Optical fiber three-dimensional force sensor and preparation method and application thereof

Abstract

The invention relates to the technical field of optical fiber sensing, and discloses an optical fiber three-dimensional force sensor and a preparation method and application thereof. According to the optical fiber three-dimensional force sensor, the end face of the optical fiber and the polygonal hollow reflection micro-cavity on the end face are used as the two reflection faces of the Fabry-Perot cavity, and the multiple optical fiber sensors are arranged around the positioning hole in the circumferential direction; the load in the vertical direction and the load in the horizontal direction can cause the displacement change of different optical fiber sensors, the displacement change of two reflecting surfaces and the movement of a Fabry-Perot interference peak, and the force and displacement of a single optical fiber sensor are detected after demodulation, so that the real-time monitoring of the three-dimensional force is realized. The optical fiber three-dimensional force sensor provided by the invention can realize wide-range detection, is small in probe size, compact in structure, high in preparation efficiency, low in preparation cost, easy in mass production, free from electromagnetic interference and relatively high in sensitivity, and can be used for detecting various micro force-displacement.

Description

Technical Field

[0001] The present application relates to the field of optical fiber sensing technology, and in particular to an optical fiber three-dimensional force sensor and a preparation method and application thereof. Background Art

[0002] Robot-assisted minimally invasive surgery has become the preferred surgical method due to its high surgical precision, strong flexibility, small incisions, and short postoperative recovery time. However, most robot-assisted minimally invasive surgeries are performed in narrow and complex environments, and surgeons usually rely only on visual cues and their surgical experience, lacking direct perception of the interaction forces between human tissue and surgical instruments, which may lead to excessive force and damage to organs. Due to the lack of force perception, surgeons need to make more efforts to ensure the accuracy of surgical operations, which makes them more susceptible to surgical fatigue. Therefore, the development of integrated force sensors to provide real-time force perception is crucial to improving the safety and efficiency of minimally invasive surgery.

[0003] There is a clear trend towards miniaturization of force sensors. Microelectromechanical system (MEMS) force sensors have attracted widespread attention due to their small size, low power consumption, easy integration with integrated circuits, and easy mass production. MEMS force sensors based on different working principles such as piezoresistive, capacitive, piezoelectric, and optical have been widely used in force detection of surgical instruments. However, conventional force sensors can often only sense vertical forces (normal forces). However, in the complex human environment, there are also lateral forces, which has imposed certain limitations on the application of existing force sensors. Summary of the invention

[0004] In view of this, the purpose of this application is to provide a fiber optic three-dimensional force sensor and a preparation method thereof, so that it can realize real-time monitoring of three-dimensional forces (normal force and lateral force);

[0005] Another object of the present application is to provide a pressure sensing device based on the above-mentioned optical fiber three-dimensional force sensor.

[0006] In order to solve the above technical problems / achieve the above objectives or at least partially solve the above technical problems / achieve the above objectives, as a first aspect of the present application, a fiber optic three-dimensional force sensor is provided, comprising a flexible cap, a positioning sheet and a fiber optic sensor;

[0007] The bottom of the side wall of the flexible cap is aligned with the positioning piece to form a cavity, a positioning column is protruding from the center of the bottom of the flexible cap, and a positioning hole is provided in the middle of the positioning piece for the positioning column to coaxially penetrate;

[0008] The positioning plate has a plurality of assembly holes arranged along the circumference of the positioning hole, and the optical fiber sensor is inserted into the assembly hole;

[0009] The optical fiber sensor includes an optical fiber and a polygonal hollow reflective microcavity vertically arranged on the end face of the optical fiber, wherein the polygonal hollow reflective microcavity has a frame parallel to the end face of the optical fiber, and the inner wall of the parallel frame can reflect the light beam of the optical fiber; the optical fiber sensor passes through the assembly hole on the positioning plate and is fixed, and the hollow polygonal frame on the optical fiber sensor is in contact with the bottom of the flexible cap.

[0010] Optionally, the flexible cap and the positioning piece are both circular.

[0011] Optionally, a plurality of raised contact points are provided on the bottom of the flexible cap, and the plurality of raised contact points are respectively in contact with the hollow polygonal frame on the optical fiber sensor.

[0012] Optionally, the polygonal hollow reflective microcavity is a regular symmetrical polygonal frame, and its symmetry axis coincides with the central axis of the optical fiber.

[0013] As a second aspect of the present application, a method for preparing the optical fiber three-dimensional force sensor is provided, comprising:

[0014] Cutting the optical fiber, focusing a femtosecond laser beam onto the end face of the optical fiber through a microscope system, and preparing a polygonal hollow reflective microcavity on the end face of the optical fiber using a two-photon polymerization processing technique, wherein the polygonal hollow reflective microcavity has a frame parallel to the end face of the optical fiber, thereby obtaining the optical fiber sensor;

[0015] A flexible cap mold is prepared by using 3D printing technology, and then a flexible material is poured into the mold for solidification to obtain the flexible cap;

[0016] A cutting technique is used to prepare a positioning piece that can be matched with the flexible cap and can abut against it, and a positioning hole and an assembly hole are opened on the positioning piece to obtain the positioning piece;

[0017] After the flexible cap, the positioning sheet and the optical fiber sensor are packaged, the optical three-dimensional force sensor is obtained.

[0018] Optionally, the flexible material comprises polydimethylsiloxane and a cross-linking agent.

[0019] As a third aspect of the present application, there is provided an application of the optical fiber three-dimensional force sensor in the preparation of a pressure sensing device.

[0020] As a fourth aspect of the present application, a pressure sensing device is provided, comprising the optical fiber three-dimensional force sensor described in the present application, as well as a broadband light source, a circulator and a spectrometer.

[0021] The fiber optic three-dimensional force sensor described in the present application utilizes the fiber end face and the reflective frame as the two reflection surfaces of the Fabry-Perot cavity, and multiple fiber optic sensors are arranged circumferentially around the positioning hole. When the fiber optic three-dimensional force sensor is subjected to external force, the vertical load and the horizontal load will cause the displacement change of different fiber optic sensors. The displacement change of the two reflection surfaces causes the Fabry-Perot interference peak to move. After demodulation, the force and displacement of a single fiber optic sensor can be detected, thereby realizing real-time monitoring of three-dimensional force. The fiber optic three-dimensional force sensor proposed in the present application can realize a large range of detection, the probe is small in size, compact in structure, high in preparation efficiency, low in preparation cost, easy to mass produce, not subject to electromagnetic interference, high in sensitivity, and can be used for the detection of various types of tiny force-displacement. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application.

[0023] Figure 1 Shown is a schematic diagram of the structure of the optical fiber sensor of this application;

[0024] Figure 2 It is a schematic diagram showing the formation of double-beam Fabry-Perot interference by the optical fiber sensor of the present application;

[0025] Figure 3 The figure shows the structure and principle diagram of the optical fiber three-dimensional force sensor of the present application;

[0026] Figure 4 The figure shows the structure schematic diagram of the positioning sheet of the present application;

[0027] Figure 5 Shown is a schematic structural diagram of the flexible cap of the present application;

[0028] Figure 6 The figure shows the structure schematic diagram of the positioning piece for assembling the optical fiber sensor of the present application;

[0029] Figure 7 The figure shows the overall exploded schematic diagram of the optical fiber three-dimensional force sensor of the present application;

[0030] Figure 8 Shown is a schematic diagram of the assembly of the pressure sensing device of the present application. DETAILED DESCRIPTION

[0031] The present application discloses a fiber optic three-dimensional force sensor and its preparation method and application. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters for implementation. It is particularly important to point out that all similar substitutions and modifications are obvious to those skilled in the art, and they are all deemed to be included in this application. The products, applications and preparation methods of this application have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods described in this article without departing from the content, spirit and scope of this application to implement and apply the technology of this application.

[0032] In a first aspect of the present application, there is provided an optical fiber three-dimensional force sensor, comprising a flexible cap, a positioning piece and an optical fiber sensor;

[0033] The bottom of the side wall of the flexible cap is aligned with the positioning piece to form a cavity, a positioning column is protruding from the center of the bottom of the flexible cap, and a positioning hole is provided in the middle of the positioning piece for the positioning column to coaxially penetrate;

[0034] The positioning plate has a plurality of assembly holes arranged along the circumference of the positioning hole, and the optical fiber sensor is inserted into the assembly hole;

[0035] The optical fiber sensor includes an optical fiber and a polygonal hollow reflective microcavity vertically arranged on the end face of the optical fiber, wherein the polygonal hollow reflective microcavity has a frame parallel to the end face of the optical fiber, and the inner wall of the parallel frame can reflect the light beam of the optical fiber; the optical fiber sensor passes through the assembly hole on the positioning plate and is fixed, and the hollow polygonal frame on the optical fiber sensor is in contact with the bottom of the flexible cap.

[0036] In some embodiments of the present application, the polygonal hollow reflective microcavity is a regular symmetrical polygon, whose horizontal width generally does not exceed the diameter of the optical fiber, and preferably its symmetry axis coincides with the central axis of the optical fiber and is arranged on the end face of the optical fiber; in some other embodiments of the present application, the polygonal hollow reflective microcavity is a hollow honeycomb hexagonal reflective microcavity, the symmetry axis of the hollow honeycomb hexagon coincides with the central axis of the optical fiber, the frame of the top of the hollow honeycomb hexagonal reflective microcavity is parallel to the end face of the optical fiber and its inner wall can reflect the light beam from the optical fiber, and the structural schematic diagram is shown in Figure 1 In some other embodiments of the present application, the frame length of the hollow honeycomb hexagonal reflective microcavity is 100 μm, and the width (thickness) is 10 μm; the core diameter of the optical fiber is 9 μm, and the cladding diameter is 125 μm.

[0037] In the optical fiber sensor, the polygonal hollow reflective microcavity has a top frame parallel to the end face of the optical fiber. Taking the hollow honeycomb hexagonal reflective microcavity as an example, in the hollow honeycomb hexagonal reflective microcavity, the end face of the optical fiber and the inner wall of its top frame respectively form a reflective surface I 1,I 2 , reflecting surface I 1 ,I 2 It forms a dual-beam Fabry-Perot interferometer (FPI) structure, as shown in the schematic diagram Figure 2 As shown, the light transmitted in the optical fiber I 0 Reflected surface I 1 ,I 2 After reflection, it re-enters the optical fiber to form double beam interference. Assume that the vertical length of the hollow honeycomb hexagonal reflective microcavity is L, and the refractive index of the air in the microcavity is n e , the central wavelength corresponding to the spectral trough position can be expressed as the following formula:

[0038] λm=(2n e L) / m; m = 1, 2, 3..., m represents the corresponding spectral trough.

[0039] When external pressure is applied, the length L of the hollow honeycomb hexagonal reflective microcavity in the vertical direction changes, resulting in the movement of the interference peak. When different pressures are applied to the sensor probe (i.e., the hollow honeycomb hexagonal reflective microcavity), the length L in the vertical direction decreases to varying degrees, resulting in different changes in the interference peak. The interference peak is monitored using a spectrometer and converted into pressure changes after demodulation.

[0040] In certain embodiments of the present application, in order to be able to sensitively sense the pressure of three-dimensional forces (normal force and lateral force) on the optical fiber sensor, the present application uses a cap made of flexible material (such as PDMS) as a flexible deformation layer to cover the optical fiber sensor. When a vertical load (normal force) is applied, the flexible cap generates a vertical force on the polygonal hollow reflective microcavity, causing all polygonal hollow reflective microcavities to undergo the same deformation. According to the above-mentioned FPI principle, relevant pressure information can be obtained; and when a horizontal load (lateral force) is applied, different areas of the flexible cap generate different forces on the polygonal hollow reflective microcavity, causing the polygonal hollow reflective microcavity of a part of the optical fiber sensors to undergo a larger deformation, while the polygonal hollow reflective microcavity of another part of the optical fiber sensors undergoes a smaller deformation. Therefore, the lateral force can be determined according to the relative deformation of different optical fiber sensors in the same direction, as shown in the schematic diagram. Figure 3 .

[0041] In some embodiments of the present application, the positioning plates are all circular. In other embodiments of the present application, the positioning plates are circular silicon wafers, such as silicon wafers with an outer diameter of 1 mm, with a positioning hole at the center of the circle, the diameter of the positioning hole can be selected to be 300-600 μm, and a number of assembly holes are opened along the circumference of the positioning hole for mounting the optical fiber sensor. The number and diameter of the assembly holes are consistent with the number and diameter (optical fiber diameter) of the optical fiber sensor, such as a circular hole with an aperture of 150 μm; the arrangement of the positioning holes can be arbitrary, preferably in a regular array arrangement, as shown in the structural schematic diagram. Figure 4 .

[0042] In certain embodiments of the present application, the flexible cap is circular, for example, a flexible cap with a diameter of 900-1200μm, a side wall length of 200-300μm, and a side wall thickness of 20-100μm. In other embodiments of the present application, in order to better transmit force, a plurality of raised contact points are provided at the bottom of the flexible cap, and the plurality of raised contact points are respectively in contact with the polygonal hollow reflective microcavity on the optical fiber sensor, or more precisely, in contact with the frame parallel to the optical fiber end face; wherein the number and position of the raised contact points correspond one-to-one to the number and position of the optical fiber sensor, and are at least 2 or more, for example, 2, 4, 6, 8, 10, etc. The specific upper limit is determined according to the needs and actual conditions, and the present application does not impose any restrictions on this. The shape of the raised contact point can be selected as a hemispherical contact point, for example, a hemispherical contact point with a diameter of 20-100μm and a height of 10-50μm. See the structural schematic diagram. Figure 5 .

[0043] In certain embodiments of the present application, the optical fiber sensor passes through the assembly hole on the positioning plate and can be fixed by a substance such as an adhesive; wherein the distance that the optical fiber end face of the optical fiber sensor exceeds the positioning plate is determined by whether the polygonal hollow reflective microcavity of the optical fiber sensor can contact the bottom of the flexible cap, for example, the distance that the optical fiber end face of the optical fiber sensor exceeds the positioning plate is 100 μm, as shown in the schematic diagram Figure 6 .

[0044] In a second aspect of the present application, a method for preparing the optical fiber three-dimensional force sensor is provided, comprising:

[0045] Cutting the optical fiber, focusing a femtosecond laser beam onto the end face of the optical fiber through a microscope system, and preparing a polygonal hollow reflective microcavity on the end face of the optical fiber using a two-photon polymerization processing technique, wherein the polygonal hollow reflective microcavity has a frame parallel to the end face of the optical fiber, thereby obtaining the optical fiber sensor;

[0046] A flexible cap mold is prepared by using 3D printing technology, and then a flexible material is poured into the mold for solidification to obtain the flexible cap;

[0047] A cutting technique is used to prepare a positioning piece that can be matched with the flexible cap and can abut against it, and a positioning hole and an assembly hole are opened on the positioning piece to obtain the positioning piece;

[0048] After the flexible cap, the positioning sheet and the optical fiber sensor are packaged, the optical three-dimensional force sensor is obtained.

[0049] In certain embodiments of the present application, the optical fiber sensor is passed through the assembly hole on the positioning sheet and fixed with ultraviolet glue, and then positioned by the engagement of the positioning column and the positioning hole, and the positioning sheet on which the optical fiber sensor is mounted is abutted against the flexible cap. See the packaging schematic diagram. Figure 7 .

[0050] In certain embodiments of the present application, the flexible material includes polydimethylsiloxane (PDMS) and a cross-linking agent; wherein the mass ratio of the PDMS to the cross-linking agent can be selected to be 15:1.

[0051] In certain embodiments of the present application, the optical fiber is a single-mode optical fiber, such as Coning SMF-28.

[0052] In certain embodiments of the present application, the polygonal hollow reflective microcavity is made of a photoinitiator (such as Irgacure 369) and a photoresist (such as SU-8) and is processed to the end face of an optical fiber by two-photon polymerization processing technology; the mass ratio of the photoinitiator to the photoresist can be selected to be 1:100.

[0053] In the third aspect of the present application, based on the excellent effect of the optical fiber three-dimensional force sensor of the present application in real time monitoring three-dimensional forces (normal force and lateral force) at the same time, the present application proposes the application of the optical fiber three-dimensional force sensor in the preparation of pressure sensing equipment.

[0054] In a fourth aspect of the present application, a pressure sensing device is provided according to an application, comprising the optical fiber three-dimensional force sensor described in the present application, as well as a broadband light source, a circulator and a spectrometer. The optical fiber three-dimensional force sensor is connected to the reflection end of the circulator, and the broadband light source and the spectrometer are both connected to the output end of the circulator.

[0055] The following is a further description of an optical fiber three-dimensional force sensor provided in the present application and its preparation method and application.

[0056] Example 1: Preparation of the optical fiber three-dimensional force sensor of the present application

[0057] S1. Dissolve the photoinitiator Irgacure 369 in propanol solvent to dissolve the initiator. Mix the dissolved photoinitiator with the photoresist SU-8 glue at a ratio of (1:100) and mix them evenly using a magnetic stirrer;

[0058] Using a high-precision fiber cutting platform to cut a single-mode fiber Coning SMF-28, the fiber core diameter is 9 μm, and the cladding diameter is 125 μm;

[0059] A silicon wafer with an outer diameter of 1 mm is used as a positioning plate. Using femtosecond cutting technology, four assembly holes with a diameter of 150 μm and a positioning hole with a diameter of 600 μm are cut out on it. The angles between the four assembly holes are 90 degrees and evenly distributed. For the schematic diagram, please refer to Figure 4 .

[0060] S2, using a femtosecond laser to generate infrared light, focusing it on the end face of the single-mode optical fiber Coning SMF-28 through a microscope, so that the SU-8 glue initiates polymerization and prepares a hollow honeycomb hexagonal reflective microcavity with a frame length of 100 μm and a width (thickness) of 10 μm;

[0061] The sample was placed in a 95°C constant temperature box for 5-10 minutes to solidify, and the unpolymerized SU-8 glue was removed with developing solution acetone for 5 minutes to obtain a fiber optic sensor.

[0062] S3, use the creative three-dimensional Halot light-curing 3D printing flexible cap mold, and mix the PDMS polymer solution and cross-linking agent (purchased from SYLGARD TM 184 polydimethylsilane) in a ratio of 15:1, poured into a mold to prepare a flexible cap, placed in a vacuum environment for 20 hours to remove bubbles, and prepared a flexible cap; wherein the flexible cap is round, refer to Figure 5 Style, with a diameter of 900μm, a side wall length of 200μm, a side wall thickness of 100μm, and 4 hemispherical raised contact points at the bottom, with a diameter of 100μm and a height of 50μm.

[0063] S4. Align the Fabry-Perot cavity of the optical fiber sensor with the center of the circle through the micro-displacement platform under the microscope, move the optical fiber sensor to a position where the distance between the optical fiber end face and the silicon wafer is 100 μm, and use ultraviolet glue to bond and cure. Repeat this step to complete the assembly of 4 optical fiber sensors.

[0064] S5. Operate under a microscope and use a micro-displacement platform to align and install the middle positioning column of the flexible cap with the positioning hole in the middle of the positioning plate.

[0065] Example 2: Pressure Sensing Device

[0066] The pressure sensing device includes the optical fiber three-dimensional force sensor described in this application, as well as a broadband light source, a circulator and a spectrometer. The optical fiber three-dimensional force sensor is connected to the reflection end of the circulator, and the broadband light source and the spectrometer are both connected to the output end of the circulator. During the test, a pneumatic device can be used to simulate pressure to detect the device. The assembly diagram is shown in FIG. Figure 8 .

[0067] The above is only a preferred implementation of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A fiber optic three-dimensional force sensor, characterized in that: It includes a flexible cover cap, a positioning piece and an optical fiber sensor; The bottom of the side wall of the flexible cap is aligned with the positioning piece to form a cavity, a positioning column is protruding from the center of the bottom of the flexible cap, and a positioning hole is provided in the middle of the positioning piece for the positioning column to coaxially penetrate; The positioning plate has a plurality of assembly holes arranged along the circumference of the positioning hole, and the optical fiber sensor is inserted into the assembly hole; The optical fiber sensor includes an optical fiber and a polygonal hollow reflective microcavity vertically arranged on the end face of the optical fiber, wherein the polygonal hollow reflective microcavity has a frame parallel to the end face of the optical fiber, and the inner wall of the parallel frame can reflect the light beam of the optical fiber; the optical fiber sensor passes through the assembly hole on the positioning plate and is fixed, and the hollow polygonal frame on the optical fiber sensor is in contact with the bottom of the flexible cap.

2. The optical fiber three-dimensional force sensor according to claim 1, characterized in that: The flexible cap and the positioning piece are both circular.

3. The optical fiber three-dimensional force sensor according to claim 1, characterized in that: The bottom of the flexible cap is provided with a plurality of raised contact points, and the plurality of raised contact points are respectively in contact with the hollow polygonal frame on the optical fiber sensor.

4. The optical fiber three-dimensional force sensor according to claim 1, characterized in that: The polygonal hollow reflective microcavity is a regular symmetrical polygon, and its symmetry axis coincides with the central axis of the optical fiber.

5. The method for preparing the optical fiber three-dimensional force sensor according to claim 1, characterized in that: include: Cutting the optical fiber, focusing a femtosecond laser beam onto the end face of the optical fiber through a microscope system, and preparing a polygonal hollow reflective microcavity on the end face of the optical fiber using a two-photon polymerization processing technique, wherein the polygonal hollow reflective microcavity has a frame parallel to the end face of the optical fiber, thereby obtaining the optical fiber sensor; A flexible cap mold is prepared by using 3D printing technology, and then a flexible material is poured into the mold for solidification to obtain the flexible cap; A cutting technique is used to prepare a positioning piece that can be matched with the flexible cap and can abut against it, and a positioning hole and an assembly hole are opened on the positioning piece to obtain the positioning piece; After the flexible cap, the positioning sheet and the optical fiber sensor are packaged, the optical three-dimensional force sensor is obtained.

6. The preparation method according to claim 5, characterized in that: The flexible material includes polydimethylsiloxane and a cross-linking agent.

7. Use of the optical fiber three-dimensional force sensor according to any one of claims 1 to 4 in the preparation of pressure sensing equipment.

8. A pressure sensing device, characterized in that: The invention comprises the optical fiber three-dimensional force sensor as claimed in any one of claims 1 to 4, as well as a broadband light source, a circulator and a spectrometer.

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