JPH07153400A - X-ray tube - Google Patents

Abstract

PURPOSE: To provide an X-ray tube including a bearing capable of rotating at a high speed by reducing a friction loss without any leakage of lubricant. CONSTITUTION: The performance and durability of a hydrodynamic slide, bearing 29 used in an X-ray tube can be improved by disposing floating inserted bodies 40, 42, 44. The hydrodynamic slide bearing 29 includes a liquid metal lubricant 38 filling clearances defined between support faces 31, 32, 33, 35, 36, 37 of the slide bearing 29. The floating inserted bodies 40, 42, 44 such as flat rings or cylindrical sleeves are soaked in the liquid metal lubricant 38 between the respective pairs of support faces in cooperation with each other. The floating inserted bodies 40, 42, 44 can freely float in the liquid metal lubricant 38 without any contact with the adjacent support faces. The floating inserted bodies 40, 42, 44 are rotated at an average speed at the support faces, thereby reducing a relative speed to 1/2. Consequently, it is possible to achieve a higher operating speed at a reduced friction loss without any leakage of the lubricant.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates generally to plain bearings for X-ray tubes, and more specifically, is disposed between bearing surfaces and immersed in a liquid metal lubricant. To a plain bearing having a floating insert.

[0002]

2. Description of the Prior Art X-ray tubes generally include a rotating anode located inside a vacuum tube. X-ray radiation is generated by irradiating the anode with electrons. To prevent its rapid deterioration, the anode is rotated at high speed. This rotation is accomplished by mounting the anode on a rotatable spindle that is coupled to the vacuum tube via a bearing assembly. Today's diagnostic x-ray procedures often require high energy exposures in quick succession. These steps are
Rapidly increase the temperature of both the anode and bearing assembly.
When approaching or exceeding the permissible temperatures of these systems, the useful life of the x-ray tube may be shortened or even fail immediately. One way to limit the anode temperature is to increase the size and / or rotational speed of the anode. However, increasing the size or rotational speed of the anode increases the axial and radial loads on the bearing assembly, which reduces bearing life.

One type of bearing system commonly used in X-ray tubes comprises two ball bearings. Ball bearings used in X-ray tubes are typically lubricated with a soft solid metal coating. This is because the more conventional ball bearing lubricants are not suitable for use in the high vacuum operating environment of X-ray tubes. Solid metal coated lubricants do not adequately dampen chattering noise in ball bearings and have no endurance when used continuously at high speeds and temperatures.

A quieter and more durable alternative to metal-coated ball bearing systems is the so-called hydrodynamic bearing or full-film bearing. Hydrodynamic plain bearings used in X-ray tubes typically include a pair of cooperating bearing surfaces with a low vapor pressure liquid metal lubricant disposed in the gap between the surfaces. Has been done. The lubricant wets the bearing surfaces and completely fills the gap, even under load, with no contact between the surfaces. A spiral groove can be provided on at least one bearing surface to increase kinematic stability and load bearing capacity. Hydrodynamic plain bearings do not cause bearing chattering and can have a long life. In addition, the liquid metal lubricants of these bearings also work well in dissipating the heat generated at the anode, while at the same time acting as contacts that supply the required high voltage.

However, at high operating speeds, instability may occur in the liquid lubricant, causing breaks in the liquid metal layer and leakage. Lubricant leakage not only causes bearing failure and breakage problems, but when liquid metal lubricant enters the vacuum tube where there is a strong electric field under operating conditions,
The wire tube may be destroyed. Furthermore, higher rotational speeds mean higher friction losses. For these reasons, conventional plain bearings have a limited range of operating speeds for which they are useful.

[0006] Therefore, there is a need for a hydrodynamic plain bearing that can rotate at high speeds without leaks and with low friction losses.

[0007]

SUMMARY OF THE INVENTION The needs set forth above are met by the present invention which provides an X-ray tube with a vacuum tube having an immovable member mounted therein. The immovable member has at least one planar bearing surface formed thereon and at least one cylindrical bearing surface. A rotating member is rotatably mounted on the immovable member so that it can rotate about an axis. The rotating member has at least one planar bearing surface formed thereon and at least one cylindrical bearing surface, the bearing surfaces comprising:
It is paired with a corresponding bearing surface on the immovable member. The corresponding bearing surfaces of each pair are facing and spaced apart, defining a gap therebetween.

Each gap is filled with a liquid metal lubricant such as gallium or a gallium-based alloy. Floating inserts are each disposed between a pair of corresponding bearing surfaces and are immersed in the lubricant therein. The insert placed between the flat bearing surfaces is
The insert, which is a flat annulus and is arranged between the cylindrical bearing surfaces, is a cylindrical sleeve. Spiral grooves can be provided on the bearing surface and / or on at least one surface of the insert to increase the kinematic stability of the bearing.

Other objects and advantages of the present invention will become apparent from the following detailed description of the drawings.
While the spirit of the invention is specifically and clearly set forth in the appended claims, the invention is best understood from the following description of the drawings.

[0010]

1 shows an X-ray tube 10 of the present invention, although the same reference numerals are used for like parts throughout the drawings. The X-ray tube 10 is equipped with a vacuum tube 12,
Is a relatively large glass envelope or bell 14 and a thin glass neck 16 extending outwardly from one end of the bell 14.
It is an integral member including and. Inside the vacuum tube 12, a cathode 18 and an anode 20 are provided. Cathode 1
8 emits an electron hitting the anode 20, and X is emitted in a known manner.
Generates linear energy.

The anode 20 is mounted on a rotor assembly 22 for rotation therewith. The rotor assembly 22 has a rotor base 24 provided at one end thereof. A bearing shroud or interface member 26 extends from the distal end of the glass neck 16 to the rotor base 24,
These elements are fixed. The interface member 26 is a thin sleeve having a somewhat conical shape, and the interface member 26 reduces the risk of neck cracking due to the different thermal properties of the rotor base 24 and the glass neck 16. It has characteristics. The rotor assembly 22 further includes a stationary shaft 28 mounted on the rotor base 24 for entry into the vacuum tube 12 along the longitudinal axis of the neck 16. The stationary shaft 28 is a substantially cylindrical member, and a circular flange 30 extends in a radial direction from an intermediate position of the cylindrical member. The axially opposite sides of the circular flange 30 are perpendicular to the longitudinal axis of the shaft 28 and define two planar bearing surfaces 31 and 32,
A portion of the cylindrical bearing surface 3 above the flange 30 is concentrically arranged along the longitudinal axis of the shaft 28.
3 is defined.

A rotary bearing housing 34 is rotatably mounted on the stationary shaft 28 by hydrodynamic plain bearings 29 (detailed in FIG. 2). Rotary bearing housing 34
Rotates about an axis that coincides with the longitudinal axis of axis 28. The anode 20 is mounted on the bearing housing 34 via the protrusion 36.
Is attached to the upper surface of. The rotation of the bearing housing 34, and thus the anode 20, is accomplished by electromechanical means (not shown) as is well known. The bearing housing 34 is a hollow cylindrical member, which is
A first part surrounding the circular flange 30 and the shaft 2
And a second portion surrounding the upper portion of 8. The axially inner surface of the first part of the bearing housing 34 defines two planar bearing surfaces 35 and 36 corresponding to the two planar bearing surfaces 31 and 32, respectively. . The inner radial surface of the second part of the bearing housing 34 defines a cylindrical bearing surface 37 corresponding to the cylindrical bearing surface 33 formed on the stationary shaft 28. For this reason, the bearing 29 consists of three pairs of corresponding bearing surfaces. The corresponding bearing surfaces of each pair are facing and spaced apart to define a gap therebetween.

As best shown in FIG. 2, each gap between the bearing surfaces is filled with a liquid metal lubricant 38. The lubricant 38 wets the bearing surfaces and completely fills the gap without allowing any contact between the corresponding bearing surfaces, either at rest or in motion. The lubricant 38 contained in the gap is used for the X-ray tube 10.
It can be any suitable low vapor pressure metal that is liquid at the normal ambient temperatures of. Metals with a melting point slightly above room temperature can be used, but this requires preheating of the X-ray tube 10 before operation. For this reason, metals that are liquid at room temperature are preferred. Further, the metal used should be low in viscosity so that viscous drag on the rotary bearing housing 34 does not noticeably increase the power required to produce the desired rotation.

Liquid metals composed of gallium or gallium alloys are particularly suitable lubricants for the present invention.
One preferred liquid metal is an alloy of gallium, indium and tin which has a melting point of about 5 ° C. Gallium-based lubricants have sufficiently low vapor pressure at normal operating temperatures that unexpected gas release does not occur. However, when using such a lubricant, the stationary shaft 28
Also, the rotary bearing housing 34 (and the insert described below) must be made of materials that can withstand gallium and gallium alloys. Such materials include tugsten, molybdenum, rhenium, and their alloys.

Bearings 29 further include floating inserts immersed in liquid lubricant 38 between each pair of corresponding bearing surfaces. Each insert is essentially the same length as the bearing surface between which it is located. Specifically, a first thin flat annulus insert 40 is disposed between the corresponding planar bearing surfaces 31 and 35, and a second thin flat annulus insert is provided. 42 is disposed between the corresponding planar bearing surfaces 32 and 36. A thin cylindrical sleeve insert 44 is arranged between the corresponding cylindrical bearing surfaces 33 and 37. All inserts are immersed in the lubricant 38 and are free to float in the lubricant 38 without contacting either of the adjacent bearing surfaces. Therefore, each one of the three gaps between the corresponding bearing surfaces is two "film gaps".
Each membrane gap is separated by one bearing surface and one surface of each insert.

In operation, the insert rotates at the average speed of the corresponding bearing surface. That is, when the rotary bearing housing 34 is rotated around the stationary shaft 28 at 10,000 RPM, the insert rotates at 5000 RPM. Therefore, at this time, 2
Although there are twice as many membranous gaps, the relative velocity of the boundary surface (the bearing surface and the surface of the insert) defining the membranous gap is
It decreases to / 2. However, since the leakage and dynamic stability of the bearing assembly 29 is a function of relative velocity, the x-ray tube 10 is made higher without leakage of lubricant from the film gap and with less friction loss. Can drive at speed.

Due to the high surface tension of the liquid metal lubricant 38, capillarity forces tend to maintain this lubricant in the film gap. Further, the surface adjacent to the interface between the liquid metal and the vacuum of the tube can be coated with an anti-wetting agent that acts as a repellent to the lubricant 38 to prevent lubricant leakage. The titanium oxide layer is very effective as an anti-wetting agent in hydrodynamic bearings using a gallium-based lubricant. The lubricant / vacuum interface is typically formed in the gap between the shaft 28 and the lowermost portion of the rotary bearing housing 34, but this interface is closer to the insert 42. It may be formed.
If the interface is formed in this gap, another sleeve insert can be placed in the gap to further protect against leakage. Furthermore, a so-called spiral groove is formed on at least one boundary surface between the film-shaped gaps,
Dynamic stability can be increased. When the interfaces rotate relative to each other, such spiral grooves tend to push the liquid lubricant into the film gap.

As can be seen in FIG. 2, the cylindrical bearing surface 33 of the shaft 28 has two chevron groove patterns 46 and 48 formed therein. The groove patterns 46 and 48 are not limited to the chevron shape of FIG. 2, but can be any type of spiral groove that has a tendency to push the lubricant into the film gap. The two groove patterns are axially spaced to provide optimum radial support. (It should be appreciated that two cylindrical sleeve inserts, one for each groove pattern, may be used instead of one cylindrical sleeve insert 44 covering both groove patterns. ) Cylindrical sleeve insert 44
Similar groove pattern on the outer surface of the (not shown in the drawing)
Are formed. For this reason, each cylindrical membranous gap has at least one boundary surface in which a groove is provided. Grooves on the cylindrical bearing surface 37 of the inner surface of the rotary bearing housing 34 instead of the outer surface of the sleeve 44 and on the inner surface of the cylindrical sleeve insert 44 instead of the cylindrical bearing surface 33 will also affect performance. Although it does not, the first-mentioned surface is considered to be a better choice simply in that it is easier to machine the groove.

The spiral groove can be provided also in the flat film-like gap. This means that a groove is provided on at least one boundary surface between the respective planar film-like gaps. Also in this case, the groove may be formed on any boundary surface of the film gap, but it is best to select the boundary surface that is the easiest to process. For example, grooves can be formed on both sides of the ring inserts 40 and 42. If the structural integrity of the thin insert is adversely affected by providing grooves on both sides, the flange 3
Other planes such as zero planar bearing surfaces 31 and 32, or inner planar bearing surfaces 35 and 36 may be used. FIG. 3 and FIG. 4 show two types that can be used in a flat film-like gap.
A groove pattern is shown. Specifically, FIG. 3 shows the insert 40 having the spiral groove pattern 41a, and FIG. 4 shows the insert 40 having the chevron groove pattern 41b. For simplicity, the term "spiral" as used herein is intended to include spirals, chevron and any other suitable groove pattern shape.

5 and 6 show another embodiment which provides both axial and radial support. Specifically, FIG. 5 shows a bearing housing 51 and a shaft 52 that are rotatably connected by a hydrodynamic plain bearing 53. As shown in FIG. 5, the shaft 52 rotates and the bearing housing 51 is stationary, but it may be reversed. Bearing housing 5
1 is formed with a hemispherical recess defining a first spherical bearing surface 54. Attached to one end of the shaft 52 is a sphere 55, which defines a second spherical bearing surface 56. The sphere 55 is arranged in a hemispherical recess so that the two bearing surfaces 54 and 56 face each other and thus define the bearing 53.

Bearing surfaces 54 and 56 are concentrically disposed and spaced from the axis of rotation and define a gap therebetween. The gap is filled with a liquid metal lubricant 57, which bears on bearing surfaces 54 and 5.
6 is wetted to completely fill the gap without allowing contact between bearing surfaces 54 and 56. A hemispherical floating insert 58 is immersed in a liquid metal lubricant 57 between bearing surfaces 54 and 56. The insert 58 is immersed in the lubricant so that it can float freely without contacting either bearing surface 54 or 56. A spiral groove 59 is formed on the outer surface of the second spherical bearing surface 56 and the insert 58,
The dynamic stability of the bearing 53 can be improved.

FIG. 6 shows a bearing housing 61 and a shaft 62 which are rotatably connected by a hydrodynamic slide bearing 63.
Indicates. As shown in FIG. 6, the shaft 62 rotates and the bearing housing 61 is stationary, but this may be reversed.
The bearing housing 61 includes a first frustoconical bearing surface 64.
A frusto-conical recess defining a. Axis 6
A frustoconical portion 65 is formed at one end of 2, and the frustoconical portion 65 defines a second frustoconical bearing surface 66. The frusto-conical portion 65 is disposed in the frusto-conical recess so that the two bearing surfaces 64 and 66 face each other and thus define the bearing 63.

Bearing surfaces 64 and 66 are concentrically disposed and spaced from the axis of rotation and define a gap therebetween. Liquid metal lubricant 6
7 and the lubricant is bearing surfaces 64 and 66.
To completely fill the gap without allowing contact between bearing surfaces 64 and 66. A hollow frustoconical floating insert 68 between the bearing surfaces 64 and 66
It is immersed in the lubricant 67. The insert 68 is immersed in the lubricant so that it can float freely without contacting either bearing surface 64 or 66. A spiral groove 69 can be formed on the second frustoconical bearing surface 66 and the outer surface of the insert 68 to improve the dynamic stability of the bearing 63.

The hydrodynamic plain bearing having a floating insert has been described above. This bearing can rotate at high speed without leakage and with reduced friction loss.
Although particular embodiments of the present invention have been described, one of ordinary skill in the art would appreciate that
It will be apparent that various modifications can be made thereto without departing from the spirit of the invention as defined by the claims.

[Brief description of drawings]

1 is a cross-sectional view of an X-ray tube having a hydrodynamic bearing of the present invention.

FIG. 2 is a sectional view of the hydrodynamic bearing of the present invention.

FIG. 3 is a view showing a spiral groove of the first embodiment used in the present invention.

FIG. 4 is a view showing a spiral groove of a second embodiment used in the present invention.

FIG. 5 is a sectional view of the spherical hydrodynamic bearing of the present invention.

FIG. 6 is a cross-sectional view of a frustoconical hydrodynamic bearing of the present invention.

[Explanation of Codes] 10 X-ray tube 12 Vacuum tube 18 Cathode 20 Anode 22 Rotor assembly 28 Immovable shaft 29 Hydrodynamic sliding bearing 30 Circular flanges 31, 32, 35, 36 Planar bearing surface 33, 37 Cylindrical bearing surface 34 Rotation Bearing housing 38 Lubricants 40, 42, 44 Inserts 46, 48 Groove pattern

Claims (19)

[Claims] 1. A vacuum tube, an immovable member mounted inside the vacuum tube and having a first bearing surface, and rotatably mounted to the immovable member so as to rotate about an axis. A rotary member having a second bearing surface facing the first bearing surface, the first and second bearing surfaces being spaced apart to define a gap therebetween. An X-ray tube including a rotating member, a lubricant that fills the gap, and an insert body that is immersed in the lubricant. 2. The X-ray tube according to claim 1, wherein the first and second bearing surfaces are flat surfaces provided perpendicular to the axis. 3. The X-ray tube according to claim 2, wherein the insert is a flat ring. 4. The X-ray tube according to claim 1, wherein the first and second bearing surfaces are cylindrical surfaces concentrically provided around the axis. 5. The X-ray tube according to claim 4, wherein the insert is a cylindrical sleeve. 6. The X-ray tube according to claim 1, wherein the first and second bearing surfaces are spherical surfaces concentric with the axis. 7. The X-ray tube according to claim 1, wherein the first and second bearing surfaces are frustoconical surfaces concentric with the axis. 8. The X-ray tube according to claim 1, further comprising a spiral groove formed in at least one of the first and second bearing surfaces. 9. The X according to claim 1, further comprising a spiral groove formed on at least one surface of the insert.
Line tube. 10. The X-ray tube according to claim 1, wherein the lubricant is a liquid metal. 11. The X-ray tube according to claim 10, wherein the liquid metal contains gallium. 12. A vacuum tube, an immovable member mounted inside the vacuum tube and having a first planar bearing surface and a first cylindrical bearing surface, and around an axis. A rotary member rotatably mounted on the immovable member so as to rotate, and having a second planar bearing surface and a second cylindrical bearing surface, the first and the The second planar bearing surfaces face and are spaced apart to define a first clearance therebetween, the first and second cylindrical bearing surfaces having a second clearance therebetween. A rotating member facing and spaced apart to define, a lubricant filling the first and second gaps, and provided between the first and second planar bearing surfaces. And a first insert body immersed in the lubricant, Together it is provided between the first and bearing surface of the second cylindrical, X-rays tube and a second insertion member is immersed in the lubricant. 13. A third flat bearing surface formed on the immovable member and a fourth flat bearing surface formed on the rotating member, wherein the third and fourth bearing surfaces are formed. A fourth planar bearing surface facing and spaced apart to define a third gap therebetween, a lubricant filling the third gap, and The X-ray tube according to claim 12, further comprising: a third insert member provided between the third and fourth planar bearing surfaces and immersed in the lubricant. 14. The X-ray tube according to claim 13, wherein the first and third inserts are flat annular bodies, and the second insert is at least one cylindrical sleeve. . 15. All of the planar bearing surfaces are provided perpendicular to the axis, and the first and second bearing surfaces are provided.
14. The X-ray tube according to claim 13, wherein the cylindrical bearing surface of is provided concentrically with respect to the axis. 16. A spiral groove formed in at least one of the first and second planar bearing surfaces, and at least one of the third and fourth planar bearing surfaces. The X-ray tube according to claim 13, further comprising: a spiral groove formed in the first side and a spiral groove formed in at least one of the first and second cylindrical bearing surfaces. 17. A spiral groove formed on at least one surface of the first insert, a spiral groove formed on at least one surface of the second insert, and the third groove. The X-ray tube according to claim 13, further comprising a spiral groove formed on at least one surface of the insert body. 18. The X-ray tube according to claim 13, wherein the lubricant is a liquid metal. 19. The X-ray tube according to claim 18, wherein the liquid metal contains gallium.