JP3235368B2 - Laser Doppler velocity measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an object to be measured in a non-contact state by irradiating an object with a plurality of laser beams and detecting a frequency shift of scattered light which is Doppler shifted in accordance with the speed of the object. The present invention relates to a laser Doppler speed measuring device for measuring a moving speed of a measurement object.

[0002]

2. Description of the Related Art Heretofore, as a non-contact type speed measuring device, a device using a laser Doppler method has been used. FIG. 14 shows the measurement principle of a speed measuring device employing the laser Doppler method. As the light source 100 of the laser Doppler type speed measuring device, H
e-Ne lasers and semiconductor lasers are often used.
The laser Doppler type velocity measuring device divides a laser beam LB emitted from the laser light source 100 into two by a beam splitter 102, and directly irradiates one of the laser beams LB to an object to be measured through the beam splitter 102, The other laser beam LB is reflected by the mirror 103 and irradiates the object 107 to be measured, so that the two laser beams LB are irradiated on the object 107 at the intersection angle θ. Then, scattered light scattered by the measured object 107 moving at a certain speed v is detected by a light receiving sensor 105 such as a photoelectric conversion element through an optical system such as a condenser lens 104, and a detection signal of the light receiving sensor 105 is detected. Amplification is performed by an amplifier, and heterodyne detection is performed via a band-pass filter (BPF) to obtain a Doppler signal. The Doppler frequency of the Doppler signal detected at this time is represented by the following equation. f _D = (2v) sin θ / λ where f _D is the Doppler frequency, v is the speed of the object to be measured, λ is the wavelength of the laser beam, and θ is the beam crossing angle.

The Doppler frequency f in the above equation
_{Since D} is proportional to the speed v of the device under test, the speed v of the device under test can be measured by extracting and processing the Doppler signal.

[0004] By the way, in the velocity measuring apparatus employing the laser Doppler system configured as described above, when measuring the velocity of an object to be measured in a two-dimensional direction or when measuring the velocity of an object to be expanded and contracted, There is a problem that a measurement error occurs.

Therefore, as a technique capable of measuring the speed of an object to be measured and the speed of the object to be expanded and contracted in two-dimensional directions, Japanese Patent Application Laid-Open No. 63-204183 and Japanese Patent Application Laid-Open No.
For example, there is one disclosed in JP-A-5991.

The reflection type laser Doppler velocity measuring apparatus disclosed in Japanese Patent Application Laid-Open No. 63-204183 is based on the Doppler shift of scattered light reflected from an object when the object is irradiated with laser light. In a reflection type laser Doppler velocity measuring apparatus for simultaneously obtaining two-dimensional components of a moving speed of an object to be measured, a laser beam for generating a first deflection and a second deflection having deflection surfaces orthogonal to each other from a common laser beam An output device, and a condenser lens for converging the first deflection and the second deflection on one point on the object to be measured, and the first deflection in a first plane including an optical axis of the condenser lens. With two beams inclined at a predetermined fixed angle with respect to the optical axis toward the one point from both sides of the optical axis, and including the optical axis and orthogonal to the first plane. Do 2 the second deflection in 2 planes inclined by a predetermined angle which is predetermined for the optical axis
A laser beam irradiating means for irradiating the beam with the one beam from both sides of the optical axis toward the one point, and a first deflection scattering corresponding to the first deflection and the second deflection from the scattered light reflected from the measured object Selecting means for selecting light and second polarized scattered light; and a moving speed of the device under test in a direction orthogonal to the optical axis in the first plane based on a beat frequency due to interference between the first polarized scattered light. Speed determining means for determining the moving speed of the DUT in the direction orthogonal to the optical axis in the second plane based on the beat frequency due to the interference between the second deflected scattered lights. It is configured to include.

[0007] This reflection type laser Doppler velocity measuring apparatus, when measuring the velocity in the two-dimensional direction, uses another set of two laser beams in a direction perpendicular to the plane of two sets of laser beams. By irradiating the object, it is possible to measure the speed of the object to be measured with high accuracy even if the angle between the moving direction of the object to be measured and the plane of the two beams is shifted.

A Doppler velocimeter according to Japanese Patent Application Laid-Open No. 4-25791 discloses a method in which an irradiating light beam having a wavelength λ is made incident on a moving object at a predetermined incident angle θ, and the frequency of scattered light from the moving object is shifted. A Doppler velocimeter that detects the speed information of the moving object based on the change of the incident angle θ according to the change of the wavelength λ of the irradiation light beam, and the irradiation light beam so that sin θ / λ becomes substantially constant. An optical system for entering the moving object, optical means for causing a plurality of the irradiation light beams to enter the moving object in the moving direction, and velocity information obtained from a plurality of positions on the moving object surface. And a calculating means for detecting speed information.

This Doppler velocimeter eliminates measurement errors by measuring multiple points in the same direction as the moving direction of the measured object when measuring the speed of the measured object that expands and contracts. Things.

[0010]

However, the prior art described above has the following problems. That is, in the case of the speed measuring device employing the laser Doppler method according to the above proposal, although it is possible to measure the speed of the object to be measured in the two-dimensional direction and the speed of the object to be expanded and contracted, Since an object to be measured for which the speed is measured has an uneven surface, noise is generated in the detected speed information due to a random change in reflectance or the like due to the unevenness of the surface of the object to be measured. Therefore, in the case of the speed measuring device adopting the conventional laser Doppler method,
There is a problem that a minute speed fluctuation component is buried in noise and cannot be detected.

Therefore, the present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to eliminate the influence of noise due to the unevenness of the surface of an object to be measured and to provide a highly accurate object to be measured. An object of the present invention is to provide a laser Doppler velocity measuring device capable of detecting a velocity fluctuation of an object.

[0012]

Means for Solving the Problems The technical problems described above are:
In the laser Doppler velocity measuring device according to claim 1 of the present invention, at a plurality of adjacent irradiation positions on the object to be measured,
At each irradiation position, the same laser light is divided into a plurality of laser beams, and two laser lights are irradiated so as to form a predetermined angle and intersect at the irradiation position. The two laser lights irradiated to the irradiation position are set so that the same laser light is separated, and the scattered light scattered at each irradiation position on the object to be measured is received by a plurality of light receiving means. A laser Doppler velocity measuring device for detecting a Doppler signal from the received light signal to measure the speed of the object to be measured, wherein a plurality of Doppler signal detecting means for detecting a Doppler signal from the received light signals output from the plurality of light receiving means; And performing a Fourier transform on each velocity signal output from the plurality of Doppler signal detection means,
Fourier transform means for obtaining the frequency component and phase of each speed signal, and phase comparison control means for detecting the same frequency component of each speed signal from the frequency components and phase of each speed signal obtained by the Fourier transform means It is solved by comprising to have.

[0013]

The noise due to the unevenness of the surface of the object mixed with the speed information is included in the light receiving signals detected by a plurality of light receiving means corresponding to a plurality of adjacent irradiation positions on the object to be measured. By the way, when attention is paid to an arbitrary measurement surface of the object to be measured, noise due to unevenness of the measurement surface occurs in a time (phase) shift in each light receiving unit. However, since the true speed fluctuation of the object to be measured occurs simultaneously at a plurality of adjacent irradiation positions on the object to be measured, the speed information output from each light receiving means is Fourier-transformed by the Fourier transform means, and the phase information is obtained. By comparing the states with the phases shifted by the comparison control means, it is possible to obtain a true speed fluctuation of the DUT.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on the illustrated embodiment.

FIG. 1 shows an embodiment of a laser Doppler velocity measuring apparatus according to the present invention.

In FIG. 1, reference numerals 1a and 1b denote laser light sources for emitting laser light, respectively. A part of the laser light LB1 emitted from one of the laser light sources 1a passes through a half mirror 2 and then a mirror 3a. The laser beam emitted from the laser light source 1a is reflected by the half mirror 2 and is reflected by the half mirror 2 at the same point on the DUT 7 while the other portion of the laser light emitted from the laser light source 1a is reflected by the half mirror 2. Irradiation is performed so as to form an intersection angle θ1 with the laser beam. Further, a part of the laser light LB2 emitted from the other laser light source 1b is transmitted through the half mirror 2, reflected by the mirror 3 and irradiated on the object 7 to be measured, and is emitted from the laser light source 1b. The other portion of the laser beam LB2 is reflected by the half mirror 2 and radiated to the same point on the DUT 7 so as to form an intersection angle θ2 with the other laser beam. Further, the two laser light beams LB1 and LB2 emitted from the two laser light sources 1a and 1b are set so as to be applied to different irradiation positions along the moving direction of the DUT 7. In this embodiment, the intersection angle θ1 and the intersection angle θ2 are f _D1 = (2v) sin θ ₁ / λ ₁ , f _D2 =
(2v) θ ₁ and θ ₂ are set so that f _D1 = f _D2 in sin θ ₂ / λ ₂ .

As the two laser light sources 1a and 1b, those which emit laser beams LB1 and LB2 having different wavelengths are used.
Are set so as to emit laser light having a wavelength of 630 nm, and the laser light source 1b emits laser light having a wavelength of 780 nm.

The two sets of laser beams emitted from the laser light sources 1a and 1b and scattered on the surface of the moving object 7 are passed through two condensing lenses 4a and 4b, respectively. 5a and 5b. At this time, the laser light sources 1a, 1b
Are used that emit laser beams LB1 and LB2 having different wavelengths.
The light receiving sensor 5b has no sensitivity to the wavelength of the laser light LB2 emitted from the laser light source 1b,
A laser beam having no sensitivity to the wavelength of the laser beam LB1 emitted from the laser beam is used. By doing so, the laser beams LB1, LB2 emitted from the laser light sources 1a, 1b
Can be completely separated and detected, and a clean Doppler signal can be obtained only by receiving the scattered light as it is. These light receiving sensors 5a, 5
The signal output from the signal b is subjected to predetermined signal processing by the signal processing means 8 and then the speed information comparison means 9 compares the speed information.

However, the two light receiving sensors 5a, 5b
1 has sensitivity to the wavelengths of the laser beams LB1 and LB2 emitted from the laser light sources 1a and 1b, respectively.
As shown in (1), by disposing the optical filters 6a and 6b in front of the condenser lenses 4a and 4b, it becomes possible to detect laser light only in a specific wavelength band. As the light receiving sensors 5a and 5b, for example, sensors having different wavelength sensitivity characteristics are used as shown in FIG.

FIG. 3 is a block diagram showing signal processing means of the laser Doppler velocity measuring device according to this embodiment.

In FIG. 3, reference numerals 5a and 5b denote scattered light receiving means comprising a light receiving sensor. Signals output from the scattered light receiving means 5a and 5b are transmitted through an amplifier and a band pass filter (not shown). The signals are input to the tracker waveform shaping circuits 10a and 10b. As shown in FIG. 4, these tracker waveform shaping circuits 10a and 10b output a pulse signal 13 shaped based on a pulse signal 12 input to the other terminal with respect to an input light receiving signal 11. As described above, the tracker waveform shaping circuits 10a and 10b perform shaping of the waveform of the signal 11 output from the scattered light receiving means 5a and 5b, and the tracker waveform shaping circuits 10a and 10b perform waveform shaping. Doppler signals 13a and 13b are output.

The Doppler frequency of the Doppler signals 13a and 13b is expressed by the following equation. f _D = (2v) sin θ / λ where f _D is the Doppler frequency, v is the moving speed of the DUT 7, λ is the wavelength of the laser beam, and θ is the beam crossing angle. Since the Doppler frequency f _D in the above equation is proportional to the speed v of the device under test, the speed v of the device under test is measured by detecting the Doppler frequency f _D that is the frequency of the Doppler signal.

The tracker waveform shaping circuit 10a,
Doppler signals 13a, 13b output from 10b
Is input to the digital counters 14a and 14b, and the digital counters 14a and 14b count the frequency of the Doppler signal. Further, the signals 15a, 15 output from the digital counters 14a, 14b
b is a fast Fourier transform (FFT).
The input signal is input to an i.e. Transform (i.e., Transform) analyzer 16 and the fast Fourier transform (FFT) analyzer 16 performs a Fourier transform on the signals output from the digital counters 14a and 14b. The Fourier-transformed signal 17 output from the fast Fourier transform (FFT) analyzer 16 is input to a frequency analysis / phase comparison circuit 18, which outputs a Doppler frequency f _D or the like. Is output based on the detected speed and the speed unevenness.

Next, a method of calculating magnitude, magnitude coefficient, and phase in the fast Fourier transform (FFT) analyzer 16 will be described.

First, a real part and an imaginary part when an FFT is performed on a signal having a certain waveform can be expressed by the following equation (1).

[0026]

(Equation 1)

The magnitude of FFT is expressed by the following equation (2). In this case, the frequencies equal to or more than a half cycle are omitted, but these frequencies mathematically include half of the entire energy. Therefore, the balance is made by the coefficient A in the following equation (2).

[0028]

(Equation 2)

Further, the magnitude coefficient of the FFT is
Indicates the peak value of the frequency component of the given waveform, and is represented by the following equation (3). Here, W1 and W2 are window coefficients, W1 is the average, and W2 is the average squared.

[0030]

(Equation 3)

The phase is represented by the following equation (4).

[0032]

(Equation 4)

By performing such calculations with the FFT analyzer 16, the frequency components and phases of the velocity-time waveform output from the digital counters 14a and 14b in FIG. 3 are obtained.

In the above configuration, the laser Doppler velocity measuring apparatus according to this embodiment eliminates the influence of noise due to the unevenness of the surface of the object to be measured and detects the speed fluctuation of the object to be measured with high precision as follows. It has become possible. That is, in the laser Doppler velocity measuring device, as shown in FIG. 1, laser beams LB1 and LB2 having different wavelengths emitted from the two laser light sources 1a and 1b,
Two different points along the moving direction are irradiated on the DUT 7 via the half mirror 2 and the mirror 3 so as to form an intersection angle θ1 = θ2. Then, the two sets of laser light scattered on the surface of the object 7 are collected by the condenser lenses 4a and 4a, respectively.
The light is detected by the light receiving sensors 5a and 5b via the line b.

As shown in FIG. 3, the detection signals output from the light receiving sensors 5a and 5b are amplified by an amplifier (not shown) and a band-pass filter (BP).
By F), signals outside the predetermined frequency band are removed and input to the tracker waveform shaping circuit. The signals input to the tracker waveform shaping circuit are shown in FIGS. 5 (a) and 6 (a).
5 (b) and FIG. 6 (b), a signal corresponding to the true speed fluctuation of the DUT 7 shown in FIG.
The signals 11a and 11b shown in FIGS. 5 (c) and 6 (c) are obtained by superimposing the noise due to the unevenness of the surface of FIG.

Next, as shown in FIG. 3, the signals 11a and 11b are input to tracker waveform shaping circuits 10a and 10b, and from the tracker waveform shaping circuits 10a and 10b, the Doppler signals 13a, 13b is output. Then, the Doppler signals 13a, 13b
Is input to the FFT analyzer 16 via the digital counters 14a and 14b, and the FFT analyzer 16 performs a predetermined Fourier transform.

In the FFT analyzer 16, FIG.
As shown in FIG. 6D and FIG. 6D, Fourier transform is performed on the digitally counted Doppler signals 15a and 15b, and a magnitude (Mag) signal corresponding to a frequency component is obtained based on the above-described equation (2). Is detected. Further, the FFT analyzer 16 detects the phase characteristic based on the above-described equation (4), and outputs the phase characteristic as shown in FIG.

By the way, the frequency and phase of the Doppler signal detected as described above are output with a phase shift corresponding to the distance between the two measurement points due to the unevenness of the surface of the object to be measured. . On the other hand, since the true speed fluctuation f ₀ of the object to be measured occurs simultaneously at two measurement points, FIG.
(A) As shown in (b), it appears in the same phase without phase shift, and the above calculation is performed on the velocity-time waveforms of the two Doppler signals, and a true velocity fluctuation component can be extracted by comparison. Becomes

That is, in the frequency analysis / phase comparison circuit 18 connected to the FFT analyzer 16, FIG.
The difference between the output 1 of the phase and the output 2 of the phase as shown in (b) is obtained from the signal of the phase difference, as shown in FIG. 8, to extract the f ₀ is a true variation frequency it can. This makes it possible to detect the fluctuation of the speed of the measured object with high accuracy by removing the influence of noise included in the Doppler signal.

FIG. 9 shows another embodiment of the present invention. The same parts as those of the above embodiment are designated by the same reference numerals. In this embodiment, the illumination optical system shown in FIG. This is a modification of the system configuration.

That is, in FIG. 9, reference numerals 1a and 1b denote laser light sources for emitting laser light, respectively. A part of the laser light LB1 emitted from one of the laser light sources 1a passes through the half mirror 2 after being transmitted. The other part of the laser light emitted from the laser light source 1a is reflected by the mirror 3b and the mirror 3a and radiated onto the DUT 7, and is reflected by the half mirror 2 and the mirror 3ca. The above same point is irradiated so as to form an intersection angle θ1 with the other laser beam. A part of the laser light LB2 emitted from the other laser light source 1b passes through the half mirror 2, is reflected by the mirror 3b and the mirror 3a, irradiates the object 7 to be measured, and also emits the laser light 1b. The other portion of the laser beam LB2 emitted from the laser beam is reflected by the half mirror 2 and the mirror 3c so as to irradiate the same point on the DUT 7 so as to form an intersection angle θ2 with the other laser beam. Has become.

Other structures and operations are the same as those of the above-described embodiment, and the description thereof will be omitted.

FIG. 10 shows another embodiment of the present invention. The same parts as those of the above embodiment are denoted by the same reference numerals. In this embodiment, a single laser light source is used. It is configured to irradiate the intersection of two beams to a plurality of positions on the measurement object.

That is, in FIG. 10, reference numeral 1a denotes a laser light source for emitting laser light LB. The laser light LB emitted from the laser light source 1a has polarization directions perpendicular to each other by the polarization beam splitter 9. The two laser beams LB1 and LB2 are separated. Two laser beams LB1, separated by the polarization beam splitter 9,
One of the laser beams LB1 of the LB2 is reflected by the mirror 3f, passes through the half mirror 2, is reflected by the mirrors 3b and 3a, irradiates the object 7 to be measured, and has the laser light source 1a. Of the same laser beam LB1 emitted from the half mirror 2 and the mirror 3c
And irradiates the same point on the DUT 7 so as to form an intersection angle θ1 with the other laser beam. Further, of the two laser beams LB1 and LB2 separated by the polarization beam splitter 9, the other laser beam LB2 is partially separated from the mirror 3d by the mirror laser beam LB2 emitted from the other laser light source 1b. After being reflected by the mirror 3e, it passes through the half mirror 2, and is reflected by the mirror mirror 3b and the mirror 3a to irradiate the object 7 to be measured, and another portion of the laser beam LB2 emitted from the laser light source 1a. Is reflected by the half mirror 2 and the mirror 3c at the same point on the DUT 7 and at the intersection angle θ with the other laser beam.
2 is formed.

The two scattered lights scattered on the object 7 are condensed by one condensing lens 4 and separated by a polarizing beam splitter 9 into two laser lights orthogonal to each other in accordance with the polarization direction. And two light receiving elements 5a and 5b
Are configured to receive light.

Other configurations and operations are the same as those of the above-described embodiment, and the description thereof will be omitted.

FIG. 11 shows another embodiment of the present invention. The same parts as those of the above embodiment are denoted by the same reference numerals. This embodiment is different from the embodiment shown in FIG. Similarly, a single laser light source irradiates the intersection of two beams to a plurality of positions on the device under test.

However, in this embodiment, as in the embodiment shown in FIG. 10, one laser beam is not separated into two laser beams LB1 and LB2 by using a polarizing beam splitter 9, but a laser light source is used. A half mirror 2b disposed immediately after 1a separates the two laser beams LB1 and LB2 into two laser beams LB1, and further comprises an AOM element or the like that changes the frequency using an ultrasonic wave or the like in the optical system of one of the laser beams LB1. Two laser beams LB1, LB with a shifter 10 interposed
The two wavelengths are configured to be different from each other.

The configuration of the light receiving sensor and the like is the same as that of the embodiment shown in FIG.

Other structures and operations are the same as those of the above-described embodiment, and the description thereof will be omitted.

FIG. 12 shows another embodiment of the present invention. The same parts as those of the above embodiment are denoted by the same reference numerals. In this embodiment, basically, FIG. As in the embodiment, a single laser light source is configured to irradiate the intersection of two beams to a plurality of positions on the object to be measured.

In this embodiment, however, the laser beam LB1 is not split into two laser beams LB1 and LB2 having polarization directions perpendicular to each other by the polarizing beam splitter 9, but is simply split by the beam splitter 9 into two laser beams LB1 and LB2. , LB2
Is to be separated. The detection of the scattered light from the DUT 7 is configured in the same manner as in the embodiment shown in FIG. 1, but in order to satisfactorily separate the two scattered lights, a separating plate for separating the scattered lights from each other is used. 8 is used.

Other structures and operations are the same as those of the above-described embodiment, and the description thereof will be omitted.

FIG. 13 shows another embodiment of the present invention. FIG. 13 is a diagram illustrating a configuration in which each beam angle φ with respect to a direction orthogonal to the moving direction of the DUT 7 is constant. Here, φ is an angle formed by each beam with respect to a direction orthogonal to the moving direction. By making each beam angle constant with respect to the direction orthogonal to the moving direction of the DUT 7, the reflected light due to the unevenness of the surface at each intersection is substantially the same.

Other configurations and operations are the same as those of the above-described embodiment, and the description thereof will be omitted.

[0056]

The present invention has the above-described structure and operation, and is capable of detecting the speed fluctuation of the object to be measured with high accuracy without being affected by noise due to the surface condition of the object to be measured. Become.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of a laser Doppler velocity measuring apparatus according to the present invention.

FIG. 2 is a graph showing a wavelength sensitivity characteristic of a light receiving sensor.

FIG. 3 is a block diagram showing signal processing means of the laser Doppler velocity measuring device according to the embodiment.

FIG. 4 is a block diagram showing a waveform shaping circuit.

FIGS. 5A to 5D are graphs respectively showing signal waveforms.

FIGS. 6A to 6D are graphs respectively showing signal waveforms.

FIGS. 7A and 7B are graphs respectively showing signal waveforms.

FIG. 8 is a graph showing a signal waveform.

FIG. 9 is a configuration diagram showing another embodiment of the laser Doppler velocity measuring device according to the present invention.

FIG. 10 is a configuration diagram showing another embodiment of the laser Doppler velocity measuring device according to the present invention.

FIG. 11 is a configuration diagram showing another embodiment of the laser Doppler velocity measuring device according to the present invention.

FIG. 12 is a configuration diagram showing another embodiment of the laser Doppler velocity measuring device according to the present invention.

FIG. 13 is a configuration diagram showing another embodiment of the laser Doppler velocity measuring device according to the present invention.

FIG. 14 is a configuration diagram showing a conventional laser Doppler velocity measuring device.

[Explanation of symbols]

1a, 1b laser light source, LB1, LB2 laser light,
5a, 5b light receiving sensor, 16 fast Fourier transform (F
FT) analyzer, 18 frequency analysis / phase comparison circuit.

──────────────────────────────────────────────────の Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G01S ⁷ /00-7/64 G01S 13/00-17/95 G01P 1/00-3/80

Claims (1)

(57) [Claims] 1. A method according to claim 1, wherein the same laser beam is divided into a plurality of laser beams at each of the plurality of irradiation positions adjacent to each other on the object to be measured at a predetermined angle. Irradiation is performed so as to intersect at the position, and at least two laser lights irradiated to the same irradiation position on the object to be measured are set so that the same laser light is separated. In a laser Doppler velocity measuring device for receiving scattered light scattered at each irradiation position by a plurality of light receiving means and detecting a Doppler signal from the received light signal to measure the speed of the object to be measured, the plurality of light receiving means A plurality of Doppler signal detecting means for detecting a Doppler signal from the received light signal output from the plurality of Doppler signals; performing a Fourier transform on each of the speed signals output from the plurality of Doppler signal detecting means; Fourier transform means for obtaining a number component and a phase, and phase comparison control means for detecting a frequency component having the same phase among the speed signals from the frequency component and the phase of each speed signal obtained by the Fourier transform means. A laser Doppler velocity measuring device, characterized in that: