Air-based contactless positioning of thin substrates

Abstract

A new concept in the field of air-based contactless positioning has been explored. The concept is based on the variation of the outlet restriction of an actuator, which controls a net air flow starting from the inlet. The object to be positioned ‘floats’ on a thin air film with a thickness in the order of tens of micrometres. Since the film thickness between actuator and object is limited and around a factor thousand smaller than the size of an actuator it can be modelled with the Reynolds equation. Combining an actuator pin, with a flat top surface and an air flow inlet in the middle, and a plate, with a hole slightly larger in diameter than the pin, creates the core of the actuator setup. Air flows from the inlet over the surface and exits through the gap between hole and actuator pin. A relative movement of the pin with respect to the hole varies the continuous outlet restriction surrounding the pin and thus the net air flow. This net air flow actuates the object due to the viscous forces of the flowing air. An actuator has been made with seven pin/hole combination and an average gap width equal to fifty micrometres, meaning that the outlet was also modelled using the Reynolds equation. Since the actuator was designed for the positioning of thin substrates with negligible weight, the average pressure in the gap between actuator and object should be around ambient pressure. This means vacuum pressure is connected to the outlet and high pressure is connected to the inlet. The created setup was able to actuate a flying object in all planar directions. The numerical model has partially been validated with measurements. It is likely that the differences between model and measurements are caused by manufacturing tolerances and inaccurate measurements.