U.S. patent application number 10/078132 was filed with the patent office on 2003-08-21 for mechanical translator with ultra low friction ferrofluid bearings.
This patent application is currently assigned to INNOVATIVE TECHNOLOGY LICENSING, LLC. Invention is credited to Cheung, Jeffrey T..
Application Number | 20030154923 10/078132 |
Document ID | / |
Family ID | 27732780 |
Filed Date | 2003-08-21 |
United States Patent
Application |
20030154923 |
Kind Code |
A1 |
Cheung, Jeffrey T. |
August 21, 2003 |
Mechanical translator with ultra low friction ferrofluid
bearings
Abstract
A mechanical translator includes at least one magnet that is
disposed on a substrate to carry a load and has a magnetic axis
generally transverse to the substrate, establishing a magnetic
field with maximum external density adjacent the substrate. An
ultra low friction interface is obtained with ferrofluid bearings,
such as a light mineral oil medium mixed with isoparaffinic acid,
which establish a critical angle of displacement from a horizontal
static position of less than 1 degree, and preferably less than 10
minutes. A controller of magnetic material can be placed on the
opposite side of the substrate to control the movement of the
magnets.
Inventors: |
Cheung, Jeffrey T.;
(Thousand Oaks, CA) |
Correspondence
Address: |
KOPPEL, JACOBS, PATRICK & HEYBL
Suite 107
555 St. Charles Drive
Thousand Oaks
CA
91360
US
|
Assignee: |
INNOVATIVE TECHNOLOGY LICENSING,
LLC
|
Family ID: |
27732780 |
Appl. No.: |
10/078132 |
Filed: |
February 19, 2002 |
Current U.S.
Class: |
118/729 |
Current CPC
Class: |
C10M 171/06 20130101;
H01F 1/44 20130101; F16C 32/0637 20130101; C10N 2020/01 20200501;
C10M 2203/1006 20130101; C10N 2010/16 20130101; H02K 7/09 20130101;
H02K 2201/18 20130101; C10N 2050/015 20200501; F16C 33/1035
20130101; C10N 2030/06 20130101; C10M 2207/12 20130101; C10M
2201/062 20130101; C10N 2020/06 20130101; C10N 2010/14 20130101;
F16C 29/02 20130101; C10N 2040/02 20130101; H02K 49/10
20130101 |
Class at
Publication: |
118/729 |
International
Class: |
C23C 016/00 |
Claims
I claim:
1. A mechanical translator, comprising: a substrate, and a magnet
disposed for movement on said substrate, said magnet arranged to
carry a load and having a magnetic axis generally transverse to
said substrate.
2. The mechanical translator of claim 1, wherein said translator
has a critical angle of displacement from a horizontal static
position of less than 1 degree.
3. The mechanical translator of claim 2, wherein said critical
angle is less than 10 minutes.
4. The mechanical translator of claim 1, further comprising a
lubricant between said magnet and substrate.
5. The mechanical translator of claim 4, wherein said lubricant
comprises a ferrofluid.
6. The mechanical translator of claim 5, wherein said ferrofluid
includes a light mineral oil medium.
7. The mechanical translator of claim 6, said ferrofluid further
comprising isoparaffinic acid mixed with said light mineral
oil.
8. The mechanical translator of claim 5, said ferrofluid having a
viscosity less than 5 cp.
9. The mechanical translator of claim 5, further comprising a
controller of magnetic material on the opposite side of said
substrate from said magnet, said controller controlling the
movement of said magnet.
10. The mechanical translator of claim 9, said substrate comprising
a portion of an enclosure, with said magnet inside and said
controller outside said enclosure.
11. A mechanical translator, comprising: a substrate, and a magnet
disposed for movement on said substrate, said magnet arranged to
carry a load and establishing a magnetic field which has its
maximum external density adjacent said substrate.
12. The mechanical translator of claim 11, wherein said translator
has a critical angle of displacement from a horizontal static
position of less than 1 degree.
13. The mechanical translator of claim 12, wherein said critical
angle is less than 10 minutes.
14. The mechanical translator of claim 11, further comprising a
lubricant between said magnet and substrate.
15. The mechanical translator of claim 14, wherein said lubricant
comprises a ferrofluid.
16. The mechanical translator of claim 15, wherein said ferrofluid
includes a light mineral oil medium.
17. The mechanical translator of claim 16, said ferrofluid further
comprising isoparaffinic acid mixed with said light mineral
oil.
18. The mechanical translator of claim 15, said ferrofluid having a
viscosity less than 5 cp.
19. The mechanical translator of claim 15, further comprising a
controller of magnetic material on the opposite side of said
substrate from said magnet, said controller controlling the
movement of said magnet.
20. The mechanical translator of claim 19, said substrate
comprising a portion of an enclosure, with said magnet inside and
said controller outside said enclosure.
21. A mechanical translator, comprising: a substrate, and a
plurality of magnets disposed for movement on said substrate and
carrying a platform, said magnets having respective magnetic axes
generally transverse to said substrate.
22. The mechanical translator of claim 21, wherein said magnets are
connected to respective fixed locations on said platform.
23. The mechanical translator of claim 21, said platform comprising
a magnetic material.
24. The mechanical translator of claim 21, said platform comprising
a nonmagnetic material.
25. The mechanical translator of claim 24, said platform comprising
a magnetic field shielding alloy.
26. The mechanical translator of claim 21, wherein said translator
has a critical angle of displacement from a horizontal static
position of less than 1 degree.
27. The mechanical translator of claim 26, wherein said critical
angle is less than 10 minutes.
28. The mechanical translator of claim 21, further comprising a
lubricant between said magnets and said substrate.
29. The mechanical translator of claim 28, said lubricant
comprising a ferrofluid.
30. The mechanical translator of claim 29, further comprising a
controller of magnetic material on the opposite side of said
substrate from said magnets and platform, said controller
controlling the movement of said magnets and platform.
31. The mechanical translator of claim 30, said substrate
comprising a portion of an enclosure, with said magnets and
platform inside said enclosure and said controller outside.
32. A mechanical translator, comprising: a substrate, and a
plurality of magnets disposed for movement on said substrate and
carrying a platform, said magnets establishing respective magnetic
fields which have their maximum external densities adjacent said
substrate.
33. The mechanical translator of claim 32, wherein said magnets are
connected to respective fixed locations on said platform.
34. The mechanical translator of claim 32, said platform comprising
a magnetic material.
35. The mechanical translator of claim 32, said platform comprising
a nonmagnetic material.
36. The mechanical translator of claim 35, said platform comprising
a magnetic field shielding alloy.
37. The mechanical translator of claim 32, wherein said translator
has a critical angle of displacement from a horizontal static
position of less than 1 degree.
38. The mechanical translator of claim 37, wherein said critical
angle is less than 10 minutes.
39. The mechanical translator of claim 32, further comprising a
lubricant between said magnets and said substrate.
40. The mechanical translator of claim 39, said lubricant
comprising a ferrofluid.
41. The mechanical translator of claim 40, further comprising a
controller of magnetic material on the opposite side of said
substrate from said magnets and platform, said controller
controlling the movement of said magnets and platform.
42. The mechanical translator of claim 41, said substrate
comprising a portion of an enclosure, with said magnets and
platform inside said enclosure and said controller outside.
43. Vapor deposition apparatus, comprising: a vacuum chamber having
a floor, at least one magnet disposed for movement on said floor
and carrying a platform for a substrate, each magnet having a
magnetic axis generally transverse to said floor, a vapor source
for depositing a thin film on a substrate carried by said platform,
and a controller of magnetic material outside said chamber on the
opposite side of said floor from said magnets, said controller
arranged to translate to impart a corresponding translation to said
magnets and platform.
44. The vapor deposition apparatus of claim 43, wherein said
translator has a critical angle of displacement from a horizontal
static position of less than 1 degree.
45. The vapor deposition apparatus of claim 44, wherein said
critical angle is less than 10 minutes.
46. The vapor deposition apparatus of claim 43, further comprising
a ferrofluid providing a lubricant between said magnets and said
floor.
47. A mechanical translator, comprising: a substrate, and at least
one magnet disposed for movement on said substrate and arranged to
carry a load, each magnet having a magnetic axis at an angle of at
least 45.degree. to said substrate and a critical angle of
displacement from a horizontal static position of less than 1
degree.
48. The mechanical translator of claim 47, wherein said critical
angle is less than 10 minutes.
49. The mechanical translator of claims 47, further comprising a
respective ferrofluidic bearing supporting each magnet.
50. The mechanical translator of claim 47, comprising a plurality
of said magnets carrying a common load platform.
51. The mechanical translator of claim 47, further comprising a
controller of magnetic material on the opposite side of said
substrate from said at least one magnet, said controller
controlling the movement of said at least one magnet.
52. The mechanical translator of claim 51, said substrate
comprising a portion of an enclosure, with said at least one magnet
inside and said controller outside said enclosure.
53. An ultra low friction ferrofluid mixture, comprising: a light
mineral oil medium, isoparaffinic acid mixed with said light
mineral oil, and magnetizable nanoparticles suspended in said
mixture.
54. The ferrofluid mixture of claim 53, said mixture having a
coefficient of static friction not greater than about 0.0012.
55. The ferrofluid mixture of claim 54, wherein the ratio of
isoparaffinic acid to light mineral oil in said mixture is in the
range of about 2:1 to about 4:1.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to magnetic-based mechanical
translators, and more particularly to mechanical translators with
ferrofluid bearings.
[0003] 2. Description of the Related Art
[0004] Ferrofluids are dispersions of finely divided magnetic or
magnetizable particles, generally ranging between about 30 and 150
Angstroms in size, dispersed in a liquid carrier. The magnetic
particles are typically covered with surfactants or a dispersing
agent. The surfactants assure a permanent distance between the
magnetic particles to overcome the forces of attraction caused by
Van der Waal forces and magnetic interaction, and also provide a
chemical composition on the outer layer of the covered particles
which is compatible with the liquid carrier and the chemicals in
the surrounding environment. Ferrites and ferric oxides employed as
magnet particles offer a number of physical and chemical properties
to the ferrofluid, including saturation magnetization, viscosity,
magnetic stability and chemical stability. Several types of
ferrofluids are provided by Ferrotec (USA) Corporation of Nashua,
N.H. A summary of patents related to the preparation of ferrofluids
is provided in U.S. Pat. No. 6,056,889, while the use of ferrofluid
bearings in a moving magnet electrical generator is discussed in
copending patent application Ser. No. ______, entitled "Electrical
Generator With Ferrofluid Bearings", filed on the same day as the
present invention by Jeffrey T. Cheung and Hao Xin, and also
assigned to Innovative Technology Licensing, LLC, the assignee of
the present invention. The contents of this copending application
are hereby incorporated herein by reference.
[0005] A ferrofluid's frictional coefficient is roughly related to
its viscosity (measured in centipoise (cp)), but not directly. For
example, a ferrofluid with a viscosity of 300 cp has been found to
have a static friction coefficient of about 0.015, the EFH1
ferrofluid from Ferrotec (USA) Corporation has a viscosity on the
order of 6 cp and a static friction coefficient of about 0.002, but
a water based ferrofluid with a viscosity of 5 cp has been found to
have a static friction coefficient of about 0.01. The higher
friction coefficient for the somewhat lower viscosity composition
has been attributed to surface tension associated with a water
based solvent.
[0006] Low friction systems can have other problems. For example,
depositing a thin film over a substrate by vapor deposition is
performed in a vacuum chamber by rotating and translating the
substrate inside the chamber to achieve uniform deposition over a
large area. The mechanism that controls this motion is cumbersome,
consisting of gears, chains, and both rotary and translational
motion vacuum feedthroughs. A simpler less expensive motion control
for the substrates would be highly desirable.
[0007] Traditional lubricants employed to assist movement of a load
bearing mechanism on a substrate, while considerably reducing the
frictional forces resisting motion, still involve a considerable
amount of friction. For example, whereas the static coefficient of
friction between unlubricated hard steel surfaces is typically
about 0.6, the corresponding coefficient is about 0.08-0.1 for
vegetable and animal oil lubricants, 0.14-0.2 for mineral oils,
0.12 for graphitised oils, 0.1 for molybdenum disulfide, 0.08 for
oleic acid, 0.4 for alcohol and benzene, and 0.2 for glycerine.
Even lower frictional coefficients, making it easier to translate a
load, would be desirable.
SUMMARY OF THE INVENTION
[0008] The present invention provides a mechanical translator
system with an ultra low degree of friction, and a novel ferrofluid
composition that can be used as a lubricant for the translator. The
term "translation" as used herein includes both changes of position
and/or rotation. In a preferred embodiment the translator includes
a moveable magnet that is arranged to carry a load and is disposed
for movement on a substrate. Its magnetic axis is generally
transverse to the substrate, such that its magnetic field has a
maximum density adjacent the substrate. A ferrofluid lubricant is
preferably provided between the magnet and substrate. A ferrofluid
composition that can be used to achieve a particularly low friction
has a viscosity substantially less than 5 cp. It consists of a
light mineral oil medium mixed with isoparaffinic acid, with the
ratio of isoparaffinic acid to light mineral oil preferably in the
range of about 2:1 to about 4:1. The resulting coefficient of
static friction has been found to be in the approximate range of
0.0008-0.0012.
[0009] A plurality of moveable magnets, each with a magnetic axis
generally transverse to the substrate, can be used to support a
platform upon which a load can be placed, or which itself can
comprise a load. The magnets are preferably connected to respective
fixed locations on the platform, which can be formed from a
magnetic material, or a nonmagnetic material which might include an
alloy that shields magnetic fields. A ferrofluid lubricant is
provided between the magnets and substrate for ultra low frictional
movement. A ferrofluid with a low vapor pressure should be selected
for environments in which other ferrofluids tend to dry out.
[0010] When applied to vapor deposition apparatus, the moveable
magnets are disposed on the floor of a vacuum chamber which
includes a vapor source for depositing a thin film on a substrate
carried by the platform. A controller formed from a magnetic
material outside the vacuum chamber, on the opposite side of the
floor from the moveable magnets, controls the movement of the
magnets and platform to achieve uniform deposition, eliminating the
need for the cumbersome control equipment and its mechanical
communication through the vacuum chamber that were previously
required.
[0011] These and other features and advantages of the invention
will be apparent to those skilled in the art from the following
detailed description, taken together with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a diagram illustrating the magnetic field lines
associated with a bar magnet;
[0013] FIG. 2 is a diagram illustrating the ultra low friction
achieved with a ferrofluid lubricant in accordance with one aspect
of the invention;
[0014] FIGS. 3a and 3b are respectively frontal and side elevation
views of a low friction, load bearing mechanical translator in
accordance with the invention; and
[0015] FIG. 4 is a diagram of a vapor deposition chamber using one
embodiment of a mechanical translator in accordance with the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0016] FIG. 1 illustrates a bar magnet 2 and its associated
magnetic field lines 4. As is well known, the field lines radiate
out mostly from the magnet's north pole, and loop around to return
to the magnet's south pole. The greatest magnetic field
concentrations external to the magnet are at its opposite poles,
and it is in these regions that a ferrofluid will tend to
accumulate when the ferrofluid is presented to the magnet. The
ferrofluid concentration formed at the opposite ends of the magnet,
indicated by dashed ovals 6 and 8 around the north and south magnet
poles, respectively, can be used as bearings to provide a
lubricated movement of the magnet along a surface. Ferrofluid
bearings would also tend to form at the opposite ends of an
electro-magnet as well as a permanent magnet.
[0017] Referring now to FIG. 2, a magnet 10 is shown supported on a
substrate 12, which in turn is on a horizontal support surface 14.
A ferrofluid bearing 16 provides an ultra low friction interface
between the magnet 10 and substrate 12. The magnet is oriented with
its magnetic axis 18 generally transverse to the substrate 12.
Thus, the magnet's magnetic field has it maximum external density
adjacent the substrate. Although for purposes of this invention the
magnet's magnetic axis will normally be orthogonal to substrate 12,
it can also be tilted at an angle up to about 45 .degree. from a
perpendicular to the substrate, preferably with a corresponding
chamfer at the end of the magnet adjacent the substrate.
[0018] With the use of an appropriate ferrofluid 16 between the
substrate and magnet, ultra low degrees of friction can be achieved
between the magnet and substrate, making the magnet highly
responsive to a tilting of the substrate or a translational force
applied to the magnet. Presently available ferrofluids from
Ferrotec (USA) Corporation are among those that can be used as low
friction bearings. For example, a water based ferrofluid designated
EMG805 has a coefficient of static friction of about 0.01 and a
viscosity of about 5 cp, while a light mineral oil ferrofluid
composition designated EFH1 has a coefficient of static friction of
about 0.002 and a viscosity slightly on the order of 6 cp.
[0019] Even lower levels of friction can be achieved with a new
formulation in which the light mineral oil EFH1 ferrofluid is mixed
(preferably for about 24 hours) with isoparaffinic acid. Two
sources of isoparaffinic acid at present are Isopar M and Isopar G
hydrocarbon fluids, both from ExxonMobil Chemical Corporation; both
appear to work equally well. With a ratio of isoparaffinic acid to
EFH1 light mineral oil ferrofluid in the range of approximately 2:1
to 4:1, ultra low static coefficients of friction in the range of
0.0008-0.0012 were achieved. The viscosity of the mixture was
significantly less than 2 cp, on the order of 1 cp. While the
mixture's static friction coefficient was even lower than for the
EFH1 ferrofluid by itself, the EFH1 composition has a somewhat
greater load bearing capability.
[0020] The static friction coefficient was measured by raising one
end of the substrate 12 off the horizontal surface 14 until a mass
supported by the ferrofluid began to slide along the substrate,
determining the substrate's critical off-horizontal angle of
displacement at which sliding movement began, returning the
substrate to horizontal, lifting its other end until the mass
started to slide in the opposite direction, determining the
critical angle of displacement from horizontal for sliding to begin
in that direction, and averaging the two angles. With the preferred
EFH1/isoparaffinic acid mixture, the mass began to slide at an
average angle of much less than 1 degree, and even considerably
less than 10 minutes. In fact, the critical angle for displacement
from a horizontal static position was found to be approximately
0.07 degree.
[0021] FIGS. 3a and 3b illustrate the invention applied to an ultra
low friction translatable load bearing platform. A set of magnets
20 are disposed with their magnetic axes generally transverse to a
substrate 22, with one end of the magnets provided with ferrofluid
bearings 24 for ultra low friction movement over the substrate, and
the other end of the magnets attached to a load bearing platform
26. A load to be carried by the platform is indicated by dashed
lines 28. The shape and size of the platform, as well as the number
of magnetic posts, are arbitrary and can be chosen depending upon
the load to be placed on the platform. The platform can be formed
from a magnetic material so that it diffuses the magnetic field,
leaving the strongest field location at the opposite end of the
magnet adjacent the substrate. This tends to concentrate the
ferrofluid away from the platform and towards the bottom of the
magnet, where it functions as a lubricant for magnet movement over
the substrate. The platform can also be formed from a nonmagnetic
material. Another option is to form the platform from a nonmagnetic
alloy that provides effective shielding of the magnetic field,
thereby creating a zone above the platform which is free of
magnetic flux. Such a material is available from Spang &
Company Corp. under the trademark MUMETAL. The magnet posts can be
attached to the platform by mechanical devices such as clamps,
bolts or adhesives.
[0022] The ferrofluid solution is applied to the bottom of the
posts where, because of their magnetic property, they bond strongly
to engulf the post bottoms. The platform thus rests on ferrofluid
"cushions", without a direct contact between the magnets and
substrate. Because of the low friction achievable with ferrofluid
bearings, the platform can be pushed to move freely with a slight
force. The movement can be controlled by either applying it
directly to the platform and/or magnets, or by moving a magnetic
control object (formed from either a magnetized or a magnetizable
material) on the other side of the substrate. The movement of the
platform can be controlled remotely by moving the external
controller on the opposite side of the substrate, without making
any direct contact to the platform assembly itself.
[0023] An application for this type of motion control is a vapor
deposition chamber, illustrated in FIG. 4. The chamber consists of
a vacuum enclosure 30, the floor 32 of which comprises a substrate
upon which a load bearing platform 34 moves via attached magnets 36
and ferrofluid bearings 38. As illustrated, the magnets 36 in FIG.
4 have a magnetic polarity opposite to that illustrated in FIGS. 3a
and 3b; the choice is arbitrary. A substrate 40 upon which a thin
film is to be deposited is placed on the platform 34.
[0024] The chamber is evacuated a vacuum pump 42, while a vapor
source generically indicated by reference number 44 provides a
material to be deposited on the substrate. In practice, the vapor
deposition process can take several forms, such as thermal
evaporation, e-beam evaporation or different forms of sputtering.
These all require that the substrate holder be able to rotate and
translate inside the vacuum chamber to achieve a uniform deposition
over a large substrate area. The prior need for gears, chains, and
both rotary and translational motion vacuum feedthroughs are
eliminated with the use of an external magnetized or magnetizable
control mass 46, placed on the opposite side of substrate 32 from
the platform 34 and aligned with its support magnets. The external
controller 46 can be translated in an x-y plane, as indicated by
arrows 48 and 50, or rotated as indicated by circular arrow 52,
imparting a corresponding movement to the interior magnets and the
platform they support. The external controller 46 is preferably a
single mass which encompasses the area subtended by the interior
magnets 38, or can equivalently be an array of separate controllers
aligned with the individual magnets 36 and moved together. The
platform and the substrate which it carries can be rotated and
translated over a large area simply by imparting the same movements
to the easily accessible external controller. If the controller is
magnetized, its polarity should be oriented in the same direction
as the internal magnets for mutual attraction.
[0025] APG S10 grade ferrofluid from Ferrotec (USA) Corporation was
used for the vapor deposition application because of its low vapor
pressure, which allows it to be used in a vacuum or ambient
atmosphere with a long operational lifetime. Some other ferrofluids
have a tendency to dry out in this environment. A 7.6 cm diameter
platform with four 0.95 cm diameter, 6.4 cm length, Grade 30 NdFeB
magnets, cushioned by the APG S10 grade ferrofluid, was found to be
capable of supporting a 250 gram load, while maintaining a low
static coefficient of friction in the range 0.01-0.02. While not as
low as the other ferrofluid compositions discussed above, this
value was still considerably lower than traditional lubricants.
[0026] In addition to providing a lower level of friction, the use
of a ferrofluid allows the movement of the platform to be
controlled externally by a moving magnet body. With traditional
lubricants, placing a magnet on the opposite side of the wall from
the platform can attract the platform's magnet posts strongly
enough that the lubricant is squeezed out, leaving the posts in a
direct high friction contact with the wall. However, due to the
attraction between the magnet posts and the magnetic nanoparticles
in a ferrofluid, a cushion of ferrofluid lubricant will remain
between the magnet posts and the chamber wall.
[0027] While various embodiments of the invention have been shown
and described, numerous variations and alternate embodiments will
occur to those skilled in the art. Accordingly, it is intended that
the invention be limited only in terms of the appended claims.
* * * * *