JPS63243929A - Automatic light controller for projector - Google Patents

Abstract

PURPOSE:To obtain a video of always adequate brightness by detecting the intensity of the light reflected from a screen and automatically controlling the light of a light source so that the specified brightness of the screen is maintained even if the size of a projection image plane or the screen is changed. CONSTITUTION:The light of the light source 1 is entered to a space modulator 3 and the incident light is modulated by video information and is imaged on the screen 10 by a projection lens 4. The light reflected from the screen 10 is received in a light receiving lens 5 having directivity, from which the light is guided to an optical sensor 6 to obtain the voltage proportional to the light reflected from the screen 10. The output voltage of the sensor 6 and the output voltage of a reference voltage device 7 are compared by a comparator 8 and the output thereof is inputted to a light quantity controller 9. The light reflected from the screen 10 is detected and the quantity of the light of the light source 1 is controlled by the controller 9 in such a manner, by which the video of always the adequate brightness is obtd. even if the size of the projection image plane or the screen is changed.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an automatic light control device for a projector, and particularly to a device that automatically controls light according to the intensity of light reflected from a screen. .

<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
(lrn), and the projected area dS (TI?) is expressed by the lower heat relation, E=d'/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 (
From equation 1), the illuminance is 25:l.

Although we assumed the screen gain to be constant here, in reality the screen gain also comes into play.

When the screen gain is Gs, the relational expression between illuminance E and brightness is L = Gs - E/π...C).

When the gain of the projection screen is 10 inches, GS=
Assuming that the image is projected onto a 50-inch screen with Gs=1, the screen brightness ratio would be 250:t.

Such extreme differences in brightness are either too bright or too dark and are not practical. Therefore, a light control device is required, and in the past, the solution was to simply insert an ND filter or manually change the light intensity of the light source.

<Problems to be Solved by the Invention> However, with the above-mentioned dimming means, it was not possible to obtain appropriate brightness, and it was necessary to manually switch the brightness.

SUMMARY OF THE INVENTION In view of the problems of the prior art described above, it is an object of the present invention to provide a light control device for a projector that automatically maintains the brightness of the screen even if the projection screen size or screen is changed.

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

The present invention includes a light sensor 6 and a light amount controller 9 having directivity for detecting the amount of reflected light from the screen 10,
The light amount controller 9 automatically adjusts the light of the light source 1 of the projector so that the detected value of the optical sensor 6 becomes a predetermined set value.

The automatic light control of such a projector allows images to be viewed at appropriate brightness even if the projection screen size or screen is changed.

<Example> Embodiments of the present invention will be described below with reference to FIG.

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
constitutes a projection system with a projection lens, and projects an image onto a screen 10. Reference numeral 5 denotes a light-receiving lens, which only allows the reflected light from the screen 10 to enter the optical sensor 6. The optical sensor 6 is an optical sensor that detects the intensity of reflected light from the screen 10. 7 is a reference voltage generator for setting the light amount; 8 is a comparator for comparing the detection value of the optical sensor 6 with the set voltage of the reference voltage generator 7; 9
is a light amount controller that controls the light amount of the light source 1 according to the output of the comparator 8.

In this embodiment with the above configuration, the light emitted from the light source 1 has its optical path adjusted by the condenser lens 2, enters the spatial modulator 3, and modulates the incident light with image information.

The light whose image is modulated by the spatial modulator 3 is transmitted to the projection lens 4
An image is formed on the screen 10, and the image of the spatial modulator 3 is projected onto the screen 10. At this time, the brightness of the screen 10 varies depending on the screen gain or the projection screen size, and the brightness is obtained by detecting the intensity of the light projected from the projection lens 4 reflected by the screen 10. . The reflected light from the screen 10 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 give directionality to the incident light so that no light other than the light reflected from the screen 10 enters the optical sensor 6, so the influence of external light can be ignored. Can be done.

A detection voltage corresponding to the intensity of screen reflected light obtained by the optical sensor 6 is compared with a reference voltage of a reference voltage device 70 set to a certain value by a comparator 8, and is inputted to a light amount controller 9. The light amount controller 9 controls the amount of light from the light source 1 according to the output from the comparator 8, so that the intensity of the reflected light from the screen 10 can be kept constant.

Furthermore, by changing the set voltage of the reference voltage generator 7, the brightness can be controlled to any desired level.

Note that instead of changing the set voltage of the reference voltage generator 7 as described above, the sensitivity of the optical sensor or the ND filter,
It goes without saying that the same function can be obtained even if a diaphragm or the like is provided.

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

<Effects of the Invention> As explained above, the present invention uses a light sensor to detect the intensity of reflected light from the screen and automatically adjusts the light source, so even if the projection screen size or the screen is changed, the screen The brightness of the screen is automatically adjusted to a constant level, which has the effect of ensuring that images are always viewed at the appropriate brightness.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an embodiment of an automatic light control device for a projector according to the present invention. DESCRIPTION OF SYMBOLS 1... Light source, 3... Spatial modulator, 4... Projection lens, 5... Light receiving lens, 6... Light sensor, 7...
Reference voltage device, 8...Comparator, 9...Light amount controller, 10...Screen Figure 1 1... Hikari Rin 3... Kukai Henkenshi 4...) Jo No. Use. 6... Light death 7... Standard voltage verification 8... Compact-7 9209 yuan Placement 1 o... Screen 7 Line

Claims (1)

[Claims] 1. A projector that can freely change the projection screen size, which is equipped with a light sensor that detects only reflected light from the screen and a light amount controller for a light source, and controls the light amount so that the detected value of the light sensor remains constant. A projector automatic light control device characterized by controlling a projector.