Patent Description:
In vehicles such as automobiles, use of head-up display apparatuses, which display information for users on windshields, is becoming widespread. In general, a head-up display apparatus magnifies and reflects video-image light by using a concave mirror, and projects the magnified and reflected video-image light onto a combiner or a windshield. In this way, the head-up display apparatus enables a user such as a driver to visually recognize virtual images.

It has been proposed to increase the display range of such a head-up display apparatus. For example, in a head-up display apparatus disclosed in Patent Literature <NUM>, light containing information emitted from light-emitting display means is magnified and diffracted by a first hologram, and a second diffracted image is magnified and diffracted by a second hologram. Then, the magnified and diffracted image is reflected by a combiner toward the observation place of a driver. Another example of relevant prior art is given by <CIT>, which discloses a windshield projecting vehicle head-up display system with a display light reflection unit comprising in some embodiments a concave mirror portion and also a transmission type volume hologram portion deposited on the windshield.

However, in the technology disclosed in Patent Literature <NUM>, the volume of the whole apparatus increases as the number of reflective components increases. Further, if the magnification of the concave mirror is increased in order to minimize the increase in size of the apparatus, the aberration of the lens increases as a consequence. As a result, virtual images recognized by the user may be distorted and/or virtual images may go out of focus.

Embodiments according to the present application have been made in order to solve such problems, and thereby to provide a head-up display apparatus capable of displaying satisfactory images while minimizing the increase in size of the apparatus.

A head-up display apparatus according to an embodiment projects a virtual image to be perceived by a user onto a virtual image display part provided in front of the user. The head-up display apparatus includes a display light emitting unit and a display light reflection unit. The display light emitting unit emits display light. The display light reflection unit reflects the display light and emits the reflected display light. The display light reflection unit includes a mirror part having a concave shape, and a transmissive-type volume hologram part provided on a surface of the mirror part.

According to the embodiment, it is possible to provide a head-up display apparatus capable of displaying satisfactory images while minimizing the increase in size of the apparatus.

For clarifying the explanation, the following descriptions and drawings are partially omitted and simplified as appropriate. Note that the same symbols are assigned to the same elements throughout the drawings and redundant explanations thereof are omitted as appropriate.

Embodiments according to the present invention will be described hereinafter with reference to the drawings. A head-up display apparatus according to this embodiment is an apparatus that projects virtual images to be perceived by a user onto a virtual image display part provided in front of the user. More specifically, the head-up display apparatus according to this embodiment is installed in an automobile, and projects virtual images containing certain information onto the windshield of the automobile while using the windshield as the virtual image display part. In this way, the head-up display apparatus displays the information for the driver, i.e., for the user.

A configuration of a head-up display apparatus according to a first embodiment will be described with reference to <FIG> is a schematic diagram showing the configuration of the head-up display apparatus according to the first embodiment. In the figure, an automobile <NUM>, a user U of the automobile <NUM>, and a head-up display apparatus <NUM> are schematically shown as viewed in the lateral direction of the automobile <NUM>.

The head-up display apparatus <NUM> is housed inside a dashboard of the automobile <NUM>. The head-up display apparatus <NUM> includes, as main components, a display light emitting unit <NUM> and a display light reflection unit <NUM>.

The display light emitting unit <NUM> generates display light and emits the generated display light to the display light reflection unit <NUM>. The display light emitting unit <NUM> includes, as main components, a light source generation part <NUM> and a display light generation part <NUM>.

The light source generation part <NUM> is a light source that generates predetermined light, such as LEDs (Light-Emitting Diodes) or a semiconductor laser. The light source generation part <NUM> emits the generated light to the display light generation part <NUM>.

The display light generation part <NUM> includes, for example, a transmissive-type liquid-crystal panel. When the transmissive-type liquid-crystal panel of the display light generation part <NUM> receives light generated by the light source generation part <NUM>, the display light generation part <NUM> generates display light containing information displayed on the liquid crystal panel. That is, the display light generation part <NUM> generates display light L10 by letting light received from the light source generation part <NUM> pass therethrough, and then emits the generated display light L10.

The display light reflection unit <NUM> receives the display light L10 coming from the display light emitting unit <NUM>, reflects the received display light L10 at a preset angle, and thereby emits reflected light L11 to a windshield WS. The reflected light L11 emitted from the display light reflection unit <NUM> is projected onto the windshield WS through a transmissive plate <NUM> disposed in the dashboard of the automobile <NUM>. The display light reflection unit <NUM> includes, as main components, a mirror part <NUM> and a transmissive-type volume hologram part <NUM>.

The mirror part <NUM> is a concave mirror formed in a concave shape. The mirror part <NUM> is, for example, a glass substrate of which a metal having a high reflectivity is deposited on the surface. The mirror part <NUM> may be aspherical or spherical. The mirror part <NUM> receives the display light L10 through the transmissive-type volume hologram part <NUM> and reflects the received display light L10.

The transmissive-type volume hologram part <NUM> is a volume hologram (or a three-dimensional hologram) formed on the surface of the mirror part <NUM>. The transmissive-type volume hologram part <NUM> is set so as to refract or diffract the display light L10. As a result, the transmissive-type volume hologram part <NUM> change the direction of the display light L10, which has traveled thereto in a straight line, to a preset direction. When the transmissive-type volume hologram part <NUM> receives the display light L10, it changes the direction of the received display light L10 and guides (i.e., directs) the light, whose traveling direction has been changed, to the mirror part <NUM>.

The transmissive-type volume hologram part <NUM> may be formed directly on the surface of the mirror part <NUM> by a method such as a coating process. The transmissive-type volume hologram part <NUM> may be formed on a film, and then the film may be tightly joined to (e.g., stuck on) the mirror part <NUM> with no space therebetween.

By the above-described configuration, the display light reflection unit <NUM> changes the direction of the display light L10 received from the display light emitting unit <NUM> and reflects the display light L10, and by doing so, emits reflected light L20 to the windshield WS.

Next, details of the display light reflection unit <NUM> will be described with reference to <FIG> is an enlarged view of the display light reflection unit in the head-up display apparatus. <FIG> shows an enlarged view of an area from the central part to the lower part of the display light reflection unit <NUM> shown in <FIG>. In <FIG>, a first area 120A of the display light reflection unit <NUM> is shown in the lower part of the drawing, and a second area 120B thereof is shown in the central part of the drawing.

The first area 120A will be described hereinafter. A light beam L101A, which constitutes a part of the display light L10, is incident on the first area 120A. The incident angle of the light beam L101A with respect to the display light reflection unit <NUM> in the first area 120A is represented as an angle A10. The angle A10 is an angle between a normal P1, which is a line perpendicular to the mirror part <NUM> in the first area 120A, and the light beam L101A.

The light beam L101A is incident on the transmissive-type volume hologram part <NUM> in the direction of the angle A10, which is the incident angle. Upon receiving the light beam L101A, the transmissive-type volume hologram part <NUM> changes the direction of the light beam L101A by diffracting the light beam L101A, and thereby generates a light beam L101B, which is the diffracted light. The angle between the light beam L101B, which is the diffracted light, and the normal P1 (i.e., the diffraction angle) is an angle A11 smaller than the angle A10.

Therefore, in the first area 120A, the incident angle of the light beam L101B with respect to the mirror part <NUM> is the angle A11 smaller than the angle A10, i.e., smaller than the incident angle of the light beam L101A with respect to the display light reflection unit <NUM>. Therefore, the reflection angle of the reflected light beam L111, i.e., the light beam that is generated as the light beam L101A is reflected by the mirror part <NUM>, is the angle A11.

The display light reflection unit <NUM> is set so that the incident angle of the light beam L101A, which is originally the angle A10, becomes the angle A11 when it is incident on the mirror part <NUM> after passing through the transmissive-type volume hologram part <NUM>. The angle A11 is smaller than the angle A10, i.e., smaller than the incident angle of the light beam L101A when the light beam L101A is incident on the mirror part <NUM> without passing through the transmissive-type volume hologram part <NUM>.

As described above, by providing the transmissive-type volume hologram part <NUM> on the surface of the mirror part <NUM>, the head-up display apparatus <NUM> can reduce the incident angle of the light beam incident on the concave mirror. Therefore, the head-up display apparatus <NUM> can reduce the aberration caused by the concave mirror.

Next, the second area 120B will be described. A light beam L102A, which constitutes another part of the display light L10, is incident on the second area 120B. The incident angle of the light beam L102A with respect to the display light reflection unit <NUM> in the second area 120B is represented as an angle A20. The angle A20 is an angle between a normal P2, which is a line perpendicular to the mirror part <NUM> in the second area 120B, and the light beam L102A.

The light beam L102A is incident on the transmissive-type volume hologram part <NUM> in the direction of the angle A20, which is the incident angle. Upon receiving the light beam L102A, the transmissive-type volume hologram part <NUM> changes the direction of the light beam L102A by diffracting the light beam L102A, and thereby generates a light beam L102B, which is the diffracted light. The angle between the light beam L102B, which is the diffracted light, and the normal P2 (i.e., the diffraction angle) is an angle A21 smaller than the angle A20.

Therefore, in the second area 120B, the incident angle of the light beam L102B with respect to the mirror part <NUM> is the angle A21 smaller than the angle A20, i.e., smaller than the incident angle of the light beam L102A with respect to the display light reflection unit <NUM>. Therefore, the reflection angle of the reflected light beam L112, i.e., the light beam that is generated as the light beam L102A is reflected by the mirror part <NUM>, is the angle A21.

The display light reflection unit <NUM> is set so that the incident angle of the light beam L102A, which is originally the angle A20, becomes the angle A21 when it is incident on the mirror part <NUM> after passing through the transmissive-type volume hologram part <NUM>. The angle A21 is smaller than the angle A20, i.e., smaller than the incident angle of the light beam L102A when the light beam L102A is incident on the mirror part <NUM> without passing through the transmissive-type volume hologram part <NUM>.

The details of the display light reflection unit <NUM> have been described above. The transmissive-type volume hologram part <NUM> is set so as to change the direction of the light beam L101A, which is originally incident at the angle A10, to the angle A11 in the first area 120A. The transmissive-type volume hologram part <NUM> is set so as to change the direction of the light beam L102A, which is originally incident at the angle A20, to the angle A21 in the second area 120B. As described above, the transmissive-type volume hologram part <NUM> is set so that the angle by which the direction of the display light is changed is set for each of the areas where the display light is received (i.e., set on an area-by-area basis) in the display light reflection unit <NUM>. Further, the incident angle of the display light, which is set in the transmissive-type volume hologram part <NUM>, is determined for each of the areas where the display light is received (i.e., determined on an area-by-area basis) based on the constraint of the place where the head-up display apparatus <NUM> is disposed and the relative positions of the display light emitting unit <NUM> and the display light reflection unit <NUM>.

The above-described head-up display apparatus <NUM>, combined with the transmissive-type volume hologram part <NUM> and the mirror part <NUM>, can reduce the curvature of the mirror part <NUM>. Therefore, the aberration caused in the mirror part <NUM> can be controlled. Further, by the above-described configuration, the head-up display apparatus <NUM> can prevent or reduce the distortion of displayed virtual images. Therefore, the head-up display apparatus <NUM> can increase the virtual-image surface.

Although an embodiment has been described above, the configuration of the head-up display apparatus <NUM> according to the embodiment is not limited to the above-described configuration. The display light emitting unit <NUM> in the head-up display apparatus <NUM> may include (i.e., generate) red, green and blue laser lights as its light sources. Further, the display light emitting unit <NUM> may include a reflective-type liquid-crystal panel, LCOS (Liquid Crystal On Silicon), or a scanning-type micro-mirror in place of the transmissive-type liquid-crystal panel in the display light generation part <NUM>. According to the embodiment, it is possible to provide a head-up display apparatus capable of displaying satisfactory images while minimizing the increase in size of the apparatus.

Note that the present invention is not limited to the above-described embodiments, and they may be modified as appropriate without departing from the scope of the invention. For example, the above-described head-up display apparatus can be applied to vehicles other than the automobiles, such as aircraft and ships. Further, the aforementioned head-up display apparatus may be applied not only to vehicles but also to driving simulators for automobiles, flight simulators for airplanes, video game consoles, and the like.

This application is based upon and claims the benefit of priority from <CIT>.

Claim 1:
A head-up display apparatus (<NUM>) configured to project a virtual image to be perceived by a user onto a virtual image display part provided in front of the user, comprising:
a display light emitting unit (<NUM>) configured to emit display light; and
a display light reflection unit (<NUM>) configured to reflect the display light and emit the reflected display light, wherein
the display light reflection unit (<NUM>) comprises a mirror part (<NUM>) having a concave shape, and a transmissive-type volume hologram part (<NUM>) provided on a surface of the mirror part (<NUM>).