The present disclosure relates to an image projection device and a head-up display device equipped with the same.
It is known that what is called a head-up display (HUD) constitutes a method of displaying various kinds of driving information on a windshield of a conveyance such as a vehicle and an airplane to enable viewing of driving information simultaneously with a background visual field outside the windshield. Meanwhile, it is known that approximately 3% to 4% of light incident on an interface between air and either of an inside and an outside of the windshield reflects off the interface and thus an image displayed on the windshield is reflected doubly, causing a deterioration in visibility.
It is known that a method for preventing the deterioration of visibility involves disposing a low reflective layer on the outside of the windshield to decrease reflectance at the interface between air and the outside of the windshield. However, if a water layer is further formed on the low reflective layer, for example, under rainy weather, the effect of decreasing reflectance cannot be produced.
In Japanese Patent Application Publication No. h02-141720, a method for preventing the generation of a double image is suggested that allows s-polarized light to be incident on a windshield at Brewster's angle using a half-wave film. However, this case poses a problem that a user cannot visually identify a display image if the user wears a pair of polarized sunglasses impervious to s-polarized light. In Japanese Patent Application Publication No. h02-141720, another method is considered that allows p-polarized light to be incident on a windshield at Brewster's angle using a half-wave plate. Unfortunately, this case poses another problem that if a water layer is formed on the outside of the windshield, for example, under rainy weather, the water layer creates another part that reflects incident light, causing the generation of a double image or a deterioration in visibility of the display image.
In Japanese Patent Application Publication No. 2009-128658, a method is suggested that involves using two half-wave plates and disposing an intermediate optical layer with a refractive index different from refractive indexes of the half-wave plates between the half-wave plates to allow incident light to reflect off the intermediate optical layer. However, in this case, incident light reflects off the intermediate optical layer and thus smoothness of the optical layer makes it difficult to produce a clear image.
A head-up display described in International Publication No. 2018/168726 includes a display unit to send out a display light of s-polarized light or p-polarized light and an optical laminate having a half-wave plate. According to a description of the head-up display, either of s-polarized light and p-polarized light is incident on the optical laminate at an angle in a neighborhood of Brewster's angle, and s-polarized light or p-polarized light is sent out from the display unit can be adjusted by disposing such as a half-wave plate disposed in addition to a light source. However, no description is given of remedies against the generation of a double image and a deterioration in visibility of the display image under rainy weather. The head-up display does not allow free switching between s-polarized light and p-polarized light to be sent out from the display unit in response to weather conditions because s-polarized light or p-polarized light sent out from the display unit is set by determining the polarized light sent out from the light source in advance or disposing an additional optical member in advance.
The present disclosure is related to providing an image projection device that prevents the generation of a double image and enables satisfactory visibility of a display image even when a user is wearing a pair of polarized sunglasses and even under rainy weather, as well as provide a head-up display device equipped with the image projection device.
According to an aspect of the present disclosure, an image projection device includes a display unit to emit a display light representing a display image in a form of either of s-polarized light and p-polarized light, and an optical laminate that the display light emitted from the display unit is incident on. The optical laminate includes at least two substrates and an optical layer to change a polarization direction of incident light by 90°. The display unit includes a polarization direction converter capable of freely switching between s-polarized light and p-polarized light.
In one embodiment of the present disclosure, the polarization direction converter includes a polarization controller to automatically switch between s-polarized light and p-polarized light.
In one embodiment of the present disclosure, the polarization controller has a detector to detect weather information. The display light to be emitted from the display unit is converted into s-polarized light or p-polarized light based on information detected with the detector.
In one embodiment of the present disclosure, the display unit emits a display light of either of s-polarized light and p-polarized light such that an angle of incidence to a surface of the optical laminate is an angle in a neighborhood of Brewster's angle.
In one embodiment of the present disclosure, the optical layer is a half-wave plate.
In one embodiment of the present disclosure, the optical laminate has an intermediate laminate in which the optical layer is sandwiched between two interlayer films, and the intermediate laminate is sandwiched between the at least two substrates.
According to another aspect of the present disclosure, a head-up display device equips with the image projection device according to the present disclosure.
The present disclosure can provide an image projection device that prevents the generation of a double image and enables satisfactory visibility of a display image even under fine weather requiring a pair of sunglasses and even under rainy weather, as well as provide a head-up display device equipped with the image projection device.
Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Description disclosed herein is merely an example, and modifications that can be designed as appropriate by the person of ordinary skill in the art should be included in the scope of the present disclosure. Constituent elements in the drawings are schematically drawn for clear description in terms of width, size, thickness, shape, and other dimension as compared to actual components, and this is merely an example. In the drawings, parts that are not essential for describing effects of the present disclosure are omitted as appropriate, and omission of them should not be construed to limit the scope of the present disclosure.
An image projection device according to the present disclosure includes a display unit to emit a display light representing a display image in a form of either of s-polarized light and p-polarized light and an optical laminate that the display light emitted from the display unit is incident on. The optical laminate includes at least two substrates and an optical layer to change a polarization direction of incident light by 90°. The optical layer is designed to convert s-polarized light emitted from the display unit into p-polarized light and p-polarized light into s-polarized light. The display unit has a polarization direction converter capable of freely switching between s-polarized light and p-polarized light and thus the emitted light from the display unit is converted into s-polarized light or p-polarized light in response to weather conditions. The image projection device thus configured is put in a head-up display device, for example.
The image projection device 100 thus configured allows incident light 110 of p-polarized light emitted from the display unit 300 to be incident on the optical laminate 200 at an incidence angle of Brewster's angle θB. The incident light 110 is propagated through the optical layer 230 and is converted into s-polarized light. The incident light 110 converted into s-polarized light reflects off an interface 251 between the second substrate 250 and air, causing reflected light 111. The reflected light 111 is propagated through the optical layer 230 and is reconverted into p-polarized light. The reflected light 111 converted into p-polarized light is propagated through an interface 211 between the first substrate 210 and the air.
An observer can visually identify the reflected light 111 as a display image. The reflected light 111 is p-polarized light. As a result, even if the observer is wearing a pair of polarized sunglasses 400 that blocks s-polarized light, the p-polarized light is transmitted as-is through the polarized sunglasses. Thus, the transmitted reflected light 114 is visually identified as a display image by the observer.
Since the incidence angle is Brewster's angle θB, reflected light 112 that reflects off the interface 211 between the first substrate 210 and the air can be substantially zero. Similarly, at the interface 251 between the second substrate 250 and the air, an angle that is formed by transmitted light 113 resulting from the incident light 110 converted into s-polarized light and a line normal to a surface of the second substrate 250 is Brewster's angle θB. As a result, the transmitted light 113 that is transmitted through the interface 251 between the second substrate 250 and the air can also be substantially zero. Thus, the image projection device 100 according to the present embodiment prevents the generation of a double image and enables satisfactory visibility of a display image even under fine weather requiring a pair of sunglasses.
<Display Unit>
As illustrated in
The display unit 300 has a polarization direction converter capable of freely switching between s-polarized light and p-polarized light. The capability to freely switch between s-polarized light and p-polarized light described herein means the capability to switch polarization directions of display lights emitted from the display unit 300 without disposing an optical member in advance in addition to a display unit that emits p-polarized light or s-polarized light and fixing a polarization direction as is disclosed in International Publication No. 2018/168726, for example. The polarization direction converter provides, for example, automated switching of a one-touch type such as by a switch or automated switching in response to output signals and the likes from a device such as a sensor for detecting rain. Hence, the polarization direction converter includes a polarization controller to automatically switch between s-polarized light and p-polarized light. A system for converting the polarization direction is, for example, a method of turning a polarizing plate in-plane at an angle of 90° or a method of converting the polarization direction by manually or mechanically inserting a phase difference plate using a switch or other tools. The method of turning a polarizing plate in-plane at an angle of 90° is simpler and thus preferable.
The polarization controller is not particularly limited, with proviso that the polarization controller is capable of automatically switching between s-polarized light and p-polarized light emitted from the display unit in response to weather conditions. In one example, such a polarization controller has a detector to detect weather information, and a display light to be emitted from a display unit is converted into s-polarized light or p-polarized light based on information detected with the detector. The weather information detected with the detector is analyzed through a computer technology such as a central processing unit (CPU) and artificial intelligence (AI), and polarized light emitted from the display unit is switched based on data about the analyzed information. For instance, the polarization controller uses a method of detecting raindrops and snow with a device such as a rain sensor that supports rain and snow or a method of detecting weather information with a device such as a capacitive sensor that uses changes in moisture amount to let a display unit emit a display light of p-polarized light under fine weather and allow the display unit to switch to emitting a display light of s-polarized light through signal output in response to an event such as detection of a raindrop or snow under rainy or snowy weather. In the case of a weather pattern, such as cloudy weather, that does not belong to fine weather and rainy weather (snowy weather), the sensor detects the weather pattern as fine weather and the display light of s-polarized light from the display unit remains unchanged.
In this way, the display unit 300 has the polarization direction converter and is thus capable of freely switching between s-polarized light and p-polarized light to be emitted in response to weather conditions without disposing an additional optical member in advance and fixing a polarization direction. Accordingly, the present disclosure can provide an image projection device that prevents the generation of a double image and enables satisfactory visibility of a display image under various weather conditions, as well as a head-up display device equipped with the image projection device.
<Optical Laminate>
The optical laminate 200 used in the image projection device 100 of the present embodiment includes the optical layer 230, the first substrate 210, and the second substrate 250 and is configured such that the optical layer 230 is sandwiched between the first substrate 210 and the second substrate 250. As illustrated in
(Substrate)
Preferably, the first substrate 210 and the second substrate 250 are transparent in a visible spectrum range to maintain visibility of display images. Specifically, the substrates satisfactorily have 50% or greater transmittance of visible light with wavelengths from 380 nm to 780 nm. The transmittance is preferably 70% or greater and is more preferably 85% or greater. The first substrate 210 and the second substrate 250 may be colored. However, it is preferred that the substrates not be colored or be colored slightly. Further, a refractive index of the first substrate 210 and the second substrate 250 preferably ranges from 1.2 to 2.0 and more preferably ranges from 1.4 to 1.8. A thickness of each of the first substrate 210 and the second substrate 250 is not particularly limited and is designed appropriately to suit an application, with proviso that the thickness is within a range that does not influence reflection of display lights. The first substrate 210 and the second substrate 250 may be identical to or be different from each other, but are preferably identical to each other.
The first substrate 210 and the second substrate 250 may each be made up of a single layer or a laminate of two or more layers. Examples of a material for the first substrate 210 and the second substrate 250 include glass, cellulose triacetate (TAC), acrylic resins, polycarbonate, polyvinyl chloride, polyolefin, and polyethylene terephthalate (PET). Of these materials, glass, cellulose triacetate (TAC), polyolefin, acrylic resins, and similar materials, which have low birefringence, are preferable to prevent a polarization axis of incident light from changing, and glass is more preferable. An enhanced reflection film made up of a multilayer film or a thin metallic layer doubling as a heat insulator may be formed on each of outer surfaces of the first substrate 210 and the second substrate 250. These films can improve reflectance to incoming polarized light. However, if the optical laminate 200 is applied to an automotive windshield, the reflectance is preferably adjusted such that visible light transmittance of the optical laminate 200 is 70% or greater. The first substrate 210 and the second substrate 250 are not particularly limited in shape and may be designed appropriately to have a shape such as a sheet shape, a film shape, a plate shape, or a curved shape suitable for an application. For instance, if the first substrate 210 and the second substrate 250 are each made of a glass plate similarly to an automotive windshield, the optical laminate may be produced by applying glue or an adhesive to both surfaces of the intermediate laminate 270 and bonding glass plates to the intermediate laminate 270 so that the intermediate laminate 270 including the optical layer 230 is bonded to the glass plates. The glue or the adhesive is not particularly limited but is preferably an agent having adhesiveness excellent in reworkability, such as silicone glue or acrylic glue, if the glass plates may be removed later.
(Optical Layer)
The optical layer 230 has a function of changing a polarization direction of incident light by 90°, i.e., a function of converting p-polarized light into s-polarized light or s-polarized light into p-polarized light. The optical layer 230 having such a function is optical rotator, for example, a half-wave plate. The optical layer 230 is, for example, made by uniaxially stretching a film of polycarbonate or a cyclo-olefin polymer film such that the phase difference is one half of the wavelength or by orienting a horizontally-aligned polymerizable liquid crystal in a thickness such that the phase difference is one half of the wavelength. Preferably, the optical layer 230 converts p-polarized light or s-polarized light in an overall visible spectrum range.
(Interlayer Film)
The first interlayer film 220 and the second interlayer film 240 are, for example, made of a thermoplastic resin. Examples of generally used thermoplastic resins include polyvinyl butyral (PVB) resins, polyvinyl alcohol (PVA) resins, and ethylene-vinyl acetate (EVA) copolymer resins, and PVB resins are preferable. A thickness and hardness of each of the first interlayer film 220 and the second interlayer film 240 are not particularly limited and may be designed appropriately to suit an application, with proviso that the thickness and hardness are within a range that does not influence reflection of display lights. The first interlayer film 220 and the second interlayer film 240 may be identical to or be different from each other, but are preferably different from each other.
The image projection device 100 thus configured allows incident light 120 of s-polarized light emitted from the display unit 300 to be incident on the optical laminate 200 at an incidence angle of Brewster's angle θB. The incident light 120 reflects off an interface 211 between the first substrate 210 and air, causing reflected light 121.
The incident light 120 that is incident on the optical laminate 200 without reflecting as the reflected light 121 is propagated through the optical layer 230 and is converted into p-polarized light. The incident light 120 converted into p-polarized light is propagated through an interface 251 between the second substrate 250 and the water layer 260 and through an interface 261 between the water layer 260 and the air at Brewster's angle θB. As a result, reflected light 122 that reflects off the interface 251 between the second substrate 250 and the water layer 260 and reflected light 123 that reflects off the interface 261 between the water layer 260 and the air can be substantially zero. Meanwhile, the incident light 120 converted into p-polarized light is transmitted as transmitted light 124 through an outer side of the water layer 260.
This allows the observer to visually identify only the reflected light 121, which reflects off the interface 211 between the first substrate 210 and the air, as a display image.
In this way, owing to the display unit 300 having the polarization direction converter, the image projection device 100 of any of the present embodiments illustrated in
The image projection device 101 illustrated in
The incident light 130 that is incident on the optical laminate 200 without reflecting as the reflected light 131 is propagated through an optical layer 230 and is converted into p-polarized light. The incident light 130 converted into p-polarized light is propagated through an interface 251 between a second substrate 250 and the air at Brewster's angle θB. As a result, reflected light 133 that reflects off the interface 251 between the second substrate 250 and the air is substantially zero. The incident light 130 converted into p-polarized light is transmitted as transmitted light 134 through an outer side of the second substrate 250.
The image projection device 101 illustrated in
The incident light 140 converted into s-polarized light reflects off an interface 251 between a second substrate 250 and a water layer 260, causing reflected light 141. The incident light 140 converted into s-polarized light also reflects off an interface 261 between the water layer 260 and the air, causing reflected light 142. Since two beams of reflected light, i.e., reflected light 141 and reflected light 142, are visible, the display image visually identified by the observer is a double image. An image visually identified owing to the reflected light 142, which reflects off the interface 261 between the water layer 260 without flatness and the air, is visually identified as an image that lacks definition.
An image projection device of the present disclosure switches types of light emitted from a display light in response to weather conditions and is thereby able to display a clear image under various weather conditions. Such an image projection device can be usefully applied to outdoor-use equipment such as head-up display devices for automobiles and other conveyances.
Number | Date | Country | Kind |
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2018-045130 | Mar 2018 | JP | national |
This is a continuation application of International Patent Application No. PCT/JP2019/010285 filed Mar. 13, 2019, which claims the benefit of Japanese Patent Application No. 2018-045130 filed Mar. 13, 2018, and the full contents of all of which are hereby incorporated by reference in their entirety.
Number | Date | Country | |
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Parent | PCT/JP2019/010285 | Mar 2019 | US |
Child | 17014413 | US |