JPS61138191A - Laser distance measuring method - Google Patents

Abstract

PURPOSE:To measure exactly and easily the distance up to an object to be measured without using an optical system for superposing laser light by dividing laser light to two optical paths, using the beat signal of the laser light passing one optical path as a reference signal and irradiating the laser light passing the other optical path to the object to be measured. CONSTITUTION:The two beams of the laser light having the frequencies different slightly from each other are projected from one laser 1 and are separated to two respective optical paths by a partial reflecting mirror 2. The beat signal of the laser light progressed in one optical path is used as the reference signal and the laser light progressed through the other optical path is irradiated to the object 5' to be measured. The beat signal of the laser light reflected by the object 5' is thereupon used as the measurement signal and the phase difference between the measurement signal and the reference signal is detected by a phase detector 10 to determine the distance up to the object 5'. The need for the optical system for superposing two beams of the laser light is thus eliminated and since the two beams of the laser light are simultaneously oscillated, there is no deviation and the need for a fine adjustment is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a method for measuring τ, the absolute distance to a desired object, using laser light in various technical fields.

2. Description of the Related Art A conventional method of measuring the absolute distance to a desired object using a laser beam will be explained with reference to FIG.

Laser beams with slightly different frequencies are projected from two lasers 101 and 102, respectively, and reflected by mirrors 1o3. and superposition using a partial reflecting mirror 104. A portion of this superimposed laser light is guided to a τ detector 106 by a partial reflection mirror 104, and the detector 105 generates two laser light beat signals. Since this beat signal serves as a reference signal for distance measurement, the frequency and intensity of the laser beams projected from the two lasers 101 and 102 are stabilized by the servo mechanism 106.

The two laser beams transmitted through the partial reflecting mirror 104 are reflected by the object 107 and guided by the reflecting mirror 10B to the °C detector 109, where the detector 109 generates beat signals of the two laser beams. Detector 106 with reference signal
The beat signal from the detector 109 and the beat signal from the detector 109 are appropriately amplified by an amplifier 110 and an amplifier 111, respectively, and then a one phase difference is detected by a phase detector 112, and a phase difference signal S is generated.

The detected phase difference ψ has the following relationship, where L is the distance to the object 10, ψ/2"=2L (1, -72), and the distance can be calculated from the phase difference ψ. However, , λ1.λ2 are the wavelengths of the two laser beams, C1.C2 are the frequencies of the two laser beams, and C is the speed of light.The frequency difference between the two laser beams (ν+"2) is the distance to be measured. Although it differs depending on the range setting, for example, if S1-S2 is 10MH1, the phase difference ψ will complete one period every time the distance to the object changes by 15m, so 15
The distance to m can be uniquely determined.

Problems to be Solved by the Invention However, this method requires the use of two lasers as light sources, superimposing the output lights from different lasers, and then obtaining a beat signal from this. Therefore, it is easily affected by deviations in the optical system, so fine adjustment is required. In addition, it is necessary to oscillate the two oscillators simultaneously with high accuracy and stability, which often leads to problems such as the device becoming large and complicated.

Therefore, in order to solve the above problems, the present invention provides a laser distance measuring method that does not require an optical system for superimposing laser beams and can easily and accurately measure the absolute distance to an object. Determine what you are trying to do.

Means for Solving the Problems The laser distance measuring method of the present invention that solves the above problems has the following features:
Two laser beams with slightly different frequencies are projected from the laser on the stand by simultaneous oscillation in transverse mode, and the laser beam is split into two optical paths using a partial reflection mirror, etc., and the beat signal of the laser beam passing through one optical path is transmitted. The object to be measured is irradiated with a laser beam that serves as a reference signal and passes through the other optical path, and the distance to the object is measured based on the phase difference between the beat signal of the reflected light and the beat signal serving as the reference signal.

Effect In the above configuration, two laser beams with slightly different frequencies are separated from one laser into two separate optical paths, and the beat signal of the laser beam traveling on one optical path is used as a reference signal, and the laser beam traveling on the other optical path is used as a reference signal. The measured laser beam is irradiated onto the measured object, and the beat signal of the reflected laser beam is used as a measurement signal to determine the distance to the measured object based on the phase difference between the two.

Therefore, there is no need for an optical system that superimposes the two laser beams, and since the two laser beams are oscillated simultaneously, there is no deviation and no fine adjustment is necessary.

1 Embodiment An embodiment of the laser distance measuring method of the present invention will be explained with reference to FIG. Two laser beams with slightly different frequencies are projected from one laser 'f-1 by simultaneous oscillation in two transverse modes, and a part of the laser beam f is projected by the partial reflecting mirror 2.
! :Y is taken out, guided to the detector 3, detected by the detector 3, and generates one beat signal. The frequency of this beat signal is kept constant by adjusting the resonator length by the servo mechanism 4. The two laser beams transmitted through the partial reflecting mirror 2 are reflected by the object 5, but are taken out by the reflecting mirror 6, guided to the detector 7, detected by the detector 7, and converted into another beat signal. to occur. The beat signal from the detector 3 and the beat signal from the detector 7 are appropriately amplified by an amplifier 8 and an amplifier 9, respectively, and then a phase difference is detected by a phase detector 1o, and a phase difference signal S is obtained.
is emitted.

The detected phase difference ψ has the relationship: ψ/2π = 2 L (---) λ, λ2 L = □ (shi1-shi2), where the distance to the object 6 is m. What you can do to find the distance from the object is the same as before.

However, λ1. λ2 is the wavelength of the two wavelengths of light, λ1. C2 is the frequency of the two laser beams, and C is the speed of light. The frequency difference between the two laser beams (Sh1-Sh2) varies depending on the setting of the distance range to be measured, but for example, if Sh1-Sh2 is 1oMHz, the difference in frequency between the two laser beams (Sh1-Sh2) changes every time the distance to the object changes by 15em. Since the phase difference ψ repeats one cycle, the distance at 15 m-4 can be uniquely determined.

Note that the frequency of the beat signal, that is, the difference in oscillation frequency between transverse modes in one l/-zer 1, can be adjusted by controlling the resonator length by the servo mechanism 4. In case, TKMoo mode and 'I'
KMo, expressed as the frequency difference between the modes. However, R1 and R2 are the curvatures of the reflecting mirror and partial reflecting mirror that constitute the resonator.

Effects of the Invention As can be seen from the above explanation, the laser distance measuring method of the present invention has the following advantages:
Since two laser beams with slightly different frequencies are projected from the laser on the stand by simultaneous oscillation in transverse mode, there is no deviation between the two laser beams and no fine adjustment is required.
The two laser beams are accurately guided to each detector, and the beat signal is extracted stably and accurately.As a result, the accurate phase difference is detected, allowing easy and accurate measurement of the absolute distance to the target. I can see the effect of being able to do it.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a laser distance measuring method according to the present invention;
FIG. 2 is a schematic diagram showing a conventional laser distance measuring method. 1...Laser, 2...Partial reflecting mirror,
3. End...Detector, 4...Servo mechanism, 6...Object, 6...Reflector, 8,
9...Amplifier, 1o...Phase detector,
S... Phase difference signal.

Claims (1)

[Claims] One laser simultaneously oscillates two transverse mode laser beams with slightly different frequencies, and each laser beam is split into two optical paths.
Obtain a beat signal, irradiate the object to be measured with a laser beam that passes through the other optical path, obtain a second beat signal from the reflected light, and determine the object to be measured based on the phase difference between the first and second beat signals. A laser distance measurement method characterized by measuring the distance to an object.