WO2019181695A1

WO2019181695A1 - Distance measuring device

Info

Publication number: WO2019181695A1
Application number: PCT/JP2019/010333
Authority: WO
Inventors: 奥田　義行
Original assignee: パイオニア株式会社
Priority date: 2018-03-23
Filing date: 2019-03-13
Publication date: 2019-09-26

Abstract

The present invention includes: an emission unit which emits laser light obtained by modulating light intensity on the basis of a first frequency signal of a first frequency and a second frequency signal of a second frequency higher than the first frequency; a light reception unit which receives laser light that has been reflected at a target object and converts the light intensity into an electrical signal; a first phase difference detection unit which detects a phase difference between a signal component of the first frequency generated from the electrical signal and the first frequency signal; a second phase difference detection unit which detects a phase difference between a signal component of the second frequency generated from the electrical signal and the second frequency signal; and a distance calculation unit which calculates the distance to the target object on the basis of the phase differences for the first frequency and the second frequency. The light intensity of the laser light is modulated by a composite wave signal obtained by adding a first sine wave of a third frequency, which is the difference between the first frequency and the second frequency, and a second sine wave of a fourth frequency, which is the sum of the first frequency and the second frequency.

Description

Ranging device

The present invention relates to a distance measuring device, and more particularly to a distance measuring device that measures the distance to an object by comparing the phases of a transmission signal and a reception signal.

A distance measuring device that measures the distance to an object by irradiating the object with laser light and receiving and analyzing the laser light reflected by the object is known (for example, Patent Document 1). . In such a distance measuring device, for example, a target is irradiated with laser light whose light intensity is modulated by a sine wave, the laser light reflected by the target is received, and the light intensity is converted into an electrical signal. Then, the phase difference between the sine wave component included in the electrical signal and the sine wave component included in the light intensity of the laser beam at the time of emission is extracted, and the extracted phase difference is converted into a delay time. The distance from the object is calculated based on the speed of light.

When modulating the light intensity of laser light based on a sine wave, in order to keep the light intensity above zero level, an offset value is added to the sine wave to set the base level of the light intensity, and the base level is oscillated. Techniques for taking the method are known.

Further, in this distance calculation method, since the distance is calculated based on the phase difference, it is possible to measure only up to a distance corresponding to one wavelength (or ½ wavelength depending on the phase difference detection method) of the sine wave to be modulated. . In order to widen the range of measurement distance, it is conceivable to use a sine wave with a long wavelength, but when it is necessary to identify a small difference in distance, the amount of phase change corresponding to the difference in distance is small. Measurement accuracy will deteriorate. Therefore, in order to achieve both a wide measurement distance range and measurement accuracy, laser light is used by combining a sine wave having a long wavelength (ie, a low frequency) and a sine wave having a short wavelength (ie, a high frequency). The intensity is being modulated.

In order to use a plurality of sine waves with different wavelengths, a plurality of sine waves are emitted after being multiplex-modulated with the light intensity of laser light from one light source (that is, one laser light). . In addition, another sine wave is modulated to the light intensity of laser light (that is, a plurality of laser lights) from a plurality of light sources and emitted simultaneously.

JP2015-129646A

As described above, in the method of multiplex-modulating a plurality of sine waves into one laser beam, the signal components of each sine wave are extracted from the electrical signal obtained by converting the received laser beam. An example of the problem is that the BPF (Band Pass する Filter) to be extracted and the BPF to extract a high frequency signal component have to be provided, and the circuit configuration of the distance measuring device becomes complicated. In addition, since consistency in distance calculation cannot be achieved unless the delay amounts between a plurality of BPFs are aligned, a configuration for aligning the delay amounts is required separately.

Further, it is conceivable to increase the light receiving sensitivity using avalanche multiplication using a light receiving element such as an APD (Avalanche Photodiode) in the light receiving unit that receives the laser light reflected by the object. However, the output signal indicating the light intensity of the received laser beam may have a signal waveform in which the non-linearity with respect to the incident light amount increases as the multiplication factor is increased and the upper side is crushed.

When a signal component of a low frequency sine wave is extracted from this output signal, the signal waveform becomes a distorted waveform whose upper side is crushed relative to the original sine wave. Since this is a second harmonic distortion, the zero cross point shifts to the front side when rising, and shifts to the rear side when falling. In this state, if the product of the sine wave before emission is taken to detect the phase difference, the phase difference appears back and forth every half cycle.

In order to avoid this, it is necessary to reduce the second-order harmonic by narrowing the passband of the BPF that extracts the signal component of the low-frequency sine wave. However, when narrowing the BPF band, there is a side effect that the delay time is increased in a trade-off manner, and an adverse effect that the time required for distance calculation is increased is an example of the problem.

In addition, in the method of simultaneously emitting a plurality of laser beams whose light intensities are modulated with sine waves of different wavelengths, a plurality of laser light sources, optical systems, and light receiving systems are required, which increases the scale of the system. As an example. In addition, if multiple laser beams are used and the optical system is misaligned, it will be difficult to collect spots at the same point on the object (detected object). One example of the problem is that they will be separated.

The present invention has been made in view of the above points, and an object of the present invention is to provide a distance measuring device capable of accurately measuring a distance to an object with a simple configuration.

The invention according to claim 1 is a distance measuring device for measuring a distance between the object and a second frequency signal having a first frequency signal having a first frequency and a second frequency higher than the first frequency. A light source that emits laser light whose light intensity is modulated based on a frequency signal toward a predetermined region, the laser light reflected by an object in the predetermined region is received, and the light intensity of the received laser light is determined. A light receiving unit for converting into an electric signal, a first phase difference detecting unit for detecting a phase difference between the signal component of the first frequency generated from the electric signal and the first frequency signal, and the electric signal generated from the electric signal A second phase difference detector that detects a phase difference between the signal component of the second frequency and the second frequency signal; a phase difference detected by the first phase difference detector; and the second phase difference detector Based on the phase difference detected by A distance calculating unit that calculates a distance to the object, wherein the laser light has a third frequency that is a difference between the first frequency and the second frequency. And a second sine wave having a fourth frequency which is a sum frequency of the first frequency and the second frequency, and having a light intensity modulated by a combined wave signal.

It is a block diagram which shows the structure of the ranging apparatus of Example 1 of this invention. It is a figure which shows the signal waveform of the optical intensity of the laser beam radiate | emitted in Example 1. FIG. It is a figure which shows typically the spectrum of the signal component of each frequency modulated by the light intensity of the laser beam radiate | emitted in Example 1. FIG. 6 is a diagram illustrating an example of a signal waveform of a light reception signal in Embodiment 1. FIG. It is a figure which shows the signal waveform of the optical intensity of the laser beam radiate | emitted in a comparative example. It is a figure which shows typically the spectrum of the signal component of each frequency modulated by the light intensity of the laser beam radiate | emitted in a comparative example. It is a figure which shows the example of the signal waveform of the light intensity of the laser beam received in a comparative example. It is a block diagram which shows the structure of the distance measuring device of a comparative example. It is a block diagram which shows the structure of the ranging apparatus of Example 2. FIG. It is a figure which shows the signal waveform of the optical intensity of the laser beam radiate | emitted in Example 2. FIG. It is a figure which shows typically the spectrum of the signal component of each frequency modulated in the light intensity of a laser beam in Example 2. FIG.

Hereinafter, preferred embodiments of the present invention will be described in detail. In the following description of each embodiment and the accompanying drawings, substantially the same or equivalent parts are denoted by the same reference numerals.

FIG. 1 is a block diagram illustrating a configuration of the distance measuring apparatus 100 according to the first embodiment. The distance measuring device 100 emits laser light whose light intensity is modulated based on a signal of a predetermined frequency toward a predetermined area, receives the laser light reflected by the object OJT in the predetermined area, The distance to the object OJT is measured based on the phase difference of the signal component of the predetermined frequency generated from the light intensity of the laser light at the time of light reception. The distance measuring device 100 includes a reference signal generating unit 10, an emitting unit 11, a light receiving unit 12, a fa to fb bandpass BPF 13, an f1 component generating unit 14, an f1 phase difference detecting unit 15, an f2 component generating unit 16, and an f2 phase difference detecting unit. A unit 17 and a distance calculation unit 18.

The reference signal generator 10 generates a reference signal used for modulation of the light intensity of the laser light at the time of emission and detection of a phase difference after light reception. The reference signal generator 10 generates a first frequency signal S1 and a second frequency signal S2 having different frequencies as reference signals. The first frequency signal S1 has a frequency f1 (for example, 1 MHz), and the second frequency signal S2 has a frequency f2 (for example, 50 MHz) higher than the frequency f1. In the following description, it is assumed that the first frequency signal S1 = sin (2π · f1 · t) and the second frequency signal S2 = sin (2π · f2 · t).

The emission unit 11 includes a laser light source 11A that emits laser light, and a laser light emission drive unit 11B that drives the laser light source 11A. The emitting unit 11 emits laser light, whose light intensity is modulated based on the first frequency signal S1 and the second frequency signal S2 supplied from the reference signal generating unit 10, toward a predetermined region. Specifically, the emitting unit 11 includes a first sine wave having a frequency fa that is the sum of the frequency f1 and the frequency f2, and a frequency fb that is a difference frequency between the frequency f1 and the frequency f2. A laser beam having a light intensity modulated by a combined wave signal obtained by adding the sine wave of 2 is emitted as the output light OL.

The light receiving unit 12 receives reflected light RL, which is laser light reflected by the object OJT in a predetermined area, and receives the reflected light RL of the received reflected light RL into an electric signal, and the light receiving element 12A. A light reception signal detection unit 12B that detects the light reception signal RS from the converted electrical signal is included. The light receiving element 12A is composed of a photodetector such as a photodiode, for example, and converts the light intensity of the received reflected light RL into an electric signal. For example, the light receiving element 12A is composed of an APD (Avalanche Photodiode).

The fa to fb band pass BPF 13 is a band pass filter whose pass band is a frequency range from the frequency fa to the frequency fb. The fa to fb band-pass BPF 13 passes signal components having frequencies from the frequency fa to the frequency fb among signal components included in the light reception signal RS, and blocks signal components in other frequency bands.

Based on the second frequency signal S2 supplied from the reference signal generator 10, the f1 component generator 14 generates (extracts) the signal component f1RS of the frequency f1 from the light reception signal RS that has passed through the fa to fb band pass BPF 13. .

The f1 phase difference detection unit 15 is a level between the signal component f1RS of the frequency f1 of the light reception signal RS generated by the f1 component generation unit 14 and the first frequency signal S1 (frequency f1) supplied from the reference signal generation unit 10. The phase difference PD1 is detected.

Based on the first frequency signal S1 supplied from the reference signal generator 10, the f2 component generator 16 generates (extracts) a signal component f2RS of the frequency f2 from the received light signal RS that has passed through the fa to fb band pass BPF 13. .

The f2 phase difference detection unit 17 compares the signal component f2RS of the frequency f2 of the light reception signal RS generated by the f2 component generation unit 16 and the second frequency signal S2 (frequency f2) supplied from the reference signal generation unit 10. The phase difference PD2 is detected.

The distance calculation unit 18 is based on the phase difference PD1 for the frequency f1 detected by the f1 phase difference detection unit 15 and the phase difference PD2 for the frequency f2 detected by the f2 phase difference detection unit 17. A distance CD from 100 to the object OJT is calculated. For example, when the frequency f1 = 1 MHz, the wavelength is about 300 m, and therefore, measurement in a range of 150 m (that is, a range of 300 m round-trip) is possible based on the phase difference PD1 for the frequency f1. On the other hand, when the frequency f2 = 50 MHz, the wavelength is about 6 m, and therefore, measurement in a range of 3 m (that is, a range of 6 m round-trip) is possible based on the phase difference PD2 for the frequency f2. The distance calculation unit 18 uses the phase difference PD1 for the frequency f1 for a rough measurement of a long distance range, and uses the phase difference PD2 for the frequency f2 for a fine measurement of a short distance range. The distance CD to OJT is calculated.

Next, the operation of the distance measuring device 100 of this embodiment will be described with reference to FIG. 1 and FIGS. 2A to 2C.

The reference signal generation unit 10 generates a first frequency signal S1 having a frequency f1, and supplies the first frequency signal S1 to the emission unit 11, the f2 component generation unit 16, and the f1 phase difference detection unit 15. In addition, the reference signal generation unit 10 generates a second frequency signal S2 having a frequency f2, and supplies the second frequency signal S2 to the emission unit 11, the f1 component generation unit 14, and the f2 phase difference detection unit 17.

The emitting unit 11 includes a first sine wave having a frequency fa that is the sum of the frequency f1 and the frequency f2, and a second sine wave having a frequency fb that is a difference frequency between the frequency f1 and the frequency f2. , And a laser beam having a light intensity modulated by the combined wave signal is emitted toward a predetermined region as an emitted light OL.

For example, when the first sine wave having the frequency fa is sin (2π · fa · t), the second sine wave having the frequency fb is sin (2π · fb · t), and the time is t, the output light OL The light intensity Semit (t) is expressed by the following equation (Equation 1).

Note that the light intensity Semit (t) needs to be kept at 0 or more. The minimum value of each of sin (2π · fa · t) and sin (2π · fb · t) is -1, and the minimum value that sin (2π · fa · t) + sin (2π · fb · t) can take. The value is -2. Therefore, in this embodiment, “+2” is added as a DC offset value (hereinafter referred to as DC offset) in order to keep the light intensity Semit (t) at 0 or more. The DC offset represents the base level of the light intensity Semit (t), and the DC offset value “2” is the average light intensity of the outgoing light OL.

As can be seen from the transformation of the equation, the light intensity of the output light OL is the same as that modulated based on sin (2π · f2 · t) × cos (2π · f1 · t), and its signal waveform is “ The beat waveform vibrates so that the amplitude changes around 2 ″.

FIG. 2A is a diagram showing a signal waveform of the light intensity of the outgoing light OL. Laser light having such a light intensity of a beat waveform is emitted from the emission unit 11 toward a predetermined region as emission light OL.

FIG. 2B is a graph schematically showing the relationship between the spectrums of the frequencies fa and fb modulated by the light intensity of the outgoing light OL and the frequencies f1 and f2 that are the frequencies of the reference signal. Assuming that f1 = 1 MHz and f2 = 50 MHz, fa = 51 MHz and fb = 49 MHz. On the graph, the spectrum of the frequency fa and the frequency fb stands near the frequency f2 and on the left and right symmetrical positions.

Referring to FIG. 1 again, the laser light (emitted light OL) emitted from the emitting unit 11 is reflected by the object OJT in a predetermined area. The light receiving unit 12 receives reflected light RL that is laser light reflected by the object OJT.

The light receiving element 12A of the light receiving unit 12 multiplies the amount of the reflected light RL and converts the light intensity of the reflected light RL into an electric signal. At this time, the nonlinearity of the reflected light RL multiplied by the light receiving element 12A with respect to the incident light amount increases. For this reason, the signal waveform of the light reception signal RS which is a signal obtained by converting the light intensity of the reflected light RL into an electric signal has a distorted shape.

FIG. 2C is a diagram illustrating an example of a signal waveform of the light reception signal RS. Here, as an extreme example of a distorted signal waveform, a signal waveform in which the light intensity of the reflected light RL is saturated and the upper half is crushed is shown.

As can be seen from the comparison between FIG. 2A and FIG. 2C, the signal waveform of the light reception signal RS retains the shape of the beat waveform of the light intensity of the emitted light OL. Specifically, the signal waveform of the light reception signal RS shown in FIG. 2C is a signal waveform obtained by adding the signal component of the frequency f1 to the light intensity of the emitted light OL shown in FIG. 2A. Therefore, by cutting the signal component of the frequency f1 from the light reception signal RS, the distorted signal waveform shown in FIG. 2C can be returned to the signal waveform similar to the signal waveform of the light intensity of the emitted light OL shown in FIG. 2A.

Referring to FIG. 1 again, the light receiving unit 12 supplies the light reception signal RS to the fa to fb bandpass BPF 13. The fa to fb band-pass BPF 13 passes signal components having frequencies from the frequency fa to the frequency fb among signal components included in the light reception signal RS, and blocks signal components in other frequency bands. Thereby, the signal component of the frequency f1 is cut, and the distortion of the signal waveform of the light reception signal RS is corrected.

The f1 component generation unit 14 generates an envelope of the signal waveform of the received light signal RS (that is, the beat waveform similar to the signal waveform of the emitted light OL shown in FIG. 2A) whose distortion has been corrected by passing through the fa to fb band pass BPF 13. By detecting, the signal component f1RS of the frequency f1 of the light reception signal RS is generated (extracted).

The f2 component generation unit 16 inverts the polarity at the node of the beat waveform in the signal waveform of the received light signal RS that has passed through the fa to fb bandpass BPF 13 and corrected for distortion, thereby A signal component f2RS having a frequency f2 is generated (extracted).

The f1 phase difference detection unit 15 detects the phase difference PD1 between the signal component f1RS of the frequency f1 of the light reception signal RS and the first frequency signal S1 (frequency f1), and supplies it to the distance calculation unit 18. Similarly, the f2 phase difference detection unit 17 detects the phase difference PD2 between the signal component f2RS of the frequency f2 of the light reception signal RS and the second frequency signal S2 (frequency f2), and supplies it to the distance calculation unit 18.

The distance calculation unit 18 uses the detected phase difference PD1 for the frequency f1 for a rough measurement of a long distance range, and uses the phase difference PD2 for the frequency f2 for a fine measurement of a short distance range. The distance CD from the object to the object OJT is calculated.

As described above, the distance measuring apparatus 100 according to the present embodiment has the first frequency fa that is the sum of the frequency f1 and the frequency f2 based on the first frequency signal S1 having the frequency f1 and the second frequency signal S2 having the frequency f2. A laser beam having a light intensity modulated by a combined wave signal obtained by adding a sine wave of 1 and a second sine wave having a frequency fb that is a difference between the frequency f1 and the frequency f2 is emitted toward a predetermined region. . Then, the distance measuring device 100 receives the laser beam reflected by the object OJT in the predetermined area and converts it into an electrical signal (light reception signal RS), and the signal component of the frequency f1 generated from the electrical signal and the first signal component. The phase difference PD1 between the first frequency signal S1 and the phase difference PD2 between the second frequency signal S2 and the signal component of the frequency f2 generated from the electrical signal are detected, and the distance CD from the object OJT based on the detection result. Is calculated.

FIG. 3A is different from the present embodiment in that the light of the laser light in the comparative example in which the laser light having the light intensity modulated by the combined wave signal obtained by adding the sine wave of the frequency f1 and the sine wave of the frequency f2 is emitted. It is a figure which shows the signal waveform of an intensity | strength. In the comparative example, laser light having a light intensity Semit (t) expressed by the following formula (Equation 2) is emitted, for example.

FIG. 3B is a graph showing the spectra of the frequencies f1 and f2 modulated by the light intensity of the laser beam of the comparative example. Assuming that f1 = 1 MHz and f2 = 50 MHz, the spectra of the frequency f1 and the frequency f2 stand at distant positions on the graph.

FIG. 4 is a block diagram showing a configuration of a distance measuring device 100A of a comparative example. The distance measuring apparatus 100A of the comparative example extracts the signal component f1RS having the frequency f1 and the signal component f2RS having the frequency f2 from the received light signal RS obtained by converting the received laser light into an electrical signal, and the respective frequencies are determined. Compare the phase difference.

As shown in FIG. 3B, since the frequency f1 and the frequency f2 are separated from each other, the distance measuring apparatus 100A of the comparative example requires two systems of BPFs (f1 component extraction BPF 13A and f2 component extraction BPF 13B shown in FIG. 4). Become. Further, in order to achieve matching in calculating the distance, it is necessary to align the delay amounts of the two systems of BPF.

On the other hand, the distance measuring apparatus 100 according to the present embodiment is unnecessary with one BPF (fa to fb bandpass BPF 13 shown in FIG. 1) because the frequency fa and the frequency fb are close as shown in FIG. 2B. It is possible to cut a signal component.

FIG. 3C is a diagram illustrating a signal waveform of a light reception signal of a comparative example. In the comparative example, the signal waveform of the light reception signal RS does not retain the shape of the signal waveform of the light intensity of the laser beam at the time of emission. Therefore, it is difficult to return to the same shape as the signal waveform at the time of emission.

Also, the signal component f1RS of the frequency f1 extracted from the received light signal RS has a distortion waveform that shifts to the front side when the zero cross point rises and shifts to the rear side when falling due to the second harmonic distortion. If an attempt is made to detect the phase difference in this state, the phase difference appears in a form shifted back and forth every half cycle. In order to avoid this, it is necessary to narrow the pass band of the BPF for extracting the signal component f1RS of the frequency f1 and remove the second harmonic. However, when trying to narrow the BPF band, there is a side effect that the delay time becomes longer in a trade-off manner, and the time required for distance calculation becomes longer.

On the other hand, in the distance measuring device 100 according to the present embodiment, the signal waveform of the light reception signal RS retains the shape of the beat waveform of the light intensity of the emitted light OL, and the signal component of the frequency f1 is cut from the light reception signal RS. Thus, the distorted signal waveform can be returned to the same signal waveform as the signal waveform of the light intensity of the outgoing light OL. Therefore, according to the distance measuring apparatus 100 of the present embodiment, it is possible to correct the distortion of the signal waveform of the light reception signal RS with a simple configuration.

Further, when compared with another distance measuring device (not shown) that measures a distance by simultaneously emitting a plurality of laser beams, the distance measuring device 100 of the present embodiment has a light source and an optical system for laser light, Since only one light receiving system, BPF, etc. are required, the scale of the apparatus can be reduced. Further, in the distance measuring device 100 according to the present embodiment, it is difficult to collect a spot at the same point or an optical axis misalignment caused by using a plurality of laser beams generated in another distance measuring device. There is no problem that long and short wavelength measurement positions are scattered.

The light intensity Semit (t) of the outgoing light OL emitted from the distance measuring device 100 of the present embodiment is “Semit (t) = sin (2π · fa · t) + sin (2π) in the above formula (Equation 1). The coefficient of each term can be arbitrarily set without being limited to the form of “fb · t) +2”. In this case, the coefficient of sin (2π · fa · t) and sin (2π · fb · t) are preferably equal, but they may be different. The DC offset may be set to an appropriate value in order to keep the light intensity Semit (t) at 0 or more. That is, the emitted light OL has only to have the light intensity Semit (t) represented by the following mathematical formula (Formula 3), where α, β, and γ are constants.

As described above, according to the distance measuring apparatus 100 of the present embodiment, it is possible to accurately measure the distance to the object with a simple configuration.

Next, the distance measuring apparatus according to the second embodiment will be described. FIG. 5 is a block diagram illustrating a configuration of the distance measuring apparatus 200 according to the second embodiment. The distance measuring device 200 includes a reference signal generator 20, an emitter 21, a light receiver 22, a fa to fb bandpass BPF 23, an f1 component generator 24, an f1 phase difference detector 25, an f2 component generator 26, and an f2 phase difference detector. Unit 27,

distance calculation unit

28, 2 × f1

band pass BPF

30, and 2 × f1 phase difference detection unit 31.

The reference signal generator 20 generates a first frequency signal S1, a second frequency signal S2, and a third frequency signal S3 as reference signals used for modulation of the light intensity of the laser light at the time of emission and detection of a phase difference after light reception. To do. The first frequency signal S1 has a frequency f1 (for example, 1 MHz), and the second frequency signal S2 has a frequency f2 (for example, 50 MHz) higher than the frequency f1. The third frequency signal S3 has a frequency twice the frequency f1 (for example, 2 MHz). In the following description, the first frequency signal S1 = sin (2π · f1 · t), the second frequency signal S2 = sin (2π · f2 · t), and the third frequency signal S3 = sin (2π · 2f1 · t) To do.

The emission unit 21 includes a laser light source 21A that emits laser light, and a laser light emission drive unit 21B that drives the laser light source 21A. The emission unit 21 emits laser light, whose light intensity is modulated based on the first frequency signal S1 and the second frequency signal S2 supplied from the reference signal generation unit 20, toward a predetermined region.

The emitting unit 21 of the present embodiment has a first sine wave having a frequency fa that is the sum of the frequency f1 and the frequency f2, and a second frequency fb that is the difference between the frequency f1 and the frequency f2. Laser light having a light intensity modulated by a combined wave signal obtained by adding the third wave having the difference between the frequency fa and the frequency fb is emitted as the emitted light OL.

The light receiving unit 22 has the same configuration as the light receiving unit 12 of the first embodiment. The light receiving unit 22 receives the reflected light RL that is the laser light reflected by the object OJT in the predetermined area, converts the light intensity of the received reflected light RL into an electric signal, and generates a light receiving signal RS.

The fa to fb band pass BPF 23 is a band pass filter whose pass band is a frequency range from the frequency fa to the frequency fb. The fa to fb band pass BPF 23 passes signal components of frequencies from the frequency fa to the frequency fb among signal components included in the light reception signal RS, and blocks signal components of other frequency bands.

Based on the second frequency signal S2 supplied from the reference signal generator 20, the f1 component generator 24 generates (extracts) the signal component f1RS having the frequency f1 from the received light signal RS that has passed through the fa to fb band pass BPF 23. .

The f1 phase difference detection unit 25 is a level between the signal component f1RS of the frequency f1 of the light reception signal RS generated by the f1 component generation unit 24 and the first frequency signal S1 (frequency f1) supplied from the reference signal generation unit 20. The phase difference PD1 is detected.

Based on the first frequency signal S1 supplied from the reference signal generator 20, the f2 component generator 26 generates (extracts) a signal component f2RS of the frequency f2 from the received light signal RS that has passed through the fa to fb band pass BPF 23. .

The f2 phase difference detection unit 27 is a level between the signal component f2RS of the frequency f2 of the light reception signal RS generated by the f2 component generation unit 26 and the second frequency signal S2 (frequency f2) supplied from the reference signal generation unit 20. The phase difference PD2 is detected.

The 2 × f1 band pass BPF 30 is a band pass filter that passes a signal of frequency 2 × f1. The 2 × f1 band pass BPF 30 passes a signal component of frequency 2 × f1 among signal components included in the light reception signal RS, and blocks signal components of other frequency bands.

The 2 × f1 phase difference detection unit 31 includes the signal component 2 · f1RS of the frequency 2 × f1 of the received light signal RS that has passed through the 2 × f1 band pass BPF 30 and the third frequency signal S3 ( The phase difference PD3 with the frequency 2 × f1) is detected.

The distance calculation unit 28 detects the phase difference PD1 for the frequency f1 detected by the f1 phase difference detection unit 25, the phase difference PD2 for the frequency f2 detected by the f2 phase

difference detection unit

27, and 2 × f1 phase difference detection. Based on the phase difference PD3 for the frequency 2 × f1 detected by the unit 31, the distance from the distance measuring device 200 to the object OJT is calculated. For example, if the frequencies f1 = 1 MHz and f2 = 50 MHz, 150 m based on the phase difference PD1 for the frequency f1, 75 m based on the phase difference PD3 for the frequency 2 × f1, and 3 m based on the phase difference PD2 for the frequency f2. It is possible to measure in each range.

Next, the operation of the distance measuring apparatus 200 of this embodiment will be described with reference to FIGS. 5, 6A and 6B.

The reference signal generation unit 20 generates a first frequency signal S1 having a frequency f1, and supplies the first frequency signal S1 to the emission unit 21, the f2 component generation unit 26, and the f1 phase difference detection unit 25. In addition, the reference signal generation unit 20 generates a second frequency signal S2 having a frequency f2, and supplies the second frequency signal S2 to the emission unit 21, the f1 component generation unit 24, and the f2 phase difference detection unit 27. Further, the reference signal generation unit 20 generates a third frequency signal S3 having a frequency 2 × f1 and supplies the third frequency signal S3 to the emission unit 21 and the 2 × f1 phase difference detection unit 31.

The emitting unit 21 includes a first sine wave having a frequency fa that is the sum of the frequency f1 and the frequency f2, and a second sine wave having a frequency fb that is a difference frequency between the frequency f1 and the frequency f2. Then, the laser beam having the light intensity modulated by the combined wave signal obtained by adding the third wave having the difference between the frequency fa and the frequency fb is emitted toward the predetermined region as the emitted light OL.

For example, the first sine wave having the frequency fa is sin (2π · fa · t), the second sine wave having the frequency fb is sin (2π · fb · t), and the frequency of the difference between the frequency fa and the frequency fb. If the third wave having 0.75 cos {2π · (fa−fb) · t} and the time is t, the light intensity Semit (t) of the emitted light OL is expressed by the following equation (Equation 4). The

As described above, in Example 1, since the minimum value that can be taken by the portion excluding the DC offset (that is, sin (2π · fa · t) + sin (2π · fb · t)) is −2, “+2” was added. However, the minimum value that can be taken by the portion excluding the DC offset in this embodiment is larger than that in the first embodiment by 0.75 cos {2π · (fa−fb) · t}. Therefore, in this embodiment, a small “+1.4” is added as the DC offset, which is smaller than that in the first embodiment.

FIG. 6A is a diagram showing a signal waveform of the light intensity of the outgoing light OL. As can be seen from the modification of the above equation (Equation 4), the light intensity of the outgoing light OL is modulated based on sin (2π · f2 · t) × cos (2π · f1 · t), and further 0.75 cos. Since (2π · 2f1 · t) is added, the signal waveform becomes a beat waveform in which the entire waveform swells upward from the 0 level.

FIG. 6B is a graph schematically showing the relationship between the spectrums of the frequencies fa, fb and 2 × f1 modulated by the light intensity of the outgoing light OL and the frequencies f1 and f2 which are frequencies of the reference signal. Assuming that f1 = 1 MHz and f2 = 50 MHz, fa = 51 MHz and fb = 49 MHz. On the graph, the spectrum of the frequency fa and the frequency fb stands near the frequency f2 and on the left and right symmetrical positions. Further, 2 × f1 = 2 MHz, and a spectrum of frequency 2 × f1 stands in the vicinity of the frequency f1 and at a frequency higher than the frequency f1.

Referring to FIG. 5 again, the laser light (emitted light OL) emitted by the emitting unit 21 is reflected by the object OJT in the predetermined area. The light receiving unit 22 receives reflected light RL that is laser light reflected by the object OJT.

The light receiving unit 22 multiplies the amount of the reflected light RL, converts the light intensity into an electric signal, and detects it as a light receiving signal RS. The light receiving unit 22 supplies the light reception signal RS to the fa to fb band pass BPF 23 and the 2 × f1 band pass BPF 30.

The fa to fb band pass BPF 23 passes signal components of frequencies from the frequency fa to the frequency fb among signal components included in the light reception signal RS, and blocks signal components of other frequency bands. Thereby, the signal component of the frequency f1 is cut, and the distortion of the signal waveform of the light reception signal RS is corrected.

The f1 component generation unit 24 generates an envelope of the signal waveform of the received light signal RS (ie, the beat waveform similar to the signal waveform of the emitted light OL shown in FIG. 6A) whose distortion has been corrected by passing through the fa to fb bandpass BPF 23. By detecting, the signal component f1RS of the frequency f1 is generated (extracted). The f1 phase difference detection unit 25 detects the phase difference PD1 between the signal component f1RS of the frequency f1 of the light reception signal RS and the first frequency signal S1 (frequency f1), and supplies it to the distance calculation unit 28.

The f2 component generation unit 26 inverts the polarity at the node of the beat waveform in the received light signal RS whose distortion has been corrected by passing through the fa to fb bandpass BPF 23, thereby obtaining the signal component f2RS of the frequency f2. Generate (extract). The f2 phase difference detection unit 27 detects the phase difference PD2 between the signal component f2RS of the frequency f2 of the light reception signal RS and the second frequency signal S2 (frequency f2), and supplies it to the distance calculation unit 28.

The 2 × f1 band pass BPF 30 passes the signal component of the frequency 2 × f1 among the signal components included in the light reception signal RS, and blocks the signal components of the other frequency bands. Thereby, the signal component 2 · f1RS having the frequency 2 × f1 of the light reception signal RS is extracted. The 2 × f1 phase difference detector 31 detects the phase difference PD3 between the extracted signal component 2 · f1RS of the frequency 2 × f1 of the received light signal RS and the third frequency signal S3 (frequency 2 × f1), and calculates the distance. Supplied to the unit 28.

The distance calculation unit 28 uses the phase difference PD1 for the frequency f1 for rough measurement of the long distance range, uses the phase difference PD2 for the frequency f2 for fine measurement of the short distance range, and further uses the phase difference PD for the frequency 2 × f1. The distance CD from the distance measuring device 200 to the object OJT is calculated by using the PD 3 for the measurement of the intermediate distance range.

As described above, the distance measuring apparatus 200 according to the present embodiment has the frequency f1 based on the first frequency signal S1 having the frequency f1, the second frequency signal S2 having the frequency f2, and the third frequency signal S3 having the frequency 2 × f1. A first sine wave having a frequency fa that is the sum of the frequency f2, a second sine wave having a frequency fb that is the difference between the frequency f1 and the frequency f2, and a first sine wave having a difference between the frequency fa and the frequency fb. A laser beam having a light intensity modulated by a combined wave signal obtained by adding the three waves is emitted toward a predetermined region.

As described above, in this embodiment, in addition to sin (2π · fa · t) and sin (2π · fb · t), 0.75 cos (2π · 2f1) is used as a composite wave signal for modulating the light intensity.・ T) is added. Therefore, the minimum value that can be taken by the portion excluding the DC offset of the synthesized wave signal is larger than that of the first embodiment by 0.75 cos (2π · 2f1 · t). Therefore, the value of the DC offset can be made smaller than that of the first embodiment (for example, “+1.4”).

The value of DC offset indicates the base level of the light intensity of the laser light, and is a value indicating the average light intensity of the laser light. From the viewpoint of safety, it is desirable that the average light intensity of the laser light is low. Therefore, according to the distance measuring apparatus 200 of the present embodiment, the distance can be measured using a laser beam with higher safety.

Further, when the amplitude of the combined wave signal used for modulating the light intensity of the laser light is large, signals used for phase difference detection (in this embodiment, the first frequency signal S1, the second frequency signal S2, and the third frequency signal S3). This improves the S / N ratio and increases the accuracy of distance measurement. Since the DC offset is an element not related to phase difference detection, and thus distance measurement, if the ratio of the DC offset to the amplitude of the synthesized wave signal can be kept small, the amplitude of the synthesized wave signal can be reduced without increasing the average light intensity. The distance measurement accuracy can be improved by increasing the distance.

In the distance measuring apparatus 200 of the present embodiment, since the ratio of the DC offset to the amplitude of the synthesized wave signal is small, the amplitude of the synthesized wave signal is relatively large and the S / N ratio of the signal used for phase difference detection is large. Therefore, according to the distance measuring apparatus 200 of the present embodiment, it is possible to perform distance measurement with high accuracy.

In addition, the distance measuring apparatus 200 according to the present embodiment receives the laser beam reflected by the object OJT and converts it into an electrical signal (light reception signal), and the signal component f1RS of the frequency f1 generated from the electrical signal and the first signal. A phase difference PD1 from the first frequency signal S1, a signal component f2RS of the frequency f2 generated from the electric signal and a phase difference PD2 of the second frequency signal S2, and a signal component 2 · f1 of the frequency 2 × f1 generated from the electric signal. The phase difference PD3 between f1RS and the third frequency signal S3 is detected, and the distance from the object OJT is calculated based on the detection result.

As described above, the distance measuring apparatus 200 according to the present embodiment calculates the distance using not only the phase difference PD1 for the frequency f1 and the phase difference PD2 for the frequency f2, but also the phase difference PD3 for the frequency 2 × f1. Therefore, the accuracy of distance measurement can be further improved.

Note that the light intensity Semit (t) of the outgoing light OL emitted from the distance measuring device 200 of the present embodiment is “Semit (t) = sin (2π · fa · t) + sin (2π) in the above equation (Equation 4). It is not limited to the form of “fb · t) +0.75 cos {2π (fa−fb) · t} +2”, and the coefficient of each term can be arbitrarily set. In this case, the coefficient of sin (2π · fa · t) and sin (2π · fb · t) are preferably equal, but they may be different. The DC offset may be set to an appropriate value in order to keep the light intensity Semit (t) at 0 or more. That is, the emitted light OL has only to have the light intensity Semit (t) represented by the following mathematical formula (Formula 5), where α, β, γ, and δ are constants.

The present invention is not limited to the above embodiment. For example, in the first embodiment and the second embodiment, the fa to fb bandpass BPF (13, 23) passes a signal component having a frequency from the frequency fa to the frequency fb among the signal components included in the light reception signal RS. The case where signal components in other frequency bands are cut off has been described as an example. However, the passband of the fa to fb bandpass BPF may be set to a slightly wider bandwidth. For example, the lower limit value of the pass band of the fa to fb band pass BPF may be set to a value smaller than the frequency fa. Further, the upper limit value of the pass band of the fa to fb band pass BPF may be set to a value larger than the frequency fb.

In the second embodiment, the distance measuring apparatus 200 includes the 2 × f1 band-pass BPF 30 and the 2 × f1 phase difference detection unit 31, and calculates the distance by detecting the phase difference of the signal component of the frequency 2 × f1. The case of using for the above has been described as an example. However, the distance measuring apparatus 200 does not use the phase difference for the signal component of the frequency 2 × f1, and calculates the distance based on the phase difference for the signal component of the frequency f1 and the frequency f2 as in the first embodiment. good. That is, the distance measuring apparatus 200 may be configured not to include the 2 × f1 band-pass BPF 30 and the 2 × f1 phase difference detecting unit 31, and according to such a configuration, only one system of the BPF is required. Can be suppressed.

In the second embodiment, the case where 0.75 cos (2π · 2f1 · t) is added as the third wave has been described as an example. However, the third wave is not limited to this, and may be a sine wave (sin wave, cos wave), a trapezoidal wave, a triangular wave, a rectangular wave, or the like.

The series of processes described in the above embodiments can be performed by computer processing according to a program stored in a recording medium such as a ROM.

100, 200

Distance measuring devices

10, 20

Reference signal generators

11, 21

Emitters

11A, 21A Laser

light sources

11B, 21B Laser

light emitting drivers

12A, 22A

Light receiving elements

12B, 22B Light receiving

signal detectors

12, 22

Light receiving units

13, 23 fa ~ fb band pass BPF
14, 24 f1

component generation unit

15, 25 f1 phase

difference detection unit

16, 26 f2

component generation unit

17, 27 f2 phase

difference detection unit

18, 28 Distance calculation unit 30 2 × f1 band pass BPF
31 2 × f1 phase difference detector

Claims

An emission unit that emits laser light whose light intensity is modulated based on a first frequency signal having a first frequency and a second frequency signal having a second frequency higher than the first frequency, toward a predetermined region;
A light receiving unit that receives the laser light reflected by the object in the predetermined region and converts the light intensity of the received laser light into an electrical signal;
A first phase difference detector that detects a phase difference between the first frequency signal component generated from the electrical signal and the first frequency signal;
A second phase difference detector that detects a phase difference between the signal component of the second frequency generated from the electrical signal and the second frequency signal;
A distance calculation unit that calculates a distance to the object based on the phase difference detected by the first phase difference detection unit and the phase difference detected by the second phase difference detection unit;
Have
The laser beam has a first sine wave having a third frequency that is a difference frequency between the first frequency and the second frequency, and a fourth frequency that is a sum of the first frequency and the second frequency. And a second sine wave having a light intensity modulated by a combined wave signal obtained by adding the second sine wave.
A filter that allows a signal component in a predetermined frequency range including the third frequency to the fourth frequency to pass, and that blocks a signal component having a frequency lower than the predetermined frequency range and a signal component having a higher frequency than the predetermined frequency range; And
2. The distance measuring apparatus according to claim 1, wherein each of the first phase difference detection unit and the second phase difference detection unit detects a phase difference based on the electrical signal that has passed through the filter.
The said laser beam has the optical intensity which added the offset value according to the amplitude of the said 1st sine wave and the said 2nd sine wave to the said synthetic wave signal, The Claim 1 or 2 characterized by the above-mentioned. Distance measuring device.
The laser light is a light intensity modulated by the following mathematical expression 1 where fb is the third frequency, fa is the fourth frequency, t is time, α, β, and γ are constants. The distance measuring apparatus according to claim 3, further comprising:
The composite wave signal is a signal obtained by adding the first sine wave, the second sine wave, and a third wave having a frequency difference between the third frequency and the fourth frequency. The distance measuring device according to claim 1 or 2.
6. The distance measuring device according to claim 5, wherein the third wave is a sine wave, a rectangular wave, a trapezoidal wave, or a triangular wave.
The laser beam was modulated by the following mathematical expression 2 where fb is the third frequency, fa is the fourth frequency, t is time, α, β, γ, and δ are constants. The distance measuring device according to claim 5, wherein the distance measuring device has light intensity.