A High-Sensitivity Force Sensor for Minimally Invasive Surgery Palpation Based on Fabry–Pérot Cavity and Rectangular Slot Hollow Structure

A palpation force sensor can provide force feedback for robot-assisted minimally invasive surgery (MIS), compensating for the lack of tactile feedback and increasing the reliability of palpation. To achieve higher sensitivity and a compact, easily manufacturable sensor structure, this article uses a single-mode optical fiber with a dual fiber Bragg grating (FBG) to form a Fabry-Pérot (FP) cavity as the sensing fiber and designs and optimizes a rectangular slot elastic structure based on the requirements of palpation applications. The sensor optical fiber is tightly suspended at the center of an elastic structure, to achieve high-sensitivity measurement of 1-D axial force. The study uses the finite element analysis for theoretical simulation to analyze the static and dynamic performance of the sensor, and experimental validation confirms its feasibility and performance. The experimental results show that the sensor exhibits a sensitivity of 124.75 pm/N within the dynamic force range of 0–5 N, with a linear response significantly superior to the conventional FBG center wavelength shift method. Furthermore, in further in vitro experiments simulating tumors, the effectiveness of the sensor in tissue palpation applications was successfully validated. This research combines the high sensitivity of the FP interferometer and the compact, easy-to-manufacture advantages of the rectangular slot hollow elastic structure, not only improving the accuracy and linearity of measurements but also making the sensor structure more compact, robust, and cost-effective. This research provides strong technical support for tactile feedback in robot-assisted MIS, with potential clinical application value.