Image projection device

Abstract

Provided is an image projection device that can be reduced in size while projecting a plurality of images onto different positions of a display unit. This image projection device (100) projects a projection image onto a display unit (WS) for displaying virtual images (P1, P2). The image projection device (100) comprises: an image irradiation unit (10) that applies first image light and second image light; and projection optical units (20, 30) that form an image of the first image light at a first distance from a viewpoint position E via the display unit (WS). The image irradiation unit (10) alternately repeats a first period during which the first image light is applied in a first direction and a second period during which the second image light is applied in a second direction.

Description

Image Projection Device

[0001] The present invention relates to an image projection device.

[0002] Conventionally, dashboards that illuminate icons have been used to display various types of information inside vehicles. 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, in order for a driver or other passenger to view the information displayed on the instrument panel, the driver or other passenger must move his or her eyes downward while driving, 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 disclosed in Patent Documents 1 and 2, an image projection unit emits light containing an image, and the light is reflected by a free-form mirror or the like, and the light reaches the viewpoint of the occupant so that the image is formed in space via a display unit such as a windshield. This allows the occupant to perceive the image as being displayed at the imaging position in the depth direction by the light incident on the viewpoint. It has also been proposed to project multiple beams of image light to form multiple virtual images at different distances from the windshield.

[0005] JP 2019-119248 A JP 2019-119262 A

[0006] However, in order to project multiple image lights at different positions on the windshield, it is necessary to use an image display device with a display area corresponding to the number of images to be formed, which makes it difficult to reduce the size.Furthermore, in order to form multiple images at positions at different distances from the viewpoint, it is necessary to provide an optical system for projecting each image light, which makes the device configuration complicated and makes it difficult to reduce the size.

[0007] SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-mentioned problems of the conventional art, and has as its object to provide an image projection device that can project a plurality of images onto different positions on a display unit while being miniaturized.

[0008] In order to solve the above problem, the image projection device of the present invention is an image projection device that projects a projection image onto a display unit for displaying a virtual image, and is equipped with an image irradiation unit that irradiates first image light and second image light, and a projection optical unit that forms an image of the first image light at a first distance from a viewpoint position via the display unit, and is characterized in that the image irradiation unit alternately repeats a first period in which it irradiates the first image light in a first direction and a second period in which it irradiates the second image light in a second direction.

[0009] In such an image projection device of the present invention, by alternating between a first period in which the image irradiation unit irradiates a first image light in a first direction and a second period in which the image irradiation unit irradiates a second image light in a second direction, it is possible to project multiple images at different positions on the display unit while achieving miniaturization.

[0010] In one aspect of the present invention, the projection optical unit is provided in the first direction, and a black reflective area formed below the display unit is provided in the extension in the second direction.

[0011] In one aspect of the present invention, the image irradiation unit includes an image display unit that displays a first image during the first period and a second image during the second period, a first light source unit that irradiates the image display unit with first irradiation light during the first period, and a second light source unit that irradiates the image display unit with second irradiation light during the second period.

[0012] In one aspect of the present invention, the image display unit is a transmissive liquid crystal display device, and the transmissive liquid crystal display device is arranged along a direction in which the light distribution of the first irradiation light and the second irradiation light is maximum, and includes a first transmission-reflection unit that reflects the first irradiation light toward a first surface of the transmissive liquid crystal display device, and a second transmission-reflection unit that reflects the second irradiation light toward a second surface of the transmissive liquid crystal display device.

[0013] In one aspect of the present invention, the first transmissive-reflective portion transmits the second image light irradiated from the first surface, and the second transmissive-reflective portion transmits the first image light irradiated from the second surface.

[0014] In one aspect of the present invention, the image display unit is a transmissive liquid crystal display device, the first light source unit has a first light-emitting unit that emits the first irradiation light and a first light-guiding reflection unit that reflects the first irradiation light toward a first surface of the transmissive liquid crystal display device, and the second light source unit has a second light-emitting unit that emits the second irradiation light and a second light-guiding reflection unit that reflects the second irradiation light toward the first surface of the transmissive liquid crystal display device.

[0015] In one aspect of the invention, the first light-guiding reflection portion reflects the first irradiation light in the first direction, and the second light-guiding reflection portion reflects the second irradiation light in the second direction.

[0016] In one aspect of the invention, the first image light is S-polarized light with respect to the display unit, and the second image light is P-polarized light with respect to the display unit.

[0017] The present invention can provide an image projection device that can project a plurality of images onto different positions on a display unit while being miniaturized.

[0018] 2A and 2B are schematic side cross-sectional views illustrating the projection of virtual images P1 and P2 using the image projection device 100 according to the first embodiment.

[0033] FIG. 2A is a schematic diagram illustrating a configuration example of the image projection unit 10 according to the first embodiment and switching between the first image light and the second image light. FIG. 2B shows a case where the first irradiation light is emitted from the light-emitting element 11a during a first period, and FIG. 2B shows a case where the second irradiation light is emitted from the light-emitting element 11b during a second period.

[0034] FIG. 3A is a schematic diagram illustrating the incidence and transmission of image light in the image projection unit 10. FIG. 3B shows a case where the first irradiation light is emitted from the light-emitting element 11a during a first period, and FIG. 3B shows a case where the second irradiation light is emitted from the light-emitting element 11b during a second period.

[0035] FIG. 3B is a graph illustrating the angle of incidence and the range of reflection of image light on the transmission-reflection units 14a and 14b.

[0036] FIG. 3C is a schematic diagram illustrating a configuration example of the image projection unit 10 according to the second embodiment and switching between the first image light and the second image light. FIG. 5(a) shows a case where the first irradiation light is emitted from the light-emitting element 11a in the first period, and FIG. 5(b) shows a case where the second irradiation light is emitted from the light-emitting element 11b in the second period.

[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, members, and processes shown in each drawing will be assigned the same reference numerals, and redundant explanations will be omitted as appropriate. In the following explanation, an embodiment in which an image projection device 100 according to the present invention is applied to a HUD mounted on a vehicle or the like will be described as an example. FIG. 1 is a schematic side cross-sectional view illustrating the projection of virtual images P1 and P2 using the image projection device 100 according to this embodiment.

[0020] As shown in FIG. 1 , the image projection device 100 includes an image projection unit 10, a first mirror 20, and a second mirror 30. The image projection device 100 is housed in a vehicle's dashboard DB and projects first and second image light onto a windshield WS and a lower windshield WSB located below the windshield WS. The first and second image light reflected by the windshield WS and the lower windshield WSB reach the driver's viewpoint E. The driver views virtual images P1 and P2 on an extension of the direction from which the first and second image light are incident. While FIG. 1 illustrates an example in which the second image light is reflected by the lower windshield WSB, a combiner or the like may be provided separately from the windshield WS to reflect the second image light. Here, the windshield WS, the lower windshield WSB, and the combiner correspond to the display unit in this invention.

[0021] In the image projection device 100, each part is controlled using a control unit (not shown) that is connected to each part so as to be able to communicate information with the parts. The configuration of the control unit is not limited, but an example includes a CPU (Central Processing Unit) for information processing, a memory device, a recording medium, an information communication device, etc. 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.

[0022] The image projection unit 10 is a part that, based on image information from the control unit, projects second image light toward the lower windshield WSB (second direction) as light containing an image, and projects first image light toward the first mirror 20 (first direction). Specific configuration examples of the image projection unit 10 will be described in detail below. The polarization direction of the first image light is not limited, but it is preferable to use S-polarized light, which has a high reflectivity on the windshield WS. Furthermore, the polarization direction of the second image light is not limited, but if the content of the second image includes information such as a speedometer, it is preferable to use P-polarized light, which ensures visibility even when the driver is wearing polarized sunglasses.

[0023] The image projection unit 10 alternately displays a far image and a near image within one display area between a first period and a second period. The far image displayed by the image projection unit 10 during the first period is reflected by the first mirror 20, the second mirror 30, and the windshield WS as far image light (first image light) and reaches the driver's viewpoint E, as shown by the solid line in FIG. 1 . The near image displayed by the image projection unit 10 during the second period is reflected by the lower windshield WSB as near image light (second image light) and reaches the driver's viewpoint E, as shown by the dashed-dotted line in FIG. 1 . Examples of far images include auxiliary information related to driving, such as attention-grabbing images and emergency information. Examples of near images include a speedometer, a volume indicator, and a driving direction guide.

[0024] The first mirror 20 is an optical element that receives the first image light emitted from the image projection unit 10 and reflects the first image light toward the second mirror 30. While FIG. 1 illustrates a flat mirror as the first mirror 20, a free-form mirror or the like may also be used. The second mirror 30 is an optical element that receives the first image light reflected by the first mirror 20 and reflects the first image light toward the windshield WS. In FIG. 1 , the second mirror 30 is illustrated as a concave free-form mirror. The first mirror 20 and the second mirror 30 are optically designed to project the first image light as a virtual image P1 through the windshield WS at a first distance from the viewpoint E. The second mirror 30 may also be configured to have an adjustable tilt angle relative to the horizontal direction, thereby changing the projection direction of the image light and moving the projection position of the virtual image P1 in the vertical direction.

[0025] The reflective surfaces of the first mirror 20 and the second mirror 30 are designed to expand the light diameter in the driver's line of sight in order to project the first image light as a virtual image P1 through the windshield WS. Here, "expanding the light diameter in the line of sight" refers not only to the case where the light diameter expands consistently after reflection, but also to 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 second mirror 30 has the function of projecting the image light through the windshield WS and corresponds to the projection optical unit in the present invention. While FIG. 1 shows an example in which the projection optical unit is composed of two mirrors, the first mirror 20 and the second mirror 30, a larger number of mirrors may be used.

[0026] The windshield WS is a part provided in front of the driver's seat of the vehicle that transmits visible light. The windshield WS reflects the first image light incident from the image projection device 100 toward the viewpoint on the inside surface of the vehicle and transmits light from outside the vehicle toward the viewpoint. While an example using the windshield WS has been shown here, a combiner may be provided separately from the windshield WS to reflect the light from the image projection device 100 toward the viewpoint. Furthermore, the windshield WS is not limited to being located at the 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.

[0027] The lower windshield WSB is a partial area of ​​the windshield WS near the boundary with the dashboard DB. The lower windshield WSB reflects the second image light incident from the image projection device 100 toward the viewpoint on the inside surface of the vehicle. The lower windshield WSB overlaps with the hood of the vehicle from the driver's viewpoint E, and therefore may be colored a dark color such as black. The dark-colored lower windshield WSB corresponds to the black reflective area in this invention.

[0028] The virtual image P1 is an image that is displayed as if it were formed in space on an extension of the path of the first image light reflected by the windshield WS when it reaches the viewpoint (eyebox) of the occupant. The position at which the virtual image P1 is formed is determined by the composite focal length of the first mirror 20, the second mirror 30, and the windshield WS included in the image projection device 100. The virtual image P2 is an image that is displayed as if it were formed in space a second distance from the viewpoint position E on an extension of the path of the second image light reflected by the lower windshield WSB when it reaches the viewpoint of the occupant. The position at which the virtual image P2 is formed is determined by the optical distance between the image projection unit 10 and the lower windshield WSB.

[0029] 1, the optical paths of the first image light and the second image light are depicted as a single straight line. However, the actual image light is displayed in a predetermined area in the image projection unit 10 and has a predetermined area in a direction perpendicular to the traveling direction. The first image light may be reflected by the first mirror 20, its light diameter reduced as it travels, and may form an intermediate image at an intermediate image position F (not shown) between the first mirror 20 and the second mirror 30.

[0030] The irradiation of the first image light and the second image light from the image irradiation unit 10 is alternately repeated in a first period and a second period, respectively. Here, by making the lengths of the first period and the second period sufficiently short, the driver can simultaneously view the virtual images P1 and P2 due to the afterimage effect. While the specific lengths of the first period and the second period are not limited, it is preferable to switch between the first image light and the second image light at 100 Hz or more (0.01 seconds or less). The first period and the second period may be the same length, or the first period may be longer than the second period to increase the brightness of the virtual image P1. Although the first period and the second period are alternately repeated, this is not limited to a 1:1 ratio, and the first period and the second period may be repeated at an n:m ratio within a predetermined period.

[0031] 2 is a schematic diagram showing an example of the configuration of the image projection unit 10 according to the present embodiment and switching between the first image light and the second image light. In the example shown in Fig. 2, the image projection unit 10 includes light-emitting elements 11a and 11b, lenses 12a and 12b, an image display unit 13, transmissive-reflective units 14a and 14b, and a heat sink 15. Fig. 2(a) shows a case where the first irradiation light is emitted from the light-emitting element 11a during a first period, and Fig. 2(b) shows a case where the second irradiation light is emitted from the light-emitting element 11b during a second period.

[0032] The light-emitting elements 11a and 11b are parts that irradiate the image display unit 13 with irradiation light. In the example shown in Fig. 2, the irradiation light travels in an in-plane direction of the transmissive image display unit 13. The light-emitting elements 11a and 11b are located on the first surface side and the second surface side of the image display unit 13, respectively. The irradiation light from the light-emitting element 11a (first irradiation light) is irradiated onto the first surface side of the image display unit 13, and the irradiation light from the light-emitting element 11b (second irradiation light) is irradiated onto the second surface side of the image display unit 13. The specific configuration of the light-emitting elements 11a and 11b is not limited, and a light-emitting diode (LED) or a laser light source can be used.

[0033] The lenses 12a and 12b are optical components disposed on the light-emitting surface sides of the light-emitting elements 11a and 11b, respectively, and refract the light emitted from the light-emitting elements 11a and 11b to adjust the light distribution. The specific configuration of the lenses 12a and 12b is not limited, but the light distribution from the light-emitting elements 11a and 11b is maximized in the direction along the display surface of the image display unit 13. One example is a collimator lens that converts the light emitted through the lenses 12a and 12b into parallel light parallel to the direction along the display surface of the image display unit 13. The combination of the light-emitting elements 11a and 11b and the lenses 12a and 12b corresponds to the first light source and the second light source of the present invention.

[0034] The image display unit 13 is a part that displays a projected image based on image information from the control unit. In the example shown in FIG. 2, a transmissive liquid crystal display device is used as the image display unit 13. As shown in FIG. 2, the image display unit 13 is arranged so that its display surface is parallel to the traveling direction of the light emitted from the light-emitting elements 11a and 11b. The side of the image display unit 13 on which the light-emitting element 11a is provided is the first surface, and the side on which the light-emitting element 11b is provided is the second surface. Because a transmissive liquid crystal display device is used as the image display unit 13, light incident from the first surface side is transmitted to the second surface side, and light incident from the second surface side is transmitted to the first surface side.

[0035] As described above, the image display unit 13 displays a first image during the first period and a second image during the second period. Therefore, as shown in Fig. 2A, the first irradiation light that passes through the image display unit 13 from the first surface side to the second surface side during the first period becomes first image light that includes the first image. Furthermore, as shown in Fig. 2B, the second irradiation light that passes through the image display unit 13 from the second surface side to the first surface side during the second period becomes second image light that includes the second image.

[0036] The transflector 14a is an optical element that reflects the first irradiation light from the light-emitting element 11a toward the first surface of the image display unit 13 and transmits the second image light irradiated from the first surface. The transflector 14b is an optical element that reflects the second irradiation light from the light-emitting element 11b toward the second surface of the image display unit 13 and transmits the first image light irradiated from the second surface. The transflector 14a and 14b are plate-shaped elements made of a light-transmitting material and have a refractive index n. As shown in FIG. 2 , the transflector 14a and 14b are arranged at a predetermined angle with respect to the traveling direction of the first irradiation light and the second irradiation light (the direction in which the light distribution is maximum) and the display surface of the image display unit 13. The angle of inclination of the transflector 14a and 14b will be described in detail below.

[0037] The first irradiation light incident on the transmission-reflection unit 14a is totally reflected due to the tilt angle and the refractive index difference, and reaches the first surface side of the image display unit 13. The first irradiation light incident on the first surface of the image display unit 13 passes through the image display unit 13 and is emitted from the second surface as first image light including the first image displayed on the image display unit 13. The first image light emitted from the second surface of the image display unit 13 passes through the transmission-reflection unit 14b and is extracted in the first direction.

[0038] The second irradiation light incident on the transmission-reflection unit 14b is totally reflected due to the tilt angle and the difference in refractive index, and reaches the second surface side of the image display unit 13. The second irradiation light incident on the second surface of the image display unit 13 passes through the image display unit 13 and is emitted from the first surface as second image light including the second image displayed on the image display unit 13. The second image light emitted from the first surface of the image display unit 13 passes through the transmission-reflection unit 14a and is extracted in the second direction.

[0039] Here, the polarization directions of the first image light and the second image light will be described when a TN (Twisted Nematic) liquid crystal display device is used as the image display unit 13. The image display unit 13 is a TN liquid crystal display. The polarization direction of the polarizer (not shown) arranged on the first surface side is P-polarized light relative to the windshield WS, and the polarization direction of the polarizer (not shown) arranged on the second surface side is S-polarized light relative to the windshield WS. In this case, the unpolarized first irradiation light emitted from the light-emitting element 11a passes only the P-polarized light through the polarizer on the first surface side, and the polarization direction is rotated by the TN liquid crystal, so that the light passes only the S-polarized light through the polarizer on the second surface side. The polarization direction of the unpolarized second irradiation light emitted from the light-emitting element 11b passes only the S-polarized light through the polarizer on the second surface side, and the polarization direction is rotated by the TN liquid crystal, so that the light passes only the P-polarized light through the polarizer on the first surface side. Therefore, the first image light emitted from the transmission-reflection unit 14b in the first direction becomes S-polarized light, and the second image light emitted from the transmission-reflection unit 14a in the second direction becomes P-polarized light.

[0040] The heat sink 15 is a part that mounts the light emitting elements 11 a, 11 b, a circuit board (not shown), a drive circuit (not shown), etc., and dissipates heat generated by irradiation with the first image light and the second image light. The material and shape of the heat sink 15 are not limited, and various heat sinks that have been proposed in the past can be used. The heat sink 15 may also be provided with a plurality of heat dissipation fins.

[0041] 3A and 3B are schematic diagrams illustrating the incidence and transmission of image light in the image irradiation unit 10. Fig. 3A shows a case where the first irradiation light is irradiated from the light-emitting element 11a in a first period, and Fig. 3B shows a case where the second irradiation light is irradiated from the light-emitting element 11b in a second period. As shown in Figs. 3A and 3B, the inclination angles of the transmission-reflection units 14a and 14b with respect to the display surface of the image display unit 13 are respectively defined as θ １ , θ ２ The angles of incidence of the first irradiation light and the second irradiation light on the transmissive-reflective portions 14a and 14b are respectively set to θ Ｓ１ , θ Ｐ１ The angles of incidence of the second image light and the first image light with respect to the transmissive-reflective portions 14a and 14b are respectively set as θ Ｓ２ , θ Ｐ２ As shown by the dashed line in the figure, the incident angle θ Ｓ１ , θ Ｐ１ , θ Ｓ２ , θ Ｐ２ are the angles formed between the normal direction of the transmission-reflection portions 14a and 14b and the traveling direction of light, respectively.

[0042] Here, the first irradiation light and the second irradiation light are reflected by the transmission-reflection portions 14a and 14b, respectively, and therefore the incident angle θ Ｓ１ , θ Ｐ１ is equal to or larger than the critical angle and satisfies the total reflection condition. In addition, since the first image light and the second image light are reflected by the transmissive-reflective portions 14b and 14a, respectively, the incident angle θ Ｓ２ , θ Ｐ２ The refractive index of the transmissive-reflective portions 14a and 14b is n, and the critical angle is θ ０ Then, the following condition must be satisfied: (Equation 1) θ Ｓ１ = π / 2 - θ １ >θ ０(Formula 2) θ Ｐ１ = π / 2 - θ ２ >θ ０ (Formula 3) | θ Ｓ２ |=|2θ １ +θ ２ -π / 2|<θ ０ (Formula 4) | θ Ｐ２ |=|2θ ２ +θ １ -π / 2|<θ ０

[0043] 4 is a graph showing the angle of incidence of image light on the transmission-reflection units 14a and 14b and the range of reflection. In the example shown in FIG. 4, acrylic plates with a refractive index n=1.5 are used as the transmission-reflection units 14a and 14b, and the critical angle θ ０ The horizontal axis in the graph shows the case where θ １ The vertical axis indicates θ ２ In addition, the critical angle θ ０ = 42°, (Equation 1', Equation 2') θ １ , θ ２ <48° (Equation 3') - 2θ １ +48°<θ ２ <-2θ １ +132° (Formula 4') -2θ ２ +48°<θ １ <-2θ ２ The area that satisfies all the inequalities of +132° is hatched.

[0044] By setting the inclination angles of the transmission-reflection units 14a and 14b so that the light falls within the hatched area in FIG. 4 , the image projection unit 10 projects S-polarized first image light from the transmission-reflection unit 14b in a first direction during a first period, and P-polarized second image light from the transmission-reflection unit 14a in a second direction during a second period. This allows the driver to view a virtual image P1 ahead from viewpoint E through the windshield WS and a virtual image P2 through the lower windshield WSB. Furthermore, because the virtual image P1 is projected as S-polarized light, the reflectivity of the windshield WS is increased, improving visibility. Furthermore, because the virtual image P2 is projected as P-polarized light, the virtual image P2 can be clearly seen even when the driver is wearing polarized sunglasses.

[0045] As described above, in the image projection device 100 of this embodiment, by alternately repeating a first period in which the image irradiation unit 10 irradiates a first image light in a first direction and a second period in which it irradiates a second image light in a second direction, it is possible to project virtual images P1 and P2 at different positions on the windshield WS and the lower windshield WSB while achieving miniaturization.

[0046] Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIG. 5 . Description of content overlapping with the first embodiment will be omitted. FIG. 5 is a schematic diagram showing a configuration example of the image projection unit 10 according to this embodiment and switching between the first image light and the second image light. In the example shown in FIG. 5 , the image projection unit 10 includes light-emitting elements 11a and 11b, light-guiding reflection units 16a and 16b, an image display unit 13, a reflecting mirror 17, and a quarter-wave plate 18. FIG. 5( a) shows a case where the first irradiation light is emitted from the light-emitting element 11a during a first period, and FIG. 5( b) shows a case where the second irradiation light is emitted from the light-emitting element 11b during a second period.

[0047] The light-guiding reflectors 16a and 16b are generally plate-shaped members made of a light-transmitting material. They are optical components that guide light incident from one end in an in-plane direction by reflecting it on the front and back surfaces, and also reflect a portion of the light by a concave-convex reflector on the back surface to extract it from the front surface. The light-guiding reflectors 16a and 16b have different light-extraction directions, but both are configured to transmit the light through the image display unit 13. The specific configuration of the light-guiding reflectors 16a and 16b is not limited, and a conventional backlight-type light guide plate known in the art can be used. While Figures 5(a) and 5(b) show an example in which the light-guiding reflector 16b is disposed closer to the image display unit 13, the positions of the light-guiding reflectors 16a and 16b may be interchanged.

[0048] The reflecting mirror 17 is a generally plate-shaped member having a reflective surface that reflects incident light while maintaining the polarization direction of the light. The reflecting mirror 17 is disposed on the optical path of the first image light emitted from the image display unit 13, and reflects the first image light in a first direction. A quarter-wave plate 18 is disposed on the reflective surface of the reflecting mirror 17.

[0049] The quarter-wave plate 18 is an optical element that is arranged on the reflecting surface of the reflecting mirror 17 and is made of a birefringent material that has different refractive indices in the slow axis and the fast axis. The thickness of the quarter-wave plate 18 is designed so that a phase difference of one-quarter of the wavelength of light occurs between the slow axis and the fast axis by the time light that is incident on one surface reaches the opposite surface. The slow axis and the fast axis of the quarter-wave plate 18 are arranged so that they are oriented in directions that differ by 45 degrees with respect to the polarization direction of the first image light.

[0050] 5A , the first irradiation light emitted from the light-emitting element 11a during the first period is guided and reflected within the light-guiding reflector 16a, passes through the light-guiding reflector 16b, and is incident on the rear surface of the image display unit 13. The first irradiation light incident on the image display unit 13 passes through the image display unit 13 and is irradiated in the direction of the reflecting mirror 17 and the quarter-wave plate 18. Here, the first irradiation light that passes through the image display unit 13 during the first period passes through the image display unit 13 and is emitted as first image light including the first image displayed on the image display unit 13. The first image light irradiated from the image display unit 13 passes through the quarter-wave plate 18 and is reflected by the reflecting mirror 17, passes through the quarter-wave plate 18 again, and is extracted in the first direction.

[0051] 5B , the second irradiation light emitted from the light-emitting element 11b during the second period is guided and reflected within the light-guiding reflection unit 16b and is incident on the rear surface of the image display unit 13. The second irradiation light incident on the image display unit 13 is transmitted through the image display unit 13 and is emitted in a second direction. Here, the second irradiation light that transmits through the image display unit 13 during the second period is transmitted through the image display unit 13 and is emitted as second image light including the second image displayed on the image display unit 13.

[0052] Here, the polarization directions of the first image light and the second image light will be described when the light transmitted through the image display unit 13 is set to be S-polarized. The image display unit 13 is made of TN liquid crystal, and the polarization direction of the polarizer (not shown) arranged on the back (first surface) side is S-polarized relative to the windshield WS, while the polarization direction of the polarizer (not shown) arranged on the front (second surface) side is P-polarized relative to the windshield WS. In this case, of the unpolarized first irradiation light and second irradiation light emitted from the light-emitting elements 11a and 11b, only S-polarized light passes through the polarizer on the first surface side, and the polarization direction is rotated by the TN liquid crystal, so that the light passes through the polarizer on the second surface side as P-polarized light. Therefore, as shown in FIG. 5B, the second image light extracted in the second direction from the image display unit 13 during the second period is P-polarized.

[0053] On the other hand, the first image light that passed through the image display unit 13 during the first period is also P-polarized light, but when reflected by the reflecting mirror 17 and extracted in the first direction, the first image light passes through the quarter-wave plate 18 twice. As described above, the slow axis and fast axis of the quarter-wave plate 18 are oriented in directions that differ by 45 degrees with respect to the polarization direction of the first image light, and therefore the polarization direction of the first image light is rotated by 90 degrees by the two transmissions, becoming S-polarized light. Therefore, as shown in FIG. 5A , the first image light extracted in the first direction from the image display unit 13 during the first period becomes S-polarized light.

[0054] Therefore, the image projection unit 10 projects the first S-polarized image light in a first direction during a first period, and the second P-polarized image light in a second direction during a second period. This allows the driver to view a virtual image P1 ahead from viewpoint E through the windshield WS and a virtual image P2 through the lower windshield WSB. Furthermore, because the virtual image P1 is projected as S-polarized light, the reflectivity on the windshield WS is increased, improving visibility. Furthermore, because the virtual image P2 is projected as P-polarized light, the virtual image P2 can be clearly viewed even when the driver is wearing polarized sunglasses.

[0055] 5A and 5B show an example in which the reflecting mirror 17 and the quarter-wave plate 18 are included in the image projection unit 10, but the reflecting mirror 17 and the quarter-wave plate 18 may be provided outside the image projection unit 10. Also, the reflecting mirror 17 may be omitted, and the quarter-wave plate 18 may be placed on the reflecting surface of the first mirror 20. Also, although an example has been shown in which the first image light passes through the quarter-wave plate 18 twice before and after reflection by the reflecting mirror 17, a half-wave plate may be used to convert P-polarized light to S-polarized light by having the first image light pass through the half-wave plate once after reflection by the reflecting mirror 17.

[0056] In the image projection device 100 of this embodiment, by alternately repeating a first period in which the image irradiation unit 10 irradiates a first image light in a first direction and a second period in which it irradiates a second image light in a second direction, it is possible to project virtual images P1 and P2 at different positions on the windshield WS and the lower windshield WSB while achieving miniaturization.

[0057] 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.

[0058] This international application claims priority based on Japanese Patent Application No. 2024-093044, filed on June 7, 2024, the entire contents of which are incorporated herein by reference.

[0059] The above descriptions of specific embodiments of the present invention have been presented for purposes of illustration. They are not intended to be exhaustive or to limit the invention to the precise forms described. Numerous modifications and variations will be apparent to those skilled in the art in light of the above description.

[0060] REFERENCE SIGNS LIST 100... image projection device 10... image irradiation section 20... first mirror 30... second mirror 11a, 11b... light emitting element 12a, 12b... lens 13... image display section 14a, 14b... transmission reflection section 15... heat sink 16a, 16b... light guiding reflection section 17... reflection mirror 18... quarter-wave plate

Claims

1. An image projection device that projects a projection image onto a display unit for displaying a virtual image, comprising: an image irradiation unit that irradiates first image light and second image light; and a projection optical unit that forms an image of the first image light at a first distance from a viewpoint position via the display unit, wherein the image irradiation unit alternately repeats a first period in which it irradiates the first image light in a first direction and a second period in which it irradiates the second image light in a second direction.

2. An image projection device according to claim 1, characterized in that the projection optical unit is provided in the first direction, and a black reflective area formed below the display unit is provided in the extension of the second direction.

3. An image projection device as described in claim 1, wherein the image irradiation unit comprises: an image display unit that displays a first image during the first period and a second image during the second period; a first light source unit that irradiates the image display unit with a first irradiation light during the first period; and a second light source unit that irradiates the image display unit with a second irradiation light during the second period.

4. An image projection device according to claim 3, wherein the image display unit is a transmissive liquid crystal display device, the transmissive liquid crystal display device is arranged along a direction in which the light distribution of the first irradiation light and the second irradiation light is maximum, and the image projection device is equipped with a first transmission-reflection unit that reflects the first irradiation light toward a first surface of the transmissive liquid crystal display device, and a second transmission-reflection unit that reflects the second irradiation light toward a second surface of the transmissive liquid crystal display device.

5. An image projection device according to claim 4, wherein the first transmission / reflection section transmits the second image light irradiated from the first surface, and the second transmission / reflection section transmits the first image light irradiated from the second surface.

6. An image projection device according to claim 3, wherein the image display unit is a transmissive liquid crystal display device, the first light source unit has a first light emitting unit that emits the first irradiation light and a first light guiding and reflecting unit that reflects the first irradiation light toward a first surface of the transmissive liquid crystal display device, and the second light source unit has a second light emitting unit that emits the second irradiation light and a second light guiding and reflecting unit that reflects the second irradiation light toward the first surface of the transmissive liquid crystal display device.

7. An image projection device according to claim 6, wherein the first light guide reflection unit reflects the first irradiation light in the first direction, and the second light guide reflection unit reflects the second irradiation light in the second direction.

8. An image projection device according to any one of claims 1 to 7, wherein the first image light is S-polarized light relative to the display unit, and the second image light is P-polarized light relative to the display unit.

Images