A fingertip three-dimensional force fiber Bragg grating sensor and optimization method

Abstract

The present invention provides a fingertip three-dimensional force fiber Bragg grating sensor and an optimization method. A plurality of LET flexible hinges are combined to form a sensor elastomer, and a plurality of fiber Bragg gratings are respectively inserted into the sensor elastomer, and half of each fiber Bragg grating is treated with chemical nickel plating and electroplating nickel processes, while the other half is not treated, thereby realizing the functions of temperature decoupling and sensing the force changes of the measured object. The present invention also processes data through Design‑expert software to establish a response surface model of the fingertip three-dimensional force fiber Bragg grating sensor elastomer, and uses the sensitivity, sensitivity isotropy, range, and natural frequency of the sensor as optimization targets, and optimizes the size of the elastomer based on the multi-objective optimization algorithm NSGAII. The present invention has a simple structure, is easy to process, can realize high-precision sensing of external force changes, and provides a solution for the precise and complex operation content of robots.

Description

Technical Field

[0001] The present invention relates to the field of multi-dimensional force optical fiber sensing technology, and in particular to a fingertip three-dimensional force optical fiber Bragg grating sensor and an optimization method thereof. Background Art

[0002] With the rapid development of intelligent robots, the force and tactile perception of robots to external information is becoming increasingly important. Robots often need to have force and tactile information feedback to more accurately complete various delicate and complex tasks. Robot fingertip multi-dimensional force sensors are an important means of force and tactile perception for robots. Their sensing performance will directly affect the accuracy of perception and control of the entire robot system. Currently studied robot fingertip multi-dimensional force sensors are mostly tubular structures, beam structures, and Stewart platform structures in terms of elastic body structure. They have disadvantages such as low axial sensitivity, poor sensitivity consistency, and complicated design and manufacturing processes. Resistance strain gauges are mostly used as sensitive elements, and the number of signal leads is large, which is not conducive to miniaturization and integration. They also have the disadvantages of weak anti-electromagnetic interference ability and poor linearity.

[0003] Robot fingertip multi-dimensional force sensors based on fiber Bragg grating (FBG) offer significant advantages over traditional resistance strain gauges, such as immunity to electromagnetic interference and fewer leads, making them more suitable for diverse and complex environments. Currently, FBG-based multi-dimensional force sensors for robotic fingertips mostly employ adhesive arrangements, resulting in low strain transfer rates and difficulty meeting the requirements for highly sensitive and high-precision force sensing. Furthermore, these designs also suffer from drawbacks such as being bulky and lacking temperature self-compensation.

[0004] In summary, in view of the above shortcomings of traditional robot fingertip multi-dimensional force sensors, it is of great significance to study a new fiber Bragg grating robot fingertip multi-dimensional force sensor with compact structure, precision and dexterity, and temperature decoupling. Summary of the Invention

[0005] In view of this, the present invention proposes a fingertip three-dimensional force fiber Bragg grating sensor with a non-strain gauge sensing element, a compact structure, and the ability to perform temperature self-compensation, and an optimization method.

[0006] The technical solution of the present invention is implemented as follows: On the one hand, the present invention provides a fingertip three-dimensional force fiber Bragg grating sensor, comprising:

[0007] Several LET flexible hinges each include an arc-shaped body, with fan-shaped ends respectively provided at both ends of the body in the axial extension direction, and the edges of the fan-shaped ends shrinking toward the central axis of the body; the bodies of the several LET flexible hinges are each provided with a radially penetrating first window near the two fan-shaped ends; and a pair of penetrating fixing holes are correspondingly provided at the fan-shaped ends at both ends of each LET flexible hinge;

[0008] A plurality of fiber gratings are respectively inserted into a pair of fixing holes at two fan-shaped ends of a plurality of LET flexible hinges and fixedly connected to the LET flexible hinges;

[0009] Finger tip covers are arranged on the same side of the axial extension direction of the plurality of LET flexible hinges and respectively abut against the fan-shaped ends of the plurality of LET flexible hinges on the side; and are used to transmit the three-dimensional force applied by the outside to the plurality of LET flexible hinges and the plurality of fiber gratings;

[0010] Among them, several LET flexible hinges are sequentially enclosed to form a hollow cylindrical structure, the fan-shaped ends at both ends of adjacent LET flexible hinges are fixed to each other, and the bodies of adjacent LET flexible hinges are spaced apart, and a radially penetrating second window is formed in the spacing area between adjacent bodies; the grating areas of the several optical fiber gratings are also provided with a nickel-plated layer.

[0011] Based on the above technical solution, preferably, the grating areas of the several optical fiber Bragg gratings are located in the middle position of the two fan-shaped ends of each LET flexible hinge, and the nickel plating layer is located on the surface area of half of the grating area close to the fingertip cover side, and the other half of the surface area of the grating area is not nickel-plated.

[0012] Preferably, the central axes of the plurality of LET flexible hinges are collinearly arranged; and the axial extension directions of the plurality of fiber gratings are parallel to the axial extension directions of the plurality of LET flexible hinges.

[0013] Preferably, the first window is a fan-shaped hole, and the projection of the first window on the outer surface of the cylindrical structure is rectangular, and the projection on the radial section of the cylindrical structure is fan-shaped.

[0014] Preferably, the second window is a stepped hole, the projection of the second window on the outer surface of the cylindrical structure is stepped, and the projection on the radial section of the cylindrical structure is fan-shaped.

[0015] On the basis of the above technical solution, preferably, it further includes a first connecting member and a second connecting member;

[0016] One end of the first connecting member is fixedly arranged at one end of the axial extension direction of the plurality of LET flexible hinges and is fixedly connected to each fan-shaped end portion on this side; an annular groove is provided at the center of the surface of the finger tip cover close to the plurality of LET flexible hinges, and the other end of the first connecting member is fixedly connected to the inner surface of the annular groove;

[0017] The second connecting member is arranged at the other end of the axial extension direction of the plurality of LET flexible hinges and is fixedly connected to each fan-shaped end on this side; the other end of the second connecting member extends outward in a direction away from the plurality of LET flexible hinges.

[0018] On the other hand, the present invention also provides a method for optimizing a fingertip three-dimensional force fiber Bragg grating sensor, comprising the following steps:

[0019] The above-mentioned fingertip three-dimensional force fiber Bragg grating sensor is configured with four LET flexible hinges and four fiber Bragg gratings, with each fiber Bragg grating arranged symmetrically in the circumference and corresponding to each LET flexible hinge. Two non-adjacent fiber Bragg gratings are coplanar with the central axis of the cylindrical structure, and the cylindrical structure formed by the combination of each LET flexible hinge serves as the sensor elastic body.

[0020] Determining input variables, output variables including the mean strain of each fiber Bragg grating, and an optimization objective, and establishing a response surface model of the sensor elastic body; wherein the input variables include the sizes of the first window and the second window; and the output variables include the mean strain of each fiber Bragg grating when the sensor elastic body is subjected to an axial force Fz, and the mean strain of each fiber Bragg grating when the sensor elastic body is subjected to a transverse force Fx or a longitudinal force Fy.

[0021] Data analysis was performed using Design-expert software, and quadratic equations were selected for fitting to obtain the algebraic expressions of each output variable;

[0022] When an arbitrary load is applied to the sensor's elastic body, each fiber Bragg grating (FBG) serving as the output channel deforms under the force, causing the center wavelength to drift. The relationship between the center wavelength drift Δλ and the load F is Δλ = C·F; C is the stress compliance matrix, C = KC1, where C1 is the strain-force conversion matrix and K is the output-strain conversion coefficient.

[0023] The strain-force conversion matrix C1 is calculated by combining the response surface model. The output-strain conversion coefficient K is obtained based on the theoretical model of the central wavelength drift, and the stress compliance matrix C of the sensor elastic body is further obtained.

[0024] The input variable size of the sensor elastomer is optimized based on the multi-objective optimization algorithm NSGAII.

[0025] Preferably, the strain-force conversion matrix C1 calculated by combining the response surface model is: for any external load F = (FxFyFz) T , after the elastic body of the sensor is subjected to force, the output of each fiber Bragg grating is Δλ=(Δλ1 Δλ2 Δλ3 Δλ4) T , Δλ1, Δλ2, Δλ3, and Δλ4 are the center wavelength drifts of the four fiber Bragg grating outputs on the sensor elastic body. For the strain-force conversion matrix C1, its parameters are only affected by the sensor structure size and can be expressed algebraically:

[0026] The elements a0, a1, a2, a3, b0, b1, b2, b3, c0, c1, c2, and c3 in the strain-force conversion matrix c1 are the variables to be determined, that is, the algebraic expression of the strain obtained by the known three-dimensional load and the response surface model. After the strain-force conversion matrix C1 is decoupled, the algebraic expression of the strain inside it corresponds to the mean strain of each fiber Bragg grating;

[0027] According to the response surface model, let the load F1=(0 0 F z ) T Corresponding to (ε a1 ε a2 ε a3 ε a4 ) T ; Load F2=(F x 00) T Corresponding to (ε b1 ε b2 ε b3 ε b4 ) T , load F3=(0 F y 0) T Corresponding to (ε b2 ε b1 ε b4 ε b3 ) T , ε a1 , ε a2 , ε a3 and ε a4 is the mean strain of each fiber Bragg grating under the axial force Fz of the sensor elastic body; ε b1 , ε b2 , ε b3 and ε b4 is the average strain of each fiber Bragg grating under the action of the transverse force Fx or the longitudinal force Fy; substituting it into the formula ε=C1·F, we can get:

[0028]

[0029]

[0030] ε refers to the matrix of the mean strain under each load;

[0031] Then the decoupled strain-force conversion matrix C1 can be calculated.

[0032] Preferably, the output-strain conversion coefficient K is obtained based on the theoretical model of the center wavelength drift, and the stress compliance matrix C of the sensor elastic body is further obtained. The center wavelength λ of the fiber Bragg grating is described as follows based on the coupled mode theory:

[0033] λ=2n eff Λ; where n eff is the effective refractive index of the fiber Bragg grating, Λ is the period of the fiber Bragg grating, and the above equation can be fully differentiated to obtain: Δλ=2n eff ·ΔΛ+2Δn eff ·Λ;

[0034] Where ΔΛ is the elastic deformation of the optical fiber under stress, Δn eff The refractive index change caused by the optical-elastic effect of optical fiber; expanding and simplifying the total differential equation, we can get the ratio of the relative wavelength drift Δλ caused by the optical-elastic effect to the central wavelength λ where k ε is the relative wavelength strain sensitivity coefficient of the fiber Bragg grating, Among them, P 11 、P 12 ,υ and n eff is the inherent parameter of fused quartz; the output-strain conversion coefficient of the sensor K = k ε Substitute K into the right side of the decoupled strain-force conversion matrix C1 to obtain the stress compliance matrix C of the sensor elastic body.

[0035] Preferably, the optimization of the input variable size of the sensor elastic body based on the multi-objective optimization algorithm NSGAII is performed by the following steps:

[0036] Step 1: Randomly generate NP individuals in the decision variable space of the multi-objective optimization problem to form the initial population P t ;

[0037] Step 2: Calculate P t The fitness function value of each individual in multiple objectives;

[0038] Step 3: For population P t Perform fast non-dominated sorting and crowding density estimation;

[0039] Step 4: Set the evolutionary generation Gen=1;

[0040] Step 5: Use the binary tournament method to obtain the value of P t Select individuals and perform crossover and mutation operations to generate the offspring population Q t ;

[0041] Step 6: By merging P t With Q t Generate a combined population R t , that is, R t =P t +Q t ;

[0042] Step 7: Rt Perform non-dominated sorting, calculate the congestion degree in layers, and select N subpopulations according to the elite strategy to form a new generation of population P t+1 ;

[0043] Step 8: Determine whether Gen is less than the set iteration value. If so, add 1 to the evolutionary generation, and repeat steps 5, 6, 7, and 8 until the termination condition is met. If not, terminate the optimization operation.

[0044] The present invention provides a fingertip three-dimensional force fiber Bragg grating sensor and optimization method, which has the following beneficial effects compared with the prior art:

[0045] (1) The fingertip force transmission module and the fingertip force sensing module are provided to achieve three-dimensional force measurement. By using fiber Bragg grating as a sensing element, the sensor has good anti-electromagnetic interference performance. By adopting a surface coating structure for the fiber Bragg grating, the sensor can achieve temperature self-compensation. By adopting a symmetrical beam structure, the coupling mode between the sensor and the measured object is more flexible and has good compatibility.

[0046] (2) The paired fiber Bragg gratings and the corresponding LET-type flexible hinges are arranged symmetrically along the axis of the sensor, so that the sensor has good isotropy; by adopting a structure in which the two ends of the fiber Bragg grating are fixed to keep the fiber Bragg grating suspended tightly, the sensor has higher sensitivity than the sensor using the fiber Bragg grating adhesive type;

[0047] (3) The data was further processed by Design-expert software to establish the response surface model of the fingertip three-dimensional force fiber Bragg grating sensor elastomer and the multi-objective optimization algorithm NSGAII, so that the size of the sensor elastomer was further optimized and the sensing performance was improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0049] Figure 1 A three-dimensional diagram of a fingertip three-dimensional force fiber Bragg grating sensor according to the present invention;

[0050] Figure 2 This is a right side view of a fingertip three-dimensional force fiber Bragg grating sensor according to the present invention;

[0051] Figure 3This is a half-section right view of a fingertip three-dimensional force fiber Bragg grating sensor according to the present invention;

[0052] Figure 4 This is a three-dimensional diagram of the assembly state of several LET flexible hinges and a first connecting member and a second connecting member of a fingertip three-dimensional force fiber Bragg grating sensor of the present invention;

[0053] Figure 5 This is a right view of the combined state of several LET flexible hinges of a fingertip three-dimensional force fiber Bragg grating sensor of the present invention;

[0054] Figure 6 A three-dimensional diagram of a fiber Bragg grating (FBG) sensor for three-dimensional fingertip force according to the present invention;

[0055] Figure 7 This is a partially enlarged schematic diagram of a fiber Bragg grating region of a fingertip three-dimensional force fiber Bragg grating sensor according to the present invention;

[0056] Figure 8 A three-dimensional diagram of a fingertip tip cover of a fingertip three-dimensional force fiber Bragg grating sensor according to the present invention;

[0057] Figure 9 A schematic diagram of a fingertip three-dimensional force fiber Bragg grating sensor and an optimization method according to the present invention;

[0058] Figure 10 A flowchart of a fingertip three-dimensional force fiber Bragg grating sensor and an optimization method for establishing a response surface model of a sensor elastic body according to the present invention;

[0059] Figure numerals: 1. LET flexible hinge; 11. main body; 12. fan-shaped end; 100. first window; 200. second window; 13. fixing hole; 2. fiber Bragg grating; 3. fingertip cover; 300. nickel plating; 4. first connecting member; 5. second connecting member; 101. first LET flexible hinge; 102. second LET flexible hinge; 103. third LET flexible hinge; 104. fourth LET flexible hinge; 21. first fiber Bragg grating; 22. second fiber Bragg grating; 23. third fiber Bragg grating; 24. fourth fiber Bragg grating. DETAILED DESCRIPTION

[0060] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0061] like Figures 1-8As shown, on the one hand, the present invention provides a fingertip three-dimensional force fiber Bragg grating sensor, comprising

[0062] Several LET flexible hinges 1 all include an arc-shaped body 11, and fan-shaped ends 12 are respectively provided at both ends of the axial extension direction of the body 11, and the edges of the fan-shaped ends 12 shrink toward the central axis direction of the body 11; the body 11 is provided with a radially penetrating first window 100 near the two fan-shaped ends 12; the fan-shaped ends 12 at both ends of each LET flexible hinge 1 are correspondingly provided with a pair of penetrating fixing holes 13; the LET flexible hinge can realize complex movements and will deform under the action of external force.

[0063] A number of fiber gratings 2 are respectively placed in a pair of fixing holes 13 of two fan-shaped ends 12 of a number of LET flexible hinges 1, and are fixedly connected to the LET flexible hinges 1. Each fiber grating 2 in this solution can be a Bragg grating FBG. Each fiber grating 2 is placed in a pair of fixing holes 13 of the LET flexible hinge 1, and the surface of the fiber grating 2 adjacent to the fixing hole 13 is provided with fixing glue, and the fixing glue fixes the outer surface of the fiber grating 2 to the inner surface of the fixing hole 13. Each fiber grating 2 is located on the side of the main body 11 of the LET flexible hinge 1 close to the central axis, and the main body 11 can protect the fiber grating. Figure 6 As shown, the fixing glue is located at both ends of the fiber Bragg grating 2. To ensure the fiber Bragg grating is taut, external weights can be used to apply a pre-tightening force to each fiber Bragg grating during the sealing process. This maintains the tension of each fiber Bragg grating 2 after the sealing is completed with the fixing hole 13 of the fan-shaped end 12. It should be noted that coated optical fibers are provided at each end of the fiber Bragg grating to extend out of the fixing hole 13 to collect and further process the optical signal.

[0064] The finger tip cover 3 is arranged on the same side of the axial extension direction of the plurality of LET flexible hinges 1, and respectively abuts against the fan-shaped ends 12 of the plurality of LET flexible hinges 1 on this side; it is used to transmit the three-dimensional force applied by the outside world to the plurality of LET flexible hinges 1 and the plurality of optical fiber gratings 2.

[0065] Among them, several LET flexible hinges 1 are sequentially enclosed to form a hollow cylindrical structure, the fan-shaped ends 12 at both ends of adjacent LET flexible hinges 1 are fixed to each other, and the bodies 11 of adjacent LET flexible hinges 1 are arranged at intervals, and a radially penetrating second window 200 is formed in the interval area between adjacent bodies 11; the grating area of several optical fiber gratings 2 is also provided with a nickel-plated layer 300.

[0066] like Figure 3 Combine Figure 6 and Figure 7As shown, the grating regions of several fiber Bragg gratings (FBGs) 2 are located midway between the two fan-shaped ends 12 of each LET flexible hinge 1. A nickel coating 300 is applied to the surface of half of the grating region near the fingertip cover 3, while the other half is unnickel-plated. This nickel coating 300 enables temperature self-compensation of the fiber Bragg gratings 2.

[0067] Figure 7 The distribution of the nickel plating layer 300 in the gate area is specifically shown. Only half of the gate area is plated with nickel, and the other half is not plated with nickel.

[0068] The several LET flexible hinges 1 of this solution are arranged in pairs. Figure 5 It can be seen that the central axes of the plurality of LET flexible hinges 1 are collinearly arranged; the axial extension directions of the plurality of fiber gratings 2 are parallel to the axial extension directions of the plurality of LET flexible hinges 1. Figure 5 A cylindrical structure composed of four LET flexible hinges 1 is shown. Of course, the number of LET flexible hinges 1 can be further adjusted as needed, which will not be described here.

[0069] like Figure 1-5 As shown, the first window 100 is a fan-shaped hole. Its projection on the outer surface of the cylindrical structure is rectangular, and its projection on the radial cross-section of the cylindrical structure is fan-shaped. Similarly, the second window 200 is a stepped hole. Its projection on the outer surface of the cylindrical structure is stepped, and its projection on the radial cross-section of the cylindrical structure is fan-shaped. The second window 200 connects the edges of two adjacent bodies 11 and the gap between them, resulting in an overall stepped change.

[0070] In order to better fix the sensor, this solution also includes a first connecting member 4 and a second connecting member 5;

[0071] One end of the first connection 4 is fixedly arranged at one end of the axial extension direction of the several LET flexible hinges 1, and is fixedly connected to each fan-shaped end 12 on this side; the tip cover 3 is provided with an annular groove near the center of the surface of the several LET flexible hinges 1, and the other end of the first connection member 4 is fixedly connected to the inner surface of the annular groove; the surface of the first connection member 4 is provided with an external thread, and the annular groove is provided with an internal thread, and the annular groove and the first connection member 4 are threadedly connected.

[0072] The second connector 5 is disposed at the other end of the axially extending LET flexible hinges 1 and is fixedly connected to each fan-shaped end portion 12 on that side. The other end of the second connector 5 extends outward, away from the LET flexible hinges 1. To facilitate the extraction of the output end of the fiber Bragg grating, the second connector 5 is provided with a through hole corresponding to the fixing hole 13. The outer surface of the second connector 5 may further be provided with external threads for fastening.

[0073] In this solution, each LET flexible hinge 1, fingertip cover 3, first connector 4, and second connector 5 are all made of aluminum alloy and fabricated integrally using metal 3D printing technology. This allows the boundaries of adjacent LET flexible hinges 1 to be directly fused, and the fan-shaped ends 12 at the ends of each LET flexible hinge 1 are fused together to form a complete plate-like structure. The design dimensions of the first window 100 and second window 200 in this solution determine the performance of the sensor.

[0074] The method for forming the nickel plating layer 300 on the surface of each fiber Bragg grating 2 specifically comprises the following steps:

[0075] Step 1: Removing the protective layer: Immerse each fiber Bragg grating in acetone at room temperature for about 10-15 minutes, remove it, gently peel off its protective layer, and then place it in an ultrasonic cleaner and wash it with deionized water for 8-12 minutes to remove the residue when removing the protective layer;

[0076] Step 2, degreasing: After removing the protective layer, scrub each fiber Bragg grating with anhydrous alcohol for several times, then place it in an ultrasonic cleaner and wash it with anhydrous alcohol for 10-12 minutes, take it out and rinse it with deionized water for several times, and then place it in an ultrasonic cleaner and wash it with deionized water for 8-10 minutes to thoroughly clean the oil;

[0077] Step 3, sensitization: Weigh 5 grams of stannous chloride and dissolve it in 5 ml of hydrochloric acid, then dilute it to 100 ml with distilled water. Sensitize each fiber Bragg grating (FBG) that has been deprotected and degreased in the sensitization solution at room temperature for 10-15 minutes, then wash it in an ultrasonic cleaner with deionized water for 2-3 minutes.

[0078] Step 4, activation: the activation solution formula is palladium chloride 0.3g / L, hydrochloric acid 3ml / L, each fiber Bragg grating treated above is soaked in the activation solution at room temperature for 10-15 minutes, and then ultrasonically cleaned for 2-3 minutes, thus completing the pretreatment operation of each fiber Bragg grating;

[0079] Step 5, chemical nickel plating: placing the pretreated fiber Bragg grating into a chemical plating device containing a chemical plating solution for chemical nickel plating, thereby obtaining a fiber Bragg grating with a surface chemically plated with nickel;

[0080] Step 6, nickel electroplating: placing the chemically nickel-plated fiber Bragg grating into an electroplating device containing an electroplating solution to electroplating nickel, thereby obtaining a fiber Bragg grating with a nickel-plated layer.

[0081] This solution provides a method for using a fingertip three-dimensional force fiber Bragg grating sensor to implement three-dimensional force monitoring, including the following:

[0082] When the elastic body of the sensor contacts the object to be measured, the following parameters are obtained: axial force Fz, lateral force Fx, and longitudinal force Fy;

[0083] Among them, when Figure 1 Combine Figure 3 、 Figure 4 、 Figure 5 and Figure 6 For example, take the rightmost LET flexible hinge, that is, Figure 5 The LET flexible hinge 101 in the figure is used as the starting position. There are two pairs of LET flexible hinges arranged in pairs in the figure. For the convenience of distinction, they are marked as the first LET flexible hinge 101, the second LET flexible hinge 102, the third LET flexible hinge 103 and the fourth LET flexible hinge 104. The four LET flexible hinges are arranged in sequence in a counterclockwise direction. Each LET flexible hinge is correspondingly provided with a fiber Bragg grating 2, which are respectively Figure 6 The first fiber Bragg grating 21, the second fiber Bragg grating 22, the third fiber Bragg grating 23 and the fourth fiber Bragg grating 24. The first LET flexible hinge 101 and the third LET flexible hinge 103 are arranged opposite to each other, and the second LET flexible hinge 102 and the fourth LET flexible hinge 104 are arranged opposite to each other.

[0084] When the first LET flexible hinge 101, the second LET flexible hinge 102, the third LET flexible hinge 103 and the fourth LET flexible hinge 104 are deformed, each fiber Bragg grating undergoes deformation of equal magnitude and the same direction, and the center wavelengths of the first fiber Bragg grating 21, the second fiber Bragg grating 22, the third fiber Bragg grating 23 and the fourth fiber Bragg grating 24 drift accordingly. The axial force Fz is measured by the center wavelength drift of each fiber Bragg grating 2;

[0085] When the first LET flexible hinge 101 and the third LET flexible hinge 103 are deformed, the first fiber Bragg grating 21 and the third fiber Bragg grating 23 are deformed in equal magnitude and opposite directions, and the center wavelengths of the first fiber Bragg grating 21 and the third fiber Bragg grating 23 drift accordingly. The lateral force Fx is measured by differential processing of the wavelength drifts of the first fiber Bragg grating 21 and the third fiber Bragg grating 23.

[0086] When the second LET flexible hinge 102 and the fourth LET flexible hinge 104 are deformed, the second fiber grating 22 and the fourth fiber grating 24 are deformed in equal magnitude and opposite directions, and the center wavelengths of the second fiber grating 22 and the fourth fiber grating 24 drift accordingly. The longitudinal force Fy is measured by differential processing of the wavelength drift amounts of the second fiber grating 22 and the fourth fiber grating 24.

[0087] In addition, if Figure 9 and Figure 10 The present invention also provides a method for optimizing a fingertip three-dimensional force fiber Bragg grating sensor, which specifically includes the following steps:

[0088] S1: Configure the above-mentioned fingertip three-dimensional force fiber Bragg grating sensor, configure four LET flexible hinges 1 and four fiber Bragg gratings 2, each fiber Bragg grating 2 is arranged circumferentially symmetrically and is set one-to-one with the LET flexible hinge 1, and two non-adjacent fiber Bragg gratings 2 are set coplanar with the central axis of the cylindrical structure, and the cylindrical structure formed by the combination of each LET flexible hinge 1 is used as the sensor elastomer.

[0089] S2: Determine input variables, output variables including the mean strain of each fiber Bragg grating 2, and optimization objectives, and establish a response surface model of the sensor elastomer; wherein the input variables include the sizes of the first window 100 and the second window 200; the output variables include the mean strain of each fiber Bragg grating 2 when the sensor elastomer is subjected to an axial force Fz, and the mean strain of each fiber Bragg grating 2 when the sensor elastomer is subjected to a transverse force Fx or a longitudinal force Fy.

[0090] Here, determining the input variables is to determine the constraint variables and the corresponding constraint conditions; determining the output variables is to determine the strain value of the fiber Bragg grating under the action of three-dimensional force, the maximum stress value of the sensor elastic body and the first-order natural frequency. Figure 4 As shown, the five input variables of the fingertip three-dimensional force fiber Bragg grating sensor are the thickness x1 of the arc rod between the first through hole 100 and the second through hole 200, the arc spanned by the first through hole 100 x2, the axial height x3 of the first through hole 100 in the sensor elastic body, the arc spanned by the second through hole 200 x4 and the axial height x5 of the second through hole 200 in the sensor elastic body, and the constraints and selection intervals are set one by one.

[0091] Common design methods for establishing models using the response surface methodology include central composite and Box-Behnken designs. Both can efficiently estimate the first- and second-order coefficients in the final fitted model. However, the Box-Behnken design has lower operating costs and is more suitable for situations where the safe operating range is known. Therefore, the Box-Behnken design method is used to determine the combination of input variables.

[0092] Determine the output variables of the fingertip three-dimensional force fiber Bragg grating sensor, mainly including the strain mean ε of each fiber Bragg grating under the action of the axial force Fz a1 , ε a2 , ε a3 and ε a4 The maximum stress value δ1 of the sensor elastic body under the action of axial force Fz; the average strain value ε of each fiber Bragg grating under the action of lateral force Fx or longitudinal force Fy b1 , ε b2 , ε b3 and ε b4; The maximum stress value δ2 of the sensor elastic body under the action of lateral force Fx or longitudinal force Fy; and the first-order natural frequency τ of the sensor.

[0093] The sensitivity, sensitivity isotropy, sensor range and sensor natural frequency of the fingertip three-dimensional force fiber Bragg grating sensor are selected as optimization targets.

[0094] The input variables were determined using a co-simulation method using SolidWorks and ANSYS. The simulation parameters were calculated using the co-simulation method and corresponded one-to-one with the input variable combinations, eliminating the need for manual calculations and saving time. When determining the design point, the output variables were the values corresponding to the sensor when subjected to three-dimensional forces.

[0095] S3: Perform data analysis using Design-expert software, select the quadratic equation for fitting, and obtain the algebraic expression of each output variable.

[0096] The algebraic expressions of the output variables are:

[0097]

[0098] Among them, Y u (X) is the expression of each output variable, and the value range of u is [1, 11]; n = 5 is the number of input variables; α0 is the unknown coefficient of the constant term; α i is the unknown coefficient of the quadratic term; α ij is the unknown coefficient of the quadratic cross term; X i and X j is the expression of each input variable, where the value range of i and j is [1, 5].

[0099] Correlation coefficient R 2 , adjusted correlation coefficient Adj R 2 , prediction coefficient Pred R 2 , coefficient of variation CV%, and predicted sum of squares Adeq Precision are used to evaluate the accuracy of the response surface model. If all coefficients meet the accuracy standards of the response surface model, it means that the obtained response surface model is reliable.

[0100] S4: After an arbitrary load is applied to the sensor elastic body, each fiber Bragg grating 2 serving as the output channel is deformed by the force, causing the central wavelength to drift. The relationship between the central wavelength drift Δλ and the load F is Δλ = C·F; C is the stress compliance matrix, C = KC1, where C1 is the strain-force conversion matrix and K is the output-strain conversion coefficient.

[0101] S5: Calculate the strain-force conversion matrix C1 by combining the response surface model; obtain the output-strain conversion coefficient K based on the theoretical model of the central wavelength drift, and further obtain the stress compliance matrix C of the sensor elastic body.

[0102] The strain-force conversion matrix C1 mentioned in this step is calculated by combining the response surface model. For any external load F = (Fx Fy Fz) T , after the elastic body of the sensor is subjected to force, the output of each fiber Bragg grating is Δλ=(Δλ1 Δλ2 Δλ3 Δλ4) T , Δλ1, Δλ2, Δλ3, and Δλ4 are the center wavelength drifts of the four fiber Bragg grating outputs on the sensor elastic body. For the strain-force conversion matrix C1, its parameters are only affected by the sensor structure size and can be expressed algebraically:

[0103] Elements a0, a1, a2, a3, b0, b1, b2, b3, c0, c1, c2, and c3 in the strain-force conversion matrix C1 represent the variables to be determined. These are the algebraic expressions for the strains obtained from the known three-dimensional loads (i.e., the three-dimensional forces) and the response surface model. After decoupling the strain-force conversion matrix C1, the algebraic expression for the strains within it corresponds to the mean strain of each fiber Bragg grating (FBG). When subjected to a three-dimensional load, the sensor's elastic body undergoes structural changes, and this structural change is the strain under the corresponding stress. Under unit stress, the smaller the strain value of the sensor's elastic body, the greater its stiffness. Stiffness is the ratio of stress to strain. Therefore, the strain-force conversion matrix C1 can be understood as the inverse of the stiffness of the sensor's elastic body.

[0104] According to the response surface model, let the load F1=(0 0 F z ) T Corresponding to (ε a1 ε a2 ε a3 ε a4 ) T ; Load F2=(F x 00) T Corresponding to (ε b1 ε b2 ε b3 ε b4 ) T , load F3=(0 F y 0) T Corresponding to (ε b2 ε b1 ε b4 ε b3 ) T ; F1, F2 and F3 are three-dimensional loads, ε a1 , ε a2, ε a3 and ε a4 is the mean strain of each fiber Bragg grating under the axial force Fz of the sensor elastic body; ε b1 , ε b2 , ε b3 and ε b4 is the average strain of each fiber Bragg grating under the action of the transverse force Fx or the longitudinal force Fy; substituting it into the formula ε=C1·F, we can get:

[0105]

[0106]

[0107] ε refers to the matrix of the mean strain under each load;

[0108] Then the decoupled strain-force conversion matrix C1 can be calculated.

[0109] The following example illustrates that, in one embodiment, the magnitudes of Fz, Fx, and Fy are all equal to F0, but their directions are different, i.e., load F1 = (0 0 F0) T Corresponding to (ε a1 ε a2 ε a3 ε a4 ) T , load F2=(F0 0 0) T Corresponding to (ε b1 ε b2 ε b3 ε b4 ) T , load F3=(0 F0 0) T Corresponding to (ε b2 ε b1 ε b4 ε b3 ) T ; F1, F2 and F3 are three-dimensional loads, ε a1 , ε a2 , ε a3 and ε a4 is the average strain of the four fiber Bragg gratings under the axial force Fz of the sensor elastic body; ε b1 , ε b2 , ε b3 and ε b4 is the mean strain of each fiber Bragg grating under the action of the transverse force Fx; ε b2 , ε b1 , ε b4 and ε b3is the mean strain of each fiber Bragg grating under the longitudinal force Fy; substituting it into the formula ε=C1·F, we can obtain:

[0110]

[0111]

[0112]

[0113] Then the decoupled strain-force conversion matrix C1 can be calculated as follows: The example here is just for illustration. In practice, the sizes of Fz, Fx and Fy can be the same or different.

[0114] Furthermore, according to the coupled mode theory, the central wavelength λ of the fiber Bragg grating is described as:

[0115] λ=2n eff Λ; where n eff is the effective refractive index of the fiber Bragg grating, Λ is the period of the fiber Bragg grating, and the above equation can be fully differentiated to obtain: Δλ=2n eff ·ΔΛ+2Δn eff ·Λ;

[0116] Where ΔΛ is the elastic deformation of the optical fiber under stress, Δn eff The refractive index change caused by the optical-elastic effect of optical fiber; expanding and simplifying the total differential equation, we can get the ratio of the relative wavelength drift Δλ caused by the optical-elastic effect to the central wavelength λ Where ε is the strain of the fiber Bragg grating, k ε is the relative wavelength strain sensitivity coefficient of the fiber Bragg grating, Among them, P 11 、P 12 ,υ and n eff is the inherent parameter of fused quartz; the output-strain conversion coefficient of the sensor K = k ε Substitute K into the right side of the decoupled strain-force conversion matrix C1 obtained in the previous step to obtain the stress compliance matrix of the sensor elastic body:

[0117] S6: Optimize the input variable size of the sensor elastic body based on the multi-objective optimization algorithm NSGAII. The following steps are used:

[0118] Step 1: Randomly generate NP individuals in the decision variable space of the multi-objective optimization problem to form the initial population P t ;

[0119] Step 2: Calculate P t The fitness function value of each individual in multiple objectives;

[0120] Step 3: For population P t Perform fast non-dominated sorting and crowding density estimation;

[0121] Step 4: Set the evolutionary generation Gen=1;

[0122] Step 5: Use the binary tournament method to obtain the value of P t Select individuals and perform crossover and mutation operations to generate the offspring population Q t ;

[0123] Step 6: By merging P t With Q t Generate a combined population R t , that is, R t =P t +Q t ;

[0124] Step 7: R t Perform non-dominated sorting, calculate the congestion degree in layers, and select N subpopulations according to the elite strategy to form a new generation of population P t+1 ;

[0125] Step 8: Determine whether Gen is less than the set iteration value. If so, add 1 to the evolutionary generation, and repeat steps 5, 6, 7, and 8 until the termination condition is met. If not, terminate the optimization operation.

[0126] After obtaining the stress compliance matrix of the sensor elastomer, that is, the relationship between the wavelength change of each fiber Bragg grating caused by the input three-dimensional force and the stress magnitude, the multi-objective optimization algorithm NSGAII is further used to iteratively search for the optimal size of the sensor elastomer within the range of input variables, thereby obtaining a better structural size of the sensor elastomer.

[0127] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A fingertip three-dimensional force fiber Bragg grating sensor, characterized in that: include: A plurality of LET flexible hinges (1) each comprise an arc-shaped body (11), wherein fan-shaped ends (12) are respectively provided at both ends of the body (11) in an axial extension direction, and the edges of the fan-shaped ends (12) are contracted toward the central axis of the body (11); the body (11) is provided with a radially penetrating first window (100) near the two fan-shaped ends (12); and a pair of penetrating fixing holes (13) are correspondingly provided at the fan-shaped ends (12) at both ends of each LET flexible hinge (1); A plurality of optical fiber gratings (2) are respectively inserted into a pair of fixing holes (13) at two fan-shaped ends (12) of a plurality of LET flexible hinges (1) and fixedly connected to the LET flexible hinges (1); The finger tip cover (3) is arranged on the same side of the axial extension direction of the plurality of LET flexible hinges (1) and respectively abuts against the fan-shaped ends (12) of the plurality of LET flexible hinges (1) on the side; and is used for transmitting the three-dimensional force applied by the outside to the plurality of LET flexible hinges (1) and the plurality of optical fiber gratings (2); A plurality of LET flexible hinges (1) are sequentially enclosed to form a hollow cylindrical structure, the fan-shaped ends (12) at both ends of adjacent LET flexible hinges (1) are fixed against each other, and the bodies (11) of adjacent LET flexible hinges (1) are arranged at intervals, and a radially penetrating second window (200) is formed in the interval area between the adjacent bodies (11); and the grating areas of the plurality of optical fiber gratings (2) are further provided with a nickel-plated layer (300).

2. The fingertip three-dimensional force fiber Bragg grating sensor according to claim 1, characterized in that: The grating areas of the plurality of fiber gratings (2) are located in the middle of the two fan-shaped ends (12) of each LET flexible hinge (1), and the nickel plating layer (300) is located on the surface area of half of the grating area close to the fingertip cover (3), and the other half of the surface area of the grating area is not nickel-plated.

3. The fingertip three-dimensional force fiber Bragg grating sensor according to claim 2, characterized in that: The central axes of the plurality of LET flexible hinges (1) are arranged collinearly; and the axial extension directions of the plurality of optical fiber gratings (2) are arranged parallel to the axial extension directions of the plurality of LET flexible hinges (1).

4. The fingertip three-dimensional force fiber Bragg grating sensor according to claim 3, characterized in that: The first window (100) is a fan-shaped hole. The projection of the first window (100) on the outer surface of the cylindrical structure is rectangular, and the projection on the radial cross section of the cylindrical structure is fan-shaped.

5. The fingertip three-dimensional force fiber Bragg grating sensor according to claim 3, characterized in that: The second window (200) is a stepped hole, and the projection of the second window (200) on the outer surface of the cylindrical structure is stepped, and the projection on the radial cross section of the cylindrical structure is fan-shaped.

6. The fingertip three-dimensional force fiber Bragg grating sensor according to claim 1, characterized in that: It also includes a first connecting member (4) and a second connecting member (5); One end of the first connecting member (4) is fixedly arranged at one end of the axial extension direction of the plurality of LET flexible hinges (1) and is fixedly connected to each fan-shaped end portion (12) on the side; an annular groove is provided on the tip cover (3) near the center of the surface of the plurality of LET flexible hinges (1), and the other end of the first connecting member (4) is fixedly connected to the inner surface of the annular groove; The second connecting member (5) is arranged at the other end of the axial extension direction of the plurality of LET flexible hinges (1) and is fixedly connected to each fan-shaped end portion (12) on this side; the other end of the second connecting member (5) extends outward in a direction away from the plurality of LET flexible hinges (1).

7. A method for optimizing a fingertip three-dimensional force fiber Bragg grating sensor, characterized in that: The steps include: A fingertip three-dimensional force fiber Bragg grating sensor according to any one of claims 1 to 6 is configured, wherein four LET flexible hinges (1) and four fiber Bragg gratings (2) are configured, each fiber Bragg grating (2) is circumferentially symmetrically arranged and arranged in a one-to-one correspondence with the LET flexible hinge (1), two non-adjacent fiber Bragg gratings (2) are arranged coplanar with the central axis of the cylindrical structure, and the cylindrical structure formed by combining the LET flexible hinges is used as a sensor elastic body; Determine input variables, output variables including the strain mean of each fiber Bragg grating (2), and optimization targets, and establish a response surface model of the sensor elastic body; wherein the input variables include the sizes of the first window (100) and the second window (200); the output variables include the strain mean of each fiber Bragg grating (2) when the sensor elastic body is subjected to an axial force Fz, and the strain mean of each fiber Bragg grating (2) when the sensor elastic body is subjected to a transverse force Fx or a longitudinal force Fy; Data analysis was performed using Design-expert software, and quadratic equations were selected for fitting to obtain the algebraic expressions of each output variable; When any load is applied to the elastic body of the sensor, each fiber Bragg grating (2) as an output channel is deformed by the force, causing the center wavelength to drift. The relationship between the center wavelength drift Δλ and the load F is Δλ=C·F; C is the stress compliance matrix, C=KC1, where C1 is the strain-force conversion matrix, and K is the output-strain conversion coefficient; The strain-force conversion matrix C1 is calculated by combining the response surface model. The output-strain conversion coefficient K is obtained based on the theoretical model of the central wavelength drift, and the stress compliance matrix C of the sensor elastic body is further obtained: The input variable size of the sensor elastomer is optimized based on the multi-objective optimization algorithm NSGAII.

8. The method for optimizing a fingertip three-dimensional force fiber Bragg grating sensor according to claim 7, characterized in that: The strain-force conversion matrix C1 calculated by combining the response surface model is: for any external load F = (Fx Fy Fz) T , after the elastic body of the sensor is subjected to force, the output of each fiber Bragg grating is Δλ=(Δλ1 Δλ2 Δλ3 Δλ4) T , Δλ1, Δλ2, Δλ3, and Δλ4 are the center wavelength drifts of the four fiber Bragg grating outputs on the sensor elastic body respectively; for the strain-force conversion matrix C1, its parameters are only affected by the sensor structure size and can be expressed algebraically as follows: The elements a0, a1, a2, a3, b0, b1, b2, b3, c0, c1, c2, and c3 in the strain-force conversion matrix C1 are the variables to be determined, that is, the algebraic expression of the strain obtained by the known three-dimensional load and the response surface model. After the strain-force conversion matrix C1 is decoupled, the algebraic expression of the strain inside it corresponds to the mean strain of each fiber Bragg grating; According to the response surface model, let the load F1=(0 0 F z ) T Corresponding to (ε a1 ε a2 ε a3 ε a4 ) T ; Load F2=(F x 0 0) T Corresponding to (ε b1 ε b2 ε b3 ε b4 ) T , load F3=(0 F y 0) T Corresponding to (ε b2 ε b1 ε b4 ε b3 ) T , ε a1 , ε a2 , ε a3 and ε a4 is the mean strain of each fiber Bragg grating under the axial force Fz of the sensor elastic body; ε b1 , ε b2 , ε b3 and ε b4 is the average strain of each fiber Bragg grating under the action of the transverse force Fx or the longitudinal force Fy; substituting it into the formula ε=C1·F, we can get: ε refers to the matrix of the mean strain under each load; Then the decoupled strain-force conversion matrix C1 can be calculated.

9. The method for optimizing a fingertip three-dimensional force fiber Bragg grating sensor according to claim 8, characterized in that: The output-strain conversion coefficient K is obtained based on the theoretical model of the center wavelength drift, and the stress compliance matrix C of the sensor elastic body is further obtained. The center wavelength λ of the fiber Bragg grating is described as follows based on the coupled mode theory: λ=2n eff Δ; where n eff is the effective refractive index of the fiber Bragg grating, Λ is the period of the fiber Bragg grating, and the above equation can be fully differentiated to obtain: Δλ=2n eff ·ΔΛ+2Δn eff ·Λ; Where ΔΛ is the elastic deformation of the optical fiber under stress, Δn eff The refractive index change caused by the optical-elastic effect of optical fiber; expanding and simplifying the total differential equation, we can get the ratio of the relative wavelength drift Δλ caused by the optical-elastic effect to the central wavelength λ where k ε is the relative wavelength strain sensitivity coefficient of the fiber Bragg grating, Among them, P 11 、P 12 ,υ and n eff is the inherent parameter of fused quartz; the output-strain conversion coefficient of the sensor K = k ε Substitute K into the right side of the decoupled strain-force conversion matrix C1 to obtain the stress compliance matrix C of the sensor elastic body.

10. The optimization method of a fingertip three-dimensional force fiber Bragg grating sensor according to claim 7, characterized in that: The optimization of the input variable size of the sensor elastic body based on the multi-objective optimization algorithm NSGAII adopts the following steps: Step 1: Randomly generate NP individuals in the decision variable space of the multi-objective optimization problem to form the initial population P t ; Step 2: Calculate P t The fitness function value of each individual in multiple objectives; Step 3: For population P t Perform fast non-dominated sorting and crowding density estimation; Step 4: Set the evolutionary generation Gen=1; Step 5: Use the binary tournament method to obtain the value of P t Select individuals and perform crossover and mutation operations to generate the offspring population Q t ; Step 6: By merging P t With Q t Generate a combined population R t , that is, R t =P t +Q t ; Step 7: R t Perform non-dominated sorting, calculate the congestion degree in layers, and select N subpopulations according to the elite strategy to form a new generation of population P t+1 ; Step 8: Determine whether Gen is less than the set iteration value. If so, add 1 to the evolutionary generation, and repeat steps 5, 6, 7, and 8 until the termination condition is met. If not, terminate the optimization operation.

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