JPH0727132B2 - Projector - Google Patents

Description

TECHNICAL FIELD The present invention relates to a projector, and more particularly to displaying an image on a screen by forming an image light by using a transmissive liquid crystal plate and projecting the image light on the screen. It was made to let.

B Outline of the Invention The present invention is a projector in which image light is formed by using a liquid crystal display plate, and the image light is projected on a screen. When the axes orthogonal to each other are the b axis and the c axis, the liquid crystal plate is tilted by a first angle with respect to the optical axis a in the direction of the maximum contrast viewing angle with the b axis as the rotation axis, and the c axis as the rotation axis. The second angle substantially equal to the first angle with respect to the optical axis a
By inclining by the angle of, the contrast of the image on the screen is improved and an image without distortion is projected at this time.

C Prior Art Conventionally, as a projector of this type, one having a structure as shown in FIG. 3 has been used (see JP-A-55-55314).

That is, a liquid crystal plate 1 in which liquid crystal cells whose transmittance changes according to an applied voltage are arranged in a matrix is arranged between a light source 2 and a screen 4, and a vertical axis passing through the center of the liquid crystal plate 1 is defined as an optical axis a. , The light LA emitted from the light source 2 is condensed and transmitted to the liquid crystal plate 1 by the condenser lens 3, and thus the image light LB with each liquid crystal cell as one pixel is formed on the liquid crystal plate 1, and this image light LB is generated. It is projected on the screen 4 via the field lens 5.

In the configuration of FIG. 3, if the voltage applied to the liquid crystal cell of the liquid crystal plate 1 is changed by, for example, a television image signal,
A corresponding image can be formed on the screen 4.

By the way, when a moving image is to be formed on the screen 4, a liquid crystal in which the transmissivity of each liquid crystal cell can be changed rapidly (that is, the response speed is fast) with respect to the change of the applied voltage of each liquid crystal cell. It is necessary to use cells.

Also, when trying to form a video with good clarity,
While displaying the black level of the video signal as dark as possible,
It is desirable to use a liquid crystal cell in which the white level is displayed as brightly as possible, that is, a liquid crystal cell having a large variation range of so-called transmittance (hence a large contrast).

As a liquid crystal cell that can practically satisfy such conditions,
In general, a liquid crystal plate 1 using a so-called TN mode (twisted nematic mode) liquid crystal cell in which parallel Nicols are provided on both sides of a nematic liquid crystal is used.

D The problem to be solved by the invention However, in the TN mode liquid crystal, the contrast changes depending on the viewing direction as shown in FIG.

That is, as shown in FIG. 5, the vertical axis passing through the center of the liquid crystal plate 1 is taken as the Z axis, and the X axis and the Y axis are taken in the alignment direction of the liquid crystal cells of the liquid crystal plate 1. Further, the viewing direction of the liquid crystal plate 1 is represented as a viewing angle θ with respect to the liquid crystal plate 1 with reference to the plane of the liquid crystal plate 1.

In such a definition, when the viewing direction changes on a virtual plane including the Y-axis direction and the Z-axis direction, the viewing angle θ corresponding to the optical axis Z direction is 90 ° as shown by the curve L1 in FIG. The contrast becomes maximum in the direction, and thereafter, the contrast gradually decreases with respect to the change of the viewing angle θ.

On the other hand, when the viewing direction changes on the virtual plane including the X-axis direction and the Z-axis direction, the viewing angle θ is 90 as shown by the curve L2.
90 ° -α (several degrees below the angle α
Is called the maximum contrast viewing angle), the contrast becomes maximum in the direction W, and thereafter, the contrast sharply decreases with respect to the change of the viewing angle θ.

Therefore, there is a problem that the image projected on the screen 4 also has a contrast lower than the state of the best contrast by a value corresponding to the viewing angle α.

Furthermore, in addition to this, there is a problem that the contrast changes abruptly when the viewing direction of the image on the screen 4 moves on a virtual plane including the X-axis direction and the Z-axis direction.

However, in general, when a person views an image on the screen 4, the change in the viewpoint in the vertical direction is significantly smaller than the change in the viewing direction in the horizontal direction (that is, the change in the viewpoint). The liquid crystal plate 1 is configured such that the direction of is the vertical direction of the projected image to prevent the change of the contrast due to the change of the viewpoint, and the contrast in the vertical direction has been improved.

That is, the direction of the best contrast point is made closer to the optical axis direction by improving the structure of the liquid crystal material and the cell.

The present invention has been made in consideration of the above points, and it is an object of the present invention to propose a projector capable of obtaining an image with significantly improved contrast as compared with a conventional projector by a simple configuration. .

E Means for Solving the Problems In order to solve the problems, the light source 2 is used in the present invention.
In the projector in which the image light LD is formed by transmitting the light LC from the image through the transmissive liquid crystal plate 1 and the image light LD is projected on the screen 4, the optical axis of the light source 2 is set to the a-axis, and When the mutually orthogonal axes in the plane 10 orthogonal to the axis 2 are the b-axis and the c-axis, the transmissive liquid crystal plate 1 is arranged with respect to the optical axis a in the direction of the maximum contrast viewing angle with the b-axis as the rotation axis. A second angle β that is substantially equal to the first angle α with respect to the optical axis a with the c-axis as the rotation axis.
Just tilt it.

By tilting the transmissive liquid crystal plate 1 with the b axis as the rotation axis by the first angle α with respect to the optical axis a in the direction of the maximum contrast viewing angle, the contrast of the image projected on the screen 4 is significantly increased. And the distortion of the image on the screen 4 can be eliminated by tilting the c-axis as the rotation axis by the second angle β that is substantially equal to the first angle α with respect to the optical axis a. .

G Example Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

In FIGS. 1 and 2 in which parts corresponding to those in FIG. 3 are designated by the same reference numerals, the optical axis a is located on the intersection of the optical axis a and the liquid crystal plate 1.
On the other hand, the vertical plane 10 is taken, the direction corresponding to the vertical direction of the screen 4 on the vertical plane 10 is defined as the c-axis, and the direction orthogonal to this is defined as the b-axis. The liquid crystal plate 1 has a screen 4
Direction corresponding to the horizontal direction of the image, that is, the b-axis direction is the Y-axis direction and the maximum contrast W (FIG. 4)
Is aligned with the optical axis a so that an angle α (FIG. 4) from the vertical surface 10 to the direction of the maximum contrast viewing angle with the b axis as the rotation axis.
Only tilted.

In addition to this, by setting the distance between the light source 2 and the condenser lens 3 to be short, the emitted light LC of the condenser lens 3 becomes substantially parallel rays.

Further, a condenser lens 11 is interposed between the liquid crystal plate 1 and the field lens 5 so that the image light LD of the liquid crystal plate 1 composed of parallel rays is condensed on the field lens 5.

In the configuration shown in FIG. 1, the light emitted from the light source 2 becomes parallel rays LC through the condenser lens 3 and enters the liquid crystal plate 1. When the applied voltage of each liquid crystal cell of the liquid crystal plate 1 changes according to a video signal, the transmitted light forms a video light LD, which is condensed by the condenser lens 11 and then the field lens 5
It is projected on the screen 4 via. Thus, the image formed by the liquid crystal plate 1 is enlarged and displayed on the screen 4.

According to the configuration shown in FIG. 1, the best contrast direction W of the liquid crystal plate 1 and the direction of the optical axis a coincide with each other, so that the image obtained on the screen 4 has a much higher contrast than the conventional one. Can be obtained.

Further, by using parallel rays as the incident light LC of the liquid crystal plate 1, it is possible to form the image forming points of the upper and lower pixels of the liquid crystal plate 1 on the same screen 4 perpendicular to the optical axis a, As a result, it is possible to prevent the local defocusing caused by tilting the liquid crystal plate 1.

It should be noted that in the above-described embodiment, by setting the distance between the light source 2 and the condenser lens 3 to be short, the parallel rays LC
However, instead of this, the same effect can be obtained by using condenser lenses having different focal lengths.

Further, in the embodiment, the liquid crystal plate 1 having the angle α with the b-axis as the rotation axis is used.
In addition to the inclination of, the liquid crystal plate 1 is inclined by the angle β with the c-axis as the rotation axis. At this time, the angle β is made equal to the angle α. This makes it possible to correct vertical image shrinkage that occurs when the liquid crystal plate 1 is tilted in the maximum contrast direction.

In the configuration of FIG. 2, the image on the screen 4 is an image smaller by cos α in the vertical direction than when the liquid crystal plate 1 is mounted perpendicularly to the optical axis a.

Similarly, in the horizontal direction of the screen 4, the image becomes smaller by cosβ.

Since the angle α and the angle β are equal to each other, the image on the screen 4 is an image shrunk in the vertical direction and the horizontal direction at the same ratio, and as a result, the image having the same aspect ratio as the image formed on the liquid crystal plate 1 is obtained. An image is formed on the screen.

According to the configuration of FIG. 2, it is possible to obtain an image having the same aspect ratio as the image formed on the liquid crystal plate 1.

Therefore, when the liquid crystal plate is tilted with respect to the optical axis in the related art, it is necessary to use the liquid crystal plate 1 which forms an image vertically extended in advance in order to obtain an image with a predetermined aspect ratio. In the example, the same shape as the liquid crystal plate 1 used in the conventional projector can be used.

In the above embodiment, the parallel rays are incident on the liquid crystal plate 1 to prevent local defocusing of the image on the screen, but instead of this, the condenser lens 11 and the field lens 4 are used. Even if an optical system having a deep depth of focus is used as the optical system, the same effect can be obtained.

Further, in the above-mentioned embodiment, the case where the present invention is applied to a projector using one liquid crystal plate has been described, but the present invention is not limited to this, and a color projector using a plurality of liquid crystal plates, etc. It can also be widely applied to. In this case, color image light may be formed by using three liquid crystal plates for red, green, and blue.

In the above-described embodiment, the tilt angle of the liquid crystal plate 1 is set to be equal to the maximum contrast viewing angle α, but instead of this, if the liquid crystal plate 1 is tilted to approach the viewing angle α, Paying attention to the fact that the above-described effect can be gradually obtained, it may be determined within a practically allowable contrast range.

H Effect of the Invention As described above, according to the present invention, the optical axis of the light source is the a-axis,
The axes orthogonal to each other in the plane orthogonal to the optical axis are the b-axis and the c-axis.
When the axis is the axis, the transmissive liquid crystal plate is tilted by a first angle with respect to the optical axis a in the direction of the maximum contrast viewing angle with the b axis as the rotation axis, and the c axis is the first axis with respect to the optical axis a 1
By tilting by a second angle that is approximately equal to the angle of
The contrast of the image projected on the screen can be remarkably improved, and an image without distortion can be projected on the screen.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of a projector of the present invention, FIG. 2 is a perspective view showing the inclination of a liquid crystal plate according to an embodiment, FIG. 3 is a sectional view showing a conventional projector, and FIG. FIG. 5 is a view angle characteristic diagram of a liquid crystal plate to be provided, and FIG. 5 is a perspective view used for the explanation. 1 ... Liquid crystal plate, 2 ... Light source, 3, 11 ... Condenser lens, 4 ... Screen, 5 ... Field lens.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 59-7928 (JP, A) JP 60-179723 (JP, A) JP 62-3227 (JP, A) JP 62- 19834 (JP, A)

Claims (1)

[Claims] 1. A projector in which image light is formed by transmitting light from a light source through a transmissive liquid crystal plate, and the image light is projected on a screen, wherein the optical axis of the light source is the a-axis. When the axes perpendicular to each other in the plane orthogonal to the axis are the b-axis and the c-axis, the transmission type liquid crystal plate has a first angle with respect to the optical axis a in the direction of the maximum contrast viewing angle with the b-axis as the rotation axis. The projector according to claim 1, wherein the projector is inclined by a second angle which is substantially equal to the first angle with respect to the optical axis a with the c-axis as a rotation axis.