Image projection device

Abstract

To provide an image projection device with which it is possible to effectively suppress the temperature rise of an image irradiation unit due to external light and secure visibility when using polarizing sunglasses or the like.SOLUTION: Provided is an image projection device (100) that projects a projection image to a display unit in order to display a virtual image. The image projection device (100) comprises an image irradiation unit (11) that irradiates image light, and an irradiation optical unit (20) that irradiates image light as a projection image in the viewpoint direction via the display unit. The irradiation optical unit (20) is provided with a polarization unit (16) that passes light in the prescribed polarization direction of image light through, the image light irradiated from the irradiation optical unit (20) including P-polarized light for the display unit.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 reflects irradiation light from an image irradiation unit to reach a viewing point.

Background Art

[0002] Conventionally, as a device for displaying various information in a vehicle, an instrument panel that lights up icons has been used. Also, with the increase in the amount of information to be displayed, proposals have 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 vehicle's front glass (windshield), in order for the driver to visually recognize the information displayed on the instrument panel, it is necessary to move the line of sight downward during driving, which is not preferable. Therefore, an image projection device such as a head-up display (hereinafter referred to as HUD: Head Up Display) has been proposed that projects an image onto the front glass so that the driver can read the information when viewing the front of the vehicle.

[0004] FIG. 7 is a schematic diagram showing the configuration of a conventional image projection device. As shown in FIG. 7, the conventional image projection device includes an image irradiation unit 1 and free-form mirrors 2 and 3. In such an image projection device, the image irradiation unit 1 irradiates irradiation light L1 including an image, and the free-form mirrors 2 and 3 reflect the irradiation light L1 so that the image is formed in space through the windshield 4 and reaches the position of the viewing point 5 of the driver or the like. As a result, the driver or the like can recognize that an image is displayed at the imaging position in the depth direction by the irradiation light L1 incident on the viewing point 5.

[0005] However, in the image projection device shown in Figure 7, if sunlight or other external light LO is incident from the outside, the external light LO is focused onto the surface of the image irradiation unit 1 by the free-form mirrors 2 and 3, potentially causing the temperature of the image irradiation unit 1 to rise and degrade. Therefore, a device has been proposed that intermediate imaging of the irradiation light L1 between multiple free-form mirrors 2 and 3 is performed, and a shielding section is placed near the intermediate imaging position to reduce the influence of external light LO reaching the image irradiation unit from the outside. (See, for example, Patent Document 1) [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2017 / 195740 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, in the structure using the light-shielding part described in Patent Document 1, it is unavoidable that ambient light reaches the image illumination part from the space used to secure the optical path of the illumination light, and there were limitations to limiting the incidence of ambient light.

[0008] Furthermore, in the reflection of light by the windshield 4, the reflectivity of the P-polarized component tends to be low, while the reflectivity of the S-polarized component tends to be high. For this reason, the polarization direction of the illumination light L1 emitted from the image illumination unit 1 is set to be S-polarized relative to the windshield 4. As a result, the illumination light L1 that reaches the position of viewpoint 5 will be S-polarized light that does not contain P-polarization.

[0009] However, in environments with strong ambient light (LO) or when driving on snowy roads, passengers may wear polarized sunglasses to view the outside through the windshield 4. In this case, the light reflected by objects outside the vehicle is also S-polarized, and polarized sunglasses are designed to cut S-polarized light and transmit P-polarized light. Therefore, for passengers wearing polarized sunglasses, the S-polarized light of the reflected light L1 from the windshield 4 is cut off by the sunglasses, making it difficult to see the image formed by the light L1.

[0010] Therefore, the present invention has been made in view of the above-mentioned conventional problems, and aims to provide an image projection device that can effectively suppress the temperature rise of the image illumination area due to ambient light, and can also ensure visibility even when using polarized sunglasses or the like. [Means for solving the problem]

[0011] To solve the above problems, the present invention provides an image projection device for projecting a projection image onto a display unit for displaying a virtual image, comprising: an image irradiation unit for irradiating image light; an irradiation optical unit for irradiating the display unit with the image light as the projection image; and a polarization reflection adjustment unit provided on the display unit, wherein the irradiation optical unit includes a polarization unit that transmits light in a predetermined polarization direction of the image light, the image light irradiated from the irradiation optical unit includes P polarization for the display unit, and the polarization reflection adjustment unit has a range in which the reflectance of the P polarization component is greater than or equal to the reflectance of the S polarization component in the range of an incident angle of 20 degrees or more and 40 degrees or less. The polarization reflection adjustment unit is attached to the inner surface of the display unit, and the angle of incidence of the image light to the polarization reflection adjustment unit is in the range of 20 degrees to 40 degrees. It is characterized by the following: Furthermore, in one aspect of the present invention, the polarization reflection adjustment unit has a saturation of 20 or less.

[0012] In the image projection apparatus of the present invention, the illumination optical unit is equipped with a polarization unit and illuminates the display unit with image light containing P-polarization. This effectively suppresses the temperature rise of the image illumination unit by cutting out a portion of the ambient light with the polarization unit, and also ensures visibility even when using polarized sunglasses or the like.

[0013] Also, in one aspect of the present invention, the irradiation optical unit includes a retardation plate on the optical path of the image light.

[0014] Also, in one aspect of the present invention, the retardation plate is disposed on the display unit side with respect to the polarizing unit.

[0015] Also, in one aspect of the present invention, the polarizing unit is disposed on the display unit side with respect to the retardation plate.

[0016] Also, in one aspect of the present invention, the retardation plate is a quarter-wave plate.

[0017] Also, in one aspect of the present invention, the image irradiation unit irradiates the image light including S-polarized light with respect to the display unit, and the retardation plate is a half-wave plate.

[0018] Also, in one aspect of the present invention, the image irradiation unit irradiates the image light including P-polarized light with respect to the display unit, and the polarizing unit transmits the P-polarized light.

[0019] Also, in one aspect of the present invention, the irradiation optical unit includes a reflection unit that reflects the image light irradiated from the image irradiation unit, and the polarizing unit is disposed between the reflection unit and the display unit.

Advantages of the Invention

[0020] In the present invention, it is possible to provide an image projection apparatus that can effectively suppress the temperature rise of the image irradiation unit due to external light and ensure visibility even when using polarized sunglasses or the like.

Brief Description of the Drawings

[0021] [Figure 1] It is a schematic diagram showing the configuration of an image projection apparatus 100 according to the first embodiment. [Figure 2] It is a graph schematically showing an example of the reflection characteristics of P-polarized light and S-polarized light in the polarization reflection adjustment unit 15. [Figure 3]It is a schematic diagram showing the configuration of the image projection device 110 according to the second embodiment. [Figure 4] It is a schematic diagram showing the configuration of the image projection device 120 according to the third embodiment. [Figure 5] It is a schematic diagram showing the configuration of the image projection device 120 according to a modified example of the third embodiment. [Figure 6] It is a schematic diagram showing the configuration of the image projection device 130 according to the fourth embodiment. [Figure 7] It is a schematic diagram showing the configuration of a conventional image projection device.

Embodiments for Carrying Out the Invention

[0022] (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 showing the configuration of the image projection device 100 according to the present embodiment.

[0023] As shown in FIG. 1, the image projection device 100 includes an image irradiation unit 11, free-form mirrors 12 and 13, and a polarization unit 16. The free-form mirrors 12 and 13 and the polarization unit 16 constitute the irradiation optical unit 20 in the present invention. In FIG. 1, the representative optical path of the irradiation light L1 irradiated from the image irradiation unit 11 is schematically shown by a solid line arrow, and the representative optical path of external light LO such as sunlight is shown by a broken line arrow. Further, a vehicle windshield 14 and a polarization reflection adjustment unit 15 are provided outside the image projection device 100, and a driver or the like visually recognizes an image by the irradiation light L1 through the polarization reflection adjustment unit 15 from the position of the viewpoint 5.

[0024] The image illumination unit 11 is a device that emits illumination light (image light) L1 containing image information when a signal containing image information is supplied from an information processing unit (not shown). The illumination light L1 emitted from the image illumination unit 11 is incident on the free-form surface mirror 12. Examples of the image illumination unit 11 include liquid crystal display devices, organic EL display devices, micro-LED display devices, DMDs (Digital Micro-mirror Devices), and projector devices using laser light sources. The illumination light L1 emitted from the image illumination unit 11 is configured to include light that is P-polarized with respect to the windshield 14, as shown by the double-headed arrow in the figure. If the illumination light L1 from the image illumination unit 11 is polarized in a specific direction, the orientation of the display surface of the image illumination unit 11 is set so that its polarization plane is P-polarized with respect to the windshield 14. Examples of the image illumination unit 11 that emits illumination light L1 with a specific polarization include liquid crystal display devices, projector devices using laser light sources, and reflective liquid crystal projector devices.

[0025] The free-form surface mirror 12 is a mirror that receives the illumination light L1 emitted from the image illumination unit 11 and reflects it in the direction of the free-form surface mirror 13. The reflective surface shape of the free-form surface mirror 12 is composed of a free-form surface whose curvature is not constant but changes in two dimensions. In Figure 1, a convex mirror is shown as the shape of the free-form surface mirror 12, but a concave mirror or a plane mirror may also be used.

[0026] The free-form surface mirror 13 is a concave mirror that receives incident light L1 reflected by the free-form surface mirror 12 and reflects it in the direction of the windshield 14 via the polarizing section 16. The reflective surface shape of the free-form surface mirror 13 is composed of a free-form surface whose curvature is not constant but changes in two dimensions. In Figure 1, a concave mirror is shown as the shape of the free-form surface mirror 13, but a convex mirror or a plane mirror may also be used. The free-form surface mirrors 12 and 13 correspond to the reflective sections in this invention.

[0027] The polarizing section 16 is an optical component having optical properties that transmit polarized light in the direction of the transmission axis and block polarized light perpendicular to the direction of the transmission axis, and a known polarizing plate or polarizing film can be used. The polarizing section 16 is positioned between the free-form mirror 13 and the windshield 14. Figure 1 shows an example in which the polarizing section 16 is positioned between the free-form mirror 13 and the windshield 14, but the position of the polarizing section 16 is not limited as long as it is on the optical path of the irradiated light L1 from the polarization reflection adjustment section 15 to the windshield 14. Furthermore, the transmission axis of the polarizing section 16 is positioned to transmit P-polarized light to the windshield 14.

[0028] The windshield 14 is located in front of the driver's seat of the vehicle and transmits light from outside the vehicle in the direction of viewpoint 5. Furthermore, since the windshield 14 transmits at least visible light from outside the vehicle, even when external light LO such as sunlight enters the vehicle from above, the external light LO reaches the polarization section 16 and the free-form mirror 13, as shown by the dashed arrow in Figure 1. In addition, a polarization reflection adjustment section 15 is provided on the inner surface of the windshield 14.

[0029] The polarization reflection adjustment section 15 is an optical element provided on the inner surface of the windshield 14 and has optical properties that reflect the S-polarized and P-polarized components of incident light to an equal degree. Furthermore, the polarization reflection adjustment section 15 has optical properties that the reflectance changes according to the angle of incidence, which is the inclination from the direction perpendicular to the incident surface. In addition, it is preferable that the saturation of the polarization reflection adjustment section 15 is 20 or less. By satisfying this condition in terms of saturation, it is possible to suppress deterioration of the quality of the projected virtual image without degrading the color of the irradiated light L1. In the example shown in Figure 1, the polarization reflection adjustment section 15 is configured as a substantially flat film shape and is attached along the curvature of the inner surface of the windshield 14. Although Figure 1 shows an example in which the polarization reflection adjustment section 15 is provided on a part of the windshield 14, it may also be attached to the front surface of the windshield 14.

[0030] Figure 2 is a schematic graph showing an example of the reflection characteristics of P-polarized and S-polarized light in the polarization reflection adjustment unit 15. The horizontal axis of the graph shows the angle of incidence, with the direction perpendicular to the surface of the polarization reflection adjustment unit 15 being 0 degrees. The vertical axis of the graph shows the reflectance of polarization (P-polarized light) in the in-plane direction including the 0-degree direction and the direction of light incidence, and the reflectance of S-polarized light perpendicular to the P-polarized light. As shown in Figure 2, the polarization reflection adjustment unit 15 has optical characteristics in which the reflectance is low (transmittance is high) for light incident at a small angle of incidence and close to the perpendicular, the reflectance increases (transmittance decreases) as the angle of incidence increases, and the reflectance becomes large above a certain angle of incidence. Also, as shown in Figure 2, the reflectance of P-polarized and S-polarized light is about the same in the polarization reflection adjustment unit 15 in the range of angle of incidence from 20 to 40 degrees.

[0031] As the polarization reflection adjustment unit 15 having optical properties as shown in Figure 2, a laminated film manufactured by Toray Industries, Inc. (product name "PICASUS® VT") or a laminated film described in Japanese Patent Publication No. 2021-54061, etc., can be used. In the example shown in Figure 2, the reflectance approaches its maximum value when the incident angle is around 40 degrees, but the maximum reflectance and the incident angle at which the maximum value is reached are not limited to this.

[0032] Furthermore, although Figure 1 shows an example in which the polarization reflection adjustment unit 15 is attached to the windshield 14 as a display unit, a combiner may be prepared separately as a display unit from the windshield 14, and the polarization reflection adjustment unit 15 may be attached to the inner surface of the combiner to reflect light from the free-form mirror 13 in the direction of the viewpoint. Also, the display unit is not limited to being located in front of the vehicle, but may be placed to the side or rear as long as it projects an image to the viewpoint 5 of the occupant. The viewpoint 5 is the eye (eyebox) of the vehicle's driver or occupant, and when the irradiated light L1 enters the eyebox and the light reaches the retina, the driver or occupant sees the formed virtual image.

[0033] The virtual image is displayed as if it were formed in space when the illuminated light L1 reflected by the polarization reflection adjustment unit 15 reaches the driver's or passenger's viewpoint (eyebox) 5. The position where the virtual image is formed is determined by the angle of spread of the light emitted from the image illumination unit 11 as it travels in the direction of the viewpoint after being reflected by the free-form mirrors 12, 13 and the polarization reflection adjustment unit 15. At this time, the driver or passenger perceives the virtual image as being located at a position farther away from the windshield 14. Here, the position where the virtual image is formed mainly depends on the combined focal length of the free-form mirrors 12 and 13. Even if the windshield 14 is a curved surface rather than a flat surface, the effect of the optical power from the windshield 14 is negligible because its radius of curvature is larger than that of the free-form mirrors 12 and 13.

[0034] As shown in Figure 1, the light L1 emitted from the image illumination unit 11 contains P-polarized light for the windshield 14, and the light L1 reflected by the free-form mirrors 12 and 13 also contains P-polarized light. Furthermore, since the polarization unit 16 is positioned to transmit P-polarized light for the windshield 14, the light L1 passes through the polarization unit 16 and reaches the polarization reflection adjustment unit 15. As shown in Figure 2, the polarization reflection adjustment unit 15 has similar reflectivity for S-polarized and P-polarized light, so the P-polarized component of the light L1 is also well reflected and reaches the viewpoint 5. Therefore, the virtual image is projected by P-polarized light, making it easily visible even when the rider is wearing polarized sunglasses. Here, as shown in Figure 2, the polarization reflection adjustment unit 15 has a small difference in reflectivity between S-polarized and P-polarized light in the range of incident angles of 20 to 40 degrees, so it is preferable to set the incident angle of the light L1 emitted from the polarization reflection adjustment unit 15 to 20 to 40 degrees.

[0035] As shown in Figure 1, ambient light LO, such as sunlight, enters from above the windshield 14, and a portion of it passes through the polarization reflection adjustment section 15 and the polarization section 16, is reflected by the free-form mirror 13 and the free-form mirror 12, and reaches the image illumination section 11. Here, ambient light LO entering from outside the vehicle is unpolarized, containing components of all polarization directions, but only the P-polarized component can pass through the polarization section 16 to the windshield 14. Therefore, the S-polarized component of the ambient light LO is cut off by the polarization section 16, and the amount of light reaching the image illumination section 11 can be suppressed. This suppresses the temperature rise caused by ambient light LO reaching the image illumination section 11 and prevents deterioration.

[0036] As described above, in the image projection device 100 of this embodiment, the illumination optical unit 20 is equipped with a polarization unit 16 and projects illumination light L1 containing P polarization onto the display unit. This effectively suppresses the temperature rise of the image illumination unit 11 by cutting off a portion of the ambient light LO with the polarization unit 16, and also ensures visibility even when using polarized sunglasses or the like.

[0037] (Second Embodiment) Next, a second embodiment of the present invention will be described with reference to Figure 3. Content that overlaps with the first embodiment will be omitted from the explanation. Figure 3 is a schematic diagram showing the configuration of the image projection device 110 according to this embodiment. As shown in Figure 3, the image projection device 110 includes an image irradiation unit 11, free-form surface mirrors 12 and 13, a polarizing unit 16, and a quarter-wave plate 17. The free-form surface mirrors 12 and 13, the polarizing unit 16, and the quarter-wave plate 17 constitute the irradiation optical unit 20 in the present invention.

[0038] The quarter-wave plate 17 is an optical element positioned on the optical path of the irradiated light (image light) L1, which generates a phase difference of one-quarter wavelength between the mutually orthogonal fast axis and slow axis, and corresponds to the phase difference plate in the present invention. The quarter-wave plate 17 is preferably positioned on the display side of the polarization unit 16, and in the example shown in Figure 3, it is positioned between the polarization unit 16 and the polarization reflection adjustment unit 15. Furthermore, the fast axis of the quarter-wave plate 17 is positioned so as to be 45 degrees different from the S-polarization component and P-polarization component of the irradiated light L1, respectively.

[0039] As shown in Figure 3, in the image projection device 110 of this embodiment, the light L1 emitted from the image irradiation unit 11 contains S-polarized light for the windshield 14, and the light L1 reflected by the free-form mirrors 12 and 13 also contains S-polarized light. Furthermore, since the polarization unit 16 is arranged to transmit S-polarized light for the windshield 14, the light L1 passes through the polarization unit 16, then through the quarter-wave plate 17, and finally reaches the polarization reflection adjustment unit 15. In the quarter-wave plate 17, the polarization direction of the S-polarized light and the fast axis are 45 degrees apart, so the light L1 emitted after passing through the quarter-wave plate 17 becomes circularly polarized light C. Circularly polarized light C is light in which the P-polarized and S-polarized components are shifted by a quarter wavelength, and therefore contains P-polarized light.

[0040] As shown in Figure 2, the polarization reflection adjustment unit 15 has similar reflectivity for S-polarized and P-polarized light. Therefore, the circularly polarized light L1 is reflected well in both its P-polarized and S-polarized components and reaches the viewpoint 5. Consequently, the virtual image is projected by the circularly polarized light C. At this time, the light L1 is S-polarized and the polarization unit 16 transmits S-polarized light, so even if the light L1 passes through the polarization unit 16 and the quarter-wave plate 17, no specific polarization component is cut off. Since polarized sunglasses transmit circularly polarized light C, the virtual image can be clearly seen even if the passenger is wearing polarized sunglasses.

[0041] As shown in Figure 3, ambient light LO, such as sunlight, enters from above the windshield 14, and a portion of it passes through the polarization reflection adjustment section 15, the quarter-wave plate 17, and the polarization section 16, and is reflected by the free-form mirror 13 and the free-form mirror 12 before reaching the image illumination section 11. Here, ambient light LO entering from outside the vehicle is unpolarized, containing components of all polarization directions, and remains unpolarized even after passing through the quarter-wave plate 17. Furthermore, the polarization section 16 can only transmit the S-polarized component to the windshield 14. Therefore, the P-polarized component of the ambient light LO is cut off by the polarization section 16, suppressing the amount of light reaching the image illumination section 11. This suppresses the temperature rise caused by ambient light LO reaching the image illumination section 11, thereby preventing deterioration.

[0042] Figure 3 shows an example where S-polarized light L1 is emitted from the image illumination unit 11 and transmitted through the polarization unit 16. However, the polarization direction is not limited as long as the polarization of the emitted light L1 can be converted to circularly polarized light C by the quarter-wave plate 17. For example, even if P-polarized light L1 is emitted from the image illumination unit 11 and transmitted through the polarization unit 16, the emitted light L1 will pass through the quarter-wave plate 17 and become circularly polarized light C, allowing the virtual image to be clearly seen even through polarized sunglasses.

[0043] As described above, in the image projection device 110 of this embodiment, the illumination optical unit 20 is equipped with a polarization unit 16 and a quarter-wave plate 17, and projects the illumination light L1 onto the display unit as circularly polarized light C containing P polarization. This effectively suppresses the temperature rise of the image illumination unit 11 by cutting off a portion of the ambient light LO with the polarization unit 16, and also ensures visibility even when using polarized sunglasses or the like.

[0044] (Third embodiment) Next, a third embodiment of the present invention will be described with reference to Figure 4. Details that overlap with the first embodiment will be omitted. Figure 4 is a schematic diagram showing the configuration of the image projection device 120 according to this embodiment. As shown in Figure 4, the image projection device 120 includes an image irradiation unit 11, free-form surface mirrors 12 and 13, a polarizing unit 16, and a half-wave plate 18. The free-form surface mirrors 12 and 13, the polarizing unit 16, and the half-wave plate 18 constitute the irradiation optical unit 20 in the present invention.

[0045] The half-wave plate 18 is an optical element positioned on the optical path of the irradiated light (image light) L1, which generates a phase difference of half a wavelength between the mutually orthogonal fast axis and slow axis, and corresponds to the phase difference plate in the present invention. The half-wave plate 18 is preferably positioned on the display side of the polarization unit 16, and in the example shown in Figure 4, it is positioned between the polarization unit 16 and the polarization reflection adjustment unit 15. Furthermore, the fast axis of the half-wave plate 18 is positioned so as to be 45 degrees different from the S-polarization component and P-polarization component of the irradiated light L1, respectively.

[0046] As shown in Figure 4, in the image projection device 120 of this embodiment, the light L1 emitted from the image irradiation unit 11 contains S-polarized light for the windshield 14, and the light L1 reflected by the free-form mirrors 12 and 13 also contains S-polarized light. Furthermore, since the polarization unit 16 is arranged to transmit S-polarized light for the windshield 14, the light L1 passes through the polarization unit 16, then through the half-wave plate 18, and finally reaches the polarization reflection adjustment unit 15. In the half-wave plate 18, the polarization direction of the S-polarized light and the fast axis are 45 degrees apart, so the light L1 emitted after passing through the half-wave plate 18 becomes P-polarized light.

[0047] As shown in Figure 2, the polarization reflection adjustment unit 15 has similar reflectivity for S-polarized and P-polarized light. Therefore, the P-polarized component of the irradiated light L1 is well reflected and reaches viewpoint 5. Consequently, the virtual image is projected by P-polarized light. Since polarized sunglasses transmit P-polarized light, the virtual image can be clearly seen even when the passenger is wearing polarized sunglasses.

[0048] As shown in Figure 4, ambient light LO, such as sunlight, enters from above the windshield 14, and a portion of it passes through the polarization reflection adjustment section 15, the half-wave plate 18, and the polarization section 16, and is reflected by the free-form mirror 13 and the free-form mirror 12 before reaching the image illumination section 11. Here, ambient light LO entering from outside the vehicle is unpolarized, containing components of all polarization directions, and remains unpolarized even after passing through the half-wave plate 18. Furthermore, the polarization section 16 can only transmit the S-polarized component to the windshield 14. Therefore, the P-polarized component of the ambient light LO is cut off by the polarization section 16, and the amount of light reaching the image illumination section 11 can be suppressed. This suppresses the temperature rise caused by ambient light LO reaching the image illumination section 11, thereby preventing deterioration.

[0049] As described above, in the image projection device 120 of this embodiment, the illumination optical unit 20 is equipped with a polarization unit 16 and a half-wave plate 18, and projects P-polarized illumination light L1 onto the display unit. This effectively suppresses the temperature rise of the image illumination unit 11 by cutting off a portion of the ambient light LO with the polarization unit 16, and also ensures visibility even when using polarized sunglasses or the like.

[0050] (Modified version of the third embodiment) Next, a modified example of the third embodiment of the present invention will be described with reference to Figure 5. Figure 5 is a schematic diagram showing the configuration of the image projection device 120 according to this modified example. In this modified example, the half-wave plate 18 is placed between the polarizing section 16 and the free-form mirror 13, and the polarizing section 16 is arranged to transmit P-polarized light to the windshield 14, which is different from the third embodiment.

[0051] As shown in Figure 5, in the image projection device 120 of this embodiment, the light L1 emitted from the image irradiation unit 11 contains S-polarized light for the windshield 14, and the light L1 reflected by the free-form mirrors 12 and 13 also contains S-polarized light. In the half-wave plate 18, the polarization direction of the S-polarized light and the fast axis are 45 degrees apart, so the light L1 transmitted through the half-wave plate 18 becomes P-polarized light. Since the polarization unit 16 is arranged to transmit P-polarized light for the windshield 14, the light L1 passes through the polarization unit 16 before reaching the polarization reflection adjustment unit 15.

[0052] As shown in Figure 2, the polarization reflection adjustment unit 15 has similar reflectivity for S-polarized and P-polarized light. Therefore, the P-polarized component of the irradiated light L1 is well reflected and reaches viewpoint 5. Consequently, the virtual image is projected by P-polarized light. Since polarized sunglasses transmit P-polarized light, the virtual image can be clearly seen even when the passenger is wearing polarized sunglasses.

[0053] As shown in Figure 5, ambient light LO, such as sunlight, enters from above the windshield 14, and a portion of it passes through the polarization reflection adjustment unit 15, the polarization unit 16, and the half-wave plate 18, and is reflected by the free-form mirror 13 and the free-form mirror 12 before reaching the image illumination unit 11. Here, in the polarization unit 16, only the P-polarized component can be transmitted to the windshield 14. Therefore, the S-polarized component of the ambient light LO is cut off by the polarization unit 16, and the amount of light reaching the image illumination unit 11 can be suppressed. Here, the P-polarized light that has passed through the polarization unit 16 is converted to S-polarized light after passing through the half-wave plate 18, but the amount of light does not change significantly. This suppresses the temperature rise caused by ambient light LO reaching the image illumination unit 11 and prevents degradation.

[0054] As described above, in this modified image projection device 120, the illumination optical unit 20 is equipped with a half-wave plate 18 and a polarization unit 16, and projects P-polarized illumination light L1 onto the display unit. This effectively suppresses the temperature rise of the image illumination unit 11 by cutting off a portion of the ambient light LO with the polarization unit 16, and also ensures visibility even when using polarized sunglasses or the like.

[0055] (Fourth Embodiment) Next, a fourth embodiment of the present invention will be described with reference to Figure 6. Content that overlaps with the first embodiment will be omitted from the explanation. Figure 6 is a schematic diagram showing the configuration of the image projection device 130 according to this embodiment. As shown in Figure 6, the image projection device 130 includes an image irradiation unit 11, free-form surface mirrors 12 and 13, a polarization unit 16, and a phase difference plate 19. The free-form surface mirrors 12 and 13, the polarization unit 16, and the phase difference plate 19 constitute the irradiation optical unit 20 in the present invention.

[0056] The phase difference plate 19 is an optical element positioned on the optical path of the irradiated light (image light) L1, and generates a phase difference between the mutually orthogonal fast axis and slow axis. The phase difference plate 19 is preferably positioned on the display side of the polarization unit 16, and in the example shown in Figure 6, it is positioned between the polarization unit 16 and the polarization reflection adjustment unit 15. Furthermore, the fast axis of the phase difference plate 19 is preferably positioned so as to be 45 degrees different from the S-polarization component and P-polarization component of the irradiated light L1, but the angle is not limited.

[0057] As shown in Figure 6, in the image projection device 130 of this embodiment, the light L1 emitted from the image irradiation unit 11 contains S-polarized light for the windshield 14, and the light L1 reflected by the free-form mirrors 12 and 13 also contains S-polarized light. Furthermore, since the polarization unit 16 is arranged to transmit S-polarized light for the windshield 14, the light L1 passes through the polarization unit 16, then through the phase difference plate 19, and finally reaches the polarization reflection adjustment unit 15. In the phase difference plate 19, the polarization direction and the fast axis are different for S-polarized light, so the light L1 that passes through the phase difference plate 19 becomes elliptically polarized light E. Elliptically polarized light E is light in which the phases of the P-polarized component and the S-polarized component are shifted, and therefore contains P-polarized light.

[0058] As shown in Figure 2, the polarization reflection adjustment unit 15 has similar reflectivity for S-polarized and P-polarized light. Therefore, the elliptically polarized light L1 is reflected well in both its P-polarized and S-polarized components and reaches the viewpoint 5. Consequently, the virtual image is projected by the elliptically polarized light E. Since polarized sunglasses transmit the elliptically polarized light E, the virtual image can be clearly seen even when the passenger is wearing polarized sunglasses.

[0059] As shown in Figure 6, ambient light LO, such as sunlight, enters from above the windshield 14, and a portion of it passes through the polarization reflection adjustment unit 15, the phase difference plate 19, and the polarization unit 16, and is reflected by the free-form mirror 13 and the free-form mirror 12 before reaching the image illumination unit 11. Here, ambient light LO entering from outside the vehicle is unpolarized, containing components of all polarization directions, and remains unpolarized even after passing through the phase difference plate 19. Furthermore, the polarization unit 16 can only transmit the S-polarized component to the windshield 14. Therefore, the P-polarized component of the ambient light LO is cut off by the polarization unit 16, and the amount of light reaching the image illumination unit 11 can be suppressed. This suppresses the temperature rise caused by ambient light LO reaching the image illumination unit 11 and prevents deterioration.

[0060] Figure 6 shows an example where S-polarized light L1 is emitted from the image illumination unit 11 and transmitted through the polarization unit 16. However, the polarization direction is not limited as long as the polarization of the emitted light L1 can be converted to elliptical polarization E by the phase difference plate 19. For example, even if P-polarized light L1 is emitted from the image illumination unit 11 and transmitted through the polarization unit 16, the emitted light L1 will pass through the phase difference plate 19 and become elliptical polarization E, allowing the virtual image to be clearly seen even through polarized sunglasses.

[0061] As described above, in the image projection device 130 of this embodiment, the illumination optical unit 20 is equipped with a polarization unit 16 and a phase difference plate 19, and projects illumination light L1 onto the display unit as elliptical polarization E including P polarization. This effectively suppresses the temperature rise of the image illumination unit 11 by cutting off a portion of the ambient light LO with the polarization unit 16, and also ensures visibility even when using polarized sunglasses or the like.

[0062] (Fifth embodiment) Next, a fifth embodiment of the present invention will be described. In the first to fourth embodiments, the polarization reflection adjustment unit 15 was used as an optical characteristic that reflected the S-polarized and P-polarized components of incident light to an equal degree. However, a polarization reflection adjustment unit 15 having optical characteristics that reflect the P-polarized component with a higher reflectivity than the S-polarized component may also be used.

[0063] In the examples shown in Figures 1, 4, and 5, the illumination light irradiated onto the windshield 14 from the image projection device is P-polarized. In the example shown in Figure 6, elliptical polarization is used as the illumination light, and it is possible to make it elliptically polarized so that the P-polarization component is larger than the S-polarization component. Therefore, even when using a polarization reflection adjustment unit 15 that reflects the P-polarization component with a higher reflectivity than the S-polarization component, it is possible to project an image with a highly reflective P-polarization component, and visibility can be ensured even when using polarized sunglasses, etc.

[0064] The present invention is not limited to the embodiments described above, 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]

[0065] 100, 110, 120, 130… Image projection devices 11…Image illumination area 12,13…Freeform surface mirrors 14... Windshield 15...Polarized reflection adjustment section 16…Polarization part 17... Quarter-wave plate 18... Half-wave plate 19...Retardation plate 20...Irradiation optical section

Claims

1. An image projection device that projects a projected image onto a display unit for displaying a virtual image, An image illumination unit that emits image light, An illumination optical unit that irradiates the display unit with the image light as the projected image, The display unit is provided with a polarization reflection adjustment unit, The illumination optical unit includes a polarization unit that transmits light in a predetermined polarization direction of the image light, The image light emitted from the illumination optical unit includes P-polarized light for the display unit. The polarization reflection adjustment unit has a range in which the reflectance of the P polarization component is equal to or greater than the reflectance of the S polarization component in the range of incident angles of 20 degrees to 40 degrees. The polarization reflection adjustment unit is attached to the inner surface of the display unit. An image projection device characterized in that the angle of incidence of the image light to the polarization reflection adjustment unit is in the range of 20 degrees to 40 degrees.

2. An image projection device according to claim 1, The image projection apparatus is characterized in that the polarization reflection adjustment unit has a saturation of 20 or less.

3. An image projection apparatus according to claim 1 or 2, The image projection device is characterized in that the illumination optical unit includes a phase difference plate in the optical path of the image light.

4. The image projection apparatus according to claim 3, The image projection apparatus is characterized in that the phase difference plate is positioned on the display side of the polarization unit.

5. The image projection apparatus according to claim 3, The image projection apparatus is characterized in that the polarization portion is positioned on the display portion side of the phase difference plate.

6. An image projection device according to any one of claims 3 to 5, The image projection apparatus is characterized in that the phase difference plate is a quarter-wave plate.

7. An image projection device according to any one of claims 3 to 5, The image illumination unit illuminates the display unit with the image light containing S-polarization, The image projection apparatus is characterized in that the phase difference plate is a half-wave plate.

8. An image projection apparatus according to claim 1 or 2, The image illumination unit illuminates the display unit with image light containing P-polarized light, The image projection device is characterized in that the polarizing portion transmits the P-polarized light.

9. An image projection device according to any one of claims 1 to 8, The illumination optical unit includes a reflecting unit that reflects the image light emitted from the image illumination unit, The image projection device is characterized in that the polarization unit is arranged between the reflective unit and the display unit.

Images