Flexible tactile sensor with double-channel structure and preparation method of flexible tactile sensor

Abstract

The invention relates to the technical field of bionic touch, in particular to a flexible touch sensor with a double-channel structure and a preparation method. According to the flexible tactile fiber sensor, a double-coaxial optical fiber structure is obtained by wrapping a cladding outside a core body, a grating is arranged at the central position of the core body to form an optical channel, and the cladding is a piezoelectric fiber to form a piezoelectric sensing channel, so that the flexible tactile sensor with optical and electrical dual channels is formed. During mechanical bending, optical wave change occurs to optical channel strain formed by the core body, and the curvature can be obtained through bending and loss mapping of the optical channel; meanwhile, the strain of an electrical channel formed by the cladding generates voltage change, strain or stretching can be obtained through piezoelectric charge or voltage response of the electrical channel, a joint model is established through electro-optical joint calibration, and real strain without temperature interference and real temperature change without strain interference can be obtained respectively; the strain contribution during bending can be accurately distinguished.

Description

Technical Field

[0001] This invention relates to the field of biomimetic tactile technology, specifically to a flexible tactile sensor with a dual-channel structure and its fabrication method. Background Technology

[0002] With the continuous development of wearable devices, wearable devices now possess flexible functions such as bending, folding, and stretching. These characteristics make flexible wearable devices highly adaptable, giving them great application potential in smart scenarios such as healthcare, sports, and daily life.

[0003] Existing flexible tactile skin typically uses piezoresistive or capacitive methods to sense normal pressure. However, these sensors suffer from zero-point drift and insufficient repeatability under temperature changes and bending conditions.

[0004] In the process of developing this invention, the inventors discovered that existing flexible tactile sensors mostly rely on a single physical quantity for detection, such as electricity or light. This makes it difficult to simultaneously achieve bending, stretching, and temperature drift compensation in microscale fiber morphology. Traditional plastic optical fibers are sensitive to bending but suffer from significant temperature drift; PVDF-type piezoelectric fibers can measure strain / stress, but calibration and temperature compensation are complex issues. Summary of the Invention

[0005] One of the objectives of this invention is to provide a flexible tactile sensor with a dual-channel structure and a method for its fabrication, so as to overcome the shortcomings of existing flexible tactile sensors that cannot detect through a single physical quantity.

[0006] To solve the above-mentioned technical problems, the embodiments of the present invention are implemented as follows: Firstly, a flexible tactile sensor with a dual-channel structure is provided, comprising: Core, wherein the core is an optical fiber core; A cladding layer, provided on the outer surface of the core, is a piezoelectric fiber layer used to output voltage signals generated by mechanical deformation; The core is equipped with an FBG grating, which is used to output the wavelength change signal generated by mechanical deformation, forming a dual-channel combined optical fiber of piezoelectric fiber and optical fiber.

[0007] Furthermore, the refractive index of the core is higher than that of the cladding.

[0008] Furthermore, the core is made of either a cyclic olefin copolymer or polymethyl methacrylate.

[0009] Furthermore, the cladding is made from a raw material including polyvinylidene fluoride (PVDF) or the copolymer PVDF-TrFE.

[0010] Furthermore, the FBG grating is located near the center of the core.

[0011] The third aspect also discloses a method for fabricating a flexible tactile sensor, the steps of which include: To prepare pre-fiber, the fiber core is dried and processed into a circular core. The cladding is heated and melted and then extruded to obtain a cladding with a sleeve structure. The core is then inserted into the cladding to obtain the pre-fiber. An FBG grating is inscribed in the core of the optical fiber near the center using a laser engraving process. After writing the FBG grating on the prefabricated optical fiber, positive and negative electrodes are set on the cladding using a magnetron sputtering coating process to obtain a flexible tactile sensor with a dual-channel structure.

[0012] Furthermore, the process of drying the optical fiber core material into a circular core involves placing the optical fiber core material in a drying device at 80°C for 12 hours to dehumidify it. The process of heating and melting the packing material and then extruding it to obtain the cladding structure is as follows: the packing material is melted at 160–180°C, and then an extrusion process is used to form the cladding structure of the sleeve structure with an inner diameter 0.05–0.2 mm larger than that of the mandrel.

[0013] Furthermore, the step of writing the FBG grating includes: The prefabricated optical fiber was focused and positioned using an immersion liquid objective lens; Femtosecond lasers are used to write on prefabricated optical fibers. The pulse energy during writing is 50-300 nJ (input to the fiber); the pulse repetition frequency is 100 kHz–1 MHz; the scanning step size is equal to the desired Λ / 2; and the writing feed rate is 0.1–1.0 mm / s. Finally, the pre-fabricated optical fiber is annealed to eliminate internal stress.

[0014] Furthermore, the steps of setting positive and negative electrodes on the cladding layer using magnetron sputtering deposition include: First, use pre-fabricated optical fibers The plasma is used for cleaning, followed by drying. Next, electrodes are deposited only on both sides of the pre-fabricated optical fiber using a mechanical masking method or photolithography. Finally, the optical fiber after the electrodes are fabricated is subjected to heat treatment to release the deposition stress.

[0015] The third aspect also discloses a sensor detection method, which uses the detection of a flexible tactile sensor with a dual-channel structure as described in any one of the above-mentioned methods, and includes the following steps: The wavelength change signal of the core and the voltage change signal of the cladding are obtained to obtain the wavelength deviation value and the voltage deviation value; Establish a joint model and express it in reverse; The wavelength deviation and voltage deviation are solved using a joint model to obtain the strain caused by mechanical bending.

[0016] The beneficial effects of the above-described technical solutions provided in the embodiments of the present invention include at least the following: This invention discloses a flexible tactile sensor with a dual-channel structure. It obtains a dual coaxial optical fiber structure by wrapping a core with a cladding. A grating is set at the center of the core to form an optical channel, and the cladding is a piezoelectric fiber to form a piezoelectric sensing channel, thus forming a flexible tactile sensor with both optical and electrical channels.

[0017] When mechanically bent, the strain of the optical channel formed by the core changes due to light wave changes. The curvature can be obtained by mapping the bending and loss of the optical channel. At the same time, the strain of the electrical channel formed by the cladding changes due to voltage changes. The strain or tension can be obtained by the piezoelectric charge or voltage response of the electrical channel. A joint model is established by electro-optic joint calibration, which can obtain the true strain and the true temperature change that are not affected by temperature, respectively, so as to accurately distinguish the strain contribution during bending.

[0018] The tactile sensor structure of this embodiment can effectively eliminate the strain effect caused by temperature factors, thereby improving the accuracy of strain acquisition.

[0019] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings.

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0021] Figure 1 A schematic diagram of a flexible tactile sensor with a dual-channel structure provided in an embodiment of the present invention; Figure 2 This is an embodiment of the present invention. Figure 1 A magnified schematic diagram of the FBG grating; Figure 3 This is a graph showing the wavelength change of the core when it undergoes tensile strain, as described in an embodiment of the present invention. Figure 4 This is a graph showing the voltage response change of the piezoelectric fiber cladding when it undergoes tensile strain, according to an embodiment of the present invention. Figure 5 The strain residual curve obtained after temperature compensation is shown in the figure after processing the joint model. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] In this application, the term "exemplary" is used to mean "used as an example, illustration, or description." Any implementation described as "exemplary" in this application is not necessarily to be construed as being more preferred or advantageous than other implementations. The following description is provided to enable any person skilled in the art to implement and use this application. Details are set forth in the following description for illustrative purposes. It should be understood that those skilled in the art will recognize that this application can be implemented without using these specific details. In other instances, well-known structures and processes are not described in detail to avoid obscuring the description of this application with unnecessary detail. Therefore, this application is not intended to be limited to the embodiments shown, but rather to be consistent with the broadest scope of the principles and features disclosed in this application.

[0024] Bionic skin is an artificial material designed to mimic the structure and function of human skin, aiming to replicate the sensory, protective, and self-healing properties of real skin. It is typically made of elastic polymer composites (such as silicone-based polymers), possessing flexibility, stretchability, and biocompatibility. Its core functions include sensing external stimuli such as pressure, temperature, and humidity, and converting this information into electrical signals for applications in robotics, intelligent prosthetics, and medical monitoring. For example, bionic electronic skin can endow robots with tactile abilities, enhancing the human-computer interaction experience. Bionic skin has enormous application potential in consumer electronics, military, and healthcare industries. With the development of flexible electronics, novel attachable, wearable, portable, and foldable flexible electronic devices have become an important development direction in recent years.

[0025] Among them, tactile sensors play a core role in bionic skin. By simulating the tactile perception mechanism of human skin, bionic skin can detect and respond to mechanical stimuli from the external environment, including pressure, shear force, and vibration, as well as physical properties such as temperature, humidity, and texture.

[0026] Existing tactile sensors struggle to combine electrical and optical physical quantities for detection while maintaining a simple structure. Traditional plastic optical fibers are sensitive to bending but exhibit significant temperature drift; PVDF-type piezoelectric fibers can measure strain / stress, but suffer from complex calibration and temperature compensation issues. Furthermore, neither of these types of sensors can combine electrical and optical physical quantities for detection.

[0027] Before describing the embodiments of the present invention in detail, the design concept of the present invention will be summarized below.

[0028] This invention provides a flexible tactile sensor with a dual-channel structure, the specific implementation of which is as follows. Figure 1 As shown, the core process of this invention includes: obtaining a dual-coaxial fiber structure by wrapping a core with a cladding layer, with a grating at the center of the core forming an optical channel, and the cladding layer being piezoelectric fibers forming a piezoelectric sensing channel, thus forming a flexible tactile sensor with both optical and electrical channels. When mechanically bent, the strain in the optical channel formed by the core changes due to light wave changes, and the curvature can be obtained by mapping the bending and loss of the optical channel; simultaneously, the strain in the electrical channel formed by the cladding changes due to voltage changes, and the strain or tension can be obtained by the piezoelectric charge or voltage response of the electrical channel. A joint model is established using electro-optical joint calibration to obtain inverse suppression of temperature interference, achieving temperature-robust curvature and tension measurement. The tactile sensor structure designed in this invention can effectively eliminate the strain influence caused by temperature factors, thereby improving the accuracy of strain acquisition.

[0029] For the first aspect, which is based on the same inventive concept, please refer to the appendix. Figure 1 and 2 The diagram also discloses a flexible tactile sensor with a dual-channel structure, comprising: Core 40, wherein the core 40 is an optical fiber core; A cladding layer 30 is disposed on the outer surface of the core 40. The cladding layer 30 is a piezoelectric fiber layer used to output voltage signals generated by mechanical deformation. The core 40 is provided with an FBG grating 20, which is used to output the wavelength change signal generated by mechanical deformation, forming a dual-channel combined optical fiber of piezoelectric fiber and optical fiber.

[0030] Understandably, in order to enable a flexible sensor to have dual physical quantities, including optical and piezoelectric signals, to detect strain caused by mechanical bending, the problem of existing flexible tactile sensors that rely on a single physical quantity being prone to temperature sensitivity crossover or complex temperature compensation can be solved.

[0031] In this embodiment, an FBG grating is placed on the fiber core of the piezoelectric fiber, thereby combining piezoelectric fiber and optical fiber. This allows a sensor to detect voltage signals through an electrical channel to obtain strain, and to detect wavelength changes in the reflected wavelength through an optical channel to obtain tensile strain. Then, a temperature-compensated strain is obtained through a matrix-calibrated temperature compensation algorithm. This reduces the cross-sensitivity of the sensor to temperature and improves the accuracy of the touch sensor. The tactile sensor structure of this embodiment can effectively eliminate the strain influence caused by temperature factors, thereby improving the accuracy of strain acquisition.

[0032] The working principle is as follows: a double-layer coaxial fiber structure is obtained by wrapping a PVDF cladding 30 around the core 40 of a COP fiber, and an FBG grating is etched on the core 40. That is, the core 40 is a COP fiber core with an FBG grating, forming an optical channel. When the core 40 undergoes mechanical bending, the wavelength of the light beam in the optical channel changes. By detecting the wavelength shift of the light wave, the corresponding strain can be obtained. Simultaneously, symmetrical electrodes 10 are arranged on the outer surface of the PVDF cladding 30, forming an electrical channel. When the cladding 30 undergoes mechanical bending, the piezoelectric fibers in the electrical channel generate a change in charge signal. The strain / tension can be detected by detecting the charge signal of the electrodes. Furthermore, the refractive index of the core 40 is greater than that of the cladding 30 to form a total internal reflection waveguide channel, thereby improving the bending sensitivity of the sensor and reducing loss.

[0033] Metal electrodes 10 are formed on the outer surface of the PVDF cladding 30. The metal electrodes 10 include at least one pair and are symmetrically arranged along the axis of the optical fiber, so that the electrodes 10 form an electrical channel for piezoelectric sensing. This electrical channel can detect the strain or stretch of the optical fiber by responding to piezoelectric charge or voltage.

[0034] Furthermore, the refractive index of the core 40 is higher than that of the cladding 30. The core 40 is made of a material with a higher refractive index, such as a COP fiber core with n of 1.53@1550nm, while the cladding 30 is made of a material with a lower refractive index, such as n of 1.42, to ensure total internal reflection and low-loss transmission.

[0035] Work process: A COP core 40 is embedded in a PVDF cladding 30 to form a coaxial touch sensor, and the refractive index of the core 40 is higher than that of the cladding 30. An electrode layer 10 is also provided on the outside of the cladding 30, and an FBG grating is inscribed on the core 40.

[0036] In this embodiment, a laser source and a photodetector are used in the tactile fiber sensor. When pressure is applied to the optical fiber, the fiber bends, causing the core 40 to bend. This causes a change in the wavelength of the light beam transmitted through the optical channel formed by the core 40, which can be detected by devices such as photodetectors. Simultaneously, since the cladding 30 of the piezoelectric fiber structure forms an electrical channel, it also undergoes mechanical bending. At this time, the cladding 30 bends in the same way; that is, when pressure is applied to the piezoelectric fiber, the internal lattice deformation of the material causes charge separation, generating a voltage. The voltage signal of the electrode 10 is detected by a photodetector. In this way, different physical quantities of the two channels can be obtained. By processing these two physical quantities, the strain of the mechanical bending after temperature compensation can be obtained. This effectively solves the problem of temperature cross-sensitivity, providing true strain unaffected by temperature and true temperature change unaffected by strain.

[0037] In a further embodiment, the core 40 is made of either a cyclic olefin copolymer or polymethyl methacrylate, and its diameter is controlled to be 6-20 μm.

[0038] Understandably, in order to make the refractive index of the core 40 higher than that of the cladding 30 and reduce loss, in this embodiment, the core 40 is made of cyclic olefin copolymer to obtain COP optical fiber, and the diameter of the core 40 should be controlled.

[0039] In some embodiments, a COP core 40 is made of a polymer and the refractive index n≈1.53@1550 nm is controlled, and the diameter of the core 40 is controlled to be 16 μm; in other embodiments, a COP core 40 is made of a polymer and the refractive index n≈1.53@1550 nm is controlled, and the diameter of the core 40 is controlled to be 6 μm; in still other embodiments, a COP core 40 is made of a polymer and the refractive index n≈1.53@1550 nm is controlled, and the diameter of the core 40 is controlled to be 20 μm.

[0040] In a further embodiment, the cladding 30 is made of one of polyvinylidene fluoride (PVDF) or the copolymer PVDF-TrFE, and the thickness is controlled to be 50–125 μm.

[0041] Understandably, in order for the cladding 30 to be a piezoelectric fiber with a refractive index lower than that of the core 40, in this embodiment, the cladding 30 is made from raw materials including polyvinylidene fluoride (PVDF) or the copolymer PVDF-TrFE, and the thickness of the cladding 30 is controlled within a certain range.

[0042] In some embodiments, the cladding 30 is made of PVDF, the thickness of the cladding 30 is controlled at 100 μm, and the refractive index n of the cladding 30 is approximately 1.42; in other embodiments, the cladding 30 is made of PVDF-TrFE, the thickness of the cladding 30 is controlled at 50 μm, and the refractive index n of the cladding 30 is approximately 1.42; in still other embodiments, the cladding 30 is made of PVDF, the thickness of the cladding 30 is controlled at 125 μm, and the refractive index n of the cladding 30 is approximately 1.42.

[0043] As described above, the core 40 is made of a material with a high refractive index, such as COP fiber core with a refractive index n of approximately 1.53@1550nm, while the cladding 30 is made of a material with a low refractive index, such as PVDF with a refractive index n of approximately 1.42, ensuring total internal reflection and low-loss transmission. The core 40 can also be made of polymethyl methacrylate with a refractive index of 1.49, and the refractive index of the core 40 is higher than that of the cladding 30.

[0044] In a further embodiment, the FBG grating 20 is disposed near the center of the core 40.

[0045] Based on the same inventive concept, a second aspect also discloses a method for fabricating a flexible tactile sensor, comprising the following steps: Step 001: Prefabricated optical fiber. After drying the optical fiber core, it is processed into a circular core 40. The cladding material is heated and melted and then extruded to obtain a cladding 30 with a sleeve structure. Then, the core 40 is inserted into the cladding 30 to obtain the prefabricated optical fiber.

[0046] In a further embodiment, the optical fiber core material is processed into a circular core 40 after drying by placing the optical fiber core material in a drying device at 80°C for 12 hours to dehumidify it. The process of heating and melting the packing material and then extruding it to obtain the cladding 30 of the sleeve structure involves: melting the packing material at 160–180°C and then using an extrusion process to form the cladding 30 of the sleeve structure with an inner diameter 0.05–0.2 mm larger than that of the mandrel.

[0047] For example: COP (carbon phosphate) was selected as the material for manufacturing the core 40. The refractive index (n) of this material is 1.53. During manufacturing, the COP particles were first dried at 80°C for 12 hours to remove moisture. Next, the COP particles were melted and extruded into cylindrical core 40 using a melt extrusion process. Further machining was also possible, ultimately achieving a diameter of 10-20 mm for the cylindrical core 40.

[0048] Using polyvinylidene fluoride copolymer PVDF-TrFE (molecular weight ≥300,000) as raw material, a tubular cladding 30 with an inner diameter 0.05-0.2 mm larger than the cylindrical core 40 was obtained by melt extrusion process at 160-180°C.

[0049] Then, a cylindrical core 40 is inserted into the PVDF cladding 30, followed by degassing in a vacuum environment (–0.09 MPa) for 30 min to remove interfacial bubbles. The PVDF cladding 30 is then pre-polarized for 10–30 min under an electric field of 40–60 MV / m and a temperature of 90–100°C to form a β-phase crystalline region, thereby improving the subsequent piezoelectric coefficient. Pre-fabricated optical fibers are obtained.

[0050] Step 002: Use laser engraving technology to engrave an FBG grating near the center of the core 40 of the pre-fabricated optical fiber.

[0051] Furthermore, the step of writing the FBG grating includes: The prefabricated optical fiber was focused and positioned using an immersion liquid objective lens; Femtosecond lasers are used to write on prefabricated optical fibers. The pulse energy during writing is 50-300 nJ (input to the fiber); the pulse repetition frequency is 100 kHz–1 MHz; the scanning step size is equal to the desired Λ / 2; and the writing feed rate is 0.1–1.0 mm / s. Finally, the pre-fabricated optical fiber is annealed to eliminate internal stress.

[0052] Understandably, a femtosecond laser or grating writing method is used to etch an FBG grating on the core 40 of the pre-fabricated optical fiber, so that the core 40 has an FBG grating 20 formed by axial periodic modulation of the refractive index, and its light wave signal is detected by a photodetector.

[0053] For example: Using femtosecond laser inscription, an FBG grating 20 is fabricated in the middle of a COP polymer core 40. Specific steps include: First, focusing and positioning are achieved by using microscopic imaging to lock the center of the prefabricated fiber core 40. The laser focusing depth is located in the middle of the core 40. In this embodiment, an oil immersion / water immersion objective lens is used to reduce spherical aberration and improve the quality of the microstructure.

[0054] Next, femtosecond laser writing is performed, with the following parameters controlled during the writing process: pulse energy controlled at 50–300 nJ (input fiber); repetition frequency at 100 kHz–1 MHz; scanning step size equal to the desired Λ / 2; and feed rate controlled at 0.1–1.0 mm / s.

[0055] Finally, the pre-fabricated optical fiber after writing is annealed at a temperature of 50–70 °C for 15–30 min to eliminate internal stress, so that the FBG grating 20 is obtained in the middle position of the core 40.

[0056] Step 003: After writing the FBG grating, the prefabricated optical fiber is coated with positive and negative electrodes 10 on the cladding using a magnetron sputtering process to obtain a flexible tactile sensor with a dual-channel structure.

[0057] Furthermore, the 10 steps of setting positive and negative electrodes on the cladding using magnetron sputtering deposition technology include: First, use pre-fabricated optical fibers The plasma is used for cleaning, followed by drying. Next, electrodes 10 are fabricated only on both sides of the cladding of the pre-fabricated optical fiber using a mechanical masking method or photolithography. Finally, the prefabricated optical fiber after electrode 10 is fabricated is subjected to heat treatment to release the deposition stress. Specific Implementation

[0058] The surface cleaning / activation treatment of prefabricated optical fibers specifically involves using... Plasma is used for treatment and activation. The cleaning power is 100 W and the cleaning time is controlled at 30–60 s to enhance the adhesion of the electrode metal. After cleaning, acetone / isopropanol is used for ultrasonic drying for 2 × 2 min.

[0059] A bilayer structure was deposited using Ti / Au (10 nm / 200 nm) or Cr / Al (20 nm / 300 nm) to ensure both conductivity and flexibility. Electrodes were deposited only on the symmetrical sides of the fiber using a rotating optical fiber and a mechanical shielding method (or photolithography), with the electrode width occupying approximately 30°–60° of the circumference. During deposition, the sputtering parameters were controlled as follows: substrate temperature below 60 °C; Ar 2–5 mTorr; power 100–300 W; and rotation speed 5–20 rpm.

[0060] Finally, a transparent insulating layer of fluorinated polymer or Parylene film is coated on the metal electrode, and the thickness of the insulating layer is controlled to <2μm for insulation and corrosion protection.

[0061] The electrode layer is polarized using a high-voltage polarization process to obtain a flexible tactile sensor with a dual-channel structure.

[0062] Furthermore, the polarization treatment of the electrode layer using a high-voltage polarization process involves subjecting the prefabricated optical fiber after electrode deposition to high-voltage polarization. The polarization temperature is controlled at 60–80°C, the electric field strength is controlled at 80–120 MV / m, and the polarization time lasts for 10–20 min, in order to release deposition stress.

[0063] For example: The optical fiber after electrode deposition is subjected to high-voltage polarization. The polarization temperature is controlled at 80–120°C, the polarization electric field strength is controlled at 80–120 MV / m, and the polarization time lasts for 10–20 min.

[0064] After high-pressure polarization, the temperature will be slowly reduced to room temperature, with the rate of temperature decrease controlled at <3°C / min during cooling to stabilize molecular orientation and internal stress, and prevent [further damage]. Attenuation was used to obtain a flexible tactile sensor with a dual-channel structure.

[0065] The third aspect also discloses a sensor detection method, which uses the detection of a flexible tactile sensor with a dual-channel structure as described in any one of the above-mentioned methods, and includes the following steps: Step 100: Obtain the wavelength change signal of the core 40 and the voltage change signal of the electrode to obtain the wavelength deviation value and the voltage deviation value.

[0066] In this embodiment, a photodetector can acquire signals of two different physical quantities generated by a dual-channel flexible tactile sensor when mechanical deformation occurs. These signals include a wavelength change signal generated by the bending strain of the core 40 and a voltage change signal generated by the bending strain of the cladding. The wavelength change signal of the core 40 is the wavelength drift of the light beam within the core 40 when mechanical deformation occurs; this wavelength change is obtained by detecting the strain of the core 40 and represents the deviation value of the wavelength of the light beam measured by the core 40. The bending strain signal of the cladding is the signal obtained when the cladding undergoes mechanical deformation; when the electrical fiber is subjected to external pressure or tension, its internal crystal structure deforms, leading to charge redistribution and a voltage across the material. This charge signal is obtained by detecting the electrode layer attached to the cladding and represents the voltage deviation value of the cladding.

[0067] Step 200: Build a joint model and perform reverse expression.

[0068] In this embodiment, the establishment of the joint model and the reverse expression are as follows: a joint model of curvature and temperature binary model is established by photoelectric joint calibration, and the joint model is expanded and expressed in reverse. The curvature κ is calculated by calibration matrix A and the influence of temperature on the measurement results is suppressed. This is used to suppress temperature interference and realize temperature-robust curvature / tension measurement.

[0069] First, by establishing a linearized joint model, the model formula is as follows: Wavelength model formula for optical sensing channel: ; The voltage model formula for an inductor channel is as follows: ; in, The deviation value of the optical channel normalized wavelength of the core is the deviation of the center wavelength measured by the photodetector; The deviation of the voltage of the electrical channel of the cladding is measured by a photodetector. The strain to be measured; Temperature deviation; The strain sensitivity coefficient represents the wavelength change caused by a unit strain, such as the strain sensitivity coefficient of a typical quartz optical fiber in the 1550nm band. Approximately 1.2 pm / με; The temperature sensitivity coefficient represents the change in wavelength caused by a unit change in temperature, such as the temperature sensitivity coefficient of FBG. Approximately 11 pm / °C; This is the sensitivity coefficient of the cladding to strain; This is the temperature sensitivity coefficient of the cladding.

[0070] The above two model formulas can be written in matrix form: ;

[0071] To solve this problem, we need to invert the matrix. The specific steps are as follows: ;

[0072] Where A is the sensitivity calibration matrix, i.e. ; For the inverse matrix A, ; Substituting the inverse matrix, we can obtain explicit expressions for ε and ΔT, as follows: ; Next, the expanded formula is expressed in reverse, and the inverse formula is: ; It should be noted that the wavelength deviation can be considered as the wavelength drift that occurs when the light beam bends along with the fiber, and the deviation value here is the amount of change in the center wavelength; the voltage deviation can be considered as the charge change that occurs when the piezoelectric fiber bends, and the deviation value here is the amount of charge change.

[0073] Step 300: Solve the deviation values ​​of the light wave and the voltage using a joint model to obtain the strain caused by mechanical bending.

[0074] The above inverse expression formula is the calculation formula for achieving temperature compensation and strain separation. By acquiring Δλ and ΔV in real time and substituting them into the above inverse expression formula, the true strain ε, which is unaffected by temperature, and the true temperature change ΔT, which is unaffected by strain, can be calculated simultaneously. Example: Through... The inputs ΔV and linearized joint model are used to obtain matrix temperature compensation, thereby accurately distinguishing the contribution of temperature and strain, and accurately obtaining the true strain.

[0075] The strain of the mechanical bending to be estimated is obtained from the above, which is the strain residual value after temperature compensation. The strain residual value is the true strain that is not affected by temperature.

[0076] Understandably, the embodiment can accurately decouple mechanical deformation (curvature) and thermal effects from simple electrical measurements, which is a common and effective signal processing method in flexible sensor systems.

[0077] In this embodiment, the above method can effectively distinguish the contributions of temperature and strain, that is, the strain obtained is the strain of accurate mechanical bending, which is not affected by temperature sensitivity.

[0078] Appendix Figure 3 The graph shows the wavelength change of the core under tensile strain. As can be seen from the graph, the wavelength change is linear with the increase or decrease of strain. (Attached) Figure 4 The graph shows the voltage response of the piezoelectric fiber cladding under tensile strain. As can be seen from the graph, the voltage response changes linearly with the increase or decrease of strain.

[0079] Appendix Figure 5 The attached figure shows the strain residual curve after temperature compensation obtained from the joint model processing. The temperature environment of the sensor application scenario is simulated at room temperature. Under temperature changes, the absolute value of the strain residual output by this sensor is less than 1με, which is close to 0. It can be seen that the effect of temperature change on the strain of mechanical bending under room temperature is very small and can be ignored. Thus, this sensor can accurately distinguish the strain of mechanical bending and obtain the true strain that is not affected by temperature.

[0080] Based on the same inventive concept, the fourth aspect also discloses an application method for a flexible tactile sensor with a dual-channel structure, which is applied in wearable health monitoring, robot tactile sensing and human-computer interaction and other application scenarios.

[0081] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. This disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims. Thus, if these modifications and variations of the invention fall within the scope of the claims of the invention and their equivalents, the invention is also intended to include these modifications and variations.

Claims

1. A flexible tactile sensor with a dual-channel structure, characterized in that, include: Core, wherein the core is an optical fiber core; A cladding layer, provided on the outer surface of the core, is a piezoelectric fiber layer used to output voltage signals generated by mechanical deformation; The core is equipped with an FBG grating, which is used to output the wavelength change signal generated by mechanical deformation, forming a dual-channel combined optical fiber of piezoelectric fiber and optical fiber.

2. The flexible tactile sensor with a dual-channel structure according to claim 1, characterized in that, The refractive index of the core is higher than that of the cladding.

3. The flexible tactile sensor with a dual-channel structure according to claim 1 or 2, characterized in that, The core is made of either a cyclic olefin copolymer or polymethyl methacrylate.

4. The flexible tactile sensor with a dual-channel structure according to claim 1 or 2, characterized in that, The cladding is made from a raw material including polyvinylidene fluoride or the copolymer PVDF-TrFE.

5. The flexible tactile sensor with a dual-channel structure according to claim 1 or 2, characterized in that, The FBG grating is located near the center of the core.

6. A method for fabricating a flexible tactile sensor, characterized in that the steps include... include: To prepare pre-fiber, the fiber core is dried and processed into a circular core. The cladding is heated and melted and then extruded to obtain a cladding with a sleeve structure. The core is then inserted into the cladding to obtain the pre-fiber. An FBG grating is inscribed in the core of the optical fiber near the center using a laser engraving process. After writing the FBG grating on the prefabricated optical fiber, positive and negative electrodes are set on the cladding using a magnetron sputtering coating process to obtain a flexible tactile sensor with a dual-channel structure.

7. The method for fabricating a flexible tactile sensor according to claim 6, characterized in that, The optical fiber core is processed into a circular core after drying by placing the optical fiber core in a drying device at 80°C for 12 hours to dehumidify. The process of heating and melting the packing material and then extruding it to obtain the cladding structure is as follows: the packing material is melted at 160–180°C, and then an extrusion process is used to form the cladding structure of the sleeve structure with an inner diameter 0.05–0.2 mm larger than that of the mandrel.

8. The method for fabricating a flexible tactile sensor according to claim 6, characterized in that, The steps for writing the FBG grating include: The prefabricated optical fiber was focused and positioned using an immersion liquid objective lens; Femtosecond lasers were used to write on prefabricated optical fibers. During writing, the pulse energy was controlled at 50-300 nJ; the pulse repetition frequency was controlled at 100 kHz–1 MHz; the scanning step size was equal to the desired Λ / 2; and the writing feed rate was controlled at 0.1–1.0 mm / s. Finally, the pre-fabricated optical fiber is annealed to eliminate internal stress.

9. The method for fabricating a flexible tactile sensor according to claim 6, characterized in that, The steps for setting positive and negative electrodes on the cladding using magnetron sputtering deposition include: First, use pre-fabricated optical fibers The plasma is used for cleaning, followed by drying. Next, electrodes are deposited only on both sides of the pre-fabricated optical fiber using a mechanical masking method or photolithography. Finally, the optical fiber after the electrodes are fabricated is subjected to heat treatment to release the deposition stress.

10. A detection method for a sensor, characterized in that, The detection is performed using the flexible tactile sensor with a dual-channel structure as described in any one of claims 1-5, and the steps include: The wavelength change signal of the core and the voltage change signal of the cladding are obtained to obtain the wavelength deviation value and the voltage deviation value; Establish a joint model and express it in reverse; The wavelength deviation and voltage deviation are solved using a joint model to obtain the strain caused by mechanical bending.

Images