Information
-
Patent Grant
-
6570961
-
Patent Number
6,570,961
-
Date Filed
Wednesday, July 25, 200122 years ago
-
Date Issued
Tuesday, May 27, 200321 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Patnode; Patrick K.
- Cabou; Christian G.
-
CPC
-
US Classifications
Field of Search
US
- 378 132
- 378 119
- 378 125
- 378 127
- 378 130
- 378 141
- 378 143
- 378 144
-
International Classifications
-
Abstract
X-ray source bearing assemblies are described herein. In an exemplary embodiment, an x-ray source includes a target anode, a rotor shaft coupled to the target anode, and a motor coupled to the rotor shaft at an end of the shaft opposite the target anode. The bearing housing, in the exemplary embodiment, includes a rotor bore, the rotor shaft extending through said rotor bore and supported therein by a plurality bearings. The housing and the shaft form a cooling medium pool so that as the shaft rotates, a cooling medium in the pool is radially displaced.
Description
BACKGROUND OF INVENTION
This invention relates generally to x-ray sources, and more particularly to an x-ray source bearing assembly for facilitating heat dissipation.
In medical x-ray imaging, an x-ray source is utilized for generating x-ray beams that pass through an object being imaged. More specifically, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as an “imaging plane”. The x-ray beam passes through an object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at a detector array is dependent upon the attenuation of the x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile.
A typical x-ray source includes an x-ray tube which emits an x-ray beam at a focal spot. Known x-ray tubes include a cathode aligned with a rotating target anode. An electron beam generated at a cathode emitter is directed towards the anode and forms a focal spot on an anode surface. As a result, x-ray beams are emitted from the anode.
The target anode is rotated by a rotor shaft coupled to a motor. Specifically, the rotor shaft extends from the motor, through a bearing housing, to the anode. The shaft is supported by bearings contained in the bearing housing, and rotates relative to the bearing housing.
During operation, the motor rotates, or drives, the rotor shaft to rotate, and the target anode rotates with the shaft. Rotation of the shaft on the bearings results in heat being generated in the bearing housing. The heat generated by the rotating shaft should be dissipated in order to avoid failure of the x-ray tube bearings.
SUMMARY OF INVENTION
In one aspect, an x-ray source including a cooling medium pool for cooling rotor shaft bearings is provided. In an exemplary embodiment, the x-ray source includes a target anode, a rotor shaft coupled to the target anode, and a motor coupled to the rotor shaft at an end of the shaft opposite the target anode. The source further includes a bearing housing including a rotor bore. The rotor shaft extends through the rotor bore and is supported therein by a plurality of bearings. The bearing housing and the rotor shaft form a cooling medium pool so that as the rotor shaft rotates, a cooling medium in the cooling medium pool is radially displaced.
In another aspect, a method for assembling a rotor shaft and a bearing housing is provided. The bearing housing has a rotor bore therethough and includes a first bearing containment section and a second bearing containment section. The method includes the steps of locating the first bearing containment section so that the rotor shaft extends therethrough and so that an outer race of the first bearing containment section aligns with an inner race of the rotor shaft, and locating the second bearing containment section so that the rotor shaft extends therethrough and so that an end section of the second bearing containment section mates with the first section, and welding the first bearing containment section to the second bearing containment section.
In yet another aspect, a bearing housing and rotor shaft is provided The bearing housing includes a rotor bore, and the rotor shaft extends through the rotor bore and is supported therein by a plurality bearings. The bearing housing and the rotor shaft form a cooling medium pool so that as the shaft rotates, a cooling medium in the pool is radially displaced.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a schematic illustration of an x-ray tube;
FIG. 2
is a cross-sectional side view of a portion of a bearing housing;
FIG. 3
is a side view of a rotor shaft;
FIG. 4
is a front view of a rotor collar;
FIG. 5
is a side view of the rotor collar shown in
FIG. 4
; and
FIG. 6
is a partial cross section of the assembly of the rotor shaft disposed in the bearing housing.
DETAILED DESCRIPTION
Although specific embodiments of a bearing housing and rotor assembly, sometimes referred to herein as a bearing housing assembly, are described herein in the context of an exemplary x-ray source, such assembly is not limited to practice with such exemplary x-ray source and can be utilized in connection with other x-ray sources. In addition, the exemplary x-ray source is sometimes described in the context of a computed tomography (CT) machine, and more specifically, a third generation CT machine. The bearing housing and rotor assembly can, however, be utilized in connection with other types of x-ray machines. Therefore, the description of the bearing housing and rotor assembly in connection with an x-ray source for a CT machine is exemplary only.
FIG. 1
is a schematic illustration of a typical x-ray source
10
, sometimes referred to as an x-ray tube. Tube
10
includes a glass envelope
12
which at one end
14
has a cathode support
16
sealed into it. The electron emissive filament of a cathode is mounted on insulators located in a focusing cup
18
which focuses an electron beam against a beveled annular focal track area
20
of a rotating x-ray target
22
. Target
22
is supported on a rotor shaft
24
that extends from a bearing housing and rotor assembly
26
.
During operation, a rotating magnetic field induced in the motor rotor causes rotor shaft
24
to rotate. In addition, an electron beam is emitted from cathode cup
18
and is focused on beveled annular focal track area
20
of x-ray target
22
. The electrons of beam collide with anode
22
and as a result, x-ray beams are generated. A focal spot is formed on the anode surface by the electron beam, and the x-ray beams emanate from the focal spot. The x-ray beams pass through a window in glass envelope
12
and pass through an object being imaged, such as a patient.
Rotor shaft
24
rotates on bearings contained within a bearing housing
28
. If the bearings deteriorate, then shaft
24
may rotate at a speed slower than an expected speed. Such deterioration also may result in undesired movement, or wobbling, of target anode
22
. Bearing deterioration therefore can adversely impact the characteristics of the x-ray beam emitted from x-ray source
10
.
Bearing deterioration can be caused, for example, by failure to dissipate heat generated as rotor shaft
24
rotates on the bearings. To facilitate such heat dissipation, an oil cooling path typically is provided within bearing housing
28
so that oil flows axially relative to shaft
24
. Heat is transferred to, and dissipated by, the axially flowing oil. While such axial flow paths have generally provided acceptable results, it would be beneficial to further enhance bearing cooling to extend bearing life.
FIG. 2
is a cross-sectional side view of a portion of an exemplary embodiment of a bearing housing
50
. Bearing housing
50
is generally cylindrical and includes a first bearing containment section
52
and a second pool containment section
54
. First bearing containment section
52
includes a bearing outer race
56
and a first section sealing cavity
58
located at an end
60
of a flange
62
. First section sealing cavity
58
, as described below in more detail, captures incidental leakage of a coolant medium
190
from a cooling medium pool
200
as described below in more detail. First section sealing cavity
58
, in the exemplary embodiment, is 2 mm ×2 mm. First bearing containment section
52
also includes an annular weld preparation groove
64
in an outer surface
66
.
Second pool containment section
54
includes an end section
70
that mates with first containment section flange
62
. Second section
54
also includes, in an outer surface
72
, a first annular weld preparation groove
74
near an end
76
and a second annular weld preparation groove
78
spaced from first groove
74
.
When end section
70
is mated with first containment section flange
62
as shown in FIG.
2
and as described in more detail below, first and second sections
52
and
54
are welded together to form bearing housing
50
. Weld preparation grooves
64
,
74
and
78
facilitate forming a reliable weld. A rotor bore
80
extends through housing
50
and is sized to receive a rotor shaft coupled at one end to a motor and at its other end to a target anode.
Second section
54
also includes a second section sealing cavity
82
located at an end
84
of a flange
86
. Second section sealing cavity
82
, in the exemplary embodiment, is 2 mm ×2 mm. A cooling medium containment wall
88
is radially outward relative to second section sealing cavity
82
. More specifically, first section sealing cavity
58
and second section sealing cavity
82
define perimeters of the cooling medium pool
200
. In addition, cooling medium containment wall
88
defines a radially outermost perimeter of the cooling medium pool
200
. As described in more detail below, first section sealing cavity
58
and second section sealing cavity
82
cooperate with annular flanges on a rotor shaft to facilitate preventing leakage of the cooling medium
190
from the cooling medium pool
200
.
Second section
54
further includes an opening
90
for facilitating the injection of a cooling medium
190
into the cooling medium pool
200
, A counter-bore
92
adjacent opening
90
is provided to facilitate securing a plug within opening
90
to prevent the leakage of the cooling medium
190
[coolant] from the cooling medium pool
200
. The plug is removable so that additional cooling medium
190
can be placed in the cooling medium pool
200
.
Referring to
FIG. 3
, which is a side view of an exemplary rotor shaft
100
, shaft
100
is sized to be inserted within rotor bore
80
of housing
50
. One end
102
of rotor shaft
100
is configured to be coupled to a motor, i.e., a motor coupling, and another end
104
of rotor shaft
100
is configured to be coupled to a target anode, i.e., a target anode coupling. The specific configuration of ends
102
and
104
is dictated by the coupling arrangements utilized for the motor and the target anode.
Rotor shaft
100
of
FIG. 6
also includes an inner race
106
and a flange
110
. A wall
108
of flange
110
and a wall
112
of target anode coupling
114
contain bearings
300
within the inner race
106
. As explained above, the bearing housing
50
includes outer race
56
, and multiple bearings
300
are trapped between the outer race
56
and the inner race
106
when rotor shaft
100
and bearing housing
50
are assembled.
Rotor shaft
100
further includes annular flange
116
, spaced apart from flange
110
with a radially inward containment wall
118
extending there between. Each flange
110
and
116
aligns with one of cavities
58
and
82
, and together with one of respective cavities
58
and
82
, forms a barrier to prevent the cooling medium
190
from leaking out of the cooling medium pool
200
.
FIG. 4
is a front view of a rotor collar
150
, and
FIG. 5
is a side view of collar
150
. Collar
150
includes a first section
152
and a second section
154
, and is sized to fit between first and second flanges
110
and
116
of rotor shaft
100
. Collar
150
facilitates maintaining the cooling medium
190
within the cooling medium pool
200
.
To assemble rotor shaft
100
of FIG.
6
and bearing housing
50
, first bearing containment section
52
of bearing housing
50
is pushed over rotor shaft
100
so that outer race
56
is positioned over inner race
106
, and so that first section sealing cavity
58
is aligned with flange
110
. Ball bearings
300
are located within, and trapped in the space between outer race
56
and inner race
106
.
End
102
of rotor shaft
100
is coupled to a motor and rotor shaft end
104
is coupled to a target anode. A cooling medium
190
is then injected into the cooling medium pool
200
via opening
90
Exemplary cooling mediums include liquid metal (e.g., gallium indium tin) and oil. Once the cooling medium pool
200
is full, a plug is then inserted into opening
90
to prevent leakage.
End
102
of rotor shaft
100
is coupled to a motor and rotor shaft end
104
is coupled to a target anode. A cooling medium is then injected into the pool via opening
90
. Exemplary cooling mediums include liquid metal (e.g., gallium indium tin) and oil. Once the pool is full, a plug is then inserted into opening
90
to prevent leakage.
Bearing housing
50
and shaft
100
are fabricated from, for example, hardened steel (e.g., Rockwell
60
62
hardened). By way of example and not limitation, and with respect to the specific embodiment illustrated in
FIGS. 2
,
3
, and
4
, the following dimensions (in mm) correspond to the dimensions indicated by corresponding letters in the figures.
a
9
.
2
+/−
0
.
001
b
4
.
6
c
4
.
69
d
4
.
9
e
31
.
98
+/−
0
.
01
f
22
.
6
+/−
0
.
1
g
28
.
6
h
9
i
18
j
4
.
5
k
18
.
0
l
22
.
50
+/−
0
.
003
m
20
.
04
min
n
5
.
3
o
9
.
0
During operation, rotor shaft
100
rotates relative to housing
50
. The bearings
300
support rotor shaft
100
and facilitate such relative rotation. Heat generated by the bearings
300
is transferred to the walls of bearing housing
50
and rotor shaft
100
. Because the cooling medium
190
is in flow communication with rotor shaft
100
, the cooling medium
190
dissipates heat from rotor shaft
100
. In addition, the cooling medium
190
is displaced within and towards the perimeter of the cooling medium pool
200
by the centrifugal forces generated by rotating shaft
100
. The cooling medium
190
; therefore, is forced against the cooling medium containment wall
88
, which facilitates heat transfer from the cooling medium
190
to the cooling medium containment wall
88
.
FIG. 6
provides a partial cross sectional view of the bearing housing/rotor assembly
26
in one embodiment of the present invention. In one particular embodiment of the present invention,
FIG. 6
provides a view of the rotor shaft
100
of Fig,
3
disposed in the rotor bore
80
of
FIG. 2
of the bearing housing
50
. The interaction of the flange
110
, the annular flange
116
, the rotor collar
150
that are disposed on the rotor shaft
100
to the first section sealing cavity
58
, the second section sealing cavity
82
, and the cooling medium containment wall
88
that are disposed on the bearing housing
50
, which forms the perimeter of the cooling medium pool
200
is discussed above with regard to
FIGS. 2 and 3
and is presented in one embodiment of the present invention in FIG.
6
. The cooling medium
190
is depicted as being disposed in the cooling medium pool
200
as discussed above with regards to FIG.
2
. Additionally,
FIG. 6
depicts the interaction between the bearing housing
50
, the bearings
300
, and the rotor shaft
100
as discussed above with regards to
FIGS. 2-3
.
The above described assembly of the bearing housing
50
and the rotor shaft
100
facilitates dissipating heat generated by the bearings
300
. As explained above, improving heat dissipation can lead to extended bearing life as well as consistent operation of the x-ray source
10
.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
Claims
- 1. An x-ray source, comprising:a target anode; a rotor shaft coupled to said target anode; a motor coupled to said rotor shaft at an end of said rotor shaft opposite said target anode; and a bearing housing comprising a rotor bore, said rotor shaft extending through said rotor bore and supported therein by a plurality of bearings, said bearing housing and said rotor shaft forming a cooling medium pool so that as said rotor shaft rotates, a cooling medium in said cooling medium pool is radially displaced, said bearing housing being generally cylindrical and comprising a first bearing containment section and a second pool containment section, said first bearing containment section comprising a bearing outer race surface and a first section sealing cavity being located at an end of a flange, said second pool containment section comprising an end section, a second section sealing cavity, and a cooling medium containment wall, said end section being disposed to mate with said first bearing containment section, said cooling medium containment wall being disposed radially outward relative to said second section sealing cavity, said first section sealing cavity and said second section sealing cavity defining perimeters of said cooling medium pool, and said cooling medium containment wall defining a radially outermost perimeter of cooling medium pool, said rotor shaft further comprises a flange and an annular flange, said flange and said annular flange being spaced apart, and a collar being disposed to extend therebetween, said flange being aligned with said first section sealing cavity, said annular flange being aligned with said second section sealing cavity, and said collar being aligned with said cooling medium containment wall.
- 2. The x-ray source according to claim 1, wherein said rotor shaft comprises an inner race, and said bearing housing comprises an outer race, and a plurality of bearings are trapped between said outer race and said inner race.
- 3. The x-ray source according to claim 1, wherein said rotor collar comprises a first section and a second section, wherein both said first section and said second section are sized to fit between said flange and said annular flange.
- 4. The x-ray source according to claim 3, wherein said first section and said second section are disposed to be fastened together.
- 5. An assembly comprising:a bearing housing; and a rotor shaft; said bearing housing comprising a rotor bore, said rotor shaft extending through said rotor bore and supported therein by a plurality of bearings, said bearing housing and said rotor shaft forming a cooling medium pool so that as said rotor shaft rotates, a cooling medium being disposed in said cooling medium pool is radially displaced. said bearing housing being generally cylindrical and comprising a first bearing containment section and a second pool containment section, said first bearing containment section comprising a bearing outer race surface and a first section sealing cavity being disposed at an end of a flange, said second pool containment section comprising a second section sealing cavity, a cooling medium containment wall, and an end section being disposed to mate with said first bearing containment section, said cooling medium containment wall being disposed radially outward relative to said second section sealing cavity, said first section sealing cavity and said second section sealing cavity defining perimeters of said cooling medium pool, and said cooling medium containment wall defining a radially outermost perimeter of cooling medium pool, said rotor shaft further comprising a flange and an annular flange, said flange and said annular flange being spaced apart, and a collar being disposed to extend therebetween, said flange being aligned with said first section sealing cavity, said annular flange being aligned with said second section sealing cavity, and said collar being aligned with said cooling medium containment wall.
- 6. The assembly according to claim 5, wherein said rotor shaft comprises an inner race, and said bearing housing comprises an outer race, and a plurality of bearings are trapped between said outer race and said inner race.
- 7. The assembly according to claim 5, wherein said rotor collar comprises a first section and a second section, wherein both said first section and said second section are sized to fit between said flange and said annular flange.
US Referenced Citations (7)