JPS5866881A - Surveying equipment by light wave - Google Patents

Abstract

PURPOSE:To reduce measurement time considerably and to improve the accuracy of measurement by making modulating frequencies variable in such a way that wavelengths are made integer times the optical path length. CONSTITUTION:A differential frequency f3 between a specific frequency f1 and a variable frequency f2 is generated and the light wave which is subjected to light intensity modulation by said frequency is emitted from an intesity modulator 4 for light source and the light wave reflectd by a reflecting mirror 5 is detected with a photodetector 6. The optical path length in this time is 2L. The received output of the photodetector 6 is applied to a phase detector 8 after amplification and with f3 as a reference signal, the output is subjected to synchronous detection. Here the wavelength of the frequency f3 is c/f[(c) is velocity of light]and therefore the phase difference phi of the photodetected light wave with respect to the emitted light wave is 4piLf3/c. Now if arrangement is so made that the f3 changes from the low frequency side where there are none of the nodes of the light wave in the path 2L, the change in the differential frequency f3 is stopped where the output from the detector 8 attains phi=pi, and the f3 is read with an operator 11, which operates L=c/(4f3) and determines the distance L. Said distance is displayed on a display 12.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light wave surveying instrument that performs surveying using a novel method.

Conventional light wave surveying instruments emit light waves that are intensity-modulated at a specific frequency and travel back and forth between the measured distances, and utilize the fact that the phase of the received light waves differs depending on the optical path length to accurately determine this phase. It was a so-called fixed frequency method. In this case, a method is usually adopted in which the received signal is converted to a frequency several orders of magnitude lower by heterodyne to expand the time scale 17 and improve measurement accuracy.

However, when the optical path length is longer than the wavelength of the light wave, the number of waves existing in the optical path becomes one or more, causing uncertainty. Furthermore, if the longest optical path length to be surveyed is set equal to the wavelength of the light wave, there is a drawback that when surveying short distances, the phase difference becomes small and measurement accuracy cannot be improved.

Therefore, in the fixed frequency method, two types of specific frequencies are usually used. is selected to have a light wave wavelength λ2 corresponding to the optical path length corresponding to the shortest measurement distance L2, and this is used as the fine signal 0. Then, these two types of signals are switched, and first, the phase in units of λ2 is determined using the fine signal. Performing high-precision measurements,
Next, the number of λ2 (integer value) included in the distance to be measured is determined from the coarse signal, and then the total distance is determined by calculation. Therefore, there are disadvantages in that the circuit configuration becomes extremely complicated and the calculation time increases, resulting in a long measurement time.

In order to solve the above-mentioned drawbacks of the conventional example, the present invention adopts a method in which the frequency of light intensity modulation is varied to a frequency where the wavelength of the light wave is an integral multiple of the optical path length, thereby simplifying the circuit configuration. The present invention provides a light wave surveying instrument designed to shorten measurement time. Hereinafter, embodiments will be described in detail with reference to the drawings.

The figure shows the configuration of an embodiment of the present invention. 1 is an oscillator that oscillates a specific frequency f1, 2 is an oscillator that oscillates a variable frequency f2, and 3 is a mixture of f+ and f2, and a difference frequency f3.
-8- A mixer that generates f2; 4 is a light source intensity modulator that emits a light wave whose light intensity is modulated by the difference frequency f3; i is a reflecting mirror; 6 is a light receiver that receives the light wave reflected by the reflecting mirror 5;
7 is an amplifier; 8 is a phase detector for synchronously detecting the received light signal using frequency f3 as a reference signal; 9 is an amplifier; 1o is a time constant circuit that performs time constant processing as required; the output of this is fed back to the oscillator 2; Ru. 11 is a computing unit, and 12 is a display.

Next, the operation of this embodiment will be explained. First, the light source intensity modulator 4 (and light receiver 6) is placed at one end of the distance to be measured, and the reflecting mirror 5 is placed at the other end.

Difference frequency f3-8- between specific frequency f and variable frequency f2
f2 is generated, a light wave whose light intensity is modulated thereby is emitted from the light source intensity modulator 4, and the light wave reflected by the reflecting mirror 5 is received by the light receiver 6. Therefore, the optical path length at this time is 2L. The received output of the photoreceiver 6 is amplified and then applied to the phase detector 8, where it is synchronously detected using f3 as a reference signal. Here, the light wave wavelengths of the difference frequency f3 are C1, f3 (however, C is the speed of light), so the phase difference φ between the received light wave and the emitted light wave is μ
and f3. Now, if we set '/f3>L, that is, 8 changes from the low frequency side where there is no node of light waves in the optical path 2L, then the phase gater, ka, et al. Since the output is proportional to the phase difference φ, the change to the difference frequency should stop when φ=π. That is, the oscillation frequency 12 of the oscillator 2 is determined by the output of the phase detector 8 at φ2π.
is kept constant, the difference frequency f3 at this time is read by the calculator 11, the L two runs are calculated, the distance is determined, and the distance can be displayed on the display 12.

As described above, according to the present invention, since the measurement time only depends on the time constant of the negative feedback control system, it can be significantly shortened compared to the conventional example, and the measurement accuracy is improved. . Furthermore, the circuit configuration is simplified, and therefore the cost is reduced, which has significant effects.

[Brief explanation of the drawing]

The figure is a block diagram showing the configuration of an embodiment of the present invention. 1...Specific frequency oscillator, 2...
・・・・・・Variable frequency oscillator, 3・・・・・・・・・
・Mixer, 4...Light source intensity modulator,
5・・・・・・・・・Reflector, 6・・・・・・・・・
Photoreceiver, 7...Amplifier, 8...
・・・・Phase detector, 9・・・・・・・・・Amplifier,
10... Time constant circuit, 11...
...Calculating machine, 12... Display device.

Claims (1)

[Claims] a frequency variable means; a means for emitting a light wave whose intensity is modulated by the output frequency of the frequency variable means; a means for receiving the light by reciprocating it over a distance to be measured; and detecting a phase difference between the received light wave and the emitted light wave; 1. A light wave surveying instrument, comprising means for feeding back to the frequency variable means, and measuring distance by determining a frequency at which the wavelength of the light wave is an integral multiple of the optical path length.