JPS62127685A - Laser distance measuring instrument - Google Patents

Abstract

PURPOSE:To accurately and precisely measure the distance to an object by imposing intensity modulation upon laser light with plural frequencies and detecting the phase lag of reflected light obtained by irradiating the object of measurement with modulated light for each frequency. CONSTITUTION:A driving circuit 13 superposes signals of different frequency from oscillators 11 and 12 upon each other to drive an optical modulator 2. The laser light from a laser 1 is modulated with two frequencies to illuminate the object of measurement through a reflecting mirror 5, and reflected light from the object is detected by a photodetector 8. The phase difference between a low frequency component from a band-pass filter and a reference signal from a low frequency oscillator 11 is detected by a phase difference between a high frequency component from a band-pass filter 15 and a signal from the high frequency oscillator 12 is detected by a phase detector 17 to obtain precise distance information, thereby finding the distance to the object accurately over a wide distance range from the two pieces of distance information.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a laser distance measuring device that uses laser light to measure the distance to a target Yanai.

BACKGROUND ART Measuring the absolute distance of an object using a laser has recently attracted attention as a visual information source for remote control of robots. Laser ranging devices such as these are broadly divided into those that use the pentagonal method and those that measure the round trip time of light, and the latter are further divided into those that use pulsed lasers and those that modulate the intensity of continuous wave lasers. It will be done. robot, l
Continuous wave laser intensity modulation is suitable for measuring relatively short distances such as vision, and David N1tzan et al.
206 pages, 1977 (Proc, IEEE Vol.
, 65.

]), 206, 1977). Hereinafter, a conventional intensity modulation type laser distance measuring device will be explained with reference to FIG.

In Figure 4, the output light from laser 1 is transferred to oscillator 3.
Intensity modulation is performed by an electro-optic light modulator 2 driven by. A part of the intensity-modulated laser beam passes through a beam splinter 4 and is directed to a target (not shown) by a reflecting mirror 5.
The other part of the laser beam is focused on the photodetector 6 by the beam splinter 4, which monitors the laser output. At the same time, the reference signal r of the distance measuring device is occurs.

The reflected light from the object is guided by a reflecting mirror 7 to a photodetector 8, which generates an information signal l. At this time, information signal 1
Since the amplitude of differs depending on the reflectance of the object to the laser beam and the distance outside the object, if the intensity of the information signal 1 is detected by the intensity detector 9 and the laser beam is scanned by the reflector 5, , image information similar to that measured by a television camera can be obtained. The phase of informationization +31 is delayed in proportion to the distance to object 1. By measuring the phase difference between the reference signal r and the information signal 1 using the phase detector 10, the distance outside the object can be measured. To measure distance by phase difference, for example, Japanese Patent Application No. 59-733
What is necessary is to perform the calculation shown in No. 57.

Problems to be Solved by the Invention In the configuration described above, distance resolution is determined by phase detection accuracy. For example, if the intensity modulation frequency of laser light is 1.5MHz, the phase shift of 360° is 1.
00 m. If the detection accuracy of the phase shift is ±1/200 cycle, that is, [18°, then the distance ill is divided by 1
Bamboo power is =t-50<:m. Furthermore, it is conceivable to increase the accuracy of distance measurement11 and lengthen the observation time to perform averaging, but in this case, the measurement time for one point becomes longer and the distance image is It would take a very long time to compile this information. Conversely, if the intensity modulation frequency is 1.50 MHz, if the phase detection accuracy is ±18°, the distance resolution is ±0.5 cm, and the distance measurement accuracy is good.

However, in the case of , a phase shift of 3600 degrees occurs for a distance of m, and an indeterminacy of an integer multiple of 1 m remains. The dimensions are 0.37?1, ], 3 m,
2.3 tn... etc. I? [-1W, 1 to -t, t
Absolute distance cannot be measured.

The present invention is intended to solve the above-mentioned problems, and has an eleventh object to provide a laser distance measuring device that measures an absolute distance outside an object with high precision.

Means for Solving the Problems In order to solve the above problems, the present invention modulates the intensity of a laser beam at a plurality of frequencies, and applies 1! This is a laser distance measuring device that detects the phase lag of the reflected light obtained by emitting α at each frequency.

Function The present invention operates as follows by virtue of the above-mentioned configuration. The approximate absolute distance is detected by phase detection using a low modulation frequency, and the relative distance is accurately measured by phase detection using a high modulation frequency, and the absolute distance is accurately determined from the distance measurement results using the above two modulation frequencies. It is something.

EXAMPLES Hereinafter, examples of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram of a laser distance measuring device of the present invention. The same parts as in the conventional example shown in FIG. 4 are given the same numbers, and detailed explanations will be omitted. This embodiment is characterized by two different frequency oscillators 11. , 1.2 to perform intensity modulation of light. For convenience, the oscillator 11 with a lower frequency will be referred to as a low-frequency oscillator, and the oscillator 12 with a higher frequency will be referred to as a high-frequency oscillator. The drive circuit 1:3 drives the optical modulator 2 by superimposing signals from two oscillators], 1, 126 and \-1. The laser light from the laser 1 can be modulated at two frequencies as shown in FIG. 2, and is irradiated onto the object to be measured by the reflecting mirror 5. The reflected light from the object to be measured is detected by a photodetector 8, and the signal from the photodetector 8 is divided into three parts. After being demodulated, the intensity is detected by the intensity detector 9 and becomes image information. In addition, the signal from the photodetector 8 is shaped by a low frequency band filter 14 and a high frequency band filter 15, which extract low frequency components and high frequency θq components, respectively. The extracted low frequency component and high frequency component signals are as shown in FIG. 3(a)(1)).

Low frequency component from bandpass filter 14 and low frequency oscillator 1
It is the same as the conventional example that the phase difference with the reference signal 1 is detected by the phase detector 16 and used as distance information, but the distance information obtained in this case cannot be used as the approximate distance and This is called distance information. On the other hand, bandpass filter 1
Similarly, the phase difference between the high frequency component from 5 and the high frequency oscillator 12 is detected by the phase detector 17, and the result is used as distance information. ? Although the distance information of −7 . Here, it will be referred to as relative distance information. From these absolute distance information and relative distance information, the distance of the object over a wide range of distances can be accurately determined. This will be explained below using specific numerical values.

Assume that the oscillation frequency of the low frequency oscillator 11 is 1.5 MHz, and the oscillation frequency of the high frequency oscillator 12 is 150 MHz.
Well, the phase measurement accuracy of phase detector 16.17 is ±18
'. Further, it is assumed that only objects within a distance of 100,771 points are measured. At this time, the phase detector 16
The output from the phase detector 17 uniquely determines the distance from 0 to 100 m4 with an accuracy of ±50 cm.13 On the other hand, the output from the phase detector 17], while containing an indeterminacy of an integer multiple of tn, Points with an accuracy of 0.5 cm. Thus, for example, if the output from the phase detector 16 is 38771, the object is within a distance range of: 38.5 m from 3757n. On the other hand, the output of phase detector 17 is 83 cm
, the exact distance at target Yanai is 37 m 8
3 cwr4-0.5cm f. In this way,
10(1+++i), the distance of a certain object can be determined with high accuracy.

In addition, the numerical values are shown as examples. ], km
Uniquely define the distance in terms of distance (if possible, set the low frequency modulation frequency to 150 kTTZ) Tsu 1: It is best to use a combination of modulation frequencies depending on the distance and accuracy you want to measure. Therefore, depending on the application, similar measurements can be made with three or more modulation frequencies.

In this embodiment, unlike the conventional example, the reference Buddha/moon is taken not from the photodetector but from the oscillators +1, ], 2, but unlike the conventional example, the reference signal is obtained by demodulating from the photodetector. 11, but there is no essential difference. /ξ, In addition to an electro-optic modulator, direct modulation of a laser oscillator or a photoacoustic modulator can be used as a means for modulating the intensity of laser light, and the present invention does not specify the means for optical modulation.

Furthermore, although the laser beam is scanned, it is clear that the present invention is effective even when distance measurement is performed only at a fixed point without scanning.

9 - 7 Effects of the Invention As stated above, the present invention measures the distance at the target object size by measuring the phase delay of laser light whose intensity is modulated at the same time at a plurality of frequencies. It is possible to accurately and accurately measure the distance of objects over a wide range of distances.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a laser distance measuring device according to an embodiment of the present invention, Figure 2 is a diagram showing the waveform of a modulated laser beam in the same embodiment, and Figure 3 (a) (1) is extracted from the signal from the photodetector in the same example. −、
FIG. 4 is a block diagram of a conventional laser distance measuring device. 1... Lator-12... Optical modulator, 3... Oscillator,
4... Beat splitter, 5, 7... Reflection/a, 6
．． 8... Photodetector, 10, 16, 1.7... Phase detector, 14.15... Bandpass filter.

Claims (1)

[Claims] an optical modulator that modulates the intensity of laser light at multiple frequencies;
means for irradiating an object to be measured with intensity-modulated laser light; a photodetector for detecting reflected light from the object; and a means for detecting frequency components corresponding to each of the plurality of frequencies from the output of the photodetector. 1. A laser ranging device comprising: means for separating; and means for detecting a phase delay of each separated frequency component.