JPH02269903A - Laser distance measuring instrument - Google Patents

Abstract

PURPOSE:To measure the movement distance of a body which passes at right angles to the irradiation direction of a laser beam with high accuracy without touching the body by converting scattered light from the body into an electric signal. CONSTITUTION:The irradiating laser light from a laser light source 1 is split by a beam splitter 2 and one laser beam is shifted in frequency by Bragg cells 3 and 4. Then the 1st and 2nd laser beams irradiate one point by an optical means, so interference fringes are formed to obtain the scattered light. This scattered light is converged and converted 17 photoelectrically to obtain a signal of frequency corresponding to the moving speed of the interference fringes and the conveyance speed of the body. A driving frequency detecting means detects the frequency difference between the laser beams to generate a reference signal and the photoelectric conversion output is supplied to 1st and 2nd change point detecting circuits of a frequency difference detecting circuit 20 as a signal corresponding to the movement distance of the body. Then the movement distance of the body can be measured according to output pulses of the detecting circuit 20.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a distance measuring device that uses laser light to detect the distance traveled by an object.

[Conventional technology]

Conventionally, a distance measuring device that measures the moving distance of an object conveyed along a conveyance path, such as a thin iron plate, in order to cut the object into predetermined lengths, uses a roller that rotates in contact with the iron plate and a roller that is connected to the roller. A rotary encoder is installed,
A device is used that detects the moving distance of an iron plate from a signal obtained from a rotary encoder.

[Problem to be solved by the invention]

However, according to such conventional distance measuring devices,
Since the roller comes into direct contact with the object to be measured, there are significant restrictions depending on the object to be measured, and the use of an encoder has the disadvantage that measurement accuracy cannot be increased very much.

The present invention has been made in view of the problems of conventional distance measuring devices, and its technical problem is to be able to detect the speed of an object with high accuracy and without contacting the object. .

[Means to solve the problem]

The present invention is a distance measuring device that detects the moving distance of an object using a laser beam, and includes a laser beam source, a first laser beam source, and a second laser beam source.
a beam splitter that separates the laser beam into a second laser beam; a Bragg cell that shifts the frequency of at least one of the separated laser beams; an optical means for causing the second laser beam to intersect at one point; A photoelectric converter that converts scattered light from an object that passes through the intersection area of the second laser beam in a direction perpendicular to the laser beam irradiation direction into an electrical signal, and a drive frequency detection that outputs a frequency difference signal given to the Bragg cell. means, a first and second change point detection circuit for detecting the change points of the reference input signal obtained from the drive frequency detection means and the photoelectric conversion signal obtained from the photoelectric converter, respectively; The output of the second change point detection circuit is given as the bit and reset input to the RS flip-flop circuit\first. a coincidence detection circuit that detects coincidence of signals of a second circuit point detection circuit;
Different outputs of the R379717071 circuit, the output of the first or second change point detection circuit, and the output of the coincidence detection circuit are respectively provided, and the first... a frequency difference detection circuit having a second output circuit, and a first output circuit of the frequency difference detection circuit. This method is characterized in that the moving distance of the object is measured based on the output pulse obtained from the second output circuit.

[Effect]

According to the present invention having such features, the laser light emitted from the laser light source is separated by the beam splitter, and the frequency of one of the laser beams (one of the laser beams is shifted by the Bragg cell. Since the laser beam is irradiated to one point by optical means,
In the intersection region, interference fringes are generated that move at a speed corresponding to the frequency difference between the laser beams. Therefore, scattered light can be obtained by transporting the object to be measured perpendicularly to the laser beam within the area of the interference fringes. By condensing this scattered light and photoelectrically converting it, a signal with a frequency corresponding to the moving speed of the interference fringes and the ll'ff moving speed of the object is obtained.

On the other hand, the frequency difference between the laser beams is detected by the drive frequency detection means and used as a reference signal, and the photoelectric conversion output is used as a signal corresponding to the moving distance of the object. It is applied to the second change point detection circuit. If you do this, number 1. R379717 by the output signal of the second change point detection circuit
071 circuit will be set or reset. Therefore, if the output of the other change point detection circuit is included between the outputs of either change point detection circuit, the output of the other change point detection circuit is outputted to the outside via the first or second output circuit. Output. Therefore, a signal having a period corresponding to the frequency difference of the input signals is outputted from the first or second output circuit depending on the magnitude thereof. The distance traveled by the object is then measured based on the output pulses obtained from these output circuits.

[Explanation of Examples]

FIG. 1 is a block diagram showing the configuration of a distance measuring device according to an embodiment of the present invention. In this figure, a laser light source 1 is a laser light source that emits monochromatic light, and uses a helium neon laser, for example.

The laser light emitted from the laser light source 1 is given to the beam splitter 2, and the first . The laser beam is separated into a second laser beam. The first of these. Bragg cells 3 and 4 and half mirrors 5 and 6 are provided on the optical axis of the second laser beam. Bragg cells 3 and 4 are Bragg cell driver 7
The laser beams are driven at different frequencies, for example, 81 MIIz and 80 MIIz, respectively, to change the frequency of the incident laser beam. The first and second laser beams that have passed through the half mirrors 5 and 6 are provided with predetermined optical means,
In this embodiment, the prisms 8 and 9 intersect at a predetermined point.

Instead of the prism 8.9, a lens may be used to cause the laser beams to intersect. At this position, as shown in FIG. 3, the object to be measured for distance is moved in the irradiation direction, that is, in FIG. Also prism 8
．． An aperture 10 having an opening in the center and a condensing lens 11 are provided in the middle of the lens 9 . The aperture 10 and the condensing lens 11 transfer the scattered light obtained from the object to the optical fiber 12.
give to

The optical fiber 12 provides the scattered light to the photoelectric converter 14 of the frequency measurement circuit section 13. The photoelectric converter 14 converts this scattered light into an electrical signal and supplies it to the AGC circuit 15 .

The AGC circuit 15 automatically controls the level of the received scattered light so that there is little change, and gives its amplified output to the waveform shaping circuit 16.On the other hand, the laser light reflected by the half mirror 5.6 is is also given to a photoelectric converter 17 such as a photodiode.The photoelectric converter 17 outputs an electrical signal with a difference in these frequencies, and the output is used as a reference signal by the waveform shaping circuit 1 of the frequency measuring circuit 13.
given to 8. Waveform shaping circuits 16 and 18 are respectively AGC
It converts the output and photoelectric conversion output into a square wave, and the output is given to the frequency difference detection circuit 20. Here, the half mirrors 5, 6 and the photoelectric converter 17 constitute drive frequency detection means for outputting a frequency difference signal applied to the Bragg cell 3.4.

Now, FIG. 2 shows a detailed block diagram of the frequency difference detection circuit 20, in which the outputs of the waveform shaping circuits 16 and 18 are applied to a pair of rising edge detection circuits 21 and 22 through input terminals 20a and 20b, respectively. The rising edge detection circuits 21 and 22 detect the change point of the input signal. Since it is the second change point detection circuit and has the same configuration, the rise detection circuit 21 will be explained. The rise detection circuit 21 has a D-type flip-flop 23 connected to its input end, and its Q output is applied to the D-input end and clock input end of D-type flip-flops 24 and 25, respectively. Flip-flop23.
A clock signal having a sufficiently faster clock than the input signal is applied from a clock signal source 26 to the clock input terminal of 24. The output of the flip-flop 24 is applied to the clear input terminal of the flip-flop 25, and the Q output of the flip-flop 25 is applied to the RS flip-flop circuit 30. Flip-flop 27 of rising edge detection circuit 22
-29 also have a similar configuration. The Q output terminal of the flip-flop 29 is connected to the RS flip-flop circuit 30
and the AND circuit 32 of the coincidence detection circuit 31. The coincidence detection circuit 31 detects coincidence of the outputs of the rising edge detection circuits 21 and 22, and the output of the AND circuit 31 is applied to a monostable multi-by-break (hereinafter referred to as MM) 33 having a fixed operating time. Inverters 34a, 34b, 35a, 35b and AND circuits 36.37 are provided at the input end of the RS Frisopfromp circuit 30 for delaying the input signals, respectively, and ant circuits 36.3.
7 outputs are applied to flip-flops 38 and 39, respectively. The output of MM33 is given to AND circuits 36 and 37 as gate signals. flip flop 38.3
Reference numeral 9 is for inverting the human input signal, and each Q output is connected to an R circuit configured with NAND circuits 40a and 40b.
It is given as ≦ and R input of the S flip-flop 41. The output (?:L output) of the NAND circuit 40b is provided as a clear input to the flip-flop 38 and also as a clear input to the flip-flop 39 via the inverter 42. Now, the Q and output of this RS flip-flop 41 are the 1st. Second output circuit 43.44
given to. Output circuits 43 and 44 are AND circuits 4 and 4, respectively.
3a and 44a, and the rise detection circuits 21 and 2
2 and the output of the coincidence detection circuit 31 are output to the output circuit 43.2.
44. Output circuits 43 and 44 are output terminals 20
c and 20d, these AND signals are outputted as a pair of signals to the frequency difference detection circuit 20.

Next, the operation of this embodiment will be explained. First, a laser beam emitted from a laser light source 1 is transmitted to a first beam splitter 2. The laser beam is separated into a second laser beam. The frequencies of these laser beams are then shifted by Bragg cells 3 and 4, respectively. Then, the signal is applied to the photoelectric converter 17 via the half mirrors 5 and 6, and is transmitted to the photoelectric converter 17 by heterodyne detection. As shown in FIG. A reference signal A having a frequency of is obtained.This signal is provided as a reference signal A' to the frequency difference detection circuit 20 via the waveform shaping circuit 18 as a reference human power.

A pair of laser beams is irradiated onto the detection area 50 by a prism 8.9. FIG. 4 shows the detection area 50. That is, it is an enlarged view showing the intersecting region of a pair of laser beams. In the intersecting region, as shown, interference fringes are formed parallel to the irradiation direction of the laser beams and move at a constant speed. The object 51 is moved into this detection area in the Y direction perpendicular to the light irradiation direction. At this time, the first. Let the angle formed by the second laser beam be θ,
If the wavelength is λ, interference fringes with a predetermined width are formed in the detection region. The interval df of this interference fringe is calculated by the following formula (1
).

λ For example, the wavelength of the laser light from the laser light source 1 is 633 nm.

When the intersection angle θ is 3.6°, the interval df of interference fringes is approximately 1
It becomes 0 μm. In the detection region 50, the interference fringes move in the Y-axis direction at a speed corresponding to the frequency difference IMllz, assuming that the frequencies of the drive signals given to the Bragg cells 3.4 are 80MIIz and 81Ml1z, respectively. That is, the interference fringes move at a speed of 10 m/s. Therefore, when the object to be detected 51 is stationary in the detection region 50, the photoelectric conversion output of the scattered light obtained from the object 51 has a frequency component of IMHz. Furthermore, if the object 51 moves in the positive direction of the Y-axis, IMt
Scattered light with a frequency lower than lz is obtained. Furthermore, if the object 51 moves in the negative direction of the Y-axis, scattered light with a frequency higher than 1M1lz will be obtained corresponding to the direction of movement. Assuming that the signal (moving signal) of this scattered light is B and its frequency is Fsg, the photoelectric converter 14 is
A movement signal as shown in bl is obtained. This signal is AG
The moving signal B' is transmitted through the C circuit 15 and the waveform shaping circuit 16.
The signal is applied to the frequency difference detection circuit 20 as a signal.

Now, the rise detection circuits 21 and 22 are shown in FIG. 5(a), respectively.
Tb) with a slightly different frequency Fref as shown in
, Fsg signals A' and B' are applied. In this case, the rising edge detection circuits 21 and 22 are used as shown in FIG. 5(C).

(As shown in d+, a signal for one clock is output at the time of each rise. This signal is sent to the RS flip-flop via the inverter 34.AND circuit 36 or inverter 35.AND circuit 37 of the RS flip 70 tube circuit 30. 41 as a set input and a reset input.
, and the RS flip-flop 41 is set at the falling edge t2 of the rising edge detection circuit 22.
A signal that is reset to 1 is output. Therefore, the RS flip-flop 41 is set and reset by this, and its Q and output terminals are shown in FIG. 5(e).

(A signal as shown in fl will be output.

Now, if the object to be measured is moving in the negative direction of the Y-axis in the detection area 50, the frequency Fsg of the movement signal B is higher than IMllz, and the period is long as shown in FIG. As shown, after the RS flip-flop 41 is reset by the output of the rise detection circuit 22, the output from the rise detection circuit 22 between the time when it is set again by the output of the rise detection circuit 21 and 4 (FIG. 5fd) A pulse signal p as shown in may be output. In this case, the output of the rising edge detection circuit 22 is applied to the output circuit 44 by the output of the flip-flop 41. Therefore, this signal causes an output pulse p as shown in FIG. 5 (hl) to be outputted via the output circuit 44. .That is, the frequencies of input signals A and B are Fref > Fsg
In this case, one pulse, that is, a frequency signal of Fref -Fsg is obtained from the output circuit 43 every one cycle, and 2
If Fref<Fsg, the output circuit 4
1 pulse every time one cycle deviates from 4, that is, Fsg-Fre
A frequency signal of f is obtained.

Next, the output signals from the rising edge detection circuits 21 and 22 may match. At this time, the rising edge detection circuit 21.22
If the output is directly given to the RS flip-flop 41, the output will be undefined, and there is a possibility that the output will appear from either 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. When the signals shown in FIGS. 6A and 6B are applied to the RS flip-flop circuit 30 from the rising edge detection circuits 21 and 22, the RS flip-flop circuit 30 is activated by the falling edge of the rising edge detection circuit 21 at time t5. 31 is sent, and the RS flip-flop 41 is operated to be reset at time L6 by the fall of the rise detection circuit 22.Now, between times t and t8, outputs are simultaneously given from the rise detection circuits 21 and 22. , the coincidence is detected by the AND circuit 32 of the coincidence detection circuit 31, and the MM 33 operates for a certain period of time.Therefore, a signal as shown in FIG. 6(d) is obtained from the coincidence detection circuit 31, and this signal causes the AND circuit 36 .37 is prohibited from being input to the flip-flops 38 and 39. Also, the output of the coincidence detection circuit 31 provides a prohibited input to the output circuits 43 and 44. Therefore, at this time, no output is provided from the output circuit 44. Since the RS flip-flop 41 maintains the reset state, a pulse as shown in FIG. Counting can be prevented.

In this way, the moving 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, one pulse obtained from either output circuit 43 or 44 is
Since it corresponds to the movement of an object of 0 μm, the movement distance can be obtained by counting the number of pulses corresponding to the movement distance.

Also, if a counter is provided on the output side of the frequency difference detection circuit 20, and the count value of each counter is N, the moving distance will be d.
It is indicated by fXN. Also, if the time taken to move this distance is T, then by dividing the distance by the time T, the moving speed (■) of the object can be obtained.

As described above, according to the present invention, the moving distance of an object can be directly measured with high accuracy in a non-contact manner. Moreover, the moving direction and moving speed can also be identified at the same time.

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

Next, a laser distance measuring device according to a second embodiment of the present invention will be explained with reference to FIG. In this example, the first
The same parts as those in the embodiment are given the same reference numerals, and detailed configurations thereof will be omitted. In this embodiment as well, the laser light from the laser light source 1 is separated by the beam sub-block 2, and its frequencies are made to differ by the Bragg cell 3.4 and the Bragg cell driver 7. Now, half mirror
A mirror 61 is provided on the optical axis of the laser beam 5 to reflect the first laser beam and irradiate it onto the half mirror 62.

In addition, the second laser beam that has passed through the half mirror 62 is directly irradiated onto the measurement area, and the reflected light from the object 64 moving on the optical axis of the second laser beam is directed to the half mirror 62 via the condensing lens 63. be returned. And the reflected light 1
portion is reflected by the half mirror 62. Therefore, the first
The difference in frequency between the laser beam and the reflected light is detected by the photoelectric converter 14.
This results in hetero gain detection. Also, the laser beam reflected by the half mirrors 5 and 6 is sent to a photoelectric converter 17.
A frequency signal representing the difference between the drive frequencies of the Bragg cell driver 7 is supplied to the waveform shaping circuit 18 as a reference signal. The configuration and operation of the detection circuit that detects the frequency difference based on the outputs of the photoelectric converters 14 and 17 are the same as in the first embodiment described above.

In this embodiment, it is possible to measure the moving distance of an object moving in the X-axis direction, which is the irradiation direction of the second laser beam. In this case, in equation (1) above, θ is approximately 180
Therefore, the interval df corresponding to the interference fringes is λ/2, that is, approximately 063 μ..., and the resolution of the moving distance can be improved.

〔Effect of the invention〕

Therefore, according to the laser distance measuring device of the present invention, it is possible to measure the moving distance of an object with high accuracy without contacting the object. In addition, in the present invention, since it is possible to measure the moving distance of an object that moves in a direction perpendicular to the irradiation direction of the laser beam of this laser distance measuring device, it is possible to continuously measure the moving distance of a long object such as a thin metal plate. can be measured.

And if the moving speed of the object changes significantly, the output frequency available to the photoelectric converter will also change accordingly. However, since the frequency difference detection circuit is entirely composed of digital circuits, its configuration does not change in response to the human frequency, and the distance traveled can be determined by counting the output pulses from the first or second output terminal. and the direction of movement can be measured simultaneously.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the overall configuration of a laser distance measuring device according to an embodiment of the present invention, Fig. 2 is a circuit diagram showing the structure of a frequency difference detection circuit, and Figs. 3 and 5 show its operation. A time chart, FIG. 4 is an enlarged view showing the detection area of this embodiment, FIG. 6 is a time chart showing the operation of the coincidence detection circuit, and FIG. 7 is a block diagram showing the laser distance measuring device according to the second embodiment of the present application. It is a diagram. ■--Laser beam iff 2--Beam splitter 3.4--Bragg cell 5.6, 62-
・−・Half mirror −° 7・−−−1−−Bragg cell driver 8, 9−−−−−−−−Prism 1
0・-------Aperture It-----1・Condensing lens 14, 1'l----Photoelectric converter 16.18-・----・Waveform shaping circuit 20・-・・
--- Frequency difference detection circuit 21.22 --- Rise detection circuit 30 --- RS flip-flop circuit
31------- Coincidence detection circuit 33-- Monostable multi-pipe rake (MM) 4l----
---RS flip-flop 43.44-----Coincidence output circuit 50--Detection area patent applicant
Representative of Nippon Kagaku Kogyo Co., Ltd. Patent attorney Yoshiki Okamoto (and 1 other person) Figure 1 3.4-------butsu, Risel 5.6----H half mirror 1B---- ---IFI Bunmaki:,! '12th Takugun 3rd
Figure 4

Claims (1)

[Claims] (1) A laser light source, a beam splitter that separates the laser beam into first and second laser beams, a Bragg cell that shifts the frequency of at least one of the separated laser beams, and a laser beam obtained through the Bragg cell. an optical means for causing the first and second laser beams to intersect at one point; and converting scattered light from an object passing through the intersection area of the first and second laser beams in a direction perpendicular to the irradiation direction of the laser beams into an electrical signal; a photoelectric converter for converting, a driving frequency detecting means for outputting a frequency difference signal given to the Bragg cell, and a change point in the reference input signal obtained from the driving frequency detecting means and the photoelectric conversion signal obtained from the photoelectric converter. first and second change point detection circuits that respectively detect the first and second change point detection circuits;
an RS flip-flop circuit to which the output of the second change point detection circuit is given as a set and reset input;
, a coincidence detection circuit that detects coincidence of the signals of the second change point detection circuit, different outputs of the RS flip-flop circuit, an output of the first or second change point detection circuit, and an output of the coincidence detection circuit. and a frequency difference detection circuit having first and second output circuits that are given to each other and output a signal when they match, and outputs obtained from the first and second output circuits of the frequency difference detection circuit. A laser distance measuring device characterized by measuring the moving distance of the object based on pulses.