X-ray or gamma ray systems or devices – Source – Electron tube
Reexamination Certificate
2002-02-22
2004-06-15
Patel, Harshad (Department: 2855)
X-ray or gamma ray systems or devices
Source
Electron tube
C378S133000
Reexamination Certificate
active
06751291
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-048641, filed Feb. 23, 2001, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rotary anode type X-ray tube, particularly, to a rotary anode type X-ray tube that permits preventing the bearing portion of the rotating mechanism rotatably supporting the anode target from being abraded.
2. Description of the Related Art
The rotary anode type X-ray tube is known as an electron tube in which a rotating anode target is irradiated with an electron beam so as to permit the anode target to emit an X-ray and is used in, for example, a medical diagnostic apparatus.
FIG. 1
is a cross sectional view schematically showing a part of the conventional rotary anode type X-ray tube. As shown in the drawing, the conventional rotary anode type X-ray tube comprises an anode target
91
arranged within a vacuum envelope (not shown). The anode target
91
is fixed to a support shaft
92
, and the support shaft
92
is joined to a rotating mechanism
93
.
The rotating mechanism
93
includes a rotor section and a stator section. The rotor section includes an intermediate rotor
94
joined to the support shaft
92
, an outside rotor
95
mounted to the outside surface of the intermediate rotor
94
, and an inside rotor
96
mounted to the inside surface of the intermediate rotor
94
. A stator
97
is inserted into the inner region of the inside rotor
96
so as to be coupled with the inside rotor
96
. That opening of the inside rotor
96
which corresponds to the right side in
FIG. 1
is sealed with a thrust ring
98
, and the stator
97
extends through the thrust ring
98
to the outside. Dynamic slide bearings which is so called as liquid film bearings or metal lubricated bearings are formed between the inside rotor
96
constituting the rotor section of the rotating mechanism
93
and the stator
97
constituting the stator section of the rotating mechanism
93
and between the thrust ring
98
and the stator
97
noted above. To be more specific, a pair of spiral grooves are formed in each of two regions apart from each other in the axial direction of, for example, the stator
97
, and a liquid metal lubricant is supplied into the spiral grooves and the peripheral regions thereof so as to form radial dynamic slide bearings
99
A and
99
B.
Also, a spiral groove of a herringbone pattern is formed on the edge surface of the stator
97
shown on the left side of
FIG. 1. A
liquid metal lubricant is also supplied into the spiral groove and the peripheral region thereof so as to form a thrust dynamic slide bearing
100
A,
100
B. Likewise, a spiral groove of a herringbone pattern is formed on the surface, which corresponds to the right side of
FIG. 1
, of the thrust ring
98
facing a stepped portion
97
A of the stator
97
, and a liquid metal lubricant is supplied into the spiral groove and the peripheral region thereof so as to form a thrust dynamic slide bearing
100
B. Incidentally, the letter “M” shown in
FIG. 1
denotes the tube axis.
In the rotary anode type X-ray tube of the construction described above, a dynamic slide bearing is used as a bearing of the rotating mechanism. However, a roller bearing such as a ball bearing is also used in the bearing of the rotating mechanism.
The dynamic slide bearing is not abraded during the rotation and, thus, burning is not generated in the bearing even where the dynamic slide bearing is rotated at a high speed. However, the rotor is brought into contact with the stator at the starting time of the rotation and when the rotation is stopped. Also, where the dynamic slide bearing is rotated at a low angular speed, the dynamic slide bearing performs its function under the state that the rotor is partly kept in contact with the stator so as to bring about a so-called “mixed lubricating state” in which the contact force and the dynamic pressure are exerted simultaneously. It follows that, if the load of the rotor is heavy, a large stress is imparted to the contact portion.
As a result, the bearing surface is abraded at the start-up time or when the rotation of the rotor is stopped. Alternatively, burning is generated, and the rotor and the stator are meshed with each other so as to bite each other in the contact portion, thereby lowering the durability. Also, where the rotor has a large moment of inertia, the energy that is generated when the rotation of the rotor is stopped is increased so as to lower the durability. Particularly, where the center of gravity of the rotating portion is positioned outside the bearing, the force applied to the contact portion is rendered greater than the actual load so as to give a detrimental effect to the durability.
It should also be noted that the dynamic slide bearing requires a large rotational torque at the start-up time of the rotation. It follows that a rotation starting apparatus generating a large torque is required so as to render the apparatus bulky and increase the power consumption. In addition, where the angular speed of rotation is increased, the heat generation derived from the shearing force of the liquid metal lubricant is increased so as to elevate the temperature of the liquid metal lubricant. If the temperature of the liquid metal lubricant is elevated, the viscosity of the liquid metal lubricant is lowered so as to shorten the life of the liquid metal lubricant.
On the other hand, the roller bearing is advantageous in that the construction of the bearing is simple so as to facilitate the manufacture of the bearing. Also, since the rotor is not brought into contact with the stator at the start-up time and when the rotation of the rotor is stopped, the abrasion of the rotor and the stator is prevented. However, the bearing surface is abraded under the state of a high speed rotation or under the state of a heavy load so as to bring about the cracking and increase the noise during the rotation, with the result that the rotational torque is increased so as to cause burning in the bearing and generate noises.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a rotary anode type X-ray tube capable of suppressing the abrasion in the bearing portion of the rotating mechanism so as to assure good rotating characteristics over a long period of time.
According to a first aspect of the present invention, there is provided a rotary anode type X-ray tube, comprising:
an anode target configured to emit an X-ray;
a rotating mechanism configured to rotatably support the anode target, including a rotor section and a stator section;
a vacuum envelope configured to house the anode target and the rotating mechanism; and
a bearing mechanism arranged between the rotor section and the stator section and including a dynamic slide bearing using a liquid metal lubricant and roller bearings.
According to a second aspect of the present invention, there is provided a rotary anode type X-ray tube, comprising:
an anode target configured to emit an X-ray;
a rotating mechanism configured to rotatably support the anode target, including a first rotor section to which the anode target is coupled, a second rotor section, a dynamic slide bearing being arranged between the first rotor section and the second rotor section, and a stator section, roller bearings being arranged between the second rotor section and the stator section; and
a vacuum envelope configured to house the anode target and the rotating mechanism.
Further, according to a third aspect of the present invention, there is provided a rotary anode type X-ray tube, comprising:
an anode target configured to emit an X-ray;
a rotating mechanism configured to rotatably supporting the anode target, including a first rotor section to which the anode target is coupled, a second rotor section, roller bearings being arranged between the first rotor section and the second rotor section, and a stato
Iwase Mitsuo
Nakamuta Hironori
Kabushiki Kaisha Toshiba
Patel Harshad
Pillsbury & Winthrop LLP
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