Stiffness-Force Feedback in UAV Tele-operation

In the tele-operation of an uninhabited aerial vehicle (UAV), the operator and vehicle are physically separated. The limited sources of information of the environment, e.g., lack of a complete outside view, sounds, vehicle motions and vibrations, often lead to poor situation awareness. Tele-operation usually involves the use of a visual interface on a ground station, providing a navigation display and an outside visual generated by a camera mounted onboard the vehicle. The visual information, however, is usually not sufficient due to for instance a limited field of view, leading to an often not very efficient and sometimes even unsafe tele-operation (Elhaij et al., 2001; McCarley & Wickens, 2005). Previous research efforts indicated that a haptic interface, using force feedback via a haptic control device, can be used to complement the visual interface. Haptic feedback provides information about the environment through the sense of touch (Lam et al., 2004; Lam et al., 2007). Indeed, the multi-sensory haptic interface improved operator performance and significantly reduced the number of collisions, leading to an overall highly increased level of safety (Lam et al., 2007). Operator control activity and workload, however, increased as well. This may be attributed to the incompatibility between the haptic interface and the operator’s intentions, based on her or his internal representation of the environment. High operator control activity and workload particularly occur in situations where the UAV is surrounded by many obstacles. Although force feedback would indeed help the operator to avoid a collision with one obstacle, through deflecting the control device away from the direction of the obstacle, it may also direct the UAV towards another obstacle located at the other side. Whereas the haptic interface does not know about the other closely-located obstacle, the operator might already have located it from the visual interface, and would prefer to adjust the direction of motion only “just enough” to avoid collision. The reported incompatibilities between the motions of the haptic device and the operator’s intentions may have been caused by the particular implementation of the haptic interface, i.e., through applying force feedback alone. Here, an external force offset will actively deflect the haptic control device, in such a way that the vehicle moves away from the direction of an obstacle. The offset force, a function of the relative position and velocity of the UAV with respect to the obstacle, still exists even after the operator releases her hand from the control device and may cause the control device to deflect to the other side of the zero deflection. For control of a UAV helicopter, the focus of our study, the control deflection represents a velocity command. Therefore, the force feedback sometimes does not allow the operator to “rest” and follow the motions of the control device, but forces the