JP2021113746A - Laser Doppler speedometer - Google Patents

Abstract

To allow identifying a location of measurement of invisible light used for measurement by aiming light using visible light with a simple configuration.SOLUTION: An invisible measuring beam emitted by a measurement laser source 1 is split into two beams by a beam splitter 3, and each beam hits a field of measurement of a measurement object 100 at each different angle. Visible aiming light emitted by an aiming laser source 8 transmits through a dichroic mirror 6, and is emitted from an objective lens 5 so that the centre of the field of measurement of the measurement object 100 is a condensing point. Reflectance of the measuring beam in the field of measurement passes through the objective lens 5, is then reflected by the dichroic mirror 6 to be condensed on a photodetector 7. A measurement device 9 measures the speed of the measurement object 100 on the basis of a beat frequency of a detection signal of the photodetector 7.SELECTED DRAWING: Figure 1

Description

The present invention relates to a laser Doppler speedometer.

As a laser Doppler speedometer, the laser beam for measurement is branched into two beams, and the two branched beams are placed in the same region on the object to be measured and two in the direction perpendicular to the moving direction of the object to be measured. The angle formed by the beams is irradiated so that it becomes + θ and -θ, the reflected light reflected on the object to be measured by the two irradiated beams is detected, and the beat frequency of the reflected light is heterodyne-detected to be measured. A laser Doppler speedometer that calculates the speed of an object is known (for example, Patent Document 1).

Further, in such a laser Doppler velocimeter, in order to perform speed measurement with higher accuracy, invisible near-infrared laser light is used while using near-infrared laser light having higher output as the laser light for measurement. A technique for emitting visible light as aiming light is known so that the irradiation position can be visually recognized (Patent Document 2).

The configuration of the laser Doppler speedometer according to this technique is shown in FIGS. 3a and 3b.
In the laser Doppler velocimeter of FIG. 3a, the measurement light, which is an invisible near-infrared laser light emitted from the measurement laser light source 301, and the aiming light, which is the visible light laser light emitted from the aiming laser light source 302, are combined. , Each of which is wavelength-synthesized by a fiber-type WDM optical coupler 303 through an optical fiber and emitted to a collimator lens 304.

The collimator lens 304 converts the measurement light and the aiming light incident from the fiber type WDM optical coupler 303 into a parallel beam and outputs the parallel beam, and the beam splitter 305 emits the measurement light and the aiming light incident from the collimator lens 304. The first laser beam group consisting of one of the branched measurement lights and the aiming light is applied to the object 100 to be measured, and the second laser composed of the other branched measurement light and the aiming light is irradiated. The light group is emitted toward the mirror 306.

Then, the mirror 306 reflects the second laser beam group incident from the beam splitter 305 and irradiates the object 100 to be measured.
Here, the first laser beam group emitted from the beam splitter 305 and the second laser beam group emitted from the mirror 306 irradiate the same region of the object to be measured 100. Further, the first laser beam group emitted from the beam splitter 305 irradiates the object to be measured 100 from a direction inclined by + θ from the direction perpendicular to the moving direction of the object to be measured 100, and is emitted from the mirror 306. The laser beam group irradiates the object to be measured 100 from a direction tilted by −θ from a direction perpendicular to the moving direction of the object to be measured 100.

Therefore, in the region where the measurement light of the first laser light group and the measurement light of the second laser light group are irradiated, the visible light spot by the aiming light of the first laser light group and the aiming light of the second laser light group Is also formed.

Next, the objective lens 307 collects the reflected light of the first laser light group and the second laser light group reflected by the object 100 to be collected by the photodetector 308, and the photodetector 308 collects the collected reflected light. Detects the measurement light of and outputs it as a detection signal.

Here, the frequency of the reflected light of the measurement light of the first laser light group and the frequency of the reflected light of the measurement light of the second laser light group have a Doppler shift of a magnitude corresponding to the speed of the object to be measured 100. Therefore, in the detection signal output by the optical detector 308, a beat of a frequency corresponding to the magnitude of the Doppler shift appears. Therefore, the velocity v of the object to be measured 100 can be calculated from the frequency of this beat.

Next, the laser Doppler velocimeter of FIG. 3b is the laser Doppler velocimeter of FIG. 3a, which uses a dichroic mirror 309 instead of the fiber type WDM optical coupler 303 used for wavelength synthesis of the measurement light and the aiming light. In the laser Doppler velocimeter of FIG. 3b, the measurement light is emitted from the measurement laser light source 301 to the dichroic mirror 309 via the collimator lens 304, and the aiming light is dichroic from the aiming laser light source 302 via the collimator lens 304. When the light is emitted to the mirror 309, the measurement light and the aiming light are coaxially wavelength-synthesized by the dichroic mirror 330 and emitted to the beam splitter 305.

Japanese Unexamined Patent Publication No. 2005-61928 Japanese Patent No. 6474270

The laser Doppler speedometer shown in FIG. 3a requires a relatively expensive fiber-type WDM optical coupler for wavelength synthesis of the measurement light and the aiming light in the same optical path. Further, in the laser Doppler velocimeter using a dichroic mirror for wavelength synthesis shown in FIG. 3b, an optical system for wavelength synthesis of the measurement light using the dichroic mirror and the aiming light in the same optical path before the branching of the measurement light. It is necessary to provide the laser Doppler speed meter, which hinders the miniaturization of the laser Doppler speed meter.

Therefore, the present invention is suitable for miniaturization and cost reduction of a laser Doppler velocimeter that emits measurement light, which is invisible light used for measurement, together with aiming light, which is visible light used for aiming the measurement light. The challenge is to realize it with a simple configuration.

In order to achieve the above object, the present invention uses a laser Doppler velocimeter for measuring the velocity of an object to be measured, a measurement laser light source that emits measurement light whose wavelength is outside the visible region, and the measurement light. A measurement region in which the beam splitter that divides the first measurement light and the second measurement light and the first measurement light and the second measurement light are regions in which the relative positions with respect to the laser Doppler velocimeter are predetermined. With a course changing optical system that emits the first measurement light and the second measurement light by changing the traveling direction of at least one of the first measurement light and the second measurement light so as to irradiate from different directions. , A light detector that detects the intensity of the reflected light of the first measurement light and the second measurement light reflected in the measurement area and outputs it as a detection signal, and emits aiming light whose wavelength is laser light in the visible region. It is provided with an aiming laser light source and a refraction optical system that refracts and emits the aiming light emitted by the aiming laser light source so that the position of the condensing point is within the measurement region.

Further, in order to achieve the above object, the present invention comprises a laser Doppler velocimeter for measuring the velocity of an object to be measured, a measuring laser light source for emitting measurement light whose wavelength is outside the visible region, and the measurement. Measurement in which the beam splitter that divides the light into the first measurement light and the second measurement light, and the first measurement light and the second measurement light are regions in which the relative positions with respect to the laser Doppler velocimeter are predetermined. Course-changing optics that emits the first measurement light and the second measurement light by changing the traveling direction of at least one of the first measurement light and the second measurement light so as to irradiate a region from different directions. The system, the aiming laser light source that emits aiming light whose wavelength is within the visible region, the spectroscopic means, the optical axis of the first measurement light emitted from the course changing optical system, and the course changing optical. It includes a lens arranged so that the optical axis is located between the optical axis of the second measurement light emitted from the system, and an optical detector. However, the reflected light of the first measurement light and the second measurement light reflected in the measurement region is incident on the lens, and the aiming light emitted from the aiming laser light source is incident on the spectroscopic means, and the said. The lens emits the incident reflected light to the spectroscopic means. Further, the spectroscopic means emits the reflected light incident from the lens toward the photodetector, and emits the aiming light incident from the aiming laser light source toward the lens. Further, the lens refracts the aiming light incident from the spectroscopic means so that the position of the condensing point is within the measurement region and emits the light, and the light detector via the spectroscopic means. The incident reflected light is refracted and emitted so that the reflected light incident on the light is condensed at the position of the light detector. Then, the photodetector detects the intensity of the reflected light incident from the spectroscopic means and outputs it as a detection signal.

In such a laser Doppler velocimeter, for example, the spectroscopic means is a dichroic mirror that reflects light having a wavelength of the measurement light and transmits light having a wavelength of the aiming light, and is incident from the lens in the spectroscopic means. The reflected light is reflected and emitted toward the light detector, and the aiming light incident from the aiming laser light source is transmitted and emitted toward the lens.

Alternatively, the spectroscopic means is a dichroic mirror that transmits light having a wavelength of the measurement light and reflects light having a wavelength of the aiming light, and the spectroscopic means transmits the reflected light incident from the lens to transmit the reflected light. In addition to emitting light toward the light detector, the aiming light incident from the aiming laser light source may be reflected and emitted toward the lens.

In the above laser Doppler speedometer, a laser beam having a wavelength of 1400 nm or more and 2600 nm or less, for example, a laser beam having a wavelength of 1550 nm may be used as the measurement light.
Further, the above laser Doppler speedometer may be provided with a measuring unit that measures the speed of the object to be measured based on the beat frequency of the detection signal detected by the photodetector.
In these laser Doppler speedometers, the laser Doppler is applied to the object to be measured so that the area on the object to be measured is a measurement area in which the invisible first measurement light and the second measurement light are commonly irradiated. When the speedometer is placed, the speed of the object to be measured can be measured correctly.

Then, this laser Doppler speedometer emits visible aiming light so that the position of the focusing point is within the measurement area, so that the position of the light spot formed on the object to be measured by the aiming light and the position of the light spot are formed. Based on the size, it is possible to identify whether the measurement area is a desired area on the object to be measured. Therefore, the aiming light can be used to aim the measurement area by the invisible first measurement light and the second measurement light, and the laser Doppler speedometer can be set to the normal arrangement capable of correctly measuring the object 100 to be measured.

In addition, a relatively expensive fiber-type WDM optical coupler and an optical system for wavelength synthesis of the measurement light and the aiming light in the same optical path, which are required before the measurement light branch, are not required, and the laser Doppler velocimeter is inexpensive. , Can be configured compactly.

As described above, according to the present invention, the laser Doppler velocimeter that emits measurement light, which is invisible light used for measurement, together with aiming light, which is visible light used for aiming the irradiation position of the measurement light, can be miniaturized. It can be realized with a simpler configuration suitable for cost reduction.

It is a figure which shows the structure of the laser Doppler speedometer which concerns on embodiment of this invention. It is a figure which shows the optical path of the laser Doppler speedometer which concerns on embodiment of this invention. It is a figure which shows the structural example of the known laser Doppler speedometer.

Hereinafter, embodiments of the laser Doppler speedometer according to the present invention will be described.
FIG. 1a shows the configuration of the laser Doppler speedometer according to the present embodiment.
As shown in the figure, the laser Doppler speedometer includes a measurement laser light source 1, a collimator lens 2, a beam splitter 3, a mirror 4, an objective lens 5, a dichroic mirror 6, a light detector 7, an aiming laser light source 8, and a measuring device 9. I have.

The measurement laser light source 1 emits near-infrared laser light as measurement light under the control of the measurement device 9. As the near-infrared laser light emitted by the measurement laser light source 1, a near-infrared laser light having a laser wavelength range of 1400 nm to 2600 nm, which is called an eye-safe laser, is used. Hereinafter, it will be described assuming that a near-infrared laser having a wavelength of 1550 nm is used as the measurement light.

The aiming laser light source 8 emits visible laser light as aiming light according to the control of the measuring device 9. In the following, the description will be made assuming that a red laser having a wavelength of 635 nm is used as the aiming light.

FIG. 1a shows a case where the laser Doppler speedometer is arranged with respect to the object to be measured 100 in a normal arrangement in which the speed of the object to be measured 100 can be measured correctly, and when the object is in the normal arrangement. The laser Doppler speedometer measures the speed v in the x direction of the object to be measured 100, with the right direction of FIG. 1a being the x direction, the upward direction being the z direction, and the direction from the front to the back of the paper surface being the y direction.

Then, the operation of the laser Doppler speedometer in the normal arrangement is as follows.
The measurement laser light source 1 emits the measurement light to the collimator lens 2, and the collimator lens 2 converts the measurement light into a parallel beam and emits it to the beam splitter 3.
The beam splitter 3 splits the measurement light incident from the collimator lens 2 into two measurement lights, the first measurement light and the second measurement light, irradiates the object 100 with the first measurement light, and the second measurement light. Is emitted toward the mirror 4.

The mirror 4 reflects the second measurement light incident from the beam splitter 3 and irradiates the object 100 to be measured.
Here, the first measurement light emitted from the beam splitter 3 and the second measurement light emitted from the mirror 4 commonly irradiate a measurement region, which is a region for measuring the velocity of the object 100 to be measured.
Further, the first measurement light emitted from the beam splitter 3 irradiates the measurement region from a direction tilted by + θ about the axis in the y direction with respect to the z direction, and the second measurement light emitted from the mirror 4 is in the z direction. The measurement area is irradiated from a direction tilted by -θ around the axis in the y direction.

Next, the objective lens 5 collects the reflected light of the first measurement light and the second measurement light reflected in the measurement region of the object to be measured 100 on the photodetector 7 via the dichroic mirror 6.
Here, the objective lens 5 is arranged at a position overlapping the measurement region of the object to be measured 100 with respect to the xy direction, and the direction of the optical axis thereof is the z direction. Further, the angle formed by the optical axis of the objective lens 5 and the optical axis of the first measurement light emitted from the beam splitter 3 is + θ, and the optical axis of the objective lens 5 and the second measurement light emitted from the mirror 4 The angle formed by the optical axis is -θ.

FIG. 1b shows the positional relationship between the first measurement light and the second measurement light reflected by the object to be measured 100, the objective lens 5, the dichroic mirror 6, and the photodetector 7 as seen in the x direction. Is shown.
As shown in the figure, the reflected light of the first measurement light and the second measurement light reflected in the measurement region of the object to be measured 100 passes through the objective lens 5 and is incident on the dichroic mirror 6 from the −z direction.
The dichroic mirror 6 reflects 100% of the light of 1550 nm, which is the wavelength of the measurement light, and 100% of the light of 635 nm, which is the wavelength of the aiming light. Further, the photodetector 7 is arranged in the y direction when viewed from the dichroic mirror 6.

Therefore, the dichroic mirror 6 reflects the reflected light of the first measurement light and the second measurement light incident on the objective lens 5 in the z direction in the direction (y direction) of the light detector 7, thereby the objective lens 5. The reflected light of the first measurement light and the second measurement light is focused on the light detector 7 via the dichroic mirror 6.

Next, the photodetector 7 outputs a detection signal obtained by photoelectrically converting the reflected light of the measurement light collected by the objective lens 5 through the dichroic mirror 6 to the measurement device 9.
Here, the frequency of the reflected light of the first measurement light and the frequency of the reflected light of the second measurement light have a Doppler shift of a magnitude corresponding to the speed v of the object to be measured 100 in opposite directions, and the light is detected. In the detection signal output by the device 7, a beat having a frequency corresponding to the magnitude of the Doppler shift is generated.
The measuring device 9 measures the beat frequency of the detection signal output from the photodetector 7, and calculates the velocity v of the object to be measured 100 from the measured beat frequency.

Next, the aiming light emitted by the aiming laser light source 8 is incident on the dichroic mirror 6 from the z direction. Then, the aiming light passes through the dichroic mirror 6 as it is and is incident on the objective lens 5.
The objective lens 5 is a chromatic aberration correction lens, and refracts the incident aiming light so that the center of the measurement region of the object to be measured 100, which is commonly irradiated by the first measurement light and the second measurement light, is the focusing point. It emits light in the -z direction.
Therefore, a visible light spot due to the aiming light is formed at the center of the measurement region of the object to be measured 100.

The operation of the laser Doppler speedometer when the laser Doppler speedometer is in the normal arrangement with respect to the object to be measured 100 so that the speed of the object to be measured 100 can be measured correctly has been described above.
As described above, as shown in FIG. 2, the laser Doppler speedometer emits the aiming light passing through the center F of the measurement region of the object to be measured 100 in the normal arrangement in the -z direction. Based on the position of the light spot formed on the object to be measured 100 in the xy direction, the arrangement of the laser Doppler speedometer can be set to the normal arrangement with respect to the xy direction.

Further, the laser Doppler speedometer emits aiming light in which the center F of the measurement region of the object to be measured 100 is the focusing point when the laser Doppler speedometer is in the normal arrangement. Therefore, the size of the light spot formed by the aiming light on the object to be measured 100 is minimized when the object is in the normal arrangement, and the laser Doppler speedometer moves from the normal arrangement to the object 100 to be measured in the z direction and the -z direction. As the deviation increases, the size of the light spot formed on the object to be measured 100 by the aiming light increases. Therefore, the arrangement of the laser Doppler speedometer can be set to the normal arrangement in the z direction based on the size of the light spot formed by the aiming light.

According to the present embodiment, the aiming light is used for aiming the measurement area by the invisible first measurement light and the second measurement light, and the laser Doppler speedometer can be correctly measured with respect to the object to be measured 100. Can be set to.
In addition, a relatively expensive fiber-type WDM optical coupler and an optical system for wavelength synthesis of the measurement light and the aiming light in the same optical path, which are required before the measurement light branch, are not required, and the laser Doppler velocimeter is inexpensive. , Can be configured compactly.

The embodiment of the present invention has been described above.
The configuration of the laser Doppler velocimeter of the present embodiment is a dichroic mirror 6 that transmits 100% of the light of 1550 nm, which is the wavelength of the measurement light, and reflects 100% of the light of 635 nm, which is the wavelength of the aiming light. 6 may be used and the arrangement of the light detector 7 and the aiming laser light source 8 may be exchanged.

1 ... Laser light source for measurement, 2 ... Collimator lens, 3 ... Beam splitter, 4 ... Mirror, 5 ... Objective lens, 6 ... Dichroic mirror, 7 ... Light detector, 8 ... Laser light source for aiming, 9 ... Measuring device, 100 … The object to be measured.

Claims (7)

A laser Doppler speedometer that measures the speed of an object to be measured.
A laser light source for measurement that emits measurement light whose wavelength is outside the visible region,
A beam splitter that splits the measurement light into a first measurement light and a second measurement light,
The first measurement light and the second measurement light so that the first measurement light and the second measurement light irradiate the measurement area, which is a region in which the relative position with respect to the laser Doppler velocimeter is predetermined, from different directions. A course changing optical system that emits light by changing the traveling direction of at least one of the first measurement light and the second measurement light.
A photodetector that detects the intensity of the reflected light of the first measurement light and the second measurement light reflected in the measurement region and outputs it as a detection signal.
An aiming laser light source that emits aiming light whose wavelength is within the visible region,
A laser Doppler speedometer characterized by having a refracting optical system that refracts the aiming light emitted by the aiming laser light source so that the position of a condensing point is within the measurement region and emits the light.
A laser Doppler speedometer that measures the speed of an object to be measured.
A laser light source for measurement that emits measurement light whose wavelength is outside the visible region,
A beam splitter that splits the measurement light into a first measurement light and a second measurement light,
The first measurement light and the second measurement light so that the first measurement light and the second measurement light irradiate the measurement area, which is a region in which the relative position with respect to the laser Doppler velocimeter is predetermined, from different directions. A course changing optical system that emits light by changing the traveling direction of at least one of the first measurement light and the second measurement light.
An aiming laser light source that emits aiming light whose wavelength is within the visible region,
Spectral means and
The optical axis is arranged so as to be located between the optical axis of the first measurement light emitted from the course changing optical system and the optical axis of the second measurement light emitted from the course changing optical system. With the lens
Has a photodetector
The reflected light of the first measurement light and the second measurement light reflected in the measurement region is incident on the lens.
The aiming light emitted from the aiming laser light source is incident on the spectroscopic means, and the aiming light is incident on the spectroscopic means.
The lens emits the incident reflected light to the spectroscopic means.
The spectroscopic means emits the reflected light incident from the lens toward the photodetector, and emits the aiming light incident from the aiming laser light source toward the lens.
The lens refracts and emits the aiming light incident from the spectroscopic means so that the position of the condensing point is within the measurement region, and is incident on the light detector via the spectroscopic means. The incident reflected light is refracted and emitted so that the reflected light is focused at the position of the light detector.
The photodetector is a laser Doppler speedometer characterized by detecting the intensity of the reflected light incident from the spectroscopic means and outputting it as a detection signal.
The laser Doppler speedometer according to claim 2.
The spectroscopic means is a dichroic mirror that reflects light having a wavelength of the measurement light and transmits light having a wavelength of the aiming light.
The spectroscopic means reflects the reflected light incident from the lens and emits it toward the light detector, and transmits the aiming light incident from the aiming laser light source and emits it toward the lens. A laser Doppler speedometer featuring.
The laser Doppler speedometer according to claim 2.
The spectroscopic means is a dichroic mirror that transmits light having a wavelength of the measurement light and reflects light having a wavelength of the aiming light.
The spectroscopic means transmits the reflected light incident from the lens and emits it toward the light detector, and reflects the aiming light incident from the aiming laser light source and emits it toward the lens. A laser Doppler speedometer featuring.
The laser Doppler speedometer according to claim 1, 2, 3 or 4.
A laser Doppler speedometer characterized in that a laser beam having a wavelength of 1400 nm or more and 2600 nm or less is used as the measurement light.
The laser Doppler speedometer according to claim 5.
A laser Doppler speedometer characterized in that a laser beam having a wavelength of 1550 nm is used as the measurement light.
The laser Doppler speedometer according to claim 1, 2, 3, 4, 5 or 6.
A laser Doppler speedometer comprising a measuring unit that measures the speed of the object to be measured based on the beat frequency of the detection signal detected by the photodetector.

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