JPH0799423B2 - Rear projection brightness variable device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to varying the brightness distribution of a rear projection screen.

[Conventional technology]

As shown in FIG. 8, the rear projection is composed of a projection tube, a projection lens, a screen and the like, and the screen is composed of a Fresnel lens and a lenticular lens.

Then, the light flux radiated from the projection tube is enlarged by the projection lens and projected on the screen, the light flux is condensed by the Fresnel lens, and the light flux is diffused by the lenticular lens to enlarge the field of view of the screen.

[Problems to be Solved by the Invention]

In the conventional rear projection, the light flux radiated from the projection tube is condensed by the Fresnel lens, and the light flux is diffused by the lenticular lens in order to expand the field of view.However, considering one of the lenticular lenses, Four
As shown in the figure, the light flux that diffuses into the light flux that enters the lenticular lens is not completely diffused uniformly at 180 °,
As shown in FIG. 5, since the light flux in the optical axis direction is strong and the light flux becomes weaker as the distance from the optical axis direction increases, the light flux in the peripheral portion of the screen is lower than that in the central portion of the screen. However, there was a defect that the brightness became dark.

Therefore, in rear projection, which is required for high image quality such as HDTV and EDTV, there is a need for a rear projection having uniform brightness without shading between the central part of the screen and the peripheral part of the screen.

[Means for solving problems]

In order to solve the above problems, in the present invention, means for making the projection tube side of the transmissive screen a Fresnel lens, and means for making the monitoring side of the screen a lenticular lens,
Between the lenticular lens and the Fresnel lens, means for enclosing a liquid crystal that is a liquid whose refractive index is variable depending on the strength of an electric field, means for installing a transparent electrode corresponding to the lenticular lens on the liquid crystal, and the same transparent electrode are provided. A control means is provided for refracting the light beam, and the refraction means makes the transmission screen uniform in luminance distribution.

Further, the liquid for changing the refractive index between the lenticular lens and the Fresnel lens depending on the strength of the electric field may be nitrobenzene or the like.

[Action]

In the rear projection brightness varying device according to the present invention configured as described above, liquid crystal is sealed between the Fresnel lens on the projection tube side of the transmissive screen and the lenticular lens on the monitoring side, and the transparent electrode corresponding to the lenticular lens is sealed. The refractive index of the liquid crystal is varied by installing the liquid crystal at both ends of the liquid crystal and controlling the transparent electrodes.

As shown in FIG. 6, when the liquid crystal has a small refractive index, the light flux incident on the lenticular lens is incident at an angle θ ₁ with respect to the optical axis, and the light flux amount of the output of the lenticular lens is (a). In the order of>(b)> (c), the luminous flux on the optical axis becomes maximum, and the luminous fluxes of (b) and (c) become substantially equal.

Further, as shown in FIG. 7, when the light flux incident on the lenticular lens has a large refractive index of the liquid crystal and the incident angle with respect to the optical axis is θ ₂ > θ ₁ , the output light flux amount of the lenticular lens is (e). >(D)> (f), the luminous flux amount of (e) is maximum, the luminous flux amount of (f) is minimum, and when the transmissive screen is monitored from the (f) side, it is very dark. Therefore, the lenticular lens 1 By controlling the refractive index of the liquid crystal corresponding to the entire surface and varying the incident angle of the light flux incident on each lenticular lens, the luminance of the transmissive screen can be varied and the luminance distribution can be made uniform.

〔Example〕

Hereinafter, a rear projection brightness varying device according to the present invention will be described with reference to the drawings.

FIG. 1 is a structural diagram of an embodiment according to the present invention, in which a light beam emitted from a projection tube 6 is enlarged by a projection lens 5 and projected on a screen A.

The screen A is composed of a Fresnel lens 3, a liquid crystal 2 and a lenticular lens 1. The light flux expanded by the projection lens 5 is condensed by the Fresnel lens 3, and the condensed light flux of the liquid crystal 2 corresponding to the lenticular lens 1. The refractive index is changed by controlling the transparent electrodes 4 provided on both ends of the grid.

FIG. 2 is a structural view showing a part of the liquid crystal 2 enclosed in the screen A, and the transparent electrodes 4 are arranged on both ends of the liquid crystal 2 on a lattice.

The liquid crystal 2 at each intersection of the transparent electrodes arranged on the lattice corresponds to the position of the lenticular lens 1, and the transparent electrodes B1, B2, B3, etc. are transparent electrodes arranged in the horizontal direction of the liquid crystal 2.
Transparent electrodes such as A1, A2, and A3 are transparent electrodes arranged in the vertical direction of the liquid crystal 2.

FIG. 3 is a block diagram of a pulse generator applied to the liquid crystal 2, and an interface for transmitting and receiving data to and from the microprocessor 9 which stores the address for controlling the pulse generated in the liquid crystal application pulse circuit 7 in advance. Supply to the circuit 8.

When the pulse of the liquid crystal application pulse circuit 7 is supplied to the interface circuit 8, the data stored in the microprocessor 9 is output to the interface circuit 8, and the interface circuit 8 outputs the liquid crystal application pulse corresponding to the address for correcting the luminous flux to the horizontal electrodes. It is supplied to the drive circuit 10 and the vertical electrode drive circuit 11.

The output pulse of the horizontal electrode drive circuit 10 is B1, B2, B3 in FIG.
The transparent electrodes in the equal horizontal direction are driven, and the vertical electrode drive circuit 11 drives the transparent electrodes in the vertical direction such as A1, A2 and A3 in FIG.

The data stored in the microprocessor 9 in advance is, for example, when the incident angle of the light beam on the lenticular lens at the intersection of A1 and B3 is small and the light beam to the outside is small and there is shading, the liquid crystal 2 at the intersection of A1 and B3 is used. Then, the output pulse of the horizontal electrode drive circuit 10 and the output pulse of the vertical electrode drive circuit 11 are supplied to correct the amount of light flux so that the light flux is refracted to the outside, and the shadenig is removed.

〔The invention's effect〕

As is clear from the above description, in the rear projection luminance variable device according to the present invention, the luminous flux emitted from the projection tube is enlarged by the projection lens and projected on the screen composed of the Fresnel lens, the liquid crystal and the lenticular lens. , Transparent electrodes are installed on the grid corresponding to the lenticular lenses on both ends of the liquid crystal enclosed between the Fresnel lens and the lenticular lens, and the transparent electrodes installed on the grid are controlled by the pulse generator to control the refractive index of the liquid crystal. Since it is variable, the incident angle of the light beam incident on each lenticular lens is variable, and the light beam diffused from each lenticular lens has directivity, so there is no shading between the center part of the screen and the peripheral part of the screen. This makes it possible to create a rear projection screen with similar brightness.

Further, by giving directivity to the light beam diffused from each lenticular lens in a certain direction, the screen field of view can be enlarged or reduced.

[Brief description of drawings]

FIG. 1 is a structural diagram showing an embodiment of the present invention, FIG. 2 is a structural diagram of a liquid crystal, FIG. 3 is a block diagram of a pulse generator, and FIGS. 4 to 7 are incident and diffused light beams of a lenticular lens. And FIG. 8 is a conventional rear projection showing the state of FIG. In the figure, A is a screen, 1 is a lenticular lens, 2 is a liquid crystal, (a), (b), (c), (d),
(E) and (f) are luminous flux, 3 is a Fresnel lens, 4, A1,
A2, A3, B1, B2, B3 are transparent electrodes, 5 is a projection lens, 6 is a projection tube, 7 is a liquid crystal application pulse circuit, 8 is an interface circuit, 9 is a microprocessor, 10 is a horizontal electrode drive circuit, and 11 is vertical. It is an electrode drive circuit.

Claims (2)

[Claims] 1. In a rear projection using a transmissive screen, a Fresnel lens is disposed on the projection tube side of the transmissive screen, a lenticular lens is disposed on the monitor side of the screen, and the lenticular lens and the Fresnel lens are disposed. A plurality of electrodes are formed on both surfaces between lenses, the transmissive screen in which a liquid whose refractive index can be changed by an electric field is sealed is disposed, and a pulse generator is provided to apply a voltage to the electrodes of the transmissive screen. Rear projection brightness variable device characterized by. 2. The rear projection brightness varying device according to claim 1, wherein the liquid to be enclosed is liquid crystal.