Power semiconductor device and method therefor

Abstract

The present invention relates to a new kind of foil bearing. The present invention relates to a bearing comprising a flexible foil with a self-aligning mechanism. The present invention furthermore relates to a foil bearing enabling a linear and / or rotary movement along / around an axis (i.e. a shaft). The present invention also relates to a foil gas / air bearing with a self-aligning mechanism. The present invention furthermore relates to the use of said foil bearing in machines, more specifically in precision and / or high-speed machines and in high-speed precision spindles.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a new kind of foil bearing. The present invention relates to a bearing comprising a flexible foil and a self-aligning mechanism. The present invention furthermore relates to a foil bearing enabling a linear and / or rotary movement along / around an axis (i.e. a shaft). The present invention also relates to a foil gas / air bearing with a self-aligning mechanism. The present invention furthermore relates to the use of said foil bearing in machines, more specifically in precision and / or high-speed machines and in high-speed precision spindles. BACKGROUND OF THE INVENTION [0002] Semiconductor fabrication, high-resolution scanning, and high-speed machinery are just some of the applications pushing (rolling-element) bearings to technical limits. One reason for this is friction and variations therein, which have always posed problems for precision positioning systems. More force is needed to initiate motion than to maintain it, lea...

AI Technical Summary

Benefits of technology

[0018] The supporting and positioning means can have any form suitable for its function. In a particular embodiment, the supporting and positioning means is cylindrical. In order to have the self-aligning system, the cylinder can be attached to the frame in a suitable way allowing the rotation of each cylinder about the two axes normal to its geometrical axis. In yet a more particular embodiment, the present invention relates to a new foil bearing comprising a foil extended between a first and a second attachment point on a frame and a means for supporting and positioning the foil, more in particular via the use of at least one cylinder, such cylinder supported or attached in such a way as to have the freedom to rotate about its support point. In a particular embodiment of the present invention, the foil bearing comprises at least two cylinders or comprises more than 2 cylinders, such as 3 or 4. In a particular embodiment of the present invention, at least one of the cylinders is self-aligning, yet more in particular, two cylinders are self-aligning. In yet another more particular embodiment, the foil bearing comprises two self-aligning cylinders, whereby the foil embraces the round rails of the cylinders. The present invention relates thus in a particular embodiment to a new foil bearing with at least one flexible foil, a frame and a self-aligning mechanism, said self-aligning system comprising (at least) two cylinders attached (to the frame) in such a way that the rotation of each cylinder about the two axes normal to its geometrical axis is possible. A particular embodiment relates to a novel foil bearing with a self-alignment system comprising cylindrical supporting and positioning means which are attached to the frame through small pins forming point contacts in blind holes drilled in the cylindrical supporting and positioning means. In another particular embodiment, the self-aligning system is obtained through the use of a spring or multiple springs, which are in a particular embodiment attached to the frame. The supporting and positioning means can comprise in a particular embodiment a spring.

[0019] Therefore, the present invention relates in a certain embodiment to a foil bearing with a flexible foil, a frame, a supporting and positioning means which is cylindrical which can rotate about the two axes normal to its geometrical axis, thereby establishing a self-aligning mechanism.

[0022] Thus, one embodiment of the present invention provides an externally pressurised foil bearing for linear and / or rotary movement along / around an axis, compromising a foil extending between a first and a second attachment point, a flexible fluid supply and two cylinders supporting and positioning the foil. More particularly, the present invention relates to an externally pressurised foil bearing for linear and / or rotary movement along / around an axis with a self-aligning mechanism, comprising a foil extending between a first and a second clamping member, a flexible gas supply and a means for supporting and positioning the foil. The present invention furthermore relates to a foil bearing wherein two cylinders support and position the foil and are constructed to have a self-aligning mechanism, giving the foil the necessary degrees of freedom it needs to cover the axis / shaft appropriately and enlarging the contact area.

[0025] In a particular embodiment, the foil bearing of the present invention comprises a foil or multiple foils wherein said foil(s) has stiffening ribs or any other texture or cross-sectional profile, to enhance stiffness and / or damping.

Problems solved by technology

One reason for this is friction and variations therein, which have always posed problems for precision positioning systems.

More force is needed to initiate motion than to maintain it, leading to an imbalance between start and stop and leading to a stick-slip action.

This problem is higher for plain bearings than for rolling bearings, because of differences in static and dynamic friction coefficients.

Friction generates heat which, in turn, causes spindles and other components to thermally grow, compromising precision.

Air bearings are however expensive and delicate.

A cheap solution of an air bearing with high performance and accuracy is problematic, especially in case of bearing around a shaft.

The special geometry of the gap between shaft and bearing surface is difficult to create and is only ideal under certain conditions.

But scratches across a groove or near orifices may cause more air to escape than orifices can supply, causing a bearing to crash at normal air-supply pressures.

In general, air bearings with hard bearing surfaces are still showing problems with reliability.

For example, since the running radial clearance between the shaft and a bearing is very small (usually less than 0.0005 inch (7.5 micron) for a 2-inch (50 mm) diameter shaft at 36,000 rpm), shaft growth caused by temperature and centrifugal force can be problematic.

In addition, damping is required to suppress any whirl instability, and there can be misalignment between various rotating parts and stationary parts.

In addition, the foils provide coulomb damping due to their relative sliding.

Currently, foil bearings are limited to rotational axes and most of the time they are working without air supply (aerodynamic), which limits their stiffness considerably: indeed, the stiffness achieved by self-acting foil bearings is negligibly small.

Furthermore, in current foil bearings, the foil does not envelop the axis in a perfect way, leading to air lost and a reduction of the capacity or a malfunction of the bearing.

This foil bearing has however also the disadvantage that because the foil is fixedly supported to have a predetermined curvature corresponding to the radius of the rotor shaft, the foil will not envelop the shaft / axis in a perfect way during the process (e.g. misalignment resulting from thermal expansion, relative motion between bearing and shaft, vibrations, etc), leading to air lost and a reduction of the capacity or a malfunction of the bearing.

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