Development of an Optic Fiber-Based Torque Sensor With a Torsion-Translation Conversion Flexure

Abstract

This work proposes a miniature and high-sensitivity torque sensor that mainly consists of a torque-sensitive flexure and one tightly suspended optic fiber with an inscribed Fiber Bragg Grating (FBG) element for application in minimally invasive surgery robots and multi-finger robotic hands. The proposed flexure can achieve a torsion-translation conversion with a linear measurement range and a solid resistance to moment loadings. It is implemented based on the hybrid design among the specially designed hyperboloid, hollow cruciform, and cross-beam structures. The mounted FBG fiber has been configured at the flexure’s central line with its two ends glued. This tight suspension configuration can improve resolution and sensitivity and avoid FBG chirping compared to the direct FBG-pasting methods. The flexure translational motion overlaps with the FBG fiber suspension direction, generating a large and uniform strain distribution on the suspended FBG. Design optimization has been performed based on finite element modeling (FEM) simulation for structural investigation and sensor sensitivity enhancement. The prototyped sensor achieved a high resolution of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.295 {\mathrm {~N}} \cdot {\mathrm {mm}}$ </tex-math></inline-formula> within [−600, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$600 {\mathrm {~N}} \cdot {\mathrm {mm}}$ </tex-math></inline-formula> ] and exhibited excellent linearity with a small linearity error of 1.24%. The dynamic experiments demonstrated small crosstalk values of 1.6% and 3.4% for Mx and My moments. Furthermore, the proposed design supports convenient customization, and it can also achieve a resolution of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.81 {\mathrm {~N}} \cdot {\mathrm {mm}}$ </tex-math></inline-formula> within [−2000, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2000 {\mathrm {~N}} \cdot {\mathrm {mm}}$ </tex-math></inline-formula> ] by structural modification.