WO2019188302A1

WO2019188302A1 - Distance measuring device

Info

Publication number: WO2019188302A1
Application number: PCT/JP2019/010335
Authority: WO
Inventors: 奥田　義行
Original assignee: パイオニア株式会社
Priority date: 2018-03-27
Filing date: 2019-03-13
Publication date: 2019-10-03

Abstract

This distance measuring device comprises: an emission unit for emitting laser light, the optical intensity of which has been modulated on the basis of a first frequency signal having a first frequency and a second frequency signal having a second frequency higher than the first frequency; a light-receiving unit for receiving the laser light reflected by an object, and converting the optical intensity of the received laser light into an electrical signal; a first phase difference detection unit for detecting the phase difference between the first frequency signal and a signal component having the first frequency and generated from the electrical signal; a second phase difference detection unit for detecting the phase difference between the second frequency signal and a signal component having the second frequency and generated from the electrical signal; and a distance calculation unit for calculating the distance to the object on the basis of the phase difference detected by the first phase difference detection unit and the phase difference detected by the second phase difference detection unit. The laser light has an optical intensity that has been modulated with a composite signal obtained by displacing the phase of a sinusoidal signal having the second frequency on the basis of a sinusoidal signal having the first 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.

According to the first aspect of the present invention, a laser beam 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 is directed to a predetermined region. Generated from the electrical signal, a light receiving unit that receives the laser light reflected by the object in the predetermined region, converts the light intensity of the received laser light into an electrical signal, and the electrical signal A first phase difference detector that detects a phase difference between the first frequency signal component and the first frequency signal; and the second frequency signal component generated from the electrical signal and the second frequency signal. A distance to the object based on a phase difference detected by the second phase difference detection unit detecting the phase difference, the phase difference detected by the first phase difference detection unit, and the phase difference detected by the second phase difference detection unit Distance calculation to calculate And the laser light has a light intensity modulated by a synthesized signal in which the phase of the sine wave signal of the second frequency is displaced based on the sine wave signal of the first frequency. To do.

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 typically the phase oscillation based on the fundamental wave of the frequency f2 of the signal modulated by the light intensity of the emitted light of Example 1. FIG. It is a figure which shows the time change of a phase. 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 typically the phase oscillation based on the fundamental wave of the frequency f2 of the light received signal of Example 1. FIG. It is a figure which shows the example of a phase shift in case a delay time is less than 1 period of a fundamental wave. It is a figure which shows the example of a phase shift in case delay time is an integral multiple of 1 period of a fundamental wave. It is a figure which shows the example of a phase shift in case a delay time exceeds one period of a fundamental wave, and is not an integral multiple. 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 figure which shows typically the phase oscillation based on the fundamental wave of the frequency f2 of the signal modulated by the light intensity of the emitted light 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 by the light intensity of the laser beam radiate | emitted in Example 2. FIG. It is a figure which shows the time change of the phase of the modulation signal in Example 2. FIG. It is a figure which shows the example of the signal waveform of the light received signal 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 included in 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 band pass BPF 13, an f1 phase difference detecting unit 15, an f2 phase difference detecting unit 17, and a distance calculating 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.

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 a laser beam, the light intensity of which is modulated by a combined signal in which the phase of the sine wave signal having the frequency f2 is displaced based on the sine wave signal having the frequency f1, toward a predetermined region. Specifically, the emitting unit 11 is a sum of the sine wave signal having the frequency f2, the first sine wave having the frequency fb that is the difference frequency between the frequency f1 and the frequency f2, and the frequency f1 and the frequency f2. Laser light whose light intensity is modulated by a combined wave signal generated by adding a second sine wave having a certain frequency fa is emitted as emitted 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 light reception signal RS that has passed through the fa to fb band pass BPF 13, the f2 phase difference detection unit 17 and the signal component of the frequency f2 of the light reception signal RS and the second frequency signal S2 ( The phase difference PD2 from the frequency f2) is detected.

The f1 phase difference detection unit 15 supplies the signal component of the frequency f1 of the received light signal RS and the reference signal generation unit 10 based on the phase difference PD2 for the signal component of the frequency f2 detected by the f2 phase difference detection unit 17. The phase difference PD1 with the first frequency signal S1 (frequency f1) 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, if the frequency f1 = 1 MHz, the wavelength is about 300 m, and therefore the range of 150 m based on the phase difference PD1 for the frequency f1 (that is, the reciprocating distance between the distance measuring device 100 and the object OJT is 300 m). Can be measured within the range. On the other hand, if the frequency f2 = 50 MHz, the wavelength is about 6 m, and therefore the range of 3 m (that is, the round-trip distance between the distance measuring device 100 and the object OJT is 6 m based on the phase difference PD2 for the frequency f2). Can be measured within the range. 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 according to the present embodiment will be described with reference to FIGS. 1, 2A, 2B, 3A to 3D, and 4A to 4C.

As shown in FIG. 1, 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 and the f1 phase difference detection unit 15. In addition, the reference signal generation unit 10 generates a second frequency signal S2 having the frequency f2 and supplies the second frequency signal S2 to the emission unit 11 and the f2 phase difference detection unit 17.

The emission unit 11 adds the sine wave signal having the frequency f2, the first sine wave having a frequency difference between the frequency f1 and the frequency f2, and the second sine wave having a frequency sum of the frequency f1 and the frequency f2. A laser beam whose light intensity is modulated by the generated composite wave signal is emitted as emitted light OL. At this time, the sine wave signal and the synthesized wave signal are added so that the phases of the first sine wave and the second sine wave are 90 degrees different from the phase of the sine wave signal having the frequency f2. Note that the phase of the first sine wave and the second sine wave and the phase of the sine wave signal having the frequency f2 do not need to be strictly different by 90 degrees, and may be 45 degrees or more and 135 degrees or less.

For example, a sinusoidal signal having a frequency f2 is cos (2π · f2 · t), and a first sinusoid having a frequency difference between the frequency f1 and the frequency f2 is 1/2 sin {2π · (f2−f1) · t}, When the second sine wave having the sum of the frequency f1 and the frequency f2 is 1/2 sin {2π · (f2 + f1) · t} and the time is t, the light intensity Semit (t) of the emitted light OL is It is expressed by a mathematical formula (Formula 1).

FIG. 2A is a diagram schematically showing a phase oscillation based on a sine wave signal of frequency f2 as a vector diagram. The horizontal axis indicates the real axis, and the vertical axis indicates the imaginary axis.

As described above, the phase of the sine wave signal having the fundamental frequency f2 (hereinafter referred to as fundamental wave f2) is the first sine wave having the frequency fb (hereinafter referred to as fb wave) and the second phase having the frequency fa. It is 90 degrees different from the phase of a sine wave (hereinafter referred to as fa wave). Therefore, if the vector of the fundamental wave f2 is the real axis direction (for example, an angle of 0 degrees), the vectors of the fb wave and the fa wave are the imaginary axis direction (for example, an angle of 90 degrees).

The vector of the fundamental wave f2 rotates counterclockwise at θ = 2π · f2 · t with the real axis direction as the start position. On the other hand, the fa wave vector rotates counterclockwise at θ = 2π · fa · t slightly earlier than the vector of the fundamental wave f2, with the imaginary axis direction as the start position. The vector of the fb wave starts at the imaginary axis direction and is slightly later than the vector of the fundamental wave f2, and rotates clockwise at θ = 2π · fb · t.

When the vector of the fundamental wave f2 is fixed at an angle of 0 degree and the relative rotation angle of the vectors of the fa wave and the fb wave is viewed with reference to this, the frequency f1 = fa−f2, and therefore the vector of the fa wave is The rotation is forward when θ = 2π · f1 · t, and the vector of the fb wave is reversely rotated when θ = −2π · f1 · t.

That is, assuming that the vector of the fundamental wave f2 is fixed to the real axis: 1.0 and the imaginary axis: 0.0, the vector of the frequency fa is the real axis: -0.5 sin (2π · f1 · t), the imaginary axis : 0.5 cos (2π · f1 · t). The vector of the frequency fb is real axis: 0.5 sin (2π · f1 · t) and imaginary axis: 0.5 cos (2π · f1 · t). A synthesized vector CV obtained by synthesizing these becomes a real axis: 1.0 and an imaginary axis: cos (2π · f1 · t).

Therefore, the phase angle θ of the composite vector CV is expressed by the following equation (Equation 2) from the deformation of tan θ = cos (2π · f1 · t).

FIG. 2B is a waveform diagram showing a time change of the phase angle θ expressed by the above mathematical formula (Formula 2). Thus, the phase angle θ changes so as to vibrate at the frequency f1.

Note that the vector obtained by combining the fa wave vector and the fb wave vector is a linear motion that reciprocates between +1 and −1 in the imaginary axis direction (that is, the range indicated by the one-dot chain line arrow in FIG. 2A). When the vector of the fundamental wave f2 is further combined with the combination of the vector of the fa wave and the vector of the fb wave, the length (amplitude) of the combined vector CV changes between 1 and √2. For this reason, as shown in (Equation 1), in this embodiment, “+ √2” is added as a DC offset value (hereinafter referred to as a DC offset). Thereby, the light intensity Semit (t) is kept 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.

FIG. 3A is a diagram showing a signal waveform of the light intensity of the outgoing light OL. Laser light having such a signal waveform of light intensity is emitted from the emitting portion 11 as emitted light OL.

FIG. 3B is a graph showing the spectra of the frequencies f2, fa, and fb that are modulated by the light intensity of the outgoing light OL. When f1 = 1 MHz and f2 = 50 MHz, fa = 51 MHz and fb = 49 MHz, and the spectrum of the frequency f2 stands on the graph, and the spectrums of the frequency fa and the frequency fb are located near the frequency f2 and symmetrically on both sides. Will stand.

Referring to FIG. 1 again, the laser light (emitted light OL) emitted by the emitting unit 11 is reflected by the object OJT. 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 electrical signal, has a distorted shape.

FIG. 3C 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 a comparison between FIG. 3A and FIG. 3C, the signal waveform of the light reception signal RS retains the shape of the waveform of the light intensity of the emitted light OL. Specifically, the signal waveform of the light reception signal RS shown in FIG. 3C 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. 3A. Therefore, by cutting the signal component of the frequency f1 from the received light signal RS, the distorted signal waveform shown in FIG. 3C can be returned to the signal waveform similar to the signal waveform of the light intensity of the emitted light OL shown in FIG. 3A.

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.

Assuming that the time from when the laser beam is emitted from the emitting unit 11 to when it is received by the light receiving unit 12 is the flight time Td of the light, the signal waveform of the received light signal RS with corrected distortion is the laser beam at the time of emission. The signal waveform of the light intensity signal (hereinafter referred to as the outgoing signal) becomes a waveform delayed by the light flight time Td on the time axis. In the following description, the flight time Td of light is also referred to as a delay time Td.

Considering the attenuation due to the reflectance and the like, the signal waveform of the light reception signal RS is a waveform obtained by translating the signal waveform of the emission signal in the positive direction by the delay time Td. When tr = t−Td, the light reception signal Srecv (t) is expressed by the following equation (Equation 3).

FIG. 4 is a diagram schematically showing a phase vibration with respect to the fundamental wave f2 in the light reception signal RS as a vector diagram. Here, the case where the vector of the fundamental wave f2 is on the imaginary axis (270 degrees in the figure) is shown as an example.

As described above, the signal waveform of the emission signal has a shape of parallel movement on the time axis when the laser beam is emitted from the emission unit 11, reflected by the object OJT, and received by the light receiving unit 12. The combined vector CV obtained by combining the fundamental wave f2, the fa wave, and the fb wave is rotated by an angle corresponding to the delay time Td while keeping the phase vibration of the outgoing signal. For example, the rotation angle θd of the vibration center of the composite vector CV is θd = 2π · f2 · Td.

Thereby, the phase angle θ of the light reception signal RS is expressed by the following equation (Equation 4).

The f2 phase difference detection unit 17 detects the phase difference PD2 between the signal component of the frequency f2 of the light reception signal RS and the second frequency signal S2 (frequency f2) based on the light reception signal RS that has passed through the fa to fb band pass BPF13. And supplied to the f1 phase difference detector 15 and the distance calculator 18. Based on the phase difference PD2 detected by the f2 phase difference detector 17, the f1 phase difference detector 15 calculates the phase difference PD1 between the signal component of the frequency f1 of the light reception signal RS and the first frequency signal S1 (frequency f1). Detected and supplied to the distance calculator 18.

The detection process of the phase difference PD2 and the phase difference PD1 by the f2 phase difference detection unit 17 and the f1 phase difference detection unit 15 will be described with reference to FIGS. 5A to 5C.

The signal waveform of the light reception signal RS is a shape in which the signal waveform of the emission signal is translated on the time axis, and the phase angle of the light reception signal RS is expressed by the above (Equation 4). Here, if the distance from the object OJT that forms the reflector is L, the flight time Td of light (that is, the delay time Td) is expressed by the following equation (Equation 5).

From Equation (Equation 4) and Equation (Equation 5), the portion of tan ⁻¹ [cos {2π · f1 · (t−Td)}] of the phase angle θ behaves such that it vibrates with a period f1 in the time axis direction. You can see that On the other hand, it can be seen that the 2π · f2 · Td portion of the phase angle θ behaves so as to be offset in a DC manner according to Td.

FIG. 5A is a diagram showing a waveform of a time change of the phase angle when the delay time Td is within one cycle of the fundamental wave f2. The solid line is the waveform of delay time Td = 0.000 (nsec), the broken line is the waveform of delay time Td = 0.625 (nsec), the one-dot chain line is the waveform of delay time Td = 1.250 (nsec), and the two-dot chain line is The waveform of delay time Td = 1.875 (nsec) is shown.

When the delay time Td is within one cycle of the fundamental wave f2, only the DC offset changes significantly. Although a shift in the horizontal direction (time axis direction) is also caused by the vibration at the frequency f1, it is not noticeable because of a small amount.

FIG. 5B is a diagram showing a waveform of a time change of the phase angle when the delay time Td is an integral multiple of one period of the fundamental wave f2. The solid line shows the waveform at Td = 0.000 (nsec). The broken line indicates the waveform of delay time Td = 60.000 (nsec), that is, 1 × f2. The alternate long and short dash line indicates a waveform of delay time Td = 120.000 (nsec), that is, 2 × f2. A two-dot chain line indicates a waveform of delay time Td = 180.000 (nsec), that is, 3 × f2.

When the delay time Td is an integral multiple of one period of the fundamental wave f2, a lateral (time axis direction) parallel movement occurs due to the vibration of the frequency f1. On the other hand, fluctuation due to DC offset does not occur.

FIG. 5C is a diagram showing a waveform of a time change of the phase angle when the delay time Td exceeds one period of the fundamental wave f2 and is not an integral multiple. The solid line is the waveform of delay time Td = 0.000 (nsec), the broken line is the waveform of delay time Td = 0.625 (nsec), the one-dot chain line is the waveform of delay time Td = 1121.250 (nsec), and the two-dot chain line is The waveform of delay time Td = 181.875 (nsec) is shown.

In a general case where the delay time Td exceeds one period of the fundamental wave f2 and is not an integral multiple, the DC offset represents a phase shift within one period of the fundamental wave f2, and the parallel movement amount of the vibration of the frequency f1 is The change represents the entire time axis shift.

The f2 phase difference detection unit 17 of the present embodiment detects the phase difference PD2 with respect to the frequency f2 by detecting the DC offset as described above. Then, the f1 phase difference detection unit 15 uses the detection result of the f2 phase difference detection unit 17 to detect the parallel movement in the horizontal direction (time axis direction) of the waveform of the phase angle, so that the phase difference with respect to the frequency f1 is detected. PD1 is detected.

The distance calculation unit 18 uses the phase difference PD1 for the frequency f1 detected by the f1 phase difference detection unit 15 for global distance calculation, and uses the phase difference PD2 for the frequency f2 detected by the f2 phase difference detection unit 17. The distance from the distance measuring device 100 to the object OJT is obtained by correcting the result of the global distance calculation using the average value as a distance calculation value in a narrow range (one wavelength range of a sine wave having the frequency f2). CD is calculated.

As described above, the distance measuring apparatus 100 according to the present embodiment uses the sine wave signal having the frequency f2, the first sine wave having the frequency difference between the frequency f1 and the frequency f2, and the sum of the frequency f1 and the frequency f2. A laser beam whose light intensity is modulated by the combined wave signal generated by adding the second sine wave is emitted toward a predetermined region. 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 f2 generated from the electrical signal and the second frequency. The phase difference PD2 between the signal S2 and the phase difference PD1 between the signal component of the frequency f1 and the first frequency signal S1 are detected. Then, the distance measuring device 100 calculates the distance CD with respect to the object OJT by using the phase difference PD1 for global distance calculation and applying correction using the phase difference PD2.

FIG. 6A 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 6) is emitted, for example.

FIG. 6B is a graph showing the spectra of the frequencies f1 and f2 modulated by the light intensity of the laser light 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. 7 is a block diagram showing a configuration of a distance measuring apparatus 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. 6B, 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. 7). 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 of the present embodiment is unnecessary with one BPF (fa to fb bandpass BPF 13 shown in FIG. 1) because the frequencies f2, fa, and fb are close as shown in FIG. 3B. It is possible to cut a signal component.

FIG. 6C 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 apparatus 100 according to the present embodiment, the signal waveform of the light reception signal RS retains the shape of the signal 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, in this embodiment, a sine wave signal cos (2π · f2 · t) having a fundamental frequency f2 is added to a first sine wave ½ sin {2π · (f2− (f2−t2)) having a frequency difference between the frequency f1 and the frequency f2. f1) · t}, the light intensity is modulated by a signal obtained by adding a second sine wave 1/2 sin {2π · (f2 + f1) · t} having the sum of the frequency f1 and the frequency f2, Since the length is √2, the DC offset value is √2. Therefore, the value of the DC offset can be reduced as compared with the comparative example.

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 100 of the present embodiment, it is possible to perform distance measurement using laser light that is safer than the distance measuring apparatus of the comparative example.

Further, when the amplitude of the composite wave signal used for modulation of the light intensity of the laser light is large, the S / N ratio of the signals used for phase difference detection (in the present embodiment, the first frequency signal S1 and the second frequency signal S2) is Improves distance measurement accuracy. 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 100 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 100 of the present embodiment, it is possible to perform distance measurement with high accuracy.

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.

Note that the light intensity Semit (t) of the outgoing light OL emitted from the distance measuring device 100 according to the present embodiment is “Semit (t) = cos (2π · f2 · t) + ½ in the above formula (Equation 1). -It is not limited to the form of [sin {2 (pi) * fb * t} + sin {2 (pi) * fa * t}] + √2 ", The coefficient of each term can be set arbitrarily. At that time, the coefficients of cos (2π · f2 · t), sin {2π · fb · t} and sin {2π · fa · t} may be equal or different. The DC offset may be set to a value corresponding to the coefficient of each term. That is, the emitted light OL only needs to have a light intensity Semit (t) expressed by the following equation (Equation 7), where α, β, γ, and δ 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, Example 2 of the present invention will be described. The distance measuring apparatus according to the present embodiment has the same configuration as the distance measuring apparatus 100 according to the first embodiment shown in FIG. 1, and the distance measuring apparatus according to the first embodiment in the method for modulating the light intensity of the laser beam emitted from the emitting unit 11. Different from the device 100.

The emitting unit 11 of the present embodiment emits laser light, whose light intensity is modulated by a composite signal in which the phase of the sine wave signal having the frequency f2 is displaced based on the sine wave signal having the frequency f1, toward a predetermined region. Specifically, the emitting unit 11 provides a phase shift term to the phase of the sine wave signal having the frequency f2, and the light is generated by a synthesized signal obtained by vibrating the phase angle of the sine wave signal having the frequency f2 with the sine wave having the frequency f1. The laser beam whose intensity is modulated is emitted as the outgoing light OL.

For example, when the width for oscillating the phase angle is 2 × θ ₀ , the phase shift amount Δθ is Δθ = θ ₀ · sin (2π · f1 · t). Then, the light intensity Semit (t) of the outgoing light OL is expressed by the following equation (Equation 8).

FIG. 8 is a diagram schematically showing a phase oscillation based on a sine wave signal (fundamental wave f2) having a frequency f2 as a vector diagram. The vector of the fundamental wave f2 rotates counterclockwise at θ = 2π · f2 · t with the real axis direction as the start position, but here shows a case where the angle is fixed at 0 °. When the vector of the fundamental wave f2 is thus fixed, the combined vector moves so as to swing within the range of the phase angle ± θ ₀ (that is, the swing width 2 × θ ₀ ), as indicated by the dashed arrow. Become.

FIG. 9A is a diagram showing a signal waveform of the light intensity of the outgoing light OL. Thus, the laser light having the light intensity of the signal waveform whose phase is shifted in the horizontal direction (time axis direction) is emitted from the emission unit 11 as the emission light OL.

FIG. 9B is a graph showing a spectrum of a frequency signal modulated by the light intensity of the outgoing light OL. The modulation of the light intensity in this embodiment is so-called PM (Phase Modulation) modulation, and a plurality of sidebands (sidebands) are provided on both sides at intervals of the frequency f1 to be modulated with the frequency f2 being a carrier wave as a center frequency. appear. Therefore, if f1 = 1 MHz and f2 = 50 MHz, the spectrum of fa = 51 MHz, fb = 49 MHz, fc = 52 MHz, fd = 48 MHz...

In the stage of receiving the reflected wave and detecting the phase difference, the frequency fc, fd,... And subsequent ones are cut off from the plurality of generated side waves, and only the center frequency f2 and the first side waves fa and fb are extracted. Even if not, the phase detection operation is possible because the phase variation can be reproduced. Therefore, the distance measuring device of the present embodiment, like the distance measuring device 100 of the first embodiment shown in FIG. 1, passes the signal components of the frequencies from the frequency fa to the frequency fb included in the light reception signal RS, and other than that. It suffices to have the fa to fb bandpass BPF 13 that blocks signal components in the frequency band. The f2 phase difference detection unit 17 can detect the phase difference PD2 for the frequency f2 based on the light reception signal RS that has passed through the fa to fb band pass BPF13.

FIG. 9C is a waveform diagram showing a time change of the phase shift amount Δθ. Here, the case where θ ₀ = 45 ° and f1 = 1 MHz is shown. Since the phase shift amount Δθ = θ ₀ · sin (2π · f1 · t), the waveform changes so as to vibrate at the frequency f1.

FIG. 9D 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 a comparison between FIG. 9A and FIG. 9D, the signal waveform of the light reception signal RS retains the shape of the waveform of the light intensity of the outgoing light OL. That is, even if the upper half of the waveform is crushed, the phase fluctuation is maintained, so that the signal component in the range of frequencies fa to fb is extracted from the received light signal RS and the low frequency noise component is cut. The distorted signal waveform shown in 9D can be returned to a signal waveform similar to the signal waveform of the light intensity of the emitted light OL shown in FIG. 9A.

As described above, the distance measuring apparatus according to the present embodiment emits the laser light whose light intensity is modulated by the combined signal obtained by oscillating the phase angle of the sine wave signal having the frequency f2 with the sine wave having the frequency f1 as the outgoing light OL. To do. The modulation of the light intensity in the present embodiment is the same as that of the first embodiment in that the light intensity is modulated by a composite signal in which the phase of the sine wave signal having the frequency f2 is displaced based on the sine wave signal having the frequency f1. is there.

In the distance measuring apparatus of the present embodiment, the light reception signal RS can be returned to the same waveform as the signal waveform at the time of emission by passing through a single BPF fa to fb band pass BPF 13, and with a simple configuration. The distortion of the signal waveform can be corrected.

Further, in the present embodiment, as shown in the above equation (Equation 8), the minimum value that cos (2π · f2 · t + Δθ) can take is “−1”, so the DC offset value is “+1”. Become. Therefore, the DC offset value can be further reduced as compared with the first embodiment.

Therefore, according to the distance measuring apparatus of the present embodiment, it is possible to perform distance measurement using laser light with higher safety. In addition, since the ratio of the DC offset to the amplitude of the synthesized wave signal can be kept small, the accuracy of distance measurement can be further improved.

The light intensity Semit (t) of the outgoing light OL emitted from the distance measuring apparatus according to the present embodiment is “Semit (t) = cos {2π · f2 · t + θ ₀ · sin (2π) in the above formula (Equation 1). The coefficient of each term can be arbitrarily set without being limited to the form of “f1 · t)} + 1”. The DC offset may be set to a value corresponding to the coefficient of each term. That is, the emitted light OL only needs to have a light intensity Semit (t) expressed by the following equation (Equation 9), where α, β, and γ are constants.

In addition, this invention is not limited to the said 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.

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 Ranging device 10 Reference signal generator 11 Emitter 11A Laser light source 11B Laser light emission driver 12A Light receiving element 12B Light received signal detector 12 Light receiver 13 fa to fb band pass BPF
15 f1 phase difference detection unit 17 f2 phase difference detection unit 18 distance calculation unit

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 distance measuring apparatus according to claim 1, wherein the laser beam has a light intensity modulated by a combined signal obtained by shifting the phase of the sine wave signal of the second frequency based on the sine wave signal of the first frequency.
The laser beam includes a sine wave signal of the second frequency, a first sine wave of a third frequency that is a difference between the first frequency and the second frequency, and the first frequency and the second frequency. A combined wave signal generated by adding the second sine wave of the fourth frequency, which is the sum frequency, and the light intensity modulated by
The range finder according to claim 1, wherein the sine wave signal of the second frequency is orthogonal to the composite wave signal.
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
3. The distance measuring apparatus according to claim 2, 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 second phase difference detection unit is a phase difference signal indicating a phase difference between the second frequency signal and the signal component of the second frequency included in the electrical signal that has passed through the filter, and indicating a time change of the phase difference. The distance measuring device according to claim 3, wherein:
The first phase difference detection unit detects a phase difference with respect to the first frequency based on the phase difference signal detected by the second phase difference detection unit. Distance measuring device.
The laser beam has a light intensity obtained by adding an offset value corresponding to the amplitude of the sine wave signal of the second frequency and the synthesized wave signal to a signal obtained by adding the sine wave signal of the second frequency and the synthesized wave signal. The distance measuring device according to claim 2, wherein the distance measuring device is provided.
The laser beam has the second frequency as f 2 , the third frequency as f b , the fourth frequency as f a , the time as t, and α, β, γ, and δ as constants as follows : The distance measuring device according to claim 6, wherein the distance measuring device has a light intensity modulated by a mathematical expression represented by Equation (1).
The laser beam is expressed by the following formula 1 where f 1 is the first frequency, f 2 is the second frequency, t is time, α, β, γ, and θ 0 are constants. The distance measuring apparatus according to claim 1, wherein the distance measuring apparatus has a modulated light intensity.