JPS63243930A - Automatic light controller for projector - Google Patents

Abstract

PURPOSE:To obtain a video of always adequate brightness by using a sensor which detects the light reflected from a screen and sensor which detects the brightness of external light and controlling the light of a projector in such a manner that the specified output difference therebetween is maintained. CONSTITUTION:Light of a light source 1 is entered to a space modulator 3 and is modulated by video information. The modulated light is imaged on a screen 11 from a projection lens 4. The light reflected from the screen 11 is received in a photodetecting lens 5 and is guided to an optical sensor 6. Directivity is provided to the lens 5 so that the lens receives only the light reflected from the screen 11. External light is diffused by a diffusion plate 7, by which the influence of the specific light is eliminated from said light. The output corresponding to the external light is obtd. by an optical sensor 8 and is inputted to a relational computing element 9. The differential signal between the sensors 6 and 8 and a set value are compared in the element 9 and the light of the light source 1 is controlled by a light quantity controller 10, by which the video of the adequate brightness having in influence of the external light is obtd.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is an automatic light control device for a projector, in particular, an automatic light control device that detects the intensity of reflected light from a screen and the brightness of external light, and automatically controls light control. The present invention relates to a device that performs this.

<Prior Art> In a conventional projector device, when the size of the screen to be projected is changed, the screen illuminance changes in inverse proportion to the area of the screen.

This is the illuminance E (lx) and the luminous flux dΦ from the projection lens
(1m) and the projected area dS(i), the following relational expression
E=dΦAs...It is expressed as (1).

Therefore, looking at the change in illuminance on the screen when changing the screen size from 10 inches to 50 inches, the screen area ratio between 10 inches and 50 inches is 1:25, so (
1) According to formula, the illuminance is 25:1. Although we assumed the screen gain to be constant here, in reality the screen gain also comes into play.

Assuming that the screen gain is G, the relational expression between illuminance E and brightness is L = as - E/π (2).

When the gain of the projection screen is 10 inches, cs
Assuming that the image is projected onto a screen with Gs = 10 and a screen with Gs = 1 when the screen is 50 inches, the screen brightness ratio at that time would be as high as 250:1.

Such an extreme difference in brightness is not practical as it may be too bright or too dark. Therefore, a light control device is required, and in the past, the solution was to simply insert an ND filter or manually switch the light intensity of the light source.

<Problems to be Solved by the Invention> However, with the above-mentioned light control means, it was not possible to obtain appropriate brightness, and it was necessary to manually switch the brightness. Furthermore, even if conditions such as the projection screen size and screen gain are the same, the optimal screen brightness differs depending on the surrounding brightness. Generally speaking, when the surroundings are bright, the screen is bright, and when it is dark, It is less tiring and the images look more beautiful when the screen is darkened, but it was difficult to obtain the appropriate brightness even with dimming, depending on the screen size, screen gain, etc.

In view of the above-mentioned problems of the prior art, the present invention provides automatic light control for a projector that can always adjust the brightness of an image to an appropriate level even if the projection screen size, screen gain, or ambient brightness is changed. The purpose is to provide equipment.

Means and operation for solving the above problems> The structure of the present invention for achieving the above-mentioned object is described in the first embodiment corresponding to the embodiment.
This will be explained using figures.

In the present invention, a projector is provided with an optical sensor 6 that detects only the amount of reflected light from a screen 11, an optical sensor 8 that detects surrounding brightness, and a light amount controller 10, and the output difference between the two optical sensors 6.8 is The light amount controller 10
The light source 1 of the projector is automatically dimmed by controlling the light source 1 of the projector.

With the automatic light control of such a projector, even if you change the projection screen size or reflectance to a different screen, the screen brightness is automatically corrected depending on the surrounding brightness, so you can always view images at the appropriate brightness. be able to.

<Example> Hereinafter, an example of the present invention will be described based on FIGS. 1 and 2.

1 is a light source; 2 is a condenser lens; 3 is a spatial modulator, such as a slide film or an LCD element, which modulates a video signal into the light from the light source 1 that has passed through the condenser lens 2; 4
A projection lens constitutes the projection system of the projector and projects an image onto the screen 11. Reference numeral 5 denotes a light-receiving lens, which allows only the light reflected from the screen 11 to enter the optical sensor 6. The optical sensor 6 is an optical sensor that detects the intensity of reflected light from the screen 11. Reference numeral 7 denotes a diffuser plate for diffusing external light, and 8 an optical sensor disposed at the rear of the diffuser plate 7, which detects the intensity of the external light. Reference numeral 9 denotes a comparator that compares and calculates the output values of both optical sensors 6.8, and as shown in FIG.
A subtracter 91 to which the output value from 8 is input, and a reference voltage generator 92
and a comparator 93 to which these output signals are input. Reference numeral 10 denotes a light amount controller that controls the amount of light from the light source 1 according to the output of the comparator 9.

The operation of this embodiment having the above configuration will be explained.

Light emitted from a light source 1 has its optical path adjusted by a condenser lens 2, enters a spatial modulator 3, and modulates the incident light with image information. The light modulated by the spatial modulator 3 is imaged onto a screen 11 by a projection lens 4, and an image of the spatial modulator 3 is projected onto the screen 11. At this time, the brightness of the screen 11 varies depending on the gain of the screen or the projection screen size, and the brightness is obtained by detecting the intensity of the light projected from the projection lens 4 and reflected by the screen 11. The reflected light from the screen 11 enters the light receiving lens 5 and is received by the optical sensor 6. At this time, the light-receiving lens 5 is set to have directionality for the incident light, and is set so that no light other than the light reflected from the screen 11 enters the optical sensor 6, so the influence of external light can be ignored. can.

Therefore, the output value corresponding to the intensity of the screen reflected light obtained by the optical sensor 6, that is, the detected voltage, is input to the comparator 9. At the same time, external light around the main body of the projector is diffused by the diffuser plate 7, eliminates the influence of specific light, and enters the optical sensor 8. The optical sensor 8 outputs an output value according to the brightness of the external light, i.e. A detected voltage is obtained and input to the comparator 9. In the comparator 9, the optical sensor 6
The output value from the optical sensor 8 and the output value from the optical sensor 8 are first subtracted by
1, the output value of the optical sensor 8 is subtracted from the output value of the optical sensor 6, and the difference signal is output. In other words, this value corresponds to the difference from the reflected light from the screen 11. The difference signal thus obtained is input to a comparator 93, where it is compared with the set voltage of the reference voltage generator 92, and the result is output. This output is input to the light amount controller 10, and the light source 1 is dimmed.

Through this series of feedback controls, the screen brightness is high when the area around the projector body is bright and low when it is dark, and it is possible to project at a constant screen brightness when the projection screen size, screen, etc. change.

Further, by changing the set voltage of the reference voltage generator 92, the brightness can be automatically adjusted to any brightness.

In addition, as mentioned above, in order to change the set voltage of the reference voltage generator 92, there is a
It goes without saying that the same function can be obtained by providing a D filter, a diaphragm, etc.

Further, in the above-described embodiment, the light intensity of the light source 1 itself is dimmed, but the light source 1 may be dimmed using an ND filter, an aperture 9, or the like.

FIGS. 3(a) and 3(b) each show a modification of the comparison calculator 9 in the above-described embodiment. Figure 3(a)
The output value of the optical sensor 6 and the output signal of the adder 91a which adds the output value of the optical sensor 8 and the set voltage of the reference voltage generator 92a are inputted to the comparator 93a and compared. In b), the output signal of the subtracter 91b that subtracts the output value of the optical sensor 6 and the set voltage of the reference voltage generator 92b and the output value of the optical sensor 8 are input to the comparator 93b and compared.

Any of the configuration examples can perform the same function as the above-mentioned embodiments.

<Effects of the Invention> As explained above, the present invention uses an optical sensor that detects only the amount of light reflected from the screen and an optical sensor that detects the brightness of the outside light, and uses a sensor that detects the brightness of the outer light so that the difference in output between them is constant. Even if you change the projection screen size or reflectivity by adjusting the projector's brightness, the screen brightness is automatically corrected depending on the surrounding brightness, so you can always view images at the appropriate brightness. It has the effect of

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of an embodiment of an automatic light control device for a projector according to the present invention, Fig. 2 is a circuit diagram of its comparator, and Fig. 3 (a) Φ) is a modification of the comparator. FIG. 2 is a circuit diagram showing an example. DESCRIPTION OF SYMBOLS 1... Light amount, 3... Spatial modulator, 4... Projection lens, 5... Light receiving lens, 6... Optical sensor for detecting screen reflected light, 7... Diffusion plate, 8... - Optical sensor for detecting external light, 9... Comparison calculator, 10... Light amount controller,
11...Screen 1 Figure 1...Light light 3...Start point 4...Projection lens 6...11 light sensor 8...Second light sensor 9... Rigid growth 10... Out of light i control 11... Step 7 Line 2 Figure 3 (a) Dan (b) Dan procedural corrector June 70, 1988 Day

Claims (1)

[Claims] 1. A projector that can freely change the projection screen size is equipped with an optical sensor that detects only the amount of light reflected from the screen, an optical sensor that detects the brightness of ambient light, and a light amount controller for the light source, and that is equipped with both. An automatic projector light control device characterized in that the light amount controller is controlled so that the difference in the output values of the optical sensors is constant.