JPH0448289A - Light wave range finder - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a light wave distance meter suitable for use in particular for short distance measurement.

(Prior art) As shown in Fig. 4, a conventional optical distance meter uses a main oscillator a
The signal converter connected to generates a signal with frequency f1 and a signal with frequency f2, and selector C selectively applies these signals to light emitting element d, and from light emitting element d, a modulation frequency f for rough measurement is generated. .

The modulated light with a modulation frequency f2 for precision measurement is sequentially emitted, the modulated light reflected by a reflecting mirror is converted into a received signal by a light receiving element e, and this received signal is phase-detected via a mixer g1 filter h and an amplifier i. In addition to the device j, this phase detector j compares the phase difference with the reference signal and measures the distance.In order to eliminate measurement errors due to the length of the optical path inside the machine, According to the above-mentioned optical distance meter, it is necessary to create signals of two frequencies f1 and f2, and furthermore, it is necessary to create signals of two frequencies f1 and f2. A circuit is required to switch between the two signals. In addition, it is necessary to switch the distance measuring light optical path [1] and the reference light optical path [2] for each of the modulation frequencies f and 12, and also to measure the phase difference for the signal of one frequency, and then for the signal of the other frequency. Since the distance measurement is performed on signals, there is a problem in that it takes time to measure the distance.

The present invention aims to solve these conventional problems.

(Means for Solving the Problems) In order to achieve the above object, the present invention transmits modulated light of different modulation frequencies, converts the modulated light reflected by a reflecting mirror into a received signal by a light receiving element, In the optical distance meter that measures distance from the phase difference between the received signal and the reference signal, the modulated light is modulated light with a rectangular wave containing a fundamental wave component for rough measurement and a harmonic component for precise measurement. , the received signal converted by the light receiving element is separated into a fundamental wave component for rough measurement and a harmonic component for precise measurement, and the phase difference between each component and the reference signal is measured in parallel to measure the distance. It is characterized by the following.

(Function) The rectangular modulated wave of the emitted light as shown in Figure 2 is expressed by the following Fourier transform equation, and as shown in Figure 3, it includes a fundamental wave component and various higher harmonic light waves. And this fundamental wave 5Irlx
is used for rough measurement, and the higher the harmonic component, the better the measurement accuracy, but the smaller the amplitude, the shorter the measurable distance. Therefore, for short-distance measurements up to about 500 m, this rectangular wave modulated light is converted into a received signal by a light-receiving element, and is then converted into a fundamental wave component and a predetermined harmonic component, such as the first harmonic component.
The first-order harmonic base is extracted, and the phase difference of each with respect to the reference signal is determined, and coarse and fine measurements are performed in parallel.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is for example 8MHz from the main oscillator 2.
This 800 KHz rectangular wave signal is applied to the light emitting element 4 via the amplifier 3. Reference numeral 5 denotes a light receiving element that converts the modulated light emitted from the light emitting element 4 and reflected by the reflecting mirror into a received signal. 5 of the fundamental wave of 800 KHz by filters 8a and 8b.
The lrl signal and the 5ffl signal of 8.8 MHz, which is the 11th harmonic, are extracted separately.

This 800KHz and 6.8MH2 received signal is sent to mixer 9.
630KHz and 6 output from signal converter 1 at a and 9b
．． 30 KHz and 1, respectively, with a 63 MHz reference signal.
3. ．． Only the 30 KHz signal, which is useful for precisely measuring the phase difference of the received signal, is converted into a 23 MHz signal and passed through the filters 10a and 10b, and this signal is passed through the amplifiers 11a and 11b, respectively, to the phase detector 12.
added to a and 12b. These phase detectors 12a and 12
b measures the phase difference between each 30 KHz received signal and the 30 KHz reference signal output from the signal converter 1, and outputs this phase difference signal to the CPU 13.

In this embodiment, as in the conventional example, a mirror 14 is provided in front of the light emitting element 4 to selectively switch the optical path from the ranging optical path L1 to the reference optical path L2 inside the machine, and the phase difference between the received signal and the reference signal is After the measurement, the mirror 14 is switched to make the reference light enter the light receiving element 5 through the reference optical path L2, and the phase difference between the reference signal converted by the light receiving element 5 and the reference signal is measured by the phase detectors 12a and 12b. , this phase difference signal is sent to the CPU
Output to 13. The CPU 13 calculates a distance value corrected for a measurement error corresponding to the length of the optical path inside the machine from the phase difference between the received signal and the reference signal and the phase difference between the reference signal and the reference signal.

In FIG. 1, 15 is, for example, a 15 MHz signal generator, and the phase detectors 12a and 12b are connected to this 15 MHz signal generator.
The MHz signal is counted for a period corresponding to the phase difference, and the counted value is output as a phase difference signal.

(Effects of the Invention) Since the present invention has the above-described configuration, rough measurement and fine measurement can be performed in parallel, and measurement time can be shortened. Further, since there is no need to create a low frequency signal for coarse measurement and a high frequency signal for precise measurement, and there is no need to output these signals alternately, the circuit configuration becomes simple. When configuring to switch between the distance measuring optical path and the reference optical path,
This switching only needs to be done once, and distance measurement time can be further shortened.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a waveform diagram of a modulated wave of the emitted light, FIG. 3 is a waveform diagram of its contained components, and FIG. 4 is a block diagram of a conventional example. 1... Signal converter 4... Light emitting element 5... Light receiving element 8a, 8b... Filter 10a, 1
0b...filter

Claims (1)

[Claims] In a light wave distance meter that transmits modulated light modulated into a rectangular wave, converts the modulated light reflected by a reflecting mirror into a received signal by a light receiving element, and measures distance from the phase difference between the received signal and a reference signal,
The modulated light is modulated light with a rectangular wave that includes a fundamental wave component for coarse measurement and a harmonic component for precise measurement, and the received signal converted by the light receiving element is combined with the fundamental wave component for coarse measurement and the harmonic component for precision measurement. A light wave distance meter characterized in that the distance is measured by separating harmonic components for measurement and measuring the phase difference between each component and a reference signal in parallel.