JPS63204182A - Method and apparatus for measuring laser doppler speed - Google Patents

Abstract

PURPOSE:To achieve a highly accurate measurement of a moving speed, by determining each one of 2-D wise components based on a Doppler shift of scattered light caused by the irradiation of polarized lights orthogonal to each other. CONSTITUTION:A laser beam from a laser oscillator 10 is divided by a polarized beam splitter 12 into two polarized lights orthogonal to each other. The polarized lights are made parallel through a polarized beam splitter 18 via mirrors 14 and 26 and beam splitters 16 and 28 and projected via a condenser lens 22 along with a polarized light positioned therein onto the point A on an object 24 to be measured along the optical axis thereof. A reflected scattered light is mixed with one of the polarized lights divided in two before the irradiation by a beam splitter 30 via a beam splitter 2 and divided in two with a beam splitter 32 to be detected with photo sensors 36 and 40 through lenses 34 and 38. A moving speed of the object 24 being measured is calculated with an arithmetic unit 42 thereby enabling highly accurate measurement.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a laser Doppler velocity measuring method and apparatus, and more particularly to a technique for simultaneously measuring two-dimensional components of the moving velocity of an object to be measured.

BACKGROUND ART When a laser beam is irradiated onto a moving object, the light reflected from the object undergoes a Doppler shift. A laser Doppler velocity measurement method has been proposed that utilizes such properties to measure the moving speed of an object by detecting changes in the frequency of light from the object. In this case, it is necessary to use an optical sensor with extremely high measurement resolution to determine minute frequency changes in the scattered light, so normally,
The beat frequency with the reference light corresponding to the Doppler shift described above or the mutual beat frequency of the scattered light is detected.

Problems to be Solved by the Invention By the way, the conventional laser Doppler velocity measurement method is carried out using, for example, the apparatus shown in FIG.
Only the moving speed of the object to be measured in one dimension could be detected. That is, in FIG. 3, the laser oscillator 11
The laser beam emitted from 0 is split into two by a beam splitter 112, and the optical path of one of the laser beams is converted by a mirror 114 and is made to enter the object to be measured 116 in the direction of the direction vector j. The other laser beam is sent to the mirror 118
and 120, the optical path is transformed into a direction hector T2
The light is made to enter the object to be measured 116 at the same incident point as above in the direction of . Scattered light from the object to be measured 116 is guided by a mirror 122 and a condensing lens 124 and detected by an optical sensor 126.

The scattered light observed by the sensor 126 is the scattered light of the laser light incident along the direction vector j, which has undergone a Doppler shift related to the moving speed of the object to be measured 116, and the scattered light of the laser light incident along the direction vector j2. Scattered light of the laser light incident along the direction , which has undergone a Doppler shift related to the moving speed of the object to be measured 116 , interferes with each other, resulting in composite scattered light. Therefore, the combined scattered light detected by the optical sensor 126 has a beat frequency corresponding to the moving speed of the object to be measured 116 due to the difference in frequency between the respective scattered lights. This beat frequency corresponds to the moving speed of the object to be measured 116 in the direction vector (LL), that is, the directional component of the moving speed of the object to be measured 116 in the direction vector (L L).
The conventional measurement method described above, which calculates based on this beat frequency, can only measure the moving speed of the object to be measured 116 in one dimension.

Therefore, in the conventional laser Doppler speed measurement method, when trying to measure the moving speed of an object to be measured with high precision, it is necessary to combine the moving direction of the object to be measured and the measurement direction of the measuring device, that is, the direction of the above-mentioned direction vector (L L). must be made to match accurately, and if the moving direction of the object to be measured changes during measurement, it becomes difficult to measure the moving speed.

First Means for Solving the Problems The present invention has been made against the background of the above circumstances.
The gist is a laser Doppler speed measurement method for determining the moving speed of an object based on the Doppler shift of scattered light obtained from the object when the object is irradiated with a laser beam, (R) A step of irradiating the object to be measured with first polarized light and second polarized light having mutually orthogonal polarization planes obtained from a common laser beam under predetermined irradiation conditions; From the scattered light, the first
(C1) determining the two-dimensional direction of the moving speed of the object based on the Doppler shift of the first polarized scattered light; determining one of the components;
and determining the other of the two-dimensional directional components based on the Doppler shift of the polarized scattered light.

Operation and Effect of the First Invention By doing this, the first light beam having mutually orthogonal polarization planes can be
The polarized light and the second polarized light are irradiated onto the object to be measured under predetermined irradiation conditions, and from the scattered light from the object to be measured, first polarized scattered light and second polarized light corresponding to the first polarized light and the second polarized light are generated.
polarized scattered light is selected, one of the two-dimensional direction components of the moving speed of the object is determined based on the Doppler shift of the first polarized scattered light, and one of the two-dimensional direction components of the moving speed of the object is determined based on the Doppler shift of the second polarized scattered light. The other of the two-dimensional directional components is determined.

Therefore, since one and the other of the two-dimensional direction components of the moving speed of the object to be measured are determined simultaneously, the moving direction of the object to be measured and the measurement direction of the measuring device, for example, the direction of the direction vector (7z 7+), can be accurately determined. Furthermore, even if the moving direction of the object to be measured changes during measurement, the moving speed of the object to be measured can be measured with high accuracy.

Second Means for Solving the Problem Furthermore, the gist of a preferred embodiment of the first invention is that when an object to be measured is irradiated with a laser beam, the laser beam is reflected from the object to be measured. A laser Doppler speed measurement device that simultaneously obtains a two-dimensional direction component of the moving speed of the object based on the Doppler shift of scattered light, the device comprising: (a)
A first beam with polarization planes orthogonal to each other from a common laser beam.
a laser light output device that generates polarized light and second polarized light;
(bl) The first polarized light is irradiated toward the object to be measured, and two beams are tilted at a predetermined angle with respect to the first polarized light in a plane including the first polarized light. (C) laser beam irradiation means for irradiating the second polarized light from both sides of the first polarized light toward the irradiation point;
a sorting means for sorting a first polarized scattered light and a second polarized scattered light corresponding to the first polarized light and the second polarized light from the scattered light from the object to be measured; Determining the moving speed of the object in the irradiation direction of the first polarized light in the plane based on the beat frequency due to interference with the polarized light, and determining the moving speed of the object in the irradiation direction of the first polarized light in the plane based on the beat frequency due to interference between the second polarized scattered lights. The method further includes a speed determining means for determining a moving speed of the object to be measured in a direction perpendicular to the irradiation direction of the first polarized light in a plane.

Operation and effect of the second invention In this way, the object to be measured is illuminated based on the beat frequency caused by the interference between the first polarized scattered light from the object to be measured and the first polarized light before irradiating the object to be measured. The moving speed of the object in the irradiation direction of the first polarized light in a plane containing the first polarized light is determined, and the object is irradiated from both sides of the first polarized light along the two beams in the plane. The moving speed of the object to be measured in the direction perpendicular to the irradiation direction of the first polarized light in the plane is determined based on the beat frequency generated by mutual interference of the scattered lights of the second polarized light irradiated toward the point. Ru. That is, the moving speed of the object to be measured is measured in a two-dimensional direction between the irradiation direction of the first polarized light and the direction orthogonal to the irradiation direction within the plane.

Therefore, it is not necessary to precisely match the moving direction of the object to be measured and the measuring direction of the measuring device, and even if the moving direction of the object to be measured changes within the plane, Speed can be measured with high precision.

Embodiment In FIG. 1, a laser beam emitted from a laser oscillator 10 is split into two by a polarizing beam splitter 12 into P-polarized light LP and S-polarized light L5, which are linearly polarized lights with mutually orthogonal polarization planes, and the P-polarized light Lp is The S polarized light LS travels in the direction B. After that, the P-polarized light LP is reflected in the j direction by the mirror 14 and enters the beam splitter 16,
The beam is split into two parallel beams in the beam direction. The two trees of parallel P-polarized light LP thus divided travel straight through the polarizing beam splitter 18 and the beam splitter 20, and are focused by the condensing lens 22 onto a point A on the object to be measured 24 at a predetermined angle. Ru.

”-Polarizing beam splitter 12.18 and 3 described below
2 is well known and allows P-polarized light with a polarization plane parallel to the plane of incidence to pass therethrough, and reflects S-polarization light with a polarization plane perpendicular to the incident plane. This plane of incidence is a plane that includes the incident ray, the surface normal of the point of incidence, the reflected ray, or the refracted ray.

The beam splitter 16 is constructed by bonding a pair of prisms together, and splits the incident beam into approximately half the amount of light on the bonded surface.
Refract the book beams so that they are parallel to each other. Furthermore, the beam splitter 20 described in "-" and the beam splitters 28 and 30 described below have a function similar to that of a so-called half mirror, and transmit a part of the incident light and reflect the rest.

The S-polarized light reflected by the polarizing beam splitter 12 travels in the positive direction by the mirror 26, and the light transmitted through the beam splitter 28 is reflected in the positive direction by the polarizing beam splitter 18.

The S-polarized light L5 reflected in the father direction is located between the two P-polarized lights Ll that are parallel to each other in the father direction, and passes through the beam splitter 20 and the condenser lens 22, and the light from the condenser lens 22 One point A on the object to be measured 24 is irradiated along the axis. That is, in a plane including S-polarized light T and g directed from the condenser lens 22 toward a point A on the object to be measured 24, the condenser lens 2
P-polarized light Lp with two beams tilted with respect to the optical axis of
is irradiated toward the irradiation point A from both sides of the S-polarized light LS. Therefore, in this embodiment, the mirror 14
．． 26, the beam splitter 16, the polarizing beam splitter 18, and the condensing lens 22 split the two P-polarized lights L under the above conditions.
The laser oscillator 10 and the polarization beam splinter 12 function as a laser beam irradiation means for irradiating p- and S-polarized light Ls toward the irradiation point A, and the laser oscillator 10 and polarization beam splinter 12 emit S-polarized light Ls perpendicular to each other.
It also functions as a laser light output device that generates P-polarized light Lp.

Scattered light reflected from one point A on the object to be measured 24 is collected by the condensing lens 22 and parallelized, and taken out by the beam splitter 20 in the negative direction. This scattered light includes two types of P-polarized scattered light Lp, in which two P-polarized lights Lp are scattered, respectively.
s and S-polarized scattered light L ss obtained by scattering the S-polarized light Ls. In this way, the scattered light including the S-polarized scattered light Lss and the two types of P-polarized scattered light Lps is mixed with the S-polarized light Ls before irradiation by the beam splitter 30, and is then sorted in this embodiment. A polarization beam splinter 32 serving as a means splits the light into a P polarization component and an S polarization component. Then, the two types of P-polarized scattered light Lps, which are P-polarized light components, are detected by the optical sensor 36 through the lens 34, and the S-polarized scattered light Lss, which is the S-polarized light component, and the S-polarized light I, S before irradiation are detected by the optical sensor 36. is detected by the optical sensor 40 through the lens 38.

As described above, the two types of P-polarized scattered light Lps included in the scattered light from the object to be measured 24 are detected by the optical sensor 36, but these two types of P-polarized scattered light I-ps are 24, the synthesized scattered light observed as a result of mutual interference between the two types of P-polarized scattered light L ps has a Doppler shift corresponding to the moving speed VX in the direction of the measured object 241. A beat frequency rbx corresponding to the speed is included, and the beat frequency rbx is detected by the optical sensor 36. The arithmetic device 42, which functions as a speed determining means in this embodiment, calculates the moving speed of the object to be measured 24 based on the beat frequency fbX. That is, the directions of the two P-polarized lights Lp heading from the condensing lens 22 toward one point A of the object to be measured 24 are 71 and 'f2, respectively.
Then, the frequencies f□1 and f11 of the two types of P-polarized scattered light L2s generated by these two P-polarized lights are
52 are each subjected to a Doppler shift, so they are expressed according to the following equations (1) and (2).

However, C is the speed of light, f is the frequency of the P-polarized light Lp, and V is the direction vector of the scattered light.

The beat frequency rhx detected by the optical sensor 36 is the frequency rps+ and f's of the two types of P-polarized scattered light, )9. Since it is the difference between , it is expressed by the following equation (3).

fbx"i (fo /C)vx ・ (L L
)...(3) In this equation (3), fo and C are known, and 1
゜and 1. can be determined in advance from the condensing conditions for the object 24 of the condenser lens 22, and since fbx is observed, the moving speed VX of the object 24 can be calculated using these values. .

The storage unit of the arithmetic unit 42 stores the above formula (3) and f. , C1(7z −7+) are stored in advance,
Beat frequency f bX detected by optical sensor 36
The moving speed vX is determined based on. This movement speed v
The direction of X is a direction ('f2-11) within a plane including j2 and 7I and perpendicular to the optical axis of the condenser lens 22, that is, the f direction.

On the other hand, the S-polarized scattered light L ss included in the scattered light from the object to be measured 24 is detected by the optical sensor 4o as described above. Since it is subjected to a Doppler shift corresponding to the moving speed, the S-polarized light L mixed by the beam splitter 3°
The synthesized scattered light as a result of interference with s includes the object to be measured 24
A beat frequency fbz corresponding to the moving speed in the father direction is observed by the optical sensor 40. Then, the calculation device 42 calculates the velocity of the object to be measured 24 in the forward direction based on the beat frequency fbz. That is, S polarization.

Regarding, since the amount of change in the optical path until reaching the optical sensor 40 is twice the amount of movement of the object to be measured 24,
When the moving speed of 4 in the father direction is v2, the beat frequency fb2 detected by the optical sensor 40 is expressed by the following equation (4).

fb-=2 fo (';'2/C) ・
...(41 Therefore, the storage section of the arithmetic unit 42 contains the above (
4) Formula, frequency f of S-polarized light L5. and the speed of light C are stored in advance, and the moving speed v2 of the object to be measured 24 in seven directions is determined based on the beat frequency fbz determined by the optical sensor 40 from them.

As described above, when the moving speed V of the object 24 in the father direction and the moving speed v2 in the father direction are determined, the moving speed V (-vX'+V,
) is calculated.

As described above, according to this embodiment, the S-polarized light and the P-polarized light LP, which have planes of polarization perpendicular to each other, are irradiated onto the object to be measured 24 under predetermined irradiation conditions, and the scattering from the object to be measured 24 is performed. S-polarized scattered light Lss and P-polarized scattered light Lps corresponding to the S-polarized light Ls and P-polarized light Lp are selected from the light, and the moving speed of the object to be measured 24 is determined based on the Doppler shift of the S-polarized scattered light Lss. One of the two-dimensional direction components v2 of V is determined, and the other two-dimensional direction component VX is determined based on the Doppler shift of the P-polarized scattered light LpS. In this way, since one of the two-dimensional direction components v2 and the other 7X of the moving speed of the object to be measured 24 are determined at the same time, the actual moving direction of the object to be measured 24 and the measurement direction of the measuring device can be accurately matched. This is not necessary, and even if the moving direction of the object to be measured changes during measurement, the moving speed V of the object to be measured 24 can be measured with high accuracy.

Next, another embodiment of the present invention will be described. In the following description, parts common to those in the above-described embodiments are designated by the same reference numerals, and the description thereof will be omitted.

In the above embodiment, the moving speed V of the object to be measured 24 was determined in a plane including the direction vectors M and A, but the moving speed V of the object to be measured 24 was determined in a plane including the direction vectors M and Y. You can also do that. In this case, as in the case where the S-polarized light Ls is the P-polarized light Lp in the embodiment shown in FIG. Object to be measured 24
irradiated against. Figure 2 shows the main part.

These two beams of S-polarized light Ls are usually located within a second plane that is perpendicular to the plane containing the two beams of P-polarized light Lp in the optical axis J, that is, in a plane that contains the directions Hectorb and A. I am made to do so. Therefore, the direction vector of the two S-polarized irradiation beams is set to 1. and j4, the two types of S-polarized scattered light L ss corresponding to the irradiation beams of these two S-polarized lights LS are subjected to a Doppler shift corresponding to the moving speed Vy of the object to be measured 24 in the direction B. The combined scattered light observed as a result of mutual interference between the two types of S-polarized scattered light L ss includes the object to be measured 24
includes a beat frequency f by corresponding to the moving speed of
The beat frequencies f and y are detected by the optical sensor 40. Note that in the case of this embodiment, the beam splitters 28 and 30 are removed.

Then, the moving speed vy of the object to be measured 24 is calculated by the calculation device 42 from the following equation (4), which is similar to the above equation (3), based on the beat frequency f by.

f by #(f o / C) ”;y' (T
4-L)...(4) One embodiment of the present invention has been described above based on the drawings, but
The invention also applies in other aspects.

For example, in the above-described embodiment, the object to be measured 24 is
Although the moving speed of the object to be measured 24 has been calculated, the moving speed of the object to be measured 24 can also be determined based on the scattered light transmitted to the side opposite to the condenser lens 22.

This method is preferably used when the object to be measured 24 is a fine particle or the like.

Further, by combining the embodiment shown in FIG. 1 and the embodiment shown in FIG. 2, the three-dimensional direction components of the moving speed of the object to be measured 24 may be simultaneously measured.

Alternatively, the frequency of the laser beam output from the laser oscillator 10 may be modulated by an optical frequency shifter, and the moving speed of the object to be measured 24 may be measured using the laser beam having the frequency modulated in this manner. good.

Furthermore, in the above-mentioned embodiment, the plane containing the two mutually parallel P-polarized light LP beams split by the beam splitter 16 was made to coincide with the plane containing the direction vectors ma and j, but they do not necessarily coincide. You don't have to do it.

Furthermore, in the embodiments described above, other optical elements such as lenses, mirrors, slits, beam splitters, etc. may be provided as appropriate.

Note that the above-mentioned embodiment is merely one embodiment of the present invention, and various modifications may be made to the present invention without departing from the spirit thereof.

[Brief explanation of the drawing]

FIG. 1 is a perspective view illustrating the configuration of an embodiment of the present invention. FIG. 2 is a diagram illustrating a main part of another embodiment of the present invention. FIG. 3 is a diagram illustrating a conventional laser Doppler velocity measuring device. 24: Object to be measured 32: Polarizing beam splitter (selecting means) 42: Arithmetic device (speed determining means) Applicant Brother Industries, Ltd. Figure 2 Figure 3

Claims (2)

[Claims] (1) A laser Doppler velocity measurement method for determining the moving speed of an object to be measured based on the Doppler shift of scattered light obtained from the object when the object is irradiated with a laser beam, which method includes a common method. irradiating the object under predetermined irradiation conditions with a first polarized light and a second polarized light having mutually orthogonal polarization planes obtained from a laser beam; a step of sorting the first polarized scattered light and the second polarized scattered light corresponding to the polarized light and the second polarized light; and determining the two-dimensional direction component of the moving speed of the object based on the Doppler shift of the first polarized scattered light. A method for measuring laser Doppler velocity, comprising: determining one of the two-dimensional direction components, and determining the other of the two-dimensional direction components based on the Doppler shift of the second polarized scattered light. (2) Laser Doppler velocity measurement that simultaneously determines the two-dimensional component of the moving speed of the measured object based on the Doppler shift of the scattered light reflected from the measured object when the measured object is irradiated with laser light. An apparatus comprising: a first laser beam with mutually orthogonal polarization planes from a common laser beam;
a laser beam output device that generates polarized light and a second polarized light; laser light irradiation means for irradiating the second polarized light from both sides of the first polarized light toward the irradiation point using two beams tilted at a certain angle; a sorting means for sorting a first polarized scattered light and a second polarized scattered light corresponding to the first polarized light and the second polarized light; determine the moving speed of the object to be measured in the irradiation direction of the first polarized light in the plane, and determine the moving speed of the object to be measured in the irradiation direction of the first polarized light in the plane, based on the beat frequency due to interference between the second polarized scattered lights. A laser Doppler speed measuring device comprising: speed determining means for determining a moving speed of the object to be measured in a direction.