JPS63253342A - Automatically for projector dimming device - Google Patents

Abstract

PURPOSE:To maintain the illuminance of a screen constant by providing a distance detector measuring a distance from a projector main body to the screen. CONSTITUTION:The oscillator 10 of the distance detector 1 oscillates by the inherent resonance frequency of a wave transmitter 14. A signal (b) that a gate circuit 11 gates with the aid of the trigger signal (a) of a trigger generator 12 is amplified and transmitted as an ultrasonic wave by the wave transmitter 14 to the screen 4. The transmitted ultrasonic wave is reflected by the screen 4. The signal detected by a wave receiver 15 generates a time difference, depending upon the distance to the screen 4. After the signal passes through the wave receiver 15, a detector 16 and a waveform shaping circuit 17, a signal (d) is obtained. On the other hand, with the aid of the previously obtained signal (d), a triangle wave generator 18 sample-holds an obtained signal (e) that the output signal of the trigger generator 12 has reset, and obtains an output voltage in proportion to the time delayed from a trigger (a) pulse, i.e. in proportion to the distance. Thus the appropriate screen illuminance can be automatically maintained.

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 control based on distance information to a screen.

<Prior Art> In conventional projector devices, 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(1
m) and projected area dS(rr?), the following relational expression
It is expressed as E=dψ/ds (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 l:25, so
From equation (1), the illuminance is 25:l. Such extreme differences in illuminance are either extremely bright or extremely dark and are not practical. Therefore, a light control device is required, and in the past, only N
The solution was to insert a D filter or manually switch the light intensity of the light source.

<Problems to be Solved by the Invention> However, appropriate brightness can be obtained with the above-mentioned dimming means. Moreover, it was necessary to manually switch the switch.

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 an automatic light control device for a projector that automatically keeps the illuminance of the screen constant even if the projection screen size is changed.

Means for Solving the Problems> The configuration of the present invention for achieving the above-mentioned object will be explained using FIG. 1 corresponding to an embodiment.

The present invention provides a projector in which the projection screen size can be changed by changing the distance on the screen, which includes a distance detector 1 for measuring the distance between the projector body and the screen, a dimmer circuit 3, and a dimmer circuit 3. Distance detector 1
and an arithmetic circuit 2 for correcting the characteristics of the dimming circuit 3.

Function> The distance between the projector body and the screen is measured by the distance detector 1, and the relationship between the distance value and the screen illuminance is corrected by the arithmetic circuit 2, and the dimmer circuit 3 is actuated based on the correction value to control the projector. Performs dimming of the light source.

Therefore, even if the projection screen size is changed according to the distance to the screen, the screen illuminance is automatically corrected to a constant value.

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

1 is a distance detector that uses ultrasonic waves to detect the distance between the projector body and the screen; 2 is an arithmetic circuit that corrects the relationship between the distance value detected by the distance detector 1 and the illuminance; and 3 is an arithmetic circuit that is obtained by the arithmetic circuit 2. This is a dimming circuit that dims the light source of the projector according to the value set.

As shown in FIG. 2, the distance detector 1 includes an oscillator 10 that generates an ultrasonic frequency, a gate circuit 11 that gates the output of the oscillator 10 by a trigger generator 12, and a triangular wave generator 18. A trigger generator 12 that sends a trigger pulse to the gate circuit 11, an amplifier 13 that amplifies the output signal of the gate circuit 11, a transmitter 14 that converts the output signal of the amplifier 13 into an ultrasonic wave, and a receiver that receives the ultrasonic wave reflected from the screen 4. a wave receiver 15 that detects the output of the wave receiver 15, a waveform shaping circuit 17 that shapes the output waveform of the wave detector 16, and generates a triangular wave in synchronization with the trigger signal of the trigger generator 12. The sampling and holding circuit 19 samples the triangular wave from the triangular wave generator 18 using the output signal of the waveform shaping circuit 17.

Regarding the operation of this embodiment having one or more configurations, the operation of the distance detector 1 will first be explained using the operation signal waveform diagram in FIG.

The oscillator 10 oscillates at the self-resonant frequency of the transmitter 14, and is gated by the gate circuit 11 by the trigger signal of the trigger generator 12, which generates the signal shown in FIG. 3(a). get. This obtained signal is amplified by an amplifier 13 and sent to the screen 4 as an ultrasonic wave by a transmitter 14. The transmitted ultrasonic waves are reflected by the screen 4,
It is detected by the receiver 15. At this time, the detected signal has a time difference depending on the distance to the screen 4, and has a waveform shown in FIG. 3(e). The signal detected by the wave receiver 15 is detected by the wave detector 16, and the signal shown in FIG. 3(d) is obtained by the waveform shaping circuit 17.

On the other hand, the triangular wave generator 18 is reset to the output signal of the trigger generator 12 to obtain the output signal shown in FIG. 3(e). By sampling and holding this signal in the sampling and holding circuit 19 using the output signal of the waveform shaping circuit 17 obtained earlier, the output voltage shown in FIG. 3(f) corresponding to the delay time from the trigger signal pulse is obtained. . In other words, an output voltage corresponding to the distance from the projector body to the screen 4 can be obtained.

Next, the obtained distance data to the screen 4 is input to the arithmetic circuit 2, and the relationship between the distance to the screen and the screen illuminance or the dimming characteristics of the next-stage dimming circuit 3 is corrected. Then, the dimming circuit 3 dims the light source of the projector body using the value corrected by the arithmetic circuit 2.

As this dimming means, any means may be used, such as means for controlling the power of the light source, or means for providing an aperture and controlling the amount of aperture.

In this way, changes in screen illuminance due to changes in the projection screen size depending on the distance to the screen can be corrected to maintain a constant illuminance.

In the above embodiment, the distance detector 1 using ultrasonic waves is used to detect the distance to the screen. may be detected.

<Effects of the Invention> As explained above, the present invention automatically corrects the screen illuminance to a constant value even if the projection screen size is changed according to the distance to the screen, and automatically maintains an appropriate screen illuminance. There is an effect that can be done0

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of a projector-automatic light control device according to the present invention, and FIG. 2 is a block diagram of its distance detector.
FIG. 3 is a signal waveform diagram illustrating the operation of the distance detector shown in FIG. 2. 1...Distance detector, 2...Arithmetic circuit, 3...Dimmer circuit, 4...Screen Figure 1 Figure 2

Claims (1)

[Claims] 1. In a projector that can change the projection screen size by changing the distance to the screen, a distance detector that measures the distance between the screen and the projector body, a dimmer circuit, and a distance detector and dimmer circuit An automatic projector light control device characterized by comprising an arithmetic circuit for correcting characteristics.