Rotating anode X-ray tube

1. A rotating anode X-ray tube comprising:

a fixed shaft comprising a small-diameter portion and a large-diameter portion; the small-diameter portion being cylindrical formed, and including a first radial bearing surface including a pair of first grooved surfaces and a first plane surface located between the first grooved surfaces; the large-diameter portion being cylindrically formed to be larger in outer diameter than the small-diameter portion, provided coaxially with the small-diameter portion, and including a second radial bearing surface including a pair of second grooved surfaces and a second plane surface located between the second grooved surfaces;

a rotor cylindrically formed to extend coaxially with the fixed shaft, and comprising a third radial bearing surface which surrounds an outer periphery of the fixed shaft, and is located opposite to the first radial bearing surface and the second radial bearing surface;

a lubricant filled in a gap between the fixed shaft and the rotor and to be drawn by the first and second grooved surfaces;

a target provided closer to the large-diameter portion than to the small-diameter portion along an axis of the fixed shaft; and

a supporting member joined to the target and part of the rotor which is located opposite to the small-diameter portion,

wherein

an entire area of the first radial bearing surface is larger than an entire area of the second radial bearing surface,

where g 1 is a gap between the first radial bearing surface and the third radial bearing surface, and g 2 is a gap between the second radial bearing surface and the third radial bearing surface, the formula “g 1 >g 2 ” is satisfied, and

where S 1 a is an entire area of each of the first grooved surfaces, S 1 b is an entire area of the first plane surface, S 2 a is an entire area of each of the second grooved surfaces, and S 2 b is an entire area of the second plane surface, the formulas “½<S 1 b /S 1 a ” and “S 2 b /S 2 a< ½” are satisfied.

2. The rotating anode X-ray tube of claim 1 , wherein where r is a radius of the large-diameter portion, an outer diameter of the small-diameter portion is smaller than an outer diameter of the large-diameter portion by ⅓×r× 1/1000 to r× 1/1000.

3. The rotating anode X-ray tube of claim 1 , wherein the formulas “½<S 1 b /S 1 a ≤5/1” and “0/1≤S 2 b /S 2 a< ½” are satisfied.

4. The rotating anode X-ray tube of claim 1 , wherein the rotor, the target and the supporting member form a rotation unit, and where D 1 is a distance from a center of gravity of the rotation unit to a center of the first radial bearing surface along the axis, S 1 is the entire area of the first radial bearing surface, D 2 is a distance from the center of gravity of the rotation unit to a center of the second radial bearing surface along the axis, and S 2 is the entire area of the second radial bearing surface, the formula “D 2 ×S 2 <D 1 ×S 1 ” is satisfied.

5. The rotating anode X-ray tube of claim 4 , wherein the formula “1.2×D 2 ×S 2 <D 1 ×S 1 ” is satisfied.

6. The rotating anode X-ray tube of claim 1 , wherein:

the first plane surface is a smooth outer peripheral surface, and

the second plane surface is a smooth outer peripheral surface.

7. The rotating anode X-ray tube of claim 1 , wherein:

each of the first grooved surfaces is an uneven surface in which a plurality of first patterned portions are formed along a smooth outer peripheral surface;

the first patterned portions are arranged along the smooth outer peripheral surface and recessed with respect to the outer peripheral surface;

each of the second grooved surfaces is an uneven surface in which a plurality of second patterned portions are formed along a smooth outer peripheral surface; and

the second patterned portions are arranged along the smooth outer peripheral surface and recessed with respect to the outer peripheral surface.

8. The rotating anode X-ray tube of claim 1 , wherein the fixed shaft includes therein space for circulating a cooling fluid.