JPS6383686A - Laser distance measuring instrument - Google Patents

Abstract

PURPOSE:To improve the accuracy of distance measurement, by obtaining a laser beam frequency-modulated by an electro-optical light modulator, radiating a part of it on an object to be measured after taking it out as a reference beam, and detecting a frequency difference between a reflected beam of light and the reference beam. CONSTITUTION:The electro-optical light modulator 11 is arranged in the resonator of a laser 1, and when a modulating power source 4 is changed, the length of the resonator is changed based on the change of reflectance due to an electro-optical effect, therefore, the frequency of an oscillating light of the laser 1 is modulated. A part of a frequency-modulated laser beam which being taken out by a beam splitter 5 as the reference beam, then being induced to a detector 9, is projected on the object 7 to be measured. The reflected light from the object 7 to be measured is reflected on a partial reflecting mirror 6, and induced to the detector 9. The detected signals of the reflected rays of light and the reference beam detected by the detector 9 are sent to a frequency analyzer 10, and the frequency of a beat signal is measured, and distance to the object 7 to be measured is calculated. In such a manner it is possible to increase the modulation quantity of a frequency and the number of repeat of modulation, and to perform a linear frequency modulation for an impressed voltage, thereby, it is possible to heighten the accuracy of the distance measurement.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a laser distance measuring device that measures the distance to an object using laser light.

BACKGROUND ART Measuring the feed distance to an object using a laser has recently attracted attention as a visual information source for remote control of robots. Among such laser distance measuring devices, F
There is a method called MCW laser radar. Regarding this method, for example, IEE Journal
Ob Kuo/Tam Electronics QE-8 Volume 9
1-92, 1972 (IEEE JQuantum
EI electronics, vol.

QE-8, PP91-92. 1972). Hereinafter, a conventional FM-CW laser radar will be explained with reference to FIG.

In FIG. 3, a total reflection mirror 2 constituting a resonator of a laser 1 is held by a piezo element 3. When the voltage applied to the piezo element 3 is changed by the modulation power source 4, the oscillation frequency of the laser beam is modulated due to the change in the resonator length. This situation is shown in FIG. When a triangular wave voltage is applied to the modulation power source 4, the oscillation frequency of the laser beam changes linearly from fl to f2 as shown in Figure 4(a). In the figure, the solid line represents the transmitted wave, and the broken line represents the reflected wave. The time Δt from transmission until receiving the reflected wave is expressed as Δt=. A laser beam modulated as shown in FIG. 3 is irradiated onto the object 7 as shown in FIG. Scattered light from the object is received by a partial reflecting mirror 6 and guided to a detector 9.

On the other hand, a part of the laser beam is extracted as a reference beam by a beam splitter 5 and guided to a detector 9.

Lens 8 is used to condense laser light.

The frequency of the detected beat signal is as shown in Fig. 4(b), and the frequency is 0, which is proportional to the distance to the target object. The relationship holds that the frequency is field, the frequency of the beat signal is fb, and the distance to the object is L. Here C is the speed of light. Therefore, by measuring the frequency of the beat signal using the frequency analyzer 1o, the distance to the object can be determined.

Problems to be Solved by the Invention In the above-mentioned configuration, the method of changing the resonator length using the total reflection mirror 2 and modulating the frequency of the laser beam is not fast and does not cause reciprocation due to the time response of the piezo element. It is possible, but the repetition frequency fm of modulation will be less than IKH2, and the distance measurement accuracy will be limited. Further, the problem that the piezo element does not change linearly with the applied voltage also reduces distance measurement accuracy. The present invention solves the above-mentioned problems and provides a highly accurate laser distance measuring device.

Means for Solving the Problems The present invention installs an electro-optic optical modulator inside a laser resonator to take out a frequency-modulated laser beam, and takes out a part of the laser beam as a reference beam. The device irradiates the reflected light and detects the frequency difference between the reflected light and the reference light.

Function: Since the present invention performs frequency modulation using the optical light modulator having the above-mentioned configuration, the amount of frequency modulation and the number of modulation cycles can be increased, and the frequency modulation can be performed linearly with respect to the applied voltage. Embodiment Hereinafter, one embodiment of the present invention will be described based on FIG. 1. The same parts as in FIG. 3 are given the same numbers.

When an electro-optic optical modulator 11 is installed inside the resonator of the laser 1 and the voltage of the modulation power source 4 is changed, the resonator length changes due to the change in refractive index due to the electro-optic effect, so the frequency of the oscillated light of the laser 1 changes. is modulated. Electro-optic light modulator 1
If a triangular wave voltage is applied to 1 by the modulation power source 4, frequency modulation similar to that shown in FIG. 4 can be performed. The configuration for measuring the beat signal of and determining the distance to the object 7 is the same as the conventional example shown in FIG. In the case of a CO2 laser, the repetition frequency fm is 500 MH2, and the frequency modulation amount △f is about I MHz/100 V, which is 1 m.
A large value of 1Δf is obtained. The distance resolution ΔL is CΔfb ΔL = −(2) 4Δffm from equation (1), where Δfb is the frequency measurement accuracy. Therefore, the larger ΔLfm is, the better the distance measurement accuracy is. Further, according to this configuration, linear frequency modulation can be performed on the applied voltage, and distance measurement accuracy is improved. As described above, according to the present invention, distance measurement can be performed with high accuracy.

FIG. 2 shows another embodiment of the invention. This example is the first
The difference from the figure is that a scanner 12 scans with frequency-modulated laser light, and the reflected light from the object 7 is detected through the same scanner 12. According to this configuration, three-dimensional information can be obtained as a distance image. Such distance images are effective for three-dimensional vision of robots.

Effects of the Invention As described above, the present invention obtains frequency-modulated laser light using an electro-optic light modulator installed inside a laser resonator, irradiates it onto a target object, and detects the frequency of the reflected light to determine the distance. The purpose of the present invention is to provide a laser distance measuring device with high accuracy for measuring.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a laser distance measuring device according to an embodiment of the present invention, FIG. 2 is a schematic diagram of a laser ranging device according to another embodiment of the present invention, and FIG. 3 is a schematic diagram of a conventional laser ranging device. The schematic diagram, FIG. 4, is a principle diagram of a frequency modulation type laser distance measuring device. 1... Laser, 2... Total reflection mirror, 3... Vieso, 4... Modulation power supply, 5... Beam splinter,
6... Partially reflecting mirror, 7... Target, 8... Lens, 9... Detector, 10... Frequency analyzer, 11...
- Electro-optic light modulator, 12...scanner. Name of agent: Patent attorney Toshio Nakao and one other person

Claims (2)

[Claims] (1) A laser light source including an electro-optic light modulator provided inside a laser oscillator, a means for extracting a part of the laser light from the laser light source as a reference light and irradiating it onto an object to be measured, 1. A laser distance measuring device comprising means for detecting a frequency difference between light reflected from an object to be measured. (2) The laser distance measuring device according to claim 1, wherein the means for irradiating the object to be measured with laser light includes a scanner.