WO2012073378A1

WO2012073378A1 - Optical distance measurement device

Info

Publication number: WO2012073378A1
Application number: PCT/JP2010/071689
Authority: WO
Inventors: 湯口翼
Original assignee: ジックオプテックス株式会社
Priority date: 2010-12-03
Filing date: 2010-12-03
Publication date: 2012-06-07

Abstract

Disclosed is an optical distance measurement device provided with: a first light projecting unit (1) which projects, to a subject to be measured, a measurement light signal being subject to high frequency modulation at a predetermined frequency; a second light projecting unit (2) which projects a reference light signal being subject to high frequency modulation at a frequency minutely different from the frequency through a light path inside the device; a light receiving unit (3) which has a single light receiving circuit (31) that outputs a beat signal obtained by receiving and mixing both the measurement light signal projected from the first light projecting unit (1) to be reflected by the subject to be measured and the reference light signal projected from the second light projecting unit (2) and a light receiving signal amplifying circuit (32) that amplifies the beat signal; a synchronous detection circuit (5) which synchronously detects the beat signal from the light receiving unit (3) to obtain synchronously detected output; and a phase consistent point extracting circuit (7) which extracts a phase consistent point of the beat signal from the synchronously detected output to obtain phase shift of the measurement light signal and the reference light signal, wherein a distance to the subject to be measured is measured on the basis of the phase shift.

Description

Lightwave ranging device

The present invention relates to a light wave distance measuring device that measures the distance to a measurement object using reflection of light.

FIG. 8A shows a basic configuration of a conventional lightwave distance measuring device, and FIG. 8B shows a measurement waveform thereof. As shown in FIG. 8A, this light wave distance measuring device projects a measurement light (light projection) signal, which is a high-frequency modulated light generated by the light projection pulse generation circuit 112 based on a predetermined frequency from the reference oscillator 110. Light is projected from the optical circuit 114, reflected by the measurement object M, received by the light receiving circuit 132 with a delay corresponding to the distance, and the received light signal is amplified to a required amplitude by the received light signal amplification circuit 133. Input to the phase detection circuit 115. In the phase detection circuit 115, as shown in FIG. A projection signal waveform (projection waveform) and b. A phase shift (c. Phase lag) from the waveform of the received light signal (received waveform) is detected, and the distance to the measuring object M is calculated by converting the phase lag measured by the delay time measuring circuit 117. The Since the travel time of light is as fast as about 3.3 microseconds at 1 km, it is necessary to measure the pulse width of the phase delay in units of 33 picoseconds if the measurement distance resolution is 10 mm. Measurement of the phase delay of both signals becomes difficult.

As an example of a conventional optical distance measuring device, the phase lag between the measurement light (projection) signal and the received light signal that is reflected by the measurement signal reflected by the measurement object is set to two slightly different frequencies. An apparatus for measuring the phase of the mixed beat signal is mentioned (for example, Patent Document 1). This apparatus can relatively easily measure the pulse width of the phase lag by expanding the phase lag between the light projection signal and the light reception signal in terms of time.

Fig. 9 (A) shows the basic configuration of a light wave distance measuring device using beat signals, and Fig. 9 (B) shows the measured waveform. As shown in FIG. 9A, the optical distance measuring device is a measurement light (high-frequency modulated light generated by the first projection pulse generation circuit 112 based on a frequency of, for example, 10 MHz generated by the first reference oscillator 111 ( A light emitting) signal is projected from the first light projecting circuit 114 having the light projecting element, reflected by the measurement object M, and received by the light receiving circuit 132 having the light receiving element with a delay corresponding to the distance, The received light signal is amplified to a required amplitude by the received light signal amplifier circuit 133 and input to the phase detection circuit 115. On the other hand, a reference signal generated by the second reference oscillator 121 and having a frequency slightly different from the frequency of the first reference oscillator 111 such as 100 Hz is also input to the phase detection circuit 115.

The phase detection circuit 115 detects the envelope of the beat signal mixed with the above slightly different frequencies, removes high frequency components by a low-pass filter (LPF) (not shown), and then outputs the detection output to the phase matching point extraction circuit 118. Is input. In the phase matching point extraction circuit 118, as shown in FIG. Delayed with respect to the waveform of the projection signal (projection waveform) of c. A light receiving signal waveform (light receiving waveform) of b. The phase shift from the reference signal waveform (reference waveform) of d. Is obtained on the basis of the phase coincidence point by phase detection of the beat signal, and the distance to the measuring object M is calculated by converting this phase shift (phase delay).

In this conventional apparatus, the phase shift of each signal waveform changes little by little by shifting the frequency of the light projection signal and the reference signal very slightly. The phase coincidence point with the waveform of the reference signal changes between the waveform of the light projection signal and the waveform of the light reception signal delayed with respect to the waveform, but the amount of change is the reference frequency f2 ÷ (reference frequency f2−light projection frequency f1). Therefore, it is possible to convert a very high speed travel time of light to a measurable time. This makes it possible to relatively easily measure the pulse width of this phase lag by expanding the phase lag between the projected signal and the reference signal in time due to a slight frequency shift between the projected signal and the reference signal. it can.

On the other hand, as a light wave distance measuring device, one that can improve the response to changes in the amount of signal light (for example, Patent Document 2), and one that can shorten the time required for distance measurement (for example, Patent Document 3). ) And those using modulated light by a PN code as a carrier wave (for example, Patent Documents 4 and 5) are also known.

Japanese Patent Application Laid-Open No. 10-068776 JP 2005-303264 A JP-A-9-252242 JP 2002-334391 A Japanese Patent No. 3055714

In FIG. 9A, the delay time from the reference oscillator 111 to the phase detection circuit 115 is the delay time of the light projection pulse generation circuit 112: Tep, the delay time of the light projection circuit 114 and the light projection element 113: Ted, Light travel time from the light projecting element 113 to the light receiving element 131 after being reflected by the measurement object: Tt, delay time of the light receiving element 131 and the light receiving circuit 132: Trd, and delay time of the light receiving signal amplifying circuit 133: Tra The total of the four delay times Tep, Ted, Trd, Tra and the optical movement time Tt 光 to the measurement object.

Further, since the phase coincidence point output from the phase detection circuit 115 is expanded by a slight difference between the two signal frequencies, assuming that the frequencies of the reference oscillators 1 and 2 are flf and f2, respectively, the delay time Tm is Tm = (Tep + Ted + Tt + Trd + Tra) × f2 ÷ (f2－ fl). That is, not only the light moving time but also the delay time generated in each circuit is extended as it is, and the measurement accuracy is lowered.

On the other hand, in the conventional optical wave distance measuring device, the problem is that the delay time on circuits such as a light projecting circuit and a light receiving circuit fluctuates. The travel time of light is only 3.3 nanoseconds per meter. In particular, in a light receiving circuit and a light receiving signal amplifier circuit, fluctuations of several nanoseconds occur naturally due to temperature changes. In other words, the measurement result greatly fluctuates, and correction means such as calculating correction by temperature at the time of manufacturing the apparatus or obtaining a difference by using two circuits simultaneously is necessary. More importantly, the light receiving circuit and the light receiving signal amplifier circuit may fluctuate so that the delay time cannot be ignored depending on the intensity of received light, that is, the signal amplitude.

Therefore, in order to correct this variation, it is necessary to add a correction calculation based on the received light amplitude and temperature, and since they have different characteristic curves for each device, the temperature and the received light amount respectively. On the other hand, calibration work is forced in the device manufacturing process.

In the above-mentioned patent document 2, in order to suppress the phase change due to the variation in the amount of received light, the light projection amount is changed and coped with. However, since the delay time of the light projection circuit changes by changing the light projection amount, This is not a preferable correction method. In addition, since there is a time difference between the determination of the amount of received light and the change in the amount of emitted light, there are cases where measurement cannot be performed correctly until the desired amount of received light is reached.

In Patent Document 3, a light receiving circuit for measurement and two light receiving circuits for internal reference are provided, and the fluctuation is corrected by the phase difference. However, since the light receiving amount for measurement and the light receiving amount for internal reference are different, It is difficult to operate the two light receiving circuits under the same conditions, that is, with the same delay time. Even if the received light amplitudes coincide, separate components are mounted on the two circuits, and the phase of the resonance circuits and filters for removing noise, in particular, fluctuates greatly with slight fluctuations in the resonance frequency. Therefore, it is practically difficult to compensate for the delay time for the purpose of use in the optical wave distance measuring device.

Further, Patent Documents 4 and 5 use modulated light by a PN code, provide a slight difference between the light projection frequency and the reference frequency, and obtain a point where the phases match, and the influence of the difference in the amount of received light is small. Although described, in principle, fluctuations in the delay time of the received light signal amplifier circuit have a great influence on the measurement result.

The present invention solves the above-described problems and provides a light wave distance measuring device capable of improving measurement accuracy by greatly reducing the influence of delay time of constituent circuits, particularly delay time fluctuation of a light receiving side circuit having large fluctuations. The purpose is to do.

In order to achieve the above object, a light wave distance measuring device according to one configuration of the present invention includes a first light projecting unit that projects a measurement light signal, which is high-frequency modulated at a predetermined frequency, onto a measurement object; A reference light signal modulated at a frequency slightly different from the frequency is projected through a light path inside the apparatus, and the light is projected from the first light projecting part and reflected by the measurement object. A single light receiving circuit that receives both the measurement light signal and the reference light signal projected from the second light projecting unit and outputs a mixed beat signal; and a light receiving signal amplification circuit that amplifies the beat signal. A light receiving unit, a synchronous detection circuit for synchronously detecting a beat signal from the light receiving unit to obtain a synchronous detection output, a phase coincidence point of the beat signal is extracted from the synchronous detection output, and the measurement light signal and the reference light Phase matching point extraction to obtain signal phase shift And a road to measure the distance to the measurement object based on the deviation of the phase.

According to this configuration, both the measurement light signal reflected by the measurement object and the reference light signal are received by the single light receiving circuit, and the beat signal received and mixed is synchronously detected by the synchronous detection circuit. The reference light signal is input to the light receiving circuit together with the measurement light signal. That is, the measurement light signal and the reference light signal which is an optical signal are mixed in the light state and input to the light receiving circuit. This is greatly different from the conventional case where the reference signal, which is an electrical signal, is input to the phase detection circuit and the measurement light signal and the reference signal are mixed in the phase detection circuit. Since the measurement light signal and the reference light signal pass through the same light receiving circuit, light receiving signal amplification circuit, and synchronous detection circuit, fluctuations in the delay time of these circuits cancel each other, and the extended phase delay on the beat signal is affected. I can not. As a result, it is possible to significantly reduce the influence of the delay time fluctuation of the light receiving unit having a particularly large fluctuation and improve the measurement accuracy.

Preferably, the light reception signal amplification circuit mixes the beat signal and a signal having a frequency different from the carrier frequency of the beat signal generated from the local oscillation circuit, and generates a beat signal having a frequency lower than the carrier wave of the beat signal. Amplify. Therefore, since the high-frequency weak signal is amplified, it is possible to prevent abnormal oscillation due to unexpected electromagnetic coupling when the received light signal is amplified as it is.

Preferably, the synchronous detection circuit includes a control circuit that resets a hold capacitor of the peak hold circuit using the carrier wave of the amplified beat signal. Therefore, the peak value of the peak of the amplitude of the high frequency signal can be accurately maintained.

In the present invention, both the measurement light signal reflected by the measurement object and the reference light signal are received by a single light receiving circuit, and the beat signal received and mixed is synchronously detected by the synchronous detection circuit. In particular, the measurement accuracy can be improved by significantly reducing the influence of the delay time fluctuation of the light receiving unit having a large fluctuation.

The present invention will be understood more clearly from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are for illustration and description only and should not be used to define the scope of the present invention. The scope of the present invention is defined by the appended claims (claims). In the accompanying drawings, the same component symbols in a plurality of drawings indicate the same parts.
It is a block diagram which shows the light wave ranging apparatus which concerns on one Embodiment of this invention. It is a block diagram which shows the detail of a reference | standard oscillator. It is an arrangement view showing an example of a light projecting / receiving element and an optical system. (A), (B) is a figure which shows an operation | movement waveform. It is a block diagram which shows the detail of a light-receiving part. (A) is a block diagram which shows the detail of a synchronous detection circuit, (B) is a figure which shows the waveform of a synchronous detection output. (A) is a block diagram which shows the detail of a phase matching point extraction circuit, (B), (C) is a figure which shows the waveform of a synchronous detection output. (A) is a basic configuration of a conventional optical wave distance measuring device, and (B) is a diagram showing the measurement waveform. (A) is a basic configuration of a conventional optical wave distance measuring device, and (B) is a diagram showing the measurement waveform.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a light wave distance measuring device according to an embodiment of the present invention. The light wave distance measuring device includes a first light projecting unit 1, a second light projecting unit 2, a light receiving unit 3, a synchronous detection circuit 5, a logarithmic conversion circuit 6, and a phase matching point extraction circuit 7.

The first light projecting unit 1 generates a light projection pulse based on a first reference oscillator 11 that generates a signal having a predetermined frequency, and outputs a measurement light signal that is high-frequency modulated at this frequency. An optical pulse generation circuit 12, a first light projection circuit 13 for projecting the measurement optical signal, and a switch 15 are provided. The second light projecting unit 2 generates a light projecting pulse based on the second reference oscillator 21 that generates a signal having a frequency slightly different from the frequency of the first reference oscillator 11, and the frequency slightly different from the first reference oscillator 11. It has a second projection pulse generation circuit 22 that outputs a modulated reference optical signal, and a second projection circuit 23 that projects the reference optical signal through an optical path inside the apparatus. The switch 15 switches the signal input from the first projection pulse generation circuit 12 to the first projection circuit 13 and the second projection circuit 23. The second light projecting circuit 23 also has a function of mixing and projecting signals given from the first light projecting pulse generating circuit 12 and the second light projecting pulse generating circuit 22.

The light receiving unit 3 receives both the measurement light signal and the reference light signal reflected by the measurement object M, and outputs a mixed beat signal, and the received and mixed beat. A received light signal amplifier circuit 32 is provided for amplifying the signal. Unlike the conventional case where the reference signal, which is an electrical signal, is input to the phase detection circuit and the measurement optical signal and the reference signal are mixed by the phase detection circuit, in the present invention, the reference optical signal is a single signal. In this case, the measurement light signal and the reference light signal, which is an optical signal, are mixed before the light receiving circuit 31, that is, in the light state, and input to the light receiving circuit 31.

FIG. 2 shows the configuration of the first and

second reference oscillators

11 and 21 in detail. For example, a well-known PLL (phase locked loop) circuit is used. In the first reference oscillator 11, the crystal oscillation circuit 51 oscillates at its inherent frequency fr, and is input to the phase comparator 53 at a frequency of fr / m by a frequency divider (M-1) 52 having a frequency division ratio m. . On the other hand, a VCO (voltage controlled oscillator) 54 oscillates at its own frequency f0 and generates a voltage v0, and is phase-shifted at a frequency of f0 / n by a frequency divider (N-1) 55 having a frequency division ratio n. Input to the comparator 53. At this time, the oscillation frequency (reference oscillation output 1) f0 is (n / m) · fr, and the desired oscillation frequency f0 is obtained from the single oscillation frequency fr by the frequency dividing ratio of the

frequency dividing circuits

52 and 55. Similarly, in the second reference oscillator 21, the crystal oscillation circuit 51, the frequency divider (M−2) 56, the phase comparator 57, the VCO (voltage controlled oscillator) 58 and the frequency divider (N−2) 59 are similarly used. Operates to obtain a desired oscillation frequency (reference oscillation output 2) f0. Various frequencies can be generated by changing the set value of the frequency divider. Since the set frequency is determined by each frequency divider, the frequency ratio is always constant.

For example, when the frequency of the crystal oscillation circuit 51 is 10.5 MHz, if the frequency dividing ratios of the frequency dividers (N-1) 55 and (M−1) 52 are 2943 and 3080, the frequency is 10.003295455MHz. Further, if the frequency dividing ratios of the frequency dividers (N-2) 59 and (M-2) 56 are 2341 mm and 2450 mm, the frequency difference is 10.3285714 MHz, and the frequency difference between them is 97.4 Hz, that is, the optical movement time is increased by 103005 times. be able to.

As shown in FIG. 1, the reference oscillation outputs from the first and

second reference oscillators

11 and 21 are input to the first and second projection pulse generation circuits 12 and 22, respectively. The light emission pulse generation circuits 12 and 22 generate a light emission pulse with an arbitrary duty ratio and output a measurement light signal and a reference light signal, and also periodically switch to prevent mutual interference with other devices. Realize that. Since this can be realized by a logic circuit, the circuit is usually configured on a logic operation element such as a gate array or FPGA (Field-Programmable Gate Array). The first and second

light projecting circuits

13 and 23 drive the measuring light projecting element 41 and the reference light projecting element 42 (FIG. 3).

FIG. 3 shows an arrangement example of the light projecting / receiving element and the optical system. The measurement light projecting element 41 and the reference light projecting element 42 are electro-optical signal conversion elements such as laser diodes and light emitting diodes. In the first and second

light projecting circuits

13 and 23, the delay time of the light projecting elements 41 and 42 occupies most of the light projecting elements 41 and 42. Therefore, the same light projecting elements 41 and 42 are used, and the drive current and the element temperature are made as close as possible. This is very important.

The light receiving circuit 31 of the light receiving unit 3 uses a photodiode as the light receiving element 43. Usually, the amount of received light of the measurement light signal (measurement light projection) is made smaller than that of the reference light signal (reference light projection). FIG. 4A shows a waveform in a state in which each light enters the photodiode 43. The solid line is the waveform for measurement and the broken line is the waveform for the reference projection. Here, in order to make the waveform easier to see, the frequency difference between the measurement light projection and the reference light projection is made larger than the actual one.

The measurement light signal and the reference light signal converted into electrical signals by the light receiving element 43 are the sum of the two light reception signals, and thus have a waveform as shown in FIG. When the phases of both waveforms coincide, the amplitude increases (α in the figure), and the amplitude decreases when the phase is shifted by 180 degrees (β in the figure).

FIG. 5 shows in detail the light receiving circuit 31 and the light receiving signal amplification circuit 32 that perform two frequency mixing in the light receiving unit 3. The beat signal mixed in the light receiving circuit 31 is used in the light receiving signal amplification circuit 32 to have the necessary amplitude. Amplify to The light receiving circuit 31 includes the light receiving element (photodiode) 43. The light receiving signal amplifying circuit 32 includes a first stage amplifying circuit 61, a frequency mixing amplifying circuit (mixer) 62, a local oscillator 63, a bandpass filter 64, and an intermediate frequency amplifier 65. Have

A beat signal amplified by the first stage amplifier circuit 61 and a signal having a frequency different from the carrier frequency of the beat signal are input to the frequency mixing amplifier circuit (mixer) 62 and lower than the beat signal carrier wave. A signal having a frequency (intermediate frequency) is output, and a signal amplified by the intermediate frequency amplifier 65 is output via the band pass filter 64. The carrier wave of the beat signal is a high-frequency signal of the measurement optical signal or the reference optical signal. In order to amplify a weak high-frequency signal, if the light reception signal is amplified as it is, abnormal oscillation may be caused by unexpected electromagnetic coupling. Therefore, the signal is once converted to an intermediate frequency and then amplified.

FIG. 6 (A) shows the configuration of the synchronous detection circuit 5, and the detection output waveform is shown by the bold line in FIG. 6 (B). The synchronous detection circuit 5 in FIG. 6A obtains a synchronous detection output by performing synchronous detection while leaving only the beat frequency component in order to detect the peak of the amplitude of the beat signal. A value circuit 72 and a hold reset control circuit 73 are provided. Conventionally, after detecting the envelope of the signal modulated at high frequency by the phase detection circuit, the high frequency component is removed by the low pass filter. Therefore, the measurement accuracy can be increased by using the synchronous detection circuit 5 that does not have this fear.

In the synchronous detection circuit 5, the high frequency signal (carrier wave) input by the binarization circuit 72 is binarized, and the hold reset control circuit 73 resets the hold capacitor of the peak hold circuit 71 at the valley of the amplitude of the original high frequency signal. . Thereafter, by charging the hold capacitor with the input signal, the peak value of the peak of the amplitude of the high-frequency signal can be accurately held as shown in FIG.

FIG. 7A shows the configuration of the phase matching point extraction circuit 7. The phase matching point extraction circuit 7 includes an A / D converter 81, a buffer memory 82, a waveform slope calculation unit 83, and a waveform peak / valley detection unit 84. The synchronous detection output from the synchronous detection circuit 5 in FIG. 1 is given to the logarithmic conversion circuit 6 and logarithmically converted, converted into digital data by the A / D converter 81 in FIG. 7A, and stored in the buffer memory 82. Is done. The waveform inclination calculation unit 83 calculates the average inclination of the waveform, and the waveform peak / valley detection unit 84 detects the peak or valley of the waveform.

As shown in FIG. 7B, the average slope of the waveform is obtained, and the point where the average slope is parallel becomes the peak or valley of the waveform. In this circuit, the position of the maximum value or the minimum value of the amplitude of the beat frequency component of the detection output is measured, and the switch 15 in FIG. 1 is switched from the first light projecting circuit 13 to the second light projecting circuit 23 on the lower side. From the difference from the result of measuring the position of the maximum value or the minimum value, it is possible to determine how much the phase is shifted (phase delay) when the measurement light projection waveform and the reference light projection waveform are received.

When the measurement distance L to the measurement object M is the frequency f1 of the measurement optical signal, the frequency f2 of the reference optical signal, the phase delay (difference of delay time) Td of both signals, and the light velocity c, Calculated.
L = (1/2) · ((f2−f1) ÷ f2) · Td · c (1)
The obtained measurement distance L is displayed on a display (not shown).

Further, when the measurement light reception amount of the measurement light signal becomes weak, the reference light signal mainly remains in the light receiving circuit 31, and the output of the reception signal amplifying circuit 32 outputs the frequency of the beat signal as shown in FIG. Ingredients decrease. The detection output after passing through the synchronous detection circuit 5 is also in a direction in which it is difficult to detect the peaks and valleys of the waveform because the amplitude is small, but the delay time variation of the light receiving circuit 31 and the light receiving signal amplifying circuit 32 due to the change in amplitude is Since it does not directly affect the waveform after the phase shift is expanded, the influence on the measurement result can be ignored.

The switch 15 in FIG. 1 switches the signal input from the first projection pulse generation circuit 12 to the first projection circuit 13 and the second projection circuit 23, and simulates the state of the measurement distance 0. It is for generating. Usually, the state of the measurement distance 0 is stored by giving the signal of the first projection pulse generation circuit 12 to the second projection circuit 23 at the time of activation. This is a work necessary to first confirm the phase relationship between the first reference oscillator 11 and the second reference oscillator 21. By switching the switch 15, the phase delay between the two signals is obtained, and the measurement distance L is calculated from the equation (1).

Here, the delay time from the first and

second reference oscillators

11 and 21 to the phase matching point extraction circuit 7 is calculated as follows. That is, delay times of the first and second projection pulse generation circuits 12 and 22: Tep1, Tep2, delay times of the first and

second projection circuits

13, 23 and the built-in projection elements 41, 42: Ted1, Ted2, the light travel time from the light projecting elements 41, 42 to the light receiving element 43 after being reflected from the measuring object: Tt, the delay time of the light receiving element 43 and the light receiving circuit 31: Trd, the light receiving signal amplification circuit 32, synchronous detection When the delay time of the circuit 5 and the logarithmic conversion circuit 6 is Tra, the delay time Tm is
Tm = (Tepl + Tedl + Tt-(Tep2 + Ted2)) x f2 ÷ (f2-fl) + Trd + Tra ... (2)
It becomes.

Explaining the above equation (2), the measurement optical signal and the reference optical signal having two slightly different frequency components generated by the first and

second reference oscillators

11 and 21 are respectively the first and second light projections. It reaches the light receiving element 43 of the single light receiving circuit 31 via the

circuits

13 and 23. An optical signal is converted into an electrical signal on the light receiving element 43, where two frequency components are mixed, and a beat signal is generated due to the phase difference between them. For example, if the frequency of the second reference oscillator is 10 MHz and the frequency of the first reference oscillator is 100 Hz slower than that, the beat signal is 100 Hz, and the first and second projection pulse generation circuits 12 and 22, the first and second projections. The difference between the delay times generated in the

optical circuits

13 and 23 and the optical movement time to the measurement object are extended by 10 MHz10 ÷ 100 Hz, that is, 100,000 times. Thereafter, the delay time of the light receiving circuit 31 and the like is added, but the influence of the delay time is only 1 / 100,000 with respect to the extended optical movement time. That is, when the measurement light signal and the reference light signal are input to the single light receiving circuit 31, the influence of the phase delay expansion due to the difference between the two signal frequencies does not reach the light receiving unit 3.

In addition, in the above formula (2), the delay time (Tepl + Ted1) and (Tep2 + Ted2) on the light emitting side remains affected, but both are in a compensation relationship, and the current flowing through the light emitting element and the temperature of the circuit element By maintaining a uniform value, the influence can be almost ignored.

In this way, the reference light signal projected from the second light projecting unit 2 is input to the single light receiving circuit 31 together with the measurement light signal projected from the first light projecting unit 1 and reflected by the measurement object M. Thus, a beat signal is generated, that is, a measurement optical signal having a minute difference between two signal frequencies and a reference optical signal which is an optical signal are mixed in the light state and input to the light receiving circuit 31. Since the measurement light signal and the reference light signal pass through the same light receiving circuit, light receiving signal amplification circuit, and phase detection circuit, fluctuations in the delay time of these circuits cancel each other, and the extended phase delay on the beat signal is affected. Not give. Conventionally, the phase detection circuit mixes two measurement optical signals having slightly different frequencies and a reference signal, which is an electrical signal. Therefore, the reference signal is obtained only by the measurement optical signal in the light receiving circuit and the light reception signal amplifying circuit. Therefore, the influence of the phase delay expansion due to the difference between the two signal frequencies is greatly different from that which has been exerted in the light receiving circuit and the light receiving signal amplifying circuit.

In the case of the configuration of FIG. 1, even if there is a difference in the received light intensity of the reference light signal and the measurement light signal, even if a fluctuation occurs in the delay time of the light receiving circuit and the subsequent circuit, the fluctuation is up to the measurement object. The effect is negligible because it is reduced to 1 / 100,000 of the light travel time (at the aforementioned frequency).

Thus, in the present invention, both the measurement light signal and the reference light signal reflected by the measurement object are received by the single light receiving circuit, and the beat signal received and mixed is synchronously detected by the synchronous detection circuit. Therefore, even if the phase delay between the measurement light signal and the reference light signal is extended due to a minute difference between the two signal frequencies, the measurement light signal mixed as the beat signal and the reference light signal are the same light receiving circuit, light receiving signal. Through the amplifier circuits, delay time fluctuations in these circuits cancel each other out and do not affect the extended phase delay on the beat signal. As a result, it is possible to significantly reduce the influence of the delay time fluctuation of the light receiving unit having a particularly large fluctuation and improve the measurement accuracy.

In this embodiment, the light reception signal amplification circuit 32 amplifies a beat signal having a frequency lower than that of the beat signal carrier by using the local oscillator 63, but a beat signal having a frequency higher than that of the beat signal carrier is used. Amplification may be performed, or this may be omitted as necessary.

As described above, the preferred embodiments have been described with reference to the drawings. However, those skilled in the art will readily consider various changes and modifications within the obvious range by looking at the present specification. Accordingly, such changes and modifications are to be construed as within the scope of the invention as defined by the appended claims.

1: first light projecting unit 2: second light projecting unit 3: light receiving unit 5: synchronous detection circuit 7: phase matching point extracting circuit 11: first reference oscillator 12: first light projecting pulse generating circuit 13: first light projecting Optical circuit 21: second reference oscillator 22: second light projection pulse generation circuit 23: second light projection circuit 31: light reception circuit 32: light reception signal amplification circuit 63: local oscillator 71: peak hold circuit 73: hold reset control circuit M : Measurement object

Claims

A first light projecting unit that projects a measurement light signal modulated at a high frequency at a predetermined frequency onto an object to be measured;
A second light projecting unit for projecting a reference optical signal modulated at a frequency slightly different from the frequency through an optical path inside the device;
Both the measurement light signal projected from the first light projecting unit and reflected by the measurement object and the reference light signal projected from the second light projecting unit are received and a mixed beat signal is output. A light receiving unit having a single light receiving circuit and a light receiving signal amplifying circuit for amplifying the beat signal;
A synchronous detection circuit that synchronously detects a beat signal from the light receiving unit to obtain a synchronous detection output; and
A phase matching point extraction circuit that extracts a phase matching point of a beat signal from the synchronous detection output and obtains a phase shift between the measurement optical signal and a reference optical signal,
A light wave distance measuring device that measures a distance to a measurement object based on the phase shift.
In claim 1,
The light reception signal amplification circuit mixes the beat signal and a signal having a frequency different from the carrier frequency of the beat signal generated from the local oscillation circuit, and amplifies a beat signal having a frequency lower than the carrier wave of the beat signal. Lightwave ranging device.
In claim 1,
The synchronous detection circuit includes a control circuit that resets a hold capacitor of a peak hold circuit using a carrier wave of the amplified beat signal.