Design and Validation of a High-Sensitivity FBG-Based Triaxial Force Sensor With Serially Configured Flexures for Percutaneous Puncture

This article introduces an innovative fiber Bragg grating (FBG)-based triaxial force sensor with high sensitivity for percutaneous puncture applications. The proposed sensor employs the serially configured axial and radial force-sensitive flexures, incorporating tightly suspended optical fibers inscribed with FBG elements. Leveraging the rigid-body replacement method, the designed flexures exhibit selective sensitivities to axial and radial loads, enabling low-coupling triaxial force sensing. The axial force-sensitive flexure combined a semi-bridge mechanism with symmetrical L-shaped levers, amplifying output force while reversing deformation direction. This design maintains the measuring fiber in a purely tensile state, obviating the need for preload adhesion, thereby streamlining assembly and augmenting fiber durability. Finite element method (FEM)-based simulation and structural parameter optimization have been implemented to further enhance the sensitivity. The sensor prototype has been calibrated employing a nonlinear decoupling algorithm based on a backpropagation neural network (BPNN), achieving high resolutions of 2.6 mN within the axial range of 8 N and 0.25 mN within the radial range of ±1 N, with the crosstalk limited to 4.36%. Puncture experiments demonstrated a root mean square error (RMSE) of 3-D resultant forces not exceeding 12.3 mN on ex-vivo tissues, validating the sensor's efficacy and potential in robotic puncture surgery.