HEAD-UP DISPLAY SYSTEM AND MOVING BODY EQUIPPED WITH HEAD-UP DISPLAY SYSTEM

Abstract

A head-up display system of the present disclosure includes a display device that displays an image and a projection optical system that projects on the display member the image displayed on the display device. The projection optical system includes mirror M.sub.L that reflects a light beam toward the display member and mirror M.sub.L1 that reflects the light beam toward mirror M.sub.L. Then, the projection optical system satisfies following condition (1):

0.01<|M.sub.LD/M.sub.LW||M.sub.L1Z/M.sub.L1W|(1) where M.sub.LD is depth of mirror M.sub.L M.sub.LW is lateral dimension of mirror M.sub.L M.sub.L1Z is maximum sag amount of mirror M.sub.L1 M.sub.L1W is lateral dimension of mirror M.sub.L1.

Such a configuration provides a head-up display system small in size that makes image distortion small in an entire viewpoint area of an observer.

Claims

1. A head-up display system configured to project an image on a display member disposed in an eye direction of an observer, the head-up display system comprising: a display device configured to display the image; and a projection optical system configured to project on the display member the image displayed on the display device, wherein the projection optical system includes, a mirror M.sub.L configured to reflect a light beam toward the display member, and a mirror M.sub.L1 configured to reflect the light beam toward mirror M.sub.L, the mirror M.sub.L and the mirror M.sub.L1 being arranged in a stated order in a direction from the display member to the display device, the display device is positioned under the mirror M.sub.L1, and the mirror M.sub.L is positioned on a side opposite to the observer with respect to the mirror M.sub.L1, and satisfies following condition (1)
0.01<|M.sub.LD/M.sub.LW||M.sub.L1Z/M.sub.L1W|(1) where M.sub.LD is a depth of the mirror M.sub.L M.sub.LW is a lateral-dimension of the mirror M.sub.L M.sub.L1Z is a maximum sag amount of the mirror M.sub.L1 M.sub.L1W is a lateral-dimension of the mirror M.sub.L1.

2. The head-up display system according to claim 1, wherein the mirror M.sub.L includes a movable mechanism configured to adjust a display position of the image to be projected on the display member.

3. The head-up display system according to claim 1, wherein a light beam emitted toward a center of a viewpoint area of the observer has a first angle and a second angle larger than the first angle, the light beam being among light beams emitted from a center of the image displayed on the display device, the first angle being made with a line parallel to a longer side of a display surface of the display device, the second angle being made with a line parallel to a shorter side of the display surface.

4. The head-up display system according to claim 1, wherein the projection optical system includes a reflection optical element, the reflection optical element including the mirror M.sub.L1 and the mirror M.sub.L.

5. The head-up display system according to claim 1, wherein the mirror M.sub.L includes a reflection surface having a free-form surface shape.

6. The head-up display system according to claim 1, wherein the mirror M.sub.L1 includes a reflection surface having a free-form surface shape.

7. The head-up display system according to claim 1, further comprising a housing, wherein the display device and the projection optical system are disposed inside the housing.

8. A moving body comprising the head-up display system according to claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0012] FIG. 1 is a schematic view illustrating a cross section of a vehicle mounting thereon a head-up display system of the present disclosure.

[0013] FIG. 2 is a schematic view for illustrating an optical cross-section for illustrating a head-up display system according to first to fourth exemplary embodiments.

[0014] FIG. 3 is a diagram for illustrating a shape of a first mirror according to another exemplary embodiment.

[0015] FIG. 4 is a view illustrating image distortion in a viewpoint area of an observer according to numerical example 1.

[0016] FIG. 5 is a view illustrating image distortion in the viewpoint area of the observer according to numerical example 2.

[0017] FIG. 6 is a view illustrating image distortion in the viewpoint area of the observer according to numerical example 3.

[0018] FIG. 7 is a view illustrating image distortion in the viewpoint area of the observer according to numerical example 4.

[0019] FIG. 8 is a diagram illustrating a coordinate system and sizes according to condition (1).

[0020] FIG. 9 is another diagram illustrating the coordinate system and the sizes according to condition (1).

[0021] FIG. 10 is a diagram illustrating a coordinate system of the numerical examples according to the first to fourth exemplary embodiments.

DESCRIPTION OF EMBODIMENTS

[0022] Hereinafter, exemplary embodiments will be described in detail with reference to the drawings as appropriate. However, a detailed description more than necessary may be omitted. For example, a detailed description of well-known matters and a duplicate description of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to make the following description easily understandable to those skilled in the art.

[0023] The applicant provides the attached drawings and the following description such that one skilled in the art can sufficiently understand the present disclosure, and therefore, they do not intend to restrict the subject matters of claims.

First to Fourth Exemplary Embodiments

[1-1. Configuration]

[1-1-1. General Configuration of Head-Up Display System]

[0024] Specific exemplary embodiments and examples of head-up display system 10 of the present disclosure will be described below with reference to the drawings.

[0025] FIG. 1 is a schematic view illustrating a cross-section of vehicle 200 mounting thereon head-up display system 10 according to the present disclosure. As illustrated in FIG. 1, head-up display system 10 is disposed inside dashboard 210 below windshield 220 of vehicle 200.

[0026] FIG. 2 is a schematic cross-sectional view of head-up display system 10 according to the first to fourth exemplary embodiments. As illustrated in FIG. 2, head-up display system 10 includes housing 100, projection optical system 120, and display device 101. Head-up display system 10 makes display image 110 displayed by display device 101 be reflected via windshield 220 to introduce the image to observer D inside vehicle 200 and provide virtual image I.

[0027] Herein, an optical path of display image 110 that forms a center of virtual image I shall be reference light beam L. Note that, a viewpoint of observer D shall exist at a center of viewpoint area 300.

[0028] Housing 100 includes opening 102. A transparent cover can be provided on opening 102. Providing the transparent cover having a lens shape makes it possible to adjust magnification of the virtual image. Head-up display system 10 according to the first exemplary embodiment includes housing 100. However, housing 100 is not a necessary component, and dashboard 210 of the vehicle may serve as the housing.

[0029] Projection optical system 120 includes first mirror 121 (an example of mirror M.sub.L1) and second mirror 122 (an example of mirror M.sub.L) in a stated order in a direction from display device 101 to windshield 220 (an example of the display member). That is, projection optical system 120 includes a reflection optical element composed of mirror M.sub.L1 and mirror M.sub.L. Display image 110 displayed by display device 101 is reflected via first mirror 121, reflected via second mirror 122, reflected via windshield 220, and reaches viewpoint area 300 of observer D. Then, observer D views display image 110 as virtual image I. Herein, viewpoint area 300 denotes an area where observer D can observe the entire of virtual image I without lacking.

[0030] Mirror M.sub.L may also have a movable mechanism for adjusting a display position of the image to be projected on the display member.

[0031] In display device 101, display image information is controlled by a controller such as a microprocessor not shown. The display image information includes, for example, a road course plan, a distance to a front vehicle, a vehicular battery remaining amount, and a present vehicle speed. The various items of display image information can be displayed on display device 101. As display device 101, a liquid crystal display device (LCD), an organic light emitting diode (electroluminescence), a plasma display, or the like is used.

[1-1-2. Configuration of Projection Optical System and Display Apparatus]

[0032] In head-up display system 10 according to the first to fourth exemplary embodiments, the position of display device 101 is disposed below first mirror 121. Furthermore, a display surface of display device 101 is oriented toward first mirror 121. In this context, display device 101 is desirably disposed such that a light beam emitted from display device 101 inclines with respect to normal line of the display surface. This makes it possible to prevent stray light caused by external light that is introduced in the housing and reflected on the display surface of display device 101.

[0033] Furthermore, first mirror 121 is disposed such that its reflection surface is eccentric in a direction in which an image displayed on display device 101 is reflected on second mirror 122.

[0034] A reflection area of second mirror 122 is larger than a reflection area of first mirror 121 to enlarge the image to display as virtual image I. Herein, the reflection area is an area of the mirror that reflects incident light, and a shape of the mirror becomes larger as the reflection area becomes larger.

[0035] Second mirror 122 is disposed in a horizontal direction of housing 100 and in a vehicle front side with respect to first mirror 121. Furthermore, second mirror 122 is disposed such that its reflection surface is eccentric in a direction in which reflection light from first mirror 121 is incident on windshield 220.

[0036] Furthermore, a light beam emitted toward a center of a viewpoint area 300 of the observer D has a first angle and a second angle larger than the first angle, the light beam being among light beams emitted from a center of the image displayed on the display device 101, the first angle being made with a line parallel to a longer side of a display surface of the display device 101, the second angle being made with a line parallel to a shorter side of the display surface.

[0037] In the first to third exemplary embodiments, first mirror 121 is a mirror having a free-form surface shape having a convex surface shape. Furthermore, second mirror 122 is a mirror having a free-form surface shape having a concave surface shape. By making first mirror 121 have the convex surface shape, asymmetric eccentric distortion generated on second mirror 122 can be successfully corrected. Furthermore, by making second mirror 122 have the concave surface shape, a virtual image magnified more than the image of display device 101 can be viewed by observer D.

[0038] Furthermore, a free-form surface shape is employed in first mirror 121 and second mirror 122. This is to correct distortion of the virtual image generated by reflection such that good virtual image I can be seen in entire viewpoint area 300. However, only any one of first mirror 121 and second mirror 122 may have a free-form surface and the other one may have a shape such as a flat surface or a toroidal shape.

[0039] In the fourth exemplary embodiment, first mirror 121 is a mirror having a free-form surface shape having a concave surface shape. Furthermore, second mirror 122 is a mirror having a free-form surface shape having a concave surface shape. By making the reflection surfaces of first mirror 121 and second mirror 122 have the concave surface shape, a virtual image magnified more than the image of display device 101 can be viewed by observer D. Furthermore, making the reflection surfaces of first mirror 121 and second mirror 122 have the concave surface makes it possible to disperse power held by one mirror, making it possible to reduce distortion aberration sensitivity during assembling.

[0040] First mirror 121 and second mirror 122 used in head-up display system 10 according to the first to fourth exemplary embodiments have a rotation asymmetric shape. However, the shape may be a surface shape of a so-called saddle type in which signs of curvatures are different in X direction and Y direction as shown in FIG. 3.

[1-2. Effects and Others]

[0041] Effects of head-up display system 10 configured above will be described below with reference to FIG. 4 to FIG. 7.

[0042] FIGS. 4 to 7 are schematic views when virtual image I is viewed from viewpoint area 300 in respective the first to fourth exemplary embodiments. In head-up display system 10 of the present disclosure, viewpoint area 300 has a rectangular shape of 130 mm in its horizontal direction40 mm in its vertical direction. A broken line is an ideal shape of virtual image I when viewed from viewpoint area 300. A solid line shows virtual image I projected by using head-up display system 10 in each exemplary embodiment.

[0043] In each of schematic views of FIGS. 4 to 7, part (1) is a view illustrating image distortion when virtual image I is viewed from the center position of viewpoint area 300 of observer D. Part (2) is a view illustrating image distortion when virtual image I is viewed from an upper left position of viewpoint area 300. Part (3) is a view illustrating image distortion when virtual image I is viewed from a lower left position of viewpoint area 300. Part (4) is a view illustrating image distortion when virtual image I is viewed from an upper right position of viewpoint area 300. Part (5) is a view illustrating image distortion when virtual image I is viewed from a lower right position of viewpoint area 300.

[0044] Using head-up display system 10 of the present disclosure successfully corrects image distortion in the entire area of viewpoint area 300. That is, in viewpoint area 300, observer D can view a good virtual image at any position.

[1-3. Desirable Conditions]

[0045] Hereinafter, desirable conditions for head-up display system 10 according to the first to fourth exemplary embodiments to satisfy will be described. Note that a plurality of preferable conditions are regulated with respect to head-up display system 10 according to each exemplary embodiment. Then, a configuration that satisfies all the plurality of conditions is most preferable. However, by satisfying individual condition, an optical system that provides an effect corresponding to the condition can be also obtained.

[0046] Head-up display system 10 according to the first to fourth exemplary embodiments includes display device 101 that displays an image, and projection optical system 120 that projects display image 110 displayed on display device 101. Then, projection optical system 120 has first mirror 121 and second mirror 122 in order of an optical path from display device 101 toward windshield 220.

[0047] Head-up display system 10 according to the first to fourth exemplary embodiments projects display image 110 displayed on display device 101 on windshield 220 to make virtual image I be viewed by observer D. This makes it possible to make observer D view the image displayed on display device 101 without interrupting forward visibility of observer D.

[0048] In head-up display system 10 of the present disclosure, first mirror 121 desirably has a free-form surface shape. This successfully corrects image distortion generated on windshield 220, making it possible to view a good image having less image distortion in entire viewpoint area 300 of observer D.

[0049] In head-up display system 10 of the present disclosure, second mirror 122 desirably has a free-form surface shape. This successfully corrects image distortion generated on windshield 220, making it possible to view a good image having less image distortion in entire viewpoint area 300 of observer D.

[0050] In head-up display system 10 of the present disclosure, the reflection surface of first mirror 121 is a concave surface or a convex surface. This makes it possible to suppress distortion of a virtual image generated by reflection as compared with a case where first mirror 121 has a flat surface.

[0051] In head-up display system 10 of the present disclosure, an outer shape of first mirror 121 is a trapezoid shape. This makes it possible to reduce an unnecessary area other than an area on which an image is reflected on first mirror 121, making it possible to downsize head-up display system 10. Note that the outer shape of first mirror 121 is not limited to the trapezoid shape, and can be appropriately changed depending on a shape of an effective area.

[0052] Head-up display system 10 of the present disclosure satisfies following condition (1) when a mirror that reflects a light beam toward windshield 220 is mirror M.sub.L, and a mirror that reflects the light beam toward mirror M.sub.L is M.sub.L1.

0.01<|M.sub.LD/M.sub.LW||M.sub.L1Z/M.sub.L1W|(1) [0053] where [0054] M.sub.LD: depth of mirror M.sub.L [0055] M.sub.LW lateral dimension of mirror M.sub.L [0056] M.sub.L1Z: maximum sag amount of mirror M.sub.L1 [0057] M.sub.L1W: lateral dimension of mirror M.sub.L1.

[0058] FIG. 8 is a diagram of housing 100 viewed from a vertical direction top side. As illustrated in FIG. 8, M.sub.LD denotes a maximum size in a vehicle front-back direction of mirror M.sub.L, M.sub.LW denotes a maximum size in a vehicle left-right direction of mirror M.sub.L, and M.sub.L1W denotes a maximum size in the vehicle left-right direction of mirror M.sub.L1.

[0059] FIG. 9 is a diagram illustrating a coordinate system and sizes according to condition (1). As illustrated in FIG. 9, a tangential plane of mirror M.sub.L1 including an intersection point between the reflection surface of mirror M.sub.L1 and reference light beam L is defined as tangential plane 170, and a maximum distance among distances from tangential plane 170 to the reflection surface of mirror M.sub.L1 shall be M.sub.L1Z.

[0060] Condition (1) defines a relationship between a size and a sag amount of mirror M.sub.L and mirror M.sub.L1. Not greater than a lower limit of condition (1) means that power of mirror M.sub.L1 is weak or inclination arrangement in the front-back direction of mirror M.sub.L is small with respect to a width of each of mirror M.sub.L1, mirror M.sub.L. When the power of mirror M.sub.L1 is weak, it becomes difficult to correct image distortion of virtual image I. Furthermore, when the inclination arrangement in the front-back direction of mirror M.sub.L is small, rotation of an image reflected on mirror M.sub.L becomes large, disadvantageously enlarging a size of mirror M.sub.L.

[0061] Furthermore, satisfying following condition (1a) makes it possible to make the above-mentioned effects further successful.

0.015<|M.sub.LD/M.sub.LW||M.sub.L1Z/M.sub.L1W|(1a)

[0062] Also, it is desirable that following condition (1b) be satisfied as well as the condition (1).

|M.sub.LD/M.sub.LW||M.sub.L1Z/M.sub.L1W|<0.04(1b)

[0063] Not lower than an upper limit of condition (1b) means that the power of mirror M.sub.L1 is strong or the inclination arrangement in the front-back direction of mirror M.sub.L is large with respect to the width of each of mirror M.sub.L1, mirror M.sub.L. When the power of mirror M.sub.L1 is strong, a zooming load of mirror M.sub.L1 becomes too large, disadvantageously enlarging mirror M.sub.L1. Furthermore, when the inclination arrangement in the front-back direction of mirror M.sub.L is large, the size of hosing 100 is disadvantageously enlarged.

[0064] Furthermore, satisfying following condition (1c) makes it possible to make the effects described above further successful.

|M.sub.LD/M.sub.LW||M.sub.L1Z/M.sub.L1W|<0.03(1c)

NUMERICAL EXAMPLES

[0065] Hereinafter, numerical examples obtained by specifically performing the head-up display system according to the first to fourth exemplary embodiments will be described. Note that in each numerical example, a unit of length in each table is all mm and a unit of angle is all . Furthermore, in each numerical example, a free-form surface is defined by the following equations.

[00001]$\begin{array}{cc}z=\frac{{\mathrm{cr}}^2}{\sqrt{1-\left(1+k\right).Math.c^2.Math.r^2}}+\underset{j=2}{.Math.}.Math..Math.c_j.Math.x^m.Math.y^n& \left[\mathrm{Equation}.Math..Math.1\right]\\ j=\frac{{\left(m+n\right)}^2+m+3.Math..Math.n}{2}+1& \left[\mathrm{Equation}.Math..Math.2\right]\end{array}$

[0066] In the equations, z is a sag amount at a position (x, y) from an axis defining a plane, r is a radius of curvature at an origin of the axis defining the plane, c is a curvature at the origin of the axis defining the plane, k is a conic constant, Cj is a coefficient in a monomial x.sup.my.sup.n.

[0067] FIG. 10 is a diagram illustrating a coordinate system of the numerical examples according to the first to fourth exemplary embodiments. In each numerical example, the coordinate origin that becomes a reference is a center of the display image on the display device, and defines X, Y, Z axes as illustrated in FIG. 10.

[0068] Further, in eccentricity data in each numerical example, ADE denotes an amount of rotation of a mirror about the X-axis from a Z-axis direction to a Y-axis direction, BDE denotes an amount of rotation of the mirror about the Y-axis from an X-axis direction to the Z-axis direction, and CDE denotes an amount of rotation of the mirror about the Z-axis from the X-axis direction to the Y-axis direction.

Numerical Example 1

[0069] Projection optical system 120 of numerical example 1 corresponds to the first exemplary embodiment. Configuration data of projection optical system 120 of numerical example 1 is shown in Table 1, and coefficients of the polynomial free-form surface of numerical example 1 are shown in Table 2.

TABLE-US-00001 TABLE 1 Radius of curvature Surface X-radius of Y-radius of Eccentricity data number Shape curvature curvature X Y Z ADE BDE CDE Display 1 0 0 0 0 0 0 surface First 2 Free- 74.5 5.083 14.834 40.755 8.474 9.699 7.666 mirror form surface Second 3 Free- 268.0 44.967 73.100 29.731 9.582 14.621 11.337 mirror form surface Windshield 4 Toroidal 2500 10000 13.504 112.063 164.894 83.432 5.696 4.059 Observer 5 31.354 263.811 757.165 143.688 2.305 12.165

TABLE-US-00002 TABLE 2 Surface number Polynomial coefficient 2 C1 0.000000E+00 C2 0.000000E+00 C3 0.000000E+00 C4 3.889322E03 C5 1.140602E03 C6 2.852333E03 C7 1.175025E05 C8 2.227307E05 C9 1.959217E05 C10 3.135374E05 C11 4.738907E07 C12 1.855805E07 C13 8.227017E07 C14 6.940548E07 C15 3.817544E07 C16 3.383532E09 C17 4.494973E09 C18 1.561764E08 C19 6.869173E08 C20 9.407151E08 C21 5.420771E08 3 C1 0.000000E+00 C2 0.000000E+00 C3 0.000000E+00 C4 3.668807E03 C5 9.397847E05 C6 3.289357E03 C7 6.805239E07 C8 2.506622E06 C9 6.289453E07 C10 2.251343E06 C11 7.722795E09 C12 1.929269E09 C13 1.668530E08 C14 6.642674E09 C15 9.160802E09 C16 2.406730E12 C17 2.410751E11 C18 2.073391E11 C19 1.825230E10 C20 1.857056E10 C21 1.027708E10

Numerical Example 2

[0070] Projection optical system 120 of numerical example 2 corresponds to the second exemplary embodiment. Configuration data of projection optical system 120 of numerical example 2 is shown in Table 3, and coefficients of the polynomial free-form surface of numerical example 2 are shown in Table 4.

TABLE-US-00003 TABLE 3 Radius of curvature Surface X-radius of Y-radius of Eccentricity data number Shape curvature curvature X Y Z ADE BDE CDE Display 1 0 0 0 0 0 0 surface First 2 Free- 97.1 5.083 14.834 40.755 2.301 7.801 7.199 mirror form surface Second 3 Free- 252.4 40.925 55.826 42.844 2.455 9.952 12.370 mirror form surface Windshield 4 Toroidal 2500 10000 41.251 105.524 176.669 84.405 4.708 1.813 Observer 5 118.274 255.017 773.713 144.892 6.903 8.405

TABLE-US-00004 TABLE 4 Surface number Polynomial coefficient 2 C1 0.000000E+00 C2 0.000000E+00 C3 0.000000E+00 C4 4.926473E03 C5 9.154287E05 C6 5.551427E03 C7 7.457614E06 C8 1.467424E05 C9 2.736122E06 C10 2.781637E05 C11 3.043821E07 C12 1.086610E08 C13 1.212193E07 C14 1.002882E07 C15 4.765067E07 C16 9.133313E10 C17 2.733132E09 C18 3.353294E09 C19 8.241253E09 C20 1.121593E08 C21 1.026651E08 3 C1 0.000000E+00 C2 0.000000E+00 C3 0.000000E+00 C4 3.544541E03 C5 1.225662E04 C6 3.164418E03 C7 1.043107E06 C8 2.340693E06 C9 7.417448E07 C10 2.540587E06 C11 4.628000E09 C12 2.606382E09 C13 1.292750E08 C14 1.254061E10 C15 1.851119E08 C16 1.819180E11 C17 2.522055E12 C18 2.254304E11 C19 3.720821E10 C20 3.847241E10 C21 1.331588E10

Numerical Example 3

[0071] Projection optical system 120 of numerical example 3 corresponds to the third exemplary embodiment. Configuration data of projection optical system 120 of numerical example 3 is shown in Table 5, and coefficients of the polynomial free-form surface of numerical example 3 are shown in Table 6.

TABLE-US-00005 TABLE 5 Radius of curvature Surface X-radius of Y-radius of Eccentricity data number Shape curvature curvature X Y Z ADE BDE CDE Display 1 0 0 0 0 0 0 surface First 2 Free- 115.5 0.019 27.571 47.754 3.190 1.570 6.588 mirror form surface Second 3 Free- 174.0 5.476 97.681 47.274 8.420 10.060 4.534 mirror form surface Windshield 4 Toroidal 2300 5000 118.115 137.045 352.969 80.116 5.067 17.331 Observer 5 348.158 242.455 820.812 142.809 20.835 2.493

TABLE-US-00006 TABLE 6 Surface number Polynomial coefficient 2 C1 0.000000E+00 C2 0.000000E+00 C3 0.000000E+00 C4 4.660058E03 C5 4.822156E04 C6 5.780335E03 C7 5.786242E06 C8 7.697644E06 C9 1.378249E05 C10 8.704499E06 C11 2.416340E07 C12 5.498882E08 C13 2.628414E07 C14 9.596673E08 C15 2.714240E07 C16 5.447252E11 C17 9.577716E10 C18 1.377973E09 C19 3.938415E10 C20 5.536787E10 C21 1.102301E09 3 C1 0.000000E+00 C2 0.000000E+00 C3 0.000000E+00 C4 4.040368E03 C5 1.238345E04 C6 3.412235E03 C7 9.536949E07 C8 4.053113E07 C9 1.969863E06 C10 1.786994E07 C11 2.312050E08 C12 9.091220E10 C13 4.427086E08 C14 8.376937E09 C15 7.592592E10 C16 1.840384E11 C17 2.206245E11 C18 1.303955E10 C19 7.721818E11 C20 1.560674E11 C21 2.128466E10

Numerical Example 4

[0072] Projection optical system 120 of numerical example 4 corresponds to the fourth exemplary embodiment. Configuration data of projection optical system 120 of numerical example 4 is shown in Table 7, and coefficients of the polynomial free-form surface of numerical example 4 are shown in Table 8.

TABLE-US-00007 TABLE 7 Radius of curvature Surface X-radius of Y-radius of Eccentricity data number Shape curvature curvature X Y Z ADE BDE CDE Display 1 0 0 0 0 0 0 surface First 2 Free- 160.6 9.303 9.974 37.225 12.971 0.632 3.257 mirror form surface Second 3 Free- 318.9 43.760 96.384 61.857 19.144 5.679 8.203 mirror form surface Windshield 4 Toroidal 2900 7000 1.175 150.019 169.581 67.776 6.563 1.004 Observer 5 103.128 476.745 735.591 127.388 7.828 11.156

TABLE-US-00008 TABLE 8 Surface number Polynomial coefficient 2 C1 0.000000E+00 C2 0.000000E+00 C3 0.000000E+00 C4 1.754483E03 C5 2.809306E04 C6 3.766153E03 C7 6.271249E06 C8 1.277670E05 C9 1.034713E07 C10 4.257452E06 C11 1.356414E07 C12 5.949794E08 C13 2.552599E08 C14 1.510860E08 C15 1.308172E08 C16 1.479740E10 C17 5.933131E10 C18 9.655838E11 C19 9.169734E10 C20 2.023240E10 C21 1.152090E10 3 C1 0.000000E+00 C2 0.000000E+00 C3 0.000000E+00 C4 2.859706E03 C5 1.679720E04 C6 2.509203E03 C7 5.110568E07 C8 1.149673E06 C9 1.770886E07 C10 1.087119E06 C11 4.014016E09 C12 5.998517E10 C13 9.308105E09 C14 1.222787E09 C15 3.812154E09 C16 8.759793E12 C17 5.780092E12 C18 1.604554E11 C19 2.995483E12 C20 1.112808E12 C21 7.255928E12

[0073] Table 9 below illustrates a display image size, a virtual image size, a distance from a pupil of observer D to virtual image I, and the value of condition (1) in each numerical example.

TABLE-US-00009 TABLE 9 Numerical Numerical Numerical Numerical example 1 example 2 example 3 example 4 Display size X 30 28.9 37.9 63.9 Y 12.3 11.6 17.8 23.8 Virtual image size X 174.6 209.6 216.6 350 Y 52.4 69.8 90.8 139.7 Distance from observer 2000 2000 2200 2800 to virtual image Condition (1) 0.016 0.010 0.015 0.012

INDUSTRIAL APPLICABILITY

[0074] A head-up display system according to the present disclosure is preferable for a head-up display system requiring high image quality such as a head-up display device for in-vehicle use or the like.

REFERENCE MARKS IN THE DRAWINGS

[0075] 10: head-up display system [0076] 100: housing [0077] 101: display device [0078] 102: opening [0079] 110: display image [0080] 120: projection optical system [0081] 121: first mirror (mirror M.sub.L1) [0082] 122: second mirror (mirror M.sub.L) [0083] 200: vehicle [0084] 210: dashboard [0085] 220: windshield (display member) [0086] 300: viewpoint area [0087] D: observer [0088] I: virtual image [0089] L: reference light beam