U.S. patent application number 12/022003 was filed with the patent office on 2008-05-22 for novel method of reducing high voltage arcs in x-ray tubes.
This patent application is currently assigned to Varian Medical Systems Technologies, Inc.. Invention is credited to David S.K. Lee, John E. Postman.
Application Number | 20080118030 12/022003 |
Document ID | / |
Family ID | 39155403 |
Filed Date | 2008-05-22 |
United States Patent
Application |
20080118030 |
Kind Code |
A1 |
Lee; David S.K. ; et
al. |
May 22, 2008 |
Novel Method of Reducing High Voltage Arcs in X-Ray Tubes
Abstract
A bearing assembly suitable for use in conjunction with x-ray
device having a rotating target anode and electron source disposed
in an evacuated enclosure. The bearing assembly includes a shaft
having a rotor hub to which the anode is mounted. The shaft
cooperates with front and rear bearing rings to define front and
rear races, and a spacer facilitates positioning of the bearing
rings. Front and rear ball sets are confined in the front and rear
races, respectively. A bearing housing receives the bearing rings,
spacer, front and rear ball sets, and part of the shaft. Finally, a
magnet is disposed near the front bearing ring to prevent escape of
foreign matter from the bearings and to prevent ingress of foreign
matter to the bearings. Consequently, the magnet serves to extend
the life of the bearings and to prevent foreign matter related
arcing of the target anode and electron source.
Inventors: |
Lee; David S.K.; (Salt Lake
City, UT) ; Postman; John E.; (Sandy, UT) |
Correspondence
Address: |
VARIAN MEDICAL SYSTEMS TECHNOLOGIES, INC.;C/O WORKMAN NYDEGGER
60 E. SOUTH TEMPLE
SUITE 1000
SALT LAKE CITY
UT
84111
US
|
Assignee: |
Varian Medical Systems
Technologies, Inc.
Palo Alto
CA
|
Family ID: |
39155403 |
Appl. No.: |
12/022003 |
Filed: |
January 29, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10358940 |
Feb 5, 2003 |
7343002 |
|
|
12022003 |
Jan 29, 2008 |
|
|
|
Current U.S.
Class: |
378/132 ;
378/210; 384/446 |
Current CPC
Class: |
F16C 2380/16 20130101;
F16C 33/82 20130101; H01J 2235/20 20130101; H01J 2235/1046
20130101; H01J 35/101 20130101; H01J 2235/108 20130101; H01J 35/103
20130101; F16C 33/66 20130101 |
Class at
Publication: |
378/132 ;
378/210; 384/446 |
International
Class: |
H01J 35/00 20060101
H01J035/00; H05G 1/00 20060101 H05G001/00; F16C 33/82 20060101
F16C033/82 |
Claims
1. An x-ray device, comprising: (a) an evacuated housing; (b) an
electron source and a target anode disposed within said evacuated
housing, said target anode positioned to receive electrons emitted
by said electron source; and (c) a bearing assembly rotatably
supporting said target anode and substantially disposed within said
evacuated housing, said bearing assembly including front and rear
bearing rings confining respective front and rear ball sets, and
said bearing assembly further including at least one magnet located
so that an open path is defined at least between said front bearing
ring and said at least one magnet.
2. An x-ray device, comprising: (a) an evacuated housing; (b) an
electron source and a target anode disposed within said evacuated
housing, said target anode positioned to receive electrons emitted
by said electron source; and (c) a bearing assembly rotatably
supporting said target anode and substantially disposed within said
evacuated housing, said bearing assembly including front and rear
bearing rings confining respective front and rear ball sets, and
said bearing assembly further including at least one magnet located
so that an open path is defined at least between said front bearing
ring and said at least one magnet; and wherein said at least one
magnet is interposed between said target anode and said front
bearing ring.
3. An x-ray device, comprising: (a) an evacuated housing; (b) an
electron source and a target anode disposed within said evacuated
housing, said target anode positioned so as to receive electrons
emitted by said electron source; and (c) a bearing assembly
substantially disposed within said evacuated housing and rotatably
supporting said target anode, said bearing assembly including: (i)
a shaft to which said anode is mounted, the shaft defining front
and rear inner races; (ii) front and rear bearing rings, the front
bearing ring and the front inner race collectively comprising a
front race, and the rear bearing ring and rear inner race
collectively comprising a rear race; (iii) a spacer interposed
between said front and rear bearing rings; (iv) a front ball set
disposed in said front race, and a rear ball set disposed in said
rear race; (v) a bearing housing, said bearing housing receiving
said front and rear bearing rings, said front and rear ball sets,
said spacer, and a portion of said shaft; and (vi) means for
controlling foreign matter, said means for controlling foreign
matter: substantially preventing escape of foreign matter from said
bearing housing; and substantially preventing ingress of foreign
matter to said bearing housing.
4. The x-ray device as recited in claim 3, wherein said means for
controlling foreign matter magnetically attracts and retains said
at least some foreign matter present in said evacuated housing.
5. The x-ray device as recited in claim 3, wherein said means for
controlling foreign matter substantially prevents escape of foreign
matter from said bearing housing.
6. The x-ray device as recited in claim 3, wherein said means for
controlling foreign matter substantially prevents ingress of
foreign matter to said bearing housing.
7. The x-ray device as recited in claim 3, wherein said means for
controlling foreign matter substantially prevents arcing of said
electron source and said target anode arising from foreign matter
present in said evacuated enclosure.
8. The x-ray device as recited in claim 3, wherein said means for
controlling foreign matter comprises at least one magnet.
9. The x-ray device as recited in claim 8, wherein said at least
one magnet substantially comprises a rare earth alloy.
10. The x-ray device as recited in claim 9, wherein said rare earth
alloy comprises a 2-17 samarium-cobalt alloy.
11. A bearing assembly, said bearing assembly comprising: (a) a
shaft having an integral bearing hub; (b) front and rear bearing
rings which cooperate with said shaft to define front and rear
races; (c) a spacer interposed between said front and rear bearing
rings such that the spacer and front and rear bearing rings are
collectively disposed in a stacked arrangement; (d) a front ball
set disposed in said front race, and a rear ball set disposed in
said rear race; (e) a bearing housing, said bearing housing
receiving said front and rear bearing rings, said front and rear
ball sets, said spacer, and a portion of said shaft, the front
bearing ring being attached to the housing; and (f) at least one
magnet located so that an open path is defined at least between
said front bearing ring and said at least one magnet.
12. The bearing assembly as recited in claim 11, wherein said shaft
includes a rotor hub, said at least one magnet being attached to
said rotor hub.
13. The bearing assembly as recited in claim 11, wherein said at
least one magnet is attached to said shaft.
14. The bearing assembly as recited in claim 11, wherein said at
least one magnet is attached to said bearing housing.
15. The bearing assembly as recited in claim 11, wherein said at
least one magnet comprises a plurality of magnets equally spaced
about an axis of rotation of said shaft.
16. The bearing assembly as recited in claim 11, further comprising
another magnet located so that an open path is defined at least
between said rear bearing ring and said another magnet.
17. The bearing assembly as recited in claim 11, wherein said at
least one magnet comprises two halves.
18. The bearing assembly as recited in claim 17, wherein a north
pole of one of said two halves is disposed adjacent to a south pole
of a remaining half.
19. The x-ray device as recited in claim 11, wherein said at least
one magnet substantially comprises a rare earth alloy.
20. The x-ray device as recited in claim 19, wherein said rare
earth alloy is selected from the group consisting of:
samarium-cobalt alloys, and neodymium-iron-boron alloys.
21. A method for controlling foreign matter within an evacuated
housing of an x-ray device, the method comprising: (a) attracting
foreign matter present within the evacuated housing of the x-ray
device to at least one predetermined location; and (b) retaining
said foreign matter at said at least one predetermined
location.
22. The method as recited in claim 21, wherein said attracting and
retaining of foreign matter are implemented by defining a magnetic
field.
23. A bearing assembly, comprising: a shaft that defines front and
rear inner races of respective front and rear ball races, and the
shaft having an integral bearing hub; front and rear bearing rings
that receive the shaft and define respective front and rear outer
races of the front and rear ball races; at least one spacer
disposed about the shaft and interposed between the front and rear
bearing rings so that the front and rear bearing rings are spaced
apart from each other by at least a length of the at least one
spacer, the spacer and front and rear bearing rings collectively
being disposed in a stacked arrangement; a front ball set partially
confined in the front ball race, and a rear ball set partially
confined in the rear ball race; a bearing housing within which the
front and rear bearing rings, front and rear ball sets, and spacer
are disposed; and means for controlling foreign matter, said means
for controlling foreign matter employing a magnetic effect to
prevent entry of at least some foreign matter, from a location
external to the bearing assembly, into the bearing assembly.
24. The bearing assembly as recited in claim 23, wherein the means
for controlling foreign matter comprises at least one magnet
located proximate the front ball race, an open path being defined
between the at least one magnet and the front ball race.
25. The bearing assembly as recited in claim 24, wherein the at
least one magnet comprises a plurality of magnets.
26. The bearing assembly as recited in claim 24, wherein the at
least one magnet comprises a rare earth material.
27. The bearing assembly as recited in claim 23, wherein the shaft
includes a rotor hub located proximate the front inner race.
28. The bearing assembly as recited in claim 23, wherein at least
one portion of the bearing assembly is magnetized.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S. patent
application Ser. No. 10/358,940 filed on Feb. 5, 2003; which is
incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. The Field of the Invention
[0003] The present invention relates generally to systems and
devices that include at least one component rotatably supported by
a bearing assembly. More particularly, embodiments of the present
invention relate to bearing assemblies that include various
features directed to controlling ingress and egress of foreign
matter to and from, respectively, the bearing assembly, and which
thereby materially reduce the incidence of foreign matter related
problems in the bearing assembly, as well as in the system or
device wherein the bearing assembly is employed.
[0004] 2. Related Technology
[0005] X-ray producing devices are valuable tools that are used in
a wide variety of industrial, medical, and other applications. For
example, such equipment is commonly used in areas such as
diagnostic and therapeutic radiology, semiconductor manufacture and
fabrication, and materials analysis and testing. While they are
used in various different applications, the different x-ray devices
share the same underlying operational principles. In general,
x-rays, or x-ray radiation, are produced when electrons are
produced, accelerated, and then impinged upon a material of a
particular composition.
[0006] Typically, these processes are carried out within a vacuum
enclosure. Disposed within the vacuum enclosure is an electron
source, or cathode, and a target anode, which is spaced apart from
the cathode. In operation, electrical power is applied to a
filament portion of the cathode, which causes a stream of electrons
to be emitted by the process of thermionic emission. A high voltage
potential applied across the anode and the cathode causes the
electrons emitted from the cathode to rapidly accelerate towards a
target surface, or focal track, positioned on the anode.
[0007] The accelerating electrons in the stream strike the target
surface, typically a refractory metal having a high atomic number,
at a high velocity and a portion of the kinetic energy of the
striking electron stream is converted to electromagnetic waves of
very high frequency, or x-rays. The resulting x-rays emanate from
the target surface, and are then collimated through a window formed
in the x-ray tube for penetration into an object, such as the body
of a patient. As is well known, the x-rays can be used for
therapeutic treatment, or for x-ray medical diagnostic examination
or material analysis procedures.
[0008] The aforementioned scheme for the production of x-rays is
relatively inefficient. It is generally acknowledged that in
typical x-ray tube operations, only about one percent of the energy
contained in the beam of electrons produced by the electron source
results in x-ray emissions from the target surface. A substantial
portion of the remaining energy of the electron beam is imparted to
the x-ray device and its component structures, such as the anode,
in the form of heat. In general, the quality and resolution of
images produced by an x-ray device increases in relation to, among
other things, the power associated with the electron beam. Thus,
improvements in image quality have often come at the cost of a
relative increase in x-ray tube operating temperatures. Various
approaches have been devised to deal with such increases in
operating temperatures.
[0009] X-ray tubes that employ rotating anodes represent one
approach that has been successful in managing the high heat levels
characteristic of many x-ray devices. In a typical rotating anode
type x-ray tube, the anode is rotatably supported by a bearing
assembly. A stator serves to rotate the shaft, and the anode
accordingly rotates as well. As the anode rotates, each point on
the focal track is rotated into and out of the path of the electron
beam generated by the cathode. In this way, the electron beam is in
contact with a given point on the focal track for only short
periods of time, thereby allowing the remaining portion of the
focal track to cool during the time that it takes such given
portion to rotate back into the path of the electron beam.
[0010] As suggested above, the bearing assembly with which the
shaft is rotatably supported is central to the operation of such
rotating anode type x-ray devices. However, many known bearing
assemblies and associated components present problems which often
act to materially impair the safety, effectiveness and reliability
of the x-ray device. In particular, the design, assembly, and
operation of typical bearing assemblies are such that many known
bearing assemblies often become contaminated by particles which
create various problems with respect to the operation of the x-ray
tube.
[0011] One example of problems caused by the presence of particles
in the x-ray tube relates to the high voltage across the cathode
and anode. In general, the presence of such particles in the x-ray
tube causes the high potential across the cathode and anode to
become unstable. This lack of high voltage stability causes
discharges of electricity, or arcs, between the cathode and anode.
High voltage arcs may cause damage to the target surface of the
anode, as well as to the cathode. Further, such high voltage arcs
may compromise image quality through the generation of x-ray image
artifacts.
[0012] Another problem associated with the presence of particles in
the x-ray tube relates to the operation of the bearing assembly. In
particular, when such particles enter, or are created in, the
bearings, the particles tend to stick between the balls, creating
rough surfaces inside the bearing. As the balls pass over the rough
surfaces thus created, noise is generated within the x-ray device.
Such noise is distracting to the operator. Further, such noise can
be unsettling to a patient, particularly in applications such as
mammography where the patient is in intimate contact with the x-ray
machine. Finally, the rough surfaces created by the particles may
serve to reduce the operating life of the bearings.
[0013] There are a variety of mechanisms by which foreign matter
contamination of the x-ray tube may occur. As suggested above, at
least some of such mechanisms concern the design, assembly, and
operation of bearing assemblies. For example, many known bearing
assemblies employ balls and/or races which are designed to include
a solid lubricant such as silver (Ag), lead (Pb), or molybdenum
disulfide (MoS.sub.2). Generally, such metal lubricants are
employed in x-ray devices at least because they are better suited
to the extreme operating temperatures of an x-ray tube than are
typical hydrocarbon-based lubricants. These solid lubricants are
applied to the balls and/or races by various chemical or physical
methods such as electroplating, ion plating, sputtering, and
evaporation. While the coating process is controlled in an effort
to ensure uniformity and adherence of the coating, the motion of
the balls rolling along the races causes the metal lubricant to
move around somewhat and form lumps. Such lumps of lubricant are
often as large as a few thousandths of an inch thick, and may be as
long as one eighth of an inch.
[0014] As the lumps of lubricant are formed in the bearing
assembly, they additionally pick up various elements, such as iron
(Fe) and nickel (Ni), from the balls and races of the bearing
assembly. As a result of the presence of the iron, the lumps of
lubricant typically exhibit magnetic properties. Typically, these
other elements migrate to the lubricant as a result of processes
such as solid state diffusion, and abrasion. As the lubricant
becomes contaminated with such elements, the desirable properties
of the lubricant are compromised. For example, the ability of the
lubricant to adhere to the balls and races is impaired, and the
lubricant thus tends to separate from the balls and races and is
then able to move about within the x-ray tube. As discussed above,
problems caused by the loose lubricant particles include arcing
between the cathode and anode, creation of noise in the bearing
assembly, and a shortening of the life of the bearing assembly and
its components.
[0015] Yet another vehicle by which foreign matter contaminates the
x-ray tube relates to the processes by which the bearing assembly
is put together. Typically, when bearing assembly components are
inserted into the bearing housing during assembly, the bearing
assembly components tend to rub against the sides of the housing.
As a result of this abrasion, metal particles are often produced
within the bearing assembly. Also, many bearing assemblies contain
threaded holes and threaded fasteners to hold the various parts of
the assembly. Pieces of metal can come loose during assembly.
Because the various components of the bearing assembly are often
constructed of various steel alloys, the particles thus produced
typically exhibit magnetic properties. As discussed above, the
presence of such particles in the x-ray tube is problematic for a
variety of reasons, and may contribute to problems such as arcing,
reduced bearing life, and noise generation within the x-ray
device.
[0016] Finally, at least one other mechanism by which foreign
matter enters the x-ray tube relates to the design of the bearing
housing of the bearing assembly. In particular, the bearing housing
in typical x-ray tube designs is at least partially open at the end
through which the bearings and shaft are inserted. Thus, there is
little to prevent foreign matter present in, or created in, the
bearing assembly, from escaping into other areas of the x-ray tube.
Correspondingly, the open end of the bearing housing allows foreign
matter present in other parts of the x-ray tube to enter the
bearings.
[0017] At least one attempt has been made to resolve the
aforementioned problems and shortcomings by employing mesh, or a
screen, intended to prevent foreign matter from escaping the
bearing assembly. The approach represented by such screens and
meshes is problematic however. For example, while such screens and
meshes may be somewhat effective in confining foreign matter within
the bearing assembly, they are generally ineffective in preventing
the movement of the foreign matter about the interior of the
bearing assembly. As discussed above, foreign matter present in, or
generated in, the bearing assembly implicates a variety of
undesirable consequences.
[0018] In particular, foreign matter in the bearing assembly may
compromise the operation of the bearings by impairing the integrity
of the bearing lubricant. As another example, the presence of
foreign matter in the bearing assembly may contribute to increased
noise levels in the x-ray device. Thus, the inability of screens,
meshes, or similar approaches, to control the foreign matter
present or created in the bearing assembly represents a significant
limitation in this attempt to resolve the problems in the art.
[0019] Another limitation of known particle control methods and
devices such as meshes, screens, and the like is that they are
incapable of effectively controlling those particles located
outside of the bearing assembly. In the x-ray tube environment, at
least, this is a significant limitation because such particles, if
not reliably controlled, may contribute to arcing of the anode and
cathode.
[0020] In view of the foregoing problems, and others, it would be
an advancement in the art to provide improved devices and systems
for trapping and controlling foreign matter present in, or created
in, an x-ray tube.
BRIEF SUMMARY OF VARIOUS FEATURES OF THE INVENTION
[0021] The present invention has been developed in response to the
current state of the art, and in particular, in response to these
and other problems and needs that have not been fully or adequately
resolved by currently available bearing assemblies. Briefly
summarized, embodiments of the present invention provide a bearing
assembly which includes features directed toward facilitating
improved control of foreign matter generated or present within, or
without, the bearing assembly.
[0022] Embodiments of the present invention are particularly well
suited for use in the context of rotating anode type x-ray tubes.
However, it will be appreciated that embodiments of the present
invention may be suitable for use in any device where it is desired
to effectively and reliably control foreign matter so as to prevent
damage to the bearing assembly and/or to the device.
[0023] In one embodiment of the invention, a bearing assembly for a
rotating anode x-ray tube is provided that includes a shaft having
a rotor hub, to which the anode is mounted, and defining front and
rear inner races. Disposed about the shaft are front and rear
bearing rings, separated by a spacer, which define, respectively,
front and rear outer races. The front and rear outer races,
respectively, defined by the front and rear bearing rings,
cooperate with the front and rear inner races, defined by the
shaft, to confine front and rear ball sets which each comprise a
plurality of balls coated with a solid metal lubricant, preferably
lead, silver, or molybdenum disulfide. The front and rear bearing
rings, spacers, and a portion of the shaft, are secured within a
bearing housing. Finally, the bearing assembly includes one or more
magnets disposed proximate to the front inner and outer races.
[0024] In operation, a stator imparts energy to the shaft, causing
the shaft to rotate at high speed. As the shaft rotates, the balls
in the front and rear ball sets travel along the front and rear
races, respectively. Motion of the balls along the races causes
some of the solid metal lubricant to clump on the balls and/or
races. Ultimately, the clumps thus formed pick up foreign particles
comprising elements such as iron (Fe) and nickel (Ni) from the
balls and the races. Typically, such foreign particles find their
way into the lubricant by way of processes such as solid state
diffusion, or abrasion of the balls and/or races. Such foreign
particles compromise the ability of the solid metal lubricant to
adhere to the balls and races. Consequently, some of the lubricant
separates from the balls and races. Because the separated lubricant
includes elements such as iron, the lubricant particles exhibit
magnetic properties. Because the particles are magnetic, the
magnets of the bearing assembly are able to attract and retain such
particles, thereby preventing them from, among other things,
impairing the operation of the bearings, or causing high voltage
arcs within the x-ray tube.
[0025] These and other features and advantages of the present
invention will become more fully apparent from the following
description and appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] In order that the manner in which the above-recited and
other advantages and features of the invention are obtained, a more
particular description of the invention briefly described above
will be rendered by reference to specific embodiments thereof which
are illustrated in the appended drawings. Understanding that these
drawings depict only typical embodiments of the invention and are
not therefore to be considered limiting of its scope, the invention
will be described and explained with additional specificity and
detail through the use of the accompanying drawings in which:
[0027] FIG. 1 is a side view illustrating various features of an
embodiment of an x-ray tube;
[0028] FIG. 2 is a section view of an embodiment of a bearing
assembly;
[0029] FIG. 3A is a section view of an embodiment of a bearing
assembly illustrating an exemplary arrangement wherein a magnet is
attached to the rotor hub;
[0030] FIG. 3B is a section view taken along Line 3B of FIG. 3A,
illustrating an exemplary magnet arrangement wherein a split magnet
(or one-piece magnet) is attached to the rotor hub;
[0031] FIG. 3C is a section view illustrating an alternative to the
split magnet arrangement illustrated in FIG. 3B, wherein the
alternative arrangement includes a plurality of individual magnets
attached to the rotor hub;
[0032] FIG. 4A is a section view of an embodiment of a bearing
assembly illustrating an exemplary magnet arrangement wherein a
single magnet is attached to the bearing housing;
[0033] FIG. 4B is a section view of an embodiment of a bearing
assembly illustrating an exemplary magnet arrangement wherein a
plurality of magnets are attached to the bearing housing;
[0034] FIG. 4C is a section view illustrating an alternative to the
split magnet arrangement illustrated in FIG. 4B, wherein the
alternative arrangement includes a plurality of individual magnets
attached to the bearing housing; and
[0035] FIG. 5 is a section view illustrating an alternative
arrangement wherein one or more magnets are attached to, and
disposed about, the shaft of the bearing assembly.
DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION
[0036] Reference will now be made to figures wherein like
structures will be provided with like reference designations. It is
to be understood that the drawings are diagrammatic and schematic
representations of various embodiments of the invention, and are
not to be construed as limiting the present invention, nor are the
drawings necessarily drawn to scale.
[0037] Reference is first made to FIG. 1, wherein an x-ray tube is
indicated generally at 100. It will be appreciated that the x-rays
produced by x-ray tube 100 may be employed in any of a variety of
applications, and embodiments of the present invention should
accordingly not be construed to be limited to any particular field
of application.
[0038] As indicated in the illustrated embodiment, x-ray tube 100
includes a vacuum enclosure 102, inside which is disposed an
electron source 104, preferably comprising a cathode or the like,
and an anode 106 arranged in a spaced-apart configuration with
respect to electron source 104 and rotatably supported by bearing
assembly 200. Anode 106 further includes a target surface 106A,
preferably comprising a refractory metal such as tungsten or the
like, arranged so as to receive electrons emitted by electron
source 104. The x-rays produced by x-ray tube 100 are directed out
of vacuum enclosure 102 by way of a window 108, preferably
comprising beryllium or the like.
[0039] With continuing attention to FIG. 1, details are provided
regarding various operational features of x-ray tube 100. In
operation, a stator (not shown) causes anode 106 to rotate at high
speed. Power applied to electron source 104 causes electrons,
denoted at "e" in FIG. 1, to be emitted by thermionic emission and
a high voltage potential applied across electron source 104 and
anode 106 causes the emitted electrons "e" to rapidly accelerate
from electron source 104 toward anode 106. Upon reaching anode 106,
electrons "e" strike target surface 106A causing x-rays, denoted at
"x" in FIG. 1 to be produced. The x-rays "x" are then collimated
and passed through window 108 and into a subject, for example, the
body of a patient.
[0040] Directing attention now to FIG. 2, and with continuing
reference to FIG. 1, various details are provided regarding an
embodiment of a bearing assembly 200. In particular, bearing
assembly 200 includes a shaft 202, preferably comprising high
temperature tool steel or the like, having rotor hub 202A and
defining front and rear inner races, 204 and 206, respectively,
disposed circumferentially about shaft 202. Front and rear inner
races 204 and 206, in turn, include respective bearing surfaces
204A and 206A. While shaft 202 preferably comprises high
temperature tool steel, it will be appreciated that various other
materials may be employed consistent with a desired
application.
[0041] In at least one embodiment of the invention, portions of
front and rear inner races 204 and 206, preferably at least bearing
surfaces 204A and 206A, are coated with a solid metal lubricant
such as lead (Pb), silver (Ag), molybdenum disulfide (MoS.sub.2),
or other suitable material. It will be appreciated however, that
while lead and silver lubricants are particularly well suited to
x-ray tube environments, different lubricants may be employed when
bearing assembly 200 is used in other environments. For example, in
relatively low temperature applications, hydrocarbon-based
lubricants such as oil and the like may be employed.
[0042] With continuing reference to FIG. 2, bearing assembly 200
additionally includes front and rear bearing rings 208 and 210
respectively, disposed about shaft 202 and separated by a spacer.
While other spacer arrangements could be used, in the illustrated
example a tubular spacer 212 is used in combination with a
"C"-shaped spacer 213, which is also shown in FIG. 2A. In
particular, the opening of the "C"-shaped spacer is large enough to
pass the shaft 202 diameter. Front and rear bearing rings 208 and
210 define front and rear outer races 214 and 216, respectively,
which in turn, include respective bearing surfaces 214A and 216A.
In at least one embodiment of the invention, portions of front and
rear inner races 214 and 216, preferably at least bearing surfaces
214A and 216A, are coated with a solid metal lubricant such as lead
(Pb), silver (Ag), molybdenum disulfide (MoS.sub.2), or other
suitable material. As in the case of shaft 202, front and rear
bearing rings 208 and 210, and spacers 212 and 213, preferably
comprise high temperature tool steel or the like. However, it will
be appreciated that various other materials may be employed
consistent with a desired application.
[0043] With more specific reference now to front and rear bearing
rings 208 and 210, and spacers 212 and 213, additional details are
provided regarding the arrangement of such components with respect
to shaft 202. In particular, front bearing ring 208, rear bearing
ring 210, as well as spacers 212 and 213, are disposed about shaft
202 so that front outer race 214 and rear outer race 216 are
substantially aligned with, respectively, front inner race 204 and
rear inner race 206 defined by shaft 202. In this way, front outer
race 214 and rear outer race 216 cooperate with, respectively,
front inner race 204 and rear inner race 206 to confine a front
ball set 218 and a rear ball set 220, respectively. Both front ball
set 218 and a rear ball set 220 comprise respective pluralities of
balls 218A . . . 218n and 220A . . . 220n. In general, front ball
set 218 and a rear ball set 220 cooperate to facilitate high speed
rotary motion of shaft 202, and thus anode 106.
[0044] It will be appreciated that the variables such as the number
and diameter of balls 218A . . . 218n and 220A . . . 220n may be
varied as required to suit a particular application. Further, in
some embodiments of the invention, balls 218A . . . 218n and 220A .
. . 220n are coated with a solid metal lubricant such as lead (Pb),
silver (Ag), molybdenum disulfide (MoS.sub.2), or other suitable
material.
[0045] Directing continuing attention to FIG. 2, bearing assembly
200 includes bearing housing 222 which serves to receive and
securely retain front and rear bearing rings 208 and 210, as well
as shaft 202. Preferably, bearing housing 222 is substantially in
the shape of a seamless hollow cylinder and preferably comprises a
durable, high strength metal or metal alloy, such as stainless
steel or the like, that is suitable for use in high temperature
x-ray tube operating environments. In one embodiment, a plurality
of bolts 209 serve to attach front bearing ring 208 to bearing
housing 222, thereby retaining rear bearing ring 210, spacers 212
and 213, and shaft 202 in position within bearing housing 222. It
will be appreciated however, that various other fasteners may
likewise be employed. Further, such fasteners may be eliminated and
one or more of the aforementioned components attached to housing
222 by way of processes including, but not limited to, welding and
brazing.
[0046] The positioning of bearing rings 208 and 210, as well as
shaft 202, within bearing housing 222 is facilitated by the spacers
212 and 213 together, which serve to, among other things, properly
orient front and rear bearing rings 208 and 210 with respect to
shaft 202. Spacers 212 and 213, front and rear bearing rings 208
and 210, and shaft 202 are securely retained in bearing housing 222
by way of fasteners 209 which secure front bearing ring 208 to
bearing housing 222, thereby substantially foreclosing axial
movement of spacers 212 and 213 and front and rear bearing rings
208 and 210.
[0047] In the illustrated example, the bearing assembly 222
includes one or more magnets 226, preferably permanent magnets,
disposed in various locations, for example, proximate to front
inner race 204 and front outer race 214. Respecting magnet(s) 226,
it will be appreciated that magnet(s) 226 comprise one exemplary
structure which serves as a means for controlling foreign matter,
and that various other structures may alternatively be employed to
provide such functionality.
[0048] For example, magnetized structures such as meshes and
screens may alternatively be employed as means for controlling
foreign matter. Likewise, such a means for controlling foreign
matter includes within its purview structures other than permanent
magnets, such as electromagnets. In view of the foregoing, it
should be understood that such structural configurations are
presented herein solely by way of example and should not be
construed as limiting the scope of the present invention in any
way.
[0049] Finally, it should be noted that while the following
discussion concerning various magnet materials, and devices and
methods for attachment of such magnets, is presented in the context
of FIG. 2, such discussion is equally germane to the various other
embodiments contemplated hereby.
[0050] In the illustrated embodiment, magnet 226 is attached to the
underside of rotor hub 202A. It will be appreciated that in cases
where rotor hub 202A comprises a magnetic material such as 400
series stainless steel, too steel, CSM Rex-20 (manufactured by
Crucible Specialty Metals, Co.), or the like, magnet 226 may be
retained in place simply by the natural magnetic attraction between
magnet 226 and rotor hub 202A. However, in the event rotor hub 202A
is composed of a non-magnetic metal alloy, such as the non-magnetic
nickel-chromium-iron (NiCrFe) alloys sold under the trademark
INCONEL.RTM. 718 (manufactured by INCO ALLOYS), magnet 226 is
preferably attached to rotor hub 202A by fasteners, examples of
which include pins, screws, snap rings, or the like, or by crimping
into place. Note that depending on the composition of magnet 226,
the magnet 226 may preferably be affixed to the rotor hub 202A with
such fastening schemes even where the hub is comprised of a
magnetic material. This will insure proper attachment, even if the
magnet is exposed to high temperatures that could affect its
magnetism.
[0051] While the illustrated embodiment indicates a single magnet
226 attached to rotor hub 202A, it will be appreciated that, as
discussed below in the context of FIGS. 3A through 4C, one or more
magnets 226 may be placed in additional or alternative locations
and arrangements as well. Generally however, embodiments of the
present invention comprise one or more magnets 226 positioned so
that magnetic particles produced in bearing assembly 200 and/or
other portions of x-ray tube 100 can freely travel, under the
influence of such attraction and/or the influence of forces such as
gravitational force, to magnet(s) 226 and be reliably retained
thereby.
[0052] As suggested earlier, at least some embodiments of bearing
assembly 200 are well suited for use in x-ray tube environments. It
will accordingly be appreciated that, when used in such
environments, magnet 226 preferably comprises a refractory, or rare
earth, magnet that retains adequate magnetic properties even when
exposed to extreme heat. Magnet materials contemplated as being
within the scope of the present invention include, but are not
limited to, rare earth alloys such as samarium-cobalt (e.g.,
SmCo.sub.5 (1-5 samarium-cobalt), Sm.sub.2Co.sub.17 (2-17
samarium-cobalt)) having a Curie temperature between about
700.degree. C. and about 800.degree. C., and possessing a magnetic
energy product, at x-ray tube operating temperatures, of about 80
kJ/m.sup.3. It will be appreciated however, that the material(s)
used for magnet 226 may be varied as required so that the
properties of the magnet suit the particular desired application.
For example, where embodiments of bearing assembly 200 are employed
in relatively low temperature applications, rare earth
neodymium-iron-boron (NdFeB) magnets may be used.
[0053] In addition to magnet(s) 226, or as an alternative thereto,
various portions of bearing assembly 200 may include, or
substantially comprise, suitable magnetic materials. For example,
in one alternative embodiment of the invention, at least a portion
of spacer 212 is magnetized and spacer 212 is thus effective in
attracting and retaining at least some of the foreign matter
produced, or present in, bearing assembly 200. In view of the
foregoing, it will be appreciated that the scope of the present
invention should not be construed to be limited solely to the
illustrated embodiments.
[0054] Directing continuing attention to FIG. 2, details are
provided regarding various operational aspects of embodiments of
the present invention. Note that while the following discussion is
presented in the context of FIG. 2, such discussion is similarly
germane to the various other embodiments contemplated hereby.
[0055] In general, rotation of shaft 202 causes front ball set 218
and rear ball set 220 to travel at high speed along the races
cooperatively defined by shaft 202 and front and rear bearing rings
208 and 210. As front ball set 218 and rear ball set 220 travel
along the races, lubricant present on front ball set 218 and rear
ball set 220, and/or front and rear inner races 204 and 206 and
front and rear outer races 214 and 216, tends to aggregate and form
clumps within bearing assembly 200. By processes such as abrasion
of front ball set 218 and rear ball set 220, and/or front and rear
inner races 204 and 206 and front and rear outer races 214 and 216,
and/or the process of solid state diffusion, such clumps entrap
bearing assembly component materials such as iron (Fe) and nickel
(Ni), thereby rendering the clumps, or particles, magnetic.
[0056] In addition to lending magnetic properties to the lubricant,
bearing component materials such as iron and nickel also compromise
the ability of the lubricant to adhere to the surface to which the
lubricant was initially applied. Consequently, the magnetic
lubricant particles tend to separate from the lubricant coated
surfaces and move about within bearing assembly 200, as well as
within the device wherein bearing assembly 200 is disposed. As a
result of the magnetic field produced by magnet 226, magnet 226
effectively and reliably attracts and retains such loose
particles.
[0057] In view of the foregoing discussion, it will be appreciated
that embodiments of the present invention serve to, among other
things, substantially foreclose many of the various problems
ascribed to the presence of foreign matter in bearing assemblies
and x-ray tubes. By way of example, it was previously noted that
foreign matter present in bearing assembly 200 may, among other
things, compromise the operation of bearing assembly 200 by
creating rough spots in the races which contribute to increased
noise levels in bearing assembly 200 and shortened operational life
of bearing assembly 200 and its constituent components.
[0058] In this regard, at least, it will be appreciated that
embodiments of the present invention present at least a twofold
benefit with respect to the operation of bearing assembly 200. In
particular, magnets 226 not only attract and retain particles
created in, or present in, bearing assembly 200, but such magnets
are also effective in attracting and retaining magnetic particles
outside of bearing assembly 200 before such magnetic particles can
make their way into bearing assembly 200.
[0059] Thus, embodiments of the present invention represent a
material improvement over known particle control methods and
devices, such as meshes and screens, at least because such known
particle control methods and devices are generally incapable of
removing harmful particles, already present, or created in, bearing
assembly 200, which may serve to compromise the safe and reliable
operation of bearing assembly 200. Known particle control methods
and devices are likewise incapable of attracting and retaining
those particles located outside of bearing assembly 200. As
suggested below, this represents a significant limitation.
[0060] It will be appreciated that embodiments of bearing assembly
200 provide additional benefits and features when employed in the
context of x-ray tubes. For example, magnet(s) 226 serve to attract
and retain particles present, or created within, bearing assembly
200, as well as attracting and retaining particles present located
elsewhere in x-ray tube 200 (not shown). Consequently, embodiments
of the present invention facilitate, among other things, the safe,
effective, and reliable operation of x-ray tube 100 by attracting
and securely retaining particles that, left unchecked, would
otherwise contribute to the occurrence of undesirable effects such
as high voltage arcing inside x-ray tube 100. By reducing or
eliminating the likelihood of high voltage arcing, embodiments of
the present invention thereby serve to improve the safety and
reliability of x-ray tube 100, as well as extend the life of
components including, but not limited to, electron source 104 (not
shown) and anode 106 (not shown), and thus contribute to a relative
increase in the operational life of x-ray tube 100 as a whole.
[0061] In this regard at least, the "active" approach represented
by embodiments of the present invention represent an advancement in
the art over more "passive" approaches such as screens, meshes and
the like which passively confine particles within a predefined
area, but which are incapable of actively attracting and retaining
particles, wherever located, that could prove detrimental to the
operation of bearing assembly 200 and/or the device within which
such bearing assembly 200 is employed.
[0062] As suggested above, the present invention contemplates as
within its scope a variety of magnet configurations and
arrangements. Accordingly, attention is directed now to FIGS. 3A
through 3C where details are provided regarding exemplary
configurations and arrangements of magnet(s) 226. With respect to
embodiments contemplated by the present invention, it will be
appreciated that regardless of the magnet arrangement employed,
magnet(s) 226 should generally be arranged symmetrically about the
axis of rotation of shaft 202 (and thus, the axis of rotation of
target anode 106) so as to foreclose unbalanced rotation, and
attendant vibration, of shaft 202 that could impair the operation
of bearing assembly 200 and x-ray tube 100.
[0063] Directing particular attention now to FIGS. 3A and 3B, a two
piece split magnet 226, preferably substantially circular in shape,
is provided which comprises first magnet portion 226A and second
magnet portion 226B, each of which is attached to the underside of
rotor hub 202A and is thereby positioned to attract and reliably
retain magnetic particles produced in bearing assembly 200 and/or
other portions of x-ray tube 100. Preferably, first magnet portion
226A and second magnet portion 226B are arranged so that the south
pole of one magnet is adjacent the north pole of the other magnet.
Such an arrangement enhances the strength of the magnetic field
produced by first magnet portion 226A and second magnet portion
226B, and thereby improves the overall effectiveness of such
magnets in attracting and retaining magnetic particles.
[0064] As suggested in FIG. 3C, the present invention also
contemplates as within its scope configurations employing a
plurality of magnets disposed in various arrangements. In the
illustrated embodiment, a total of six magnets, 226A through 226F,
each being preferably cylindrical in shape, are equally spaced
about the underside of rotor hub 202A. Finally, while not
specifically illustrated, it will be appreciated that in an
alternative embodiment, a cylindrical magnet 226, comprising one or
more segments, may be attached about shaft 202, proximate front
bearing ring 208, so as to reliably attract and retain particles
present, or generated, within or without bearing assembly 200.
[0065] Directing attention now to FIGS. 4A through 4C, details
regarding various other exemplary configurations and arrangements
of magnet(s) 226 are provided. In the illustrated embodiments, one
or more magnet(s) 226 are attached to bearing housing 222 of
bearing assembly 200, proximate front bearing ring 208. As in the
case of the various embodiments illustrated in FIGS. 3A and 3B, it
will be appreciated that magnet(s) 226 may comprise a single magnet
having one or more constituent portions, or alternatively, a
plurality of smaller magnets arranged in a desired configuration,
such as magnets 226A through 226F (FIG. 4C). Finally, magnet(s) 226
may, as in the case of other embodiments contemplated hereby, be
attached to bearing housing 222 by magnetic attraction or, if
required, by various types of fasteners, such as crimping them in
place or by metallurgical bonding, such as brazing.
[0066] Finally, directing attention to FIG. 5, yet another
alternative embodiment is indicated. In particular, one or more
magnet(s) 226 are disposed about the circumference of shaft 202.
Magnet(s) 206 are thus well positioned to attract and retain
foreign matter present or created in bearing assembly 200, as well
as foreign matter outside of bearing assembly 200.
[0067] It will be appreciated that in view of the discussion
presented herein, embodiments of the present invention provide for
considerable latitude regarding aspects such as the design and
employment of magnet(s) 226. For example, it will be appreciated
that variables pertaining to magnet(s) 226 including, but not
limited to, size, number, location, positioning, geometry,
orientation of magnetic polarization, magnetic strength,
composition, and the like may be varied either alone or in various
combinations as required to suit a particular application and/or to
facilitate achievement of one or more desired results. Accordingly,
the embodiments of the invention discussed and illustrated herein
are exemplary only and should not be construed to limit the scope
of the present invention in any way.
[0068] The present invention may be embodied in other specific
forms without departing from its spirit or essential
characteristics. The described embodiments are to be considered in
all respects only as illustrative and not restrictive. The scope of
the invention is, therefore, indicated by the appended claims
rather than by the foregoing description. All changes which come
within the meaning and range of equivalency of the claims are to be
embraced within their scope.
* * * * *