JP2529616B2 - Distance measuring device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a distance measuring device for measuring a distance to an object using laser light, and more particularly to distance measuring using laser light modulated by a pseudo random signal. is there.

[Prior Art] Measuring the absolute distance to an object by using laser light is useful as distance measurement for civil engineering and construction, distance measurement for collision prevention of moving objects, and visual information for remote control of robots. It has a wide range of applications such as distance measurement and distance measurement to measure the degree of wear of refractory bricks inside a converter or ladle inside a ladle used in the steelmaking process.

The laser distance measuring methods are roughly classified according to the laser light modulation method, and there are a phase comparison method, a pulse modulation method, and a pseudo-random signal modulation method. Next, those conventional techniques will be described.

(1) Phase comparison method Regarding the phase comparison method, for example, there is a method described in JP-A-62-75363. This will be described with reference to FIG.

The laser light from the laser oscillator 21 is split into two optical paths by the half mirror 27, and one of them is incident on the acousto-optic light modulator 22.
The acousto-optic light modulator 22 generates diffracted light whose frequency is shifted by the interaction with the high frequency signal from the high frequency oscillator 23, and irradiates the object 17 via the reflecting mirror 44. Detector
At 43, the laser light is monitored. The reflected light from the object 17 enters the heterodyne detector 40 by the half mirror 28. On the other hand, the other laser light split by the half mirror 27 passes through the half mirror 28 and enters the heterodyne detector 40 as reference light. The heterodyne detector 40 heterodyne-detects a difference frequency signal between the reflected wave from the object and the reference wave from the half mirror 28 and outputs it. Since the phase of the difference frequency signal is delayed in proportion to the distance to the object, if the phase detector 42 detects the phase difference between the reference signal from the high frequency oscillator 23 and the difference frequency signal, the distance to the object can be obtained. .

(2) Pulse Modulation Method Regarding the pulse modulation method, for example, there is a method described in JP-A-58-76784. This will be described below with reference to FIG.

The laser light from the laser oscillator is 2 by the half mirror 27.
The light is divided into optical paths, one of which is incident on the acousto-optic modulator 22 driven by the high-frequency oscillator 23, passes through the striation 29 as diffracted light whose frequency is shifted, is condensed by the lens 54, and is incident on the optical modulator 24. To do. In the optical modulator 24, the incident laser light is pulse-modulated by the pulse signal from the pulse generator 50, and the pulse-modulated laser light is transmitted by the transmission optical system 11
The object 17 is irradiated with the light passing through. The reflected wave from the object 17 passes through the receiving optical system 12 and the half mirror 28, and the light receiving element.
Incident on 25. The other laser beam split by the half mirror 27 is reflected by the half mirror 28 and enters the light receiving element 25 as reference light. The light receiving element 25 heterodyne-detects the reflected wave having the pulse waveform from the object with the reference light, and outputs the pulse waveform of the difference frequency signal between them. The pulse waveform of this difference frequency signal is amplified by the intermediate frequency amplifier 51 and then detected by the detector 52 to be a pulse waveform. Since this pulse waveform is delayed by the propagation time of the laser light to the target object 17, it is obtained by receiving the pulse generation time of the original pulse generator 50 and the reflected wave from the target object 17 in the information processing circuit 53. The time to the time of the pulse waveform is measured and the distance to the object 17 is obtained.

(3) Pseudo Random Signal Modulation Method Regarding the pseudo random signal modulation method, for example, Japanese Patent Laid-Open No.
There is a method described in JP-A-166281. This will be described below with reference to FIG.

The laser light output from the laser oscillator 21 is intensity-modulated by the modulator 24 with the pseudo-random signal generated by the pseudo-random signal generator 60, and is irradiated onto the object 17. The reflected light from the object 17 is received by the light receiving element 25, converted into an electric signal, and the waveform thereof is stored in the high speed storage device 62. The delay correlator 61 calculates the correlation with the received pseudo random signal stored in the high speed storage device 62 while sequentially delaying the pseudo random signal generated by the pseudo random signal generator 60, and calculates the result. Output to the display recorder 63. The phase of the pseudo-random signal obtained by being received as the reflected light from the object 17 is delayed by the propagation time of the light to the object 17, and thus is generated by the pseudo-random signal generator 60.
When the phase of the pseudo random signal used as the transmission signal is sent for the propagation time, the correlation between the two becomes large. Therefore, the distance to the object 17 can be obtained by measuring the delay time that maximizes the correlation.

[Problems to be Solved by the Invention] Each of the above-described conventional laser distance measuring devices has the following problems.

(1) Phase comparison method First, since the phase comparison method is a method of transmitting a continuous wave, if there is unnecessary light such as reflected light or leaked light from a place other than the object, it cannot be distinguished and a large error occurs. There is a problem that causes. In particular, when the sensitivity is increased and even weak reflected light can be detected, even weak leak light from the optical system that irradiates the laser light is detected as being incident on the receiving optical system, There is a possibility that the reflected light from the laser light is superposed and interferes with each other, the phase is disturbed, and a large error occurs.

(2) Pulse modulation method Since the pulse modulation method is a method of sending an intermittent wave, even if there is unnecessary light from other than the object, it can be distinguished from the reflected light from the object in terms of time, The power of light is small on average, and increasing the peak power of the laser light to be sent is also limited due to device or safety issues. There is a problem that you cannot do it. Therefore, when the reflectance of the object is low, a reflective tape having a large number of minute reflectors attached to the surface of the tape may be attached to the object in order to increase the amount of reflected light, but this work is complicated. There is also a problem that becomes.

(3) Pseudo-random modulation method The pseudo-random modulation method is a method of transmitting a continuous wave and has a high sensitivity, and even if unnecessary light from other than the target object is present, it is targeted in terms of the delay time when performing the correlation calculation. Although it is possible to distinguish the reflected wave from the object and the unnecessary wave, there are problems that the configuration of the device is complicated and the signal processing time is delayed. That is, the high-speed storage device and the delay correlation device are specifically configured with analog circuits or digital circuits. In the former case, the number of used elements is extremely large and the configuration is complicated, and in the latter case, the complex circuit is complicated. Since arithmetic processing is executed, there is a problem that the processing speed becomes slow.

It is an object of the present invention to provide a distance measuring device that solves the above-mentioned problems such as sensitivity, influence of unnecessary light, complexity of device configuration, and signal processing time.

[Means for Solving the Problem] A distance measuring device according to one aspect of the present invention has a means for generating a first pseudo-random signal having a clock frequency of f1 and the same pattern as the first pseudo-random signal. , Means for generating a second pseudo-random signal having a clock frequency f2 slightly different from the clock frequency f1,
A first multiplier that multiplies the first pseudo-random signal and the second pseudo-random signal, a laser light generation unit that generates laser light, and an output of the laser light generation unit based on the first pseudo-random signal. Modulating means for modulating, irradiating means for irradiating the object with the output of the modulating means, light receiving means for receiving the reflected light from the object and converting it into an electric signal, the output of this light receiving means and the second pseudo. A second multiplier that multiplies with a random signal, a time difference between the time series pattern output from the first multiplier and the time series pattern output from the second multiplier is measured, and based on the time difference, And distance measuring means for obtaining the distance to the object. And
The laser light generating means includes a laser light source, a high frequency generator,
An acousto-optic light modulator driven by the output of the high-frequency generator and receiving the output light of the laser light source as input, and the light receiving means, and a branching means for branching a part of the output laser light of the laser light source, And a light receiving element that combines the output light from the object and the reflected light from the object to perform heterodyne detection and output as an electric signal. The distance measuring means includes a first low-pass filter that inputs the output of the first multiplier and performs low-pass filtering, and a second low-pass filter that inputs the output of the second multiplier and performs low-pass filtering. , Measuring means for measuring the time between the time when the maximum value of the output signal of the first low-pass filter occurs and the time when the maximum value of the output signal of the second low-pass filter occurs.

A distance measuring device according to another aspect of the present invention uses a semiconductor laser instead of the above laser light generating means and modulating means, and drives this semiconductor laser with a first pseudo random signal signal to directly A laser beam whose intensity is modulated is obtained.

A distance measuring device according to still another aspect of the present invention, in each of the distance measuring devices described above, is provided with biaxial direction measuring means for measuring the irradiation direction and the receiving direction of the laser beam,
The 3D shape can be measured.

[Operation] In the present invention, the first and second pseudo-random signals are code strings having the same pattern, but since the clock frequencies of both signals are slightly different, the phases of both signals are Even if they match, they will gradually shift over time,
If this shifts by one code or more, there is no correlation between the two signals, the multiplication result of both signals becomes random, and no output is generated in the low-pass filter. When the time further passes and the phase between the first and second pseudo-random signals deviates by exactly one period of one pseudo-random signal, the phases of both again match and the correlation between both signals becomes maximum. In this case, the peak signal is obtained when the output of the multiplier passes through the low pass filter. This phenomenon is repeated and a periodic pulse signal is obtained at the output of the low pass filter. The pulse obtained by the direct multiplication of the first and second pseudo random signals is used as the time reference signal, and on the other hand, it is obtained from the product value of the received signal of the laser reflected wave from the object and the second pseudo random signal. By detecting the difference between the pulse generation time of the low-pass filter and the pulse generation time, the distance to the object can be measured with a simple device configuration.

 The above description is formulated as follows.

The clock frequency of the first pseudo-random signal is f1, the second
The clock frequency of the pseudo random signal is set to f2, and the pattern of each pseudo random signal is set to be the same. Where f1
> F2 Letting T _B be the period at which the reference signal obtained by correlating the transmitted pseudo-random signal and the second pseudo-random signal has the maximum value, the first pseudo-random signal and the second pseudo-random signal included in this T _B are included. The difference in the wave number of the pseudo random signal becomes the wave number N of exactly one cycle. That is, T _B · f1 = T _B · f2
It becomes + N. Here, rearranging the above equation, T _B is given by the following equation (1).

T _B = N / (f1−f2) (1) From this equation (1), it is understood that the smaller the difference between the two clock frequencies, the larger the period T _{B at} which the reference signal becomes the maximum value.

Next, the propagation time until the laser light whose amplitude is modulated by the first pseudo random signal is transmitted, reflected by the object, and received again is τ, and this received signal is referred to as the second pseudo random signal. The time when the pulse-like signal of the object detection signal is obtained, which is obtained by multiplying and passing through the low-pass filter,
Letting T _{D be} the time difference measured from the generation time of the pulse-shaped signal of the time reference signal, the wave number of the second pseudo random signal generated during this T _D is the same as that of the first pseudo random signal generated during T _D. Since the number of waves is small, the following equation holds.

T _D · f2 = T _D · f1 − τ · f1 Organizing the above equation, T _D is given by the following equation (2).

T _D = τ · f1 / (f1−f2) (2) That is, the propagation time τ is measured as T _D which is expanded by f1 / (f1−f2) times or slowed. Since the measurement time is extended in this way, it can be said that the present invention is essentially a device suitable for short distance measurement. Here, the propagation time τ is τ = 2x / v, where v is the propagation velocity and x is the distance to the object. Therefore, the following expression (3) is obtained from the expression (2).

The distance x can be measured by measuring the time difference T _D by the above formula (3).

In this way, the measurement time between the time reference signal and the object detection signal is greatly expanded on the time axis, so that the distance to the object can be accurately measured from a short distance.
In addition, even if unnecessary light such as leaked light from the optical system exists,
The pulse generation time on the detection signal due to this unnecessary light is different from the pulse generation time due to the reflected light from the target object, so it is possible to distinguish between the two, and the stable distance measurement of the target object is not affected. Is possible.

[Embodiment] FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention. In the figure, 1 and 2 are clock generators, and 3
Is a pseudo random signal generator that outputs a first pseudo random signal, and 4 is a pseudo random signal generator that outputs a second pseudo random signal. Clock generator 1 is, for example, its frequency f ₁ is f ₁ = 100.004MH _Z, the clock generator 2
The frequency f ₂ a f ₂ = 99.996MH _Z, it retains a stable frequency by a crystal oscillator. The pseudo random signal generators 3 and 4 have exactly the same circuit configuration and generate an M-sequence signal which is one of pseudo random signals by a 7-bit shift register. A semiconductor laser 9 has a wavelength of 780 nm, for example, and outputs a laser beam whose intensity is modulated by a signal from the pseudo random signal generator 3. This laser light is applied to the object 17 via the lens of the transmission optical system 11. The reflected wave from the object 17 enters the photodiode 10 through the lens of the receiving optical system 12, the optical filter, etc., and the intensity of light is converted into an electric signal to obtain a received signal. This received signal is multiplied by the second pseudo random signal output from the pseudo random signal generator 4 by the balanced mixer 8, and this multiplied signal is input to the distance converter 13 as an object detection signal via the low pass filter 6. To be done.

On the other hand, the first and second pseudo random signals output from the pseudo random signal generators 3 and 4 are multiplied by the balanced mixer 7, and the multiplied signal is passed through the low pass filter 5 and converted into distance as a time reference signal. Input to the device 13. The distance converter 13 has a function of detecting the peak of the object detection signal and the peak of the time reference signal, measuring the generation time difference between these peaks, and thereby converting the distance to the object 17. There is.

As described above, the first and second pseudo-random signals generated by the pseudo-random signal generators 3 and 4 are code strings having the same pattern, but these two are different due to the difference in clock frequency for driving them. The periods of the signals are slightly different. When the phases of both signals match at a certain point in time, the phases gradually shift with the passage of time, and if they shift by more than one sign of the signals, the correlation between these two pseudo random signals disappears. If there is no phase shift correlation between the received signal of the reflected wave of the laser light intensity-modulated by the first pseudo random signal from the object 17 and the second pseudo random signal, this 2 The result of the multiplication of the two signals by the balanced mixer 8 becomes a random signal and has no DC component, so the output signal of the low-pass filter 6 is a zero value.

When the time further passes and the phase between these first and second pseudo-random signals deviates by exactly one period of one pseudo-random signal, both phases match and the correlation between the two signals is Since it becomes the maximum, a peak signal is obtained when the multiplication output of the balanced mixer 8 passes through the low pass filter 6. FIG. 2 (a) is a diagram showing the input / output signal of the low-pass filter 6, but the same applies to the low-pass filter 5 described later.

The phenomenon in which the phases coincide with each other is repeated at regular intervals, and a periodic pulse signal as shown in FIG. 2B is obtained as a detection signal of the reflected wave of the object 17. on the other hand,
To set the time reference signal for measuring the time when the object detection signal is obtained, the first pseudo random signal and the second pseudo random signal are set.
By directly multiplying the pseudo-random signal by the balanced mixer 7 and extracting the time-series pattern that is the multiplication result via the low-pass filter 5, a pulse-like signal having the same period as the object detection signal is obtained. The time reference signal shown in FIG.

Therefore, the time from the pulse generation time of the time reference signal to the pulse generation time of the object detection signal is a distance proportional to the round-trip propagation time of the laser light to the object 17 between the transmission optical system 11 and the reception optical meter 12. Obtained as information, the distance converter 13 calculates the distance to the object 17.

Further, in this embodiment, the transmission optical system 11 and the reception optical system 12
Detects the direction in which the laser beam is emitted and receives the laser beam by the angle information from the biaxial angle measuring device using two rotary encoders, that is, the θ direction meter 14 and the φ direction meter 15, and the signal processing unit 16 The object 17 can be measured as a three-dimensional shape.

By the way, in this embodiment, the distance measurement accuracy is about
At 15 mm, the response speed was 0.1 seconds per point, and the distance could be measured.

FIG. 3 is a block diagram showing the configuration of a distance measuring device according to another embodiment of the present invention. In this embodiment, pseudo-random signal processing is applied to a laser range finder of the heterodyne detection type to further increase the sensitivity. In the figure, the clock frequency of the clock generator 1 is, for example,
200.010MH _Z, the clock frequency of the clock generator 2 is 200.
Is 000MH _Z. The pseudo random signal generators 3 and 4 have the same circuit configuration and generate an M-sequence signal which is one of pseudo random signals by an 8-stage shift register. Laser oscillator 21
Is a He-Ne laser oscillator, and the output laser light is split into two directions by a half mirror 27, and one of them is incident on an acousto-optic modulator 22 driven by a high frequency oscillator 23. Here, the diffracted light shifted by the high-frequency frequency passes through the slit 29 and enters the optical modulator 24. In the optical modulator 24, the incident laser light is intensity-modulated by the M-sequence signal generated by the pseudo random signal generator 3, and is irradiated onto the object 17 via the transmission optical system 11.

The laser beam reflected by the object 17 is received by the receiving optical meter 12, enters the light receiving element 25 through the half mirror 28, heterodyne-detects the received laser beam, and has an amplitude corresponding to the intensity of the received laser beam. A high-frequency electrical signal having is obtained. The amplitude-modulated high-frequency signal is detected by the detector 26, multiplied by the M-sequence signal generated by the pseudo-random signal generator 4 by the balanced mixer 8, and passed through the low-pass filter 5 to detect the distance as an object detection signal. Input to the converter 13. On the other hand, the outputs of the pseudo random signal generators 3 and 4 are multiplied by the balanced mixer 7 and input to the distance converter 13 as a time reference signal via the low pass filter 6. The distance converter 13 detects the peaks of the object detection signal and the time reference signal, and measures the difference in their generation time,
Convert this to a distance.

Also in this embodiment, the θ direction meter 14 and the φ direction meter 15 to which a rotary encoder is applied to measure the directions of the transmission and reception optical systems are provided, and biaxial angle information is input to the signal processing unit 16. It The signal processing unit 16 can measure the three-dimensional shape of the object 17 from this angle information and the calculated distance value of the distance converter 13.

In addition, in this embodiment, the distance measurement accuracy is about 10 mm.
Then, the response speed was 0.14 seconds per point, and the distance could be measured.

By the way, the biaxial goniometers 14 and 15 shown in FIGS.
The angle information obtained by is combined with the distance information obtained by the distance measuring device and used to measure the three-dimensional shape as follows.

FIG. 4 (a) is a side view of the entire laser rangefinder, FIG. 4 (b) is a top view thereof, FIG. 4 (c) is a front view thereof, and FIG. It is explanatory drawing showing a coordinate system. In the figure, 14 is the θ direction angle meter, 15 is φ
It is a directional angle meter, and is a highly accurate incremental rotary encoder that generates 360,000 pulses per revolution. Reference numeral 74 denotes a laser rangefinder main body (containing the circuit configuration of FIG. 1 or FIG. 3), which emits laser light in the direction of the arrow and receives it to perform distance measurement to the object. 75 is a stand.
Reference numeral 76 is a yoke for supporting the laser rangefinder main body 74 so that it can rotate in the θ direction. The yoke itself is a φ direction angle meter 15
You can rotate on.

For example, if distance measurement is performed in a certain direction (θ, φ) and r is obtained as a measurement value of the distance to the object, the signal processing unit 16 causes the three-dimensional position (x, y, z) of the object. Is calculated by the following formula.

x = r · cos θ · cos φ y = r · cos θ · sin φ z = r · sin θ By repeating the above measurement and calculation while scanning θ and φ, the three-dimensional shape of the object is (x, y, z ) It can be obtained as coordinate information.

As described above, according to the present invention, the patterns are the same,
Since a pseudo-random signal with a slightly different frequency is applied to the laser distance measuring device to measure the distance, unnecessary light is distinguished on the time of the object detection signal and its influence is eliminated, so the sensitivity is high, And the signal processing time until the object detection signal is obtained is short, the distance can be measured in real time, and the measurement time is extended as described above, so that the device can be realized by the low-speed circuit element, It is possible to reduce the size and cost of the device.

[Brief description of drawings]

1 is an apparatus configuration diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the operation of FIG. 1, FIG. 3 is an apparatus configuration diagram showing another embodiment of the present invention, Figure 4 (a),
(B), (c), (d) are side views of the entire laser rangefinder,
FIG. 4 is an explanatory view showing a top view, a front view, and a coordinate system of laser light irradiation and light receiving directions. FIG. 5, FIG. 6 and FIG. 7 are block diagrams showing a distance measuring device according to the prior art. 1,2 …… Clock generator, 3, 4 …… Pseudo random signal generator, 5, 6 …… Low pass filter, 7, 8 …… Balanced mixer, 9 …… Semiconductor laser, 10 …… Photo diode, 11
...... Transmission optical system, 12 …… Reception optical system, 13 …… Distance converter, 14 …… θ direction meter, 15 …… φ direction meter, 16 …… Signal processing unit, 17 …… Target object, 21 …… Laser oscillator, 22 ... Acousto-optic light modulator, 23 ... High-frequency oscillator, 24 ... Optical modulator, 25
...... Light receiving element, 26 ...... Detector, 27,28 ...... Half mirror, 2
9 …… Slit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A 64-25080 (JP, A) JP-A 48-90554 (JP, A) JP-A 62-54189 (JP, A) JP-A 58- 166281 (JP, A) JP 6-16080 (JP, B2) JP 58-6156 (JP, B2) JP 6-64141 (JP, B2) JP 6-16081 (JP, B2)

Claims (3)

(57) [Claims] 1. A means for generating a first pseudo-random signal having a clock frequency of f1, and a frequency f2 having the same pattern as that of the first pseudo-random signal and slightly different from the clock frequency f1 as the clock frequency. Means for generating a second pseudo-random signal; a first multiplier for multiplying the first pseudo-random signal by the second pseudo-random signal; laser light generation means for generating a laser light; Modulating means for intensity-modulating the output of the laser light generating means by a first pseudo-random signal, irradiating means for irradiating the output of the modulating means to an object, and electric signals for receiving reflected light from the object. A light receiving means for converting the light into the light receiving means, a second multiplier for multiplying the output of the light receiving means by the second pseudo random signal, and a time series pattern output from the first multiplier. And a time measuring means for measuring a time difference between the time series pattern output from the second multiplier and a distance to an object based on the time difference, and the laser light generating means is a laser A light source, a high-frequency generator, and an acousto-optic light modulator driven by the output of the high-frequency generator and receiving the output light of the laser light source as an input. And a light-receiving element that combines the output light of the branching means and the reflected light from the object by heterodyne detection and outputs as an electrical signal, the distance measuring means comprising: A first low-pass filter for inputting the output of the multiplier and low-pass filtering; a second low-pass filter for inputting the output of the second multiplier and low-pass filtering; and the first low-pass filter. The distance measuring device is provided with a measuring means for measuring the time between the time when the maximum value of the output signal of the second low-pass filter occurs and the time when the maximum value of the output signal of the second low-pass filter occurs. 2. A semiconductor laser is used instead of the laser light generating means and the modulating means, and the semiconductor laser is driven by the first pseudo-random signal to directly intensity-modulate the laser light. Claim 1 adapted to obtain
The described distance measuring device. 3. The distance measuring device according to claim 1 or 2, further comprising biaxial direction measuring means for measuring an irradiation direction and a reception direction of the laser beam so that a three-dimensional shape can be measured.