Adaptive Hybrid Force/Position Admittance Control With a Velocity-Level Correction for Robotic Grinding Contact Tasks

Robotic grinding and related surface-contact tasks require smooth contact establishment and stable force regulation during sustained interaction. Fixed-parameter admittance control often cannot meet both requirements, because damping that suppresses initial impact may compromise compliant behavior after contact. This article presents an applied adaptive hybrid force/position admittance framework for robotic grinding. It integrates velocity-level admittance correction with a projection-constrained adaptive update law and a σ-modification term. The velocity-level correction maps normal-force error directly to corrective velocity commands, suiting industrial robots with Cartesian or joint velocity interfaces. The adaptive law regulates virtual inertia and damping online while keeping the estimates inside a physically meaningful feasible set under weak excitation. Lyapunov-based analysis establishes uniform ultimate boundedness of the high-level normal-contact channel under stated local contact and bounded velocity-servo assumptions. UR5-based grinding experiments under 23 N and 3 N target forces show that the proposed controller reduces force-tracking root mean square error (RMSE) and contact-force fluctuation relative to the tested baselines, while also reducing the mean maximum impact force in the evaluated contact-transition stage. The results also show a normal-motion trade-off, since the heuristic adaptive controller produced the smallest mean Z-axis position standard deviation.