Rotary anode type X-ray tube

1. A rotary anode X-ray tube, comprising:

a vacuum envelope;

a cathode arranged within the vacuum envelope, which emits an electron beam;

a rotary anode arranged within the vacuum envelope, on which the electron beam impinges to generate X-rays;

a rotary structure supporting the rotary anode, including a cylindrical portion having two open ends and a rotor section provided for generating a rotating force to rotate the cylindrical portion together with the rotary anode, the rotary anode fixed to the cylindrical portion and arranged within the vacuum envelope, the rotary anode being arranged around the cylindrical portion so that a center of gravity of the rotary anode with the rotary structure is in the cylindrical portion;

a stationary shaft having two ends and an axis, and including a middle section having two ends, which is fitted into the cylindrical portion, a first section extending along the axis between one end of the middle section and one end of the stationary shaft and having a first shaft length, a second section extending along the axis between the other end of the middle section and the other end of the stationary shaft and having a second shaft length, the first shaft length being larger than the second shaft length, a transverse stiffness of the second section being larger than a transverse stiffness of the first section, and the center of gravity is positioned in the middle section;

a dynamic pressure radial bearing arranged between the cylindrical portion and the middle section of the stationary shaft; and

first and second supporting sections arranged within and fixed to the vacuum envelope, the second supporting section fixedly supporting the second section such that the second section does not slide, and the first supporting section supporting the first section in such a manner that the first section is configured to slide on the first supporting section.

2. The rotary anode X-ray tube according to claim 1 , wherein a bending rigidity of the first section is smaller than a bending rigidity of the second section.

3. The rotary anode X-ray tube according to claim 1 , wherein the stationary shaft is columnar, and a diameter of the first section is smaller than a diameter of the second section.

4. The rotary anode X-ray tube according to claim 1 , wherein the first section is in a form of a hollow cylinder having a void formed therein.

5. The rotary anode X-ray tube according to claim 2 , wherein the first section is formed of a first material having a first Young's modulus, and the second section is formed of a second material having a second Young's modulus.

6. The rotary anode X-ray tube according to claim 1 , wherein the first section of the stationary shaft is capable of tilting at the first supporting section.

7. The rotary anode X-ray tube according to claim 1 , wherein the stationary shaft is deformed due to a centrifugal force applied to the rotary anode in such a way that a peak of displacement distribution along the axis of the stationary shaft is located in the first section of the stationary shaft.

8. The rotary anode X-ray tube according to claim 1 , further comprising:

a second dynamic pressure radial bearing arranged between the cylindrical portion and the middle section of the stationary shaft, the center of gravity of the rotary anode and the rotary structure being positioned between the first and the second radial bearings.

9. The rotary anode X-ray tube according to claim 8 , wherein the stationary shaft is deformed due to a centrifugal force applied to the rotary anode in such a way that a peak of displacement distribution along the axis of the stationary shaft is located in the radial bearing closer to the first section of the stationary shaft.

10. The rotary anode X-ray tube according to claim 8 , wherein the stationary shaft is deformed due to a centrifugal force applied to the rotary anode in such a way that a peak of displacement distribution along the axis of the stationary shaft is located in the first section of the stationary shaft.

11. A computed tomography apparatus comprising:

a rotary anode X-ray tube including:

a vacuum envelope;

a cathode arranged within the vacuum envelope, which emits an electron beam;

a rotary anode arranged within the vacuum envelope, on which the electron beam impinges to generate X-rays;

a rotary structure supporting the rotary anode, including a cylindrical portion having two open ends and a rotor section provided for generating a rotating force to rotate the cylindrical portion together with the rotary anode, the rotary anode fixed to the cylindrical portion and arranged within the vacuum envelope, the rotary anode being arranged around the cylindrical portion so that a center of gravity of the rotary anode with the rotary structure is in the cylindrical portion;

a stationary shaft having two ends and an axis, and including a middle section having two ends, which is fitted into the cylindrical portion, a first section extending along the axis between one end of the middle section and one end of the stationary shaft and having a first shaft length, a second section extending along the axis between the other end of the middle section and the other end of the stationary shaft and having a second shaft length, the first shaft length being larger than the second shaft length, a transverse stiffness of the second section being larger than a transverse stiffness of the first section, and the center of gravity is positioned in the middle section;

a dynamic pressure radial bearing arranged between the cylindrical portion and the middle section of the stationary shaft; and

first and second supporting sections arranged within and fixed to the vacuum envelope, the second supporting section fixedly supporting the second section such that the second section does not slide, and the first supporting section supporting the first section in such a manner that the first section is configured to slide on the first supporting section.