U.S. patent application number 14/552643 was filed with the patent office on 2015-03-26 for high speed ball bearing for dental or medical handpieces.
The applicant listed for this patent is The Timken Company. Invention is credited to Paul J. Carabello, Frank J. Damato, Ryan D. Evans, Martin S. Galehouse, Joseph P. Greathouse, Steven R. Morel, John A. Zannotti.
Application Number | 20150086146 14/552643 |
Document ID | / |
Family ID | 40732114 |
Filed Date | 2015-03-26 |
United States Patent
Application |
20150086146 |
Kind Code |
A1 |
Damato; Frank J. ; et
al. |
March 26, 2015 |
HIGH SPEED BALL BEARING FOR DENTAL OR MEDICAL HANDPIECES
Abstract
A bearing assembly for use in a medical, surgical, or dental
handpiece that enables spindle rotation for a supported rotary tool
at high speeds. The bearing assembly incorporates annular gap
shields at each axial end to prevent contaminate ingress and to
retain lubricating grease within the bearing assembly to avoid
re-lubrication after each use or sterilization cycle.
Inventors: |
Damato; Frank J.; (Keene,
NH) ; Greathouse; Joseph P.; (Nelson, NH) ;
Carabello; Paul J.; (Dublin, NH) ; Evans; Ryan
D.; (North Canton, OH) ; Galehouse; Martin S.;
(Muskegon, MI) ; Morel; Steven R.; (Swanzey,
NH) ; Zannotti; John A.; (West Chesterfield,
NH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Timken Company |
North Canton |
OH |
US |
|
|
Family ID: |
40732114 |
Appl. No.: |
14/552643 |
Filed: |
November 25, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12988194 |
Nov 24, 2010 |
8931960 |
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PCT/US2009/040907 |
Apr 17, 2009 |
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14552643 |
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61045773 |
Apr 17, 2008 |
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61122624 |
Dec 15, 2008 |
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Current U.S.
Class: |
384/462 |
Current CPC
Class: |
F16C 33/58 20130101;
F16C 33/44 20130101; F16C 33/585 20130101; F16C 27/066 20130101;
F16C 33/767 20130101; F16C 33/56 20130101; F16C 2316/13 20130101;
F16C 33/7816 20130101; F16C 33/7846 20130101; F16C 33/583 20130101;
F16C 2208/42 20130101; F16C 33/80 20130101; F16C 2208/36 20130101;
F16C 2208/40 20130101; A61C 1/181 20130101; F16C 19/547 20130101;
F16C 33/6633 20130101; F16C 19/163 20130101 |
Class at
Publication: |
384/462 |
International
Class: |
F16C 33/78 20060101
F16C033/78; F16C 33/66 20060101 F16C033/66; F16C 33/58 20060101
F16C033/58; F16C 33/44 20060101 F16C033/44 |
Claims
1. A medical, surgical, or dental handpiece bearing assembly
comprising: an outer ring defining an outer raceway and an inner
ring defining an inner raceway; said inner and outer rings defining
a radial distance between said inner and outer rings; a first
shield proximate a first axial end of said bearing assembly and
extending from and integral with one of said inner and outer rings
towards the other of said inner and outer rings; a second shield
proximate a second axial end of said bearing assembly and extending
from one of said inner and outer rings towards the other of said
inner and outer rings; wherein said second shield is snap fit with
one of said inner and outer rings to interlock said second shield
and said ring together; said second shield being comprised of an
engineering plastic of an amorphous polyetherimide to withstand
temperatures of approximately 134.degree. C.; wherein said first
and second shields each have a length equal to at least about 50%
of the radial distance between said inner and outer rings; a
plurality of balls installed between said inner and outer rings and
positioned to contact said inner and outer raceways; a retainer
positioned between said inner and outer rings defining a plurality
of pockets which receives said balls, said retainer comprising an
engineering plastic having a base material selected from either a
polyamide-imide (PAI) or a polyetheretherketone (PEEK) to withstand
repeated sterilization, autoclaving, and application temperatures
without degradation of mechanical properties; and a lubricating
grease being disposed between the first shield and the second
shield, adjacent to the plurality of balls, the lubricating grease
comprising a mineral base oil with polyurea thickener.
2. The bearing assembly of claim 1 wherein said second shield is
mounted to an outer diameter axial surface of said inner ring, an
inner diameter axial surface of said outer ring, or an outer
diameter axial surface of said outer ring; said inner or outer ring
defining a groove which receives said second shield.
3. The bearing assembly of claim 1 wherein said first and second
shields extend substantially the full radial distance between said
inner and outer rings.
4. The bearing assembly of claim 1 wherein said engineering plastic
of the second shield further includes glass filler.
5. The bearing assembly of claim 1 wherein the material for the
retainer includes carbon fillers.
6. The bearing assembly of claim 5 wherein said carbon fillers
comprise graphite and/or carbon fibers.
7. The bearing assembly of claim 5 where in the carbon is present
in amounts greater than, or equal to, about 10% by weight.
8. The bearing assembly of claim 1 wherein the material for the
retainer comprises fillers, said fillers including fluoropolymer
particles, and wherein said fluoropolymer is a
polytetrafluoroethylene.
9. The bearing assembly of claim 8 wherein the fluoropolymer
particles are present in amounts greater than, or equal to, about
1% by weight.
10. The bearing assembly of claim 1 wherein said plurality of balls
are supported in an angular contact configuration.
11. The bearing assembly of claim 1 wherein one of said inner and
outer rings has a relieved configuration; and wherein said retainer
has a one-piece configuration fully encompassing the equator of
each of said plurality of balls.
12. The bearing assembly of claim 1 wherein said first shield is
integrally formed with said outer ring and said second shield snap
fits with said outer ring.
13. The bearing assembly of claim 1 wherein said lubricating grease
has a viscosity of at least about 110 centristrokes at
approximately 104 degrees Fahrenheit.
14. The bearing assembly of claim 2 wherein said second shield is
mounted to an outer diameter surface of said outer ring.
15. The bearing assembly of claim 1 wherein the engineering plastic
of said second shield is a material which remains as a barrier and
preserves shield integrity at temperatures of approximately 134
degrees Centigrade and exposure to steam.
16. The bearing assembly of claim 1 wherein the thermal expansion
properties of the engineering plastic of said second shield
maintain a mechanical interlock at temperatures of approximately
134 degrees Centigrade and exposure to steam.
17. The bearing assembly of claim 1 wherein said second shield is
mounted to an inner diameter surface of said outer ring.
18. The bearing assembly of claim 1 wherein said second shield is
mounted to an outer diameter surface of said outer ring.
19. A medical, dental, or surgical handpiece containing a driven
member and incorporating at least one bearing assembly of claim 1
to support said driven member.
20. The medical, dental, or surgical handpiece of claim 19 wherein
said handpiece comprises a head defining a cavity housing said
driven member; said cavity including upper and lower recesses
axially opposite said driven member with each recess receiving one
of said bearing assemblies; and each of said bearing assemblies
orientated in said recesses such that said second shield faces
axially inward toward said driven member.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/988,194 filed on Nov. 24, 2010, now U.S.
Pat. No. ______, which is the United States National Stage under 35
U.S.C. 371 of International Application No. PCT/US2009/040907,
having an international filing date of Apr. 17, 2009, and claims
priority from U.S. Provisional Patent Application No. 61/045,773
filed on Apr. 17, 2008 and U.S. Provisional Patent Application No.
61/122,624 filed on Dec. 15, 2008, each of which are herein
incorporated by reference.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] Not Applicable.
BACKGROUND OF THE INVENTION
[0003] This invention relates to medical, dental, and surgical
handpieces, and in particular to a high-speed ball bearing for use
in such handpieces.
[0004] Medical, dental, and surgical handpieces containing rotary
tools supported on high-speed bearings are typically powered by an
air turbine or electric motor. In either case, there are some
common challenges to long bearing life. During operation, the
bearings in such handpieces may be exposed to contamination in the
form of both solid and liquid biological matter, as well as in the
form of synthetic debris. The handpiece must be cleaned and
sterilized between each patient. Typical cleaning and sterilization
procedures require flushing of the head of the handpiece with
solvents followed by high pressure steam sterilization in an
autoclave system. Handpieces can reach temperatures
.about.134.degree. C. in autoclaving processes. Both procedures are
detrimental to the life of the bearings in that they degrade the
properties of many lubricants and retainer materials, as well as
remove the lubricant remaining in the bearings. In addition, the
cleaning process requires that the head of the handpiece be
disassembled so that any foreign matter can be removed from the
handpiece head. This is time consuming and can be complicated. For
this reason, cleaning of foreign matter (as opposed to
sterilization) of medical, dental, and surgical handpieces may not
be performed as often as is necessary.
[0005] In order to replenish the lubricant within the bearings, the
user must inject oil into the drive system of the handpiece,
operate the handpiece to expel excess oil and clean any oil residue
from the exterior of the handpiece. In addition to the time and
expense required to relubricate the handpiece, there is the
unwanted added risk that excess lubrication can contaminate the
working environment. Unwanted lubricant can be expelled within the
handpiece body cavity during patient treatment and can contaminate
the surface of the tooth or bone being treated, risking infection
or resulting in poor adhesion of a amalgam or "filling" material,
such as employed in dental procedures.
[0006] For medical, surgical, or dental handpieces having a rotary
tool powered by an air driven turbine, air is discharged from
exhaust vents located near the top and bottom of the of the
handpiece head during use. This exhaust air may pass through the
bearings on the way out of the head and accelerate the expulsion of
lubricant from the handpiece. While the handpiece is slowing to a
stop, the air flow physics of the handpiece are reversed. As the
handpiece shuts down, the low pressure caused by the rotating
turbine draws debris, into the head of the handpiece and the
bearings within.
[0007] Accordingly, there is a need for an improved high-speed
bearing suitable for application medical, surgical, or dental
handpeices to provide support for rotary tools, and which is
adapted for easy cleaning, exclusion of external contaminates, and
which is configured to facilitate the retention of lubricants
within the bearing assembly.
BRIEF SUMMARY OF THE INVENTION
[0008] Briefly stated, the present disclosure provides a bearing
assembly for use in a medical, surgical, or dental handpiece that
enables spindle rotation for a supported rotary tool at high speeds
which may approach 500,000 rpm in dental handpieces. The bearing
assembly incorporates annular gap shields at each axial end to
prevent contaminate ingress and to retain lubricating grease within
the bearing assembly to avoid re-lubrication after each use or
sterilization cycle.
[0009] In one embodiment, the bearing assembly comprises an inner
ring, an outer ring, a plurality of stainless steel or ceramic
balls, and a retainer that separates the balls. The bearing
assembly has an angular contact design, whereby one of the rings is
relieved for assembly, and the retainer is a one-piece design which
fully encompasses the equator of each ball. The retainer cannot be
assembled into the bearing after the rings and balls are assembled,
and the retainer is necessarily of a "non-crown" or "non-pronged"
design. The bearing assembly further includes two shield closures,
with the first shield preferably integral to the inner or outer
ring, or non-integral and attached to the bearing in some other
way. The first single shield is disposed to protect the interior of
the bearing assembly from external debris and contaminates, with
the shield directly adjacent to the exterior openings of the
housing. The second shield, is mounted to either the inner or outer
ring on either the ID or OD of the ring such that the original
standard bearing chassis cross-section is not changed. The second
shield is positioned between the interior of the bearing assembly
(balls, retainer, and grease) and the driven member or rotary tool,
without altering the external configuration of the bearing
assembly. This second shield substantially encloses the annular gap
between the inner and outer bearing rings, and prevents forced air
that drives the turbine from driving lubricant out of the bearing
assembly. The second shield also prevents ingress of cleaning
solutions, foreign material, and contamination into the bearing
that can compromise, degrade, dissolve, or otherwise remove the
initial lubricant from the bearing. In non-air-turbine powered
handpieces, the second shield encloses the interior of the bearing
assembly more effectively than a single shield design, thus
retaining factory-applied grease lubricant more effectively than
prior art designs. The bearing can be sized for use in a variety of
medical or dental handpiece applications.
[0010] In an embodiment of the present disclosure, the second
shield component of the bearing assembly is a molded or machined
component comprised of an engineering plastic (or polymer),
composite or other material, such as an amorphous polyetherimide,
with or without a glass filler. The second shield is capable of
withstanding repeated sterilization, autoclaving, and exposure to
associated high temperatures without degradation of mechanical
properties, while maintaining a rigid barrier, and while preserving
shield integrity.
[0011] In an embodiment of the present disclosure, the second
shield component of the bearing assembly is configured as a "snap"
shield, such that it will mechanically interlock with the inner
bearing ring in an operational position, such as by snapping over a
grove on the bearing ring outer diameter, or mechanically interlock
with the outer bearing ring, such as by snapping into a groove on
the bearing ring inner diameter. The "snap" mechanical interlocking
approach eliminates the need for other fastening methods such as
welding or affixing the shield with wire and provides for easy
assembly. The shield is preferably made of an engineering plastic
material that will elastically deflect sufficiently during
installation to permit a "snap" mechanical interlocking action
which return the shield to an undeflected configuration when the
shield is disposed at the operational position.
[0012] In an embodiment of the present disclosure, the retainer
(cage) component of the bearing assembly is composed of an
engineering plastic with a composition selected to withstand
repeated sterilization and autoclaving procedures and temperatures
without degradation of mechanical or tribological properties,
similar to the second shield component.
[0013] In one embodiment, the retainer (cage) component of the
bearing assembly is composed of a base material such as
polyamide-imide (PAI), containing fillers including carbon
(graphite or carbon fiber) present in amounts equal to, or greater
than 10% of the component weight, and fluoropolymer particles in
amounts equal to, or greater than, 1% of the component weight. The
fluoropolymer particles may be polytetrafluoroethylene (PTFE, such
as Teflon.TM.). The presence of fillers enhance the tribological
performance (low friction and wear) of the retainer.
[0014] In one embodiment, the retainer (cage) component of the
bearing assembly is composed of a base material such as
polyetheretherketone (PEEK), containing fillers including carbon
(graphite or carbon fiber) present in amounts equal to, or greater
than 10% of the component weight, and fluoropolymer particles in
amounts equal to, or greater than, 5% of the component weight. The
fluoropolymer particles may be polytetrafluoroethylene (PTFE, such
as Teflon.TM.).
[0015] The foregoing features, and advantages set forth in the
present disclosure as well as presently preferred embodiments will
become more apparent from the reading of the following description
in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0016] In the accompanying drawings which form part of the
specification:
[0017] FIG. 1 is a perspective view of a medical, surgical, or
dental handpiece;
[0018] FIG. 2 is an enlarged cross-sectional view of a head of the
handpiece shown in FIG. 1, incorporating a bearing assembly of the
present disclosure;
[0019] FIG. 3 is an enlarged cross-sectional view of the bearing
assembly of the present disclosure;
[0020] FIG. 4 is an enlarged cross-sectional view of an alternative
embodiment of the bearing assembly of the present disclosure;
[0021] FIG. 5 is an exemplary graph illustrating a normalized life
improvement of the bearing assembly of FIG. 3, as compared to a
prior art bearing in the same handpiece under identical test
conditions; and
[0022] FIG. 6 is an exemplary graph comparing relative life
improvement of the bearing assembly of FIG. 4, as compared to a
prior art bearing in the same handpiece under identical test
conditions.
[0023] Corresponding reference numerals indicate corresponding
parts throughout the several figures of the drawings. It is to be
understood that the drawings are for illustrating the concepts set
forth in the present disclosure and are not to scale. Before any
embodiments of the invention are explained in detail, it is to be
understood that the invention is not limited in its application to
the details of construction and the arrangement of components set
forth in the following description or illustrated in the
drawings.
DETAILED DESCRIPTION
[0024] The following detailed description illustrates the invention
by way of example and not by way of limitation. The description
enables one skilled in the art to make and use the present
disclosure, and describes several embodiments, adaptations,
variations, alternatives, and uses of the present disclosure,
including what is presently believed to be the best mode of
carrying out the present disclosure.
[0025] Turning to the Figures, and to FIG. 1 in particular, powered
hand-held instruments 10 (handpieces) for supporting rotary driven
tools, that are used frequently in medical, surgical, or dental
typically have a sleeve 12 and an end portion (or head) 14. As
shown in FIG. 2, the head 14 comprises a body 16 and a cap 18
which, in combination, define an interior cavity 20. A bore 22
extends downwardly from the interior cavity 20 to the bottom of the
head 14. The body 16 and cap 18 include aligned recesses 24 and 26,
respectively, which each receive a bearing assembly 28.
Circumferential channels 30 can be formed in the recesses 24, 26 to
receive O-rings 32 which form seals around the outer circumference
of each bearing assembly 28. A preload device 17 configured to
exert an axial preload on each bearing assembly 28 is fitted in the
recess 24, between the bearing assembly 28 and the cap 18.
[0026] In an air-driven handpiece, a driven member 34, such as a
turbine or impeller as shown in FIG. 2, is received in the cavity
20. Correspondingly, for a motor-driven handpiece, the driven
member 34 is a gear. The head 14 receives a spindle shaft 36, to
which a rotary tool (or bit) can be attached, which extends through
the head bore 22 into the cavity 20 to be received by each of the
bearings 28 and engaged with the driven member 34 so that the
driven member can rotationally drive the spindle and attached tool
during use.
[0027] Turning to FIG. 3, an illustrative bearing assembly 28 made
in accordance with the present disclosure consists of an inner ring
40 and outer ring 42, both of which can be made of stainless steel.
The inner ring 40 has an outer circumferential surface 44, with a
curved or arcuate channel 46 formed in the surface 44. The curved
channel 46 defines an inner raceway. The outer ring 42 has an inner
circumferential surface 48 having a first portion 48a and a second
portion 48b. The first and second portions 48a and 48b are both
generally cylindrical, with the portion 48b having a larger
diameter than the portion 48a. The two portions are joined by a
curved or arcuate section 48c which defines an outer raceway.
[0028] The outer ring 42 further includes an integrated shield 50
at one axial end of the ring which extends radially inwardly toward
the inner ring 40. The shield 50 has a length equal to at least 50%
of the radial distance between the inner and outer rings. The
radial distance between the inner and outer rings is defined as the
difference between the outermost surface of the inner ring and
innermost surface of the outer ring when the two rings are
positioned coaxially. Preferably, the shield 50 extends
substantially the full width of this radial distance to effectively
close the axial end of the bearing assembly 28 without actually
contacting the other ring during normal operation. That is, the
shield 50 as defined in this disclosure is not a contact seal, such
as an elastomeric lip seal which can be designed to contact and
slide against a shaft.
[0029] A circumferential groove 52 is formed on the second portion
48b of the inner circumferential surface 48, proximate to the
opposite axial end of the outer ring 42 from the integrated shield
50. A second shield 54 is received in the groove 52 to close the
second axial end of the bearing assembly 28. The second shield 54
is generally L-shaped, and includes a radially inward extending leg
54a and an axially extending head portion 54b sized and shaped to
be received in the circumferential groove 52. Preferably, the
second shield 54 is a "snap" shield adapted to be snapped into
place in the circumferential groove 52 as the shield head portion
54b mechanically interlocks with the groove 52. This mechanical
interlocking as shown defines a "snap" shield design in this
disclosure, and is will be understood to refer to a shield
component which may elastically deform from an operating
configuration or shape during installation, enabling the shield to
be distorted from a rest configuration by the bearing ring
component during installation, and to "snap" back to the rest
configuration upon proper positioning adjacent the groove 52. The
shield leg 54a is sized similarly to the first shield 50, and thus
has a length equal to at least about 50% of the radial distance
between the inner and outer rings, and preferably, has a length
substantially the full width of this radial distance to close the
second axial end of the bearing assembly 28. As with shield 50, the
shield leg 54a effectively closes the axial end of the bearing
assembly 28 without actually contacting the opposite ring during
normal operation. That is, the shield 54 as defined in this
disclosure is not a contact seal, such as an elastomeric lip seal
which can be designed to contact and slide against a shaft.
[0030] As can be seen from FIG. 2, the shields 50 and 54
substantially close the opposite axial ends of each bearing
assembly 28 contained within the head 14. The shields 50 and 54 are
sized to allow clearance of the inner ring, and hence, although it
is preferred that the shields extend at least about 50% of the
width of the space between the inner and outer rings, and
preferably as much of the distance as possible, the shields will
not cover 100% of the annular gap between the inner and outer rings
40, 42. Although the second shield 54 is shown the be mounted to
the inner circumferential surface of the outer ring 42, those of
ordinary skill in the art will recognize that the second shield 54
could be mounted to the outer circumferential surface 44 of the
inner ring 40 in substantially the same manner, without departing
from the scope of the present disclosure.
[0031] The second shield 54 is made by molding or machining an
engineering plastic, composite or other material that can withstand
repeated sterilization, autoclaving, and application temperatures
without degradation of mechanical properties. The engineering
plastic, composite, or other material is selected to remain rigid
and strong enough to function as a barrier to preserve shield
integrity at any application or sterilization temperature which may
be experienced by the handpiece 10 during normal usage. An example
autoclaving sterilization temperature is .about.134.degree. C., and
the preferred embodiment materials can accommodate this temperature
level. The thermal expansion properties of the engineering plastic,
composite, or other material are selected to ensure proper shield
fit or retention occurs at any temperature within the normal
operating range. One exemplary engineering plastic for forming the
second shield 54 consists primarily of an amorphous polyetherimide,
with or without glass filler, such as that sold under the
registered trademark ULTEM containing no fillers.
[0032] Within the interior space of the bearing assembly 14,
axially between the first and second shields 50, 54, a plurality of
balls 60 are positioned within the curved channels 46 and 48c which
define the inner and outer raceways. The curvatures of the raceways
46 and 48c each define a radius, with the radius of each being
substantially the same, and as seen in FIG. 3, the curvature of the
raceways corresponds substantially to the curvature of the balls
60. The curvature of the raceway 46 subtends an arc of between
about 80.degree. and about 90.degree., and preferably about
85.degree.. The curvature of the raceway 48c, on the other hand,
subtends an arc of between about 40.degree. and about 50.degree.,
and preferably about 45.degree.. The two arcs begin at
approximately the same axial position. That is, one end of the arcs
is the same distance from an axial end of the rings. The plurality
of balls 60 are preferably formed from a ceramic such as silicon
nitride (Si.sub.3N.sub.4) or steel, and are held in place between
the raceways and relative to each other by a retainer or cage 62
having optimized dimensions and clearances for the intended
operating conditions of the application.
[0033] The bearing assembly 28, including the balls 60, is
preferably lubricated with a grease consisting of a mineral base
oil and polyurea thickener. Nominal properties of a preferred
grease or lubricant include a specific gravity of 0.9, a dropping
point temperature of 470.degree. F., a viscosity (cSt at
104.degree. F.) of 110, penetration (unworked) of 195, and
penetration (worked after 60 strokes) of 280. Those of ordinary
skill will recognize that different greases or lubricants having
desired properties may be utilized without departing from the scope
of the present disclosure.
[0034] As seen in FIG. 3, the bearing assembly 28 has an angular
contact design, whereby one of the rings is relieved for assembly
and the one piece retainer or cage 62 is fitted that fully
encompasses the equator of each ball. The retainer cannot be
assembled into the bearing after the rings and balls are assembled,
and the retainer is necessarily of the "non-crown" or "non-pronged"
design.
[0035] As with the second shield 54, the retainer or cage 62 is
designed to withstand repeated sterilization, autoclaving, and
application temperatures without degradation of mechanical
properties. The retainer can be made from an engineering plastic
base material such as polyamide-imide (PAI), such as that sold
under the registered trademark TORLON, or from polyetheretherketone
(PEEK). In either case, the material preferably contains fillers,
including carbon (graphite and or carbon fibers) and fluropolymer
particles such as polytetrafluoroethylene (PTFE, such as the
trademarked TEFLON). The carbon filler is preferably present in
amounts greater than or equal to about 10 wt %, while the
fluoropolymer particle filler is preferably present in amounts
greater than or equal to 1 wt % if the retainer is made from a PAI,
or in amounts greater than or equal to about 5 wt % if the retainer
is made from PEEK.
[0036] An exemplary composition of the retainer or cage 62 having a
PAI base such as that sold under the registered trademark TORLON,
consisting of about 20 wt. % carbon (graphite or fiber), about 3
wt. % fluoropolymer (such as polytetrafluoroethylene), and balance
(about 77%) polyamide-imide-type polymer with respect to the total
weight of the article.
[0037] An exemplary composition of the retainer or cage 62 having a
PEEK base consists of about 15 wt. % PTFE, about 15 wt. % carbon
fiber, and balance (70 wt. %) PEEK with respect to the total weight
of the article.
[0038] The following table sets forth an example of nominal
properties suitable for an embodiment of the second shield 54 and
retainer 62:
TABLE-US-00001 Property Second "snap" shield Retainer General
Density (lb/in.sup.3) 0.046 0.054 Water Absorption, 0.25 0.33 24
hrs (%) Mechanical Tensile Strength (psi) 16,500 19,000 Tensile
Modulus (psi) 475,000 1,130,000 Flexural Strength (psi) 20,000
30,200 Flexural Modulus (psi) 500,000 1,060,000 Compressive
Strength (psi) 22,000 17,800 Compressive Modulus (psi) 480,000
580,000 IZOD Notched Impact 0.5 1.6 (ft-lb/in) Thermal Heat
Deflection Temp (.degree. F.) 392 536 at 264 psi Max Operating Temp
(.degree. F.) 340 450
[0039] When assembled in the handpiece head 14, each bearing
assembly 28 is oriented along the axis of the spindle shaft 36 such
that the second shield 54 is positioned between the interior of the
bearing assembly (including the balls 60, retainer 62, and internal
grease) and the driven member 34. In an air powered device, the
second shield 54 prevents air that drives the turbine from entering
the bearing assembly and blowing grease out of the bearing assembly
28. The second shield 54 also prevents ingress of cleaning
solutions, foreign material, and contamination into the bearing
assembly 28 that can compromise, degrade, dissolve, or otherwise
remove the initial lubricant from the bearing. In non-air-turbine
powered handpieces, the second shield 54 encloses the interior of
the bearing assembly 28 more effectively than prior single shield
designs, thus retaining factory-applied grease lubricant more
effectively than prior designs.
[0040] The second shield 54 works in combination with synergies
achieved by retainer materials and grease specifications, as
highlighted above. The synergies achieved by combining the three
elements (i.e., a second shield, the retainer material, and grease
selection) cooperatively function to extend the operational life of
the bearing assemblies 28 when used in medical, surgical, or dental
handpieces 10 subjected to repeated sterilization and autoclaving
procedures. However, it is believed that some benefits could be
realized by incorporating only a second shield; more benefits could
be realized by incorporating the second shield and the retainer
material; and the highest benefits could be achieved by
incorporating all three elements (i.e., the second shield, the
retainer material and the specified grease) as discussed above with
respect to handpiece operation in the absence of periodic
re-lubrication. Those of ordinary skill in the art will recognized
that the bearing assemblies 28 of the present disclosure can be
incorporated in older handpieces 10 as a retrofit option to
dramatically improve performance of such older handpieces without
redesigning the handpiece head 14.
[0041] Turning to FIG. 4, and alternate embodiment 128 of the
bearing assembly is shown. The bearing 128 is generally similar to
bearing assembly 28 shown in FIG. 3, which can be described as an
outer ring relieved design. In contrast, the bearing 128, as will
become apparent from the description below, can be described as an
inner ring relieved design. In this description of the bearing
assembly 128, only the elements which are different from the
corresponding elements in the bearing assembly 28 will be
described.
[0042] The bearing assembly 128 comprises an inner ring 140 and
outer ring 142 which can be made of stainless steel. The outer ring
142 has an inner circumferential surface 148 with a curved or
arcuate channel 149 formed in the surface 148. The channel 149
defines an outer raceway. The inner ring 140 has an outer
circumferential surface 144 having a first portion 144a and a
second portion 144b. The first and second portions 144a and 144b
are both generally cylindrical, with the portion 144a having a
larger diameter than the portion 144b. The two portions are joined
by a curved or arcuate section 144c which defines an inner raceway
on the inner ring 140.
[0043] The curvatures of the raceways 149 and 144c each define a
radius, with the radius of each being substantially the same,
corresponding substantially to the curvature of the balls 60. The
curvature of the raceway 144c subtends an arc of between about
45.degree. and about 55.degree., and preferably about 50.degree..
The curvature of the raceway 149, on the other hand, subtends an
arc of between about 85.degree. and about 95.degree., and
preferably about 90.degree.. The two arcs begin at approximately
the same axial position. That is, one end of the arcs is the same
distance from an axial end of the inner and outer rings 140,
142.
[0044] Like the bearing assembly 28, the bearing assembly 128 has
an angular contact design, whereby one of the rings is relieved for
assembly and the one piece retainer 62 is fitted that fully
encompasses the equator of each ball 60. The difference is that in
the bearing assembly 28, the outer ring is relieved and in the
bearing assembly 128, the inner ring is relieved. In each
embodiment, the retainer 62 cannot be assembled into the bearing
assembly 28, 128 after the rings and balls are assembled, and the
retainer 60 is necessarily of the "non-crown" or "non-pronged"
design.
[0045] An exemplary test program was conducted to evaluate air
turbine driven handpieces 10 incorporating the bearing assemblies
28 (i.e., containing a second shield enclosure 54) and other design
modifications including new retainer material and grease options.
The retainer 62 of the tested bearing 28 was comprised of about 15
wt. % PTFE, about 15 wt. % carbon fiber, and balance (about 70 wt.
%) PEEK. The goal was for the bearing characteristic life to exceed
200 hours without additional lubrication in a handpiece test
including a cyclic steam sterilization procedure. Prior art
bearings were assembled and tested under identical conditions as
the bearings 28. All test bearings passed a torque test prior to
life testing. All test bearings were sterilized for 25 cycles in an
autoclave at 134.degree. C. prior to life testing. Handpieces 10
containing the test bearings were mounted in special testers with a
simulated burr (pin or rotary tool) affixed to the head. Air
pressure was first set to achieve a free running speed of 350,000
rpm (air pressure typically around 3 bar). A 170 g normal load was
then applied to the simulated burr in a cyclic manner to simulate
actual handpiece use by a dentist. After 50 load cycles, the
sequence was paused for 30 seconds by shutting off the air pressure
that drives the turbine 34 in the head 14. After the pause, another
interval of load cycling began. After each 5,000 cycle period,
technicians evaluated the condition of the test handpieces. Every
10,000 load cycles, each handpiece 10 was removed from the testers
and sterilized for 10 cycles at 134.degree. C. in an autoclave. The
test was stopped once a handpiece 10 was unable to reach a free
running speed of 280,000 rpm, was excessively loud, or had
excessive run-out of the simulated burr. A 2-parameter Weibull
approach was used to calculate characteristic lives of the test
bearings. Results are shown in FIG. 5. Handpieces 10 incorporating
prior art bearing assemblies were unable to meet the 200 hour test
life goal, whereas handpieces 10 incorporating the bearing assembly
28 of the present invention surpassed the test goal and exceeded
the prior art bearing assembly operational life by more than 10
times.
[0046] A second test program was conducted to evaluate air turbine
driven handpieces 10 incorporating the bearing assemblies 128
(i.e., containing a second shield enclosure) and other design
modifications including new retainer material and grease options.
The retainer 62 of the tested bearing 128 was comprised of a
polyamide-imide (PAI) polymer, such as that sold under the name
TORLON.RTM., containing normally about 20% graphite and about 3%
fluoropolymer fillers. The goal was for the bearing characteristic
life to exceed 200 hours without additional lubrication in a
handpiece test including a cyclic steam sterilization procedure.
Handpieces 10 included prior art bearing assemblies were tested
under identical conditions as handpieces 10 containing the bearing
assemblies 128. All test bearings passed a torque test prior to
life testing. All test bearings were sterilized for 25 cycles in an
autoclave at 134.degree. C. prior to life testing. Handpieces 10
containing the test bearings were mounted in special testers with a
simulated burr (pin or rotary tool) affixed to the head. Air
pressure was first set to achieve a free running speed of 350,000
rpm (air pressure typically around 3 bar). A 170 g normal load was
then applied to the simulated burr in a cyclic manner to simulate
actual handpiece 10 use by a dentist. After 50 load cycles, the
sequence was paused for 30 seconds by shutting off the air pressure
that drives the turbine 34 in the head 14. After the pause, another
interval of load cycling began. After each 5,000 cycle period,
technicians evaluated the condition of the test handpieces. Every
10,000 load cycles, the handpieces 10 were removed from the testers
and sterilized for 10 cycles at 134.degree. C. in an autoclave. The
test was stopped once a handpiece 10 was unable to reach a free
running speed of 280,000 rpm, was excessively loud, or had
excessive run-out of the simulated burr. A 2-parameter Weibull
approach was used to calculate characteristic lives of the test
bearings. Results are shown in FIG. 6. Handpieces 10 incorporating
the prior art bearing assemblies were unable to meet the 200 hour
test life goal, whereas handpieces 10 incorporating the bearing
assembly 128 surpassed the test goal and exceeded the prior art
bearing life by approximately 10 times.
[0047] In view of the above, it will be seen that the present
disclosure sets forth a bearing assembly 28, 128 for use in
high-speed medical, surgical or dental handpieces 10 that can
withstand routine autoclave steam sterilization (typically around
temperatures of 134.degree. C.) and requires no maintenance or
re-lubrication during its extended useful life.
[0048] As various changes could be made in the above constructions
without departing from the scope of the claimed invention, it is
intended that all matter contained in the above description or
shown in the accompanying drawings shall be interpreted as
illustrative and not in a limiting sense. For example, although the
first shield 50 is shown to be integral with the outer ring, the
shield 50 could be integral with the inner ring. Alternatively, the
shield 50 could be a snap fitted shield, similar to the second
shield 54, which is snapped into place in the outer diameter
surface of the inner ring, the inner diameter surface of the outer
ring, or the outer diameter surface of the outer ring. The examples
set forth herein, and the accompanying test results, are
illustrative only, and do not limit the present disclosure to the
specific features or properties set forth therein.
* * * * *