Hardness recognition using a fiber Bragg grating flexible tactile sensor

Accurate hardness recognition is crucial for reliable robotic precision assembly. Traditional tactile sensors, constrained by electromagnetic sensitivity and poor flexibility, cannot achieve reliable hardness detection. Fiber Bragg grating (FBG) sensors offer an innovative solution for robotic hardness recognition, leveraging their anti-interference capability, high sensitivity, and flexibility. In this study, an object hardness recognition method based on FBG sensors was proposed using the force–longitudinal deformation mapping relationship. First, the force–longitudinal deformation mapping relationship of objects with different hardnesses in contact with encapsulated materials was established by theoretically analyzing the force and deformation of two objects in contact and optimizing the sensor structure using finite element modeling. Subsequently, the FBG flexible tactile sensor was fabricated and an experimental system for hardness detection was developed. The performance of the sensor was verified using pressure calibration experiments, and horizontal comparison experiments were conducted for objects comprising different materials. Longitudinal comparison experiments were also conducted for objects of the same material but different hardnesses. The experimental findings reveal significant differences in the rate of central wavelength shift over time for the FBG tactile sensor when in contact with different materials (iron: 144.86 pm/s; soap: 87.66 pm/s; eraser: 60.03 pm/s; foam: 35.34 pm/s) and across a range of hardness levels for the same material (A10–A80 silicone rubber: 32.27, 60.06, 68.71, 76.32, 96.05, 108, 115.92, and 135.9 pm/s). The results highlight the potential of FBG tactile sensors for hardness recognition, offering new approaches for advancing electronic skin and intelligent robotics technologies.