Image projection device

Abstract

To provide an image projection device that can be made compact while reducing astigmatism by a display portion.SOLUTION: An image projection device (100) comprises: an image irradiation portion (10) that radiates an image for forming a virtual image (P) as image display light; and a projection optical portion that projects the image display light onto a display portion (WS). The projection optical portion includes: a first concave mirror (20) that reflects the image display light radiated from the image irradiation portion; and a second concave mirror (30) that reflects the image display light reflected by the first concave mirror (20). The curvature of the first concave mirror (20) in a predetermined direction is greater than the curvature of the second concave mirror (30) in the predetermined direction. A component of the image display light in the predetermined direction forms an intermediate image between the first concave mirror (20) and the second concave mirror (30). The optical path length from the image irradiation portion (10) to the second concave mirror (30) at the center position of the image display light is greater than 1 mm and less than 130 mm.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 projects a projection image onto a display unit for displaying a virtual image. [Background technology]

[0002] Conventionally, dashboards that light up icons have been used as devices for displaying various types of information inside a vehicle. As the amount of information to be displayed increases, it has been proposed to embed an image display device in the dashboard or to configure the entire dashboard with an image display device.

[0003] However, since the instrument panel is located below the vehicle's windshield, the driver must move his or her eyes downward while driving in order to see the information displayed on the instrument panel, which is undesirable. Therefore, a head-up display (hereinafter referred to as HUD) has been proposed that projects an image onto the windshield so that the driver can read information when looking ahead of the vehicle (see, for example, Patent Documents 1 and 2).

[0004] In such conventional image projection devices, image display light is projected from an image projection unit onto the vehicle's windshield (display unit), allowing the driver to visually recognize the image display light reflected by the windshield superimposed on the background in front of the vehicle. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-119248 A [Patent Document 2] JP 2019-119262 A Summary of the Invention [Problem to be solved by the invention]

[0006] In such an image projection device, in order to improve the visibility of the image projected through the windshield, a projection optical system such as a concave mirror or a lens is used to enlarge and project the image display light at a desired optical magnification. In addition, the windshield also functions as an optical member having a curvature. Therefore, in order to make the optical path length from the image irradiation unit to the windshield appropriate, it becomes necessary to use multiple mirrors in the projection optical system, which makes it difficult to reduce the size. In addition, the windshield (display unit) generally has different curvatures in the vertical and horizontal directions, which causes the problem of astigmatism.

[0007] SUMMARY OF THE PRESENT DISCLOSURE The present invention has been made in consideration of the above-mentioned problems in the conventional art, and has an object to provide an image projection device that can be made compact while reducing astigmatism caused by a display unit. [Means for solving the problem]

[0008] In order to solve the above problem, the image projection device of the present invention is an image projection device that projects a virtual image via a display unit, and includes an image irradiation unit that irradiates an image for forming the virtual image as image display light, and a projection optical unit that projects the image display light onto the display unit, wherein the projection optical unit includes a first concave mirror that reflects the image display light irradiated from the image irradiation unit, and a second concave mirror that reflects the image display light reflected by the first concave mirror, wherein a curvature of the first concave mirror in a predetermined direction is larger than a curvature of the second concave mirror in the predetermined direction, a component of the image display light in the predetermined direction forms an intermediate image between the first concave mirror and the second concave mirror, and an optical path length from the image irradiation unit to the second concave mirror at a central position of the image display light is greater than 1 mm and smaller than 130 mm.

[0009] In the image projection device of the present invention, the curvature of the first concave mirror in a specified direction is made larger than that of the second concave mirror to form an intermediate image, and the optical path length from the image irradiation unit to the second concave mirror is greater than 1 mm and less than 130 mm, making it possible to reduce the size while reducing astigmatism caused by the display unit.

[0010] In one aspect of the present invention, the predetermined direction is a height direction or a lateral direction of the virtual image.

[0011] In one aspect of the invention, in a region on the display unit where the image display light is irradiated, a curvature in a direction perpendicular to the predetermined direction is larger than a curvature in the predetermined direction.

[0012] In one aspect of the invention, a component of the image display light in a direction perpendicular to the predetermined direction between the first concave mirror and the second concave mirror does not form an intermediate image.

[0013] In addition, in one aspect of the present invention, when the width of the image display light at the imaging position of the virtual image in the specified direction is Y0, the width of the image display light in the image irradiation unit is Y1, the optical path length from the display unit to the imaging position of the virtual image is L0, the optical path length from the second concave mirror to the display unit is L3, and the focal length of the display unit is f, the relationship fY0<(fL3-L0L3-fL0)Y1<130fY0 is satisfied. Effect of the Invention

[0014] The present invention can provide an image projection device that can be made compact while reducing astigmatism caused by a display unit. [Brief description of the drawings]

[0015] [Figure 1] 1 is a schematic diagram illustrating projection of a virtual image P using the image projection device 100 according to the first embodiment. [Diagram 2] 1 is a schematic diagram illustrating intermediate imaging of image display light in an image projection device 100. FIG. [Diagram 3] 2 is a schematic diagram illustrating the optical path length and optical magnification in the image projector 100. FIG. [Figure 4] 11 is a schematic diagram illustrating projection of a virtual image P using an image projection device 200 according to a second embodiment. FIG. [Diagram 5]10 is a schematic diagram illustrating intermediate imaging of image display light in the image projection device 200. FIG. [Figure 6] 2 is a schematic diagram for explaining the optical path length and optical magnification in the image projector 200. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] (First embodiment) Hereinafter, an embodiment 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 given the same reference numerals, and duplicated descriptions are omitted as appropriate. FIG. 1 is a schematic diagram for explaining the projection of a virtual image P using an image projection device 100 according to this embodiment. As shown in FIG. 1, the image display light projected from the image projection device 100 is reflected by a windshield (display unit) WS and irradiated to the driver's viewpoint position. The driver visually recognizes the virtual image P formed on the extension (broken line direction) of the optical path from which the image display light is incident. In this embodiment, an example is shown in which the image projection device 100 projects the image display light to form one virtual image P, but the number of virtual images P is not limited.

[0017] As shown in Fig. 1, the image projection device 100 includes an image projection unit 10, a first concave mirror 20, and a second concave mirror 30. In the image projection device 100, each part is controlled using a control unit (not shown) connected to each part so as to be able to communicate information. The configuration of the control unit is not limited, but an example includes a CPU (Central Processing Unit) for performing information processing, a memory device, a recording medium, an information communication device, and the like. The control unit controls the operation of each part according to a predetermined program, and sends information including an image (image information) to the image projection unit 10.

[0018] The windshield WS is a part provided in front of the driver's seat of the vehicle and transmits visible light. The windshield WS corresponds to the display unit in the present invention because the inner surface of the vehicle reflects the image display light incident from the image projection device 100 toward the viewpoint and transmits light from the outside of the vehicle toward the viewpoint. Here, an example is shown in which the windshield WS is used as the display unit, but a combiner may be prepared as a display unit separate from the windshield WS and may reflect the light from the image projection device 100 toward the viewpoint. In addition, the display unit is not limited to being located in front of the vehicle, and may be located to the side or rear as long as it projects an image toward the passenger's viewpoint EP.

[0019] The curvature of the windshield WS is smaller in a predetermined direction in the virtual image P than in a direction perpendicular to the predetermined direction, and the optical power in the predetermined direction is greater. For example, when the curvature Rv of the windshield WS in the vehicle height direction is smaller than the curvature Rh in the width direction, the predetermined direction is the height direction, and the direction perpendicular to the predetermined direction is the width direction. When the curvature Rv of the windshield WS in the vehicle height direction is larger than the curvature Rh in the width direction, the predetermined direction is the width direction, and the direction perpendicular to the predetermined direction is the height direction.

[0020] The image projection unit 10 is a part that projects light containing an image onto the first concave mirror 20 as image display light based on image information from the control unit. Details of the image projection unit 10 will be described later. The specific configuration of the image projection unit 10 is not limited, and 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 projects light from a light emitting diode (LED) from the rear side of the liquid crystal display device is used.

[0021] The first concave mirror 20 is an optical member that reflects the image display light arriving from the image projection unit 10 toward the second concave mirror 30. In the example shown in Fig. 1, the first concave mirror 20 is a free-form mirror having an optically designed concave shape necessary for projecting the image display light as a virtual image P.

[0022] The second concave mirror 30 is an optical member that reflects the image display light arriving from the first concave mirror 20 toward the windshield WS. In the example shown in Fig. 1, the second concave mirror 30 is a free-form mirror having an optically designed concave shape necessary for projecting the image display light as a virtual image P.

[0023] The curvature of the first concave mirror 20 and the second concave mirror 30 is smaller in a predetermined direction than in a direction perpendicular to the predetermined direction, and the optical power in the predetermined direction is greater. Here, the predetermined direction in the first concave mirror 20 and the second concave mirror 30 corresponds to the predetermined direction in the windshield WS described above. Also, the curvature of the first concave mirror 20 in the predetermined direction is set to be larger than the curvature of the second concave mirror 30 in the predetermined direction.

[0024] The reflecting surfaces of the first concave mirror 20 and the second concave mirror 30 are designed to expand the light diameter in the driver's viewpoint direction in order to project the image display light as a virtual image P through the windshield WS. Here, the expansion of the light diameter in the viewpoint direction includes not only the case where the light diameter expands consistently after reflection, but also the case where the light diameter shrinks and expands after forming an image at an intermediate point. The combination of the first concave mirror 20 and the second concave mirror 30 has the function of projecting the image display light through the windshield WS, and corresponds to the projection optical unit in the present invention.

[0025] The virtual image P is an image that is displayed as if it were formed in space when the image display light reflected by the windshield WS reaches the passenger's viewpoint EP (eyebox). The position where the virtual image P is formed is determined by the combined focal length of the projection optical unit included in the image projection device 100 and the windshield WS.

[0026] Fig. 2 is a schematic diagram for explaining intermediate imaging of the image display light in the image projection device 100. In Fig. 1, the optical path of the image display light is depicted as a single straight arrow. However, the actual image display light is displayed in a predetermined area in the image projection unit 10, and has a predetermined area (width) in the direction perpendicular to the traveling direction.

[0027] As shown in Fig. 2, the image light irradiated from the image irradiation unit 10 reaches the first concave mirror 20. The image display light is reflected by the first concave mirror 20, and the component in the predetermined direction travels while the light diameter is reduced, and an intermediate image is formed at an intermediate imaging position F between the first concave mirror 20 and the second concave mirror 30 (intermediate imaging). After the component in the predetermined direction is imaged at the intermediate imaging position F, the image display light travels while the light diameter is expanded, and reaches the second concave mirror 30. The image display light reflected by the second concave mirror 30 is reflected by the windshield WS and reaches the driver's viewpoint position.

[0028] In the image projection device 100, the component of the image display light in a predetermined direction is intermediately imaged at the intermediate imaging position F, improving the optical freedom in the predetermined direction and reducing astigmatism caused by the difference in curvature between the height direction and the width direction of the windshield WS. In addition, since the light diameter of the component in the predetermined direction becomes small near the intermediate imaging position F, the image projection unit 10 can be arranged close to the vacant space, allowing for effective use of space and miniaturization.

[0029] FIG. 3 is a schematic diagram for explaining the optical path length and optical magnification in the image projection device 100. In the figure, the horizontal axis indicates the optical path length of the image display light, and the vertical axis indicates the horizontal width. Here, the optical path length of the image display light refers to the length of the path of the light at the center position in the height direction and the width direction when the image display light is projected as a virtual image P. In other words, it is the length of the optical path of the light irradiated from the center position of the image display light in the image irradiation unit 10, reflected by the first concave mirror 20, the second concave mirror 30, and the windshield WS, and reaching the driver's viewpoint position. In FIG. 3, the case where the above-mentioned predetermined direction is the height direction is shown and described, but when the predetermined direction is the horizontal direction, the relationship between the height direction and the horizontal direction (width direction) can be considered interchangeably.

[0030] In FIG. 3, the optical path length from the windshield WS to the viewpoint EP is L1. The distance from the windshield WS to the imaging position of the virtual image P is L0. The optical path length from the image projection unit 10 to the second concave mirror 30 after being reflected by the first concave mirror 20 is L2. The optical path length from the second concave mirror 30 to the windshield WS is L3. The width of the image projection light at the imaging position of the virtual image P is Y0. The width of the image projection light immediately after being irradiated from the image projection unit 10 is Y1. Assuming that the image projection light reflected by the second concave mirror 30 is not incident on the windshield WS and is imaged, the distance to the virtual imaging position is L, and the width of the image projection light at the virtual imaging position is Y0'.

[0031] In the image projector 100 of this embodiment, the curvature in a predetermined direction of the first concave mirror 20 is larger than the curvature of the second concave mirror 30, and an intermediate image is formed. In the case of having such a projection optical system, by setting the optical path length L2 from the image projection unit 10 to the second concave mirror 30 in the range of more than 1 mm and less than 130 mm, it is possible to reduce the size while reducing the astigmatism caused by the windshield WS.

[0032] In addition, if the focal length of the windshield WS is f and the lateral magnification is m, then (Formula 1) m=Y0 / Y0' By transforming Equation 1, we get (Formula 2) Y0'=Y0 / m=fY0 / (L0-f) Furthermore, if the lateral magnification of the second concave mirror 30 is m', then (Formula 3) m'=Y0' / Y1=L / L2 Transforming Equation 3 gives us (Formula 4) L=L2Y0' / Y1 The lens formula for the windshield WS is: (Formula 5) 1 / L0+1 / (L+L3)=1 / f Therefore, by transforming Equation 4, we get (Formula 6) L={f(L3-L0)-L0L3} / (f-L0)=L3-fL0 / (f-L0) Furthermore, from Equation 2 and Equation 4, (Formula 7) L=L2fY0 / Y1(L0-f)=L3-fL0 / (f-L0) Further transforming Equation 7 gives us (Formula 8) L2=(fL3-L0L3-fL0)Y1 / fY0 Satisfy the relationship.

[0033] Therefore, in a predetermined direction, the optical path length at the image formation position of the image projection unit 10, the first concave mirror 20, the second concave mirror 30, the windshield WS, and the virtual image P is given by (Formula 9) fY0<(fL3-L0L3-fL0)Y1<130fY0 By satisfying this relationship, the curvature of the first concave mirror 20 in a predetermined direction is larger than the curvature of the second concave mirror 30, and in the projection optical system that forms an intermediate image, it is possible to reduce the size while reducing astigmatism caused by the display unit.

[0034] As described above, in the image projection device 100 of this embodiment, the curvature in a specified direction of the first concave mirror 20 is made larger than that of the second concave mirror 30 to form an intermediate image, and the optical path length L2 from the image irradiation unit 10 to the second concave mirror 30 is greater than 1 mm and less than 130 mm, thereby making it possible to achieve compactness while reducing astigmatism due to the windshield WS.

[0035] Second embodiment Next, a second embodiment of the present invention will be described with reference to Figs. 4 to 6. Description of contents overlapping with the first embodiment will be omitted. Fig. 4 is a schematic diagram for explaining the projection of a virtual image P using an image projection device 200 according to this embodiment. As shown in Fig. 4, the image projection device 200 includes an image projection unit 10, a lens 40, and a second concave mirror 30.

[0036] The lens 40 is an optical member that transmits the image display light irradiated from the image irradiation unit 10 and refracts the light with a predetermined optical power. The image display light transmitted through the lens 40 reaches the second concave mirror 30. The specific configuration of the lens 40 is not limited, but a convex lens having a positive optical power and converging the image irradiation light can be used. The combination of the lens 40 and the second concave mirror 30 has a function of projecting the image display light through the windshield WS, and corresponds to the projection optical unit in the present invention.

[0037] 5 is a schematic diagram for explaining intermediate imaging of the image display light in the image projection device 200. As shown in FIG. 5, the image light irradiated from the image irradiation unit 10 reaches the lens 40. The image display light also passes through the lens 40, and the component in a predetermined direction travels while the light diameter is reduced, and an intermediate image is formed at an intermediate imaging position F between the lens 40 and the second concave mirror 30 (intermediate imaging). After the component in the predetermined direction is imaged at the intermediate imaging position F, the image display light travels while the light diameter is expanded, and reaches the second concave mirror 30. The image display light reflected by the second concave mirror 30 is reflected by the windshield WS and reaches the driver's viewpoint position.

[0038] FIG. 6 is a schematic diagram for explaining the optical path length and optical magnification in the image projection device 200. In FIG. 6, the optical path length from the windshield WS to the viewpoint EP is L1. The distance from the windshield WS to the imaging position of the virtual image P is L0. The optical path length from the image projection unit 10 to the second concave mirror 30 after being refracted by the lens 40 is L2. The optical path length from the second concave mirror 30 to the windshield WS is L3. The width of the image projection light at the imaging position of the virtual image P is Y0. The width of the image projection light immediately after being irradiated from the image projection unit 10 is Y1. Assuming that the image projection light reflected by the second concave mirror 30 does not enter the windshield WS and forms an image, the distance to the virtual imaging position is L, and the width of the image projection light at the virtual imaging position is Y0'. Although an example using a combination of lens 40 and second concave mirror 30 has been shown here, the second concave mirror 30 may be replaced with a convex lens, and image illumination light may be irradiated onto the windshield WS using a combination of lens 40 and a convex lens.

[0039] In the image projector 200 of this embodiment, the intermediate image is formed by refracting the image display light by the lens 40. When such a projection optical system is used, the optical path length L2 from the image projection unit 10 to the second concave mirror 30 is set in the range of more than 1 mm and less than 130 mm, thereby making it possible to reduce the size while reducing the astigmatism caused by the windshield WS.

[0040] Furthermore, in the image projection device 200 of this embodiment, by satisfying the relationship of Equation 9, the curvature in a specified direction of the first concave mirror 20 is greater than the curvature of the second concave mirror 30, and in the projection optical system that forms an intermediate image, it is possible to reduce the astigmatism caused by the display unit while achieving miniaturization.

[0041] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of 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 symbols]

[0042] 100,200...Image projection device 10...Image irradiation unit 20…First concave mirror 30…Second concave mirror 40…Lens WS…Windshield P...Virtual image

Claims

1. An image projection device that projects a virtual image through a display unit, an image irradiating unit that irradiates an image for forming the virtual image as image display light; a projection optical unit that projects the image display light onto the display unit, The projection optical unit includes: a first concave mirror that reflects the image display light emitted from the image irradiation unit; a second concave mirror that reflects the image display light reflected by the first concave mirror, a curvature of the first concave mirror in a predetermined direction is greater than a curvature of the second concave mirror in the predetermined direction, a component of the image display light in the predetermined direction forms an intermediate image between the first concave mirror and the second concave mirror, an optical path length from said image projection unit to said second concave mirror at a central position of said image display light being greater than 1 mm and smaller than 130 mm;

2. 2. The image projection device according to claim 1, 13. An image projection device, wherein the predetermined direction is a height direction or a lateral direction of the virtual image.

3. 2. The image projection device according to claim 1, In a region on the display unit where the image display light is irradiated, 13. An image projection device, comprising: an image projection device having a curvature in a direction perpendicular to the predetermined direction that is greater than a curvature in the predetermined direction.

4. 2. The image projection device according to claim 1, an intermediate image is not formed between the first concave mirror and the second concave mirror by a component of the image display light in a direction perpendicular to the predetermined direction;

5. 2. The image projection device according to claim 1, In the predetermined direction, The width of the image display light at the imaging position of the virtual image is defined as Y ０ year, The width of the image display light in the image irradiation unit is defined as Y １ year, The optical path length from the display unit to the imaging position of the virtual image is L ０ year, The optical path length from the second concave mirror to the display unit is L ３ year, When the focal length of the display unit is f, fY ０ <(fL ３ -L ０ L ３ -fL ０ )Y １ <130fY ０ An image projection device, characterized in that the following relationship is satisfied.

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