Displacement Sensor

Abstract

A displacement sensor is provided, which can suppress the decrease in motion resolution and light receiving amount and achieve appropriate measurement accuracy and measurement speed. The displacement sensor (11) includes: a light source (110) that outputs white light; a light guide (201) that includes at least one optical fiber; a sensor head (300) that houses a diffraction lens (310) that causes the white light incident through the light guide (201) to generate chromatic aberration along the optical axis direction, and irradiates the chromatic aberration light onto a measurement object (TA); and a spectrometer (120) that obtains reflected light reflected by the measurement object (TA) and converged by the sensor head (300) through the light guide (201), and measures the spectrum of the reflected light. The optical fiber connected to the sensor head (300) has a larger core diameter than the optical fiber connected to the spectrometer (120).

Description

Technical Field

[0001] The present invention relates to a displacement sensor. Background Art

[0002] Conventionally, a confocal measuring device using a confocal optical system has been used as a device for measuring the displacement of a measurement object in a non-contact manner.

[0003] For example, the confocal measurement device described in Patent Document 1 below includes a confocal optical system using a diffraction lens between a light source and a measurement object. In this confocal measurement device, light emitted from the light source passes through the confocal optical system and strikes the measurement object at a focal length corresponding to its wavelength. By detecting the peak wavelength of the reflected light, the displacement of the measurement object can be measured.

[0004] Furthermore, Patent Document 2 below discloses a technology related to a confocal measurement device that improves the accuracy of detecting the position of a measurement object. In this confocal measurement device, the core diameters of the second optical fiber connected to the spectrometer and the third optical fiber connected to the sensor head are 5 μm to 25 μm. Furthermore, the document describes that the core diameters of the second and third optical fibers may be different.

[0005] Furthermore, as mentioned above, measurement accuracy indicators for confocal measurement devices include linearity, static resolution, and dynamic resolution. When performing displacement measurement, these are summed to form the final measurement error. In point-based displacement sensors, dynamic resolution generally contributes the most to these measurement accuracy indicators, making its improvement a key challenge.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: U.S. Patent No. 5,785,651

[0009] Patent Document 2: Japanese Patent Application Publication No. 2019-66343 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] However, in confocal measurement devices, in order to improve the motion resolution, it is conceivable to reduce the core diameter of the optical fiber. However, if the core diameter is reduced, the amount of received light decreases, resulting in a problem of a decrease in measurement speed.

[0012] Therefore, an object of the present invention is to provide a displacement sensor that can suppress a decrease in motion resolution and light reception amount and achieve appropriate measurement accuracy and measurement speed.

[0013] Means for solving problems

[0014] A displacement sensor according to one embodiment of the present invention comprises: a light source that outputs white light; a light guide portion that includes at least one optical fiber; a sensor head that houses a diffraction lens that causes chromatic aberration of the white light incident through the light guide portion along the optical axis, and irradiates the chromatically aberrated light onto a measurement object; and a spectrometer that obtains reflected light from the measurement object through the light guide portion and converges by the sensor head, and measures the 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 spectrometer.

[0015] According to this aspect, the displacement sensor of one embodiment 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 spectrometer. This can suppress a decrease in motion resolution and light reception amount while achieving appropriate measurement accuracy and speed.

[0016] In the above aspect, the optical fiber disposed between the sensor head and the spectrometer may include a tapered portion in which the core diameter continuously changes.

[0017] According to this aspect, since the optical fiber disposed between the sensor head and the spectrometer 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 spectrometer.

[0018] In the above embodiment, the light guiding portion may include: a first optical fiber connected to the light source; a second optical fiber connected to the sensor head; a third optical fiber connected to the spectrometer; and an optical coupler to which the first optical fiber, the second optical fiber, and the third optical fiber are connected.

[0019] According to this aspect, the light guide includes the first optical fiber, the second optical fiber, the third optical fiber, and the optical coupler. Therefore, the optical fiber connected to the sensor head can have a larger core diameter than the optical fiber connected to the spectrometer.

[0020] In the above aspect, the second optical fiber may include a tapered portion in which the core diameter continuously changes.

[0021] According to this aspect, since the second 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 spectrometer.

[0022] In the above aspect, the third optical fiber may include a tapered portion in which the core diameter continuously changes.

[0023] According to this aspect, since the third 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 spectrometer.

[0024] In the above aspect, the second optical fiber may have a larger core diameter than the third optical fiber.

[0025] According to this aspect, the second optical fiber and the third optical fiber can be used so that the optical fiber connected to the sensor head has a larger core diameter than the optical fiber connected to the spectrometer.

[0026] In the above aspect, the optical fiber connected to the sensor head may have the same numerical aperture as that of the diffraction lens.

[0027] According to this embodiment, the optical fiber connected to the sensor head has the same numerical aperture as the diffraction lens, thereby suppressing a decrease in motion resolution and increasing the amount of light received. As a result, the displacement sensor according to one embodiment of the present invention can suppress a decrease in measurement accuracy and increase measurement speed.

[0028] In the above aspect, the optical fiber connected to the sensor head may have a numerical aperture larger than that of the diffraction lens.

[0029] According to this embodiment, the optical fiber connected to the sensor head has a larger numerical aperture than the diffraction lens, thereby suppressing a decrease in the amount of light received and improving motion resolution. As a result, the displacement sensor according to one embodiment of the present invention can suppress a decrease in measurement speed and improve measurement accuracy.

[0030] Effects of the Invention

[0031] According to the present invention, it is possible to provide a displacement sensor that can suppress a decrease in motion resolution and light reception amount and achieve appropriate measurement accuracy and measurement speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 1 is a structural diagram showing an example of a schematic structure of the displacement sensor 10 according to each embodiment of the present invention.

[0033] Figure 2 It is a diagram schematically showing the structure of a displacement sensor 11 according to the first embodiment of the present invention.

[0034] Figure 3A This is a diagram showing a specific example of an optical fiber having a tapered portion.

[0035] Figure 3B It is a diagram showing the internal structure of an optical fiber having a tapered portion.

[0036] Figure 4 Yes Figure 2 Graph showing the evaluation of the displacement sensor 11.

[0037] Figure 5 This diagram shows the relationship between the sensor head waveform, spectrometer waveform, and received light waveform.

[0038] Figure 6This diagram shows the relationship between the half-value width of the sensor head waveform, the half-value width of the spectrometer waveform, and the amount of received light.

[0039] Figure 7 It is a diagram schematically showing the structure of a displacement sensor 12 according to a second embodiment of the present invention.

[0040] Figure 8 Yes Figure 7 Graph showing the evaluation of the displacement sensor 12.

[0041] Figure 9 It is a diagram schematically showing the structure of a displacement sensor 13 according to a third embodiment of the present invention.

[0042] Figure 10 It is a diagram schematically showing the structure of a displacement sensor 14 according to a fourth embodiment of the present invention. DETAILED DESCRIPTION

[0043] The preferred embodiments of the present invention are described below in detail with reference to the accompanying drawings. The embodiments described below are merely examples for implementing the present invention and are not intended to limit the present invention. To facilitate understanding, identical components are denoted by the same reference numerals throughout the drawings, and duplicate descriptions may be omitted.

[0044] First, the basic structure of the displacement sensor according to each embodiment of the present invention will be described.

[0045] [Basic structure of displacement sensor]

[0046] Figure 1 1 is a structural diagram showing an example of a schematic structure of a displacement sensor 10 according to each embodiment of the present invention. Figure 1 As shown, the displacement sensor 10 includes a controller 100 , a light guide unit 200 , and a sensor head 300 , and measures the distance to a measurement target object TA using a confocal optical system.

[0047] The controller 100 includes a light source 110 , a spectrometer 120 , and a processing unit 130 . The spectrometer 120 includes a collimating lens 121 , a diffraction grating 122 , an adjustment lens 123 , and a light receiving element 124 .

[0048] The light guide unit 200 is disposed between the controller 100 and the sensor head 300 and includes, for example, a first optical fiber 210 , a second optical fiber 220 , a third optical fiber 230 , and an optical coupler 240 , and propagates light.

[0049] 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 .

[0050] The light source 110 outputs, for example, white light to the first optical fiber 210. The light source 110 may also adjust the amount of white light based on a command from the processing unit 130. Furthermore, the light emitted by the light source 110 is not limited to white light, as long as it includes multiple wavelength components and falls within a wavelength range that covers the measurement distance range required by the displacement sensor 10.

[0051] One end of the first optical fiber 210 is optically connected to the light source 110, one end of the second optical fiber 220 is optically connected to the sensor head 300, and one end of the third optical fiber 230 is optically connected to the spectrometer 120. Furthermore, the other ends of the first optical fiber 210 and the third optical fiber 230 are optically coupled to the other end of the second optical fiber 220 via an optical coupler 240.

[0052] The optical coupler 240 transmits light (irradiated light) incident from the first optical fiber 210 to the second optical fiber 220, and splits the light (reflected light) incident from the second optical fiber 220 and transmits the split light to the first optical fiber 210 and the third optical fiber 230, respectively. The light transmitted from the second optical fiber 220 to the first optical fiber 210 via the optical coupler 240 ends at the light source 110.

[0053] The white light output from the light source 110 is incident on the sensor head 300 via the first optical fiber 210, the optical coupler 240, and the second optical fiber 220. The sensor head 300 houses a diffraction lens 310 that chromatically aberrates the white light emitted from the end face of the second optical fiber 220 along the optical axis, and an objective lens 320 that focuses the chromatically aberrated light on the measurement object TA, thereby irradiating the measurement object TA with the chromatically aberrated light.

[0054] exist Figure 1 In the example shown, the focal lengths of the light beams are arranged in ascending order from the shortest to the longest: light beam 410 of the first wavelength, light beam 420 of the second wavelength, and light beam 430 of the third wavelength. Light beam 420 of the second wavelength is focused on the surface of the object TA (second focal position), while light beam 410 of the first wavelength is focused on the front side of the object TA (first focal position), and light beam 430 of the third wavelength is focused on the back side of the object TA (third focal position).

[0055] Light reflected from the surface of the measurement object TA is collected by the objective lens 320, converged by the diffraction lens 310, and then sent back to the core of the second optical fiber 220. Light 420 of the second wavelength in the reflected light is focused on the end face of the second optical fiber 220, and therefore, most of it enters the second optical fiber 220. However, light of other wavelengths is not focused on the end face of the second optical fiber 220, and therefore, most of it does not enter the second optical fiber 220. The reflected light entering the second optical fiber 220 is transmitted to the third optical fiber 230 via the optical coupler 240 and input into the spectrometer 120. Furthermore, the reflected light entering the second optical fiber 220 is also transmitted to the first optical fiber 210 via the optical coupler 240, but terminates at the light source 110.

[0056] The spectrometer 120 receives reflected light from the measurement object TA and converged by the sensor head 300 via the second optical fiber 220, the optical coupler 240, and the third optical fiber 230, and measures the spectrum of the reflected light. The spectrometer 120 includes a collimator lens 121 that converges the reflected light emitted from the third optical fiber 230, a diffraction grating 122 that separates the reflected light, an adjustment lens 123 that converges the separated reflected light, and a light receiving element 124 that receives the separated reflected light.

[0057] The processing unit 130 detects the position of the object to be measured TA based on a light reception amount distribution signal indicating the wavelength and amount of light received by the light receiving element 124. Specifically, the position of the object to be measured TA can be measured by detecting a wavelength peak in the received light waveform using the spectrometer 120. In this example, the second wavelength light 420 focused by the optical fiber, among the light reflected by the object to be measured TA, appears as a peak at the spectrometer 120, enabling the position of the object to be measured TA to be detected.

[0058] [Motion resolution and light intensity]

[0059] Here, the following describes the motion resolution, which significantly influences measurement errors, in relation to the measurement accuracy of the displacement sensor 10. Since motion resolution is affected by the depth of field and the averaging effect, it is believed that reducing the core diameter of the optical fiber and the numerical aperture (hereinafter sometimes referred to as "NA") of the diffraction lens 310 improves it.

[0060] On the other hand, the amount of received light, which affects the measurement speed of the displacement sensor 10, is affected by the coupling efficiency of the sensor head 300. Therefore, it is believed that increasing the numerical aperture (NA) of the diffraction lens 310 can improve this, contradicting the aforementioned measure for improving motion resolution. Furthermore, when calculating the received light waveform (received light intensity distribution signal) through a convolution operation combining the waveform of the light focused by the sensor head 300 (hereinafter sometimes referred to as the "sensor head waveform") with the device characteristic waveform generated by a device such as the spectrometer 120 (hereinafter sometimes referred to as the "speculator waveform"), the received light intensity may also decrease.

[0061] Here, the inventors of the present invention have found that the second optical fiber 220 connected to the sensor head 300 has a larger core diameter than the third optical fiber 230 connected to the spectrometer 120 .

[0062] Hereinafter, specific embodiments of the optical fiber and the like constituting the light guide unit 200 will be described in detail.

[0063] <First embodiment>

[0064] Figure 2 1 is a diagram schematically showing the structure of a displacement sensor 11 according to a first embodiment of the present invention. Figure 2 In the figure, the displacement sensor 11 includes a light source 110, a spectrometer 120, and a sensor head 300, each of which transmits light through a light guide 201. The light guide 201 includes a first optical fiber 211, a second optical fiber 221, a third optical fiber 231, and an optical coupler 241. Each optical fiber has the following core diameter and numerical aperture (NA).

[0065] First optical fiber 211: core diameter = 50 μm, NA = 0.2

[0066] Second optical fiber 221: core diameter = 50 μm, NA = 0.2 (optical coupler 241 side)

[0067] Second optical fiber 221: core diameter = 100 μm, NA = 0.1 (sensor head 300 side)

[0068] Third optical fiber 231: core diameter = 50 μm, NA = 0.2

[0069] Here, the second optical fiber 221 has a core diameter of 50 μm on the optical coupler 241 side and a core diameter of 100 μm on the sensor head 300 side. A portion between the optical coupler 241 and the sensor head 300 includes a tapered portion in which the core diameter continuously changes.

[0070] Figure 3A is a diagram showing a specific example of an optical fiber having a tapered portion, Figure 3B : is a diagram showing the internal structure of an optical fiber having a tapered portion. Figure 3A As shown, in a 3 m optical fiber, the diameter of the optical fiber changes continuously and gradually within a range of 1 m, thereby forming a tapered portion.

[0071] In addition, Figure 3A In the specific example shown, a tapered portion is formed at the end of the optical fiber, but the present invention is not limited thereto. For example, a tapered portion may be formed in the center, and the two end portions may be cylindrical with diameters of 50 μm and 100 μm, respectively.

[0072] Furthermore, the range where the tapered portion is formed is not limited to approximately 1 / 3 of the length of the optical fiber or 1 m, and may be appropriately set depending on the core diameters at both ends and the like.

[0073] In addition, if Figure 2 As shown, the core diameter of the second optical fiber 221 is 50 μm on the optical coupler 241 side and 100 μm on the sensor head 300 side. Therefore, NA is 0.2 on the optical coupler 241 side and 0.1 on the sensor head 300 side (Lagrange invariant).

[0074] Furthermore, in the present embodiment, the diffraction lens 310 housed in the sensor head 300 has NA=0.1, which is set to be the same as the NA of the second optical fiber 221 connected to the sensor head 300 .

[0075] [Evaluation of Displacement Sensor 11]

[0076] Figure 4 Yes Figure 2 The evaluation diagram of the displacement sensor 11 is shown. Figure 4 As shown, in the displacement sensor 11, compared with the comparative example (optical fiber with all core diameters = 50 μm and NA = 0.2), the decrease in motion resolution is suppressed and the amount of received light is greatly increased (5.5 times).

[0077] More specifically, the half-value 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. The motion resolution is also affected by the half-value width of the sensor head 300 and the spot diameter. In the displacement sensor 11, the NA of the diffraction lens 310 is the same as in the comparative example, at 0.1. Furthermore, the core diameter of the optical fiber on the sensor head 300 side of the displacement sensor 11 is 100 μm, double that of the comparative example, and the spot diameter is also doubled accordingly. Consequently, the displacement sensor 11 can minimize the decrease in motion resolution compared to the comparative example.

[0078] Here, the half-value width of the received light waveform (received light amount distribution signal), the waveform of light focused by the sensor head 300 (sensor head waveform), and the device characteristic waveform (spectrometer waveform) caused by devices such as the spectrometer 120 will be described.

[0079] Figure 5 This figure shows the relationship between the sensor head waveform, spectrometer waveform, and received light waveform. Figure 5 In each waveform, the vertical axis represents the light intensity, and the horizontal axis represents the wavelength. Figure 5 As shown, the received light waveform is obtained by convolution operation of the sensor head waveform and the spectrometer waveform. The half-value width of the received light waveform is roughly calculated based on the half-value width of the sensor head waveform and the half-value width of the spectrometer waveform.

[0080] The half-value width (FWHM) is the length (width) of the two intersections of the line representing 50% of the peak (maximum) value of the received light intensity and the light intensity distribution signal. It is an indicator of the spread of the Gaussian distribution. The received light waveform represents the wavelength of light focused on the measurement object TA as a peak. Therefore, by more clearly representing this peak, the position of the measurement object TA can be accurately measured. In other words, a smaller FWHM indicates higher measurement accuracy.

[0081] On the other hand, in the relationship between the half-value width of the sensor head waveform and the half-value width of the spectrometer waveform, the amount of received light may decrease.

[0082] Figure 6 This is a graph showing the relationship between the half-value width of the sensor head waveform and the half-value width of the spectrometer waveform and the amount of received light. Figure 6 As shown in , as the half-value width of the sensor head waveform / half-value width of the spectrometer waveform decreases, the amount of received light decreases. Figure 5 As shown in (B), when the half-value width of the sensor head waveform is reduced, the half-value width of the received light waveform is reduced, and the half-value width of the sensor head waveform / half-value width of the spectrometer waveform is also reduced. As a result, the amount of received light is significantly reduced.

[0083] In addition, Figure 4 , a comparative example is shown in which an optical fiber with a core diameter of 50 μm and NA of 0.2 is used to evaluate the displacement sensor 11. However, it is also possible to use an optical fiber with a core diameter of 100 μm and NA of 0.1. However, in this case, both the half-value width of the sensor head waveform and the half-value width of the spectrometer waveform become larger, so the half-value width of the received light waveform is different from the half-value width of the optical fiber. Figure 4 As compared to the comparative example shown, the linearity and static resolution are deteriorated, and the measurement accuracy is significantly reduced.

[0084] As described above, according to the displacement sensor 11 of the first embodiment of the present invention, the light guide 201 includes the second optical fiber 221 having a tapered portion. Therefore, the optical fiber connected to the sensor head 300 has a larger core diameter than the optical fiber connected to the spectrometer 120. This significantly increases the amount of light received while suppressing a decrease in motion resolution. Consequently, the displacement sensor 11 can improve measurement speed while suppressing a decrease in measurement accuracy.

[0085] In addition, the optical fiber used in this embodiment can be either a single-core having a single fiber core or a multi-core having multiple fiber cores, but the above-mentioned effect can be obtained even when a single-core is used, thereby reducing the cost burden caused by the use of multi-cores.

[0086] Hereinafter, second to fourth embodiments will be described. In each embodiment, the configuration different from the first embodiment of the present invention will be mainly described in detail, and descriptions of matters common to the first embodiment will be omitted or simplified.

[0087] <Second embodiment>

[0088] Figure 7 : is a diagram schematically showing the structure of a displacement sensor 12 according to a second embodiment of the present invention. Figure 7 In the displacement sensor 12, the NA of the diffraction lens 310 in the sensor head 300 is different from that of the displacement sensor 11 in the first embodiment. In this embodiment, the NA of the diffraction lens 310 is 0.05.

[0089] Figure 8 Yes Figure 7 The evaluation diagram of the displacement sensor 12 is shown. Figure 8 As shown, in the displacement sensor 12 , compared with the comparative example (optical fiber with all core diameters = 50 μm and NA = 0.2), a decrease in the amount of received light is suppressed and the motion resolution is significantly improved (twice).

[0090] More specifically, in the displacement sensor 12, the NA of the diffraction lens 310 is half the NA of the optical fiber on the sensor head 300 side, the same as in the comparative example. Therefore, the coupling efficiency (ratio) between the displacement sensor 12 and the sensor head of the comparative example is also the same, suppressing a decrease in the amount of received light. Meanwhile, in the displacement sensor 12, the core diameter of the optical fiber on the sensor head 300 side is 100 μm, double that of the comparative example, and the NA of the diffraction lens 310 is 0.05, half that of the comparative example. Therefore, the half-value width of the sensor head 300 is the same as in the comparative example. Furthermore, since the core diameter of the optical fiber on the sensor head 300 side is doubled, the spot diameter is doubled compared to the comparative example. Therefore, the motion resolution is significantly improved through averaging within the spot.

[0091] As described above, the displacement sensor 12 according to the second embodiment of the present invention has the same structure as the light guide 201 in the displacement sensor 11 according to the first embodiment, but the NA of the diffraction lens of the sensor head 300 is set to be smaller than the NA of the optical fiber on the sensor head 300 side. This significantly improves motion resolution while suppressing a decrease in the amount of received light. As a result, the displacement sensor 12 can suppress a decrease in measurement speed while improving measurement accuracy.

[0092] <Third embodiment>

[0093] Figure 9 : is a diagram schematically showing the structure of a displacement sensor 13 according to a third embodiment of the present invention. Figure 9 In FIG, the displacement sensor 13 includes a light source 110, a spectrometer 120, and a sensor head 300, each of which transmits light through a light guide 203. The light guide 203 includes a first optical fiber 213, a second optical fiber 223, a third optical fiber 233, and an optical coupler 243. Each optical fiber has the following core diameter and numerical aperture (NA).

[0094] First optical fiber 213: core diameter = 100 μm, NA = 0.1

[0095] Second optical fiber 223: core diameter = 100 μm, NA = 0.1

[0096] Third optical fiber 233: core diameter = 100 μm, NA = 0.1 (optical coupler 243 side)

[0097] Third optical fiber 233: core diameter = 50 μm, NA = 0.2 (beam splitter 120 side)

[0098] like Figure 9 As shown in FIG. 1 , the optical fiber having a tapered portion among the optical fibers included in the light guide portion 203 of the displacement sensor 13 is the third optical fiber 233. Figure 2 The displacement sensor 11 of the first embodiment shown is different (the second optical fiber 221 includes a tapered portion).

[0099] More specifically, the third optical fiber 233 has a core diameter of 100 μm on the optical coupler 243 side and a core diameter of 50 μm on the optical splitter 120 side. A portion between the optical coupler 243 and the optical splitter 120 includes a tapered portion with a continuously changing core diameter. Furthermore, the third optical fiber 233 has an NA of 0.1 on the optical coupler 243 side and an NA of 0.2 on the optical splitter 120 side (Lagrange invariant).

[0100] In addition, the first optical fiber 213 and Figure 2Compared to the displacement sensor 11 of the first embodiment shown, the first optical fiber 211 has a doubled core diameter, resulting in a quadrupled cross-sectional area, but a NA of 1 / 2. Consequently, the amount of light output from the light source 110 and propagating through the first optical fiber 213 is the same as that of the displacement sensor 11 of the first embodiment.

[0101] The optical coupler 243 couples two optical fibers having a core diameter of 100 μm.

[0102] As described above, the third optical fiber 233 includes the tapered portion, and thereby the optical fiber connected to the sensor head 300 has a larger core diameter than the optical fiber connected to the spectrometer 120 .

[0103] [Evaluation of Displacement Sensor 13]

[0104] Regarding the diffraction lens 310 housed in the sensor head 300, when NA=0.1 is set to be the same as the NA of the second optical fiber 223 connected to the sensor head 300, as shown in FIG. Figure 4 As shown, the displacement sensor 13 achieves the same effects as the displacement sensor 11 of the first embodiment.

[0105] That is, the displacement sensor 13 can significantly increase the amount of light received (5.5 times) while suppressing a decrease in motion resolution. As a result, the displacement sensor 13 can improve the measurement speed while suppressing a decrease in measurement accuracy.

[0106] In addition, regarding the diffraction lens 310 housed in the sensor head 300, when NA=0.05, the NA of the diffraction lens 310 is set to 1 / 2 of the NA of the optical fiber on the sensor head 300 side. Figure 8 As shown, the displacement sensor 13 exhibits the same effects as the displacement sensor 12 of the second embodiment.

[0107] That is, the displacement sensor 13 can significantly improve the motion resolution (by a factor of 2) while suppressing a decrease in the amount of light received. As a result, it can improve the measurement accuracy while suppressing a decrease in the measurement speed.

[0108] <Fourth embodiment>

[0109] Figure 10 : is a diagram schematically showing the structure of a displacement sensor 14 according to a fourth embodiment of the present invention. Figure 10 In FIG, the displacement sensor 14 includes a light source 110, a spectrometer 120, and a sensor head 300, each of which transmits light through a light guide 204. The light guide 204 includes a first optical fiber 214, a second optical fiber 223, a third optical fiber 233, and an optical coupler 244. Each optical fiber has the following core diameter and numerical aperture (NA).

[0110] First optical fiber 214: core diameter = 50 μm, NA = 0.2

[0111] Second optical fiber 223: core diameter = 100 μm, NA = 0.1

[0112] Third optical fiber 233: core diameter = 100 μm, NA = 0.1 (optical coupler 244 side)

[0113] Third optical fiber 233: core diameter = 50 μm, NA = 0.2 (beam splitter 120 side)

[0114] like Figure 10 As shown, in the displacement sensor 14, the optical fiber having the tapered portion among the optical fibers included in the light guide portion 204 is the third optical fiber 233. Figure 2 The displacement sensor 11 of the first embodiment shown is different (the second optical fiber 221 has a tapered portion). In this respect, the displacement sensor 14 of the fourth embodiment is the same as the displacement sensor 13 of the third embodiment.

[0115] On the other hand, the first optical fiber 214 and Figure 9 The first optical fiber 213 of the displacement sensor 13 of the third embodiment shown is different from Figure 2 The first optical fiber 211 in the displacement sensor 11 of the first embodiment shown is the same.

[0116] The optical coupler 244 couples an optical fiber having a core diameter of 50 μm and an optical fiber having a core diameter of 100 μm.

[0117] As described above, the third optical fiber 233 has a tapered portion, so that the optical fiber connected to the sensor head 300 has a larger core diameter than the optical fiber connected to the spectrometer 120 . In this respect, the third optical fiber 233 is similar to the displacement sensor 13 of the third embodiment and has the same effect as the displacement sensor 13 .

[0118] Specifically, regarding the diffraction lens 310 housed in the sensor head 300, when NA=0.1, the displacement sensor 14 is as follows: Figure 4 As shown, the displacement sensor 14 can achieve the same effect as the displacement sensor 11 of the first embodiment, suppressing a decrease in motion resolution and significantly increasing the amount of received light (5.5 times). As a result, the displacement sensor 14 can suppress a decrease in measurement accuracy and increase measurement speed.

[0119] In addition, regarding the diffraction lens 310 housed in the sensor head 300, when NA=0.05, the displacement sensor 14 is as follows: Figure 8As shown, the displacement sensor 14 can achieve the same effects as the displacement sensor 12 of the second embodiment, suppressing a decrease in the amount of received light and significantly improving the motion resolution (by a factor of 2). As a result, the displacement sensor 14 can suppress a decrease in measurement speed and improve measurement accuracy.

[0120] Furthermore, in the first to fourth embodiments of the present invention, a tapered portion is provided in any of the optical fibers included in the light guide, thereby ensuring that the optical fiber connected to the sensor head 300 has a larger core diameter than the optical fiber connected to the spectrometer 120. However, this alternative approach can also be achieved using an optical coupler. For example, a configuration can be employed in which the core diameter of the second optical fiber connecting the optical coupler to the sensor head 300 is set to 100 μm, while the core diameter of the second optical fiber connecting the optical coupler to the spectrometer 120 is set to 50 μm, with the optical coupler absorbing the core diameter difference.

[0121] The embodiments described above are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The various elements and their configurations, materials, conditions, shapes, and dimensions of the various embodiments are not limited to those illustrated and may be appropriately modified. In addition, the structures shown in the different embodiments may be partially replaced or combined with each other.

[0122] [Note]

[0123] A displacement sensor (10, 11, 12, 13, 14) comprises: a light source (110) that outputs white light; a light guide (200, 201, 202, 203, 204) that includes at least one optical fiber; a sensor head (300) that houses a diffraction lens (310) that causes the white light incident through the light guide to generate chromatic aberration along an optical axis direction, and irradiates the chromatically aberrated light onto a measurement object (TA); and a spectrometer (120) that obtains reflected light reflected by the measurement object and converged by the sensor head through the light guide, and measures the spectrum of the reflected light. The optical fiber (220, 221, 223) connected to the sensor head has a larger core diameter than the optical fiber (230, 231, 233) connected to the spectrometer.

[0124] Label Description

[0125] 10, 11, 12, 13, 14: displacement sensor; 110: light source; 120: spectrometer; 200, 201, 202, 203, 204: light guide; 210, 211, 213, 214: first optical fiber; 220, 221, 223: second optical fiber; 230, 231, 233: third optical fiber; 240, 241, 243, 244: optical coupler; 300: sensor head; 310: diffraction lens; 410: light of the first wavelength; 420: light of the second wavelength; 430: light of the third wavelength; TA: measured object.

Claims

1. A displacement sensor comprising: a light source that outputs white light; a light guide portion comprising at least one optical fiber; a sensor head housing a diffraction lens for causing chromatic aberration of the white light incident through the light guide portion along an optical axis direction, and irradiating the chromatically aberrated light onto a measurement object; and a spectrometer that receives reflected light reflected by the measurement object and converged by the sensor head via the light guide portion and measures 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 spectrometer includes a tapered portion whose core diameter continuously changes.

3. The displacement sensor according to claim 1 or 2, wherein: The light guide portion includes: a first optical fiber connected to the light source; a second optical fiber connected to the sensor head; a third optical fiber connected to the optical splitter; and An optical coupler to which the first optical fiber, the second optical fiber, and the third optical fiber are connected.

4. The displacement sensor according to claim 3, wherein: The second optical fiber includes a tapered portion whose core diameter continuously changes.

5. The displacement sensor according to claim 3, wherein: The third optical fiber includes a tapered portion whose core diameter continuously changes.

6. The displacement sensor according to claim 3, wherein: The second optical fiber has a larger core diameter than the third optical fiber.

7. The displacement sensor according to claim 1, wherein: The optical fiber connected to the sensor head has the same numerical aperture as that of the diffraction lens.

8. The displacement sensor according to claim 1, wherein: The optical fiber connected to the sensor head has a numerical aperture larger than that of the diffraction lens.

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