JP6902902B2 - Light wave rangefinder - Google Patents

Description

In the present invention, the phase difference or time difference between the reference light passing through the internal optical path serving as the reference optical path and the distance measuring light that is irradiated on the measurement object, reflected by the measurement object and passes through the external optical path, to the measurement object. It is related to a light wave range finder that measures the distance of.

In order to perform distance measurement with high accuracy in a light wave rangefinder, a predetermined amount of received light is required for the reflected distance measurement light from the measurement target, and the peak value of the distance measurement light irradiating the measurement target is Light intensity corresponding to the distance measurement is required.

On the other hand, the light emitting element that emits a laser beam (distance measuring light) has a light emitting load factor (Duty), and the peak value of the distance measuring light is also limited due to the limitation of the light emitting load factor.

Therefore, a burst light emission method that intermittently emits modulated light (burst light emission) is adopted.

In addition, the burst light emission method has two aspects. That is, the surface in which the modulated light in burst light emission is regarded as pulse light emission in the burst light emission cycle, and the surface in which the inside of the section in which burst light emission is regarded as the modulated light for obtaining the phase difference.

In the burst emission method, a coarse distance value is measured using the entire burst section that is regarded as pulse emission, a precise distance value is measured using the modulated light in the burst section, and they are combined. Distance values can be calculated.

However, in the burst light emission method, since the modulated light for phase difference measurement is sampled, the analog-to-digital converter has a relatively slow sampling time. On the other hand, when it is regarded as pulse emission, it is necessary to improve the temporal resolution of the waveform and the sampling time must be short. For this reason, there is a problem that the measurement accuracy is poor in the distance measurement which is regarded as the pulse light emission in the burst light emission method.

Japanese Unexamined Patent Publication No. 2011-185707 Japanese Unexamined Patent Publication No. 2016-1614111

The present invention provides a burst light wave rangefinder that intermittently emits modulated light, which enables highly accurate light wave distance measurement without shortening the sampling time. ..

The present invention emits a reference signal generator that emits a reference signal, a light emitting element that emits distance measuring light, a modulation signal generator that generates a modulation signal based on the reference signal, and an intermittent light emission drive signal based on the modulation signal. The distance to the measurement target is calculated based on the light emitting element drive circuit that causes the light emitting element to burst light at a predetermined cycle, the light receiving element that receives the reflected distance measurement light from the measurement target, and the light receiving signal from the light receiving element. The light emitting element drive circuit has a control calculation unit that performs the above-mentioned, and the light emitting element drive circuit emits a signal obtained by synthesizing a modulation signal and a modulation signal in which the modulation signal is phase-shifted by 90 ° as the intermittent light emission drive signal. The received signal is subjected to DFT arithmetic processing, the obtained intermediate frequency, the phase and amplitude of the sideband with respect to the intermediate frequency are obtained, and the burst period corresponds to the burst period based on the intermediate frequency and the two frequencies included in the sideband. It relates to a light wave distance meter that obtains the phase of a frequency and calculates a distance based on the phase of the frequency.

Further, in the present invention, the received light signal is input to the light receiving circuit via the light receiving signal processing unit, and the light receiving signal processing unit branches the received light signal and mixes a reference signal with one of the branched received light signals. The present invention relates to a light wave distance meter that mixes a reference signal phase-shifted by 90 ° with the other branched received signal signal and inputs the signal to the control calculation unit.

Further, in the present invention, the light receiving signal processing unit adds and subtracts the branched bifurcated light receiving signals, further synthesizes them, and inputs them to the control calculation unit, and the control calculation unit inputs an intermittent light receiving signal as a pulse signal. It relates to a light wave distance meter that calculates the distance to the object to be measured by the TOF method.

According to the present invention, a reference signal generator that emits a reference signal, a light emitting element that emits distance measuring light, a modulation signal generator that generates a modulation signal based on the reference signal, and an intermittent light emission drive signal based on the modulation signal. A light emitting element drive circuit that emits light to burst the light emitting element at a predetermined cycle, a light receiving element that receives reflected distance measurement light from the light receiving element, and a distance to the measurement target based on the light receiving signal from the light receiving element. The light emitting element drive circuit has a control calculation unit for calculating the above, and the light emitting element drive circuit emits a signal obtained by synthesizing a modulation signal and a modulation signal obtained by phase-shifting the modulation signal by 90 ° as the intermittent light emission drive signal. , The received signal is processed by DFT calculation, the obtained intermediate frequency and the phase and amplitude of the sideband with respect to the intermediate frequency are obtained, and the burst period is set based on the intermediate frequency and the two frequencies included in the sideband. Since the phase of the corresponding frequency is obtained and the distance is calculated based on the phase of the frequency, the sampling time of analog-digital conversion is not shortened in the burst emission type light wave distance meter that emits modulated light intermittently. , It exerts an excellent effect that it enables highly accurate light wave distance measurement.

It is a conceptual diagram which shows the basic structure of the light wave distance measuring apparatus. It is a schematic block diagram of the distance measuring part which concerns on embodiment of this invention. (A) is an explanatory diagram showing the distance measuring light emitted from the light emitting element in the distance measuring unit, and (B) is an explanatory diagram showing the intermittent light receiving signal emitted from the light receiving element in the distance measuring unit. .. (A) is a diagram showing an intermittent light receiving signal of internal reference light, (B) is a diagram showing an intermittent light receiving signal of ranging light, and (C) is a diagram showing a primary frequency extracted from each intermittent light receiving signal. is there. It is a graph about the amplitude and frequency obtained by DFT calculation processing, and is particularly the graph which enlarged the vicinity of the emission frequency. The phases of the frequencies of two adjacent points with respect to the frequencies included in the sideband are shown, and the DFT calculation of the sideband is represented on a single core circle. The arithmetic expression for performing the discrete Fourier transform (DFT) is shown. It is a graph which shows the result when the burst interval is discrete Fourier transform. It is a graph which shows the state which carried out the present invention and removed an unnecessary alias component. It is a figure which shows the flow of signal processing. (A) shows the formula (2) for obtaining a beatdown signal by adding up the signals obtained by signal processing, and (B) shows a phase shift by signal subtraction obtained by signal processing and further beatdown. Equation (3) for obtaining a signal is shown.

Hereinafter, examples of the present invention will be described with reference to the drawings.

First, the basic configuration of the light wave distance measuring device will be described with reference to FIG.

The light emitting element 1 (for example, a laser diode: LD) emits a laser beam whose intensity is modulated to a predetermined frequency by the light emitting element drive circuit 12. The laser beam is divided into a distance measuring light 3 and an internal reference light 4 by a half mirror 2, and the distance measuring light 3 transmitted through the half mirror 2 is irradiated to an object to be measured (not shown) through an objective lens 5. The reflected ranging light 3'reflected by the measurement object is received by the light receiving element 7 through the objective lens 5 and the half mirror 8. A photodiode, for example, an avalanche photodiode (APD) is used as the light receiving element.

The light emitting element 1, the light emitting element drive circuit 12, and the like constitute a ranging light emitting unit, and the light receiving element 7, an amplifier 19 (see FIG. 2), a light receiving circuit 13, and the like constitute a light receiving signal generating unit.

The internal reference light 4 reflected by the half mirror 2 is reflected by the half mirror 8 on the optical path of the reflected distance measuring light 3'and is received by the light receiving element 7. The optical path from the half mirror 2 to the light receiving element 7 constitutes an internal reference optical path and has a known optical path length.

An optical path switching device 9 is provided across the optical path of the ranging light 3 and the optical path of the internal reference light 4, and the optical path of the optical path switching device 9 is switched by the drive circuit 14, and the reflected ranging light 3'. And the internal reference light 4 are alternately received by the light receiving element 7. The light receiving signal of the light receiving element 7 is input to the light receiving circuit 13.

The optical path switch 9 is a means for allowing the light receiving element 7 to separate the internal reference light 4 and the distance measuring light 3 and receive light, and the light is applied to the optical path of the internal reference light 4. The optical path switching device 9 can be omitted if an optical path adjusting member such as a fiber is provided so that a time difference occurs when the light receiving element 7 receives the internal reference light and the distance measuring light.

The light receiving circuit 13 executes necessary signal processing such as amplification of the light receiving signal from the light receiving element 7 by an amplifier, frequency conversion (beatdown) by a mixer, and A / D conversion, and controls and calculates the processed signal. Input to unit 15.

The control calculation unit 15 controls the light emitting element driving circuit 12, and controls the light emitting state of the light emitting element 1 via the light emitting element driving circuit 12. Further, the control calculation unit 15 controls the drive circuit 14 to switch between the reflected distance measuring light 3 ′ incident on the light receiving element 7 and the internal reference light 4.

Further, the control calculation unit 15 calculates the distance by obtaining the phase difference (light receiving time difference) between the internal reference light 4 and the reflected distance measuring light 3'from the received light signal. Further, by obtaining the phase difference between the internal reference light 4 and the reflected distance measuring light 3', unstable elements on the circuit such as drift of the light receiving circuit 13 are removed.

FIG. 2 shows a schematic configuration diagram of a distance measuring unit according to an embodiment of the present invention. In FIG. 2, those equivalent to those shown in FIG. 1 are designated by the same reference numerals.

In FIG. 2, reference numeral 16 denotes a reference signal generator, which emits a predetermined reference frequency. In the following description, 120 MHz is exemplified as the reference frequency, 7.5 MHz as the beatdown frequency (intermediate frequency), and 60 MHz as the sampling frequency for analog-to-digital conversion. As each frequency, a frequency obtained by multiplying the sampling frequency by an integer, such as 240 MHz, is used, and a reference frequency is appropriately selected according to the accuracy and ability required by the light wave range finder.

A frequency division signal is generated with respect to the reference frequency emitted from the reference signal generator 16, and a modulation frequency is generated by the division frequency signal and the reference frequency. The frequency division signal is obtained by dividing the reference frequency by an integral multiple for the convenience of calculation, and since the divisor depends on the S / N ratio, it is preferably about 8 to 20. In the following description, the divisor is 16, and a 7.5 MHz division frequency signal is generated.

As the reference signal from the reference signal generator 16, two adjacent modulation signals 120 MHz + 7.5 MHz and 120 MHz-7.5 MHz are generated by the modulation frequency generators 17a and 17b.

The modulated signal 120 MHz + 7.5 MHz is input to the light emitting element drive circuit 12, and the phase shifter 18a shifts the phase by 90 °, and the modulated signal 120 MHz + 7.5 MHz with the 90 ° phase shifted is the light emitting element drive circuit 12 Is entered in.

Similarly, the modulated signal 120 MHz-7.5 MHz is input to the light emitting element drive circuit 12, and the phase shifter 18b shifts the phase by 90 °, and the modulated signal 120 MHz-7.5 MHz whose phase is shifted by 90 °. Is input to the light emitting element drive circuit 12.

The light emitting element drive circuit 12 causes the light emitting element 1 to burst light (intermittent light emission) by the modulated signal 120 MHz + 7.5 MHz and the modulated signal 120 MHz + 7.5 MHz whose phase is shifted by 90 °. For example, as shown in FIG. 3A, the burst emission period is 10 μs (10 kHz), and the burst emission time is 933.33 ns.

Further, the light emitting drive signal emitted from the light emitting element drive circuit 12 is the first composite signal of IQ modulation by adding the modulated signal 120 MHz + 7.5 MHz whose phase is shifted by 90 ° to the modulated signal 120 MHz + 7.5 MHz. There is.

Similarly, in the light emitting element drive circuit 12, the modulation signal 120 MHz-7.5 MHz whose phase is shifted by 90 ° is added to the modulation signal 120 MHz-7.5 MHz, and the light emission is performed by the second composite signal of IQ modulation. The element 1 is made to emit burst light (intermittent light emission).

Further, the light emitting element drive circuit 12 is time-divided, and the light emitting element 1 is alternately emitted by the first composite signal and the second composite signal (see FIG. 3 (see)).

Therefore, from the light emitting element 1, the combined ranging light 3a modulated to 120 MHz-7.5 MHz with 120 MHz-7.5 MHz and 90 ° phase shifted, and 120 MHz + 7 with 120 MHz + 7.5 MHz and 90 ° phase shifted. The synthetic ranging light 3b modulated to .5 MHz is alternately burst-emitting with a burst emission period (10 μs).

The reference signal generator 16, the modulation frequency generators 17a and 17b, the phase shifters 18a and 18b and the like constitute a modulation signal generation unit 20.

Further, the control calculation unit 15 executes various programs stored in the storage unit 21 and executes necessary calculations necessary for distance measurement.

The storage unit 21 stores various programs for calculations necessary for measurement. For example, a signal processing program for executing signal processing such as amplifying and analog-digital conversion (A / D conversion) of the signal output from the light receiving circuit 13, and a discrete Fourier transform (DFT) for a burst signal. An arithmetic program for executing (transform), a program for converting the DFT result into phase and amplitude, a primary frequency obtained by executing DFT, a secondary frequency, etc .... (described later) is extracted from the phase and amplitude. The arithmetic program for the operation is stored.

Further, various data such as a distance measurement result and a calculation result are stored in the storage unit 21.

The main control unit 22 controls the distance measurement operation of the light wave range finder (not shown) and also controls the calculation process of the control calculation unit 15. The main control unit 22 and the control calculation unit 15 may be integrated into a control unit.

Since the signal processing for the distance measuring light 3 and the signal processing for the internal reference light are the same, the distance measuring light will be described below.

Intermittent light receiving signals 27a and 27b (see FIG. 3B) are alternately emitted from the light receiving element 7, and the intermittent light receiving signals 27a and 27b correspond to the combined ranging light 3a and 3b, and the intermittent light receiving signals 27a and 27b correspond to the combined ranging light 3a and 3b. The light-receiving signal 27a is an IQ-modulated light-receiving signal in which a signal width of 933.33 ns and 120 MHz-7.5 MHz with a phase shift of 120 MHz-7.5 MHz and 90 ° are combined.

Similarly, the intermittent light receiving signal 27b is an IQ-modulated light receiving signal in which a signal width of 933.33 ns and 120 MHz + 7.5 MHz with a phase shift of 120 MHz + 7.5 MHz and 90 ° are combined.

As described above, the light emitting period of the light emitting element 1 is 10 μs (100 kHz). Therefore, the generation period (generation interval) of the two intermittent light receiving signals 27a and 27b is 10 μs. The light emission interval is set sufficiently longer than the time it takes for the ranging light to reciprocate with respect to the object to be measured, and is appropriately set according to the required maximum ranging distance.

The intermittent light receiving signals 27a and 27b are mixed with the reference signal of 120 MHz in the mixing circuits 26a and 26b, respectively, and beat down to the intermittent modulation signals of +7.5 MHz and −7.5 MHz. Further, the 120 MHz reference signal whose phase is shifted by 90 ° by the phase converter 24 is mixed by the intermittent light receiving signals 27a and 27b and the mixing circuits 26a and 26b and demodulated by IQ, and 90 ° by the phase converter 24. It is beatdown to a phase-shifted ± 7.5 MHz intermittent modulation signal.

IQ demodulation separates the intermittently modulated signals of +7.5 MHz and -7.5 MHz and the intermittently modulated signals of + 7.5 MHz and -7.5 MHz with the 90 ° phase shifted.

The mixing circuits 26a and 26b, the phase converter 24 and the like constitute an IQ demodulation unit.

The intermittent modulation signal beatdown to ± 7.5 MHz is amplified by the amplifier 28a, and the intermittent modulation signal of ± 7.5 MHz whose phase is shifted by 90 ° is amplified by the amplifier 28b and input to the light receiving circuit 13. The intermittent modulation signal is subjected to necessary signal processing such as A / D conversion by the light receiving circuit 13, and is input to the control calculation unit 15.

Further, the light receiving element 7 includes an internal reference light in which 120 MHz + 7.5 MHz and 120 MHz + 7.5 MHz with a 90 ° phase shift are combined, and 120 MHz-7.5 MHz with a 120 MHz-7.5 MHz and a 90 ° phase shift. The combined internal reference light is incident in a time-division manner, and the light receiving signal emitted from the light receiving element 7 is also processed in the same manner as the distance measuring light 3.

The light emitting element drive circuit 12, the reference signal generator 16, the modulation frequency generators 17a and 17b, the phase shifters 18a and 18b and the like constitute a light emitting drive signal generation unit 34, and the amplifier 19 and the amplifier 19. The mixing circuits 26a and 26b, the amplifiers 28a and 28b, the phase converter 24, the light receiving circuit 13 and the like constitute a light receiving signal processing unit 35.

Regarding the internal reference light, the optical path length is constant, and when the circuit such as the light receiving circuit 13 is stable, the generation timing of the light emission drive signal and the light receiving circuit 13 receive the internal reference light. The generation timing of the light receiving signal to be emitted is fixed. Therefore, when the circuit such as the light receiving circuit 13 is stable, the light receiving circuit 13 receives the internal reference light and emits the intermittent light receiving signal 31 (see FIG. 4), and the generation timing of the light emitting drive signal. The relationship is also fixed, and the light receiving signal of the internal reference light emitted by the light receiving circuit 13 becomes a signal based on the light emitting drive signal.

Therefore, the light emission drive signal emitted by the light emitting element drive circuit 12 may be used as a reference signal.

FIG. 4 (A) shows the intermittent light receiving signal 31 of the internal reference light 4 when burst light emission is performed in a cycle of 10 μs, and FIG. 4 (B) shows the intermittent light receiving signal of the ranging light 3. 27a is shown, and FIG. 4C shows the primary frequencies (1 cycle 10 μs) 27a'and 31'extracted from the intermittent light receiving signal 27a and the intermittent light receiving signal 31 by DFT arithmetic processing and sideband processing. Shown.

In FIG. 4, the intermittent light receiving signals having a modulation frequency of 120 MHz + 7.5 MHz of the distance measuring light 3 (3a, 3b) and the internal reference light 4 are omitted. Further, the case where the light emitting element 1 is burst-emitting with 120 MHz-7.5 MHz alone, omitting 120 MHz-7.5 MHz whose phase is shifted by 90 °, will be described below.

Assuming that the intermittent light is pulsed light, the time difference between the emission timing of the ranging light 3 and the emission of the intermittent light receiving signal 31 is t1 for the intermittent light receiving signal 31, and the intermittent light 3 is intermittently emitted from the emission timing of the ranging light 3. Assuming that the time difference until the light receiving signal 27 is emitted is t2, t2-t1 = Δt is the time for the distance measuring light 3 to reciprocate to the object to be measured, and the distance to the object to be measured can be measured by the speed of light and Δt. .. However, unlike the single-pulse light, the intermittent light includes the modulated light of 120 MHz ± 7.5 MHz, so that the received modulated light (the emitted modulated signal) changes its shape depending on the distance. Therefore, the sampling position with respect to the modulated light varies, and as a result, the time difference Δt includes an error, and the measurement accuracy deteriorates. Therefore, in reality, the distance measurement is performed based on the phase difference between the received signal of the reflected ranging light and the received signal of the internal reference light.

However, as described above, since the received signal of the reflected distance measuring light and the received signal of the internal reference light are both intermittent light, the phase difference between the received signal of the reflected distance measuring light and the received signal of the internal reference light can be obtained. I can't. Therefore, the phase is obtained when the entire burst section is set to the burst period (frequency 100 kHz) of 2π, but when the frequency is converted, the amplitude of the spectrum appearing at 100 kHz (10 μs) becomes small.

For example, when the burst waveform (the section of FIG. 3A (burst period 10 μs)) is subjected to a discrete Fourier transform (DFT: discrete Fourier transform), the frequency and the amplitude and phase with respect to the frequency can be obtained. FIG. 5 shows a curve 32 showing the relationship between frequency and amplitude.

Note that FIG. 5 is a graph in which the vicinity of the emission frequency (7.5 MHz) is particularly enlarged. As shown in the figure, a large amplitude (hereinafter referred to as sideband 33) can be obtained in the vicinity centered on the emission frequency (7.5 MHz), but the amplitude sharply decreases as the distance from the intermediate frequency (7.5 MHz) increases. , There is almost no amplitude at 100 kHz (primary frequency), which is the light emission cycle.

The plot on the curve 32 in FIG. 5 shows the discrete interval processed by the DFT calculation.

This is because the light emitting drive signal emitted from the light emitting element drive circuit 12 is a sine wave having a frequency orthogonal to the primary frequency, and the signal included in the burst section (the section in which the signal exists) is also orthogonal to the primary frequency. This is because it becomes a sine wave of the frequency and is canceled out, and a valid amplitude does not appear in the primary frequency.

On the other hand, the present inventor pays attention to the fact that the sideband 33 having a large amplitude appears before and after the emission frequency (7.5 MHz) of the intermediate frequency, and uses the sideband 33 for this intermediate frequency with respect to the intermediate frequency. It has been found that the phase and amplitude of the sideband are obtained, and the phase of the 1st to 4th order wavelengths is further obtained.

The primary frequency is a frequency in which the burst light emission cycle is 2π, and is a frequency that rotates one cycle with the length of the data to be DFTed.

When there is a frequency in the entire DFT range, ideally only the emission frequency peaks and the frequencies before and after that peak are 0, but the burst waveform (see FIGS. 4 (A) and 4 (B)) is used for the DFT for the burst period. Then, since there is only a part of the waveform, the amplitude related to the frequency deviation from the emission frequency appears.

Since the amplitude of the sideband 33 is also a relational expression of the frequency deviation with the emission frequency (7.5 MHz), the phase of the frequency difference can be obtained from this. Since the frequency interval required for DFT is the same over the entire range (that is, the frequency interval is the burst emission frequency), the frequency difference between the emission frequency P1 and the emission frequency P1 and the closest emission frequency P2 included in the sideband 33 = The primary frequency is the difference between the emission frequency P1 and the emission frequency P3 closest to the second = the secondary frequency, and similarly the difference between the emission frequency P4 close to the third = the third frequency and the emission frequency P5 close to the fourth. Difference from and = 4th frequency. This makes it possible to obtain the phase of low-order (for example, 1st to 4th-order) frequencies (see FIG. 4C).

Further, a plurality of primary frequencies obtained by obtaining a plurality of primary frequencies using different adjacent emission frequencies Pn and Pn + 1 such as obtaining a primary frequency from the light emitting frequency P2 and a light emitting frequency P3 adjacent to the light emitting frequency P2 are obtained. The accuracy of the desired primary frequency may be improved by weighting the primary frequency of the above. Similarly, for the secondary frequency, the tertiary frequency, and the like, a plurality of frequencies may be obtained by changing the combination of emission frequencies, and the accuracy may be improved by weighting or the like.

Long-distance measurement can be performed by obtaining this primary frequency. Further, by obtaining the secondary frequency, the tertiary frequency, and the quaternary frequency, it is possible to measure a distance with high accuracy for a medium distance and a short distance.

FIG. 6 shows the phases of the frequencies P1 and P2 of two adjacent points with respect to the frequency included in the sideband 33, and represents the DFT calculation of the sideband 33 on a single core circle.

In FIG. 6, ω t is the angular velocity of the emission frequency (7.5 MHz, P1 in FIG. 5), and ω ₀ t is the angular velocity of the frequency of the sideband 33 (P2 in FIG. 5).

Due to the difference in angular velocity between the emission frequency and the sideband, the difference in angular velocity ((ω−ω ₀ ) t) phase rotates with respect to the phase of the emission frequency.

Since ω and ω ₀ exist at discrete intervals of DFT, the phase ((ω−ω ₀ ) t) obtained by the difference between adjacent frequencies is equal to the phase of the primary frequency of DFT. Therefore, the phase of the primary frequency can be obtained by obtaining the difference between adjacent frequencies.

DFT can also be performed on the intermittent received signal of the internal reference light, and the phase of the primary frequency can be obtained using the sideband. The phase of the primary frequency of the internal reference light is the phase of the reference primary frequency for obtaining the phase difference from the distance measuring light, and the phase of the reference primary frequency and the intermittent light receiving signal of the distance measuring light. The phase difference between the internal reference light and the distance measurement light is obtained from the phase of the primary frequency obtained in the sideband, and the measurement distance is calculated.

FIG. 7 shows an arithmetic expression (1) that performs DFT arithmetic processing for the burst period.

FIG. 8 shows the result of arithmetic processing based on the equation (1).

The sideband 33 is obtained by the DFT calculation process, but at the same time, the alias component 33'having the same waveform is also obtained. This alias component 33'corresponds to the a term and the b term in the equation (1).

The primary frequencies 27a'and 31'can be obtained by using either the sideband 33 or the alias component 33', but the sideband 33 and the alias component 33' are mutually exclusive. Since it has an effect, it is preferable to delete one of them in order to improve the accuracy. The case where the alias component 33'is removed will be described below.

As shown in the formula (1), the terms a and b depend on cos and sin, respectively. Therefore, the burst signal whose phase is shifted by π / 2 (90 °) is arithmetically processed by the equation (1) with respect to the burst signal which is arithmetically processed by the equation (1), and the obtained result is added. Item and item b can be removed.

In the present invention, based on such attention, a burst signal whose phase is shifted by π / 2 (90 °) is created, that is, 120 MHz ± 7.5 MHz whose phase is shifted by 90 ° is created, and this 90 ° phase is used. The light emitting element 1 is driven to emit light by a modulated signal obtained by combining the shifted 120 MHz ± 7.5 MHz and 120 MHz ± 7.5 MHz.

The reflected distance measuring light 3'reflected by the object to be measured is received by the light receiving element 7, and the intermittent light receiving signals emitted from the light receiving element 7 are beaten down by the mixing circuits 26a and 26b, and further, the phase converter 24 IQ demodulated by the signal from.

The beatdown received signal is separated into + 7.5 MHz and 90 ° phase-shifted + 7.5 MHz intermittent received signal, and the -7.5 MHz and 90 ° phase-shifted -7.5 MHz intermittent received signal is DFT. The alias component 33'is removed by performing arithmetic processing and further adding up the obtained results. FIG. 9 shows a state in which the alias component 33'has been removed.

Next, the above-mentioned signal processing will be specifically described with reference to FIG.

A signal that is 90 ° out of phase with respect to the 120 ± 7.5 MHz modulated signal is created, and further, an intermittent signal is input from the control calculation unit 15, so that the 120 ± 7.5 MHz and 90 ° phase are out of phase. 120 ± 7.5 MHz is combined, and an intermittent modulation signal is output as a Burst signal.

An intermittent light receiving signal is emitted from the light receiving element 7 that receives the reflected ranging light (and internal reference light) emitted by the burst signal. A reference signal (120 MHz) is mixed with one of the branched intermittent light receiving signals to beat down, and waveform data A (Waveform data A) is obtained. Further, a reference signal that is 90 ° out of phase is mixed with the other branched received signal, IQ demodulated and beatdown to obtain waveform data B (Waveform data B).

By adding the waveform data A and the waveform data B (FIG. 11 (A), equation (2)), cos (ω−ω ₀ ) t (a signal beatdown to 7.5 MHz) can be obtained.

Further, by subtracting the waveform data B from the waveform data A (FIG. 11 (B), equation (3)), sin (ω-ω ₀ ) t (beat down to 7.5 MHz and 90 ° phase shift). Signal) is obtained.

In the process of addition and subtraction, sin (ω + ω ₀ ) t and cos (ω + ω ₀ ) t appear, but ω + ω ₀ = 480 ± 7.5 MHz is a high frequency and is removed by a low-pass filter.

Further, by synthesizing the (A + B) signal and the (AB) signal and performing the DFT calculation processing, the sideband 33 from which the alias component 33'has been removed can be obtained (see FIG. 9).

Therefore, in the present embodiment, the intermittent modulation signal and the intermittent modulation signal whose phase is shifted by 90 ° with respect to the modulated signal are used as the light emission drive signal for burst light emission, thereby causing interruption. When the received signal is subjected to DFT calculation processing, the sideband 33 can be left and the alias component 33'which is an unnecessary signal can be removed.

Furthermore, the primary frequency with the burst section as one cycle can be obtained from the adjacent frequency included in the sideband 33, and the burst light emission method does not require a complicated circuit configuration, and high-precision distance measurement is possible. It becomes.

1 Light emitting element 2 Half mirror 3 Distance measuring light 3'Reflected distance measuring light 7 Light receiving element 12 Light emitting element Drive circuit 13 Light receiving circuit 14 Drive circuit 15 Control calculation unit 16 Reference signal generator 17a, 17b Modulation frequency generator 18a, 18b Phase Shifter 19 Amplifier 20 Modulation signal generator 21 Storage unit 22 Main control unit 24 Phase converter 26a, 26 Mixing circuit 27a, 27b Intermittent light receiving signal 31 Intermittent light receiving signal 32 Curve 33 Sideband 35 Light receiving signal processing unit

Claims (3)

A reference signal generator that emits a reference signal, a light emitting element that emits distance measuring light, a modulation signal generator that generates a modulation signal based on the reference signal, and an intermittent light emission drive signal that emits an intermittent light emission drive signal based on the modulation signal. A light emitting element drive circuit that bursts light at a predetermined cycle, a light receiving element that receives reflected distance measurement light from the measurement target, and a control calculation unit that calculates the distance to the measurement target based on the light receiving signal from the light receiving element. The light emitting element drive circuit emits a signal obtained by synthesizing a modulated signal and a modulated signal whose phase shift of the modulated signal by 90 ° as the intermittent light emitting drive signal, and the control calculation unit outputs the received light signal to DFT. arithmetic processing, obtains an intermediate frequency obtained, the sidebands with respect to the intermediate frequency phase, determine the amplitude, the phase of the frequency corresponding to the burst period based on the two frequency included before Symbol sideband, the frequency A light wave distance meter that calculates the distance based on the phase of. The received light signal is input to the light receiving circuit via a light receiving signal processing unit, and the light receiving signal processing unit branches the received light signal, mixes a reference signal with one of the branched received light signals, and branches the other. The light wave distance meter according to claim 1, wherein a reference signal whose phase is shifted by 90 ° is mixed with the received signal and input to the control calculation unit. The light-receiving signal processing unit adds, subtracts, and further synthesizes the branched bi-branched light-receiving signals and inputs them to the control calculation unit. The control calculation unit uses the intermittent light-receiving signal as a pulse signal and measures it by the TOF method. The light wave distance meter according to claim 2, which calculates the distance to an object.

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