JPH01113688A - Measuring apparatus of distance by laser - Google Patents

Abstract

PURPOSE:To facilitate the correction of a zero-point drift, by a method wherein comparison is made with a theoretical phase difference of a known distance by a phase comparator and the position of interactions of an ultrasonic wave and a laser light in an acoustooptic modulator is shifted on the basis of a signal of this phase comparator. CONSTITUTION:A laser light reflected on a reference object is reflected by a reflector 5 and detected by a photodetector 8 for measuring a distance. A phase difference between a signal obtained by the photodetector 8 and a reference signal from an oscillator 3 is found by a phase detector 10. A distance to a measuring object 7 is calculated from this phase difference, an output phase difference of the phase detector 10 is given to a phase comparator 11 and compared with a theoretical phase difference corresponding to a known distance, and a signal corresponding to the phase difference thus compared is outputted. A phase correction element 12 is controlled by this output to correct a phase slippage. By this constitution, the correction of a zero-point drift can be corrected every easily and a distance can be measured with excellent accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a laser distance device that measures the distance to an object using laser light.

2. Description of the Related Art Conventional laser distance measuring devices of this type include, for example, Grosseings of the IE, Vol. 65, pp. 206-220, 1977 (Proc.
EFiEVo, L 65. pp206-220.1
977) is known. below,
A conventional laser distance measuring device will be explained with reference to FIG.

In FIG. 4, a laser beam emitted from a laser oscillator 1 is intensity-modulated by an acousto-optic modulator 2 driven by an oscillator 3. In FIG. The intensity-modulated laser beam is sent to the beam splitter 4.
One enters the photodetector 6 for reference signal, and the other is reflected by one surface of the reflecting mirror 5 for laser beam irradiation and is irradiated onto the measurement object 7. The laser beam reflected from the object to be measured 7 is reflected again by the other surface of the reflecting mirror 5 and enters the photodetector 8 for distance measurement. The output r of the reference signal photodetector 6 and the output i of the ranging photodetector 8 are guided to a phase detector 10, and the phase detector 10 performs phase measurement. The phase difference φ at this time increases in proportion to the distance between the measurement object and the original 7, and if the speed of light is C1 and the modulation frequency in the acousto-optic modulator 2 is fm, then 1)=Cφ/4π □ ...... It is represented by (1), and the distance to the measurement object 7 can be measured from the phase difference φ.

If distance measurement is performed by scanning the reflecting mirror 5 two-dimensionally, a distance image based on distance information can be obtained. The output i of the photodetector 8
By detecting the intensity with the intensity detector 9, intensity image information similar to that measured by a television camera can be obtained.

Problems to be Solved by the Invention However, in the conventional laser distance measuring device as described above, the distance measuring accuracy is determined by the phase detection accuracy of the phase detector 10. Then, a temporal zero point drift occurs due to the temperature characteristics of the circuit system, etc.

As a result, the accuracy of distance measurement decreases, making it impossible to accurately measure the distance to the object 7 to be measured.

The present invention solves the problems of the conventional examples as described above, and provides a laser distance measuring device that can easily correct the zero point drift and accurately measure the distance to the object to be measured. The purpose is to

Means for solving the problems and technical means of the present invention for solving the above problems are as follows:
A laser oscillator, an acousto-optic modulator for intensity modulating the laser beam emitted from the laser oscillator, a means for irradiating the intensity-modulated laser beam onto a measurement object, and detecting reflected light from the measurement object. A phase detector that calculates the distance from the phase difference of the reflected light signal, and a phase detector that compares the measured phase difference of the object at a known distance with the theoretical phase difference determined by equation (1). The apparatus includes a comparator and a phase correction means comprising a moving mechanism that moves at least one of the optical axes of the laser light emitted from the acousto-optic modulator and the laser oscillator in response to a signal from the phase comparator.

action The effect of this technical means is as follows.

That is, when intensity modulating a laser beam using an acousto-optic modulator, the initial phase difference between the reference signal for modulation and the modulated laser beam is determined by the modulation propagating through the acousto-optic modulator. It is determined by which phase of the generated ultrasonic wave the laser light is modulated. In other words, by moving the position where the ultrasound and laser light interact,
The phase difference between the reference signal and the laser beam is adjustable. Therefore, when a zero point drift occurs in phase measurement, the output of the phase comparator is used to adjust the distance between at least one of the acousto-optic modulator and the optical axis of the laser beam so that the phase difference at a known distance is always the actual value. Errors due to zero point drift can be corrected by moving the position of and controlling the interaction position between the ultrasonic wave and the laser beam.

Example Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a block diagram showing the overall configuration of a laser ranging device according to an embodiment of the present invention. In FIG. 1, ■ is a laser oscillator, 2 is an acousto-optic modulator that modulates the intensity of the laser beam emitted from the laser oscillator 1, 3 is an oscillator that drives the acousto-optic modulator 2, and 5 is an intensity-modulated laser. a reflector that reflects light and irradiates it onto the measurement target 7; 8 a photodetector for distance measurement that detects the laser beam reflected by the measurement target 7 and reflected by the reflector 5; 10 a distance measurement photodetector; A phase detector 11 detects the phase difference between the signal obtained by the photodetector 8 and the reference signal from the oscillator 3, and 11 is a phase detector 100 used when measuring an object at a known distance as the measurement object 7. phase difference and
A phase comparator 12 performs a comparison with a theoretical phase difference determined by equation (1) corresponding to the known distance; 12 is a phase comparator 11;
This is a phase correction unit that controls the acousto-optic modulator 2 based on the way the signal is output from the acousto-optic modulator 2.

Next, the operation of the above embodiment will be explained. First, a reference object at a known distance is measured as the measurement object 7.

The laser beam emitted from the laser oscillator 1 is transmitted by the oscillator 3,
The intensity is modulated by the driven acousto-optic modulator 2, and the reflecting mirror 5
The object to be measured 7 is irradiated with the light. The laser beam reflected by the reference object is reflected by a reflecting mirror 5 and detected by a photodetector 8 for distance measurement. The phase difference between the signal obtained by the photodetector 8 and the reference signal from the oscillator 3 is determined by the phase detector 10. The distance to the measurement object 7 is calculated from this phase difference. The output phase difference of the phase detector 10 is added to the phase comparator 11, and (
It compares it with a theoretical phase difference corresponding to a known distance determined by Equation 11, and outputs a signal according to the phase shift. This phase shift corresponds to zero point drift. The output of the phase comparator 11 controls a phase correction section 12 to correct the phase so that the above-mentioned phase shift does not occur.

This phase correction will be described later.

After the phase correction is completed, the distance of the object 7 whose distance is unknown is measured. The measurement method may be carried out in the same manner as in the case of the object to be measured at a known distance, in which the laser beam from the laser oscillator 1 whose intensity is modulated by the acousto-optic modulator 2 is irradiated onto the object to be measured 7 using the reflecting mirror 5. , the phase difference φ between the signal obtained by detecting the reflected light by the photodetector 8 and the reference signal from the oscillator 3 is determined by the phase detector 10, and the distance to the object to be measured 7 is calculated. The distance at this time can be obtained as an accurate value without zero point drift because the phase has been corrected by the acousto-optic modulator 2.

Next, the phase correction operation will be explained in more detail.

FIG. 2 shows a principle diagram of the acousto-optic modulator 2. As shown in FIG. In FIG. 2, 13 is an acousto-optic modulator, which is a CO2
For laser light, germanium (Ge) is used. 14 is a piezoelectric element attached to one side of the acousto-optic modulator 13. Then, high frequency power is applied from the oscillator 3 to the piezoelectric element 14 to generate ultrasonic waves in the acousto-optic modulation element 13. The ultrasound propagates through the acousto-optic modulator 13 at a velocity V and interacts with the laser beam 15 at a certain distance, producing diffracted light 16 and transmitted light 17.

The diffracted light 16 is intensity-modulated at a modulation frequency fm, and the phase difference between the electric signal detected by the photodetector (not shown) and the reference signal from the oscillator 3 is determined by the phase detector 1.
It is obtained as 0 and Φ.

Here, when the interaction position between the ultrasonic wave and the laser beam 15 is moved by a minute distance Δt (m), the phase difference output Φ changes by Δ〆. The amount of change in △〆 is the ultrasonic propagation velocity v (m)
, if the modulation frequency is fm (Hz), △〆/△t=3
6 (lfm/v (degrees/m)), fm is 5MH
If z, then Δ〆/△2=0.327 (degrees/μm). In Figure 3, 18 is pace, 1
9 is a movable table equipped with an acousto-optic light modulator 2;
8, it is slidably supported by a precise slide mechanism with little mechanical play. 20 is a driving means;
21 is a transmission mechanism that transmits the driving force of the driving means 20 to the movable table 19.

In this embodiment, a piezoelectric element is used as the driving means 20, and 5
A displacement of 20 μm is obtained with a voltage of 00 V. This is a correction amount of 6.54 degrees as a phase angle, which corresponds to 0.545 m when converted to the distance measured by 5 MHz modulation.

In this way, the amount of movement is practically small at several tens of micrometers,
It is possible to use a piezoelectric element such as a piezo for the driving means 20, thereby making it possible to downsize the device.

In addition to this, a pulse motor or a servo motor may be used as the driving means 20, and a ball screw or the like may be used as the transmission mechanism 21.

In the above example, the case where the acousto-optic modulator 2 is moved was explained, but since the phase is corrected by changing the interaction position between the ultrasonic wave and the laser beam 15, the laser beam 15 Exactly the same effect can be obtained even if the optical axis position is moved and all phase correction is performed.

Effects of the Invention As described above, according to the present invention, a laser beam emitted from a laser oscillator is intensity-modulated by an acousto-optic modulator and irradiated onto an object to be measured at a known distance. The reflected light is detected by a photodetector, the phase difference of the reflected light signal is detected by a phase detector, this phase difference output is compared with the theoretical phase difference of a known distance by a phase comparator, and the output from this phase comparator is The signal moves the interaction position of the ultrasonic wave and laser light in the acousto-optic modulator to correct the phase. Since the movement angle and the corrected phase angle are in a proportional relationship, it is possible to perform correction that is much simpler and more stable than the method of correcting the phase by changing electric circuit constants. Therefore, zero point drift can be easily corrected and distance measurement can be performed with high accuracy.

[Brief explanation of the drawing]

1 to 3 show a laser distance measuring device according to an embodiment of the present invention, and FIG. 1 is a block diagram showing the overall configuration,
FIG. 2 is a principle diagram of an acousto-optic modulator, FIG. 3 is a side view showing the detailed configuration of a phase correction section, and FIG. 4 is a block diagram showing the overall configuration of a conventional laser distance measuring device. ■... Laser oscillator, 2... Acousto-optic light modulator, 3
...Oscillator, 5...Reflector, 7...Measurement object,
8... Photodetector, 10... Phase detector, 11...
Phase comparator, 12... Phase correction unit, 13... Acousto-optic modulation element, 14... Piezoelectric element, 19... Moving table,
20... Drive means, 21... Transmission mechanism. Patent applicant: Director of the Agency of Industrial Science and Technology Yuki Iizuka Mitaka 1 figure 2 sounds τ Hikaru Kumugi style S i! Gootsu φ Fig. 3 20 canter + steps, /

Claims (1)

[Claims] A laser oscillator, an acousto-optic modulator for intensity modulating the laser light emitted from the laser oscillator, a means for irradiating the measurement object with the intensity-modulated laser light, and detecting the reflected light from the measurement object. a phase detector that calculates the distance from the phase difference of the reflected optical signal, a phase comparator that compares the measured phase difference and the theoretical phase difference of an object at a known distance, and a phase detector that calculates the distance from the phase difference of the reflected optical signal. A laser distance measuring device comprising: a phase correction means comprising a moving mechanism that moves at least one of the acousto-optic modulator and the optical axis of the laser beam emitted from the laser oscillator in response to a signal from a comparator.