Image projection device

Abstract

To provide an image projection device capable of heightening the use efficiency of irradiation light.SOLUTION: Provided is an image projection device comprising: a light source (11) for irradiating non-polarized irradiation light; an image display unit (18) for receiving irradiation light entered from the rear and emitting image light from a display surface; a reflecting polarization unit (13) for reflecting polarized light in a first direction as first light and passing polarized light in a second direction crossing the first direction through as second light; and a half-wavelength plate (14) located on the optical path of the first light or the second light. The first light is irradiated in a first display region and the second light is irradiated in a second region of the image display unit (18). Assuming that S1 represents the area of the first display region, S2 represents the area of the second display region, Pr represents the reflection rate of the first light in the reflecting polarization unit (13), and Pt represents the transmission rate of the second light, the ratio Pr / Pt is proportionate to the ration S2 / S1.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an image projection device. [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 windshield of the vehicle, passengers such as the driver must move their eyes downward while driving in order to view the information displayed on the instrument panel, which is undesirable. Therefore, image projection devices such as head up displays (hereinafter referred to as HUDs) have been proposed that project images onto the windshield so that passengers can read information when they view the area ahead of the vehicle (see, for example, Patent Documents 1 and 2).

[0004] In the image projection devices of Patent Documents 1 and 2, an image projection unit projects light containing an image, and the light is reflected by a free-form mirror or the like to reach the viewpoint of the passenger so that the image is formed in space via a display unit such as a windshield. This allows the passenger to perceive the image as being displayed at the imaging position in the depth direction by the light incident on the viewpoint. [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 conventional image projection devices, a projection image is displayed using an image display unit such as a liquid crystal display device, and image light is projected by irradiating irradiation light from the rear side of the image display unit. However, since an image display unit such as a liquid crystal display device transmits only polarized light in a specific direction, when unpolarized irradiation light is incident, polarized light in directions other than the specific direction is not used to project the image, and the light utilization efficiency decreases.

[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 capable of improving the utilization efficiency of irradiated light. [Means for solving the problem]

[0008] In order to solve the above problem, the image projection device of the present invention comprises a light source that irradiates unpolarized irradiation light, an image display unit into which the irradiation light enters from the back and which emits image light from a display surface, a reflective polarization unit that reflects light polarized in a first direction as a first light and transmits light polarized in a second direction intersecting the first direction as a second light, and a half-wave plate arranged on the optical path of the first light or the second light, wherein the first light is irradiated onto a first display region of the image display unit and the second light is irradiated onto a second display region, the area of ​​the first display region is S1, the area of ​​the second display region is S2, the reflectance of the first light in the reflective polarization unit is Pr, the transmittance of the second light is Pt, and Pr / Pt is proportional to S2 / S1.

[0009] In such an image projection device of the present invention, the light irradiated from the light source is polarized and separated by a reflective polarizing section, and the polarization direction of one of the separated illumination lights is rotated by a half-wave plate. The ratio Pr / Pt of the reflectance Pr of the first light in the reflective polarizing section to the transmittance Pt of the second light is proportional to the ratio S2 / S1 of the area S1 of the first display area to the area S2 of the second display area, thereby increasing the utilization efficiency of the illumination light and making it possible to align the brightness of the first display area and the second display area.

[0010] In addition, in one aspect of the present invention, the half-wave plate is arranged on the optical path of the first light, and a reflective portion that reflects the second light is provided on the optical path of the second light, and when the transmittance of the half-wave plate is Ph, the reflectance of the reflective portion is Rm, and a constant is α, the relationship Pr / Pt=α·Rm·(1 / Ph)·(S2 / S1) is satisfied.

[0011] In addition, in one aspect of the present invention, the half-wave plate is arranged on the optical path of the second light, and a reflective portion that reflects the second light is provided on the optical path of the second light, and when the reflectance of the reflective portion is Rm, the transmittance of the half-wave plate is Ph, and a constant is α, the relationship Pr / Pt=α·Rm·Ph·(S2 / S1) is satisfied.

[0012] In addition, in one aspect of the present invention, the half-wave plate is arranged on the optical path of the first light, and a reflective portion that reflects the first light is provided on the optical path of the first light, and when the transmittance of the half-wave plate is Ph, the reflectance of the reflective portion is Rm, and a constant is α, the relationship Pr / Pt=α·(1 / Rm)·(1 / Ph)·(S2 / S1) is satisfied.

[0013] In addition, in one aspect of the present invention, the half-wave plate is arranged on the optical path of the second light, and a reflective portion that reflects the first light is provided on the optical path of the first light, and when the reflectance of the reflective portion is Rm, the transmittance of the half-wave plate is Ph, and a constant is α, the relationship Pr / Pt=α·(1 / Rm)·Ph·(S2 / S1) is satisfied.

[0014] In addition, in one embodiment of the present invention, when the solid angle of the first light irradiated from the first display area is ω1 and the solid angle of the second light irradiated from the second display area is ω2, the constant α=ω2 / ω1.

[0015] In one aspect of the invention, the first display area and the second display area are provided adjacent to each other on one image display unit.

[0016] In one aspect of the invention, the first display area and the second display area are provided separately in the single image display section. Effect of the Invention

[0017] The present invention can provide an image projection device capable of improving the efficiency of use of irradiated light. [Brief description of the drawings]

[0018] [Figure 1] FIG. 2 is a schematic diagram illustrating projection of a virtual image using the image projection device 100 according to the first embodiment. [Diagram 2] FIG. 2 is a schematic cross-sectional view illustrating an overview of an image projection unit 10 according to the first embodiment. [Diagram 3] FIG. 11 is a schematic cross-sectional view illustrating an overview of an image projection unit 10 according to a second embodiment. [Figure 4] FIG. 11 is a schematic cross-sectional view illustrating an overview of an image projection unit 10 according to a third embodiment. [Diagram 5] FIG. 11 is a schematic cross-sectional view illustrating an overview of an image projection unit 10 according to a fourth embodiment. [Figure 6] FIG. 13 is a schematic cross-sectional view illustrating an overview of an image projection unit 10 according to a fifth embodiment. [Figure 7] FIG. 13 is a schematic cross-sectional view illustrating an overview of an image projection unit 10 according to a sixth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] (First embodiment) Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The same or equivalent components, parts, and processes shown in each drawing are given the same reference numerals, and duplicated explanations will be omitted as appropriate. In the following explanation, an image projection device 100 according to the present invention will be described by taking as an example a form in which it is applied to a HUD mounted on a vehicle or the like.

[0020] FIG. 1 is a schematic diagram for explaining the projection of a virtual image using an image projection device 100 according to this embodiment. The dashed line in FIG. 1 indicates the optical path of a first image light L1, which will be described later, and the dashed line indicates the optical path of a second image light L2. As shown in FIG. 1, the first image light L1 and the second image light L2 projected from the image projection device 100 are reflected by a windshield (display unit) WS and irradiated to the driver's viewpoint position. The driver visually recognizes virtual images P1 and P2 formed on the extension of the optical path on which the first image light L1 and the second image light L2 are incident. In this embodiment, an example is shown in which the image projection device 100 projects the first image light L1 and the second image light L2 to form two images P1 and P2, but the number of virtual images is not limited.

[0021] The windshield WS is a part provided in front of the driver's seat of the vehicle and transmits visible light. The windshield WS reflects the first image light L1 and the second image light L2 incident from the image projection device 100 toward the viewpoint direction on the inner surface of the vehicle and transmits light from the outside of the vehicle toward the viewpoint direction, and therefore corresponds to the display unit in the present invention. 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 light from the image projection device 100 toward the viewpoint direction. 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 viewpoint of the passenger.

[0022] The virtual images P1 and P2 are images that are displayed as if they were formed in space when the first image light L1 and the second image light L2 reflected by the windshield WS reach the viewpoint (eyebox) of the passenger. The positions at which the virtual images P1 and P2 are formed depend on the composite focal length of the projection optical unit included in the image projection device 100 and the windshield WS.

[0023] In the image projection device 100 of this embodiment, a far image displayed in the far display area of ​​the image projection unit 10 is irradiated as a first image light L1, and a near image displayed in the near display area is irradiated as a second image light L2. Examples of the far image displayed in the far display area include images calling attention and auxiliary information related to driving, such as emergency information. Examples of the near image displayed in the near display area include a speed and volume indicator, a driving direction guide, and the like.

[0024] In the example shown in FIG. 1, the image projection device 100 includes an image projection unit 10, a first mirror 20, a second mirror 30, and a housing 40. 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.

[0025] The image irradiation unit 10 is a part that irradiates the first mirror 20 with light containing an image as image light based on image information from the control unit. In this embodiment, an example is shown in which two image lights displayed in two image display areas are irradiated onto the first mirror 20 as a first image light L1 and a second image light L2.

[0026] The first mirror 20 is an optical member that reflects the first image light L1 and the second image light L2 arriving from the image irradiation unit 10 toward the second mirror 30. In the example shown in Fig. 1, the first mirror 20 is a flat reflecting mirror, but a concave or convex reflecting mirror may be used. In addition, when the first mirror 20 is configured with a curved surface, it is not limited to a surface with a constant curvature, and a paraboloid of revolution, an ellipsoid, a free curved surface mirror, or the like may be used.

[0027] The second mirror 30 is an optical member that reflects the first image light L1 and the second image light L2 arriving from the first mirror 20 toward the windshield WS. In the example shown in Fig. 1, the second mirror 30 is a free-form mirror having an optically designed concave shape necessary for projecting the first image light L1 and the second image light L2 as virtual images P1, P2.

[0028] The reflecting surfaces of the first mirror 20 and the second mirror 30 are designed to expand the light diameter in the driver's viewpoint direction in order to project the first image light L1 and the second image light L2 as virtual images P1, P2 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 mirror 20 and the third mirror 30 has a function of projecting the first image light L1 and the second image light L2 through the windshield WS, and corresponds to the irradiation optical unit in the present invention.

[0029] 1, the optical paths of the first image light L1 and the second image light L2 are depicted as a single straight line. However, the actual first image light L1 and the second image light L2 are displayed in a predetermined area in the image projection unit 10, and have a predetermined area in a direction perpendicular to the traveling direction. In addition, the first image light L1 and the second image light L2 may be reflected by the first mirror 20 and travel with their light diameters reduced, and may be intermediately imaged at an intermediate image position F (not shown) between the first mirror 20 and the second mirror 30.

[0030] The housing 40 is a container that constitutes the outer shape of the image projection device 100 and houses each component. The housing 40 is provided with a light exit port for emitting the first image light L1 and the second image light L2. An angle adjustment unit for adjusting the angle of the second mirror 30 may be provided in the housing 40 to adjust the irradiation angle of the first image light L1 and the second image light L2 projected onto the windshield WS and change the imaging height of the virtual images P1 and P2. The housing 40 may also be provided with an optical filter that cuts ultraviolet light and infrared light contained in light (external light) arriving from the outside.

[0031] Fig. 2 is a schematic cross-sectional view for explaining an overview of the image projection unit 10 according to this embodiment. As shown in Fig. 2, the image projection unit 10 of this embodiment includes a light source 11, a primary lens 12, a reflective polarizing unit 13, a half-wave plate 14, a reflecting mirror 15, a diffusion plate 17, an image display unit 18, and a meniscus lens 19. Here, the combination of the reflective polarizing unit 13, the half-wave plate 14, and the reflecting mirror 15 constitutes the polarization conversion element 50 of the present invention.

[0032] The light source 11 is a member that irradiates the image display unit 18 with irradiation light via the primary lens 12, the reflective polarizing unit 13, the half-wave plate 14, the reflecting mirror 15, the meniscus lens 19, and the diffusion plate 17. The light source 11 is, for example, a semiconductor light-emitting element such as an LED (Light Emitting Diode), and is arranged in a predetermined direction (the depth direction of the paper surface in FIG. 2). The color of the light emitted by the light source 11 is not particularly limited, but in this embodiment, the light is white as an example. Note that, in this embodiment, the number of rows of the light source 11 is one, but it may be two or more rows. The irradiation light emitted from the light source 11 is non-polarized.

[0033] The primary lens 12 is an optical member arranged in the light emission direction of the multiple light sources 11, and has a function of concentrating the light emitted from the light sources 11 and emitting it as, for example, parallel light or light close to parallel light (hereinafter, both are collectively referred to as "approximately parallel light"). The primary lens 12 is extended along the arrangement direction of the multiple light sources 11. In this embodiment, as an example of the primary lens 12, a TIR (Total Internal Reflection) lens is used, which has a refracting part in the center that refracts light and reflecting parts on both sides of the refracting part that reflect light. Although FIG. 2 shows a shape extended in the arrangement direction of the light sources 11 as the primary lens 12, multiple collimating lenses may be provided for each light source 11. In addition, as long as the light from the light source 11 can be made into approximately parallel light, the lens is not limited to a lens, and a configuration in which a combination of a reflector and a lens or a reflector alone is used to make the light into approximately parallel light may be adopted.

[0034] The polarization conversion element 50 is an optical member disposed on the light exit side of the primary lens 12, and converts the unpolarized irradiated light into a polarized light direction along a specific direction and emits the light as backlight. The specific configuration of the polarization conversion element 50 is not limited, but Fig. 2 shows an example in which a reflective polarizing unit 13, a half-wave plate 14, and a reflecting mirror 15 are attached to each surface of a prism.

[0035] The reflective polarizing unit 13 is an optical member that reflects polarized light in a first direction and transmits polarized light in a second direction perpendicular to the first direction. The polarization direction of the light transmitted by the reflective polarizing unit 13 is not limited, and it is necessary to match the polarization direction required for the backlight light finally irradiated to the image display unit 18. As an example, the reflective polarizing unit 13 may transmit polarized light in the horizontal direction in FIG. 2 (e.g., p-polarized light) and reflect polarized light in a direction perpendicular to the paper surface (e.g., s-polarized light). The reflective polarizing unit 13 is disposed at a predetermined angle with respect to the traveling direction of the light irradiated from the light source 11. Here, the light reflected by the reflective polarizing unit 13 out of the irradiated light corresponds to the first light in the present invention, and the light transmitted through the reflective polarizing unit 13 corresponds to the second light in the present invention.

[0036] The half-wave plate 14 is an optical element arranged between the reflecting mirror 15 and the meniscus lens 19, and is made of a birefringent material with different refractive indices in the slow axis and the fast axis. The half-wave plate 14 is designed so that a phase difference of half the wavelength of the light occurs between the slow axis and the fast axis before the incident light is emitted. The slow axis and the fast axis of the half-wave plate 14 are arranged in directions that differ by 45 degrees with respect to the polarization direction of the irradiated light that has passed through the reflective polarizing unit 13.

[0037] Reflecting mirror 15 is an optical member that reflects incident light. In the example shown in Fig. 2, it is arranged so as to be inclined at a predetermined angle with respect to the traveling direction of light transmitted through reflective polarizing unit 13. In the example shown in Fig. 2, reflective polarizing unit 13 and reflecting mirror 15 are inclined at different angles with respect to the traveling direction of light irradiated from light source 11. More specifically, they are arranged so that the traveling directions of light reflected by reflective polarizing unit 13 and reflecting mirror 15 are different, and the inclination angle is set so as to reflect light in a direction away from the center of image display unit 18.

[0038] 2 shows an example in which the inclination angles of the reflective polarizing unit 13 and the reflecting mirror 15 are different, but the reflective polarizing unit 13 and the reflecting mirror 15 may be arranged substantially parallel to each other. In this case, the reflective polarizing unit 13 and the reflecting mirror 15 are arranged at an inclination of, for example, 45 degrees with respect to the traveling direction of the light emitted from the light source 11, and the traveling direction of the light reflected by the reflective polarizing unit 13 in the backlight light and the light reflected by the reflecting mirror 15 are the same.

[0039] The diffusion plate 17 is an optical member disposed on the rear side of the image display unit 18, which diffuses and transmits backlight. The diffusion plate 17 diffuses the highly directional light deflected by the primary lens 12 and the meniscus lens 19 and outputs the light to the image display unit 18, so that the image display unit 18 is illuminated more uniformly. As the diffusion plate 17, it is preferable to use an optical member which diffuses and transmits the backlight converted by the polarization conversion element 50 while maintaining the polarization direction of the backlight.

[0040] The image display unit 18 functions as a spatial light modulation unit in which backlight irradiated from the polarization conversion element 50 enters from the rear surface and emits light modulated by image information from the exit surface. The specific configuration of the image display unit 18 is not limited, but as an example, a transmissive liquid crystal display device that transmits light incident from the rear surface and emits it from the front surface can be used. In a transmissive liquid crystal display device, only polarized light of a specific direction that is incident on the rear surface side is transmitted, so the polarization direction in the polarization conversion element 50 is made to coincide with the specific direction.

[0041] The meniscus lens 19 is an optical member that adjusts the light distribution of the backlight irradiated from the polarization conversion element 50. The meniscus lens 19 is formed by stretching in a direction perpendicular to the paper surface of FIG. 2. In the example shown in FIG. 2, the meniscus lens 19 has a first lens region 19a and a second lens region 19b, and the light reflected by the reflective polarizing unit 13 enters the first lens region 19a, and the light reflected by the reflecting mirror 15 enters the second lens region 19b. The optical characteristics of the first lens region 19a and the second lens region 19b are not limited, but the example shown in FIG. 2 shows an example in which the light reflected by the reflective polarizing unit 13 and the reflecting mirror 15 is refracted so that the traveling direction of the light is further away from the center of the image display unit 18.

[0042] In the above-described image projection device 100, the light emitted from the light source 11 is unpolarized light whose polarization direction is not limited. The light emitted from the light source 11 is incident on the primary lens 12 and collimated, and then incident on the incident surface of the polarization conversion element 50. The light incident on the polarization conversion element 50 is polarized in a first direction by the reflective polarizing unit 13 toward the lens region 19a of the meniscus lens 19, and is polarized in a second direction by the reflective polarizing unit 13. Here, the polarization of the light reflected by the reflective polarizing unit 13 is polarized in a first direction through which the image display unit 18 passes. Moreover, the polarization of the light passing through the reflective polarizing unit 13 is polarized in a second direction that is substantially perpendicular to the first direction.

[0043] Furthermore, the light irradiated from the light source 11 is polarized in the second direction (second light) through the reflective polarizing unit 13, reflected by the reflecting mirror 15, and transmitted through the half-wave plate 14. At this time, the polarization of the irradiated light transmitted through the half-wave plate 14 is rotated by 90 degrees in-plane and converted into polarization in the first direction. As a result, the first light reflected by the reflective polarizing unit 13 and the second light transmitted through the reflective polarizing unit 13, reflected by the reflecting mirror 15, and transmitted through the half-wave plate 14 are irradiated as backlight light having the same polarization direction, that is, the first direction. Furthermore, the half-wave plate 14 does not need to have a phase difference of exactly 50% with respect to the wavelength of light, and as long as it generates a phase difference close to 50%, it can exhibit the function of rotating the polarization direction in-plane.

[0044] The second light transmitted through the half-wave plate 14 is irradiated in the direction of the lens area 19b of the meniscus lens 19 as backlight light polarized in the first direction. The backlight light that reaches the lens areas 19a and 19b of the meniscus lens 19 has its light distribution adjusted and reaches the diffusion plate 17. The diffusion plate 17 diffuses and transmits the backlight light polarized in the first direction. As a result, the backlight light polarized in the first direction is uniformly irradiated on the rear surface of the image display unit 18.

[0045] In the example shown in FIG. 2, the backlight refracted by the first lens region 19a and the backlight refracted by the second lens region 19b are irradiated to different regions of the image display unit 18 and travel in directions away from each other. Therefore, by irradiating the light transmitted through the first lens region 19a and the light transmitted through the second lens region 19b to the far display region and the near display region of the image display unit 18, respectively, the first image light L1 transmitted through the far display region and the second image light L2 transmitted through the near display region can be separated. This makes it possible to omit an additional optical member for separating the first image light L1 and the second image light L2, thereby making it possible to reduce the size of the image projection device 100. Here, the near display region and the far display region correspond to either the first display region or the second display region in the present invention, respectively.

[0046] 2 shows an example in which the inclination angles of the reflective polarizing unit 13 and the reflecting mirror 15 are different, but the reflective polarizing unit 13 and the reflecting mirror 15 may be arranged substantially parallel to each other. In this case, the reflective polarizing unit 13 and the reflecting mirror 15 are arranged at an inclination of, for example, 45 degrees with respect to the traveling direction of the light emitted from the light source 11, and the traveling direction of the light reflected by the reflective polarizing unit 13 in the backlight light is the same as that of the light reflected by the reflecting mirror 15. In addition, the backlight light refracted by the first lens region 19a and the backlight light refracted by the second lens region 19b are irradiated onto the adjacent first and second display regions of the image display unit 18.

[0047] In the example shown in FIG. 2, the second light transmitted through the reflective polarizing unit 13 and reflected by the reflector 15 has a longer optical path length until it reaches the image display unit 18 than the first light reflected by the reflective polarizing unit 13. The light emitted from the light source 11 is made into a substantially parallel light by the primary lens 12, but is not a strictly parallel light beam and travels with a changing light diameter. Therefore, the irradiation area of ​​the first light irradiated on the first display region of the image display unit 18 is different from the irradiation area of ​​the second light irradiated on the second display region. The second light is partially attenuated when passing through the half-wave plate 14. This may cause a luminance difference between the first light irradiating the first display region of the image display unit 18 and the second light irradiating the second display region.

[0048] Therefore, in the image projection device 100 of this embodiment, the luminance difference between the first display region and the second display region is suppressed and display is performed at approximately the same luminance by appropriately setting the relationship between the reflectance Pr of the first light and the transmittance Pt of the second light in the reflective polarizing unit 13. The appropriate relationship between the reflectance Pr of the first light and the transmittance Pt of the second light is such that the area of ​​the first display region of the image display unit 18 is S1, the area of ​​the second display region is S2, and the ratio Pr / Pt is proportional to S2 / S1.

[0049] Here, the reflectance of the reflecting mirror 15 is Rm, the transmittance of the half-wave plate 14 is Ph, and the amount of light emitted from the light source 11 is LA. The solid angle of the first light emitted from the first display region is ω1, and the solid angle of the second light emitted from the second display region is ω2. The amount of the first light reflected by the reflective polarizing unit 13 is Lr=LA·Pr. The amount of the second light transmitted through the reflective polarizing unit 13, reflected by the reflecting mirror 15, and transmitted through the half-wave plate 14 is Lt=LA·Pt·Rm·Ph. The luminance of the first display region is Lr / (S1·ω1), and the luminance of the second display region is Lt / (S2·ω2).

[0050] Therefore, in order to make the luminance of the first display area and the second display area the same, (Formula 1) Lr / (S1 ω1)=Lt / (S2 ω2) This can be transformed into (Formula 2) LA·Pr / (S1·ω1)=LA·Pt·Rm·Ph / (S2·ω2) Further transformation results in (Formula 3) Pr / Pt=Rm·Ph·(S2·ω2 / S1·ω1) Here, if (ω2 / ω1) is a constant α, (Formula 4) Pr / Pt=α·Rm·Ph·(S2 / S1) It can be expressed as: Therefore, when the relationship between the reflectance Pr of the first light and the transmittance Pt of the second light in the reflective polarizing unit 13 satisfies the above-mentioned equation 4, virtual images P1 and P2 can be projected with the same brightness even if the optical paths of the first light and the second light are different and the areas of the first display area and the second display area are different.

[0051] In addition, if it can be assumed that there is no significant difference between the solid angles ω1 and ω2 in the first and second display areas, the constant α is assumed to be 1, and (Equation 5) Pr / Pt=Rm Ph (S2 / S1) The relationship between the reflectance Pr of the first light and the transmittance Pt of the second light in the reflective polarizing section 13 can be set simply based on this relationship, and the optical design can be simplified.

[0052] As described above, in the image projection device 100 of this embodiment, the light emitted from the light source 11 is converted by the polarization conversion element 50 into backlight light polarized in the first direction. In addition, since the polarization direction of the backlight light reaching the image display unit 18 matches the polarization direction used for image display in the image display unit 18, the amount of polarized component in the second direction that is absorbed by the image display unit 18 is small, and it is possible to improve the light utilization efficiency. In addition, by reflecting the light from the light source 11 by the reflective polarizing unit 13 and the reflecting mirror 15, the light irradiation area can be expanded, and the image irradiation unit 10 can be made smaller.

[0053] In addition, the light irradiated from light source 11 is polarized and separated by reflective polarizing unit 13, and the polarization direction of one of the separated light beams is rotated by half-wave plate 14. The ratio Pr / Pt of the reflectance Pr of the first light to the transmittance Pt of the second light in reflective polarizing unit 13 is proportional to the ratio S2 / S1 of the area S1 of the first display area to the area S2 of the second display area, thereby increasing the efficiency of use of the irradiated light and making it possible to align the brightness of the first display area and the second display area.

[0054] Second embodiment Next, a second embodiment of the present invention will be described with reference to Fig. 3. Descriptions of contents overlapping with the first embodiment will be omitted. Fig. 3 is a schematic cross-sectional view for explaining an overview of an image projection unit 10 according to this embodiment. This embodiment differs from the first embodiment in that a half-wave plate 14 is disposed between a reflective polarizing unit 13 and a meniscus lens 19.

[0055] In this embodiment, the light emitted from the light source 11 is incident on the primary lens 12 and collimated, and is incident on the incident surface of the polarization conversion element 50. Of the light incident on the polarization conversion element 50, the polarized light in the first direction (first light) is reflected by the reflective polarizing unit 13 toward the half-wave plate 14, and the polarized light in the second direction (second light) is transmitted through the reflective polarizing unit 13. The second light transmitted through the reflective polarizing unit 13 is irradiated toward the lens region 19b of the meniscus lens 19 as backlight polarized in the second direction.

[0056] Light emitted from light source 11 is polarized in a first direction and reflected by reflective polarizing unit 13, and passes through half-wave plate 14. At this time, the polarization of the irradiated light that passes through half-wave plate 14 is rotated 90 degrees in-plane and converted into polarization in a second direction. As a result, the first light reflected by reflective polarizing unit 13 and transmitted through half-wave plate 14, and the second light transmitted through reflective polarizing unit 13 and reflected by reflecting mirror 15 are irradiated as backlight light having the same polarization direction, that is, the second direction.

[0057] In this embodiment, the amount of first light reflected by the reflective polarizing unit 13 and transmitted through the half-wave plate 14 is Lr=LA·Pr·Ph. The amount of second light transmitted through the reflective polarizing unit 13 and reflected by the reflecting mirror 15 is Lt=LA·Pt·Rm. Furthermore, the luminance of the first display region is Lr / (S1·ω1), and the luminance of the second display region is Lt / (S2·ω2).

[0058] Therefore, the condition for making the luminance of the first display area and the second display area the same is (Formula 6) Pr / Pt=Rm·(1 / Ph)·(S2·ω2 / S1·ω1) Here, if (ω2 / ω1) is a constant α, (Formula 7) Pr / Pt=α·Rm·(1 / Ph)·(S2 / S1) It can be expressed as: Therefore, when the relationship between the reflectance Pr of the first light and the transmittance Pt of the second light in the reflective polarizing unit 13 satisfies the above-mentioned equation 7, virtual images P1 and P2 can be projected with the same brightness even if the optical paths of the first light and the second light are different and the areas of the first display area and the second display area are different.

[0059] In addition, if it can be assumed that there is no significant difference between the solid angles ω1 and ω2 in the first and second display areas, the constant α is assumed to be 1, and (Formula 8) Pr / Pt=Rm (1 / Ph) (S2 / S1) The relationship between the reflectance Pr of the first light and the transmittance Pt of the second light in the reflective polarizing section 13 can be set simply based on this relationship, and the optical design can be simplified.

[0060] Third embodiment Next, a third embodiment of the present invention will be described with reference to FIG. 4. Descriptions of contents overlapping with the first embodiment will be omitted. FIG. 4 is a schematic cross-sectional view for explaining an outline of an image projection unit 10 according to this embodiment. This embodiment differs from the first embodiment in that a light source 11 and a primary lens 12 are disposed below a polarization conversion element 50. Therefore, the second light transmitted through the reflective polarizing unit 13 is incident on the first lens region 19a of the meniscus lens 19. In addition, the first light reflected by the reflective polarizing unit 13 reaches a reflecting mirror 15.

[0061] In this embodiment, the light emitted from the light source 11 is incident on the primary lens 12 and collimated, and then incident on the incident surface of the polarization conversion element 50. Of the light incident on the polarization conversion element 50, the light polarized in a first direction (first light) is reflected by the reflective polarizing unit 13 toward the reflecting mirror 15, and the light polarized in a second direction (second light) passes through the reflective polarizing unit 13. The second light that passes through the reflective polarizing unit 13 is irradiated in the direction of the lens area 19a of the meniscus lens 19 as backlight light polarized in the second direction.

[0062] Light emitted from light source 11 is polarized in a first direction and reflected by reflective polarizing unit 13, then reflected by reflecting mirror 15, and transmitted through half-wave plate 14. At this time, the polarization of the irradiated light transmitted through half-wave plate 14 is rotated 90 degrees in-plane and converted into polarization in a second direction. As a result, the first light reflected by reflective polarizing unit 13 and transmitted through half-wave plate 14, and the second light transmitted through reflective polarizing unit 13 are irradiated as backlight light having the same polarization direction, the second direction.

[0063] In this embodiment, the amount of first light reflected by the reflective polarizing unit 13, reflected by the reflecting mirror 15, and transmitted through the half-wave plate 14 is Lr=LA·Pr·Rm·Ph. The amount of second light transmitted through the reflective polarizing unit 13 is Lt=LA·Pt. Furthermore, the luminance of the first display region is Lr / (S1·ω1), and the luminance of the second display region is Lt / (S2·ω2).

[0064] Therefore, the condition for making the luminance of the first display area and the second display area the same is (Formula 9) Pr / Pt=(1 / Rm)·(1 / Ph)·(S2·ω2 / S1·ω1) Here, if (ω2 / ω1) is a constant α, (Formula 10) Pr / Pt=α (1 / Rm) (1 / Ph) (S2 / S1) It can be expressed as: Therefore, when the relationship between the reflectance Pr of the first light and the transmittance Pt of the second light in the reflective polarizing unit 13 satisfies the above-mentioned equation 10, virtual images P1 and P2 can be projected with the same brightness even if the optical paths of the first light and the second light are different and the areas of the first display area and the second display area are different.

[0065] In addition, if it can be assumed that there is no significant difference between the solid angles ω1 and ω2 in the first and second display areas, the constant α is assumed to be 1, and (Formula 11) Pr / Pt=(1 / Rm) (1 / Ph) (S2 / S1) The relationship between the reflectance Pr of the first light and the transmittance Pt of the second light in the reflective polarizing section 13 can be set simply based on this relationship, and the optical design can be simplified.

[0066] (Fourth embodiment) Next, a fourth embodiment of the present invention will be described with reference to FIG. 5. Descriptions of contents overlapping with the third embodiment will be omitted. FIG. 5 is a schematic cross-sectional view for explaining an overview of an image projection unit 10 according to this embodiment. This embodiment differs from the third embodiment in that a half-wave plate 14 is disposed between a reflective polarizing unit 13 and a meniscus lens 19.

[0067] In this embodiment, the illumination light emitted from the light source 11 is incident on the primary lens 12 and collimated, and is incident on the incident surface of the polarization conversion element 50. Of the illumination light incident on the polarization conversion element 50, the polarized light in the first direction (first light) is reflected by the reflective polarizing unit 13 toward the reflecting mirror 15, and the polarized light in the second direction (second light) is transmitted through the reflective polarizing unit 13. The second light transmitted through the reflective polarizing unit 13 is transmitted through the half-wave plate 14 and is irradiated in the direction of the lens region 19a of the meniscus lens 19. At this time, the polarization of the illumination light transmitted through the half-wave plate 14 is rotated 90 degrees in-plane and converted into polarization in the first direction.

[0068] The light emitted from the light source 11 is polarized in the first direction and reflected by the reflective polarizing unit 13, then reflected by the reflecting mirror 15, and is emitted in the direction of the lens region 19b of the meniscus lens 19. As a result, the first light reflected by the reflective polarizing unit 13 and the second light transmitted through the reflective polarizing unit 13 and the half-wave plate 14 are irradiated as backlight light having the same polarization direction, that is, the first direction.

[0069] In this embodiment, the amount of first light reflected by the reflective polarizing unit 13 and then reflected by the reflecting mirror 15 is Lr=LA·Pr·Rm. The amount of second light transmitted through the reflective polarizing unit 13 and then through the half-wave plate 14 is Lt=LA·Pt·Ph. Furthermore, the luminance of the first display region is Lr / (S1·ω1), and the luminance of the second display region is Lt / (S2·ω2).

[0070] Therefore, the condition for making the luminance of the first display area and the second display area the same is (Formula 12) Pr / Pt=(1 / Rm)·Ph·(S2·ω2 / S1·ω1) Here, if (ω2 / ω1) is a constant α, (Formula 13) Pr / Pt=α (1 / Rm) Ph (S2 / S1) It can be expressed as: Therefore, when the relationship between the reflectance Pr of the first light and the transmittance Pt of the second light in the reflective polarizing unit 13 satisfies the above-mentioned equation 13, virtual images P1 and P2 can be projected with the same brightness even if the optical paths of the first light and the second light are different and the areas of the first display area and the second display area are different.

[0071] In addition, if it can be assumed that there is no significant difference between the solid angles ω1 and ω2 in the first and second display areas, the constant α is assumed to be 1, and (Formula 14) Pr / Pt=(1 / Rm)·Ph·(S2 / S1) The relationship between the reflectance Pr of the first light and the transmittance Pt of the second light in the reflective polarizing section 13 can be set simply based on this relationship, and the optical design can be simplified.

[0072] Fifth embodiment Next, a fifth embodiment of the present invention will be described with reference to FIG. 6. Descriptions of contents overlapping with the first embodiment will be omitted. FIG. 6 is a schematic cross-sectional view for explaining an outline of the image projection unit 10 according to this embodiment. This embodiment differs from the first embodiment in that the polarization conversion element 50 is separated into a first portion 50a and a second portion 50b, and a half-wave plate 14 is disposed between the first portion 50a and the second portion 50b.

[0073] In this embodiment, the illumination light emitted from the light source 11 is incident on the primary lens 12 and collimated, and is incident on the incident surface of the polarization conversion element 50. Of the illumination light incident on the polarization conversion element 50, polarized light in a first direction (first light) is reflected by the reflective polarizing unit 13 toward the first lens region 19a of the meniscus lens 19.

[0074] Of the light emitted from the light source 11, the second light polarized in the second direction is transmitted through the reflective polarizing unit 13. The second light transmitted through the reflective polarizing unit 13 is transmitted through the half-wave plate 14, reflected by the reflecting mirror 15, and irradiated in the direction of the second lens region 19b of the meniscus lens 19 as backlight light polarized in the second direction. At this time, the polarization of the irradiated light transmitted through the half-wave plate 14 is rotated 90 degrees in-plane and converted into polarization in the first direction. As a result, the first light reflected by the reflective polarizing unit 13 and the second light transmitted through the reflective polarizing unit 13, transmitted through the half-wave plate 14, and reflected by the reflecting mirror 15 are irradiated as backlight light having the same polarization direction, that is, the first direction.

[0075] In this embodiment, the amount of first light reflected by the reflective polarizing unit 13 is Lr=LA·Pr. The amount of second light transmitted through the reflective polarizing unit 13, transmitted through the half-wave plate 14, and reflected by the reflecting mirror 15 is Lt=LA·Pt·Ph·Rm. Furthermore, the luminance of the first display region is Lr / (S1·ω1), and the luminance of the second display region is Lt / (S2·ω2).

[0076] Therefore, the condition for making the luminance of the first display area and the second display area the same is, as in the first embodiment, (Formula 3) Pr / Pt=Rm·Ph·(S2·ω2 / S1·ω1) Here, if (ω2 / ω1) is a constant α, (Formula 4) Pr / Pt=α·Rm·Ph·(S2 / S1) It can be expressed as:

[0077] In addition, if it can be assumed that there is no significant difference between the solid angles ω1 and ω2 in the first and second display areas, the constant α is assumed to be 1, and (Formula 5) Pr / Pt=Rm (1 / Ph) (S2 / S1) The relationship between the reflectance Pr of the first light and the transmittance Pt of the second light in the reflective polarizing section 13 can be set simply based on this relationship, and the optical design can be simplified.

[0078] Sixth embodiment Next, a sixth embodiment of the present invention will be described with reference to FIG. 7. Descriptions of contents overlapping with the fifth embodiment will be omitted. FIG. 7 is a schematic cross-sectional view for explaining an outline of the image projection unit 10 according to this embodiment. This embodiment is the same as the fifth embodiment except that the light source 11 and the primary lens 12 are disposed below the polarization conversion element 50. Therefore, the second light transmitted through the reflective polarizing unit 13 is incident on the first lens region 19a of the meniscus lens 19. In addition, the first light reflected by the reflective polarizing unit 13 is transmitted through the half-wave plate 14 and reaches the reflecting mirror 15.

[0079] In this embodiment, the light emitted from the light source 11 is incident on the primary lens 12 and collimated, and is incident on the incident surface of the polarization conversion element 50. Of the light incident on the polarization conversion element 50, the polarized light in the first direction (first light) is reflected by the reflective polarizing unit 13 toward the half-wave plate 14, and the polarized light in the second direction (second light) is transmitted through the reflective polarizing unit 13. The second light transmitted through the reflective polarizing unit 13 is irradiated toward the lens region 19a of the meniscus lens 19 as backlight light polarized in the second direction.

[0080] The light emitted from the light source 11 is polarized in a first direction and reflected by the reflective polarizing unit 13, passes through the half-wave plate 14, and is reflected by the reflecting mirror 15 to be emitted in the direction of the lens region 19b of the meniscus lens 19. At this time, the polarization of the irradiated light that passes through the half-wave plate 14 is rotated 90 degrees in-plane and converted into polarization in a second direction. As a result, the first light reflected by the reflective polarizing unit 13 and passed through the half-wave plate 14, and the second light passed through the reflective polarizing unit 13 and reflected by the reflecting mirror 15 are irradiated as backlight light having the same polarization direction, that is, the second direction.

[0081] In this embodiment, the amount of first light reflected by the reflective polarizing unit 13, transmitted through the half-wave plate 14, and reflected by the reflecting mirror 15 is Lr=LA·Pr·Ph·Rm. The amount of second light transmitted through the reflective polarizing unit 13 is Lt=LA·Pt. Furthermore, the luminance of the first display region is Lr / (S1·ω1), and the luminance of the second display region is Lt / (S2·ω2).

[0082] Therefore, the condition for making the luminance of the first display area and the second display area the same is, as in the third embodiment, (Formula 9) Pr / Pt=(1 / Rm)·(1 / Ph)·(S2·ω2 / S1·ω1) Here, if (ω2 / ω1) is a constant α, (Formula 10) Pr / Pt=α (1 / Rm) (1 / Ph) (S2 / S1) It can be expressed as:

[0083] In addition, if it can be assumed that there is no significant difference between the solid angles ω1 and ω2 in the first and second display areas, the constant α is assumed to be 1, and (Formula 11) Pr / Pt=(1 / Rm) (1 / Ph) (S2 / S1) The relationship between the reflectance Pr of the first light and the transmittance Pt of the second light in the reflective polarizing section 13 can be set simply based on this relationship, and the optical design can be simplified.

[0084] 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]

[0085] 100...Image projection device 10...Image irradiation unit 20…1st mirror 30…2nd mirror 40…Housing 50...Polarization conversion element 11...Light source 12…Primary lens 13...Reflective polarizing section 14...Half-wave plate 15...Reflector 17…Diffusion plate 18...Image display section 19...Meniscus lens 19a...First lens region 19b...Second lens area

Claims

1. A light source that emits unpolarized irradiation light; an image display unit into which the irradiation light is incident from a rear surface and which emits image light from a display surface; a reflective polarizing unit that reflects light polarized in a first direction as a first light and transmits light polarized in a second direction intersecting the first direction as a second light; a half-wave plate disposed on an optical path of the first light or the second light, the first light is irradiated onto a first display area of ​​the image display unit, and the second light is irradiated onto a second display area of ​​the image display unit; The area of ​​the first display region is S １ and the area of ​​the second display region is S ２ year, The reflectance of the first light in the reflective polarizing unit is denoted as Pr and the transmittance of the second light in the reflective polarizing unit is denoted as Pt, Pr / Pt is S ２ / S １ An image projection device characterized in that the image projection angle is proportional to

2. 2. The image projection device according to claim 1, the half-wave plate is disposed on an optical path of the first light, a reflecting portion that reflects the second light is provided on an optical path of the second light, The transmittance of the half-wave plate is Ph, The reflectance of the reflective portion is Rm, When the constant is α, t0.834597 t0.834597 t0.834597 t0.834597 ２ / S １ , An image projection device, characterized in that the following relationship is satisfied.

3. 2. The image projection device according to claim 1, the half-wave plate is disposed on an optical path of the second light, a reflecting portion that reflects the second light is provided on an optical path of the second light, The reflectance of the reflective portion is Rm, The transmittance of the half-wave plate is Ph, When the constant is α, t0.834597 t0.834597 t0.834597 ２ / S １ , An image projection device, characterized in that the following relationship is satisfied.

4. 2. The image projection device according to claim 1, the half-wave plate is disposed on an optical path of the first light, a reflecting portion that reflects the first light is provided on an optical path of the first light, The transmittance of the half-wave plate is Ph, The reflectance of the reflective portion is Rm, When the constant is α, t0.834597°N -8.434597°W(8.4 ...N -8.434597°W(8.434597°N ２ / S １ , An image projection device, characterized in that the following relationship is satisfied.

5. 2. The image projection device according to claim 1, the half-wave plate is disposed on an optical path of the second light, a reflecting portion that reflects the first light is provided on an optical path of the first light, The reflectance of the reflective portion is Rm, The transmittance of the half-wave plate is Ph, When the constant is α, t0.834597 t0.834597 t0.834597 ２ / S １ , An image projection device, characterized in that the following relationship is satisfied.

6. 6. The image projection device according to claim 2, The solid angle of the first light emitted from the first display region is defined as ω １ and the solid angle of the second light emitted from the second display region is ω ２ When Prefix α = ω ２ / ω １ 1. An image projection device comprising:

7. 2. The image projection device according to claim 1, The image projection device, characterized in that the first display area and the second display area are provided adjacent to each other on one of the image display sections.

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

Images