light incident along the reference ray Lc is reflected at the incident or exit surface, the reflected light does not enter the first mirror 122 or the second mirror 124. More preferably, the above inclination is such that when ambient light incident from the first mirror 122 to the second lens 121 or the first lens 123 is reflected at the incident or exit surface of the second lens 121 or the first lens 123, the reflected light does not incident on the first mirror 122. Note that when the second lens 121 and the first lens 123 are inclined with respect to the reference ray Lc, it means that the points where the optical refractive surfaces of the second lens 121 and the first lens 123 intersect with the reference ray Lc are not horizontal with respect to a plane perpendicular to the reference ray Lc.

[0084] In this embodiment, similar to Embodiment 1, the positions of the thicker and thinner portions of 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 Embodiment 1, 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 portion of the light rays passing through the second lens 121 and the first lens 123.

[0085] [4-2. Effects, etc.] The head-up display 100, as an example of a head-up display according to Embodiment 4, is a head-up display that allows an observer D to view a virtual image I. The head-up display 100 comprises 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 the function of forming an intermediate image M of the image displayed by the display device 110. The first lens 123 included in the projection optical system 140 is arranged at an angle with respect to the reference ray Lc. Therefore, even when ambient light is incident into the projection optical system 140, stray light due to reflection of ambient light by the fifth lens 128, etc., can be suppressed. The projection optical system 140 also comprises, in the order of the optical path from the display device 110, a first lens 123 with a light-gathering effect and a second mirror 124 as an example of a first optical element with a diverging effect. Thus, in the head-up display 100 according to Embodiment 4, a first lens 123 having positive power is placed before the second mirror 124, which has negative power and forms an intermediate image M, in the optical path from the display device 110, resulting in 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, thereby reducing the size of the head-up display 100. Furthermore, a fifth lens 128 is placed before the first lens 123 in the optical path from the display device 110. As a result, the negative refractive power of the fifth lens 128 can suppress chromatic aberration generated in the first lens 123.

[0086] In the head-up display 100 according to Embodiment 4, a first mirror 122 is used as an example of a second optical element, and a second mirror 124 is used as an example of a first optical element. Therefore, it is possible to sufficiently enlarge the image displayed on the small display device 110 to create an intermediate image M, and then further enlarge the intermediate image M and project it onto the observer D.

[0087] In the head-up display 100 according to Embodiment 4, at least one surface of the second lens 121, the first lens 123, and the fifth lens 128 is a free-form surface. Therefore, in an imaging optical system such as the head-up display 100, good optical characteristics can be achieved while suppressing reflection of ambient light.

[0088] In the head-up display 100 according to Embodiment 4, 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 ray Lc, the optical path length of the light ray passing through the first lens 123 and the second lens 121 can be adjusted.

[0089] The head-up display 100 according to Embodiment 4 includes a second lens 121 between the display device 110 and the first mirror 122. The second lens 121 has a wedge shape, and at least one surface is a free-form surface. Furthermore, in the head-up display 100 according to Embodiment 4, the first lens 123 and the second lens 121 are arranged such that light rays passing through the thinner part of one lens pass through the thicker part of the other lens, and light rays passing through the thicker part of one lens pass through the thinner part of the other lens. Therefore, even when the first lens 123 and the second lens 121 are tilted with respect to the reference light ray Lc, the optical path length of the light rays passing through the first lens 123 and the second lens 121 can be made uniform.

[0090] In the head-up display 100 according to Embodiment 4, the intermediate image M is an aerial image formed in the air along the optical path from the display device 110 to the virtual image I. Therefore, without adding a member to form 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 then further enlarge the intermediate image M and project it onto the observer D.

[0091] (Embodiment 5) Next, Embodiment 5 will be described using Figure 8.

[0092] [5-1. Structure] Figure 8 is a schematic diagram illustrating the optical path for explaining the head-up display 100 according to Embodiment 5. As shown in Figure 8, the head-up display 100 of this embodiment includes a sixth lens 129 after the intermediate image M in the optical path from the second mirror 124 to the third mirror 125.

[0093] The sixth lens 129 is a free-form surface lens with different curvatures in the X-axis and Y-axis directions. In the sixth lens 129, the surface on the third mirror 125 side is a planar exit surface, and the surface on the intermediate image M side is a concave incident surface that is concave towards the first lens 123 in the X-axis direction. The curvature of the incident surface of the second mirror 124 in the Y-axis direction is smaller than the curvature in the X-axis direction. That is, the shape of the sixth lens 129 in the Y-axis direction is a concave, convex, or planar shape with a curvature smaller than the curvature in the X-axis direction.

[0094] In this embodiment, as shown in Figure 8, the incident and exit surfaces of the sixth lens 129 are tilted counterclockwise with respect to the reference ray Lc in the XZ plane view in Figure 8. As a result, the reflected light is reflected downward from the sixth lens 129. Therefore, the reflected light can be prevented from entering the viewpoint area 300. Here, it is desirable that the tilt of the sixth lens 129 with respect to the reference ray Lc be such that when ambient light incident along the reference ray Lc is reflected at the incident or exit surface, the reflected light does not enter the third mirror 125 and the second mirror 124. More preferably, the tilt is such that when ambient light incident from the second mirror 124 to the sixth lens 129 is reflected at the incident or exit surface of the sixth lens 129, the reflected light does not enter the second mirror 124 and the third mirror 125. Furthermore, when we say that the sixth lens 129 is tilted with respect to the reference ray Lc, it means that the point where the optical refractive surface of the sixth lens 129 intersects with the reference ray Lc is not horizontal with respect to a plane perpendicular to the reference ray Lc.

[0095] The sixth lens 129 is a lens element with negative refractive power. In the optical path from the display device 110 to the third mirror 125, this sixth lens 129 is positioned behind the optical elements of the relay optical system 120. This reduces the aberration correction burden on the optical elements and improves image quality.

[0096] In the projection optical system 140 of this embodiment, a first mirror 122, which serves as a second optical element with a light-gathering effect, and a second mirror 124, which serves as a first optical element for forming an intermediate image M, are arranged in the order of the optical path from the display device 110. By arranging the first lens 123 in front of the second mirror 124 that forms the intermediate image M in the order of the optical path from the display device 110, the intermediate image M can be formed closer to the output side of the first lens 123. As a result, the first lens 123 itself can be miniaturized. Consequently, the head-up display 100 can be miniaturized. Furthermore, a sixth lens 129 is arranged behind the intermediate image M. As a result, the burden of aberration correction on the optical elements in the relay optical system 120 can be reduced, and image quality can be improved.

[0097] Furthermore, in the relay optical system 120 of this embodiment, a first lens 123 having positive power and a second mirror 124 having negative power are arranged from the display device 110 toward the intermediate image M. In other words, the relay optical system 120 has a so-called telephoto arrangement. By using this 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 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.

[0098] Furthermore, in this embodiment, as shown in Figure 8, the incident and exit surfaces of the second lens 121 are tilted counterclockwise with respect to the reference ray Lc in the XZ plan view of Figure 8. Also, the incident and exit surfaces of the first lens 123 are tilted clockwise with respect to the reference ray Lc in the XZ plan view of Figure 8. As a result, the light reflected from ambient light by the first lens 123 is reflected downward from the second mirror 124, and the light reflected from ambient light by the second lens 121 is reflected downward from the first mirror 122. Therefore, reflected light can be prevented from entering the viewpoint area 300. Here, it is desirable that the inclination of the second lens 121 and the first lens 123 with respect to the reference ray Lc be such that when ambient light incident along the reference ray Lc is reflected at the incident or exit surface, the reflected light does not enter the first mirror 122 or the second mirror 124. More preferably, the above inclination is such that when ambient light incident from the first mirror 122 to the second lens 121 or the first lens 123 is reflected at the incident or exit surface of the second lens 121 or the first lens 123, the reflected light does not incident on the first mirror 122. Note that when the second lens 121 and the first lens 123 are inclined with respect to the reference ray Lc, it means that the points where the optical refractive surfaces of the second lens 121 and the first lens 123 intersect with the reference ray Lc are not horizontal with respect to a plane perpendicular to the reference ray Lc.

[0099] In this embodiment, similar to Embodiment 1, the positions of the thicker and thinner portions of 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 Embodiment 1, 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 portion of the light rays passing through the second lens 121 and the first lens 123.

[0100] [5-2. Effects, etc.] The head-up display 100, as an example of a head-up display according to Embodiment 5, is a head-up display that allows an observer D to view a virtual image I. The head-up display 100 comprises 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 the function of forming an intermediate image M of the image displayed by the display device 110. The first lens 123 included in the projection optical system 140 is arranged at an angle with respect to the reference ray Lc. Therefore, even when ambient light is incident into the projection optical system 140, stray light caused by the ambient light being reflected by the sixth lens 129, etc., can be suppressed. The projection optical system 140 also comprises, in the order of the optical path from the display device 110, a first lens 123 having a light-gathering effect and a second mirror 124 as an example of a first optical element having a diverging effect. Thus, in the head-up display 100 according to Embodiment 5, the first lens 123, which has positive power, is placed before the second mirror 124, which has negative power and forms an intermediate image M, in the optical path from the display device 110, resulting in 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, thereby reducing the size of the head-up display 100. Furthermore, the sixth lens 129 is placed after the relay optical system 120 in the optical path from the display device 110. As a result, the burden of aberration correction on the optical elements of the relay optical system 120 can be reduced, and image quality can be improved.

[0101] In the head-up display 100 according to Embodiment 5, a first mirror 122 is used as an example of a second optical element, and a second mirror 124 is used as an example of a first optical element. Therefore, it is possible to sufficiently enlarge the image displayed on the small display device 110 to create an intermediate image M, and then further enlarge the intermediate image M and project it onto the observer D.

[0102] In the head-up display 100 according to Embodiment 5, at least one surface of the second lens 121, the first lens 123, and the sixth lens 129 is a free-form surface. Therefore, in an imaging optical system such as the head-up display 100, good optical characteristics can be achieved while suppressing reflection of ambient light.

[0103] In the head-up display 100 according to Embodiment 5, 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 ray Lc, the optical path length of the light ray passing through the first lens 123 and the second lens 121 can be adjusted.

[0104] The head-up display 100 according to Embodiment 5 includes a second lens 121 between the display device 110 and the first mirror 122. The second lens 121 has a wedge shape, and at least one surface is a free-form surface. In the head-up display 100 according to Embodiment 4, the first lens 123 and the second lens 121 are arranged such that light rays passing through the thinner part of one lens pass through the thicker part of the other lens, and light rays passing through the thicker part of one lens pass through the thinner part of the other lens. Therefore, even when the first lens 123 and the second lens 121 are tilted with respect to the reference light ray Lc, the optical path length of the light rays passing through the first lens 123 and the second lens 121 can be made uniform.

[0105] In the head-up display 100 according to Embodiment 5, the intermediate image M is an aerial image formed in the air along the optical path from the display device 110 to the virtual image I. Therefore, without adding a member to form 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 then further enlarge the intermediate image M and project it onto the observer D.

[0106] (Embodiment 6) Next, Embodiment 6 will be described using Figure 9.

[0107] [6-1. Structure] Figure 9 is a schematic diagram illustrating the optical path for explaining the head-up display 100 according to Embodiment 6. As shown in Figure 9, the head-up display 100 of this embodiment includes a seventh lens 150 as another example of the first optical element.

[0108] The first mirror 122 in this embodiment has the same configuration as the first mirror 122 in Embodiments 1 and 2. However, its position differs from those in the embodiments described above. In this embodiment, as shown in Figure 9, the first mirror 122 is positioned at the rearmost position of the vehicle 200 within the head-up display 100. Also, the display device 110 and the second lens 121 in this embodiment have the same configuration as the display device 110 and the second lens 121 in the embodiments described above. However, their position differs from those in the embodiments described above. In this embodiment, as shown in Figure 9, the display device 110 and the second lens 121 are positioned further forward of the vehicle 200 than the first mirror 122.

[0109] The first lens 123 in this embodiment has the same configuration as the first lens 123 in Embodiments 1 and 3. However, its position is different. In this embodiment, the first lens 123 is located further rearward from the vehicle 200 than the seventh lens 150, which is the first optical element.

[0110] The seventh lens 150 is a free-form surface lens with different curvatures in the X-axis and Y-axis directions. In the seventh lens 150, the surface on the first lens 123 side is a planar incident surface, and the surface on the third mirror 125 side is a concave exit surface that is concave towards the third mirror 125 in the X-axis direction. The curvature of the exit surface of the seventh lens 150 in the Y-axis direction is smaller than the curvature in the X-axis direction. That is, the shape of the seventh lens 150 in the Y-axis direction is a concave, convex, or planar shape with a curvature smaller than that in the X-axis direction.

[0111] In this embodiment, as shown in Figure 9, the incident and exit surfaces of the seventh lens 150 are tilted counterclockwise with respect to the reference ray Lc in the XZ plane view in Figure 9. As a result, the reflected light is reflected downward from the seventh lens 150. Therefore, the reflected light can be prevented from entering the viewpoint area 300. Here, it is desirable that the tilt of the seventh lens 150 with respect to the reference ray Lc be such that when ambient light incident along the reference ray Lc is reflected at the incident or exit surface, the reflected light does not enter the first mirror 122 and the third mirror 125. More preferably, the tilt is such that when ambient light incident from the first mirror 122 to the seventh lens 150 is reflected at the incident or exit surface of the seventh lens 150, the reflected light does not enter the first mirror 122. Furthermore, when we say that the seventh lens 150 is tilted with respect to the reference ray Lc, it means that the point where the optical refractive surface of the seventh lens 150 intersects with the reference ray Lc is not horizontal with respect to a plane perpendicular to the reference ray Lc.

[0112] Furthermore, the emission surface of the seventh lens 150 has a wedge shape in the XZ plan view shown in Figure 9. By making the cross-sectional shape of the seventh lens 150 along the Y-axis wedge-shaped, the optical path length of light passing above the seventh lens 150 becomes longer than the optical path length of light passing below the seventh lens 150. In other words, the optical path length from the image light emitted from the display device 110 to the formation of the intermediate image M can be changed according to the position in the Y-axis direction. This makes it possible to effectively correct the eccentric image plane curvature that occurs in the first mirror 122.

[0113] In the projection optical system 140 of this embodiment, a first mirror 122, which serves as a second optical element with a light-gathering function, and a seventh lens 150, which serves as a first optical element for forming an intermediate image M, are arranged in the order of the optical path from the display device 110. A first lens 123, which serves as a light-gathering function, is positioned between the first mirror 122 and the seventh lens 150. By positioning the first lens 123 between the first mirror 122, which creates the intermediate image M, and the seventh lens 150, which forms the intermediate image M, the intermediate image M can be formed closer to the output side of the first lens 123. As a result, the first lens 123 itself can be miniaturized. Consequently, the head-up display 100 can be miniaturized.

[0114] Furthermore, in the relay optical system 120 of this embodiment, a first lens 123 having positive power and a seventh lens 150 having negative power are arranged from the display device 110 toward the intermediate image M. In other words, the relay optical system 120 has a so-called telephoto arrangement. By using this telephoto arrangement, the first lens 123 increases the negative power of the seventh lens 150, and the seventh lens 150 increases the positive power of the first lens 123. That is, the first lens 123 and the seventh lens 150 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.

[0115] Furthermore, in this embodiment, as shown in Figure 9, the incident and exit surfaces of the second lens 121 are tilted clockwise with respect to the reference ray Lc in the XZ plan view of Figure 9. Also, the incident and exit surfaces of the first lens 123 are tilted counterclockwise with respect to the reference ray Lc in the XZ plan view of Figure 9. As a result, the reflected light from ambient light in the first lens 123 is reflected upward from the first mirror 122, and the reflected light from ambient light in the second lens 121 is reflected downward from the first mirror 122. Therefore, reflected light can be prevented from entering the viewpoint area 300. Here, it is desirable that the inclination of the second lens 121 and the first lens 123 with respect to the reference ray Lc be such that when ambient light incident along the reference ray Lc is reflected at the incident or exit surface, the reflected light does not enter the first mirror 122. More preferably, the above inclination is such that when ambient light incident from the first mirror 122 to the second lens 121 or the first lens 123 is reflected at the incident or exit surface of the second lens 121 or the first lens 123, the reflected light does not incident on the first mirror 122. Note that when the second lens 121 and the first lens 123 are inclined with respect to the reference ray Lc, it means that the points where the optical refractive surfaces of the second lens 121 and the first lens 123 intersect with the reference ray Lc are not horizontal with respect to a plane perpendicular to the reference ray Lc.

[0116] In this embodiment, similar to Embodiment 1, the positions of the thicker and thinner portions of 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 Embodiment 1, 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 portion of the light rays passing through the second lens 121 and the first lens 123.

[0117] [6-2. Effects, etc.] The head-up display 100, as an example of a head-up display according to Embodiment 6, is a head-up display that allows an observer D to view a virtual image I. The head-up display 100 comprises 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 the function of forming an intermediate image M of the image displayed by the display device 110. The first lens 123 included in the projection optical system 140 is arranged at an angle with respect to the reference ray Lc. Therefore, even when ambient light enters the projection optical system 140, stray light caused by the ambient light being reflected by the seventh lens 150, etc., can be suppressed. The projection optical system 140 also comprises, in the order of the optical path from the display device 110, the first lens 123 which has a light-gathering function and the seventh lens 150 as an example of a first optical element. Thus, in the head-up display 100 according to Embodiment 6, the first lens 123, which has positive power, is placed before the seventh lens 150, which has negative power and forms an intermediate image M, in the optical path from the display device 110, thus creating 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, thereby reducing the size of the head-up display 100.

[0118] As an example of the second optical element according to Embodiment 6, a first mirror 122 is used, and a third mirror 125 is used in the projection optical system 130. Therefore, it is possible to sufficiently enlarge the image displayed on the small display device 110 to create an intermediate image M, and then further enlarge the intermediate image M and project it onto the observer D.

[0119] The head-up display 100 according to Embodiment 6 uses a seventh lens 150 having negative power as an example of a first optical element near the intermediate image M. As a result, the seventh lens 150 acts as a so-called field lens. Therefore, the first lens 123, the first mirror 122, and the second lens 121 can be miniaturized.

[0120] In the head-up display 100 according to Embodiment 6, at least one surface of the first lens 123, the second lens 121, and the seventh lens 150 is a free-form surface. Therefore, in an imaging optical system such as the head-up display 100, good optical characteristics can be achieved while suppressing reflection of ambient light.

[0121] In the head-up display 100 according to Embodiment 6, the first lens 123, the second lens 121, and the seventh lens 150 have a wedge shape. Therefore, even when the first lens 123, the second lens 121, and the seventh lens 150 are tilted with respect to the reference ray Lc, the optical path length of the light rays passing through the first lens 123, the second lens 121, and the seventh lens 150 can be adjusted.

[0122] The head-up display 100 according to Embodiment 6 includes a second lens 121 between the display device 110 and a first mirror 122, which is an example of a second optical element. The second lens 121 has a wedge shape, and at least one surface is a free-form surface. In addition, in the head-up display 100 according to Embodiment 6, the first lens 123 and the second lens 121 are arranged such that light rays passing through the thinner part of one lens pass through the thicker part of the other lens, and light rays passing through the thicker part of one lens pass through the thinner part of the other lens. Therefore, even when the first lens 123 and the second lens 121 are tilted with respect to the reference light ray Lc, the optical path length of the light rays passing through the first lens 123 and the second lens 121 can be made uniform.

[0123] In the head-up display 100 according to Embodiment 6, the intermediate image M is an aerial image formed in the air along the optical path from the display device 110 to the virtual image I. Therefore, without adding a member to form 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 then further enlarge the intermediate image M and project it onto the observer D.

[0124] (Other embodiments) As described above, Embodiments 1 to 6 have been explained as examples of the technology disclosed in this application. However, the technology in this disclosure is not limited thereto and can be applied to embodiments that have been modified, replaced, added, or omitted. Furthermore, it is possible to create new embodiments by combining the components described in Embodiments 1 to 6 above.

[0125] In embodiments 1 to 6, a second lens 121 was shown as an example of a 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 consist of multiple lens elements arranged between the display device 110 and the first mirror 122. When there are multiple lens elements, it is desirable that the lens element to which the light emitted from the display device first enters has positive power.

[0126] In embodiments 1 to 6, one third mirror 125 is arranged as the projection optical system 140. However, two or more mirrors may be arranged. In addition, the additional mirrors may be positioned in front of the third mirror 125, or in the direction inward or outward of the vehicle, that is, in the direction perpendicular to the plane of the paper in Figures 1, 2, and 4 to 9.

[0127] In embodiments 1 to 6, a lens element was 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 added and placed between the third mirror 125 and the windshield 220.

[0128] In embodiments 1 to 6, the first mirror 122, second mirror 124, and third mirror 125 of the head-up display 100 were described using mirrors with rotationally asymmetrical shapes. However, these mirrors are not limited to these. For example, these mirrors may have a so-called saddle-shaped surface where the sign of curvature differs in the X-axis direction and the Y-axis direction.

[0129] The surface shape of the lens element used in Embodiments 1 to 6 is not limited to a free-form surface shape. For example, the surface shape of the lens element may be toroidal, anamorphic, or cylindrical. Furthermore, lenses of these shapes may be arranged eccentrically with respect to the reference ray Lc.

[0130] The exit surface of the fifth lens 128 in Embodiment 4, the incident surface of the sixth lens 129 in Embodiment 5, and the exit surface of Embodiment 6 do not necessarily have to be entirely concave in the X-axis direction; they may have a locally convex shape.

[0131] The planar surfaces of the lens elements used in Embodiments 1 to 6 may be convex or concave, or they may have a locally curved shape.

[0132] The reflective surfaces of the first mirror 122, the second mirror 124, and the third mirror 125 in Embodiments 1 to 5 are not limited to free-form shapes. The reflective surfaces of these mirrors may be spherical, aspherical, toroidal, or anamorphic. Furthermore, these mirrors may be arranged eccentrically with respect to the reference ray Lc.

[0133] In embodiments 1 to 6, the head-up display 100 is positioned below the dashboard 210, but it may also be positioned above the dashboard 210.

[0134] As described above, embodiments have been explained as examples of the technology in this disclosure. For this purpose, attached drawings and a detailed description have been provided. Therefore, among the components described in the attached drawings and detailed description, there may be not only components that are essential for solving the problem, but also components that are not essential for solving the problem, in order to illustrate the above technology. For this reason, the mere fact that these non-essential components are described in the attached drawings and detailed description should not be immediately assumed to be essential.

[0135] Furthermore, since the embodiments described above are for illustrative purposes of the technology described herein, various modifications, substitutions, additions, omissions, etc., can be made within the claims or their equivalents.

[0136] (Summary of the embodiment) (1) The head-up display of the present disclosure is a head-up display that projects an image onto a transparent reflective member to allow an observer to view a virtual image, and comprises a display device for displaying the image, and a projection optical system for projecting the image displayed on the display device as a virtual image to the observer. The projection optical system comprises a first lens having a focusing function and an intermediate image-forming function, and a first optical element having a diverging function. The first lens and the first optical element are arranged in the order of the optical path from the display device. When a ray that reaches the center of the observer's viewpoint region and corresponds to the center of the virtual image is taken as a reference ray, the first lens is positioned at an angle with respect to the reference ray.

[0137] In this configuration, a projection optical system is constructed by arranging a first lens with a focusing effect and a first optical element with a diverging effect in the order of the optical path from the display device, with the first lens positioned at an angle to the reference ray. Therefore, even when ambient light enters the projection optical system, stray light caused by reflection of ambient light from the first lens can be suppressed. Furthermore, the projection optical system is arranged in a telephoto configuration, with a first lens having positive power positioned before the first optical element having negative power and forming an intermediate image in the order of the optical path from the display device. Consequently, the overall length of the relay optical system can be shortened, and the first lens itself can be miniaturized, thereby enabling a smaller head-up display.

[0138] (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 a small display device to create an intermediate image, and then further enlarge the intermediate image and project it onto the observer.

[0139] (3) In the head-up display of (1) or (2), 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 achieved while suppressing reflection of ambient light.

[0140] (4) In any one of the head-up displays described in (1) to (3), the first lens has a wedge shape. Therefore, even when the first lens is tilted with respect to the reference ray, the optical path length of the ray passing through the first lens can be adjusted.

[0141] (5)(4) In the head-up display, the projection optical system comprises a second optical element having a light-gathering function and a second lens having a light-gathering function. The second lens, the second optical element, and the first lens are arranged in the order of the optical path from the display device. 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 the thin part of the first lens pass through the thick part of the second lens, and light rays passing through the thick part of the first lens pass through the thin part of the second lens. Therefore, even when the first lens and the second lens are tilted with respect to a reference ray, the optical path length of the light rays passing through the first lens and the second lens can be made uniform.

[0142] In the head-up display of (6)(5), the first lens and the second lens are formed integrally. Therefore, the number of parts can be reduced, and the manufacturing cost of the head-up display can be lowered.

[0143] In the head-up display of (7)(5), the projection optical system includes a lens having negative refractive power, which is positioned in the optical path from the second optical element to the first optical element, in front of the first lens, at an angle with respect to the reference ray. Therefore, the burden of aberration correction on the optical elements can be reduced, and image quality can be improved.

[0144] In the head-up display of (8)(5), the projection optical system includes a lens having negative refractive power, which is positioned after the intermediate image in the optical path from the first optical element to the virtual image and is tilted with respect to the reference ray. Therefore, the burden of aberration correction on the optical element can be reduced, and image quality can be improved.

[0145] (9) In any one of the head-up displays described in (1) to (8), the intermediate image is an aerial image formed in the air along the optical path. Therefore, without adding any additional components for forming the intermediate image, it is possible to enlarge an image displayed on a small display device to create an intermediate image, and then further enlarge the intermediate image and project it onto the observer. [Industrial applicability]

[0146] This disclosure is applicable to head-up displays using refractive optical systems such as lenses. Specifically, this disclosure is applicable to head-up displays for vehicles and the like. [Explanation of Symbols]

[0147] 100 Head-Up Displays 110 Display Devices 120 Relay Optics 121 Second lens 122 First Mirror 123 First Lens 124 Second Mirror 125 Third Mirror 126 Third Lens 127 Fourth Lens 128 Fifth Lens 129. Lens No. 6 130 Projection optical system 140 Projection optical system 150 7th lens 200 vehicles 210 Dashboard 220 Windshield 300 viewpoint areas D Observer Illusion M intermediate image L-ray Lc reference ray

Claims

1. A head-up display that projects a projected image formed from an original image onto a transparent reflective material to allow an observer to see a virtual image, A device that emits a light ray to convert the original image into the projected image, The system comprises a projection optical system that forms the projected image from the original image and projects the projected image as a virtual image to the observer, The aforementioned projection optical system is A first lens having a refractive surface into which light rays emitted from the device are received, A second mirror that reflects light rays downwards, The system comprises a third mirror that reflects the light reflected by the second mirror as the projected image to the reflective member, The first lens, the second mirror, and the third mirror are arranged in the order of the optical path to the reflective member. When the ray that reaches the center of the observer's viewpoint region and corresponds to the center of the virtual image is taken as the reference ray, the first lens is positioned at an angle with respect to the reference ray. The projection optical system has the function of forming the original image as an intermediate image on the optical path between the second mirror and the third mirror using light rays emitted from the device, and forming the projected image from the intermediate image. The optical path between the second mirror and the third mirror is in the air. The aforementioned intermediate image is an aerial image. Head-up display.

2. The first lens is positioned at an angle with respect to the reference ray such that its upper side is closer to the second mirror than its lower side. The head-up display according to claim 1.

3. The first lens is positioned at an angle between 15 and 30 degrees with respect to a plane perpendicular to the reference ray. The head-up display according to claim 2.

4. The aforementioned intermediate image is formed at a position closer to the second mirror than to the third mirror. The head-up display according to claim 1.

5. The second mirror is a convex mirror. The head-up display according to claim 1.

6. The third mirror is a concave mirror. The head-up display according to claim 1.

7. The third mirror has a freeform surface shape. The head-up display according to claim 5.

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