JP2007114002A - Laser distance measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem wherein high precision for measurement is difficult to be compatible with quick measurement in conventional laser distance measurement. <P>SOLUTION: In this laser distance measuring method, a pulse signal of a transmission laser beam LT is varied at a prescribed period to serve as a low-frequency periodic signal, a rough primary distance data is obtained, based on the low-frequency periodic signal of the transmission laser beam LT emitted to a target T and a low-frequency periodic signal of a reception laser beam LR reflected by the target T, a detail secondary distance data is obtained, based on the pulse signal of the transmission laser beam LT and a pulse signal of the reception laser beam LR, the primary distance data is thereafter combined with the secondary distance data to calculate a distance up to the target T, and the high precision for the measurement is thereby made compatible with the quick measurement. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a laser distance measuring method used for measuring a distance to a target using a laser beam.

Laser distance measurement irradiates the target with pulsed transmission laser light, receives the reception laser light reflected by the target, and determines the distance to the target based on the time difference between the transmission laser light and the reception laser light and the speed of light. Measure.
“Latest Defense Technology Taisei” R & D Planning, Inc., February 11, 1985, p. 287,288

  By the way, in the laser distance measurement as described above, high accuracy and high speed of measurement are always required, and in order to achieve high accuracy of measurement, there is a method of repeating measurement and averaging.

  In addition to increasing the accuracy of the above measurement, it is conceivable to increase the number of repetitions of measurement per unit time by increasing the frequency of the pulse signal of the transmission laser light in order to increase the measurement speed. However, if the frequency of the pulse signal is made higher than the time required for the laser beam to reciprocate at the maximum distance to be measured, a plurality of pulse signals for the transmission laser beam and the reception laser beam are included in the above-described round-trip time. In some cases, absolute values could not be measured.

  For this reason, in the conventional laser distance measurement, there has been a demand for improvement in achieving both high accuracy and high speed of measurement.

  The present invention has been made in view of the above-described conventional situation, and an object of the present invention is to provide a laser distance measuring method capable of realizing both high accuracy and high speed of measurement.

  The laser distance measurement method of the present invention changes the pulse signal of the transmission laser beam at a predetermined period when measuring the distance to the target based on the time difference between the pulsed transmission laser beam and the reception laser beam reflected by the target. This is used as a low-frequency periodic signal, and primary distance data is acquired based on the low-frequency periodic signal of the transmission laser light and the low-frequency periodic signal of the reception laser light, and based on the pulse signal of the transmission laser light and the pulse signal of the reception laser light. Then, after acquiring the secondary distance data, the distance to the target is calculated by combining the primary distance data and the secondary distance data.

  Note that the low-frequency periodic signal means that the pulse signal is changed at a predetermined cycle as described above, and therefore means that the frequency is lower than the frequency of the pulse signal. It does not indicate a signal.

  In the laser distance measuring method of the present invention, as a more preferred embodiment, the low-frequency periodic signal is a signal obtained by modulating the pulse height of the pulse signal of the transmission laser light at a predetermined period, and the low-frequency periodic signal of the transmission laser light The primary distance data is acquired based on the time difference between the low frequency periodic signal of the received laser beam and the received laser beam, and the secondary distance data is acquired based on the phase difference between the pulse signal of the transmitted laser beam and the pulse signal of the received laser beam. It is said.

  Furthermore, in the laser distance measurement method of the present invention, as a more preferred embodiment, a pulsed reference clock signal for determining the transmission timing of the transmission laser beam is set, and the low frequency periodic signal is synchronized with the reference clock signal. The transmission laser light pulse signal is transmitted for a predetermined time and is stopped for a predetermined time, and the signal has one cycle. The first pulse signal of the low frequency periodic signal of the transmission laser light is transmitted and then the received laser light The number of pulse signals until the first pulse signal of the low frequency periodic signal is received is measured, the primary distance data to the target is obtained based on the measured value, the reference clock signal and the pulse signal of the received laser beam The secondary distance data is acquired based on the phase difference between and.

  Furthermore, in the laser distance measuring method of the present invention, as a more preferred embodiment, a range gate corresponding to a stop time in the low-frequency periodic signal is set simultaneously with the start of transmission of the transmission laser beam, and reception is performed within this range gate. It is characterized in that acquisition of primary distance data is executed only when a laser beam is received.

  The laser distance measuring method of the present invention is a low-frequency periodic signal obtained by changing the pulse signal of a transmission laser beam at a predetermined period, for example, a low-frequency periodic signal obtained by modulating the pulse height of a pulse signal at a predetermined period, or a pulse signal at a predetermined time. By using a low-frequency periodic signal that is transmitted and stopped for a predetermined period of time, a rough distance data that is primary distance data is acquired, and a secondary signal is obtained by using a pulse signal. Detailed distance data is acquired, and by combining these distance data and calculating the distance to the target, highly accurate measurement can be performed without reducing the distance measurement rate.

  In addition, since the laser distance measurement method naturally has a frequency of the low frequency periodic signal lower than the frequency of the pulse signal, the laser distance measurement method tries to measure even if the frequency of the pulse signal of the transmission laser light is increased. Multiple low-frequency periodic signals do not coexist within the time that the laser beam travels back and forth over the maximum distance, which ensures that the primary distance data is acquired and then the secondary distance data is acquired and absolute value measurement is performed. It can be carried out.

  In addition, the laser distance measurement method can further increase the measurement accuracy by repeating and averaging the measurements, while reducing the number of measurement repetitions per unit time as the above-described measurement becomes more accurate. Therefore, it is possible to realize high-speed measurement. Therefore, according to the laser distance measuring method of the present invention, it is possible to realize both high accuracy and high speed of measurement.

  Further, the laser distance measurement method is particularly useful when acquiring primary distance data using a low-frequency periodic signal whose operation is a period in which a pulse signal of a laser beam is transmitted for a predetermined time and stopped for a predetermined time. By acquiring the primary distance data only when the received laser beam is received within the range gate of the time corresponding to the stop time in the periodic signal, the maximum distance to be measured is within the time that the laser beam reciprocates. A situation in which a plurality of low-frequency periodic signals are mixed can be reliably prevented.

  FIG. 1 is a diagram for explaining a laser distance measuring apparatus applicable to the laser distance measuring method of the present invention.

  The outline of the laser distance measuring apparatus includes a laser diode 1, a laser diode driving circuit 2, a high frequency clock circuit 3, and a low frequency clock circuit 4 as a laser beam transmission system. Then, pulsed transmission laser light LT is irradiated.

  The laser distance measuring device also includes a light receiving element (APD) 5, a preamplifier 6, a high-frequency bandpass filter 7, and a low-frequency bandpass filter 8 as a laser beam receiving system, and is reflected at the target T. Received laser light LR is received.

  Further, the laser distance measuring apparatus includes a high-frequency quadrature detection circuit 9, a low-frequency quadrature detection circuit 10, and an arithmetic processing circuit 11 as a signal processing system, and a time difference between the transmission laser light LT and the reception laser light LR. The distance to the target T is calculated based on the (phase difference) and the speed of light.

  Here, in the laser light transmission system, the high frequency clock circuit 3 outputs the pulsed reference clock signal shown in the upper part of FIG. 2 to the laser diode drive circuit 2. In this embodiment, The frequency of the reference clock signal is 50 MHz.

  The low-frequency clock circuit 4 changes the pulse signal of the transmission laser light LT at a predetermined cycle with respect to the laser diode driving circuit 2, and in this embodiment, the pulse height of the pulse signal is modulated into a sinusoidal cycle. This is used as a low frequency periodic signal, and the frequency of the low frequency periodic signal is set to 750 kHz. This frequency corresponds to the case where the maximum distance to the target is about 200 m.

  As a result, the transmission laser light LT oscillated from the laser diode 1 is a pulse signal having a frequency of 50 MHz, as shown in the middle part of FIG. 2, and at the same time a low frequency of 750 kHz in which the pulse height of the pulse signal is modulated in a sine wave shape. A frequency periodic signal is included. In the case of the exemplified frequency, 66 pulse signals are included in one cycle of the low frequency periodic signal.

  In the laser light receiving system, the high-frequency bandpass filter 7 extracts a 50 MHz signal (pulse signal), which is a high-frequency component, from the received laser light LR signal amplified by the preamplifier 6.

  The low-frequency band-pass filter 8 extracts a 750 kHz signal (low-frequency periodic signal), which is a low-frequency component, from the received laser light LR signal amplified by the preamplifier 6.

  Further, in the signal processing system, the high-frequency quadrature detection circuit 9 compares the high-frequency component signal (pulse signal) extracted by the high-frequency band-pass filter 7 with the reference clock signal of the high-frequency clock 3, and the phase difference And secondary distance data to be described later based on the speed of light.

  The low-frequency quadrature detection circuit 10 compares the low-frequency component signal (low-frequency periodic signal) extracted by the low-frequency band-pass filter 8 with the output signal of the low-frequency clock 4, and determines the time difference and the speed of light. Based on this, primary distance data to be described later is calculated.

  The arithmetic processing circuit 11 combines the secondary distance data from the high-frequency quadrature detection circuit 9 and the primary distance data from the low-frequency quadrature detection circuit 10 to calculate the distance to the target T.

  Next, a laser distance measuring method using the above laser distance measuring device will be described.

  In the laser distance measuring method, a pulsed transmission laser light LT including a low frequency periodic signal is irradiated toward a target T by a laser light transmission system, and reflected light (scattered light) from the target T, that is, received laser light. LR is received by a laser beam receiving system.

  At this time, as shown in the lower part of FIG. 2, the received laser beam LR is a pulse-like signal including a low-frequency periodic signal, similar to the transmitted laser beam LT, and reaches the target T with respect to the transmitted laser beam LT. It has a time difference (phase difference) corresponding to the distance. In FIG. 2, for the sake of easy understanding, the deviation of the reception laser beam LR from the transmission laser beam LT is greatly illustrated.

  Next, in the laser distance measurement method, in the laser beam receiving system, the received laser beam LR is received and amplified, and a pulse signal that is a high frequency component in the signal of the received laser beam LR and a low frequency component that is a low frequency component are received. Extract periodic signals individually.

  Thereafter, the low-frequency quadrature detection circuit 10 compares the output signal of the low-frequency clock 4 that is equivalent to the low-frequency periodic signal of the transmission laser beam LR with the low-frequency periodic signal of the reception laser beam LR, Primary distance data, which is rough distance data, is obtained based on the time difference (phase difference) and the speed of light.

  On the other hand, in the high-frequency quadrature detection circuit 9, the reference clock signals P1 to P4 of the high-frequency clock 3 equivalent to the pulse signal of the transmission laser light LT shown in the upper part of FIG. 3 and the reception laser light shown in the middle part of FIG. The LR pulse signals p1 to p4 are compared, and secondary distance data, which is detailed distance data, is obtained based on both phase differences and light speeds shown in the lower part of FIG.

  In the laser distance measurement method, the arithmetic processing circuit 11 combines primary distance data that is rough distance data and secondary distance data that is detailed distance data, and calculates the distance to the target T. .

  As described above, according to the laser distance measurement method described above, primary distance data, which is rough distance data acquired using a low-frequency periodic signal obtained by modulating the pulse height of a pulse signal, and a pulse signal are used. By combining the secondary distance data, which is the detailed distance data, and calculating the distance to the target T, highly accurate measurement can be performed without reducing the distance measurement rate.

  In the laser distance measurement method, the frequency of the reference clock signal is changed and the frequency of the pulse signal of the transmission laser beam LT is set high. At this time, the laser beam reciprocates within the maximum distance to be measured. Even if a plurality of pulse signals of the transmission laser beam LT and the reception laser beam LR are mixed, the frequency of the low frequency periodic signal is clearly lower than that of the pulse signal. Low-frequency periodic signals are not mixed, so that the primary distance data can be reliably acquired and then the secondary distance data can be acquired and the absolute value of the distance to the target T can be measured.

  Furthermore, the laser distance measurement method can further increase the measurement accuracy by repeating and averaging the above measurement, while the number of repetitions of measurement per unit time as the above-described measurement becomes more accurate. In this case, the measurement speed can be increased, and when a distance image is created by scanning the transmission laser beam LT within a predetermined range, the image creation speed is increased. Can contribute.

  FIG. 4 is a diagram for explaining another laser distance measuring apparatus applicable to the laser distance measuring method of the present invention.

  An outline of the laser distance measuring apparatus is as follows. As a laser beam transmission system, a laser diode 21, a laser diode driving circuit 22, a clock circuit 23 for generating a pulsed reference clock signal, and a gate circuit 24 for setting a range gate. And irradiating the target T with the pulsed transmission laser light LT.

  Further, the laser distance measuring device includes a light receiving element 25, a preamplifier 26 for amplifying a pulse signal of the received laser light, and a comparator 27 as a laser light receiving system, and receives the received laser light LR reflected by the target T. To do. The comparator 27 compares the output of the preamplifier 26 with a reference voltage, and raises the digital level (for example, 5 V) when the output of the preamplifier 26 exceeds the reference voltage.

  Further, the laser distance measuring apparatus includes, as a signal processing system, a multivibrator 28 on the transmission system side for inputting a reference clock signal and a range gate, a multivibrator 29 on the reception system side for inputting a pulse signal of the received laser light LR, A counter 31 that receives signals from the vibrators 28 and 29 via a logic element (EXOR) 30, a phase detection circuit 32 that compares the phase difference between the reference clock signal and the pulse signal of the received laser light LR, and a phase detection circuit 32 An AD converter 33 for digitizing an analog signal is provided.

  In the signal processing system, the reference clock signal of the clock circuit 23 is directly input to the counter 31. The counter 31 and the AD converter 33 are connected via a connector 34 to an arithmetic processing circuit 35 that synthesizes primary distance data and secondary distance data described later.

  Here, the clock circuit 23 generates the pulsed reference clock signal shown in FIG. 5A and changes the pulse signal of the transmission laser light LT at a predetermined cycle with respect to the laser diode driving circuit 22. In addition, a low-frequency periodic signal having an operation of transmitting a pulse signal of the laser light LT synchronized with the reference clock signal for a predetermined time and stopping for a predetermined time is generated through the gate circuit 24. Further, the number of pulses of the laser beam LT transmitted during this period is N3.

  In this embodiment, the frequency of the reference clock signal is 50 MHz, the frequency of the low frequency periodic signal is 500 kHz (2 μs), the transmission time in the low frequency periodic signal is 666 ns, and the stop time is 1.334 μs. This setting corresponds to the case where the maximum distance to the target is about 200 m.

  As a result, the transmission laser light LT oscillated from the laser diode 1 is a pulse signal having a frequency of 50 MHz, as shown in FIG. A low frequency periodic signal is included. Therefore, the number of pulses N3 transmitted during this period is 33.

  As shown in FIG. 5D, the multivibrator 28 sets a range gate for a time corresponding to the stop time (1.334 μs) in the low-frequency periodic signal simultaneously with the start of transmission of the transmission laser light LT. .

  The counter 31 is turned on simultaneously with the start of transmission of the transmission laser light LT as shown in FIG. 5E, and the pulse signal (reference clock signal of the reference clock signal) of the transmission laser light LT is turned on as shown in FIG. When the received laser beam LT shown in FIG. 5B is input, the number of pulse signals is turned off, and the measurement of the number of pulse signals is stopped.

  Next, a laser distance measuring method using the above laser distance measuring device will be described.

  In the laser distance measuring method, a pulsed transmission laser light LT including a low frequency periodic signal is irradiated toward a target T by a laser light transmission system, and reflected light (scattered light) from the target T, that is, received laser light. LR is received by the laser beam receiving system. At this time, the counter 31 transmits the first pulse signal of the low frequency periodic signal of the transmission laser beam LT, and then the low frequency periodic signal of the reception laser beam LR. The number of pulse signals until the first pulse signal is received is measured.

  That is, since the frequency (50 MHz) of the pulse signal is known in advance, the arithmetic processing circuit 35 obtains primary distance data, which is rough distance data to the target T, based on the measured value (N1) of the number of pulse signals. Can be acquired.

  In the laser distance measurement method, the phase detection circuit 32 compares the phase difference (ΔTi) between the pulse signal of the reference clock signal and the pulse signal of the received laser beam LR as shown in FIG. The arithmetic processing circuit 35 acquires secondary distance data, which is detailed distance data, based on the phase difference (ΔTi) and the speed of light (c).

Then, the arithmetic processing unit 35, based on the above primary distance data and secondary distance data, to calculate the distance R ₁ to the target T using the following equation.

  As described above, according to the laser distance measurement method described above, the primary distance that is the approximate distance data obtained by using the low-frequency periodic signal having one cycle of transmission and stop of the pulse signal and the measured value of the number of pulse signals. By combining the data and secondary distance data, which is detailed distance data acquired using a pulse signal, and calculating the distance to the target T, the distance measurement rate is reduced as in the previous embodiment. It is possible to measure the absolute value of the distance to the target T without making it, and to increase the measurement speed.

  In the laser distance measuring method, as described above, a range gate for a time (1.334 μs) corresponding to the stop time in the low-frequency periodic signal is set simultaneously with the start of transmission of the transmission laser light LT. The primary distance data is acquired only when the received laser beam LR is received.

  As a result, it is possible to reliably prevent a plurality of low-frequency periodic signals from being mixed within the time during which the laser beam reciprocates the maximum distance to be measured, and to obtain primary distance data more reliably.

  When the maximum distance to the target to be measured is 200 m as in this embodiment, in addition to setting the range gate as described above, the counter 31 has 66 or more pulse signals corresponding to 200 m. When measured, it may be possible not to execute acquisition of primary distance data, and the same effect can be obtained.

  In the laser distance measuring method of the present invention, the detailed configuration and applicable laser distance measuring apparatus are not limited to the above embodiments. Further, since the frequency of the low frequency periodic signal and the frequency of the low frequency periodic signal are set, the number of pulse signals included in one cycle is determined. It is good also as what changed the wave height etc. of the at least 1 pulse signal of the signals.

It is explanatory drawing which shows an example of the laser distance measuring apparatus applicable to the laser distance measuring method of this invention. It is explanatory drawing which shows a reference clock signal, the pulse signal of a transmission laser beam, and the pulse signal of a reception laser beam. It is explanatory drawing which shows the time difference of the pulse signal of a transmission laser beam which modulated the wave height, the reference clock signal, the pulse signal of a reception laser beam, and a pulse signal. It is explanatory drawing which shows the other example of the laser distance measuring apparatus applicable to the laser distance measuring method of this invention. Reference clock signal (A), transmission laser light signal (B), reception laser light signal (C), gate signal (D), counter ON / OFF signal (E), measurement value (F), reference clock signal and reception laser It is explanatory drawing which shows the comparison (G) with a signal.

Explanation of symbols

LR reception laser beam LT transmission laser beam T target

Claims (4)

  When measuring the distance to the target based on the time difference between the pulsed transmitted laser beam and the received laser beam reflected by the target, the pulse signal of the transmitted laser beam is changed at a predetermined cycle to make it a low frequency periodic signal, and transmitted After acquiring the primary distance data based on the low frequency periodic signal of the laser light and the low frequency periodic signal of the received laser light, and after acquiring the secondary distance data based on the pulse signal of the transmitted laser light and the pulse signal of the received laser light A method of measuring a laser distance, comprising calculating a distance to a target by combining primary distance data and secondary distance data.   The low frequency periodic signal is a signal obtained by modulating the pulse height of the pulse signal of the transmission laser light at a predetermined period, and the primary distance data based on the time difference between the low frequency periodic signal of the transmission laser light and the low frequency periodic signal of the reception laser light. The laser distance measuring method according to claim 1, further comprising: acquiring secondary distance data based on a phase difference between a pulse signal of a transmission laser beam and a pulse signal of a reception laser beam.   A pulse-shaped reference clock signal for determining the transmission timing of the transmission laser beam is set, and the low-frequency periodic signal transmits a pulse signal of the transmission laser beam synchronized with the reference clock signal for a predetermined time and stops for a predetermined time. A signal whose operation is one cycle, and is a pulse from when the first pulse signal of the low frequency periodic signal of the transmission laser beam is transmitted until the first pulse signal of the low frequency periodic signal of the reception laser beam is received Measuring the number of signals, obtaining primary distance data to the target based on the measured value, and obtaining secondary distance data based on the phase difference between the reference clock signal and the pulse signal of the received laser beam The laser distance measuring method according to claim 1.   Set the range gate for the time corresponding to the stop time in the low-frequency periodic signal at the same time as the start of transmission of the transmission laser beam, and execute the acquisition of primary distance data only when the reception laser beam is received within this range gate. The laser distance measuring method according to claim 3.

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