Image projection device

Abstract

To provide an image projection device that improves accuracy of aberration correction, and that enhances visibility of a formed virtual image.SOLUTION: An image projection device for projecting image light onto a display part (WS) for displaying a virtual image comprises: an image irradiation part (10) for emitting image light; a primary mirror (20) for reflecting image light that is incident from the image irradiation part (10); and a secondary mirror (30) for reflecting image light that is incident from the primary mirror (20). A reflection plane of the primary mirror (20) has a saddle type shape with a recessed shape in a first direction and a protruding shape in a second direction.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an image projection device, and more particularly to an image projection device that irradiates a projection image onto a display unit for displaying a virtual image.

Background Art

[0002] Conventionally, an instrument panel that lights up icons has been used as a device for displaying various types of information inside a vehicle. In addition, with the increase in the amount of information to be displayed, proposals have also been made to embed an image display device in the instrument panel or to configure the entire instrument panel with an image display device.

[0003] However, since the instrument panel is located below the front windshield (windshield) of the vehicle, it is not preferable because the driver needs to move their line of sight downward during driving in order to visually recognize the information displayed on the instrument panel. Therefore, a head-up display (hereinafter referred to as HUD: Head Up Display) that projects an image onto the front windshield so that the driver can read the information when viewing the front of the vehicle has also been proposed (see, for example, Patent Documents 1 and 2).

[0004] In such a conventional image projection device, image light is irradiated from an image irradiation unit onto the windshield (display unit) of the vehicle, and the driver can visually recognize the image light reflected by the windshield and the background in front of the vehicle by overlapping them.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in conventional image projection devices, since a free-form mirror and a windshield WS reflect image light to form a virtual image in space, the paths of the image light incident on the left and right eyes are displaced due to aberration, resulting in vertical and horizontal parallax and a decrease in the visibility of the virtual image.

[0007] Therefore, the present invention has been made in view of the above-described conventional problems, and an object thereof is to provide an image projection device capable of improving the correction accuracy of aberration and enhancing the visibility of the formed virtual image.

Means for Solving the Problems

[0008] In order to solve the above problems, an image projection device of the present invention is an image projection device that projects image light onto a display unit for displaying a virtual image, and includes an image irradiation unit that irradiates the image light, a primary mirror that reflects the image light incident from the image irradiation unit, and a secondary mirror that reflects the image light incident from the primary mirror, wherein a reflection surface of the primary mirror has a saddle shape that is concave in a first direction and convex in a second direction.

[0009] In such an image projection device of the present invention, since the reflection surface of the primary mirror has a saddle shape that is concave in the first direction and convex in the second direction, and the image light reflected by the primary mirror is reflected by the secondary mirror, it is possible to improve the correction accuracy of aberration and enhance the visibility of the formed virtual image.

[0010] Also, in one aspect of the present invention, a component in the first direction of the image light reflected by the primary mirror is intermediate-imaged between the primary mirror and the secondary mirror.

[0011] Also, in one aspect of the present invention, a distance from the image irradiation unit to the primary mirror is smaller than a distance from the primary mirror to the secondary mirror.

[0012] Also, in one aspect of the present invention, a distance from the image irradiation unit to the primary mirror is in a range of 30 mm or more and 100 mm or less.

[0013] In addition, in one aspect of the present invention, the image irradiation unit irradiates near-field image light from the near-field display region and far-field image light from the far-field display region, and includes a first planar mirror that reflects the far-field image light, and a second planar mirror that reflects the far-field image light reflected by the first planar mirror. The near-field image light from the near-field display region is incident on the primary mirror, and the far-field image light is incident on the primary mirror from the second planar mirror.

Effects of the Invention

[0014] In the present invention, it is possible to provide an image projection apparatus capable of improving the correction accuracy of aberration and improving the visibility of a virtual image to be formed.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0016] (First Embodiment) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same or equivalent components, members, and processes shown in each drawing are denoted by the same reference numerals, and repeated explanations will be omitted as appropriate. FIG. 1 is a schematic diagram for explaining the projection of virtual images P1 and P2 using the image projection apparatus 100 according to the present embodiment. As shown in FIG. 1, the image projection apparatus 100 includes an image irradiation unit 10, a primary mirror 20, and a secondary mirror 30. In FIG. 1, the direction perpendicular to the paper surface is defined as the x-axis direction, the vertical direction is defined as the y-axis direction, and the horizontal direction is defined as the z-axis direction. Here, the x-axis direction corresponds to the left-right direction (width direction) of the vehicle on which the image projection apparatus 100 is mounted, the y-axis direction corresponds to the up-down direction (vertical direction), and the z-axis direction corresponds to the front-rear direction.

[0017] As shown in FIG. 1, the image light projected from the image projection apparatus 100 is reflected by the windshield (display unit) WS and irradiated to the driver's viewpoint position. The driver visually recognizes the virtual images P1 and P2 formed on the extension of the optical path (dashed line direction) where the image light is incident. In the present embodiment, an example is shown in which the image projection apparatus 100 projects image display light and two virtual images P1 and P2 are formed, but the number of virtual images is not limited.

[0018] In the image projection apparatus 100 of the present embodiment, far-field image light and near-field image light are irradiated from the image irradiation unit 10, and each is formed as virtual images P1 and P2. The dashed line shown in FIG. 1 schematically shows the path (reference ray) of the center position of the far-field image light, and the dashed-dotted line schematically shows the path (reference ray) of the center position of the near-field image light. Examples of the far-field image projected by the far-field image light include auxiliary information related to driving such as attention-arousing images and emergency information. Examples of the near-field image projected by the near-field image light include a speed and volume indicator, a travel direction guide, and the like.

[0019] As shown in FIG. 1, the far-field image light and the near-field image light irradiated from the image irradiation unit 10 are reflected by the primary mirror 20, the secondary mirror 30, and the windshield WS and reach the viewpoint 40. At this time, the trajectory of the light reaching the viewpoint 40 from the direction of visually recognizing the virtual images P1 and P2 is defined as the reference ray. In other words, this reference ray can be regarded as being substantially the same as the trajectory when the light irradiated from the center of the effective area where the light is emitted in the image irradiation unit 10 reaches the viewpoint 40. The actual image light is irradiated from the image irradiation unit 10 over a predetermined area and is light whose light beam spreads from each position on the display surface, and is condensed or enlarged by the optical power of the reflecting surfaces of the primary mirror 20 and the secondary mirror 30. Therefore, the reference ray shown in FIG. 1 does not indicate the path traveled by the irradiation light in the entire area of the image irradiation unit 10.

[0020] The image irradiation unit 10 is a part that irradiates image light including image information when a signal including image information is supplied from an information processing unit (not shown). Details of the image irradiation unit 10 will be described later. The image light irradiated from the image irradiation unit 10 enters the primary mirror 20. The specific configuration of the image irradiation unit 10 is not limited, and for example, a conventionally known device such as a liquid crystal display device, an organic EL display device, or a combination of a laser light source and an optical modulation element can be used. In the example shown in FIG. 1, a device that irradiates light with a light emitting diode (LED: Light Emitting Diode) from the back side of the liquid crystal display device is used.

[0021] The primary mirror 20 is an optical member on which the image light irradiated from the image irradiation unit 10 is incident and is reflected in the direction of the secondary mirror 30. In the example shown in FIG. 1, a free-form mirror optically designed to project the image light as virtual images P1 and P2 is shown as the primary mirror 20. Details of the reflecting surface of the primary mirror 20 will be described later, but it has a concave shape in the short side direction (the first direction) which is the height direction and a convex shape in the long side direction (the second direction) which is the width direction, that is, a saddle shape. Also, the reflecting surface of the primary mirror 20 is set such that only the y-axis component is intermediate-imaged before reaching the secondary mirror 30.

[0022] The secondary mirror 30 is an optical member onto which the image light reflected by the primary mirror 20 is incident and which reflects the light in the direction of the windshield WS. In the example shown in FIG. 1, the secondary mirror 30 is a free-form surface mirror with a concave shape that is optically designed to project the image light as virtual images P1 and P2. The reflecting surface of the secondary mirror 30 has different focal lengths in the x-axis component and the y-axis component in the plane, and is set such that the x-axis component and the y-axis component of the irradiated light are imaged at the same position after being reflected by the secondary mirror 30.

[0023] The windshield WS is provided in front of the driver's seat of the vehicle and functions as an optical member that reflects the image light incident from the secondary mirror 30 in the direction of the viewing point 40 on the inner surface of the vehicle and transmits the light from the outside of the vehicle in the direction of the viewing point 40. Therefore, the windshield WS corresponds to the display unit in the present invention. Here, an example in which the windshield WS is used as the display unit is shown, but a combiner may be prepared as the display unit separately from the windshield WS, and the light from the secondary mirror 30 may be reflected in the direction of the viewing point 40. Further, it is not limited to being located in front of the vehicle, and it may be arranged on the side or the rear as long as it projects an image toward the viewing point 40 of the passenger.

[0024] The viewing point 40 is the eye (eyebox) of the driver or passenger of the vehicle. When the image light enters the eyebox and the light reaches the retina, the driver or passenger visually recognizes the formed virtual images P1 and P2.

[0025] The virtual images P1 and P2 are displayed as if they are formed in space when the image light reflected by the windshield WS reaches the viewing point (eyebox) 40 of the driver or the like. The position where the virtual images P1 and P2 are formed is determined by the spreading angle when the light irradiated from the image irradiation unit 10 travels in the direction of the viewing point 40 after being reflected by the primary mirror 20 and the secondary mirror 30. At this time, the driver or passenger at the viewing point 40 recognizes that the virtual images P1 and P2 exist at an imaging position farther from the windshield WS.

[0026] FIG. 2 is a schematic diagram for explaining the structure of the primary mirror 20. FIG. 2(a) is a schematic perspective view, FIG. 2(b) is a cross-sectional view in the horizontal direction, and FIG. 2(c) is a cross-sectional view in the vertical direction. The white arrows shown in FIGS. 2(b) and 2(c) schematically indicate the traveling direction of the image light incident on the primary mirror 20. As shown in FIGS. 2(a) to 2(c), the reflecting surface of the primary mirror 20 is convex in the width direction (second direction) and concave in the height direction (first direction), and has a saddle shape. Therefore, the reflecting surface of the primary mirror 20 provides positive optical power in the height direction and negative optical power in the width direction with respect to the image light.

[0027] FIG. 3 is a schematic diagram showing a configuration example of the image irradiation unit 10. As shown in FIG. 3, the image irradiation unit 10 includes a light source unit 11, an image display unit 12, a first planar mirror 13, and a second planar mirror 14. The image display unit 12 includes a far display region 12a and a near display region 12b. The dashed arrow shown in FIG. 3 schematically indicates the path (reference ray) of the center position of the far image light, and the dashed-dotted arrow schematically indicates the path (reference ray) of the center position of the near image light.

[0028] The light source unit 11 is a part that irradiates the image display unit 12 with irradiation light. In the example shown in FIG. 3, the light source unit 11 is arranged on the back side of the transmissive image display unit 12 to show a configuration in which the irradiation light passes through the image display unit 12. However, it is also possible to irradiate the irradiation light from the display surface side using a reflective image display unit 12. The specific configuration of the light source unit 11 is not limited, and a light emitting diode (LED: Light Emitting Diode) or a laser light source can be used. When an organic EL display device is used as the image display unit 12, the light source unit 11 and the image display unit 12 are integrally configured.

[0029] The image display unit 12 is a part that displays a projection image based on the image information from the control unit. The specific configuration of the image display unit 12 is not limited, and for example, a conventionally known device such as a liquid crystal display device, an organic EL display device, or an optical modulation element can be used. In the example shown in FIG. 3, a liquid crystal display device is used as the image display unit 12. As will be described later, the image display unit 12 includes a far - distance display area 12a and a near - distance display area 12b that respectively display a far - distance image and a near - distance image. The far - distance image displayed in the far - distance display area 12a is irradiated as far - distance image light, and the near - distance image displayed in the near - distance display area 12b is irradiated as near - distance image light. Here, the far - distance display area 12a and the near - distance display area 12b may be configured by different display devices, but it is preferable to use a single display device divided into two areas.

[0030] The first planar mirror 13 is an optical member having a flat reflecting surface. The reflecting surface of the first planar mirror 13 is arranged at a position where the far - distance image light irradiated from the far - distance display area 12a is incident. Also, the reflecting surface of the first planar mirror 13 is arranged to be inclined by a predetermined angle with respect to the far - distance display area 12a, and reflects the incident far - distance image light in the direction of the second planar mirror 14.

[0031] The second planar mirror 14 is an optical member having a flat reflecting surface. The reflecting surface of the second planar mirror 14 is arranged at a position where the far - distance image light reflected by the first planar mirror 13 is incident. Also, the reflecting surface of the second planar mirror 14 is arranged to be inclined by a predetermined angle with respect to the image display unit 12, and reflects the incident far - distance image light in the direction of the primary mirror 20.

[0032] As shown in Fig. 3, the first planar mirror 13 and the second planar mirror 14 are not arranged on the path of the near-field image light irradiated from the near-field display area 12b. Therefore, the near-field image light irradiated from the near-field display area 12b travels in the direction of the primary mirror 20 through the space between the first planar mirror 13 and the second planar mirror 14. While the near-field image light is directly irradiated onto the primary mirror 20, the far-field image light is reflected by the first planar mirror 13 and the second planar mirror 14 and then irradiated onto the primary mirror 20. As a result, an optical path difference occurs between the near-field image light and the far-field image light before they reach the primary mirror 20, and the imaging positions of the virtual images P1 and P2 are different.

[0033] Here, an example using the first planar mirror 13 and the second planar mirror 14 is shown to cause an optical path difference between the near-field image light and the far-field image light, but the specific configuration for causing the optical path difference is not limited. As an example, there are configurations such as using a prism to branch the optical paths of the far-field image light and the near-field image light and changing the optical path lengths after branching, or using a reflecting prism to reflect the far-field image light twice and transmit the near-field image light.

[0034] Fig. 4 is a schematic diagram for explaining the positional relationship among the image irradiation unit 10, the primary mirror 20, and the secondary mirror 30 and the path of the image light. Fig. 4(a) is a side view, and Fig. 4(b) is a top view. The dashed lines shown in Fig. 4 schematically indicate the paths of the light irradiated from the ends of the image irradiation unit 10. Also, the double-headed arrows shown in Fig. 4(a) indicate the distance d1 between the center of the image irradiation unit 10 and the center of the reflecting surface of the primary mirror 20, and the distance d2 between the center of the reflecting surface of the primary mirror 20 and the center of the reflecting surface of the secondary mirror 30.

[0035] As shown in Fig. 4(a), the y-axis component of the image light is reflected by the primary mirror 20, condensed with positive optical power, and intermediate-imaged at the intermediate imaging position f, and then reaches the secondary mirror 30 while expanding. Also, as shown in Fig. 4(b), the x-axis component of the image light is reflected by the primary mirror 20 and expanded with negative optical power and reaches the secondary mirror 30.

[0036] FIG. 5 is a schematic diagram for explaining the parallax caused by aberration. FIG. 5(a) shows the horizontal parallax, and FIG. 5(b) shows the vertical parallax. When aberration occurs, the virtual image viewed with the left eye is drawn as a solid line triangle PL, and the virtual image viewed with the right eye is drawn as a dashed-dotted line triangle PR. Also, the virtual image in the ideal case where no aberration occurs and can be viewed at the same position with both eyes is drawn as a dashed line triangle PI.

[0037] As shown in FIGS. 5(a) and 5(b), when aberration occurs in the primary mirror 20 and the secondary mirror 30, parallax occurs in the image light reaching the viewpoint 40. When horizontal parallax as shown in FIG. 5(a) occurs, it is possible to eliminate the parallax by changing the convergence angle of both eyes, and the influence of the decrease in visibility is small. However, when vertical parallax as shown in FIG. 5(b) occurs, it is difficult to eliminate the parallax by the operation of both eyes, and the influence of the decrease in visibility is large.

[0038] In the image projection apparatus 100 of the present embodiment, since the reflecting surface of the primary mirror 20 has a saddle shape that is convex in the width direction and concave in the height direction, the aberration in the width direction is reduced, and the design freedom of the secondary mirror 30 is improved. Thereby, when designing the reflecting surface of the secondary mirror 30, it is possible to prioritize aberration correction in the height direction and improve the aberration correction accuracy in the height direction.

[0039] Also, since the primary mirror 20 has a saddle shape and the aberration correction accuracy in the height direction is improved, even if the distance d1 from the image irradiation unit 10 to the primary mirror 20 is reduced, the aberration can be corrected well. Therefore, by making the distance d1 smaller than the distance d2 and satisfying the relationship d1 < d2, the image projection apparatus 100 can be made smaller and thinner.

[0040] Further, although the specific lengths of the distances d1 and d2 are not limited, the distance d1 from the image irradiation unit 10 to the primary mirror 20 is preferably in the range of 30 mm or more and 100 mm or less, and more preferably in the range of 50 mm or more and 70 mm or less. When the distance d1 is smaller than these ranges, the angle at which the image light irradiated from the image irradiation unit 10 expands over the entire reflecting surface of the primary mirror 20 becomes large, making aberration correction difficult. When the distance d1 is larger than these ranges, it becomes difficult to reduce the size and thickness of the image projection apparatus 100.

[0041] In the present embodiment, the far-field image light is irradiated from the far-field display area 12a, and the near-field image light is irradiated from the near-field display area 12b. Further, the positions where the far-field image light and the near-field image light are incident on the reflecting surface of the primary mirror 20 are different in the height direction. Therefore, at least one of the positions where the far-field image light and the near-field image light are reflected deviates from the central positions of the primary mirror 20 and the secondary mirror 30, and the aberration in the height direction tends to increase. However, by making the primary mirror 20 have a saddle shape and improving the accuracy of aberration correction in the height direction, the parallax generated in the virtual images P1 and P2 can be reduced, and the visibility can be improved.

[0042] As described above, in the image projection apparatus 100 of the present embodiment, the reflecting surface of the primary mirror 20 has a saddle shape that is concave in the first direction and convex in the second direction. Since the image light reflected by the primary mirror 20 is reflected by the secondary mirror 30, it is possible to improve the correction accuracy of aberration and improve the visibility of the virtual images P1 and P2 formed. (Second Embodiment)

[0043] Next, a second embodiment of the present invention will be described. Descriptions of the contents overlapping with the first embodiment will be omitted. In the first embodiment, the far-field image light and the near-field image light are irradiated from the image irradiation unit 10 to form two virtual images P1 and P2 at different imaging positions. However, it is also possible to irradiate only one image light to form one virtual image.

[0044] Even in the image projection apparatus 100 of the present embodiment, the reflecting surface of the primary mirror 20 has a saddle shape that is concave in the first direction and convex in the second direction. Since the image light reflected by the primary mirror 20 is reflected by the secondary mirror 30, it is possible to improve the correction accuracy of aberration and improve the visibility of the virtual image to be formed.

[0045] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope indicated by the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

Explanation of Reference Numerals

[0046] 100... Image projection apparatus 10... Image irradiation unit 20... Primary mirror 30... Secondary mirror 40... Viewpoint 11... Light source unit 12... Image display unit 12a... Distant display area 12b... Near display area 13... First planar mirror 14... Second planar mirror

Claims

1. An image projection device that projects image light onto a display unit for displaying a virtual image, an image irradiating unit that irradiates the image light; a primary mirror that reflects the image light incident from the image irradiation unit; a secondary mirror that reflects the image light incident from the primary mirror, 11. An image projection device, comprising: a reflecting surface of the primary mirror having a saddle shape that is concave in a first direction and convex in a second direction.

2. 2. The image projection device according to claim 1, An image projection device, characterized in that the image light reflected by the primary mirror has a component in the first direction formed as an intermediate image between the primary mirror and the secondary mirror.

3. 2. The image projection device according to claim 1, 13. An image projection device, comprising: a projection unit for projecting an image from said first mirror to said second mirror; a projection unit for projecting an image from said first mirror to said second mirror;

4. 4. The image projection device according to claim 3, An image projection device, wherein a distance from the image irradiation unit to the primary mirror is in a range of 30 mm to 100 mm.

5. 5. The image projection device according to claim 1, the image irradiating unit irradiates near image light from a near display region and irradiates far image light from a far display region; a first plane mirror that reflects the far-field image light; a second plane mirror that reflects the far-distance image light reflected by the first plane mirror, 13. An image projection device, comprising: said primary mirror receiving said near image light from said near display area; and said second plane mirror receiving said far image light.

Images