HEAD MOUNTED DISPLAY DEVICE

Abstract

The purpose of the present invention is to provide a head mounted display for aircraft in which astigmatism is reduced so that a display image with a wide visual field can be observed. A reflection surface (10a) of a visor (10), onto which display light is projected from a projection optical system (12), does not have a spherical shape but an aspherical shape whose curvature in the vertical direction is smaller than in the horizontal direction. This difference in curvature eliminates the difference in optical power due to a difference in the incident angle on the reflection surface (10a) and reduces the amount of astigmatism. An intermediate image is formed in both the vertical and horizontal directions within the projection optical system (12) or in the middle of an optical path from the projection optical system (12) to the reflection surface (10a). This increases the degree of freedom of the arrangement of optical elements and allows for the reduction in size and weight of the device.

Claims

1. A head mounted display device comprising: a helmet to be mounted on a head of a user; a visor connected to the helmet, the visor having a curved surface protruding outward and configured to be placed in front of eyes of the user; a display section for creating a display image; and a projection optical system for projecting display light onto a reflecting surface of the visor, the display light containing, as a piece of information, the display image created by the display section, the head mounted display device configured to create a virtual image originating from the display image within a view of an external scene that is visible through the visor, wherein: an intermediate image is formed within the projection optical system or on an optical path between the projection optical system and the reflecting surface; the visor is rotatable with respect to the helmet about an axis parallel to an X axis and is slidable upward to allow the user to put the helmet on or remove the helmet, while an upper portion of the reflecting surface is held in an inclined position tilting outward in front of the eyes of the user when the visor is in use; and the reflecting surface of the visor has an aspherical shape whose curvature in a Y-Z plane is smaller than the curvature in an X-Z plane, where: a central position between the right and left eyes of the user facing horizontally frontward is defined as an origin O; an axis extending frontward from the origin O as viewed from the user is defined as the Z axis; an axis orthogonal to the Z axis and directed upward as viewed from the user is defined as the Y axis; an axis orthogonal to both the Z axis and the Y axis is defined as the X axis; a point at which an optical axis of a light beam incident on the reflecting surface of the visor intersects with the reflecting surface is defined as an intersection point O; a normal to the reflecting surface at the intersection point O is defined as the Z axis; an axis which is orthogonal to the Z axis and forms, with the Z axis, a plane containing the optical axis of the incident light beam and an optical axis of an outgoing light beam resulting from the incident light beam reflected by the reflecting surface and travelling toward an eye of the user, is defined as the Y axis; and an axis orthogonal to both the Y axis and the Z axis is defined as the X axis.

2. The head mounted display device according to claim 1, wherein: the reflecting surface of the visor has an aspherical shape whose curvature in the Y-Z plane is smaller than the curvature in the X-Z plane by an amount corresponding to a difference in optical power due to a difference in the incident angle of the display light to the reflecting surface.

3. The head mounted display device according to claim 1, wherein: the reflecting surface of the visor is a free-form surface having a plane-symmetrical shape with respect to the Y axis corresponding to each of the eyes of the user.

4. The head mounted display device according to claim 1, wherein: the reflecting surface of the visor is an aspherical surface which is rotationally symmetrical with respect to a vertex located on a Z-Y plane.

5. The head mounted display device according to claim 1, therein: the reflecting surface of the visor is a toroidal surface whose curvature in the Y-Z plane is different from the curvature in the X-Z plane.

6. The head mounted display device according to claim 1, wherein: an inclination angle of the reflecting surface at the intersection point O is equal to or larger than 10 degrees, a radius of curvature of the reflecting surface is within a range from 50 to 500 mm in both the Y-Z plane and the X-Z plane, and a thickness of the visor is within a range from 0.1 to 10 mm.

7. The head mounted display device according to claim 6, wherein: the visor has a surface layer formed on an inner surface or outer surface, the surface layer made of a material different from a base material of the visor.

8. The head mounted display device according to claim 1, wherein: the projection optical system includes at least one reflection mirror, and a reflecting surface of the reflection mirror has an aspherical shape.

9. The head mounted display device according to claim 8, wherein: the reflecting surface of the reflection mirror is a concave surface.

10. The head mounted display device according to claim 9, wherein: the reflection mirror is a back-surface reflection mirror having a refracting effect in addition to a reflecting effect.

11. The head mounted display device according to claim 10, wherein: the surface having the refracting effect has an aspherical shape.

12. The head mounted display device according to claim 1, wherein: the projection optical system includes at least one lens having a refracting effect on both surfaces, and at least one surface of the lens has an aspherical shape.

13. The head mounted display device according to claim 12, wherein: the lens has a refractive index and equal to or higher than 1.58.

14. The head mounted display device according to claim 1, wherein: the display section is configured to display information in two or more colors.

15. The head mounted display device according to claim 1, wherein: the display section and the projection optical system are arranged so that a principal ray corresponding to a center of a visual field of the display light emitted from the display section is emitted at an angle which is not orthogonal to the display surface of the display section.

16. The head mounted display device according to claim 1, wherein: the display section and the projection optical system are arranged so that a principal ray corresponding to a center of a visual field of the display light emitted from the display section is emitted from a position displaced from a center of the display surface of the display section.

17. The head mounted display device according to claim 1, wherein: the display section includes a transmission-type display element and a backlight illumination unit for illuminating the display element with light from behind.

18. The head mounted display device according to claim 1, wherein: the display section includes a reflection-type display element, an illumination section for emitting illumination light, and a reflection-type optical system configured to illuminate the display surface of the display element with the illumination light and to guide the light reflected by the display surface.

19. The head mounted display device according to claim 1, wherein: the display section includes a light-emitting display element.

20. The head mounted display device according to claim 1, wherein: the display section includes a small projector and a small screen.

21. The head mounted display device according to claim 14, wherein: the display section includes a transmission-type display element and a backlight illumination unit for illuminating the display element with light from behind, where at least a portion of the backlight illumination unit is a small projector.

22. The head mounted display device according to claim 1, wherein: two sets of the display sections and the projection optical systems are respectively provided on right and left sides corresponding to both eyes of the user, where a portion of the optical elements constituting the right and left projection optical systems is shared for both eyes.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0053] FIGS. 1A and 1B are schematic configuration diagrams of an optical system including a visor in an HMD as one embodiment of the present invention, where FIG. 1A is a schematic vertical-sectional view, and FIG. 1B is a schematic horizontal-sectional view.

[0054] FIG. 2 is a detailed configuration diagram in the vertical direction of the display section and the projection optical system in the HMD according to the present embodiment.

[0055] FIG. 3 is a detailed configuration diagram in the horizontal direction of the display section and the projection optical system in the HMD according to the present embodiment.

[0056] FIG. 4 is a perspective view schematically showing an optical path of the display light in the HMD according to the present embodiment.

[0057] FIG. 5 is a diagram showing another configuration example of the display section in the HMD according to the present embodiment.

[0058] FIG. 6 is a diagram showing another configuration example of the display section in the HMD according to the present embodiment.

[0059] FIG. 7 is a diagram showing another configuration example of the display section in the HMD according to the present embodiment.

[0060] FIGS. 8A and 8B are schematic configuration diagrams of an optical system including a visor in a conventional HMD, where FIG. 1A is a schematic vertical-sectional view, and FIG. 1B is a schematic horizontal-sectional view.

DESCRIPTION OF EMBODIMENTS

[0061] An HMD as one embodiment of the head mounted display device according to the present invention is hereinafter described with reference to the attached drawings.

[0062] FIGS. 1A and 1B are schematic configuration diagrams of an optical system including a visor in the HMD according to the present embodiment, where FIG. 1A is a schematic vertical-sectional view, and FIG. 1B is a schematic horizontal-sectional view. FIGS. 2 and 3 are more detailed diagrams showing the configuration of the optical system in FIGS. 1A and 1B, respectively. FIG. 4 is a perspective view schematically showing an optical path of the display light. It should be noted that the visor and other components are omitted in FIG. 4.

[0063] As a typical use of the HMD 1 according to the present embodiment, the HMD 1 is mounted on the head of a pilot operating an aircraft. The HMD 1 includes a visor 10, an image display section 11, and a projection optical system 12. The visor 10 is connected to a helmet (not shown) in a manner to be rotatable about an axis parallel to the X axis (which will be described later) and vertically slidable. The helmet covers the head of the user H, leaving an open area in front of the face of the user H. The image display section 11 creates a display image based on image data received from an image processing unit (not shown). The projection optical system 12 projects display light containing a display image as a piece of information onto a predetermined area of the visor 10. As shown in FIG. 3, two sets of image display sections 11 and projection optical systems 12 are respectively provided on the left and right sides corresponding to both eyes (left eye EL and right eye ER) of the user H. The display section and the projection optical system for the right eye ER are respectively denoted by reference signs 11R and 12R, while the display section and the projection optical system for the left eye EL are respectively denoted by reference signs 11L and 12L.

[0064] The visor 10 has a reflection surface 10a formed on the side which faces the user H. The reflection surface 10a is a coating layer which reflects a portion of the display light while allowing a portion of the light coming from the external world to pass through. This coating layer is made of a material different from the base material of the visor 10. For example, the base material of the visor 10 is polycarbonate, while the coating layer forming the reflection surface 100a is made of a material selected from SiO, SiO.sub.2, Al.sub.2O.sub.3, MgO, Ta.sub.2O.sub.5, TiO.sub.2 and other compounds, or a combination of two or more of those compounds. The thickness of the visor 10, which varies depending on the kind of base material, normally falls within a range from 0.1 to 10 mm.

[0065] The two beams of display light containing display images formed by the image display sections 11L and 11R exit from the projection optical systems 12L and 12R, and are projected onto the reflection surface 10a of the visor 10. The thereby reflected beams of light reach the left eye EL and right eye ER of the user H, respectively. A portion of the light coming from the external world and passing through the visor 10 also reaches the eyes EL and ER of the user H. Consequently, a virtual image of the display image is created in front of the eyes of the user H, being superposed on a view of the external scene. The overall configuration of such a basic optical system is the same as before.

[0066] For convenience of explanation, the X, Y and Z axes as well as the X, Y and Z axes in the present embodiment are defined as follows:

[0067] As shown in FIGS. 1A, 1B and 4, an central position between the left eye EL and right eye ER of the user H is defined as the origin O. An axis extending from the origin O toward the front side as viewed from the user H is defined as the Z axis. An axis orthogonal to the Z axis and directed upward as viewed from the user H is defined as the Y axis. An axis orthogonal to both the Z axis and the Y axis as well as extending in the left-outward direction as viewed from the user H is defined as the X axis. A point at which the optical axis C1 of a light beam emitted from the optical projection system 12 (12L or 12R) and reaching the visor intersects with the reflecting surface 10a of the visor 10 is defined as the intersection point O. An axis extending in the direction normal to the visor 10 at the intersection point O and directed outward as viewed from the user H is defined as the Z axis. An axis which is orthogonal to the Z axis and directed so as to form a Y-Z plane on which both the optical axis C1 of the light beam before being reflected by the visor 10 and the optical axis C2 of the light beam after the reflection are present. An axis which is orthogonal to both the Y and Z axes is defined as the X axis. The intersection point O is present for each of the left and right eyes EL and ER. Therefore, the system of X, Y and Z axes is also present for each of the left and right eyes, as shown in FIG. 4.

[0068] As opposed to the conventional HMD shown in FIGS. 8A and 8B in which the reflection surface 100a of the visor 100 has a spherical shape, the reflection surface 10a of the visor 10 in the HMD according to the present embodiment has a rotationally symmetrical and aspherical shape (axially symmetrical aspherical shape) expressed by the following equation (1), with its vertex U located on the Y-Z plane:

[00001]$\begin{array}{cc}z=\frac{c.Math..Math.r^2}{1+\sqrt{1-\left(1+k\right).Math.c^2.Math..Math.r^2}}+\underset{i=1}{\overset{n}{.Math.}}.Math..Math.A_i.Math..Math.r^{2.Math.i}.Math..Math.c.Math.\text{:}.Math..Math.\mathrm{Curvature}.Math..Math.k.Math.\text{:}.Math..Math.\mathrm{Conic}.Math..Math.\mathrm{Constant}.Math..Math.r^2=x^2+y^2.Math..Math.A_i.Math.\text{:}.Math..Math.\mathrm{Aspheric}.Math..Math.\mathrm{Coefficient}& \left(1\right)\end{array}$

[0069] Since this surface is aspherical, the curvature in the Y-axis direction at the intersection point O is different from the curvature in the X-axis direction. As will be described later, the former curvature is set to be smaller than the latter (i.e. the radius of curvature in the Y-axis direction is larger than the radius of curvature in the X-axis direction).

[0070] A detailed configuration of the optical system in the HMD according to the present embodiment is hereinafter described.

[0071] The visor 10 is connected to a helmet (not shown) in such a manner that it is rotatable about the X axis. As shown in FIGS. 1A and 2, when the visor 10 is completely lowered (i.e. when in use), the upper portion of the reflection surface 10a is in an inclined position tilting frontward in front of the eyes of the user H. Its inclination angle at the intersection point O (the angle formed by the vertical plane and the tangential plane to the reflection surface 10a at the intersection point O) is equal to or larger than 10 degrees.

[0072] As shown in FIG. 2, the image display section 11 includes a transmission-type display element 112, such as a transmission-type color liquid crystal display element, and a backlight illumination unit 111. The light emitted from the backlight illumination unit 111 passes through the display surface of the transmission-type display element 112, whereby an image formed on the display surface of the transmission-type display element 112 is emitted as display light. This image is completely symmetrical (i.e. plane-symmetrical with respect to the Y-Z plane). The projection optical system 12 includes a plurality of lenses 121, a back-surface reflection mirror 122 (122L or 122R) with a concave reflection surface, and a flat mirror 123. These components are also completely symmetrical. However, it should be noted that the lenses 121 and the back-surface reflection mirror 122 are independently provided for each of the right and left eyes, while the flat mirror 123 is placed so as to perpendicularly traverse the Y-Z plane and be shared by the two projection optical systems 12L and 12R.

[0073] The display light emitted from the image display section 1 passes through the lenses 121 (two lenses are used in FIG. 2, although there is no limitation on the number of lenses) and reaches the back-surface reflection mirror 122. Then, the light is refracted at the refraction surface 122a on the incident side of the back-surface reflection mirror 122 and subsequently reaches the reflection surface 122b, to be reflected by the reflection surface 122b while being focused. The reflected light is once more reflected by the flat mirror 123 into the direction toward the reflection surface 10a of the visor 10. Due to the focusing effect of the reflection surface 122b of the back-surface reflection mirror 122, the reflected light temporarily forms an intermediate image on the optical path between the flat mirror 123 and the reflection surface 10a. The imaging plane on which the intermediate image is formed is denoted by reference sign Q in FIG. 2. At this plane, the intermediate image is formed in both the vertical direction (i.e. in a plane parallel to the Y-Z plane) and the horizontal direction (i.e. in a plane parallel to the X-Z plane). It should be noted that the intermediate image may be formed within the projection optical system 12 including the flat mirror 123 instead of being formed on the optical path between the flat mirror 123 and the reflection surface 10a.

[0074] As shown in FIG. 2, the optical axis of the display light emitted from the image display section 11 and incident on the lenses 121 of the projection optical system 12 is not orthogonal to the display surface of the transmission-type display element 112 of the image display section 11. In other words, the configuration of a non-coaxial optical system is adopted. Therefore, a display image which is asymmetrically blurred is formed. To address this problem, at least one of the refraction surface 122a and reflection surface 122b of the back-surface reflection mirror 122, or the lenses 121, are given an aspherical shape so as to correct the aforementioned blurring of the display image.

[0075] The display light emitted from the projection optical system 12, or more exactly, the display light which travels from the imaging plane Q of the intermediate image while gradually expanding, hits the reflection surface 10a of the visor 10 and is reflected by the concave surface while being focused. The incident angle of the optical axis of the incident light in the Y-Z plane is not the same as that of the optical axis of the incident light in the X-Z plane. Therefore, if the reflection surface were spherical, a difference in optical power would occur between these two planes and cause astigmatism. To avoid this problem, in the HMD according to the present embodiment, the curvature of the reflection surface 10a in the Y-Z plane is made to be smaller than the curvature in the X-Z plane by an amount corresponding to the aforementioned difference in the incident angle of the optical axis of the incident light so that the optical power will be almost equal in both planes. In practice, this difference in curvature is considerably small. The radius of curvature is normally within a range from 50 to 500 mm in both planes.

[0076] Since the optical power is made to be almost equal in both the Y-Z plane and the X-Z plane, the problem of astigmatism is practically eliminated when the beams of display light respectively reach the eyes EL and ER. Accordingly, the user H can observe a display image with a wide visual field in the form of a virtual image in both the vertical and horizontal directions.

[0077] The shape of the reflection surface 10a of the visor 10 is not limited to the previously described kind of rotationally symmetrical aspherical shape having point U as its vertex; it may be any shape that is aspherical. For example, it may be shaped like a toroidal surface defined by the following equation (2):

z={square root over ((RxRy+{square root over (Ry.sup.2y.sup.2)}).sup.2x.sup.2)}(2)

[0078] It may also be a free-form shape which is defined by the following equation (3) and is plane-symmetrical with respect to the Y axis corresponding to each of the eyes EL and ER

[00002]$\begin{array}{cc}a=\underset{i=0}{.Math.}.Math.\underset{j=0}{.Math.}.Math.A_{\mathrm{ij}}.Math..Math.x^{i-j}.Math..Math.y^j.Math..Math.A_{\mathrm{ij}}.Math.\text{:}.Math..Math.\mathrm{Free}.Math.\text{-}.Math.\mathrm{Form}.Math..Math.\mathrm{Surface}.Math..Math.\mathrm{Coefficient}& \left(3\right)\end{array}$

[0079] The configuration of the image display section 11 or projection optical system 12 in the HMD according to the previously described embodiment can be appropriately changed.

[0080] FIGS. 5-7 are schematic diagrams each of which shows a different configuration example of the display section.

[0081] The image display section 11A shown in FIG. 5 includes an illumination section 11A1, a reflection-type display element 11A2 (e.g. reflection-type color liquid crystal display element), as well as a reflection-type optical element 11A3 including a beam splitter and other related components. The light emitted from the illumination section 11A1 is reflected by the reflection-type optical element 11A3 and directed toward the reflection-type display element 11A2. When reflected by the display surface of the reflection-type display element 11A2, the light receives image information formed on the display surface and is eventually emitted through the reflection-type display element 11A3 to the outside as the display light.

[0082] The image display section 11B shown in FIG. 6 includes a light-emitting display element 11B1, such as an organic electroluminescent display. According to this configuration, it is unnecessary to provide a separate illumination section, since the display element 11B1 itself emits light and produces display light.

[0083] The image display section 11C shown in FIG. 7 includes a small projector 11C1 and a small screen 11C2. The display light emitted from the small projector 11C1 is projected onto the small screen 11C2 and forms an enlarged version of the display image on the small screen 11C2. The display image on this small screen 11C2 is directly emitted as the display light.

[0084] In the configuration of the previously described embodiment shown in FIG. 2, a display image which is effectively a colored image or an image with two or more colors can be created by using a monochromatic display element as the display element 112 and a small projector emitting colored light or light with two or more colors as the backlight illumination unit 111.

[0085] The previously described embodiment is a mere example of the present invention. Its variations are not limited to the already described ones. Any change, modification or addition appropriately made within the spirit of the present invention will naturally fall within the scope of claims of the present application.

REFERENCE SIGNS LIST

[0086] 1 . . . Helmet Mounted Display (HMD) [0087] 10 . . . Visor [0088] 10 10a . . . Reflection Surface [0089] 11, 11A, 11B, 11C, 11L, 11R . . . Image Display Section [0090] 111 . . . Backlight Illumination Unit [0091] 112 . . . Transmission-Type Display Element [0092] 12, 12L, 12R . . . Projection Optical System [0093] 15 121 . . . Lens [0094] 122 (122L, 122R) . . . Back-Reflection Mirror [0095] 122a . . . Refraction Surface [0096] 122b . . . Reflection Surface [0097] 123 . . . Flat Mirror [0098] C1 . . . Optical Axis of Bundle of Incident Light [0099] C2 . . . Optical Axis of Bundle of Outgoing Light [0100] EL . . . Left Eye [0101] ER . . . Right Eye [0102] H . . . User