JP2667501B2 - Laser distance measuring device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring device that detects a moving distance of an object using a laser beam.

[Conventional technology]

Conventionally, as a distance measuring device that measures the moving distance of an object conveyed along a conveying path, for example, a thin iron plate or the like to cut a thin iron plate at a predetermined length, the distance measuring device is connected to a roller that rotates in contact with the iron plate. There is used a device which is provided with a rotary encoder and detects the moving distance of the iron plate from a signal obtained from the rotary encoder.

[Problems to be solved by the invention]

However, according to such a conventional distance measuring device, since the roller comes into direct contact with the object to be measured, there is a large restriction due to the object to be measured, and the measurement accuracy cannot be made too high by using an encoder. There was a drawback.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems of the conventional distance measuring apparatus, and has been developed to provide a technique for detecting the moving amount and speed of an object with high accuracy and without contact with the object. Make it an issue.

[Means for solving the problem]

The present invention is a distance measuring device for detecting a moving distance of an object using laser light, wherein a laser light source and a laser light are
A beam splitter for separating the laser beam into a second laser beam, a Bragg cell for shifting the frequency of at least one of the separated laser beams, and optical means for intersecting the first and second laser beams obtained through the Bragg cell at one point. Scattered light from an object passing in the direction perpendicular to the bisector of the angle formed by the laser beams in the plane formed by the first and second laser beams in the intersection area of the first and second laser beams A driving frequency detecting means for outputting a signal of a frequency difference given to the Bragg cell, and a reference input signal obtained from the driving frequency detecting means and a change time point of the photoelectric conversion signal obtained from the photoelectric converter, respectively. No. to detect
1, an RS flip-flop circuit in which the outputs of the first and second transition point detection circuits, the outputs of the first and second transition point detection circuits are given as set and reset inputs, and the coincidence of the signals of the first and second transition point detection circuits. A match detection circuit for detection, a different output of the RS flip-flop circuit, an output of the first or second change point detection circuit, and an output of the match detection circuit are respectively provided, and first and second outputs of a signal at the time of the match. And a frequency difference detection circuit having an output circuit, wherein the moving distance of the object is measured based on output pulses obtained from the first and second output circuits of the frequency difference detection circuit. It is.

[Action]

According to the present invention having such characteristics, the laser light emitted from the laser light source is split by the beam splitter, and the frequency of at least one of the laser beams is shifted by the Bragg cell. Then, since the first and second laser beams are irradiated to one point by the optical means,
In the intersection region, an interference fringe moving at a speed corresponding to the frequency difference of the laser beam is generated. Therefore, scattered light can be obtained by transporting the object to be measured perpendicularly to the laser beam within the region of the interference fringes. By condensing the scattered light and performing photoelectric conversion, a signal having a frequency corresponding to the moving speed of the interference fringes and the transport speed of the object is obtained. On the other hand, the frequency difference of the laser beam is detected by the driving frequency detecting means and used as a reference signal, and the photoelectric conversion output is given to the first and second change point detecting circuits of the frequency difference detecting circuit as a signal corresponding to the moving distance of the object. I have. In this way, the RS flip-flop circuit is set or reset by the output signals of the first and second change point detection circuits. Therefore, when the output of the other change point detection circuit between the outputs of any one of the change point detection circuits is included, the output of the other change point detection circuit is output to the outside via the first or second output circuit. Is output. Therefore, a signal having a cycle corresponding to the frequency difference of the input signal is output from the first or second output circuit according to the magnitude.
Then, the moving distance of the object is measured based on the output pulses obtained from these output circuits.

[Explanation of Example]

FIG. 1 is a block diagram showing the configuration of a distance measuring device according to an embodiment of the present invention. In FIG. 1, a laser light source 1 is a laser light source that emits monochromatic light, and uses, for example, a helium neon laser. The laser light emitted from the laser light source 1 is given to the beam splitter 2 and separated into first and second laser beams. Bragg cells 3 and 4 and half mirrors 5 and 6 are provided on the optical axes of the first and second laser beams. The Bragg cells 3 and 4 are driven by the Bragg cell driver 7 at different frequencies, for example, 81 MHz and 80 MHz, respectively, to change the frequency of the incident laser beam. Half mirror 5,6
The first and second laser beams that have passed through are given optical means,
In the present embodiment, the prisms 8 and 9 intersect at a predetermined point. Laser beams may be crossed using lenses instead of the prisms 8 and 9. In this position, as shown in FIG. 3, the object to be measured is moved in the Y-axis direction, that is, as shown in FIGS.
In the plane formed by the second laser beam, the angle θ formed by the first and second laser beams is moved in the Y-axis direction perpendicular to the X-axis direction, which divides the angle θ equally into two. An aperture 10 having an opening at the center and a condenser lens 11 are provided at an intermediate portion between the prisms 8 and 9. The aperture 10 and the condenser lens 11 provide the scattered light obtained from the object to the optical fiber 12. The optical fiber 12 supplies the scattered light to the photoelectric converter 14 of the frequency measurement circuit unit 13. The photoelectric converter 14 converts this scattered light into an electric signal and
It is given to the AGC circuit 15. The AGC circuit 15 automatically controls the change in the level of the received scattered light to be small, and supplies the amplified output to the waveform shaping circuit 16. On the other hand, the laser beams reflected by the half mirrors 5 and 6 are both provided to a photoelectric converter 17 such as a photodiode. The photoelectric converter 17 outputs an electric signal having a difference between these frequencies, and its output is used as a reference signal as a waveform shaping circuit of the frequency measuring circuit 13.
Given to 18. The waveform shaping circuits 16 and 18 convert the AGC output and the photoelectric conversion output into a square wave, respectively, and the outputs are supplied to the frequency difference detection circuit 20. Here, the half mirrors 5 and 6 and the photoelectric converter 17 constitute driving frequency detecting means for outputting a signal of a frequency difference given to the Bragg cells 3 and 4.

FIG. 2 is a detailed block diagram of the frequency difference detection circuit 20, and the outputs of the waveform shaping circuits 16 and 18 are supplied to a pair of rising detection circuits 21 and 22 from input terminals 20a and 20b, respectively. The rise detection circuits 21 and 22 are first and second change point detection circuits for detecting a change time point of the input signal, and have the same configuration. Therefore, the rise detection circuit 21 will be described. The rising detection circuit 21 has an input terminal connected to a D-type flip-flop 23 and its Q output connected to a D-type flip-flop 2.
4,25 D input terminals and clock input terminals, respectively.
A clock signal having a clock that is sufficiently faster than the input signal is provided from a clock signal source 26 to clock input terminals of the flip-flops 23 and 24. The output of the flip-flop 24 is given to the clear input terminal of the flip-flop 25, and the Q output of the flip-flop 25 is connected to the RS flip-flop circuit 30.
Given to. Flip-flop 27 of rising detection circuit 22
The same applies to ~ 29. The Q output terminal of the flip-flop 29 is given to the RS flip-flop circuit 30 and the AND circuit 32 of the coincidence detection circuit 31. The coincidence detection circuit 31 detects the coincidence of the outputs of the rise detection circuits 21 and 22. The output of the AND circuit 31 is supplied to a monostable multivibrator (hereinafter, referred to as MM) 33 having a constant operation time. At the input end of the RS flip-flop circuit 30, inverters 34a, 34b and 3 for delaying the input signal respectively are provided.
5a, 35b and AND circuits 36, 37 are provided, and AND circuits 36, 37
Are supplied to flip-flops 38 and 39, respectively. MM3
The output of 3 is provided to AND circuits 36 and 37 as gate signals. Flip-flops 38 and 39 are for inverting the input signal, and their outputs are NAND circuits 40 and 39, respectively.
a, 40b and are provided as inputs of an RS flip-flop 41. The output (output) of the NAND circuit 40b is provided as a clear input of the flip-flop 38 and as a clear input of the flip-flop 39 via the inverter 42. The Q and output of the RS flip-flop 41 are supplied to first and second output circuits 43 and 44. The output circuits 43 and 44 are composed of AND circuits 43a and 44a, respectively. The outputs of the rise detection circuits 21 and 22 and the output of the coincidence detection circuit 31 are supplied to the output circuits 43 and 44. Output circuit 4
Reference numerals 3 and 44 output the logical product signals of these signals from the output terminals 20c and 20d as a pair of signals of the frequency difference detection circuit 20.

Next, the operation of this embodiment will be described. First, the laser light emitted from the laser light source 1 is split by the beam splitter 2 into first and second laser beams. The frequency of this laser beam is shifted by the Bragg cells 3 and 4, respectively. Then, the signal is given to the photoelectric converter 17 via the half mirrors 5 and 6, and is subjected to heterodyne detection. As shown in FIG. A reference signal A having a frequency of 1 MHz is obtained. This signal is supplied to the frequency difference detection circuit 20 as A 'as a reference signal via the waveform shaping circuit 18 as a reference input. The pair of laser beams are applied to the detection area 50 by the prisms 8 and 9. 4th
The figure is an enlarged view showing the detection region 50, that is, the intersection region of a pair of laser beams. In the intersection region, as shown, an interference fringe is formed parallel to the irradiation direction of the laser beam and moves at a constant speed. The object 51 is moved to the detection area in the Y direction perpendicular to the light irradiation direction. At this time, assuming that the angle formed by the first and second laser beams is θ and the wavelength is λ, an interference fringe having a predetermined width is formed in the detection area. The interval df of the interference fringes is represented by the following equation (1).

For example, if the wavelength of the laser beam from the laser light source 1 is 633 nm and the crossing angle θ is 3.5 °, the interval df between the interference fringes is about 10 μm. And in the detection area 50, this interference fringe is a Bragg cell 3,
Assuming that the frequencies of the drive signals given to 4 are 80 MHz and 81 MHz, respectively, Y is determined at a speed corresponding to the frequency difference of 1 MHz.
Move in the axial direction. That is, the interference fringes move at a speed of 10 m / s. Therefore, when the detected object 51 is stationary in the detection area 50, the photoelectric conversion output of the scattered light obtained from the object 51 has a frequency component of 1 MHz. Also, object 51 is Y
If you move in the positive direction of the axis, 1M H
Scattered light having a frequency lower than z will be obtained. If the object 51 moves in the negative direction of the Y axis, scattered light having a frequency higher than 1 MHz is obtained corresponding to the moving direction. The scattered light signal (moving signal) is B, and its frequency is
If Fsg is set, a movement signal as shown in FIG. 3 (b) is obtained in the photoelectric converter 14. This signal is supplied to the frequency difference detection circuit 20 as the movement signal B 'via the AGC circuit 15 and the waveform shaping circuit 16.

Now, the rise detection circuits 21 and 22 are respectively shown in FIG.
As shown in (b), signals A 'and B' having slightly different frequencies Fref and Fsg are provided. In this case, as shown in FIGS. 5 (c) and 5 (d), signals for one clock are output from the rising edge detection circuits 21 and 22 at each rising edge. This signal is supplied as a set input and a reset input to the RS flip-flop 41 via the inverter 34, the AND circuit 36 or the inverter 35 and the AND circuit 37 of the RS flip-flop circuit 30. The RS flip-flop 41 at time t ₁ is a falling time point of the rising edge detection circuit 21 is set, signal the flip-flop 41 at the falling time t ₂ of the rising edge detection circuit 22 is reset is output. Accordingly, the RS flip-flop 41 is set and reset by this, and the signal as shown in FIGS. 5 (e) and 5 (f) is output to its Q and output terminal.

Now, the measured object is moving in the negative direction of the Y axis in the detection area 50, and the frequency Fsg of the moving signal B is higher than 1 MHz, and the fifth
The, as shown at time t ₃ when its period as shown in FIG. Long, RS flip-flop at the output of the rising detection circuit 22
After 41 has been reset, there is a pulse signal p shown in FIG. 5 (d) from the rising edge detection circuit 22 is output until time t ₄ when the set again by the output of the rising detection circuit 21 . In this case, the output of the rise detection circuit 22 is given to the output circuit 44 by the output of the flip-flop 41. Therefore, an output pulse p as shown in FIG. 5 (b) is output through the output circuit 44 by this signal. This pulse has a timing corresponding to the frequency difference between the input signals A and B. That is, the frequencies of the input signals A and B are Fre
When f> Fsg, a pulse, that is, a frequency signal of Fref−Fsg, is obtained every time the output circuit 43 is shifted by one cycle, and when two frequencies are Fref <Fsg, each time the output circuit 43 is shifted by one cycle. , A frequency signal of Fsg-Fref is obtained.

Next, the output signals from the rise detection circuits 21 and 22 may coincide. At this time, if the outputs of the rise detection circuits 21 and 22 are directly supplied to the RS flip-flop 41, the output is undefined, and there is a possibility that the output appears from one of the output circuits 43 and 44. A coincidence detection circuit 31 is provided to inhibit such output. FIG. 6 is a diagram showing the operation. 6 (a) and 6 (b) from the rise detection circuits 21 and 22
When the signal shown in the given RS flip-flop circuit 30, at time t ₅ is set RS flip-flop 31 by the falling of the rising edge detection circuit 21, the time by the falling of the rising edge detection circuit 22 t RS flip-flop 41 to ₆
Works as if they were reset. Now the same time the output from the rising edge detection circuit 21, 22 between times t ₇ ~t ₈ is given, the AND circuit 32 that matches the is detected MM33 coincidence detection circuit 31 is operated a certain time. Therefore, the match detection circuit
A signal as shown in FIG. 6 (d) is obtained from 31. By this signal, the flip-flop 38,
Input to 39 is prohibited. Also, the output of the coincidence detection circuit 31 provides an inhibition input to the output circuits 43 and 44. Therefore, at this time, no output is given from the output circuit 44. And RS
Since the flip-flop 41 to maintain the reset state, then miss the time t ₉ ~t ₁₀ the signal from the rising edge detection circuit 22 is supplied become the pulse as shown in Figure No. 6 (e) is output count Can be prevented.

In this case, the movement state of the object 51 passing through the detection area 50 can be detected by the output obtained from the frequency difference detection circuit 20. That is, as shown in FIG. 3, since one pulse obtained from one of the output circuits 43 and 44 corresponds to the movement of an object of 10 μm each, the movement is performed by counting the number of pulses corresponding to the movement distance. The distance is obtained. If counters are provided on the output side of the frequency difference detection circuit 20, if the count value of each counter is N, the moving distance L is df × N
Indicated by Further, assuming that the time of moving the distance is T, the moving speed V of the object can be obtained by dividing the time of the distance L by the time T.

According to the present invention, the moving distance of the object can be directly measured with high accuracy without contact. Further, the moving direction and the moving speed can be identified at the same time.

In this embodiment, the signal of the reference frequency is obtained by heterodyne detection of the frequency difference between the laser beams obtained from the half mirrors 5 and 6 by the photoelectric converter 17. A difference signal may be output.

Next, a laser distance measuring apparatus according to a second embodiment of the present invention will be described with reference to FIG. 7. In this embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals, and the details are omitted. I do. Also in the present embodiment, the laser light of the laser light source 1 is split by the beam splitter 2, and the frequencies thereof are made different by the Bragg cells 3, 4 and the Bragg cell driver 7. Now, a mirror 61 is provided on the optical axis of the half mirror 5 so that the first laser beam is reflected and irradiated to the half mirror 62. The second laser beam that has passed through the half mirror 62 is irradiated onto the measurement area as it is, and the reflected light from the object 64 moving on the optical axis of the second laser beam is transmitted to the half mirror 62 via the condenser lens 63. Will be returned. And part of the reflected light is a half mirror
Reflected by 62. Therefore, the difference between the frequencies of the first laser beam and the reflected light is heterodyne-detected by the photoelectric converter 14. The laser beams reflected by the half mirrors 5 and 6 are supplied to a photoelectric converter 17, and a frequency signal of a difference between the driving frequencies of the Bragg cell driver 7 is supplied to a waveform shaping circuit 18 as a reference signal. The structure and operation of the detection circuit for detecting the frequency difference based on the outputs of the photoelectric converters 14 and 17 are the same as those in the first embodiment.

In this embodiment, X is the irradiation direction of the second laser beam.
The moving distance of the object moving in the axial direction can be measured. In this case, in equation (1), θ is about 180.
Since ゜, the interval df corresponding to the interference fringes is λ / 2, that is, about 0.
3 μm, and the resolution of the moving distance can be improved.

〔The invention's effect〕

Therefore, according to the laser distance measuring device of the present invention, it is possible to measure the moving distance of the object without contacting the object and with high accuracy. Further, in the present invention, since the moving distance of an object moving in the direction perpendicular to the irradiation direction with the laser beam of the laser distance measuring device can be measured, the moving distance of a long object such as a thin metal plate can be continuously measured. Can be measured. And when the moving speed of the object changes greatly,
The output frequency obtained by the photoelectric converter also changes correspondingly. However, since the frequency difference detection circuit is entirely composed of a digital circuit, its configuration does not change in accordance with the input frequency, and the distance traveled by counting output pulses from the first or second output terminal. And, it becomes possible to measure the moving direction at the same time.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the overall configuration of a laser distance measuring device according to one embodiment of the present invention, FIG. 2 is a circuit diagram showing the configuration of a frequency difference detection circuit, and FIGS. 3 and 5 show the operation thereof. FIG. 4 is an enlarged view showing the detection area of the present embodiment, FIG. 6 is a time chart showing the operation of the coincidence detecting circuit, and FIG. 7 is a block diagram showing a laser distance measuring apparatus according to the second embodiment of the present invention. FIG. 1 ... laser light source, 2 ... beam splitter, 3,4 ...
Bragg cell, 5, 6, 62… Half mirror, 7… Bragg cell driver, 8, 9… Prism, 10… Aperture, 1
1… Condenser lens, 14,17… Photoelectric converter, 16,18 …… Waveform shaping circuit, 20 …… Frequency difference detection circuit, 21,22… Rising detection circuit, 30 …… RS flip-flop circuit, 31: Match detection circuit, 33: Monostable multivibrator (MM),
41 …… RS flip-flop, 43,44 …… Output circuit, 50…
… Detection area

Claims (1)

(57) [Claims] A laser beam source; a beam splitter for separating the laser beam into first and second laser beams; a Bragg cell for shifting a frequency of at least one of the separated laser beams; An optical means for causing the obtained first and second laser beams to intersect at a single point; and an angle formed by the laser beam in a plane formed by the first and second laser beams in an intersection region of the first and second laser beams. A photoelectric converter that converts scattered light from an object passing in the direction perpendicular to the bisector of the optical signal into an electric signal, a driving frequency detecting unit that outputs a signal of a frequency difference given to the Bragg cell, and the driving frequency detecting unit A first and a second change point detection circuit for detecting a change time point of a reference input signal obtained from the photoelectric conversion signal and a change time point of the photoelectric conversion signal obtained by the photoelectric converter;
An RS flip-flop circuit in which the output of the change point detection circuit is provided as a set and reset input, a match detection circuit for detecting a match between the signals of the first and second change point detection circuits,
Different outputs of the RS flip-flop circuit;
Alternatively, the output of the second change point detection circuit and the output of the coincidence detection circuit are respectively provided, and a signal is output when the coincidence occurs.
A frequency difference detection circuit having a first output circuit and a second output circuit, wherein the moving distance of the object is measured based on output pulses obtained from the first and second output circuits of the frequency difference detection circuit. A laser distance measuring device characterized by the above.