JP2018059789A - Distance measuring apparatus and distance measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distance measuring apparatus and the like capable of accurately measuring in a wide range with a simple configuration.SOLUTION: The distance measuring apparatus includes: a light generating part that generates laser light with modulated intensity; an intensity modulator that modulates the intensity of a beam of return light which is reflected by a measurement object at a modulated frequency identical to the modulated frequency of the laser light; a signal generator that outputs a modulated signal to the light generating part and the intensity modulator; a photodetector that detects the return light the intensity of which is modulated by the intensity modulator; and a control unit that controls a signal generator and calculates the distance up to the measurement object based on the detection signal from the photodetector.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a distance measuring device and a distance measuring method.

  Conventionally, a technique is known in which intensity-modulated laser light is emitted toward a measurement object, and the distance is measured by taking an intensity correlation between reflected light from the measurement object and a reference signal (for example, non-patent literature). 1, see Patent Document 1).

Koichi Matsumoto, “High-precision ranging technology”, optics, vol. 23, no. 3, pp. 170-175, 1994

JP 2007-205949 A

  In principle, a distance measurement method using intensity-modulated laser light can perform a wide range of measurements with high accuracy. However, in the method disclosed in Non-Patent Document 1, the return light from the measurement target is converted into an electric signal by a photodetector and the intensity correlation with the electric signal (reference signal) serving as a reference is obtained. Therefore, it is difficult to measure a wide range with a single device. Further, the technique disclosed in Patent Document 1 that takes the intensity correlation between the return light and the reference optical signal by the nonlinear response of the light receiving element enables a receivable signal band to be extremely wide and a wide range of measurements to be performed. However, in this method, it is necessary to amplify the optical power using an optical amplifier in order to cause a nonlinear response, and it is necessary to use two light sources in order to prevent interference noise with reference light.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a distance measuring device and the like capable of performing a wide range of measurement with high accuracy with a simple configuration. is there.

  (1) The present invention includes a light generation unit that generates intensity-modulated laser light, an intensity modulator that modulates the intensity of the return light reflected by the measurement target at the same modulation frequency as the modulation frequency of the laser light, A signal generator for outputting a modulation signal to the light generator and the intensity modulator; a photodetector for detecting return light intensity-modulated by the intensity modulator; and controlling the signal generator to detect the light And a control unit that calculates a distance to the measurement object based on a detection signal from the device.

  The present invention also provides a light generation step for generating an intensity-modulated laser beam by the light generation unit and an intensity of the return light reflected by the measurement target at the same modulation frequency as the modulation frequency of the laser beam by the intensity modulator. An intensity modulation step for modulating, a light detection step for detecting return light intensity-modulated by the intensity modulator by a photodetector, and a control for calculating a distance to the measurement object based on a detection signal from the photodetector And a distance measuring method.

According to the present invention, the return light is intensity-modulated at the same modulation frequency as that of the light source (laser light), and the distance is calculated based on the detection signal of the intensity-modulated return light. Can be measured with high accuracy.

  (2) In the distance measuring apparatus and the distance measuring method according to the present invention, a photodetector having a cutoff frequency lower than the modulation frequency may be used as the photodetector.

  According to the present invention, it is not necessary to separately perform signal processing on the detection signal, and the high-frequency component of the return light whose intensity is modulated with a simple configuration can be removed.

  (3) In the distance measuring apparatus and the distance measuring method according to the present invention, the control unit (in the control step) is configured to measure the distance to the measurement object based on a change in the detection signal when the modulation frequency is swept. May be calculated.

  According to the present invention, it is possible to accurately measure the distance to a plurality of reflection points over a wide range with a simple configuration.

It is a figure which shows typically the structure of the distance measuring device which concerns on this embodiment. It is a figure which shows the relationship between a modulation frequency and the intensity | strength of a detection signal. It is a figure which shows typically the structure of the distance measuring device which concerns on other embodiment.

  Hereinafter, this embodiment will be described. In addition, this embodiment demonstrated below does not unduly limit the content of this invention described in the claim. In addition, all the configurations described in the present embodiment are not necessarily essential configuration requirements of the present invention.

1. Configuration FIG. 1 is a diagram schematically illustrating a configuration of a distance measuring apparatus according to the present embodiment. The distance measuring apparatus 1 includes a laser light source 10 that functions as a light generation unit, an intensity modulator 20, a signal generator 30, a photodetector 40, a control unit 50 that includes an arithmetic processing unit (processor) and a storage unit. including.

Laser light source 10 generates an intensity modulated laser beam at the modulation frequency f _m. Laser light emitted from the laser light source 10 is converted into parallel light by the lens 11, passes through the half mirror 12, and reaches the measurement target T. The return light reflected from the measurement target T (reflected light from the measurement target T) is reflected by the half mirror 12 and enters the intensity modulator 20.

The intensity modulator 20 modulates the intensity of the return light reflected by the measurement target T at a modulation frequency f _m (the same modulation frequency as that of the laser light source 10).

Signal generator 30 based on the control signal from the control unit 50, and outputs a modulated signal of the modulation frequency f _m to the laser light source 10 and intensity modulator 20.

The photodetector 40 detects the return light whose intensity is modulated by the intensity modulator 20. A detection signal (electric signal) from the photodetector 40 is converted into digital data by an AD converter (not shown) and output to the control unit 50. Here, the cutoff frequency of the optical detector 40 is lower than the modulation frequency f _m, the photodetector 40 detects only the DC component of the intensity-modulated return light.

The control unit 50 controls the signal generator 30 and calculates the distance L to the measurement target T based on the detection signal from the photodetector 40 (output signal of the AD converter). Control unit 50 discretely sweeping the modulation frequency f _m at a constant frequency interval controls the signal generator 30 (e.g., up to several tens MHz~ number GHz, swept several tens kHz step), and the modulation frequency may be calculated the distance L based on a change of the detection signal when the sweep f _m (first method). In addition, the control unit 50 controls the signal generator 30 to sweep the phase of the modulation signal output to either the laser light source 10 or the intensity modulator 20 and detect the detection signal when the phase of the modulation signal is swept. The distance L may be calculated based on the change in the second (second method).

2. Laser light from the method the laser light source 10 of this embodiment is intensity modulated at a frequency f _m. The intensity I of the intensity-modulated laser beam is expressed by the following formula (1).

ここで、α、ａは定数であり、ｔは時間である。

Here, α and a are constants, and t is time.

Return light reflected by the measurement target T is intensity modulated again frequency f _m in the intensity modulator 20. The intensity I ′ of the intensity-modulated return light is expressed by the following formula (2).

ここで、β、ｂは定数であり、θは初期位相であり、Ｌは、所与の基準位置から測定対象Ｔまでの距離であり、ｎは周囲（光が伝播する媒質）の屈折率であり、ｃは光速である。

Here, β and b are constants, θ is the initial phase, L is the distance from a given reference position to the measurement target T, and n is the refractive index of the surroundings (the medium through which light propagates). C is the speed of light.

The intensity-modulated return light, the narrow band detected by (cutoff frequency modulation frequency f lower than _m) photodetector 40, a high frequency component (the term including t in the third row of Equation (2)) is Only the DC component is obtained. The intensity S of the detection signal obtained by the photodetector 40 is expressed by the following formula (3).

ここで、γは定数である。

Here, γ is a constant.

In a first approach of the present embodiment calculates the distance L based on a change in detection signal when sweeping the modulation frequency f _m. When sweeping the modulation frequency f _m, as shown in FIG. 2, the intensity S of the detection signal (when the reflection point is one point) which varies sinusoidally with frequency sweep width c / 2nL as a cycle. The distance L can be obtained immediately from the reciprocal of this period. Actually, the distance L is calculated by Fourier-transforming the detection signal that periodically changes according to the frequency sweep. In the first method, the distance L to all the reflection points can be calculated from the frequency spectrum of the detection signal, including the case where there is a translucent reflector or the like on the propagation path of the laser light.

In the second method of the present embodiment, the distance L is calculated based on the change in the detection signal when the phase of the modulation signal output to either the laser light source 10 or the intensity modulator 20 is swept. When the phase of the modulation signal is swept, the intensity of the detection signal changes in a sine wave shape. If the phase of the detection signal when the phase of the modulation signal is 0 is ΔΦ (f _m ), the distance L is expressed by the following equation (4).

ここで、ｋは整数である。変調周波数ｆ_ｍが高く、強度変調されたレーザー光の１周期分の波長が測定距離に比べて小さい場合、空間分解能は向上するが、ｋが０以外の整数となり、測定値に波長の整数倍の不定性が生じる。そこで、まず、低い変調周波数ｆ_ｍ，ｌ（１周期分の波長が測定距離よりも大きくなる変調周波数）によってｋ＝０のときについて低分解能で距離Ｌ（ｆ_ｍ，ｌ）を測定する。その上で、高い変調周波数ｆ_ｍ，ｈ（１周期分の波長が測定距離よりも小さくなる変調周波数）によって測定を行い、変調信号の位相が０であるときの検出信号の位相ΔΦ（ｆ_ｍ，ｈ）を求めるとともに、以下の式（５）によりｋを求める。

Here, k is an integer. The modulation frequency f _m is high, when the wavelength of one cycle of the intensity-modulated laser beam is smaller than the measured distance, although the spatial resolution is improved, k is an integer other than 0, an integer number of wavelengths to the measured value Indeterminacy occurs. Therefore, first, the distance L (f _{m, l} ) is measured with low resolution when k = 0 by the low modulation frequency f _{m, l} (the modulation frequency at which the wavelength for one period is larger than the measurement distance). Then, measurement is performed with a high modulation frequency f _{m, h} (a modulation frequency in which the wavelength for one period is smaller than the measurement distance), and the phase ΔΦ (f _m of the detection signal when the phase of the modulation signal is 0 _{, H} ) and k in accordance with the following equation (5).

ここで、ＦＬ［ｘ］は、ｘを超えない最大の整数を与える関数である。式（５）で得られたｋを式（４）に代入すると、高い変調周波数ｆ_ｍにより距離Ｌを求めることができる。第２の手法では、高い変調周波数ｆ_ｍを用いることができるため、空間分解能を向上することができる。また、限られた範囲の位相掃引を行うだけで距離を測定することができるため、測定時間を短縮することができる。

Here, FL [x] is a function that gives the maximum integer not exceeding x. Substituting k obtained in formula (5) into equation (4), can determine the distance L by a high modulation frequency f _m. In the second approach, it is possible to use a high modulation frequency f _m, it is possible to improve the spatial resolution. In addition, since the distance can be measured simply by performing a phase sweep within a limited range, the measurement time can be shortened.

  According to the method of the present embodiment, the intensity of the return light is modulated using the intensity modulator 20 (optical modulator) at the same frequency as the modulation frequency of the laser light source 10, and the intensity-modulated return light is narrow in bandwidth. Intensity correlation can be obtained only by detection with the photodetector 40 (thus inexpensive). The band of the intensity modulator that modulates the intensity of light is extremely wide, and the optical loss is small. Therefore, accurate distance measurement over a wide range can be performed with a simple configuration without using an optical amplifier or a plurality of light sources.

In actual measurement, first, the laser light from the laser light source 10 is directly incident on the intensity modulator 20 (without the reciprocating optical path from the half mirror 12), and at this time, the calculation is performed by the equation (3). The distance to be measured is L ₁ and L ₁ is a reference value. On top of that, was measured in a state in which a half mirror 12 there is an optical path of the previous round-trip, the distance calculated by the equation (3) at this time as L _2, the difference between L ₂ and the reference value L ₁ (L ₂ −L ₁ ) is determined as the distance L to the measurement target T.

3. Modifications The present invention is not limited to the above-described embodiment, and various modifications can be made. The present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations that have the same functions, methods, and results, or configurations that have the same objects and effects). In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that exhibits the same operational effects as the configuration described in the embodiment or a configuration that can achieve the same object. Further, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

  For example, in the above-described embodiment, the case where the direct modulation method that outputs the modulation signal to the laser light source 10 and modulates the laser light has been described. However, the light generation unit includes the laser light source and the modulator, and the modulation signal It is also possible to adopt an external modulation system that outputs laser to the modulator and modulates the laser light.

  In the above-described embodiment, the configuration has been described in which the high-frequency component of the intensity-modulated return light is removed (only the DC component is detected) using the narrow-band photodetector 40. However, the detection from the photodetector is performed. The signal may be input to a filter (for example, a low-pass filter) to remove the high-frequency component of the intensity-modulated return light. In addition, the control unit 50 may process the detection signal (digital data) from the photodetector to remove the high-frequency component of the intensity-modulated return light.

In the above embodiment, the configuration for sweeping the frequency or phase of the modulation signal has been described. However, instead of sweeping the frequency or phase of the modulation signal, the modulation signal may be phase-modulated. FIG. 3 is a diagram schematically showing the configuration of the distance measuring device when the modulated signal is phase-modulated. In FIG. 3, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted as appropriate. The distance measuring device 1 shown in FIG. 3 further includes a phase modulator 60 and a filter 70. Phase modulator 60, the modulated signal output from the signal generator 30 to the intensity modulator 20 phase-modulates the phase [Phi _m. When the fundamental frequency of the modulation signal is f ₀ , the modulation frequency is f _m , and the amplitude is V _m , the phase-modulated modulation signal S _m is represented by V _m cos (2πf ₀ t + Φ _m cos 2πf _m t). Note that the modulation signal generated by the signal generator 30 is represented by V _m cos (2πf ₀ t).

  At this time, the intensity S of the detection signal obtained by the photodetector 40 is expressed by the following equation (6).

ここで、Ｊ_１、Ｊ_２はベッセル関数であり、式（６）の２行目はベッセル関数による展開式（周波数ｆ_ｍ成分及び周波数２ｆ_ｍ成分を抜粋）を示している。この実施形態では、検出信号の周波数ｆ_ｍ成分と周波数２ｆ_ｍ成分の振幅をフィルタ７０（ロックインアンプ）を用いて測定し、制御部５０において、両者の比を算出し、算出した比から距離Ｌを算出する。検出信号の周波数ｆ_ｍ成分の振幅と周波数２ｆ_ｍ成分の振幅の比をＲとすると、比Ｒは、以下の式（７）で表され、距離Ｌは、以下の式（８）で表される。

_Here, J 1, _{J 2} is a Bessel function, the second line of Equation (6) shows the deployable by Bessel function (excerpt frequency _{f m} component and frequency 2f _m component). In this embodiment, the distance the amplitude of the frequency f _m component and frequency 2f _m component of the detected signal was measured using a filter 70 (lock-in amplifier), the control unit 50 calculates the ratio of the two, from the calculated ratio L is calculated. When the amplitude ratio of the amplitude and frequency 2f _m component of the frequency f _m component of the detection signal is R, the ratio R is expressed by the following equation (7), the distance L is expressed by the following equation (8) The

この実施形態によれば、測定対象までの凡その距離が既知である場合に、変調信号の周波数や位相の掃引を行うことなく、距離Ｌを測定することができる。変調信号の基本周波数ｆ_０は、例えば数ＭＨｚ〜数ＧＨｚの範囲で設定し、変調周波数ｆ_ｍは、例えば数百ｋＨｚ〜数ＭＨｚの範囲で設定する。例えば、位相Φ_ｍを０．５ｒａｄ、基本周波数ｆ_０を９１０ＭＨｚ、変調周波数ｆ_ｍを６２ｋＨｚとした場合、凡そ１〜３ｍｍの範囲で距離Ｌを測定することができる。また、基本周波数ｆ_０を低くすれば、より長い距離を測定することができる。例えば、上記の条件で基本周波数ｆ_０を９１０ｋＨｚとした場合、凡そ１〜３ｍの範囲で距離Ｌを測定することができる。

According to this embodiment, when the approximate distance to the measurement target is known, the distance L can be measured without sweeping the frequency and phase of the modulation signal. The fundamental frequency _{f 0} of the modulated signal, for example, set in the range of several MHz~ number GHz, the modulation frequency _{f m} is set in the range of hundreds kHz~ several MHz, for example. For example, the phase [Phi _m 0.5 rad, 910 MHz fundamental frequency _{f 0,} if the modulation frequency _{f m} was 62 kHz, it is possible to measure the distance L in a range of approximately 1 to 3 mm. Further, if lowering the basic frequency f _0, it is possible to measure a longer distance. For example, when the fundamental frequency f ₀ is 910 kHz under the above conditions, the distance L can be measured in a range of approximately 1 to 3 m.

DESCRIPTION OF SYMBOLS 1 ... Distance measuring device, 10 ... Laser light source, 11 ... Lens, 12 ... Half mirror, 20 ... Intensity modulator, 30 ... Signal generator, 40 ... Photo detector, 50 ... Control part, 60 ... Phase modulator, 70 ... Filter, T ... Measurement target

Claims (4)

A light generator that generates intensity-modulated laser light;
An intensity modulator that modulates the intensity of the return light reflected by the measurement target at the same modulation frequency as the modulation frequency of the laser beam;
A signal generator for outputting a modulation signal to the light generator and the intensity modulator;
A photodetector for detecting return light intensity-modulated by the intensity modulator;
And a control unit that controls the signal generator and calculates a distance to the measurement object based on a detection signal from the photodetector. In claim 1,
The distance measuring device, wherein a cutoff frequency of the photodetector is lower than the modulation frequency. The control unit according to claim 1 or 2,
A distance measuring device that calculates a distance to the measurement object based on a change in the detection signal when the modulation frequency is swept. A light generation step of generating intensity-modulated laser light by a light generation unit;
An intensity modulation step of intensity-modulating the return light reflected by the measurement object with an intensity modulator at the same modulation frequency as the modulation frequency of the laser beam;
A light detection step of detecting the return light intensity-modulated by the intensity modulator with a photodetector;
And a control step of calculating a distance to the measurement object based on a detection signal from the photodetector.

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