X-ray or gamma ray systems or devices – Source – Target
Reexamination Certificate
2001-06-14
2002-09-10
Porta, David P. (Department: 2882)
X-ray or gamma ray systems or devices
Source
Target
C378S141000, C378S132000
Reexamination Certificate
active
06449339
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a rotary anode type X-ray tube and an x-ray tube apparatus provided with the same, particularly, to a rotary anode type X-ray tube equipped with a hydrodynamic type slide bearing having a spiral groove and an X-ray tube apparatus having the rotary anode type X-ray tube incorporated therein.
A rotary anode type X-ray tube comprises a rotary anode disk provided with a target region for emitting an X-ray, a rotary mechanism rotatably supporting the rotary anode disk directly or with a supporting shaft arranged therebetween, and a cathode for irradiating the target region with an electron beam. This rotary anode disk, the rotary mechanism and the cathode are arranged within a vacuum envelope. The rotary mechanism for supporting the rotary anode disk comprises a rotary structure having bearing sections formed between the rotary anode disk and the rotary mechanism and a stationary structure.
In the X-ray tube apparatus comprising the rotary anode type X-ray tube described above, a rotating magnetic field is generated from a stator electromagnetic coil arranged outside the vacuum envelope of the X-ray tube so as to rotate the rotary anode disk jointed to the rotating mechanism at high speed using the principle of an electromagnetic induction motor. As a result, the target region of the rotary anode disk is irradiated with the electron beam generated from the cathode so as to allow an X-ray to be emitted from the target region.
The rotary mechanism of the conventional rotary anode type X-ray tube, which rotatably supports the rotary anode disk, will now be described with reference to
FIGS. 1 and 2
. As shown in
FIGS. 1 and 2
, the rotary mechanism comprises a supporting shaft
31
. A rotary anode disk (not shown) provided with a target region made of a heavy metal and emitting an X-ray is fixed to the supporting shaft
31
. Also, a cylindrical rotor
32
for rotatably supporting the rotary anode disk is coupled with the supporting shaft
31
.
The rotor
32
is of a triple coaxial structure consisting of an outer cylinder
32
a
, an intermediate cylinder
32
b
, and an inner cylinder
32
c
having a bottom. The outer cylinder
32
a
and the intermediate cylinder
32
b
are brazed to each other to form an integral structure in an upper open region B
1
shown in FIG.
1
. Incidentally, the upper portion of the intermediate cylinder
32
b
is bonded directly to the supporting shaft
31
.
Further, the intermediate cylinder
32
b
and the inner cylinder
32
c
are brazed to each other to form an integral structure in a lower open portion shown in FIG.
1
. To be more specific, as apparent from
FIG. 2
showing a lateral cross section along the line II—II shown in
FIG. 1
, the outer cylinder
32
a
, the intermediate cylinder
32
b
and the inner cylinder
32
c
are arranged coaxial, and the intermediate cylinder
32
b
and the inner cylinder
32
c
are integrally bonded to each other by a brazed portion B
2
over the entire circumferential region in a lower end portion of the rotary mechanism.
A columnar stator (not shown) is inserted into the inner cylinder
32
c
of the rotor
32
with a small bearing clearance of about 20 &mgr;m provided between the outer circumferential surface of the stator and the inner circumferential surface of the inner cylinder
32
c
. The intermediate cylinder
32
b
is formed of, for example, a ferromagnetic material and also performs the function of a magnetism guiding section of the rotary magnetic field generated from a stator electromagnetic coil (not shown).
A heat insulating clearance G
1
having a size of, for example, about 0.5 mm in the radial direction is formed between the outer cylinder
32
a
and the intermediate cylinder
32
b
. Also, a heat insulating clearance G
2
having a size of, for example, about 1 mm in the radial direction is formed between the intermediate cylinder
32
b
and the inner cylinder
32
c.
During operation of the rotary anode type X-ray tube, the target region of the rotary anode disk is irradiated with an electron beam, with the result that the rotary anode disk is heated to one thousand and several hundred degrees centigrade. The heat of the rotary anode disk is transmitted to the rotor via the supporting shaft, etc. so as to elevate the temperature of the hydrodynamic type slide bearing portion arranged between the inner cylinder
32
c
and the stator, thereby impairing the rotating characteristics of the rotor.
Such being the situation, the intermediate cylinder
32
b
that is bonded directly to the supporting shaft is generally formed of a material having a low heat conductivity in order to prevent the heat of the rotary anode disk from being transmitted to the bearing section as much as possible. Also, since heat is generated in the bearing section during operation, it is said to be desirable for the inner cylinder constituting the bearing surface to be formed of a material having a high heat conductivity in order to permit the generated heat to be dispersed and released efficiently to the outside.
As described above, the intermediate cylinder is formed of a material having a low heat conductivity, and the inner cylinder is formed of a material having a high heat conductivity. Naturally, the intermediate cylinder and the inner cylinder are formed of different materials, and the intermediate cylinder and the inner cylinder differ from each other in the thermal expansion coefficient in many cases. It follows that it is difficult in some cases to bond the intermediate cylinder and the inner cylinder by means of brazing.
To be more specific, where these cylinder members are bonded to each other by a welding material, e.g., by a gold brazing, it is necessary to heat the welding material to about 1100° C. Also, in the case of silver brazing, the welding material must be heated to about 800° C. What should be noted is that, if the intermediate cylinder and the inner cylinder differ from each other in the thermal expansion coefficient, a large difference is generated between the coupled size between the intermediate and inner cylinders at room temperature and the coupled sizes of the intermediate and inner cylinders at brazing temperature.
Suppose, for example, that the thermal expansion coefficient of the intermediate cylinder is higher than that of the inner cylinder. If the brazing is performed under the state that the intermediate and inner cylinders are exactly coupled at room temperature, the inner diameter of the intermediate cylinder is rendered larger than the outer diameter at the brazed portion of the inner cylinder under the high brazing temperature, with the result that it is possible for the intermediate and inner cylinders to be brazed to each other with a non-uniform clearance provided therebetween and with the axes of the intermediate and inner cylinders deviated from each other.
To be more specific, it is certainly possible for the intermediate cylinder and the inner cylinder to be brazed to each other with the axes of these two cylinders substantially aligned. Alternatively, it is also possible for an inconvenience to take place as shown in FIG.
3
. To be more specific, it is considered possible for the intermediate and inner cylinders to be brazed to each other with the axis Cr of the intermediate cylinder
32
b
inclined by a certain angle &agr; relative to the axis Co of the inner cylinder
32
c
with respect to the axis of the brazed portion B
1
.
Where the axes of the inner cylinder and the intermediate cylinder are deviated from each other, it is certainly possible to correct to some extent the unbalanced rotation by the processing after the brazing step. However, where the rotary structure is processed at room temperature, the balance of rotation is rendered poor at the high temperature during operation of the X-ray tube so as to render the rotation characteristics poor. Particularly, in a rotary anode type X-ray tube comprising a hydrodynamic slide bearing for high speed rotation having an angular speed of, for example, 6,000 rpm to 10,0
Gemmell Elizabeth
Kabushiki Kaisha Toshiba
Pillsbury & Winthrop LLP
Porta David P.
LandOfFree
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