Real-Time Fingertip Force Estimation from Lateral Deformation for Precision Manipulation Task

This study proposes a wearable fingertip force estimation approach that employs a single three-axis force sensor mounted on the side of the fingernail, enabling measurements under natural contact conditions without obscuring the fingerpad. Fingertip deformation during contact is captured by the sensor, and calibration experiments are performed using a table-mounted force sensor to relate the measured lateral deformation to actual normal and tangential forces. Two modeling approaches—a 6th-order multi-input multi-output transfer function model and an 8th-order state-space model—are identified from the calibration data. The transfer function model achieves high offline accuracy (R²≈ 0.9, RMSE ≤ 7%FS), while the state-space model offers smoother, low-latency output suitable for real-time feedback. These results clarify the relationship between fingertip deformation and applied forces, providing a scientific basis for improving skill transfer, training protocols, and haptic simulation in precision manual tasks.