FBG-based 3D micro-force sensor integrated into ophthalmic microsurgical robotic forceps

Posterior segment ophthalmic surgery requires precise manipulation of handheld instruments while avoiding injury to delicate fundus tissues. In procedures such as internal limiting membrane (ILM) peeling, even experienced clinicians using dedicated ophthalmic surgical robots struggle to maintain appropriate contact force without inducing tissue damage. This difficulty arises primarily from the absence of precise three-dimensional (3D) intraoperative force measurements. In this paper, we design a rhombus-shaped Force-sensitive Mechanism (FSM) that amplifies the FBG strain under axial loading. Guided by an intraoperative force analysis of surgical forceps, we further propose a parameter optimization method that improves sensor resolution and accuracy. Moreover, by evenly distributing four FBGs around the outer tube of the forceps, we achieve accurate measurement of intraoperative lateral forces and implement a robust and computationally efficient temperature compensation strategy. We also construct a strain-transfer model comprising the “FBG–adhesive layer–deformable body”, and theoretically analyze the strain-transfer rate from the deformable bodies to the FBGs along with its governing factors. Experiments show that optimization increases the strain at FBG5 by 94.32% relative to the unoptimized design. The sensor attains a sensitivity of 0.45 pm/mN and a resolution of 0.05 mN over a 5–25 mN range, with hysteresis and repeatability errors of 3.4% and 3.3%, respectively. In ILM-simulant peeling experiments, the sensor accurately captures both lateral and axial contact forces of the forceps, providing actionable force information for robotic-assisted fundus surgery.