JPH0843413A - Speedometer - Google Patents

Abstract

PURPOSE:To obtain a speedometer capable if carrying out highly-accurate detection of speed information on an moving object by utilizing a Doppler effect. CONSTITUTION:A light flux from a light source 1 provided in a case body is cast on a moving object through an optical member fitted removably to the case body. The light flux based on the deviation of frequencies of a scattered light from the moving object 7 is detected by a detecting means provided in the case body. On the occasion of detecting a speed information on the moving object 7 by utilizing a signal from the detecting means, the optical member IC has members being different in a refracting power mutually in terms of the direction of detection of the speed of the moving object 7 and the direction intersecting it perpendicularly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speedometer, for example, irradiating a moving object or fluid (hereinafter referred to as "moving object") with a laser beam and performing a Doppler shift according to the moving speed of the moving object. The present invention relates to a speedometer using the Doppler effect, which detects displacement information about displacement of a moving object and moving speed of the moving object in a non-contact manner by detecting a shift in frequency of received scattered light.

[0002]

2. Description of the Related Art Conventionally, a laser Doppler velocimeter has been used as a device for measuring the moving speed of a moving object in a non-contact and highly accurate manner. The laser Doppler velocimeter irradiates a moving object with a laser beam, and the frequency of scattered light from the moving object uses the effect of shifting (shifting) in proportion to the moving speed of the moving object (Doppler effect), The moving speed of a moving object is measured.

As an example, FIG. 3 shows a Japanese Patent Application No. 2-130590.
The schematic diagram of the main part of the laser Doppler speedometer proposed in No. In the figure, 101 is a laser Doppler velocimeter. 1 is a laser, 2 is a collimator lens, 7 is an object to be measured as a moving object, 10 is a diffraction grating with a grating pitch d, and 11 and 12 are convex lenses with a focal length f. Has become. When the distance from the diffraction grating 10 to the lens 11 is a and the distance b from the lens 12 to the object to be measured 7 is a, b is a + b.
= 2f is satisfied.

A laser beam from a laser diode 1 having a wavelength λ of about 0.68 μm is converted into a parallel light beam 3 having a diameter of 1.2 mmφ by a collimator lens 2 and a grating pitch d.
Is incident perpendicularly to the grating arrangement direction of the transmission type diffraction grating 10 having a thickness of 3.2 μm. At this time, the ± 1st-order diffracted lights 5a and 5b are emitted at a diffraction angle θ1 = 12 °.

The light beams 5a and 5b have a focal length f (= 15 m).
When incident on the convex lens 11 of FIG.
a and 13b are obtained. The luminous fluxes 13a and 13b are 2f (=
When it enters another convex lens 12 that is 30 mm apart, parallel rays 14a and 14b are obtained again, and a spot diameter of 1.2 mmφ is formed at an angle equal to the diffraction angle θ1 from the diffraction grating 10 described above and the velocity V (mm / Sec) to be measured 7 is irradiated.

The scattered light from the object 7 to be measured is converted into a convex lens 12.
And the light-collecting section 9a of the photodetector 9 efficiently by the condenser lens 8.
Then, the optical signal containing the Doppler signal represented by the formula (a1) is detected. Then, the speed information of the moving object 7 is obtained by the calculating means 24.

F = 2V / d = V / 1.6 (kHz) (a1) Here, a = 10 mm and b = 20 mm, where b is relatively long and the working distance is increased to increase the speed. The degree of freedom in installing the meter is increased.

Here, if the wavelength λ of the laser light from the laser diode 1 changes, the diffraction angle θ changes corresponding to dsin θ = λ, but the Doppler signal does not change. Also, in this device, the position 25 of the two-beam spot is fixed. That is, the object to be measured 7 is set to the arrangement shown in FIG. 3, the positions of the spots of the two light fluxes on the object to be measured 7 are immovable, and the positional deviation between the spots does not occur. It keeps a good intersection.

[0009]

In the laser Doppler velocimeter having the structure shown in FIG. 3, it is necessary that the object to be measured 7 exists in a range where interference fringes occur at the intersection of the laser beams. In the case of the configuration of the laser Doppler velocimeter of FIG. 3, the diameter of the laser beam is set to 1.2 mmφ and the laser crossing angle is set to 12 °, and the range where interference fringes sufficient for measurement, that is, the measurable range is actually measured. By convex lens 1
It becomes 20 ± 1 mm from 2. For example, when measuring the moving speed of a steel plate, even if there is unevenness on the surface or warpage of the plate, 2
It is also specified that only depth irregularities of mm are allowed.

If the diameter of the luminous flux emitted from the laser Doppler velocimeter main body 101 is enlarged, the crossing distance of the luminous flux is enlarged. However, since the light / dark pattern of light due to the unevenness of the reflection surface of the DUT 7 increases, the signals are averaged in the photodetector 9, and the output level as the Doppler frequency signal becomes low, and the S / N decreases. . Therefore, it is very difficult to expand the measurable range in the conventional device.

It is an object of the present invention to provide a speedometer utilizing the Doppler effect that can obtain highly accurate speed information while expanding the measurable range.

[0012]

The speedometer of the present invention comprises: (1-1) Injecting a light beam from a light source provided in a housing into a moving object through an optical member detachably attached to the housing. When detecting the light flux based on the frequency shift of the scattered light from the moving object by the detecting means provided in the housing, and detecting the velocity information of the moving object using the signal from the detecting means, The optical member is characterized in that it has members having different refractive powers in the speed detection direction of the moving object and the direction orthogonal to the speed detection direction.

In particular, the optical member has a cylindrical lens having a negative refracting power only in a direction orthogonal to the speed detection direction of the moving object, and a positive lens having a spherical surface, and the optical member has the above-mentioned structure. Cylindrical lens having negative refractive power only in the velocity detection direction of a moving object,
It is characterized in that it has a cylindrical lens having a negative refractive power only in a direction orthogonal to the speed detection direction of the moving object, and a positive lens made of a spherical surface.

(1-2) The light flux from the light source means is made incident on the moving object, the light flux based on the frequency shift of the scattered light from the moving object is detected by the detecting means, and the signal from the detecting means is used. Then, in the device for detecting the speed information of the moving object, when the light beam is incident on the moving object through the optical member, the optical member has a refractive power in the speed detection direction of the moving object and in a direction orthogonal to the speed detection direction. Is characterized in that the diameter of the light beam in the speed detection direction is expanded by a different configuration.

In particular, the optical member has a cylindrical lens having a negative refracting power only in a direction orthogonal to the speed detecting direction of the moving object, and a positive lens having a spherical surface, and the optical member has the above-mentioned structure. Cylindrical lens having negative refractive power only in the velocity detection direction of a moving object,
It is characterized in that it has a cylindrical lens having a negative refractive power only in a direction orthogonal to the speed detection direction of the moving object, and a positive lens made of a spherical surface.

(1-3) A light beam having a wavelength λ from a light source means in the detection body is incident on a moving object through an optical member detachable from the detection body at an incident angle θ according to a change in the wavelength λ of the light beam. When the incident angle θ changes, the light is made incident so that sin θ / λ becomes substantially constant, the deviation of the frequency of the scattered light flux from the moving object is detected by the detection means in the detection body, and the signal from the detection means is detected. When the velocity information of the moving object is detected by utilizing, the optical member is characterized by having members having different refractive powers in the velocity detecting direction of the moving object and the direction orthogonal thereto.

[0017]

1 (A) and 1 (B) are a plan view and a sectional view of a main part of a first embodiment of the present invention.

In the present embodiment, the case where the moving object 7 is moving at the velocity V in the plane of the paper (moving plane) of FIG. 1A as shown by the arrow 7a is shown. In FIG. 1, 1A is a speedometer. 1B is the detection body of the speedometer 1A, 1C is the body 1B
It is an optical member that can be attached to and detached from.

Reference numeral 1 denotes a light source, which is composed of, for example, a laser diode (hereinafter referred to as "laser"), and emits laser light having a wavelength λ = 685 nm. Reference numeral 2 denotes a collimator lens, which transforms the light flux from the laser 1 into a parallel light flux 3 having a diameter of 1.8 mm. Reference numeral 4 denotes a diffraction grating, which is, for example, a transmissive diffraction grating having a grating pitch d of 3.2 μm, and the ± first-order diffracted lights 12a and 12b have a diffraction angle θ1.
It is set to diffract at (θ1 = 12 °).

Reference numeral 5 denotes a lens group, which is ± from the diffraction grating 4.
The first-order diffracted lights 12a and 12b are condensed to form light beams 13a and 13b.
b, and the light is guided to the lens group 6 after being condensed at the point P. The lens group 6 has two lenses 6a and 6b, and makes incident light beams 13a and 13b parallel light beams 14a and 14b.
Is ejected from the main body 1B. Parallel light flux 1 at this time
Reference numerals 4a and 14b denote optical members 1C as spots having an angle θ2 equal to the diffraction angle θ1 from the diffraction grating 4 and a diameter of 1.8 mm.
Is incident on.

The lens groups 5 and 6 each have a focal length f.
Are equal lens groups. The two lens groups 5 and 6 are arranged with an interval twice the focal length f. 7
Is a moving object or a moving fluid (hereinafter referred to as "moving object"), and is moving at a moving speed V in the direction of arrow 7a.

The optical member 1C can be attached to and detached from the main body 1B. The optical member 1C has a movement detection direction 7a of the moving object 7.
It has two lenses, a cylindrical lens 21 having a negative refractive power and a positive lens 22 made of a spherical surface only in a direction orthogonal to (in the plane of FIG. 1A).

In the moving surface, which is the speed detection direction in FIG. 1A, the cylindrical lens 21 causes the parallel light beam 14a,
14b as divergent light beams 15a and 15b, and the positive lens 22 causes the divergent light beams 15a and 15b from the cylindrical lens 21.
b is incident on the moving object 7 as parallel light beams 16a and 16b.

On the plane orthogonal to the moving surface of FIG. 1B, the cylindrical lens 21 allows the parallel light beams 14a and 14b to pass through as it is, and the positive lens 22 collects the parallel light beam from the cylindrical lens 21 to move the moving object 7. Is incident on.

In this embodiment, the luminous flux 16 in FIG.
The elements a and 16b are set so that the intersection angle θm on the surface of the moving object 7 is θm = sin ⁻¹ (685 / 2Pm) when the interference fringe pitch is Pm.

The direction perpendicular to the speed detection direction is shown in FIG.
In the plane of, the intersecting position of the center of the light beam substantially coincides with the light collecting position of the light beam.

A condenser lens 40 condenses the reflected light from the moving object 7 through the optical member 1C and the lens group 6 and guides it to the photodetector 60.

In this embodiment, the laser light emitted from the laser 1 is made into a parallel light flux 3 by the collimator lens 2 and is vertically incident on the diffraction grating 4. Then, the ± first-order diffracted lights 12a and 12b from the diffraction grating 4 are emitted at a diffraction angle θ1, enter the lens group 5, are condensed at the point P by the lens group 5, and then diverge and enter the lens group 6. . The parallel light fluxes 14a and 14b emitted from the lens group 6 enter the optical member 1C at an angle θ2, and then enter the moving object 7 at an angle θm via the optical member 1C.

The object to be measured 7 moving at the speed V
The measurement point M is irradiated from different directions. The scattered light from the measurement point M of the measured object 7 is detected by the photodetector 60 via the optical member 1C, the lens group 6, and the condenser lens 40. Here, θ1 = θ2.

At this time, the frequency of the scattered light by the two light beams is
Each is subjected to Doppler shifts of + Δf and −Δf in proportion to the moving speed V. Here, if the wavelength of the laser light is λ, the frequency change Δf can be expressed by the following equation (1).

Δf = V · sin (θm) / λ (1) The scattered light subjected to the Doppler shift of + Δf, −Δf is
They interfere with each other to cause a change in brightness and darkness on the light receiving surface of the photodetector 60, and the frequency F thereof is given by the following equation (2).

F = 2 · Δf = 2 · V · sin (θm) / λ (2) The frequency F of the photodetector 60 (hereinafter referred to as “Doppler frequency”) is measured from the equation (2). Then, the moving speed V of the moving object 7 is obtained.

In this system, if the angles θ1 and θm are not substantially different from each other, the angle of emergence of the diffracted light from the diffraction grating 4 ( Diffraction angle) θ1 and incident angle θ to the moving object 7
m is always θ1≈θm even if the diffraction angle varies due to wavelength variation.

If the diffracted light is the nth order light, then sin θ1 = nλ / d (3)

Therefore, from the equations (2) and (3), the Doppler frequency F is F = 2V.sin θm / λ ≈2V · sin θ1 / λ = 2nV / d (4) As is apparent from the equation (4), this system can obtain the Doppler frequency F that is substantially unaffected by wavelength fluctuation.

That is, in the system shown in FIG. 1, since sin θm / λ is a substantially constant value, the Doppler frequency F that is substantially unaffected by wavelength fluctuation is obtained.

In the present embodiment, when the wavelength λ of the laser light changes, the diffraction angle θ of the diffracted light of a predetermined order also changes. At this time, however, the value of sin θm / λ is made substantially constant by the configuration as described above. I am trying to become.

In this embodiment, the grating pitch dm of the diffraction grating 4
Is dm = 3.2 μm, the intersection angle θm of the light beams 16a and 16b on the moving object 7 surface is θm = 7.87 °, the interference fringe pitch Pm = 2.5 μm, and the beam diameter is 3 mm.
As a result, the distance at which the laser light flux intersects is expanded by a factor of about 5 compared to the conventional device.

The laser beam diameter on the surface of the moving object 7 is 1 /
It is set to about 5 to 1/10 to reduce the averaging of the light-dark signal of light due to the unevenness on the surface of the moving object 7 and improve the S / N ratio.

2 (A) and 2 (B) are a plan view and a sectional view of a main part of a second embodiment of the present invention. In the figure, the same elements as those shown in FIG. 1 are designated by the same reference numerals.

In this embodiment, as compared with the first embodiment, in addition to the cylindrical lens 21 and the positive lens 22 shown in FIG. 1, in addition to the cylindrical lens 21 and the positive lens 22, the optical member 1C is in a plane perpendicular to the moving surface which is the speed detecting direction of FIG. Only the structure shown in FIG. 2B is different in that the cylindrical lens 23 having a negative refractive power is provided on the main body 1B side of the cylindrical lens 21 as a dedicated lens for condensing, and the other configurations are the same.

In the present embodiment, the optical member 1C is composed of the three lenses having the above-mentioned shapes, so that the measurement light (measurable range) is further expanded as compared with the first embodiment, and the scattered light from the moving object 7 is generated. A large amount of light is made incident on the photodetector 60, so that even if the reflecting surface is a moving object having a low reflectance, movement information can be detected with high accuracy.

[0043]

As described above, according to the present invention, it is possible to achieve a speedometer utilizing the Doppler effect that can obtain highly accurate speed information while expanding the measurable range.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

FIG. 2 is a schematic view of the essential portions of Embodiment 2 of the present invention.

FIG. 3 is a schematic view of a main part of a conventional laser Doppler speedometer.

[Explanation of symbols]

 1 Light source 1A Speedometer 1B Detection body 1C Optical member 2 Collimator lens 4 Diffraction grating 5,6 Lens group 7 Moving object 21,23 Cylindrical lens 22 Positive lens 24 Computational means 40 Condenser lens 60 Photodetector

Claims (7)

[Claims] 1. A light flux based on a frequency shift of scattered light from the moving object, which is caused by entering a light flux from a light source provided in the housing into a moving object through an optical member detachably attached to the housing. Is detected by the detection means provided in the housing, and when the speed information of the moving object is detected by using the signal from the detection means, the optical member detects the speed detection direction of the moving object and a direction orthogonal thereto. A speedometer characterized by having members having different refracting powers from each other. 2. The optical member has a cylindrical lens having a negative refracting power only in a direction orthogonal to a velocity detection direction of the moving object, and a positive lens having a spherical surface. Speedometer. 3. The cylindrical member, wherein the optical member has a negative refractive power only in a velocity detection direction of the moving object,
2. The speedometer according to claim 1, further comprising a cylindrical lens having a negative refractive power only in a direction orthogonal to the speed detection direction of the moving object, and a positive lens having a spherical surface. 4. A light flux from a light source means is made incident on a moving object, a light flux based on a frequency shift of scattered light from the moving object is detected by a detecting means, and a signal from the detecting means is used to detect the light flux. A device for detecting speed information of a moving object, wherein when a light beam is incident on the moving object through an optical member, the optical member has different refractive powers in a speed detecting direction of the moving object and a direction orthogonal to the speed detecting direction. A speedometer characterized in that the beam diameter in the speed detection direction is expanded by. 5. The optical member has a cylindrical lens having a negative refracting power only in a direction orthogonal to a velocity detection direction of the moving object, and a positive lens having a spherical surface. Speedometer. 6. The cylindrical member, wherein the optical member has a negative refracting power only in a velocity detection direction of the moving object,
5. The speedometer according to claim 4, further comprising a cylindrical lens having a negative refractive power only in a direction orthogonal to the speed detection direction of the moving object, and a positive lens having a spherical surface. 7. A light beam having a wavelength λ from a light source means in the detection body is incident on a moving object at an incident angle θ via an optical member which is attachable to and detachable from the detection body, and the incident angle θ is changed according to the change of the wavelength λ of the light beam. Is incident so that sin θ / λ becomes substantially constant, the deviation of the frequency of the scattered light flux from the moving object is detected by the detection means in the detection main body, and the signal from the detection means is used. When detecting the speed information of the moving object by means of the optical member, the optical member has members having different refractive powers in the speed detecting direction of the moving object and in a direction orthogonal to the speed detecting direction.