Modelling and experimental validation of dynamic characteristics of porous-walled air film for non-contact conveyor system

Abstract

Air film conveyors equipped with porous pads have been developed to bring the liquid crystal display into a non-contact state during transportation process. In this study, a theoretical model of one porous-walled radial flow, considering the effects of velocity slip at the surface of the porous medium, is established within a representative region, and its validity is verified by vibrating a moveable plate close to the porous surface to conduct investigations on pressure dynamic response. Due to the air damping effects, an apparent pressure hysteresis is observed when the air film subjected to periodic sinusoidal squeeze, and particularly for a given gap thickness, the pressure show approximate proportion to the squeezing velocities. A slip coefficient valued 0.004 is determined and applied to the theoretical model to study the air damping characteristics. In accordance with the experimental results, it is found that the air damping is greatly affected by the region radius, but little by the supply flow rate. Also, it is confirmed that the velocity slip is capable of inhibiting the damping effect. Moreover, free-decay oscillation of a suspended workpiece is inspected. The results indicate that the oscillating amplitude continuously attenuates until the workpiece finally becomes stable, and any change to the region radius or the supply flow rate can exert direct or indirect impact on the decay speed.