Image projection device

Abstract

To provide an image projection device that can prevent an increase in the temperature of an image display unit due to external light, while ensuring the brightness of a virtual image.SOLUTION: An image projection device (100) projects image light on a display (WS) for displaying a virtual image, and the image projection device (100) has: a light source unit that radiates radiation light including a first wavelength and a second wavelength; an image display unit (10) that displays an image with the radiation light and emits image light; and a wavelength filter (50) that is arranged on a path of the image light from the image display unit (10) to the display (WS), transmits at least the first wavelength and second wavelength within a visible light range, and cuts wavelengths different from the first wavelength and second wavelength.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

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

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

[0004] [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]

[0005] In such a conventional image projection device, in order to project an image through the windshield, which is a display unit, a projection optical unit is provided that irradiates light from below the windshield upward. Therefore, when external light such as sunlight enters from above the windshield, the external light reaches the image display unit that displays the image through the projection optical unit. In this case, the external light that reaches the image display unit through the projection optical unit is concentrated by the optical power of the projection optical unit, causing a problem of deterioration due to temperature rise.

[0006] In order to suppress such a temperature rise, it has been proposed to place a wavelength filter such as an infrared light filter or an ultraviolet light filter between the windshield and the projection optical unit as an external light cut unit to cut wavelengths other than visible light that reach the image display unit and suppress the temperature rise. However, in order to ensure the brightness of the virtual image, it is necessary to transmit the wavelength range of visible light, and it has been difficult to sufficiently suppress the temperature rise caused by external visible light that reaches the image display unit.

[0007] Therefore, the present invention has been made in consideration of the above-mentioned conventional problems, and aims to provide an image projection device that can suppress the temperature rise of the image display unit due to external light while ensuring the brightness of the virtual image. [Means for solving the problem]

[0008] In order to solve the above problems, the image projection device of the present invention is an image projection device that projects image light onto a display unit for displaying a virtual image, and is characterized in having a light source unit that irradiates irradiation light including a first wavelength and a second wavelength, an image display unit that displays an image with the irradiation light and emits the image light, and a wavelength filter that is arranged on the path of the image light from the image display unit to the display unit, and transmits at least the first wavelength and the second wavelength in the visible light range and cuts wavelengths different from the first wavelength and the second wavelength.

[0009] In the image projection device of the present invention, a wavelength filter that transmits the first wavelength and the second wavelength contained in the light irradiated from the light source unit and cuts wavelengths different from the first wavelength and the second wavelength is placed on the path of the image light, so that it is possible to suppress the temperature rise of the image display unit due to external light while maintaining the brightness of the virtual image.

[0010] In one aspect of the invention, the wavelength filter transmits a wavelength range of 1.2 to 4.0 times the half-width of the first wavelength and the second wavelength.

[0011] In addition, in one aspect of the present invention, the wavelength filter cuts wavelengths between the first wavelength and the second wavelength.

[0012] In one aspect of the present invention, the wavelength filter cuts wavelengths not less than 470 nm and not more than 505 nm.

[0013] In one aspect of the present invention, the wavelength filter cuts wavelengths not less than 540 nm and not more than 620 nm.

[0014] In one aspect of the present invention, the wavelength filter also blocks infrared light and ultraviolet light.

[0015] In one embodiment of the present invention, the first wavelength and the second wavelength have peak wavelengths in a red, green, or blue wavelength band.

[0016] In one aspect of the present invention, the image light includes polarized light in a predetermined direction, and a polarizing filter is disposed on the path of the image light from the image display unit to the display unit, which transmits polarized light in the predetermined direction and cuts polarized light in a direction intersecting the predetermined direction. Effect of the Invention

[0017] The present invention can provide an image projection device capable of suppressing a temperature rise in an image display unit due to external light while ensuring the brightness of a virtual image. [Brief description of the drawings]

[0018] [Figure 1] 1 is a schematic diagram showing projection of a virtual image P using the image projection device 100 according to the first embodiment. [Diagram 2] 2A and 2B are graphs showing schematic wavelength characteristics of a light source unit and a wavelength filter 50 according to the first embodiment, where FIG. 2A shows the intensity of light irradiated from the light source unit, and FIG. 2B shows the transmittance of the wavelength filter 50. [Diagram 3] 11 is a schematic diagram showing projection of a virtual image P using an image projection device 100 according to a second embodiment. FIG. [Figure 4] FIG. 11 is a schematic diagram showing projection of a virtual image P using an image projection device 100 according to a third embodiment. [Diagram 5] 5A and 5B are graphs showing schematic wavelength characteristics of a wavelength filter 50 according to a fourth embodiment, in which FIG. 5A shows an example of cutting blue-green wavelengths, and FIG. 5B shows an example of cutting yellow wavelengths. 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, members, and processes shown in each drawing are given the same reference numerals, and duplicated descriptions are omitted as appropriate. FIG. 1 is a schematic diagram showing the projection of a virtual image P using an image projection device 100 according to this embodiment. As shown in FIG. 1, the image projection device 100 includes an image display unit 10, a first mirror 20, a second mirror 30, a polarizing filter 40, and a wavelength filter 50. As shown in FIG. 1, the image light projected from the image projection device 100 is reflected by a windshield (display unit) WS and irradiated to the driver's viewpoint position. The driver visually recognizes the virtual image P formed on the extension of the optical path along which the image light is incident.

[0020] In the image projection device 100 shown in Fig. 1, each part is controlled by a control unit connected to each part so as to be able to communicate information with the other parts. 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 display unit 10.

[0021] The image display unit 10 is a part that irradiates image light containing an image based on image information from the control unit. The specific configuration of the image display unit 10 is not limited, and a conventionally known one such as a liquid crystal display device or an organic electroluminescence display device can be used. As an example, a liquid crystal display device that irradiates light from a back side thereof using a light emitting diode (LED: Light Emitting Diode) is used. Here, when a combination of a liquid crystal display device and a light emitting diode is used as the image display unit 10, the light emitting diode corresponds to the light source unit in the present invention. Also, when an organic electroluminescence display device is used as the image display unit 10, the organic electroluminescence element itself corresponds to the light source unit in the present invention. Also, a semiconductor laser may be used as the light source unit.

[0022] The first mirror 20 is an optical member that receives the image light emitted from the image display unit 10 and reflects the image light in the direction of the second mirror 30. In the example shown in FIG. 1, the first mirror 20 is a free-form surface mirror with a concave shape optically designed to project the image light as a virtual image P. The second mirror 30 is an optical member that receives the image light reflected by the first mirror 20 and reflects the image light in the direction of the windshield WS. In the example shown in FIG. 1, the second mirror 30 is a free-form surface mirror with a concave shape optically designed to project the image light as a virtual image P.

[0023] 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 image light as a virtual image P through the windshield WS. Here, the expansion of the light diameter in the viewpoint direction includes not only the case where the light diameter expands consistently after reflection, but also the case where the light diameter shrinks and expands after forming an image at an intermediate point. The combination of the first 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.

[0024] The polarizing filter 40 is an optical member having optical properties of transmitting polarized light in the transmission axis direction and cutting (reflecting or absorbing) polarized light perpendicular to the transmission axis direction. FIG. 1 shows an example in which the polarizing filter 40 is disposed between the image display unit 10 and the first mirror 20, but the position is not limited as long as it is on the path of the image light between the image display unit 10 and the windshield WS. When a liquid crystal display device is used as the image display unit 10, the transmission axis of the polarizing filter 40 is set to transmit polarized light of the image light irradiated from the liquid crystal display device. FIG. 1 shows an example in which the polarizing filter 40 is used, but when an organic EL display device or the like is used as the image display unit 10 and the image light is unpolarized, it is preferable to omit the polarizing filter 40.

[0025] The wavelength filter 50 is an optical member that is disposed on the path of the image light between the image display unit 10 and the windshield WS and cuts a part of the external light that reaches the inside of the image projection device 100 from the outside. The specific configuration of the wavelength filter 50 is not limited, but the wavelength filter 50 having a plurality of transmission bands can be designed by stacking known dielectric multilayer films. The wavelength characteristics of the wavelength filter 50 will be described in detail later. Although FIG. 1 shows an example in which the wavelength filter 50 is disposed between the second mirror 30 and the windshield WS, the position of the wavelength filter 50 is not limited as long as it is disposed on the path of the image light between the image display unit 10 and the windshield WS.

[0026] In Fig. 1, the optical path of the image light is depicted as a single straight line. However, the actual image light is displayed with a predetermined area on the image display unit 10, and has a predetermined area in a direction perpendicular to the traveling direction. The image light may be reflected by the first mirror 20 and travel with its light diameter reduced, and may be intermediately imaged at an intermediate imaging position F (not shown) between the first mirror 20 and the second mirror 30. When the image light reflected by the first mirror 20 is imaged at the intermediate imaging position F, the cross-sectional area through which the image light passes is minimized at the intermediate imaging position F between the first mirror 20 and the second mirror 30.

[0027] The windshield WS is a part provided in front of the driver's seat of the vehicle and transmits visible light. The windshield WS corresponds to the display unit in the present invention because the inner surface of the vehicle reflects the image light incident from the second mirror 30 toward the viewpoint and transmits light from outside the vehicle toward the viewpoint. Here, an example is shown in which the windshield WS is used as the display unit, but a combiner may be prepared as a display unit separate from the windshield WS and may reflect light from the second mirror 30 toward the viewpoint. In addition, the display unit is not limited to being located in front of the vehicle, and may be located to the side or rear as long as it projects an image toward the viewpoint of the passenger.

[0028] The virtual image P is an image that is displayed as if it were formed in space when the image light reflected by the windshield WS reaches the viewpoint (eyebox) of the driver or the like. The position at which the virtual image P is formed is determined by the spread angle of the light irradiated from the image display unit 10 as it travels toward the viewpoint after being reflected by the first mirror 20, the second mirror 30, and the windshield WS. The display contents of the image projected as the virtual image P include auxiliary information related to driving such as a warning image or emergency information, a volume indicator, a driving direction guide, and the like.

[0029] Fig. 2 is a graph showing a schematic diagram of the wavelength characteristics of the light source unit and the wavelength filter 50 according to this embodiment, with Fig. 2(a) showing the intensity of the irradiated light irradiated from the light source unit, and Fig. 2(b) showing the transmittance of the wavelength filter 50. The horizontal axis of Fig. 2 shows the wavelength, the vertical axis of Fig. 2(a) shows the relative light intensity with the maximum light intensity taken as 1, and the vertical axis of Fig. 2(b) shows the relative light transmittance with the maximum light transmittance taken as 1.

[0030] The example shown in FIG. 2(a) shows a case where a red LED, a green LED, and a blue LED are used in the light source section of the image display section 10. In FIG. 2(a), the red LED has an emission peak wavelength of 640 nm, the green LED has an emission peak wavelength of 535 nm, and the blue LED has an emission peak wavelength of 460 nm. As shown in FIG. 2(a), the red LED, the green LED, and the blue LED of the light source section have a steep emission spectrum with a half-width of about 10 to 20 nm, and the light intensity is maximum at the peak wavelength. Here, an example is shown in which a red LED, a green LED, and a blue LED are used as the light source section, but when a red laser, a green laser, and a blue laser are used as the light source section, the emission spectrum has an even narrower half-width. In this case, the LED or semiconductor laser of the light source section is advantageous in mixing colors by mounting three primary colors in one package. In addition, a combination of a blue LED, a green phosphor, and a red phosphor, or a combination of an ultraviolet LED, a blue phosphor, a green phosphor, and a red phosphor may be used as the light source section.

[0031] In the example shown in FIG. 2(b), the wavelength filter 50 has a light transmittance that transmits the wavelength range corresponding to the emission peak wavelength of the light source unit and cuts off the other wavelength ranges. More specifically, it transmits the wavelength ranges of 630 to 650 nm, 520 to 560 nm, and 440 to 480 nm corresponding to the emission peak wavelengths of the red LED, green LED, and blue LED, respectively. It also cuts off the wavelength range over 650 nm including infrared light and the wavelength range less than 440 nm including ultraviolet light. It also cuts off the wavelength ranges of 480 to 520 nm and 560 to 630 nm between the emission peak wavelengths of the light source unit.

[0032] As shown in Fig. 2(a) and (b), the transmission wavelength band of the wavelength filter 50 includes wavelengths contained in the light emitted from the light source unit. Therefore, the image light projected from the image display unit 10 by the light emitted from the light source unit passes through the wavelength filter 50 and is reflected by the windshield WS to form a good virtual image P. In addition, the wavelength filter 50 cuts out part of the wavelength range of visible light as well as infrared light and ultraviolet light from the external light traveling from the windshield WS to the image display unit 10, and the amount of transmitted energy is significantly reduced. This makes it possible to suppress the temperature rise of the image display unit 10 caused by external light while maintaining the brightness of the virtual image P.

[0033] As an example, when the energy in the spectral distribution of sunlight is taken as 100%, if a normal external light filter that blocks only infrared and ultraviolet light is used, the entire visible light band is transmitted, resulting in an energy attenuation rate of approximately 44%. If the wavelength filter 50 shown in FIG. 2(b) is used, a portion of the visible light can be blocked, resulting in an energy attenuation rate of 18%. Therefore, when the wavelength filter 50 is used, the energy of external light that reaches the image display unit 10 is less than half that when a normal external light filter is used, and the temperature rise of the image display unit 10 can be effectively suppressed.

[0034] 1, by using the wavelength filter 50 and the polarizing filter 40 in combination, it is possible to cut half of the polarized light contained in the external light, reducing the total attenuation rate to 9%, and further effectively suppressing the temperature rise of the image display unit 10. At this time, since the transmission axis of the polarizing filter 40 coincides with the polarization direction contained in the image light from the image display unit 10, the image light for projecting the virtual image P is not attenuated, and the brightness of the virtual image P can be ensured.

[0035] 2(a) and 2(b), the transmission band of the wavelength filter 50 is wider than the emission peak wavelength of the light source unit. This is because the emission peak wavelength of an LED or semiconductor laser varies depending on the temperature and current value. By making the transmission bandwidth of the wavelength filter 50 wider than the emission peak wavelength of the light source unit, the wavelength filter 50 can transmit the image light well and ensure the brightness of the virtual image P even if the emission peak wavelength from the light source unit varies.

[0036] Table 1 shows the results of simulating the transmittance of light from the light source unit and the transmittance of sunlight when the width of the transmission band of the wavelength filter 50 is changed. The filter wavelength width magnification in the table indicates the ratio of the width of the transmission band of the wavelength filter 50 to the half-width of the emission peak wavelength of the light source unit. The "2 peaks" column in the table indicates a case where there are two transmission bands, a red wavelength transmission band and blue and green wavelength transmission bands. The "3 peaks" column in the table indicates a case where there are three transmission bands corresponding to red wavelengths, blue wavelengths, and green wavelengths, respectively.

[0037] In the table, the transmittance A of the light from the light source and the transmittance B of the sunlight are expressed as (A / B). When an infrared cut filter was used, the transmittance A of the light from the light source and the transmittance B of the sunlight were A=82.0% and B=77.2%. Therefore, for the transmission band of the wavelength filter 50, a transmittance of 82% or more of the light from the light source was deemed to be acceptable, and a transmittance of 76% or less of the sunlight was deemed to be acceptable, and a judgment of good was made when both conditions were met.

[0038] [Table 1]

[0039] As shown in Table 1, when the transmission bandwidth of the wavelength filter 50 is in the range of 1.2 to 4.0 times the half-width of the emission peak wavelength of the light source unit, the transmittance A of the light from the light source unit and the transmittance B of the sunlight are better than those of an infrared cut filter. Therefore, the transmission band of the wavelength filter 50 is preferably 1.2 to 4.0 times the half-width of the light from the light source unit.

[0040] Moreover, the wavelength filter 50 preferably cuts wavelengths between a plurality of emission peak wavelengths of the light source unit, and preferably cuts a wavelength width of at least 10 nm or more, and more preferably cuts a wavelength width of 20 nm or more. If the wavelength width cut by the wavelength filter 50 in the visible light range is smaller than this range, the energy of external light reaching the image display unit 10 cannot be sufficiently reduced, making it difficult to effectively suppress a rise in temperature.

[0041] As described above, in the image projection device 100 of this embodiment, a wavelength filter 50 that transmits multiple emission peak wavelengths contained in the light irradiated from the light source unit and cuts wavelengths different from the emission peak wavelengths is arranged on the path of the image light, so that it is possible to suppress a temperature rise in the image display unit 10 due to external light while maintaining the brightness of the virtual image P.

[0042] Second embodiment Next, a second embodiment of the present invention will be described with reference to Fig. 3. Descriptions of contents overlapping with those of the first embodiment will be omitted. Fig. 3 is a schematic diagram showing projection of a virtual image P using an image projection device 100 according to this embodiment. In this embodiment, a wavelength filter 50 is disposed on the path of image light between the first mirror 20 and the second mirror 30.

[0043] In the image projection device 100 of this embodiment, a wavelength filter 50 that transmits multiple emission peak wavelengths contained in the light irradiated from the light source unit and cuts wavelengths different from the emission peak wavelengths is placed on the path of the image light, so that it is possible to suppress the temperature rise of the image display unit 10 due to external light while maintaining the brightness of the virtual image P.

[0044] Third embodiment Next, a third embodiment of the present invention will be described with reference to FIG. 4. Description of contents overlapping with the first embodiment will be omitted. FIG. 4 is a schematic diagram showing projection of a virtual image P using an image projection device 100 according to this embodiment. In this embodiment, a wavelength filter 50 is disposed on the path of image light between the image display unit 10 and the first mirror 20. FIG. 4 shows an example in which a polarizing filter 40 is disposed between the wavelength filter 50 and the image display unit 10, but the polarizing filter 40 may be disposed between the first mirror 20 and the wavelength filter 50.

[0045] In the image projection device 100 of this embodiment, a wavelength filter 50 that transmits multiple emission peak wavelengths contained in the light irradiated from the light source unit and cuts wavelengths different from the emission peak wavelengths is placed on the path of the image light, so that it is possible to suppress the temperature rise of the image display unit 10 due to external light while maintaining the brightness of the virtual image P.

[0046] (Fourth embodiment) Next, a fourth embodiment of the present invention will be described with reference to Fig. 5. Descriptions of contents overlapping with the first embodiment will be omitted. Fig. 5 is a graph showing a schematic wavelength characteristic of a wavelength filter 50 according to this embodiment, Fig. 5(a) shows an example of cutting blue-green wavelengths, and Fig. 5(b) shows an example of cutting yellow wavelengths.

[0047] In the example shown in Fig. 5(a), the wavelength filter 50 transmits wavelength ranges of 520 to 650 nm and 440 to 480 nm corresponding to the emission peak wavelengths of the red LED, green LED, and blue LED, respectively. It also cuts wavelengths over 650 nm including infrared light and wavelengths below 440 nm including ultraviolet light. It also cuts wavelengths between the emission peak wavelengths of the light source unit, that is, 480 to 520 nm.

[0048] In the example shown in Fig. 5(b), the wavelength filter 50 transmits wavelength ranges of 630 to 650 nm and 440 to 560 nm corresponding to the emission peak wavelengths of the red LED, green LED, and blue LED, respectively. It also cuts wavelength ranges over 650 nm including infrared light and wavelength ranges below 440 nm including ultraviolet light. It also cuts wavelength ranges of 560 to 630 nm between the emission peak wavelengths of the light source unit.

[0049] In the image projection device 100 of this embodiment, a wavelength filter 50 that transmits multiple emission peak wavelengths contained in the light irradiated from the light source unit and cuts wavelengths different from the emission peak wavelengths is placed on the path of the image light, so that it is possible to suppress the temperature rise of the image display unit 10 due to external light while maintaining the brightness of the virtual image P.

[0050] (Modification of the fourth embodiment) Next, a modified example of the fourth embodiment of the present invention will be described. In the first to fourth embodiments, an LED or a semiconductor laser that emits light in the three primary colors of red, green, and blue has been described as the light source unit, and the wavelength filter 50. However, as long as the light emitted from the light source unit includes a plurality of emission peak wavelengths and the transmission band of the wavelength filter 50 corresponds to the emission peak wavelengths, the specific wavelengths are not limited.

[0051] As an example, a white LED using a blue LED and a yellow phosphor has a steep emission peak at 460 nm corresponding to the primary light from the blue LED and an emission peak of the secondary light with a wide wavelength range obtained by wavelength conversion using the yellow phosphor. When such a white LED is used as a light source, a narrow range of blue light and a wide range of yellow light can be transmitted to project an image by using a wavelength filter 50 having a transmission band as shown in Fig. 5(a).

[0052] 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]

[0053] 100...Image projection device 10...Image display section 20…1st mirror 30…2nd mirror 40...Polarizing filter 50...Wavelength filter

Claims

1. An image projection device that projects image light onto a display unit for displaying a virtual image, A light source unit that irradiates irradiation light including a first wavelength and a second wavelength; an image display unit that displays an image using the irradiation light and emits the image light; An image projection device comprising: a wavelength filter disposed on a path of the image light from the image display unit to the display unit, the wavelength filter transmitting at least the first wavelength and the second wavelength in the visible light range and cutting wavelengths different from the first wavelength and the second wavelength.

2. 2. The image projection device according to claim 1, wherein the wavelength filter transmits a wavelength range of 1.2 to 4.0 times the half-width of the first wavelength and the second wavelength.

3. 2. The image projection device according to claim 1, The image projection device, wherein the wavelength filter cuts wavelengths between the first wavelength and the second wavelength.

4. 4. The image projection device according to claim 3, The image projection device, wherein the wavelength filter cuts wavelengths of 470 nm or more and 505 nm or less.

5. 4. The image projection device according to claim 3, The image projection device, wherein the wavelength filter cuts wavelengths of 540 nm or more and 620 nm or less.

6. 2. The image projection device according to claim 1, The image projection device, wherein the wavelength filter also blocks infrared light and ultraviolet light.

7. 2. The image projection device according to claim 1, 13. An image projection device, wherein the first wavelength and the second wavelength have peak wavelengths in a red, green or blue wavelength band.

8. 8. The image projection device according to claim 1, the image light includes polarization in a predetermined direction; an image projection device comprising: a polarizing filter disposed on a path of the image light from the image display unit to the display unit, the polarizing filter transmitting polarized light in the specified direction and cutting polarized light in a direction intersecting the specified direction.

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