JP2924754B2 - Optical differential velocity meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical differential velocimeter for measuring the speed of a moving object using laser light.

[0002]

2. Description of the Related Art Conventionally, as a speedometer for measuring the speed of a moving body in a non-contact manner, a laser using the Doppler effect of light has been used.
There is a Doppler speedometer (for example, "Applied Optics-Introduction to Optical Measurements", written by Toyohiko Yatakai, published by Maruzen kk, Showa 63
Year issuance etc.). This laser Doppler speedometer
The velocity measurement is performed by heterodyne detection of the Doppler shift of the scattered light generated by the movement of the moving body.

A conventional laser Doppler velocimeter will be described with reference to the drawings. FIG. 3 is an explanatory diagram showing a conventional laser Doppler velocimeter. In the figure, (1) shows the configuration of a reference beam method, (2) shows the configuration of a laser Doppler velocimeter using the two-incident light method (differential method), and (3) shows the configuration of a laser Doppler velocimeter using the one-incident light method.
1a and 1b are half mirrors that transmit part of incident light and reflect the rest, 2 is a mirror, 3 is a photodetector, 4 is a beam splitter, 5, 5a and 5b are lenses, 6, 7, and 8 are slits. , The vector v is the velocity vector of the moving object, the vector k
s, ks ₁ and ks ₂ are wave number vectors of incident light, and vectors ko, ko ₁ and ko ₂ are wave number vectors of scattered light.

The operation of the conventional example having the above configuration will be described for each method. (1) Reference light method The incident light having the wave number vector ks is divided into two by the half mirror 1a, the reflected light is irradiated to the mirror 2 as the reference light, reflected by the half mirror 1b, and made incident on the photodetector 3.
Further, the transmitted light is applied to the moving body moving at the velocity vector v, and the scattered light of the wave vector ko is incident on the photodetector 3 via the half mirror 1b. These two laser beams incident on the photodetector 3 overlap each other to generate interference fringes. Therefore, the speed of the moving body can be obtained by measuring the interval between the interference fringes.

(2) Two incident light method (differential method) The incident light is converted into a wave vector ks by the beam splitter 4.
_After splitting into two beams of ₁ and ks ₂ , the beam is irradiated to the moving object of the velocity vector v via the lens 5 a. The scattered light from the moving object is incident on the photodetector 3 via the slit 6, the lens 5b, and the slit 7. The incident scattered light produces interference fringes in the same manner as in (1), and the speed of the moving body can be obtained by measuring the interval.

(3) One incident light method A moving object having a velocity vector v is irradiated with incident light having a wave number vector ks, and scattered light having wave number vectors ko ₁ and ko ₂ is transmitted through a slit 8, a lens 5, and a slit 7. The light is incident on the detector 3. The incident scattered light produces interference fringes in the same manner as in (1), and the speed of the moving body can be obtained by setting this interval.

As described above, in any of (1), (2) and (3), the speed of the moving body can be obtained by measuring the interval between the interference fringes generated in the optical measuring device 3. However, since all of them utilize the Doppler effect of light, the relative speed between the measurer and the moving body in the direction of the line of sight of the measurer cannot be determined. That is, it is impossible to measure a velocity component orthogonal to the line of sight of the measurer.

[0008]

As described above, the conventional speedometer utilizing the Doppler effect of light has a problem that a speed component perpendicular to the line of sight of a measurer cannot be measured. The present invention has been made to solve such a problem, and an object of the present invention is to provide a speedometer that can measure a speed component orthogonal to a line of sight of a measurer.

[0009]

In order to achieve the above object, an optical differential velocimeter according to the present invention irradiates an object to be measured with irradiation light, and outputs the irradiation light and the irradiation light from the object to be measured. Interference fringe detecting means for detecting the interval between interference fringes generated by superimposing the reflected light on the light beam, calculating the light line difference from the interval between the interference fringes, and calculating the speed of the DUT in a direction orthogonal to the irradiation light Speed calculation means. With this configuration, the present invention can measure the optical path difference generated between the irradiation light applied to the moving body and the reflected light, and from the optical path difference, it is orthogonal to the line of sight of the measurer. The speed component of the moving object can be measured.

[0010]

Next, details of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram showing one embodiment of the present invention. In FIG. 1, reference numeral 10 denotes a moving object which is an object to be measured, 11 denotes a corner cube provided on the moving object 10 and reflects light, 12 denotes a velocity vector of the moving object 10, 13 denotes a laser light source, and 14 denotes an incident light. A half mirror that transmits through the part and reflects the rest, 15 is a CCD (Charge Cou
pled Device), 16 is a mirror, 17 is a laser light source 13
Fringe detecting means composed of a half mirror 14, a CCD 15, and a mirror 16, 18 is irradiation light, 19 is reflected light, 20 is interference fringes, ε is a light line difference between irradiation light 18 and reflected light 19, θ Is the incident angle of the irradiation light 18 on the CCD 15, and ΔL is the interval between the interference fringes.

The operation of the present invention having the above configuration will be described in detail. The moving body 10 is moving upward from below in the figure with the velocity vector 12. When the moving body 10 comes to a position orthogonal to the line of sight of the measurer (the irradiation direction of the irradiation light 18), the irradiation light 18 is irradiated from the laser light source 13 to the half mirror 14. A part of the irradiation light 18 passes through the half mirror 14 and irradiates the CCD 15, and the remaining laser light is reflected by the half mirror 14 and irradiates the corner cube 11 provided on the moving body 10. The irradiation light 18 is reflected by the corner cube 11 and is irradiated as reflected light 19 on the half mirror 14. The reflected light 19 passes through the half mirror 14, irradiates the mirror 16, is reflected, is further reflected by the half mirror 14, and irradiates the CCD 15.

At this time, assuming that the relative speed between the moving body 10 and the interference fringe detecting means (measurement person) 17 is v, the irradiation light 18 to the corner cube 11 and the reflected light 19 are not parallel, and An optical line difference ε as shown in FIG. ε = v / c (ε << 1) (1) Here, c is the speed of light, and the relative speed v is the speed in the direction orthogonal to the irradiation light 18.

Next, a method of detecting the optical path difference ε will be described with reference to FIG. FIG. 2 is an explanatory diagram showing interference fringes generated on the CCD 15 of FIG. If there is a relative velocity v between the moving body 10 and the interference fringe detecting means (measurer) 17, a light line difference ε occurs between the irradiation light 18 and the reflected light 19, and the CCD 15
Interference fringes 20 occur on the surface. The interval between the interference fringes 20 is Δ
L, the wavelength λ of the irradiation light 18, the optical line difference ε, and the irradiation light 1
ΔL = λ / (sin ε + sin θ) holds from the angle of incidence θ on the CCD 15.

Here, if θ = 0 and ε << 1, ΔL
= Λ / ε, and ε = λ / (ΔL) (2) As described above, Δ is obtained by substituting ΔL detected by the CCD 15 and the wavelength λ of the irradiation light 18 into equation (2), and the relative velocity v can be obtained by substituting ε into equation (1). . The above calculation is performed by a speed calculation unit (not shown).

[0015]

As described above, according to the present invention, the light path difference generated between the irradiation light to the object to be measured and the reflected light thereof is obtained, and the speed of the object to be measured is calculated from the light path difference. Therefore, it is possible to measure the velocity component of the DUT in a direction orthogonal to the line of sight of the measurer. Further, by measuring the interval between interference fringes between the irradiation light and the reflected light, highly accurate speed measurement can be performed.

[Brief description of the drawings]

FIG. 1 is a sectional view and an explanatory view showing one embodiment of the present invention.

FIG. 2 is an explanatory diagram showing interference fringes generated in the CCD of FIG.

FIG. 3 is an explanatory diagram showing a conventional example.

[Explanation of symbols]

1a, 1b, 14 ... half mirror, 2, 16 ... mirror,
3: photodetector, 4: beam splitter, 5, 5a, 5b
... Lens, 6, 7, 8 ... Slit, 10 ... Moving body, 11
... corner cube, 12 ... moving direction of the moving body 10, 13
... Laser light source, 15 ... CCD, 17 ... Interference fringe detecting means,
18: irradiation light, 19: reflection light, 20: interference fringe, ε: light line difference, θ: light line difference generated between irradiation light 18 and reflection light 19, ΔL: interval of interference fringe.

Claims (4)

(57) [Claims] 1. An interference fringe detecting means for irradiating an object to be irradiated with irradiation light and detecting an interval of interference fringes generated by superimposing the irradiation light and the reflected light of the irradiation light from the object to be measured; An optical path difference velocimeter, comprising: a velocity calculating unit that determines an optical path difference from an interval between interference fringes and calculates a velocity of the device under test in a direction orthogonal to the irradiation light. 2. The apparatus according to claim 1, wherein the interference fringe detecting means includes: a laser light source for irradiating a laser beam of a predetermined wavelength; A half mirror to irradiate, a mirror to reflect laser light reflected by the object to be measured and then transmitted through the half mirror, a laser beam reflected by the mirror and reflected by the half mirror and a laser beam reflected by the half mirror And a light receiving element for receiving light. 3. The method according to claim 1, wherein the speed calculating means obtains a light path difference by dividing a wavelength of the irradiation light by an interval of interference fringes generated in the light receiving element, and multiplies the light path difference by the light speed. An optical differential velocimeter characterized by determining the velocity of an object by measuring. 4. The optical line speedometer according to claim 2, wherein the light receiving element is a CCD.