JPH06258436A - Electro-optical distance measuring equipment - Google Patents

Abstract

PURPOSE:To provide a highly accurate electro-optical distance measuring equipment requiring no optical diaphragm. CONSTITUTION:An emitted intensity modulated light 4 modulated by a modulator 2 and having the same phase as a reference signal emitted from a light emitter 3 is passed through a transmission optical system 5 and reflected by an object 7 and then received, as a reflected intensity modulated light 10, by a light receiving means 11 through a light receiving optical system 9. The light receiving means 11 comprising an avalanche diode, for example, outputs a detection signal having externally controllable level which is controlled by a control means 15 to come within a predetermined range. A phase difference detector 14 detects phase difference between the reflected intensity modulated light 14 and the reference signal and a distance calculator 16 determines the distance. Since the level of detected signal is not susceptible to the quantity of light received by the light receiver 11, it is matched with that of the reference signal without requiring any optical diaphragm thus realizing highly accurate measurement.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lightwave rangefinder for obtaining a distance from a phase difference between a transmitted light modulated wave and a received light modulated wave.

[0002]

2. Description of the Related Art In general, a light wave range finder emits a brightness-modulated light having the same phase as a reference signal from a light emitter, is reflected by an object to be measured and becomes reflected light, and a light receiving means receives the reflected light and The detection signal synchronized with the phase of the reflected light is output, and the phase difference detector detects the phase difference between the phase of the detection signal and the phase of the reference signal, and measures the distance to the target from the phase difference. ing.

When attempting to measure a distance using such an optical distance meter, the intensity of reflected light is low when the distance between the optical distance meter and the object to be measured is long, and the intensity is high when the distance is short. Etc., due to the difference in perspective of the measurement object,
The light quantity of the reflected light received by the light receiving means changes, and the level of the detection signal changes accordingly. However, the level of the reference signal is irrelevant to the amount of received light and is always at a constant level. Therefore, the intensity of the incident modulated light fluctuates due to the length of the distance, which causes a mismatch between the reference signal level and the detection signal level, which is one of the causes of the detection error of the phase difference detection circuit.

Therefore, in the prior art, an optical diaphragm such as an optical filter is provided between the light emitter and the object to be measured or between the object to be measured and the light receiving means, and the light amount received by the light receiving means is small. If the aperture is large, the aperture is closed, and if it is large, the optical aperture is controlled by controlling the optical aperture according to the amount of light received by the light-receiving means, and the level of light received is constant regardless of the distance. The amount of light is secured, and the discrepancy between the reference signal level and the detection signal level is tried to be solved by this.

Further, the detection signal output from the light receiving means is amplified by an amplifier having an AGC function (voltage gain automatic control function) according to the level, and the level of the detection signal is made equal to the level of the reference signal. The phase difference was also detected.

As a reference of such a prior art, Japanese Examined Patent Publication No. 51-8340 can be cited.

[0007]

In the conventional optical distance meter, the optical diaphragm such as an optical filter is controlled in order to make the amount of received light constant. To this end, a driving device such as a motor is used. I need. Such a drive device has poor responsiveness and is inconvenient to handle. Also in terms of reliability, as a result of such a drive having a moving part,
There are many failures due to deterioration due to wear of moving parts, and
There were problems such as requiring maintenance work. Further, since the optical diaphragm has a large volume and a large weight, it has been an obstacle to reducing the size and weight of the entire apparatus.

Also in the amplifier having the AGC function, since the light receiving means placed in the preceding stage is outside the feedback loop, when the light receiving means is saturated, the AGC function is not useful and an auxiliary when an optical diaphragm is provided. It was just a means.

The present invention has been made in view of the above problems of the prior art, and an object thereof is to provide an optical distance meter which does not require a light receiving amount adjuster such as an optical diaphragm.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention receives reflected brightness modulated light in which emitted brightness modulated light having the same phase as a reference signal is reflected by an object to be measured, and the reflected brightness modulated light is received. In a light-wave distance meter that measures a distance to a measurement object from a light receiving unit that outputs a detection signal in the same phase as the light and a phase difference between the phase of the detection signal and the phase of the reference signal, the light receiving unit outputs the detection signal. The signal level can be controlled by an external signal, and a control means for controlling the light receiving means based on the level of the detection signal to keep the level of the detection signal at a constant value is provided.

When an avalanche photodiode is used as the light receiving means, a control means for controlling the voltage applied to the diode to keep the output current of the diode at a constant value is provided.

[0012]

According to the invention described in claim 1, since the detection signal level output by the light receiving means can be controlled by a signal from the outside, the control means has a low detection signal level because the light receiving amount is small. Controls the light receiving means so as to raise it, and conversely controls the light receiving means so as to reduce it when the detection signal level is high because the amount of received light is large.

According to a second aspect of the present invention, when an avalanche photodiode (hereinafter referred to as "APD") is used as the light receiving means, the control means controls the voltage applied to the APD so that the light is emitted. Control electromotive force
It acts to keep the output current, which is the detection signal output by D, constant.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

Referring to FIG. 1, reference numeral 1 is a reference signal generator, which is composed of an oscillator.

Reference numeral 2 denotes a modulator, which modulates the brightness of the emitted light emitted from the light emitter 3 based on the reference signal. The emitted brightness-modulated light 4 emitted from the light emitter 3 after being subjected to the brightness modulation is made into an emitted parallel light beam bundle 6 by the light transmission optical system 5, and is reflected by a measuring object 7 such as a reflecting mirror to become a reflected parallel light beam bundle 8. ,
The reflected brightness modulated light 10 is transmitted through the light receiving optical system 9 to the light receiving means 1.
Incident on 1.

The reference signal obtained from the modulator 2 is the amplifier 1
The signal is amplified by 2a, waveform-shaped by the waveform shaper 13a, and then output to the phase difference detector 14.

The detection signal output from the light receiving means 11 composed of an avalanche photodiode or phototransistor is amplified by the amplifier 12b, and the waveform shaper 13b and the control means 1 are amplified.
Input to 5.

The waveform shaper 13b shapes the signal output from the amplifier 12b and outputs it to the phase difference detector 14.

The phase difference detector 14 includes waveform shapers 13a and 1a.
The signals input from 3b are compared with each other to detect the phase difference between the two signals, and the distance calculator 16 calculates the distance from the phase difference to the measurement target. The distance calculator 16 also controls the switch control means 18 to obtain the internal optical path by the optical path switch 19 including a mirror and a lens, and corrects the distance to the object to be measured.

The control means 15 monitors the magnitude of the signal output from the amplifier 12b and controls the light receiving means 11 so that the signal level of the detection signal output from the light receiving means 11 is kept constant. FIG. 2 is an internal block diagram of the control means 15. A rectifier circuit 21 rectifies the output of the amplifier 12b and outputs a DC voltage to the A / D converter 22. The A / D converter 22 digitizes the DC voltage and outputs a digital signal to the arithmetic unit 23. The arithmetic unit 23 compares the value of the digital signal with the set value stored in the storage means 24 to detect the difference, and controls the voltage controlled voltage source 26 via the D / A converter 25 to receive the light receiving means. The detection signal level output by 11 is controlled.

When the light receiving means 11 is composed of APD, A
By increasing or decreasing the voltage applied to the PD, the output current of the APD, which is a detection signal, can be controlled.
When the output value of the A / D converter 22 is larger than the set value stored in the storage means 24, the U23 calculates the calculation means 2
3 operates so as to lower the bias voltage by the voltage control voltage source 26 via the D / A converter 25 to reduce the detection signal level output from the light receiving means 11, and conversely the A / D converter 2
When the output value of 2 is smaller than the set value, the bias voltage is increased to increase the detection signal level output by the light receiving means 11. In this way, the distance can be measured by controlling the light receiving sensitivity of the APD with the voltage with respect to the light amount of the reflected brightness modulated light.

In this embodiment, the light receiving means 11 and the control means 15
Although a negative feedback loop is formed via the amplifier 12b, the control means 15 can directly control the light receiving means 11 by using the detection signal output from the light receiving means 11 as an input signal.

[0024]

As described above, according to the present invention,
Even if the received light amount adjuster such as an optical diaphragm is not provided to adjust the received light amount, the measurement error caused by the mismatch between the detection signal level and the reference signal level does not occur.

As a result of eliminating the need for a light receiving amount adjuster such as an optical diaphragm, a mechanical driving device such as a motor is not necessary, and mechanical parts therefor are also unnecessary. Therefore, it is possible to obtain a product having excellent performance such as reduction in size and weight of the device, high-speed response, high reliability, and maintenance-free.

Furthermore, since the gain of the first stage of the amplifier circuit can be controlled, the circuit will not be saturated and the dynamic range can be widened. .

When the light receiving means is composed of an avalanche photodiode, a highly accurate lightwave distance meter can be realized by using an inexpensive and simple circuit structure, which further contributes to reduction of manufacturing cost and weight and size reduction of the device. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a block diagram of control means.

[Explanation of symbols]

4 Emission brightness modulated light 10 Reflection brightness modulated light 11 Light receiving means 15 Control means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tatsuyuki Matsumoto 260-63 Yanagicho, Hase, Atsugi, Kanagawa Prefecture Sokia Atsugi Factory (72) Inventor, Koji Sasaki 260-63, Yanagicho, Hase, Atsugi, Kanagawa Prefecture Stock Company Sokia Atsugi Factory

Claims (2)

[Claims] 1. Light receiving means for receiving the reflected brightness modulated light reflected by the emitted brightness modulated light having the same phase as the reference signal and irradiating the object to be measured, and outputting a detection signal in phase with the reflected brightness modulated light. In the lightwave rangefinder for measuring the distance to the object to be measured from the phase difference between the phase of the detection signal and the phase of the reference signal, the light receiving means can control the level of the detection signal output by an external signal. An optical distance meter, characterized in that control means for maintaining the level of the detection signal at a constant value is provided by controlling the light receiving means based on the level of the detection signal. 2. The light wave according to claim 1, wherein an avalanche photo diode is used for the light receiving means, and a control means for controlling a voltage applied to the diode to keep an output current of the diode at a constant value is provided. Rangefinder.