JPS6060576A - Laser distance measuring device - Google Patents

Abstract

PURPOSE:To set a laser distance measuring device to optimum sensitivity automatically according to the level of background light by measuring the amount of noise in a receiver output in a time zone except a distance measurement period, and adjusting the reception sensitivity automatically. CONSTITUTION:A gate circuit 9 is opened in a laser distance measurement interruption period which extends from the laser emission of a laser oscillator 1, etc., by the specific reception time lapse of a receiving optical system 4. Then, the noise in the output of a variable gain video amplifier 12 is supplied to a detecting circuit 10 and the amplifier 12 is brought under feedback control through a holding circuit 11 to adjust the reception sensitivity automatically so that the amount of receive noise is nearly constant. Therefore, the reception sensitivity of the laser distance measuring device is set to the best value automatically; even when the receiving optical system has a large diameter, the sensitivity is displayed sufficiently with the small quantity of background light and there is no malfunction due to noise at the time of an increase in the quantity of background light.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a distance measuring device using pulsed laser light.

Pulsed laser distance measuring equipment generates a gigantic laser pulse in an extremely short period of time, irradiates it towards the target to be measured, receives the reflected laser light, and measures the time between emitting the laser light and receiving it. It attempts to measure the distance to the target by measuring time.

First, related parts of a conventional device of this type will be explained with reference to FIG. 8g1.

In Figure 1, (1) is a laser oscillator that generates a pulsed laser beam, (2) is a beam splitter that reflects a part of the laser beam, and (3) is a converter that converts the laser pulse beam from the beam splitter into an electrical signal. Photodiode,(
4) is a receiving optical system that focuses the reflected laser light from the target;
(5) is a photodetector that converts the received laser pulse light into an electrical signal, (6) is a video amplifier that amplifies the receiver No. 4, and (7) is a photodetector that converts the received laser pulse light into an electrical signal.
) is a comparator that outputs a pulse when the value of receiver No. 4 exceeds a reference value, and (8) is a counting circuit that measures the time interval from laser emission to reception of reflected pulsed light.

In the above device, when a laser pulse light is emitted from a laser oscillator (1) toward a target, a beam splitter (2
), a part of the laser light is given to the photodiode (3). The laser firing timing pulse detected by the photodiode (3) is given to the counting circuit (8), and the counting circuit (8) starts measuring time. When the laser beam hits the target and a part of it is reflected back, the receiving optical system (4
) and applied to a photodetector (5). Photodetector (
The received pulse signal of 5) is amplified by a video amplifier (6) and given to a comparator (7). When the magnitude of the received pulse signal exceeds a reference value, the comparator (7) generates a pulse signal and stops the time measurement operation of the counting circuit (8). In addition, the reference value of the comparator (7) is.

The level is set to such a level that malfunctions due to noise will not occur.

At this time, the distance R to the target is determined from the time t measured by the counting circuit (8).

■-c-t/2(t) Here C: Speed of light is given by

By the way, in a device using this type of laser light.

A YAG laser is generally used as the laser, and in that case, an avalanche photodiode (hereinafter referred to as rAPDJ) is used as the photodetector (5) because of its excellent sensitivity. Even when an APD is used as a photodetector (5), this type of device has traditionally been used toward the ground, so noise as a laser receiver is normally generated by the video amplifier (6) behind it. The comparator (7) is conventionally used because the value generated from
A method was used in which once the standard value of was adjusted, it was fixed at that value.

However, if this type of device is to be used primarily for anti-aircraft targets, it is necessary to measure even small targets at long distances, and to increase reception sensitivity.

It becomes necessary to increase the aperture of the receiving optical system (4).

Furthermore, in the case of anti-aircraft use, high-luminance objects 2, such as bright white clouds illuminated by sunlight, will be in the background. Those background lights cause a strong photocurrent to flow through the APD of the photodetector (5), resulting in large shot noise.

Figure 2 shows an example of the receiving optical system aperture versus noise when a bright cloud background is used.
If the noise level exceeds 100 degrees, background noise becomes dominant in the noise of the receiver. Therefore.

In conventional equipment, the reference value of the comparator (7) must be increased or the gain of the video amplifier (6) must be lowered to prevent the equipment from malfunctioning even in situations where the reception There was a drawback that the sensitivity did not improve significantly even if the aperture of the receiving optical system (4) was increased.

In order to improve the above-mentioned conventional drawbacks, the present invention automatically adjusts the reception sensitivity so that the amount of noise in the receiver remains constant.
This is intended to automatically set higher reception sensitivity when there is less background light.

The present invention will be explained below with reference to two drawings.

Figure 3 shows an embodiment of the present invention. Figure 2 shows a laser oscillator (1), a beam splitter (2), a photodiode (3), a receiving optical system (4), a photodetector (5), and a comparison. The counter (7) and the counting circuit (8) are the same as the conventional ones.

(9) is a gate circuit that passes signals only during a predetermined time period, 00
is a detection circuit that converts the output from the gate circuit (9) into DC, 0υ is a hold circuit that holds the DC value from the detection circuit +11 for a predetermined period, and a'a is a signal that responds to the DC voltage from the hold circuit 011. This is a variable gain video amplifier that changes the amplification gain.

In FIG. 3, the output of the variable gain video amplifier is given to a comparator (7) and a gate circuit (9).

The gate circuit (9) opens the gate during the period when the laser distance measurement is stopped after a predetermined reception time (usually about 100 μS) has elapsed since the laser emission, and the variable gain video amplifier α
The output noise is guided to the detection circuit αQ.

The detection circuit 00) detects input noise and sends it to the hold circuit αυ1 as a DC output. The hold circuit u11 amplifies the DC input to an appropriate magnitude, holds that value for a predetermined period, and changes the amplification gain of the variable gain video amplifier.

Therefore, according to the laser distance measuring device 6 having such a configuration, the receiver noise amount is measured using the pause period for laser distance measurement, and the variable gain video amplifier u2 is adjusted so that the noise amount becomes a constant value. Since the gain can be controlled, even with this device, which has a large-diameter receiving optical system and improved sensitivity, the sensitivity can be adjusted to a sufficient level when there are no bright ghosts in the background and the amount of background light is relatively low. In addition, even when background light increases, the optimal receiving sensitivity state is automatically set without malfunction due to noise.

In the above embodiment, the method of adjusting the receiving sensitivity was explained by changing the gain of the video amplifier.

A similar effect can be obtained by adjusting the aperture p of the optical system or changing the bias of the APD of the photodetector.

As described above, according to the present invention, it is possible to provide a laser ranging device that automatically sets the optimal reception sensitivity according to the level of background light.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing a conventional laser distance measuring device, Figure 2 is a block diagram showing a conventional laser distance measuring device.
The figure is a diagram explaining the relationship between receiving aperture and noise. FIG. 3 is a block diagram showing the laser distance measuring device of the present invention. In the figure, (1) is a laser emitter, (2) is a beam splitter, (3) is a photodiode, (4) is a receiving optical system, (5) is a photodetector, (6) is a video amplifier, ( 7
) is a comparator, (8) is a counting circuit, (9) is a gate circuit,
(Lull is a detection circuit, U is a hold circuit, and 02 is a variable gain video amplifier. In Figure 2, the same or equivalent parts are indicated by the same symbols. Agent: Masuo Oiwa No. 1 .IX+ Figure 2 Ukeka Kutenya Caliber No. 314

Claims (1)

[Claims] A laser oscillator that generates a pulsed laser beam. The reflected light from the target of the above laser beam is focused. A receiver that converts and amplifies the received No. 4 pulse into an electrical signal, a comparator that compares the received No. 4 pulse with a threshold value and sends it out as a signal if it is above a predetermined value, and a comparator that counts the time between the two emitted laser pulses and the received No. 4 pulse. A means for measuring the amount of noise in the receiver output during a time period other than the distance measurement period from laser emission to the passage of a predetermined received signal in a laser range finder that measures the distance to a target. and a means for adjusting the reception sensitivity of the receiver so that the amount of noise becomes a substantially constant value.