Rotating anode type X-ray tube

1. A rotating anode type X-ray tube, comprising:

a fixed shaft having a first surface intersecting a direction parallel to a rotation axis;

a rotor supported by dynamic pressure bearings including a lubricant put into a gap between the fixed shaft and the rotor to rotate about the rotation axis around the fixed shaft;

a cathode emitting electrons; and

an anode target provided at the rotor to generate X-rays by electrons emitted from the cathode colliding with the anode target,

wherein

the rotor comprises:

a first cylinder having a second surface intersecting a direction parallel to the rotation axis;

a second cylinder being in contact with the second surface and facing the first surface via the lubricant; and

a third cylinder facing the second cylinder, the second cylinder being located between the third cylinder and the first and second surfaces,

a first threaded portion is provided on an inner surface of the first cylinder,

a second threaded portion is provided on an outer peripheral surface of the third cylinder,

the second threaded portion is screwed into the first threaded portion, and

a screw member is screwed in a third threaded portion provided on an inner peripheral surface of a hole which penetrates the third cylinder in the direction parallel to the rotation axis, and a tip portion of the screw member presses the second cylinder against the second surface.

2. The rotating anode type X-ray tube of claim 1 , wherein

the fixed shaft has a first outer peripheral surface, a second outer peripheral surface, and a third outer peripheral surface,

the third outer peripheral surface is provided between the first outer peripheral surface and the second outer peripheral surface,

the third outer peripheral surface has a diameter larger than each of the first outer peripheral surface and the second outer peripheral surface,

the first cylinder has a first inner peripheral surface facing the first outer peripheral surface, a second inner peripheral surface having a diameter larger than the first inner peripheral surface and provided with the first threaded portion, and a third inner peripheral surface which has a diameter larger than the first inner peripheral surface and smaller than the second inner peripheral surface,

the third inner peripheral surface faces the third outer peripheral surface, and

the first surface includes a surface connecting the second outer peripheral surface with the third outer peripheral surface, and the second surface includes a surface connecting the second inner peripheral surface with the third inner peripheral surface.

3. The rotating anode type X-ray tube of claim 1 , wherein

the fixed shaft has a first outer peripheral surface extending from a tip of the fixed shaft, and a second outer peripheral surface having a diameter smaller than the first outer peripheral surface,

the first cylinder has a first inner peripheral surface facing the first outer peripheral surface via the lubricant, and a second inner peripheral surface having a diameter larger than the first inner peripheral surface,

the first threaded portion is provided on the second inner peripheral surface, and

the first surface includes a surface connecting the first outer peripheral surface with the second outer peripheral surface, and the second surface includes a surface connecting the first inner peripheral surface with the second inner peripheral surface.

4. A rotating anode type X-ray tube, comprising:

a fixed shaft having a first surface intersecting a direction parallel to a rotation axis;

a rotor supported by dynamic pressure bearings including a lubricant put into a gap between the fixed shaft and the rotor to rotate about the rotation axis around the fixed shaft;

a cathode emitting electrons; and

an anode target provided at the rotor to generate X-rays by electrons emitted from the cathode colliding with the anode target,

wherein

the rotor comprises:

a first cylinder having a second surface intersecting a direction parallel to the rotation axis;

a second cylinder being in contact with the second surface and facing the first surface via the lubricant;

a third cylinder facing the second cylinder, the second cylinder being located between the third cylinder and the first and second surfaces; and

a fourth cylinder connected to the first cylinder,

a first threaded portion is provided on an inner surface of the fourth cylinder,

a second threaded portion is provided on an outer peripheral surface of the third cylinder,

the second threaded portion is screwed into the first threaded portion, and

a screw member is screwed in a third threaded portion provided on an inner peripheral surface of a hole which penetrates the third cylinder in the direction parallel to the rotation axis, and a tip portion of the screw member presses the second cylinder against the second surface.

5. The rotating anode type X-ray tube of claim 4 , wherein

the fixed shaft has a first outer peripheral surface, a second outer peripheral surface, and a third outer peripheral surface,

the third outer peripheral surface is provided between the first outer peripheral surface and the second outer peripheral surface,

the third outer peripheral surface has a diameter larger than each of the first outer peripheral surface and the second outer peripheral surface,

the first cylinder has a first inner peripheral surface facing the first outer peripheral surface, a second inner peripheral surface having a diameter larger than the first inner peripheral surface and provided with the first threaded portion, and a third inner peripheral surface which has a diameter larger than the first inner peripheral surface and smaller than the second inner peripheral surface,

the third inner peripheral surface faces the third outer peripheral surface, and

the first surface includes a surface connecting the second outer peripheral surface with the third outer peripheral surface, and the second surface includes a surface connecting the second inner peripheral surface with the third inner peripheral surface.

6. The rotating anode type X-ray tube of claim 4 , wherein

the fixed shaft has a first outer peripheral surface extending from a tip of the fixed shaft, and a second outer peripheral surface having a diameter smaller than the first outer peripheral surface,

the first cylinder has a first inner peripheral surface facing the first outer peripheral surface via the lubricant, and a second inner peripheral surface having a diameter larger than the first inner peripheral surface,

the first threaded portion is provided on the second inner peripheral surface, and

the first surface includes a surface connecting the first outer peripheral surface with the second outer peripheral surface, and the second surface includes a surface connecting the first inner peripheral surface with the second inner peripheral surface.