Investigation of air film conveyor pressurised through multiple holes
TL;DR: In this article, the authors investigated the pressure distribution, load capacity and air requirements to maintain a load carrying air film of variable thickness with the help of the finite element method, and established the usefulness of the FEM for designing load-carrying air films and enabled some general design recommendations to be made.
About: This article is published in Finite Elements in Analysis and Design.The article was published on 1990-02-01. It has received 17 citations till now.
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TL;DR: In this paper, a simple air slit levitating conveyor was devised to lower the equipment cost and to reduce the air consumption, and the air consumptions between the air conveyor with the air slit and that with the porous pad were compared.
42 citations
TL;DR: In this article, a new air bearing element called as vortex bearing is introduced and investigated in comparison to the conventional orifice bearing, the new bearing is characterized by blowing air through tangential nozzles to form a vortex flow.
Abstract: A new air bearing element called as vortex bearing is introduced and investigated in this study. In comparison to the conventional orifice bearing, the new bearing is characterized by blowing air through tangential nozzles to form a vortex flow. The study focuses on one vortex-bearing element to investigate its basic characteristics (flow rate characteristics, pressure and velocity distributions, load capacity, and static stiffness). We show that the vortex bearing uses vortex flow to form a sunken negative pressure distribution at the central area, so that it can narrow the gap clearance between the workpiece and the bearing and thereby improve the flotation stiffness. Moreover, blowing air tangentially instead of emitting onto the workpiece directly can avoid the formation of intense pressure distribution on the workpiece’s surface, which would reduce the partial stress concentration acting on the workpiece. For these reasons, the new vortex bearing is applicable in air conveyors that float and transport workpieces such as glass substrates and silicon wafers.
40 citations
TL;DR: In this paper, a theoretical analysis of the fluid mechanics of the air cushion of air reversers used in web-handling systems is presented and conditions that maximize the air pressure supporting the web are analyzed and design guidelines are deduced.
Abstract: A theoretical analysis of the fluid mechanics of the air cushion of the air reversers used in web-handling systems is presented. A two-dimensional model of the airflow is derived by averaging the equations of conservation of mass and momentum over the clearance between the web and the reverser. The resulting equations are Euler's equations with nonlinear source terms representing the air supply holes in the surface of the reverser. The equations are solved analytically for the one-dimensional case and numerically for the two-dimensional case. Results are compared with an empirical formula and the one-dimensional air-jet theory developed for hovercraft. Conditions that maximize the air pressure supporting the web are analyzed and design guidelines are deduced.
13 citations
TL;DR: A completely contactless air conveyor system for transporting and positioning planar objects that forms a thin film underneath the object for support and simultaneously generates a controlled airflow that results in viscous traction is developed.
Abstract: In this study, we developed a completely contactless air conveyor system for transporting and positioning planar objects. The air conveyor forms a thin film underneath the object for support and simultaneously generates a controlled airflow that results in viscous traction. It is potentially applicable in the manufacturing process for semiconductor wafer or flat foodstuffs, where mechanical contact is expected to be avoided during transportation of the products to minimize contamination. The air conveyor employs duplicated arrays of actuating cells that are square pockets with a surrounding dam. A simple model is proposed to characterize the viscous force. The theoretical analysis reveals that the total force is the composition of an actuating force generated in the pocket areas and the side areas and a drag force generated in the dam areas. Experimental investigations are conducted on the basic characteristics of the film pressure distribution and the viscous force. The results show that the air film pressure is symmetrically distributed in the width direction but nonsymmetrically distributed in the length direction. The viscous force increases if the suction flow rate is enlarged or the gap thickness is narrowed. Comparison of the experimental results and the calculated results indicates that the model can provide an accurate prediction. A proportional⁻integral⁻derivative (PID) controller is applied for 1D-position control and position tracking. The actuating direction is selected using fast switching valves and the amplitude of the actuating force is adjusted using a control valve to vary the suction flow rate. The simulated and the experimental results verify the feasibility of the air conveyor system and the control method.
9 citations
TL;DR: In this article, a contactless air film system with aligned porous pads is proposed and experiments and analysis of its basic characteristics are conducted, and it is confirmed that the flow rate characteristics of the porous pads can be represented by a modified Forchheimer equation with determined permeability and inertial coefficient.
Abstract: Recently, the development of displays requires large, thin glass substrates, and air film conveyors equipped with porous pads have been developed to transport the substrates in a noncontact state. In this study, a contactless air film system with aligned porous pads is proposed. Experiments and analysis of its basic characteristics are conducted. First, it is confirmed that the flow rate characteristics of the porous pads can be represented by a modified Forchheimer equation with the determined permeability and inertial coefficient. Then, a theoretical model based on the Reynolds equation is established to analyze the film pressure distribution. The results indicate a parabola-like shape distributed along the radial direction in the porous area and an approximately linear curve in the periphery area. Furthermore, the experimental results indicate that the bearing force and static stiffness increase if the clearance decreased with a given flow rate. Finally, a numerical calculation performed by solving the...
7 citations
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32 citations
TL;DR: In this article, the authors investigated theoretically the pressure distribution in externally pressurized circular thrust gas bearings with a circular recess by assuming the generation of a normal shock wave in the bearing recess, and good quantitative agreement was found between the analytical results and available experimental data except the case of small bearing clearance height or deep recess.
Abstract: In externally pressurized gas-lubricated circurlar thrust bearings, the occurrence of depression in the pressure profile is observed under some working conditions. Following the previous paper on the theoretical investigation of pressure depression, this paper investigates theoretically the pressure distribution in externally pressurized circular thrust gas bearings with a circular recess by assuming the generation of a normal shock wave in the bearing recess. Good quantitative agreement is found between the analytical results and available experimental data except the case of small bearing clearance height or deep recess. In order to prevent the pressure depression just after the gas supply hole, it is effective to provide a round or tapered chamfer at the entrance edge of the hole to the bearing clearance or to make the recess tapered doubly. Through these alternations, the shape of pressure distribution becomes flatter so that the load capacity can increase remarkably.
10 citations
TL;DR: In this article, the externally pressurized rectangular pad with multiple supply holes is analyzed theoretically by use of complex potential theory, and an appropriate potential function which satisfies the boundary conditions, is found by using infinite arrays of infinite sources and sinks.
Abstract: The externally pressurized rectangular pad with multiple supply holes are analyzed theoretically by use of complex potential theory. An appropriate potential function, which satisfies the boundary conditions, is found by using infinite arrays of infinite sources and sinks. Then, the pressure distribution can be obtained theoretically, which leads to the determination of load capacity and flow. Results are given for both incompressible and compressible fluids. Experimental results coincide very well with theory concerning pressure distribution and load capacity if secondary effects owing to the compressibility of the fluid and pressure loss at supply holes is accounted for. Contributed by the ASLE Technical Committee on Bearings and Bearing Lubrication and presented at the Annual Meeting of the American Society of Lubrication Engineers held in Pittsburgh, Pa., May 3–5, 1966.
5 citations