Fuzzy-Adaptive Force-Compliant Control and Sensorless Estimation of a Hybrid Aerial Manipulator for Contact-Based Pipeline Repair

Aerial manipulators offer a compelling solution for maintenance tasks in hazardous or hard-to-reach environments. Contact-based operations, such as pipeline crack repair, demand not only precise trajectory tracking but also stable and controlled force application when interacting with cylindrical surfaces subject to friction. These dual objectives are challenging due to the aerial system’s inherent instability, strong nonlinearities, and sensitivity to disturbances. While impedance control enables direct interaction, it replaces the position control loop that can reduce robustness under dynamic conditions. In contrast, conventional admittance control wraps around existing loops but suffers from limited adaptability and challenging gain tuning. This paper proposes a unified force-compliant control framework for a quadrotor equipped with a hybrid manipulator. An adaptive backstepping-adaptive fast terminal sliding mode controller (AB-AFTSMC) governs the inner trajectory loop, ensuring reliable tracking performance. Over this structure, a fuzzy-admittance outer loop modulates the desired reference trajectories based on desired force, enabling compliant interaction during contact without altering the underlying control architecture. Interaction forces are estimated using a lightweight disturbance observer (DOB), enabling low-computation, sensorless feedback without the weight or complexity of force sensors. Validation is carried out in MATLAB Simscape through a 3D physics-based model. The results demonstrate reliable tracking, compliant force build-up, and consistent free-flight-to-contact transitions.