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Aerial Manipulator Interactions With Trees for Canopy Sampling

Aerial manipulation applications involve a physical interaction between an unmanned aerial vehicle and its operating environment. This paper presents the novel application of physical coupling between an aerial manipulator and tree toward semiautonomous canopy sampling. Interactions with unconstrained objects have been studied extensively; however, trees are a complex environment with unique and naturally varying mechanical characteristics. Such interactions have not appeared in the previous literature so the effects remain unknown, thus warranting this study. First, an aircraft-tree branch interaction model is introduced using known aircraft dynamic modeling methods and a specially developed tree branch mechanical model, representing environmental disturbances to the aircraft. Coupling behavior with a range of canopy branches is investigated in both simulation, and experimentally with the aid of motion capture. The case of interactions with a swaying quasi-rigid tree stem is also explored. These respective studies have revealed station-keeping flight performance while coupled with flexible branches, and bounded environmental motion interactions where force closure does not exist. The use of conventional PID control is also validated for branch-coupled flight. Furthermore, a comparison of simulation and experimental results has shown that coupling behavior is adequately represented by mechanical effects captured in the developed tree branch model.