Flexible needle curvature measurement and shape reconstruction method based on piezoelectric ceramics

Abstract

The invention relates to the technical field of flexible needle shape measurement and reconstruction, in particular to a flexible needle curvature measurement and shape reconstruction method based on piezoelectric ceramics, which comprises the following specific steps: S1, sensor installation and signal acquisition; s2, data processing and curvature calculation; s3, performing interpolation calculation and a continuous curvature model; s4, carrying out segmented RMF reconstruction; and S5, verifying and optimizing curve splicing. According to the invention, the plurality of piezoelectric ceramic sensors are installed in a distributed manner, so that real-time and accurate local curvature and deflection of the flexible needle are realized, and high-precision multi-point measurement is realized; the RMF frame is adopted to replace a traditional Frenet frame, the frame sudden change problem caused by curve torsion is avoided, therefore, accumulative errors are reduced, and the reconstruction precision is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible needle shape measurement and reconstruction, and specifically to a method for measuring the curvature and reconstructing the shape of a flexible needle based on piezoelectric ceramics. Background Art

[0002] Existing shape reconstruction and puncture techniques mainly rely on imaging techniques such as MRI, CT, and ultrasound. Although these methods can provide three-dimensional image information with high resolution, they have obvious defects: MRI and CT devices are large in volume, expensive, have long scanning times, and are prone to artifacts for metal instruments, which is not conducive to real-time dynamic monitoring; while ultrasound technology has the advantages of real-time and radiation-free, but its resolution is limited, and the imaging quality is unstable in complex tissue or gas interference environments, making it difficult to accurately capture the local deformation information of flexible needles.

[0003] In view of such deficiencies, a flexible needle shape reconstruction technique based on piezoelectric ceramic sensors has been proposed. Piezoelectric ceramics utilize the piezoelectric effect and can quickly generate charge signals proportional to local strain when the flexible needle bends. It has a small volume, low cost, fast response speed, and strong anti-electromagnetic interference ability, and can realize real-time monitoring of the local curvature at multiple positions of the needle body, providing an efficient and economical solution for the three-dimensional shape reconstruction of flexible needles. Summary of the Invention

[0004] To solve the above problems, the present invention proposes a method for measuring the curvature and reconstructing the shape of a flexible needle based on piezoelectric ceramics.

[0005] The method for measuring the curvature and reconstructing the shape of a flexible needle based on piezoelectric ceramics is specifically as follows:

[0006] S1. Sensor installation and signal acquisition;

[0007] Five groups of piezoelectric ceramic sensors are evenly arranged on the flexible needle, connected to an analog-to-digital converter, the amplified analog signal is converted into a digital signal, and the data is transmitted to data processing;

[0008] S2. Data processing and curvature calculation:

[0009] Perform data processing on the charge signal Q of each group of sensors , , , , , , ,

[0012] ,

[0011] ,

[0006] , i ,

[0010] ,

[0009] ,

[0008] ,

[0007] ,

[0013] ;

[0010] S3. Interpolation calculation and continuous curvature model:

[0011] After obtaining the discrete curvature and torsion of five measurement points, generate the continuous curvature function κ(s) and torsion function au(s) of the needle body along the axis;

[0012] S4. Piecewise RMF reconstruction:

[0013] Taking the fixed base coordinate system at the root of the needle, i.e., the 20 cm end, as the initial frame {T0, N0, B0}, where T0 is the axial direction of the base. Starting from the 17 cm to 20 cm section, the interpolated κ(s) and τ(s) sequences are discretized with a step size of Δs = 1 mm. According to the RMF differential equation, the frame is updated step by step:

[0014]

[0015] Calculate the current point coordinate: r i+1 = r i + Δs·T i ;

[0016] S5. Curve splicing verification and optimization:

[0017] Check the coordinate deviation of the endpoints of adjacent paragraphs: ||r prev_end - r next_star || < ∈∈ = 0.01 mm

[0018] Verify the included angle between adjacent frames: cosθ = T prev_end ·T next_star > 0.99.

[0019] The piezoelectric ceramic sensor in step S1 consists of two sensors, one for measuring curvature and the other for measuring torsion.

[0020] The installation positions of the piezoelectric ceramic sensors in step S1 are located at 1 cm, 5 cm, 9 cm, 13 cm, and 17 cm away from the tip of the needle respectively.

[0021] The charge signal Q κ of the curvature sensor in step S2 and the relationship with the local curvature κ are determined by a calibration experiment.

[0022] The charge signal Q au of the torsion sensor in step S2 and the relationship with the local torsion au are also obtained through calibration. The formula is as follows:

[0023] Q κi = k κ ·κ i + ∈ κi

[0024] Q aui = k au ·au i + ∈ aui

[0025] The generation method in step S3 is interpolation by the spline interpolation method.

[0026] The s in step S3 is the arc length coordinate of the needle body.

[0027] The initial frame in step S4 ensures the frame continuity between adjacent paragraphs. Repeat this step along the needle body towards the tip direction until the 1 cm node.

[0028] Based on the frame {T1, N1, B1} at the 1 cm node, assuming the curvature of the needle tip segment is constant κ(s) = κ1, calculate the 0 cm - 1 cm trajectory through integration:

[0029]

[0030] The beneficial effects of the present invention are as follows: By installing multiple piezoelectric ceramic sensors in a distributed manner, real-time and accurate local curvature and torsion of the flexible needle are achieved, realizing high-precision multi-point measurement for detection; Using the RMF frame to replace the traditional Frenet frame avoids the frame mutation problem caused by curve torsion, thereby reducing the cumulative error and improving the reconstruction accuracy. Description of the Drawings

[0031] The present invention will be further described below in conjunction with the drawings and embodiments.

[0032] Figure 1 It is the distribution diagram of the piezoelectric ceramics on the needle body of the present invention;

[0033] Figure 2 It is the cross-sectional view of the needle where the piezoelectric ceramic group of the present invention is located;

[0034] Figure 3 It is the curve reconstruction flow chart of the flexible needle of the present invention;

[0035] Reference numerals: 1, flexible needle; 2, piezoelectric ceramic sensor; 3, wire. Detailed Embodiments

[0036] In order to make the technical means, creative features, achieved purposes and functions of the present invention easy to understand, the present invention will be further described below.

[0037] As Figures 1 to 3 shown, for the flexible needle curvature measurement and shape reconstruction method based on piezoelectric ceramics, the specific steps are as follows:

[0038] S1. Sensor installation and signal acquisition

[0039] Five groups of piezoelectric ceramic sensors 2 are evenly arranged on the flexible needle 1. Each group consists of two sensors, one for measuring curvature and the other for measuring torsion. The installation positions of the sensors are located at 1 cm, 5 cm, 9 cm, 13 cm, and 17 cm away from the tip of the needle respectively. The sensors are connected to a high-impedance charge amplifier through flexible wires 3 to ensure the stable transmission of weak charge signals. Then, an analog-to-digital converter is connected to convert the amplified analog signal into a digital signal and transmit the data to data processing;

[0040] S2. Data Processing and Curvature Calculation

[0041] For the charge signal Q of each group of sensors i perform data processing. The relationship between the charge signal Q of the curvature sensor κ and the local curvature κ is determined by a calibration experiment. The relationship between the charge signal Q of the torsion sensor au and the local torsion au is also obtained through calibration. Before deployment, each piezoelectric ceramic sensor 2 is statically bent and pre-calibrated to establish a mapping relationship model between charge and curvature, torsion. The formula is as follows:

[0042] Q κi = k κ ·κ i + ∈ κi

[0043] Q aui = k au ·au i + ∈ aui ;

[0044] k κ and k au are the sensor sensitivity coefficients, κ i is the local curvature at the corresponding position of the i-th sensor, au i is the local torsion at the corresponding position of the i-th sensor, ∈ i is the environmental noise compensation term;

[0045] S3. Interpolation Calculation and Continuous Curvature Model

[0046] Real-time collect the charge signals of each sensor, and convert them into discrete local curvature values κ i through the pre-calibration model. Use the cubic spline interpolation algorithm to generate the continuous curvature function κ(s) and torsion function τ(s) of the needle body along the axis, where s ∈ [0, 20] is the axial coordinate of the needle body. This method ensures that the curvature distribution is smooth and effective, and can effectively avoid the Runge phenomenon. After obtaining the discrete curvature and torsion at five measurement points, use the spline interpolation method for interpolation to generate the continuous curvature function κ(s) and torsion function au(s) of the needle body along the axis, where s is the arc length coordinate of the needle body;

[0047] S4. Piecewise RMF Reconstruction: The RMF frame is used to replace the traditional Frenet frame, avoiding the problem of frame mutation caused by curve torsion, thus reducing the cumulative error and improving the reconstruction accuracy. The RMF frame has good stability during the smooth transition of the curve, which helps to ensure the morphological measurement accuracy of the flexible needle 1 during dynamic movement;

[0048] Taking the fixed base coordinate system at the 20 cm end of the needle root as the initial frame {T0, N0, B0}, where T0 is the axial direction of the base. Starting from the 17 cm - 20 cm segment, the interpolated κ(s), τ(s) sequences are discretized with a step size of Δs = 1 mm; According to the RMF differential equation, the frame is updated step by step:

[0049]

[0050] Calculate the current point coordinate: r i+1 = r i + Δs·T i ,

[0051] When iterating to the end point of the paragraph at 17 cm, save the frame {T end , N end , B end} of this point as the initial frame for the next 13 cm - 17 cm segment, ensuring the continuity of the frames between adjacent segments. Repeat this step along the needle body towards the tip direction until the 1 cm node;

[0052] Based on the frame {T1, N1, B1} at the 1 cm node, assuming a constant curvature κ(s) = κ1 for the needle tip segment, calculate the 0 cm - 1 cm trajectory through integration:

[0053]

[0054] S5. Curve Stitching Verification and Optimization

[0055] Check the coordinate deviation of adjacent paragraph endpoints: ||r prev_end - r next_star || < ∈∈ = 0.01 mm

[0056] Verify the included angle of adjacent frames: cosθ = T prev_end ·T next_star > 0.99;

[0057] If the deviation exceeds the limit, change the interpolation method for the segment with excessive error and introduce a rotation compensation term during the reconstruction process to make the frame of the current segment connect well with the adjacent segment. After complete stitching, output the complete curve. By using the piecewise reconstruction and stitching method, each small segment is calculated independently and stitched step by step, which can reduce the error accumulation and improve the overall reconstruction accuracy.

[0058] In the step S1, five groups of rectangular piezoelectric ceramic sensors 2 are installed at equal intervals along the axial direction on the surface of a flexible needle 1 with a total length of 20 cm. By installing multiple piezoelectric ceramic sensors 2 in a distributed manner, real-time accuracy of the local curvature and torsion of the flexible needle 1 is achieved, and high-precision multi-point measurement for detection is realized.

[0059] The piezoelectric ceramic sensors in the step S1 are fixed with double-sided epoxy resin glue and connected to a charge amplifier through a flexible circuit to achieve dynamic signal acquisition synchronized with the surface strain of the needle body.

[0060] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification is only the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for measuring the curvature and reconstructing the shape of a flexible needle based on piezoelectric ceramics, characterized in that: The specific steps are as follows: S1. Sensor installation and signal acquisition; Five groups of piezoelectric ceramic sensors (2) are evenly arranged on the flexible needle (1), connected to an analog-to-digital converter to convert the amplified analog signal into a digital signal, and transmit the data to data processing. S2. Data processing and curvature calculation: Process the charge signal Q for each group of sensors i and perform data processing; S3. Interpolation calculation and continuous curvature model: After obtaining the discrete curvature and torsion of five measurement points, generate the continuous curvature function κ(s) and torsion function au(s) of the needle body along the axial direction. S4. Piecewise RMF reconstruction: Taking the fixed base coordinate system at the root of the needle, i.e., the 20 cm end, as the initial frame {T0, N0, B0}, where T0 is the axial direction of the base, starting from the 17 cm - 20 cm section, discretize using the interpolated κ(s), τ(s) sequences with a step size of Δs = 1 mm; according to the RMF differential equation, gradually update the frame: Calculate the coordinates of the current point: r i+1 = r i + Δs·T i ; S5. Curve stitching verification and optimization: Check the coordinate deviation of adjacent paragraph endpoints: ||r prev_end -r next_star || <∈ ∈=0.01mm Verify the included angle between adjacent frames: cosθ = T prev_end ·T next_star > 0.99 2. The method for measuring the curvature and reconstructing the shape of the flexible needle based on piezoelectric ceramics according to claim 1, wherein: The piezoelectric ceramic sensor (2) in step S1 is composed of two sensors, one for measuring curvature and the other for measuring torsion.

3. The method for measuring the curvature and reconstructing the shape of a flexible needle based on piezoelectric ceramics according to claim 1, wherein: The installation positions of the piezoelectric ceramic sensors (2) in step S1 are respectively located at 1 cm, 5 cm, 9 cm, 13 cm, and 17 cm away from the needle tip.

4. The method for measuring the curvature and reconstructing the shape of a flexible needle based on piezoelectric ceramics according to claim 1, wherein: The charge signal Q of the curvature sensor in step S2 κ The relationship with the local curvature κ is determined by a calibration experiment.

5. The method for measuring the curvature and reconstructing the shape of a flexible needle based on piezoelectric ceramics according to claim 1, wherein: The charge signal Q of the torsion sensor in step S2 au The relationship with the local torsion au is also obtained through calibration, and the formula is as follows: Q κi = k κ ·κ i + ∈ κi Q aui = k au · au i + ∈ aui .

6. The method for measuring the curvature and reconstructing the shape of a flexible needle based on piezoelectric ceramics according to claim 1, characterized in that: The generation method in step S3 is interpolation using the spline interpolation method.

7. The method for measuring the curvature and reconstructing the shape of a flexible needle based on piezoelectric ceramics according to claim 1, wherein: In step S3, s is the arc length coordinate of the needle body.

8. The method for measuring the curvature and reconstructing the shape of a flexible needle based on piezoelectric ceramics according to claim 1, characterized in that: The initial frame in step S4 ensures frame continuity between adjacent paragraphs. Repeat this step along the needle body towards the tip direction until the 1 cm node; Based on the frame {T1, N1, B1} at the 1 cm node, assuming a constant curvature in the needle tip section (κ(s) = κ1), calculate the 0 cm - 1 cm trajectory through integration:

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