CN116601459A - Displacement sensor - Google Patents

Abstract

Provided is a displacement sensor which can suppress the decline of the movement resolution and the light receiving amount, and realize proper measurement accuracy and measurement speed. The displacement sensor (11) comprises: a light source (110) that outputs white light; a light guide (201) comprising at least one optical fiber; a sensor head (300) which houses a diffraction lens (310) that causes chromatic aberration in the optical axis direction of white light incident via a light guide (201) and irradiates the object (TA) to be measured with light having chromatic aberration generated; and a beam splitter (120) that obtains reflected light reflected by the object to be measured (TA) via the light guide (201) and collected by the sensor head (300), measures the spectrum of the reflected light, and an optical fiber connected to the sensor head (300) has a larger core diameter than an optical fiber connected to the beam splitter (120).

Description

Displacement sensor

Technical Field

The present invention relates to displacement sensors.

Background

Conventionally, as a device for measuring displacement of a measurement object in a noncontact manner, a confocal measurement device using a confocal optical system has been used.

For example, the confocal measurement device described in patent document 1 below has a confocal optical system using a diffraction lens between a light source and a measurement object. In this confocal measurement device, the light emitted from the light source is irradiated to the measurement object through the confocal optical system at a focal length corresponding to the wavelength of the light. Further, by detecting the peak value of the wavelength of the reflected light, the displacement of the measurement target can be measured.

Further, patent document 2 below discloses a technique related to a confocal measurement device in which the detection accuracy of the position of the measurement target is improved, and the core diameters of the 2 nd optical fiber connected to the spectroscope and the 3 rd optical fiber connected to the sensor head are 5 μm to 25 μm. It is described that the core diameters may be different between the 2 nd optical fiber and the 3 rd optical fiber.

As the index of the measurement accuracy of the confocal measurement device described above, there are, for example, linearity, stationary resolution, moving resolution, and the like, and when displacement measurement is performed, these are added to form the final measurement error. Among the indices of these measurement accuracy, the displacement sensor for point measurement generally has one of the important problems to be improved because the measurement error due to the movement resolution is the largest.

Prior art literature

Patent literature

Patent document 1: U.S. Pat. No. 5785651 Specification

Patent document 2: japanese patent laid-open publication No. 2019-66343

Disclosure of Invention

Problems to be solved by the invention

However, in the confocal measurement device, in order to improve the movement resolution, it is conceivable to reduce the core diameter of the optical fiber, but if the core diameter is reduced, the light receiving amount is reduced, and as a result, there is a problem that the measurement speed is reduced.

Accordingly, an object of the present invention is to provide a displacement sensor capable of realizing appropriate measurement accuracy and measurement speed while suppressing a decrease in movement resolution and light receiving amount.

Means for solving the problems

The displacement sensor according to one embodiment of the present invention includes: a light source that outputs white light; a light guide section including at least one optical fiber; a sensor head that houses a diffraction lens that causes chromatic aberration in an optical axis direction of white light incident via a light guide unit, and irradiates the object to be measured with light that causes chromatic aberration; and a spectroscope which acquires reflected light reflected by the object to be measured and converged by the sensor head via the light guide section, and measures the spectrum of the reflected light, wherein an optical fiber connected to the sensor head has a larger core diameter than an optical fiber connected to the spectroscope.

According to this aspect, the displacement sensor according to one aspect of the present invention is configured such that the optical fiber connected to the sensor head has a larger core diameter than the optical fiber connected to the spectroscope, and therefore, it is possible to realize appropriate measurement accuracy and measurement speed while suppressing a decrease in the movement resolution and the light receiving amount.

In the above aspect, the optical fiber disposed between the sensor head and the spectroscope may include a tapered portion having a continuously changing core diameter.

According to this aspect, since the optical fiber disposed between the sensor head and the spectroscope includes the tapered portion, the optical fiber connected to the sensor head can be configured to have a larger core diameter than the optical fiber connected to the spectroscope.

In the above aspect, the light guide portion may include: a 1 st optical fiber connected to a light source; a 2 nd optical fiber connected to the sensor head; a 3 rd optical fiber connected to the optical splitter; and an optical coupler to which the 1 st optical fiber, the 2 nd optical fiber, and the 3 rd optical fiber are connected.

According to this aspect, since the light guide section includes the 1 st optical fiber, the 2 nd optical fiber, the 3 rd optical fiber, and the optical coupler, the optical fiber connected to the sensor head can have a larger core diameter than the optical fiber connected to the optical splitter.

In the above aspect, the 2 nd optical fiber may include a tapered portion having a continuously changing core diameter.

According to this aspect, since the 2 nd optical fiber includes the tapered portion, the optical fiber connected to the sensor head can be configured to have a larger core diameter than the optical fiber connected to the spectroscope.

In the above aspect, the 3 rd optical fiber may include a tapered portion having a continuously changing core diameter.

According to this aspect, since the 3 rd optical fiber includes the tapered portion, the optical fiber connected to the sensor head can be configured to have a larger core diameter than the optical fiber connected to the spectroscope.

In the above aspect, the 2 nd optical fiber may have a larger core diameter than the 3 rd optical fiber.

According to this aspect, the 2 nd and 3 rd optical fibers can be used to provide the optical fiber connected to the sensor head with a larger core diameter than the optical fiber connected to the spectroscope.

In the above aspect, the optical fiber connected to the sensor head may have the same numerical aperture as the diffraction lens.

According to this aspect, since the optical fiber connected to the sensor head has the same numerical aperture as the diffraction lens, it is possible to suppress a decrease in the movement resolution and to increase the light receiving amount. As a result, the displacement sensor according to one embodiment of the present invention can increase the measurement speed while suppressing a decrease in the measurement accuracy.

In the above aspect, the optical fiber connected to the sensor head may have a numerical aperture larger than that of the diffraction lens.

According to this aspect, since the optical fiber connected to the sensor head has a numerical aperture larger than that of the diffraction lens, it is possible to suppress a decrease in the amount of light received and to improve the movement resolution. As a result, the displacement sensor according to one embodiment of the present invention can suppress a decrease in the measurement speed and improve the measurement accuracy.

Effects of the invention

According to the present invention, it is possible to provide a displacement sensor capable of realizing appropriate measurement accuracy and measurement speed while suppressing a decrease in movement resolution and light receiving amount.

Drawings

Fig. 1 is a block diagram showing an example of a schematic configuration of a displacement sensor 10 according to each embodiment of the present invention.

Fig. 2 is a diagram schematically showing the structure of a displacement sensor 11 according to embodiment 1 of the present invention.

Fig. 3A is a diagram showing a specific example of an optical fiber having a tapered portion.

Fig. 3B is a diagram showing an internal structure of an optical fiber having a tapered portion.

Fig. 4 is a diagram showing evaluation of the displacement sensor 11 shown in fig. 2.

Fig. 5 is a diagram showing the relationship between the sensor head waveform and the beam splitter waveform and the light receiving waveform.

Fig. 6 is a diagram showing the relationship between the half-value width of the sensor head waveform and the half-value width of the beam splitter waveform and the light receiving amount.

Fig. 7 is a diagram schematically showing the structure of a displacement sensor 12 according to embodiment 2 of the present invention.

Fig. 8 is a diagram showing the evaluation of the displacement sensor 12 shown in fig. 7.

Fig. 9 is a diagram schematically showing the structure of a displacement sensor 13 according to embodiment 3 of the present invention.

Fig. 10 is a diagram schematically showing the structure of a displacement sensor 14 according to embodiment 4 of the present invention.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments described below are merely specific examples for carrying out the present invention, and the present invention is not limited thereto. In order to facilitate understanding of the description, the same reference numerals are given to the same components as much as possible in the drawings, and duplicate descriptions may be omitted.

First, the basic structure of the displacement sensor according to each embodiment of the present invention will be described.

[ basic Structure of Displacement sensor ]

Fig. 1 is a block diagram showing an example of a schematic configuration of a displacement sensor 10 according to each embodiment of the present invention. As shown in fig. 1, the displacement sensor 10 includes a controller 100, a light guide 200, and a sensor head 300, and measures the distance to the measurement object TA by using confocal optical system statistics.

The controller 100 includes a light source 110, a beam splitter 120, and a processing unit 130, and the beam splitter 120 includes a collimator lens 121, a diffraction grating 122, an adjustment lens 123, and a light receiving element 124.

The light guide 200 is disposed between the controller 100 and the sensor head 300, and includes, for example, the 1 st optical fiber 210, the 2 nd optical fiber 220, the 3 rd optical fiber 230, and the optical coupler 240, and propagates light. A part of the light guide 200 may be housed in the controller 100.

The sensor head 300 is configured to be detachable from the controller 100 via the light guide unit 200, and includes, for example, a diffraction lens 310 and an objective lens 320.

The light source 110 outputs white light to, for example, the 1 st optical fiber 210. The light source 110 may adjust the light amount of the white light based on the instruction of the processing unit 130. The light emitted from the light source 110 is not limited to white light, as long as it includes a plurality of wavelength components and includes a wavelength range covering a measurement distance range required by the displacement sensor 10.

One end of the 1 st optical fiber 210 is optically connected to the light source 110, one end of the 2 nd optical fiber 220 is optically connected to the sensor head 300, and one end of the 3 rd optical fiber 230 is optically connected to the beam splitter 120. The other ends of the 1 st and 3 rd optical fibers 210 and 230 and the other end of the 2 nd optical fiber 220 are optically coupled via an optical coupler 240.

The optical coupler 240 transmits light (irradiation light) incident from the 1 st optical fiber 210 to the 2 nd optical fiber 220, and splits light (reflected light) incident from the 2 nd optical fiber 220 and transmits the split light to the 1 st optical fiber 210 and the 3 rd optical fiber 230, respectively. Light transmitted from fiber 2 220 to fiber 1 210 through optical coupler 240 terminates at light source 110.

White light output from the light source 110 is incident on the sensor head 300 through the 1 st optical fiber 210, the optical coupler 240, and the 2 nd optical fiber 220. The sensor head 300 houses a diffraction lens 310 that causes chromatic aberration to occur in the optical axis direction in the white light emitted from the end face of the 2 nd optical fiber 220, and an objective lens 320 that causes chromatic aberration to be condensed in the object to be measured TA, and irradiates the object to be measured TA with the chromatic aberration-occurring light.

In the example shown in fig. 1, the light 410 of the 1 st wavelength, the light 420 of the 2 nd wavelength, and the light 430 of the 3 rd wavelength are arranged in order of focal length from short to long. The light 420 of the 2 nd wavelength is focused on the surface of the object TA to be measured (2 nd focal position), but the light 410 of the 1 st wavelength is focused on the front side of the object TA to be measured (1 st focal position), and the light 430 of the 3 rd wavelength is focused on the back side of the object TA to be measured (3 rd focal position).

The light reflected on the surface of the measurement object TA is collected by the objective lens 320, condensed by the diffraction lens 310, and returned to the core of the 2 nd optical fiber 220. Since the light 420 of the 2 nd wavelength among the reflected light is focused on the end surface of the 2 nd optical fiber 220, most of the light is incident on the 2 nd optical fiber 220, but the light of other wavelengths is not focused on the end surface of the 2 nd optical fiber 220, and most of the light is not incident on the 2 nd optical fiber 220. The reflected light incident on the 2 nd optical fiber 220 is transmitted to the 3 rd optical fiber 230 via the optical coupler 240, and is input to the beam splitter 120. In addition, the reflected light incident on the 2 nd optical fiber 220 is also transmitted to the 1 st optical fiber 210 via the optical coupler 240, but is terminated at the light source 110.

The beam splitter 120 obtains reflected light reflected by the object to be measured TA and converged by the sensor head 300 via the 2 nd optical fiber 220, the optical coupler 240, and the 3 rd optical fiber 230, and measures the spectrum of the reflected light. The beam splitter 120 includes a collimator lens 121 that condenses the reflected light emitted from the 3 rd optical fiber 230, a diffraction grating 122 that splits the reflected light, an adjustment lens 123 that condenses the split reflected light, and a light receiving element 124 that receives the split reflected light.

The processing unit 130 detects the position of the measurement object TA based on a light receiving amount distribution signal indicating the wavelength and the amount of light received by the light receiving element 124. Specifically, the position of the measurement object TA can be measured by detecting the peak of the wavelength in the received optical waveform by the spectroscope 120, and in this example, the 2 nd wavelength light 420 focused through the optical fiber among the light reflected by the measurement object TA appears as a peak in the spectroscope 120, and the position of the measurement object TA can be detected.

[ movement resolution and light receiving amount ]

Here, the measurement accuracy of the displacement sensor 10 will be described with respect to the movement resolution that has a large influence on the measurement error. Since the movement resolution is affected by the depth of field and the averaging effect, it is considered that the improvement is achieved by setting the core diameter of the optical fiber and the numerical aperture (hereinafter, also referred to as "NA (numerical aperture)") of the diffraction lens 310 to be small.

On the other hand, since the light receiving amount that affects the measurement speed of the displacement sensor 10 is affected by the coupling efficiency of the sensor head 300, it is considered that if the Numerical Aperture (NA) of the diffraction lens 310 is set large, improvement is achieved, contrary to the countermeasure for improving the movement resolution. In addition, when a light receiving waveform (light receiving amount distribution signal) is obtained by a convolution operation of combining a waveform of light converged by the sensor head 300 (hereinafter, also referred to as a "sensor head waveform" or the like) and a device characteristic waveform (hereinafter, also referred to as a "spectroscope waveform" or the like) caused by a device such as the spectroscope 120, the light receiving amount may be reduced.

Here, the inventors of the present invention have found the following: the 2 nd optical fiber 220 connected to the sensor head 300 is made to have a larger core diameter than the 3 rd optical fiber 230 connected to the spectroscope 120.

Hereinafter, specific embodiments of the optical fiber and the like constituting the light guide 200 will be described in detail.

Embodiment 1

Fig. 2 is a diagram schematically showing the structure of a displacement sensor 11 according to embodiment 1 of the present invention. In fig. 2, the displacement sensor 11 includes a light source 110, a beam splitter 120, and a sensor head 300, and transmits light through a light guide 201. The light guide 201 includes a 1 st optical fiber 211, a 2 nd optical fiber 221, a 3 rd optical fiber 231, and an optical coupler 241, each of which has the following core diameter and Numerical Aperture (NA).

Fiber 1 211: core diameter=50 μm, na=0.2

Fiber 2, 221: core diameter=50 μm, na=0.2 (optocoupler 241 side)

Fiber 2, 221: core diameter=100 μm, na=0.1 (sensor head 300 side)

Fiber 3, 231: core diameter=50 μm, na=0.2

Here, the 2 nd optical fiber 221 has a core diameter=50 μm on the optical coupler 241 side and a core diameter=100 μm on the sensor head 300 side, and a part of the optical coupler 241 and the sensor head 300 has a tapered portion in which the core diameter continuously changes.

Fig. 3A is a diagram showing a specific example of an optical fiber having a tapered portion, and fig. 3B is a diagram showing an internal structure of an optical fiber having a tapered portion. As shown in fig. 3A, the diameter of the optical fiber continuously gradually changes in the range of 1m among the 3m optical fibers, thereby forming a tapered portion.

In the specific example shown in fig. 3A, the tapered portion is formed at the end portion of the optical fiber, but the present invention is not limited thereto, and for example, the tapered portion may be formed at the center portion or the like, and both end portions may have a cylindrical shape of 50 μm and 100 μm, respectively.

The range of forming the tapered portion is not limited to about 1/3 or 1m of the length of the optical fiber, and may be appropriately set according to the core diameters of both ends.

As shown in fig. 2, the 2 nd optical fiber 221 has a core diameter=50 μm on the optical coupler 241 side and a core diameter=100 μm on the sensor head 300 side, and therefore na=0.2 on the optical coupler 241 side and na=0.1 on the sensor head 300 side (lagrangian invariant).

In the present embodiment, na=0.1 for the diffraction lens 310 housed in the sensor head 300 is set to be the same as NA of the 2 nd optical fiber 221 connected to the sensor head 300.

[ evaluation of Displacement sensor 11 ]

Fig. 4 is a diagram showing evaluation of the displacement sensor 11 shown in fig. 2. As shown in fig. 4, in the displacement sensor 11, the decrease in the movement resolution was suppressed and the light receiving amount (5.5 times) was greatly increased as compared with the comparative example (optical fibers having total core diameters=50 μm and na=0.2).

More specifically, the half width of the sensor head 300 is affected by the core diameter of the optical fiber on the sensor head 300 side and the NA of the diffraction lens 310, and the movement resolution is affected by the half width of the sensor head 300 and the spot diameter, and in the displacement sensor 11, the na=0.1 of the diffraction lens 310 is the same as that of the comparative example. The core diameter=100 μm of the optical fiber on the sensor head 300 side of the displacement sensor 11 was 2 times as large as that of the comparative example, and the spot diameter was also 2 times as large. In this way, the displacement sensor 11 can suppress a decrease in the movement resolution as compared with the comparative example.

Here, a description will be given of a light receiving waveform (light receiving amount distribution signal), a waveform of light converged by the sensor head 300 (sensor head waveform), and a half-value width of a device characteristic waveform (spectroscope waveform) caused by devices such as the spectroscope 120.

Fig. 5 is a diagram showing the relationship between the sensor head waveform and the beam splitter waveform and the light receiving waveform. In fig. 5, the vertical axis of each waveform represents the light amount, and the horizontal axis represents the wavelength. As shown in fig. 5, the light receiving waveform is obtained by a convolution operation of synthesizing the beam splitter waveform with the sensor head waveform, and the half-value width of the light receiving waveform is calculated substantially based on the half-value width of the sensor head waveform and the half-value width of the beam splitter waveform.

The half width is the length (width) of the intersection between the line of the light receiving amount 50% of the peak value (maximum value) of the light receiving amount and the light receiving amount distribution signal, and is an index indicating the degree of expansion of the gaussian distribution. Since the received light waveform exhibits a peak in the wavelength of light focused on the object to be measured TA, the position of the object to be measured TA can be appropriately measured by expressing the peak more clearly. That is, it can be said that if the half width is small, the measurement accuracy is high.

On the other hand, in the relationship between the half-value width of the sensor head waveform and the half-value width of the beam splitter waveform, the light receiving amount may be reduced.

Fig. 6 is a diagram showing the relationship between the half-value width of the sensor head waveform and the half-value width of the beam splitter waveform and the light receiving amount. As shown in fig. 6, as the half width of the sensor head waveform/the half width of the spectroscope waveform becomes smaller, the light receiving amount decreases. For example, as shown in fig. 5 (B), when the half-value width of the sensor head waveform is reduced, the half-value width of the light receiving waveform becomes small, and the half-value width of the sensor head waveform/the half-value width of the spectroscope waveform also becomes small. This significantly reduces the light receiving amount.

In fig. 4, a comparative example is shown in which optical fibers having total core diameters=50 μm and na=0.2 are used in evaluating the displacement sensor 11, but optical fibers having total core diameters=100 μm and na=0.1 are also conceivable. However, in this case, since both the half width of the sensor head waveform and the half width of the beam splitter waveform become large, the half width of the light receiving waveform is approximately 2 times as large as that of the comparative example shown in fig. 4. This deteriorates linearity and static resolution, and significantly reduces measurement accuracy.

As described above, according to the displacement sensor 11 of embodiment 1 of the present invention, since the light guide 201 includes the 2 nd optical fiber 221 having the tapered portion, the optical fiber connected to the sensor head 300 has a larger core diameter than the optical fiber connected to the optical splitter 120. This can suppress a decrease in the movement resolution and greatly increase the light receiving amount. As a result, the displacement sensor 11 can suppress a decrease in measurement accuracy and increase the measurement speed.

The optical fiber used in the present embodiment may be a single core having a single core or may be a multicore having a plurality of cores, but the above-described effects can be obtained even when a single core is applied, and therefore the cost burden due to the application of the multicore is reduced.

Hereinafter, embodiments 2 to 4 will be described, but in each embodiment, mainly the configuration different from embodiment 1 of the present invention will be described in detail, and description of the same matters as embodiment 1 will be omitted or simplified.

< embodiment 2 >

Fig. 7 is a diagram schematically showing the structure of a displacement sensor 12 according to embodiment 2 of the present invention. In fig. 7, the displacement sensor 12 is different from the displacement sensor 11 of embodiment 1 in NA of the diffraction lens 310 in the sensor head 300. In the present embodiment, na=0.05 of the diffraction lens 310.

Fig. 8 is a diagram showing the evaluation of the displacement sensor 12 shown in fig. 7. As shown in fig. 8, in the displacement sensor 12, the decrease in the light receiving amount was suppressed and the displacement resolution (2-fold) was greatly improved as compared with the comparative example (optical fibers having total core diameters=50 μm and na=0.2).

More specifically, in the displacement sensor 12, the NA of the diffraction lens 310 is 1/2 of the NA of the optical fiber on the sensor head 300 side, as in the comparative example. Therefore, the coupling efficiency (ratio) of the displacement sensor 12 is also the same as that of the sensor head of the comparative example, and the drop in the light receiving amount is suppressed. On the other hand, in the displacement sensor 12, the core diameter of the optical fiber on the sensor head 300 side is 100 μm, which is 2 times as large as that of the comparative example, and na=0.05 of the diffraction lens 310 is 1/2 as compared with the comparative example, so the half-value width of the sensor head 300 is the same as that of the comparative example. Since the core diameter of the optical fiber on the sensor head 300 side is 2 times and the spot diameter is 2 times as compared with the comparative example, the movement resolution is significantly improved by the averaging in the spot.

As described above, the displacement sensor 12 according to embodiment 2 of the present invention has the same configuration as the light guide 201 in the displacement sensor 11 according to embodiment 1, and the NA of the diffraction lens of the sensor head 300 is set smaller than the NA of the optical fiber on the sensor head 300 side. This can suppress a decrease in the amount of light received and can greatly improve the movement resolution. As a result, the displacement sensor 12 can suppress a decrease in the measurement speed and improve the measurement accuracy.

Embodiment 3

Fig. 9 is a diagram schematically showing the structure of a displacement sensor 13 according to embodiment 3 of the present invention. In fig. 9, the displacement sensor 13 includes a light source 110, a beam splitter 120, and a sensor head 300, and transmits light through a light guide 203. The light guide 203 includes a 1 st optical fiber 213, a 2 nd optical fiber 223, a 3 rd optical fiber 233, and an optical coupler 243, each of which has the following core diameter and Numerical Aperture (NA).

Fiber 1 213: core diameter=100 μm, na=0.1

Fiber 2, 223: core diameter=100 μm, na=0.1

3 rd optical fiber 233: core diameter=100 μm, na=0.1 (optocoupler 243 side)

3 rd optical fiber 233: core diameter=50 μm, na=0.2 (beam splitter 120 side)

As shown in fig. 9, the optical fiber having a tapered portion among the optical fibers included in the light guide portion 203 of the displacement sensor 13 is a 3 rd optical fiber 233, which is different from the displacement sensor 11 (the 2 nd optical fiber 221 has a tapered portion) of embodiment 1 shown in fig. 2.

More specifically, the 3 rd optical fiber 233 has a core diameter=100 μm on the side of the optical coupler 243 and a core diameter=50 μm on the side of the optical splitter 120, and a part of the optical coupler 243 and the optical splitter 120 has a tapered portion in which the core diameter continuously changes. The 3 rd optical fiber 233 has na=0.1 on the optical coupler 243 side and na=0.2 on the optical splitter 120 side (lagrangian invariant).

The 1 st optical fiber 213 has a core diameter 2 times as large as that of the 1 st optical fiber 211 in the displacement sensor 11 of embodiment 1 shown in fig. 2, and thus has a cross-sectional area 4 times, but NA is 1/2. Thus, the amount of light outputted from the light source 110 and transmitted through the 1 st optical fiber 213 is the same as that of the displacement sensor 11 of embodiment 1.

The optical coupler 243 is a coupler for coupling two optical fibers having a core diameter of 100 μm.

As described above, the 3 rd optical fiber 233 has a tapered portion, and thus the optical fiber connected to the sensor head 300 has a larger core diameter than the optical fiber connected to the optical splitter 120.

[ evaluation of Displacement sensor 13 ]

When na=0.1, the diffraction lens 310 housed in the sensor head 300 is set to be the same as NA of the 2 nd optical fiber 223 connected to the sensor head 300, as shown in fig. 4, the displacement sensor 13 has the same effect as the displacement sensor 11 of embodiment 1.

That is, the displacement sensor 13 can suppress a decrease in the movement resolution and greatly increase the light receiving amount (5.5 times). As a result, the displacement sensor 13 can suppress a decrease in measurement accuracy and increase the measurement speed.

In addition, regarding the diffraction lens 310 housed in the sensor head 300, when na=0.05, and NA of the diffraction lens 310 is set to 1/2 of NA of the optical fiber on the sensor head 300 side, as shown in fig. 8, the displacement sensor 13 exhibits the same effect as the displacement sensor 12 of embodiment 2.

That is, the displacement sensor 13 can suppress a decrease in the light receiving amount and greatly improve the movement resolution (by a factor of 2). As a result, the measurement accuracy can be improved while suppressing the decrease in the measurement speed.

Embodiment 4

Fig. 10 is a diagram schematically showing the structure of a displacement sensor 14 according to embodiment 4 of the present invention. In fig. 10, the displacement sensor 14 includes a light source 110, a beam splitter 120, and a sensor head 300, and transmits light through the light guide 204. The light guide section 204 includes a 1 st optical fiber 214, a 2 nd optical fiber 223, a 3 rd optical fiber 233, and an optical coupler 244, each of which has the following core diameter and Numerical Aperture (NA).

Fiber 1 214: core diameter=50 μm, na=0.2

Fiber 2, 223: core diameter=100 μm, na=0.1

3 rd optical fiber 233: core diameter=100 μm, na=0.1 (optocoupler 244 side)

3 rd optical fiber 233: core diameter=50 μm, na=0.2 (beam splitter 120 side)

As shown in fig. 10, the optical fiber having a tapered portion among the optical fibers included in the light guide portion 204 in the displacement sensor 14 is a 3 rd optical fiber 233, which is different from the displacement sensor 11 (the 2 nd optical fiber 221 has a tapered portion) of embodiment 1 shown in fig. 2. In this regard, the displacement sensor 14 of embodiment 4 is identical to the displacement sensor 13 of embodiment 3.

On the other hand, the 1 st optical fiber 214 is different from the 1 st optical fiber 213 of the displacement sensor 13 of embodiment 3 shown in fig. 9, and is the same as the 1 st optical fiber 211 of the displacement sensor 11 of embodiment 1 shown in fig. 2.

The optical coupler 244 is a coupler for coupling an optical fiber having a core diameter of 50 μm and an optical fiber having a core diameter of 100 μm.

As described above, the 3 rd optical fiber 233 has a tapered portion, and thus the optical fiber connected to the sensor head 300 has a larger core diameter than the optical fiber connected to the optical splitter 120, and in this regard, the same effects as those of the displacement sensor 13 of embodiment 3 are obtained as those of the displacement sensor 13.

Specifically, in the case where na=0.1, the displacement sensor 14 exhibits the same effect as the displacement sensor 11 of embodiment 1 as shown in fig. 4, and can significantly increase the light receiving amount (5.5 times) while suppressing the decrease in the movement resolution with respect to the diffraction lens 310 housed in the sensor head 300. As a result, the displacement sensor 14 can suppress a decrease in measurement accuracy and increase the measurement speed.

In addition, in the case where na=0.05, the diffraction lens 310 housed in the sensor head 300 has the same effect as the displacement sensor 12 of embodiment 2 as shown in fig. 8, and can significantly improve the movement resolution (2 times) while suppressing the decrease in the light receiving amount. As a result, the displacement sensor 14 can suppress a decrease in the measurement speed and improve the measurement accuracy.

Furthermore, in embodiments 1 to 4 of the present invention, the taper portion is provided in any of the optical fibers included in the light guide portion, so that the optical fiber connected to the sensor head 300 has a larger core diameter than the optical fiber connected to the optical splitter 120, but the present invention can be realized by an optical coupler. For example, the following structure may be adopted: the core diameter of the 2 nd optical fiber connecting the optical coupler and the sensor head 300 was set to 100 μm, the core diameter of the 2 nd optical fiber connecting the optical coupler and the spectroscope 120 was set to 50 μm, and the difference in core diameter was absorbed by the optical coupler.

The embodiments described above are for easy understanding of the present invention, and are not intended to limit the explanation of the present invention. The elements and their arrangement, materials, conditions, shapes, sizes, and the like in each embodiment are not limited to those exemplified, and can be changed as appropriate. In addition, the structures shown in the different embodiments can be partially replaced or combined with each other.

[ additionally remembered ]

A displacement sensor (10, 11, 12, 13, 14) is provided with: a light source (110) that outputs white light; a light guide (200, 201, 202, 203, 204) comprising at least one optical fiber; a sensor head (300) which houses a diffraction lens (310) for generating chromatic aberration in the optical axis direction of the white light incident via the light guide unit, and irradiates the object (TA) with light generated chromatic aberration; and a spectroscope (120) that obtains reflected light reflected by the object to be measured and collected by the sensor head via the light guide section, and measures a spectrum of the reflected light, wherein optical fibers (220, 221, 223) connected to the sensor head have a larger core diameter than optical fibers (230, 231, 233) connected to the spectroscope.

Description of the reference numerals

10. 11, 12, 13, 14: a displacement sensor; 110: a light source; 120: a beam splitter; 200. 201, 202, 203, 204: a light guide section; 210. 211, 213, 214: 1 st optical fiber; 220. 221, 223: a 2 nd optical fiber; 230. 231, 233: a 3 rd optical fiber; 240. 241, 243, 244: an optical coupler; 300: a sensor head; 310: a diffraction lens; 410: light of wavelength 1; 420: light of wavelength 2; 430: light of wavelength 3; TA: and measuring the object.

Claims (8)

1. A displacement sensor is provided with:

a light source that outputs white light;

a light guide section including at least one optical fiber;

a sensor head that houses a diffraction lens that causes chromatic aberration in an optical axis direction of the white light incident through the light guide unit, and irradiates the object to be measured with light that causes chromatic aberration; and

a beam splitter for acquiring reflected light reflected by the object to be measured and collected by the sensor head via the light guide unit, measuring a spectrum of the reflected light,

the optical fiber connected to the sensor head has a larger core diameter than the optical fiber connected to the beam splitter.

2. The displacement sensor according to claim 1, wherein,

the optical fiber disposed between the sensor head and the spectroscope includes a tapered portion having a continuously changing core diameter.

3. The displacement sensor according to claim 1 or 2, wherein,

the light guide section includes:

a 1 st optical fiber connected to the light source;

a 2 nd optical fiber connected to the sensor head;

a 3 rd optical fiber connected to the optical splitter; and

and the optical coupler is connected with the 1 st optical fiber, the 2 nd optical fiber and the 3 rd optical fiber.

4. A displacement sensor according to claim 3, wherein,

the 2 nd optical fiber includes a tapered portion having a continuously changing core diameter.

5. A displacement sensor according to claim 3, wherein,

the 3 rd optical fiber includes a tapered portion having a continuously changing core diameter.

6. A displacement sensor according to claim 3, wherein,

the 2 nd optical fiber has a larger core diameter than the 3 rd optical fiber.

7. The displacement sensor according to any one of claims 1 to 6, wherein,

the optical fiber connected to the sensor head has the same numerical aperture as the diffraction lens.

8. The displacement sensor according to any one of claims 1 to 6, wherein,

an optical fiber connected to the sensor head has a numerical aperture larger than the diffraction lens.