JP5245218B2 - Projector, transmissive screen, and rear projection display device - Google Patents

Description

  The present invention relates to a projector and a rear projection display device.

A rear projection television is known as a rear projection display device having a transmissive screen.
FIG. 1 is a side sectional view of a rear projection television.
The rear projection TV projects image light from a projector 12 as a light source, reflects the image light by reflecting mirrors 13 and 14, and makes the image light enter the back surface of a transmission screen 20 having a substantially rectangular flat plate shape.

FIG. 4 is a cross-sectional view showing a configuration example of a transmissive screen serving as a display screen of a rear projection television.
The transmissive screen 20 is configured by combining two lens sheets having different optical functions. A Fresnel lens 30 that converts image light into substantially parallel light is disposed on the light source side, and the image light is diverged for each unit lens. A lenticular lens array (diffuse lens array) 40 is arranged on the viewer side.
Thus, an observer located in front of the transmission screen can observe the transmitted image light (see, for example, Patent Documents 1 and 2).

As for projectors, high brightness and miniaturization are required, and miniaturization of projection lenses and high F-numbers are progressing. Liquid crystal (LCD) projectors and reflective light valves (DMD, DLP: trademarks of Texas Instruments Incorporated) For example, a projection tube having a small projection pupil is used.
However, the conventional transmissive screen has a problem that flickering of an image called scintillation or speckle appears when such a projection tube having a small projection pupil is used.
Scintillation is a phenomenon in which the brightness of the image light changes with the change of the observer's viewpoint, and the image appears to flicker.

In order to prevent flickering of the image due to scintillation or speckles, it is necessary to change the projector body or add an additional device.
Further, when the above flicker is eliminated by improving the screen, there is a problem that when a large amount of a diffusing agent is added to the screen, the gain is reduced or the resolution is unnecessarily reduced.

  The proposal of Patent Document 3 states that “the lens sheet or optical sheet having a plurality of diffusing parts spaced apart from each other via a non-diffusing part and the diffusing part of the lens sheet or optical sheet located on the light source side is located on the observation side. The transmission screen is characterized in that the degree of light diffusion is smaller than that of the sheet diffusion portion. "In the configuration example shown in FIG. 6, the first diffusion portion (plate) 33 on the Fresnel lens sheet 30 side and When light diffusing fine particles are dispersed and mixed in each of the second diffusing parts (plates) 43 on the lenticular sheet 40 side, the material and particle size of the light diffusing fine particles, the refractive index difference with the surrounding binder resin, the amount of dispersion, etc. In addition to various designs, it is necessary to control the degree of diffusion as desired.

Recently, it is required to reduce the thickness of the transmissive screen 20. This is because the transmission screen 20 can be reduced in weight and cost, and the resolution and sharpness of the transmission screen 20 can be improved.
In Patent Documents 4 and 5, making a Fresnel lens into a film has been studied.
However, when the transmission screen 20 is thinned, the thickness of the first diffusion plate 33 and the second diffusion plate 43 is reduced, and the distance between the Fresnel lens 30 and the lenticular lens array 40 is shortened. Scintillation may occur.

JP 2002-236319 A US Pat. No. 6,307,675 Japanese Patent No. 3606862 Japanese Patent No. 3002477 Japanese Utility Model Publication No. 1-111734

The present invention has been made to solve the above-described problem, and is a rear projection display using a projector using an LCD or a DLP while reducing the weight and cost by reducing the thickness of the transmissive screen. The main purpose of the apparatus is to provide a projector capable of preventing scintillation of images.
It is another object of the present invention to provide a rear projection display device with excellent display quality.

In order to achieve the above object, a projector according to the present invention provides:
A light source;
A light modulation element for modulating light from the light source;
In a projector having a projection optical system that projects image light modulated by a light modulation element onto a screen,
Spatial scattering means is provided between the light source and the light modulation element, and the scattering means varies with time.

Spatial scattering means indicates that light from a light source is incident on the scattering means with a fixed area rather than a narrow area like a beam, and the width of the light incident on the scattering means is that of the light modulation element. The scattering means is disposed at a position where the image of the scattering means is formed in the vicinity of the image position of the light modulation element projected by the projection optical system. The effect is improved.
If the structure of the scattering means is made random, moire defects with periodic structures such as light modulation elements and screens are less likely to occur.
If the image of the scattering means completely coincides with the position of the light modulation element, if there is a defect on the scattering means, the defect will appear remarkably in the display image, so it may be better to shift the imaging position. is there.

The size p of the pixel structure of the light modulation element on the screen is often 1 mm or less, and if the size of the scattering structure becomes too small, there may be problems such as coloring.
If the average size of the scattering structure of the scattering means is d, the width of the light incident on the scattering means is W, and the projected screen size is H,
The effect is also improved when 0.00001 mm <d and d × H / W <1 mm.
Desirably, the effect increases if d × H / W <p.

When a liquid crystal phase modulation element that temporally modulates the phase is used as the scattering means, there is no working part, which is advantageous for durability and noise.
In addition, when the screen is a transmissive screen, scintillation defects appear remarkably. However, a spatial scattering means is provided between the light source and the light modulation element, and the scattering means is effective because it varies with time. It is possible to reduce scintillation.

Further, when the coherence distance of the light source is 0.17 mm or more, scintillation defects appear more remarkably, but a spatial scattering means is provided between the light source and the light modulation element, and the scattering means varies with time. By doing so, it becomes possible to reduce scintillation more effectively.
When the size of the pupil of the projection optical system is a and the distance between the pupil of the projection optical system and the screen is Z, the relationship of A / Z> 1.15 × 10 ⁻³ is satisfied, thereby further improving the scintillation reduction effect. It becomes possible.
Further, when the phase at the time of incidence on the screen, which fluctuates due to the scattering means, is a minute interval on the screen, p, the maximum fluctuation amount Δφ of the phase difference at p satisfies Δφ> 1.15 × 10 ⁻³ × p. In this way, it is possible to increase the scintillation reduction effect.
Further, if the surface of the scattering means is subjected to antireflection treatment on one side or both sides, it is possible to reduce scintillation while suppressing a reduction in brightness.

According to this configuration, it is possible to change the brightness of the image light projected from the projector at high speed, and to prevent scintillation of the image. Further, in the transmissive screen, the total thickness of the scattering layer of the screen can be reduced. Even if it is 1 mm or less, scintillation of the image can be prevented.

In the projector of the present invention,
A spatial scattering means is provided between the light source and the light modulation element, and the scattering means temporally varies, so that the phase of the projection light incident on the screen can be changed at high speed. Scintillation can be prevented.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Rear projection type display device)
FIG. 1 is a side sectional view of a rear projection television which is an example of a rear projection display device.
A rear projection television 10 shown in FIG. 1 includes a projector 12 that projects video light, reflecting mirrors 13 and 14 that reflect video light, a transmissive screen 20 that displays video on the front side by allowing the video light to enter from the back, The casing 11 is mainly configured to cover the whole while exposing the front surface of the transmission screen 20 to the outside.
FIG. 2 is a schematic configuration diagram of a three-plate projector.
The projector 112 includes a white light source 110 such as a high-pressure mercury lamp. An integrator 115 made up of a lens array or the like is disposed on the downstream side of the light source 110. The integrator 115 uniformly illuminates the light modulation region of the liquid crystal light valves 136, 146, and 156 arranged on the downstream side thereof. Downstream of the integrator 115, a blue light spectral mirror 132 that transmits only the blue light 130, a green light spectral mirror 142 that reflects green light 140 and transmits red light, and a red light spectral mirror 152 that reflects red light 150. Are provided in order.

On the downstream side of the blue light spectral mirror 132, a parallel light conversion lens 134 that converts the blue light 130 into parallel light, and a blue light modulation liquid crystal as a light modulation element that modulates the blue light 130 to create blue image light. A light valve (hereinafter referred to as “blue light LV”) 136 and a blue light collecting mirror 138 that reflects blue light are provided. Similarly, on the downstream side of the green light spectroscopic mirror 142, a parallel light conversion lens 144, a green light modulation liquid crystal light valve (hereinafter referred to as “LV for green light”) 146, and reflects green light to blue light. And a green light collecting mirror 148 that transmits the light. On the downstream side of the red light spectral mirror 152, a parallel light conversion lens 154, a red light modulation liquid crystal light valve (hereinafter referred to as “red light LV”) 156, and a red light collection that transmits only the red light 150. An optical mirror 158 is provided.
A projection lens 160 for enlarging and projecting image light is provided on the downstream side of each color light collecting mirror 138, 148, 158.

  In the present invention, the projector 112 has a scattering means 164 on the optical system that scatters the light spread from the optical system to a certain surface precision device over time. The scattering means 164 includes a diffusion plate that rotates or vibrates with time, a phase modulation element such as liquid crystal, and the like. When the scattering means rotates, the rotation axis and the optical axis may coincide with each other, but since the phase fluctuation of the rotation center is reduced, it is desirable to arrange the rotation center at a position different from the optical axis.

The scattering means is arranged so that light is incident on the spatially constant area. For example, when the light from the light source is a thin light beam after passing through an optical fiber or a light pipe, the light is emitted by a lens or a curved mirror. It is desirable that the light is incident on the scattering means after spreading.
This is because, in the reduction of scintillation, the larger the phase inclination change on the screen, the greater the effect. Therefore, when the area of light incident on the scattering means is reduced, the amount of phase inclination change on the screen cannot be obtained. It is desirable that the width of the light incident on the scattering means is 1/2 or more of the width of the light modulation element, and it is even better if it is substantially equal to the width of the light modulation element.

Scintillation occurs more strongly in transmissive screens. This is because the transmissive screen is less diffusive than the reflective screen.
Since the present invention is a method for compensating for the low scattering of the transmission screen, a higher effect can be obtained. At this time, by setting the thickness of the scattering layer of the transmission screen (the distance between the scattering layer position closest to the light source and the scattering layer position closest to the viewer) to 1 mm or less, an image with excellent resolution and low scintillation can be obtained. I can do it.

  When the incident light greatly fluctuates from the pupil of the projection optical system due to the scattering means, the light fluctuated more than the pupil is absorbed and the light use efficiency is lowered. For this reason, it is desirable that the variation of the light beam by the scattering unit is smaller than the pupil of the projection optical system. It is desirable that the amount of light is 70% or more when there is scattering variation compared to the case where there is no scattering. In order to prevent a decrease in the amount of light, it is desirable to apply an antireflection treatment to the surface of the variable element. However, if the amount of fluctuation is small, both the scintillation reduction and the effect are small. Therefore, the larger the pupil of the projection optical system, the more effective the scintillation reduction.

A desirable pupil size of the projection optical system is obtained as follows.
When the observer observes the screen at a distance of 1 m from the screen and the size of the observer's eye pupil is 4 mm, at least 0.17 mm in diameter on the screen from the diffraction limit of the eye pupil size. You are observing the area. Therefore, assuming that the light within the range of 0.17 mm has coherence, scintillation occurs due to the interference pattern of the observer's retina. The coherence in the range of R = 0.17 mm on the screen is obtained as follows.
When the distance from the pupil of the projection optical system to the screen is Z, the wavelength of the light source is λ, and the size of the pupil of the projection optical system is a, the coherence degree γ (R) is

It is expressed as Incidentally _{J 1} shows the first-order Bessel function.
When λ is 500 nm and R = 0.17 mm, a / Z needs to be 1.15 × 10 ⁻³ or more in order to make γ indicating the contrast of the interference pattern 0.5 or less.
Although this example shows a case where the pupil of the projection optical system is fixed with respect to the screen, the relationship between the distance between the pupil of the projection optical system and the screen is a / Z of 1.15 × 10 ^−3. Even in the case where the pupil position fluctuates with time or has a plurality of pupils, the expected angle of the incident light on the screen may be optically 1.15 × 10 ⁻³ or more. .
This means that when the phase at the time of incidence on the screen, which fluctuates by the fluctuating means, is a minute interval on the screen, p, the maximum fluctuation amount Δφ of the phase difference at p is Δφ> 1.15 × 10 ⁻³ × p. It shows that it satisfies.

(Specific configuration)
Next, a video projection method using the projector according to the first embodiment will be described with reference to FIG.
The light projected from the light source enters the lens L1.
The light transmitted through L1 and spread to a certain area is incident on a diffusion plate that is a scattering and scattering means.
The light incident on the diffuser plate passes through the lenses L2 and L3, and then enters a light modulation element such as a high-temperature polysilicon liquid crystal.
At this time, if the focal length of the lens L2 is f2 and the focal length of the lens L3 is f3, the distance between the lens L2 and the lens L3 is L2 + L3, a diffusion plate is disposed at the rear focal position of L2, and the front focal position of L3 is set. A 4f optical system in which the light modulation element is arranged is used.

In the above arrangement, the diffusion plate as the scattering modulation means forms an image in the vicinity of the spatial modulation element.
The light transmitted through the light modulation element forms an image on the screen by the projection optical system.
The diffusion plate has a rotating structure and can vary the scattering of light transmitted through the diffusion plate.
Variation in scattering by the diffusion plate causes phase variation on the screen by forming an image of the diffusion plate in the vicinity of the screen. Phase fluctuation on the screen corresponds to changing the direction of the light incident on the screen minutely, so the scintillation pattern fluctuates at high speed, and as a result, the observer observes the scintillation with reduced scintillation. .
When a diffusion plate is used as the scattering modulation means and rotation is used as the scattering means, it is desirable that the rotation axis of the diffusion plate does not coincide with the optical axis. Further, in this embodiment, scattering fluctuation due to rotation is used, but fluctuation due to vibration caused by a piezo element or the like may be used.

As in this embodiment, when a 4f optical system is used, the light emitted from the light modulation element is substantially parallel to the optical axis, so that the efficiency of the telecentric optical system often used in the projection optical system of the projector is improved. . However, not only the 4f optical system but also the effect of scintillation reduction can be obtained when the scattering and scattering means forms an image near the screen.
In this embodiment, the image of the scattering means is formed in the vicinity of the screen. With this structure, it is possible to enhance the scintillation reduction effect due to scattering fluctuations. Defects tend to occur as image defects on the screen. In that case, the image position of the scattering means may be shifted from the screen position.

In this embodiment, a diffusion plate that fluctuates as the phase scattering means is used and the 4f optical system is used to image the scattering means in the vicinity of the imaging screen. However, the present invention is not limited to this. Or a reflective diffuser. Further, the scattering means does not necessarily need to form an image near the screen.
These combinations are not fixed and can be realized by different combinations.
In this embodiment, the phase scattering means is realized by having an operating part such as rotation or vibration. However, a means such as liquid crystal that causes a change in refractive index with time may be used. If liquid crystal or the like is used, there is an advantage that there are no moving parts and problems such as vibration and sound are less likely to occur.

In this embodiment, for the sake of explanation, the light from the light source is described as being incident on the light modulation element without being separated. Naturally, after color separation as described in FIG. You may use for the optical system which injects into the sheet of spatial modulation element.
In this case, three phase modulation means may be prepared separately for each spatial modulation element, but if an optical system that passes through the phase modulation means before one spatial modulation element is color-separated, the phase modulation means One modulation means is sufficient, which is effective for cost reduction and miniaturization.

In the present invention, it is possible to meet the demand for thinning the entire screen, such as forming a film of the Fresnel lens 30 in the transmissive screen 20.
This is because the first diffusion portion is formed by roughening the surface of the light source side of the base material 32, the first diffusion plate 33 is eliminated, and the Fresnel lens 30 is thinned to a thickness of 0.8 mm or less. is there.
Thereby, the transmissive screen 20 can be lightened and reduced in cost. By so doing, it becomes possible to reduce the diffusion layer thickness to 1 mm or less when viewed in combination with a Fresnel lens and a lenticular lens, and the resolution and sharpness of the transmissive screen 20 can be improved.

However, when the transmissive screen 20 is thinned, the thickness of the first diffusing portion is reduced, and the distance between the Fresnel lens 30 and the lenticular lens array 40 is shortened, so that image scintillation occurs in a general projector. There is a fear.
The optical system is equipped with a means for temporally changing the phase of the light from the light source, and by using a projector characterized in that the phase changing means forms an image near the screen, the scintillation is reduced, resulting in high image quality. Can be observed.

Side surface sectional drawing of a rear projection television. 1 is a schematic configuration diagram of a three-plate projector. 1 is a schematic configuration diagram of a projector according to the present invention. The plane sectional view of a transmission type screen.

Explanation of symbols

10 Rear Projection Television 12 Projector 13, 14 Reflector 20 Transmissive Screen 30 Fresnel Lens 40 Lenticular Lens Array (Diffusion Lens Array)

Claims (11)

White light source of high-pressure mercury lamp,
A light modulation element for modulating light from a white light source of the high-pressure mercury lamp;
In a projector having a projection optical system that projects image light modulated by a light modulation element onto a screen,
A spatial scattering means is provided between the white light source of the high-pressure mercury lamp and the light modulation element, and the scattering means varies with time,
The scattering means is a diffusion plate rotating in time;
A projector characterized in that a rotation center is arranged at a position different from the optical axis.   2. The projector according to claim 1, wherein a width W of light incident on the scattering means is not less than ½ of a width O of the light modulation element. If the average size of the scattering structure of the scattering means is d, the width of the light incident on the scattering means is W, and the projected screen size is H,
The projector according to claim 1, wherein 0.00001 mm <d and d × H / W <1 mm.   The projector according to claim 1, wherein the scattering means has a spatially random structure.   It is arranged so that a projection image of the scattering means is formed in the vicinity of the light modulation element, and the projection light and the image light modulated by the light modulation element are formed in the vicinity of the screen by the projection optical system. The projector according to claim 1.   The projector according to claim 1, wherein the scattering means is a liquid crystal phase modulation element that temporally modulates the phase.   The projector according to claim 1, wherein the screen is a transmissive screen.   The projector according to claim 1, wherein the coherence distance of the light source is 0.17 mm or more. If the size of the pupil of the projection optical system is a and the distance between the pupil of the projection optical system and the screen is Z,
The projector according to claim 1, wherein a relationship of a / Z> 1.15 × 10 ⁻³ is satisfied.   The projector according to claim 1, wherein the scattering means surface is subjected to an antireflection treatment on one side or both sides.   A rear projection display comprising: the projector according to any one of claims 1 to 9; and a transmissive screen that displays the image on the front side by allowing the image light projected from the projector to enter from the rear surface. apparatus.