JPH11118928A - Electrooptical distance meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a distance meter whose measuring time does not become long by a method wherein a quantity-of-light modulation is performed by a signal which is modulated by a modulation circuit, a carrier wave signal and a modulating wave signal are separated from reflected distance-measuring light by a demodulation circuit, a distance is measured and computed regarding the carrier wave signal and the modulating wave signal and a distance up to a reflecting mirror is found. SOLUTION: A modulating signal F in which a carrier wave signal F1 is modulated by a modulating wave signal F2 is quantity-of-light-modulated by a quantity-of-light modulation circuit 3, and laser light is radiated to a reflecting mirror as distance measuring light BF. Reflected distance-measuring light BB is converted into an electric signal by a photoelectric element 41 so as to be demodulated into the carrier wave signal F1 and the modulating wave signal F2 by a demodulation circuit 4. The phase of the carrier wave signal F1 with reference to a signal F1 which is not modulated is found by a phase detection circuit 51. The phase of the modulating wave signal F2 with reference to a signal F2 which is not modulated before modulation is found by a phase detection circuit 52. Regarding reference light which is reflected by mirrors M1, M2, its phase is found in the same manner. The phase difference of the carrier wave signal F1 and the phase difference of the modulating wave signal F2 regarding the distance measuring light BB and the reference light are found by a distance computing circuit 6, and a distance up to the reflecting mirror is computed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lightwave distance meter that emits modulated light toward a reflecting mirror and determines the distance to the reflecting mirror from the phase difference between the light before emission and the reflected light.

[0002]

2. Description of the Related Art Conventionally, modulated light, which is modulated in light quantity at a predetermined frequency oscillated by an oscillation circuit, is emitted as distance measuring light toward a reflecting mirror installed at a measuring point, and the reflected light is reflected by the reflecting mirror. 2. Description of the Related Art There is known a light wave distance meter that calculates a distance to a reflecting mirror from a phase difference between a distance light and a modulated light by calculation. By the way, the oscillation frequency of the oscillation circuit which is the predetermined frequency is set to, for example,
If the frequency is set to Hz, the wavelength is 20 m, so that it is not possible to obtain a portion exceeding 10 m in the distance to the reflecting mirror. Therefore, as known from Japanese Patent Application Laid-Open No. Hei 5-323029, for example, 1/10 of 15 MHz
The distance is measured with light modulated at a frequency of 150 KHz, which is a frequency of 0, and 150 KHz is applied to a portion exceeding 10 m.
The value measured with the light whose light intensity has been modulated is used.

[0003]

SUMMARY OF THE INVENTION In the above prior art,
The distance is measured with the light intensity modulated at 15 MHz, and
Since the distance is measured with the light modulated at 0 KHz, the time required for the measurement becomes longer.

In view of the above problems, an object of the present invention is to provide a lightwave distance meter that does not require a long measurement time when measuring the distance by modulating the light quantity with a plurality of frequencies.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is directed to a reflecting mirror installed at a measuring point, using modulated light, which is modulated in light quantity at a predetermined frequency oscillated by an oscillation circuit, as distance measuring light. In a light wave distance meter that measures the distance to the reflecting mirror from the phase difference between the ranging light and the modulated light reflected by the reflecting mirror, the oscillation circuit includes a carrier signal and a modulated wave signal having different frequencies from each other. A modulation circuit that modulates a carrier signal with a modulation signal, performs the light quantity modulation by the signal modulated by the modulation circuit, and performs a carrier signal and a modulation signal from the reflected distance measuring light. And a distance measuring operation for the carrier wave signal and a distance measuring operation for the modulated wave signal are performed, and the distance to the reflecting mirror is obtained from both operation results.

[0006] By using the modulated signal, distance measurement using signals of a plurality of frequencies can be performed at once,
The time required for the measurement is not longer than that of the conventional one that performs measurement for each frequency.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, reference numeral 1 denotes an oscillation circuit. In this embodiment, a carrier signal F1 having a frequency of 15 MHz and a modulated signal F2 having a frequency of 150 KHz are output. It can be set appropriately according to the surveying accuracy and the like. The carrier signal F1 and the modulation signal F2 are both input to the modulation circuit 2, and the carrier signal F1 is
2 is output to the light quantity modulation circuit 3. A laser diode 31 is connected to the light quantity modulation circuit 3 and emits a laser beam whose light quantity is modulated according to a modulation signal from the modulation circuit 2 to a reflecting mirror installed at a measurement point (not shown) as distance measurement light BF. . The light reflected by the reflecting mirror returns to the photoelectric device 41 as distance measuring light BB. Distance measuring light B
B is converted into an electric signal by the photoelectric element 41 and input to the demodulation circuit 4. The demodulation circuit 4 demodulates the input electric signal into a carrier signal F1 and a modulated signal F2. The demodulated carrier signal F1 and modulated wave signal F2 are output to phase detection circuits 51 and 52, respectively. The carrier wave signal F1 and the modulation wave signal F2 before modulation are branched and input from between the oscillation circuit 1 and the modulation circuit 2 to each of the phase detection circuits 51 and 52. In the phase detection circuit 51, the phase of the demodulated carrier signal F1 with respect to the carrier signal F1 before modulation is obtained. Further, in the phase detection circuit 52, the phase of the demodulated modulated wave signal F2 with respect to the modulated wave signal F2 before modulation is obtained. On the other hand, in front of the laser diode 31, an optical path switch C
Is provided, and the distance measuring light emitted from the laser diode 31 is transferred to a mirror M1
The light is reflected by M2 and sent to the photoelectric element 41 as reference light. The reference light is demodulated by the demodulation circuit 4 into a carrier signal F1 and a modulated wave signal F2 in the same manner as the distance measurement light BB, and sent to each of the phase detection circuits 51 and 52 as reference signals (indicated by chain lines). Is required.

The distance measuring light BB detected by the phase detecting circuit 51
The phase of the carrier signal F1 and the phase of the carrier signal F1 of the reference light are sent to the distance calculation circuit 6 where the difference between the two phases is obtained.
From the phase difference, the distance to the not-shown reflecting mirror is calculated. Similarly, the phase of the modulated wave signal F2 of the ranging light BB detected by the phase detection circuit 52 and the phase of the modulated wave signal F2 of the reference light are sent to the distance calculation circuit 6, and the phase difference between the two modulated wave signals is obtained. Then, the distance to the above-mentioned not-shown reflecting mirror is calculated from the phase difference.

The frequency of the carrier signal F1 is 15
Since the frequency is MHz, the wavelength is 20 m, and a number up to a distance of 10 m to the reflecting mirror can be obtained. Further, since the frequency of the modulated wave signal F2 is 150 KHz, the wavelength is 2000 m, and a number up to 1000 m, which is the distance to the reflecting mirror, can be obtained. When the distance to the reflecting mirror is, for example, 123.456 m, 3.456 m can be obtained from the carrier signal F1. Also, the modulated wave signal F
2 gives 123.4 m. The calculation based on the carrier wave signal F1 and the calculation based on the modulated wave signal F2 are both performed in parallel and simultaneously by the distance calculation circuit 6. Then, both calculation results are superimposed to obtain 123.456 m, and the result is displayed on the display 61.

The modulation method by the modulation circuit 2 is such that when the modulation signal F2 is an analog signal with respect to the carrier signal F1, amplitude modulation (AM modulation) or frequency modulation (F modulation) is performed.
M modulation), and in the case of a digital signal, a conventionally known modulation method such as phase shift keying (PSK modulation) may be used. Further, in the above-described embodiment, signals of two kinds of frequencies, that is, the carrier wave signal F1 and the modulated wave signal F2, are used. However, signals having further different frequencies may be used according to the distance to the reflector to be measured.

[0011]

As is apparent from the above description, according to the present invention, when measuring distance by lightwave using signals of a plurality of frequencies, it is not necessary to perform measurement for each frequency, and measurement is performed at once. Can be shortened.

[Brief description of the drawings]

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

[Explanation of symbols]

 31 laser diode 41 photoelectric element

Claims (1)

[Claims] 1. A modulated light having a light quantity modulated at a predetermined frequency oscillated by an oscillation circuit is emitted as distance measuring light toward a reflecting mirror installed at a measuring point, and the distance measuring light reflected by the reflecting mirror and the modulation light are modulated. In a light wave distance meter that measures the distance to a reflecting mirror from the phase difference with light, the oscillation circuit outputs a carrier signal and a modulation signal having different frequencies, and modulates the carrier signal with the modulation signal. A modulation circuit that modulates the amount of light with a signal modulated by the modulation circuit, and a demodulation circuit that separates a carrier wave signal and a modulation wave signal from the reflected ranging light, An electro-optical distance meter that performs a measurement operation and a distance measurement operation on a modulated wave signal, and obtains a distance to a reflector from both operation results.