Physical-Virtual Impedance Control in Ultralightweight and Compliant Dual-Arm Aerial Manipulators

Dual-arm aerial manipulation requires the design and development of high performance robotic arms in terms of safety, robustness, and force/torque/impedance control, taking into account the integration in the aerial platform, the strong weight constraints, and the technological limitations of the servo actuators. A compliant joint arm also improves the response of the aerial manipulator to collisions and external forces during the flight operation. This letter evaluates the control capabilities in a lightweight manipulator built with smart servo actuators and a spring-lever transmission mechanism that provides joint compliance and deflection measurement. The dynamic model of a compliant joint is validated through frequency identification, demonstrating how virtual variable impedance can be achieved without a second motor. Mechanical joint compliance is the base of the Cartesian impedance control scheme of the dual-arm system, integrated with the controller of the aerial platform. A stereo vision system provides the Cartesian deflection of the end effector, derived from the definition of an equivalent stiff joint manipulator, allowing the estimation and control of the contact forces. Experimental results validate the developed concepts.