U.S. patent application number 10/557135 was filed with the patent office on 2007-03-15 for power semiconductor device and method therefor.
Invention is credited to RobertB Davies.
Application Number | 20070057289 10/557135 |
Document ID | / |
Family ID | 34798857 |
Filed Date | 2007-03-15 |
United States Patent
Application |
20070057289 |
Kind Code |
A1 |
Davies; RobertB |
March 15, 2007 |
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.
Inventors: |
Davies; RobertB; (Tempe,
AZ) |
Correspondence
Address: |
HVVI SEMICONDUCTORS, INC.
c/o PORTFOLIOIP
P.O. BOX 52050
MINNEAPOLIS
MN
55402
US
|
Family ID: |
34798857 |
Appl. No.: |
10/557135 |
Filed: |
January 6, 2005 |
PCT Filed: |
January 6, 2005 |
PCT NO: |
PCT/US05/00205 |
371 Date: |
November 17, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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60535956 |
Jan 10, 2004 |
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60535955 |
Jan 10, 2004 |
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Current U.S.
Class: |
257/202 ;
257/E29.022; 257/E29.023; 257/E29.027; 257/E29.066; 257/E29.118;
257/E29.121; 257/E29.134; 257/E29.135; 257/E29.136 |
Current CPC
Class: |
H01L 2224/48091
20130101; H01L 2924/01061 20130101; H01L 2924/01322 20130101; H01L
23/047 20130101; H01L 24/06 20130101; H01L 2223/6644 20130101; H01L
2924/1306 20130101; H01L 2924/14 20130101; H01L 2924/01006
20130101; H01L 21/32055 20130101; H01L 29/41766 20130101; H01L
29/4238 20130101; H01L 2224/0401 20130101; H01L 21/56 20130101;
H01L 29/66719 20130101; H01L 2924/0105 20130101; H01L 21/768
20130101; H01L 23/552 20130101; H01L 29/7811 20130101; H01L
2224/83193 20130101; H01L 2924/01033 20130101; H01L 23/66 20130101;
H01L 2924/01023 20130101; H01L 21/823481 20130101; H01L 29/41741
20130101; H01L 29/7817 20130101; H01L 2924/0002 20130101; H01L
21/2815 20130101; H01L 2924/01074 20130101; H01L 21/76838 20130101;
H01L 21/823412 20130101; H01L 2924/01005 20130101; H01L 25/50
20130101; H01L 27/0296 20130101; H01L 29/0696 20130101; H01L
2924/01019 20130101; H01L 2924/1305 20130101; H01L 2924/1306
20130101; H01L 29/42376 20130101; H01L 29/66727 20130101; H01L
2924/16152 20130101; H01L 2924/13091 20130101; H01L 29/66681
20130101; H01L 2924/30107 20130101; H01L 29/0657 20130101; H01L
2924/01029 20130101; H01L 23/3675 20130101; H01L 23/49844 20130101;
H01L 2224/04042 20130101; H01L 2224/06136 20130101; H01L 2924/01022
20130101; H01L 2924/00 20130101; H01L 2924/00 20130101; H01L
2924/00 20130101; H01L 2924/00014 20130101; H01L 2924/01014
20130101; H01L 2924/00 20130101; H01L 2924/01082 20130101; H01L
2924/04941 20130101; H01L 2924/14 20130101; H01L 21/76224 20130101;
H01L 2924/3011 20130101; H01L 29/0878 20130101; H01L 23/051
20130101; H01L 23/4824 20130101; H01L 2924/014 20130101; H01L
29/1095 20130101; H01L 23/36 20130101; H01L 29/402 20130101; H01L
24/83 20130101; H01L 2224/83801 20130101; H01L 21/823487 20130101;
H01L 29/66712 20130101; H01L 2924/01079 20130101; H01L 2224/48091
20130101; H01L 2924/1305 20130101; H01L 21/823437 20130101; H01L
23/10 20130101; H01L 2924/0106 20130101; H01L 2924/19041 20130101;
H01L 29/42372 20130101; H01L 2924/3025 20130101; H01L 29/0661
20130101; H01L 2924/0002 20130101; H01L 21/823475 20130101; H01L
2924/01013 20130101 |
Class at
Publication: |
257/202 |
International
Class: |
H01L 27/10 20060101
H01L027/10 |
Claims
1. A foil bearing comprising a frame and a foil, characterised in
that the foil bearing has a self-aligning mechanism which allows
the foil to self-adapt its position.
2. The foil bearing according to claim 1, wherein the foil is
attached to the frame and extended between a first and a second
attachment point.
3. The foil bearing according to claim 1, further comprising a
supporting and positioning means for optimally positioning and
supporting the foil, wherein the supporting and positioning means
allows for a self-aligning mechanism.
4. The foil bearing according to claim 3, wherein the supporting
and positioning means is cylindrical and can rotate around two axes
normal to its geometrical axis.
5. The foil bearing according to claim 3, wherein the supporting
and positioning means comprises two cylinders attached to the frame
and which can rotate around two axes normal to their geometrical
axes.
6. The foil bearing according to claim 4, wherein the cylindrical
supporting and positioning means are attached to the frame through
small pins forming point contacts in blind holes drilled in the
cylindrical supporting and positioning means.
7. The foil bearing according to claim 3, wherein the supporting
and positioning means comprises a spring.
8. The foil bearing according to claim 1, wherein the foil bearing
is externally pressurised.
9. The foil bearing according to claim 8, wherein the external
pressurisation is obtained through fluid supplied via the
shaft.
10. The foil bearing according to claim 8, wherein the external
pressurisation is obtained through fluid supplied via the foil.
11. The foil bearing according to claim 8, wherein the external
pressurisation is obtained through one or multiple flexible fluid
supplies.
12. The foil bearing according to claim 11, wherein said flexible
fluid supply is a rubber or a plastic hose.
13. The foil bearing according to claim 9, wherein the fluid is
gas, more in particular air.
14. The foil bearing according to claim 3, wherein the foil is
additionally fixed to the middle of the frame.
15. The foil bearing according to claim 14, comprising two
additional cylindrical supporting and positioning means allowing
for the self-alignment of the foil and thereby supporting and
positioning the foil on a different position than the other
supporting and positioning means.
16. The foil bearing according to claim 1, comprising a second
foil, attached to the frame at two attachment points.
17. The foil bearing according to claim 16, wherein the two foils
are interwoven.
18. The foil bearing according to claim 1, wherein said foil has
stiffening ribs or any other texture or cross-sectional profile, to
enhance stiffness and/or damping.
19. The foil bearing according to claim 1, wherein said foil is
supported by electromagnetic, magnetostrictive, piezoelectric or
any suitable type of actuator, so that the foil could be moved
statically or dynamically during operation, whereby its
characteristics could be controlled.
20. The foil bearing according to claim 1, wherein said foil is
made of metal.
21. The foil bearing according to claim 1, wherein said foil is
made from a "smart" material, e.g. PVD or piezoelectric material,
so that the characteristic of the foil could be changed during
operation, by controlling an electric current that is fed to the
foil.
22. The foil bearing according to claim 10, wherein the fluid is
gas, more in particular air.
23. The foil bearing according to claim 1, wherein the foil is
additionally fixed to the middle of the frame.
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, 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.
[0003] An option to circumvent the friction problem is the use of
fluid, liquid or air bearings, in which solid-solid contact is
eliminated. Fluid, i.e. hydrodynamic, hydrostatic, aerodynamic or
aerostatic bearings eliminate the stick-slip problem, because
static friction is zero, making infinite-motion resolution
theoretically possible and reducing the power loss. Most large
turbines today use oil-based hydrodynamic bearings, though many new
microturbines employ aerodynamic bearings to improve
efficiency.
[0004] Besides smoothing stop and starts, air bearings offer less
resistance (friction) to steady-state motion. Friction generates
heat which, in turn, causes spindles and other components to
thermally grow, compromising precision. Fluid bearings, in
particular, air bearings generate much less heat in a given
application than rolling-element or plain bearings in most cases.
In fact, relative speeds must exceed about 100 ft/sec (30 m/s)
before air bearings generate any significant heat at normal air
gaps. Air bearings excel in applications requiring tight velocity
control such as scanning and wafer inspection, because they
eliminate force ripples from recirculating ball bearings loading
and unloading.
[0005] Air bearings have been operated in process fluids other than
air, such as helium, xenon, air-conditioner refrigerants, liquid
oxygen, and liquid nitrogen. For applications in vapor cycles, the
refrigerant can be used to cool and support the air bearings
without the need for oil lubricants that can contaminate the system
and reduce efficiency.
[0006] The trend to make machines faster and more precise leads to
an increasing demand for gas or more specifically air bearings. 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. Furthermore,
traditional air bearings for axial movement have a rigid form. The
special geometry of the gap between shaft and bearing surface is
difficult to create and is only ideal under certain conditions.
[0007] An attempt to overcome some of the problems has been
undertaken by using air bearings made with, for example, orifice or
with porous technology, in order to achieve a more uniform pressure
distribution. Orifice compensation distributes pressurised air
across a bearing face through strategically placed, precisely sized
orifices and grooves. 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.
[0008] 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.
[0009] In the prior art, this problem is solved by foil bearings.
While the shaft is stationary, there is a small amount of preload
between the shaft and the bearing. As the shaft turns, hydrodynamic
pressure is generated, pushing the foils away from the shaft and
making the shaft completely airborne. This phenomenon occurs
instantly during start-up at a very low speed. When the shaft is
airborne, the friction loss due to shaft rotation is quite small.
As the shaft grows, the foils get pushed further away, keeping the
film clearance relatively constant. In addition, the foils provide
coulomb damping due to their relative sliding. This damping is
essential for the stability of the machine.
[0010] 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.
[0011] U.S. Pat. No. 4,251,119 describes a gas foil bearing for
textile machines comprising a foil, means for fixedly supporting
the foil and means for fixedly securing the foil, so configured
that the foil has a predetermined curvature substantially
corresponding to the radius of curvature of the rotatable member
(rotor shaft). Furthermore, also a movable hose attached to the
foil in order to create a gas film is described. 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.
[0012] As a summary, there is still a need for foil (fluid/gas/air)
bearings with a high performance and accuracy and with different
and multiple movement possibilities around an axis (rotary and
linear movement). Therefore, a goal of the present invention is to
satisfy this need by creating a new foil air bearing enabling a
linear and rotary movement along/around an axis (i.e. shaft) with a
high performance, in regard to load capacity, stiffness and
damping, and with a self-aligning mechanism.
SUMMARY OF THE INVENTION
[0013] In the present invention, a new foil bearing is being
provided. The present invention provides new foil bearings, in a
particular embodiment fluid or more specifically gas foil bearings
and deals with their use. The new foil bearings can be used in
machines, more specifically in precision and/or high-speed machines
and in high-speed precision spindles.
[0014] The present invention relates to a new kind of bearing. The
present invention relates to a foil bearing comprising a flexible
foil and a rigid frame or base structure. More in particular, the
present invention relates to a foil bearing enabling a linear
and/or rotary movement along/around an axis (i.e. a shaft). The
present invention furthermore relates to a new foil bearing in
which the foil envelops the axis perfectly during operation. This
perfect fitting of the foil is obtained due to the provision of a
self-aligning mechanism, more in particular through the provision
of means for supporting and/or positioning the foil, such means
allowing self-alignment (i.e. because of a kinematic support). The
self-aligning mechanism allows the foil to adapt itself during the
process to envelop the shaft/axis in an optimal way. The present
invention relates to a foil bearing with a self-aligning mechanism,
thus relates to a foil bearing comprising a rigid frame, at least
one flexible foil and a self-aligning mechanism. In another
embodiment, the present invention relates to a new foil bearing
with a self-aligning mechanism comprising a rigid frame, at least
one flexible foil and supporting and/or positioning means.
[0015] The present invention relates to a foil bearing with a
self-aligning mechanism, comprising a foil, wherein the foil can be
made of metal, plastic or any other convenient material. The
foil(s) is extended between a first and a second attachment point
on the frame. These attachment points can be outside or inside of
the frame. In a more particular embodiment, at least one attachment
point is on the outside of the frame. The foil can be attached or
fixed to the frame by clamping members, by welding or by
gluing.
[0016] In yet another embodiment, the foil bearing comprises
multiple foils or at least one or more than one foil, wherein
multiple foils are attached to the frame, in a particular
embodiment through clamping means, yet in another particular
embodiment with one end of each foil attached at the outside of the
frame and the other end attached at the inside of the frame. In yet
another particular embodiment, the foils are cutting each other or
are woven into each other, in order to allow optimal contact
between the foils and the shaft. The present invention therefore
also relates to a foil bearing, comprising two different foils
within one frame. Another yet more particular embodiment of the
present invention relates to a foil bearing with a self aligning
mechanism, comprising two foils, wherein one end of the first foil
is attached to the outside of one end of the frame, the other end
of the first foil is attached to the inner side of the frame, more
in particular at the top of the frame, while one end of the second
foil is attached at the opposite outside part of the frame and the
other end of the second foil is attached at the inner side of the
frame, more in particular at the top of the frame.
[0017] The present invention relates to a new foil bearing for
linear and/or rotary movement along/around an axis. In a particular
embodiment, the present invention relates to a new foil bearing
with a self-aligning mechanism, comprising supporting and
positioning means, attached to the frame, which allow the foil to
adapt its position during the process in order to envelop the
shaft/axis in an optimal way. In a particular embodiment, the
self-aligning mechanism comprises a kinematic support arrangement,
wherein in a particular embodiment, the supporting and positioning
means have a kinematic support arrangement, with in yet another
more particular embodiment with 2.times.3 degrees of freedom. In a
particular embodiment, the supporting and positioning means have
the freedom to rotate or move (i.e. about their support point) in
order to align the foil in an optimal way. In a particular
embodiment, there can be 1, 2, 3, 4 or more supporting and
positioning means.
[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.
[0020] The present invention relates to a novel foil bearing with
or without an external fluid supply. Therefore, a particular
embodiment of the present invention relates to a new foil bearing
which is externally provided with a fluid or externally
pressurised, so that a fluid (gas or liquid) foil bearing is
obtained. The fluid can be a gas or a liquid (i.e. oil), while the
gas can be air or other gases as known in the art, such as xenon,
helium, etc. The fluid or gas can be supplied through the foil or
through the shaft. In a particular embodiment, the invention
relates to an externally pressurised gas foil bearing wherein the
gas is supplied through at least one gas supply, which can be a
hose attached to the foil or to the shaft. In a particular
embodiment, multiple gas supplies are provided which deliver gas
through the foil or through the shaft or a combination of both.
Therefore, the present invention also relates to a gas foil bearing
with multiple or more than one gas supply, which can be 2, 3, 4 or
more. The gas supplies can be flexible or rigid. In a particular
embodiment, the invention relates to a gas foil bearing with a
self-aligning mechanism and which comprises at least one flexible
gas supply, yet in a more particular embodiment, the gas supply is
delivered through the shaft. In a particular embodiment, the gas
supply can be rigid or not flexible and could also be used to fix
the foil to the frame. In yet another particular embodiment of the
present invention, the flexible supply is made of plastic, rubber
or any other convenient material. In another embodiment of the
present invention, the air of the foil air bearing is supplied via
the shaft.
[0021] In any of the previously mentioned embodiments, the empty
space between the foil and the rigid frame may be filled with
flexible material, such as a flexible sponge, foam or rubber
material, which adheres to the foil and housing (frame) and serves
to hold the foil approximately in concave form to facilitate for
example storage and assembly.
[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.
[0023] In another embodiment of the invention, the foil of the foil
bearing is additionally fixed to the frame at the internal side,
more in particular at or around the middle of the frame.
[0024] One particular embodiment of the present invention relates
to a foil bearing with a foil or at least one foil, a frame,
whereas the foil is attached to the frame, and at least one
supporting and positioning means, characterised in that the
supporting and positioning means allows for a self-aligning system,
in a particular embodiment because the supporting or positioning
means can rotate around two axes normal to its geometrical axis. In
a particular embodiment, the supporting and positioning means is
cylindrical or the supporting and positioning means is attached to
the frame and thereby points out of the frame.
[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.
[0026] Another more particular embodiment relates to a foil bearing
with a self-aligning mechanism, comprising a foil which is
supported by electromagnetic, magnetostrictive, piezoelectric or
any suitable type of actuator, so that the foil could be moved
statically or dynamically during operation, whereby its
characteristics could be controlled.
[0027] Yet in another embodiment of the invention, the foil is made
from a "smart" material, e.g. PVD or piezoelectric material, so
that the characteristic of the foil could be changed during
operation, by controlling an electric current that is fed to the
foil.
[0028] An embodiment of the present invention relates to a foil
bearing with at least one foil attached to a frame and at least one
supporting and positioning means for the foil, characterised in
that: [0029] the foil is attached to the outside of the frame at
two different attachment points at the opposite sides of the frame;
[0030] the supporting and positioning means allows for a
self-aligning system and the foil embraces the supporting and
positioning means and extends over the shaft; and [0031] there is a
flexible gas supply, in one embodiment attached to the foil, yet in
another embodiment, attached to the shaft.
[0032] Another specific embodiment relates to a foil bearing with
at least one foil attached to a frame and at least one supporting
and positioning means for the foil, characterised in that: [0033]
there is only one foil attached to the outside of the frame at two
different attachment points at the opposite sides of the frame;
[0034] there are two cylindrical supporting and positioning means
attached at the opposite sides of the frame whereby the foil
embraces the round rails of the two cylinders and extends over the
shaft, whereby in a particular embodiment, the cylinders can rotate
around two axes normal to its geometrical axis, allowing for a
self-aligning system; and [0035] there is a flexible gas supply, in
one embodiment attached to the foil, yet in another embodiment,
attached to the shaft.
[0036] Yet another specific embodiment relates to the foil bearing
as described herein, characterised in that the foil is additionally
fixed to the middle of the frame. The fixation of the foil in the
middle of the frame at the internal side can be achieved through
clamping means or gluing or welding and in a particular embodiment,
the additional fixation point could also allow the supply of gas or
liquid through this fixation point. In yet another particular
embodiment, two gas supplies are attached to the foil, one at each
side of the fixation point in the middle of the frame.
[0037] Yet another more particular embodiment relates to a foil
bearing with a foil attached to a frame and a supporting and
positioning means for the foil, characterised in that: [0038] there
are two foils each of them attached with one end to the outside of
the frame and the other end attached to the inside of the frame,
whereby the foils are interwoven or are cutting each other; [0039]
there are two cylindrical supporting and positioning means attached
at the opposite sides of the frame whereby each foil embraces one
cylinder and extends over a part of the shaft, whereby in a
particular embodiment, the cylinders can rotate around two axes
normal to its geometrical axis, allowing for a self-aligning
system; and [0040] there are two flexible gas supplies, in one
embodiment attached to the foil, yet in another embodiment,
attached to the shaft, one for each foil.
[0041] In yet another specific embodiment, the invention relates to
the foil bearing as described herein, characterised in that there
are two additional (cylindrical) supporting and positioning means
attached directly or indirectly to the frame (i.e. to an additional
plate attached to the frame) so that in total four cylindrical
supporting and positioning means attached to the frame or to an
additional base plate attached to the frame are present whereby
each of them could allow and at least one allows a self-aligning
mechanism. In a particular embodiment, the foil is additionally
fixed to the frame. In yet another particular embodiment, the two
extra cylindrical supporting and positioning means are attached in
such a way that they support and position the foil around the
middle of the foil, in a particular embodiment next to the
additional fixation point of the foil to the frame.
[0042] Another aspect of the invention relates to the use of said
novel foil bearing in machines, more specifically in precision
and/or high-speed machines and in high-speed precision spindels.
The invention furthermore provides a new kind of air bearing for
precise and/or rapidly moving parts along or around a shaft. The
new foil bearings can be used in slideways for precision machine
tools, precise measuring machines, high-speed machinery and test
equipment. High-speed precision spindles for turning, milling or
grinding are other applications the foil bearing could be used
for.
BRIEF DESCRIPTION OF THE FIGURES
[0043] FIG. 1 is a lateral view of the standard embodiment of the
air bearing.
[0044] FIG. 2 is a longitudinal cross-sectional view of this
embodiment taken along line II-II.
[0045] FIG. 3 is a longitudinal cross-sectional view of an
embodiment with fluid supplied through the shaft.
[0046] FIG. 4 is a lateral view of an embodiment of the air bearing
with multi-directional stiffness only using a fixation.
[0047] FIG. 5 is a longitudinal cross-sectional view of the
embodiment in FIG. 4 along line V-V.
[0048] FIG. 6 is a lateral cross-sectional view of the embodiment
of FIG. 7 along the line VI-VI. It is an air bearing with
multi-directional stiffness using additional positioning parts.
[0049] FIG. 7 is a longitudinal cross-sectional view of the
embodiment of FIG. 6 taken along the VII-VII.
[0050] FIG. 8 is a lateral view of an embodiment of the air bearing
with multi-directional stiffness using two separate foils cutting
each other.
[0051] FIG. 9 is a longitudinal cross-sectional view of the
embodiment of FIG. 8 along the line IX-IX.
[0052] FIG. 10 is an illustration of a possible configuration of
the two cutting foils.
[0053] FIG. 11: Foil bearing prototype of an embodiment of the
present invention.
[0054] FIG. 12: Test system to investigate the behaviour of
aerostatic foils.
[0055] FIG. 13: Graphical representation of the theoretical and
experimental results obtained with the foil bearing prototype.
DETAILED DESCRIPTION OF THE INVENTION
Definitions
[0056] "Flexible supply" as used herein shall mean that the means
for supply shall be bendable, in a particular embodiment for more
than 1.degree., more in particular more than 5.degree. and yet more
in particular more than 20.degree. and yet more in particular more
than 45.degree., under standard conditions. "Foil" shall mean any
(thin) plate of material that is flexible in bending so that it can
be folded around a shaft, cylinder, or rotatable member.
[0057] With "self-aligning mechanism" or "self-aligning system" is
meant a mechanism allowing the self-adaptation of the position or
alignment of the foil, in order to envelop the shaft/axis in an
optimal way (and this without intervention from the outside).
Description
[0058] Application of conventional rigid radial aerostatic bearings
has two main drawbacks: a technical one and an economic one, which
are interconnected. The technical drawback lies in the inherent
problem of "conformity" between shaft and bearing (bush). In
contrast to flat bearings, where the gap does not change in
character (i.e. convex, concave or parallel) with the relative
normal displacement of bearing to platen, the gap between a shaft
and a bush will change from convex, through parallel to concave,
with the relative eccentricity. This is a geometry existing in
presently available bearings. The economic or cost side lies in the
fact that radial bearings, both of the full and partial type, are
very costly to produce owing to the close tolerances that have to
be observed. As an example, bearing bushes have to be produced for
an "exact" given size of shaft, which makes their
interchangeability well-nigh impossible.
[0059] With our invention, a low-cost (fluid) bearing type that can
overcome both hereinabove outlined problems simultaneously has been
developed. The present invention provides a novel foil bearing with
a self-aligning mechanism. The foil bearing comprises a mechanism
allowing the self-adaptation of the position or alignment of the
foil, in order to envelop the shaft/axis in an optimal way (and
this without intervention from the outside).
[0060] Research in foil bearings dates back to many decades ago,
the greatest effort being devoted to self-acting (aerodynamic)
bearings. Two basic categories were considered: (i) moving-web type
bearings, including tape-recording applications [1], with which
there has been little preoccupation since then, and (ii) leaf and
bump type [2], which continues to evolve till now, with important
applications in the aviation and general high speed rotor systems.
This type of bearings can achieve very high load capacity, however
with very low stiffness. The foil bearing type described in this
patent is an (externally pressurised) development of the first
category above. It has the advantage of compliant surface, possibly
combined with the high stiffness obtainable from external
pressurisation. Possible applications of the new foil bearings are
linear slideway systems, e.g. for high speed pick-and-place
machines, where they could form a viable alternative to
conventional precision bearing types, but also to a variety of
radial and axial bearing applications where the loads are high,
stiffness requirements medium and friction low.
[0061] The present invention provides a new kind of bearing, more
specifically (fluid) foil bearing, for precise and/or rapidly
moving parts along or around a shaft wherein the bearing has the
advantage of lower cost along with minimal requirements on the
shaft's surface. In particular, one and the same foil bearing unit
(frame and foil) can be used on a range of shaft sizes, since the
foil, unlike a rigid bearing, can adapt itself to fit the new size
of shaft. The bearing can also be used in precise and high-speed
spindles.
[0062] Traditional flat gap air bearings have start-up problems, as
the air pressure will only push on the surface beneath the supply
hole. Temporary lift of the load is needed for operation. Our foil
bearing however does not have this problem because the supply
pressure will lift the foil locally. This increases the surface on
which the pressure is pushing and the foil will gradually rise
until a continuous air gap is built up in the whole bearing.
[0063] For good working conditions it is preferred that the foil
envelops the axis perfectly during operation. If not, air will be
lost and the loading capacity of the bearing will be reduced or the
bearing will malfunction. To avoid aligning problems when using
foil bearings a mechanism of supporting and positioning means, in a
particular embodiment comprising two cylinders, has been developed
that enables fixation of the foil and provides sufficient degrees
of freedom for the foil to surround the axis. The supporting means,
e.g. small cylinders, support the foil and position it in a good
way, while giving it the possibility to move and thereby allows an
optimal positioning of the foil during movement.
[0064] Stiffness in different radial directions is achieved by
placing several foil bearings relatively rotated with respect to
each other or by integrating two bearings in one frame.
[0065] U.S. Pat. No. 4,251,119 describes a gas foil bearing for
textile machines comprising a foil, means for fixedly supporting
the foil and means for fixedly securing the foil, so configured
that the foil has a predetermined curvature substantially
corresponding to the radius of curvature of the rotatable member
(rotor shaft). Furthermore, also a movable hose attached to the
foil in order to create a gas film is described. This foil bearings
has however the disadvantage that because the foil is fixedly
supported to have a predetermined curvature corresponding to the
radius of the rotor shaft, the foil can not envelop the shaft/axis
in a perfectly and can not adapt itself to envelop the shaft/axis
in a perfect way, for example when needed owing to misalignment of
the foil or of its supporting frame or means, or when changing to a
different shaft diameter, which leads to air lost and a reduction
of the capacity or a malfunction of the bearing. The position of
the foil in U.S. Pat. No. 4,251,119 will not be self-adapting
during changes in the process (e.g. misalignment resulting from
thermal expansion, relative motion between bearing and shaft,
vibrations, etc.). This self-adaptation is necessary because as
stated before, with the relative normal displacement of bearing to
shaft the gap between a shaft and foil will change from convex,
through parallel to concave, with the relative eccentricity.
[0066] Thus, in the present invention, a type of foil
(fluid/gas/air) bearings has been developed which delivers a better
positioning of the foil to the shaft and even during rotation, the
foil can be adapted to embrace the shaft in a better way by a
self-aligning mechanism. The foil bearing can also be externally
pressurised. The foil bearing of the invention comprises
cylindrical supporting and positioning means which can be movable
in two directions due to specific construction, allowing the better
positioning of the foil. The foil bearing enables a linear or
rotary movement along/around an axis (i.e. a shaft) with very low
friction. It is very suited for precise positioning tools and
high-speed machines.
[0067] The foil bearing of the present invention comprises a foil,
a frame and a self-aligning mechanism, in particular obtained
through movable supporting and positioning means. The frame can be
of any arbitrary form allowing the functionality of the foil
bearing of the invention. In a particular prototype, the frame is
U-shaped.
[0068] The foil can be of different thickness, but has to be
flexible. It can be made of metal, plastic or any other material
which is suited for this purpose. The foil is attached to the frame
at different attachment points and can be attached through
different means. Also foil bearings comprising multiple foils are
provided. The construction is made in this way so that each foil
embraces the shaft on a different side. The foils are therefore
interwoven. The invention is based on the use of a flexible foil
instead of a hard bearing surface. The air spreads through the gap
between axis and foil thereby lifting the load. If the air is
supplied through the foil, the hose must be sufficiently flexible
not to affect the shape of the air gap.
[0069] The supporting and positioning means are present in order to
position the foil. In a particular prototype, these means for
supporting and positioning the foil allow for the self-aligning
mechanism. This can be obtained through any kinematic support
arrangement, so that the foil's flexibility and its kinematic
support allow an optimal air-gap geometry at all times. The
kinematic support comprises supporting and positioning means which
have the freedom to rotate or move (i.e. about their support point)
in order to align the foil in an optimal way. The supporting and
positioning means have to be constructed in such a way to allow for
this rotation or movement. For example they can be movable around
their attachment or support point. There can be one, two or
multiple (3, 4, 5, 6, etc.) means for supporting and positioning
the foil, like in a specific example there are 4 such supporting
and positioning means. In FIG. 1 for example, there are two means
ensuring the support and position of the foil (designated with no.
5), while in FIG. 6 the foil bearing comprises at least an extra
two of such means (designated with no. 11).
[0070] In a particular prototype, the supporting and positioning
means are cylindrical, but can have any form suitable for their
function. Cylinders deliver a good positioning and support, due to
a good contact with the foil, which embraces the round rail
partially. The cylinders are movable in two directions so that an
adaptation of the foil position and support is possible when
necessary during the process. To obtain the freedom to rotate for
the cylinders, the cylinders can be attached to the frame through
small pins forming point contacts in blind holes drilled in the
cylinders. The point contact connection between the frame and
alignment cylinders does not impair the stiffness.
[0071] Another possibility for supporting and positioning means
which would allow self-adaptation of the foil, would be the use of
a spring or multiple springs. The spring can be attached to the
shaft at one side and could support and position the foil at the
other side. The spring will need to be flexible in order to allow
the self-alignment system, but will also need to be stiff in order
to deliver the right positioning and/or support for the foil. Also
other possibilities exist in order to obtain the self-alignment
system in the foil bearing. A combination of different mechanisms
is furthermore also possible.
[0072] The invention relates mainly to externally pressurised fluid
foil bearings. However, the self-aligning mechanism is also
applicable for non-externally pressurised foil bearings. Fluid,
i.e. hydrodynamic, hydrostatic, aerodynamic or aerostatic bearings
eliminate the stick-slip problem. The fluid can be a liquid (i.e.
oil) or a gas and can be other than air, such as helium, xenon,
air-conditioner refrigerants, liquid oxygen, liquid nitrogen, etc.
The fluid/gas supply can be obtained via the shaft or via the foil
and multiple fluid supplies can be present. Also a combination of
fluid supply through the shaft and the foil is possible. Supply
through the shaft has the advantage that no fluid supply has to be
attached to the foil, so that problems associated with this fluid
supply through the foil, such as the movement of the supply during
the process, are not encountered.
[0073] The present invention thus provides a foil bearing
comprising a frame and a foil, characterised in that the foil
bearing has a self-aligning mechanism which allows the foil to
self-adapt its position. In a particular embodiment, the foil is
attached to the frame and extended between a first and a second
attachment point. The foil bearing further comprises in another
embodiment a supporting and positioning means for optimally
positioning and supporting the foil, wherein the supporting and
positioning means allows for a self-aligning mechanism. Another
embodiment relates to the foil bearing wherein the supporting and
positioning means is cylindrical and can rotate around two axes
normal to its geometrical axis. The foil bearing comprises in a
particular embodiment two cylinders attached to the frame which can
rotate around two axes normal to their geometrical axes. The
cylindrical supporting and positioning means can be 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 supporting and positioning means
comprises a spring.
[0074] Another embodiment provides a foil bearing which is
externally pressurised, more in particular through fluid supplied
via the shaft or via the foil more in particular through one or
multiple flexible fluid supplies, which in a particular embodiment
are from rubber of plastic.
[0075] In another particular embodiment, two additional cylindrical
supporting and positioning means are present. Also a second foil
can be present, which more particularly is interwoven with the
other foil.
EXAMPLES
Example 1
Externally Pressurised Foil Bearing with One Air Supply Through the
Foil and One Foil
[0076] A specific example of the foil bearing includes a rigid
frame of any convenient shape (e.g. .pi.), a flexible foil, a
flexible gas/air supply line and two small self-aligning cylinders.
The foil embraces the round rail partially. Liquid or gas is
supplied via the flexible hose that is attached to the foil at one
or several points. Small holes in the foil (the restrictors or
supply holes) enable the fluid to enter the gap between shaft and
foil. The thin foil is fixed to the frame by clamping plates,
gluing, welding or any convenient way.
[0077] Two self-aligning cylinders guide and support the foil. They
are attached to the frame by appropriate hinges. As these axes can
rotate freely, for a certain amount, they make sure the foil is
embracing the shaft correctly at all times, reducing alignment
problems.
[0078] FIGS. 1 a and 1 b illustrate the embodiment of the present
invention, which is suited for all applications. Multidirectional
stiffness can be accomplished by placing several foil bearings
relatively rotated to each other. A flexible foil 1 embraces the
shaft 2 partially. The foil is made from a suitable material,
metal, plastic, composite material, . . . , preferably with high
bending flexibility and high tensile stiffness. The foil surface is
required to be flat and smooth only on one side, namely the fluid
film side or the side facing the shaft. (On the opposite side, it
could be allowed to have "ribs", or any other suitable profile, to
increase tensile stiffness and/or to increase damping. The foil is
fixed to a frame 3 by means of clamping plates 4, by welding or by
gluing. The frame can be of any arbitrary form with the same
functionality (e.g. n). To make sure the foil is surrounding the
shaft appropriately a positioning system is added. Two small
cylinders S support and guide the foil during operation. They are
attached to the frame by suitable means allowing the rotation of
each cylinder about the two axes normal to its geometrical axis. In
this case, this is achieved by means of two small pins 6 forming
point contacts in blind holes drilled in the cylinders.
[0079] A flexible hose 7 attached to the foil supplies the
necessary fluid. For example pressured air is pressed between the
foil and shaft thereby creating a small air gap enabling the
relative displacement of bearing and shaft. Larger bearings may
need several fluid inlets.
[0080] This foil bearing consists thus of a (thin) foil, which
partially envelopes a shaft, while air is supplied through a
flexible hose attached to the foil. The foil's flexibility and its
kinematic support allow an optimal air-gap geometry at all times.
Design theory has also been formulated in order to enable
prediction of the characteristics and their optimisation. Tests on
prototypes indicate that the foil bearing is far superior to
conventional (rigid surface) bearings, in particular regarding load
capacity and air consumption. Furthermore the production cost is
much lower owing to simplicity of construction.
[0081] FIG. 11 shows a foil bearing prototype. The foil bearing
consists of a thin metal foil, equipped with feeding hole(s), which
enfolds the shaft (see FIG. 2). A flexible hose is attached to each
feeding hole to supply pressurised air, in such a way as not to
affect the foil shape. The foil is fixed to the rigid frame (body
of the bearing) at both ends, passing over alignment cylinders
Cinematic support system with 2.times.3 d.o.f.). In this way, the
foil can wrap around the shaft correctly at all times. By virtue of
its flexibility, the foil continuously adapts its geometry to
different working conditions generating an optimal air gap.
Furthermore such a bearing can accommodate a relatively wide range
of shaft sizes without any alignment problem and is suitable for
rotary as well as linear sliding applications.
[0082] The design parameters to be selected are: the supply air
pressure, the foil geometry and material, the wrap angle, and the
restrictor diameter(s) and location(s). Results show that very high
load factors could be achieved; stiffness, however, is a major
concern. The total stiffness of the bearing system can be
represented as a serial connection of the air-gap stiffness and the
foil stiffness. A "thick" foil results in a higher foil stiffness,
but the load capacity may deteriorate owing to loss of wrap angle,
and the air-gap stiffness may decrease owing to loss of flexibility
of the foil. One measure to increase foil stiffness, without
jeopardising load and film stiffness, is to minimise the total
length of the foil.
Example 2
[0083] FIG. 3 shows an implementation in which the air is supplied
through the shaft. Several air inlets 8 in the shaft replace the
need for a hose in the foil, thus overcoming the difficulty of air
supply through the foil. This configuration can be useful for small
stroke applications.
Example 3
Foil Bearing with an Extra Fixation of the Foil to the Frame
[0084] FIGS. 4 and 5 show a configuration enabling multidirectional
stiffness in a single frame. This has the advantage of demanding
less space than placing two separate bearings with stiffness in
only one direction rotated with respect to each other. A negative
aspect of this structure is the reduction in total stiffness.
Fixation 9 of the foil in the middle of the frame results in two
separately operating foil bearings rotated with respect to each
other. Naturally, at least two supply holes are needed 10.
Example 4
Foil Bearing with Extra Cylindrical Supporting and Positioning
Means and Extra Fixation to the Frame
[0085] FIGS. 6 and 7 illustrate an additional embodiment of the
previous foil bearing. Two extra cylinders 11 ensure the proper
placement of the foil and enlarge the contact area between foil and
shaft. Fixation 12 of the foil in the middle is still present to
avoid mutual influence. Parts can be added to shorten the length of
the small pins 13. In this figure this is done by two cylinders 14
attached to the frame by plates 15 at the end of the frame.
Example 5
Foil Bearing with Two Foils
[0086] FIGS. 8 and 9 show a construction of a multidirectional
bearing with two foils and one frame. Both foils are attached to
the frame with one side on the outside and one side at the inside
16. In order to get a large area of contact between foils and shaft
the foils are cutting each other as illustrated in FIG. 10.
Example 6
[0087] In order to verify the externally pressurised foil bearing
of the present invention, a test rig was built as depicted in FIG.
12 to investigate the basic behaviour of aerostatic foils. In this
set-up, the air was fed through the shaft and the foil extension as
well as the gap geometry could be measured. A number of prototype
bearings were tested for their load capacity, air consumption and
stiffness characteristics. The load capacity and air consumption
turn out to be far superior to conventional bearings. The stiffness
is comparable to rigid bearings of the same dimensions. As an
example, a foil bearing prototype (FIG. 11) with a 50 mm wide and
0.08 mm thick, steel foil on a 40 mm diameter shaft, (wrap angle
180 degrees) was supplied with a 6 bar air pressure. The
measurements show a load capacity of more than 800 N, a radial
stiffness of 8.5 N/micron, and air consumption of around 2 N/min.
FIG. 13 illustrates the good agreement between theoretical
prediction and experiment showing how the total stiffness is the
resultant of the foil and air-gap stiffness, in series. Obviously,
this bearing is not well optimised since the latter stiffness
values are not well matched (the air gap is much stiffer than the
foil). With better optimisation, a resultant stiffness of around 25
N/micron may be achievable.
REFERENCES TO THE APPLICATION
[0088] (1) Wildman, M. "Foil Bearings", ASME, J. Lubrication
Technology, Jan. 69, pp. 37-44. [0089] (2) S. Gray, H. Heshmat, B.
Bhushan, "Technology progress on compliant foil air bearing systems
for commercial applications," 8th Gas Bearting Symposium, Leicester
Polytechnic, BHRA Fluid Engineering, 1981, paper 6, pp. 69-97.
* * * * *