Modular and Fault-Tolerant Three-Axial FBG-Based Force Sensing for Transoral Surgical Robots

Transoral robotic surgery (TROS) has met a significant challenge to precise control of surgical instruments and depress the injury risks without force feedback. Therefore, we develop a modular high-precision three-axial fiber Bragg grating (FBG) force sensor with nonlinear decoupling, fault tolerance, and temperature compensation (TC) for seamless integration into transoral robots. The sensor comprises a one-body elastomer housing four optical fibers engraved with FBG each, arranged at a constant interval of 90° along the circumference to enhance three-axial force perception through redundancy. A novel dung Beetle optimization extreme learning machine (DBO-ELM) algorithm is proposed to tackle nonlinear coupling, FBG fracture, and temperature interference challenges leading to excellent performances of accurate and reliable measurement. The maximum full-scale error is less than 4% in each dimension, and the maximum MSE is only 1.8 mN at various spatial angles. The combination of four redundant FBGs and the DBO-ELM fault-tolerant model enables high-precision fault tolerance with maximum full-scale relative errors below 6% in case of one FBG damage. After TC, the maximum force measurement error is within 4% of the range. These merits confirm the effectiveness and dependability of the proposed sensor and algorithms in TROS applications.