Patent Description:
Generally, an X-ray tube assembly is used as an X-ray source in medical and industrial equipment that uses X-rays to diagnose a subject. As the X-ray tube assembly, a rotating anode X-ray tube assembly including a rotating anode type X-ray tube is known.

The rotating anode X-ray tube assembly comprises a rotating anode X-ray tube that emits X-rays, a stator coil, and a housing that houses the rotating anode X-ray tube and stator coil. The rotating anode X-ray tube comprises a stationary shaft, a cathode that generates electrons, an anode target, a rotor, and an envelope. The rotor is formed in a cylindrical shape. The anode target is fixed to the rotor. A gap between the stationary shaft and the rotor is filled with a lubricant. The rotating anode X-ray tube uses dynamic pressure sliding bearings. The rotor rotates with the anode target due to a magnetic field generated by the stator coil. Furthermore, X-rays are emitted when electrons emitted from the cathode collide with the anode target.

Embodiments described herein aim to provide a sliding bearing unit that can obtain good bearing operation and a rotating anode X-ray tube provided with this sliding bearing unit.

According to one embodiment, there is provided a sliding bearing unit comprising: a stationary shaft that extends along a rotation axis and includes a first radial bearing surface on an outer peripheral surface; a rotor that is rotatable around the stationary shaft; and a lubricant. The rotor includes: a first cylinder extending along the rotation axis and formed in a tubular shape, and located surrounding the stationary shaft; and a second cylinder extending along the rotation axis and formed in a tubular shape, located between the stationary shaft and the first cylinder, including a second radial bearing surface on an inner peripheral surface, and whose operation is restricted so as not to rotate relative to the first cylinder. The lubricant is filled in a plurality of gaps between the stationary shaft, the first cylinder, and the second cylinder, and forms a dynamic pressure radial sliding bearing together with the first radial bearing surface and the second radial bearing surface.

According to another embodiment, there is provided a rotating anode X-ray tube comprising: a sliding bearing unit comprising a stationary shaft extending along a rotation axis and including a first radial bearing surface on an outer peripheral surface, a rotor rotatable around the stationary shaft, and a lubricant; an anode target; a cathode arranged facing the anode target; and an envelope housing the sliding bearing unit, the anode target, and the cathode, and fixing the stationary shaft. The rotor includes: a first cylinder extending along the rotation axis and formed in a tubular shape, and located surrounding the stationary shaft; and a second cylinder extending along the rotation axis and formed in a tubular shape, located between the stationary shaft and the first cylinder, including a second radial bearing surface on an inner peripheral surface, and whose operation is restricted so as not to rotate relative to the first cylinder. The lubricant is filled in a plurality of gaps between the stationary shaft, the first cylinder, and the second cylinder, and forms a dynamic pressure radial sliding bearing together with the first radial bearing surface and the second radial bearing surface. The anode target surrounds an outer peripheral surface of the first cylinder, and is fixed to the first cylinder.

Embodiments and comparative examples will be described hereinafter with reference to the accompanying drawings. Note that the disclosure is merely an example, and proper changes within the spirit of the invention, which are easily conceivable by a skilled person, are included in the scope of the invention as a matter of course. In addition, in some cases, in order to make the description clearer, the widths, thicknesses, shapes, etc., of the respective parts are schematically illustrated in the drawings, compared to the actual modes. However, the schematic illustration is merely an example, and adds no restrictions to the interpretation of the invention. Besides, in the specification and drawings, the same or similar elements as or to those described in connection with preceding drawings or those exhibiting similar functions are denoted by like reference numerals, and a detailed description thereof is omitted unless otherwise necessary.

In each of the following embodiments and comparative examples, a sliding bearing unit and a rotating anode X-ray tube assembly comprising this sliding bearing unit are described. The rotating anode X-ray tube assembly comprises a rotating anode X-ray tube and the like. Hereinafter, the rotating anode X-ray tube assembly is simply referred to as an X-ray tube assembly, and the rotating anode X-ray tube is simply referred to as an X-ray tube. The X-ray tube comprises the sliding bearing unit, an anode target, a cathode, and an envelope. The sliding bearing unit comprises a stationary shaft, a rotor, and a liquid metal (metal lubricant) as a lubricant, and uses a sliding bearing.

First, an X-ray tube assembly according to Comparative Example <NUM> will be described. <FIG> is an enlarged cross-sectional view showing a part of an X-ray tube <NUM> of Comparative Example <NUM>, and shows a state before heat is input to an anode target <NUM>. <FIG> is an enlarged cross-sectional view showing a part of the X-ray tube <NUM> of Comparative Example <NUM>, and shows a state until which heat is input to the anode target <NUM> and the anode target <NUM> is cooled.

As shown in <FIG>, the X-ray tube assembly according to Comparative Example <NUM> comprises the X-ray tube <NUM>. The X-ray tube <NUM> comprises a sliding bearing unit U, the anode target <NUM>, and the like. The sliding bearing unit U comprises a stationary shaft <NUM>, a rotor <NUM>, a liquid metal LM, and the like.

The stationary shaft <NUM> is formed in a tubular shape and extends along a rotation axis a. A radial bearing surface S11a is formed on an outer peripheral surface of the stationary shaft <NUM>. The rotor <NUM> is formed in a tubular shape, extends along the rotation axis a, and surrounds the stationary shaft <NUM>. A radial bearing surface S21a is formed on an inner peripheral surface of the rotor <NUM>. The liquid metal LM is filled in a gap between the stationary shaft <NUM> and the rotor <NUM>. The liquid metal LM forms a dynamic pressure radial sliding bearing Ba together with the radial bearing surface S11a and the radial bearing surface S21a.

The anode target <NUM> has an anode target main body <NUM> and a target layer <NUM> provided on a part of an outer surface of the anode target main body <NUM>. The anode target main body <NUM> has an annular shape, is connected to an outer peripheral surface of the rotor <NUM>, is fixed to the rotor <NUM>, and is integrated with the rotor <NUM>. The target layer <NUM> has a target surface (electron collision surface) S52 on which electrons emitted from a cathode collide.

The potential of the rotor <NUM> and the stationary shaft <NUM> is the same as that of the anode target <NUM>. In the case of an anode grounded X-ray tube, the anode target <NUM>, the rotor <NUM>, the stationary shaft <NUM>, and the metal part of an envelope (not shown) have a grounding potential.

In an operating state of the X-ray tube <NUM>, the rotor <NUM> and the anode target <NUM> rotate together. Furthermore, the cathode irradiates an electron beam to the anode target <NUM>. As a result, the anode target <NUM> emits X-rays when it collides with an electron.

When the target surface S52 is continuously irradiated with the electron beam for a certain period of time, heat is accumulated in the anode target <NUM>, and the temperature of the target surface S52 rises. When the amount of heat generated by the electron beam exceeds the heat capacity of the anode target <NUM> and exceeds the allowable temperature of the anode target <NUM>, there is a problem that the target surface S52 starts to be damaged. This problem is solved by increasing the size of the anode target <NUM> and increasing the heat capacity of the anode target <NUM>. Increasing the size of the anode target <NUM> also has the effect of increasing the cooling rate of the anode target <NUM> by radiation.

However, as the size of the anode target <NUM> increases, the size, weight, and cost of the X-ray tube <NUM> increase. Therefore, in order to solve the above problem, it is not a preferable means to increase the size of the anode target <NUM>.

Therefore, by using the liquid metal LM of the dynamic pressure sliding bearing (radial sliding bearing Ba) as a heat transfer medium, heat is transferred from the anode target <NUM> to the stationary shaft <NUM>, and the heat can be transferred to a coolant flowing through a heat transfer portion 10a formed inside of the stationary shaft <NUM>. The heat generated in the anode target <NUM> can be removed by the above cooling means. In order to improve the cooling performance, it is necessary to increase the heat transfer rate from the anode target <NUM> to the stationary shaft <NUM>. Therefore, the anode target <NUM> is firmly coupled to the rotor <NUM>.

As shown in <FIG>, however, stress due to thermal expansion when the anode target <NUM> is at a high temperature propagates to the rotor <NUM>. Note that the heat (heat energy) generated by the collision of electrons with the target surface S52 is transferred from the target surface S52 to the inside of the target layer <NUM>, a portion of the anode target main body <NUM> close to the target layer <NUM>, and a portion of the anode target main body <NUM> close to the rotor <NUM> in this order, and the temperature of the anode target <NUM> rises. Therefore, in the X-ray tube <NUM> of Comparative Example <NUM>, when the anode target main body <NUM> is at a high temperature, the gap (bearing gap) between the radial bearing surface S11 and the radial bearing surface S21a changes (enlarges), causing the performance of the radial sliding bearing Ba to deteriorate.

Next, an X-ray tube assembly according to Comparative Example <NUM> will be described. <FIG> is an enlarged cross-sectional view showing a part of an X-ray tube <NUM> of Comparative Example <NUM>, and shows a state until which heat is input to an anode target <NUM> and the anode target <NUM> is cooled.

As shown in <FIG>, an anode target main body <NUM> has a circumferential notch 51a. The notch 51a is located at the root of the anode target main body <NUM>, and is located on an inner peripheral side of a target layer <NUM>. By forming the notch 51a in the anode target main body <NUM>, an adverse effect of a thermal expansion of the anode target <NUM> on the rotor <NUM> can be reduced in comparison to a case where the notch 51a is not formed in the anode target main body <NUM>.

However, since the anode target <NUM> is firmly coupled to a rotor <NUM>, the adverse effect of the thermal expansion of the anode target <NUM> on the rotor <NUM> remains strong. Therefore, even in the X-ray tube <NUM> of Comparative Example <NUM>, the performance of a radial sliding bearing Ba is deteriorated as in the case of the X-ray tube <NUM> of Comparative Example <NUM>.

As shown in <FIG>, a stationary shaft <NUM> is formed in a columnar shape. An anode target main body <NUM> is held in a state of being pressed against a protruding portion <NUM> of a rotor <NUM> by a nut <NUM> of the X-ray tube <NUM>. From the above, the anode target <NUM> is fixed to the rotor <NUM>. The anode target main body <NUM> is located at intervals from the rotor <NUM> in a radial direction of the anode target <NUM>. A protrusion <NUM> is formed on the outer peripheral surface side of the rotor <NUM>. The protrusion <NUM> extends toward the anode target main body <NUM> and is not in contact with the anode target main body <NUM>. A liquid contact material <NUM> of the X-ray tube <NUM> is enclosed in a space surrounded by the rotor <NUM>, the anode target <NUM>, and the nut <NUM>. Heat generated in the anode target <NUM> can be transferred to the rotor <NUM> via the liquid contact material <NUM>.

As described above, the anode target main body <NUM> is located at intervals from the rotor <NUM> in the radial direction of the anode target <NUM>. Therefore, it is possible to reduce an adverse effect of the thermal expansion of the anode target <NUM> on the rotor <NUM> while transferring the heat generated in the anode target <NUM> to the rotor <NUM>.

However, the structure of the X-ray tube <NUM> in Comparison Example <NUM> is complicated. Furthermore, since the anode target <NUM> is firmly coupled to the rotor <NUM>, the adverse effect of the thermal expansion of the anode target <NUM> on the rotor <NUM> remains. Therefore, even in the X-ray tube <NUM> of Comparative example <NUM>, the performance of the radial sliding bearing Ba is deteriorated as in the case of the X-ray tube <NUM> of Comparative Examples <NUM> and <NUM>.

As can be seen from Comparative Examples <NUM> to <NUM> described above, there is a demand for an X-ray tube <NUM> in which the thermal expansion of the anode target <NUM> does not adversely affect the bearing. Furthermore, there is a demand for a sliding bearing unit U and an X-ray tube <NUM> capable of obtaining a good bearing operation. Furthermore, there is a demand for an X-ray tube <NUM> that is compact and has excellent thermal characteristics.

Next, an X-ray tube assembly according to a first embodiment will be described. <FIG> is a cross-sectional view of the X-ray tube assembly according to the first embodiment. <FIG> is an enlarged cross-sectional view showing a part of an X-ray tube <NUM> shown in <FIG>. <FIG> is a side view showing a part of a stationary shaft <NUM> shown in <FIG>. <FIG> is a perspective view of a second cylinder <NUM> shown in <FIG>. <FIG> is a perspective view of a first restriction member <NUM> shown in <FIG>.

As shown in <FIG>, the X-ray tube assembly comprises a rotating anode type X-ray tube <NUM>, a stator coil <NUM> as a coil for generating a magnetic field, and the like. The X-ray tube <NUM> comprises a sliding bearing unit U, an anode target <NUM>, a cathode <NUM>, and an envelope <NUM>. The sliding bearing unit U comprises a stationary shaft <NUM>, a rotor (rotating shaft) <NUM>, and a liquid metal LM, and uses sliding bearings.

As shown in <FIG>, the stationary shaft <NUM> is formed in a columnar shape, extends along a rotation axis a, and has radial bearing surfaces S11a and Sllb formed on the outer peripheral surface and a heat transfer portion 10a. The stationary shaft <NUM> comprises a large diameter portion <NUM>, a first small diameter portion <NUM>, and a second small diameter portion <NUM>. The large diameter portion <NUM>, the first small diameter portion <NUM>, and the second small diameter portion <NUM> are coaxially integrally formed. The stationary shaft <NUM> is made of a metal such as a Fe (iron) alloy or a Mo (molybdenum) alloy.

The large diameter portion <NUM> of the stationary shaft <NUM> is located in an area A1, an area A2, an area A3, an area A4, and an area A5 arranged along the rotation axis a. Note that the area A1 is an area surrounded by the anode target <NUM>. The area A2 is located at a distance from the area A1 in the direction along the rotation axis a. The area A3 is located between the area A1 and the area A2, and is adjacent to each of the area A1 and the area A2. The area A4 is located beyond the area A1 from the area A3 and is adjacent to the area A1. The area A5 is located beyond the area A2 from the area A3 and is adjacent to the area A2.

The large diameter portion <NUM> is formed in a columnar shape and has the radial bearing surface S11a, the radial bearing surface Sllb, a concave surface Sllc, a concave surface S11d, and a concave surface Slle located on the outer peripheral surface, respectively. Furthermore, the large diameter portion <NUM> has a thrust bearing surface Slli at one end and a thrust bearing surface Sllj at another end. The radial bearing surface S11a and the radial bearing surface Sllb are each formed on the outer peripheral surface of the large diameter portion <NUM> over the entire circumference. In the first embodiment, the concave surface Sllc, the concave surface S11d, and the concave surface Slle are each formed on the outer peripheral surface of the large diameter portion <NUM> over the entire circumference. However, the concave surface Sllc, the concave surface S11d, and the concave surface Slle may be formed intermittently in the circumferential direction, respectively.

The radial bearing surface S11a is formed on the large diameter portion <NUM> in the area A1. The radial bearing surface Sllb is formed on the large diameter portion <NUM> in the area A2. The radial bearing surface S11a and the radial bearing surface Sllb are located at intervals in the direction along the rotation axis a.

The radial bearing surface S11a has a plane surface Sa and a plurality of patterned portions Pa. The plane surface Sa has a smooth outer peripheral surface. The plurality of patterned portions Pa are formed by recessing the plane surface Sa, and are arranged on the outer peripheral surface of the large diameter portion <NUM> in the area A1 over the entire circumference. Each patterned portion Pa is arranged so as to extend diagonally with respect to the circumferential direction.

The plurality of patterned portions Pa are formed at intervals in the direction along the rotation axis a. However, the plurality of patterned portions Pa may be connected in the direction along the rotation axis a.

The radial bearing surface Sllb has a plane surface Sb and a plurality of patterned portions Pb. The plane surface Sb has a smooth outer peripheral surface. The plurality of patterned portions Pb are formed by recessing the plane surface Sb, and are arranged on the outer peripheral surface of the large diameter portion <NUM> in the area A2 over the entire circumference. The patterned portions Pb are arranged so as to extend diagonally with respect to the circumferential direction.

The plurality of patterned portions Pb are formed at intervals in the direction along the rotation axis a. However, the plurality of patterned portions Pb may be connected in the direction along the rotation axis a.

Each patterned portion Pa and each patterned portion Pb are formed of grooves having a depth of several tens of um. The plurality of patterned portions Pa and the plurality of patterned portions Pb each form a herringbone pattern. Therefore, the radial bearing surfaces S11a and Sllb are uneven surfaces, respectively, and can scrape the liquid metal LM therein, allowing dynamic pressure due to the liquid metal LM to be easily generated.

The concave surface Sllc is formed on the large diameter portion <NUM> in the area A3. The concave surface Slid is formed on the large diameter portion <NUM> in the area A4. The concave surface Slle is formed on the large diameter portion <NUM> in the area A5. The concave surface Sllc, the concave surface S11d, and the concave surface Slle are located at intervals in the direction along the rotation axis a and are separated from the radial bearing surface S11a and the radial bearing surface Sllb.

The concave surface Sllc is arranged side by side with each of the radial bearing surface S11a and the radial bearing surface Sllb in the direction along the rotation axis a. The concave surface Slid is arranged side by side with the radial bearing surface S11a in the direction along the rotation axis a. The concave surface Slle is arranged side by side with the radial bearing surface Sllb in the direction along the rotation axis a. Each of the concave surfaces Sllc, S11d, and Slle is a smooth outer peripheral surface and a plane surface.

The concave surface Sllc, the concave surface S11d, and the concave surface Slle are formed to be recessed as compared with the radial bearing surface S11a and the radial bearing surface Sllb. In other words, the concave surfaces Sllc, S11d, and Slle are located on the rotation axis a side of virtual extension surfaces Se of the radial bearing surfaces S11a and Sllb. In other words, in the stationary shaft <NUM>, an outer diameter DO2 of the section where the concave surfaces Sllc, S11d, Slle are formed is smaller than a minimum outer diameter DO1 of the outer diameters of the sections where the radial bearing surfaces S11a and Sllb are formed.

In a direction perpendicular to the rotation axis a, the gap between the concave surface (concave surfaces Sllc, S11d, and Slle) and the second cylinder <NUM> is larger than the gap between the radial bearing surface S11a (plane surface Sa) and the second cylinder <NUM>, and is larger than the gap between the radial bearing surface Sllb (plane surface Sb) and the second cylinder <NUM>.

In the present first embodiment, the gap between the radial bearing surface S11a (plane surface Sa) and the second cylinder <NUM> and the gap between the radial bearing surface Sllb (plane surface Sb) and the second cylinder <NUM> in a direction perpendicular to the rotation axis a are <NUM> to <NUM>, respectively. Note that the gaps may be less than <NUM>. Furthermore, the gap between the concave surface (concave surfaces Sllc, S11d, and Slle) and the second cylinder <NUM> in a direction perpendicular to the rotation axis a is <NUM> to <NUM>.

The space between the concave surface Sllc and the second cylinder <NUM>, the space between the concave surface Slid and the second cylinder <NUM>, and the space between the concave surface Slle and the second cylinder <NUM> can be made to function as a reservoir for accommodating the liquid metal LM. Since the liquid metal LM can be supplied to each of the radial bearing surfaces S11a and Sllb from both sides, the depletion of the liquid metal LM in the bearing gap can be suppressed.

It is possible to suppress contact between the radial bearing surfaces that occurs in a case where the liquid metal LM becomes diluted in the bearing gap or the liquid metal LM does not exist. Furthermore, since it is possible to suppress the generation of a foreign matter itself caused by scraping at least one of the bearing surfaces, it is possible to suppress the mixing of the foreign matter into the liquid metal LM.

The first small diameter portion <NUM> is formed in a columnar shape having an outer diameter smaller than the large diameter portion <NUM>, and is located on one end side of the large diameter portion <NUM>. The first small diameter portion <NUM> is located on the rotation axis a side with respect to the thrust bearing surface S11i.

The second small diameter portion <NUM> is formed in a columnar shape having an outer diameter smaller than the large diameter portion <NUM>, and is located on the other end side of the large diameter portion <NUM>. The second small diameter portion <NUM> is located on the rotation axis a side with respect to the thrust bearing surface Sllj.

The stationary shaft <NUM> includes a first bottom surface 10b1, a second bottom surface 10b2, and the heat transfer portion 10a. The second bottom surface 10b2 is located on the opposite side of the first bottom surface 10b1 in the direction along the rotation axis a. In the present first embodiment, the first bottom surface 10b1 is located on the first small diameter portion <NUM>, and the second bottom surface 10b2 is located on the second small diameter portion <NUM>.

The heat transfer portion 10a extends along the rotation axis a and is open to at least one of the first bottom surface 10b1 and the second bottom surface 10b2. In the present first embodiment, the heat transfer portion 10a is a heat transfer hole and is open to the second bottom surface 10b2. The heat transfer portion 10a forms a flow path for a cooling fluid. The heat transfer portion 10a transfers heat to the cooling fluid flowing inside by forced convection. In the present first embodiment, the cooling fluid is a coolant L. The cooling rate of the anode target <NUM> of the X-ray tube <NUM> can be improved by water cooling or oil cooling. However, the cooling fluid may be air, and the cooling rate of the anode target <NUM> may also be improved by air cooling.

It is desirable that the heat transfer portion 10a is located at least in the area A1. As a result, it is possible to cool a portion of the stationary shaft <NUM> where the heat of the anode target <NUM> is easily transferred.

As shown in <FIG> and <FIG>, the rotor <NUM> is configured to be rotatable around the stationary shaft <NUM>. The rotor <NUM> comprises a first cylinder <NUM>, the second cylinder <NUM>, the first restriction member <NUM>, a second restriction member <NUM>, and a tubular portion <NUM>. The first cylinder <NUM>, the second cylinder <NUM>, the first restriction member <NUM>, and the second restriction member <NUM> are each made of a metal such as an Fe alloy or a Mo alloy. The tubular portion <NUM> is made of a metal such as copper (Cu) or a copper alloy. In the rotor <NUM>, the first cylinder <NUM> is an outer cylinder located on the outer side, and the second cylinder <NUM> is an inner cylinder located relatively on the inner side.

The first cylinder <NUM> extends along the rotation axis a, is formed in a tubular shape, and is located so as to surround the stationary shaft <NUM> (large diameter portion <NUM>). In the present first embodiment, the first cylinder <NUM> has a uniform inner diameter and outer diameter over the entire length.

As shown in <FIG>, <FIG> and <FIG>, the second cylinder <NUM> extends along the rotation axis a and is formed in a tubular shape. The second cylinder <NUM> is located between the stationary shaft <NUM> and the first cylinder <NUM>. In the present first embodiment, the second cylinder <NUM> has a uniform inner diameter and outer diameter over the entire length. The inner diameter of the second cylinder <NUM> is larger than the stationary shaft <NUM> (large diameter portion <NUM>), and the outer diameter of the second cylinder <NUM> is smaller than the inner diameter of the first cylinder <NUM>.

The second cylinder <NUM> includes a radial bearing surface S22 on the inner peripheral surface. The radial bearing surface S22 is located at least in the area A1 and the area A2. In the present first embodiment, the radial bearing surface S22 is a smooth inner peripheral surface and is a plane surface. Due to the gap between the second cylinder <NUM> and the stationary shaft <NUM> and the gap between the second cylinder <NUM> and the first cylinder <NUM>, the second cylinder <NUM> can move to an eccentric position with respect to each of the stationary shaft <NUM> and the first cylinder <NUM>. The operation of the second cylinder <NUM> is restricted so that the second cylinder <NUM> does not rotate relative to the first cylinder <NUM>. Therefore, the rotation speed of the second cylinder <NUM> is the same as the rotation speed of the first cylinder <NUM>.

In the direction along the rotation axis a, the length of the second cylinder <NUM> is shorter than the length of the large diameter portion <NUM>. The length of the second cylinder <NUM> is adjusted so as not to impair the functions of the radial sliding bearing and the thrust sliding bearing described later.

The second cylinder <NUM> includes a first end surface 22e1, a second end surface 22e2, and one or more recesses 22r. The first end surface 22e1 is located at the end of the second cylinder <NUM> in the direction along the rotation axis a. The second end surface 22e2 is located at the end of the second cylinder <NUM> in the direction along the rotation axis a, and is on the opposite side of the first end surface 22e1. In the present embodiment, the second cylinder <NUM> has three recesses 22r. These recesses 22r are located at intervals from each other in the circumferential direction. Each recess 22r opens in the first end surface 22e1 and is recessed in the direction along the rotation axis a.

In the present first embodiment, the gap between the first cylinder <NUM> and the second cylinder <NUM> in a direction perpendicular to the rotation axis a is from <NUM> to <NUM>.

As shown in <FIG>, <FIG> and <FIG>, the first restriction member <NUM> has a first member 23a and one or more second members 23b. In the present embodiment, the first restriction member <NUM> has three second members 23b. The first member 23a has an annular shape and is fixed to the first cylinder <NUM>. For example, as in the present first embodiment, in order to fix the relative position of the first member 23a with respect to the first cylinder <NUM>, an annular step portion may be formed on the outer peripheral side of the first member 23a. The step portion of the first member 23a can be fitted to the first cylinder <NUM>.

By holding the first member 23a in a state of being pressed against the first cylinder <NUM> in the direction along the rotation axis a, the first member 23a can be fixed to the first cylinder <NUM>. Alternatively, the first member 23a may be fixed to the first cylinder <NUM> by welding or brazing, or the first member 23a may be detachably fixed to the first cylinder <NUM> by using a screw.

The first member 23a faces the first end surface 22e1 of the second cylinder <NUM>. Thereby, the first member 23a can restrict the movement of the second cylinder <NUM> in the direction along the rotation axis a. The first member 23a includes a thrust bearing surface S23a facing the thrust bearing surface Slli of the stationary shaft <NUM> in the direction along the rotation axis a. The thrust bearing surface S23a is located on the inner peripheral side of the first member 23a and has an annular shape. Note that, in <FIG>, the thrust bearing surface S23a is denoted by a dot pattern.

Each second member 23b protrudes from the first member 23a in a direction along the rotation axis a. The second member 23b is provided in a one-to-one correspondence with the recess 22r of the second cylinder <NUM>. Each second member 23b is fitted in the recess 22r of the second cylinder <NUM>. In the present first embodiment, a sufficient gap for fitting is secured between the second member 23b and the recess 22r. Therefore, the second member 23b can be fitted into the recess 22r without using a tightening fit. Furthermore, the gap between the second member 23b and the recess 22r can be used for a circulation path of the liquid metal LM.

The second member 23b is configured to restrict an operation of the second cylinder <NUM> together with the recess 22r of the second cylinder <NUM>. The second cylinder <NUM> is restricted so as not to rotate with respect to the first cylinder <NUM>.

The gap (clearance) between the first restriction member <NUM> (first member 23a) and the stationary shaft <NUM> (first small diameter portion <NUM>) is set to a value that can maintain the rotation of the rotor <NUM> and suppress the leakage of the liquid metal LM. From the above, the gap is slight, and the first member 23a functions as a labyrinth seal ring.

As shown in <FIG> and <FIG>, the second restriction member <NUM> has an annular shape and is fixed to the first cylinder <NUM>. In the present first embodiment, the second restriction member <NUM> is integrally molded with the same material as the first cylinder <NUM>. The second restriction member <NUM> faces the second end surface 22e2 of the second cylinder <NUM>. As a result, the second restriction member <NUM> can restrict the movement of the second cylinder <NUM> in the direction along the rotation axis a.

The second restriction member <NUM> includes a thrust bearing surface S24 facing the thrust bearing surface Sllj of the stationary shaft <NUM> in the direction along the rotation axis a. The thrust bearing surface S24 is located on the inner peripheral side of the second restriction member <NUM> and has an annular shape.

Furthermore, the gap (clearance) between the second restriction member <NUM> and the stationary shaft <NUM> (second small diameter portion <NUM>) is set to a value that can maintain the rotation of the rotor <NUM> and suppress the leakage of the liquid metal LM. From the above, the gap is small, and the second restriction member <NUM> functions as a labyrinth seal ring.

The tubular portion <NUM> is joined to the outer peripheral surface of the first cylinder <NUM> and is fastened to the first cylinder <NUM>. Note that, in <FIG>, the tubular portion <NUM> is not shown.

When assembling to the sliding bearing unit U, the second cylinder <NUM> is inserted into an integral body of the first cylinder <NUM> and the second restriction member <NUM>, and then the stationary shaft <NUM> is fitted to the second cylinder <NUM>. Subsequently, the first restriction member <NUM> is fixed to the first cylinder <NUM> to be covered by the first restriction member <NUM>.

In the present embodiment, the second restriction member <NUM> is formed integrally with the first cylinder <NUM>, and the first restriction member <NUM> is a lid that is physically independent of the first cylinder <NUM>.

However, the first restriction member <NUM> may be formed integrally with the first cylinder <NUM>, and the second restriction member <NUM> may be a lid that is physically independent of the first cylinder <NUM>.

Alternatively, the first restriction member <NUM> and the second restriction member <NUM> may each be a lid physically independent of the first cylinder <NUM>.

The stationary shaft <NUM> and the rotor <NUM> are provided with a gap between them in all facing areas. The large diameter portion <NUM> is covered with the rotor <NUM>. The first small diameter portion <NUM> and the second small diameter portion <NUM> protrude to the outside of the rotor <NUM>. The stationary shaft <NUM> rotatably supports the rotor <NUM>.

The liquid metal LM fills a plurality of gaps between the stationary shaft <NUM> (large diameter portion <NUM>), the first cylinder <NUM>, the second cylinder <NUM>, the first restriction member <NUM>, and the second restriction member <NUM>. As the liquid metal LM, a material such as a GaIn (gallium-indium) alloy or a GaInSn (gallium-indium-tin) alloy can be used. An appropriate amount of the liquid metal LM is filled in the plurality of gaps. During the operation of the rotor <NUM>, the liquid level of the liquid metal LM on the rotation axis a side is located on the rotation axis a side with respect to the radial bearing surfaces S11a and Sllb. This makes it possible to suppress the depletion of the liquid metal LM in the bearing gap.

The liquid metal LM forms a dynamic pressure sliding bearing together with the bearing surface of the stationary shaft <NUM> and the bearing surface of the rotor <NUM>.

The liquid metal LM forms a dynamic pressure radial sliding bearing Ba together with the radial bearing surface S11a and the radial bearing surface S22. The radial sliding bearing Ba is located in the area A1.

The liquid metal LM forms a dynamic pressure radial sliding bearing Bb together with the radial bearing surface Sllb and the radial bearing surface S22. The radial sliding bearing Bb is located in the area A2.

The liquid metal LM forms a dynamic pressure thrust sliding bearing Bc together with the thrust bearing surface S11i and the thrust bearing surface S23a.

The liquid metal LM forms a dynamic pressure thrust sliding bearing Bd together with the thrust bearing surface Sllj and the thrust bearing surface S24.

The gap between the first end surface 22e1 (recessed portion 22r) of the second cylinder <NUM> and the first restriction member <NUM> is connected to the gap between the stationary shaft <NUM> and the second cylinder <NUM> and the gap between the first cylinder <NUM> and the second cylinder <NUM> so as to configure a circulation path for the liquid metal LM. The gap between the second end surface 22e2 of the second cylinder <NUM> and the second restriction member <NUM> is connected to the gap between the stationary shaft <NUM> and the second cylinder <NUM> and the gap between the first cylinder <NUM> and the second cylinder <NUM> so as to configure a circulation path for the liquid metal LM.

From the above, the liquid metal LM can move through the plurality of gaps between the stationary shaft <NUM> (large diameter portion <NUM>), the first cylinder <NUM>, the second cylinder <NUM>, the first restriction member <NUM>, and the second restriction member <NUM>.

The anode target <NUM> is formed in an annular shape and is provided coaxially with the stationary shaft <NUM>, the first cylinder <NUM>, and the second cylinder <NUM>. The anode target <NUM> has the anode target main body <NUM> and the target layer <NUM> provided on a part of the outer surface of the anode target main body <NUM>. The anode target main body <NUM> is formed in an annular shape. The anode target main body <NUM> surrounds the outer peripheral surface of the first cylinder <NUM> and is fixed to the first cylinder <NUM>. In the present embodiment, the anode target main body <NUM> is fixed to the first cylinder <NUM>.

The anode target main body <NUM> is formed of molybdenum, tungsten, or an alloy using these. The melting point of the metal forming the target layer <NUM> is the same as the melting point of the metal forming the anode target main body <NUM>, or higher than the melting point of the metal forming the anode target main body <NUM>. In the present first embodiment, the anode target main body <NUM> is made of a molybdenum alloy, and the target layer <NUM> is made of a tungsten alloy.

The anode target <NUM> is rotatable together with the rotor <NUM>. When an electron collides with a target surface S52 of the target layer <NUM>, a focal point is formed on the target surface S52. As a result, the anode target <NUM> emits X-rays from the focal point.

Here, the materials of the stationary shaft <NUM>, the first cylinder <NUM>, the second cylinder <NUM>, and the anode target main body <NUM> will be described.

The degree of freedom in selecting the materials for the first cylinder <NUM> and the second cylinder <NUM> is high. Therefore, the second cylinder <NUM> may be formed of the same material as the first cylinder <NUM>, or may be formed of a material different from that of the first cylinder <NUM>.

The second cylinder <NUM> may be made of the same material as the stationary shaft <NUM>. The coefficient of thermal expansion of the second cylinder <NUM> and the coefficient of thermal expansion of the stationary shaft <NUM> can be matched. For example, fluctuations in the radial bearing gap can be suppressed.

The first cylinder <NUM> may be made of the same material as the stationary shaft <NUM>. The coefficient of thermal expansion of the first cylinder <NUM> and the coefficient of thermal expansion of the stationary shaft <NUM> can be matched. For example, fluctuations in the thrust bearing gap can be suppressed.

Note that the stationary shaft <NUM> may be made of a material different from that of the first cylinder <NUM> or may be made of a material different from that of the second cylinder <NUM>. For example, the stationary shaft <NUM> may be formed of a metal softer than the first cylinder <NUM>, or the stationary shaft <NUM> may be formed of a metal softer than the second cylinder <NUM>. Since the stationary shaft <NUM> can be easily machined, the productivity of the stationary shaft <NUM> can be improved.

In a case where the anode target main body <NUM> is located on the outer peripheral surface of the first cylinder <NUM> at a distance, the first cylinder <NUM> may be formed of the same material as the anode target main body <NUM> or may be formed of a material different from the anode target main body <NUM>.

In a case where the anode target main body <NUM> is connected to the outer peripheral surface of the first cylinder <NUM>, and the anode target main body <NUM> is fastened to the outer peripheral surface of the first cylinder <NUM>, the first cylinder <NUM> is made of the same material as the anode target main body <NUM>. The coefficient of thermal expansion of the anode target main body <NUM> can be matched with the coefficient of thermal expansion of the first cylinder <NUM>. For example, it is possible to suppress a situation where the anode target main body <NUM> is detached from the first cylinder <NUM> or at least one of the first cylinder <NUM> and the anode target main body <NUM> is damaged.

As shown in <FIG>, the cathode <NUM> is arranged to face the target layer <NUM> at a distance from the target layer <NUM> of the anode target <NUM>. The cathode <NUM> is attached to the inner wall of the envelope <NUM>. The cathode <NUM> has a filament <NUM> as an electron emission source that emits electrons to irradiate the target layer <NUM>.

The envelope <NUM> is formed in a cylindrical shape. The envelope <NUM> is made of glass, ceramic and metal. In the envelope <NUM>, the outer diameter of a part facing the anode target <NUM> is larger than the outer diameter of a part facing the tubular portion <NUM>. The envelope <NUM> has openings <NUM> and <NUM>. The envelope <NUM> is hermetically sealed and houses the sliding bearing unit U, the anode target <NUM>, and the cathode <NUM>. The inside of the envelope <NUM> is maintained in a vacuum state (decompressed state).

The opening <NUM> is airtightly joined to one end (first small diameter portion <NUM>) of the stationary shaft <NUM>, and the opening <NUM> is airtightly joined to the other end (second small diameter portion <NUM>) of the stationary shaft <NUM> so as to maintain the airtight state of the envelope <NUM>. In the present embodiment, the X-ray tube <NUM> adopts a bearing structure supported at both ends. The envelope <NUM> fixes the first small diameter portion <NUM> and the second small diameter portion <NUM> of the stationary shaft <NUM>. That is, the first small diameter portion <NUM> and the second small diameter portion <NUM> function as a double-sided support portion of the bearing.

The X-ray tube <NUM> comprises a tube portion <NUM> provided inside the stationary shaft <NUM>. An annulus portion <NUM> is liquid-tightly joined to the second bottom surface 10b2 of the stationary shaft <NUM>. The outer peripheral surface of the tube portion <NUM> is liquid-tightly joined to the opening of the annulus portion <NUM>, and the tube portion <NUM> extends to the outside of the stationary shaft <NUM>. The stationary shaft <NUM> forms a flow path of the coolant L together with the tube portion <NUM>.

The tube portion <NUM> has an inlet 40a for taking in the coolant and a discharge port 40b for discharging the coolant L to the inside of the stationary shaft <NUM>. The inlet 40a is located on the side extending outward from the second bottom surface 10b2 of the stationary shaft <NUM>. Furthermore, the discharge port 40b is located with a gap on the bottom surface of the heat transfer portion 10a in the direction along the rotation axis a.

On the outside of the envelope <NUM>, an opening is formed in the stationary shaft <NUM>, and a tube portion <NUM> is liquid-tightly joined to the opening. The tube portion <NUM> has an outlet 45a for taking out the coolant L to the outside. From the above, the coolant L circulating inside the X-ray tube <NUM> is taken in from the inlet 40a, passes through the inside of the tube portion <NUM>, is discharged from the discharge port 40b to the inside of the stationary shaft <NUM>, passes between the tube portion <NUM> and the stationary shaft <NUM>, and is taken out from the outlet 45a of the tube portion <NUM>. Note that the coolant L may be circulated in the opposite direction. In this case, the tube portion <NUM> forms an inlet for the coolant L, and the tube portion <NUM> forms an outlet for the coolant L.

The stator coil <NUM> is provided so as to face the outer peripheral surface of the rotor <NUM>, more specifically, the outer peripheral surface of the tubular portion <NUM>, and surround the outside of the envelope <NUM>. The shape of the stator coil <NUM> is annular. The stator coil <NUM> generates a magnetic field to be applied to the tubular portion <NUM> (rotor <NUM>) and rotates the rotor <NUM> and the anode target <NUM>.

The X-ray tube assembly comprising the X-ray tube <NUM> is formed in the manner described above.

In the operating state of the above X-ray tube assembly, the stator coil <NUM> generates a magnetic field to be applied to the rotor <NUM> (particularly the tubular portion <NUM>) to rotate the second cylinder <NUM>. As a result, the first cylinder <NUM> and the anode target <NUM> also rotate together. Furthermore, a current is applied to the cathode <NUM> to apply a negative voltage, and a relatively positive voltage is applied to the anode target <NUM>.

This creates a potential difference between the cathode <NUM> and the anode target <NUM>. The filament <NUM> emits electrons. The electrons are accelerated and collide with the target surface S52. As a result, a focal point is formed on the target surface S52, and the focal point emits X-rays when colliding with an electron. The electrons (thermoelectrons) that collide with the anode target <NUM> are converted into X-rays, and the rest are converted into heat energy. Note that the electron emission source of the cathode <NUM> is not limited to the filament, and may be, for example, a flat emitter. Furthermore, the X-ray tube <NUM> may be a cold cathode X-ray tube instead of a hot cathode X-ray tube.

<FIG> is an enlarged cross-sectional view showing a part of the X-ray tube <NUM> according to the first embodiment, and shows a state until which heat is input to the anode target <NUM> and the anode target <NUM> is cooled.

As shown in <FIG>, when heat is generated in the anode target <NUM>, the anode target <NUM> thermally expands. Then, stress due to the thermal expansion propagates to a portion integral with the anode target <NUM> or firmly coupled to the anode target <NUM>, and causes thermal deformation to occur. In the present first embodiment, thermal deformation is likely to occur in the portion of the first cylinder <NUM> located in the area A1. For example, the portion of the first cylinder <NUM> located in the area A1 can be expanded outward in the radial direction by a maximum of <NUM>.

However, in the present first embodiment, the second cylinder <NUM> is not physically fixed to the first cylinder <NUM>. The second cylinder <NUM> has a gap therebetween the first cylinder <NUM>. Since the second cylinder <NUM> is not firmly coupled to the first cylinder <NUM>, the stress due to the deformation of the first cylinder <NUM> is difficult to propagate to the second cylinder <NUM>. Deformation of the second cylinder <NUM> due to thermal expansion of the anode target <NUM> can be suppressed, and deterioration of bearing performance can be suppressed.

Furthermore, since the volume between the first cylinder <NUM> and the second cylinder <NUM> increases, the liquid metal LM gathers on the first cylinder <NUM> side due to the centrifugal force, and a vacuum space is generated on the large diameter portion <NUM> side. However, since the concave surfaces Sllc, S11d, and Slle form a reservoir space of the liquid metal LM in advance, the liquid metal LM can be supplied to the gap between the first cylinder <NUM> and the second cylinder <NUM> and the bearing gap. From the above, it is possible to suppress the deterioration of bearing performance. Furthermore, heat transfer from the anode target <NUM> to the large diameter portion <NUM> side will not be inhibited.

Note that, in the case where the second member 23b is fitted into the recess 22r, unlike the present first embodiment, the second member 23b may be fitted into the recess 22r by using a tightening fit. Also in this case, the deformation of the second cylinder <NUM> due to the thermal expansion of the anode target <NUM> can be suppressed. This is because the end portion of the first cylinder <NUM> is not easily deformed even if the anode target <NUM> is thermally expanded, and the second cylinder <NUM> is indirectly fixed to the end portion of the first cylinder <NUM> where it is not easily deformed.

As described above, the relative position of the second cylinder <NUM> with respect to the first cylinder <NUM> may be fixed by the tightening fit. In that case, the second cylinder <NUM> can be prevented from moving to a position eccentric with respect to the first cylinder <NUM>. Note that the method of fixing the relative position of the second cylinder <NUM> with respect to the first cylinder <NUM> is not limited to the tightening fit, and may be performed by brazing, welding, or using screws.

In the present embodiment, the end portion of the second cylinder <NUM> on the first end surface 22e1 side is indirectly fixed to the first cylinder <NUM> via the first restriction member <NUM>.

However, in order to fix the relative position of the second cylinder <NUM> with respect to the first cylinder <NUM>, it is not necessary to fix the end portion of the second cylinder <NUM> on the first end surface 22e1 side. The end portion of the second cylinder <NUM> on the second end surface 22e2 side may be indirectly fixed to the first cylinder <NUM> via the second restriction member <NUM>. Since the heat transfer path from the anode target <NUM> to the second end surface 22e2 is longer than to the first end surface 22e1, the deformation of the second cylinder <NUM> can be further suppressed.

Alternatively, the end portion of the second cylinder <NUM> on the first end surface 22e1 side may be indirectly fixed to the first cylinder <NUM> via the first restriction member <NUM>, and the end portion of the second cylinder <NUM> on the second end surface 22e2 side may be indirectly fixed to the first cylinder <NUM> via the second restriction member <NUM>.

According to the X-ray tube assembly according to the first embodiment configured as described above, the X-ray tube assembly comprises the rotating anode type X-ray tube <NUM>. The X-ray tube <NUM> comprises the sliding bearing unit U, the anode target <NUM>, the cathode <NUM>, and the envelope <NUM>. The sliding bearing unit U comprises the stationary shaft <NUM> extending along the rotation axis a and including radial bearing surfaces S11a and Sllb on the outer peripheral surface, the rotor <NUM> rotatable around the stationary shaft <NUM>, and the liquid metal LM.

The rotor <NUM> has the first cylinder <NUM> and the second cylinder <NUM>. The first cylinder <NUM> extends along the rotation axis a and is formed in a tubular shape, and is located surrounding the stationary shaft <NUM>. The second cylinder <NUM> extends along the rotation axis a and is formed in a tubular shape, is located between the stationary shaft <NUM> and the first cylinder <NUM>, includes the radial bearing surface S22 on the inner peripheral surface, and has the operation restricted so as not to rotate relative to the first cylinder <NUM>. The second cylinder <NUM> may be movable to a position eccentric with respect to each of the stationary shaft <NUM> and the first cylinder <NUM>.

The liquid metal LM is filled in a plurality of gaps between the stationary shaft <NUM>, the first cylinder <NUM>, and the second cylinder <NUM>, forms the dynamic pressure radial sliding bearing Ba together with the radial bearing surface S11a and the radial bearing surface S22, and forms the dynamic pressure radial sliding bearing Bb together with the radial bearing surface Sllb and the radial bearing surface S22. The anode target <NUM> surrounds the outer peripheral surface of the first cylinder <NUM> and is fixed to the first cylinder <NUM>.

The rotor <NUM> has a double cylindrical structure. The first cylinder <NUM> that is firmly coupled to the anode target <NUM> or is formed integrally with the anode target <NUM> and the second cylinder <NUM> that forms the radial sliding bearings Ba and Bb are physically independent. The second cylinder <NUM> is less susceptible to the adverse effects of thermal expansion of the anode target <NUM>.

According to the X-ray tube assembly according to the first embodiment configured as described above, the sliding bearing unit U capable of obtaining good bearing operation and the X-ray tube <NUM> comprising the sliding bearing unit U can be obtained.

Next, an X-ray tube assembly according to a second embodiment will be described. An X-ray tube <NUM> has the same configuration as that in the above first embodiment, except for the configurations described in the present second embodiment. <FIG> is an enlarged cross-sectional view showing a part of the X-ray tube assembly according to the present second embodiment.

As shown in <FIG>, a second cylinder <NUM> further has a plurality of circulation holes h22. Each circulation hole h22 penetrates from the outer peripheral surface to the inner peripheral surface of the second cylinder <NUM>. In the present second embodiment, each circulation hole h22 extends linearly in a direction perpendicular to a rotation axis a. Each circulation hole h22 is located outside the area A1 where a radial bearing surface S11a and a radial bearing surface S22 face each other, and the area A2 where a radial bearing surface Sllb and the radial bearing surface S22 face each other.

The plurality of circulation holes h22 are located in areas A3, A4, and A5, and are provided at intervals in a direction along a rotation axis a. Although not shown, the plurality of circulation holes h22 may be provided in each of the areas A3, A4, and A5 at intervals in a circumferential direction.

The plurality of circulation holes h22 are connected to a gap between a stationary shaft <NUM> and the second cylinder <NUM> and a gap between a first cylinder <NUM> and the second cylinder <NUM>, and form a circulation path for a liquid metal LM. Therefore, the liquid metal LM can be moved rapidly between both of the above gaps.

According to the second embodiment configured as described above, the same effect as that of the above first embodiment can be obtained. It is possible to obtain a sliding bearing unit U capable of obtaining good bearing operation and an X-ray tube <NUM> provided with this sliding bearing unit U.

Next, an X-ray tube assembly according to a third embodiment will be described. An X-ray tube <NUM> has the same configuration as that in the above second embodiment, except for the configurations described in the present third embodiment. <FIG> is an enlarged cross-sectional view showing a part of the X-ray tube assembly according to the present third embodiment.

As shown in <FIG>, a stationary shaft <NUM> (large diameter portion <NUM>) further has a plurality of groove portions 11r. Each groove portion 11r is opened in a concave surface Sllc, a concave surface S11d, or a concave surface Slle, and is recessed toward a rotation axis a side. In the present third embodiment, each groove portion 11r is not formed over the entire circumference of the large diameter portion <NUM>. The plurality of groove portions 11r are provided in an area facing a circulation hole h22, and are provided at intervals from each other in a direction along the rotation axis a and in a circumferential direction.

However, the groove portion 11r may also be formed over the entire circumference of the large diameter portion <NUM>. Furthermore, the second cylinder <NUM> may also be formed without the circulation hole h22.

According to the third embodiment configured as described above, the same effect as that of the above second embodiment can be obtained. It is possible to obtain a sliding bearing unit U capable of obtaining good bearing operation and an X-ray tube <NUM> provided with this sliding bearing unit U.

Next, an X-ray tube assembly according to a fourth embodiment will be described. An X-ray tube <NUM> has the same configuration as that of the above second embodiment except for the configurations described in the present fourth embodiment. <FIG> is a cross-sectional view showing an X-ray tube assembly according to the present fourth embodiment. <FIG> is a perspective view showing a stationary shaft <NUM> shown in <FIG>.

As shown in <FIG> and <FIG>, the stationary shaft <NUM> has an accommodating portion and a circulation hole. The accommodating portion is provided inside the stationary shaft <NUM> and accommodates a liquid metal LM. The circulation hole penetrates from the accommodating portion to the outer peripheral surface of the stationary shaft <NUM>, and is located to be separated from radial bearing surfaces S11a and Sllb. In the present fourth embodiment, the stationary shaft <NUM> has an accommodating portion 10c, an accommodating portion 10d, an accommodating portion 10e, and a plurality of circulation holes h11.

The accommodating portions 10c, 10d, and 10e are each provided inside the stationary shaft <NUM> and are formed by through holes extending linearly in the direction along the rotation axis a. In the present fourth embodiment, the accommodating portions 10c, 10d, and 10e extend from at least the area A4 to the area A5. The accommodating portions 10c, 10d, and 10e are provided at intervals in the circumferential direction. Openings of the accommodating portions 10c, 10d, and 10e located on a first bottom surface 10b1 are sealed with a sealing material <NUM> to prevent the liquid metal LM from leaking to the outside of the X-ray tube <NUM>.

The plurality of circulation holes h11 communicate with the accommodating portion 10c, the accommodating portion 10d, or the accommodating portion 10e, and extend linearly in a direction perpendicular to the rotation axis a. The plurality of circulation holes h11 are opened in any one of a concave surface Sllc, a concave surface S11d, and a concave surface Slle. The circulation holes h11 can circulate the liquid metal LM between the accommodating portions 10c, 10d, and 10e and the gap between the stationary shaft <NUM> and the second cylinder <NUM>.

The accommodating portions 10c, 10d, and 10e can function as a reservoir for accommodating the liquid metal LM. Therefore, the liquid metal LM temporarily accommodated in the accommodating portions 10c, 10d, and 10e can be supplied to the gap between the stationary shaft <NUM> and the second cylinder <NUM>, and thus supplied to the gap between a first cylinder <NUM> and the second cylinder <NUM>.

In the present fourth embodiment, the circulation holes h11 are provided at intervals in the direction along the rotation axis a and in the circumferential direction. The circulation hole h11 is located on the same straight line as the corresponding circulation hole h22. However, the circulation hole h11 does not have to be located on the same straight line as the circulation hole h22. Furthermore, the plurality of circulation holes h11 do not have to be provided in all of the areas A3, A4, and A5. For example, the plurality of circulation holes h11 may be provided only in the area A3 and may be opened only in the concave surface Sllc.

Note that the circulation holes h11 may be located on at least one of the radial bearing surfaces S11a and Sllb.

According to the fourth embodiment configured as described above, the same effect as that of the above second embodiment can be obtained. Furthermore, the depletion of the liquid metal LM in the bearing gap can be further suppressed. It is possible to obtain a sliding bearing unit U capable of obtaining good bearing operation and an X-ray tube <NUM> provided with this sliding bearing unit U.

Next, an X-ray tube assembly according to a fifth embodiment will be described. An X-ray tube <NUM> has the same configuration as that of the above third embodiment, except for the configurations described in the present fifth embodiment. <FIG> is an enlarged cross-sectional view showing a part of the X-ray tube assembly according to the present fifth embodiment.

As shown in <FIG>, a second cylinder <NUM> may have a plurality of areas having different outer diameter dimensions. The inner diameter of a first cylinder <NUM> is uniform over the entire length. From the above, there are a plurality of areas Aa, Ab, Ac, Ad, Ae, Af, and Ag having different gaps between the first cylinder <NUM> and the second cylinder <NUM> in the direction along a rotation axis a. The second cylinder <NUM> has a plurality of concave surfaces 22c. The plurality of concave surfaces 22c are formed on the outer peripheral surface of the second cylinder <NUM> over the entire circumference in each of the areas Ab, Ad, and Af. The concave surface 22c is formed by being recessed toward the rotation axis a side.

A circulation hole h22 is open to the concave surface 22c.

Here, a gap between the first cylinder <NUM> and the second cylinder <NUM> in each of the areas Aa and Ag is g1, a gap between the first cylinder <NUM> and the second cylinder <NUM> in each of the areas Ac and Ae is g2, and a gap between the first cylinder <NUM> and the second cylinder <NUM> in each of the areas Ab, Ad, and Af is g3.

Whereupon, g1 ≤ g2 < g3 is established. In the present fifth embodiment, g1 = g2, but may also be g1 < g2. This allows the positions of the first cylinder <NUM> and the second cylinder <NUM> to be aligned in the areas Aa and Ag. The areas Ac and Ae can form a path for transferring heat from the first cylinder <NUM> to the second cylinder <NUM>. The area Ab, Ad, and Af can function as a reservoir to accommodate liquid metal LM.

Note that g2 < g3 = g1 may also be established. In other words, the outer diameter of the second cylinder <NUM> in each of the areas Aa and Ag may be identical to the outer diameter of the second cylinder <NUM> in each of the areas Ab, Ad, and Af.

The second cylinder <NUM> has an outer diameter DO3 in the area Ac and an outer diameter DO4 in the area Ad. The outer diameter DO3 is also the outer diameter of an area of the second cylinder <NUM> surrounded by an anode target <NUM>. The outer diameter DO4 is also the outer diameter of an area of the second cylinder <NUM> adjacent to the area Ac (an area surrounded by the anode target <NUM>). The outer diameter DO3 is larger than the outer diameter DO4.

According to the fifth embodiment configured as described above, the same effect as that of the above third embodiment can be obtained. It is possible to obtain a sliding bearing unit U capable of obtaining good bearing operation and an X-ray tube <NUM> provided with this sliding bearing unit U.

Next, an X-ray tube assembly according to a sixth embodiment will be described. An X-ray tube <NUM> has the same configuration as the above fifth embodiment except for the configurations described in the present sixth embodiment. <FIG> is an enlarged cross-sectional view showing a part of the X-ray tube assembly according to the present sixth embodiment.

As shown in <FIG>, a first cylinder <NUM> has a plurality of portions having different inner diameter dimensions. The first cylinder <NUM> has a first portion 21A having an inner diameter DI1 and a second portion 21B having an inner diameter DI2. The inner diameter DI1 is larger than the inner diameter DI2. The first portion 21A is located in areas Aa, Ab, Ac and Ad. The second portion 21B is located in areas Ae, Af, and Ag.

The second cylinder <NUM> has a plurality of portions having different outer diameter dimensions. The second cylinder <NUM> comprises a first portion 22A having an outer diameter DOS and a second portion 22B having an outer diameter DO6 that is smaller than the outer diameter DOS. The first portion 22A is located in the areas Aa, Ab, and Ac. The second portion 22B is located in the areas Ad, Ae, Af, and Ag.

Whereupon, g1 ≤ g2 < g3 is established. In the present sixth embodiment, g1 = g2, but may also be g1 < g2. This allows the positions of the first cylinder <NUM> and the second cylinder <NUM> to be aligned in the areas Aa and Ag. The areas Ac and Ae can form a path for transferring heat from the first cylinder <NUM> to the second cylinder <NUM>. The areas Ab, Ad, and Af can function as a reservoir to accommodate a liquid metal LM.

As described above, the first cylinder <NUM> has the first portion 21A with a relatively large inner diameter DI1, and the second cylinder <NUM> has the second portion 22B with a relatively small outer diameter DO6. Therefore, when assembling to a sliding bearing unit U, the second cylinder <NUM> can be easily inserted into an integral body of the first cylinder <NUM> and a second restriction member <NUM>.

According to the sixth embodiment configured as described above, the same effect as that of the above fifth embodiment can be obtained. Since the first portion 21A has a relatively large inner diameter DI1, the liquid metal LM can be less likely depleted in the gap between the first portion 21A and the first portion 22A. In other words, in the area surrounded by an anode target <NUM>, the liquid metal LM can be less likely depleted in the gap between the first cylinder <NUM> and the second cylinder <NUM>. It is possible to obtain a sliding bearing unit U capable of obtaining good bearing operation and an X-ray tube <NUM> provided with this sliding bearing unit U.

Note that, unlike the above sixth embodiment, the inner diameter of the first cylinder <NUM> may be uniformly formed over the entire length. In other words, the first cylinder <NUM> may have the inner diameter DI1 over the entire length. Even in that case, the same effect as that of the above sixth embodiment can be obtained.

Next, an X-ray tube assembly according to a seventh embodiment will be described. An X-ray tube <NUM> has the same configuration as that of the above first embodiment, except for the configurations described in the present seventh embodiment. <FIG> is an enlarged cross-sectional view showing a part of the X-ray tube assembly according to the present seventh embodiment. Note that, in <FIG>, for convenience, a recess 22r and a second member 23b are not shown.

As shown in <FIG>, a second cylinder <NUM> has a plurality of concave surfaces 22c. The plurality of concave surfaces 22c are formed on the outer peripheral surface of the second cylinder <NUM> over the entire circumference. The concave surface 22c is formed by being recessed toward a rotation axis a side.

The X-ray tube <NUM> has an annular spring <NUM>. In the seventh embodiment, the X-ray tube <NUM> has two springs <NUM>. The spring <NUM> is located between a first cylinder <NUM> and the second cylinder <NUM>, an end portion on the inner side presses the concave surface 22c, and an end portion on the outer side presses the inner peripheral surface of the first cylinder <NUM>.

The gap between the concave surface 22c and the inner peripheral surface of the first cylinder <NUM> can function as a reservoir for accommodating a liquid metal LM, or can be used as a space for arranging the spring <NUM>. Thereby, for example, the coaxiality between the first cylinder <NUM> and the second cylinder <NUM> can be maintained.

According to the seventh embodiment configured as described above, the same effect as that of the above first embodiment can be obtained. It is possible to obtain a sliding bearing unit U capable of obtaining good bearing operation and an X-ray tube <NUM> provided with this sliding bearing unit U.

Next, an X-ray tube assembly according to an eighth embodiment will be described. An X-ray tube <NUM> has the same configuration as that of the above first embodiment, except for the configurations described in the present eighth embodiment. <FIG> is an enlarged cross-sectional view showing a part of the X-ray tube assembly according to the present eighth embodiment.

As shown in <FIG>, the operation of a second cylinder <NUM> may be further restricted by a second restriction member <NUM>.

The second cylinder <NUM> further includes one or more recesses 22t. In the present eighth embodiment, the second cylinder <NUM> has three recesses 22t. These recesses 22t are located at intervals from each other in the circumferential direction. Each recess 22t opens in a second end surface 22e2 and is recessed in the direction along a rotation axis a.

The second restriction member <NUM> is configured in the same manner as the first restriction member <NUM> shown in <FIG> and the like. The second restriction member <NUM> has a first member 24a and one or more second members 24b. In the present eighth embodiment, the second restriction member <NUM> has three second members 24b. The first member 24a has an annular shape and is fixed to a first cylinder <NUM>.

The first member 24a faces the second end surface 22e2 of the second cylinder <NUM>. Thereby, the first member 24a can restrict the movement of the second cylinder <NUM> in a direction along the rotation axis a. The first member 24a includes a thrust bearing surface S24. The thrust bearing surface S24 is located on the inner peripheral side of the first member 24a and has an annular shape.

Each second member 24b protrudes from the first member 24a in a direction along the rotation axis a. The second member 24b is provided in a one-to-one correspondence with the recess 22t of the second cylinder <NUM>. Each second member 24b is fitted in the recess 22t of the second cylinder <NUM>. In the present eighth embodiment, the second member 24b can be fitted into the recess 22t without using a tightening fit. However, the second member 24b may also be fitted into the recess 22t by using the tightening fit. The second member 24b is configured to restrict the operation of the second cylinder <NUM> together with the recess 22t of the second cylinder <NUM>.

According to the eighth embodiment configured as described above, the same effect as that of the above first embodiment can be obtained. It is possible to obtain a sliding bearing unit U capable of obtaining good bearing operation and an X-ray tube <NUM> provided with this sliding bearing unit U.

Next, an X-ray tube assembly according to a ninth embodiment will be described. An X-ray tube <NUM> has the same configuration as that of the above first embodiment, except for the configurations described in the present ninth embodiment. <FIG> is a cross-sectional view showing the X-ray tube assembly according to the present ninth embodiment.

As shown in <FIG>, the X-ray tube <NUM> is formed without a tube portion <NUM>, an annulus portion <NUM>, and a tube portion <NUM>. A heat transfer portion 10a is a heat transfer hole. The heat transfer portion 10a is open to both a first bottom surface 10b1 and a second bottom surface 10b2, extends along a rotation axis a, and penetrates a stationary shaft <NUM>. A cooling fluid (coolant L) flows into the stationary shaft <NUM> from the first bottom surface 10b1 side and flows out from the second bottom surface 10b2 side to the outside of the stationary shaft <NUM>. Alternatively, the cooling fluid (coolant L) flows into the stationary shaft <NUM> from the second bottom surface 10b2 side and flows out from the first bottom surface 10b1 side to the outside of the stationary shaft <NUM>.

According to the ninth embodiment configured as described above, the same effect as that of the above first embodiment can be obtained. It is possible to obtain a sliding bearing unit U capable of obtaining good bearing operation and an X-ray tube <NUM> provided with this sliding bearing unit U.

Next, an X-ray tube assembly according to a tenth embodiment will be described. An X-ray tube <NUM> has the same configuration as that of the above first embodiment, except for the configurations described in the present tenth embodiment. <FIG> is a cross-sectional view showing the X-ray tube assembly according to the present tenth embodiment.

As shown in <FIG>, the X-ray tube <NUM> adopts a single-ended support bearing structure. An envelope <NUM> fixes a second small diameter portion <NUM> of a stationary shaft <NUM>. That is, the second small diameter portion <NUM> functions as a cantilever support portion of the bearing.

The stationary shaft <NUM> comprises a large diameter portion <NUM> and the second small diameter portion <NUM>, and is configured without a first small diameter portion <NUM>. A first bottom surface 10b1 is located on the large diameter portion <NUM>, and a thrust bearing surface Slli is located on the first bottom surface 10b1. A first restriction member <NUM> is formed in a disk shape and liquid-tightly closes one end side of a first cylinder <NUM>. The first restriction member <NUM> has a thrust bearing surface S23a facing the thrust bearing surface S11i.

In the present tenth embodiment, a second cylinder <NUM> has a recess 22t, and a second restriction member <NUM> has a first member 24a and a second member 24b. The second restriction member <NUM> is detachably fixed to the first cylinder <NUM> using, for example, a screw. The operation of the second cylinder <NUM> is restricted so that it does not rotate relative to the first cylinder <NUM>.

According to the tenth embodiment configured as described above, the same effect as that of the above first embodiment can be obtained. It is possible to obtain a sliding bearing unit U capable of obtaining good bearing operation and an X-ray tube <NUM> provided with this sliding bearing unit U.

Next, an X-ray tube assembly according to an eleventh embodiment will be described. An X-ray tube <NUM> has the same configuration as the above tenth embodiment except for the configurations described in the present eleventh embodiment. <FIG> is a cross-sectional view showing the X-ray tube assembly according to the present eleventh embodiment.

As shown in <FIG>, a stationary shaft <NUM> further comprises a flange portion <NUM>. The flange portion <NUM> is located on the outer peripheral surface side of a large diameter portion <NUM> and is integrally formed with the large diameter portion <NUM>.

A rotor <NUM> further comprises a bearing member <NUM>. The bearing member <NUM> is formed by a tubular portion surrounding the flange portion <NUM> and an annular portion facing the flange portion <NUM> in a direction along a rotation axis a being integrally formed. For example, a second restriction member <NUM>, together with the bearing member <NUM>, is detachably fixed to a first cylinder <NUM> using screws. Note that the configuration of the rotor <NUM> and the method of assembling a sliding bearing unit U are not limited to the example shown in <FIG>, and can be variously modified.

The second restriction member <NUM> and the flange portion <NUM> form a dynamic pressure thrust sliding bearing Bc together with a liquid metal LM. On the other hand, the bearing member <NUM> and the flange portion <NUM> also form a dynamic pressure thrust sliding bearing Bd together with the liquid metal LM.

According to the eleventh embodiment configured as described above, the same effect as that of the above tenth embodiment can be obtained. It is possible to obtain a sliding bearing unit U capable of obtaining good bearing operation and an X-ray tube <NUM> provided with this sliding bearing unit U.

Next, an X-ray tube assembly according to a twelfth embodiment will be described. An X-ray tube <NUM> has the same configuration as the above first embodiment, except for the configurations described in the present twelfth embodiment. <FIG> is a cross-sectional view showing the X-ray tube assembly according to the present twelfth embodiment.

As shown in <FIG>, a stationary shaft <NUM> is formed in a columnar shape and may be a solid member. The stationary shaft <NUM> can be cooled at a portion of the stationary shaft <NUM> exposed to the outside of an envelope <NUM>.

According to the twelfth embodiment configured as described above, the same effect as that of the above tenth embodiment can be obtained. It is possible to obtain a sliding bearing unit U capable of obtaining good bearing operation and an X-ray tube <NUM> provided with this sliding bearing unit U.

Claim 1:
A sliding bearing unit (U) comprising:
a stationary shaft (<NUM>) that extends along a rotation axis (a) and includes a first radial bearing surface (S11a) on an outer peripheral surface;
a rotor (<NUM>) that is rotatable around the stationary shaft (<NUM>); and
a lubricant (LM),
wherein
the rotor (<NUM>) includes:
a first cylinder (<NUM>) extending along the rotation axis (a) and formed in a tubular shape, and located surrounding the stationary shaft (<NUM>); and
a second cylinder (<NUM>) extending along the rotation axis (a) and formed in a tubular shape, located between the stationary shaft (<NUM>) and the first cylinder (<NUM>), including a second radial bearing surface (S22) on an inner peripheral surface, and whose operation is restricted so as not to rotate relative to the first cylinder (<NUM>), and
the lubricant (LM) is filled in a plurality of gaps between the stationary shaft (<NUM>), the first cylinder (<NUM>), and the second cylinder (<NUM>), and forms a dynamic pressure radial sliding bearing (Ba) together with the first radial bearing surface (S11a) and the second radial bearing surface (S22) .