JPH0735507A - Signal processing circuit for laser distance measuring device - Google Patents

Abstract

PURPOSE:To provide a laser processing circuit for a laser distance measuring device, which can perform measurements with a high degree of accuracy and which can enhance the reliability of the laser distance measuring device. CONSTITUTION:A time measuring counter 130 and a time measuring counter 132 connected to a reference optical system simultaneously measure a time of a reference beat signal and a time of a distance measuring beat signal in accordance with clock pulses which are produced from one and the same clock generator 122, errors caused by time-fluctuation of the clock generator 122 are canceled out. In accordance with count values obtained from the time measuring counters 130, 132 and the wave number counter 123, a computer 11 calculates a distance to an object to be measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to FA (Factory).
The present invention relates to a laser range finder used in the field of automation and the like, and particularly to a signal processing circuit thereof.

[0002]

2. Description of the Related Art As a conventional example of a laser distance measuring device, a semiconductor laser is time-frequency-modulated and incident on an interference optical system.
By coherent heterodyne detection of the reference light and the measurement light generated by the two optical systems having different distance differences, a beat signal is obtained from the frequency difference according to the difference in the distance between the reference light and the measurement light. There is known a device for measuring the distance to an object to be measured based on the above.

As an example of such a laser distance measuring device, the one described in Japanese Patent Application Laid-Open No. 61-223577 and the document "FM heterodyne length measuring method using a semiconductor laser, Takaro Kobayashi et al., IEICE. Technical research briefing
OQE87-153 ”.

FIG. 3 shows the configuration of such a laser distance measuring device. Laser light emitted from a semiconductor laser 201 serving as a light source is collimated by a collimator lens 202, enters a beam splitter 203, and is split into two by the beam splitter 203. One of the split lights is incident on an optical system (reference optical system) having an optical path difference that serves as a stable reference. This reference optical system is composed of a beam splitter 204, two reflectors 205, 205, and a detector 207, and operates as described below. First, the beam splitter 204 splits the incident light into a reference light and a measurement light, and guides the reference light to a reflector 205 (reflection mirror) provided on an extension of the optical axis of the incident light. In addition, the measurement light is guided to a reflector 205 provided in a direction forming 90 degrees with the optical axis of the incident light. In the figure, R _r represents the optical path length of the reference light, and L _r represents the optical path length of the measurement light.

The reference light and measurement light reflected by the respective reflectors 205, 205 are re-incident on the beam splitter 204 to be combined, and then guided to a detector 207 for coherent heterodyne detection. A beat signal is obtained by this detection.

On the other hand, the other light split by the beam splitter 203 is incident on the distance measuring optical system. The structure of this distance measuring optical system is substantially the same as the structure of the reference optical system. That is, the configuration is the same as that of the reference optical system except that the measurement light is guided to the measurement object 216 instead of being guided to the reflector, and the beam splitter 214 and the reflector 21.
5 and a detector 217 are similarly provided. The detector 217 of this distance measuring optical system similarly outputs the beat signal in this interference optical system.

Here, the frequency f _b of the beat signal is expressed by the following equation (1).

[0008] _{f b = (dν / dt)} · τ = 4f m · Δν · (R-L) / c ... (1) where, [nu: frequency of the laser beam tau: time of the measuring light and the reference light delays f _m : Modulation frequency Δν (GHz / mA): Frequency modulation amount of laser light R: Distance of reference light L: Distance of measurement light c: Speed of light

FIG. 4 shows the frequency modulation amount of the laser light and the waveform of the beat signal.

Further, in this optical system, the measurement object 2
The distance L to 16 is represented by the following equation (2).

L = (f _s / f _r ) · (R _r −L _r ) + R (2) = [(N _clr / N _r ) / (N _cls / N _s )] · (R _r −L _r ) + R (2) where N _s : wave number of frequency of beat signal of distance measuring optical system N _r : wave number of frequency of beat signal of reference optical system R _r : optical path length of reference light of reference optical system L _r : Optical path length of measuring light of reference optical system R: Optical path length of reference light of distance measuring optical system N _clr : Number of pulses of clock generator of reference optical system for time measurement N _cls : _Distance measuring optical system of time measurement It is the number of pulses in the clock generator.

The distance calculation is performed by the computer 211 including a personal computer or the like. More specifically, the beat signals obtained by the detectors 207 and 217 as described above are amplified to a predetermined level by the amplifiers 208 and 218 connected to the detectors 207 and 217, respectively, and then the waveform shaper 209. Two
After the waveform is shaped by 19, the frequency is counted by the counter 210. Then, the computer 211 calculates (measures) the distance L based on this count value.

FIG. 5 shows a circuit configuration of the counter 210 which counts the frequency of the beat signal. Wave shaper 20
The beat signals of the reference optical system and the distance measuring optical system (hereinafter referred to as the reference beat signal and the distance measuring beat signal) whose waveforms have been respectively shaped by 9, 219 are the number of integer waves of each beat signal, that is, the wave number for counting the wave number. Counter 22
3 and 224, respectively. An integer set value is preset in the wave number counter 223 to which the distance measurement beat signal is input by the wave number setting device 226 connected thereto, and the wave number counter 223 is shown in FIG.
Counting is performed until the wave number of the distance measurement beat signal of the signal waveform shown in (3) reaches the set value. During this time, the wave number counter 224
Counts the wave number of the reference beat signal having the signal waveform shown in FIG.

When the count value reaches the set value, the wave number counter 223 stops counting and outputs a count stop signal to the wave number counter 224. This allows
The wave number counter 224 stops counting the wave number of the reference beat signal input from the waveform shaper 209.

At this time, the wave number counter 224 can count only an integral number of wave numbers of the reference beat signal.
Phase counter 2 to measure the wave number below the decimal point
25 counts the phase of the reference beat signal. This counting is performed by counting clock pulses (see FIG. 6 (d)) having a frequency much higher than the frequency of the reference beat signal provided from the clock generator 222. Then, the wave number counter 224 outputs the phase counter 2 every time the wave number of the reference beat signal is counted.
A reset signal is output to 25 to reset the phase counter 225 (see FIG. 6C). In this way, the phase counter 225 counts the wave number within one cycle of the reference beat signal, that is, the value (phase angle) corresponding to the wave number below the decimal point.

The count value of the wave number counter 224 is displayed on the wave number display 227. Also, the phase counter 22
The count value of 5 is displayed on the phase angle display 228.

[0017]

By the way, in the signal processing circuit of the laser distance measuring apparatus as described above, the phase portion of the reference beat signal is measured based on the clock pulse generated from the clock generator 222. Therefore, the measurement accuracy of this measurement system is determined by the clock accuracy.

To explain the signal processing circuit in more detail, the method of calculating the phase angle is performed by the ratio of the number of clock pulses for one cycle and the decimal part of the wave number by the phase counter. The frequency stability is about ± 50 ppm, and there is a problem that due to this error, a measurement frequency error of only about 10 ⁻⁴ is obtained.

The present invention solves the problems of the prior art as described above, and automatically changes fluctuations caused by environmental changes such as the temperature of a clock generator used for measuring the time of a beat signal. It is an object of the present invention to provide a signal processing circuit for a laser range finder, which can be cancelled, and which enables highly accurate distance measurement.

[0020]

A signal processing circuit for a laser range finder according to the present invention is incident on an interference optical system having two optical systems and is beat generated by a frequency difference caused by an optical path difference between the two optical systems. A signal processing circuit for a laser range finder, which is used in a laser range finder for measuring a distance to a measurement object or a displacement of the measurement object based on a signal, has two interference optical systems, and one interference optical system. The system is a distance measuring optical system that measures the distance to the object to be measured, and the other interference optical system is a reference optical system in which the distance difference between the two optical systems is known.
A beat signal processing circuit that calculates the frequency of the beat signal by measuring the wave number and time of the beat signal of each interference optical system is provided, and the beat signal processing circuit generates a clock signal generated from the same clock generator. It is a signal processing circuit that measures the time of each beat signal substantially simultaneously according to a pulse, and thereby achieves the above object.

Preferably, the wave number of the reference optical system is set, and the time between the set wave numbers is measured by a time measuring counter based on the clock pulse from the clock generator, while the wave number is set between the set wave numbers. The wave number of the beat signal obtained from the distance measuring optical system and the time based on the clock pulse from the clock generator are measured by a time measuring counter, and each beat signal frequency is measured.

[0022]

As described above, according to the circuit configuration in which the time measurement of the beat signal of each of the reference optical system and the distance measuring optical system is performed almost simultaneously based on the clock pulse generated from the same clock generator, the clock generator Even if the generated clock pulse changes due to environmental changes such as temperature, that is, it fluctuates in time, the effect appears equally in both optical systems. Therefore, the error with respect to the measurement value of each optical system is canceled and canceled.

This is also clear from the equation (2).
It That is, in equation (2), N_{cl r}, N_clsMeasured from the ratio of
Since the distance L to the fixed item is measured, N_clr, N_clsTo
Error in measuring the absolute time of the clock generator
You can see that you can cancel the difference.

[0024]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a signal processing circuit for a laser range finder according to the present invention. This signal processing circuit is mounted on a laser distance measuring device having a reference optical system and a distance measuring optical system similar to the conventional example. The reference beat signal generated by the reference optical system and the distance measurement beat signal generated by the distance measurement optical system in the same manner as above are respectively amplified and waveform-shaped by the analog circuit portion including the amplifier and the waveform shaper, and TT
After being converted to an L level output, it is input to the digital circuit portion.

That is, the reference beat signal generated by the reference optical system is amplified to a predetermined level by an amplifier (not shown) and then input to the waveform shaper 109,
Here, waveform shaping is performed and converted into the rectangular wave shown in FIG. Similarly, the distance measurement beat signal is generated by the waveform shaper 1
The waveform is shaped by 19 and converted into a rectangular wave shown in FIG.

The signal converted into a rectangular wave by the waveform shaper 109 is input to the wave number counter 124 of the reference system. An integer set value is preset in the wave number counter 124 by the wave number setting device 126 connected thereto. The wave number counter 124 is used for the waveform shaper 10.
The number of waves of the input signal from 9 is counted, and the gate is opened until the count value reaches the set value.
More specifically, during this period, the wave number counter 124 outputs the "H" level gate open signal (reference system gate signal) to the reference system time measurement counter 130 at the timing as shown in FIG. 2B. It has become so.

The time measuring counter 130 is provided with a clock signal of the waveform shown in FIG.
A pulse is input. The time measurement counter 130 counts the number of clock pulses from the clock generator 122 and measures time while the reference system gate signal from the wave number counter 124 is in the gate open state (FIG. 2 (d. )reference).

The reference system gate signal is the synchronizing circuit 1
It is input to 31. The synchronizing circuit 131 generates a distance measuring system gate signal (see FIG. 2F) synchronized with the reference beat signal based on the reference system gate signal, and supplies it to the wave number counter 123 and the time measuring counter 132 of the distance measuring system. The output of the waveform shaper 119 is input to the synchronization circuit 131. This output is also input to the time measurement counter 132.

The wave number counter 123 counts the wave number (see FIG. 2 (g)) of the distance measurement beat signal while the distance measurement system gate signal is in the "H" level gate open state. Further, a clock pulse (see FIG. 2 (h)) is input from the same clock generator 122 to the time measurement counter 132, and the distance measurement system gate signal is "
While the gate is open at H ”level, this clock
Pulses are counted and time is measured.

With the above count values, the beat frequencies of the beat signals of the distance measuring optical system and the reference optical system are measured,
Thereafter, in the same manner as in the conventional example, the computer 111 calculates the above equation (2) to calculate the distance L to the measurement object.

As is clear from comparing FIGS. 2D and 2H, in the signal processing circuit for the laser range finder of the present invention, the clock pulse from the same clock generator 122 is used as a reference. The time is measured by counting almost simultaneously by the time measuring counters 130 and 132 provided in the optical system and the distance measuring optical system, respectively. At the same time, the distance L is measured according to the equation (2). Therefore, it is possible to perform highly accurate distance measurement in which the error caused by the temporal fluctuation of the clock generator is canceled.

[0032]

According to the signal processing circuit for the laser distance measuring apparatus of the present invention, beat signals generated by the reference optical system and the distance measuring optical system are generated in accordance with the clock pulses generated from the same clock generator. Since the time measurement is performed, the time of both beat signals can be measured almost simultaneously. Therefore, even if the clock pulse fluctuates temporally due to environmental changes such as temperature, the effect appears equally in both optical systems, and the error for the measured value of each optical system is canceled and canceled. It Therefore, highly accurate measurement is possible, and the reliability of the laser range finder can be significantly improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration of a signal processing circuit for a laser range finder according to the present invention.

FIG. 2 is a timing chart showing signal waveforms of signals processed by a signal processing circuit for a laser range finder according to the present invention.

FIG. 3 is a schematic diagram showing a conventional example of a laser distance measuring device.

FIG. 4 is a signal waveform diagram showing a laser frequency modulation amount and a beat signal.

FIG. 5 is a block diagram showing a part of a conventional signal processing circuit for a laser distance measuring device.

FIG. 6 is a timing chart showing signal waveforms of signals processed by a conventional signal processing circuit for laser range finder.

[Explanation of symbols]

 109, 119 Waveform shaper 111 Computer 122 Clock generator 123, 124 Wave number counter 130, 132 Time measurement counter 131 Synchronous circuit 201 Semiconductor laser 203, 204, 214 Beam splitter 205, 215 Reflector 207, 217 Detector 208, 218 Amplifier

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsushi Shimonaka 22-22 Nagaike-cho, Abeno-ku, Osaka City, Osaka Prefecture

Claims (2)

[Claims] 1. A distance to a measurement object or a displacement of the measurement object is measured based on a beat signal which is incident on an interference optical system having two optical systems and is generated by a frequency difference caused by an optical path difference between the two optical systems. A signal processing circuit for a laser range finder used in a laser range finder, comprising: two interferometer optical systems, one interferometer optical system being a range finder optical system for measuring a distance to an object to be measured. While the other interference optical system is a reference optical system in which the distance difference between both optical systems is known, the frequency of the beat signal is measured by measuring the wave number and time of the beat signal of each interference optical system. A beat signal processing circuit for calculating is provided, and the beat signal processing circuit,
A signal processing circuit for a laser range finder, which is a signal processing circuit that measures the time of each beat signal almost simultaneously in accordance with clock pulses generated from the same clock generator. 2. A wave number of the reference optical system is set, and a time between set wave numbers is measured by a time measuring counter based on a clock pulse from the clock generator, while the wave number is measured during the set wave number. A signal for a laser range finder according to claim 1, wherein the wave number of the beat signal obtained from the range optical system and the time based on the clock pulse from the clock generator are measured by a time measuring counter to measure the frequency of each beat signal. Processing circuit.