JPH06186337A - Laser distance measuring equipment - Google Patents

Abstract

PURPOSE:To enhance the accuracy in the measurement of distance by eliminat ing an electric signal processing circuit which causes error in distance measure ment information thereby preventing fluctuation of measurements. CONSTITUTION:A laser beam emitted from a laser unit 21 is split by a beam splitter 22 and then subjected to intensity modulation by means of first and second modulators 23, 25. The laser beam subjected to intensity modulation through the first modulator 23 is then split into a reference light 27 and a distance measuring light 28 by means of a beam splitter 26 and the distance measuring light 28 is directed to an object to be measured equipped with a reflector. A laser beam returned from the object and the reference light 27 then interfere with a laser beam subjected to intensity modulation through the modulator 25 thus producing beating lights 33, 34 having a frequency equal to the difference of modulation frequencies between the modulators 23, 25 and different phases. The beating lights 33, 34 are converted by optical detectors 35, 36 into electric signals which are delivered to a measuring unit 37 where the distance upto the object is calculated based on the phase difference between the electric signals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser distance measuring device for measuring a distance to an object to be measured by using a laser beam.

[0002]

2. Description of the Related Art A conventional laser distance measuring device is constructed as shown in FIG.

That is, the laser light emitted from the laser device 1 is intensity-modulated by the modulator 2 and then split into two by the beam splitter 3 into a reference light 4 and a distance measuring light 5. Reference light 4 above
Directly enters the photodetector 6, and the distance measuring light 5 enters the photodetector 9 through the corner cube 7 and the reflection mirror 8 attached to the object to be measured.

The reference light 4 and the distance measuring light 5 are converted into electric signals by the photodetectors 6 and 9, respectively, and the filter 1
0, 11 and amplifiers 12, 13 and then mixer 1
At 4 and 15, the signals from the local oscillator 16 are mixed with signals having different frequencies, converted into low frequency signals, and then sent to the measuring instrument 17. This measuring instrument 17 includes a mixer 14,
The distance from the low-frequency signal sent via 15 to the object to be measured is measured.

[0005]

As described above, in the conventional laser distance measuring apparatus, the frequency reduction processing of the distance measuring signal is performed after the signal is converted from light to electricity. However, there is a problem in that the electronic circuit that performs the frequency reduction processing of the distance measurement signal is likely to cause fluctuations, which causes an error in the obtained distance measurement information.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a laser measuring device capable of omitting an electronic circuit for frequency reduction processing which causes an error in distance measuring information and improving distance measuring accuracy. A distance device is provided.

[0007]

A laser range finder according to the present invention comprises a laser device for generating a laser beam for range finding, a beam splitter for splitting the laser beam emitted from the laser device into two, and a beam splitter for this beam. A first modulator and a second modulator having different modulation frequencies for intensity-modulating the laser beam split by the splitter, and a laser beam intensity-modulated by the first modulator, which is provided with a reflection mirror. The laser light emitted to the range object and returned from the range object and the second
Means for producing beat light having a frequency which is the difference between the modulation frequencies of the first and second modulators by interfering with the laser light intensity-modulated by the modulator, and the beat light produced by this means It is characterized by comprising a photodetector for detecting and converting it into an electric signal, and a measuring means for obtaining distance information to the object to be measured from the output signal of the photodetector.

[0008]

The laser beam emitted from the laser device is split into two by the beam splitter, one is intensity-modulated by the first modulator and the other is intensity-modulated by the second modulator. The laser light intensity-modulated by the first modulator is emitted as distance measuring light to a distance-measuring object provided with a reflecting mirror. Then, the laser light returned from the object to be measured interferes with the laser light intensity-modulated by the second modulator, so that the low-frequency laser light having the frequency of the difference frequency between the first and second modulators is interfered with. Produces beat light. This low-frequency beat light is detected by the photodetector and converted into an electric signal, and then sent to the measuring means to obtain distance information for the object to be measured.

The signal detected by the photodetector is already a low-frequency signal, so that the frequency-reducing process at the stage of the electric signal is unnecessary, and the distance measuring accuracy can be improved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a laser distance measuring apparatus according to an embodiment of the present invention.

In FIG. 1, reference numeral 21 denotes a laser device, and a laser beam emitted from the laser device 21 is split into two by a beam splitter 22. One of the two laser beams divided by the beam splitter 22 is intensity-modulated by a modulator 23 having a modulation frequency f1 to generate a frequency f1.
Intensity modulated light, and the other laser light is reflected by the reflection mirror 2
After passing 4, the intensity is modulated by the modulator 25 having the modulation frequency f2 and becomes intensity-modulated light of the frequency f2.

The laser beam having the modulation frequency f1 is split into two beams, a reference beam 27 and a distance measuring beam 28, by the beam splitter 26. The reference light 27 is incident on the beam splitter 29,
The distance-measuring light 28 is applied to a distance-measuring object (not shown), is reflected by a corner cube 30 attached to the distance-measuring object, passes through a reflection mirror 31 and the beam splitter 3
Incident on 2. In addition, the beam splitter 29 and the beam splitter 32 enter the modulated light of the modulation frequency f2 output from the modulator 25.

In the beam splitter 29 and the beam splitter 32, the reference light 27 having the modulation frequency f1
And the distance measuring light 28 interferes with the intensity-modulated light of the modulation frequency f2 to generate the beat light 3 of the frequency "f1-f2".
Yields 3,34. Beat light 33 by this reference light 27
Is input to the photodetector 35, and the beat light 34 generated by the distance measuring light 28 is input to the photodetector 36.

Since the beat light 33, 34 generated by the reference light 27 and the distance measuring light 28 contains phase information, the beat light 33, 34 is converted into an electric signal in the photodetector 35 and the photodetector 36. Then, the signal is phase-measured by the measuring instrument 37 to obtain the distance to the object to be measured.
Next, the principle of obtaining the phase difference between the reference light 27 and the distance measuring light 28 from the beat lights 33 and 34 will be described with reference to FIG.

FIG. 2A shows the waveform of the intensity-modulated light having the modulation frequency f1, which corresponds to the reference light 27 and the distance measuring light 28 in FIG. When the respective phases are φs and φr, the reference light 27 and the distance measuring light 28 have the following expressions. Reference light: Er = Ar cos (2πf1 t + φr) (1) Distance measuring light: Es = As cos (2πf1 t + φs) (2) where Ar is the amplitude of the reference light 27 and As is the amplitude of the distance measuring light 28. is there. FIG. 2B shows the waveform of the intensity-modulated light having the modulation frequency f2, which is expressed by the following equation. E = A cos (2πf2 t + φ) (3)

By interfering the reference light 27 and the distance measuring light 28 of FIG. 2A with the intensity-modulated light of FIG.
Beat lights 33 and 34 as shown in (c) are generated. The beat lights 33 and 34 are converted into electric signals by the photodetectors 35 and 36. Since the photodetectors 35 and 36 perform square-law detection of the beat lights 33 and 34, electric signals as shown in FIG. 2D are obtained. An electric signal obtained from the beat lights 33 and 34 generated by the reference light 27 and the distance measuring light 28 is expressed by the following equation. That is, the electric signal obtained from the beat light 33 of the reference light 27 is

[0017]

[Equation 1] And the electric signal obtained from the beat light 34 of the distance measuring light 28 is

[0018]

[Equation 2] It is represented by.

As described above, the electric signals obtained by detecting the beat lights 33 and 34 by the photodetectors 35 and 36 have already been converted into low frequency signals f1 -f2 at the time of photoelectric conversion. And the original reference light 27 and distance measuring light 28
The phase difference of is calculated by measuring the phase of the electric signal obtained from the beat light by the following equation. When the phase difference between the reference light 27 and the distance measuring light 28 is Δθ, (φs−φ) − (φr−φ) = φs−φr = Δθ (6) Next, the principle of obtaining the distance to the object to be measured from the phase obtained as described above will be described with reference to FIG.

As shown in FIG. 3A, the reference light 27 and the distance measuring light 28 have an optical path length difference of "L1 + 2L2 + L3". Here, if the point on the optical path of the distance measuring light 28 that intersects the extension of the optical paths of the photodetector 36 and the beam splitter 32 is A, then L1 is the distance from the beam splitter 26 to point A, and L2 is the point A and The distance from the beam splitter 32 to the corner cube 30, L3 is the distance between the light incident point and the light exit point of the corner cube 30, and the values of L1 and L3 are known.

As described above, since the reference light 27 and the distance measuring light 28 have different optical path lengths, the reference light 27 detected by the photodetector 35 and the distance measuring light detected by the photodetector 36. At 28, a time delay ΔT occurs as shown in FIG. When the period of the laser light is T, the time delay ΔT is obtained as a phase difference Δθ as shown in the following equation. Δθ = (ΔT / T) × 360 (degree) (7) Here, when the wavelength of the laser light is λ, the optical path difference between the reference light 27 and the distance measuring light 28 is Δθ = φs−φr, and Δθ × λ = (Φs-φr) × λ = L1 + 2L2 + L3 (8) In this case, since the values of L1 and L3 are known as described above, the distance L2 to the object to be measured is L2 = {(φs-φr) × λ-L1-L3} / 2 (9) It can be obtained by a formula.

For example, if an apparatus for measuring a signal of 100 KHz with a phase resolution of 1 degree is used to obtain a distance measurement resolution of 1 mm, it is necessary to modulate the intensity of the distance measurement light 28 with a high frequency of about 100 MHz.

In the conventional method, since this high frequency signal is directly converted into an electric signal and then converted into 100 KHz,
High frequency compatible filter, amplifier, mixer and 100.1
A local oscillator of KHz is required. However, in the present invention, the difference frequency 100.1 MHz-100 MHz = 0.1 MHz = 10 is obtained by causing the intensity modulated light of 100.1 MHz and the reference light 27 and the distance measuring light 28 of 100 MHz to interfere with each other.
Since the beat light of 0 KHz is produced and converted into an electric signal, an electric signal of 100 KHz is directly obtained. As described above, in the present invention, the frequency reduction is performed at the light stage, and as a result, the frequency reduction process at the electric signal stage is not necessary.

[0024]

As described above in detail, according to the present invention, it is possible to reduce the frequency at the stage of light, omit the processing circuit for reducing the frequency at the stage of electric signals, and generate by the signal processing circuit. It is possible to improve the distance measurement accuracy by eliminating the fluctuation of the measured value, and to simplify the circuit configuration. Further, the present invention, by improving the distance measurement accuracy, eliminates the need for the correction / averaging process that was conventionally required as a measure against fluctuations.
It is possible to speed up the distance measurement.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a laser distance measuring apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing the principle of beat light generation and detection in the embodiment.

FIG. 3 is a diagram showing a principle of distance measurement in the embodiment.

FIG. 4 is a configuration diagram of a conventional laser distance measuring device.

[Explanation of symbols]

21 ... Laser device, 22 ... Beam splitter, 2
3 ... Modulator, 24 ... Reflecting mirror, 25 ... Modulator, 26 ... Beam splitter, 27 ... Reference light, 28 ... Distance measuring light, 29 ... Beam splitter, 30 ... Corner cube, 31 ... Reflecting mirror,
32 ... Beam splitter, 33, 34 ... Beat light, 3
5, 36 ... Photodetector, 37 ... Measuring instrument.

Claims (1)

[Claims] 1. A laser device for generating a laser beam for distance measurement, a beam splitter for dividing the laser beam emitted from the laser device into two, and a modulation frequency for intensity-modulating the laser beam divided by the beam splitter. Of the first modulator and the second modulator different from each other, and the laser light intensity-modulated by the first modulator is emitted to a distance-measuring object equipped with a reflection mirror, and returns from the distance-measuring object. Means for making beat light having a frequency of a difference between the modulation frequencies of the first and second modulators by causing the laser light and the laser light intensity-modulated by the second modulator to interfere with each other; A laser comprising: a photodetector for detecting the beat light created by the means and converting it into an electric signal; and a measuring means for obtaining distance information with respect to the object to be measured from the output signal of the photodetector. Ranging device .