JPH07229913A - Speedometer - Google Patents

Abstract

PURPOSE:To obtain a speedometer which can obtain highly accurate speed data without being influenced by a reflectance of a moving body. CONSTITUTION:A collimator lens 2 changes a luminous flux from a laser 1 into a parallel luminous flux. An optical system 16 with a diffraction grating 10 is comprised of lens groups 11, 12 of two single lenses having approximately equal focal lengths or a plurality of lenses. The two lens groups 11, 12 are separated a distance twice the focal length. A moving body 7 or moving fluid moves in a direction of an arrow 7a. A condenser lens 8 condenses a scattering light subjected to the Doppler shift from the moving body 7 onto a detecting face 9a of a photodetector 9 which is a detecting means. A surface of the moving body 7 and the detecting face 9a are generally conjugate. An operating means 20 such as a calculator or the like operates and obtains a moving speed of the moving body 7 with the use of a Doppler signal from a high pass filter 19.

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.

FIG. 2 is an explanatory view showing an example of a conventional laser Doppler velocimeter.

In FIG. 1, a laser beam emitted from a laser 1 is collimated by a collimator lens 2 into a parallel light beam 3
The beam splitter 4 splits the transmitted light 5a and the reflected light 5b into two light beams, which are reflected by the reflecting mirrors 6a and 6b. It is irradiated with two light fluxes. The scattered light from the moving object 7 is detected by the photodetector 9 via the condenser lens 8. At this time, the frequencies of the scattered light due to the two light beams undergo Doppler shifts of + Δf and −Δf, respectively, 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 (θ) / λ (1) The scattered light subjected to the Doppler shift of + Δf and −Δf is
They interfere with each other to cause changes in brightness and darkness on the light receiving surface of the photodetector 9, and the frequency F thereof is given by the following equation (2).

F = 2 · Δf = 2 · V · sin (θ) / λ (2) From equation (2), the frequency F of the photodetector 9 (hereinafter referred to as “Doppler frequency”) is measured. And the moving speed V of the moving object 7
Are seeking.

[0007]

In the conventional laser Doppler velocimeter, generally, the frequency of the change in brightness and darkness due to the flow of the speckle pattern and the moving object (inspected object).
The frequency of the change in the transmittance (or the reflectance) is lower than the Doppler frequency represented by the above equation (2). For this reason, a method is used in which the output of the photodetector is passed through a high-pass filter to electrically remove low-frequency components, and only the Doppler signal is extracted.

However, when the reflectance of the moving object is low, the S / N is lowered, and a sufficient signal for electrical processing cannot be obtained. On the contrary, when the reflectance of the moving object is high. Had a problem that the photodetector became saturated and the Doppler frequency could not be obtained.

As described above, the conventional Doppler velocimeter has a problem that it becomes impossible to measure the velocity with high accuracy depending on the reflectance of the moving object.

According to the present invention, a light-receiving device is configured so that the amount of light received by a photodetector is constant irrespective of the magnitude of the reflectance of a moving object, so that a highly accurate velocity information can always be obtained without being influenced by the reflectance. For the purpose of provision.

[0011]

The speedometer of the present invention comprises: (1-1) Injecting a light beam from a light source means into a moving object,
A signal obtained by the detecting means when detecting the light flux based on the frequency shift of the scattered light from the moving object and detecting the speed information of the moving object using the signal from the detecting means. The control means controls the output intensity of the luminous flux emitted from the light source means based on the DC component of the.

In particular, the control means controls the output of the light source means so that the intensity of scattered light obtained by the photodetector becomes substantially constant.

(1-2) An optical system in which two lenses or lens groups having substantially the same focal length for the light flux of wavelength λ from the light source means are arranged in the optical axis direction at intervals of approximately twice the focal length. Through the moving object at an incident angle θ in accordance with the change of the wavelength λ of the light beam so that sin θ / λ becomes substantially constant, and the light beam from the moving object is detected by the detecting means. Then, when the speed information of the moving object is detected using the signal from the detection means, the DC of the signal obtained by the detection means
The control means controls the output intensity of the light flux emitted from the light source means based on the component.

(1-3) An irradiation light flux having a wavelength λ is incident on a moving object at a predetermined incident angle θ, and velocity information of the moving object is detected based on the frequency shift of scattered light from the moving object. In the speedometer, the incident angle θ changes according to the change of the wavelength λ of the irradiation light flux, and the irradiation light flux is made incident on the moving object so that sin θ / λ becomes substantially constant, and at the same time, it is obtained by the detection means. The control means controls the output intensity of the luminous flux emitted from the light source means on the basis of the DC component of the generated signal.

(1-4) A light flux having a wavelength λ from a light source is made incident on a diffraction grating, and the + nth order and the −nth order (n
, 1, 2, 3 ...) and two different diffracted lights on the moving object surface through an optical system in which two lens groups having substantially equal focal lengths are arranged at intervals of twice the focal length. The two diffracted lights intersect at an incident angle θ from the direction near the moving object plane,
Moreover, each element is set and irradiated so that sin θ / λ becomes substantially constant when the incident angle θ changes in accordance with the change of the wavelength λ, and the Doppler shift from the moving object surface is received.
When one of the scattered lights is detected by the detection means and the moving speed of the moving object is detected by using the signal obtained by the detection means, the light source is controlled by the control means based on the DC component of the signal obtained by the detection means. It is characterized in that the output intensity of the luminous flux emitted from the means is controlled.

[0016]

Embodiment 1 FIG. 1 is a schematic view of the essential portions of Embodiment 1 of the present invention.

In FIG. 1, reference numeral 1 denotes a light source (light source means), which is composed of, for example, a laser diode or a semiconductor laser (hereinafter referred to as "laser"). A collimator lens 2 collimates the light flux from the laser 1 into a parallel light flux 3. Reference numeral 10 denotes a diffraction grating, which transmits the transmission type ± 1st-order diffracted light having a grating pitch d of 3.2 μm to a diffraction angle θ ₁ (θ ₁ =
It is set to diffract at 12 degrees.

Reference numeral 16 denotes an optical system, which is a lens group 1 composed of two single lenses or a plurality of lenses having substantially equal focal lengths f.
1 and 12 (generally referred to as “lens group” hereinafter). The two lens groups 11 and 12 are arranged with an interval twice the focal length f. A moving object or a moving fluid (hereinafter referred to as “moving object”) 7 is moving at a moving speed V in the direction of arrow 7a.

In this embodiment, the diffraction grating 10 and the lens group 11
Is a and the distance between the moving object 7 and the lens group 12 is b.
Then, a <b and a + b = 2f are set. This extends the working distance.

A condenser lens 8 condenses scattered light, which has undergone the Doppler shift from the moving object 7, on a detection surface 9a of a photodetector 9 as a detection means. The surface of the moving object 7 and the detection surface 9a have a substantially conjugate relationship.

Reference numeral 17 is a low-pass filter, which extracts the DC component signal from the signal from the photodetector 9. Here, the signal of the DC component is the amount of change in the amount of light due to the change in the reflectance of the moving object 7.

Reference numeral 18 denotes a laser output controller, which controls the light source 1 based on the DC component signal from the low-pass filter 17.
The output intensity of the laser light emitted from the photodetector 9 is controlled so that the intensity of the scattered light obtained by the photodetector 9 becomes substantially constant regardless of the reflectance of the moving object 7. The low pass filter 17 and the laser output controller 18 form one element of the control means 21.

Reference numeral 19 denotes a high-pass filter, which extracts the AC component signal from the signal from the photodetector 9.
This AC component signal corresponds to the Doppler frequency signal. Reference numeral 20 denotes a computing means such as a calculator, which uses the Doppler signal from the high pass filter 19 to move the moving object 7
Is calculated and calculated.

In this embodiment, the laser light emitted from the laser 1 (laser diode, wavelength λ = 0.68 μm) becomes a parallel light beam 3 having a diameter of about 1.2 mm by the collimator lens 2 and the transmission type diffraction grating 10 is provided. It is incident perpendicularly to the lattice array direction. Then, the ± n-order (n = 1 in this embodiment) diffracted lights 5a and 5b diffracted by the diffraction grating 10 at the diffraction angle θ ₁ are condensed by the lens group 11 at the position 11a, and then diverge. And the parallel light beams 14a and 14b
And shoot. Then, they are made incident on the moving object 7 from different directions at the same angle θ ₂ as the diffraction angle θ ₁ (that is, θ ₁ = θ ₂ ).

In this embodiment, the diffraction angle θ ₀ of the diffracted light when the laser light I is incident on the transmission type diffraction grating 10 having the grating pitch d perpendicularly to the array direction of the grating is given by the following equation.

Sin θ ₀ = mλ / d where m is the diffraction order (0, 1, 2, ...) And λ is the wavelength of the laser light.

Of these, the ± n-order light other than the 0th-order light is expressed by the following equation.

Sin θ ₀ = ± nλ / d (3) (n is 1, 2, ...) Light when two moving light beams are applied to the moving object 7 from different directions so that the incident angle becomes θ _0. The Doppler frequency F of the detector 9 is F = 2Vsin θ ₀ / λ = 2nV / d (4) from the equations (2) and (3). That is, it does not depend on the wavelength of the laser light, but is inversely proportional to the grating pitch d of the diffraction grating 10 and proportional to the moving speed of the moving object 7. Since the grating pitch d can be made sufficiently stable, the Doppler frequency F becomes a frequency proportional to only the moving speed of the moving object 7. Note that the diffraction grating 10 is exactly the same for a reflection type diffraction grating.

In the present embodiment, when the wavelength λ of the laser light changes, the diffraction angle θ of the diffracted light of the predetermined order also changes. At this time, the value of sin θ ₂ / λ is made constant by the configuration as described above. I have to.

Further, the two diffracted lights 14a and 14b are incident on the surface of the moving object 7 so that their spots overlap each other so as to intersect with each other.

In this embodiment, the focal lengths f of the lens group 11 and the lens group 12 of the optical system 16 are made substantially equal to each other, and the diffraction grating 1 is used.
The optical system 16 configures 0 and the moving object 7 so as to have a unity-scale conjugate relationship. At this time, 2 on the moving object 7 surface
The two diffracted lights 14a and 14b have a spot diameter of about 1.2 mm.

Further, even when the wavelength λ of the laser light changes and the diffraction angle θ ₁ of the ± n-order diffracted light from the diffraction grating 10 changes to the diffraction angle θ ₁ ′, the lens group 11 is used in this embodiment. The incident ± nth order diffracted light is imaged on the surface of the position 11a (a position where the image height is slightly different from that of the diffracted lights 5a and 5b having the diffraction angle θ ₁ ) and then diverges to become a parallel light flux in the lens group 12 and the angle θ ₁ At ′, the light is incident on the surface of the moving object 7. Then, the spots of the two light fluxes at this time are maintained in a state of overlapping each other.

The condenser lens 8 is proportional to the moving speed V of the moving object 7, and the Doppler shifts Δf and −Δf shown in the equation (1).
The scattered light of the received frequency is condensed on the detection surface 9a of the photodetector 9. At this time, Doppler shift Δf, −Δf
The two scattered lights received interfere with each other on the detection surface 9a. The photodetector 9 detects the amount of light based on the brightness of the interference fringes at this time. That is, the photodetector 9 has n = 1 in the equation (4).
The Doppler frequency F proportional to the moving speed V, F = 2V / d (5) The Doppler signal independent of the oscillation wavelength λ of the laser 1 is detected. Then, the calculating means 20 uses the output signal from the photodetector 9 to obtain the moving speed V from the equation (5).

When the scattered light from the moving object 7 changes depending on the reflectance of the moving object 7 and the amount of light received by the photodetector 9 changes, the control means 21 feeds back the light source 1 to the light source 1. The output intensity from 1 is adjusted so that the scattered light received by the photodetector 9 becomes substantially constant.

As a result, a Doppler frequency signal having a good S / N ratio is obtained, so that highly accurate speed information can always be obtained.

[0036]

According to the present invention, by setting each element as described above, the amount of light received by the photodetector becomes constant regardless of the magnitude of the reflectance of the moving object, and the reflectance is affected. It is possible to achieve a speedometer that can always obtain highly accurate speed information without being disturbed.

[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 a main part of a conventional Doppler speedometer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 light source 2 collimator lens 6a, 6b mirror 7 moving object 8 condensing lens 9 photodetector 10 diffraction grating 11, 12 lens system 20 computing means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Jun Asuwa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Shujiro Kadowaki 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (72) Inventor Makoto Takamiya 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (5)

[Claims] 1. A light flux from a light source means is 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 speedometer characterized in that, when detecting speed information of a moving object, the control means controls the output intensity of the luminous flux emitted from the light source means based on the DC component of the signal obtained by the detecting means. 2. The speedometer according to claim 1, wherein the control means controls the output of the light source means so that the intensity of scattered light obtained by the photodetector becomes substantially constant. 3. An optical system in which two lenses or lens groups having substantially the same focal length for a light flux having a wavelength λ from a light source means are arranged at an interval of approximately twice the focal length in the optical axis direction, The incident angle θ changes at the incident angle θ according to the change of the wavelength λ of the light flux so that sin θ / λ becomes substantially constant, and the luminous flux from the moving object is detected by the detection means.
When detecting the velocity information of the moving object using the signal from the detecting means, the control means controls the output intensity of the luminous flux emitted from the light source means based on the DC component of the signal obtained by the detecting means. A speedometer characterized by doing. 4. A speedometer for detecting a velocity information of a moving object based on a deviation of a frequency of scattered light from the moving object by causing an irradiation light flux having a wavelength λ to enter the moving object at a predetermined incident angle θ. , The incident angle θ changes according to the change of the wavelength λ of the irradiation light flux, and the irradiation light flux is made incident on the moving object so that sin θ / λ becomes substantially constant, and the signal obtained by the detection means is detected. A speedometer characterized in that the control means controls the output intensity of the light flux emitted from the light source means based on the DC component. 5. A light beam having a wavelength λ from a light source is made incident on a diffraction grating, and the + nth order and the −nth order (n = 1, n) from the diffraction grating.
2, 3 ...) Two different diffracted light beams have different focal directions on the moving object plane through an optical system in which two lens groups having substantially equal focal lengths are arranged at intervals of twice the focal length. Angle of incidence θ
When the two diffracted lights intersect near the moving object surface and the incident angle θ changes in accordance with the change of the wavelength λ, sin
Irradiate by setting each element so that θ / λ is almost constant,
When the detection means detects the two scattered lights that have undergone the Doppler shift from the surface of the moving object, and when the moving speed of the moving object is detected using the signal obtained by the detection means, it is obtained by the detection means. A speedometer characterized in that the control means controls the output intensity of the luminous flux emitted from the light source means based on the DC component of the signal.