Speed-related puncture characteristic modeling method for SMA flexible driving puncture device

Abstract

The invention discloses a speed-related puncture characteristic modeling method for an SMA flexible drive puncture device, and the method comprises the following steps: researching the characteristics of the SMA flexible drive puncture device in a skin tissue puncture process, firstly controlling a puncture needle to puncture skin tissues at different speeds, and obtaining puncture force data and input voltage and puncture displacement data; according to the puncture process, puncture force is divided into rigid force, shear force and friction force, and a speed-related puncture force equation is designed to describe speed-related characteristics of the rigid force and the friction force; a kinetic equation of the SMA flexible driving puncture device is established, a modulation GPI algorithm is used for describing the driving force of an SMA wire, and a puncture force equation related to the speed is combined into the kinetic equation; and performing parameter identification on the speed-related puncture force equation and the kinetic equation by using a least square algorithm to obtain an actual speed-related puncture characteristic model of the SMA flexible driving puncture device.

Description

Technical Field

[0001] The present invention belongs to the technical field of nonlinear modeling, and particularly relates to a method for modeling the speed-related puncture characteristics of an SMA flexible drive puncture device. Background Art

[0002] The shape memory alloy (SMA) flexible drive puncture device is a high-precision puncture device driven by SMA flexible material. As an intelligent material, SMA has the advantages of light weight, high power-to-weight ratio, and large strain range. Relatively, the main disadvantage of SMA material is its hysteretic nonlinear response, especially the nonlinear relationship between material strain and input voltage. This nonlinear response shows an asymmetric hysteresis and strong saturation characteristics, which lead to problems such as low positioning accuracy and instability during the driving process of SMA material. Moreover, for the SMA flexible drive puncture device, during the process of puncturing skin tissue, due to the viscoelasticity of skin tissue and muscle, the puncture needle will be subjected to resistance, thereby reducing the positioning accuracy of the SMA flexible drive puncture device. Therefore, in order to overcome the negative impact of the nonlinear characteristics of the SMA flexible drive puncture device, it is necessary to accurately model the hysteresis characteristics and the nonlinear puncture force during the puncture process.

[0003] Currently, for the hysteresis characteristics of SMA materials, many mathematical models have been proposed by scholars. The commonly used modeling strategies are mainly divided into physical models and phenomenological models. Among them, the physical model is relatively complex, which needs to start from the real physical principle of the hysteresis phenomenon and obtain accurate material parameters. Therefore, it is more difficult to practice; while the phenomenological model is based on the hysteresis phenomenon for modeling, without considering the cause of the hysteresis phenomenon, and is more universal and practical. In addition, the modeling of the force during the process of the puncture needle piercing into the skin tissue is also an important research topic. These puncture force equations can be used for surgical simulation, preoperative planning, and autonomous or robot-assisted medical procedures. By modeling the hysteresis characteristics and the speed-related puncture process, the influence of these nonlinear characteristics can be weakened or even eliminated, which is of great significance for improving the control accuracy of the SMA flexible drive puncture device. Summary of the Invention

[0004] The object of the present invention is to propose a method for modeling the speed-related puncture characteristics of an SMA flexible drive puncture device for the hysteretic nonlinear characteristics between the input and output of the SMA flexible drive puncture device and the nonlinear characteristics during the puncture process, so as to accurately describe the nonlinear dynamic characteristics of the SMA flexible drive puncture device. Based on the modulated GPI algorithm, the hysteretic nonlinear characteristics of the SMA flexible drive puncture device are described, and the speed-related puncture process is modeled to compensate for the nonlinearity of the puncture device.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A method for modeling the speed-related puncture characteristics of an SMA flexible drive puncture device, the speed-related puncture characteristics modeling method comprising the following steps: S1. Establish an SMA flexible drive puncture device: The SMA flexible drive puncture device is driven by 3 SMA wires and 1 linear deflection spring for the puncture needle. In the initial state, the deflection spring applies prestress to the 3 SMA wires to cause pre-strain in the 3 SMA wires. When the 3 SMA wires are subjected to an externally applied voltage and heat up, due to the characteristics of the SMA material itself, the SMA wires tend to return to their original length. During this process, the SMA wires generate a driving force, driving the puncture needle to generate displacement and puncture the skin tissue. When the input voltage becomes smaller, the driving force of the 3 SMA wires becomes smaller, and the elastic force of the deflection spring causes the puncture needle to return to its original position; S2. Collect the open-loop data of the puncture needle in the SMA flexible drive device at different speeds: First, control the puncture needle to puncture the skin tissue at different speeds, and then collect the puncture displacement data, puncture force data, and input voltage data of the puncture needle during the puncture process; S3. Establish a speed-related puncture force equation: According to the puncture process of the skin tissue, the puncture force of the puncture needle is divided into a rigid force, a shear force, and a frictional force. Among them, the rigid force occurs before the puncture needle pierces the skin tissue, and after the skin tissue is pierced, the rigid force disappears, and the frictional force and the shear force appear. Before the skin tissue is pierced, the rigid force is mainly generated by the antagonism between the puncture needle and the skin tissue membrane, and the limit value of the rigid force is related to the speed.

[0006] The rigid force equation related to speed is as follows: (1) Where is the puncture displacement of the puncture needle, is the puncture displacement when the skin tissue membrane ruptures, is the puncture speed of the puncture needle, are the first parameter and the second parameter describing the characteristics of the rigid force respectively, are the first parameter, the second parameter, and the third parameter describing the speed-related characteristics of the rigid force respectively; In addition, after the skin tissue is pierced, there is a sudden drop process force for the rigid force, and the defined expression is as follows: (2) Where are the first parameter and the second parameter describing the sudden drop process force respectively, is the puncture displacement at the end of the sudden drop process; The friction force equation related to speed is as follows: (3) wherein are the first parameter, the second parameter, the third parameter, and the fourth parameter for describing the characteristics of the speed-related frictional force; The shear force equation is as follows: (4) wherein is the shear force after the puncture needle penetrates the skin tissue; Combining Equation (3) and Equation (4), the overall frictional force equation and shear force equation are as follows: (5) wherein is the first parameter for describing the characteristics of the overall frictional force and shear force; In summary, the speed-related puncture force equation is as follows: (6); S4. Establish the dynamic equation of the SMA flexible drive puncture device: The expression of the dynamic equation of the SMA flexible drive puncture device is as follows: (7) wherein is the displacement of the puncture needle, are respectively the first derivative and the second derivative of, is the input voltage value of the SMA flexible drive puncture device, are respectively the first parameter, the second parameter, the third parameter, and the fourth parameter for describing the electromechanical characteristics of the SMA flexible drive puncture device; is the driving force of the SMA wire, described by the modulated GPI algorithm, represents time, and the expression of the modulated GPI algorithm is as follows: (8) wherein is the input shape function, and a linear input shape function is adopted, defined as follows: (9) wherein are respectively the first parameter and the second parameter for describing the linear input shape function; In Equation (8) is the Play operator of the modulated GPI algorithm, is the number of Play operators, is the weight of the Play operator, is the coefficient of the weight of the Play operator, is the threshold of the Play operator, is the coefficient of the threshold of the Play operator, and the definition of the Play operator is as follows: (10) is the m-th time step of the Play operator. When at that time becomes , indicating the initial time step, is the (m + 1)-th time step, is the number of time steps, is the input for modulating the GPI algorithm, is the mapping function of the Play operator, is the input of the mapping function, are the left and right envelope functions respectively, and the definitions are as follows: (11) where are the first, second, and third parameters of the left envelope function, are the first, second, and third parameters of the right envelope function; S5. Perform parameter identification: For the open-loop data collected in step S2, use the least squares algorithm to perform parameter identification on the velocity-related puncture force equation in step S3 and the dynamic equation in step S4, so as to obtain the velocity-related puncture characteristic model of the SMA flexible drive puncture device.

[0007] Furthermore, the SMA flexible drive puncture device further includes a signal acquisition unit and a control unit. The signal acquisition unit includes: a high-precision laser displacement sensor, a tensile and compressive force sensor, and a force transmitter; the control unit includes: a dsPACE simulation experiment platform and a power amplifier. The SMA flexible drive puncture device collects puncture displacement data and puncture force data through the signal acquisition unit and transmits them to the dsPACE simulation experiment platform for processing, generates a control signal and transmits it to the power amplifier to form an input voltage signal, and finally controls the puncture needle of the SMA flexible drive puncture device to generate a puncture displacement. Through the cooperation of the signal acquisition unit and the control unit, real-time monitoring and precise control of the puncture displacement and puncture speed are achieved, thereby ensuring the uniform puncture process of the puncture needle.

[0008] Furthermore, the velocity-related puncture characteristic model has the characteristics of many parameters and difficult parameter identification. In order to improve the performance of parameter identification, the parameter identification process in step S5 is as follows: S51. Perform least squares algorithm parameter identification on the velocity-related puncture force equation in step S3; S52. Apply the speed-related puncture force equation obtained by parameter identification to the dynamic equation of the SMA flexible drive puncture device in step S4, and perform parameter identification using the least squares algorithm.

[0009] Identifying the speed-related puncture force equation and the dynamic equation separately is beneficial to improving the efficiency and accuracy of parameter identification.

[0010] Furthermore, in the parameter identification process, the sum of squared errors function is used as the objective function. The objective function is iteratively minimized using the least squares algorithm, and the parameter vector corresponding to the minimum value of the objective function is the result of parameter identification. The expression of the objective function is as follows: (12) where is the objective function for parameter identification of the speed-related puncture force equation in step S51, is the parameter vector of the speed-related puncture force equation, is the objective function for parameter identification of the dynamic equation in step S52, is the parameter vector of the dynamic equation, is the puncture displacement data collected in step S2, is the puncture force data collected in step S2, is the number of data points collected, is the predicted puncture displacement value of the dynamic equation in step S4, is the predicted puncture force value of the speed-related puncture force equation in step S3.

[0011] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. In the modeling method proposed by the present invention, by segmenting the puncture force into a rigid force, a frictional force, and a shear force in the speed-related puncture force equation, the mechanical behavior of different stages during the puncture of skin tissue can be clearly described, facilitating precise control and optimization of the puncture process.

[0012] 2. In the modeling method of the present invention, by introducing a speed variable into the puncture force equation, the changing trends of the rigid force and the frictional force of the puncture needle at different speeds can be accurately captured, improving the dynamic response ability of the model.

[0013] 3. In the modeling method of the present invention, by using a linear input shape function in the modulation GPI algorithm, not only the number of parameters of the traditional GPI algorithm is reduced, thereby improving the efficiency of parameter identification, but also it is ensured that the speed-related puncture characteristic model of the SMA flexible drive puncture device is an affine nonlinear system, facilitating the design of control algorithms.

[0014] 4. To more accurately characterize the non-linear dynamic characteristics of the SMA flexible drive puncture device, the puncture force equation related to speed and the modulated GPI algorithm are combined with the kinetic equation to improve the prediction ability of the established model for non-linear characteristics such as saturation, asymmetry, and hysteresis. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0016] Figure 1 is the model structure diagram of the SMA flexible drive puncture device in the present invention; Figure 2 is the system structure diagram of the SMA flexible drive puncture device in the present invention; Figure 3 is the comparison diagram of the puncture forces of the puncture needle of the SMA flexible drive puncture device in the present invention at different puncture speeds; Figure 4 is the comparison diagram of the experimental data and the prediction of the puncture force equation related to speed at the puncture speed of 4 mm / s in the present invention; Figure 5 is the comparison diagram of the experimental data and the prediction of the puncture force equation related to speed at the puncture speed of 3 mm / s in the present invention; Figure 6 is the comparison diagram of the experimental data and the prediction of the puncture force equation related to speed at the puncture speed of 2.5 mm / s in the present invention; Figure 7 is the comparison diagram of the experimental data and the prediction of the puncture force equation related to speed at the puncture speed of 1.5 mm / s in the present invention; Figure 8 is the input signal frequency in the present invention under the comparison diagram of the experimental data and the prediction of the kinetic equation; Figure 9 is the input signal frequency in the present invention under the comparison diagram of the experimental data and the prediction of the kinetic equation. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] To enable those skilled in the art to better understand the solution of this application, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of this application.

[0018] In this application, the mention of "embodiment" means that the specific features, structures or characteristics described in connection with the embodiment can be included in at least one embodiment of this application. The phrase appears in various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described in this application can be combined with other embodiments.

[0019] Embodiment 1 This embodiment proposes a method for modeling the speed-related puncture characteristics of an SMA flexible drive puncture device, including the following steps: S1. Establish an SMA flexible drive puncture device As Figure 2 shown, the SMA flexible drive puncture device drives the puncture needle with 3 SMA wires and 1 linear deflection spring. In the initial state, the deflection spring applies prestress to the 3 SMA wires to generate prestrain in the 3 SMA wires. When the 3 SMA wires are subjected to an externally applied voltage and heat up, due to the characteristics of the SMA material itself, the SMA wires tend to return to their original length. During this process, the SMA wires generate a driving force, driving the puncture needle to generate displacement and puncture the skin tissue. When the input voltage becomes smaller, the driving force of the 3 SMA wires becomes smaller, and the elastic force of the deflection spring causes the puncture needle to return to its original position; S2. Collect the open-loop data of the puncture needle at different speeds First, control the puncture needle to puncture the skin tissue at different speeds, and then collect the puncture displacement data, puncture force data, and input voltage value during the puncture process; S3. Establish a speed-related puncture force equation According to the puncture process of the skin tissue, the puncture force of the puncture needle is divided into a rigid force, a shear force, and a frictional force. The rigid force occurs before the puncture needle pierces the skin tissue, and after piercing the skin tissue, the rigid force disappears, and the frictional force and shear force appear. Before the skin tissue is pierced, the rigid force is mainly generated by the antagonism between the puncture needle and the skin tissue membrane, and the value of the rigid force is related to the speed. The expression of the rigid force related to the speed is as follows: (1) Where is the puncture displacement of the puncture needle, is the puncture displacement when the skin tissue membrane ruptures, is the puncture speed of the puncture needle; are the first parameter and the second parameter describing the characteristics of the rigid force respectively; are the first parameter, the second parameter and the third parameter describing the characteristics related to the rigid force speed respectively.

[0020] In addition, after the skin tissue is punctured, there is a sharp drop process force of the rigid force, and the definition expression is as follows: (2) where are the first parameter and the second parameter describing the sharp drop process force, is the puncture displacement at the end of the sharp drop process; After the puncture needle punctures the skin tissue, the puncture needle begins to cut the punctured skin tissue, thus generating a shear force, and due to the adhesion force inside the skin tissue, the puncture needle will be affected by the frictional force. The expression of the frictional force related to speed is as follows: (3) where are the first parameter, the second parameter, the third parameter and the fourth parameter describing the characteristics of the frictional force related to speed; The expression of the shear force is as follows: (4) where is the shear force after the puncture needle penetrates the skin tissue; Combining formula (3) and formula (4), the expressions of the overall frictional force and shear force are obtained as follows: (5) where is the first parameter describing the characteristics of the overall frictional force and shear force; To sum up, the expression of the puncture force equation related to speed is as follows: (6); S4. Establish the dynamic equation of the SMA flexible drive puncture device The expression of the dynamic equation of the SMA flexible drive puncture device is as follows: (7) where is the displacement of the puncture needle, are respectively the first derivative and the second derivative of, is the input voltage value of the SMA flexible drive puncture device, They are the first parameter, the second parameter, the third parameter, and the fourth parameter that describe the electromechanical characteristics of the SMA flexible drive puncture device; is the driving force of the SMA wire, described by the modulated GPI algorithm, represents time, and the expression of the modulated GPI algorithm is as follows: (8) where is the input shape function, and a linear input shape function is adopted, defined as follows: (9) where are the first parameter and the second parameter that describe the linear input shape function, respectively; In equation (8) is the Play operator of the modulated GPI algorithm, is the number of Play operators, is the weight of the Play operator, is the coefficient of the weight of the Play operator, is the threshold of the Play operator, is the coefficient of the threshold of the Play operator, and the definition of the Play operator is as follows: (10) where is the m-th time step of the Play operator. When at this time becomes , representing the initial time step, is the (m + 1)-th time step, is the number of time steps, is the input of the modulated GPI algorithm, is the mapping function of the Play operator, is the input of the mapping function, are the left and right envelope functions, respectively, defined as follows: (11) where are the first parameter, the second parameter, and the third parameter of the left envelope function, are the first parameter, the second parameter, and the third parameter of the right envelope function; S5. Perform parameter identification For the open-loop data collected in step S2, the least squares algorithm is used to perform parameter identification on the velocity-related puncture force equation in step S3 and the dynamic equation in step S4, so as to obtain the velocity-related puncture characteristic model of the SMA flexible drive puncture device.

[0021] At this time, the system for collecting the open-loop data of the SMA flexible driving puncture device in step S2 includes a signal acquisition unit and a control unit. The signal acquisition unit includes: a high-precision laser displacement sensor, a tensile and compressive force sensor, and a force transmitter; the control unit includes: a dsPACE simulation experiment platform and a power amplifier. The SMA flexible driving puncture device collects the puncture displacement data and the puncture force data through the signal acquisition unit, and transmits them to the dsPACE simulation experiment platform for processing, generates a control signal and transmits it to the power amplifier to form an input voltage signal, and finally controls the puncture needle of the SMA flexible driving puncture device to generate a puncture displacement. Through the cooperation of the signal acquisition unit and the control unit, the real-time monitoring and precise control of the puncture displacement and puncture speed are realized, so as to ensure the uniform puncture process of the puncture needle.

[0022] At this time, the velocity-related puncture characteristic model has the characteristics of many parameters and difficult parameter identification. In order to improve the performance of parameter identification, the parameter identification process in step S5 is as follows: S51. Perform parameter identification on the velocity-related puncture force equation in step S3 using the least squares algorithm; S52. Apply the velocity-related puncture force equation obtained by parameter identification to the dynamic equation of the SMA flexible driving puncture device in step S4, and perform parameter identification using the least squares algorithm.

[0023] Identifying the velocity-related puncture force equation and the dynamic equation separately is beneficial to improving the efficiency and accuracy of parameter identification.

[0024] At this time, the parameter identification process uses the sum of squared errors function as the objective function. The objective function is iteratively obtained by the least squares algorithm to obtain the minimum value. The parameter vector corresponding to the minimum value of the objective function is the result of parameter identification. The expression of the objective function is as follows: (12) Where is the objective function for parameter identification of the velocity-related puncture force equation in step S51, is the parameter vector of the velocity-related puncture force equation, is the objective function for parameter identification of the dynamic equation in step S52, is the parameter vector of the dynamic equation, is the puncture displacement data collected in step S2, is the puncture force data collected in step S2, is the number of data points collected, is the puncture displacement prediction value of the dynamic equation in step S4, is the puncture force prediction value of the velocity-related puncture force equation in step S3.

[0025] Based on the above-mentioned speed-related puncture characteristic modeling method, the following implementation plan is proposed: To verify the effectiveness of the proposed modeling method, for the SMA flexible drive puncture device, the puncture force, puncture displacement, and input voltage data during the puncture of the simulated skin tissue are collected, a speed-related puncture force equation and the dynamic equation of the SMA flexible drive puncture device are established, and parameter identification is carried out to obtain the speed-related puncture characteristic model of the SMA flexible drive puncture device. The model structure is as Figure 1 shown. The input voltage passes through the modulated GPI algorithm to output the driving force to the dynamic equation. The dynamic equation outputs the puncture displacement and puncture speed, which are then transmitted to the speed-related puncture force equation. The puncture force equation outputs the puncture force and inputs it back into the dynamic equation, thus forming the overall speed-related puncture characteristic model of the SMA flexible drive puncture device.

[0026] (1) SMA flexible drive puncture device The system structure diagram of the SMA flexible drive puncture device is as Figure 2 shown, which includes the SMA flexible drive puncture device, the signal acquisition unit, and the control unit. The signal acquisition unit collects the puncture displacement and puncture force data and transmits them to the control unit. The control unit generates the input voltage signal and transmits it to the SMA flexible drive puncture device, thereby realizing the monitoring of the open-loop data and the control of the puncture needle. The specific information of each component in the system of the SMA flexible drive puncture device is as follows: SMA drive element: The No. 8 Ni-Ti alloy wire of Fort Wayne Metals Company is used as the drive element to provide the driving force, and a biasing spring is used for biasing drive.

[0027] Puncture object: The puncture object is a simulated skin tissue made of silicone material, which has a soft skin layer, a tough fascia layer, and an elastic sponge layer and other multi-layer structures, and can simulate the non-linear characteristics of the soft tissue puncture process.

[0028] Signal acquisition unit: The HG-C1000 series laser displacement sensor of Panasonic Company is used; the tension and compression sensor and the force transmitter are the DYLY-108 tension and compression sensor and the DY510 force transmitter of Dayang Company.

[0029] Control unit: The dSPACE1104 real-time simulation system developed by dSPACE Company of Germany is used, which can monitor the parameter data in real time through the ControlDesk software and realize the real-time control of the SMA flexible drive puncture device through the connection with MATLAB / Simulink; the power amplifier selects the OPA549 model power amplification module of Conway Technology Company, with a maximum output current of 8A and a maximum output power of 100W, which can meet the SMA drive requirements.

[0030] (2)Parameter identification of the velocity-related puncture force equation According to the velocity-related puncture force equation created in step S3, open-loop experiments are carried out at different puncture speeds and open-loop data are collected for parameter identification. The puncture speeds are set to 4 mm / s, 3 mm / s, 2.5 mm / s, and 1.5 mm / s. The collected open-loop data are as Figure 3 shown. It can be seen that the smaller the puncture speed, the larger the puncture displacement when the skin tissue membrane ruptures, the greater the corresponding puncture force at this time, and after piercing the skin tissue, the friction force and shear force in the stable state are also greater. The velocity-related puncture characteristic model established in the present invention conforms to the described puncture force characteristics. The effect of the velocity-related puncture force equation on predicting experimental data at a puncture speed of 4 mm / s is as Figure 4 shown. It can be seen that the prediction curve of the velocity-related puncture force equation can accurately fit the actual experimental data, and the root mean square error of the prediction is 0.1299 N, and the prediction result is accurate; the effect of the velocity-related puncture force equation on predicting experimental data at a puncture speed of 3 mm / s is as Figure 5 shown, and it also has an excellent fitting effect, and the root mean square error of the prediction is 0.1103 N; Figure 6 is the effect of the velocity-related puncture force equation on predicting experimental data at a puncture speed of 2.5 mm / s, and the root mean square error of the prediction is 0.1331 N, and the prediction result is accurate; Figure 7 is the effect of the velocity-related puncture force equation on predicting experimental data at a puncture speed of 1.5 mm / s, and the root mean square error of the prediction is 0.1292 N. The root mean square error value is small, and the prediction result of the velocity-related puncture force equation is good. The velocity-related puncture force equation established in the present invention can accurately describe the puncture force change characteristics at different speeds, which proves the effectiveness of the prediction of the velocity-related puncture force equation. In the above four groups of puncture force experiments, the parameters of the velocity-based friction force equation in formula (6) are respectively: ; the parameters of the velocity-based friction force and shear force equations are respectively: ; the parameters obtained by other parameter identifications are shown in Table 1.

[0031] Table 1. Parameter identification results of the velocity-related puncture force equation

[0032] (3)Parameter identification of the dynamic equation For the dynamic equation of the SMA flexible drive puncture device created in step S4, combined with the already identified velocity-related puncture force equation, parameter identification is carried out. Select the decaying input voltage signal as the input signal of the SMA flexible drive puncture device,Figure 8 It is the effect diagram of the prediction of the kinetic equation for the experimental data at Figure 9 It is the effect diagram of the prediction of the kinetic equation for the experimental data at

[0033] Table 2. Parameter identification results of the kinetic equation

[0034] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0035] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for modeling the speed-dependent puncture characteristics of an SMA flexible drive puncture device, characterized in that: The speed-dependent puncture characteristic modeling method comprises the following steps: S1. Establish an SMA flexible driven puncture device: The SMA flexible driven puncture device is driven by three SMA wires and a linear bias spring to drive the puncture needle. In the initial state, the bias spring applies prestress to the three SMA wires to make the three SMA wires produce prestrain. When the three SMA wires are subjected to an external voltage and heated up, a driving force is generated to drive the puncture needle to move and puncture the skin tissue. When the input voltage becomes smaller, the driving force of the three SMA wires becomes smaller, and the elastic force of the bias spring restores the puncture needle to its original position. S2, collecting open-loop data of the puncture needle at different speeds in the SMA flexible drive device: first, controlling the puncture needle to puncture the skin tissue at different speeds, and then collecting the puncture displacement data, puncture force data and input voltage data of the puncture needle during the puncture process; S3. Establishing the velocity-dependent puncture force equation: According to the puncture process of skin tissue, the puncture force of the puncture needle is divided into rigid force, shear force and friction force. Among them, the velocity-dependent rigid force equation is as follows: (1) Where x is the puncture displacement of the puncture needle, x max is the puncture displacement when the skin tissue membrane ruptures, v is the puncture speed of the puncture needle, are the first and second parameters that describe the rigid force characteristics, They are the first, second and third parameters describing the velocity-dependent characteristics of the rigid force; In addition, after piercing the skin tissue, the rigid force has a shaking-down process force, and the definition expression is as follows: (2) in are the first and second parameters describing the shaking process force, x s1 is the puncture displacement at the end of the shaking-down process; The velocity-dependent friction equation is as follows: (3) in are the first parameter, the second parameter, the third parameter and the fourth parameter describing the speed-dependent friction characteristics; The shear force equation is as follows: (4) in It is the shear force after the puncture needle penetrates the skin tissue; Combining equations (3) and (4), the overall friction force equation and shear force equation are as follows: (5) in It is the first parameter that describes the overall friction and shear characteristics; In summary, the velocity-dependent puncture force equation is as follows: (6) S4. Establish the dynamic equation of the SMA flexible driven puncture device: The expression of the dynamic equation of the SMA flexible driven puncture device is as follows: (7) where x is the displacement of the puncture needle, are the first and second derivatives of x, respectively, u is the input voltage value of the SMA flexible drive puncture device, They are the first parameter, the second parameter, the third parameter and the fourth parameter describing the electromechanical characteristics of the SMA flexible driven puncture device; is the driving force of the SMA wire, which is described by the modulated GPI algorithm. t represents the time. The expression of the modulated GPI algorithm is as follows: (8) in is the input shape function, which uses a linear input shape function and is defined as follows: (9) in are the first and second parameters describing the linear input shape function, respectively; In formula (8) is the Play operator that modulates the GPI algorithm, N is the number of Play operators, is the weight of the Play operator, is the coefficient of the weight of the Play operator, is the threshold of the Play operator, is the coefficient of the threshold of the Play operator. The definition of the Play operator is as follows: (10) where t m is the mth time step of the Play operator. When m=0, t m becomes t0, indicating the initial time step, t m+1 is the m+1th time step, M is the number of time steps, u(t) is the input of the modulated GPI algorithm, is the mapping function of the Play operator, is the input of the mapping function, They are the left and right envelope functions, defined as follows: (11) in are the first, second and third parameters of the left envelope function, are the first, second and third parameters of the right envelope function; S5. Perform parameter identification: For the open-loop data collected in step S2, a least squares algorithm is used to perform parameter identification on the speed-dependent puncture force equation in step S3 and the dynamic equation in step S4, thereby obtaining a speed-dependent puncture characteristic model of the SMA flexible drive puncture device.

2. The method for modeling the speed-dependent puncture characteristics of the SMA flexible drive puncture device according to claim 1, characterized in that: The SMA flexible driven puncture device also includes a signal acquisition unit and a control unit. The signal acquisition unit includes: a high-precision laser displacement sensor, a tension and pressure sensor, and a force transmitter; the control unit includes: a dsPACE simulation experiment platform and a power amplifier. The SMA flexible driven puncture device collects puncture displacement data and puncture force data through the signal acquisition unit, and transmits them to the dsPACE simulation experiment platform for processing, generates a control signal and transmits it to the power amplifier to form an input voltage signal, and finally controls the SMA flexible driven puncture device to generate puncture displacement.

3. The speed-dependent puncture characteristic modeling method for the SMA flexible drive puncture device according to claim 1, characterized in that: The parameter identification process in step S5 is as follows: S51, performing least squares algorithm parameter identification on the speed-related puncture force equation in step S3; S52, applying the velocity-related puncture force equation obtained by parameter identification to the dynamic equation of the SMA flexible drive puncture device in step S4, and performing least squares algorithm parameter identification.

4. The method for modeling the speed-dependent puncture characteristics of the SMA flexible drive puncture device according to claim 3, characterized in that: The objective function of the selected least squares algorithm parameter identification is as follows: (12) in is the objective function for parameter identification of the velocity-dependent puncture force equation in step S51, is the parameter vector of the velocity-dependent puncture force equation, is the objective function for parameter identification of the dynamic equation in step S52, is the parameter vector of the dynamic equation, X k is the puncture displacement data collected in step S2, P k is the puncture force data collected in step S2, K is the number of data points collected, is the predicted value of the puncture displacement of the kinetic equation in step S4, is the predicted puncture force value of the velocity-dependent puncture force equation in step S3.

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