Admittance-based bilateral teleoperation with time delay for an unmanned aerial vehicle involved in an obstacle avoidance task

The paper focuses on the implementation of an admittance based control scheme in a bilateral teleoperation set-up for an Unmanned Aerial Vehicle (UAV) under time delay. The goal of this study is to assess and improve the stability characteristics of the bilateral teleoperator. Computer simulations were conducted to evaluate the effectiveness of the admittance-based control scheme. A commercial impedance-like haptic device was chosen to simulate the control stick: the master device. The slave system is constituted by the dynamics of the aircraft under control; in order to maximize the pilot attention on its task, only the lateral aircraft dynamics was considered. A virtual environment was displayed during the experiments to produce the visual cues. In order to evaluate the system, we prepared a control task where the aircraft had to be flown in a virtual urban canyon with buildings placed irregularly (non Manhattanlike) along the desired path by avoiding the collisions with them. A repulsive force field was associated to the obstacles and a force was sent back to the operator through the communication link. A compensator capable of flying autonomously the aircraft through the buildings with satisfactory performance was designed first using linear techniques then the haptic augmentation system was derived from the compensator by splitting it in two parts: the actual haptic cueing for the pilot and the simulated the pilot effort. The latter component was used only for the preliminary assessment of the system and was removed in simulations where a real pilot operated the stick (the master device). Experimental results and analytical motivations as well have shown that a haptic force which is simply proportional to the distance from the obstacles cannot stabilize the system: a relevant anticipatory effect or phase lead (as the derivative effect of standard industrial controllers) is needed. In order to manage the degradation of performance and overall stability when a delay is present in the communication paths, an admittance-based controller was designed together with an observer for the force generated by the human operator on the stick. The admittance-based Force Position teleoperation scheme was shown by simulations and tests with real pilots to improve the performance of the system under consideration.