Development of a Distal Tri-Axial Force Sensor for Minimally Invasive Surgical Palpation

The current study highlights the development of a novel and high-accuracy Fiber Bragg Grating (FBG)-enabled tri-axial distal force sensor for minimally invasive surgical palpation. This tri-axial sensor designs the primary flexure/elastomer consisting of axial and radial force-sensitive structures in a serial configuration, based on the method of freedom and constraint topology (FACT) from the perspective of the mechanism. This method provides general guidelines for designing multidimensional sensor design, achieving excellent sensitivity and a large measurement range, depressing crosstalks and couplings among different axes, and keeping the sensitivity of the three directions at the same order of magnitude. Five tightly suspended optical fibers embedded with one FBG element each have been assembled with the proposed flexure. They are configured with one arranged at the axial flexure's central line and four distributed along the circumference of the radial flexure. This tight suspension configuration generates uniform and constant strain distribution on the FBG element, thus improving resolution and repeatability and further avoiding FBG chirping. Finite element modeling (FEM)-based simulation has been conducted for performance investigation and design optimization to improve the sensor sensitivity. Static calibration experiments and in-vitro and ex-vivo palpation experiments have been performed to investigate the proposed design's performances and feasibility. The optimized sensor prototype achieves excellent resolution values of 1.18mN and 1.81mN in the x- and y-directions within [-5N, 5N], and 2.61mN in the z-direction within [0, 5N], realizing the same order of sensitivity magnitude at each axis.