JP7115738B2 - Rangefinder, distance measuring method, and optical three-dimensional shape measuring machine - Google Patents

Description

The present invention relates to a rangefinder, a distance measuring method, and an optical three-dimensional shape measuring machine for measuring distance from the time difference between an interference signal of reference light and an interference signal of measurement light.

2. Description of the Related Art Conventionally, distance measurement based on optical principles using laser light has been known as an active distance measurement method capable of precise point distance measurement. A laser rangefinder, which measures the distance to an object using a laser beam, detects the distance to the object based on the difference between the time when the laser beam is emitted and the time when the light receiving element detects the laser beam that hits and is reflected from the object to be measured. is calculated (see Patent Document 1, for example). In addition, for example, the driving current of the semiconductor laser is modulated with a triangular wave or the like, and the reflected light from the object is received using a photodiode embedded in the semiconductor laser element, and the sawtooth that appears in the photodiode output current is obtained. Distance information is obtained from the dominant wave number of the square wave.

A laser rangefinder is known as a device that measures the absolute distance from a certain point to a measurement point with high accuracy. For example, Patent Literature 1 describes a rangefinder that measures a distance from a time difference between an interference signal of reference light and an interference signal of measurement light.

With conventional absolute distance meters, it is difficult to achieve a practical absolute distance meter that can measure long distances with high accuracy. I had no choice but to use an unsuitable method.

The inventors of the present invention detect the interference light between the reference light irradiated on the reference surface and the measurement light irradiated on the measurement surface with a reference light detector, and detect the reference light reflected by the reference surface and the measurement surface. Interference light with the measurement light reflected by the measurement light detector is detected by the measurement photodetector, and the distance to the reference plane and the measurement We have previously proposed a rangefinder, a distance measuring method, and an optical three-dimensional shape measuring machine that can be performed with high precision and in a short time by obtaining the difference in distance to the surface (see, for example, Patent Document 2.)

JP-A-2001-343234 Japanese Patent No. 5231883

By the way, when looking at the shape of a material with low reflectance, such as a rough material surface, in optical shape measurement, a high-gain light receiving system is prepared so that even minute reflected light falls within the proper signal amplitude range. system design from light reception to signal processing.

With this setting, the gain becomes excessive for clean processed surfaces or mirror surfaces with high reflectivity, and phenomena such as exceeding the input range of the A/D converter and signal waveform saturation occur, resulting in measurement errors. cause growth.

Conversely, if the gain is set on the assumption that a surface with a high reflectivity such as a mirror surface is used, the sensitivity on the rough material surface will be insufficient, resulting in a problem of degraded measurement accuracy.

If the reflectance of the object to be measured is biased towards one or the other, it is possible to switch the gain for measurement. I can't help it.

SUMMARY OF THE INVENTION In view of the conventional circumstances as described above, an object of the present invention is to provide a rangefinder and a distance measuring method capable of continuously measuring a reflected light level over a wide dynamic range from a low-reflecting material to a high-reflecting material. An object of the present invention is to provide an optical three-dimensional shape measuring machine.

Other objects of the present invention and specific advantages obtained by the present invention will become clearer from the description of the embodiments described below.

The present invention is based on the phase difference between the first interference light obtained by combining the reference light and the measurement light and the second interference light obtained by combining the reflected light of the measurement light from the measurement object and the reference light. , a rangefinder for calculating a distance to the object to be measured, the first interference light obtained by combining the reference light and the measurement light, reflected light of the measurement light from the object to be measured, and the reference light. a first interference signal generating means for generating a first interference signal from the first interference light generated by the optical comb interferometer, a first interference signal generated by the optical comb interferometer; second interference signal generating means for generating a low-gain second interference signal and a high-gain second interference signal from the second interference light generated by the optical comb interferometer; and the first interference signal. first phase comparison means for comparing the phases of the first interference signal generated by the generation means and the low-gain second interference signal generated by the second interference signal generation means; and the first interference. a second phase comparison means for comparing the phases of the first interference signal generated by the signal generation means and the high-gain second interference signal generated by the second interference signal generation means; The first phase difference information obtained by the first phase comparison means and the second phase difference information obtained by the second phase comparison means are output as distance information indicating the distance to the object. and

In the rangefinder according to the present invention, the first interference signal generating means includes, for example, a reference photodetector to which the first interference light is incident, and a reference light detector for detecting the incident first interference light. The second interference signal generating means comprises a measuring photodetector to which the second interference light is incident, and the second interference signal to which the second interference light is incident. can be composed of a low gain amplifier circuit and a high gain amplifier circuit to which a first interference signal obtained by detecting the interference light from the measuring photodetector is inputted.

Further, in the rangefinder according to the present invention, the second interference signal generating means is, for example, the measurement light detector, in which the second interference light is incident via a measurement light distributor having a predetermined distribution ratio. A second interference signal obtained by the first measurement photodetector is incident on the low-gain amplifier circuit, and the high-gain amplification circuit is provided. A second interference signal obtained by the second measurement photodetector may be incident on the circuit.

Also, in the rangefinder according to the present invention, the distribution ratio of the measurement light distributor can be set to, for example, 1:1.

Further, in the rangefinder according to the present invention, for example, the distribution ratio of the measuring optical distributor is 1:N (N is any positive number greater than 1), and the low gain amplifier circuit and the high gain amplifier circuit are , may be equal in gain to each other.

Further, the rangefinder according to the present invention adjusts, for example, the delay time difference or phase difference between the second interference signal amplified by the low gain amplifier circuit and the second interference signal amplified by the high gain amplifier circuit. It may be provided with a delay adjusting means for

Further, the distance meter according to the present invention, for example, compares the first phase difference information obtained by the first phase comparison means and the second phase difference information obtained by the second phase comparison means to the measurement object. Additional information generating means for outputting additional information for selection as distance information indicating the distance to the destination may be provided.

Further, in the rangefinder according to the present invention, for example, based on the additional information generated by the additional information generation means, the distance information indicating the distance to the measurement object is obtained by the first phase comparison means. A distance information selection means for selectively outputting one phase difference information and the second phase difference information obtained by the second phase comparison means may be provided.

Further, the present invention provides a first interference light obtained by combining a reference light and a measurement light by an optical comb interferometer, and a second interference light obtained by combining the reflected light of the measurement light from a measurement object and the reference light. and calculating the distance to the measurement object from the phase difference between the first interference light and the second interference light, the distance measurement method comprising: generating a first interference signal, generating a low-gain second interference signal and a high-gain second interference signal from the second interference light, and generating the first interference signal and the low-gain second interference signal; and comparing the phases of the first interference signal and the second interference signal of the high gain, and comparing the phases of the first interference signal and the second interference signal of the low gain. The first phase difference information obtained as the phase comparison output of and the second phase difference information obtained as the phase comparison output of the first interference signal and the high-gain second interference signal of the measurement object It is characterized by outputting as distance information indicating the distance to an object.

Furthermore, the optical three-dimensional shape measuring machine according to the present invention combines the first interference light obtained by combining the reference light and the measurement light, and the reflected light of the measurement light from the measurement object and the reference light. A distance meter for calculating the distance to the measurement object from the phase difference between the second interference light and the measurement object, wherein the first interference light obtained by combining the reference light and the measurement light and the measurement object an optical comb interferometer that generates second interference light by combining the reflected light of the measurement light and the reference light; and a first interference signal that is generated from the first interference light generated by the optical comb interferometer. and a second interference signal generating means for generating a low-gain second interference signal and a high-gain second interference signal from the second interference light generated by the optical comb interferometer. a signal generating means for phase-comparing a first interference signal generated by the first interference signal generating means and a second low-gain interference signal generated by the second interference signal generating means; and a phase comparison means for comparing the phases of the first interference signal generated by the first interference signal generation means and the high-gain second interference signal generated by the second interference signal generation means. 2 phase comparison means, wherein the first phase difference information obtained by the first phase comparison means and the second phase difference information obtained by the second phase comparison means are used as the distance information indicating the distance to the object to be measured. an optical scanning device that scans a target object with measurement light emitted from the rangefinder and returns the measurement light reflected by the target object to the rangefinder; The optical scanning device is controlled to scan the laser beam, and at the same time, the absolute distance information based on the first phase difference information or the second phase difference information measured by the rangefinder is acquired, and the beam irradiation position and the place are obtained. and a signal processing device for measuring the three-dimensional shape of an object without contact by accumulating absolute distances for a plurality of points.

In the present invention, the output of the measurement photodetector of the optical comb interferometer is separated into the low-gain side and the high-gain side, and phase comparison is performed in parallel, thereby continuously reflecting light from low-reflecting materials to high-reflecting materials. It is possible to provide a distance meter, a distance measuring method, and an optical three-dimensional shape measuring machine capable of performing measurement with a wide dynamic range of levels.

1 is a block diagram showing the basic configuration of a laser range finder according to the present invention; FIG. FIG. 4 is a characteristic diagram showing the relationship between the reflected light level and the measurement light level in the laser rangefinder. 1 is a block diagram showing the configuration of a laser range finder to which the present invention is applied; FIG. FIG. 4 is a schematic diagram of a case in which the time of a reference light pulse and a measurement light pulse, which are proportional to the distance to be measured, are measured by interference between two coherent pulse light sources having different modulation periods. FIG. 4 is a schematic diagram of an optical spectrum and a beat signal spectrum; FIG. 4 is a cross-sectional view schematically showing the structure of an optical frequency comb generator used as a light source in the laser range finder; It is a figure which shows typically the output of the said optical frequency comb generator. FIG. 4 is a block diagram schematically showing a configuration of a light source using two optical frequency comb generators in the laser rangefinder; It is a figure which shows typically the output of two optical frequency comb generators which comprise the said light source. FIG. 4 is a diagram showing an example of an interference waveform when the distance measured by the laser rangefinder is near; FIG. 4 is a block diagram showing another configuration example of the laser range finder according to the present invention; FIG. 4 is a characteristic diagram showing delay time errors between a low-gain second interference signal and a high-gain interference signal in the laser rangefinder according to the present invention; FIG. 4 is a block diagram showing another configuration example of the essential part of the laser range finder according to the present invention; FIG. 4 is a block diagram showing another configuration example of the essential part of the laser range finder according to the present invention; FIG. 4 is a block diagram showing another configuration example of the essential part of the laser range finder according to the present invention; FIG. 4 is a block diagram showing another configuration example of the essential part of the laser range finder according to the present invention; FIG. 4 is a block diagram showing another configuration example of the essential part of the laser range finder according to the present invention; FIG. 4 is a block diagram showing another configuration example of the essential part of the laser range finder according to the present invention; FIG. 19 is a characteristic diagram showing hysteresis given to the switching characteristic between the first distance information and the second distance information by the output information selection unit in the laser rangefinder shown in FIG. 18; 1 is a block diagram showing the configuration of an optical three-dimensional shape measuring machine using a laser rangefinder according to the present invention; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that common constituent elements will be described by attaching common reference numerals in the drawings. Further, the present invention is not limited to the following examples, and can be arbitrarily modified without departing from the gist of the present invention.

FIG. 1 is a block diagram showing the basic configuration of a laser rangefinder 10 according to the present invention.

This laser rangefinder 10 includes an optical comb interferometer 50, a reference photodetector ₃ into which a first interference light S3 obtained by the optical comb interferometer 50 is incident, and a second detector 3 obtained by the optical comb interferometer 50. A first interference signal _fb1 obtained by the reference photodetector 3 and a second interference signal _fb2 obtained by the measurement photodetector ₆ are inputted. It is applied to a laser rangefinder configured as shown in FIG. 3, for example.

The reference photodetector ₃ receives the first interference light S3 emitted from the optical comb interferometer 50 and photoelectrically converts it to generate a first interference signal _fb1 from the first interference light _S3 . do.

Further, the measurement light detector 6 receives the second interference light S4 emitted from the optical comb interferometer 50 and photoelectrically converts it into a second interference signal _fb2 from the _second interference light _S4 . to generate

The signal processing unit 7 includes an amplifier circuit 31A to which the first interference signal _fb1 obtained by the reference photodetector 3 is input, and a low frequency signal to which the second interference signal _fb2 obtained by the measurement photodetector 6 is input. It has a gain amplifier circuit 31B and a high gain amplifier circuit 31C.

The amplifier circuit 31A amplifies the _first interference signal _fb1 generated by the reference photodetector 3 with a predetermined gain A1. The first interference signal _fb1A amplified by this amplifier circuit 31A is supplied to the A/D converter 32. FIG.

In this laser rangefinder 10, the reference photodetector 3 and the amplifier circuit 31A form a first interference signal _fb1A from the first interference light _S3 generated by the optical comb interferometer 50. It functions as signal generation means.

A low gain amplifier circuit 31B amplifies the _second interference signal _fb2 generated by the measurement photodetector 6 with a predetermined gain A2. The second interference signal _fb2L amplified by the amplifier circuit 31B is supplied to the A/D converter 32. FIG. Also, the high-gain amplifier circuit 31C amplifies the second interference signal _fb2 generated by the measurement photodetector ₆ with a predetermined gain A3. The second interference signal _fb2H amplified by this amplifier circuit 31C is supplied to the A/D converter 32. FIG.

In this laser rangefinder 10, the measurement photodetector 6, the low gain amplifier circuit 31B and the high gain amplifier circuit 31C convert the second interference light S4 generated by the optical comb interferometer 50 into a low gain _second It functions as second interference signal generating means for generating an interference signal f _b2L and a high gain second interference signal f _b2H .

Further, the signal processing unit 7 in the laser rangefinder 10 outputs the first interference signal _fb1A output from the reference photodetector 3 through the amplifier circuit 31A and the measurement photodetector 6 through the low gain amplifier circuit 31B. a first phase comparator 33A for phase-comparing the low-gain second interference signal _fb2L output from the measuring photodetector 6 via a high-gain amplifier circuit 31C; and a second phase comparator 33B for phase-comparing the interference signal _fb2H .

In this laser range finder 10, the first phase comparator 33A and the second phase comparator 33B combine the first interference signal f _b1A digitized by the A/D converter 32 with the low-gain second interference signal. A phase comparison between the signal _fb2L and the high-gain second interference signal _fb2H is performed by digital signal processing.

The first phase comparator 33A generates phase difference information by comparing the phases of the first interference signal f _b1 amplified by the amplifier circuit 31A and the low-gain second interference signal f _b2L . It functions as phase comparison means. The phase difference information obtained by the first phase comparator 33A is output as first distance information _Dp1 indicating the distance to the measurement object 5 via the first phase/distance information output section 34A.

The second phase comparator 33B functions as second phase comparison means for generating phase difference information by comparing the phases of the first interference signal _fb1A and the high-gain second interference signal _fb2H . The phase difference information obtained by the second phase comparator 33B is output as second distance information _Dp2 indicating the distance to the measurement object 5 via the second phase/distance information output section 34B.

In this laser rangefinder ₁₀ , the measurement light S2 is irradiated from the optical comb interferometer 50 to the measurement object 5, and the measurement light S2 is reflected by the measurement object ₅ and enters the optical comb interferometer 50. The measurement photodetector 6 detects the light S ₂ ′, the light power level (reflected light level), and the second interference light S 4 emitted from the optical comb interferometer 50 into which the reflected light S ₂ ′ is incident. _The signal strength of the low-gain second interference signal _fb2L and the high-gain second interference signal _fb2H output via the low-gain amplifier circuit 31B and the high-gain amplifier circuit 31C (Measurement signal level) relationship is shown in FIG.

FIG. 2 is a characteristic diagram showing the relationship between the reflected light level and the measurement signal level in this laser rangefinder 10 in double-logarithmic representation.

In this laser range finder 10, the second interference signal _{fb2 obtained by the measuring photodetector 6 is converted into two-channel second interference signals fb2 having} different gains by means of a low gain amplifier circuit 31B and a high gain amplifier circuit 31C. By setting the second interference signal _fb2L with a high gain and the second interference signal _fb2H with a high gain _, the high gain amplifier circuit 31C with a high gain A3 generates the second interference signal _fb2 in a region where the reflected light level is low. can be amplified to obtain a high-gain second interference signal _fb2H , and in a region where the reflected light level is high, the second interference signal _fb2 is amplified by the low-gain amplifier circuit 31A with a low gain _A2 . can obtain the second interference signal f _b2L with a low gain, the effective range for the reflected light level can be expanded, and the high gain circuit effective range and the low gain amplifier circuit by the high gain amplifier circuit 31C shown in FIG. Both low-gain circuit coverages according to 31B can be coverages for reflected light levels.

The measurement signal level shown on the vertical axis in FIG. 2 may be the average power of the signal obtained by integrating the sum of squares of the data for one waveform of the signal period.

Thus, in the laser rangefinder ₁₀ , the optical comb interferometer 50 generates the _first interference light S3 obtained by combining the reference light S1 and the measurement light S2 _, and the measurement light S2 from the measurement object ₅ . and the reference light S1 to generate a _second interference light _S4 , and from the phase difference between the _first interference light _S3 and the _second interference light S4, , in calculating the distance to the measurement object 5, a first interference signal _fb1A is generated from the first interference light S3 _, and a second interference signal _fb1A with a low gain is generated from the second interference light S4. generating a signal f _b2L and a high-gain second interference signal f _b2H ; comparing the phases of the first interference signal f _b1A and the low-gain second interference signal f _b2L ; The interference signal _fb1A and the high-gain second interference signal _fb2H are phase-compared to obtain a phase-comparison output between the first interference signal _fb1 and the low-gain second interference signal _fb2L . The first phase difference information D _p1 and the second phase difference information D _p2 obtained as a phase comparison output between the first interference signal f _b1 and the high-gain second interference signal f _b2H are used for the measurement. By using the distance information indicating the distance to the object 5, distance measurement with a wide dynamic range of reflected light levels can be continuously performed from a low-reflection material to a high-reflection material.

That is, for example, like the laser range finder 10 shown in FIG. Distance measurement with a wide dynamic range of the reflected light level can be continuously performed up to the reflecting material.

The first and second light sources 1 and 2 are periodically modulated in intensity or phase, respectively, and emit coherent reference light S ₁ and measurement light S ₂ having mutually different modulation periods, _Two light sources equipped with optical modulators for emitting coherent reference light S1 and measurement light S2, _each of which is periodically modulated in intensity or phase and whose modulation periods are different from each other. It consists of two different optical frequency comb generators or two pulse sources with different optical pulse repetition frequencies.

The first and second light sources 1 and 2 are periodically modulated in intensity or phase, respectively, and emit coherent reference light S ₁ and measurement light S ₂ having mutually different modulation periods, _Two light sources equipped with optical modulators for emitting coherent reference light S1 and measurement light S2, _each of which is periodically modulated in intensity or phase and whose modulation periods are different from each other. It consists of two different optical frequency comb generators or two pulse light sources with different optical pulse repetition frequencies.

The reference light S1 and the measurement light S2 emitted from the first and second light sources ₁ and ₂ are mixed and superimposed by a light mixing element 11 consisting of a semitransparent mirror or a polarizing beam splitter. The separation element 12 separates the light directed toward the reference photodetector 3 and the light directed toward the object to be measured.

Here, the reference light S1 and the measurement light S2 emitted from the first and second light sources 1 and ₂ are assumed to have orthogonal planes of polarization, and are mixed by a light mixing element 11 made up of a semitransparent mirror. The mixed light is reflected by the light separation element 12 and enters the reference photodetector 3 via the polarizer 13, and the mixed light that has passed through the light separation element 12 is polarized by the polarization beam splitter 14 according to the polarization. The reference light S ₁ and the measurement light S ₂ are separated into the reference light S ₁ and the measurement light S 2 to enter the reference surface 4 and the measurement light S ₂ to the measurement surface 5 , respectively.

Here, the planes of polarization of the reference light S1 and the measurement light S2 emitted from the first and second light sources 1 and 2 are assumed to be perpendicular to each other. may be used to mix the components of the reference light S1 and the measurement light S2 whose planes of polarization are orthogonal to _each other.

Further, the reference light S ₁ ′ reflected by the reference surface 4 and the measurement light S ₂ ′ reflected by the measurement surface 5 are mixed by the polarization beam splitter 14 , and the mixed light is the light separation element 12 . , and enters the measuring photodetector 6 via the polarizer 15 .

The reference photodetector 3 receives the mixed light of the reference light S1 and the measurement light S2 incident through the polarizer 13, thereby detecting the _first and second light sources 1 and 2. _Interference light _S3 between the reference light _S1 and the measurement light S2 emitted from the .

Further, the measurement light detector 6 receives the mixed light of the reference light S ₁ ′ and the measurement light S ₂ ′ incident through the polarizer 15 and reflected by the reference surface 4 . Interference light S ₄ between the reference light S ₁ ′ and the measurement light S ₂ ′ reflected by the measurement surface 5 is detected.

_In this laser rangefinder ₁₀ , in the optical path from the light mixing element 11 to the polarizing beam splitter 14 indicated by the thick line in FIG. The polarizing beam splitter 14 splits the reference light S ₁ and the measurement light S ₂ according to the polarization and makes them incident on the reference plane 4 and the measurement plane 5 . Then, the reference light S ₁ ′ and the measurement light S ₂ ′ reflected by the reference surface 4 and the measurement surface 5 are mixed by the polarization beam splitter 14, and the mixed light is reflected by the light separation element 12. The measurement light detector 6 detects the interference light S ₄ of the reference light S 1 ′ reflected by the reference surface 4 and the measurement light S ₂ ′ reflected by the measurement surface 5 . do.

Here, the reference light S1 and the measurement light S2 included in the mixed light guided to the reference photodetector ₃ via the light separation element ₁₂ provided in the optical path from the light mixing element 11 to the polarization beam splitter 14 , the polarization is orthogonal to each other, and no interference signal can be obtained even if the light enters the reference detector 3 as it is. By adjusting the direction of the polarizer _{13 so} that the reference detector ₃ is , and the reference detector 3 obtains an interference signal. Similarly, since the reference light S ₁ ′ and the measurement light S ₂ ′ contained in the mixed light guided to the measurement light detector 6 via the light separation element 12 have orthogonal polarizations, Therefore, a polarizer 15 is inserted and the orientation of the polarizer 15 is adjusted so that it is oblique to the polarization of the reference light S ₁ ′ and the measurement light S ₂ ′. By doing so, interference light S4, which is _a mixture of the components of the reference light S1' and the measurement light S2' as the transmission component of the polarizer 15, is incident on the measurement light detector ₆ . An interference signal is obtained by a measurement detector 6 . A half-wave plate and a polarizing beam splitter may be used instead of the polarizer.

The interference signal obtained by the reference photodetector 3 has a carrier frequency which is the difference between the carrier optical frequencies of the reference light S1 and the measurement light S2 emitted from the _first and _second light sources 1 and 2. _The same interference waveform is repeated at _a frequency that is the difference between the optical pulse repetition frequencies of the reference light S1 and the measurement light S2.

In this laser range finder 10, the role of the reference photodetector 3 is to generate a reference for delay time measurement. The reference light S1 and the measurement light S2 emitted from the _first and second light sources 1 and ₂ have unequal repetition frequencies. , and there will always be _an instant where the light pulse of the reference light S1 and the light pulse of the measurement light S2 _overlap . Moreover, the overlapping _instants appear periodically at the repetition frequency of the difference between the repetition frequencies of the reference light _S1 and the measurement light S2. The moment when the optical pulses overlap with each other is the reference for delay time measurement.

The interference signal obtained by the measurement photodetector 6 has the same carrier frequency as that of the interference signal obtained by the reference photodetector 3, which is the difference between the carrier frequencies of the reference light S ₁ ' and the measurement light S ₂ '. It has the same repetition frequency as the difference between the optical pulse repetition frequencies of the reference light S1 and the measurement light S2. However, the light pulse input to the measurement light detector 6 is equal to the absolute value of the distance difference (L ₂ −L ₁ ) between the distance L ₁ to the reference reflector 4 and the distance L ₂ to the measurement reflector 5. Since the timing of the light pulse is delayed by the amount, the moment when the light pulses overlap is delayed compared to the interference signal obtained by the reference photodetector 3 . This delay time is the delay time due to the light pulse propagating through a distance that is twice the absolute value of the distance difference (L _{2 −L 1} ). gives the distance.

In this way, when distance measurement is performed by interference between two pulsed light sources with different periods, the reference photodetector 3 for the interference signal that provides the time reference is indispensable. Distance measurement becomes possible only by comparing the time difference of each interference signal obtained.

Therefore, in the laser rangefinder 10, the signal processing unit 7 detects an interference signal obtained by detecting the interference light S3 with the reference photodetector ₃ and the interference light S4 with the measurement light detector 6. From the time difference of the interference signal obtained by , the absolute value of the distance difference between the distance L ₁ from the speed of light and the refractive index at the measurement wavelength to the reference surface 4 and the distance L ₂ to the measurement surface 5 (L ₂ - L ₁ ) Perform the requested processing.

That is, in this laser range finder 10, the reference light S1 and the measurement light emitted from the _first and second light sources 1 and 2 are periodically modulated in intensity or phase, and have coherence with mutually different modulation periods. S2 is applied to the reference surface ₄ and the measurement surface ₅ , and interference light _S3 between the reference light S1 and the measurement light S2 applied to the reference surface 4 and the measurement surface 5 is detected by the reference photodetector ₃ . , the interference light S4 between the reference light S ₁ ′ reflected by the reference surface 4 and the measurement light S ₂ ′ reflected by the measurement surface 5 is detected by the measurement light detector 6, and the signal processing unit 7 The distance from the speed of light and the refractive index at the measurement wavelength to the reference plane 4 is obtained from the time difference between the interference signal obtained by detecting the interference light S3 by the reference photodetector 3 and the interference signal obtained by detecting the interference light S4 by the measurement photodetector 6. and the distance to the measurement surface 5 is obtained.

Here, the principle of distance measurement in this laser rangefinder 10 will be described.

The principle of distance measurement conforms to a rangefinder that obtains the distance from the time delay of light pulses. That is, by measuring the time delay ΔT=2×n _g ×(L ₂ −L ₁ )/c when reciprocating the distance (L ₂ −L ₁ ), the group refractive index n _g of the optical path, the speed of light in vacuum Calculate (L ₂ −L ₁ ) from c.

An optical pulse with envelope waveform f(t) and carrier frequency ω ₀ =2πf ₀ can be expressed as follows.

Assuming that this optical pulse is a reference pulse, the Fourier transform of the reference pulse is expressed by the following equation (1) using the Fourier transform F(ω) of the envelope pulse f(t).

The calculation of Fourier transform is represented by FFT[ ]. Assuming that the reference pulse is affected by the delay due to propagation over the measured distance, the waveform of the delayed pulse and its Fourier transform are expressed in the following equation (2).

Here, the time ΔT is the delay time. To measure the absolute distance, find ΔT from the time waveform f(t−ΔT) of the envelope curve on the time axis, or find the phase characteristic e ^−jB on the frequency axis indicated by term B on the right side of equation (2). good. ω is an angular frequency, and there is a relationship of ω=2πf where f is the frequency. The jA term on the left side of equation (2) represents the phase shift of the carrier component. This term is a sensitive component that changes 2π radians at a distance of half the wavelength of light and is used for displacement measurements.

In order to increase the resolution of distance measurement from 1 μm, the time resolution for finding the delay time ΔT from the time waveform f(t−ΔT) of the envelope or the phase characteristic e ^−jB on the frequency axis must be increased to the order of femtoseconds. must. Considering that the upper limit of the frequency band of electric circuits is several tens of GHz, it is difficult. Therefore, it is preferable to prepare two light sources that generate coherent reference light S1 and measurement light S2 with mutually different modulation cycles and cause them to interfere with each other, reduce the frequency to a frequency that can be electrically processed, and measure the delay time ΔT. This is a method of distance measurement by the laser rangefinder 10. FIG.

When the time ΔT between the reference light pulse P ₁ and the measurement light pulse P ₂ , which is proportional to the measurement distance (L ₂ −L ₁ ), is measured by the interference of two coherent pulse light sources with different modulation periods. Schematic diagrams are shown in FIGS. 4A and 4B.

FIG. 4A shows a light pulse train received by the reference photodetector 3. FIG. S ₁ and S ₂ are time waveforms of envelope curves of the reference light pulse and the measurement light pulse, respectively. Assume that the repetition frequency is f _m +Δf _m for the reference light pulse S ₁ and f _m for the measurement light pulse S ₂ . The repetition period is T′=1/(f _m +Δf _m ) for S ₁ and T=1/f _m for S ₂ . Let N be the value obtained by normalizing the time measured based on the overlapping pulses by each repetition period, and the N _- th pulse of _each pulse of S1 and S2 arrives at the detector at the time when N is an integer. It will be. Comparing the arrival times of the Nth pulses of S ₁ and S ₂ , the reference optical pulse S ₁ arrives earlier by N times the period difference (TT′) of the pulse train. The deviation of the pulse arrival time increases in proportion to N, and for a certain Nth pulse, (T−T′)N=T, and the Nth reference optical pulse S ₁ becomes the (N−1)th measurement optical pulse S It catches up with ₂ and arrives at the same time.

The number N of pulses until the timings of S ₁ and S ₂ match is obtained by the following equation (3).

_The interference signals of S1 and S2 _are generated at the timing when the pulses overlap each other. Therefore, the period Tb of the interference signal is represented by the following equation (4 ₎ and is equal to the reciprocal of the repetition frequency difference _Δfm between the two pulse trains.

Moreover, since S ₁ and S ₂ are pulse trains each having a constant repetition frequency, the interference signal also repeats the same waveform at a constant cycle T _b . If the repetition frequency difference .DELTA.fm is too large, the overlapping time of the optical pulses will be shortened, making it difficult to obtain an interference signal. To avoid this, the repetition frequency difference is set such that Δf _m <<f _m .

4B represents a pulse train received by the measuring photodetector 6. FIG. Compared to the pulse shown in FIG. 4A, the measurement light pulse S ₂ arrives with a delay of time ΔT due to the round trip of the optical path length (L ₂ −L ₁ ). _In this case, the number N' at which the pulses of S1 and S2 overlap is the moment when the _sum of the period deviation that increases in proportion to N' and ΔT coincides with the period T of the measurement light pulse. ) can be expressed as

Therefore, N' is given by the following equation (6).

However, δ=ΔTf _m . δ varies linearly from 0 to 1 while ΔT varies from 0 to the repetition period T of the measurement light pulse.

When the time at which the pulses S ₁ and S ₂ of the measurement photodetector overlap is measured based on the time N=0 at which the pulse received by the reference photodetector overlaps, the time is N′ given by the following equation (7). is given by T'.

When δ varies from 0 to 1 during one period of the measurement light pulse, N'T' varies linearly from Tb to 0. Even if there is a delay time .DELTA.T, an interference signal is always obtained between 0 and _Tb because there is always one point in time between 0 and Tb where the S1 pulse overtakes the S2 pulse. The delay time .DELTA.T is obtained by comparing the time of the interference signal of the reference photodetector generated at the time of N=0 with the time of the interference signal of the measurement photodetector generated with a delay due to the delay time .DELTA.T.

For example, if the repetition frequency of the reference light pulse is 25 GHz+100 kHz and the repetition frequency of the measurement light pulse is 25 GHz, the generation time of the interference signal changes between 10 μs and 0 when ΔT changes in the range of 0-40 ps. A change that occurs within a time of 40 ps can be extended to a time width of 10 μs and measured. Since even a time difference of 1 femtosecond can be observed as 250 ps, it can be handled by an electrical circuit of a much lower frequency band than direct time measurement with femtosecond resolution.

_The relationship between the sign of the time delay given to the measurement light pulse and the sign of the _time delay of the beat signal depends on the magnitude relationship between the repetition frequency of S1 and S2 and the carrier frequency.

FIG. 5A is a schematic diagram of an optical spectrum. S ₁ represents the spectrum of the reference light and S ₂ represents the spectrum of the measurement light. S ₁ and S ₂ have comb-like modes that match the repetition frequency of the optical pulse, and the mode intervals are f _m +Δf _m for S ₁ and f _m for S ₂ , respectively. In (A) of FIG. 5, mode numbers are assigned around the mode in the center of the spectrum, and it is assumed that the frequency of the interference signal between modes with N ₌ 0 is fa. Although the interference waveforms of _S1 and _S2 contain the difference frequencies between various modes, the difference frequencies between the same mode numbers appear in the lowest frequency band. The difference frequency component is excluded from the detected signal. In this case, only interference waveforms with the same mode number are extracted from the photodetector as beat signals.

FIG. 5B is a schematic diagram of the beat signal spectrum. A comb-shaped electrical signal spectrum is obtained centered on the frequency f _a with an interval of Δf _m . The time waveform of the beat signal is obtained by superimposing each frequency component. In order to obtain the phase characteristic e ^-jB on the frequency axis, the reference phase characteristic is obtained from the spectrum of the output beat signal of the reference photodetector, and at the same time, the phase characteristic obtained from the output beat signal spectrum of the measurement photodetector is obtained. , to compare them. Since the phase characteristics of the beat signal spectra, which depend on the optical path difference up to the optical separation element 12, are common, the difference in the phase characteristics obtained by comparison is due to propagation over the measured distance (L ₂ -L ₁ ). Phase difference information of each mode of the measurement light spectrum and the reference light spectrum is reflected in the phase of each mode number of the beat signal spectrum. Replacing the relationship between the mode number and the phase of the beat signal spectrum with the relationship between the mode number and the phase difference of the measured optical spectrum, the relationship ωΔT between the optical frequency and the phase difference is obtained, and ΔT is calculated from the coefficient obtained by differentiating the straight line with ω. Ask.

If distance measurement using optical comb interference is performed by frequency analysis of beat signals, the wide band of the optical spectrum can be compressed to Δf _m /f _m and analyzed electrically. High resolution can be obtained.

Assuming that _Δf , which is one period Tb of the interference signal, is 100 kHz, the period _Tb is 10 μs, and the distance can be measured in a short period of time.

Therefore, in the laser range finder 10 having such a configuration, the reference light beams S emitted from the first and second light sources 1 and 2 are periodically modulated in intensity or phase, and have coherence with different modulation periods. ₁ and measurement light S2 are applied to the reference surface ₄ and the measurement surface ₅ , and the interference light _S3 between the reference light S1 and the measurement light S2 applied to the reference surface 4 and the measurement surface 5 is detected by the reference photodetector ₃ . and an interference light S ₄ between the reference light S ₁ ′ reflected by the reference surface 4 and the measurement light S ₂ ′ reflected by the measurement surface 5 is detected by a measurement light detector 6. The signal processor ₇ detects the interference light S3 from the reference photodetector ₃ and the interference light S4 from the measurement photodetector 6, and the time difference between the interference signal detects the interference light S4. By obtaining the difference between the distance to the reference surface 4 and the distance to the measurement surface 5 from the refractive index at the measurement wavelength, a long distance can be measured with high accuracy and in a short time.

Here, as the first and second light sources 1 and 2 in the laser range finder 10, for example, two optical frequency comb generators having different mode frequency intervals, or cyclically modulated intensity or phase. In addition, two light sources with stabilized carrier frequencies can be used.

The performance as a rangefinder is determined by the performance of the first and second light sources ₁ and ₂ that emit substantially the reference light S1 and the measurement light S2. The resolution of distance measurement depends on the width of the optical spectrum or the width of the optical pulse, and the wider the width of the optical spectrum or the narrower the width of the optical pulse, the higher the resolution of distance measurement. Also, the accuracy of absolute distance measurement depends on the accuracy of the frequency interval of the optical comb mode or the repetition frequency of the optical pulse. The higher the absolute frequency accuracy of the microwave, the higher the accuracy of the absolute distance measurement. Furthermore, the dispersion of measured values depends on the stability of f _m and f _m +Δf _m .

Further, in the laser rangefinder 10, the distance is measured using the interference of the light emitted from the two light sources 1 and 2. Alternatively, the optical pulse repetition frequency or modulation period should be different and the coherence should be good.

Pulsed lasers that oscillate independently usually have different center frequencies and repetition frequencies of laser oscillation, and there is no correlation between the fluctuations. Therefore, when distance measurement is performed using two independent pulse lasers, it is important to relatively fix the oscillation wavelength, optical phase, and pulse repetition frequency in order to improve accuracy.

Using two externally modulated light sources or two optical frequency comb generators is relatively easy to implement a light source that meets the rangefinder requirements. In particular, an optical frequency comb generator in which two oscillators are synchronized has characteristics such as good mutual interference, stable repetition frequency, wide spectrum spread and short pulse width. It is the best light source for

The optical frequency comb generator 20, for example, as shown in FIG. When light of a single frequency continuous wave (frequency: ν) is input and the optical phase modulator 22 is driven at a frequency that is an integer multiple of the free spectral range (FSR) of the optical resonator 21, Since the cycle of multiple round trips and the modulation signal cycle can be synchronized, modulation is performed with extremely high efficiency compared to an optical phase modulator without a resonator. can be obtained as an output optical frequency comb with a spectral spread of . The optical frequency comb generator 20 can generate short pulses in terms of time, and can generate optical pulses with a time width of 1 picosecond or less. The output of the optical frequency comb generator 20 is comb-shaped light whose center frequency is equal to the input frequency and whose frequency interval is equal to the modulation _frequency . is a pulse train. A pulse with a shorter time width can be obtained by increasing the modulation index to widen the spread of the spectrum.

Here, when two optical frequency comb generators are used as the first and second light sources 1 and 2 in the laser range finder 10, the light source 100 is configured as shown in FIG. 8, for example.

That is, in this light source 100, laser light emitted from a single-frequency oscillation laser light source 101 is split by a beam splitter 102 and input to two optical frequency comb generators (OFCG1, OFCG2) 20A, 20B. It is designed to be

The two optical frequency comb generators 20A and 20B are driven by oscillators 103A and 103B that oscillate _at different frequencies fm+ _Δfm and _fm . The respective oscillators 103A and 103B are phase-locked by a common reference oscillator 104 to stabilize the relative frequencies of _fm + _Δfm and _fm . A frequency shifter 105 such as an acousto-optical frequency shifter (AOFS) is provided in front of the optical frequency comb generator ( _OFCG1 ) 20A, and an optical frequency shift of frequency fa is applied to the input laser light by this frequency shifter 105. It is designed to give As a result, the beat frequency between the carrier frequencies becomes an AC signal of frequency fa instead of _a DC signal. As a result, the beat signal in the high-frequency side band of the carrier frequency and the beat signal in the low-frequency side band of the carrier frequency are generated in opposing frequency regions across the beat frequency _fa between the carrier frequencies of the beat signal, which is inconvenient for phase comparison. good.

Two optical frequency comb generators (OFCG1, OFCG2) 20A and 20B constituting the light source 100 output optical frequency combs having frequencies as shown in FIGS. 9A and 9B.

That is, in the output of the optical frequency comb generator ( _OFCG2 ) 20B, as shown in FIG. 9A, comb-like modes are arranged in the center at frequency intervals of fm. As shown in FIG. 9B, the output of the optical frequency comb generator ( _OFCG1 ) 20A has comb-like modes arranged _at frequency intervals of fm+ _Δfm around the frequency ν+fa.

In the laser rangefinder 10 having the light source 100 having such a configuration as the first and second light sources 1 and 2, the amplitude e _n ( t) is represented by the following equation (8).

Here, ER _n represents the electric field of the reference light S1 emitted from the optical frequency comb generator (OFCG1) 20A, and ET _n represents the electric field of the measurement light S2 emitted from the optical frequency comb generator (OFCG2) 20B. represents Interference signals between modes of different orders appear at and around the modulation frequency _fm . Therefore, if the bandwidth of the photodetector is set sufficiently broader than f _a or Δf but smaller than f _m or a filter is used to remove the high frequency components, only beat frequencies between modes of the same order remain. θn is the n-th mode phase difference. It represents the relative phase of the nth mode of the measurement light with respect to the phase of the nth mode of the reference light.

Also, the output current i _n (t) of the photodetector can be expressed by the following equation (9) using a as a coefficient.

In the case of the reference photodetector 3, the time delay that gives _θn in the equation (9) depends on the optical path difference between the beam splitter 102 and the light mixing element 11, and the length of the signal cable. Dependent. Since this time delay is common to the reference photodetector 3 and the measurement photodetector 6, it is removed by subtracting the output _θn of the reference photodetector 3 from the output _θn of the measurement photodetector 6. FIG. The time waveform of the output current from the photodetector is the result of superimposing all n-order currents and can be represented by _Σin (t). The waveform of the output current is a waveform obtained by modulating _a signal of carrier frequency fa with a period of _Δfm , and _θn determines the time of the envelope curve. In terms of time, the influence of θn can be removed by comparing the generation time of the beat signal output from the reference photodetector 3 and the generation time of the beat signal output from the measurement photodetector 6 . Assuming that θ _n of the output of the measurement photodetector 6 is θ _n ', the time difference between each interference signal obtained as detection by the reference photodetector 3 and the measurement photodetector 6 is (θ _n '-θ _n ) with respect to n. Therefore, the distance (L ₂ -L ₁ ) can be obtained by obtaining (θ _n '-θ _n ) for each mode.

Here, FIG. 10 shows an example of waveform obtained by waveform observation of the interference signal obtained as detection by the reference photodetector 3. In FIG. This is the case when optical comb generators (OFCG1, OFCG2) 20A and 20B with fm=25 GHz, Δf=100 kHz, and fa=40 MHz are used. The interference signal has a waveform in which the period _Tb is 10 μsec and the carrier of 40 MHz is intensity-modulated.

In this laser rangefinder 10, when the distance (L ₂ -L ₁ ) changes, the timing of the signal obtained as the detection output from the measuring photodetector 6 changes. L ₂ -L ₁ ) can be determined.

_In the laser rangefinder ₁₀ , the _first interference light S3 obtained by combining the reference light S1 and the measurement light S2, the reflected light _S2 ' of the measurement light S2 from the measurement object ₅ , and the In calculating the distance to the measurement object 5 from the phase difference between the reference light S ₁ ′ and the second interference light S ₄ multiplexed with the reference light S 1 ′, the signal processing unit 7 configured as shown in FIG. be done.

In the signal processing unit 7, the detection output of the reference photodetector ₃ , into which the first interference light S3 is incident, is amplified with a gain A1 by the amplification circuit 31A to obtain a _first interference signal _fb1 as a result. A detection output from the measurement photodetector 6 into which the interfering light S4 of No. ₂ is incident is amplified by the low gain amplifier circuit 31B and the high gain amplifier circuit 31C with the low gain _A2 and the _high gain A3. and a high-gain second interference signal _fb2H are obtained, and the _phases of the first interference signal _fb1 and the low-gain second interference signal _fb2L are compared by a first phase comparator 33A. At the same time, the phases of the first interference signal _fb1 and the high-gain second interference signal _fb2H are compared by the second phase comparator 33B, and the first interference signal f First phase difference information obtained as a phase comparison output between _b1 and a low-gain second interference signal _fb2L , the first interference signal _fb1 and a high-gain second By using the second phase difference information obtained as the phase comparison output with the interference signal f _b2H as the distance information indicating the distance to the measurement object 5, the reflected light level can be continuously adjusted from the low reflectance material to the high reflectance material. distance measurement with a wide dynamic range.

The signal processing unit 7 in this laser range finder 10 can be configured by hardware such as FPGA and DSP, and can also be realized by software on a PC. Further, the functions of the first and second phase comparators 33A and 33B provided in the signal processing unit 7 may be a calculation function of Fourier transform or a calculation by a phase difference calculation method, or a cross-correlation function which can obtain an equivalent effect. It may be a modulus calculation.

_In the laser rangefinder 10 shown in the block diagram of FIG. From the _time difference (phase difference) of the interference signal that detected S4, the difference between the distance L1 to the reference surface ₄ and the distance L2 to the measurement surface ₅ is obtained from the speed of light and the refractive index at the measurement wavelength. Alternatively, the reference surface 4 may be provided with a reference optical path that provides an optical path length difference corresponding to the distance L ₁ to the surface 4 between the reference light S ₁ and the measurement light S ₂ .

Here, in the basic configuration of the laser range finder 10 according to the present invention shown in the block diagram of FIG. 1, the first interference light _S3 and the _second interference light S4 obtained by the optical comb interferometer 50 are In the incident signal processing unit 7, the detection output from one measurement photodetector ₆ that detects the second interference light S4 is converted to low gain _A2 and high gain A by a low gain amplifier circuit 31B and a high gain amplifier circuit 31C. ₃ to obtain a low-gain second interference signal _fb2L and a high-gain second interference signal _fb2H . The second interference light S4 obtained by the optical comb interferometer 50 is supplied to the _two measurement light detectors 6A and 6B at a predetermined distribution ratio by the measurement light distributor 35, and the two measurement light detectors 6A and 6B The obtained second interference signals _fb2L and _fb2H may be amplified by the low gain amplifier circuit 31B and the high gain amplifier circuit 31C.

In the signal processing section 7A of the laser rangefinder 10A, for example, when the measurement light distributor 35 with a distribution ratio of 1:1 is provided, the second signal levels distributed by the measurement light distributor 35 are equal to each other. The interference signal _fb2 is amplified with the low gain _A2 and the high gain A3 by the low gain amplifier circuit 31B and the high gain amplifier circuit 31C, resulting in a low gain _second interference signal _fb2L and a high gain second interference signal. f _b2H can be obtained, and when the measurement optical splitter 35 with a split ratio of 1:N (N is a positive number greater than 1) is provided, the low gain amplifier circuit 31B and the high gain amplifier circuit 31B with equal gains The amplification circuit 31C can obtain a low-gain second interference signal _fb2L and a high-gain second interference signal _fb2H to obtain the first interference signal _fb1 and the low-gain second interference signal. A first phase difference information D _p1 obtained as a phase comparison output with f _b2L , and a second phase difference information D p1 obtained as a phase comparison output between the first interference signal f _b1 and the high-gain second interference signal f _b2H . By using the phase difference information D _p2 as distance information indicating the distance to the measurement object 5, distance measurement with a wide dynamic range of the reflected light level can be continuously performed from a low-reflection material to a high-reflection material. can.

In this laser rangefinder 10A, the reference photodetector 3 and the amplifier circuit 31A generate the first interference signal _fb1A from the first interference light _S3 generated by the optical comb interferometer 50. A measurement light splitter 35, a first measurement photodetector 6A, a second measurement photodetector 6B, a low gain amplifier circuit 31B and a high gain amplifier circuit 31C were generated by an optical comb interferometer 50. It functions as second interference signal generation means for generating a low gain second interference signal _fb2L and a high gain second interference signal _fb2H from the second interference light _S4 .

Other components of the laser rangefinder 10A are the same as those of the laser rangefinder 10 shown in the block diagram of FIG.

In addition, in the laser range finders 10 and 10A according to the present invention, the first phase comparator 33A and the second phase comparator 33B have a low-gain second phase detector obtained by the low-gain amplifier circuit 31B and the high-gain amplifier circuit 31C. and the high-gain interference signal _fb2H are simultaneously phase-compared with the first _interference signal _fb1 . It is preferable to take measures so that the interference signal _fb2 does not have a time lag.

That is, here, the delay time error between the low-gain second interference signal _fb2L and the high-gain interference signal _fb2H obtained by the low-gain amplifier circuit 31B and the high-gain amplifier circuit 31C, that is, the phase/distance error As shown in FIG. 12, the offset .DELTA.L is caused by the difference in the delay time of each circuit, the difference in the length of the optical fiber, the difference in the length of the wire that transmits the interference signal, and the like.

The delay time error between the low-gain second interference signal f _b2L and the high-gain interference signal f _b2H can be reduced by adjusting the physical signal path length, offsetting the data sampling time, and using a phase comparator. can be corrected by shifting the positions of the waveforms input to , or by offsetting the phases of the two phase comparator outputs.

It is desirable to obtain the offset between the low-gain second interference signal f _b2L and the high-gain interference signal f _b2H from the phase/distance values obtained simultaneously at valid input levels. Phase can be converted to distance by multiplying by a factor.

For example, in the laser rangefinder 10B shown in the block diagram of FIG. 13 and the laser rangefinder 10C shown in the block diagram of FIG. Delay adjusters 37A and 37B are provided.

That is, like the laser range finder 10B shown in the block diagram of FIG. 13, the high-gain second interference signal _fb2H amplified by the high-gain amplifier circuit 31B is passed through the delay adjuster 37A to the A/D converter 32. The second interference signal _fb2L of low gain amplified by the low gain amplifier circuit 31B and the high gain amplified by the high gain amplifier circuit 31B are provided. By making the analog delay adjuster 37A function as a delay adjusting means for adjusting the delay time difference or phase difference with the second interference signal _fb2H , the first phase comparator 33A and the second phase comparator 33B It is possible to prevent a time lag from occurring in the second interference signal _fb2 that is input, and to continuously measure the distance with a wide dynamic range of the reflected light level from a low-reflection material to a high-reflection material with high accuracy. It can be carried out.

As the analog delay adjuster 37A, for example, a phase adjuster that mechanically changes the length of the waveguide can be used.

The delay adjuster 37A may be placed on the output side of the low gain amplifier circuit 31B. Moreover, it may be provided in both the output side of the high-gain amplifier circuit 31C and the output side of the low-gain amplifier circuit 31B.

Other components in this laser range finder 10B are the same as the components denoted by the same reference numerals in the laser range finder 10 shown in the block diagram of FIG.

Further, like the laser range finder 10C shown in the block diagram of FIG. 14, a delay adjuster 37B is provided after the A/D converter 32 to provide a high-gain second signal input to the second phase comparator 33B. A signal processing unit 7C configured to adjust the delay amount of the interference signal _fb2H may be provided by digital processing. Other components of the laser range finder 10C are the same as those of the laser range finder 10 shown in the block diagram of FIG.

In this laser range finder 10C as well, the second interference signal _fb2 input to the first phase comparator 33A and the second phase comparator 33B can be prevented from being time-shifted. Distance measurement with a wide dynamic range of reflected light levels can be performed with high accuracy continuously from reflective materials to highly reflective materials.

Further, like the laser rangefinder 10D shown in the block diagram of FIG. 37C gives an offset to the phase of the sampling clock to give a lag to the sampling time, thereby sampling the low-gain second interference signal _fb2L in the A/D converter 32 and the high-gain second interference signal f A signal processing unit 7D configured to synchronize _b2H sampling may be provided.

A sampling phase adjuster 37C may be placed on the channel side of the low gain second interference signal f _b2L . Also, it may be put in both the channel side of the low-gain second interference signal f _b2L and the channel side of the high-gain second interference signal f _b2H .

Other components of the laser rangefinder 10D are the same as the components denoted by the same reference numerals as those of the laser rangefinder 10 shown in the block diagram of FIG. 1, so description thereof will be omitted.

In this laser range finder 10D as well, the second interference signal _fb2 input to the first phase comparator 33A and the second phase comparator 33B can be prevented from being time-shifted. Distance measurement with a wide dynamic range of reflected light levels can be performed with high accuracy continuously from reflective materials to highly reflective materials.

Furthermore, like the laser range finder 10E shown in the block diagram of FIG. 16, in the signal processing section 7E, a phase adjuster 37D is provided on the output side of the first phase comparator 33A, so that differences in circuit characteristics, etc. Unremovable errors can also be removed by phase/distance offset correction. The phase adjuster 37D adjusts the phase by adding or subtracting the offset value to the phase value obtained by the first phase comparator 33A.

The phase adjuster 37D may be provided on the output side of the second phase comparator 33B. Also, it may be provided on both the output side of the first phase comparator 33A and the output side of the second phase comparator 33B.

Further, in the laser rangefinder 10E, by recording the obtained offset value in the ROM of the signal processing unit 7 or the like, phase adjustment can be performed by the phase adjuster 37D. When performing signal processing with PC software, it is also possible to load the initial values of the software.

If the sampling period is sufficiently short, the delay can be adjusted by shifting the calculation range of the digital data.

Other components of the laser range finder 10E are the same as those of the laser range finder 10 shown in the block diagram of FIG.

In this laser range finder 10E as well, the second interference signal _fb2 input to the first phase comparator 33A and the second phase comparator 33B can be prevented from being time-shifted. Distance measurement with a wide dynamic range of reflected light levels can be performed with high accuracy continuously from reflective materials to highly reflective materials.

In the laser rangefinders 10, 10A to 10E according to the present invention, the distance to the measurement object 5 output via the first phase/distance information output section 34A and the second phase/distance information output section 34B is shown. The first distance information D _p1 and the second distance information D _p2 are determined and selected by software in subsequent processing units that use these information.

The following information is used singly or in combination for determination and selection of the first distance information D _p1 and the second distance information D _p2 to be used.
・Signal strength (sum of squares): Valid if the signal strength is within a certain range.
・Signal amplitude: Valid if the signal amplitude is within a certain range.
・Power distribution of signal waveform: Effective if the power distribution of the signal waveform is similar to the reference signal (within a certain error).
・Correlation value with reference signal waveform: Effective if the correlation value with the reference signal is high.

Further, like the laser rangefinder 10F shown in the block diagram of FIG. 17, information necessary for determination and selection of the first distance information D _p1 and the second distance information D _p2 to be used is output as additional information D _add . A configuration including an additional information generation unit 38 is also possible.

The additional information generator 38 obtains the signal strength as follows.

That is, the low-gain second interference signal f _b2L input to the first phase comparator 33A on the output side of the A/D converter 32 or the high-gain second interference signal f b2L input to the second phase comparator 33B on the output side of the A/D converter 32 A value proportional to the signal strength can be obtained by accumulating the square of the value of the interference signal f _b2H of 2 over one period of the signal.

When the second interference signal f _b2 is given as an AC signal, the low-gain second interference signal f _b2L input to the first phase comparator 33A or the second interference signal f b2L input to the second phase comparator 33B A value proportional to the signal strength is obtained by accumulating the square of the value of the high-gain second interference signal _fb2H from which the DC offset is removed for one period of the signal. Further, the intensity maximum value of the envelope of the AC signal is obtained by obtaining the quadrature phase component of the original waveform by Hilbert transform of the value of the low gain second interference signal f _b2L or the value of the high gain second interference signal f _b2H . , is obtained from the peak value of the square waveform of the envelope obtained by summing the squares of the original waveform and the Hilbert transform waveform.

Further, the additional information generator 38 obtains the signal amplitude as follows.

That is, when the second interference signal f _b2 is given as an AC signal, the low gain second interference signal f _b2L input to the first phase comparator 33B or the second interference signal f b2L input to the second phase comparator 33C The value obtained by subtracting the minimum peak value from the maximum peak value of the signal waveform of the input high-gain second interference signal _fb2H is taken as the signal amplitude.

Further, the maximum amplitude value of the envelope of the AC signal is obtained by obtaining the quadrature phase component of the original waveform by Hilbert transform of the low-gain second interference signal f _b2L or the high-gain second interference signal f _b2H . The squared waveform of the envelope is obtained from the sum of the squares of the signal and the Hilbert transform waveform, and is obtained from the square root of the peak value.

Further, the additional information generator 38 obtains the power distribution of the signal waveform as follows.

That is, one period of the signal is divided into a plurality of finite intervals, and the signal intensity of each interval is calculated. In order to obtain the power distribution, it is desirable to set the time width of the section to the same width as or slightly narrower than the time width of the main lobe of the assumed measurement signal waveform.

After aligning the positions of the waveforms so that the peak values of the signal amplitudes of the reference signal and the measurement signal match at the center, the power distribution is calculated for each.

Further, the additional information generator 38 obtains the correlation value with the reference signal waveform as follows.

That is, the normalized cross-correlations are calculated.

If the waveform of the measurement signal is similar to that of the reference signal, a sharp peak with a maximum value of 1 will be obtained. The peak value becomes smaller than 1 when the waveform is buried in noise, distorted, or in an abnormal region.

Since the laser range finder 10F outputs the additional information D _add generated by the additional information generation unit 38 in this manner, the first distance information D _p1 or the second distance information D p1 to be used in the subsequent processing device is output. _Dp2 can be determined and selected easily and appropriately based on the additional information _Dadd .

Other components of the laser range finder 10F are the same as those of the laser range finder 10 shown in the block diagram of FIG.

In this laser range finder 10F as well, the second interference signal _fb2 input to the first phase comparator 33A and the second phase comparator 33B can be prevented from being time-shifted. Distance measurement with a wide dynamic range of reflected light levels can be performed with high accuracy continuously from reflective materials to highly reflective materials.

Furthermore, like the laser range _{finder 10G} shown in the block diagram of FIG. 2 distance information _Dp2 may be provided.

In the laser rangefinder 10G, the output information selection unit 39 provided in the signal processing unit 7G selects the first distance from the second distance information D _p2 based on the additional information D _add generated by the additional information generation unit 38. A first threshold sh ₁ for switching to the information D _p1 and a second threshold sh ₂ for switching from the first distance information D _p1 to the second distance information D _p2 are determined, and the first distance information D It functions as distance information selection means for selectively outputting _p1 or second distance information _Dp2 .

Other components of the laser range finder 10G are the same as those of the laser range finder 10F shown in the block diagram of FIG.

Since this laser range finder 10G selectively outputs the first distance information D _p1 or the second distance information D _p2 , the user can continuously adjust the dynamic range of the reflected light level from a low-reflection material to a high-reflection material. It can be treated as a rangefinder that measures a wide range of distances and outputs distance information of one channel.

Further, as shown in FIG. 19, the output information selection unit 39 shifts the thresholds sh ₁ and sh ₂ for selectively outputting the first distance information D _p1 or the second distance information D _p2 to obtain a switching characteristic. By giving hysteresis to the boundary area, the frequency of data selection switching due to minute fluctuations in the reflected light level is reduced, and the data can be stabilized.

The output information selection unit 39 can also determine and select the first distance information D _p1 or the second distance information D _p2 to be output based on an externally set threshold value.

Also, using the laser range finder 10 (10A to 10G) according to the present invention, for example, an optical three-dimensional shape measuring machine 200 as shown in FIG. 20 can be constructed.

This optical three-dimensional shape measuring machine 200 includes an optical scanning device 220 that scans a target object ₂₅₀ with the measurement light S2 in the laser rangefinder 10 according to the present invention, a reference photodetector 3 of the laser rangefinder 10 and the measurement light. A signal processing device 230 is provided for measuring absolute distances to a plurality of points on the target object 250 based on each detection output of the detector 6 to obtain a stereoscopic image.

In this optical three-dimensional shape measuring machine 200, the measurement light S2 from the laser rangefinder 10 is irradiated from the optical scanning device 220 toward the target object 250, the reflected light from the target object 250 returns to the laser rangefinder 10, The absolute distance to the object surface is measured by signal processor 230 . The signal processing device 230 controls the optical scanning device 220 to scan the laser beam, and at the same time obtains the absolute distance information measured by the laser rangefinder 10 in a wide dynamic range, and obtains a plurality of absolute distances to the beam irradiation position and its place. The three-dimensional shape of the object is measured without contact by accumulating the points.

Note that the target object 250 may be moved instead of scanning the light beam with the optical scanning device 220 .

1 first light source, 2 second light source, 3 reference photodetector, 5 measurement surface, 6, 6A, 6B measurement photodetector, 7, 7A to 7G signal processing section, 11 light mixing element, 14 polarizing beam splitter , 12 optical separation element, 13 polarizer, 10, 10A to 10G laser rangefinder, 31A amplifier circuit, 31B low gain amplifier circuit, 31C high gain amplifier circuit, 32 A/D converter, 33A first phase comparator, 33B second phase comparator 34A first phase/distance information output section 34B second phase/distance information output section 35 measuring optical distributor 37A, 37B delay adjuster 37C sampling phase adjuster 37D phase adjuster 38 additional information generator 39 output information selector 50 optical comb interferometer

Claims (10)

The measurement target is determined from the phase difference between the first interference light obtained by combining the reference light and the measurement light and the second interference light obtained by combining the reflection light of the measurement light from the measurement target and the reference light. A rangefinder for calculating the distance to an object,
an optical comb interferometer that generates a first interference light obtained by combining the reference light and the measurement light, and a second interference light obtained by combining the reflection light of the measurement light from the measurement object and the reference light; ,
first interference signal generating means for generating a first interference signal from the first interference light generated by the optical comb interferometer;
second interference signal generating means for generating a second interference signal with a low gain and a second interference signal with a high gain from the second interference light generated by the optical comb interferometer;
a first phase comparison means for comparing the phases of the first interference signal generated by the first interference signal generation means and the second interference signal of low gain generated by the second interference signal generation means; ,
a second phase comparison means for comparing the phases of the first interference signal generated by the first interference signal generation means and the high-gain second interference signal generated by the second interference signal generation means; with
outputting first phase difference information obtained by the first phase comparison means and second phase difference information obtained by the second phase comparison means as distance information indicating the distance to the object to be measured; A rangefinder characterized by: The first interference signal generating means includes a reference photodetector to which the first interference light is incident, and a first interference signal obtained by the reference photodetector from the incident first interference light. It consists of an input amplifier circuit,
The second interference signal generating means includes a measurement light detector into which the second interference light is incident, and a second interference signal obtained by detecting the incident second interference light with the measurement light detector. 2. The rangefinder according to claim 1, comprising a low gain amplifier circuit and a high gain amplifier circuit to which the interference signal is input. The second interference signal generating means includes, as the measurement light detector, a first measurement light detector into which the second interference light is incident via a measurement light distributor having a predetermined distribution ratio, and a second measurement light detector. with a measuring photodetector,
A second interference signal obtained by the first measurement photodetector is incident on the low gain amplifier circuit,
3. The rangefinder according to claim 2, wherein a second interference signal obtained by said second measurement photodetector is incident on said high gain amplifier circuit. 4. The rangefinder according to claim 3, wherein the distribution ratio of said measuring light distributor is 1:1. 3. The measuring optical splitter has a distribution ratio of 1:N (N is any positive number greater than 1), and the low gain amplifier circuit and the high gain amplifier circuit have the same gain. 3. The rangefinder according to 3. and delay adjusting means for adjusting a delay time difference or a phase difference between the second interference signal amplified by the low gain amplifier circuit and the second interference signal amplified by the high gain amplifier circuit. The rangefinder according to any one of claims 1 to 5, characterized by: for selecting the first phase difference information obtained by the first phase comparison means and the second phase difference information obtained by the second phase comparison means as the distance information indicating the distance to the measurement object; 7. The rangefinder according to claim 1, further comprising additional information generating means for outputting additional information. Based on the additional information generated by the additional information generation means, the first phase difference information obtained by the first phase comparison means as distance information indicating the distance to the measurement object and the second phase comparison. 8. A rangefinder according to claim 7, further comprising distance information selection means for selectively outputting the second phase difference information obtained by said means. An optical comb interferometer generates a first interference light obtained by combining the reference light and the measurement light, and a second interference light obtained by combining the reflected light of the measurement light from the object to be measured and the reference light. , a distance measurement method for calculating a distance to the measurement object from the phase difference between the first interference light and the second interference light,
generating a first interference signal from the first interference light and generating a second interference signal with a low gain and a second interference signal with a high gain from the second interference light;
comparing the phases of the first interference signal and the second interference signal of low gain, and comparing the phases of the first interference signal and the second interference signal of high gain;
First phase difference information obtained as a phase comparison output between the first interference signal and the second interference signal with a low gain, and information between the first interference signal and the second interference signal with a high gain A distance measuring method, wherein second phase difference information obtained as a phase comparison output is output as distance information indicating a distance to the object to be measured. The measurement target is determined from the phase difference between the first interference light obtained by combining the reference light and the measurement light and the second interference light obtained by combining the reflection light of the measurement light from the measurement target and the reference light. A rangefinder for calculating a distance to an object, wherein the first interference light is obtained by combining the reference light and the measurement light, and the reflected light of the measurement light from the measurement object and the reference light are combined. An optical comb interferometer that generates second interference light, a first interference signal generating means that generates a first interference signal from the first interference light generated by the optical comb interferometer, and the optical comb interference a second interference signal generating means for generating a low-gain second interference signal and a high-gain second interference signal from the second interference light generated by the meter; and the first interference signal generating means. a first phase comparison means for phase-comparing the first interference signal generated by the second interference signal generation means with a second interference signal of low gain generated by the second interference signal generation means; and the first interference signal generation means a second phase comparison means for comparing the phases of the generated first interference signal and the high-gain second interference signal generated by the second interference signal generation means; a rangefinder that outputs first phase difference information obtained by the first phase comparison means and second phase difference information obtained by the second phase comparison means as distance information indicating distance;
an optical scanning device that scans a target object with measurement light emitted from the rangefinder and returns the measurement light reflected by the target object to the rangefinder;
While controlling the optical scanning device to scan the laser beam, obtaining absolute distance information based on the first phase difference information or the second phase difference information measured by the rangefinder, and obtaining the beam irradiation position and its place and a signal processing device that measures the three-dimensional shape of an object in a non-contact manner by accumulating absolute distances to a plurality of points.

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