JPH0843764A - Projection type image display device - Google Patents

Abstract

PURPOSE:To obtain a smooth picture where stripes by a light shielding mask are made inconspicuous at low cost. CONSTITUTION:In this projection type picture display device displaying the picture by forming transmitted light from a liquid crystal display panel 2 where picture elements are arrayed in a matrix state into a picture on a projection screen 7; a parallel plate glass 1 shifting the optical path of incident light is provided at least at a part of an optical path between the liquid crystal display panel 2 and the projection screen 7, and the picture based on the display panel 2 and the picture based on the display panel 2 positionally deviated by a specified shift amount are superimposed to be projected on the screen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display device for displaying an image by making light from a light source incident on a transmissive display element or the like and projecting the transmitted light on a screen.

[0002]

2. Description of the Related Art A transmissive display panel does not emit light by itself, but its transmissivity is changed by a drive signal, and an intensity of light from a light source is modulated to display an image or a character. Examples of such a transmissive display panel include a liquid crystal display panel, an electrochromic display, and a PLZT (Plumbum Lanthanum Zirconium Titanium).
oxide) and other transparent ceramics. Among them, liquid crystal display panels are widely and generally used for pocketable TVs, word processors, and the like.

In such a liquid crystal display panel, a minimum display unit called a picture element is regularly arranged, and by applying an independent driving voltage to each of the picture elements, the optical characteristics of the liquid crystal are improved. It changes, which causes images and characters to be displayed. As a method of applying an independent drive voltage to each picture element, a simple matrix method and an active matrix method are known.

According to the above active matrix system, each pixel is provided with a thin film transistor or an MI of a diode.
It is necessary to provide an element such as M (Metal Insulator Metal) and to provide a line for supplying a driving signal to these elements between the picture elements. Therefore, the ratio of the picture element area in the screen (called the aperture ratio) becomes small. Further, of the light emitted to the liquid crystal display panel, the light incident on the area other than the pixel area is not modulated by the display signal. In a display panel in which the display operation mode is a normally black mode (an operation mode in which light does not pass through when an electric field is not applied to the liquid crystal layer), light incident on a region other than the pixel region does not pass through the liquid crystal display panel. Does not penetrate. In a liquid crystal display panel in which the display operation mode is a normally white mode (an operation mode in which light is transmitted when an electric field is not applied to the liquid crystal layer), the light incident on the area other than the pixel area is the liquid crystal display panel. , The black level of the display screen rises and the contrast decreases.

In order to prevent the deterioration of the contrast, a light-shielding mask (Blackout Mask) is provided in a matrix form in a region other than the picture elements as necessary to absorb or reflect light which does not contribute to display. Is known to do. Therefore, when this panel is projected, stripes due to the light-shielding mask are conspicuous on the screen, and the image quality is significantly deteriorated. Therefore, a diffraction grating is inserted in the light path on the exit side of the liquid crystal display panel to diffract the light emitted from the liquid crystal display panel and pass through the picture element aperture of the liquid crystal display panel at the position where the light-shielding mask should be focused on the screen. It is possible to form an image of the formed light so that the light-shielding mask is not conspicuous, for example, JP-A-59-214825 and JP-A-63-114.
It is disclosed in Japanese Patent Laid-Open No. 475,475 and Japanese Patent Laid-Open No. 3-148622.

According to the color display device (first prior art) disclosed in Japanese Patent Laid-Open No. 59-214825, a front surface of a pixel group in which three types of pixels corresponding to three primary colors are linearly arranged alternately. In addition, a transmissive plane diffraction grating is provided, and the light emitted from each pixel is diffracted by this diffraction grating and divided into three (0th-order diffracted light and ± 1st-order diffracted light).
Therefore, a real image and two virtual images of each pixel can be seen. Therefore, even if pixels of a single color are scattered (even if the pixels are arranged at a low density), they do not appear to be scattered but appear to be dense. In addition, when two or more pixels emit light, it appears that the pixels of the combined color emit light, and the image becomes clear. Similar technology
It is also disclosed in Japanese Patent Laid-Open No. 3-148622.

According to the image display device (second prior art) disclosed in Japanese Patent Laid-Open No. 63-114475, an optical low-pass filter having a diffraction grating is provided between the image display and the eyepiece. It is arranged at a predetermined position on the optical axis and at a predetermined angle with respect to a plane perpendicular to the optical axis (may be integrally formed on the surface of the image display). The image display has dot-shaped display segments arranged two-dimensionally, and an optical low-pass filter cuts frequency components of (1 / 2p) or more (the pitch of the display segments is p).
Therefore, only the information regarding the display image is displayed. Therefore, the roughness due to the dot pitch is eliminated, and an easily viewable image can be reproduced. The optical low-pass filter only needs to have a blurring effect, and examples thereof include a polished glass and a milky white resin plate.

In addition, as a third conventional technique, a plurality of projection type image display devices are used so that an opening of a picture element of one liquid crystal display panel overlaps a light-shielding mask of a picture element of another display panel. When superimposing images, it is known to insert a parallel plate element into the entire optical path near the projection lens and change the tilt angle to make fine adjustments (picture element matching) of multiple images on the screen. (For example, Japanese Patent Laid-Open No.
-123868 gazette).

[0009]

However, according to the above-mentioned first and second prior arts, both use diffraction gratings. In this case, the diffraction angle β of light is as shown in FIG.
, The diffracted light is largely dependent on the order of the diffracted light, so that the diffracted light of each order (0th, 1st, and 2nd order diffracted light) is formed on the screen according to each diffraction angle. To be imaged.

Further, the diffraction angle of light largely depends on the grating spacing of the diffraction grating, as shown in the following equation (1). That is, if the lattice spacing is D, α is the angle formed by the incident light with respect to the optical axis, β is the angle formed by the diffracted light with respect to the optical axis, m is the order of the diffracted light, and λ is the wavelength of the incident light. Formula (1)
Is established.

Sin α-sin β = m · λ / D (1) Therefore, it is necessary to prepare a specific diffraction grating having a corresponding grating interval for each display panel having a different pixel pitch. In this case, since the manufacturing cost of the diffraction grating is high, there is a problem that the cost of the device equipped with this diffraction grating increases.

Further, according to the above-mentioned third conventional technique, since all the light projected from one projection type image display device onto the screen is shifted, the images of a plurality of projection type image display devices are simultaneously displayed on the screen. This is effective only in the case of projection, causes a significant increase in cost, and makes the configuration of the apparatus itself complicated and large-scale.

From the above, the present invention has been made in view of the above problems, and an object thereof is to maintain a fineness of a display panel and obtain a smooth and natural image at a low cost. To provide a device.

[0014]

In order to solve the above-mentioned problems, the projection-type image display device according to the present invention forms an image of the transmitted light from the liquid crystal display means in which picture elements are arranged in a matrix on a screen. The following means are taken in the projection-type image display device that displays an image.

That is, the above-mentioned projection type image display device is provided with an optical path shift means provided in at least a part of the optical path between the liquid crystal display means and the screen to shift the optical path of incident light. .

In order to solve the above-mentioned problems, the projection type image display device according to a second aspect of the invention is characterized in that, in the structure of the first aspect, the optical path shifting means is a transparent parallel plate element.

In order to solve the above-mentioned problems, the projection type image display apparatus according to a third aspect of the present invention has the structure of the second aspect, in which the transparent parallel plate element is arranged such that the shift amount of the optical path is approximately half the pixel pitch. The refractive index and thickness of are set,
The transparent parallel plate element is tilted at a predetermined angle with respect to a plane perpendicular to the optical axis.

In order to solve the above-mentioned problems, a projection type image display device according to a fourth aspect of the present invention is the structure according to the first or second aspect, wherein the optical path shifting means comprises a plurality of surfaces, and at least one surface method is used. The line is not parallel to the optical axis.

According to a fifth aspect of the present invention, in order to solve the above-mentioned problems, in the structure of the first or second aspect, the optical path shifting means comprises a plurality of surfaces, and each surface has its surface. In this configuration, the normal line is arranged so as to make a symmetrical angle with respect to the optical axis.

In order to solve the above-mentioned problems, the projection type image display device according to a sixth aspect of the present invention is the structure according to the first aspect, wherein the optical path shifting means is made of a birefringent substance.

In order to solve the above-mentioned problems, the projection type image display device according to a seventh aspect displays an image by forming an image of transmitted light from a liquid crystal display means in which picture elements are arranged in a matrix on a screen. The following means are taken in the projection type image display device.

That is, an optical path shift means provided on the optical axis between the liquid crystal display means and the screen for shifting the optical path of incident light, and an optical axis between the liquid crystal display means and the screen. The optical path difference correction means is provided on the upper side and corrects the optical path difference caused by the optical path shift means.

[0023]

According to the structure of the first aspect, the transmitted light from the liquid crystal display means is projected on the screen through the optical path shifting means, and is also projected on the screen without passing through the optical path shifting means. In other words, an image based on the liquid crystal display means (an image formed without passing through the optical path shift means) and an image based on the liquid crystal display means that is displaced in parallel by a predetermined shift amount (via the optical path shift means). The projected image is projected onto the screen so that it is superposed.

According to the structure of claim 2, in addition to the operation of claim 1, since the optical path shifting means is a transparent parallel plate element, a smooth image can be obtained at low cost.

According to the structure of claim 3, in addition to the function of claim 2, since the shift amount of the optical path is approximately half of the pixel pitch, the pixel becomes a double image on the screen and is smooth. An image is obtained.

According to the structure of claim 4, claim 1 or 2
In addition to the effect of, the number of picture elements to be imaged increases, and a smooth image can be obtained.

According to the configuration of claim 5, claim 1 or 2
In addition to the effect of, the number of picture elements to be imaged increases, and a smooth image can be obtained.

According to the structure of claim 6, in the operation of claim 1, the shift of the incident light is 2 due to the birefringent substance.
This is done by splitting into two polarized lights.

According to the structure of claim 7, the transmitted light from the liquid crystal display means is projected on the screen through the optical path shift means. At this time, an optical path difference is generated between the light passing through the optical path shift means and the light not passing therethrough, but the optical path difference correction means corrects the optical path difference. Therefore, on the screen, between the image formed through the optical path difference correcting means without passing through the optical path shifting means and the image formed by shifting in parallel by a predetermined amount through the optical path shifting means. Has no optical path difference and is projected on the screen so that these images are superimposed.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS. 1 to 8.

[Embodiment 1] As shown in FIG. 1, a projection type image display apparatus of this embodiment converts a light source 4 for emitting light for projection and a light emitted from the light source 4 into parallel light. A parabolic mirror 3 that guides the liquid crystal display panel 2 (liquid crystal display means), a field lens 5 that guides the transmitted light of the liquid crystal display panel 2 to a projection lens 6, and a projection screen 7 that forms an image of the light from the projection lens 6 ( Screen).

In the present projection type image display device, a parallel plate glass 1 (optical path shifting means) is further provided on at least a part of the optical path between the liquid crystal display panel 2 and the projection screen 7. For example, parallel plate glass 1
Is provided on the optical axis l between the liquid crystal display panel 2 and the projection screen 7, as shown in FIG. 1, and has a predetermined angle θ with respect to the normal line of the incident surface (see FIG. 2). The optical path of the incident light is shifted only by tilting. The shift amount of the optical path differs depending on the thickness of the parallel plate glass 1, the refractive index, and the angle θ.

In this embodiment, the liquid crystal display panel 2 having the following specifications was used. That is, the diagonal line of the display screen is 75 mm, the pixel pitch is 160 μm × 130 μm in length × width, the pixel region is 80 μm × 75 μm in length × width, and the aperture ratio (the size of the pixel region in the screen is The ratio) is 29%. Although the twisted nematic is used as the operation mode of the liquid crystal, it is also possible to use other modes.

Examples of the light source 4 include a metal halide lamp, a xenon lamp and a halogen lamp.

According to the above structure, the light emitted from the light source 4 is collimated by the parabolic mirror 3 and is then incident on the liquid crystal display panel 2, and further is transmitted to the projection lens 6 via the field lens 5. Be guided. Here, since the parallel plate glass 1 is obliquely arranged at a part of the pupil position of the projection lens 6, the parallel plate glass 1 refracts the incident light as shown in FIG.

That is, as shown in FIG. 2, the light incident on the point A at an angle of θ with respect to the normal to the plane of incidence of the parallel flat glass 1 is refracted in the parallel flat glass 1 according to Snell's law. After that, go out from point B into the air. At this time, the incident light and the outgoing light of the parallel flat plate glass 1 are parallel to each other, and a predetermined shift amount d is generated between them.

Now, referring to FIG. 2, the shift amount d generated between the incident light and the emitted light of the parallel flat plate glass 1 will be determined.

As described above, the incident angle of the incident light on the parallel flat plate glass 1 is θ, the refraction angle in the parallel flat plate glass 1 is α, the thickness of the parallel flat plate glass 1 is D, and the refraction of the parallel flat plate glass 1 is made. When the ratio is n, α = sin ⁻¹ (1 / n · sin θ) (2), and the line segment AB corresponding to the length of the optical path in the parallel plate glass 1 is AB = D / cos (sin ⁻¹ (1 / n · sin θ)) (3), and the shift amount d of the light generated by the incident light passing through the parallel flat glass 1 is d = AB · sin (θ−α) = D · sin (θ− It is expressed by sin ^-1 (1 / n · sin θ)) / cos (sin ⁻¹ (1 / n · sin θ)) (4).

The shift amount d is adjusted such that the thickness of the parallel flat plate glass 1 and the inclination angle of the parallel flat plate glass 1 are adjusted so that the shift amount d is approximately half the pixel pitch of the liquid crystal display panel 2, and the projection lens 6 is used.
It is preferable to dispose near the pupil position. With this setting, the picture element is formed as a double image on the projection screen 7, so that the stripes due to the light shielding mask become inconspicuous.

As described above, when the parallel flat plate glass 1 is viewed from the projection lens 6 side, it seems that the liquid crystal display panel 2 is shifted by d. Therefore, on the projection screen 7, an image based on the original liquid crystal display panel 2 (an image based on transmitted light that does not pass through the parallel flat plate glass 1) and an image based on the liquid crystal display panel 2 (parallel plate based on the transmitted light that does not pass through the parallel flat plate glass 1). Glass 1
The image based on the transmitted light that has passed through) was projected so as to be superimposed, and a smooth image was obtained.

Specifically, from the above equations (2) to (4), d
When the thickness D of the parallel flat plate glass 1 is set to 1.3 mm, the incident angle θ is set to 10 °, and the refractive index n is set to 1.52 so that it is approximately half the pixel pitch (about 80 μm in this embodiment), Figure 3
As shown in FIG. 3, the image of the picture element aperture portion is superposedly formed at the position where the image of the light-shielding mask is originally formed (see the shaded portion in FIG. 3A) (see the shaded portion in FIG. 3B). ), The stripes due to the light-shielding mask became inconspicuous, and a smooth image was obtained. 3 (a) shows the state of the projection screen 7 before the parallel flat plate glass 1 is arranged, and FIG. 3 (b) shows the state of the projection screen 7 after the parallel flat plate glass 1 is arranged (picture element image). Is shown.

In the present embodiment, as described above, the parallel flat glass 1 is arranged so as to be inclined with respect to the vertical direction of the liquid crystal display panel 2 (the surface perpendicular to the optical axis 1). The present invention is not limited to this. For example, the liquid crystal display panel 2 may be arranged so as to be oblique with respect to the left-right direction or the diagonal direction, or the liquid crystal display panel 2 may be arranged in the vertical direction. You may respectively provide the parallel plate glass 1 in the left-right direction.

[Embodiment 2] Another embodiment of the present invention will be described below with reference to FIG. The members having the same functions as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted here.

As shown in FIG. 4, in the projection type image display apparatus of this embodiment, as in the case of the first embodiment, the incident light is incident at a predetermined angle with respect to the normal to the incident surface. The parallel plate glass 1 (optical path shifting means) is arranged on one side of the optical axis l (upper side from the optical axis l in FIG. 4), and is parallel to the liquid crystal display panel 2 on the other side of the optical axis l. Direction (Fig. 4
In the above, the case where the parallel flat plate glass 8 (optical path difference correction means) is arranged below the optical axis 1 is illustrated, but the other configurations are the same as those in the first embodiment.

According to the configuration of the first embodiment, with the optical axis 1 as a boundary, the side on which the parallel flat plate glass 1 is arranged (the upper side from the optical axis 1) and the side on which the parallel flat plate glass 1 is not arranged ( Optical axis l
From the lower side).

This is because the light passing through the parallel flat plate glass 1 has a longer optical path than that of the light not passing through the parallel flat plate glass 1 due to refraction, resulting in an optical path difference. Defocusing occurs in the image formed on the projection screen 7 based on the optical path difference thus generated. In order to correct the out-of-focus condition, in the present embodiment, a parallel plate glass 8 for correcting the optical path difference is provided on the portion where the parallel plate glass 1 is not provided, as shown in FIG. It is provided parallel to the panel 2.

In this embodiment, the parallel flat plate glass 1 is used.
Is arranged at a part of the pupil position of the projection lens 6 at a predetermined angle (for example, 10 °) with respect to the perpendicular of the optical axis l, and the parallel plate glass 8 is vertically downward from the optical axis l. It is provided in the direction. Since the parallel flat glass 1 has a small inclination angle of 10 °, the thickness of the parallel flat glass 8 and the thickness of the parallel flat glass 1 are set to be the same so that the optical path length is the same (the optical path difference is zero). There is.

According to the above construction, the light passing through the parallel flat plate glass 1 and the light passing through the parallel flat plate glass 8 both have the same optical path length, so that there is no optical path difference between them. As a result, the light passing through the parallel plate glass 1
The light that has passed through the parallel plate glass 8 is condensed and imaged on the projection screen 7 in a state where there is no optical path difference, so that a smooth and defocused image is obtained.

By the way, as the optical path shifting means and the optical path difference correcting means, in addition to the parallel plate glass shown in the first and second embodiments, for example, FIGS. 5A and 5B and FIG.
A polygonal pyramid such as a quadrangular pyramid and a quadrangular pyramid, and a polygonal pyramid may be used. The polygonal pyramid shape has a common feature that it has a plurality of surfaces, and the surface normal of at least one surface is not parallel to the optical axis l. The polygonal frustum shape has a plurality of surfaces, and each surface has a common feature that the normal to the surface forms a symmetrical angle with respect to the optical axis.

When a quadrangular pyramid shape as shown in FIGS. 5A and 5B is used as the parallel flat plate glass 1 (or the parallel flat plate glass 8), an image is formed as shown in FIG. 5C. The number of picture elements is increased from 1 (the number in the case where the parallel flat glass 1 is not used) to 4 which is equal to the number of picture elements around the same, and along with this, a smooth image can be obtained. Also, FIG.
When a rectangular truncated pyramid shape as shown in (a) and (b) is used as the parallel flat plate glass 1 or the parallel flat plate glass 8,
As shown in FIG. 6C, the number of picture elements to be imaged is increased from one (when the parallel flat glass 1 is not used) to five, which is equal to the number of picture elements in the surrounding area. Along with this, a smooth image is obtained. Note that FIGS. 5B and 6B are FIGS. 5A and 6A, respectively.
FIG.

[Embodiment 3] Still another embodiment of the present invention will be described below with reference to FIGS. 7 and 8. The members having the same functions as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted here.

In this embodiment, as shown in FIG.
Instead of the parallel plate glass 1 of Example 1, the birefringent element 9 (birefringent substance) is orthogonal to the optical axis l (parallel to the liquid crystal display panel 2), and the upper side and the lower side of the optical axis l. It is different from the first embodiment in that it is provided over the side.

Liquid crystal display panel 2 utilizing polarized light
In this case, since polarizing plates (both not shown) are provided on the light incident side and the light emitting side, respectively, the light passing through the liquid crystal display panel 2 becomes linearly polarized light vibrating in a specific direction. Therefore, the vibration direction of this linearly polarized light and the axial direction of the birefringent element are set to be inclined by 45 °, or the emitted light from the liquid crystal display panel 2 is converted into circularly polarized light via a wave plate (not shown), Birefringence effect when incident on the birefringent element 9 (eg, Tetsuo Sueda "How to Use Optical Components and Points to Note")
Separation into ordinary rays and extraordinary rays (see pages 69 to 86, published by Optronics), and the same effects as those of the parallel flat glass 1 of Examples 1 and 2 can be obtained.

The birefringent element 9 of this embodiment is composed of a Savart plate. Specifically, a uniaxial crystal such as quartz or calcite is cut from an oblique direction with respect to the optical axis of the crystal and finished into a parallel plate. Although the birefringent element 9 is used in this embodiment, this utilizes a phenomenon that the traveling direction of the extraordinary ray changes when the Savart plate makes the light obliquely incident on the optical axis. Is.

When the angle between the normal of the Savart plate and the optical axis of the crystal is θ, the light incident on the Savart plate at the angle of θ is separated into two polarizations P and Q orthogonal to each other. At this time, the polarized light Q corresponding to the extraordinary ray (the wavefront and the light traveling direction are not perpendicular) travels obliquely in the Savart plate against the Snell's law and is emitted from the Savart plate. On the other hand, the polarized light P corresponding to an ordinary ray (where the wavefront and the traveling direction of the light are perpendicular to each other) goes straight through the Savart plate and is emitted from the Savart plate. Both of these separated polarizations P
The separation width d between −Q is obtained as follows.

As shown in FIG. 8, the angle between the normal of the Savart plate and the optical axis of the crystal is θ, the refractive index for ordinary rays is n _o, and the refractive index for extraordinary rays is n, as shown in FIG.
_{Assuming e} , the separation width d between the extraordinary ray and the ordinary ray is represented by d = [(b ² −a ² ) / 2c ² ] · t · sin 2θ (5). _{Here, a = 1 / n e,} b = 1 / n o, and ^{c 2 = a 2 sin 2 θ} + b 2 cos 2 θ, and t is the thickness of the Savaru plate.

According to the above configuration, when the transmitted light of the liquid crystal display panel 2 is incident on the birefringent element 9, the birefringent element 9
The ordinary ray and the extraordinary ray pass through different optical paths in the inside, and are separated into two polarizations P and Q.
Image on top, respectively. As a result, when the birefringent element 9 is viewed from the projection lens 6 side, it is as if the liquid crystal display panel 2
Appears to have shifted by d. Therefore, on the projection screen 7, the original image by the liquid crystal display panel 2 and d
The image on the liquid crystal display panel 2 which was displaced by a certain amount was projected so as to be superimposed, and a smooth image was obtained.

[0058] In this case, calcite _{(n e = 1.6584, n o} =
If the thickness of the Savart plate (θ = 45 °) created from 1.4864) is set to 0.37 mm, the separation width d between the polarized light P and Q is approximately
The thickness was 80 μm, and similar to Examples 1 and 2, a smooth image with no out-of-focus was obtained.

In the present embodiment, the birefringent element 9 has been described as being arranged at the pupil position of the projection lens 6, but the present invention is not limited to this, and it is on the exit side of the liquid crystal display panel 2. Therefore, it may be provided on a part of the optical path.

In the above-described first to third embodiments, the case where the image shift amount is set to half the picture element pitch has been described, but the shift amount may be any value as long as the resolution does not decrease, and the picture element is It does not matter if the parts overlap.

Further, Examples 1 to 3 are as an illumination method,
Telecentric lighting is used, but other lighting methods,
For example, it can be applied to critical lighting and Koehler lighting systems.

Further, in the first to third embodiments, the case of the single plate type has been described for the sake of convenience of explanation, but the present invention is not limited to this, and can be applied to a three plate type projection image display device.

[0063]

As described above, the projection type image display apparatus according to the present invention is provided in at least a part of the optical path between the liquid crystal display means and the screen and shifts the optical path of incident light. This is a configuration including means.

Therefore, it is possible to provide a low-cost projection type image display device irrespective of the picture element pitch with a simple structure in which only the optical path shift means is provided. An image based on the liquid crystal display means (an image formed without passing through the optical path shift means)
And an image based on the liquid crystal display means (an image formed via the optical path shift means) that is displaced by a predetermined shift amount are projected on the screen so as to be superposed, so that the conventional diffraction grating is used. In the same manner as in the above case, the effect is obtained that the stripes due to the light-shielding mask become inconspicuous and a smooth image is obtained.

As described above, the projection type image display device according to the second aspect has the configuration according to the first aspect, in which the optical path shifting means is a transparent parallel plate element.

Therefore, in addition to the effect of the first aspect, since the transparent parallel plate element is used as the optical path shifting means, there is an effect that a lower cost projection type image display device can be provided.

As described above, in the projection type image display device according to the third aspect, in the structure according to the second aspect, the refractive index of the transparent parallel plate element is set so that the shift amount of the optical path is approximately half the pixel pitch. , And the thickness are set, and the transparent parallel plate element is inclined at a predetermined angle with respect to a plane perpendicular to the optical axis.

Therefore, in addition to the effect of the second aspect, as compared with the conventional diffraction grating, optimization can be achieved simply by adjusting the tilt angle, thickness and refractive index of the transparent parallel plate element, resulting in a significant cost reduction. Can be achieved. In addition, 2 pixels on the screen
Since it becomes a double image, the effect that the stripe due to the light-shielding mask becomes less conspicuous and a smoother image can be obtained.

As described above, in the projection type image display device according to a fourth aspect of the present invention, in the structure of the first or second aspect, the optical path shifting means is composed of a plurality of surfaces, and the surface normal of at least one surface is the optical axis. It has a configuration that is not parallel to.

Therefore, in addition to the effect of claim 1 or 2, since the number of picture elements to be imaged is increased, an effect that a smoother image can be obtained is also obtained.

As described above, in the projection type image display device according to a fifth aspect of the present invention, in the structure of the first or second aspect, the optical path shift means is composed of a plurality of surfaces, and each surface has its surface normal on the optical axis. It has the composition arranged so that it may make a symmetrical angle to it.

Therefore, in addition to the effect of claim 1 or 2, since the number of picture elements to be imaged is increased, the effect that a smoother image can be obtained is also obtained.

As described above, the projection type image display device according to the sixth aspect has the configuration according to the first aspect, in which the optical path shifting means is made of a birefringent substance.

Therefore, the projection type image display device can be provided at a low cost because it has a simple structure in which only the optical path shifting means made of a birefringent substance is provided. Further, when the incident light passes through the birefringent substance, it is separated into two parallel polarized lights, so that the image based on one polarized light and the image based on the other polarized light are projected on the screen so as to be superposed on each other. As in the case of using the conventional diffraction grating, the effect is obtained that the stripes due to the light-shielding mask become inconspicuous and a smooth image is obtained.

As described above, the projection type image display device according to claim 7 is provided on the optical axis between the liquid crystal display means and the screen, and the optical path shift means for shifting the optical path of the incident light. The optical path difference correcting means is provided on the optical axis between the liquid crystal display means and the screen and corrects the optical path difference generated by the optical path shifting means.

Therefore, since the optical path difference correction means corrects the optical path difference generated by the optical path shift means, the transmitted light from the liquid crystal display means has no optical path difference on the screen without complicating the structure. An image is formed, and a smooth image with no out-of-focus is obtained. In addition, it has an effect that it can be applied to a liquid crystal display panel of any picture element pitch.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration example of a main part of a projection type image display device of the present invention.

FIG. 2 is an explanatory diagram showing a relationship between incident light and outgoing light of the parallel flat plate glass when the parallel flat plate glass is used as the optical path shifting means in FIG.

3A and 3B are explanatory views showing a state of stripes by a light-shielding mask based on the presence or absence of the parallel flat plate glass of FIG. 1, and FIG. 3A shows a state of a projection screen before disposing the parallel flat plate glass,
(B) shows the state of the projection screen after the parallel flat glass is arranged.

FIG. 4 is an explanatory diagram showing a configuration example of a main part of another projection-type image display device of the present invention.

FIG. 5 is an explanatory diagram showing changes in the number of picture elements to be imaged when a quadrangular pyramid is used as the optical path shifting means of the present invention.

FIG. 6 is an explanatory view showing a change in the number of picture elements to be imaged when a quadrangular truncated pyramid is used as the optical path shifting means of the present invention.

FIG. 7 is an explanatory diagram showing a configuration example of a main part of still another projection-type image display device of the present invention.

FIG. 8 is an explanatory diagram showing a relationship between incident light and outgoing light of the birefringent element when the optical path shift means is composed of the birefringent element in FIG.

FIG. 9 is an explanatory diagram for explaining a problem of the conventional technique.

[Explanation of symbols]

 1 parallel flat glass (optical path shifting means) 2 liquid crystal display panel (liquid crystal display means) 3 parabolic mirror 4 light source 5 field lens 6 projection lens 7 projection screen (screen) 8 parallel flat glass (optical path difference correcting means) 9 birefringence Element (optical path shift means)

Claims (7)

[Claims] 1. A projection type image display device for displaying an image by forming an image of transmitted light from liquid crystal display means in which picture elements are arranged in a matrix on a screen, wherein the liquid crystal display means and the screen are provided. A projection-type image display device, comprising: an optical path shift unit that is provided in at least a part of an optical path between the two and shifts an optical path of incident light. 2. A projection type image display apparatus according to claim 1, wherein the optical path shifting means is a transparent parallel plate element. 3. The refractive index and the thickness of the transparent parallel plate element are set so that the shift amount of the optical path is approximately half the pixel pitch, and the transparent parallel plate element has a surface perpendicular to the optical axis. The projection type image display device according to claim 2, wherein the projection type image display device is tilted at a predetermined angle with respect to. 4. The optical path shifting means comprises a plurality of surfaces,
3. The projection type image display device according to claim 1, wherein the surface normal of at least one surface is not parallel to the optical axis. 5. The optical path shifting means comprises a plurality of surfaces,
3. The projection type image display device according to claim 1, wherein each surface is arranged such that its surface normal line forms a symmetrical angle with respect to the optical axis. 6. The projection type image display apparatus according to claim 1, wherein the optical path shifting means is made of a birefringent material. 7. A projection type image display device for displaying an image by forming an image of transmitted light from a liquid crystal display means in which picture elements are arranged in a matrix on a screen, the liquid crystal display means and the screen. Between the liquid crystal display means and the screen, and an optical path difference generated by the optical path shift means, which is provided on the optical axis between the liquid crystal display means and the screen. A projection-type image display device, comprising: an optical path difference correction unit for correction.