Optical fiber-based force and distance measurement sensor and manufacturing method thereof

Abstract

The present invention relates to an optical fiber-based force and distance measurement sensor and a manufacturing method thereof. According to the present invention, an optical fiber-based force and distance measurement sensor comprises: an optical fiber or an optical waveguide; an optical material positioned in front of the optical fiber or the optical waveguide and separated from the optical fiber or the optical waveguide by a cavity of a predetermined size; and a capillary surrounding the optical fiber or the optical waveguide and the optical material, and may further comprise a coupling module for coupling to an object such as a needle. According to the present invention, the one sensor is used to simultaneously or separately measure force and distance, thus making it possible to minimize size, and can be coupled to a device such as a fine needle. Accordingly, the present invention can assist in miniaturizing and modularizing the structure of an intelligent micro-surgical tool. Here, the one sensor includes one or more light sources and one or more detectors, and the slope, thickness, and the like of a reflective surface in the sensor can be easily adjusted as selected by a user.

Description

Optical fiber-based force and distance measurement sensor and manufacturing method thereof

[0001] The present invention relates to an optical fiber-based force and distance measuring sensor and a method for manufacturing the same, and more specifically, to an optical fiber-based force and distance measuring sensor that simultaneously or individually measures an applied force and a distance to an object located in front using reflected light from an optical fiber or an optical waveguide, and a method for manufacturing the same.

[0002] A force measuring sensor based on an optical fiber or optical waveguide is a sensor that has a fiber Bragg grating (FBG) engraved on an optical fiber or optical waveguide. It can be easily integrated with sensors that measure temperature, pressure, acceleration, displacement, etc., and has the advantage of being unaffected by electromagnetic interference.

[0003] Prior art 1 (Tianci Zhang, Baojun Chen, and Siyang Zuo. (2022). A Novel 3-DOF Force Sensing Microneedle With Integrated Fiber Bragg Grating for Microsurgery. IEEE Transactions on Industrial Electronics, 69(1), 940-949.) relates to an intraocular microsurgical needle system capable of measuring three-axis force using three fiber Bragg gratings. The present invention discloses a technology for measuring micro-force by utilizing the characteristic that the distance between the gratings can change depending on temperature and applied force (strain), and the central wavelength value of the reflected light changes accordingly.

[0004] In addition, prior art 2 (Mo, Z., Li, J. and Xu, W., 2021. Tactile needle probe for minimally invasive tissue identification during epidural space insertion. Optik, 242, p.167285.) relates to a needle system for epidural space detection using an interferometer-based force sensor, and discloses a technology for utilizing the measured spectrum as a force sensor value by performing Fourier transform and phase analysis since the phase of the interference signal spectrum changes depending on the change in the distance between the optical fiber or optical waveguide and the reflector.

[0005] In addition, prior art 3 (US Patent No. 10,039,530) relates to an interferometer for measuring angle and displacement, and discloses a technology for using three sensors that measure force using an interferometer by spacing them apart at a certain distance and using them as a single detector.

[0006] In addition, prior art 4 (Ourak, M., Smits, J., Esteveny, L., Borghesan, G., Gijbels, A., Schoevaerdts, L., Douven, Y., Scholtes, J., Lankenau, E., Eixmann, T. and Schulz-Hildebrandt, H., 2019. Combined oct distance and fbg force sensing cannulation needle for retinal vein cannulation: in vivo animal validation. International journal of computer assisted radiology and surgery, 14, pp.301-309.) relates to a microsurgical needle utilizing one fiber Bragg grating and two optical coherence tomography-based distance sensors, and discloses a technique for measuring distance and force simultaneously by using optical coherence tomography to measure distance and using interferometry to measure force.

[0007] However, the above-described prior arts have the following limitations.

[0008] In the case of the fiber Bragg grating of the microsurgical needle disclosed in prior art 1, distance measurement is not possible and it is difficult to obtain a good signal because it is vulnerable to temperature changes.

[0009] In addition, in the case of the surgical needle disclosed in prior art 2, the sensor is constructed by using an interferometer using a single mode optical fiber or optical waveguide and a coreless optical fiber or optical waveguide, so the sensor manufacturing process is complicated and distance measurement is not possible.

[0010] In addition, in the case of the microsurgical needle disclosed in prior art 3, a high-reflectance needle tip is positioned in front of a single-mode optical fiber or optical waveguide, making it impossible to measure the distance to an object positioned in front.

[0011] In addition, in the case of the microsurgical needle disclosed in prior art 4, only one piece of information, either force or distance, can be derived for each optical fiber or optical waveguide, and it is inefficient to obtain various pieces of information with a limited number of optical fibers or optical waveguides.

[0012] Thus, according to the present invention, an optical fiber-based force and distance measuring sensor and a method for manufacturing the same are provided that simultaneously or individually measure an applied force and a distance to an object located in front using reflected light from an optical fiber or an optical waveguide.

[0013] According to an embodiment of the present invention for achieving such technical tasks, a fiber-optic-based force and distance measuring sensor may include: an optical fiber or an optical waveguide; an optical material positioned in front of the optical fiber or the optical waveguide and spaced apart by a cavity of a predetermined size; and a capillary formed in a shape that surrounds the optical fiber or the optical waveguide and the optical material.

[0014] The above optical fiber or optical waveguide may be a hybrid optical fiber or optical waveguide structure in which a coreless optical fiber or optical waveguide and a gradient refractive index optical fiber or optical waveguide are fused to the front of the optical fiber or optical waveguide.

[0015] The above optical material may have a preset polishing angle at the front or rear end.

[0016] A sensor system according to one embodiment of the present invention may include an optical fiber-based force and distance measuring sensor; a light source unit that applies light to an optical fiber or an optical waveguide; and a measuring unit that measures force or distance based on reflected light reflected from an end of the optical fiber or optical waveguide, reflected light reflected from an optical material front end, and reflected light reflected from an object, or from an interference signal.

[0017] The above measurement unit removes noise from a signal obtained from reflected light reflected from the end of the optical fiber or optical waveguide and reflected light reflected from the front end of the optical material using a band filter, and obtains a complex signal spectrum using zero padding and Fourier transform, and can measure force or calculate force from an interference signal using the obtained complex signal spectrum.

[0018] The above measuring unit can measure force using the following mathematical formula:

[0019]

[0020] Here, Φ is the phase value of the signal spectrum in complex form, S is the signal spectrum, and I is the signal spectrum converted to complex form through Fourier transform.

[0021] The above measurement unit can measure the distance by using the common path interference between the reflected light reflected from the end of the optical fiber or optical waveguide and the reflected light reflected from an object by passing through an optical material, or can calculate the distance from the interference signal.

[0022] The above measuring unit can measure the distance using the following mathematical formula:

[0023]

[0024] Here, A is the frequency component of the signal spectrum in complex form, S is the signal spectrum, and I is the signal spectrum converted to complex form through Fourier transform.

[0025] In another embodiment of the present invention, a method for manufacturing an optical fiber-based force and distance measuring sensor may include: a step of polishing a front surface of a temporary optical fiber or optical waveguide for molding at a preset polishing angle; a step of inserting the polished temporary optical fiber or optical waveguide for molding into a capillary and positioning an optical material at the front end of the capillary; and a step of inserting the optical fiber or optical waveguide so as to have a cavity of a preset size apart from the optical material and positioning the material at the rear.

[0026] Thus, according to the present invention, by simultaneously or individually measuring force and distance using a single sensor, the size can be minimized and the device can be combined with devices such as microneedles. This can contribute to the miniaturization and modularization of intelligent microsurgical tool structures. Here, a single sensor includes one or more light sources and one or more detectors, allowing the user to easily adjust the slope, thickness, etc. of the reflective surface within the sensor according to their choice.

[0027] Additionally, a single sensor can be manufactured for various purposes, such as a three-axis stage, a microscope for observing materials, and an optical fiber polisher, by implementing it using a reflector or a transmissive material, thereby improving cost-effectiveness and reducing risk.

[0028] Figure 1 is a configuration diagram of a sensor system to which a force and distance measuring sensor is applied according to one embodiment of the present invention.

[0029] FIG. 2 is a conceptual diagram of a force and distance measuring sensor according to one embodiment of the present invention.

[0030] FIG. 3 is a drawing illustrating an example of measuring force or distance according to one embodiment of the present invention.

[0031] FIG. 4 is a drawing showing a force and distance measuring sensor structure depending on whether there is a polishing angle according to one embodiment of the present invention.

[0032] FIG. 5 is a drawing showing the structure of a force and distance measuring sensor using a hybrid optical fiber or optical waveguide according to one embodiment of the present invention.

[0033] FIG. 6 is a drawing showing the results of simultaneously measuring force and distance using a force and distance measuring sensor according to one embodiment of the present invention.

[0034] FIG. 7 is a drawing illustrating a process for manufacturing a force and distance measuring sensor according to another embodiment of the present invention.

[0035] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. In this process, the thickness of lines and the sizes of components depicted in the drawings may be exaggerated for clarity and convenience of explanation.

[0036] Furthermore, the terms described below are defined based on their functions within the present invention, and may vary depending on the intent or custom of the user or operator. Therefore, the definitions of these terms should be based on the overall content of this specification.

[0037] Figure 1 is a configuration diagram of a sensor system to which a force and distance measuring sensor is applied according to one embodiment of the present invention.

[0038] As illustrated in FIG. 1, the sensor system (100) may include a proposed force-distance sensor (110), a light source (Source) (120), a detector (130), and an interferometer (140).

[0039] First, a force and distance measuring sensor (110) is located at the end and can measure the force applied to the sensor or the distance to an object located in front using light applied from a light source (120). At this time, the light source (120) can apply light using a low-coherence source, etc.

[0040] Specifically, the force and distance measuring sensor (110) includes an optical fiber or waveguide (111), a capillary (112), and an optical material (113), and is coupled to an object such as a needle, a syringe, or a scalpel as needed, and may include various optical fibers or waveguides such as a coreless optical fiber or waveguide (111-1, see FIG. 5) and a gradient-index optical fiber or waveguide (GIF) (111-2, see FIG. 5). Here, the optical fiber or waveguide (111) includes a core at the center thereof and a cladding surrounding the core, so that light is transmitted through total internal reflection between the two surfaces.

[0041] Additionally, a force and distance measuring sensor (110) can be coupled to the end of the sensor system (100).

[0042] In the following embodiment, the structure of the force and distance measuring sensor (110) will be described in more detail.

[0043] Additionally, the measuring unit (130) can measure force or distance based on reflected light reflected from the force and distance measuring sensor (110) or from an interference signal.

[0044] Specifically, the measuring unit (130) can measure force or distance by using common-path interference between the reflected light reflected from the end of an optical fiber or optical waveguide (111) and the reflected light reflected from the front end of an optical material (113).

[0045] When measuring force, the measuring unit (130) can receive the size of the cavity from the common path interference between the reflected light reflected from the end of the optical fiber or optical waveguide (111) and the reflected light reflected from the front end of the optical material (113). At this time, the size of the cavity transmitted is the size of the cavity that has undergone a microscopic displacement due to an external force.

[0046] According to one embodiment of the present invention, the measuring unit (130) can calculate and measure the distance from the interference signal.

[0047] In addition, the measuring unit (130) removes noise from the signal obtained from the reflected light reflected from the end of the optical fiber or optical waveguide (111) and the reflected light reflected from the front end of the optical material (113) using a band-pass filter, applies zero-padding and Fourier transform to obtain a complex-type signal spectrum, and can measure force using the obtained complex-type signal spectrum.

[0048] Here, the measuring unit (130) can calculate the phase value of the signal spectrum in complex form using [Mathematical Formula 1] below.

[0049]

[0050] Here, Φ is the phase value of the signal spectrum in complex form, S is the signal spectrum, and I is the signal spectrum converted to complex form through Fourier transform. At this time, Φ is any value in [-nπ ~ nπ] or [0 ~ 2nπ], and n is an integer.

[0051] When measuring the distance to an object located in front of a capillary (112), the measuring unit (130) can receive a signal spectrum including information on the distance to the object located in front of the capillary (112) from the common path interference between the reflected light reflected from the end of an optical fiber or optical waveguide (111) and the reflected light reflected from the object through an optical material (113). Here, if the distance to the object is close, a low frequency band may be indicated, and if the distance to the object is far, a high frequency band may be indicated.

[0052] In addition, the measuring unit (130) can apply the signal spectrum to [Mathematical Formula 2] below to calculate the frequency components of the spectrum and measure the distance to the object.

[0053]

[0054] Here, A is the frequency component of the signal spectrum in complex form, S is the signal spectrum, and I is the signal spectrum converted to complex form through Fourier transform.

[0055] In addition, the interference unit (140) can assist the force or distance measurement of the measuring unit (130) by using the common path interference or interference generated from a combination of two of the reflected light reflected from the end of the optical fiber or optical waveguide (111), the reflected light reflected from the front end of the optical material (113), and the reflected light reflected from an object located in front of the capillary (112).

[0056] In other words, the force and distance measurement sensor (110) can measure force and distance information simultaneously or individually.

[0057] Hereinafter, a force and distance measuring sensor (110) according to an embodiment of the present invention will be described in more detail using FIGS. 2 to 7.

[0058] FIG. 2 is a conceptual diagram of a force and distance measuring sensor according to one embodiment of the present invention.

[0059] As illustrated in FIG. 2, the force and distance measuring sensor (110) may include an optical fiber or an optical waveguide (111), an optical material (113) positioned in front of the optical fiber or the optical waveguide (111) and spaced apart by a cavity of a preset size, and a capillary (112) formed in a shape that surrounds the optical fiber or the optical waveguide (111) and the optical material (113). At this time, the capillary (112) may be made of various glass materials such as silica, quartz, and borosilicate, and may perform at least one of inner diameter, outer diameter, and length adjustment in a tube shape.

[0060] Additionally, the optical material (113) has little foreign matter and has a specified reflectance and transmittance.

[0061] FIG. 3 is a drawing illustrating an example of measuring force or distance according to one embodiment of the present invention.

[0062] Referring to (a) of Fig. 3, when using a force and distance measuring sensor (110), the distance between the object (2) and the force and distance measuring sensor (110) can be measured before contact with the object (2).

[0063] Additionally, when an object (2) and a force and distance measuring sensor (110) come into contact, the force and distance measuring sensor (110) can measure the force applied to the force and distance measuring sensor (110).

[0064] Referring to (b) of FIG. 3, when a force and distance measurement sensor (110) is coupled to a predetermined object (e.g., a needle) (3), the distance between the object (2) and the force and distance measurement sensor (110) can be measured before the object (3) and the object (2) come into contact.

[0065] In addition, when an object (3) and an object (2) come into contact, the force and distance measuring sensor (110) can simultaneously measure the distance between the object (2) and the force and distance measuring sensor (110) and the applied force.

[0066] FIG. 4 is a drawing showing a force and distance measuring sensor structure depending on whether there is a polishing angle according to one embodiment of the present invention.

[0067] As shown in (a) of FIG. 4, when there is no polishing angle, the force and distance measuring sensor (110) may have a reflective surface whose angle of the cavity is perpendicular to the optical axis.

[0068] As shown in (b) of Fig. 4, when there is a polishing angle, the front or rear end of the optical material (113) may have a preset polishing angle.

[0069] Due to this, the force and distance measurement sensor (110) can reduce noise by minimizing interference (e.g., co-path interference, Fabry-Perot interference, etc.) in the signal for measuring force and distance.

[0070] FIG. 5 is a drawing showing the structure of a force and distance measuring sensor using a hybrid optical fiber or optical waveguide according to one embodiment of the present invention.

[0071] As illustrated in FIG. 5, the force and distance measuring sensor (110) may be a composite single mode fiber (cSMF) structure in which a coreless optical fiber or optical waveguide (111-1) and a gradient refractive index optical fiber or optical waveguide (111-2) are fusion-spliced ​​in front of an optical fiber or optical waveguide (111).

[0072] In this way, the force and distance measuring sensor (110) may be a hybrid optical fiber or optical waveguide structure in which various optical fibers or optical waveguides, such as a coreless optical fiber or optical waveguide (111-1) or a gradient refractive index optical fiber or optical waveguide (111-2), are fused in front of an optical fiber or optical waveguide (111).

[0073] Here, the force and distance measuring sensor (110) can expand incident light incident through a coreless optical fiber or optical waveguide (111-1), and generate or focus the expanded incident light into parallel light according to the purpose through an inclined refractive optical fiber or optical waveguide (111-2). As a result, the divergence angle of light can be reduced, and the shape of the laser beam can be maintained to a relatively distant space compared to the past, thereby improving the performance of distance measurement.

[0074] That is, the limitation of resolution reduction in distance measurement through a divergence angle of approximately 10° of a conventional single-mode optical fiber or optical waveguide structure can be resolved.

[0075] FIG. 6 is a drawing showing the results of simultaneously measuring force and distance using a force and distance measuring sensor according to one embodiment of the present invention.

[0076] As shown in (a) of Fig. 6, the force and distance measurement sensor (110) has a force measurement resolution of about 1.7 mN or less, and the distance between the object (2) and the force and distance measurement sensor (110) was measured to be about 8 μm.

[0077] As illustrated in (b) of Fig. 6, it can be seen that force can be measured simultaneously while measuring the distance to an object (Balance) in front of a needle (Needle) that is coupled using a coupling module. At this time, the force and distance measurement sensor (110) can simultaneously measure force and distance at a high speed of about 10 Hz or more.

[0078] FIG. 7 is a drawing illustrating a process for manufacturing a force and distance measuring sensor according to another embodiment of the present invention.

[0079] As shown in (a) of Fig. 7, the front surface of the dummy optical fiber for molding or optical waveguide (4) is polished at a preset polishing angle using a polisher (5).

[0080] As shown in (b) of Fig. 7, a temporary optical fiber or optical waveguide (4) for polished molding is inserted into the capillary (112), and an optical material (113) is positioned and included at the front end of the capillary (112).

[0081] As shown in (c) of Fig. 7, an optical material (113) is positioned on the shear as needed.

[0082] As shown in (d) of Fig. 7, the front end of the optical material (113) and the capillary (112) is polished at a preset polishing angle. At this time, the polishing angle may be different from the polishing angle of (a) of Fig. 7.

[0083] As shown in (e) of Fig. 7, the temporary optical fiber or optical waveguide (4) for molding production is removed.

[0084] As illustrated in (f) of Fig. 7, an optical fiber or optical waveguide (111) is inserted with a gap between the optical material (113) and a cavity of a preset size, and the material is injected and fixed at the rear. Here, the optical fiber or optical waveguide (111) may have a hybrid optical fiber or optical waveguide structure using various types of optical fibers or optical waveguides according to the user's choice.

[0085] According to the embodiments of the present invention described above, by simultaneously or individually measuring force and distance using a single sensor, the size can be minimized and the device can be combined with devices such as microneedles. This can contribute to the miniaturization and modularization of intelligent microsurgical tool structures. Here, a single sensor includes one or more light sources and one or more detectors, allowing the user to easily adjust the slope, thickness, etc. of the reflective surface within the sensor according to their choice.

[0086] Additionally, a single sensor can be manufactured for various purposes, such as a three-axis stage, a microscope for observing materials, and an optical fiber polisher, by implementing it using a reflector or a transmissive material, thereby improving cost-effectiveness and reducing risk.

[0087] While the present invention has been described with reference to the embodiments illustrated in the drawings, these are merely exemplary, and those skilled in the art will understand that various modifications and equivalent embodiments are possible. Therefore, the true technical protection scope of the present invention should be determined by the technical spirit of the following claims.

Claims

1. Optical fiber or optical waveguide; An optical material positioned in front of the optical fiber or optical waveguide and spaced apart by a cavity of a preset size; and An optical fiber-based force and distance measuring sensor comprising a capillary formed in a form that surrounds the optical fiber or optical waveguide and the optical material.

2. In paragraph 1, The above optical fiber or optical waveguide, An optical fiber-based force and distance measuring sensor having a hybrid optical fiber or optical waveguide structure in which a coreless optical fiber or optical waveguide or a gradient refractive index optical fiber or optical waveguide is fused in front of the optical fiber or optical waveguide.

3. In paragraph 1, The above optical material is, A fiber-optic based force and distance measuring sensor with a preset grinding angle at the front or rear end.

4. An optical fiber-based force and distance measuring sensor according to any one of claims 1 to 3; A light source unit that applies light to an optical fiber or optical waveguide; and A sensor system including a measuring unit that measures force or distance based on reflected light reflected from the end of the optical fiber or optical waveguide, reflected light reflected from the front end of the optical material, and reflected light reflected from an object, or from an interference signal.

5. In paragraph 4, The above measuring unit, A sensor system that removes noise from a signal obtained from reflected light reflected from the end of the optical fiber or optical waveguide and reflected light reflected from the front end of an optical material using a band filter, obtains a complex-type signal spectrum using zero padding and Fourier transform, and measures force or calculates force from an interference signal using the obtained complex-type signal spectrum.

6. In paragraph 5, The above measuring unit, A sensor system that measures force using the following mathematical formula: Here, Φ is the phase value of the signal spectrum in complex form, S is the signal spectrum, and I is the signal spectrum converted to complex form through Fourier transform.

7. In paragraph 4, The above measuring unit, A sensor system that measures distance by utilizing common path interference between reflected light reflected from the end of the optical fiber or optical waveguide and reflected light reflected from an object through an optical material, or calculates distance from an interference signal.

8. In paragraph 7, The above measuring unit, A sensor system that measures distance using the following mathematical formula: Here, A is the frequency component of the signal spectrum in complex form, S is the signal spectrum, and I is the signal spectrum converted to complex form through Fourier transform.

9. A step of polishing the front surface of a temporary optical fiber or optical waveguide for molding production at a preset polishing angle; A step of inserting the polished temporary optical fiber or optical waveguide for molding manufacturing into the capillary and positioning the optical material at the front end of the capillary to contain it; and A method for manufacturing an optical fiber-based force and distance measuring sensor, comprising the steps of inserting an optical fiber or an optical waveguide so as to have a cavity of a predetermined size and spaced apart from the optical material and positioning the material at the rear.

Images