A four-dimensional puncture force / torque sensor based on FBG

Abstract

The application provides a four-dimensional FBG-based puncture force / torque sensor, and relates to the field of puncture force measuring sensors, which is composed of a 16G puncture needle, a radial force / torque measuring unit, an axial force measuring unit and a base, the puncture needle is connected to the radial force / torque measuring unit, the radial force / torque measuring unit and the axial force measuring unit are arranged in series, and the base is connected to the rear end of the axial force measuring unit, so that the decoupling measurement of the axial force and the radial force / torque is realized in structure. The axial force sensitive structure is developed by deforming the traditional parallelogram linear guide mechanism. By arranging the original parallelogram guide mechanism in series, symmetry and ring, an axial force measuring sensitive structure with strong anti-interference ability, large motion range and excellent force-deformation linearity is designed, and the sensitivity and precision of the axial force measurement of the sensor are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of puncture force measurement sensors, in particular to a Bragg grating fiber sensor that can realize low crosstalk, high precision and high sensitivity measurement of four-dimensional interaction force and torque between a puncture needle and human tissue in minimally invasive percutaneous puncture surgery. BACKGROUND

[0002] With the continuous rise in cancer incidence, percutaneous puncture is increasingly applied to biopsy sampling, radiofrequency ablation, radioactive particle implantation and other modern clinical cancer diagnosis and treatment methods. Compared with traditional open surgery, percutaneous puncture has the advantages of small trauma, light pain, low risk of infection, fewer complications and short postoperative recovery time, and robot-assisted puncture has obvious advantages in operation precision, stability and safety. However, the master-slave operation mode of the puncture robot makes it impossible for the doctor to perceive the end interaction force information through tactile feedback, which may lead to the surgeon applying excessive force during the operation and introducing unsafe factors. Precise puncture force feedback helps surgeons assess tissue properties and adjust operations in a timely manner, which is crucial to improving surgical outcomes and reducing surgical risks.

[0003] Researchers have developed a large number of sensors to measure puncture force in percutaneous puncture surgery, which can be divided into distal measurement methods and proximal measurement methods according to the integrated position of the sensor. The distal measurement method integrates the sensing element on the surface of the puncture needle or at the puncture needle axis, but due to the small diameter of the puncture needle, it is difficult to optimize the design of the force-sensitive structure, resulting in the distal measurement scheme usually having the problems of low axial force sensitivity and serious multi-dimensional force coupling. The proximal measurement method integrates the sensor at the needle seat, which reduces the size requirement of the integrated space, and the design and packaging of the sensor are significantly less difficult, making it easier to achieve low coupling and high precision measurement of multi-dimensional force. The FBG-based optical fiber sensor is more popular in the medical sensor field in recent years due to its small size, immunity to electromagnetic interference, good flexibility, good biocompatibility and high measurement accuracy.

[0004] Ambastha et al. developed an axial force sensor for lumbar spinal needle, they pasted FBG on a cylindrical rod located on the sensor axis, the sensor achieved 21 mN measurement resolution in the range of [0, 20N], but due to the full pasting arrangement of the sensor, the sensor measurement accuracy is easily affected by the chirp effect caused by the uneven strain of the optical fiber, and the anti-interference ability of the force sensitive structure is poor, resulting in the sensor has a large radial crosstalk. Shi et al. developed a puncture axial force sensor with good linearity, high sensitivity and strong anti-interference ability by using double-layer planar spring, which adopts a suspended optical fiber arrangement form, avoiding the influence of chirp effect, effectively improving the measurement resolution, accuracy and robustness of the sensor. The sensor achieves a high resolution of 1.5 mN in the range of [0, 6N]. However, these two sensors only support axial force measurement, which is difficult to meet the demand of providing real force feedback to doctors in clinical practice.

[0005] To meet the demand of more dimensional interactive force measurement in percutaneous puncture process, Xiong et al. proposed a FBG sensor that can measure axial force and torque, by designing grooves on the surface of the puncture needle to paste FBG optical fibers to measure axial force, and designing spoke-shaped flexible beam structures near the needle tip to measure torque, and designing temperature compensation optical fibers to improve measurement accuracy. The sensor achieves an axial force resolution of 30 mN and a torque resolution of 0.8 N·mm, with low repeatability error and hysteresis error. However, the size of the sensor is relatively large, which limits its application in actual clinical operation. Liu et al. developed a three-dimensional puncture force sensor for prostate biopsy surgery based on S-shaped folded beams, which configures one force measurement optical fiber and one temperature compensation optical fiber in each of the three folded beam modules. Simulation results show that the axial force and radial force resolutions of the sensor are 32.5 mN and 7.2 mN, respectively.

[0006] In summary, although many researchers have developed puncture force measurement sensors, there is still a lack of mature force sensing equipment applied in commercial puncture robots. The main technical difficulties faced are: ① The puncture needle has a large aspect ratio, with a much higher axial stiffness than radial stiffness, making it difficult to achieve high sensitivity axial force measurement, and the radial force applied at the end of the puncture needle is easily amplified due to the lever effect, resulting in a large difference in axial / radial sensitivity and reducing the measurement accuracy of the sensor. ② The size of the sensor design and integration is strictly limited, making it difficult to achieve decoupled measurement of multi-dimensional force / torque through force sensitive structure design. SUMMARY

[0007] (I) Technical problems solved

[0008] In view of the deficiencies of the prior art, the application provides a four-dimensional puncture force / torque sensor based on FBG, which solves the problems of few measurement dimensions, low sensitivity and serious inter-dimension coupling in the traditional percutaneous puncture force sensor.

[0009] (II) Technical scheme

[0010] To achieve the above object, the application is implemented by the following technical scheme: a four-dimensional puncture force / torque sensor based on FBG: composed of a 16G puncture needle, a radial force / torque measurement unit, an axial force measurement unit and a base, the puncture needle is connected to the radial force / torque measurement unit, the radial force / torque measurement unit and the axial force measurement unit are configured in series, and the base is connected to the rear end of the axial force measurement unit, which realizes decoupled measurement of axial force and radial force / torque in structure.

[0011] Preferably, the axial force measurement unit comprises an annular axial guide structure, an FBG optical fiber, a connecting flange and a connecting cylinder, the annular axial guide structure is connected to the base through the connecting cylinder, the connecting flange is arranged inside the annular axial guide structure, the upper end of the connecting flange is connected to the radial force / torque measurement unit, and the FBG optical fiber is arranged in the middle of the axial force measurement unit.

[0012] Preferably, the annular axial guide structure is composed of parallelogram linear motion flexible structure and is configured in annular parallel connection by three symmetrical composite modules, the symmetrical composite modules are reversely configured in series by two parallelogram guide mechanisms and are symmetrically arranged.

[0013] Preferably, the radial force / torque measurement unit comprises a spoke type sensitive structure, four radially arranged optical fibers and a needle seat, the needle seat is arranged in the center of the spoke type sensitive structure, four sticking columns are arranged at equal angles on the outer ring of the spoke type sensitive structure, and the two ends of the four radially arranged optical fibers are respectively connected to the needle seat and the sticking columns by glue.

[0014] Preferably, the spoke type sensitive structure is a sensitive structure configured by three spokes, and the spokes are arranged at equal angles in a circle.

[0015] Preferably, the four optical fibers are arranged at equal intervals of 90° along the radial direction of the structure and are suspended on the needle seat of the central puncture needle and the outer ring of the spoke type sensitive structure, which realizes low-coupling measurement of radial forces Fx and Fy and torque Mz.

[0016] Preferably, the optical fibers are fixed on both sides of the force sensitive structure in a two-point suspension type configuration to improve sensitivity and avoid chirping.

[0017] (III) Beneficial effects

[0018] The application provides a four-dimensional puncture force / torque sensor based on FBG.

[0019] The application develops an axial force sensitive structure by deforming a traditional parallelogram linear guide mechanism. By successively connecting, symmetrically arranging and circularly arranging the original parallelogram guide mechanism, an axial force measurement sensitive structure with strong anti-interference ability, large movement range and excellent force-deformation linearity is designed, thereby improving the sensitivity and accuracy of the sensor in axial force measurement.

[0020] In addition, the traditional spoke force sensitive structure is improved for radial force and torque measurement. The cross-sectional size design with a beam height greater than a beam width is adopted to improve the torque measurement sensitivity of the sensor, meanwhile, the ability of the structure to resist axial force is enhanced, the radial force and torque measurement accuracy is improved, and the sensitivity of each measurement direction is balanced.

[0021] In addition, four optical fibers are suspended and arranged at 90° intervals along the radial direction of the structure at the central puncture needle holder and the outer ring of the structure, thereby realizing low coupling measurement of the radial forces Fx and Fy and the torque Mz. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 FIG. 1 is a structural schematic diagram of a four-dimensional puncture force / torque sensor based on FBG according to the application;

[0023] Figure 2 FIG. 2 is a structural schematic diagram of an axial force measurement unit of the four-dimensional puncture force / torque sensor based on FBG according to the application;

[0024] Figure 3 FIG. 3 is a structural schematic diagram of a radial force / torque measurement unit of the four-dimensional puncture force / torque sensor based on FBG according to the application; Figure 1

[0025] Figure 4 FIG. 4 is a structural schematic diagram of a radial force / torque measurement unit of the four-dimensional puncture force / torque sensor based on FBG according to the application; Figure 2

[0026] Figure 5 FIG. 5 is a design flowchart of a ring-shaped axial guide structure of the four-dimensional puncture force / torque sensor based on FBG according to the application;

[0027] Figure 6 FIG. 6 is a performance simulation result schematic diagram of the four-dimensional puncture force / torque sensor based on FBG according to the application;

[0028] Figure 7 FIG. 7 is a specific embodiment schematic diagram of the four-dimensional puncture force / torque sensor based on FBG according to the application.​​

[0029] Figure: 1, 16G puncture needle; 2, radial force / torque measurement unit; 21, spoke type sensitive structure; 211, spoke; 212, sticking column; 22, needle seat; 23, optical fiber two; 24, optical fiber three; 25, optical fiber four; 26, optical fiber five; 3, axial force measurement unit; 31, ring-shaped axial guide structure; 311, symmetric composite module; 312, parallelogram guide mechanism; 32, connecting flange; 33, connecting cylinder; 34, optical fiber one; 4, base. DETAILED DESCRIPTION

[0030] The embodiment of the present application provides a Bragg grating fiber sensor which can realize low crosstalk, high precision and high sensitivity measurement of four-dimensional puncture force and torque in a percutaneous puncture operation, as shown in the figure. Figure 1 The embodiment of the present application provides a Bragg grating fiber sensor which can realize low crosstalk, high precision and high sensitivity measurement of four-dimensional puncture force and torque in a percutaneous puncture operation, as shown in the figure. Figure 1 The radial force / torque measurement unit 2 and the axial force measurement unit 3 are configured in series, and the decoupling measurement of the axial force and the radial force / torque is realized in structure. The axial force measurement unit 3 comprises a ring-shaped axial guide structure 31, an FBG optical fiber 34, a connecting flange 32 and a connecting cylinder 33; the radial force / torque measurement unit 2 comprises a spoke type sensitive structure 21, four radially arranged optical fibers (23-26) and a needle seat 22. The optical fibers are fixed on both sides of the force sensitive structure in a two-point suspension type configuration to improve the sensitivity and avoid chirp.

[0031] The ring-shaped axial guide structure 31 is composed of a parallelogram linear motion flexible structure composite, as shown in the figure. Figure 5 The classical parallelogram guide module has horizontal movement along the x-axis direction and rotational parasitic motion around the z-axis during its vertical movement along the y-axis direction. The present application firstly configures two parallelogram guide modules in reverse series, and the horizontal movement parasitic motions of the two modules offset each other; then symmetrically designs the composite parallelogram guide module to eliminate the rotational parasitic motion; finally, the three symmetric composite guide modules are configured in ring parallel, to obtain the proposed ring-shaped axial guide structure 31, which provides high-precision axial guiding capability, improves the anti-interference ability of the sensor and the axial force measurement precision. In addition, the series design of the multi-layer plane beam increases the deformation of the structure when subjected to axial force, thereby improving the sensitivity of the sensor.

[0032] The radial force / torque measurement unit 2 adopts a three-spoke configuration sensitive structure, as shown in the figures. Figure 3 and Figure 4As shown, it also includes four radially arranged optical fibers, a needle seat 22 arranged at the center of the spoke sensitive structure 21, four adhesive columns 212 arranged around the needle seat 22, and four radially arranged optical fibers (23-26) respectively connected to the needle seat 22 and the adhesive columns 212 by glue. Compared with the traditional four-spoke cross beam design, the design has greater torque flexibility, improves the torque measurement sensitivity; each spoke 211 adopts a rectangular cantilever beam design with a height greater than the width of the cross-sectional size, which improves the axial deformation stiffness and bending-torque stiffness ratio of the sensor, limits the deformation of the force sensitive structure under the axial force, reduces the inter-axis coupling of the radial force / torque measurement under the axial force, balances the sensitivity of each measurement direction, and improves the measurement accuracy.

[0033] Based on the multi-objective genetic algorithm, the key size parameters of the FBG puncture force sensor are optimized and designed, the sensor model after structure parameter optimization is added to ANSYS Workbench for simulation analysis, and the relationship between the stress of the sensor and the center wavelength shift of the optical fiber can be calculated, as shown in Figure 6

[0034] Under the action of the radial force of the sensor, the maximum radial force Fx is loaded as 1.5N, the center wavelength shift of the optical fiber two 23 and the optical fiber four 25 is 1198pm and 1264pm respectively, and the sensitivity of the radial force Fx of the sensor can be calculated as 1984pm / N, and the corresponding resolution is 0.5mN. Similarly, the sensitivity and resolution of Fy can be calculated as 2512pm / N and 0.40mN respectively. Under the condition of radial force loading, the center wavelength shift of the optical fiber one 34 is small, so the influence of the radial loading of the sensor on the axial force measurement is small.

[0035] Under the action of the axial force Fz of the sensor, within the measurement range of 0-6N, only the optical fiber one 34 has a significant center wavelength shift, the sensitivity and resolution of Fz can be calculated as 559pm / N and 1.79mN respectively, and the influence of the axial force loading on the radial force and torque measurement is small.

[0036] Under the action of the torque Mz of the sensor, within the measurement range of 0-60N·mm, the optical fiber two 23 to the optical fiber five 26 all show obvious and basically consistent wavelength shift, while the wavelength shift of the optical fiber one 34 is very small, the sensitivity and resolution of the torque measurement can be calculated as 148pm / (N·mm) and 6.7mN·mm respectively, and the sensor has good axial force and torque measurement decoupling ability.

[0037] In addition, under all full-scale loading conditions, the safety factor of the sensor is always greater than 2, which ensures that the sensor has sufficient structural strength.

[0038] ​Based on the characteristics of high sensitivity and strong anti-interference ability of the sensor, the four-dimensional puncture force sensor can provide high-precision real-time interactive force / torque feedback when the doctor performs percutaneous puncture operation, overcoming the problem of loss of end-touch interactive force in master-slave operation mode of robot-assisted surgery. The doctor can adjust the puncture operation and penetration path in time according to the end force feedback to improve the puncture precision and surgical safety and reduce the incidence of surgical complications.

[0039] The specific implementation of the designed puncture force sensor is shown in Figure 7 As shown in the figure, the physical characteristics of the reflected light of the Bragg grating fiber of the sensor are detected on the fiber demodulator, and the fiber demodulator is connected with a computer system to read the fiber center wavelength shift data, and relevant data processing can convert the center wavelength shift of the five fibers into the force and torque received by the tip of the puncture needle 1.

[0040] Working principle: when the sensor is subjected to axial force, the axial force is transmitted to the annular axial guide structure 31 through the radial force / torque measuring unit 2, causing the structure to deform, and the optical fiber 34 and FBG grating area suspended at both ends of the structure to produce compression strain, causing the center wavelength of the FBG fiber reflection to shift, and the wavelength shift is measured by the fiber demodulator. Based on the conversion formula of grating strain and wavelength shift, the size of the axial force received by the sensor can be measured; and the spoke sensitive structure 21 has a large axial stiffness, so the strain on the optical fibers 2-5 is small, realizing the decoupling of axial force and radial force / torque measurement.

[0041] When the sensor is subjected to radial force, for example Fx, the external force Fx makes the spoke force sensitive structure produce deflection around the y axis, so that the optical fiber two 23 and the optical fiber four 25 are subjected to pressure and tension respectively, producing center wavelength shifts of the same size and opposite directions, while the optical fiber three 24 and the optical fiber five 26 produce a small offset along the radial direction of the optical fiber, and the strain is much smaller than that of the optical fiber two 23 and the optical fiber four 25. Difference operation of the wavelength shift of the optical fiber two 23 and the optical fiber four 25, the optical fiber three 24 and the optical fiber five 26 can improve the measurement sensitivity and reduce the crosstalk error. Similarly, when the sensor is subjected to Fy, the optical fiber three 24 and the optical fiber five 26 are compressed and stretched respectively, and the strain on the optical fiber two 23 and the optical fiber four 25 is small. After differential calculation, the sensitivity of the sensor to Fy can be obtained. In addition, since the optical fiber one 34 is arranged along the axis of the sensor, it is on the neutral axis of the sensor bending under radial force, so the strain of the optical fiber one 34 under radial force is small, realizing the decoupling of radial force and axial force measurement.

[0042] When the sensor is subjected to torque, the four optical fibers of the radial force / torque measuring unit 2 are simultaneously subjected to tension or compression, resulting in the same central wavelength shift in size and direction. The sum of the wavelength shifts of the optical fibers two 23 to the optical fiber five 26 can be calculated to obtain the torque sensitivity of the sensor. In addition, due to the large torsional stiffness of the designed ring-shaped axial guide mechanism, the strain of the optical fiber one 34 under the action of torque is very small, realizing the decoupling of torque and axial force measurement.

[0043] In summary, the present application develops an axial force sensitive structure by deforming the traditional parallelogram linear guide mechanism. By arranging the original parallelogram guide mechanism 312 in series, symmetrically and circularly, a sensitive structure for axial force measurement is designed, which has strong anti-interference ability, large movement range and excellent force-deformation linearity, and improves the sensitivity and accuracy of the sensor axial force measurement. In addition, by optimizing the number and size of the spokes of the spoke structure and using it as a radial force / torque sensitive structure, the torque measurement sensitivity is improved, the sensitivity of each measurement direction of the sensor is balanced, and the decoupling measurement of axial force and radial force / torque is realized.

[0044] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A FBG based four-dimensional puncture force / torque sensor, characterized in that: A 16G puncture needle (1), a radial force / torque measurement unit (2), an axial force measurement unit (3) and a base (4) are composed, the puncture needle (1) is connected on the radial force / torque measurement unit (2), the radial force / torque measurement unit (2) and the axial force measurement unit (3) are configured in series, the base (4) is connected at the rear end of the axial force measurement unit (3), and the axial force and the radial force / torque are decoupled and measured in structure; The axial force measurement unit (3) comprises a ring-shaped axial guide structure (31), an FBG optical fiber, a connecting flange (32) and a connecting cylinder (33), the ring-shaped axial guide structure (31) is connected with the base (4) through the connecting cylinder (33), the connecting flange (32) is arranged in the ring-shaped axial guide structure (31), and the upper end of the connecting flange (32) is connected with the radial force / torque measurement unit (2); the FBG optical fiber is arranged at the axial position of the axial force measurement unit (3); The ring-shaped axial guide structure (31) is composed of parallelogram linear motion flexible structures and is arranged in a ring-shaped parallel connection mode by three symmetrical composite modules (311), the symmetrical composite modules (311) are reversely connected in series by two parallelogram guide mechanisms (312) and are symmetrically arranged.

2. The FBG-based four-dimensional puncture force / torque sensor according to claim 1, characterized in that: The radial force / torque measurement unit (2) comprises a spoke type sensitive structure (21), four radially arranged optical fibers and a needle seat (22), the needle seat (22) is arranged at the center of the spoke type sensitive structure (21), four adhesive columns (212) are arranged around the needle seat (22), and the four radially arranged optical fibers are connected with the needle seat (22) and the adhesive columns (212) by glue.

3. The FBG-based four-dimensional puncture force / torque sensor according to claim 2, characterized in that: The spoke type sensitive structure (21) is a sensitive structure comprising three spokes (211), and the spokes (211) are arranged at equal angles along the circumference, and each spoke (211) is designed as a rectangular cantilever beam with a height greater than a width.

4. The FBG-based four-dimensional puncture force / torque sensor according to claim 2, characterized in that: The four optical fibers are arranged in a 90° equidistant interval along the radial direction of the structure, and are suspended outside the needle seat (22) and the spoke type sensitive structure (21) of the central puncture needle, so that the radial forces Fx and Fy and the torque Mz are measured with low coupling.

5. A four-dimensional puncture force / torque sensor based on FBG according to any one of claims 2-4, characterized in that: The optical fibers are fixed on both sides of the force sensitive structure in a two-point suspension mode to improve sensitivity and avoid chirping.

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