Force-stiffness Feedback in UAV Tele-operation with Time Delay

This study investigates the application of force-stiffness feedback, a combination of force offset and extra spring load, to a haptic interface for UAV tele-operation with time delay. Force feedback is based on applying force offsets that induce operator stick deflections that guide the UAV away from obstacles. Additional stiffness feedback limits the operator from deviating the stick too much from the guidance offered by the force feedback. The goal of this study is to increase safety of tele-operation, while reducing operator workload with force-stiffness feedback. A theoretical analysis shows that force-stiffness feedback improves the stability in the human control loop, and allows for lower force feedback gains, possibly reducing operator workload. An experiment was conducted to evaluate the effectiveness of force-stiffness feedback as compared to conditions without haptic feedback and force feedback using force offsets alone. Results indicate that force-stiffness feedback reduces the number of collisions as compared to conventional force feedback; workload, however, remains the same. Introducing a timepenalty each time a collision occurred, led operators to rate their workload to be lower when using either one of the haptic feedback conditions. This finding is in contrast with results from earlier experiments, which indicated higher workload with haptic feedback, and shows the importance of creating realistic test conditions when using subjective workload ratings.