JP6924029B2 - LCD projector - Google Patents

Description

The present invention relates to a liquid crystal projector that uses a ferroelectric liquid crystal panel to project an image by a field sequential color method.

A field sequential color method (hereinafter referred to as "FSC") in which one image is divided into a red image, a green image, and a blue image based on color, the divided images are displayed in a time-divided manner at high speed, and the one image is reconstructed. Method) is known. In this FSC system, a liquid crystal projector that displays a full-color image by projecting a red, green, and blue image time-divided on a liquid crystal panel onto a screen has been proposed (for example, Patent Document 1).

Therefore, FIG. 5 of Patent Document 1 is reprinted in FIG. 3, and the liquid crystal projector 100 shown in Patent Document 1 will be described. In FIG. 3, the reference numerals are changed. FIG. 3 is a schematic view of the liquid crystal projector 100 shown as a conventional example. As shown in FIG. 3, the liquid crystal projector 100 includes small arc type CNT light sources 108, 109, 110, a reflector 114, a polarizing beam splitter 115, a reflective liquid crystal panel 116, and a projection lens 112.

The small arc type CNT light sources 108, 109, and 110 emit light in red, green, and blue, respectively. The reflector 114 efficiently sends light to the reflective liquid crystal panel 116. The polarization beam splitter 115 splits light into P and S polarized light, transmits one and reflects the other. The reflective liquid crystal panel 116 displays a red image, a green image, and a blue image in a time-division manner. The projection lens 112 projects an image drawn on the reflective liquid crystal panel 116 onto a screen.

In the liquid crystal projector 100, when the reflective liquid crystal panel 116 is displaying a red image, the small arc type CNT light source 108 that emits red light is turned on, and the red image is projected on the screen. Similarly, when the reflective liquid crystal panel 116 is displaying a green image (blue image), the small arc type CNT light source 109 (110) that emits green (blue) is lit, and the green (blue) image is projected on the screen. NS. Note that () indicates replacement. In the FSC method, a natural full-color image (one image) can be obtained by switching between a red image, a green image, and a blue image at high speed. In addition, moving images can be displayed by continuously switching full-color images.

JP-A-2002-40388 (Fig. 5)

As described above, in the FSC type liquid crystal projector, the image displayed on the liquid crystal panel must be rewritten at high speed. Ferroelectric liquid crystal panels are known as liquid crystal panels that can rewrite display images at high speed (hereinafter, may be referred to as "FLC panels"). This FLC panel can rewrite an image at a speed of about 10 to 100 times that of a widely used TN (twisted nematic) liquid crystal panel.

However, since the FLC panel is a so-called AC drive, when one image is displayed, a voltage having a reverse sign must be applied to the liquid crystal display for the same period. The image is not displayed normally during the period when the voltage having the opposite sign is applied. Therefore, in the liquid crystal projector adopting the FSC method, the FLC panel is not illuminated during this period. That is, when the FLC panel is applied to the liquid crystal projector shown in FIG. 3, a non-display period having the same length as the display period appears on the screen. This non-display period causes flicker and makes color breaks (color noise generated at the edges of moving images) stand out on the screen. In particular, it is known that color breaks are remarkable in moving image display.

Therefore, the present invention has been made in view of the above problems, and provides a liquid crystal projector suitable for moving image display even though it has a simple configuration when an image is projected by a field sequential color method using a ferroelectric liquid crystal panel. The purpose is to do.

In a liquid crystal projector that projects an image displayed on a dielectric liquid crystal panel by a field sequential color method, one image is a first image, a second image, and a third image based on the first color, the second color, and the third color. When the period for decomposing into an image and reconstructing the one image is set as the frame period, the first light source that emits light in the first color, the second light source that emits light in the second color, and the third color A third light source that emits light, a first strong dielectric liquid crystal panel, and a second strong dielectric liquid crystal panel are provided, and the first light source is turned on during the first period of projecting the first image, and the second light source is projected. The light source is lit in the second period of projecting the second image, the third light source is lit in the third period of projecting the third image, and one frame period for reconstructing the one image is It is composed of two first period, one second period and one third period, and in the first period, the light emission intensity of the first light source is the light emission of the second light source and the third light source. It is a liquid crystal projector that is controlled to be half the intensity.

The first color may be green.

The liquid crystal projector of the present invention decomposes one image into a first image corresponding to the first color, a second image corresponding to the second color, and a third image corresponding to the third color, and uses the FSC method. Reconstruct one image on the screen. Of course, one frame period consists of four fields. Two of these four fields are the first period for projecting the first image, and the rest are the second period for projecting the second image and the third period for projecting the third image, respectively. For example, the second image is projected onto the screen, then the first image is projected, then the third image is projected, and then the first image is projected again.

Further, in the liquid crystal projector of the present invention, when one ferroelectric liquid crystal panel displays an image for projection, the other ferroelectric liquid crystal panel displays an image not projected in order to satisfy the condition of AC drive. do. By swapping the relationship between one and the other for each field, there is no hidden period on the screen.

That is, flicker and motion break are greatly improved by making it possible to increase the speed of the frame frequency by configuring one frame period with a small number of fields and eliminating the non-display period on the screen.

As described above, when the liquid crystal projector of the present invention uses a ferroelectric liquid crystal panel and projects an image by a field sequential color method, it is possible to display a good moving image with a simple configuration.

It is the schematic of the liquid crystal projector shown as the 1st Embodiment of this invention. It is a timing chart of the liquid crystal projector shown in FIG. It is the schematic of the liquid crystal projector shown as a prior art. It is the schematic of the liquid crystal projector shown as the 2nd Embodiment of this invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to Attachments 1 and 2. In addition, the matters specifying the invention shown in the claims are described in parentheses.

(First Embodiment)
FIG. 1 is a schematic view of a liquid crystal projector 10 shown as a first embodiment of the present invention. The rays L1 and L2 are added in the figure. The liquid crystal projector 10 includes an LED 11 (first light source) that emits green light (first color), an LED 21 (second light source) that emits red light (second color), and an LED 31 (third color) that emits blue light (third color). A third light source), an FLC panel 14 (first ferroelectric liquid crystal panel) that displays a green image (first image), and an FLC panel that displays a red image (second image) and a blue image (third image). 24 (second ferroelectric liquid crystal panel) is provided.

The LED 11 is arranged in the reflector 12. The reflecting mirror 12 sets the light emission of the LED 11 to a parallel light ray L1. The light beam L1 is reflected by the beam splitter 13 (first beam splitter) and reaches the FLC panel 14. Further, the light ray L1 is reflected by the FLC panel 14, passes through the beam splitter 13, is reflected by the dichroic prism 15, and is imaged by the projection lens 16 on a screen (not shown).

The beam splitter 13 reflects one polarization component and transmits the other polarization component. Therefore, only one polarization component of the light ray L1 reaches the FLC panel 14. In the FLC panel 14, the polarization state changes due to the retardation of the FLC layer, and the other polarization component appears. The other polarization component passes through the beam splitter 13 and reaches the dichroic prism 15. The dichroic prism 15 reflects green, which is the emission color of the LED 11, and transmits other colors. That is, the distribution of the other polarization component on the FLC panel 14 corresponds to displaying a green image. The green image can be seen through the beam splitter 13.

In the liquid crystal projector 10, parallel light rays L1 are obtained by the reflecting mirror 12. However, when the LED 11 adopts a package in which its light emission is emitted only to the front (beam splitter 13 side), a lens may be used instead of the reflector 12 to obtain parallel light rays. Further, the dichroic prism 15 may be a dichroic mirror.

Similarly, the LEDs 21 and 31 are arranged in the reflector 22. The reflector 22 uses parallel light rays L2 to emit light from the LEDs 21 and 31. The light beam L2 is reflected by the beam splitter 23 (second beam splitter) and reaches the FLC panel 24. Further, the light ray L2 is reflected by the FLC panel 24, passes through the beam splitter 23, passes through the dichroic prism 15, and is imaged by the projection lens 16 on a screen (not shown).

The beam splitter 23 reflects one polarization component and transmits the other polarization component. Therefore, only one polarization component of the light ray L2 reaches the FLC panel 24. Even in the FLC panel 24, the polarization state changes due to the retardation of the FLC layer, and the other polarization component appears. The other polarization component passes through the beam splitter 23 and reaches the dichroic prism 15. The dichroic prism 15 transmits blue and red, which are the emission colors of the LEDs 21 and 31, and reflects other colors. That is, similarly to the FLC panel 14, the distribution of the other polarization component in the FLC panel 24 corresponds to a red image or a blue image.

The reflector 22 is replaced with a lens if the LED 21 and 31 are a package that emits only forward (beam splitter 23 side). Further, since the LEDs 21 and 31 must be arranged near the focal point of the reflecting mirror 22 (or lens), they may be packaged as one that can switch between red and blue light emission.

The FLC panels 14 and 24 are referred to as so-called LCOS (Liquid Crystal on Silicon).
A ferroelectric liquid crystal display (FLC) is used for the liquid crystal layer of Silicon). The LCOS has a display area and a circuit area on a Si substrate. The display area is provided with reflective electrodes (pixels) arranged in a matrix and switch elements connected to each reflective electrode, and a liquid crystal layer and transparent glass are laminated. The switch element conducts when the voltage held by each reflecting electrode is rewritten. The circuit area includes an image memory, a timing control circuit, a level shifter, and the like.

The controller 17 generates a green image containing only a green component, a red image containing only a red component, and a blue image containing only a blue component from one image, and converts the green image data into the FLC panel 14, the red image data, and the blue image. The data is sent to the FLC panel 24. Further, the controller 17 controls the display timing of the FLC panels 14 and 24, and controls the lighting of the LEDs 11, 21 and 31 in synchronization with this timing.

FIG. 2 is a timing chart of the liquid crystal projector 10. FIG. 2A shows the display state of the FLC panel 24, and FIG. 2B shows the display state of the FLC panel 14. In FIG. 2, R1 +, G1 +, and B1 + indicate periods for displaying a red image, a green image, and a blue image for one image, respectively. R1-, G1-, and B1- are periods in which a voltage of opposite polarity is applied at the same time after the period R1 +, G1 +, and B1 + in order to satisfy the condition of AC drive. The voltage of opposite polarity means that the absolute value is the same in each pixel and the positive and negative are reversed. The period in which the numbers are different is the period in which the red (green or blue) image constituting the other image indicated by the number is displayed (or the period in which a voltage having the opposite polarity is applied).

As described above, in the FSC method, a red image (red field), a green image (green field), and a blue image (blue field) obtained by decomposing one image (frame) based on color are displayed in chronological order. Reconstruct one image. In FIG. 2, the one-frame period shown by A is, in order, a period for projecting a red image (second period), a period for projecting a green image (first period), and a period for projecting a blue image (third period). , It consists of a period for projecting a green image (first period). That is, during the second, first, third, and first periods, the LEDs 21, 11, 31, and 11 (see FIG. 1) are lit, respectively. At this time, a red image, a green image, a blue image, and a green image are projected on the screen in chronological order, and one image is reconstructed in one frame period. That is, in the driving method shown in FIG. 2, one frame is composed of four fields, and there is a period (first period) in which the green image is displayed twice in one frame.

In the first field B1 of the frame period A, when a red image is displayed on the FLC panel 24, the LED 21 that emits red light is turned on. In the field B1, the reverse polarity voltage of the green image constituting the other image indicated by 0 is applied to the FLC panel 14.

In the second field B2, when a green image is displayed on the FLC panel 14, the LED 11 that emits green light is turned on. In the field B2, the reverse polarity voltage of the red image constituting one image is applied to the FLC panel 24. Since the green image display period G1 + exists twice during the frame period A, the emission intensity of the LED 11 is halved from the emission intensity of the LED 21.

In the third field B3, when a blue image is displayed on the FLC panel 24, the LED 31 that emits blue light is turned on. In the field B3, the reverse polarity voltage of the green image constituting one image is applied to the FLC panel 14.

In the final field B4, when a green image is displayed on the FLC panel 14, the LED 11 that emits green light is turned on. In the field B4, the reverse polarity voltage of the blue image constituting one image is applied to the FLC panel 24. Further, similarly to the field B2, since the green image display period G1 + exists twice during the frame period A, the light emission intensity of the LED 11 is halved from the light emission intensity of the LEDs 21 and 31.

The arrangement of the first, second and third periods in the frame period A is not limited to the above. For example, in the frame period A, the display periods of the FLC panels 14 and 24 are displayed, respectively.
R1 +, R1-, B1-, B1 +,
And G1-, G1 +, G1 +, G1-,
May be.

Further, if only the non-display period is to be eliminated, two FLC panels may be prepared and one frame period may be composed of even-numbered fields. For example, when one frame period is composed of 6 fields, the display periods of FLC panels 14 and 24 are set respectively.
R1 +, R1-, G1 +, G1-, B1 +, B1-,
When,
R1-, R1 +, G1-, G1 +, B1-, B1 +,
Is conceivable. However, in such a field configuration, the frame period becomes long, so that flicker and color breaks become conspicuous. Further, referring to FIG. 1, the reflecting mirrors 12 and 22 must be provided with LEDs that emit red, green, and blue, respectively, which complicates the component configuration.

As described above, the liquid crystal projector 10 projects a red image in the field B1, a green-red image in the field B2, a blue image in the field B3, and a green image in the field B4 on the screen to reconstruct one image. There is. That is, the liquid crystal projector 10 has no display period on the screen and can shorten the frame period A. As a result, flicker and color breaks are less noticeable in the projected image.

The period for rewriting the voltage held by each pixel of the FLC panels 14 and 24 is assigned to the first part of one field. This period causes display noise for a short time in one field. In order to make this noise inconspicuous, the liquid crystal projector 10 turns off the LEDs 11, 21, and 31 during the rewriting period.

Further, in order to clarify the action and effect of the liquid crystal projector 10, it is compared with the liquid crystal projector 100 shown in FIG. In the liquid crystal projector 100, one frame period must be composed of 6 fields in order to satisfy the AC drive. On the other hand, the liquid crystal projector 10 is composed of four fields for one frame period. Therefore, the frame frequency can be increased. If the frame frequency can be increased, flicker and color breaks will not be noticeable.

Further, in the liquid crystal projector 100, half of the one frame period was the non-display period, whereas in the liquid crystal projector 10, there is no non-display period on the screen. Therefore, in the liquid crystal projector 10, the brightness of the LEDs 21 and 31 at the time of lighting can be reduced to 2/3 as compared with the liquid crystal projector 100. That is, it becomes possible to loosen the required specifications of the LED 21 and the like.

Further, in the liquid crystal projector 10, a field for displaying a green image appears twice in one frame period A (fields B2 and B4). As a result, the emission intensity of the LED 11 that emits green light can be halved from the emission intensity of the LEDs 21 and 31 that emit red and blue light. This works favorably on the green light emitting LED (LED11), which has lower luminous efficiency than the red and blue light emitting LEDs (LEDs 21 and 31). That is, the liquid crystal projector 10 can effectively utilize the green light emitting LED (LED11).

Further, in the liquid crystal projector 10, the FLC panels 14 and 24 were reflective type. In the liquid crystal projector of the present invention, the FLC panel may be a transmissive type. At this time, since the first to third light sources can be used as rear illumination and the first and second beam splitters can be used as polarizing plates, the structure is simplified.

(Second Embodiment)
The liquid crystal projector 10 shown in FIG. 1 uses beam splitters 13 and 14 and a dichroic prism 15 for polarization processing and light synthesis. Polarization processing and light synthesis are not limited to this configuration, and can be realized by, for example, only one beam splitter. Therefore, with reference to FIG. 4, a liquid crystal projector 40 that performs polarization processing and light synthesis by one beam splitter 45 will be described as a second embodiment of the present invention.

FIG. 4 is a schematic view of the liquid crystal projector 40. The rays L3 and L4 are added in the figure. The liquid crystal projector 40 includes an FLC panel 43 (first strong dielectric liquid crystal panel) that displays a green image (first image), and an FLC panel 44 that displays a red image (second image) and a blue image (third image). (Second strong dielectric liquid crystal panel), square columnar beam splitter 45 (third beam splitter), LED 41g (first light source) that emits green (first color), and red (second color). It includes an RGB light source 41 including an LED 41r (second light source) and an LED 41b (third light source) that emits light in blue (third color), and a projection lens 16.

The FLC panel 43, the FLC panel 44, the RGB light source 41, and the projection lens 46 are arranged to face each other on the four side surfaces (first, second, third, and fourth side surfaces) of the beam splitter 45, respectively. The RGB light source 41 is arranged at the focal position of the reflector. A polarizing plate 48 and a FLC panel 49 (third ferroelectric liquid crystal panel) are arranged between the side surface (third side surface) of the beam splitter 45 and the RGB light source 42.

The reflecting mirror 42 uses parallel light rays L3 and L4 to emit light from the RGB light source 41. The polarizing plate 48 and the FLC panel 49 switch between emitting a p wave and emitting an s wave. That is, when the FLC panel 49 is emitted, the light ray L3 is a p wave (called one polarized light in the first embodiment), and the light ray L4 is an s wave (called the other polarized light in the first embodiment). Is. The ray L3 passes through the beam splitter 45 and reaches the FLC panel 43. Further, the light ray L3 is reflected by the FLC panel 43 and the beam splitter 45, and is imaged by the projection lens 46 on a screen (not shown). The ray L4 reflects off the beam splitter 45 and reaches the FLC panel 44. Further, the light ray L4 is reflected by the FLC panel 44, then transmitted through the beam splitter 45, and is imaged by the projection lens 46 on a screen (not shown).

The method by which the FLC panel 49 switches between emitting the p wave and emitting the s wave is as follows. The FLC panel 49 has a ferroelectric liquid crystal display sandwiched between two glass plates provided with solid electrodes. Further, it will be described as assuming that the p wave is incident on the FLC panel 49 from the polarizing plate 48. In order to perform sp conversion of polarized light on the FLC panel 49, the FLC panel 49 is used as a retardation plate. For this purpose, the amount of birefringence of the ferroelectric liquid crystal layer is set to 1 / 2λ (λ is the wavelength of light in the medium). Specifically, the cell gap is set to about 1.4 μm in the liquid crystal materials currently available. Further, the linearly polarized light (p wave) incident on the FLC panel 49 is made perpendicular or parallel to the liquid crystal molecules. Further, when a voltage is applied to the ferroelectric liquid crystal layer, the liquid crystal molecules are switched by 45 °. In this way, the p wave is emitted from the FLC panel 45 when no voltage is applied, and the s wave is emitted when the voltage is applied.

The beam splitter 45 transmits the p wave and reflects the s wave. Therefore, the light ray L3 reaching the FLC panel 43 becomes a p wave. In the FLC panel 43, the polarization state changes due to the retardation of the FLC layer, and s waves appear. This s wave component is reflected by the beam splitter 45 and reaches the screen via the projection lens 46. Similarly, the light ray L3 reaching the FLC panel 44 becomes an s wave. In the FLC panel 44, the polarization state changes due to the retardation of the FLC layer, and a p wave appears. This p-wave component passes through the beam splitter 45 and reaches the screen via the projection lens 46.

In the liquid crystal projector 40, parallel rays L3 and L4 are obtained by the reflecting mirror 42. However, when the RGB light source 41 adopts a package in which the light emission is emitted only to the front (beam splitter 45 side), a lens may be used instead of the reflector 42 to obtain parallel light rays.

The FLC panels 43 and 44 are the same as the FLC panels 14 and 24 included in the liquid crystal projector 10 shown in FIG. The controller 47 is the same as the controller 17 included in the liquid crystal projector 10 except that it has a function of applying or not applying a voltage to the FLC panel 49 for sp conversion.

The operation of the liquid crystal projector 40 will be described with reference to FIG. That is, FIG. 2 is regarded as a timing chart of the liquid crystal projector 40. FIG. 2A shows the display state of the FLC panel 44, and FIG. 2B shows the display state of the FLC panel 43. In FIG. 2, R1 + and the like, A and B1 to 4, are the same as the period in the projector 10.

In the first field B1 of the frame period A, when a red image is displayed on the FLC panel 44, the LED 41r that emits red light is turned on. In the field B1, the FLC panel 43 is applied with the reverse polarity voltage of the green image constituting the other image indicated by 0.

In the second field B2, when a green image is displayed on the FLC panel 43, the LED 41g that emits green light is turned on. In the field B2, the reverse polarity voltage of the red image constituting one image is applied to the FLC panel 44. Since the green image display period G1 + exists twice during the frame period A, the emission intensity of the LED 41g is halved from the emission intensity of the LED 41r.

In the third field B3, when a blue image is displayed on the FLC panel 44, the LED 41b that emits blue light is turned on. In the field B3, the reverse polarity voltage of the green image constituting one image is applied to the FLC panel 43.

In the final field B4, when a green image is displayed on the FLC panel 43, the LED 41g that emits green light is turned on. In the field B4, the reverse polarity voltage of the blue image constituting one image is applied to the FLC panel 44. Further, similarly to the field B2, since the green image display period G1 + exists twice during the frame period A, the emission intensity of the LED 41g is halved from the emission intensity of the LEDs 41r and 41b.

As described above, the liquid crystal projector 40 can simplify the optical system by using the polarizing plate 48 and the FLC panel 49 that enable sp conversion as compared with the liquid crystal projector 10 shown in FIG.

10, 40 ... LCD projector,
11, 41g ... LED (first light source),
12, 22, 42 ... Reflector,
13, 23, 45 ... Beam splitters (first, second, third beam splitters),
14, 43 ... FLC panel (first ferroelectric liquid crystal panel),
15 ... Dichroic prism,
16, 46 ... Projection lens,
17, 47 ... Controller,
21, 41r ... LED (second light source),
24, 44 ... FLC panel (second ferroelectric liquid crystal panel),
31, 41b ... LED (third light source),
41 ... RGB light source,
48 ... Polarizing plate,
49 ... FLC panel (third ferroelectric liquid crystal panel)
L1, L2, L3, L4 ... Rays,
R1 + ... During the period when the red image is displayed,
G1 + ... Period for displaying a green image,
B1 + ... During the period when the blue image is displayed,
R1-... Period for satisfying AC drive conditions for red image display,
G1-… Period for satisfying AC drive conditions for green image display,
B1-… Period for satisfying AC drive conditions for blue image display,
A ... Frame period,
B1 ... Field for projecting a red image (second period),
B2, B4 ... Field for projecting a green image (first period),
B3 ... A field for projecting a blue image (third period).

Claims (2)

In a liquid crystal projector that projects an image displayed on a ferroelectric liquid crystal panel by the field sequential color method,
When one image is decomposed into a first image, a second image, and a third image based on the first color, the second color, and the third color, and the period for reconstructing the one image is set as the frame period.
The first light source that emits light in the first color and
A second light source that emits light in the second color,
A third light source that emits light in the third color,
The first ferroelectric liquid crystal panel and
Equipped with a second ferroelectric liquid crystal panel
The first light source is turned on during the first period of projecting the first image.
The second light source is turned on during the second period of projecting the second image.
The third light source is turned on during the third period of projecting the third image.
The one-frame period for reconstructing the one image comprises two said first periods, one said second period, and one said third period.
In the first period, the emission intensity of the first light source is controlled to be half the emission intensity of the second light source and the third light source.
A liquid crystal projector characterized by this. The liquid crystal projector according to claim 1, wherein the first color is green.

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