Six-dimensional force tactile sensor based on mode-interference fiber structure and preparation method

Abstract

The present application relates to the technical field of tactile sensing, in particular to a six-dimensional force tactile sensor based on mode interference fiber structure and a preparation method thereof. The six-dimensional force tactile sensor comprises a rigid substrate, a flexible elastomer arranged on the substrate, and a sensing group arranged in the flexible elastomer. The sensing group is composed of at least three mode interference fibers uniformly arranged around the center of the sensing area. One end of the fiber extends from the bottom to the top of the flexible elastomer. By measuring the change of the light wave interference of each fiber, combining the temperature compensation of the reference fiber and the sensitivity matrix obtained by calibration, the six-dimensional force and torque vector is calculated by using the regularization least square method. The embodiment can solve the shortcomings of the six-dimensional force sensor in terms of electromagnetic interference resistance, flexible integration and miniaturization, and improve the multi-dimensional force demodulation accuracy and stability.

Description

Technical Field

[0001] This invention relates to the field of tactile sensing technology, specifically to a six-dimensional force tactile sensor based on a mode interference fiber structure and its fabrication method. Background Technology

[0002] Traditional six-dimensional force sensors mostly use strain gauges, capacitors, or piezoelectric structures. Although they are widely used in the field of industrial robots, they have certain limitations in terms of flexible integration, miniaturization, and resistance to electromagnetic interference.

[0003] In the process of realizing this invention, the inventors discovered that in the prior art, six-dimensional force sensors still face challenges in terms of anti-electromagnetic interference, flexible integration and miniaturization, making it difficult to meet the needs of high-precision measurement in complex environments, and the decoupling accuracy and stability of multi-dimensional forces need to be improved. Summary of the Invention

[0004] One of the objectives of this invention is to provide a six-dimensional force tactile sensor based on a modal interference fiber structure and its fabrication method, in order to address the challenges that existing six-dimensional force sensors still face in terms of electromagnetic interference resistance, flexible integration, and miniaturization, making it difficult to meet the needs of high-precision measurement in complex environments.

[0005] To solve the above-mentioned technical problems, the embodiments of the present invention are implemented as follows: In the first aspect, a six-dimensional force-tactile sensor based on a mode interference fiber structure is provided, comprising: a rigid substrate; A flexible elastomer is disposed on the side of the rigid substrate; A sensing group is disposed within the flexible elastic body and is arranged corresponding to the sensing area; The sensing group includes at least three mode interference optical fibers, which are uniformly arranged around the center of the sensing area. One end of each mode interference optical fiber extends from the side of the flexible elastomer close to the rigid substrate to the side away from the rigid substrate, and is used to sense forces and torques from different directions.

[0006] The second aspect also discloses a method for fabricating a tactile sensor, the steps of which include: The end faces of the mode interference fiber and the reference fiber were cut using a fiber optic cleaver and the surfaces were cleaned with anhydrous ethanol. A silver reflective film was deposited at the end of the mode interference fiber using vacuum physical coating technology, and a grating was photolithographically written on the reference fiber using femtosecond laser. A flexible tactile elastomer mold with fiber optic channels was fabricated, and fiber optic grooves were machined in a rigid substrate for arranging reference fiber optic components. The mode interference fiber is embedded in the flexible tactile elastomer along the prefabricated fiber channel and a slight pretension is applied. At the same time, the reference fiber is placed horizontally in the fiber groove and fixed. Liquid elastomer is poured into the mold, and after vacuum degassing, it is cured in an environment of 60~80℃. After curing, the flexible tactile elastomer is connected to the rigid substrate, and the lead-out ends of the mode interference fiber and the reference fiber are connected to the optical path system.

[0007] The third aspect also discloses a demodulation method for a six-dimensional force-tactile sensor based on a mode interference fiber structure, the steps of which include: Acquire the optical interference of each mode of the interferometric fiber in the sensing group, and the temperature center wavelength drift of the reference fiber component; The temperature change is obtained by calculating the temperature center wavelength drift, and then the temperature change is used to compensate for the optical wave interference to obtain the wavelength drift vector of the induction group. The sensitivity matrix is ​​obtained by calibrating the sensing group, and the wavelength drift vector is combined with the sensitivity matrix to establish a linear model; The linear model is solved by regularized least squares method to obtain the estimated values ​​of the six-dimensional force and torque vectors.

[0008] 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 six-dimensional force-tactile sensor based on a mode interference fiber structure, comprising: a rigid substrate; a flexible elastomer disposed on the side of the rigid substrate; and a sensing group disposed within the flexible elastomer and corresponding to the sensing area. The sensing group includes at least three mode interference fibers, which are uniformly arranged around the center of the sensing area. One end of each mode interference fiber extends from the side of the flexible elastomer close to the rigid substrate to the side away from the rigid substrate, for sensing forces and torques from different directions.

[0009] In this embodiment, modal interferometry fiber is used as the sensing element, which has excellent anti-electromagnetic interference capability, ultra-small size and lightweight characteristics, solving the problems of signal distortion and difficulty in miniaturization of traditional electrical six-dimensional force sensors in strong electromagnetic environments. Three or more modal interferometry fibers are evenly arranged around the center of the sensing area and extend in a spatially symmetrical manner, which can decouple the non-uniform strain field caused by the six-dimensional load into multiple independent optical response channels, improving the resolution and measurement accuracy of force and torque components. The flexible elastomer is set on the side of the rigid substrate and is firmly connected to it, which not only ensures the overall structural stability of the sensor, but also realizes flexible adaptation to the curved contact interface, expanding its applicability in robot grippers, wearable devices and medical palpation devices.

[0010] 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.

[0011] 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

[0012] Figure 1 A partial cross-sectional view of a six-dimensional force-tactile sensor based on FBG provided for an embodiment of the present invention; Figure 2 This is an embodiment of the present invention. Figure 1 A diagram from another perspective; Figure 3 This is a schematic diagram of an embodiment of the present invention, specifically an induction group; Figure 4 This is a schematic diagram of a demodulation system according to an embodiment of the present invention; Figure 5 The calibration curve of the normal force Fz; Figure 6 The calibration curve for the tangential force Fx; Figure 7 The calibration curve for the tangential force Fy; Figure 8 The torque Mx calibration curve is shown. Figure 9 The torque My calibration curve is shown. Figure 10 The torque Mz calibration curve is shown.

[0013] Markings in the image: 10. Mode interference fiber; 11. Reference fiber component; 20. Rigid substrate; 30. Flexible elastomer; 40. Broadband light source; 50. 1×2 coupler; 60. 1×4 coupler; 70. Single-channel FBG demodulator; H, included angle; F, sensing area. Detailed Implementation

[0014] 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.

[0015] 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.

[0016] Six-dimensional force sensors are key sensors commonly used in industrial production control and robot motion. Their measurement range includes three torque components (Mx, My, and Mz) and three force components (Fx, Fy, and Fz). As sensors that measure the forces and torques experienced by a robot's end effector when it interacts with the external environment or grasps a workpiece, six-dimensional force and torque sensors provide force-sensing information for robot force and motion control, playing a crucial role in realizing robot intelligence. They enable precise measurement of force and motion control in robots, thereby improving their operational accuracy and level of intelligence.

[0017] Modal interference fiber refers to an optical fiber structure that works based on the principle of multimode interference (MMI). The following modal interference fiber mainly refers to the single-mode-multi-mode-single-mode (SMS) optical fiber structure.

[0018] Before describing the embodiments of the present invention in detail, the design concept of the present invention will be summarized below.

[0019] This invention provides a six-dimensional force-tactile sensor based on a modal interference fiber structure, the specific implementation of which is as follows. Figure 1 As shown, the core of the inventive concept of this invention includes: using a rigid substrate 20 to provide mechanical anchoring and temperature reference, using a flexible elastomer 30 as a force-deformation conversion medium, embedding at least three mode interference optical fibers 10 in a spatially symmetrical manner, so that the axial strain response of the optical fiber and the six degrees of freedom (Fx, Fy, Fz, Mx, My, Mz) of the applied load form a calibrable coupling relationship; by demodulating the wavelength shift of the optical interference spectrum, the electrical signal path is avoided, the influence of electromagnetic interference is fundamentally eliminated, and the compact structure and flexible conformal integration are achieved by relying on the microscale characteristics of optical fiber.

[0020] The technical problem this embodiment aims to solve is that existing six-dimensional force sensors mostly employ electrical measurement methods such as resistance strain gauges, capacitance, or piezoelectricity. These methods have significant limitations in terms of electromagnetic interference resistance, flexible integration, and miniaturization, making it difficult to achieve highly stable and accurate synchronous measurement of six-dimensional force / torque in environments with strong electromagnetic interference, confined working spaces, or robot tactile perception scenarios requiring conformal fitting with curved flexible bodies. Especially in applications such as human-robot collaboration, minimally invasive surgical robots, and intelligent prostheses, sensors need to possess mechanical robustness, biocompatible interface adaptability, and electromagnetic silence. However, traditional electrical sensors are susceptible to stray field interference, difficult to embed in soft structures, and exhibit significant long-term drift.

[0021] For the first aspect, which is based on the same inventive concept, please refer to the appendix. Figure 1 , 2 Figure 3 also discloses a six-dimensional force-tactile sensor based on a mode interference fiber 10 structure, comprising: a rigid substrate 20; a flexible elastomer 30 disposed on the side of the rigid substrate 20; and a sensing group disposed within the flexible elastomer 30 and corresponding to the sensing area F. The sensing group includes at least three mode interference fibers 10, which are uniformly arranged around the center of the sensing area F. One end of each mode interference fiber 10 extends from the side of the flexible elastomer 30 near the rigid substrate 20 to the side away from the rigid substrate 20, for sensing forces and torques from different directions.

[0022] In this embodiment, the rigid substrate 20 provides mechanical support and thermal stability reference for the sensor, and is used to fix the flexible elastomer 30 and support the reference fiber optic component 11. The rigid substrate 20 is made of metal or hard alloy material, such as stainless steel, titanium alloy or aluminum alloy, and its surface is processed with fiber optic grooves to arrange the reference fiber optic component 11.

[0023] The flexible elastomer 30 is a polymer material layer disposed on the side of the rigid substrate 20, used to transmit external forces and undergo reversible elastic deformation; the flexible elastomer 30 is a silicone rubber or polyurethane elastomer with a Shore hardness range of 20A-60A and a thickness of 1mm-5mm set according to actual sensitivity and range requirements; it has a pre-fabricated optical fiber channel inside to accommodate and position the mode interference optical fiber 10; the flexible elastomer 30 is connected to the rigid substrate 20 by adhesive or mechanical fixation, and the connection interface ensures the continuity of force transmission and avoids slippage or debonding.

[0024] The sensing group is an optical sensing unit set within the flexible elastomer 30, corresponding to the sensing area F. The sensing group includes at least three mode interference fibers 10, the number of which can be three, four, or six, with three being optional, to reduce system complexity while ensuring decoupling capability. The mode interference fibers 10 are single-mode-multimode-single-mode (SMS) structure fibers, with the length of the multimode fiber sensitive section being 5 mm-10 mm, such as 6 mm, 7.5 mm, or 9 mm. The end face of the mode interference fibers 10 is coated with a silver reflective film to form a Fabry-Perot (FP) type reflective interference cavity, enhancing the contrast of the interference signal. The thickness of the silver reflective film is set to 80 nm-150 nm according to the optimization requirements of reflectivity in the visible to near-infrared band.

[0025] The mode interference fibers 10 are uniformly arranged around the center of the sensing region F. Within the cross-section of the flexible elastic body 30, the projections of each fiber axis are centrally symmetrical, and the included angles of adjacent fiber axes are equal. When the sensing group includes three mode interference fibers 10, the included angle of their projections in the cross-section is 120°. When it includes four fibers, the included angle H is 90°. This arrangement ensures a balanced response sensitivity to the force components in the x, y, and z directions and the moment components around the x, y, and z axes. The included angle H between each mode interference fiber 10 and the rigid substrate 20 is set to 30°-60°, and can be selected as 45°, to balance axial strain sensitivity and lateral disturbance rejection capability.

[0026] The modal interference fiber 10 extends from one end of the flexible elastomer 30 near the rigid substrate 20 to the side away from the rigid substrate 20. The fiber is inclinedly disposed within the flexible elastomer 30, with its proximal end fixed to the region near the rigid substrate 20 and its distal end extending to the top surface of the flexible elastomer 30. This extension method allows each fiber to generate differentiated axial strain due to local bending, shearing, and compression deformation of the elastomer when an external force is applied to the upper surface of the flexible elastomer 30, thereby exhibiting a distinguishable wavelength drift response in the spectral domain. The embedding depth, pretension, and cladding state of the fiber within the flexible elastomer 30 are adjusted according to actual process conditions, with the pretension controlled within the range of 0.1 N-0.5 N to avoid slack or overload.

[0027] In this embodiment, a three-level mechanical-optical coupling structure is constructed, consisting of a rigid substrate 20, a flexible elastomer 30, and a spatially symmetric mode interference fiber 10 array. The rigid substrate 20 provides a zero-point reference for temperature and displacement, the flexible elastomer 30 realizes the nonlinear mapping from macroscopic force / torque to microscopic strain field, and the spatially uniformly arranged mode interference fiber 10 deconstructs the strain field into multiple orthogonal optical channel responses, thereby simultaneously acquiring six-dimensional mechanical information in a single sensor.

[0028] The working process and principle are as follows: When the external six-dimensional load (Fx, Fy, Fz, Mx, My, Mz) acts on the upper surface of the flexible elastomer 30, the flexible elastomer 30 undergoes composite elastic deformation, including overall compression, local bending and shear torsion; this deformation is transmitted to each mode interference fiber 10 embedded therein, causing changes in its length, curvature and microbending degree, which in turn causes a shift in the characteristic valley wavelength in the multimode interference spectrum; since each fiber has a different spatial orientation, the direction of its strain principal axis is different, so the wavelength shift is directionally selective; by synchronously acquiring the wavelength shift vector of the interference spectrum of each fiber and combining it with the pre-calibrated sensitivity matrix, the original six-dimensional load components are calculated.

[0029] For example: Using a rigid rectangular stainless steel substrate 20 as a support, a layer of flexible silicone rubber elastomer 30 with a thickness of 3-mm and a Shore hardness of 40A is bonded to its side with silicone adhesive; three inclined optical fiber channels evenly distributed at 120° are prefabricated in a silicone rubber mold, with the channel axis making an angle H of 45° with the substrate plane; three SMS structure mode interference optical fibers with a multimode segment length of 7.5mm and a core diameter of 50μm are used, the far end face of the optical fibers is flatly cut with a fiber cleaver, and 100% of the fiber is coated using vacuum physical coating technology. A nm thick silver reflective film is embedded along the channel, and after applying a pretension of 0.3 N, liquid silicone rubber is injected. The film is then degassed under vacuum and cured at 70 °C for 4 hours. Finally, the three optical fiber leads are connected to a broadband light source, a 1×2 coupler, a 1×4 coupler, and a spectrometer to form a reflective wavelength demodulation system. The initial interference spectrum of each optical fiber is recorded in the unloaded state. Then, uniaxial forces and torques of known magnitudes are applied for calibration, and a linear sensitivity matrix S (3×6) between the six-dimensional load and the wavelength drift vector is established to achieve real-time demodulation of the six-dimensional force / torque.

[0030] In this embodiment, a modal interferometric fiber 10 is used as the sensing element, which has excellent anti-electromagnetic interference capability, ultra-small size and lightweight characteristics, solving the problems of signal distortion and difficulty in miniaturization of traditional electrical six-dimensional force sensors in strong electromagnetic environments. Three or more modal interferometric fibers 10 are uniformly arranged around the center of the sensing area F and extend in a spatially symmetrical manner, which can decouple the non-uniform strain field caused by the six-dimensional load into multiple independent optical response channels, improving the resolution and measurement accuracy of force and torque components. The flexible elastomer 30 is disposed on the side of the rigid substrate 20 and is firmly connected to it, which not only ensures the overall structural stability of the sensor, but also realizes flexible adaptation to the curved contact interface, expanding its applicability in robot grippers, wearable devices and medical palpation devices.

[0031] In a further embodiment, the six-dimensional force tactile sensor includes a reference fiber optic component 11, which is disposed within a rigid substrate 20.

[0032] In this embodiment, effective separation and compensation of temperature interference are achieved through the reference fiber optic component 11: since the reference fiber optic component 11 is rigidly encapsulated inside the substrate and does not participate in the mechanical response, its wavelength drift only reflects the pure temperature effect; since the reference signal shares the same optical path and demodulation hardware with the sensing group, common-mode interference such as light source fluctuation and coupling loss can be eliminated; thus, this application improves the long-term stability and measurement reliability of the six-dimensional force tactile sensor under non-constant temperature conditions without adding a complex temperature control device.

[0033] In this embodiment, the reference fiber optic component 11 is used to monitor changes in ambient temperature. It is completely encapsulated within the rigid substrate 20, does not contact the flexible elastomer 30, and does not bear externally applied mechanical loads. The reference fiber optic component 11 is a fiber Bragg grating. The reference fiber optic element 11 is a temperature-sensitive fiber optic device, such as a long-period fiber grating (LPFG) or a temperature sensing unit based on microstructured fiber optics. This embodiment does not impose any special limitations on this. The axial direction of the reference fiber optic element 11 is parallel to the surface of the rigid substrate 20, or it can be set to other orientations according to the internal spatial layout of the rigid substrate 20, as long as it does not participate in mechanical response and only responds to temperature changes. The reference fiber optic element 11 is fixed in the rigid substrate 20 by adhesive bonding, slotted snap-fit, or laser welding. Its installation position is set in any stress-free area inside the substrate according to actual processing requirements, such as in a fiber optic groove reserved on the sidewall of the substrate. The size and shape of this fiber optic groove are designed to adapt to the outer diameter and bending radius of the selected reference fiber optic element 11. For example, when the outer diameter of the reference fiber optic element 11 is 125 μm, the width of the fiber optic groove is set to 130~150 μm and the depth to 80~100 μm to ensure that the fiber is laid straight and is not deformed by compression.

[0034] For example, during the sensor assembly stage, a straight fiber optic groove with a depth of 90μm and a width of 140μm is first machined on the surface of the rigid metal substrate 20, with the groove extending along the length of the substrate. The FBG reference fiber component 11, with a center wavelength of 1550nm and a grating length of 10mm, is horizontally placed into the groove, and both ends are fixed with UV-curable adhesive. After the flexible elastomer 30 is bonded to the rigid substrate 20, the free ends of the three mode interference fibers 10 are led out through the inclined channel inside the elastomer and connected to a 1×4 coupler together with the reference fiber component 11, and finally connected to the spectrometer demodulator. When the ambient temperature rises from 25℃ to 45℃, the center wavelength of the reference FBG drifts about 200pm in the long-wave direction. Based on this, ΔT = 20℃ is deduced, and the original drift data of the three sensing fibers are corrected simultaneously, so that the fluctuation amplitude of the six-dimensional force calculation result is reduced.

[0035] In a further embodiment, the axis of the mode interference fiber 10 forms an angle H with the side surface of the rigid substrate 20; The included angle H is an acute angle, and the angle of the included angle is controlled between 30° and 60°.

[0036] In this embodiment, the angle H between the axis of the mode interference fiber 10 and the side surface of the rigid substrate 20 is limited to an acute angle range of 30°-60°. Therefore, while ensuring sufficient axial strain response to the normal force Fz, the coordinated sensing capability of the tangential forces Fx and Fy and the rotational moments Mx, My, and Mz around each axis is significantly enhanced. Combined with the spatial configuration of the three fibers evenly distributed at 120° within the cross section, the information redundancy and decoupling stability of the six-dimensional force signal are improved, thereby improving the overall measurement accuracy and robustness of the sensor.

[0037] In this embodiment, the angle formed between the axis of the mode interference fiber 10 and the side surface of the rigid substrate 20 can refer to the angle H between the arrangement direction of the mode interference fiber 10 in the flexible elastomer 30 and the normal direction of the side surface of the adjacent rigid substrate 20. The angle H can be 30°, 35°, 40°, 45°, 50°, 55° or 60°, or any angle value in the range of 30°–60°. Specifically, it can be set according to the sensor's response sensitivity balance requirements for the normal force Fz and the tangential forces Fx and Fy. This embodiment does not impose any special limitation on this.

[0038] For example, during the fabrication process, the angle control is achieved by prefabricating an inclined optical fiber channel in a flexible tactile elastomer mold; the optical fiber channel is inclined at 30°-60° to the plane of the rigid substrate 20 and is evenly distributed along the center of the sensing area F; when the mode interference optical fiber 10 is embedded into the flexible elastomer 30 along the channel, a slight pretension is applied to ensure that it maintains a stable tilt angle after curing; after curing, the tilt angle is covered and fixed by the elastomer material to maintain its geometric consistency and mechanical transmission reliability during the sensor's service.

[0039] In a further embodiment, the flexible elastomer 30 is silicone rubber or polyurethane elastomer; the rigid substrate 20 is metal or hard alloy material; and the rigid substrate 20 is provided with fiber optic slots for arranging the reference fiber optic component 11.

[0040] In this embodiment, the flexible elastomer 30 is made of silicone rubber or polyurethane elastomer, which has moderate mechanical compliance and deformation transmission fidelity, and can accurately respond to small six-dimensional loads; the rigid substrate 20 is made of metal or hard alloy material, which can provide a high-rigidity support reference and suppress parasitic deformation in non-target directions; the rigid substrate 20 is provided with fiber optic grooves, which can realize the precise positioning of the reference fiber optic component 11, stress-free encapsulation and long-term mechanical stability assurance, thereby improving the temperature compensation accuracy and the overall repeatability of the sensor.

[0041] The flexible elastomer 30 and the rigid substrate 20 are spatially coordinated through an optical fiber groove structure: the flexible elastomer 30 covers the side of the rigid substrate 20 and wraps the sensitive section of the mode interference fiber 10, while the reference fiber 11 is constrained in the optical fiber groove inside the rigid substrate 20, and is in a state of no strain or near zero strain; when an external six-dimensional force is applied to the surface of the flexible elastomer 30, its deformation is mainly concentrated inside the flexible elastomer 30, and the mode interference fiber 10 undergoes axial tension / compression and bending coupling strain, while the reference fiber 11 is rigidly constrained by the rigid substrate 20 and far away from the force-bearing area, and is basically unaffected by mechanical loads, only responding to changes in ambient temperature, thereby providing a stable reference for subsequent temperature drift compensation.

[0042] For example, in the fabrication process, a rectangular fiber groove with a depth of 180 μm and a width of 160 μm is first processed on the surface of the rigid metal substrate 20 using micro-milling or laser etching. The groove length is adapted to the length of the reference FBG and a margin is reserved for lead-out at both ends. Then, the reference FBG is horizontally placed into the groove and fixed by spot application of UV-curable adhesive. Next, three SMS mode interference fibers 10 are embedded in the silicone rubber mold channel with a 45° tilt angle and a 120° circumferential uniform distribution and a pretension of 0.5%. After mold closing, liquid silicone rubber is injected, and the mixture is vacuum degassed and cured at 70°C for 6 hours. Finally, the cured flexible elastomer 30 is bonded to the rigid substrate 20 with the fiber groove using structural adhesive, so that the root of the mode interference fiber 10 forms a stable transition connection with the side of the substrate, and the end face of the reference FBG is flush with the port of the fiber groove, which facilitates optical path docking.

[0043] Based on the same inventive concept, a second aspect also discloses a method for fabricating a tactile sensor, the method comprising the following steps: Step 01: Cut the end faces of the mode interference fiber 10 and the reference fiber 11 with a fiber optic cleaver and clean the surfaces with anhydrous ethanol. The mode interference fiber 10 can be a special optical fiber composed of a single-mode-multimode-single-mode (SMS) structure, capable of supporting multiple propagation modes and generating a stable interference spectrum. The reference fiber component 11 can be an optical fiber component used to provide a temperature and long-term drift reference, specifically a Bragg grating (FBG) type reference fiber in this embodiment. End face cleaving refers to using a high-precision fiber cleaver to make a flat cut along the direction perpendicular to the fiber axis of the mode interference fiber 10 and the reference fiber component 11 to obtain an end face with good optical performance. Anhydrous ethanol cleaning refers to using anhydrous ethanol as an organic solvent to remove residual cutting debris, grease, and oxides from the end face, ensuring the cleanliness of the interface for subsequent coating or grating writing. The purpose of this step is to provide an initial optical end face foundation with high reflectivity and high diffraction efficiency for subsequent coating and grating writing, avoiding the introduction of impurities that would lead to attenuation of the reflection signal or degradation of the grating quality.

[0044] For example, in a clean operating table, a Fujikura CT-30 fiber optic cleaver can be used to cut the end faces of three mode interference fibers 10 and one reference fiber 11, respectively. The cutting blade depth is set to 12μm and the feed speed is 0.8mm / s. After cutting, the ends of each fiber are immersed in an ultrasonic cleaning tank containing analytical grade anhydrous ethanol, with the ultrasonic power set to 80W and the frequency 40kHz, and the cleaning is carried out for 120s. Then, they are dried with high-purity nitrogen and placed in a Class 1000 clean environment for later use.

[0045] Step 02: A silver reflective film is deposited on the end of the mode interference fiber 10 using vacuum physical coating technology, and a grating is photolithographically written on the reference fiber 11 using a femtosecond laser. In this embodiment, the vacuum physical coating technology refers to a coating process in which silver atoms are deposited on the end face of an optical fiber to form a continuous metal thin film through heating evaporation or sputtering within a vacuum chamber. This results in a high-reflectivity metal film layer with a thickness controlled within the range of 80-120 nm at the end of the mode interference fiber 10, with an average reflectivity greater than 95% in the visible to near-infrared band. The femtosecond laser photolithography grating refers to using femtosecond laser pulses to induce periodic modulation of the refractive index within the fiber core, thereby forming a Bragg grating structure with a stable center wavelength. The purpose of this step is to separately construct the temperature / strain dual-parameter decoupling reference for the reflective interference cavity of the mode interference fiber 10 and the reference fiber 11, enabling effective separation of wavelength drift caused by load and drift caused by environmental disturbances.

[0046] For example, the three mode interference fibers 10, after the above treatment, can be fixed on the sample stage of a vacuum coating machine, and a vacuum can be drawn until... After that, with A 95nm thick silver film was deposited on the end face at a certain rate. During the deposition process, high-purity argon gas was simultaneously introduced to maintain stable chamber pressure. At the same time, the reference fiber optic component 11 was clamped on a three-dimensional precision displacement platform. A femtosecond laser with a center wavelength of 1030nm and a pulse width of 350fs was used to write a uniform FBG with a period of 532.6nm in the fiber core region at a single pulse energy of 2.1μJ and a scanning speed of 0.8mm / s. After writing, the grating was annealed to improve its thermal stability.

[0047] Step 03: Fabricate a flexible tactile elastomer mold with fiber optic channels, and machine fiber optic grooves in the rigid substrate 20 for arranging reference fiber optic components 11; In this embodiment, the flexible tactile elastomer mold with fiber optic channels refers to a silicone or polyurethane negative mold designed according to the target sensor structure. The mold contains a pre-set through-channel microchannel that perfectly matches the spatial orientation of the mode interference fiber 10. The channel diameter is slightly larger than the fiber's outer diameter, for example, 10-20 μm larger. The channel axis forms a 30°-60° angle H with the side of the rigid substrate 20 and is uniformly distributed within the cross-section. The fiber optic groove refers to a rectangular or U-shaped groove machined on or inside the rigid substrate 20 to accommodate and limit the reference fiber optic component 11. The groove depth matches the outer diameter of the fiber cladding, and the groove width has a 0.05-0.1 mm assembly allowance. This step aims to ensure the spatial arrangement accuracy of the mode interference fiber 10 in the elastomer and the repeatability of the reference fiber optic component 11's installation in the substrate through the structured guidance of the mold and substrate, providing a geometric constraint basis for subsequent integrated molding.

[0048] The optical fiber channel is inclined at an angle H of 30°-60° to the side of the rigid substrate 20, and uniformly distributed at 120° along the center of the sensing region F, so that the three mode interference fibers 10 form a spatially non-coplanar sensitive array structure within the flexible elastomer 30. This inclined arrangement ensures that after the mode interference fibers 10 are embedded in the flexible elastomer 30, their multimode fiber sensitive segments are no longer parallel to the surface of the rigid substrate 20, but rather obliquely pierce the flexible elastomer 30 at a preset angle. Therefore, when subjected to a normal force (Fz) perpendicular to the substrate plane or a torsional moment (Mz) normal to the substrate plane, they produce a distinguishable axial strain response. In this embodiment, when external forces or moments in different directions act on the sensing region F, the fibers produce differentiated strain responses due to differences in spatial orientation, resulting in identifiable differences in the wavelength shift of their interference spectra. Embedding the mode interference fiber 10 into the flexible tactile elastomer along the prefabricated fiber channel to form a synergistic effect not only enhances the independent sensing capability of the normal force Fz and the torsional torque Mz, but also strengthens the decoupling degree between the six-dimensional force signals, providing a reliable physical basis for subsequent linear modeling and regularized least squares solution based on the sensitivity matrix.

[0049] In one embodiment, a flexible elastomer 30 mold with a channel position error of less than ±15 μm can be obtained by using a CNC engraving machine to process the microchannels of the mold based on 3D modeling data. A rigid substrate 20 with fiber optic groove depth tolerance controlled within ±2 μm can be obtained by using laser confocal scanning to obtain the surface morphology of the rigid substrate 20 and adaptively correcting the milling path. Furthermore, an elastomer preform with 100% channel integrity can be obtained by using a microfluidic-assisted casting process to pre-place temporary support wires within the mold channel to prevent channel collapse during glue pouring. This application obtains a high-fidelity, reproducible fiber optic spatial guidance structure based on any of the above methods, ensuring the consistency of the multi-channel response of the sensor and the repeatability of calibration.

[0050] For example: it can be based on Figure 3 Based on the spatial relationship shown, a 3D model of the mold containing three channels, an inclination angle of 45°, and a circumferential interval of 120° was created using SolidWorks. The model was then imported into a CNC engraving machine, and a silicone master mold material with a hardness of Shore A 40 was selected to process a female mold with channels. Simultaneously, a straight fiber optic groove with a length of 15 mm, a width of 0.25 mm, and a depth of 0.125 mm was milled on the surface of an aluminum rigid substrate 20, with a groove bottom roughness Ra≤0.4 μm.

[0051] Step 4: Embed the mode interference fiber 10 into the flexible tactile elastomer along the prefabricated fiber channel and apply a slight pretension. At the same time, place the reference fiber 11 horizontally in the fiber groove and fix it. Pour liquid elastomer into the mold, degas it under vacuum, and then cure it in an environment of 60~80℃. In this embodiment, applying slight pre-tension when embedding the mode interference fiber 10 into the flexible tactile elastomer refers to the initial axial tension applied during the fiber embedding process, the magnitude of which is controlled within the range of 0.5% to 2.0% of the fiber's breaking strength, for example, approximately 0.05 to 0.2 N for a single-mode fiber, to eliminate slack bending and ensure that the fiber remains straight during the elastomer's curing and shrinkage process. An uncured silicone rubber or polyurethane precursor mixture, with a viscosity controlled at 2000 to 5000 cP to balance flowability and air bubble removal, is poured into a mold. The mold is then left to stand for 10 to 15 minutes under a vacuum better than −0.095 MPa to allow the incorporated air to escape fully. The mold is then placed in a constant temperature oven, heated to 70°C at a rate of 2°C / min, and held for 90 minutes to complete the crosslinking reaction. This step achieves integrated encapsulation of the fiber and the flexible substrate, ensuring the fiber's mechanical zero-point stability while endowing the sensor with good flexibility and impact resistance.

[0052] For example: Three silver-coated mode interference optical fibers 10 are sequentially inserted into the corresponding channels of the mold. A miniature tension meter is connected to the end of each fiber. A pretension of 0.12N is applied and locked by adjusting the knob. The reference optical fiber 11 is horizontally embedded into the fiber groove of the rigid substrate 20, and a small amount of UV adhesive is applied to fix both ends. Then, liquid silicone rubber with components A and B mixed in a 10:1 ratio is slowly injected into the mold, tilted at 15° and gently shaken to remove air bubbles. After being vacuumed in a vacuum drying oven for 12 minutes, it is transferred to a 70° oven and kept at a temperature of 90 minutes to complete the curing.

[0053] Step 5: After curing, connect the flexible tactile elastomer to the rigid substrate 20, and connect the mode interference fiber 10 and the reference fiber lead-out end to the optical path system.

[0054] The connection between the flexible tactile elastomer and the rigid substrate 20 refers to the structural integration of the two through interface bonding or mechanical fixation. The connection interface must cover the fiber optic exit and have sealing and mechanical buffering functions. The optical path system can be a reflective wavelength detection system composed of a broadband light source, a 1×2 fiber coupler, a 1×4 fiber coupler, a circulator, and a spectral demodulator. It is used to collect the wavelength shift of the interference spectral valleys of each mode interference fiber 10 and the center wavelength drift of the reference FBG. This step completes the physical packaging of the sensor and the construction of the optical link, enabling each fiber channel to have independent measurability and providing a standardized input interface for subsequent demodulation.

[0055] In one embodiment, interfacial bonding can be achieved by applying two-component epoxy resin adhesive along the contact edge between the elastomer and the substrate and accelerating curing with UV assistance, with the adhesive layer thickness controlled at 0.1~0.3mm; alternatively, mechanical fixing can be achieved by using a micron-level positioning clamp in conjunction with M2.5 stainless steel screws to press the elastomer into the pre-reserved mounting holes on the substrate, with the pre-tightening torque set at 0.15N·m.

[0056] For example: Place the cured flexible tactile elastomer on top of the rigid substrate 20, align the exit positions of the three mode interference optical fibers 10 with the fiber slot outlet of the substrate, apply epoxy glue evenly along the circumference, irradiate with ultraviolet light for 30 seconds for initial curing, and then place it in a 70℃ oven for post-curing for 60 minutes; connect the reference optical fiber 11 and the exit ends of the three mode interference optical fibers 10 to the input ports of a 1×2 coupler, and connect them to the spectrometer after being split by a 1×4 coupler to complete the optical path connection.

[0057] In this embodiment, through the coordinated control of key processes such as fiber end-face processing, silver film coating, FBG writing, mold guidance, pre-tension embedding, gradient curing, and structural integration, high-precision, low-stress, and repeatable integrated packaging of the mode interference fiber 10 and the flexible elastomer 30 is achieved. By utilizing the spatial arrangement constraints and pre-tension mechanism of the fiber channel, fiber bending instability caused by the shrinkage of the flexible substrate is effectively suppressed. Based on the functional division of labor between the reference fiber 11 and the mode interference fiber 10, a temperature-strain decoupled optical measurement architecture is constructed. Ultimately, a fiber optic tactile sensor with six-dimensional force / torque resolution, excellent long-term operational stability, and high feasibility for mass production is obtained.

[0058] Based on the same inventive concept, a third aspect also discloses a demodulation method for a six-dimensional force-tactile sensor based on a mode interference fiber structure, the steps of which include: Step 100: Obtain the optical interference of each mode interference fiber 10 in the sensing group, and the temperature center wavelength drift of the reference fiber 11.

[0059] Wherein, the optical wave interference quantity of each mode interference fiber 10 in the sensing group refers to the center wavelength position value (unit: nm) of the main interference valley in the reflection interference spectrum generated by each mode interference fiber 10 under broadband light source excitation. The center wavelength shifts with the axial strain of the multimode segment of the fiber. The optical wave interference quantity characterizes the comprehensive deformation response of the corresponding fiber under the current load.

[0060] The temperature center wavelength drift of the reference fiber component 11 can refer to the Bragg wavelength shift of the reference fiber Bragg grating embedded inside the rigid substrate 20 and unaffected by mechanical loads in the same temperature field. It is only sensitive to temperature changes and does not respond to six-dimensional forces or torques; this parameter is used to characterize the degree of common-mode interference of ambient temperature fluctuations on the entire sensing system.

[0061] In this embodiment, the reflection spectra of each mode of the interferometric fiber 10 are acquired in real time by a broadband spectral demodulator, and the center wavelengths of each interference valley are extracted by Gaussian fitting or centroid algorithm to obtain the first set of initial state optical wave interference quantity sequences. Compared with the current state The difference between the two is used to obtain the interference of each optical fiber wave. In another embodiment, the initial reference wavelength can be obtained by synchronously acquiring the center wavelength of the reference FBG reflection peak using the built-in wavelength calibration channel of the spectrometer. Compared with the current reference wavelength The difference between the two values ​​indicates the temperature center wavelength shift. Furthermore, four optical signals are coupled in parallel to the same spectrometer via a 1×4 fiber coupler, connecting three induction fibers and one reference FBG respectively. All four wavelength data sets are acquired simultaneously in a single scan. The raw spectral response data used for subsequent temperature compensation and modeling are obtained based on any of the above methods.

[0062] For example, when the six-dimensional force tactile sensor is integrated into the tip of a robot finger, and the finger touches a heat source surface with a temperature rise of 5°C and applies normal pressure, the spectrometer simultaneously collects the interference valley wavelengths of the three mode interference fibers 10. At this time, the wavelengths drift by +8.2 pm, +7.9 pm, and +8.5 pm, respectively. And with reference to the FBG wavelength, the wavelength drifts by +12.6 pm. Thus, the uncompensated set of light wave interference quantities and independent temperature perturbation parameters are obtained.

[0063] Step 200: Calculate the temperature change by measuring the temperature center wavelength drift, and then compensate the light wave interference by measuring the temperature change to obtain the wavelength drift vector of the induction group.

[0064] In a further embodiment, the calculation of the temperature change by the temperature center wavelength drift involves substituting the temperature center wavelength drift into a formula to calculate the temperature change of the ambient temperature. The formula is as follows: ,in, This is the temperature sensitivity coefficient. This is the wavelength shift. This refers to the change in temperature. The method of temperature compensation for optical wave interference by temperature change to obtain the wavelength drift vector of the sensing group is to subtract the temperature change from the total wavelength drift of each mode interference fiber 10 of the sensing group to obtain the wavelength drift vector caused only by the load.

[0065] The optical wave interference quantity can refer to the center wavelength position value corresponding to the main interference valley in the reflection interference spectrum generated by each mode interference fiber 10 under broadband light source excitation. The center wavelength shifts with the axial strain of the multimode segment of the fiber. The optical wave interference quantity characterizes the comprehensive deformation response of the corresponding fiber under the current load.

[0066] The calculation of temperature change by the temperature center wavelength drift can refer to using the temperature and wavelength response relationship of the reference fiber optic component 11 to calculate the actual temperature change. This is converted to the corresponding ambient temperature change ΔT. This conversion is based on the fundamental principle of FBG temperature sensing, namely, the linear relationship between center wavelength drift and temperature change. Temperature compensation for the optical interference can be achieved by subtracting the drift component caused by temperature change from the total wavelength drift of each mode interference fiber 10, thereby separating the effective wavelength drift caused only by mechanical load. The wavelength drift vector of the sensing group can be a three-dimensional column vector reflecting only the six-dimensional mechanical response after temperature compensation, denoted as... .

[0067] An embodiment may be based on The relationship is used to inversely deduce ΔT, and then substituted into... This application can also perform channel-by-channel compensation; for example, it can also use a method of joint lookup table and interpolation based on the temperature sensitivity coefficients of multiple channels to perform compensation. Dynamic temperature term stripping is performed; furthermore, this application can also use a method based on online updated temperature drift baseline and sliding window deviation correction to... Real-time temperature compensation is performed. The pure mechanical wavelength drift vector, after eliminating temperature interference, is obtained based on any of the above methods. This ensures that it only carries six-dimensional load information: Fx, Fy, Fz, Mx, My, and Mz.

[0068] In this embodiment, a reproducible quantitative inversion mechanism for ΔT is established by combining the temperature center wavelength drift of the reference fiber 11 with the calibration coefficient. Then, based on the differentiated temperature response characteristics of each mode interferometric fiber 10, the measured total drift is subtracted in a targeted manner, and the final output is a wavelength drift vector caused only by the load. This collaborative process achieves accurate identification and channel-level separation of temperature crosstalk, ensuring the physical purity and engineering reproducibility of the wavelength drift vector, and providing a pollution-free, high-fidelity original data foundation for subsequent sensitivity matrix modeling and regularization solution in this application.

[0069] For example: when measured by reference FBG Substitute have to If the original interferometric quantity of a certain mode interferometric fiber 10 is +8.2 pm, then after compensation... = 8.2 -10.5×1.2 =-4.4pm; similarly calculate the other two channels to finally form The three-dimensional wavelength drift vector is used as a clean input for subsequent modeling.

[0070] Step 300: The sensitivity matrix is ​​obtained by calibrating the sensing group, the optical wave interference quantity is combined with the sensitivity matrix, and a linear model is established.

[0071] The sensitivity matrix obtained by the induction group calibration can refer to the following: during the calibration phase, a known uniaxial load is applied to each independent degree of freedom (Fx, Fy, Fz, Mx, My, Mz) in the six-dimensional load space, and the corresponding wavelength drift response is recorded simultaneously. A 3×6-dimensional mapping matrix S is constructed through linear regression or least squares fitting, with each column characterizing the comprehensive influence weight of a certain load component on the optical wave interference of the three mode interferometric fibers 10. Combining the optical wave interference with the sensitivity matrix can refer to the above-obtained... As the observed output, S serves as the system response parameter, and a linear equation is established with the six-dimensional load W as the unknown variable; the linear model can refer to the mapping relationship being expressible under the assumptions of small deformation and linear elasticity as follows: ,in To measure the noise vector. This model embodies the differentiated coupling response mechanism of three tilted mode interferometric fibers 10 under a geometric constraint of 120° circumferential distribution and approximately 45° tilt angle to a six-dimensional load.

[0072] In this embodiment, S is constructed using a method of uniaxial successive loading and least squares fitting; alternatively, S can also be constructed using a method of multiaxial collaborative loading and orthogonal experimental design; furthermore, S can be constructed using a method of physical modeling initial value guidance and iterative correction based on measured data. This application obtains a sensitivity matrix S with good condition number and physical interpretability based on any of the above methods, making... A stable and reversible mathematical relationship is formed between W and W.

[0073] For example, loads of Fx = 1 N, 2 N, and 3 N can be applied sequentially on a calibration platform, and the corresponding values ​​can be recorded. The sample was fitted to obtain the first column of S. Similarly, the remaining five columns were calibrated to finally obtain the S sensitivity matrix. The above results... Substitution This constitutes the linear model to be solved.

[0074] Appendix Figure 5 The calibration curve of the tangential force Fz shows that linear fitting yields a sensitivity of approximately 14.96 pm / N, and a correlation coefficient R² of approximately 0.9975; (See attached image) Figure 6 The calibration curve of the tangential force Fx shows that the fitting results indicate a sensitivity of approximately 10.31 pm / N and a correlation coefficient of... Approximately 0.9951; Appendix Figure 7 The tangential force Fy calibration curve shows that the fitting results indicate a sensitivity of approximately 9.58 pm / N and a correlation coefficient R² of approximately 0.9939. (See attached image.) Figure 8 The torque Mx calibration curve shows that the fitting results indicate a sensitivity of approximately 39.42 pm / (N·m) and a correlation coefficient R² of approximately 0.9219. (See attached image.) Figure 9 The torque My calibration curve shows that the fitting results indicate a sensitivity of approximately 40.12 pm / (N·m) and a correlation coefficient R² of approximately 0.8185. (See attached...) Figure 10 The torque Mz calibration curve shows that the fitting results indicate a sensitivity of approximately 46.27 pm / (N·m) and a correlation coefficient R² of approximately 0.9265. These curves not only verify the sensor's linear response to normal force but also lay the foundation for subsequent decoupled calculations of multi-dimensional force / torque, ensuring the accuracy and stability of the six-dimensional force measurement results.

[0075] In a further embodiment, the step of combining the wavelength drift vector with the sensitivity matrix calibrated by the sensing group and establishing a linear model is as follows: The sensitivity matrix is ​​obtained by applying known loads to the sensing group from six directions. The six directions can refer to the six degrees of freedom components of a six-dimensional force / torque, i.e., three-dimensional translational forces. , , and triaxial torque , , ; In one embodiment, the elements of each column of the sensitivity matrix S are determined by applying a uniaxial load and acquiring the corresponding wavelength drift. Alternatively, this application may determine the elements of each column of the sensitivity matrix S by controlling a mechanical loading platform to apply a stepped force / torque along a specified degree of freedom direction based on a preset load sequence, and simultaneously recording the wavelength drift response of the three mode interference fibers 10. Furthermore, this application may also determine the elements of each column of the sensitivity matrix S by outputting a load signal with known amplitude and direction from a high-precision six-dimensional force calibration stage, stabilizing the load value under closed-loop feedback, and acquiring steady-state wavelength drift data.

[0076] In this embodiment, a six-dimensional force-tactile sensor based on FBG is fixed on a calibration platform, with the sensing area F facing the loading direction; standard weights or servo actuators are sequentially applied along the positive x-axis with pure force loads of 0.5N, 1.0N, 1.5N, and 2.0N. The remaining degrees of freedom are strictly constrained; the wavelength drift of the three mode interferometric fibers after temperature compensation under each loading is simultaneously acquired. , , ;right Load and each Perform linear fitting to obtain the slope , , The first column of the sensitivity matrix S ; and so on, until completion. , , , , A total of six single-axis calibrations were performed, which were then spliced ​​together to form a 3×6 sensitivity matrix S, the mathematical form of which is as follows: .

[0077] In a further embodiment, the rows of the sensitivity matrix correspond to the working channels of the mode interference fiber 10, and the columns correspond to the six components of the six-dimensional force. As shown in the sensitivity matrix S above, each row represents a working channel of the mode interference fiber 10, i.e., the first row is FBG1, the second row is FBG2, and the third row is FBG3; the columns represent... , , , , A total of six single-axis calibrations were performed.

[0078] In this embodiment, the wavelength drift vector is combined with the sensitivity matrix to obtain a linear model; the linear model is as follows: ,in, Let W be the compensated wavelength drift vector, and W be the six-dimensional force / torque vector to be determined. This is the sensitivity matrix; To measure the noise vector.

[0079] In an example, the temperature-compensated wavelength drift vector was obtained during an actual measurement. ; Call up the sensitivity matrix S obtained from calibration; Substitute it into the model That is, to construct an overdetermined linear system with 3 equations and 6 unknowns, providing input for subsequent regularized least squares solution.

[0080] In the embodiment, the physical driven calibration of the sensitivity matrix S and the wavelength drift vector The model combines structural alignment with S with linear modeling of the noise term ε. This model inherits the experimental reliability of uniaxial calibration while preserving the integrity of the six-dimensional coupled response, avoiding the simplification distortion introduced by theoretical modeling. Based on this, the model is formed... The relationship forms the only mathematical bridge from optical measurement signals to six-dimensional mechanical vector calculations, supporting the feasibility and accuracy of regularized least squares solutions.

[0081] Step 400: Solve the linear model using the regularized least squares method to obtain the estimated value of the six-dimensional force / torque vector.

[0082] In a further embodiment, the method of solving the linear model using regularized least squares involves constructing an objective function from the linear model formula using regularized least squares, then differentiating the objective function to derive the analytical solution formula, and finally obtaining the estimated value of the six-dimensional force / torque vector based on the analytical solution formula.

[0083] Regularized least squares can refer to introducing regularized least squares into the traditional least squares objective function. Norm regularization terms are used to suppress noise amplification and matrix ill-conditioned effects during the solution process of underdetermined systems; this method does not rely on pseudo-inverse operations on the sensitivity matrix S, but ensures the numerical stability of the solution by constructing a constrained optimization problem; the estimates of the six-dimensional force and moment vectors can refer to the solutions obtained from the solution. Each of its components is the optimal unbiased estimate of the true load.

[0084] The derivative of the objective function is as follows: In practice, this can be achieved using several sets of known loads. and the corresponding measurement wavelength drift Constructing the calibration dataset: Let It is a 3×N matrix. Given a 6×N matrix, the sensitivity matrix S can be estimated using the following formula in the least squares sense: .

[0085] For measurements under unknown load conditions, given the temperature-compensated wavelength drift vector Δλ', the six-dimensional load estimation vector W should satisfy... .because It is a 3×6 matrix, and the system of equations is underdetermined.

[0086] To obtain a unique and stable solution from an underdetermined system, the objective function is solved using the Tikhonov regularization framework: , Among them, the first item The second term represents the residual between the model's predicted values ​​and the actual measured values, and is required to be minimized. This is the regularization term. Here, α>0 is the regularization parameter, used to suppress noise and avoid dedivergence.

[0087] When α→0 and When the solution has full row rank, it degenerates into a weighted least squares pseudo-inverse, leading to the derivation of the analytical solution formula: , in, This is the transpose of the sensitivity matrix. It is a 6×6 identity matrix.

[0088] In this embodiment, a six-dimensional demodulation algorithm is used for calculation. The specific steps include: First, during the calibration phase, a sufficient number of sets of six-dimensional loads are collected. and corresponding ,calculate Next, during the online measurement phase, ΔT is calculated based on the FBG wavelength change of the reference fiber optic component 11, and temperature compensation is performed on the FBG of the three mode interferometric fibers 10 to obtain... Furthermore, based on the pre-selected α and ,according to Calculate the six-dimensional load estimate; finally, optionally... Perform physical constraint corrections, such as saturation and symmetry constraints, to improve the physical consistency of the results.

[0089] For example: We could set the regularization parameter α = 0.01, and then... Substitution Calculated This means that the system identifies the current normal pressure of 0.29N, the lateral thrust of 0.12N, and the torsional moment about the Z-axis of 0.07N·m.

[0090] In summary, by acquiring the interference of the sensing group's optical waves and the temperature wavelength drift of the reference fiber, dual-channel synchronous acquisition of the original optical response is achieved. The temperature change is calculated based on the temperature center wavelength drift, and this is used to uniformly compensate each sensing channel, effectively eliminating common-mode temperature interference. A linear mapping relationship between wavelength drift and six-dimensional load is established using the calibrated sensitivity matrix, transforming the physical sensing problem into a mathematical inversion problem. Finally, the regularized least squares method is used to solve the underdetermined linear system, which, while ensuring the physical interpretability of the solution, significantly suppresses the estimation distortion caused by measurement noise and matrix ill-conditioning, thereby achieving high-precision, high-robustness, and temperature-drift-resistant real-time demodulation of six-dimensional force-tactile information.

[0091] Based on the same inventive concept, the fourth aspect also discloses an application method for a six-dimensional force tactile sensor based on a mode interference fiber 10 structure. The six-dimensional force tactile sensor based on the mode interference fiber 10 structure is applied in wearable health monitoring, robot tactile sensing and human-computer interaction and other application scenarios.

[0092] 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 six-dimensional force-tactile sensor based on a modal interference fiber structure, characterized in that, include: Rigid substrate; A flexible elastomer is disposed on the side of the rigid substrate; A sensing group is disposed within the flexible elastic body and is arranged corresponding to the sensing area; The sensing group includes at least three mode interference optical fibers, which are uniformly arranged around the center of the sensing area. One end of each mode interference optical fiber extends from the side of the flexible elastomer close to the rigid substrate to the side away from the rigid substrate, and is used to sense forces and torques from different directions.

2. The six-dimensional force-tactile sensor according to claim 1, characterized in that, The six-dimensional force-tactile sensor based on the mode interference fiber structure also includes a reference fiber element disposed within the rigid substrate.

3. The six-dimensional force-tactile sensor according to claim 1, characterized in that, The axis of the mode interference fiber forms an angle with the side surface of the rigid substrate; The included angle is an acute angle, and the angle of the included angle is controlled between 30° and 60°.

4. The six-dimensional force-tactile sensor according to claim 1, characterized in that, The flexible elastomer is silicone rubber or polyurethane elastomer; the rigid substrate is metal or hard alloy material; the rigid substrate is provided with fiber slots for arranging reference fiber optic components.

5. The six-dimensional force-tactile sensor according to claim 1, characterized in that, The end face of the mode interference fiber is coated with a silver reflective film.

6. The six-dimensional force-tactile sensor according to claim 1, characterized in that, The length of the sensitive section of the multimode fiber in the mode interference fiber is 5~10 mm.

7. A method for fabricating a tactile sensor, characterized in that the steps include... include: The end faces of the mode interference fiber and the reference fiber were cut using a fiber optic cleaver and the surfaces were cleaned with anhydrous ethanol. A silver reflective film was deposited at the end of the mode interference fiber using vacuum physical coating technology, and a grating was photolithographically written on the reference fiber using femtosecond laser. A flexible tactile elastomer mold with fiber optic channels was fabricated, and fiber optic grooves were machined in a rigid substrate for arranging reference fiber optic components. The mode interference fiber is embedded in the flexible tactile elastomer along the prefabricated fiber channel and a slight pretension is applied. At the same time, the reference fiber is placed horizontally in the fiber groove and fixed. Liquid elastomer is poured into the mold, and after vacuum degassing, it is cured in an environment of 60~80℃. After curing, the flexible tactile elastomer is connected to the rigid substrate, and the lead-out ends of the mode interference fiber and the reference fiber are connected to the optical path system.

8. The preparation method according to claim 7, characterized in that, The optical fiber channels are inclined to the rigid substrate plane and are evenly distributed along the center of the sensing area.

9. The preparation method according to claim 7, characterized in that, The connection between the flexible tactile elastomer and the rigid substrate includes bonding or mechanical fixation.

10. A demodulation method for a six-dimensional force-tactile sensor based on a mode interference fiber structure, characterized in that the steps include... include: Acquire the optical interference of each mode of the interferometric fiber in the sensing group, and the temperature center wavelength drift of the reference fiber component; The temperature change is obtained by calculating the temperature center wavelength drift, and then the temperature change is used to compensate for the optical wave interference to obtain the wavelength drift vector of the induction group. The sensitivity matrix is ​​obtained by calibrating the sensing group, and the wavelength drift vector is combined with the sensitivity matrix to establish a linear model; The linear model is solved by regularized least squares method to obtain the estimated values ​​of the six-dimensional force and torque vectors.

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