3-Axial Force Self Fault-Tolerant Decoupling of Surgical Forceps Integrating Step-Coated FBG for Spinal Endoscopic Robot

This work proposed surgical forceps as a sensor that integrated step-coated Fiber Bragg Grating (FBG) for the 3-axial force sensing in the percutaneous spinal endoscopic robot. The step-coated FBG achieved a reflection spectrum with double wavelength peaks, providing more wavelength signals for fault-tolerant decoupling. The temperature and force sensitivity were regulated by adjusting the coating size to reduce decoupling error to 3.68% F.S, solving the span temperature (≥ 20°) disturbance from the operating room to the operative area. The optical fiber metallization and laser welding package was proposed to achieve stable connections between the quartz optical fiber and metal forceps. The innovative package made the forceps tolerate 180° dry-heat sterilization and aqueous erosion, allowing for sterilized reuse (11 times with error lower than 4.98% F.S) and long-term stability (one month with error lower than 4.36% F.S). A Wavelet Fuzzy Entropy (WFE) and Extreme Learning Machine (ELM) based dynsamic fault-tolerant decoupling strategy was proposed. The WFE-ELM reduced the sensor error to 4.42% F.S. under the influence of spectrum chirp noise and single-branch FBG breakage, and the fault-tolerant recovery rate within 10% F.S. error was raised to 40.23%. The designed surgical instruments were integrated with a spinal endoscopic surgical robot to conduct the spine model and pig experiments, verifying its force-sensing effectiveness. Note to Practitioners - This paper aims to address clinical applications of optical fiber force sensors in spinal endoscopic surgery, such as preoperative sterilization, aqueous erosion, temperature perturbations, and stability of reused. Most optical fiber sensors in the medical field are often packaged with adhesives, which make it difficult to withstand high-temperature sterilization environments and are prone to debonding under aqueous erosion. Moreover, FBG force sensors increase interaction force sensing errors under large-span temperature perturbations between the operating room and the body. These limitations hinder the development of fiber optic sensors in clinical applications. To address these issues, this work proposed step-coated FBG and their laser welding package method. Unlike conventional temperature compensation methods by increasing FBGs, the step-grid region microstructure is designed to provide extra twinned wavelength signals, improving temperature and force decoupling accuracy. Laser welding enables robust integration of metalized optical fibers with titanium alloy substrates, ensuring the resultant sensor exhibits exceptional resistance to high-temperature sterilization (up to 180°C) and prolonged aqueous erosion in biomedical environments. In addition, a fault-tolerant measurement method based on WFE and ELM was proposed to improve long-term service stability, which solves the problem of increased measurement error and failure due to degradation of sensing performance and link breakage failure. The results of sterilization and liquid erosion experiments show that the sensor can be reused 11 times with an error of 4.98%, reducing its cost in medical clinical applications.