JPS6275363A - Laser distance measuring apparatus - Google Patents

Abstract

PURPOSE:To enable accurate measurement free from effects of background noise, by performing a heterodyne detection with combination of a signal light subjected to a frequency shift and a reference light not subjected to the same. CONSTITUTION:A laser light from a laser oscillator 1 is divided with a beam splitter 4 and one thereof is supplied to a heterodyne detector 16 via a reflecting mirror 15 as reference light. The other thereof is inputted to an acousto-optical light modulation element 13 and subjected to a frequency shift by interaction with a high frequency signal from a high frequency oscillator 5 to generate a diffraction light with a stressed intensity, which irradiates an object 20 via reflecting mirrors 51 and 52. A detector 16 performs a heterodyne detection of a differential frequency signal 17 between the reflected light from the object 20 and the reference light. The phase of the signal 17 is delayed in proportion to the distance to the object 20. A phase difference between the reference signal 5 from an oscillator 5 and the signal 17 is detected with a phase detector 12. This enables measurement of the distance to the object 20 even with a weak reflected light free from effects of any background noise.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application Prior Art Measuring the absolute distance to an object using a laser has recently attracted attention as a source of visual information for remote control of robots. Such laser distance measuring devices are broadly divided into those that use trigonometry and those that measure the round trip time of light, and the latter can be further divided into those that use pulsed lasers and those that modulate the intensity of continuous wave lasers. . Continuous wave laser intensity modulation is suitable for measuring relatively short distances such as robot vision, and this method is described in, for example, Proceedings of the I.E.
E Vol. 65, pp. 206-220 (Proc.

IEEE vol, 55, [)I) 206-220
, 1977). Hereinafter, a conventional intensity modulation type laser distance measuring device will be explained with reference to FIG.

In FIG. 2, the output light from a laser 1 is intensity-modulated by an electro-optic light modulator 2 driven by an oscillator 3. The intensity-modulated laser beam is irradiated onto the object 20 by the reflecting mirror 5. A portion of the laser light is guided by a beam splitter 4 to a detector 6, which monitors the laser output and generates a reference signal 7 for ranging. The reflected light from the object 20 is guided to a detector 9 by a reflecting mirror 8, and a signal wave 10 is generated. At this time,
Since the amplitude of the signal wave 10 differs depending on the reflectance of the object 20 with respect to the laser beam and the distance to the object 20, the intensity of the signal wave 10 is detected by the intensity detector 11, while the intensity of the signal wave 10 is detected by the reflector 5. If you scan the light,
The same image information as that measured by a TV camera can be obtained.

Further, the phase of the signal wave 10 is delayed in proportion to the distance to the object 20. Therefore, by measuring the phase difference between the reference signal 7 and the signal wave 10 using the phase detector 12, the distance to the object can be measured.

Problems to be Solved by the Invention However, with the above configuration, the light existing in the bank ground affects noise, so weak reflected light cannot be measured and good measurement accuracy cannot be obtained. Was. The present invention solves the above problems, and aims to provide a laser distance measuring device that is resistant to noise and has high measurement accuracy.

In order to achieve the second object of "Means for Solving the Problems", the present invention inputs laser light into an acousto-optic modulator (hereinafter referred to as AOM) to shift the frequency and generate intensity-modulated light. This laser beam is irradiated onto an object to obtain a signal light, and distance measurement is performed by heterodyne detection of this signal light and a reference light whose frequency has not been shifted, and based on the phase delay of the difference frequency signal obtained. It is a distance device.

Function: With the above configuration, the present invention irradiates only the light frequency-shifted by the AOM onto the measured object as signal light, and performs heterodyne detection using this and the reference light whose frequency has not been shifted, so it is not affected by background noise. Therefore, highly accurate measurements can be performed.

EXAMPLES Hereinafter, examples of the present invention will be described in detail with reference to the drawings. FIG. 1 is an overall configuration diagram showing an embodiment of a laser distance measuring device according to the present invention. The laser beam from the laser oscillator 1 is split into two optical paths by the beam sub-block 4, and one of the beams enters the AOM 13. The AOM 13 generates frequency-shifted and intensity-modulated diffracted light due to interaction with the high-frequency signal from the high-frequency oscillator 5, and the reflected mirrors 51 and 52
The target object 20 is irradiated with the light. At this time, undiffracted light that is not diffracted passes through the AOM 13, and this transmitted light is detected by a detector 14 to monitor the laser output.

The reflected light from the object 20 is reflected by the partial reflecting mirror 15 and enters the heterodyne detector 16 .

The other laser beam split by the beam splitter 4 is supplied as a reference beam to a heterodyne detector 16 through a partially reflecting mirror 15. The heterodyne detector 16 heterodyne detects the difference frequency signal 17 between the reflected light from the object 20 and the reference light from the beam subric-4,
The intensity of this difference frequency signal 17 is detected by the intensity detector 11 to obtain image information. The phase of the difference frequency signal 17 is
Since the delay is proportional to the distance to the object, the distance to the object can be determined by detecting the phase difference between the reference signal 7 from the high frequency oscillator 5 and the difference frequency signal 17 using the phase detector 12. That is, if the phase difference is Da, the difference frequency is ν, and the speed of light is C, the distance to the object is 4 π ν Thus, according to this embodiment, the laser beam is transmitted by the AOM only at the frequency generated by the high-frequency oscillator 5. Only the frequency-shifted light is selected and used as the signal light from the target object, and heterodyne detection is performed between this and the non-frequency-shifted laser light, eliminating the influence of light existing in the bank ground and detecting weak signals. Measurement can also be performed using reflected light.

Effects of the Invention As described above, the present invention injects a laser beam into an acousto-optic light modulation element to obtain frequency-shifted light, irradiates the object to be measured with the light, and adds the resulting reflected light to a heterogain detector. ,
This is a laser ranging device that heterodyne detects the difference frequency signal between the frequency-shifted laser beam and the laser beam, and measures the distance based on the phase delay of this signal. Since the present invention uses heterodyne detection, it is possible to provide a laser distance measuring device with high measurement accuracy, which is not affected by background noise, and can also measure weak reflected light.

FIG. 1 is a schematic diagram of a laser ranging device according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of a conventional laser ranging device.

1... Laser oscillator, 5... High frequency oscillator, 7...
-Reference signal, 12. Phase detector, 13.. Acousto-optic optical modulator, 16.. Heterodyne detection, 17. Difference frequency signal.

Name of agent: Patent attorney Toshio Nakao (1st person)
Figure 2

Claims (1)

[Claims] A laser beam is intensity-modulated by an acousto-optic light modulation element to generate frequency-shifted diffracted light, which is irradiated onto the target object, and the reflected light is generated by a phase delay between the non-frequency-shifted reference light and the heterodyne-detected signal. A laser distance measuring device that measures the distance to an object.