Design and Control of a Fully-actuated Multirotor-based Aerial Manipulator with Series-Elastic Actuators for Stable Aerial Physical Interaction

Unlike terrestrial robots, aerial manipulation systems are inherently vulnerable to external forces due to their airborne nature, often resulting in flight instability and significant control errors. Control strategies that employ compliance control methods have shown promise in effectively dampening these external forces; however, they rely on sensors and computer-based operations, which can introduce response delays, often compromising control objectives and causing instability within the flight system. To address these challenges, in this research, we introduce an aerial manipulation technique that utilizes modified series-elastic actuators and new flight hardware. Series-elastic actuators allow for an immediate reaction to external forces through spring deformation before the compliance control algorithm is activated. However, implementing series-elastic actuators presents issues such as undesired system vibrations caused by the spring element (referred to as "bandwidth limitation" problems) and resulting control performance degradation. To mitigate these issues, we propose the implementation of a mechanical rotary damper within the series-elastic actuator to reduce vibrations while maintaining compliance performance within the desired frequency ranges. The proposed manipulation technique is applied to a fully-actuated multirotor platform named "Palletrone, " which can maintain a constant attitude during flight, enabling much more stable aerial physical interaction. Flight experiments validate the effectiveness and stability of the proposed methods by demonstrating stable trajectory tracking of the manipulator's end-effector in an unloaded state and confirming the efficacy of series-elastic actuator-based compliance control during interactions with external objects.