Design of an FBG-Based Tension Sensor with High Sensitivity and Linearity for Cable-Driven Continuum Robots

Tension-force sensing of driving cables is essential for continuum surgical robots to ensure operational safety and enhance surgical quality and outcomes. This paper presents a fiber Bragg grating (FBG)-based force sensor with high sensitivity and accuracy for cable tension measurement in continuum robots. The proposed sensor comprises a force-sensitive flexure with a trapezoidal-shaped beam and a suspended optical fiber inscribed with an FBG element. The force-sensing flexure is developed from a conceptual lever displacement amplification model, and its specific shape is determined by topology optimization to achieve high stiffness and compactness. It transforms the tension input into the flexure deformation, which is further amplified to stretch the FBG optical fiber. The optical fiber adopts a two-point suspended configuration to avoid chirping failure and enhance sensitivity, taking advantage of the flexure’s lever amplification capability. Finite element method (FEM)-based simulation has been implemented to investigate the proposed sensor’s performance, and structural size optimization has been conducted for optimal design parameters and enhanced sensitivity. The sensor prototype has been calibrated to demonstrate a high resolution of 10.1 mN within [0, 50 N] and excellent linearity with a slight error of 0.25% FS. Dynamic loading experiments have been conducted to verify the prototype’s high accuracy with a root mean square error (RMSE) of 0.33% FS. The cable tension measurement experiment integrated into a continuum robot has been implemented to validate the effectiveness of the proposed sensor.