Three-Dimensional Manipulation of a Spherical Object Using Ultrasound Plane Waves

In this letter, we demonstrate a new robotic framework where a lightweight balloon with no onboard actuators or batteries acts as a mid-air robot that travels three-dimensionally within a workspace. The workspace contains five sparsely arranged ultrasound transducer arrays emitting steerable plane waves that cause acoustic radiation forces on the balloon and actuate it. The fabricated system performs a dynamic PID control of the movement of the balloon based on visual feedback. For practical operation of the system, we experimentally modeled the acoustic radiation force applied on a sphere. Based on the model, we developed the system dynamics model and a control law. We constructed a prototype system and demonstrated meter-scale three-dimensional manipulation of a 200 mm-diameter spherical object. Our proposed methodology is beneficial for long-term mid-air robotic applications, such as 24-h indoor surveillance system with no blind spots caused by battery limitation.