A rotational traveling wave based levitation device – Modelling, design, and control

Described is a device acting on an acoustically levitated object by manipulating the pressure and flow of a thin layer of air such that its rotation can be precisely controlled without mechanical contact. Virtual work analysis assists in simplifying the multi-actuator control problem into one governed by a single controllable parameter. Actuation is accomplished by a vibrating annulus capable of producing ultrasonic standing and traveling waves. Thus creating the acoustic excitation that affects the pressure in a thin, intermediate layer of gas. A distinctive vibration pattern is required to generate the temporal and spatial pressure field of the squeezed air layer that gives rise to both acoustic levitation force and rotational torque. Described are the physical and design development stages leading to an optimized structure, all followed by verifying and dynamics-calibration experiments. Moreover, by precisely controlling the ratio of standing and traveling waves in the annulus, in a closed-loop, one can control the shear forces applied by the squeezed air layer, thus creating a non-contacting levitated object manipulation mechanism. Through an algebraic transformation, the over-actuated setup is converted to a simplified single control-parameter problem. The transformation links the standing waves ratio, and hence the rotational torque, to the amplitudes and phases of the actuators. This arrangement leads to an effective closed loop methodology that was implemented experimentally, showing good performance and exhibiting rapid angular positioning.