Mnf flexible tactile sensing system mimicking fingertip skin microstructure and method of manufacture

Abstract

The application particularly relates to a MNF flexible tactile sensing system simulating fingertip skin microstructure and a manufacturing method. The system comprises a sensing layer for sensing a space-time tactile stimulus, a micro-nano optical fiber and a polydimethylsiloxane encapsulation structure; a top layer elastic annular ridge layer, the side away from the sensing layer being provided with an annular ridge structure; a bottom layer elastic annular ridge layer, the side in contact with the sensing layer being provided with an annular ridge structure; the sensing layer is clamped and fixed between the top layer elastic annular ridge layer and the bottom layer elastic annular ridge layer; the annular ridge structure comprises a plurality of annular ridges with different diameters and arranged concentrically and protruding upward; the annular ridges on the top layer elastic annular ridge layer and the annular ridges of the bottom layer elastic annular ridge layer are staggered to form an interlocking microstructure. The bionic microstructure design formed by the top layer elastic annular ridge layer, the sensing layer and the bottom layer elastic annular ridge layer can improve the tactile sensitivity and the sensing range of the tactile sensing and better protect the MNF.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical fiber sensing technology, in particular to a MNF flexible tactile sensing system simulating fingertip skin microstructure and a manufacturing method. BACKGROUND

[0002] Bionic flexible tactile sensors can better simulate human tactile perception, perceive and quantify tactile stimuli such as stress, hardness and surface texture, achieve precise, fast and flexible perception, and thus improve the perception and response capabilities of robots. In recent years, flexible tactile sensors based on electrical sensing schemes, including capacitive, resistive, piezoelectric and triboelectric mechanisms, have been widely reported in the past decade. These electronic tactile sensors usually simulate the biological characteristics of fine touch in human skin, such as epidermis-dermis interface, sensory receptors, fingerprint patterns and ion stimulation in afferent neurons.

[0003] In the prior art, multi-modal sensing capabilities and other special features such as self-healing, self-powering, energy harvesting, stimulus visualization to environmental adaptation have also been tried in electronic tactile sensors, but they still have some defects, including high manufacturing cost, parasitic effect, complex circuit, signal crosstalk, etc., which may limit their practical application in robots.

[0004] Flexible tactile sensors based on optical sensing schemes are a promising approach, in which micro-nano optical fibers (MNF) have the advantages of small size, strong flexibility, high sensitivity, resistance to electromagnetic interference, easy to manufacture, etc., and have unique advantages in the field of flexible tactile sensing. In recent years, several types of micro-nano tactile sensors have been developed in the prior art to achieve single-parameter detection of stress, strain, sliding, object hardness and dual-mode detection of stress-temperature, stress-humidity, and further explore applications in human-machine interaction and physiological parameter detection, including gesture recognition, pulse wave detection, etc.

[0005] At present, flexible tactile sensors based on micro-nano optical fibers mostly use polydimethylsiloxane (PDMS) single material to package MNF, which leads to the problem that the sensing range and tactile sensitivity cannot be considered at the same time, and the packaging structure is easy to wear and cause damage to MNF. Therefore, how to improve the tactile sensitivity and sensing range of tactile sensing and better protect MNF is a technical problem to be solved. SUMMARY

[0006] In view of the deficiencies of the prior art, the technical problem to be solved by the present application is how to provide a MNF flexible tactile sensing system simulating fingertip skin microstructure, which can improve the tactile sensing sensitivity and sensing range of tactile sensing, better protect the MNF, and effectively detect static pressure, dynamic pressure, vibration and other mechanical stimuli, thereby improving the sensing performance of the FIMF sensor.

[0007] To solve the above technical problems, the present application adopts the following technical solutions:

[0008] The MNF flexible tactile sensing system simulating fingertip skin microstructure comprises:

[0009] The perception layer is used for perceiving spatiotemporal tactile stimuli;

[0010] The perception layer comprises micro-nano optical fibers for converting the perceived spatiotemporal tactile stimuli into a form of transmitted light output intensity variation, and a polydimethylsiloxane packaging structure for packaging the micro-nano optical fibers;

[0011] The top elastic annular ridge layer is arranged on the side of the perception layer for perceiving spatiotemporal tactile stimuli, and the side facing away from the perception layer is provided with an annular ridge structure;

[0012] The bottom elastic annular ridge layer is arranged on the side of the perception layer facing away from the top elastic annular ridge layer, and the side in contact with the perception layer is provided with an annular ridge structure;

[0013] The perception layer is clamped and fixed between the top elastic annular ridge layer and the bottom elastic annular ridge layer;

[0014] The annular ridge structure comprises a plurality of annular ridges with different diameters and arranged concentrically and protruding upward;

[0015] The annular ridges on the top elastic annular ridge layer and the annular ridges of the bottom elastic annular ridge layer are staggered, so that the annular ridge structures of the top elastic annular ridge layer and the bottom elastic annular ridge layer can form interlocking microstructures.

[0016] Preferably, the micro-nano optical fiber of the perception layer is a non-adiabatic tapered micro-nano optical fiber obtained by fusing and tapering a single-mode optical fiber.

[0017] Preferably, the diameter of the micro-nano optical fiber of the perception layer is 1-10 μm, and the waist taper length is 100-2200 μm.

[0018] Preferably, the polydimethylsiloxane packaging structure comprises two layers of polydimethylsiloxane film layers arranged in parallel, and the micro-nano optical fiber is clamped and packaged between the two layers of polydimethylsiloxane film layers.

[0019] Preferably, the thickness of the upper and lower polydimethylsiloxane film layers is 10-100 microns.

[0020] Preferably, the annular ridge structures on the top and bottom elastic annular ridge layers are integrally formed.

[0021] Preferably, the thickness of the top elastic annular ridge layer is 0.2-0.4 mm, and the thickness of the bottom elastic annular ridge layer is 0.3-0.5 mm.

[0022] Preferably, the diameter of the largest annular ridge in the annular ridge structure on the top and bottom elastic annular ridge layers is 10-14 mm, the annular ridge spacing is 0.3-0.7 mm, the annular ridge thickness is 0.1-0.3 mm, and the annular ridge width is 0.4-0.6 mm.

[0023] The application also discloses a manufacturing method of the MNF flexible tactile sensing system, comprising:

[0024] S1: preparing a micro-nano optical fiber;

[0025] S2: bending the prepared micro-nano optical fiber into a U-shaped structure with a bending radius of 0.3-0.5 mm;

[0026] S3: clamping and packaging the micro-nano optical fiber by the upper and lower polydimethylsiloxane film layers to obtain a sensing layer;

[0027] S4: preparing a top elastic annular ridge layer and a bottom elastic annular ridge layer with protruding annular ridge structures; the annular ridges on the top elastic annular ridge layer are staggered with the annular ridges on the bottom elastic annular ridge layer, so that the annular ridge structures of the top and bottom elastic annular ridge layers can form interlocking microstructures;

[0028] S5: clamping and fixing the sensing layer between the top and bottom elastic annular ridge layers to obtain the MNF flexible tactile sensing system.

[0029] Preferably, the micro-nano optical fiber with a non-adiabatic taper structure is obtained by using a single-mode optical fiber fusion taper;

[0030] Specifically, first, the single-mode optical fiber is stripped of the coating layer and wiped with alcohol; then the treated single-mode optical fiber is placed in a fiber fusion machine for discharge operation to obtain a tapered optical fiber structure with a diameter of 60-80 microns; finally, the tapered optical fiber structure is stretched by a fiber tapering machine through a flame fusion tapering method to obtain a micro-nano optical fiber with a non-adiabatic taper structure.

[0031] Compared with the prior art, the MNF flexible tactile sensing system simulating the fingertip skin microstructure has the following beneficial effects:

[0032] The MNF flexible tactile sensing system (FIMF) of the present application comprises a three-layer structure compounded in turn from top to bottom, namely a top elastic annular ridge layer, a sensing layer and a bottom elastic annular ridge layer. The top elastic annular ridge layer can simulate the fingerprint structure of the human fingertip, effectively enhance the surface roughness and strengthen the detection ability of the FIMF to the mechanical stimulation caused by sliding / friction, thereby improving the tactile sensitivity of the FIMF. The middle sensing layer converts the sensed spatio-temporal tactile stimulation into the form of transmitted light output intensity change through micro-nano optical fibers (MNF) to realize sensing, and the low Young's modulus, biocompatibility and excellent optical properties of the PDMS material in the PDMS packaging structure enable the packaging structure to protect the micro-nano optical fibers and enhance the mechanical stimulation, thereby further improving the sensitivity and reducing the interference of the FIMF. The annular ridge structure of the bottom elastic annular ridge layer is staggered with the annular ridge structure of the bottom elastic annular ridge layer, so that the annular ridge structures of the top and bottom elastic annular ridge layers can form interlocking microstructures, which can better simulate the epidermis / dermis interlocking microstructure in the skin of the fingertip, thereby more effectively amplifying the tactile stimulation and improving the sensing range of the FIMF.

[0033] In summary, the bionic microstructure design formed by the top, middle and bottom elastic annular ridge layers can improve the tactile sensitivity and sensing range of the tactile sensing, and the elastic annular ridge layers of the top and bottom layers can better protect the MNF. At the same time, the MNF converts the sensed spatio-temporal tactile stimulation into the form of transmitted light output intensity change, so that the sensed tactile stimulation (such as pressure and vibration) is converted into the deformation and bending of the optical microfiber, which can reflect the change of the guided mode evanescent field energy on the change of the output light intensity, thereby more effectively detecting mechanical stimuli such as static pressure, dynamic pressure and vibration, and further improving the sensing performance of the FIMF sensor. In addition, the elastic resin has flexibility, high efficiency, high precision and customizability, and the two-layer elastic resin annular ridge structure can better simulate the fingerprint structure of the human fingertip, thereby effectively enhancing the surface roughness and strengthening the detection ability to the mechanical stimulation caused by sliding / friction.

[0034] Experiments show that the MNF flexible tactile sensing system (FIMF) of the present application has a wider pressure response range (0-16N) compared with existing sensors, can obtain higher sensitivity (20.58%N-1) in the low touch pressure range (0-2N), has shorter response time (86ms), longer service life, lower manufacturing cost and other advantages.

[0035] It is found that the FIMF sensor can distinguish soft and hard objects, perceive object texture, measure clamping force, etc. by connecting the FIMF sensor directly to the robot manipulator, and the sensor is suitable for robot clamping operation, i.e. the new type of flexible tactile sensor has similar structure and functional characteristics to the skin of the fingers, and has potential application prospects in bionic artificial skin and advanced robot technology.

[0036] The effects of pressure and sliding speed on the texture perception of the FIMF are studied by combining the pressing stroke with the feedback of the FIMF transmitted light intensity for perceiving the hardness of the object, and perceiving the object texture according to the FIMF response oscillation waveform. The experiments prove the feasibility and universal applicability of the FIMF sensor in object hardness / roughness perception. BRIEF DESCRIPTION OF DRAWINGS

[0037] In order to make the purpose, technical scheme and advantages of the application clearer, the application will be further described in detail below with reference to the drawings, in which:

[0038] Figure 1 It is a schematic diagram of the structure of the skin of the human finger;

[0039] Figure 2 It is a schematic diagram of the structure of the MNF flexible tactile sensing system (FIMF);

[0040] Figure 3 It is a side sectional view of the MNF flexible tactile sensing system (FIMF);

[0041] Figure 4 It is the effect of the thickness of each layer of the sensor on the performance: (a) the effect of the thickness of the PDMS on the stress; (b) the effect of the elastic annular ridge layer on the stress.

[0042] Figure 5 It is the mechanical response of the sensor: (a) the deformation distribution of the plane where the micro-nano optical fiber is located; (b) the stress distribution under different conditions; (c) the output response of the sensor under finger pressing and sliding;

[0043] Figure 6 It is a schematic diagram of the dual-mode interference MNF structure;

[0044] Figure 7 It is a micro-nano optical fiber: (a) when the wavelength is 1550 nm, the effective refractive index of the HE11 and HE12 modes varies with the diameter of the MNF; (b) the simulation spectrum of the MNF with a diameter of 10 μm, 5 μm and 2.3 μm; (c) the change of the FSR of the MNF with different diameters near 1550 nm;

[0045] Figure 8 It is a physical diagram of the sensor: (a) a microscope diagram of the MNF with a diameter of 5 μm; (b) a physical diagram of the FIMF; (c) the transmission spectrum before and after packaging;

[0046] Figure 9 For mechanical property comparison and calibration: (a) mechanical property test experimental system diagram; (b) comparison of sensors with different structures; (c) FIMF pressure spectrum response; (d) FIMF sensitivity; (e) repeatability; (f) response / recovery time;

[0047] Figure 10 For mechanical property test: (a) incremental pressure response curve; (b) repeatability test; (c) different frequency sensor response under 1N pressure; (d) different pressure sensor response under 0.5HZ;

[0048] Figure 11 For hardness perception: (a) experimental system diagram; (b) hardness change and transmission intensity relationship of 3 cycles; (c) intensity change and hardness change relationship of a single cycle; (d) hardness and transmission intensity relationship of 30 cycles; (e) FIMF integrated into a mechanical hand; (f) intensity change waveform when using a mechanical hand integrated with FIMF to grasp different objects;

[0049] Figure 12 For texture perception: (a) experimental system diagram; (b) test object with a pitch of 4mm; (c) response waveform of contact scanning; (d) response waveform of scanning under different pressures; (e) response waveform under 50mm / s, 100mm / s scanning speed

[0050] Figure 13 For different scanning speeds: (a) response waveform; (b) frequency spectrum diagram of FFT transform; (c) time-frequency diagram of FFT transform

[0051] Figure 14 For different texture test objects: (a) texture pitch 1mm, 0.5mm test object real object diagram; (b) response waveform; (c) time-frequency diagram of FFT transform. DETAILED DESCRIPTION

[0052] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0053] It should be noted that like reference numerals and characters refer to like elements throughout the following description with like reference numerals and characters referring to like elements throughout the following description and the appended figures, it being also noted that, once an element is defined in one figure, it is not necessary to further define and explain it in the subsequent figures. In the description of the application, it needs to be explained that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the application is usually placed during use, and are only for the convenience of describing the application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the application. In addition, the terms "first", "second", "third", and the like are only used to distinguish the description and cannot be understood as indicating or implying relative importance. In addition, the terms "horizontal", "vertical", and the like do not mean that the parts must be absolutely horizontal or vertical, but can be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but can be slightly inclined. In the description of the application, it also needs to be explained that, unless otherwise explicitly specified and limited, the terms "arrangement", "installation", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication between two elements inside. For those skilled in the art, the specific meaning of the above terms in the application can be understood according to the specific circumstances.

[0054] The following will be further described in detail through specific embodiments:

[0055] Example one:

[0056] The applicant found that the skin of the human fingertip is a special type of skin with high tactile sensitivity, the ability to perceive and distinguish static and dynamic forces, friction, vibration and other spatiotemporal tactile stimuli, and to recognize pressure / slip, perceive the shape, hardness and texture of the object being grasped. For example, Figure 1As shown, the skin of the human fingertips has a multi-layered structure, including the epidermis, dermis, and subcutaneous tissue. The interlocking microstructures between the epidermis and dermis amplify and effectively transfer tactile stimuli to the skin's mechanoreceptors. The outermost layer of the epidermis, with its high elastic modulus, provides resilience, and the fingerprint microstructures on its surface enhance friction and amplify friction-induced vibrations, facilitating fingertip manipulation and texture perception. The lower dermis contains low elastic modulus collagen. Slow-adapting receptors (such as Merkel and Ruffini corpora) respond to continuous touch and pressure on the skin, while fast-adapting receptors (such as Meissner and Pacinian corpora) respond to dynamic touch and vibration stimuli. They perceive and transmit tactile stimuli through nerve fibers in the form of frequency-encoded action potentials. Due to the stimulus-specific sensing behavior of sensory receptors and nerve fibers, similar to bandpass filters, vibrational information caused by sliding and friction is encoded as frequency-time correlated tactile information and finely perceived by the skin.

[0057] Inspired by the unique biological microstructure and tactile conduction mechanism of human fingertip skin, this application proposes a flexible tactile sensing system (hereinafter referred to as FIMF) with fingerprint structure and interlocking microstructure.

[0058] Specifically, this embodiment discloses an MNF flexible tactile sensing system that simulates the microstructure of fingertip skin.

[0059] like Figure 2 As shown, the MNF flexible tactile sensing system, which simulates the microstructure of fingertip skin, includes:

[0060] The sensory layer is used to perceive spatiotemporal tactile stimuli.

[0061] The sensing layer includes micro / nano fiber (hereinafter also referred to as MNF) for converting perceived spatiotemporal tactile stimuli into changes in the intensity of transmitted light output, and polydimethylsiloxane (hereinafter also referred to as PDMS) encapsulation structure for encapsulating the micro / nano fiber.

[0062] In this embodiment, the output of the micro-nano fiber (MNF) is connected to the back-end processing circuit, which includes a miniaturized photodetector circuit and a data processing circuit.

[0063] The top elastic annular ridge layer is set on the side of the sensing layer used to sense spatiotemporal tactile stimuli, and the side facing away from the sensing layer is provided with an annular ridge structure.

[0064] The bottom elastic annular ridge layer is located on the side of the sensing layer away from the top elastic annular ridge layer, and the side in contact with the sensing layer is provided with an annular ridge structure.

[0065] The sensing layer is clamped and fixed between the top elastic annular ridge layer and the bottom elastic annular ridge layer;

[0066] The annular ridge structure comprises a plurality of annular ridges with different diameters and arranged concentrically and protruding upward;

[0067] The annular ridges on the top layer of elastic annular ridges are staggered with the annular ridges of the bottom layer of elastic annular ridges, so that the annular ridge structures of the top layer of elastic annular ridges and the bottom layer of elastic annular ridges can form interlocking microstructures.

[0068] In combination Figure 3 As shown, the staggered arrangement of the annular ridges refers to that, after the top layer of elastic annular ridges and the bottom layer of elastic annular ridges are compounded with the perception layer, the annular ridges of the bottom layer of elastic annular ridges are staggered and do not correspond to the annular ridges of the top layer of elastic annular ridges, that is, the position of the annular ridges on the bottom layer of elastic annular ridges corresponds to the position without annular ridges on the top layer of elastic annular ridges, and correspondingly, the position of the annular ridges on the top layer of elastic annular ridges corresponds to the position without annular ridges on the bottom layer of elastic annular ridges.

[0069] The MNF flexible tactile sensing system (FIMF) of the application comprises a three-layer structure compounded from top to bottom, that is, a top layer of elastic annular ridges, a perception layer and a bottom layer of elastic annular ridges. The top layer of elastic annular ridges can simulate the fingerprint structure of the human fingertip, effectively enhance the surface roughness and strengthen the detection ability of the FIMF to mechanical stimulation caused by sliding / friction, thereby improving the tactile sensitivity of the FIMF. The perception layer in the middle converts the perceived spatiotemporal tactile stimulation into a change in transmitted light output intensity through micro-nano optical fibers (MNF) to realize perception, and the low Young's modulus, biocompatibility and excellent optical properties of the PDMS material in the PDMS packaging structure enable the packaging structure to protect the micro-nano optical fibers and enhance the mechanical stimulation, thereby further improving the sensitivity of the FIMF and reducing interference. The annular ridge structure of the bottom layer of elastic annular ridges is staggered with the annular ridge structure of the bottom layer of elastic annular ridges, so that the annular ridge structures of the top layer of elastic annular ridges and the bottom layer of elastic annular ridges can form interlocking microstructures, which can better simulate the epidermis / dermis interlocking microstructure in the skin of the fingertip, thereby more effectively amplifying the tactile stimulation, thereby improving the sensing range of the FIMF.

[0070] In summary, the bionic microstructure design formed by the top elastic annular ridge layer, the sensing layer and the bottom elastic annular ridge layer can improve the sensitivity and sensing range of the tactile sensing of the tactile sensor, and the elastic annular ridge layers of the top layer and the bottom layer can better protect the MNF. Meanwhile, the time-space tactile stimulation perceived by the MNF is converted into the change form of the transmission light output intensity, so that the tactile stimulation (such as pressure and vibration) perceived is converted into the deformation bending of the optical microfiber, the change of the guided mode evanescent field energy can be shown on the change of the output light intensity, so that the mechanical stimulation such as static pressure, dynamic pressure and vibration can be more effectively detected, and the sensing performance of the FIMF sensor is improved. In addition, the elastic resin has flexibility, high efficiency, high precision and customization, and the two-layer elastic resin annular ridge structure can better simulate the fingerprint structure of the human fingertip, so as to effectively enhance the surface roughness and strengthen the detection ability of the mechanical stimulation caused by sliding / friction.

[0071] Experiments prove that the MNF flexible tactile sensing system (FIMF) of the application has a wider pressure response range (0-16N) compared with the existing sensor, can obtain higher sensitivity (20.58%N-1) in the low touch pressure range (0-2N), has shorter response time (86ms), longer service life, lower manufacturing cost and other advantages.

[0072] It is found through demonstration of directly connecting the FIMF sensor to the robot manipulator that the FIMF sensor can distinguish between soft and hard objects, perceive object texture and measure clamping force, and the sensor is suitable for robot clamping operation, that is, the new type of flexible tactile sensor has similar structure and functional characteristics to the skin of the finger, and has potential application prospects in bionic artificial skin and advanced robot technology.

[0073] The effects of pressure and sliding speed on the texture perception of the FIMF are studied by combining the pressing stroke with the FIMF transmission light intensity feedback for perceiving the hardness of the object, and perceiving the object texture according to the response oscillation waveform of the FIMF. Experiments prove the feasibility and universal applicability of the FIMF sensor in object hardness / roughness perception.

[0074] I. Mechanical simulation of the sensing system

[0075] 1、To further study the sensing characteristics of FIMF and optimize the sensing performance, the finite element software COMSOL is used to parameterize modeling and mechanical simulation of the FIMF tactile sensor. The simulation parameters are as follows: the elastic resin is a super-elastic material, the simulation adopts the Mooney-Rivlin double-parameter super-elastic model, wherein C10=3.7*105pa, C01=1.1*105pa, bulk modulus K=1*107pa, density p=1.1*104kg / m3, the prepared micro-nano fiber diameter is below 10um, which is one order of magnitude smaller than the size of each level, so the simulation model does not include the micro-nano fiber itself.

[0076] Specifically, the polydimethylsiloxane packaging structure includes two layers of polydimethylsiloxane (PDMS) film layers arranged in parallel, and the micro-nano fiber is clamped and packaged between the two layers of polydimethylsiloxane film layers (hereinafter also referred to as PDMS film layer).

[0077] Considering the influence of the thickness of the upper and lower PDMS film layers in the packaging structure on the performance of the FIMF, the thickness of the two layers of PDMS film layers is set to be 0-1mm, wherein the PDMS contact layer is the plane where the MNF is located, and the average stress of the MNF is used to characterize the stress of the MNF. The simulation results are shown in Figure 4 (a), it can be seen that the average stress of the MNF plane decreases with the increase of the thickness of the upper PDMS contact layer from 0-1mm, which means that the thinner the upper PDMS contact layer, the greater the stress on the plane where the MNF is located, and the lower PDMS contact layer has little effect on the average stress of the MNF plane within the thickness of 0-1mm. The results show that when the MNF is packaged with the PDMS contact layer, the thinner the cover layer, the higher the sensitivity.

[0078] Secondly, the thickness of the two elastic annular ridge layers is set to be 0.1-1mm, and the simulation results are shown in Figure 4 (b), it can be seen that when the thickness of the bottom elastic annular ridge layer is 0.1-0.2mm, the average stress of the layer where the MNF is located increases, 0.2-0.55mm decreases, and 0.55-1mm increases; and the thinner the top elastic annular ridge layer, the greater the stress, so different feature size combinations of the packaging structure can be adjusted to be applied to different touch stress occasions. However, considering that the interlocking structure is to improve the strain bending ability of the MNF, and the top elastic annular ridge layer is to improve the sensitivity of the FIMF to sliding friction, therefore, the introduction of the top elastic annular ridge layer is necessary.

[0079] The PDMS film in the application has a thickness of 10-100 μm (the maximum value in the embodiment is 50 μm), the top elastic annular ridge layer has a thickness of 0.2-0.4 mm (the maximum value in the embodiment is 0.2 mm), and the bottom elastic annular ridge layer has a thickness of 0.3-0.5 mm (the maximum value in the embodiment is 0.4 mm).

[0080] 2. A 1N normal force was applied to the FIMF in simulation, and the results are shown in Figure 5 (a). A small amplitude multi-scale bending deformation occurred in the sensing layer where the MNF was located, which indicated that the interlocking structure could introduce more micro-bending, and the bending degree showed an increasing trend with the increase of the normal force, thereby causing the MNF to produce more severe bending with the increase of the force, which would be reflected in the change of the transmission intensity. Among them, Figure 5 (b) is the simulation under the condition of 1N normal force and 0.5N tangential force. In the case of applying pressure (Fz=1N), the maximum stress is located below the annular ridge. On the other hand, by applying friction force (Fz=1N, Fx=0.5N), the position of the maximum stress moves from the annular ridge area, and the size of the maximum stress also increases.

[0081] The finite element simulation results show that in the above two cases, the change of stress distribution will lead to different output responses of the FIMF. A preliminary experiment was further carried out, in which an adult repeatedly scanned and pressed the sensor surface with the index finger. As shown in Figure 5 (c), the triangular wave generated by the finger pressing (pressure ≈0.8N) has an average intensity change of 18%, while the burst pulse generated by the finger scanning (sliding friction ≈1N) has an average intensity change of 82%, which indicates that the MNF flexible tactile sensing system of the application has higher sensitivity to friction / slip.

[0082] II. Preparation of the sensing system

[0083] In the specific implementation process, the micro-nano optical fiber of the sensing layer is a micro-nano optical fiber with a non-adiabatic taper structure obtained by using a single-mode optical fiber fusion taper.

[0084] 1. The MNF with a non-adiabatic taper structure can be obtained by using a single-mode optical fiber fusion taper. Previous studies have shown that when the diameter of the MNF is less than 12 μm, mode interference mainly occurs between HE 11 and HE 12 modes. Figure 6 The schematic diagram of the bimodal interference MNF structure is shown in FIG. 1. The spectral intensity of the bimodal interference MNF can be expressed as:

[0085]

[0086] In the formula, I 11 and I12 respectively, HE 11 and HE 12 mode, Δn eff is the difference of effective refractive index between two modes, λ is wavelength, L is the interference length.

[0087] The phase difference change Δφ is expressed as:

[0088]

[0089] where ΔL is the length change of MNF, Δ(Δn eff ) is the change of the difference of effective refractive index between two modes.

[0090] The mode effective refractive index is obtained by the dispersion equation of micro-nano fiber:

[0091]

[0092] where J1 is the first-order first-type Bessel function, K1 is the first-order second-type modified Bessel function, n MF and n air are the refractive index of micro-nano fiber and air respectively, β is the propagation constant of HE1m mode, k0 is the wave number, d is the waist diameter of MNF.

[0093] The effective refractive index of HE 11 , HE 12 mode is positively correlated with the diameter of MNF at 1550 nm wavelength (as shown in (a)), the free spectral range (FSR) change rule of interference peak near 1550 nm is explored by simulating the spectrum of MNF with different diameters (as shown in (b)), and it can be known from (c) that when the diameter of MNF is 3-10 μm, the FSR is positively correlated with the diameter, and when the diameter of MNF is 2.2-2.5 μm, the FSR is negatively correlated with the diameter. Figure 7 Figure 7 Therefore, in the process of making MNF, we can estimate the diameter of MNF by the FSR of interference spectrum. Figure 7

[0094] Therefore, in the process of making MNF, we can estimate the diameter of MNF by the FSR of interference spectrum.

[0095] ​​2、FIMF fabrication process: stripping the single-mode fiber of the coating layer and wiping it clean with alcohol, then putting it into the optical fiber fusion splicer, setting the discharge amount to 105 bit, the discharge time to 2000 ms, the discharge times to 2 times, and performing the discharge operation to obtain a tapered structure with a diameter of 70 μm. Then, using the flame fusion tapering method, a non-adiabatic abrupt taper is further prepared by an optical fiber tapering machine, the hydrogen flow rate of the optical fiber tapering machine is set to 225 sccm, the pre-drawing speed is 120 μm / s, and the pre-drawing length is 10000 μm. The diameter of the prepared MNF is 5 μm, and the waist taper length of the MNF is 2200 μm. The microscope image of the MNF is shown in Figure 8 (a). It can be seen that the prepared MNF has a smooth surface and good flexibility, and can effectively guide light under bending conditions.

[0096] In order to further improve the sensing area of the FIMF and simplify the in-out structure of the sensor, improve the integration simplicity, the prepared MNF is pre-bent into a U-shaped structure with a bending radius of 4 mm by using a PDMS rod, then the MNF is clamped by two layers of PDMS film with a thickness of 50 μm, and then the MNF is placed into a drying oven and cured at a temperature of 80°C for 20 minutes to obtain the final sensing layer.

[0097] Subsequently, the upper and lower two layers of elastic annular ridge layers of the simulated fingertip skin microstructure are prepared by using 3D printing technology through an elastic resin material. The diameter of the largest annular ridge in the annular ridge structure on the top layer of elastic annular ridge layer and the bottom layer of elastic annular ridge layer is 10 mm-14 mm (the maximum value in this embodiment is 12 mm), the annular ridge spacing is 0.3 mm-0.7 mm (the maximum value in this embodiment is 0.5 mm), the annular ridge thickness is 0.1 mm-0.3 mm (the maximum value in this embodiment is 0.2 mm), and the annular ridge width is 0.4 mm-0.6 mm (the maximum value in this embodiment is 0.5 mm), which is comparable to the ridge line of adult fingerprints (distance: 0.4-0.5 mm, thickness 0.2 mm). It should be noted that the annular ridge structures protruding on the top layer of elastic annular ridge layer and the bottom layer of elastic annular ridge layer are integrally formed by 3D printing technology.

[0098] Finally, the two layers of elastic annular ridge layers and the soft sensing (PDMS) layer are firmly assembled together by inserting RTV glue into the elastic resin layer to prepare a FIMF tactile sensor (as shown in Figure 8 (b)), thereby ensuring strong adhesion between different layers and enhancing the mechanical robustness of the clamped sensor.

[0099] The transmission spectrum of the MNF with a diameter of 5 μm before and after packaging is shown in Figure 8 (c). It can be seen that the periodic spectrum of the MNF after packaging almost becomes a straight line, which is due to the high refractive index of the PDMS film layer, which changes the waveguide mode structure of the MNF, thereby making the double-mode interference phenomenon disappear.

[0100] III. In order to better illustrate the advantages of the designed MNF flexible tactile sensing system (FIMF), the following experiments are disclosed in this embodiment.

[0101] 1. Mechanical performance experiment and analysis

[0102] As shown in Figure 9 (a), in the designed FIMF tactile sensing mechanical performance test system, the light signal is provided by a broadband light source (ASE, CONOUER, C-L), passes through a tunable filter (OTF, Santec, 1530-1570 nm) to reach the sensing test optical fiber, and couples the 1550 nm light signal with the MNF; a precision force gauge (MPT, Mark-10 ESM303) is used to provide static pressure and dynamic pressure signals, and the light loaded with mechanical signals is converted into an output signal by an oscilloscope through a photodetector (PD, CONOUER, 200 kHz), which monitors the transmitted light intensity in real time.

[0103] By preparing three kinds of MNF sensors with different structure encapsulation (including only PDMS film encapsulation, top layer elastic ring ridge layer plus PDMS film encapsulation, and interlocking microstructure plus PDMS film encapsulation), the influence of each part of the FIMF structure on the performance of the sensor is compared and studied. The experimental results are shown in Figure 9 (b), it can be seen that when the MNF is encapsulated with a top layer elastic ring ridge layer plus PDMS, the mechanical detection range is comparable to that of the FIMF, but the corresponding sensitivity is lower; when only PDMS film is encapsulated, higher sensitivity is obtained but the sensing range is lower; the introduction of the artificial fingertip microstructure expands the detection range and improves the sensitivity. Figure 9 (c) shows the transmission spectrum obtained under different pressures (0-16N, step 1N), from which it can be seen that the intensity of the transmitted light gradually decreases with the increase of the pressure. This is because the increase of the pressure leads to the increase of the bending degree of the MNF, and the energy leakage occurs in the transition of the guided mode to the radiation mode. Figure 9(d) The relative intensity change (ΔΙ / Ι0, Ι0 is the initial output intensity under no pressure) as a function of the applied normal force at 1550 nm wavelength can be seen in Figure 6. The pressure sensitivity of the sensor in the range of 0-2 N is 20.58% N-1, in the range of 2-8 N is 5.63% N-1, and in the range of 8-16 N is 2.54% N-1. The difference in sensitivity in different pressure ranges can be attributed to the fact that large applied force causes the top ring ridge to be compressed, increasing the effective contact area of the sensor surface with the object, and secondly because excessive force causes the MNF to be excessively bent, thus, the intensity change under large force (8-10 N) is much smaller than that under small force (0-2 N). In addition, according to the pressure calculation formula P = F / s, where P is the pressure on the unit area of the object (Pa), F is the pressure perpendicular to the object (N), and s is the contact area of the measured object with the pressure (N / m2). The FIMF sensor can detect the pressure range of 0-16 N, and the pressure range of 0-141 kPa. Figure 9 (e) The response curves of three FIMF sensors prepared repeatedly to pressure are shown in Figure 7, and the correlation coefficients are close to 1, the curves are highly coincident, and the pressure response of repeated preparation is consistent. The FIMF sensor shows an instant response to external loading and unloading, as shown in Figure 8 (c) The response and recovery time is less than 100 ms, as shown in Figure 8, so that the sensor can timely perceive mechanical stimulation.

[0104] Table 1 compares the designed FIMF with other MNF tactile sensors. From the results, it can be seen that without microstructure, the NMF sensor (referring to LI Yu-jie, LUO Bin-bin, ZOU Xue, et al. Optical Vernier sensing characteristics based on double-helix micro-nano fiber coupler) obtains extremely high sensitivity, but is limited by the sensing range which is not suitable for the daily grasping task of the robot (0-10N). When the parallel ridge (referring to Jiang C P, Zhang Z, Pan J, et al. Finger-skin-inspired flexible optical sensor for force sensing and slip detection in robotic grasping) microstructure is introduced, it can effectively improve the pressure sensing range of the MNF (0-20N), but the sensitivity in the small touch pressure range (0-2N) is lower. In this work, the FIMF sensor introduced by the interlocking bionic ring microstructure effectively improves the sensitivity in the small touch pressure range (0-2N) on the basis of expanding the sensing range, which is about 4 times that of the recently reported MNF tactile sensor (referring to Jiang C P, Zhang Z, Pan J, et al. Finger-skin-inspired flexible optical sensor for force sensing and slip detection in robotic grasping). In addition, due to the introduction of the microstructure, the tactile mechanical stimulus can be effectively amplified and converted into the deformation of the MNF, which does not need to taper the MNF to below 2μm, which simplifies the tapering process and preparation difficulty of the MNF, and enhances the overall toughness of the structure. The designed FIMF has great application potential in robot grasping tasks.

[0105] Table 1 Comparison of the performance of other micro-nano fiber tactile sensors

[0106]

[0107] The light transmission intensity gradually decreases with the increase of the pressure value of the FIMF in turn, showing stable and continuous fluctuations (as shown in Figure 10 (a)). In the loading-unloading cycle test, the optical signal of the sensor still shows stable output after 1000 cycles (as shown in Figure 10(b) shows), without obvious performance degradation, such high durability and stability benefit from the robust encapsulation of MNF in PDMS and the strong adhesion of the multi-layer structure in the sensor. Further, the dynamic force response of the sensor was evaluated by applying cross-mechanical signals, cyclic forces with different frequencies (1, 0.5, 0.25, 0.1 Hz) under 1 N normal force and different amplitudes (1, 3, 5, 7 N) under 0.5 Hz, and the results are shown in Figure 10 (c) and Figure 10 (d), respectively. The results show that the pressure response of the sensor is quite stable, the baseline intensity does not fluctuate obviously, and the output intensity changes easily with the frequency or amplitude of the applied force. The FIMF tactile sensor in the present application has excellent durability and high static / dynamic stability, and is suitable for robotic grasping applications. If the sensor structure is optimized by reducing the fiber diameter (see Ma S Q, Wang X Y, Li P, et al. Optical Micro / Nano Fibers Enabled Smart Textiles for Human-Machine Interface) and reducing the thickness of the PDMS encapsulation layer, the touch pressure sensitivity can be further improved.

[0108] 2. Hardness perception experiment and analysis

[0109] Under certain conditions, there is an approximate linear relationship between hardness and elastic modulus, when the Hooke's law defines the elastic deformation, the deformation x of the elastic body is proportional to the contact force F, i.e. F = k x. Where k is the elastic modulus of the elastic body, this formula can be used to describe the relatively simple elastic deformation process. For the measured object, k is a constant, which means that under the same extrusion stroke (keeping x constant) the force value feedback is related to k, and the k value of different objects gives different feedback forces F. Based on this principle, a combination of mechanical finger stroke and FIMF force value feedback is used to identify the hardness characteristics of the object. The test system is shown in Figure 11 (a), first, a precision force gauge (MPT, Mark-10 ESM303) is used to extrude the FIMF into contact with different Shore hardness blocks (A10-A80), the extrusion stroke is fixed at 2 mm, and the oscilloscope is used to monitor the change of light intensity. The test results are shown in Figure 11 (b), which records the intensity change waveform of 3 cycles. It can be seen that as the hardness increases, the transmission intensity decreases, which is because the harder the object, the greater its stiffness, and the greater the k value, which will result in greater force value feedback under the same x, which is reflected in the FIMF receiving greater stress causing greater light intensity attenuation. Due to the stickiness and resilience of the measured object surface, the FIMF response waveform will have a hysteresis effect (as shown in Figure 11(c)), but this does not affect the ability of the FIMF to identify the hardness of the object. To test the reliability of the FIMF in identifying hardness, the negative peak value of each sample was recorded over 30 trials and the statistical data plotted in Figure 11 (d). It is clear that these standard hardness blocks can be distinguished by the output signal of the FIMF.

[0110] Next, the FIMF was integrated into a two-fingered robot hand (as shown in Figure 11 (e)) to detect the hardness of several common laboratory items, including a rubber dropper, a leather wallet, a piece of foam, an empty plastic bottle and a packet of paper towels. During each test, the robot hand was controlled by the host computer to approach and clamp the target and compress to a specified depth (set to 2 mm) for 4 s, with three cycles. The output signal is shown in Figure 11 (f). It can be observed that there is a slight fluctuation in the light intensity due to the instability of the robot fingers, but the FIMF is still able to distinguish between the objects according to the results of the light intensity response.

[0111] 3. Texture perception experiment and analysis

[0112] When using the FIMF to perceive the texture of an object, the perception object is the change in the small geometry of the surface of the object. In this work, the texture is represented based on the spatial frequency. The experimental system is shown in Figure 12 (a). The FIMF is fixed on an optical platform, and a precision motorized slide table (PST, Z-Mod-SE-44-10SE) is rigidly connected with a precision Z-axis displacement table (PSD, LZ1000). The test object is rigidly connected with the PST, and the PST is controlled by the host computer to drive the test object to contact and scan the FIMF. This test method can effectively reduce the mechanical vibration interference of the PST. Figure 12 (b) is a photograph and a side view diagram of a test object with a texture pitch of 4 mm. The response waveform of the transmitted light intensity as a function of time when the test object is in contact with the FIMF (1 mm / s) is recorded in Figure 12 (c). When the test object is in contact with the FIMF, the bending of the MNF causes the conversion of the transmission light base mode to the radiation mode, resulting in a decrease in the transmitted light intensity. According to the relationship between the change in the transmitted light intensity and the pressure, the normal force at this time can be calculated to be about 2 N; when the test object scans the FIMF, it can be observed that the response waveform is periodically oscillated, which is due to the introduction of the annular ridge that amplifies the vibration caused by the texture. When the contact pressure is increased, the response waveform generated by scanning the FIMF is basically consistent in amplitude and period, and the median value corresponding to the oscillation waveform decreases Figure 12 (d), indicating that the FIMF can be used for contact force detection and object texture perception at the same time. As shown in Figure 12(e) As shown, periodic changes in transmitted light intensity can still be observed at higher scanning speeds (50, 100 mm / s), and FIMF can capture the texture features of the object and convert them into waveforms of transmitted intensity versus time at different sliding speeds.

[0113] Figure 13 (a) At lower scanning speeds (0.5 to 2 mm / s), the transmitted light intensity versus time when the FIMF is scanned with a test object with a texture pitch of 4 mm is shown. The frequency spectrum of each waveform is calculated by fast Fourier transform (FFT), as shown in Figure 13 (b) As shown, the significant frequencies in the spectrum power map are 0.125 Hz, 0.175 Hz, 0.25 Hz, and 0.5 Hz, respectively, where the significant frequency (f) is defined as the frequency with the highest power as the mean square amplitude (MSA). The wavelength of the texture (λ = v / f) is calculated by dividing the sliding speed by the significant frequency. The texture wavelengths corresponding to the four low-speed scanning results are all 4 mm, which is basically consistent with the true value measured. The short-time Fourier transform (STFT) of the transmitted light intensity signal further describes the intensity versus time Figure 13 (c) Scanning on a regular surface pattern causes the light intensity signal to induce a periodic pattern versus time in the frequency range below 10 Hz, and the number and frequency position increase with the increase of the scanning speed in the same time domain.

[0114] Finally, in order to verify the universal applicability of the FIMF sensor, a more fine texture test object is prepared by using 3D printing technology, and the test object is scanned at a scanning speed of 1 mm / s. Figure 14 (a) The real object images of the test objects with texture pitches of 1 mm and 0.5 mm, and their sliding response waveforms Figure 14 (b) appear periodic oscillations as expected, and the corresponding significant frequencies Figure 14 (c) are 1 Hz and 2 Hz, respectively. According to the relationship between the sliding speed, the significant frequency and the texture wavelength, it is deduced that the texture wavelengths are consistent with the true values. The amplitudes of the sliding response waveforms of different test objects are different, which is caused by the height difference of the corresponding textures, but it does not hinder us from perceiving the texture pitch according to the significant frequency results.

[0115] Example Two:

[0116] A manufacturing method of the MNF flexible tactile sensing system in Example One is disclosed in this embodiment.

[0117] The manufacturing method of the MNF flexible tactile sensing system comprises the following steps:

[0118] S1: preparing a micro-nano optical fiber;

[0119] S2: the prepared micro-nano fiber is bent into a U-shaped structure with a bending radius of 0.3-0.5 mm;

[0120] S3: the micro-nano fiber is clamped and packaged by the upper and lower two layers of polydimethylsiloxane film layers to obtain a sensing layer;

[0121] S4: a top elastic annular ridge layer and a bottom elastic annular ridge layer with a convex annular ridge structure are prepared; the annular ridges on the top elastic annular ridge layer and the bottom elastic annular ridge layer are staggered to form an interlocking microstructure;

[0122] S5: the sensing layer is clamped and fixed between the top elastic annular ridge layer and the bottom elastic annular ridge layer to obtain a MNF flexible tactile sensing system.

[0123] In the specific implementation process, a single-mode optical fiber is used to obtain a micro-nano fiber with a non-adiabatic taper structure by fusion tapering;

[0124] Specifically, first, the single-mode optical fiber is stripped of the coating layer and wiped with alcohol; then the treated single-mode optical fiber is placed in an optical fiber fusion machine for discharge operation (the discharge amount of the optical fiber fusion machine is set to 105 bit, the discharge time is 2000 ms, and the discharge frequency is 2 times); a tapered optical fiber structure with a diameter of 60-80 μm (the maximum value in this embodiment is 70 μm) is obtained; finally, the flame fusion tapering method is used to stretch the tapered optical fiber structure by an optical fiber tapering machine (the hydrogen flow rate of the optical fiber tapering machine is set to 225 sccm, the pre-drawing speed is 120 μm / s, and the pre-drawing length is 10000 μm) to obtain a micro-nano fiber with a non-adiabatic taper structure.

[0125] The MNF flexible tactile sensing system (FIMF) manufactured by the above steps comprises a three-layer structure compounded in turn from top to bottom, namely a top elastic annular ridge layer, a sensing layer and a bottom elastic annular ridge layer. The top elastic annular ridge layer can simulate the fingerprint structure of a human fingertip, effectively enhance the surface roughness and strengthen the detection ability of the FIMF to mechanical stimulation caused by sliding / friction, thereby improving the tactile sensitivity of the FIMF. The middle sensing layer converts the sensed spatio-temporal tactile stimulation into a change in the intensity of transmitted light output to realize sensing, while the low Young's modulus, biocompatibility and excellent optical properties of the PDMS material in the PDMS packaging structure enable the packaging structure to protect the micro-nano optical fiber, enhance the mechanical stimulation, thereby further improving the sensitivity of the FIMF and reducing interference. The annular ridge structure of the bottom elastic annular ridge layer is arranged in a staggered manner with the annular ridge structure of the bottom elastic annular ridge layer, so that the annular ridge structures of the top and bottom elastic annular ridge layers can form an interlocking microstructure, which can better simulate the epidermis / dermis interlocking microstructure in the skin of the fingertip, thereby more effectively amplifying the tactile stimulation, thereby improving the sensing range of the FIMF.

[0126] In summary, the bionic microstructure design formed by the top, middle and bottom elastic annular ridge layers can improve the tactile sensitivity and sensing range of the tactile sensing, and the elastic annular ridge layers of the top and bottom layers can better protect the MNF. Meanwhile, the MNF converts the sensed spatio-temporal tactile stimulation into a change in the intensity of transmitted light output, so that the sensed tactile stimulation (such as pressure and vibration) is converted into the deformation and bending of the optical microfiber, which can reflect the change in the guided mode evanescent field energy on the change in the output light intensity, thereby more effectively detecting mechanical stimulation such as static pressure, dynamic pressure and vibration, thereby improving the sensing performance of the FIMF sensor. In addition, the elastic resin has flexibility, high efficiency, high precision and customizability, and the two-layer elastic resin annular ridge structure can better simulate the fingerprint structure of the human fingertip, thereby effectively enhancing the surface roughness and strengthening the detection ability to mechanical stimulation caused by sliding / friction.

[0127] Specifically, the diameter of the micro-nano optical fiber is 1-10 μm (the maximum value in the embodiment is 5 μm), and the waist taper length is 100-2200 μm (the maximum value in the embodiment is 2200 μm).

[0128] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit the technical solutions. Those skilled in the art should understand that modifications or equivalent replacements to the technical solutions of the present application without departing from the spirit and scope of the technical solutions should be covered in the scope of the claims of the present application.

Claims

1. A flexible tactile sensing system using MNF (Micro-Nutrition Matrix) to simulate the microstructure of fingertip skin, characterized in that, include: The sensory layer is used to perceive spatiotemporal tactile stimuli. The sensing layer includes micro- and nano-fibers for converting perceived spatiotemporal tactile stimuli into variations in the intensity of transmitted light output, and a polydimethylsiloxane encapsulation structure for encapsulating the micro- and nano-fibers. The top elastic annular ridge layer is set on the side of the sensing layer used to sense spatiotemporal tactile stimuli, and the side facing away from the sensing layer has an annular ridge structure; the top elastic annular ridge layer simulates the fingerprint structure of human fingertips, enhances surface roughness and strengthens the MNF flexible tactile sensing system's ability to detect mechanical stimuli caused by sliding / friction. The bottom elastic annular ridge layer is located on the side of the sensing layer away from the top elastic annular ridge layer, and the side in contact with the sensing layer is provided with an annular ridge structure. The sensing layer is clamped and fixed between the top elastic annular ridge layer and the bottom elastic annular ridge layer; The ring-shaped ridge structure consists of several concentric ring-shaped ridges of different diameters that bulge upwards. The staggered arrangement of the ring ridges on the top elastic ring ridge layer and the bottom elastic ring ridge layer allows the ring ridge structures of the top elastic ring ridge layer and the bottom elastic ring ridge layer to form an interlocking microstructure. The interlocking microstructure simulates the interlocking microstructure of the epidermis / dermis in the fingertip skin, amplifying tactile stimulation.

2. The MNF flexible tactile sensing system for simulating the microstructure of fingertip skin as described in claim 1, characterized in that: The micro / nano fiber of the sensing layer is a non-insulated tapered micro / nano fiber obtained by fused tapering of single-mode fiber.

3. The MNF flexible tactile sensing system for simulating the microstructure of fingertip skin as described in claim 2, characterized in that: The diameter of the micro-nano optical fiber in the sensing layer is 1μm-10μm, and the waist cone length is 100μm-2200μm.

4. The MNF flexible tactile sensing system for simulating the microstructure of fingertip skin as described in claim 1, characterized in that: The polydimethylsiloxane encapsulation structure includes two parallel polydimethylsiloxane thin film layers, with micro / nano optical fibers sandwiched and encapsulated between the two polydimethylsiloxane thin film layers.

5. The MNF flexible tactile sensing system for simulating the microstructure of fingertip skin as described in claim 4, characterized in that: The thickness of the upper and lower polydimethylsiloxane film layers is 10μm-100μm.

6. The MNF flexible tactile sensing system for simulating the microstructure of fingertip skin as described in claim 1, characterized in that: The protruding annular ridge structures on the top elastic annular ridge layer and the bottom elastic annular ridge layer are all integrally molded.

7. The MNF flexible tactile sensing system for simulating the microstructure of fingertip skin as described in claim 1, characterized in that: The thickness of the top elastic annular ridge layer is 0.2mm-0.4mm; the thickness of the bottom elastic annular ridge layer is 0.3mm-0.5mm.

8. The MNF flexible tactile sensing system for simulating the microstructure of fingertip skin as described in claim 1, characterized in that: The diameter of the largest annular ridge in the annular ridge structure on the top elastic annular ridge layer and the bottom elastic annular ridge layer is 10mm-14mm, the spacing between the annular ridges is 0.3mm-0.7mm, the thickness of the annular ridge is 0.1mm-0.3mm, and the width of the annular ridge is 0.4mm-0.6mm.

9. The method for manufacturing the MNF flexible tactile sensing system as described in any one of claims 1 to 8, characterized in that, include: S1: Fabrication of micro / nano optical fibers; S2: The prepared micro / nano optical fiber is bent into a U-shaped structure with a bending radius of 0.3mm-0.5mm; S3: The sensing layer is obtained by sandwiching and encapsulating micro-nano optical fibers with two layers of polydimethylsiloxane thin film. S4: Prepare a top elastic annular ridge layer and a bottom elastic annular ridge layer with a raised annular ridge structure; The staggered arrangement of the annular ridges on the top elastic annular ridge layer and the annular ridges on the bottom elastic annular ridge layer allows the annular ridge structures of the top elastic annular ridge layer and the bottom elastic annular ridge layer to form an interlocking microstructure. S5: The sensing layer is clamped and fixed between the top elastic annular ridge layer and the bottom elastic annular ridge layer to obtain the MNF flexible tactile sensing system.

10. The manufacturing method of the MNF flexible tactile sensing system as described in claim 9, characterized in that: In step S1, a non-insulated tapered micro / nano fiber is obtained by fusion tapering of single-mode fiber. Specifically: First, the coating layer of the single-mode fiber is stripped and wiped with alcohol; then, the treated single-mode fiber is placed in a fiber fusion splicer for discharge operation to obtain a tapered fiber structure with a diameter of 60μm-80μm; finally, the tapered fiber structure is stretched by a fiber tapering machine using the flame melting tapering method to obtain a non-insulated tapered micro / nano fiber.

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