A Contactless Stage Based on Near-Field Acoustic Levitation for Object Handling and Positioning-Concept, Design, Modeling, and Experiments

A technology demonstrating a stage capable of positioning an object in the X-Y plane and performing rotation on a thin layer of air without contact is presented. By creating ultrasonic vibrations in an annulus structure, a thin air layer develops a dynamic acoustic pressure field able to levitate a planar object and to control its position. Motion is obtained by creating traveling pressure waves within the acoustic field giving rise to directional forces acting on the levitated object. The novel configuration is based on three independent acoustic levitation motors. Each capable of levitating and positioning the object simultaneously. Closed-loop control of the object's position is made possible by incorporating several sensors. In particular, the motion and rotation of the mirror-like reflective surface such as the silicon wafers were realized with optical sensors based on a laser mouse. The necessary forces for manipulating the acoustic vibrations and, therefore, the pressure fields are generated by an H-infinity controller. The controller is robust enough to handle the strong coupling of the system and the model uncertainties. A laboratory prototype in which the concept was developed is described and validated by a series of experiments. This paper demonstrates the ability of the acoustic levitation systems to manipulate objects without contact.