Controlled Shaking of Trees With an Aerial Manipulator

In recent years, the fields of application of aerial manipulators have expanded, ranging from infrastructure inspection to physical interaction with flexible elements, such as branches and trees. This article presents the controlled shaking of a tree with an aerial manipulator. Our work aims at contributing to applications like the identification of tree parameters for environmental health monitoring or the collection of samples and fruits by vibration. To this end, we propose a control strategy for controlled shaking of flexible systems. We adopt a self-excited oscillation strategy that induces vibrations at the natural frequency of the system, at which the greatest amplification and therefore the greatest vibrations occur. Likewise, this work presents a simplified 1 degree of freedom (DoF) model based on the Rayleigh–Ritz method to analyze dynamic interaction between a tree and the aerial manipulator with the controlled shaking strategy. The proposed control strategy is evaluated through indoor experiments, where an aerial manipulator shakes an indoor tree made of bamboo canes. Experimental results show how the proposed model can estimate properly the amplitude of the vibration and the frequency of the vibration, depending on the grasping point and the control gain of the self-excited oscillation strategy.