Passive Orientation Control of Nozzle Unit With Multiple Water Jets to Expand the Net Force Direction Range for Aerial Hose-Type Robots

Fluid injection has promising potential as a novel actuation approach for robots to enable the rapid switching of large forces. We have proposed a nozzle unit with multiple active rotating nozzles for controlling the magnitude and direction of the net force simultaneously. However, a new fundamental challenge arises when multiple nozzle units are connected to a long flexible robot, hence addressing the need to expand the injection range caused by twisting. The proposed nozzle unit can drastically expand the injection range using a passive rotation mechanism to automatically follow the intended injection direction. Concretely, the nozzle unit consists of the passive joint to rotate and two active rotating nozzles to realize the net force. If the unit emits the jets inwardly, the nozzle posture converges to the direction of net force without any additional control. By modeling the proposed nozzle unit, we theoretically validate the global stability of the proposed unit and derive sufficient conditions for geometric parameters. Moreover, we demonstrate that some geometrical parameters could modify the responsiveness of the posture. The developed nozzle unit experimentally verifies that the nozzle unit can direct the net force direction in the range of 180 degrees from the upward to the downward direction. In addition, we observe the step responses of the posture for several gains and confirm that responsiveness could be tuned by geometrical parameters. The results of the experiments agree well with the model trends.