JPH09311307A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a display device capable of displaying a bright color virtual image. SOLUTION: This headup display is provided with a cold cathode tube 2 and a transmission type liquid crystal display element 3 on which driving voltage is impressed to change the wavelength of transmitted light in a housing 1, and light emitted from the cold cathode tube 2 and transmitted through the display element 3 is diffracted toward a viewer through a hologram 5 sealed in a laminated glass 6 whose end is attached to the housing 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device for allowing a viewer to visually recognize information, and more particularly to a head-up display device for a vehicle.

[0002]

2. Description of the Related Art A head-up display (hereinafter referred to as HUD) is used as a method for displaying information to a driver in a vehicle.
What is called is recently used. This is to display the optical information projected from the light emitting display means such as a liquid crystal display device on a combiner composed of a half mirror etc. so that the driver can superimpose it on the background outside the vehicle with almost no movement of the line of sight from the driving state. The information can be read.

FIG. 5 is a conceptual diagram showing the structure of such a vehicle-mounted HUD. Here, 41 is a driver's observation position, 42 is a combiner with a half mirror, 43 is light containing information, 44 is a lens system, 45 is a transmissive liquid crystal display (LCD) as a display, and 46 is a halogen lamp. Is a light source, 47 is a windshield, and 48 is a display image (virtual image) formed at a distance.

Light emitted from a light source 46 passes through a lens system 44, which is a collimator, and a transmissive liquid crystal display element 45, and is applied to a combiner 42 formed by a half mirror formed on a windshield 47 of a vehicle, reflected and driven. It is visually recognized at the observation position 41 by a viewer as a hand. At this time, the display information is recognized by the driver as a virtual image at position 48.

As such a HUD display element, in addition to the above-mentioned transmission type liquid crystal display element, a fluorescent display tube (VFD) or CR
Although T can be used, a fluorescent display tube or a liquid crystal display element is often used due to problems such as space and price.

Further, with the diversification, sophistication and increase of display information, not only fixed pattern display such as single warning display but also various displays at the same place are required, and colorization and dot matrix type display are required. There is a strong demand for display.

The fluorescent display tube has an advantage of being self-luminous and capable of reducing the number of parts, but has a drawback as compared with the transmissive liquid crystal display element in that it is difficult to display in color and to perform dot matrix type display.

On the other hand, a hologram is used as the above combiner because of its simplicity as an optical element and the abundance of added functions. The combiner consisting of this hologram can have not only the reflection function (diffraction function) but also the lens function and the like, so that the optical information is diffracted in the driver's visual field direction, or another optical system such as a lens is used. It is possible to form a display virtual image at an arbitrary position without using it, and it is possible to reduce the size of the optical system and the size of the entire apparatus. Another feature is that a high-luminance display image can be obtained without impairing the foreground luminance.

As described above, when a hologram is used as a combiner, there is a drawback in that a virtual display image is blurred or blurred when a fluorescent display tube having a wide wavelength band is used as a display information source due to the wavelength selectivity of the hologram. Therefore, when a hologram is used as a combiner, a light source with high monochromaticity is often used as a light source in combination with a transmissive liquid crystal display element. Specifically, a bright line spectrum of a hot cathode tube or a cold cathode tube is used. It is used in combination with a light source having a transparent liquid crystal display element.

This HUD includes a so-called stationary HUD in which the light emitting means and the combiner are integrated and installed later on the dashboard of the vehicle, in addition to the one in which the combiner is formed on the windshield as described above.
As a basic configuration, the same configuration as above is used.

[0011]

By the way, as a method of displaying in multiple colors using a transmissive liquid crystal display element, each pixel or region is divided into R (red), G (green), and B (blue). Three
This is possible by arranging a plurality of color filters such as colors, but there is a problem that the display becomes dark because the color filters absorb a lot of light. For example, in a liquid crystal display device of the TFT drive system, the aperture ratio is small and the transmittance is 3 to
4%. On the other hand, the HUD needs to obtain sufficient brightness of the display image in order for the viewer to visually recognize the display information so that the display information is superimposed on a bright background. Therefore, it is necessary to increase the light amount of the light source, which is not only efficient and wasteful, but also a measure to prevent the display element from being thermally damaged by the light source.

On the other hand, when the driver visually recognizes a display image superimposed on the background while driving, it is necessary that the display image has a color pattern that is simpler than a fine display and is easily visible. is there.

Further, JP-A-6-219184 and JP-A-6-219184.
As shown in -265812, a method using an LCD for display and a LCD for color change has been proposed, but both have a drawback that the configuration is complicated.

As described above, there has been a demand for a display device suitable for HUD applications, capable of dot matrix display corresponding to diversification of display and capable of color display, and particularly suitable for HUD using a hologram.

[0015]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and includes a light source and a transmissive display element for transmitting light emitted from the light source, and a light containing information from the light source. And a combiner arranged so as to reflect or diffract the light toward the viewer so that the display virtual image formed by the combiner can be viewed in front of the viewer. In the display device, there is provided a display device, wherein the transmissive display element changes a wavelength of transmitted light when a driving voltage is applied.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described in more detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing the basic configuration of a stationary HUD as an example of the display device of the present invention. Here, 1 is a housing, 2 is a cold cathode tube, 3
Is a transmissive liquid crystal display element, 5 is a hologram, 6 is laminated glass, 7 is a viewer, and 12 is light containing information. The case 1 is provided with a cold cathode tube 2 and a transmissive liquid crystal display element 3, and the cold cathode tube via the hologram 5 enclosed in the laminated glass 6 whose end is attached to the case 1. The light emitted from 2 and transmitted through the transmissive liquid crystal display element 3 is diffracted toward the viewer. In this example, the cold cathode tube 1
Has a length of 60 mm, a diameter of Φ2.6 mm, and a brightness of 4
A three-wavelength type of 000 cd / m ² was used.

FIG. 2 is a perspective view schematically showing the transmissive liquid crystal display element 3 used in the present invention. 3 and 4 are similar to FIG.
The transmission axis direction of the transmission type liquid crystal display element 3 shown in FIG. 1 is viewed from above, the absorption axis direction of the upper polarizing plate, the slow axis direction of the plurality of birefringent plates, the long axis direction of the liquid crystal molecules above the liquid crystal layer, and the lower direction. FIG. 3 is a plan view showing relative positions in the absorption axis direction of the side polarizing plate and in the long axis direction of liquid crystal molecules below the liquid crystal layer.

In FIG. 2, 21 and 22 are a pair of polarizing plates, 23 is a liquid crystal layer for displaying characters and figures, 24 is a birefringent plate laminated on the liquid crystal layer, and 25 is an upper polarizing plate. Absorption axis, 26 is the absorption axis of the lower polarizing plate, 27 is the major axis direction of liquid crystal molecules above the liquid crystal layer (substantially one orientation direction), and 28 is the major axis of liquid crystal molecules below the liquid crystal layer. The direction (remaining one orientation direction) 29 represents the axial direction (slow axis) of the laminated birefringent plates. The liquid crystal layer 23 has Δn ₁ ·
A nematic liquid crystal having a value of d ₁ of 1.2 to 2.5 μm and a positive dielectric anisotropy, and a liquid crystal layer having a twist angle of 160 to 300 °. Here, Δn ₁ represents the refractive index anisotropy of the liquid crystal layer, and d ₁ represents the thickness of the liquid crystal layer.

3 and 4, the absorption axis 25 of the upper polarizing plate as viewed from the long axis direction of the liquid crystal molecules 27 on the upper side of the liquid crystal layer.
Is measured in the clockwise direction by θ ₁ , and the axial direction (slow axis) 29 of the birefringent plate 24 on the upper side (polarizing plate side) viewed from the long axis direction of the liquid crystal molecules 27 on the upper side of the liquid crystal layer is watched. The value measured in the clockwise direction is θ ₂ , and the value measured in the clockwise direction of the absorption axis 26 of the lower polarizing plate viewed from the long axis direction of the liquid crystal molecules 28 on the lower side of the liquid crystal layer is θ ₃ .

This θ ₁ , θ ₂ , θ ₃ and Δn ₁ ·.
d ₁ , twist angle of liquid crystal layer, Δn ₂ · d ₂ of birefringent plate
(Δn ₂ is the refractive index anisotropy of the birefringent plate and d ₂ is the thickness of the birefringent plate) is optimized to display an almost achromatic color when no voltage is applied and to display a red color when a voltage is applied. It is possible to fabricate a transmissive color liquid crystal display element device capable of producing blue, green and blue colors.

In the following description, the liquid crystal layer will be described by taking the left spiral as an example. However, even if the spiral is reversed, the long axis direction of the liquid crystal molecules of the liquid crystal layer, the polarization axis direction of the polarizing plate, and the slow axis of the birefringent plate. By setting the relations θ ₁ , θ ₂ , and θ ₃ with the phase axis direction to be counterclockwise, color display can be easily obtained as in the case of the left spiral example.

The liquid crystal cell was formed as follows. The ITO transparent electrode provided on the glass substrate was patterned into a stripe shape, an insulating film was formed, a polyimide overcoat was formed, and this was rubbed to prepare a substrate on which an orientation control film was formed. A liquid crystal cell is formed by sealing the periphery of the two substrates thus manufactured with a sealing material, and nematic liquid crystal having a positive dielectric anisotropy is injected into the liquid crystal cell to seal the injection hole. It was sealed with a material.

More specifically, in the liquid crystal display element used in this example, Δn ₁ and d ₁ are adjusted, and Δn _{1 of} the liquid crystal layer is adjusted.
・ D _{1 is set} to 1.35 μm. Also, Δn ₂ · d ₂
Is 1.46 μm, the twist angle of the liquid crystal layer is 240 °, θ ₁
= 140 °, θ ₂ = 100 °, θ ₃ = 135 °, θ ₄ =
The angle was set to 30 ° and the central orientation direction was set to the 3 o'clock direction. The liquid crystal used has physical properties of Δn ₁ = 0.206 and viscosity η = 1.
It is 6.8 cSt (ambient temperature Ta = 20 ° C.). Also,
The size of the display screen is 64 × 32 dots.

The hologram 5 in this embodiment has a thickness of 2
A Lippmann type volume / phase hologram composed of a 0 μm acrylic photopolymer and having a size of 74 mm square was used. In addition to the above, various photosensitive materials such as polyvinylcarbazole-based photopolymers, dichromated gelatin, photoresists, and silver salts can be used as the hologram material. Further, as the hologram, a volume / phase type hologram such as a Lippmann type is preferable in that high diffraction efficiency can be obtained, but a so-called hologram such as an embossed type or a rainbow type can be widely used. The size of the hologram varies depending on the size of the display image to be obtained, the magnification, etc., but is usually an area of about several tens of mm to several hundreds of mm square, and the thickness is appropriately selected to be several μm to several tens of μm. To be done.

In this example, the hologram 5 is used for numerical calculation, experiment and photo in order to match the emission spectrum and intensity of the cold cathode tube which is the light source of the light emitting display means and the light transmission characteristics of the transmissive liquid crystal display element 3. Considering polymer characteristics and luminosity factor, center wavelength 436 nm, half width 10 nm, diffraction efficiency 6
0% and center wavelength 545 nm, half width 10 nm, diffraction efficiency 60% and center wavelength 613 nm, half width 10 nm, and diffraction efficiency 50% were prototyped. Center wavelength 437 nm, half width 7 nm, diffraction efficiency 50% and center wavelength 543 nm A hologram having a half value width of 9 nm, a diffraction efficiency of 55% and a central wavelength of 613 nm, a half value width of 12 nm, and a diffraction efficiency of 43%. As the configuration of this hologram, in addition to the multiple exposure of a plurality of wavelengths on one sheet as described above, a plurality of holograms separately exposed at each wavelength may be laminated, but the deviation of the image of each color, It is preferable to perform multiple exposure on one sheet of the light-sensitive material from the viewpoint that the decrease in the transmittance of the combiner is small.

The hologram 5 is enclosed in laminated glass, and the hologram 5 is attached to the other surface of the glass plate to prevent the plasticizer contained in polyvinyl butyral from affecting the hologram 5 on the surface of the hologram 5. Another glass plate is laminated via a polyvinyl alcohol film for the above purpose, and further via a laminated interlayer film of polyvinyl butyral.

The hologram may be provided on the surface of glass, but in view of protection of the hologram,
It is preferable to use it by enclosing it inside the laminated glass.
Therefore, it is preferable that the hologram has a small thickness and is excellent in weather resistance in that it is used for vehicles, and the photopolymer as used in the examples of the present invention is preferable.

The laminated glass is made by laminating and adhering a resin film such as a polyvinyl butyral film or a polyurethane film on at least one glass plate. Examples of its form include a glass plate / resin film and a glass plate / resin. There are a film / glass plate and a glass plate / resin film / resin substrate. The hologram is enclosed at the boundary between these glass plates or resin films. The glass plate may be colored to some extent or may be provided with a black ceramics, a heat ray reflective film or the like on the surface in addition to the antireflection film, but it is desirable that the glass plate does not affect the displayed virtual image. Further, a glass plate is most suitable for holding a hologram because it is less likely to be thermally deformed and has excellent scratch resistance, but a resin substrate may be used instead of the glass plate in terms of cost, weight reduction, and breakage. it can. Also in this case, it is preferable to seal the hologram between the two resin substrates with an adhesive or the like in view of protection from external factors. Furthermore, a combination of a resin substrate and a resin film may be used, and an antireflection film or a hard coat film for protecting the substrate may be formed on the surface thereof.

As the resin substrate and the resin film, polymethylmethacrylate (PMMA), polycarbonate, polyolefin,
Diethylene glycol bisallyl carbonate, polystyrene, rigid polyvinyl chloride, methyl methacrylate-
Examples thereof include styrene copolymer resin, styrene-acrylonitrile copolymer resin, poly (4-methylpentene-1) and the like.

As for the optical characteristics of the above-mentioned substrate, it is desirable that the refractive index is close to that of a hologram, and the value of the refractive index in the range of 1.44 to 1.64 is due to the reflection generated at the interface between the substrate and the hologram. It is preferable in that it has less noise.

In the case of a resin substrate, it is preferable that the substrate has a low birefringence, a small haze and a high light transmittance. When the birefringence is high, the display virtual image is deteriorated due to the deterioration of the matching of the polarization planes, and when the haze is large and the light transmittance is small, it is difficult for light to enter the hologram and the display virtual image is It is difficult to see.

The thickness of the substrate is preferably 0.5 to 3.0 mm. If it is less than 0.5 mm, handling may be difficult in terms of strength.

The transmissive liquid crystal display element 3 is driven to display 8 gradations at a duty of 1/32, and the light emitted from the cold cathode fluorescent lamp 2 is applied to the hologram 5 through the liquid crystal display element 3 as a result. By changing the voltage, red,
It became possible to display green and blue, and it became possible to display a virtual image of a color with good color purity.

Further, by using the display device of this example, the pattern indicating the road is green, the arrow is red, and the distance is blue.
As a result of performing the route guidance display as a color display, the visibility was excellent as compared with the simple binary display.

As described above, by controlling the drive voltage applied to the transmissive liquid crystal display element 3, the color of the display light can be changed and the color of the display virtual image can be changed, but the cold cathode tube 2 emits light. By further optimizing the characteristics, the characteristics of the transmissive liquid crystal display element 3, the driving method, and the characteristics of the hologram 5, it is possible to display a color virtual image with high visibility.

Although the stationary HUD is exemplified in the above example, the display device of the present invention can be used in the HUD shown in FIG. In this case, when the transmissive liquid crystal display element 45 has the above-mentioned configuration of the display element,
Highly visible color display is possible without using a color filter, and color display with brightness comparable to the background brightness can be realized without increasing the light amount of the light source.

The display device of the present invention can be used not only as a HUD for vehicles but also as a display device for other purposes.

[0038]

According to the present invention, a transmission type liquid crystal display device having a high transmittance and a bright line spectrum capable of color display can be obtained by changing the driving voltage applied to one pixel without using a color filter. A display device capable of displaying a virtual image in a bright color, which is suitable for HUD and has good visibility, can be configured by using the light source included therein and the combiner using the hologram. In this case, it is possible to obtain a display having a brightness comparable to the brightness of the background without increasing the light amount of the light source used, and it is possible to downsize the device and prevent deterioration of the liquid crystal display element due to heat of the light source.

In particular, in the present invention, by combining these, it is possible to display a very good color virtual image with less blurring and bleeding.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration of a stationary HUD which is an example of a display device of the present invention.

FIG. 2 is a perspective view schematically showing a liquid crystal display element according to the present invention.

FIG. 3 is a plan view showing the relative positions of the liquid crystal display element of the present invention viewed from above in the major axis direction of the upper liquid crystal molecules, the absorption axis direction of the polarizing plate, and the slow axis direction of the birefringent plate.

FIG. 4 is a plan view showing relative positions in the long axis direction of liquid crystal molecules on the lower side and the absorption axis direction of a polarizing plate when the liquid crystal display element of the present invention is viewed from above.

FIG. 5 is a conceptual diagram showing an example of a vehicle-mounted HUD.

[Explanation of symbols]

 1: Case 2: Cold cathode tube 3: Transmission type liquid crystal display element 5: Hologram 6: Laminated glass 7, 41: Viewer 12, 43: Light containing information 21, 22: A pair of polarizing plates 23: Liquid crystal layer 24: Birefringent plate 25: Absorption axis of upper polarizing plate 26: Absorption axis of lower polarizing plate 27: Liquid crystal molecule on upper side of liquid crystal layer (one orientation direction) 28: Liquid crystal molecule on lower side of liquid crystal layer ( Second orientation direction) 29: Slow axis direction of laminated birefringent plates 42: Combiner 44: Lens system 45: Transmissive liquid crystal display element 46: Light source 47: Windshield 48: Display virtual image

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G09F 9/00 359 G09F 9/00 359A

Claims (7)

[Claims] 1. A display unit which has a light source and a transmissive display element for transmitting light emitted from the light source and emits the light as information-containing light from the light source, and the light is reflected or diffracted toward a viewer. A display device having at least a combiner arranged so that a display virtual image formed by the combiner can be visually recognized in front of a viewer, wherein the transmissive display element transmits light when a drive voltage is applied. A display device characterized by changing the wavelength of light. 2. The transmissive display element comprises two substrates, each of which has a transparent electrode and an alignment film and which are provided substantially parallel to each other, and an optical anisotropy material sandwiched between the substrates. A liquid crystal layer composed of a positive nematic liquid crystal, a pair of polarizing plates disposed outside the liquid crystal layer, a birefringent plate interposed between the liquid crystal layer and at least one of the pair of polarizing plates, and a transparent At least a drive circuit for applying a drive voltage between the electrodes, the twist angle of the liquid crystal layer depending on the alignment direction of the liquid crystal molecules formed by the alignment film of each substrate is 160 to 300 °, and the liquid crystal is refracted in the liquid crystal layer. The product Δn ₁ · d ₁ of the refractive index anisotropy Δn ₁ and the thickness d _{1 of the} liquid crystal layer is 1.2 to 2.5 μm, and the total of the birefringence in the vertical direction due to the refractive index anisotropy of the birefringent plate and the thickness. Δ
n ₂ · d ₂ is 1.2 to 2.5 μm, a voltage value of three values or more is selected, and a voltage is applied between the transparent electrodes by multiplex driving, whereby color display is possible. The display device according to claim 1. 3. The display device according to claim 2, wherein the birefringent plate is a twisted phase difference plate. 4. The twist angle of the liquid crystal layer is 220 to 260.
The angle θ ₂ between the axial direction of the birefringent plate and the alignment direction of the liquid crystal molecules on the one substrate side is 75 to 110 °, and the polarization axis or absorption axis of the polarizing plate on the one substrate side and the alignment direction. Angle θ ₁ is 120 to 165 °, and the angle θ ₃ between the polarization axis or absorption axis of the polarizing plate on the other substrate side and the alignment direction of the liquid crystal molecules on the other substrate side is 115 to 155 °. The display device according to claim 2, wherein the display device is a display device. 5. Δn ₁ · d ₁ and Δn ₂ · d ₂ are 1.
0 × Δn ₁ · d ₁ <Δn ₂ · d ₂ <1.2 × Δn ₁ · d
The display device according to claim 2, wherein the relationship of ₁ is satisfied. 6. The display device according to claim 1, wherein the transmissive display element is driven by a multiplex drive with a duty of 1/32 or more. 7. The display device according to claim 1, wherein the drive circuit is provided with means for detecting an ambient temperature and changing a drive voltage to be applied according to the detected temperature. .