Floating image display device

Abstract

A floating image display device according to the present disclosure comprises: a display unit having a display surface; a first concave mirror that reflects image light emitted from the display surface in a direction different from a direction toward the display unit; and a second concave mirror that reflects the image light reflected by the first concave mirror in a direction different from a direction toward the first concave mirror and forms an image as a floating image of a real image. A first inclination angle of the first concave mirror with respect to a first virtual plane encompassing the display surface has a size equal to or greater than a second inclination angle of the second concave mirror with respect to a second virtual plane encompassing a virtual image formation surface for the floating image.

Description

Floating Image Display

[0001] The present disclosure relates to a floating image display device.

[0002] 2. Description of the Related Art A floating image display device is known from the past, for example, as described in Patent Document 1.

[0003] Japanese Patent Application Laid-Open No. 2020-177221

[0004] The floating image display device of the present disclosure comprises: a display unit having a display surface; a first concave mirror that reflects image light emitted from the display surface in a direction different from the direction toward the display unit; and a second concave mirror that reflects the image light reflected by the first concave mirror in a direction different from the direction toward the first concave mirror and forms a floating image of a real image, wherein a first tilt angle of the first concave mirror with respect to a first imaginary plane including the display surface is equal to or greater than a second tilt angle of the second concave mirror with respect to a second imaginary plane including a virtual imaging plane of the floating image.

[0005] Objects, features, and advantages of the present disclosure will become clearer from the following detailed description and drawings.

[0023] Fig. 1 is a side view showing the configuration of a main part of a floating image display device according to an embodiment of the present disclosure. Fig. 2 is a cross-sectional view of a first concave mirror for explaining the curvature of a first reflecting surface of the first concave mirror. Fig. 3 is a front view of a first concave mirror for explaining the geometric center of the first reflecting surface of the first concave mirror. Fig. 4 is a front view of a first concave mirror for explaining the geometric center of the first reflecting surface of the first concave mirror. Fig. 5 is a front view of a floating image for explaining distortion of the floating image viewed by a user. Fig. 6 is a front view of a floating image showing an example of a floating image viewed by a user of the floating image display device of Fig. 1. Fig. 7 is a front view of a floating image showing an example of a floating image viewed by a user of the floating image display device of Fig. 1. FIG. 2 is a front view of a floating image, showing an example of a floating image visually recognized by a user of the floating image display device of FIG. 1;

[0006] Patent Document 1 describes a floating image display device that uses a reflection optical system to form an image light emitted from a display device as a floating image in the air.

[0007] In conventional floating image display devices, the floating image visually recognized by the user may be distorted or the brightness of the floating image may be reduced. Therefore, there is a demand for a floating image display device with improved display quality of the floating image.

[0008] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Each of the drawings referred to below shows the main components of a floating image display device according to an embodiment. The display device according to the embodiment may include well-known components such as an optical element holding member and a camera, which are not shown. Each of the drawings referred to below is schematic, and the dimensional ratios and the like in the drawings do not necessarily correspond to the actual ones. In addition, in some of the drawings, for convenience, a Cartesian coordinate system XYZ is defined, and the positive and negative sides of the Y-axis direction are sometimes referred to as up and down, respectively. The X-axis direction, the Y-axis direction, and the Z-axis direction are also referred to as the first direction, the second direction, and the third direction, respectively.

[0009] FIG. 1 is a side view showing the configuration of a main part of a floating image display device according to an embodiment of the present disclosure. FIG. 2 is a cross-sectional view of a first concave mirror illustrating the curvature of the reflective surface of the first concave mirror. FIGS. 3A, 3B, and 3C are front views of the first concave mirror illustrating the geometric center of the reflective surface of the first concave mirror. FIG. 4 is a front view of a floating image illustrating the distortion of the floating image visually perceived by a user. FIGS. 5A, 5B, 5C, and 5D are front views of a floating image showing an example of a floating image visually perceived by a user of the floating image display device of FIG. 1. In FIGS. 4, 5A, 5B, 5C, and 5D, the direction from left to right on the virtual imaging plane of the floating image is the positive direction in the X-axis direction, and the direction from bottom to top is the positive direction in the Y-axis direction.

[0010] As shown in FIG. 1, the floating image display device 1 of this embodiment includes a display unit 2, a first concave mirror 3, and a second concave mirror 5.

[0011] The display unit 2 has a display surface 2a, and displays on the display surface 2a an image that propagates through space as image light L. In other words, the display unit 2 emits the image light L from the display surface 2a.

[0012] The display unit 2 may be a transmissive display device. The transmissive display device may be, for example, a liquid crystal display device including a backlight and a liquid crystal panel. The backlight may be a direct backlight having multiple light sources arranged two-dimensionally on the rear side of the liquid crystal panel. The backlight may be an edge-lit backlight having multiple light sources arranged on the periphery of the liquid crystal panel. The edge-lit backlight may have a lens array, a light guide plate, a diffusion plate, etc. for uniformly illuminating the liquid crystal panel. The light source of the backlight may be, for example, a light-emitting diode (LED) element, a cold cathode fluorescent lamp, a halogen lamp, a xenon lamp, etc.

[0013] The liquid crystal panel may be a known liquid crystal panel, such as an IPS (In-Plane Switching) type, an FFS (Fringe Field Switching) type, a VA (Vertical Alignment) type, or an ECB (Electrically Controlled Birefringence) type liquid crystal panel.

[0014] The display unit 2 is not limited to a transmissive display device, but may be a self-luminous display device including light-emitting elements such as LED elements, organic light-emitting diode (OLED) elements, semiconductor laser (LD) elements, etc. The self-luminous display device can improve the brightness of the floating image R compared to a transmissive liquid crystal display device equipped with a backlight.

[0015] The first concave mirror 3 and the second concave mirror 5 are a reflective optical system that focuses the image light L emitted from the display unit 2 within the field of view of the user 7. Hereinafter, the first concave mirror 3 and the second concave mirror 5 may be collectively referred to as a reflective optical system 8.

[0016] The first concave mirror 3 is located on the optical path of the image light L emitted from the display unit 2. The first concave mirror 3 is configured to reflect the image light L emitted from the display unit 2 in a direction different from the direction toward the display unit 2.

[0017] The second concave mirror 5 is located on the optical path of the image light L reflected by the first concave mirror 3. The second concave mirror 5 is configured to reflect the image light L reflected by the first concave mirror 3 in a direction different from the direction toward the first concave mirror 3, and form the image as a real floating image R. The second concave mirror 5 is configured to form the floating image R on a virtual image plane 9 in the air.

[0018] The relative position of the first concave mirror 3 with respect to the display unit 2 (e.g., distance from the display unit 2, tilt angle with respect to the display unit 2, etc.) is adjusted so that the first concave mirror 3 reflects the image light L emitted from the display unit 2 in a direction different from the direction toward the display unit 2. The floating image display device 1 may include an adjustment member for adjusting the relative position of the first concave mirror 3 with respect to the display unit 2. The adjustment member may include, for example, a support member such as a rod provided on the back side of the first concave mirror 3, an axis member provided on the support member for rotating the support member and the first concave mirror 3, and a slide mechanism for translating the support member and the first concave mirror 3 along a predetermined direction. The relative position of the first concave mirror 3 with respect to the display unit 2 may be adjusted manually or electrically using a stepping motor or the like.

[0019] The relative position of the second concave mirror 5 with respect to the first concave mirror 3 (for example, the distance from the first concave mirror 3, the tilt angle with respect to the first concave mirror 3, etc.) is adjusted so that the second concave mirror 5 reflects the image light L reflected by the first concave mirror 3 in a direction different from the direction toward the first concave mirror 3. The floating image display device 1 may include an adjustment member for adjusting the relative position of the second concave mirror 5 with respect to the first concave mirror 3. The adjustment member for adjusting the relative position of the second concave mirror 5 may have the same configuration as the adjustment member for adjusting the relative position of the first concave mirror 3.

[0020] The first concave mirror 3 has a first reflecting surface 3a. The first concave mirror 3 may be a free-form concave mirror in which the first reflecting surface 3a is defined by a free-form surface. The second concave mirror 5 has a second reflecting surface 5a. The second concave mirror 5 may be a free-form concave mirror in which the second reflecting surface 5a is defined by a free-form surface. When the first concave mirror 3 and the second concave mirror 5 are free-form concave mirrors, it becomes easy to give the first reflecting surface 3a and the second reflecting surface 5a shapes that reduce distortion of the floating image R, and as a result, it becomes possible to reduce distortion of the floating image R.

[0021] The second concave mirror 5 may be a free-form concave mirror, and the apex of the curvature of the second reflecting surface 5 a of the second concave mirror 5 may be located at the same position as the geometric center of the second reflecting surface 5 a or near the center. In this case, the second reflecting surface 5 a of the second concave mirror 5, which forms the floating image R of a real image, has geometric symmetry, thereby reducing distortion of the floating image R. When the apex of the curvature of the second reflecting surface 5 a of the second concave mirror 5 is located near the geometric center of the second reflecting surface 5 a, the deviation between the apex and the center may be approximately 0.1% to 20%, approximately 0.1% to 10%, or approximately 0.1% to 5% of the diameter (which may be the maximum diameter) of the second reflecting surface 5 a, but is not limited to these ranges.

[0022] The size of the second concave mirror 5 may be larger than the size of the first concave mirror 3. In this case, the size of the floating image R defined by the size of the second concave mirror 5 can be increased. The size of the second concave mirror 5 may be more than 1 time but not more than about 10 times the size of the first concave mirror 3, or more than 1 time but not more than about 5 times, but is not limited to these ranges. The size of the first concave mirror 3 may be the length of the maximum diameter of the first reflecting surface 3a, or may be the average value of the diameters of the first reflecting surface 3a. The same applies to the second concave mirror 5.

[0023] The degree of curvature of the first reflecting surface 3 a of the first concave mirror 3 may be greater than the degree of curvature of the second reflecting surface 5 a of the second concave mirror 5. In this case, the distance between the display unit 2 and the first concave mirror 3 can be shortened. Also, the imaging distance of the floating image R formed by the second concave mirror 5 (the distance between the second concave mirror 5 and the floating image R) can be lengthened. The degree of curvature of the first reflecting surface 3 a of the first concave mirror 3 may be from 1 to about 5 times, or from 1 to about 3 times, the degree of curvature of the second reflecting surface 5 a of the second concave mirror 5, but is not limited to these ranges.

[0024] The free-form surfaces defining the first reflecting surface 3a and the second reflecting surface 5a may be XY polynomial surfaces (also called SPS XYP surfaces) defined by the following formulas (1) and (2). The XY polynomial surfaces are expanded into polynomials of up to the tenth degree that are added to the reference conic surface. Therefore, in formulas (1) and (2), the sum of m and n is 10 or less. In formula (1), z is the sag of the surface parallel to the z axis (optical axis), c is the vertex curvature, and r is the radial distance (i.e., r 2 = x 2 +y 2 ), k is the conic constant, and C ｊ is a monomial x ｍ y ｎ is the coefficient of

[0025] A free-form concave mirror can be produced by, for example, cutting the surface of a metal plate such as aluminum (Al) into a free-form concave surface using a cutting method under computer numerical control. Alternatively, the free-form concave mirror may have a structure in which a reflective layer made of aluminum or the like is formed on the surface of a base material made of resin molded by injection molding or the like. The reflective layer may be formed by vapor deposition, plating, CVD (Chemical Vapor Deposition), or the like.

[0026] The first concave mirror 3 and the second concave mirror 5 are not limited to free-form concave mirrors, and at least one of the first concave mirror 3 and the second concave mirror 5 may be a spherical concave mirror or an aspherical concave mirror.

[0027] The first reflecting surface 3a may have a first curvature S1 and a second curvature S2. The first curvature S1 and the second curvature S2 are defined as follows. As shown in FIG. 2 , a plane tangent to the first reflecting surface 3a at a vertex O (e.g., the origin of the free-form surface) of the first reflecting surface 3a is defined as a tangent plane T1. Furthermore, in a cross section of the first concave mirror 3 passing through the vertex O and cut by a cutting plane parallel to the propagation direction of the image light L, points located at both ends of the first reflecting surface 3a are defined as E1 and E2, and the intersections of perpendicular lines drawn from points E1 and E2 perpendicularly to the tangent plane T1 with the tangent plane T1 are defined as H1 and H2, respectively. Furthermore, the distance between the vertex O and point H1 is defined as L1, the distance between the vertex O and point H1 is defined as L2, the distance between points E1 and H1 is defined as D1, and the distance between points E2 and H2 is defined as D2. Note that distance L1 is equal to or greater than distance L2. When the distances L1, L2, D1, and D2 are set as described above, the first curvature S1 is defined by D1 / L1, and the second curvature S2 is defined by D2 / L2. If the first curvature S1 varies depending on how the cross section is taken, the maximum value of D1 / L1 obtained when the position of the cross section is changed may be defined as the first curvature S1. If the second curvature S2 varies depending on how the cross section is taken, the maximum value of D2 / L2 obtained when the position of the cross section is changed may be defined as the second curvature S2.

[0028] The first curvature S1 may be smaller than the second curvature S2. In this case, since the apex O of the curvature of the first reflecting surface 3a is located closer to the display unit 2 than the geometric center C of the first reflecting surface 3a, the length L2 of the portion with a relatively large curvature (the portion with the second curvature S2) is shorter than the length L1 of the portion with a relatively small curvature (the portion with the first curvature S1). As a result, the increase in distortion of the floating image R due to the increase in the overall curvature of the first reflecting surface 3a can be suppressed. Furthermore, since most of the image light L is reflected by the portion with the first curvature S1, which has a relatively small curvature, the increase in distortion of the floating image R can be further suppressed. The first curvature S1 may be, for example, approximately 0.165, and the second curvature S2 may be, for example, approximately 0.244, but are not limited to these values.

[0029] The distribution of reflection points of image light L on first reflecting surface 3a, i.e., whether the image light L is reflected more at the portion with first curvature S1 or the portion with second curvature S2, may be found as follows: The component of image light L emitted from each light-emitting point on display surface 2a in a direction perpendicular to display surface 2a is taken as the chief ray, and from the distribution (number) of reflection points at which the chief ray reaches first reflecting surface 3a and is reflected, it may be found whether the image light L is reflected more at the portion with first curvature S1 or the portion with second curvature S2.

[0030] The curvature of the first reflecting surface 3a (i.e., the curvature of the entire first reflecting surface 3a) may be defined by a first curvature S1 and a second curvature S2. The curvature of the first concave mirror 3 may be defined by the average value of the first curvature S1 and the second curvature S2. The curvature of the first concave mirror 3 may be defined by the larger of the first curvature S1 and the second curvature S2.

[0031] The second reflecting surface 5a may have a third curvature S3 and a fourth curvature S4. The third curvature S3 is defined similarly to the first curvature S1. The fourth curvature S4 is defined similarly to the second curvature S2.

[0032] The first concave mirror 3 is inclined at a first tilt angle θ1 with respect to a first imaginary plane Pi1 including the display surface 2a. The first tilt angle θ1 is the angle between the display surface 2a and a tangent plane T1 of the first concave mirror 3. The second concave mirror 5 is inclined at a second tilt angle θ2 with respect to a second imaginary plane Pi2 including a virtual imaging plane 9 of the floating image R. The second tilt angle θ2 is the angle between the virtual imaging plane 9 of the floating image R and a tangent plane T2 of the second concave mirror 5. The tangent plane T2 is defined in the same manner as the tangent plane T1 (see FIG. 2). That is, the tangent plane T2 is a plane tangent to the second reflecting surface 5a at the vertex O' (e.g., the origin of the free-form surface) of the second concave mirror 5. Hereinafter, viewing the second reflecting surface 5a in the normal direction of the tangent plane T2 may be referred to as a front view.

[0033] The first virtual plane Pi1, the second virtual plane Pi2, the tangent plane T1, and the tangent plane T2 are surfaces that exist virtually in space, but can be clearly illustrated in design drawings displayed on the display device of a personal computer (PC) terminal using computer-aided design (CAD) program software, etc.

[0034] The floating image display device 1 is configured such that the first tilt angle θ1 is equal to or greater than the second tilt angle θ2. With this configuration, the floating image display device 1 has a relatively small second tilt angle θ2, and the virtual image plane 9 and the tangential plane T2 are nearly parallel to each other, so that the optical path difference between the light rays traveling from the second reflecting surface 5a to the virtual image plane 9 can be reduced. As a result, the image aberration of the reflective optical system 8 can be reduced, and the distortion of the floating image R can be reduced.

[0035] Furthermore, because the floating image display device 1 has a relatively large first tilt angle θ1, even when the second tilt angle θ2 is small, it is possible to prevent a portion of the image light L reflected by the first concave mirror 3 from being undesirably reflected by the display unit 2. That is, it is possible to prevent the display unit 2 from overlapping with the optical path of the image light L. As a result, it is expected that the following problems can be prevented: a portion of the image light L is reflected by the display unit 2 and becomes stray light, resulting in the generation of ghost light (ghost image); a portion of the image light L is blocked by the display unit 2, resulting in a decrease in the brightness of the floating image R; and a portion of the image light L is blocked by the display unit 2, resulting in the loss of a portion of the floating image R. This improves the display quality of the floating image R. Furthermore, because it is expected that the display unit 2 is prevented from overlapping with the optical path of the image light L, it is possible to increase the size of the display unit 2 and the size of the first concave mirror 3. As a result, it is possible to increase the size of the floating image R and reduce distortion of the floating image R. Furthermore, since it is possible to prevent the display unit 2 from overlapping with the optical path of the image light L, it is also possible to place the display unit 2 close to the first concave mirror 3 and the second concave mirror 5. In this case, it is possible to make the floating image display device 1 compact.

[0036] The first reflecting surface 3a of the first concave mirror 3 has a geometric center (also referred to as the geometric center) C (shown in FIGS. 1 and 2). The geometric center C of the first reflecting surface 3a may be the center (centroid) of the first reflecting surface 3a when viewed in the normal direction of the tangent plane T1. The geometric center C of the first reflecting surface 3a does not have to coincide with the vertex O of the first reflecting surface 3a. Hereinafter, viewing the first reflecting surface 3a in the normal direction of the tangent plane T1 may be referred to as a front view.

[0037] 3A, 3B, and 3C are front views of the first reflecting surface 3a of the first concave mirror 3, illustrating the geometric center C of the first reflecting surface 3a. These views show the shape of the first reflecting surface 3a in front view. As shown in FIG. 3A, if the shape of the first reflecting surface 3a in front view is a circle or an ellipse, the geometric center C may be the center of the circle or the ellipse. If the shape of the first reflecting surface 3a in front view is a circle, the geometric center C is the center point of the diameter. If the shape of the first reflecting surface 3a in front view is an ellipse, the geometric center C is the intersection of the major axis (maximum diameter) and the minor axis (minimum diameter). Furthermore, as shown in FIG. 3B, if the shape of the first reflecting surface 3a in front view is a square or a rectangle, the geometric center C may be the intersection of two diagonals of the square or rectangle. Furthermore, as shown in Figure 3C, when the shape of the first reflecting surface 3a in front view is hexagonal, the geometric center C may be any point within the region CR surrounded by the four diagonal lines of the hexagon, or may be the center point of the approximately diamond-shaped region CR (the intersection of the major axis (maximum diameter) and the minor axis (minimum diameter)).

[0038] The apex O of the curvature of the first reflecting surface 3a may not coincide with the geometric center C of the first reflecting surface 3a, but may be located offset within the first reflecting surface 3a. As shown in FIGS. 1 and 2 , the apex O of the curvature of the first reflecting surface 3a may be located closer to the display unit 2 from the geometric center C of the first reflecting surface 3a. By positioning the apex O of the curvature closer to the display unit 2, it becomes easier to correct the image aberration of the reflective optical system 8, and as a result, it is possible to reduce distortion of the floating image R. In other words, since most of the image light L is reflected by a portion having the first curvature S1 with a relatively small degree of curvature (close to flat), it is possible to reduce the optical path difference between the light rays reflected at each portion of the first reflecting surface 3a.

[0039] As shown in FIG. 1 , the first reflecting surface 3 a has a portion (also referred to as a first portion) 31 on the opposite side of the vertex O from the display unit 2 side, and a portion (also referred to as a second portion) 32 on the display unit 2 side from the vertex O. The first portion 31 is located on the negative side of the vertex O in the third direction, and the second portion 32 is located on the positive side of the vertex O in the third direction. In the first reflecting surface 3 a, the curvature S1 of the first portion 31 may be equal to or less than the curvature S2 of the second portion 32. In this case, it is possible to prevent light rays contained in the image light L that move away from the optical axis center of the image light L and are likely to cause distortion of the floating image R from entering a portion with a large degree of curvature (i.e., a portion where aberration is difficult to correct), and as a result, distortion of the floating image R can be reduced. Furthermore, in the floating image display device 1, since the second portion 32, which has a relatively large curvature S2, is located close to the display unit 2, it is easy to correct the aberration caused by the second portion 32, and therefore the distortion of the floating image R caused by the second portion 32 can be reduced.

[0040] 1 , the second reflecting surface 5a has a portion 51 (also referred to as a third portion) on the opposite side of the vertex O′ from the floating image R side, and a portion 52 (also referred to as a fourth portion) on the floating image R side of the vertex O′. The third portion 51 is located on the negative side of the vertex O′ in the second direction, and the fourth portion 52 is located on the positive side of the vertex O′ in the second direction. On the second reflecting surface 5a, the degree of curvature of the third portion 51 may be equal to or greater than the degree of curvature of the fourth portion 52, or the degree of curvature of the third portion 51 may be equal to or less than the degree of curvature of the fourth portion 52.

[0041] The display unit 2 may be disposed so that the optical axis at the center of the display surface 2a passes through the first portion 31 of the first reflecting surface 3a. In this case, most of the rays of the image light L emitted from the display unit 2 are incident on the first portion 31, which has a relatively small curvature S1 and makes it easy to correct aberration. As a result, distortion of the floating image R caused by the first portion 31 can be effectively reduced.

[0042] The first tilt angle θ1 of the first concave mirror 3 may be approximately 40° to 50°. If the first tilt angle θ1 is less than 40°, a portion of the image light L emitted from the display surface 2a and reflected by the first concave mirror 3 tends to return to the display surface 2a without heading toward the second concave mirror 5. Furthermore, if the first tilt angle θ1 exceeds 50°, distortion of the image light L reflected by the first concave mirror 3 tends to increase. The second tilt angle θ2 of the second concave mirror 5 may be approximately 20° to 45°. If the second tilt angle θ2 is less than 20°, the virtual image plane 9 of the floating image R tends to be tilted with respect to the line of sight of the user 7. Furthermore, if the second tilt angle θ2 exceeds 45°, distortion of the image light L reflected by the second concave mirror 5 tends to increase. Note that the first tilt angle θ1 and the second tilt angle θ2 may change depending on factors such as the shape or size of the display surface 2a and the angle of view of the image light L (the spread of the image light L), and are therefore not necessarily limited to the above ranges.

[0043]

[0044] Table 1 shows the values ​​of the first tilt angle θ1, the second tilt angle θ2, the first curvature S1, the second curvature S2, the third curvature S3, and the fourth curvature S4 for several examples (device Nos. 1 to 4) of the floating image display device 1. For example, for device No. 1, a curvature S1 of 0.165 (-) means that the first portion 31 located on the negative side of the vertex O in the third direction (the Z-axis direction in FIG. 1) has a curvature S1 of 0.165. Furthermore, a curvature S2 of 0.244 (+) means that the second portion 32 located on the positive side of the vertex O in the third direction has a curvature S2 of 0.244. Furthermore, a curvature S3 of 0.188 (-) means that the third region 51 located on the negative side of the vertex O' in the second direction (the Y-axis direction in FIG. 1) has a curvature S3 of 0.188, and a curvature S4 of 0.192 (+) means that the fourth region 52 located on the positive side of the vertex O' in the second direction has a curvature S2 of 0.192. The same applies to the first curvature S1, second curvature S2, third curvature S3, and fourth curvature S4 of Devices No. 2 to 4.

[0045] Next, the distortion of the floating image R visually recognized by the user 7 will be described with reference to Figs. 4, 5A, 5B, 5C, and 5D. First, the definition of the distortion of the floating image R will be described with reference to Fig. 4. Fig. 4 is a front view of the floating image R to explain the distortion of the floating image R. Furthermore, in Fig. 4, in order to facilitate visual understanding of the distortion of the floating image R, the floating image R is depicted as a floating image with a grid pattern, and coordinate axes indicating the direction and amount of distortion are depicted. In Fig. 4, the floating image R visually recognized by the user 7 is indicated by a solid line, and an ideal floating image IR without distortion is indicated by a dashed line.

[0046] 4, distortion of the floating image R is likely to occur in the outer periphery of the floating image R, and distortion is particularly likely to be large at the four corners (lower right corner LR, upper right corner UR, lower left corner LL, and upper left corner UL) of the floating image R. Table 2 shows distortion from the ideal floating image IR at the corners LR, UR, LL, and UL for the floating image R in FIG.

[0047] In Table 2, the distortion of the floating image R is defined as a positive value in the X-axis direction and a negative value in the Y-axis direction when the floating image R is distorted outward from the ideal floating image IR. For example, at the lower right corner LR, the outward direction in the X-axis direction (rightward: expanding direction) is defined as the + (plus) direction, the inward direction in the X-axis direction (leftward: shrinking direction) is defined as the - (minus) direction, the outward direction in the Y-axis direction (downward: expanding direction) is defined as the + (plus) direction, and the inward direction in the Y-axis direction (upward: shrinking direction) is defined as the - (minus) direction. The same applies to the upper right corner UR, the lower left corner LL, and the upper left corner UL. The same applies to the following tables showing the distortion of the floating image R.

[0048] The distortion at the corners LR, UR, LL, and UL is calculated as follows. The distortion in the X-axis direction at the corners LR, UR, LL, and UL is defined as the offset length in the X-axis direction relative to the length LX of the top edge (the bottom edge is the same length as the top edge) of an ideal rectangular floating image IR. Because the length of the bottom edge of the floating image IR is the same as the length LX of the top edge, the length LX of the top edge is used as the reference. For example, the distortion in the X-axis direction at the corner UR is defined as the offset length ΔXUR in the X-axis direction from the upper right corner CUR of the floating image IR relative to the length LX of the top edge. In other words, the distortion in the X-axis direction at the corner UR is defined as (ΔXUR / LX) × 100 (%). Because the corner UR is distorted toward the outside of the floating image IR in the X-axis direction, a positive value is obtained. The distortion in the X-axis direction at the corners LR, LL, and UL is defined similarly. When the floating image IR has a shape other than a rectangle, the reference length in the X-axis direction may be an average length or a maximum length.

[0049] The distortion of the corners LR, UR, LL, and UL in the Y-axis direction is defined as the deviation length in the Y-axis direction relative to the length LY of the right side (the left side is the same length as the right side) of an ideal rectangular floating image IR. Because the length of the left side of the floating image IR is the same as the length LY of the right side, the length LY of the right side is used as the reference. For example, the distortion of the corner UR in the Y-axis direction is defined as the deviation length ΔYUR in the Y-axis direction from the upper right corner CUR of the floating image IR relative to the length LY of the right side. That is, the distortion of the corner UR in the Y-axis direction is defined as (ΔYUR / LY) × 100 (%). Because the corner UR is distorted inward of the floating image IR in the Y-axis direction, it has a negative value. The distortion of the corners LR, LL, and UL in the Y-axis direction is defined similarly. If the floating image IR has a shape other than rectangular, the reference length in the Y-axis direction may be the average length or the maximum length.

[0050]

[0051] Table 2 shows the distortion of the corners of the floating image R in Fig. 4. As shown in Table 2, in the floating image R in Fig. 4, the magnitude of the Y component of the distortion (distortion in the Y-axis direction) at the corners UL and UR exceeds 10%.

[0052] 5A, 5B, 5C, and 5D, the distortion of the floating image R visually recognized by the user 7 of the floating image display device 1 will be described.

[0053] Fig. 5A shows the floating image R viewed by the user 7 of device No. 1, and Table 3 shows the distortion at the corners of the floating image R in Fig. 5A. As shown in Table 3, the user 7 of device No. 1 can view the floating image R in which the magnitude of distortion at all corners is reduced to 5% or less.

[0054]

[0055] Fig. 5B shows the floating image R viewed by user 7 of device No. 2, and Table 4 shows the distortion at the corners of the floating image R in Fig. 5B. As shown in Table 4, user 7 of device No. 2 can view the floating image R in which the magnitude of distortion at all corners is reduced to 5% or less.

[0056]

[0057] Fig. 5C shows the floating image R viewed by user 7 of device No. 3, and Table 5 shows the distortion at the corners of the floating image R in Fig. 5C. As shown in Table 5, user 7 of device No. 3 can view the floating image R in which the magnitude of distortion at all corners is reduced to 5% or less.

[0058]

[0059] Fig. 5D shows the floating image R viewed by user 7 of device No. 4, and Table 6 shows the distortion at the corners of the floating image R in Fig. 5D. As shown in Table 6, user 7 of device No. 4 can view the floating image R in which the magnitude of distortion at all corners is reduced to 5% or less.

[0060]

[0061] As described above, the floating image display device 1 can reduce distortion of the floating image R visually recognized by the user 7. Therefore, according to the floating image display device 1, it is possible to provide a floating image display device with improved display quality of the floating image R.

[0062] As shown in FIG. 1 , the floating image display device 1 includes a control device 6. The control device 6 is connected to each component of the floating image display device 1 and controls each component. The control device 6 may have functions such as turning the display unit 2 on and off, transmitting an image signal to the display unit 2, and adjusting the brightness, chromaticity, frame frequency, etc. of the image. Furthermore, if the display unit 2 includes a heat dissipation member or a cooling member, the control device 6 may have a function to adjust the temperature of the heat dissipation member or the cooling member. The control device 6 may have a function to control an adjustment member for adjusting the relative position of the first concave mirror 3 with respect to the display unit 2, and an adjustment member for adjusting the relative position of the second concave mirror 5 with respect to the first concave mirror 3.

[0063] The control device 6 may be configured to include one or more processors. The processor may include a general-purpose processor configured to load a specific program and execute a specific function, and a dedicated processor specialized for a specific process. The dedicated processor may include an ASIC (Application Specific Integrated Circuit). The processor may include a PLD (Programmable Logic Device). The PLD may include an FPGA (Field-Programmable Gate Array). The control device 6 may be a SoC (System-on-a-Chip) or SiP (System-in-a-Package) in which one or more processors are configured to work together.

[0064] Because the floating image display device 1 is configured to display the floating image R using the reflective optical system 8, appropriate design of the shapes of the first reflective surface 3a and the second reflective surface 5a can reduce distortion of the floating image R. Furthermore, because the floating image display device 1 does not include an optical element (e.g., a beam splitter, a polarizing filter, etc.) that transmits a portion of the image light L incident on the reflective optical system 8, reduction in brightness of the floating image R can be reduced. For example, if a beam splitter is located on the optical axis of the reflective optical system 8, the beam splitter may split off approximately half of the image light L, resulting in approximately half the brightness of the floating image R. The floating image display device 1 can suppress such a reduction in brightness. Alternatively, the floating image display device 1 can reduce the brightness of the image displayed on the display unit 2 while maintaining sufficient brightness of the floating image R, thereby reducing the power consumption of the floating image display device 1.

[0065] The second concave mirror 5 may be larger in size than the first concave mirror 3. In this case, it becomes easier to display an enlarged floating image R. That is, the second concave mirror 5 easily reflects the rays of the image light L, which are reflected by the first concave mirror 3 and have an enlarged diameter, toward the virtual imaging plane 9 of the floating image R. Furthermore, when the second concave mirror 5 is relatively large, it becomes easier to shape the second reflecting surface 5a in accordance with each of the multiple rays contained in the image light L. As a result, it becomes possible to effectively reduce distortion of the floating image R.

[0066] The size of the first concave mirror 3 may be defined by the maximum diameter of the first reflecting surface 3a. The size of the second concave mirror 5 may be defined by the maximum diameter of the second reflecting surface 5a. For example, if the first concave mirror 3 is partially spherical, the shape of the first reflecting surface 3a of the first concave mirror 3 is circular in front view. In this case, the size of the first concave mirror 3 may be the sum of L1 and L2 (see FIG. 2). If the first concave mirror 3 is partially ellipsoidal, the shape of the first reflecting surface 3a of the first concave mirror 3 is elliptical in front view. In this case, the size of the first concave mirror 3 may be the length of the major axis of a line segment that passes through the center of the first reflecting surface 3a and connects both ends E1 and E2. If the shape of the first reflecting surface 3a of the first concave mirror 3 is rectangular or other shape in front view, the size of the first concave mirror 3 may be the maximum length (e.g., the length of a diagonal) of a line segment that passes through the center of the first reflecting surface 3a and connects both ends E1 and E2. The center of the first reflecting surface 3a is defined by the lowest point (maximum protruding point) of the curved first reflecting surface 3a. The size of the second concave mirror 5 is defined in the same way as the size of the first concave mirror 3. The size of the first concave mirror 3 may be, for example, approximately 150 mm to 200 mm. The size of the second concave mirror 5 may be, for example, approximately 200 mm to 350 mm.

[0067] The size of the first concave mirror 3 may be defined by the area of ​​the first reflecting surface 3 a or the area of ​​the first reflecting surface 3 a in a front view. The size of the second concave mirror 5 may be defined by the area of ​​the second reflecting surface 5 a or the area of ​​the second reflecting surface 5 a in a front view.

[0068] The floating image display device 1 may be configured so that the image light L reflected by the first concave mirror 3 propagates through the space between the first concave mirror 3 and the second concave mirror 5. In other words, the optical path of the image light L between the first concave mirror 3 and the second concave mirror 5 may be a spatial propagation optical path in which no other optical components exist, as shown in FIG. 1 . In this case, the loss of the image light L in the optical path between the first concave mirror 3 and the second concave mirror 5 can be reduced, and as a result, a decrease in the brightness of the floating image R can be suppressed. Alternatively, the brightness of the image displayed on the display surface 2a can be reduced while maintaining sufficient brightness of the floating image R, thereby making it possible to reduce the power consumption of the floating image display device 1.

[0069] When the second concave mirror 5 is viewed from its rear side along a direction parallel to the virtual imaging plane 9 of the floating image R (approximately the Y-axis direction in FIG. 1 ), the second concave mirror 5 may overlap the display unit 2 and the first concave mirror 3. In this case, the space occupied by the display unit 2 and the reflection optical system 8 can be reduced, thereby making it possible to miniaturize the floating image display device 1. Furthermore, the optical path length of the image light L inside the floating image display device 1 can be shortened, thereby reducing loss of the image light L due to undesired scattering, interference, etc., and improving the display quality of the floating image R. The second reflecting surface 5a of the second concave mirror 5 may overlap the display surface 2a of the display unit 2 and the first reflecting surface 3a of the first concave mirror 3.

[0070] In the floating image display device 1, the user 7 views the floating image R from a direction approximately perpendicular to the virtual image plane 9, so the direction parallel to the virtual image plane 9 is the height direction of the floating image display device 1, and the direction perpendicular to the virtual image plane 9 is the thickness direction (depth direction) of the floating image display device 1. As described above, by having the second concave mirror 5 overlap the display unit 2 and the first concave mirror 3, the thickness (depth) of the floating image display device 1 can be made thinner.

[0071] When the second concave mirror 5 is viewed from its rear side along a direction parallel to the virtual imaging plane 9 of the floating image R (approximately the Y-axis direction in FIG. 1 ), the second concave mirror 5 may contain the display unit 2 and the first concave mirror 3. In this case, the space occupied by the display unit 2 and the reflection optical system 8 can be made smaller, thereby making the floating-image display device 1 more compact. As a result, the optical path length of the image light L inside the floating-image display device 1 can be made shorter, effectively reducing loss of the image light L due to undesired scattering, interference, etc., thereby effectively improving the display quality of the floating-image display device 1. The second reflecting surface 5a of the second concave mirror 5 may contain the display surface 2a of the display unit 2 and the first reflecting surface 3a of the first concave mirror 3. In this case, the thickness (depth) of the floating-image display device 1 can be made thinner.

[0072] 1, the distance between the first concave mirror 3 and the second concave mirror 5 may be smaller than the vertical length of the display surface 2a. In this case, it is possible to prevent light from leaking from the display surface 2a toward the distance. Furthermore, the vertical length of the floating image display device 1 can be shortened, making it more compact.

[0073] The end of the first concave mirror 3 on the side of the second concave mirror 5 and the end of the second concave mirror 5 on the side of the first concave mirror 3 may be in contact with each other. In this case, it is possible to prevent light from leaking from the display surface 2a toward the gap. Also, the vertical length of the floating image display device 1 can be made shorter, making it more compact.

[0074] The floating image display device 1 may be mounted on a moving object such as a vehicle, ship, or aircraft, i.e., a vehicle on which a user boards. Examples of vehicles include automobiles, industrial vehicles, railroad vehicles, residential vehicles, and fixed-wing aircraft traveling on runways. Examples of automobiles include passenger cars, trucks, buses, motorcycles, and trolleybuses. Examples of industrial vehicles include agricultural and construction vehicles. Examples of industrial vehicles include forklifts and golf carts. Examples of agricultural industrial vehicles include tractors, cultivators, transplanters, binders, combines, and lawn mowers. Examples of construction industrial vehicles include bulldozers, scrapers, excavators, crane trucks, dump trucks, and road rollers. Examples of vehicles may include human-powered vehicles. Examples of ships include marine jets, boats, and tankers. Examples of aircraft include fixed-wing aircraft and rotary-wing aircraft. The floating image display device 1 may be disposed in the dashboard of a moving object.

[0075] A moving body including the floating image display device 1 can allow a user 7 (for example, a driver of the moving body) to view a high-brightness floating image R with reduced distortion. The floating image R may include information about the state of the moving body (for example, the speed, acceleration, and posture of the moving body), the surrounding situation of the moving body, etc., in which case, driving safety can be improved.

[0076] The floating image display device 1 may be a head-up display installed in a vehicle. In this case, for example, a part of the front windshield of the vehicle may be used as a reflective member, and the reflective member may be used as the second concave mirror 5. The reflective member may be a semi-transmissive reflective member that transmits a part (e.g., approximately half) of the incident light and reflects the other part (e.g., approximately half) of the incident light.

[0077] The floating image display device 1 may be configured such that the display unit 2 is located between the first concave mirror 3 and the second concave mirror 5 in a side view as shown in Fig. 1. In other words, the floating image display device 1 may be configured such that the first concave mirror 3 is located at the bottom and the second concave mirror 5 is located at the top. In this case, it becomes easier to reduce the height of the floating image display device 1 and make it smaller.

[0078] The floating image display device 1 may be configured such that the display unit 2 is positioned so as not to overlap with the image light L (i.e., not to block the image light L). In this case, it is possible to prevent the display unit 2 from obstructing the floating image R, causing a portion of the floating image R to be missing or a portion of the floating image R to become dark. The distance (shortest distance) between the display unit 2 and the ray of the image light L closest to the display unit 2 may be 2 mm or more, or may be 10 mm or more, but is not limited to these ranges.

[0079] The floating image display device 1 may be configured such that the display surface 2a of the display unit 2 becomes larger as the first tilt angle θ1 becomes larger. In other words, the display unit 2 may have the largest size of the display surface 2a within a range that does not block the image light L, and in this case, the size of the floating image R visually recognized by the user 7 can be changed over a wide range.

[0080] The floating image display device 1 may be configured such that the first concave mirror 3 is contained in a curved space (also called a three-dimensional space) formed by extending the second concave mirror 5 into space. In this case, the reflection optical system 8 is made smaller, and as a result, the floating image display device 1 is made smaller. The floating image display device 1 may also be configured such that the display unit 2 and the first concave mirror 3 are contained in a three-dimensional space. In this case, the reflection optical system 8 is made even smaller, and as a result, the floating image display device 1 is made even smaller.

[0081] The floating image display device 1 may include a camera that captures an image of the face of the user 7. The camera may be an infrared camera or a visible light camera. The camera may include a CCD image sensor or a CMOS image sensor. The control device 6 may detect the eye position of the user 7 based on the image data output from the camera. The control device 6 may deform the image displayed on the display surface 2a based on the detected eye position. In this case, it is possible to reduce distortion of the floating image R even when the eye position of the user 7 moves. When the floating image display device 1 is mounted on a mobile object, the camera may be attached to the mobile object. The camera may be attached at any position inside or outside the mobile object. For example, the camera may be located inside or on the dashboard of the mobile object.

[0082] The floating image display device 1 may include a drive device that moves at least one of the first concave mirror 3 and the second concave mirror 5 of the reflective optical system 8. The drive device may be configured to include the above-mentioned adjustment member. The control device 6 may move at least one of the first concave mirror 3 and the second concave mirror 5 based on the detected eye position. In this case, even if the eye position of the user 7 moves, it is possible to reduce distortion of the floating image R visually recognized by the user 7. The drive device may be configured to include, for example, a motor, a piezoelectric element, etc.

[0083] According to the floating image display device of the present disclosure, it is possible to provide a floating image display device with improved display quality of floating images.

[0084] Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to the above embodiments, and various modifications and improvements are possible within the scope of the gist of the present disclosure. For example, the floating image display device 1 of the present disclosure is not limited to one that forms a floating image in space, but may also form a floating image in water, in a solid medium such as glass or transparent plastic, in outer space, etc.

[0085] The present disclosure can be implemented with the following configurations (1) to (17).

[0086] (1) A floating image display device comprising: a display unit having a display surface; a first concave mirror that reflects image light emitted from the display surface in a direction different from the direction toward the display unit; and a second concave mirror that reflects the image light reflected by the first concave mirror in a direction different from the direction toward the first concave mirror and forms a floating image of a real image, wherein a first tilt angle of the first concave mirror with respect to a first imaginary plane including the display surface is equal to or greater than a second tilt angle of the second concave mirror with respect to a second imaginary plane including a virtual image formation plane of the floating image.

[0087] (2) The floating image display device according to (1) above, wherein the apex of the curvature of the first reflecting surface of the first concave mirror is located closer to the display unit than the geometric center of the first reflecting surface.

[0088] (3) The floating image display device according to (2), wherein the curvature of the first reflecting surface at a portion of the first reflecting surface opposite the vertex to the display unit is equal to or less than the curvature of the portion of the first reflecting surface opposite the vertex to the display unit.

[0089] (4) The floating image display device according to (3) above, wherein an optical axis at the center of the display surface passes through a portion of the first reflecting surface opposite the vertex of the first reflecting surface to the display unit.

[0090] (5) The floating image display device according to any one of (2) to (4) above, wherein the first concave mirror is a free-form concave mirror, and the vertex is the origin of the free-form surface of the first concave mirror.

[0091] (6) The floating image display device according to any one of (1) to (5), wherein the second concave mirror is a free-form concave mirror, and the apex of the curvature of the second reflecting surface of the second concave mirror is at the same position as the geometric center of the second reflecting surface or in the vicinity of the center.

[0092] (7) The floating image display device according to any one of (1) to (6) above, wherein the second concave mirror is larger in size than the first concave mirror.

[0093] (8) The floating image display device according to any one of (1) to (7) above, wherein the curvature of the first reflecting surface of the first concave mirror is greater than the curvature of the second reflecting surface of the second concave mirror.

[0094] (9) The floating image display device according to any one of (1) to (8), wherein the display unit is located between the first concave mirror and the second concave mirror, and the display unit is located at a position that does not overlap with the optical path of the image light from the first concave mirror to the second concave mirror.

[0095] (10) The floating image display device according to any one of (1) to (8) above, wherein the size of the display surface is set to increase as the first tilt angle increases.

[0096] (11) The floating image display device according to any one of (1) to (8) above, wherein the first tilt angle is equal to or greater than 40° and equal to or less than 50°, and the second tilt angle is equal to or greater than 20° and equal to or less than 45°.

[0097] (12) The floating image display device according to any one of (1) to (8) above, wherein the image light reflected by the first concave mirror propagates only through the space between the first concave mirror and the second concave mirror.

[0098] (13) The floating image display device according to any one of (1) to (12) above, wherein the distance between the first concave mirror and the second concave mirror is smaller than the length of the display surface in the vertical direction.

[0099] (14) The floating image display device according to (13) above, wherein the end of the first concave mirror on the side of the second concave mirror and the end of the second concave mirror on the side of the first concave mirror are in contact with each other.

[0100] (15) The floating image display device according to any one of (1) to (14) above, wherein the display unit is of a self-luminous type.

[0101] (16) The floating image display device according to any one of (1) to (15) above, wherein the display unit includes a light-emitting diode element.

[0102] (17) The floating image display device according to (16), wherein the light-emitting diode element is an organic light-emitting diode element. Industrial application fields

[0103] The floating image display device of the present disclosure allows touchless operation of floating images, and as a result can be used in various product fields such as, but not limited to, a communication device for conversation, communication, etc., accompanied by a floating image, a medical interview device in which a doctor interviews a patient through a floating image, a navigation device and operation control device for vehicles such as automobiles, an order placement and reception device and cash register device for stores, etc., an operation panel for buildings, elevators, etc., a learning device for teaching or taking classes accompanied by a floating image, an office machine for business communication, instructions, etc. accompanied by a floating image, an amusement machine for playing games accompanied by a floating image, a projection device for projecting images onto the ground, walls, etc. at amusement parks, game centers, etc., a simulator device for conducting simulation experiments, etc., using floating images at universities, medical institutions, etc., a large display that displays prices, etc. at markets, stock exchanges, etc., and a video viewing device for viewing images of floating images.

[0104] REFERENCE SIGNS LIST 1 Floating image display device 2 Display unit 2a Display surface 3 First concave mirror 3a First reflecting surface 31 First portion 32 Second portion 5 Second concave mirror 5a Second reflecting surface 51 Third portion 52 Fourth portion 6 Control device 7 User 8 Reflection optical system 9 Virtual image plane L Image light R Floating image θ1 First tilt angle θ2 Second tilt angle

Claims

1. A floating image display device comprising: a display unit having a display surface; a first concave mirror that reflects image light emitted from the display surface in a direction different from the direction toward the display unit; and a second concave mirror that reflects the image light reflected by the first concave mirror in a direction different from the direction toward the first concave mirror and forms a floating image of a real image, wherein a first tilt angle of the first concave mirror with respect to a first imaginary plane including the display surface is greater than or equal to a second tilt angle of the second concave mirror with respect to a second imaginary plane including a virtual imaging plane of the floating image.

2. The floating image display device according to claim 1, wherein the apex of the curvature of the first reflecting surface of the first concave mirror is located closer to the display unit than the geometric center of the first reflecting surface.

3. The floating image display device according to claim 2, wherein the curvature of the first reflecting surface at a portion from the apex opposite the display unit is equal to or less than the curvature of a portion from the apex on the display unit side.

4. The floating image display device according to claim 3, wherein an optical axis at the center of said display surface passes through a portion of said first reflecting surface opposite said display unit from said vertex.

5. A floating image display device according to any one of claims 2 to 4, wherein the first concave mirror is a free-form concave mirror, and the vertex is the origin of the free-form surface of the first concave mirror.

6. A floating image display device as described in any one of claims 1 to 5, wherein the second concave mirror is a free-form concave mirror, and the apex of the curvature of the second reflecting surface of the second concave mirror is located at the same position as the geometric center of the second reflecting surface or in the vicinity of the center.

7. The floating image display device according to any one of claims 1 to 6, wherein the size of said second concave mirror is larger than that of said first concave mirror.

8. The floating image display device according to any one of claims 1 to 7, wherein the curvature of said first concave mirror is greater than the curvature of said second concave mirror.

9. A floating image display device as described in any one of claims 1 to 8, wherein the display unit is located between the first concave mirror and the second concave mirror, and the display unit is located in a position that does not overlap with the optical path of the image light from the first concave mirror to the second concave mirror.

10. The floating image display device according to any one of claims 1 to 8, wherein the size of the display surface is set to increase as the first tilt angle increases.

11. The floating image display device according to any one of claims 1 to 8, wherein the first tilt angle is greater than or equal to 40° and less than or equal to 50°, and the second tilt angle is greater than or equal to 20° and less than or equal to 45°.

12. A floating image display device according to any one of claims 1 to 8, wherein the image light reflected by the first concave mirror propagates only through the space between the first concave mirror and the second concave mirror.

13. The floating image display device according to any one of claims 1 to 12, wherein the distance between said first concave mirror and said second concave mirror is smaller than the vertical length of said display surface.

14. The floating image display device according to claim 13, wherein an end of said first concave mirror on the side of said second concave mirror and an end of said second concave mirror on the side of said first concave mirror are in contact with each other.

15. The floating image display device according to any one of claims 1 to 14, wherein the display section is of a self-luminous type.

16. The floating image display device according to any one of claims 1 to 15, wherein the display section includes a light emitting diode element.

17. The floating image display device according to claim 16, wherein the light emitting diode element is an organic light emitting diode element.

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