Rollable coated multi-point force sensing film, execution arm and force sensing method

Abstract

The invention belongs to the technical field of medical robots, and particularly relates to a rollable coating type multi-point force sensing film, an execution arm and a force sensing method. The piezoelectric film comprises a lower high-elasticity base film, a distributed heterogeneous lower electrode layer, a PVDF piezoelectric film, a distributed heterogeneous upper electrode layer and a lower high-elasticity base film which are sequentially laminated from bottom to top, the PVDF piezoelectric film comprises a dense sensing section located at the far end, a uniform distribution section located in the middle and a sparse sensing section located at the near end. When in use, the coiled coated multi-point force sensing film is coiled by taking the length direction of the film as a coiling shaft. The flexible film integrated with the distributed PVDF piezoelectric unit is directly used as electronic skin to cover the side wall of the catheter, so that the space sensing efficiency is remarkably improved, and the optimal balance between the sensing precision and the sensing range is realized under the condition that the number of the sensing units is limited; therefore, the flexible operation execution arm has gradient tactile perception capability similar to biological nerves.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of medical robots, and particularly relates to a rollable coated multi-point force sensing film, an execution arm and a force sensing method. BACKGROUND

[0002] Force sensing of a flexible surgical robot is one of the key problems to be solved in the field of medical robots. At present, related researches mainly focus on two technical paths: one is to integrate sensors at the distal end of a surgical instrument or a driving joint to obtain distal mechanical information through direct measurement or indirect mechanical modeling; the other is to estimate the interaction force by means of mechanical modeling or intelligent algorithm to obtain approximate force information in an indirect way.

[0003] In the aspect of integrated sensors, Xu et al. developed a steerable catheter integrated with fiber Bragg gratings (FBG), which realizes real-time contact force sensing by monitoring the reflected total power without relying on spectral analysis, and has good temperature robustness. Li et al. designed a remote center of motion (RCM) mechanical arm with 4 degrees of freedom, which can perform orientation, insertion, rotation and linear motion of a needle, and focuses on realizing accurate force sensing during puncture and evaluating the operator's perception of puncture force.

[0004] In the aspect of force estimation model, Wu et al. constructed a subclavian vein puncture force model for a puncture surgical robot, which divides the needle-tissue interaction into four stages. The model can accurately describe the mechanical characteristics of each stage, find that the puncture force increases with the increase of needle diameter and insertion angle, and decreases with the increase of vein pressure, and reveals the coupling effect between vein pressure and vessel diameter. Back et al. proposed a multi-element dynamic-static model for flexible catheters based on the Bernoulli-Euler hypothesis, which considers tendon friction, compression effect and Young's modulus change caused by spiral structure, and realizes real-time prediction of catheter three-dimensional shape and contact force under given tendon tension.

[0005] Although the existing researches have made certain progress in force sensing of surgical robots, most of them still focus on force sensing at the distal end of the actuator, and the research on interaction force sensing of the side wall of the flexible catheter is still insufficient. At present, the identification of the side wall force mainly relies on physical modeling estimation method, which has the problems of limited accuracy, complex model and large calculation burden, and it is urgent to develop new sensing strategies to improve the accuracy and practicality of force sensing. SUMMARY

[0006] The purpose of the present application is to overcome the defects of relying on complex physical models and insufficient accuracy of side wall force sensing in the prior art, and to provide a rollable coated multi-point force sensing film based on PVDF piezoelectric film, which can directly and accurately sense the contact force of the side wall in a distributed heterogeneous manner.

[0007] The technical scheme adopted by the present application to solve its technical problems is:

[0008] As a first aspect, the present application provides a rollable coated multi-point force sensing film, comprising a lower high-elasticity base film, a distributionally heterogeneous lower electrode layer, a PVDF piezoelectric film, a distributionally heterogeneous upper electrode layer and a lower high-elasticity base film arranged in order from bottom to top.

[0009] The PVDF piezoelectric film is divided into three functional zones along its length direction, including a dense sensing segment at the distal end, a uniformly distributed segment at the middle and a sparse sensing segment at the proximal end; the dense sensing segment includes three parallelly arranged stress unit groups, the uniformly distributed segment includes two parallelly arranged stress unit groups, and the sparse sensing segment includes one stress unit group.

[0010] The corresponding stress units of the distributionally heterogeneous lower electrode layer and the distributionally heterogeneous upper electrode layer are respectively connected in conduction with the PVDF piezoelectric film, and are provided with a silk-screen silver paste electrode for leading out an electrical signal.

[0011] In use, it is rolled into a rollable coated multi-point force sensing film with its length direction as the rolling axis.

[0012] Further, the material thickness of the PVDF piezoelectric film is 26 ~ 30 ; the Young's modulus Y of the PVDF piezoelectric film is .

[0013] Further, the segment length L1 of the dense sensing segment and the segment length L2 of the uniformly distributed segment are equal, and the segment length L3 of the sparse sensing segment is greater than L1 or L2.

[0014] Among them, the total length L1+L2+L3 is less than 300mm.

[0015] Further, the dense sensing segment includes 30 piezoelectric sensitive units; the uniformly distributed segment includes 20 piezoelectric sensitive units; and the sparse sensing segment includes 14 piezoelectric sensitive units.

[0016] Further, the lower high-elasticity base film and the lower high-elasticity base film both adopt thermoplastic polyurethane film; the thickness of the lower high-elasticity base film and the lower high-elasticity base film is both 45 ~ 55 , the Young's modulus of which is both 9.5~10.5Mpa, and the elongation at break of which is both 1450%~1550%.

[0017] Further, the distributionally heterogeneous lower electrode layer and the distributionally heterogeneous upper electrode layer both adopt silver paste electrodes.

[0018] As a second aspect, the present invention provides a flexible surgical arm that passes through the body's natural cavities, including a robotic arm, a flexible catheter disposed at the distal end of the robotic arm, and a rollable, multi-point force sensing film as described above, rolled up on the sidewall of the flexible catheter.

[0019] The rollable, wrap-around multi-point force sensing film is rolled onto the sidewall of the flexible conduit to form a rollable, wrap-around multi-point force sensing film, the length direction of which is consistent with the axial direction of the flexible conduit.

[0020] Furthermore, an external flexible circuit board is provided at the proximal end of the sparse sensing segment of the force sensing film, and the signal lead is electrically connected to the external flexible circuit board.

[0021] The external flexible circuit board is electrically connected to the multi-channel charge conditioner. When any PVDF piezoelectric sensing unit is subjected to external pressure, it generates a charge signal. This signal is transmitted to the multi-channel charge conditioner via the external flexible circuit board and is converted into a voltage signal for output.

[0022] As a third aspect, the present invention also provides a force sensing method employing a flexible surgical arm via a natural human body cavity as described above, comprising the following:

[0023] The rollable, multi-point force-sensing film is rolled up, wrapped, and attached to the sidewall of the flexible conduit, thereby constructing a biomimetic nerve bundle with a heterogeneous distribution density on the sidewall of the flexible conduit.

[0024] When the flexible catheter is used to perform surgical operations, the various piezoelectric sensitive units in the bionic nerve bundle synchronously capture the multi-dimensional contact force signals generated when the sidewall of the flexible catheter comes into contact with human tissue in three-dimensional space;

[0025] The captured multi-dimensional contact force signals are acquired and processed through signal leads and subsequent signal processing circuits to sense and locate the force on the sidewall of the flexible conduit.

[0026] Furthermore, the step of rolling up and covering the flexible, multi-point force-sensing film and attaching it to the sidewall of the flexible conduit includes the following:

[0027] The sparse sensing segment begins at the proximal end of the flexible catheter and its thin film plane covers and adheres to the sidewall along the axial direction of the flexible catheter, while the distal end of the dense sensing segment is close to the distal end of the flexible catheter.

[0028] Furthermore, in the multi-dimensional contact force signal processing, the signal is calibrated and compensated based on the voltage sensitivity of the piezoelectric sensitive unit. The calculation formula for the voltage sensitivity of the force unit group is as follows:

[0029] ;

[0030] In the formula, The piezoelectric strain constant of the PVDF piezoelectric film is... The piezoelectric strain constant of PVDF piezoelectric thin film, The Poisson's ratio of the PVDF piezoelectric film. The Young's modulus of the PVDF piezoelectric film. The thickness of the PVDF piezoelectric film. The vacuum permittivity, The relative permittivity of the PVDF piezoelectric film is... W represents the wall thickness of the flexible conduit, and W represents the width of the stress-bearing unit group.

[0031] The beneficial effects of the rollable, wrap-around multi-point force sensing film, actuator, and force sensing method of the present invention are as follows:

[0032] This invention abandons the traditional indirect approach of relying on complex and simplified physical models for force estimation. By directly covering the catheter sidewall with a flexible film integrating distributed PVDF piezoelectric units, it achieves direct, in-situ measurement of interactive forces, reducing indirect errors. The PVDF piezoelectric film is designed as a biomimetic nerve bundle structure, dense at the distal end, sparse at the proximal end, and uniform in the middle. This innovative layout highly matches the force characteristics of the flexible surgical arm in actual operation: the distal end, as the leading part, has the most frequent and complex contact with tissue, requiring higher sensing resolution to identify fine anatomical structures and navigation information; the proximal end mainly undertakes support and transmission functions, with relatively less contact, and the sparse layout optimizes system complexity while ensuring basic sensing coverage; the uniform middle section achieves a smooth transition and full coverage of force sensing, significantly improving spatial sensing efficiency and achieving the best balance between sensing accuracy and sensing range with a limited number of sensing units. This gives the flexible surgical arm a gradient tactile sensing capability similar to that of biological nerves.

[0033] Both the lower and upper highly elastic base membranes of this invention are made of thermoplastic polyurethane material. Combined with silver paste electrodes, this imparts excellent flexibility to the sensing film, enabling it to withstand large deformations of the conduit without cracking or peeling, ensuring long-term, stable mechanical and electrical reliability within complex cavities. The PVDF piezoelectric film has a thickness of 26 mm. ~30 The thickness of both the lower high-elasticity basement membrane and the lower high-elasticity basement membrane is 45. ~55 This gives it an ultra-thin characteristic, so that when rolled onto a flexible conduit, it hardly changes the original configuration of the conduit, thus achieving seamless integration of sensing functions. Attached Figure Description

[0034] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0035] Figure 1 This is an exploded view of the rollable, multi-point force sensing film in Embodiment 1 of the present invention.

[0036] Figure 2 This is a distribution diagram of the PVDF piezoelectric film in Embodiment 1 of the present invention.

[0037] Figure 3 yes Figure 1 Detailed diagram of the medium-voltage sensitive unit.

[0038] Figure 4 This is a cross-sectional view of a rollable, multi-point force sensing film rolled onto the outer wall of a flexible conduit, according to Embodiment 1 of the present invention.

[0039] Figure 5 This is a flowchart of the roll-up process for the rollable, multi-point force sensing film in Embodiment 2 of the present invention.

[0040] Figure 6 This is a schematic diagram of the connection between the external flexible circuit board and the rolled-up multi-point force sensing film in Embodiment 2 of the present invention.

[0041] Figure 7 This is a schematic diagram illustrating the working principle of the PVDF piezoelectric film in Embodiment 2 of the present invention.

[0042] Figure 8 This is a flowchart of the force sensing method of the actuator arm in Embodiment 3 of the present invention.

[0043] In the figure: 1. Rollable, multi-point force sensing film; 11. Lower high-elasticity base film; 12. Distributed heterogeneous lower electrode layer; 13. PVDF piezoelectric film; 131. Dense sensing section; 132. Uniformly distributed section; 133. Sparse sensing section; 134. Piezoelectric sensing unit; 14. Distributed heterogeneous upper electrode layer; 15. Upper high-elasticity base film; 2. Flexible conduit; 3. External flexible circuit board; 4. Pin; 5. Multi-channel charge conditioner. Detailed Implementation

[0044] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0045] Example 1

[0046] like Figures 1-4The embodiment of a rollable, encapsulated multi-point force sensing film 1 of the present invention shown includes a lower highly elastic base film 11, a distributed heterogeneous lower electrode layer 12, a PVDF piezoelectric film 13, a distributed heterogeneous upper electrode layer 14, and the lower highly elastic base film 11 stacked sequentially from bottom to top. The PVDF piezoelectric film 13 is divided into three functional regions distributed along its length: a dense sensing section 131 at the far end, a uniformly distributed section 132 in the middle, and a sparse sensing section 133 at the near end. The dense sensing section 131 includes three parallel force-receiving unit groups, the uniformly distributed section 132 includes two parallel force-receiving unit groups, and the sparse sensing section 133 includes one force-receiving unit group. The corresponding force-receiving units of the distributed heterogeneous lower electrode layer and the distributed heterogeneous upper electrode layer are electrically connected to the PVDF piezoelectric film, and the electrode layers are equipped with screen-printed silver paste electrodes to lead out electrical signals. The structure of each layer of the encapsulated rollable, encapsulated multi-point force sensing film 1 is as follows. Figure 1 and Figure 4 As shown, in use, the sensing film 1 is rolled up along its length as the winding axis to form a rolled-up, multi-point force sensing film. In practical applications, this sensing film 1 is rolled up along its length as the axis and wrapped around the surface of a flexible conduit or other actuator. It can be understood that the inner side of the rolled-up sensing film can be composed of either a lower highly elastic base film 11 or an upper highly elastic base film 15. Both have the same material and properties, and both can provide good adhesion and interface protection.

[0047] This embodiment abandons the traditional indirect path of force estimation relying on complex and simplified physical models. By directly covering the catheter sidewall with a flexible film integrating distributed PVDF piezoelectric units as electronic skin, it achieves direct, in-situ measurement of interactive forces, reducing indirect errors. The PVDF piezoelectric film 13 is designed as a biomimetic nerve bundle structure with dense distal end, sparse proximal end, and uniform middle section. This innovative layout is highly compatible with the force characteristics of the flexible surgical arm in actual operation: the distal end, as the leading part, has the most frequent and complex contact with tissue, requiring higher sensing resolution to identify fine anatomical structures and navigation information; the proximal end mainly undertakes support and transmission functions, with relatively less contact, and the sparse layout can optimize system complexity while ensuring basic sensing coverage; the uniform middle section achieves a smooth transition and full coverage of force sensing, which not only significantly improves spatial sensing efficiency, but also achieves the best balance between sensing accuracy and sensing range with a limited number of sensing units, enabling the flexible surgical arm to have a gradient tactile sensing capability similar to that of biological nerves.

[0048] Here, the PVDF piezoelectric film 13 is further defined, including its material thickness. 26 ~30 The Young's modulus Y of the PVDF piezoelectric film 13 is: In this embodiment, both the lower highly elastic base membrane 11 and the upper highly elastic base membrane 15 are made of thermoplastic polyurethane material. Combined with silver paste electrodes, this imparts excellent flexibility to the sensing film, enabling it to withstand large deformations of the conduit without breaking or peeling, ensuring long-term, stable mechanical and electrical reliability within complex cavities. The PVDF piezoelectric film 13 has a thickness of 26 mm. ~30 The thickness of both the lower high-elasticity base film 11 and the lower high-elasticity base film 11 is 45. ~55 This gives it an ultra-thin characteristic, and when rolled onto the flexible conduit 2, it hardly changes the original configuration of the conduit, thus achieving seamless integration of sensing functions.

[0049] As a specific implementation method, the material parameters of the PVDF piezoelectric film 13 are: thickness 28 Young's modulus Y is Relative permittivity The ratio is 12, Poisson's ratio The piezoelectric strain constant is 0.4. The piezoelectric strain constant is 23 PC / N. With a 4PC / N ratio, the acoustic impedance of the PVDF piezoelectric film 13 with these material parameters is close to that of water or biological tissue. It has wide-band acoustic properties, excellent flexibility, and can be formed into large-area films. It can also be coated on substrates of various shapes and materials.

[0050] The rollable, multi-point force sensing film 1 of this invention has 64 acquisition points arranged in a gradually decreasing pattern: dense at the far end, uniform in the middle, and sparse at the near end. This focuses on key areas and optimizes channel resources. Specifically, for example... Figure 3 As shown, the three functional areas are the dense sensing segment 131 at the far end, the uniformly distributed segment 132 in the middle, and the sparse sensing segment 133 at the near end. The length L1 of the dense sensing segment 131 is equal to the length L2 of the uniformly distributed segment 132, and the length L3 of the sparse sensing segment 133 is greater than L1 or L2. It should be further noted that the total length L1+L2+L3 is less than 300mm. The dense sensing section 131 includes 30 piezoelectric sensing units 134, arranged in three parallel force-receiving unit groups, with each force-receiving unit group corresponding to 10 piezoelectric sensing units 134 arranged along the length of the sensing film; the uniformly distributed section 132 includes 20 piezoelectric sensing units 134, arranged in two parallel force-receiving unit groups, with each force-receiving unit group corresponding to 10 piezoelectric sensing units 134 arranged along the length of the sensing film; the sparse sensing section 133 includes 14 piezoelectric sensing units 134, arranged along the length of the sensing film. Specific design and signal channel numbering are as follows... Figure 2As shown.

[0051] In use, the rollable, multi-point force sensing film 1 is rolled up along its length as the rolling axis to form a rollable, multi-point force sensing film. The rolling process is as follows: Figure 5 As shown.

[0052] In actual surgery, the dense sensing segment 131 needs to enter the segmental bronchus and subsegmental bronchus, where the lumen is narrow, the bends are frequent, the contact force is the greatest and the risk is the highest. Taking all factors into consideration, the total length of this segment is designed to be 80mm. The piezoelectric sensitive units 134 in this segment are evenly distributed along the axial direction with a piezoelectric unit width of 5mm and a spacing of 3mm. Three force unit groups are arranged in the circumferential direction. The dense sensing segment 131 has a total of 30 piezoelectric sensitive units 134.

[0053] The uniformly distributed section 132 in the middle is the central bending sensitive area, which is used to withstand the side wall extrusion and friction distribution force during bending adjustment. Its total length is 80mm. The piezoelectric sensitive unit 134 is evenly distributed along the axial direction with a piezoelectric unit width of 5mm and a spacing of 3mm. Two force-bearing unit groups are arranged in the circumferential direction. The uniformly distributed section 132 has a total of 20 piezoelectric sensitive units 134.

[0054] When in use, the sparse sensing segment 133 at the proximal end is mainly located in the main trachea and lobar bronchus. The lumen is thick and can withstand contact force greater than other parts. It is divided into segments along the axial direction of the rolled-up multi-point force sensing film with a piezoelectric unit width of 5mm and a spacing of 3mm. One force unit group is arranged along the circumference of the rolled-up multi-point force sensing film. This segment has a total of 14 piezoelectric sensitive units 134.

[0055] In a preferred embodiment, both the lower highly elastic base film 11 and the lower highly elastic base film 12 in this embodiment are made of thermoplastic polyurethane film; the thickness of both the lower highly elastic base film 11 and the lower highly elastic base film 12 is 45. ~55 The Young's modulus of these materials is 9.5–10.5 MPa, and their elongation at break is 1450%–1550%. The selection of a TPU film with a low Young's modulus of approximately 10 MPa and a high elongation at break of nearly 1500% gives the entire sensing film excellent flexibility and elasticity. Like a second skin, it can elastically deform without plastic fracture or delamination when the flexible catheter 2 undergoes extensive bending and torsional deformation, ensuring long-term mechanical reliability during operation in complex cavities.

[0056] At the same time, such as Figure 1As shown, both the distributed heterogeneous lower electrode layer 12 and the distributed heterogeneous upper electrode layer 14 in this embodiment use silver paste electrodes. Utilizing the excellent conductivity of the silver paste electrodes, the weak charges generated by the PVDF can be effectively collected, reducing signal loss during transmission. Simultaneously, the flexibility of the silver paste material itself allows it to deform synchronously with the TPU substrate and the PVDF film layer, avoiding electrode breakage or a sharp increase in resistance under repeated bending.

[0057] In this embodiment, the silver paste electrode forms a strong physical and chemical bond with the thermoplastic polyurethane film substrate and the PVDF film layer through printing or coating processes, thus forming a stable multilayer composite structure of thermoplastic polyurethane film-silver electrode-PVDF-silver electrode-thermoplastic polyurethane film. This prevents the layers from peeling off during use and ensures the integrity of the sensing unit.

[0058] Example 2

[0059] This second embodiment provides an application of rolling up a rollable, coverable multi-point force sensing film 1 with its length direction as the rolling axis to form a rollable, coverable multi-point force sensing film. A flexible surgical arm that passes through a natural human cavity includes a robotic arm, a flexible catheter 2 disposed at the distal end of the robotic arm, and the aforementioned rollable, coverable multi-point force sensing film 1 rolled onto the sidewall of the flexible catheter 2. The rollable, coverable multi-point force sensing film 1 is rolled onto the sidewall of the flexible catheter 2 to form a rollable, coverable multi-point force sensing film. The length direction of the rollable, coverable multi-point force sensing film 1 is aligned with the axial direction of the flexible catheter 2. See details [link to documentation]. Figure 4 and Figure 5 .

[0060] For details, see Figure 6 In this embodiment, an external flexible circuit board 3 is provided near the sparse sensing segment 133 of the rollable, wrap-around multi-point force sensing film 1, and signal leads are electrically connected to the external flexible circuit board 3. The external flexible circuit board 3 is electrically connected to the multi-channel charge conditioner 5; when any piezoelectric sensing unit 134 is subjected to external pressure, a charge signal is generated, which is transmitted to the multi-channel charge conditioner 5 via the external flexible circuit board 3 and converted into a voltage signal for output.

[0061] In detail, the external flexible circuit board 3 is provided with two pins 4, one of which is connected to a 32-channel charge conditioner.

[0062] This second embodiment uses a bronchoscopic surgical arm as an example. The surgical arm is made of composite material, and the flexible catheter 2 is the external bronchoscope tube. The external bronchoscope tube is typically sized as follows: Wall thickness During surgery, the dense sensing segment 131 of the rollable, wrap-around multi-point force sensing film 1 is placed at the proximal end of the bronchoscope tube, close to the surgical target point, and the sparse sensing segment 133 is placed at the distal end of the bronchoscope tube. The slight contact between the bronchoscope tube and the airway mucosa usually results in a force value of 0.1 to 5 N. The material parameters of the PVDF piezoelectric film 13 are set as follows, as shown in Table 1.

[0063] Table 1:

[0064] piezoelectric strain constant 23 PC / N piezoelectric strain constant 4 PC / N Young's modulus Y thickness 28 Relative dielectric constant 12 Poisson's ratio 0.4

[0065] like Figure 7 As shown, assuming the length and width of a single PVDF piezoelectric sensing element 134 are respectively... and The wall thickness of the flexible segment of the surgical arm is The effective cross-sectional area of ​​PVDF circumferential tension is... Represented as

[0066]

[0067] The elastic force equilibrium external force of circumferential tension can be expressed as:

[0068]

[0069] in, This represents the elastic modulus of the surgical arm's outer tube (to distinguish it from electric field strength, the symbol commonly used to represent the elastic modulus is not used here). ), This indicates the circumferential strain of the tube. Indicates circumferential displacement. Indicates the outer radius of the surgical arm.

[0070] United and You can obtain:

[0071]

[0072] The PVDF attached to the outer wall of the surgical arm undergoes circumferential strain and axial strain due to the Poisson effect. For isotropic materials, Poisson's ratio can be expressed as...

[0073]

[0074] in, This represents the axial strain of the PVDF pipe; the negative sign indicates that the circumferential strain is opposite to the axial strain. (Simultaneous equations) and You can obtain:

[0075]

[0076] Therefore, according to the stress-electric field constitutive equation of PVDF, the electric displacement matrix... With stress matrix electric field strength The relationship can be represented as:

[0077]

[0078] in, It is the piezoelectric constant matrix. It is the dielectric constant under constant stress. Generally expressed as:

[0079]

[0080] in, Its absolute value is relatively or It is nearly two orders of magnitude smaller, so it can be considered as .

[0081] Since PVDF is an orthotropic piezoelectric material, its radial electric displacement vector can be expressed as:

[0082]

[0083] in, , and These represent the circumferential, axial, and radial stresses of the PVDF, respectively.

[0084] Because the surgical arm that operates through the body's natural cavities is a flexible arm, not a rigid tube, when an external force is applied to a certain location, the compression in the thickness direction of the PVDF is extremely small, far less than the in-plane strain. The third item on the right can be ignored. Therefore, It can be represented as

[0085]

[0086] in, and These represent the circumferential and axial elastic moduli of PVDF, respectively. They are approximately equal and can be considered as... Combination and You can obtain:

[0087]

[0088] Furthermore, the capacitance of the PVDF sensing cell can be expressed as:

[0089]

[0090] in, The vacuum permittivity, Here is the relative permittivity of the PVDF. The thickness of the PVDF.

[0091] Because of electric displacement It can also be done through electric charge With the area of ​​force Represented as:

[0092]

[0093] Combination , and The magnitude of the generated voltage can be calculated as follows:

[0094]

[0095] Therefore, the voltage sensitivity expression of the PVDF sensing element can be calculated as follows:

[0096]

[0097] In this embodiment, the value of the bronchoscopy surgical arm is... Wall thickness If the width of the PVDF piezoelectric sensing element 134 is taken... Then the voltage sensitivity can be calculated to be approximately The theoretical voltage sensitivity value is within a safe range, ensuring signal strength for small forces without causing excessive voltage due to slight fluctuations in force, thus preventing interference with judgment.

[0098] Example 3

[0099] The force sensing method of the flexible surgical arm through the natural cavities of the human body, as described in Embodiment 2 above, is employed. Figure 8 As shown, it includes the following:

[0100] S1: The rollable wrap-around multi-point force sensing film 1 is rolled up and attached to the side wall of the flexible conduit 2 to construct a biomimetic nerve bundle with heterogeneous distribution density on the side wall of the flexible conduit 2.

[0101] S2: When the flexible catheter 2 is performing a surgical procedure, the multi-dimensional contact force signal generated when the sidewall of the flexible catheter 2 comes into contact with human tissue in three-dimensional space is simultaneously captured by each piezoelectric sensitive unit 134 in the bionic nerve bundle.

[0102] S3: The captured multi-dimensional contact force signals are collected and processed through signal leads and subsequent signal processing circuits to sense and locate the force on the sidewall of the flexible conduit 2.

[0103] In this embodiment, step one, which involves rolling up and covering the flexible, multi-point force-sensing film 1 and attaching it to the sidewall of the flexible conduit 2, includes the following:

[0104] The sparse sensing segment 133 begins at the proximal end of the flexible catheter 2, and its thin film plane wraps around and adheres to the sidewall along the axial direction of the flexible catheter 2. The distal end of the dense sensing segment 131 is close to the distal end of the flexible catheter 2. After being wound up, it is glued to the corresponding sidewall of the flexible catheter 2 or overlapped and glued to the corresponding rollable, multi-point force sensing film 1, as shown in the details. Figure 5 As shown, one type of rollable multi-point force sensing film completely covers the flexible catheter 2. This is the ideal situation. However, it should be understood that even if the rollable multi-point force sensing film 1 overlaps after covering the flexible catheter 2, it will not affect its performance.

[0105] In step S3, during the multi-dimensional contact force signal processing, the signal is calibrated and compensated based on the voltage sensitivity of the piezoelectric sensitive unit 134. The calculation formula for the voltage sensitivity of the force unit group is as follows:

[0106] ;

[0107] In the formula, The piezoelectric strain constant of the PVDF piezoelectric film is... The piezoelectric strain constant of PVDF piezoelectric thin film, The Poisson's ratio of the PVDF piezoelectric film. The Young's modulus of the PVDF piezoelectric film. The thickness of the PVDF piezoelectric film. The vacuum permittivity, The relative permittivity of the PVDF piezoelectric film is... Let W be the wall thickness of the flexible conduit 2, and W be the width of the force-bearing unit group. The specific derivation process of its calculation formula is as described above, and will not be elaborated here.

[0108] This embodiment constructs a stable and reliable biomimetic nerve bundle for the sidewall of the flexible catheter 2 by defining a coverage path where the sparse sensing segment 133 starts proximally and the dense sensing segment 131 is fixed distally. This design ensures coordinated movement of the sensing membrane and the catheter under complex bending and twisting deformations, effectively preventing membrane slippage, wrinkling, or peeling, and providing structural protection for signal continuity and reliability. Whether the membrane is ideally aligned or partially overlapped after coverage, it maintains full-range sensing capability, which greatly reduces the installation difficulty in clinical operations and improves the robustness and reproducibility of the method.

[0109] Simultaneously, a voltage sensitivity calculation model based on physical parameters was introduced into the signal processing stage, realizing the scientific conversion from raw charge signals to precise force information. This model comprehensively considers the characteristics of the PVDF material itself and the influence of the flexible catheter 2 structure. By performing personalized signal calibration and compensation for each unit group, it effectively eliminates systematic errors introduced by batch differences in materials, fine-tuning of unit dimensions, and variations in catheter wall thickness. This unifies the distributed multi-channel signals onto a precise mechanical benchmark, ultimately achieving high-precision, quantitative perception of the magnitude and location of sidewall contact force, rather than remaining at a qualitative judgment level, enabling the flexible surgical arm to acquire true tactile feedback.

[0110] It should be understood that the specific embodiments described above are for illustrative purposes only and are not intended to limit the scope of the invention. Obvious variations or modifications derived from the spirit of the invention are still within the protection scope of the invention.

Claims

1. A rollable, multi-point force sensing film, characterized in that, It includes a lower highly elastic base film, a distributed heterogeneous lower electrode layer, a PVDF piezoelectric film, a distributed heterogeneous upper electrode layer, and a lower highly elastic base film stacked sequentially from bottom to top; The PVDF piezoelectric film is divided into three functional regions distributed along its length: a dense sensing section at the far end, a uniformly distributed section in the middle, and a sparse sensing section at the near end. The dense sensing section includes three parallel force unit groups, the uniformly distributed section includes two parallel force unit groups, and the sparse sensing section includes one force unit group. The corresponding force-bearing units of the distributed heterogeneous lower electrode layer and the distributed heterogeneous upper electrode layer are respectively connected to the PVDF piezoelectric film, and the screen-printed silver paste electrodes of the electrode layer lead out the electrical signal. In use, it is rolled up along its length as the winding axis to form a rolled-up, multi-point force sensing film.

2. The rollable, multi-point force sensing film according to claim 1, characterized in that, The material thickness of the PVDF piezoelectric film 26 ~30 The Young's modulus Y of the PVDF piezoelectric film is: .

3. The rollable, encapsulated multi-point force sensing film according to claim 1, characterized in that: The length L1 of the dense sensing segment is equal to the length L2 of the uniformly distributed segment, and the length L3 of the sparse sensing segment is greater than L1 or L2. The total length L1+L2+L3 is less than 300mm.

4. The rollable, encapsulated multi-point force sensing film according to claim 1, characterized in that: The dense sensing segment includes 30 piezoelectric sensing units; the uniformly distributed segment includes 20 piezoelectric sensing units. The sparse sensing segment includes 14 piezoelectric sensing units.

5. The rollable, encapsulated multi-point force sensing film according to claim 1, characterized in that: Both the lower high-elasticity base film and the lower high-elasticity base film are made of thermoplastic polyurethane film; the thickness of both the lower high-elasticity base film and the lower high-elasticity base film is 45. ~55 Their Young's modulus is 9.5 to 10.5 MPa, and their elongation at break is 1450% to 1550%.

6. The rollable, encapsulated multi-point force sensing film according to claim 1, characterized in that: Both the distributed heterogeneous lower electrode layer and the distributed heterogeneous upper electrode layer use silver paste electrodes.

7. A flexible surgical arm that passes through natural human cavities, characterized in that, It includes a robotic arm, a flexible conduit disposed at the distal end of the robotic arm, and a rollable, multi-point force sensing film as described in any one of claims 1-6, rolled up on the sidewall of the flexible conduit. The rollable, wrap-around multi-point force sensing film is rolled onto the sidewall of the flexible conduit to form a rollable, wrap-around multi-point force sensing film, the length direction of which is consistent with the axial direction of the flexible conduit.

8. The flexible surgical arm that passes through the natural cavities of the human body according to claim 7, characterized in that: An external flexible circuit board is provided at the proximal end of the sparse sensing segment of the force sensing film, and the signal lead is electrically connected to the external flexible circuit board. The external flexible circuit board is electrically connected to the multi-channel charge conditioner. When any PVDF piezoelectric sensing unit is subjected to external pressure, it generates a charge signal. This signal is transmitted to the multi-channel charge conditioner via the external flexible circuit board and is converted into a voltage signal for output.

9. The force sensing method using a flexible surgical arm via a natural human body cavity as described in claim 8, characterized in that, Includes the following: The rollable, multi-point force-sensing film is rolled up, wrapped, and attached to the sidewall of the flexible conduit, thereby constructing a biomimetic nerve bundle with a heterogeneous distribution density on the sidewall of the flexible conduit. When the flexible catheter is used to perform surgical operations, the various piezoelectric sensitive units in the bionic nerve bundle synchronously capture the multi-dimensional contact force signals generated when the sidewall of the flexible catheter comes into contact with human tissue in three-dimensional space; The captured multi-dimensional contact force signals are acquired and processed through signal leads and subsequent signal processing circuits to sense and locate the force on the sidewall of the flexible conduit.

10. The force sensing method using a flexible surgical arm via a natural human body cavity as described in claim 9, characterized in that, The step of rolling up and covering the flexible, multi-point force-sensing film and attaching it to the sidewall of the flexible conduit includes the following: The sparse sensing segment begins at the proximal end of the flexible catheter and its thin film plane covers and adheres to the sidewall along the axial direction of the flexible catheter, while the distal end of the dense sensing segment is close to the distal end of the flexible catheter.

11. The force sensing method for a flexible surgical arm via a natural human body cavity according to claim 9, characterized in that: In the multi-dimensional contact force signal processing, the signal is calibrated and compensated based on the voltage sensitivity of the piezoelectric sensitive unit. The calculation formula for the voltage sensitivity of the force unit group is as follows: ； In the formula, The piezoelectric strain constant of the PVDF piezoelectric film is... The piezoelectric strain constant of PVDF piezoelectric thin film, The Poisson's ratio of the PVDF piezoelectric film. The Young's modulus of the PVDF piezoelectric film. The thickness of the PVDF piezoelectric film. The vacuum permittivity, The relative permittivity of the PVDF piezoelectric film is... W represents the wall thickness of the flexible conduit, and W represents the width of the stress-bearing unit group.

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