Vertical attractive force generated in a noncontact chuck using ultrasonic vibration

•The air flows inward toward the gap center at greater velocity than it flows out.•The inflow behavior at the outer edge generates the inflow resistance.•The inflow resistance causes the lower pressure area and the attractive force.•The attractive force is affected by the squeeze number σ and increases with σ.

Squeeze-film chucks using ultrasonic vibration are attracting considerable attention because of their ability to vertically and horizontally support an object placed on their vibrating surface without any contact. In addition, it has been shown experimentally that an attractive force is exerted on an object set under the vibrating surface. Although the cause of the vertical and horizontal forces has been determined using computational fluid dynamics (CFD) calculations, the cause of the attractive force generated by the vibrating surface has not yet been clarified in detail. This paper investigates numerically and experimentally the cause of this attractive force generation. In the numerical calculations, CFD was used to obtain the pressure distribution both in the air gap between the object and the vibrating plate and in the space surrounding the object. The attractive force acting on the object was found to be generated by the inflow resistance at the outer edge of the object when the air flows into the narrow air gap from the outside, which lowers the pressure in the air gap around the outer edge of the object to below ambient.