A finger touch force sensing device based on fiber grating and a sensing and detecting method thereof

Abstract

The application provides a finger touch force sensing device based on a fiber grating and a sensing and detecting method thereof. The sensing device is a split structure in which a finger tip sensing sleeve is rotationally connected with a finger body sleeve, and a rotation gap formed between the two is adapted to the bending track of a finger joint. The cavity structure of the finger tip sensing sleeve is adapted to the shape of a finger head, and a touch force sensing curved surface is arranged at the finger palm part, so that the touch force sensing area is conformally attached to the finger, and external touch force can be efficiently transmitted to a sensing element. The sensing fiber grating is embedded in the touch force sensing curved surface along the finger axis, one end of the sensing fiber grating is fixed to the inner side wall of the touch force sensing curved surface, the other end of the sensing fiber grating is sequentially arranged outside the curved surface and the sensing sleeve body, and then is connected with a demodulator in communication, so as to form a stable and continuous optical signal transmission link, and ensure that the wavelength drift signal of the grating due to the touch force can be accurately transmitted to the demodulation device, and a reliable signal source is provided for subsequent touch force calculation.

Description

Technical Field

[0001] This invention relates to the field of strain sensing technology, and in particular to a finger touch force sensing device based on fiber Bragg grating and its sensing and detection method. Background Technology

[0002] With the rapid development of intelligent manufacturing, medical rehabilitation, and human-computer interaction technologies, flexible sensors, as a core technology for achieving high-precision sensing and real-time feedback, are receiving increasing attention. Fiber Bragg grating (FBG) sensing technology, with its inherent safety, strong resistance to electromagnetic interference, high sensitivity, small size, and ease of reuse, has become an important development direction in the current sensing field. Among them, finger-type fiber Bragg grating sensors, as an innovative achievement deeply integrating fiber Bragg grating technology with ergonomics and wearable device concepts, are gradually becoming an important solution for fine finger movement sensing and biomechanical tactile force monitoring.

[0003] Fingers are the primary organs for humans to interact with the outside world in fine detail. The tactile force and tactile distribution information they exert contain rich operational intentions, physiological and pathological data. Finger-mounted fiber Bragg grating (FBG) sensors, deeply integrating FBG technology with wearable technology, can meet the practical needs of high-precision, non-invasive monitoring of finger tactile force. However, existing finger-mounted FBG sensors still have several technical shortcomings: poor adaptability between the sensor and finger joints, and the overall rigid connection can restrict finger joint movement; the structural design of the tactile force sensing area does not conform to the natural curvature of the human fingertip, making it difficult to achieve accurate multi-location detection of tactile force. Furthermore, existing FBG tactile force detection methods do not match the actual mechanical transmission and optical sensing characteristics, resulting in significant detection errors.

[0004] Therefore, how to provide a finger force sensing device and its sensing and detection method based on fiber optic gratings to improve the sensitivity and positional accuracy of force sensing and achieve accurate detection of the magnitude and distribution of fingertip force is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the aforementioned problems, this invention aims to provide a finger touch force sensing device and its sensing and detection method based on fiber optic gratings, thereby solving at least one of the aforementioned technical problems.

[0006] To at least solve the above-mentioned technical problems, in a first aspect, the present invention provides a finger force sensing device based on a fiber Bragg grating, the finger force sensing device based on a fiber Bragg grating comprising: A fingertip sensing sleeve and a finger body sleeve, wherein the fingertip sensing sleeve and the finger body sleeve are rotatably connected, and a rotational gap is formed between the fingertip sensing sleeve and the finger body sleeve to accommodate the movement of the finger joints. The fingertip sensing sleeve includes a sensing sleeve body, a tactile sensing surface, and a sensing fiber optic grating. The sensing sleeve body and the tactile sensing surface together form a cavity structure adapted to the shape of the fingertip. The cavity structure has a fingertip receiving cavity, and the tactile sensing surface is disposed at the fingertip of the fingertip receiving cavity. The sensing fiber optic grating is embedded in the tactile sensing surface along the finger axis. The end of the sensing fiber optic grating near the fingertip is fixedly connected to the inner wall of the tactile sensing surface, and the end near the finger joint passes through the tactile sensing surface and the sensing sleeve body in sequence and is then connected to the demodulator for communication.

[0007] Preferably, the tactile sensing surface is a three-segment continuous curved surface structure along the finger axis, with the longitudinal radius of curvature of the three segments gradually increasing from the fingertip to the finger joint and the transverse radius of curvature being the same; the sensing fiber grating has three interconnected sensing segments, which are sequentially and correspondingly arranged in the three segments of the curved surface structure along the finger axis, and the curvature of each sensing segment matches the transverse curvature of the corresponding curved surface structure.

[0008] Preferably, the tactile sensing surface is an integrated composite structure formed by bonding an inner rigid support layer and an outer flexible sensing layer. The inner rigid support layer is fixedly connected to the sensing sleeve body to fix and shape the tactile sensing surface, and the sensing fiber grating is embedded in the outer flexible sensing layer.

[0009] Preferably, the sensing sleeve body has connecting protrusions on both sides of the end near the finger joint, and the finger sleeve has corresponding mating protrusions on both sides of the end near the finger tip. The connecting protrusions and the mating protrusions are rotatably connected by a rotating shaft.

[0010] Preferably, the fiber optic grating is positioned on the side of the outer flexible sensing layer near the thickness midline, close to the inner rigid support layer.

[0011] Preferably, the device further includes a temperature compensation fiber grating, which is embedded in the finger sleeve, and one end of the temperature compensation fiber grating extends out from the finger sleeve and is communicatively connected to the demodulator.

[0012] Secondly, this application provides a touch force detection method, applied to the finger touch force sensing device based on fiber optic grating as provided in the first aspect, the method comprising: Based on the sensing characteristics of fiber optic gratings, a nonlinear expression is determined for the actual wavelength shift of the sensing segment caused solely by the contact force. Based on the curvature radius parameters of the three-segment surface structure of the tactile sensing surface, and combined with the bending strain effect of the fiber grating, the initial wavelength drift caused by structural bending in each of the sensing segments is calculated. The total wavelength drift of each sensing segment is collected in real time by a demodulator, and the actual wavelength drift of each sensing segment is calculated based on the total wavelength drift and the corresponding initial wavelength drift. Substituting the actual wavelength drift of each sensing segment into the nonlinear expression, the magnitude of the contact force at the corresponding position of each sensing segment is calculated respectively; Based on the contact force detection results of each sensing segment, and combined with the positional distribution of the three curved surface structures, the distribution of fingertip contact force is analyzed.

[0013] Preferably, the calculation process for the initial wavelength drift of any one of the sensing segments is as follows: Calculate the deformation of the sensing segment as it changes from a straight state to a curved state. The calculation formula is: ; The neutral layer length and the actual length of the induction segment after bending are obtained based on the arc length calculation formula: , ; Substituting the above formula into the bending strain formula The expression for bending strain is obtained from this: ; The initial wavelength drift is calculated using the correlation formula between fiber grating strain and wavelength drift: ; Where L is the neutral layer length of the surface where the sensing segment is located; L h This is the actual length of the sensing segment after it has been bent. R is the bending strain of the sensing segment; R is the longitudinal radius of curvature of the curved surface structure where the sensing segment is located; h is the vertical distance between the sensing segment and the neutral layer of the outer flexible sensing layer. The central angle of the surface structure where the sensing segment is located; This is the Bragg center wavelength of the sensing segment in a straight line state; The effective photoelastic coefficient of the optical fiber core; This represents the initial wavelength shift of the sensing segment.

[0014] Preferably, the nonlinear expression for the contact force experienced by any one of the sensing segments and its actual wavelength drift is: ; in, ; ; The contact force experienced by the sensing segment; This represents the actual wavelength shift of the sensing segment. This is the proportionality coefficient between the strain of the sensing segment based on the contact force and the surface deformation of the flexible sensing layer on its outer side; The Poisson's ratio of the outer flexible sensing layer; E1 is the Poisson's ratio of the external contact object; E2 is the Young's modulus of the outer flexible sensing layer; E3 is the Young's modulus of the external contact object. and For intermediate quantities in mechanical derivation; The longitudinal radius of curvature of the surface structure where the sensing segment is located; The longitudinal radius of curvature of the surface profile of the contacting object.

[0015] Preferably, the formula for calculating the actual wavelength drift of any one of the sensing segments is: ; in, This is the center wavelength of the sensing segment in a straight line. Temperature-based wavelength shift of fiber Bragg gratings for temperature compensation.

[0016] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a finger tactile sensing device and its sensing detection method based on fiber optic gratings. The sensing device is designed as a separate structure of a fingertip sensing sleeve and a finger body sleeve, with a rotating connection. The rotational gap between the two precisely adapts to the bending trajectory of the finger joint, breaking the rigid limitations of traditional integrated finger sleeve sensors on joint movement and significantly improving the flexibility and comfort of wearing the device. The cavity structure of the fingertip sensing sleeve is adapted to the shape of the fingertip, and a tactile sensing surface is provided on the fingertip to enhance tactile sensing. The area conforms to the shape of the finger, ensuring that external tactile force can be efficiently transmitted to the sensing element, laying the structural foundation for accurate tactile force detection. The sensing fiber grating is embedded in the tactile force sensing surface along the finger axis. One end of the sensing fiber grating is fixed to the inner wall of the tactile force sensing surface, and the other end passes through the surface and the sensing sleeve body in sequence and communicates with the demodulator, forming a stable and continuous optical signal transmission link. This ensures that the wavelength drift signal generated by the grating due to tactile force can be accurately transmitted to the demodulation device, providing a reliable signal source for subsequent quantitative calculation of tactile force.

[0017] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this specification or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of the finger touch force sensing device based on fiber optic grating in an embodiment of the present invention; Figure 2 This is a schematic diagram of the layout structure of the sensing fiber grating in an embodiment of the present invention; Figure 3 This is a cross-sectional view of the finger touch force sensing device based on fiber Bragg grating in an embodiment of the present invention; Figure 4 This is a schematic flowchart of the sensing and detection method in an embodiment of the present invention; Figure 5 This is a schematic diagram of the contact surface contour between the tactile sensing surface and the contacting object in an embodiment of the present invention.

[0020] Figure label: 1. Finger tip sensor sleeve; 11. Sensor sleeve body; 111. Connect the raised edge; 12. Tactile sensing curved surfaces; 13. Application of fiber Bragg gratings; 2. Finger sleeve; 21. Matching the raised edge. Detailed Implementation

[0021] The technical solutions in the embodiments of this specification 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 specification, and not all of the embodiments. Based on the embodiments in this specification, all other embodiments obtained by those skilled in the art are within the scope of protection of this invention. The keyword "and / or" involved in this embodiment indicates two situations: and or. In other words, A and / or B mentioned in the embodiments of this specification indicates two situations: A and B, or A or B. It describes three states of A and B. For example, A and / or B means: only A is included but not B; only B is included but not A; and A and B are included.

[0022] Furthermore, in the embodiments of this specification, when a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be an intervening component present. When a component is considered to be "set on" another component, it can be directly set on the other component or there may be an intervening component present.

[0023] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0024] Example 1 Please see Figures 1-3 Specifically, in this embodiment of the fiber optic grating-based finger force sensing device, the fiber optic grating-based finger force sensing device includes: a fingertip sensing sleeve 1 and a finger body sleeve 2, the fingertip sensing sleeve 1 and the finger body sleeve 2 being rotatably connected, and a rotational gap adapted to the movement of the finger joint being formed between the fingertip sensing sleeve 1 and the finger body sleeve 2; the fingertip sensing sleeve 1 includes a sensing sleeve body 11, a force-sensing curved surface 12, and a sensing fiber optic grating 13, the sensing sleeve body 11 and the force-sensing curved surface... The 12 components enclose a cavity structure that conforms to the shape of the fingertip. The cavity structure contains a fingertip receiving cavity, and the tactile sensing surface 12 is located at the fingertip of the fingertip receiving cavity. The sensing fiber optic grating 13 is embedded in the tactile sensing surface 12 along the finger axis. The end of the sensing fiber optic grating 13 near the fingertip is fixedly connected to the inner wall of the tactile sensing surface 12, and the end near the finger joint passes through the tactile sensing surface 12 and the sensing sleeve body 11 in sequence and then communicates with the demodulator.

[0025] Specifically, this application designs the sensing device as a separate structure of fingertip sensing sleeve 1 and finger body sleeve 2, with a rotating connection design. The rotational gap formed between the two precisely adapts to the bending trajectory of the finger joint, breaking the rigid limitation of traditional integrated finger sleeve sensors on joint movement and greatly improving the flexibility and comfort of wearing the device. The cavity structure of the fingertip sensing sleeve 1 is adapted to the shape of the fingertip, and a tactile sensing surface 12 is set at the fingertip, so that the tactile sensing area conforms to the shape of the finger, ensuring external... The tactile force can be efficiently transmitted to the sensing element, laying a structural foundation for accurate tactile force detection. The sensing fiber grating 13 is embedded in the tactile force sensing surface 12 along the finger axis. One end of the sensing fiber grating 13 is fixed to the inner wall of the tactile force sensing surface 12, and the other end passes through the surface and the sensing sleeve body 11 in sequence and is connected to the demodulator to form a stable and continuous optical signal transmission link. This ensures that the wavelength drift signal generated by the grating due to tactile force can be accurately transmitted to the demodulation device, providing a reliable signal source for subsequent quantitative calculation of tactile force.

[0026] As one possible approach, multiple application fiber Bragg gratings 13 can be provided in this application. The multiple application fiber Bragg gratings 13 are uniformly and parallelly embedded in the force-sensing curved surface 12. The end of each application fiber Bragg grating 13 near the fingertip is fixedly connected to the inner wall of the force-sensing curved surface 12, and the end near the finger joint passes through the force-sensing curved surface 12 and the sensing sleeve body 11 in sequence and then communicates with the demodulator.

[0027] Specifically, by setting up multiple fiber optic gratings 13, an array-style sensing layout for the fingertip area can be achieved, enabling differentiated detection of touch force at different lateral positions of the fingertip and avoiding blind spots in touch force position recognition caused by a single grating layout.

[0028] As one feasible approach, the tactile sensing surface 12 is a three-segment continuous curved surface structure along the finger axis. The longitudinal radius of curvature of the three curved surface structures gradually increases from the fingertip to the finger joint, while the lateral radius of curvature is the same. The sensing fiber grating 13 has three interconnected sensing segments. The three sensing segments of the sensing fiber grating 13 are sequentially and correspondingly arranged in the three curved surface structures along the finger axis, and the curvature of each sensing segment matches the lateral curvature of the corresponding curved surface structure.

[0029] Specifically, the tactile sensing surface 12 is designed as a three-segment continuous curved structure along the finger axis, with the longitudinal radius of curvature gradually increasing from the fingertip to the finger joint, while the lateral radius of curvature remains consistent. This conforms to the natural curvature distribution characteristics of the human fingertip, achieving a high degree of adaptation between the tactile sensing area and the fingertip. This significantly improves the transmission efficiency of tactile force from the fingertip surface to the internal fiber optic grating, ensuring that even minute tactile forces can be effectively sensed. Each sensing fiber optic grating 13 has three interconnected sensing segments, which are sequentially positioned along the finger axis within the three-segment curved structure, realizing the sensing of the fingertip, middle, and root of the finger. Independent detection of touch force zones at key locations overcomes the technical deficiency of traditional sensors that cannot identify the axial distribution of touch force in a single sensing area. Matching the curvature of each sensing segment with the transverse curvature of the corresponding surface structure avoids prestress caused by bending mismatch in the grating, thus protecting the structural integrity of the fiber Bragg grating and eliminating invalid wavelength drift caused by prestress, thereby improving the initial accuracy of touch force detection. The three sensing segments are integrated into the same fiber Bragg grating 13, realizing multi-position sensing integration of a single fiber, simplifying the grating layout and signal transmission structure, and reducing the overall complexity and manufacturing difficulty of the device.

[0030] As one feasible approach, the tactile sensing surface 12 is an integrated composite structure formed by bonding an inner rigid support layer and an outer flexible sensing layer. The inner rigid support layer is fixedly connected to the sensing sleeve body 11 to fix and shape the tactile sensing surface 12. The sensing application fiber optic grating 13 is embedded in the outer flexible sensing layer. The end of the sensing application fiber optic grating 13 near the fingertip is fixed in the outer flexible sensing layer, and the end near the finger joint passes through the outer flexible sensing layer and the sensing sleeve body 11 in sequence and is then connected to the demodulator for communication.

[0031] Specifically, the tactile sensing surface 12 adopts an integrated composite structure formed by bonding an inner rigid support layer and an outer flexible sensing layer. The inner rigid support layer is fixedly connected to the sensing sleeve body 11, providing stable structural support and shaping effect for the tactile sensing surface 12, and preventing the sensing surface from undergoing irregular deformation due to external forces. The outer flexible sensing layer has excellent deformation capability, which can efficiently convert the small external tactile force deformation into its own strain and quickly transmit it to the sensing fiber optic grating 13 embedded therein, so as to achieve high sensitivity sensing of small tactile forces.

[0032] Furthermore, to improve the efficiency of normal force transmission, the outer flexible sensing layer can be made of highly flexible silicone-like materials (such as Ecoflex or PDMS), with an elastic modulus of approximately 0.1~0.3MPa, which can fully deform and convert external force into internal strain.

[0033] The inner rigid support layer can be made of epoxy resin with relatively high hardness and an elastic modulus in the range of 0.5~2MPa, in order to provide structural support and prevent the finger sleeve from collapsing as a whole.

[0034] The upper and lower layers are bonded together to form a composite structure. Simulation analysis shows that the outer flexible sensing layer is 2.5 mm thick, and the inner rigid support layer is 1 mm thick. The fiber grating is embedded in the lower middle part of the outer flexible sensing layer (beyond the centerline and close to the finger joint), approximately 0.3-0.5 mm from the equivalent neutral axis. This design effectively senses strain while avoiding excessive prestress under pressure.

[0035] As one possible approach, the sensor sleeve body 11 has connecting flanges 111 on both sides of the end near the finger joint, and the finger sleeve 2 has corresponding mating flanges 21 on both sides of the end near the finger tip. The connecting flanges 111 and the mating flanges 21 are rotatably connected by a rotating shaft.

[0036] Specifically, by rotating the connecting protrusion 111 of the sensing sleeve body 11 to the mating protrusion 21 of the finger sleeve 2, a double-sided symmetrical hinge structure is constructed, which provides stable mechanical support for the rotation of the fingertip sensing sleeve 1 and ensures the smoothness of the device rotation when the finger joint is bent.

[0037] As an feasible approach, the fiber grating 13 is positioned near the inner rigid support layer, close to the centerline of the outer flexible sensing layer. This fully utilizes the bending strain effect, allowing the grating at this location to generate greater axial strain when the outer flexible sensing layer deforms under tactile force. This significantly enhances the fiber grating's sensitivity to tactile deformation, enabling precise capture and detection of minute tactile forces. This placement avoids structural damage caused by direct external pressure and friction to the grating when it is too close to the outer flexible layer, effectively extending its lifespan. It also prevents the grating from being too close to the rigid support layer, thus ensuring effective sensing of strain changes in the flexible layer. This achieves a dual optimization of grating structure protection and sensing sensitivity. Positioning the grating along this location allows the deformation of the flexible layer caused by tactile force to be directly converted into axial tensile / compressive strain of the grating, reducing interference from non-axial strain and ensuring that the wavelength drift signal of the grating is only related to the tactile force, improving the purity and accuracy of the tactile force detection signal.

[0038] As one possible approach, the device also includes a temperature compensation fiber grating, which is embedded in the finger sleeve 2, and one end of the temperature compensation fiber grating is led out from the finger sleeve 2 and communicates with the demodulator.

[0039] Specifically, a temperature compensation fiber optic grating is added to the device and embedded inside the finger sleeve 2. This location is in the non-touch-sensing area of ​​the device, where the grating is not affected by touch deformation and only responds to changes in ambient temperature. It can accurately collect the wavelength drift signal caused by temperature, providing an accurate compensation basis for eliminating temperature interference. One end of the temperature compensation fiber optic grating is led out from the finger sleeve 2 and communicates with the demodulator, forming a unified signal acquisition system with the sensing fiber optic grating 13. The demodulator can subtract the temperature-induced drift from the wavelength drift signal of the sensing fiber optic grating 13, achieving effective and accurate elimination of temperature interference. This solves the technical problem of large touch detection errors caused by changes in ambient temperature, and significantly improves the detection accuracy and environmental adaptability of the device under different temperature environments.

[0040] Example 2 Please see Figures 4-5 Specifically, this sensing and detection method is implemented in a finger tactile force sensing device based on a fiber optic grating as described in any one of Embodiment 1, and the method includes the following steps S110 to S150: Step S110: Determine the nonlinear expression for the actual wavelength shift of the sensing segment caused solely by the contact force based on the fiber optic grating sensing characteristics; As a feasible approach, the nonlinear expression for the contact force experienced by any sensing segment and its actual wavelength drift is as follows: ; in, ; ; The contact force experienced by the sensing segment; This represents the actual wavelength shift of the sensing segment. This is the proportionality coefficient between the strain of the sensing segment based on the contact force and the surface deformation of the flexible sensing layer on its outer side; The Poisson's ratio of the outer flexible sensing layer; E1 is the Poisson's ratio of the external contact object; E2 is the Young's modulus of the outer flexible sensing layer; E3 is the Young's modulus of the external contact object. and For intermediate quantities in mechanical derivation; The longitudinal radius of curvature of the surface structure where the sensing segment is located; The longitudinal radius of curvature of the surface profile of the contacting object.

[0041] The specific derivation process of the above nonlinear expression is as follows: During the strain transmission process, when the tactile sensing surface of the fingertip sensing area touches other objects, the tactile force first causes local strain in the outer flexible sensing layer with lower hardness. The surface material undergoes compressive deformation in the local area and indents inward. Stress concentration occurs in the area around the bottom sink, thereby forming tensile or compressive strain in the fiber grating axis.

[0042] The contact contour of the tactile sensing surface is represented as: ; The outer contour of the contacting object is represented as follows: ; The expression is based on a three-dimensional coordinate system with the contact point as the origin. The normal direction of the common tangent at the contact point is the z-axis of the three-dimensional coordinate system, and the plane containing the x-axis and y-axis is the common tangent at the contact point. The longitudinal radius of curvature of the surface structure where the contact point is located. The radius of curvature of the surface structure where the contact point is located; and The preset radius for the curved contour of the contacting object. The longitudinal radius of curvature of the surface profile of the contacting object. The lateral radius of curvature of the surface profile of the contacting object; As can be seen from the sensing characteristics of fiber optic gratings (FBG), the changes in the phase grating period and finite refractive index of an FBG under axial stress are much greater than the effects of radial stress. Therefore, the influence of radial stress on the sensing wavelength drift of the FBG can be ignored, and the influence of axial stress should be considered.

[0043] Therefore, modeling and analyzing the xz plane is performed, and the semi-ellipsoid is scaled to a coordinate system. For analysis of a hemispherical shape with radius of curvature, when the fingertip touches a flexible object, a tactile force is generated, causing local deformation, such as... Figure 5 The diagram shows a cross-sectional profile of the sensing device just as it comes into contact with an external object. N1 is an arbitrary point on the outer contour of the contact surface of the force-sensing surface, and the coordinates of this point on the x-axis are... N2 is a point on the outer contour of the contacting object, and line segment N1N2 is perpendicular to the xy plane. The distance between N1 and the common tangent plane of the contact point is... The distance between N2 and the common tangent plane of the contact point is ,because Much smaller than r1, Much smaller than r2, therefore: ; ; Then line segment ; Under the action of contact force F, deformation occurs near the contact point, and N1N2 coincide to a point N on the x-axis, with deformations of ω1 and ω2 respectively; according to Hertzian contact, the elastic convergence of the two is δ, and from geometric relationships, we know that: (Formula 1) To determine the deformation at point N, we take a differential area ds = μdμdφ within the contact circle of radius a under a uniformly distributed normal load q. Treating the contact surface as a problem of distributed load acting on a circular region of an elastic semi-infinite body, we can obtain the following solution from the Businesk equation: ; ; but, ; ; To determine the amount of each compression, the value of q needs to be determined. According to Hertz's contact principle, the height of each point on the hemispherical surface where the contact surface is located can represent the magnitude of the pressure q at that point. That is, at the origin, q0=ka, where k is the proportionality coefficient. Then, the pressure at a height z on the hemispherical surface is q=kz.

[0044] The length l of the chord containing N is: ; The pressure distributed along the chord l is the pressure on the hemisphere containing the chord: ; Due to symmetry, when integrating over φ, we can take φ∈(0, 90°), then: (Formula 2) Based on Formula 1 and Formula 2, we can obtain: (Formula 3) The pressure distribution on the contact surface can be represented as a hemisphere of radius *a*, where the pressure *q* at any point is equal to the height of that point multiplied by the proportionality constant *k*, where *k* = *q0* / *a*. The total force on the entire contact surface is equivalent to performing a double integral over the pressure *q*, which geometrically equates to calculating the volume of the hemisphere and multiplying it by *k*. Therefore, the contact pressure *F* can be expressed as: (Formula 4) Based on formulas three and four, we can obtain: (Formula 5) The deformation d of the flexible body directly above the fiber grating is: (Formula 6) In summary, the relationship between the contact force and the deformation d of the flexible body directly above the fiber grating can be obtained. (Formula 7) It is known that, under ideal conditions, the strain transmitted to the optical fiber can be expressed by its surface deformation as follows: We can obtain: (Formula 8) Furthermore, based on formulas five, six, seven, and eight, the nonlinear expression for the applied contact force and its actual wavelength drift is obtained: .

[0045] Step S120: Based on the curvature radius parameters of the three-segment surface structure of the tactile sensing surface, and combined with the bending strain effect of the fiber optic grating, calculate the initial wavelength drift of each sensing segment caused by structural bending. As one possible approach, the calculation process for the initial wavelength drift of any sensing segment involved in step S120 above is specifically as follows: Calculate the deformation of the sensing segment as it changes from a straight state to a curved state. The calculation formula is: ; The neutral layer length and the actual length of the induction segment after bending are obtained based on the arc length calculation formula: , ; Substituting the above formula into the bending strain formula The expression for bending strain is obtained from this: ; The initial wavelength drift is calculated using the correlation formula between fiber grating strain and wavelength drift: ; Where L is the neutral layer length of the surface where the sensing segment is located, and is equal to the length of the fiber grating embedded in the curve in its straight-line state; L h This is the actual length of the sensing segment after it has been bent. R is the bending strain of the sensing segment; R is the longitudinal radius of curvature of the curved surface structure where the sensing segment is located; h is the vertical distance between the sensing segment and the neutral layer of the outer flexible sensing layer. The central angle of the surface structure where the sensing segment is located; This is the Bragg center wavelength of the sensing segment in a straight line state; The effective photoelastic coefficient of the optical fiber core; This represents the initial wavelength shift of the sensing segment.

[0046] Specifically, the initial wavelength drift is calculated independently for any single sensing segment. This is adapted to the structural design of three segments with different curvatures of the tactile sensing surface, achieving precise and differentiated decoupling of drift interference in sensing segments at different locations. This avoids local errors caused by uniform compensation and further improves the overall accuracy of tactile force detection. The calculation process has a simple formula and clear logic, and can be quickly implemented using the demodulator's matching algorithm. It can adapt to the real-time detection requirements of tactile force, enhancing the practicality and engineering application value of the method.

[0047] It is understandable that the vertical distance between the sensing segments of multiple fiber Bragg gratings and the neutral layer of the outer flexible sensing layer is the same, which is h.

[0048] Step S130: The total wavelength drift of each sensing segment is collected in real time by the demodulator, and the actual wavelength drift of each sensing segment is calculated based on the total wavelength drift and the corresponding initial wavelength drift. As an feasible method, the formula for calculating the actual wavelength drift of any sensing segment is: ; in, The center wavelength of the sensing segment in a straight line state. Temperature-based wavelength shift of fiber Bragg gratings for temperature compensation.

[0049] When the tactile sensing surface of the fingertip sensing area comes into contact with another object, the tactile force initially causes localized strain in the softer outer sensing layer. The surface material undergoes compressive deformation and indents in a localized area, while stress concentration occurs around the bottom groove. This results in tensile or compressive strain along the fiber grating axis. This strain causes a change in the center wavelength of the fiber grating, which is the actual wavelength shift. When a fiber grating changes from a straight to a bent state, its wavelength also changes; this wavelength change is the initial wavelength shift. Meanwhile, since the human body temperature is higher than room temperature, when the sensing device is worn on a person's finger, the temperature change will cause a certain wavelength change in the fiber optic grating, which is... This wavelength drift can be obtained by demodulating the signal of the temperature-compensated fiber grating using a demodulator.

[0050] Step S140: Substitute the actual wavelength drift of each sensing segment into the nonlinear expression to calculate the magnitude of the contact force at the corresponding position of each sensing segment. Step S150: Based on the contact force detection results of each sensing segment and the positional distribution of the three curved surface structures, analyze the distribution of the fingertip contact force.

[0051] In summary, this embodiment determines the nonlinear expression for the actual wavelength drift of the sensing segment caused solely by the touch force based on the actual sensing characteristics of the fiber optic grating. This breaks the traditional assumption that the two are simplified to a linear relationship, making the correlation between touch force and wavelength drift more consistent with the actual laws of mechanical transmission and optical sensing conversion, fundamentally reducing the theoretical error in touch force calculation. Based on the curvature radius parameters of the three curved surface structures of the touch-sensing surface, combined with the bending strain effect, the initial wavelength drift of each sensing segment is calculated separately, achieving quantitative identification of the invalid drift caused by structural curvature, providing a precise basis for subsequent drift interference decoupling. The demodulator... The total wavelength drift of each sensing segment is collected in real time, and the actual wavelength drift is obtained by subtracting the corresponding initial wavelength drift and the wavelength drift caused by temperature. This achieves precise decoupling of structural curvature interference, eliminates detection errors caused by the device's own structural features, and ensures that the wavelength drift signal used for force calculation is a valid signal caused by pure force. The actual wavelength drift of each sensing segment is calculated independently and substituted into a nonlinear expression to obtain the corresponding force magnitude. Combined with the positional distribution of the three curved surface structures, the distribution of fingertip contact force is analyzed, achieving precise quantification of contact force at different fingertip positions and clear identification of distribution characteristics, meeting the actual needs of fine fingertip contact force detection.

[0052] It should be noted that the structures, proportions, sizes, etc., illustrated in the accompanying drawings are merely for illustrative purposes to aid those skilled in the art and to facilitate understanding and reading. They are not intended to limit the scope of the invention and therefore have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effectiveness and purpose of the invention, should still fall within the scope of the technical content disclosed herein. Furthermore, the terms "upper," "lower," "left," "right," "middle," and "one" used in this specification are merely for clarity and not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A finger tactile force sensing device based on a fiber Bragg grating, characterized in that, include: The system comprises a fingertip sensing sleeve and a finger body sleeve, the fingertip sensing sleeve and the finger body sleeve being rotatably connected, with a rotational gap between them adapted to the movement of the finger joint; the fingertip sensing sleeve includes a sensing sleeve body, a tactile sensing surface, and a sensing fiber optic grating, the sensing sleeve body and the tactile sensing surface together forming a cavity structure adapted to the shape of the fingertip, the cavity structure having a fingertip receiving cavity, the tactile sensing surface being disposed at the fingertip of the fingertip receiving cavity; the sensing fiber optic grating is embedded in the tactile sensing surface along the finger axis; one end of the sensing fiber optic grating near the fingertip is fixedly connected to the inner wall of the tactile sensing surface, and the other end near the finger joint passes through the tactile sensing surface and the sensing sleeve body in sequence and is then connected to a demodulator for communication.

2. The finger touch force sensing device based on fiber Bragg grating according to claim 1, characterized in that: The tactile sensing surface is a three-segment continuous curved surface structure along the finger axis. The longitudinal radius of curvature of the three segments gradually increases from the fingertip to the finger joint, while the lateral radius of curvature is the same. The sensing fiber grating has three interconnected sensing segments. The three sensing segments of the sensing fiber grating are sequentially and correspondingly arranged in the three segments of the curved surface structure along the finger axis, and the curvature of each sensing segment matches the lateral curvature of the corresponding curved surface structure.

3. The finger touch force sensing device based on fiber Bragg grating according to claim 2, characterized in that: The tactile sensing surface is an integrated composite structure formed by bonding an inner rigid support layer and an outer flexible sensing layer. The inner rigid support layer is fixedly connected to the sensing sleeve body, and the sensing fiber grating is embedded in the outer flexible sensing layer.

4. The finger touch force sensing device based on fiber Bragg grating according to claim 1, characterized in that: The sensor sleeve body has connecting protrusions on both sides of the end near the finger joint, and the finger sleeve has corresponding mating protrusions on both sides of the end near the finger tip. The connecting protrusions and the mating protrusions are rotatably connected by a rotating shaft.

5. The finger touch force sensing device based on fiber Bragg grating according to claim 4, characterized in that: The fiber grating for sensing applications is positioned on the side of the outer flexible sensing layer near the thickness midline, close to the inner rigid support layer.

6. The finger touch force sensing device based on fiber Bragg grating according to claim 4, characterized in that, The device also includes a temperature compensation fiber grating, which is embedded in the finger sleeve, and one end of the temperature compensation fiber grating extends out from the finger sleeve and is communicatively connected to the demodulator.

7. A tactile force detection method, applied to the finger tactile force sensing device based on a fiber optic grating as described in any one of claims 1-6, characterized in that, The method includes: Based on the sensing characteristics of fiber optic gratings, a nonlinear expression is determined for the actual wavelength shift of the sensing segment caused solely by the contact force. Based on the curvature radius parameters of the three-segment surface structure of the tactile sensing surface, and combined with the bending strain effect of the fiber grating, the initial wavelength drift caused by structural bending in each of the sensing segments is calculated. The total wavelength drift of each sensing segment is collected in real time by a demodulator, and the actual wavelength drift of each sensing segment is calculated based on the total wavelength drift and the corresponding initial wavelength drift. Substituting the actual wavelength drift of each sensing segment into the nonlinear expression, the magnitude of the contact force at the corresponding position of each sensing segment is calculated respectively; Based on the contact force detection results of each sensing segment, and combined with the positional distribution of the three curved surface structures, the distribution of fingertip contact force is analyzed.

8. The contact force detection method according to claim 7, characterized in that, The calculation process for the initial wavelength drift of any of the aforementioned sensing segments is as follows: Calculate the deformation of the sensing segment as it changes from a straight state to a curved state. The calculation formula is: ； The neutral layer length and the actual length of the induction segment after bending are obtained based on the arc length calculation formula: ， ； Substituting the above formula into the bending strain formula The expression for bending strain is obtained from this: ; The initial wavelength drift is calculated using the correlation formula between fiber grating strain and wavelength drift: ； Where L is the neutral layer length of the surface where the sensing segment is located; L h This is the actual length of the sensing segment after it has been bent. R is the bending strain of the sensing segment; R is the longitudinal radius of curvature of the curved surface structure where the sensing segment is located; h is the vertical distance between the sensing segment and the neutral layer of the outer flexible sensing layer. The central angle of the surface structure where the sensing segment is located; This is the Bragg center wavelength of the sensing segment in a straight line state; The effective photoelastic coefficient of the optical fiber core; This represents the initial wavelength shift of the sensing segment.

9. The contact force detection method according to claim 8, characterized in that, The nonlinear expression for the contact force experienced by any of the sensing segments and its actual wavelength drift is: ； in, ; ; The contact force experienced by the sensing segment; This represents the actual wavelength shift of the sensing segment. This is the proportionality coefficient between the strain of the sensing segment based on the contact force and the surface deformation of the flexible sensing layer on its outer side; The Poisson's ratio of the outer flexible sensing layer; E1 is the Poisson's ratio of the external contact object; E2 is the Young's modulus of the outer flexible sensing layer; E3 is the Young's modulus of the external contact object. and For intermediate quantities in mechanical derivation; The longitudinal radius of curvature of the surface structure where the sensing segment is located; The longitudinal radius of curvature of the surface profile of the contacting object.

10. The contact force detection method according to claim 8, characterized in that, The formula for calculating the actual wavelength drift of any of the aforementioned sensing segments is as follows: ； in, This is the center wavelength of the sensing segment in a straight line. Temperature-based wavelength shift of fiber Bragg gratings for temperature compensation.

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