Design and Validation of a Miniature Fiber Bragg Grating-Enabled High-Sensitivity Torque Sensor

This paper presents a Fiber Bragg Grating (FBG)-based torque sensor with high sensitivity and miniature size for MIS instruments and multi-finger hands. The proposed sensor design mainly consists of a torque-sensitive flexure structure and two diagonally arranged optical fibers embedded with FBG sensing elements. An improved hollow hexaform structure with flexible hinges has been utilized to design the torque-sensitive flexure with an excellent linear measurement range and a solid capacity to resist non-torsion loading. Two optical fibers with an FBG inscribed each adopt a two-point gluing configuration with a tightly stretched status, and they are arranged diagonally along the hyperboloid surface. This configuration can obtain improved sensitivity and resolution and avoid the drawbacks of FBG chirping and low repeatability. Finite element modeling (FEM)-enabled simulation has been implemented to perform design optimization for further sensor sensitivity improvement and performance investigation. The prototyped sensor has been calibrated and achieves a high resolution of 0.062N.mm within [-100, 100N.mm] and excellent linearity with a small linearity error of 0.68%. The crosstalk experiments on the bending moment of Mx and My and the axial force have been conducted to validate the anti-interference capacity on the basis of the small values of 0.47%, 0.31%, and 1.78%. The proposed design also supports convenient customization to achieve the adjustable measuring range and torque sensitivity, which has been validated by another sensor version with a resolution of 0.26 N.mm within [-500, 500N.mm].