Rotating anode x-ray tube

Abstract

To provide a rotating anode type X-ray tube capable of improving cooling performance of an anode target and stabilizing rotation of a rotating body.SOLUTION: A rotary anode type X-ray tube 11 includes a cathode 22 for emitting electrons, an anode target 25 for generating X-rays by collision of the electrons emitted from the cathode 22, a cylindrical rotor 24 for supporting the anode target 25, a fixed shaft 23 for rotatably supporting the rotor 24, and a sliding bearing 34. The sliding bearing 34 includes a first bearing portion 36 and a second bearing portion 37 that rotatably support the rotating body 24 with respect to the fixed shaft 23, a third bearing portion 38 provided at a position corresponding to a region of the rotating body 24 to which the anode target 25 is connected, and a liquid metal 39 interposed in a gap between the fixed shaft 23 and the rotating body 24. The gap between the fixed shaft 23 and the rotating body 24 in the third bearing portion 38 is larger than the gap in the first bearing portion 36 and the second bearing portion 37.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a rotating anode X-ray tube. [Background technology]

[0002] In X-ray tubes, X-rays are generated by bremsstrahlung radiation, which occurs when electrons emitted from a cathode collide with an anode target. The conversion efficiency during this process is approximately 1%, with the remaining 99% converted into heat. This causes the anode target to heat up. To obtain higher-power X-rays, more electrons must be collided with the anode target, which results in a significant increase in the anode target's temperature. The anode target's temperature must be kept below its melting point, and to prevent localized temperature increases in the anode target, rotating anode X-ray tubes are commonly used. A hydrodynamic sliding bearing with liquid metal as a lubricant is widely used to rotate the anode target. The sliding bearing consists of two elements: a rotating body (outer) containing the anode target, and a fixed shaft (inner) that rotatably supports this rotating body.

[0003] In the case of a computed tomography system (hereafter referred to as a CT system) equipped with a rotating anode X-ray tube, the rotating anode X-ray tube revolves at high speed along with the CT system for scanning. The centrifugal force generated by the CT system's revolution places a load on the rotating anode X-ray tube. This centrifugal force causes stress deformation in the fixed shaft, but the tube must be able to rotate stably even under these conditions. Furthermore, because a faster revolution speed allows for the creation of diagnostic images with higher time resolution, there is a demand for CT systems that revolve at higher speeds, and therefore for rotating anode X-ray tubes that can withstand higher centrifugal force loads. For these reasons, load-bearing capacity is important when installing a rotating anode X-ray tube in a CT system.

[0004] For this reason, in rotating anode X-ray tubes, the sliding bearing that supports the rotor equipped with the anode target uses a two-point support structure with a first bearing section and a second bearing section located in two places to support the mass load of the rotor and prevent tilt due to moments.

[0005] In this case, the shape and position of the first and second bearing parts of the sliding bearing are designed to appropriately support the load and moment of the rotating body. Also, to cool the anode target, a conduction cooling structure is used to conduct the heat of the anode target from the sliding bearing to the fixed shaft side.

[0006] However, because neither the first nor second bearing of the sliding bearing is located in the heat transfer path area (directly below the heat conduction surface) where the anode target of the rotor is connected and heat is transferred, it is difficult to retain the liquid metal heat transfer medium between the heat transfer path area of ​​the rotor and the fixed shaft, which could reduce the efficiency of conductive cooling between the rotor and fixed shaft.In addition, a decrease in conductive cooling efficiency could cause the rotor and fixed shaft to heat up and undergo thermal deformation, increasing the possibility of contact between the rotor and fixed shaft due to this thermal deformation or of instability in the rotation of the rotor due to bearing deformation. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6620348 [Patent Document 2] Patent No. 7070976 Summary of the Invention [Problem to be solved by the invention]

[0008] The problem to be solved by the present invention is to provide a rotating anode X-ray tube that can improve the cooling performance of the anode target and stabilize the rotation of the rotor. [Means for solving the problem]

[0009] The rotating anode X-ray tube of this embodiment includes a cathode that emits electrons, an anode target that generates X-rays when the electrons emitted from the cathode collide with it, a cylindrical rotor that supports the anode target, a fixed shaft that rotatably supports the rotor, and a plain bearing. The plain bearing includes a first bearing that rotatably supports the rotor relative to the fixed shaft, a second bearing that rotatably supports the rotor relative to the fixed shaft at a position spaced apart from the first bearing, a third bearing provided on the rotor at a position corresponding to the region where the anode target is connected, and a lubricant disposed in the gap between the fixed shaft and the rotor. The gap between the fixed shaft and the rotor at the third bearing is larger than the gaps between the fixed shaft and the rotor at the first bearing and the second bearing. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view of a rotating anode X-ray tube showing a first embodiment. [Figure 2] FIG. 10 is a cross-sectional view of a rotating anode X-ray tube showing a second embodiment. [Figure 3] FIG. 10 is a cross-sectional view of a rotating anode X-ray tube showing a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] The first embodiment will be described below with reference to FIG.

[0012] 1 shows a rotating anode X-ray tube assembly 10. The rotating anode X-ray tube assembly 10 includes a rotating anode X-ray tube 11, a stator coil 12 that generates a magnetic field for rotating the rotating part of the rotating anode X-ray tube 11, and the like.

[0013] The rotating anode X-ray tube 11 includes a vacuum envelope 21, a cathode 22, a fixed shaft 23, a rotor 24, an anode target 25, and a rotor 26. The cathode 22, the fixed shaft 23, the rotor 24, the anode target 25, and the rotor 26 are arranged inside the vacuum envelope 21, and the stator coil 12 is arranged outside the vacuum envelope 21.

[0014] The inside of the vacuum envelope 21 is maintained at a vacuum. The vacuum envelope 21 is provided with an X-ray transmission window through which X-rays generated by the anode target 25 pass and are output to the outside.

[0015] The cathode 22 emits electrons toward the anode target 25 .

[0016] The fixed shaft 23 is formed in a substantially cylindrical shape, with one end fixed to the vacuum envelope 21. The fixed shaft 23 has a fixed shaft portion 31 and support shaft portions 32, each of which has a smaller diameter than the fixed shaft portion 31 and is provided on each end of the fixed shaft portion 31. A cooling passage 30 is formed inside the fixed shaft 23, through which a refrigerant, which is a coolant for cooling, passes. The refrigerant is circulated between the cooling passage 30 and the heat exchanger by a cooling device equipped with a heat exchanger (not shown).

[0017] The rotor 24 is cylindrical and rotatably disposed around the fixed shaft portion 31 of the fixed shaft 23 with a gap 33 therebetween.

[0018] The rotating body 24 is rotatably supported by bearings on the fixed shaft 23. The bearings include a hydrodynamic plain bearing 34, which is a radial bearing that rotatably supports the radial direction of the rotating body 24 on the fixed shaft 23, and a thrust bearing 35 that rotatably supports both axial ends of the rotating body 24 on the fixed shaft 23.

[0019] The sliding bearing 34 comprises a first bearing portion 36, a second bearing portion 37 and a third bearing portion 38 which are respectively spaced apart at three locations in the axial direction of the fixed shaft 23 and the rotating body 24, and a liquid metal 39 which is a lubricant interposed in the gap between the fixed shaft 23 and the rotating body 24.

[0020] The first bearing portion 36 is provided at a position closer to one end (cathode 22 side) in the axial direction of the fixed shaft 23 and the rotor 24 than the heat transfer path area 40, which is the connection area (joining area) within the range where the anode target 25 of the rotor 24 is connected (joined) and is the path through which heat from the anode target 25 is transferred.

[0021] The second bearing portion 37 is spaced apart from the first bearing portion 36 and is located closer to the other axial end (rotor 26 side) of the fixed shaft 23 and the rotating body 24 than the heat transfer path area 40 through which heat is transferred from the anode target 25 of the rotating body 24.

[0022] The third bearing portion 38 is provided between the first bearing portion 36 and the second bearing portion 37 at a position corresponding to a heat transfer path region 40 through which heat is transferred from the anode target 25 of the rotating body 24. The third bearing portion 38 is provided apart from the first bearing portion 36 and the second bearing portion 37, and therefore the first bearing portion 36, the second bearing portion 37 and the third bearing portion 38 are provided independently.

[0023] The first bearing portion 36, the second bearing portion 37 and the third bearing portion 38 have a first bearing forming portion 41, a second bearing forming portion 42 and a third bearing forming portion 43 which are large diameter portions protruding from the outer peripheral surface of the fixed shaft portion 31 of the fixed shaft 23, a first fixed side bearing surface 44, a second fixed side bearing surface 45 and a third fixed side bearing surface 46 provided on the outer peripheral surfaces of these first bearing forming portion 41, second bearing forming portion 42 and third bearing forming portion 43, and a first rotating side bearing surface 47, a second rotating side bearing surface 48 and a third rotating side bearing surface 49 provided on the inner peripheral surface of the rotating body 24 facing these first fixed side bearing surface 44, second fixed side bearing surface 45 and third fixed side bearing surface 46.

[0024] The first fixed-side bearing surface 44 and the second fixed-side bearing surface 45 have the same outer diameter, and the third fixed-side bearing surface 46 has a smaller outer diameter than the first fixed-side bearing surface 44 and the second fixed-side bearing surface 45. The first rotation-side bearing surface 47, the second rotation-side bearing surface 48, and the third rotation-side bearing surface 49 are provided with the same inner diameter of the rotating body 24.

[0025] The dimension L1 of the first gap, which is the gap between the first fixed side bearing surface 44 and the first rotating side bearing surface 47 in the first bearing portion 36, and the dimension L2 of the second gap, which is the gap between the second fixed side bearing surface 45 and the second rotating side bearing surface 48 in the second bearing portion 37, are the same dimension, for example, approximately 20 μm.

[0026] The dimension L3 of the third gap, which is the gap between the third fixed side bearing surface 46 and the third rotating side bearing surface 49 in the third bearing portion 38, is larger than the dimension L1 of the first gap and the dimension L2 of the second gap, and is set to, for example, approximately 30 μm.

[0027] Groove patterns 50 in the shape of grooves for holding the liquid metal 39 are formed on the first fixed-side bearing surface 44 and the second fixed-side bearing surface 45. The groove patterns 50 are formed at positions spaced apart in the axial direction of each of the first fixed-side bearing surface 44 and the second fixed-side bearing surface 45, are inclined with respect to the axial direction, and have a symmetrical or asymmetrical shape.

[0028] The liquid metal 39 is sealed in the gap 33 between the fixed shaft 23 and the rotor 24, and is made of a fluid lubricant material such as a gallium-indium (Galn) alloy or a gallium-indium-tin (GaInSn) alloy.

[0029] The thrust bearing 35 has a disk-shaped thrust bearing member 51 attached to the end of the rotating body 24, and is composed of a thrust bearing surface 52 of this thrust bearing member 51, the end face of the fixed shaft portion 31, and liquid metal 39 interposed between them. The thrust bearing 35 has a hole 53 in the center through which the fixed shaft 23 is inserted, and a thrust seal portion 54 is provided on the inner peripheral surface of this hole 53 to seal against the peripheral surface of the fixed shaft 23.

[0030] The anode target 25 is provided in a disk shape and protrudes from the outer circumferential surface of the rotor 24. An anode 55 that generates X-rays when electrons emitted from the cathode 22 collide with the anode target 25 on the surface facing the cathode 22. The anode 55 is made of a heavy metal with a high melting point, such as molybdenum (Mo), tungsten (W), or an alloy of these.

[0031] The rotor 26 is cylindrical and is provided around the rotating body 24 .

[0032] The stator coil 12 is disposed at a position facing the rotor 26 across the vacuum envelope 21, and generates a magnetic field that rotates the rotor 26.

[0033] In the rotating anode X-ray tube 11, the anode target 25 rotates together with the rotor 24, and electrons emitted from the cathode 22 collide with the anode 55 of the anode target 25 to generate X-rays. The heat generated by the electron collisions causes the temperature of the anode target 25 to rise, and the heat of the anode target 25 is conducted from the rotor 24 to the fixed shaft 23 via the sliding bearing 34 and is absorbed by the coolant circulating inside the fixed shaft 23, thereby suppressing the temperature rise of the anode target 25.

[0034] In the rotating anode X-ray tube 11 of this embodiment, the third bearing portion 38 is provided between the first bearing portion 36 and the second bearing portion 37 at a position corresponding to the heat transfer path region 40 through which heat is transferred from the anode target 25 of the rotor 24. Therefore, when the rotor 24 rotates, liquid metal 39 can be drawn into and retained in the gap between the fixed shaft 23 (third fixed-side bearing surface 46) and the rotor 24 (third rotation-side bearing surface 49) in the third bearing portion 38. This ensures a heat transfer path for transferring heat from the rotor 24 to the fixed shaft 23, improving the efficiency of conductive cooling from the rotor 24 to the fixed shaft 23. In addition, the improved conductive cooling efficiency can suppress thermal deformation due to a rise in temperature of the rotor 24 and the fixed shaft 23. This suppresses contact between the rotor 24 and the fixed shaft 23 due to thermal deformation and unstable rotation of the rotor 24 due to bearing deformation, thereby stabilizing the rotation of the rotor 24.

[0035] Incidentally, because the third bearing 38 serves as a heat transfer path for transferring heat from the rotor 24 to the fixed shaft 23, it is more susceptible to the effects of thermal stress than the first bearing 36 or the second bearing 37, and may induce rotational instability of the rotor 24 due to contact between the rotor 24 and the fixed shaft 23 or unevenness in the bearing gap caused by thermal deformation. Furthermore, when the third bearing 38 is provided, when the anode target 25 is rotated at high speed, various resonance modes occur, compared to a normal two-point support bearing structure, increasing the possibility of inducing rotational instability of the rotor 24.

[0036] Therefore, by making the gap between the fixed shaft 23 (third fixed side bearing surface 46) and the rotating body 24 (third rotating side bearing surface 49) in the third bearing portion 38 wider than the gap in the first bearing portion 36 and the second bearing portion 37, it is possible to reduce the induction of rotational instability in the rotating body 24, and it has the effect of increasing the amount of thermal deformation that can be tolerated due to contact between the rotating body 24 and the fixed shaft 23.

[0037] If the spring force maintaining the gaps between the first bearing portion 36, the second bearing portion 37, and the third bearing portion 38 is considered as a bearing spring constant, by widening the gap of the third bearing portion 38, it is possible to make the bearing spring constant of the third bearing portion 38 sufficiently small relative to the bearing spring constants of the first bearing portion 36 and the second bearing portion 37, thereby making it possible to reduce the induction of rotational instability of the rotating body 24 due to resonance.

[0038] In this way, it is possible to provide a rotating anode X-ray tube 11 that can improve the cooling performance of the anode target 25 and stabilize the rotation of the rotor 24.

[0039] Furthermore, cold work tool steel (e.g., SKD11) or molybdenum-based metals can be used as materials for the bearings (fixed shaft 23, rotating body 24), but because the third bearing portion 38 serves as a heat transfer path, it is more susceptible to thermal effects than the first bearing portion 36 and the second bearing portion 37. Therefore, by forming the fixed shaft 23 from a tungsten carbide-based alloy and the rotating body 24 from SKD11 or a molybdenum alloy, it is possible to improve conduction cooling performance by improving thermal conductivity while suppressing thermal deformation of the third bearing portion 38.

[0040] Next, FIG. 2 shows a second embodiment.

[0041] In order to make the gap between the fixed shaft 23 (third fixed-side bearing surface 46) and the rotating body 24 (third rotation-side bearing surface 49) in the third bearing portion 38 wider than the gaps in the first bearing portion 36 and the second bearing portion 37, this can also be achieved by making the inner diameter of the third rotation-side bearing surface 49 of the rotating body 24 in the third bearing portion 38 larger than the inner diameters of the first rotation-side bearing surface 47 and the second rotation-side bearing surface 48 in the first bearing portion 36 and the second bearing portion 37. In this case, the outer diameters of the first fixed-side bearing surface 44, the second fixed-side bearing surface 45, and the third fixed-side bearing surface 46 may be the same.

[0042] In addition, the gap between the fixed shaft 23 (third fixed side bearing surface 46) and the rotating body 24 (third rotating side bearing surface 49) in the third bearing portion 38 may be made wider than the gap in the first bearing portion 36 and the second bearing portion 37 by both making the outer diameter of the third fixed side bearing surface 46 smaller than that of the first fixed side bearing surface 44 and the second fixed side bearing surface 45 and making the inner diameter of the third rotating side bearing surface 49 larger than that of the first rotating side bearing surface 47 and the second rotating side bearing surface 48.

[0043] Next, a third embodiment is shown in FIG.

[0044] The third fixed-side bearing surface 46 of the third bearing portion 38 may be provided with groove patterns 58 in the shape of grooves for holding the liquid metal 39. The groove patterns 58 are formed at positions spaced apart in the axial direction of the third fixed-side bearing surface 46, are inclined with respect to the axial direction, and have a symmetrical or asymmetrical shape.

[0045] By providing the groove pattern 58 on the third fixed-side bearing surface 46, the liquid metal 39 is more easily retained in the third bearing portion 38, and the conductive cooling performance from the rotating body 24 to the fixed shaft 23 can be further improved.

[0046] In each of the above-described embodiments, the third bearing portion 38 is installed between the first bearing portion 36 and the second bearing portion 37, but by appropriately designing the center of gravity, the third bearing portion 38 may also be installed outside the first bearing portion 36 and the second bearing portion 37.

[0047] Furthermore, the third fixed side bearing surface 46 is not limited to being provided independently and spaced apart from the first bearing portion 36 and the second bearing portion 37, but may also be provided over the entire area between the first bearing portion 36 and the second bearing portion 37.

[0048] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0049] 11 Rotating anode X-ray tube 22 Cathode 23 Fixed axis 24 Rotating Body 25 Anode target 34 Plain bearing 36 1st bearing part 37 Second bearing part 38 3rd bearing part 39 Liquid metal as a lubricant 44 1st fixed side bearing surface 45 2nd fixed side bearing surface 46 3rd fixed side bearing surface 47 First rotating side bearing surface 48 Second rotation side bearing surface 49 Third rotation side bearing surface 58 Groove Patterns

Claims

1. a cathode that emits electrons; an anode target that generates X-rays when struck by the electrons emitted from the cathode; a cylindrical rotor supporting the anode target; a fixed shaft that rotatably supports the rotating body; a first bearing portion that rotatably supports the rotating body relative to the fixed shaft; a second bearing portion that rotatably supports the rotating body relative to the fixed shaft at a position spaced apart from the first bearing portion; and a plain bearing having a lubricant interposed in a gap between the fixed shaft and the rotating body; Equipped with The sliding bearing has a third bearing portion provided at a position corresponding to a region of the rotating body to which the anode target is connected, and a gap between the fixed shaft and the rotating body at the third bearing portion is larger than gaps between the fixed shaft and the rotating body at the first bearing portion and the second bearing portion. A rotating anode X-ray tube characterized by:

2. the first bearing portion, the second bearing portion, and the third bearing portion have a first fixed-side bearing surface, a second fixed-side bearing surface, and a third fixed-side bearing surface provided on the fixed shaft, respectively; The outer diameter of the third fixed-side bearing surface is smaller than the outer diameters of the first fixed-side bearing surface and the second fixed-side bearing surface.

2. The rotating anode X-ray tube according to claim 1.

3. the first bearing portion, the second bearing portion, and the third bearing portion have a first rotation-side bearing surface, a second rotation-side bearing surface, and a third rotation-side bearing surface provided on the rotating body, respectively; The inner diameter of the third rotation-side bearing surface is larger than the inner diameters of the first rotation-side bearing surface and the second rotation-side bearing surface.

2. The rotating anode X-ray tube according to claim 1.

4. The third bearing portion has a third fixed-side bearing surface provided on the fixed shaft and a groove pattern provided on the third fixed-side bearing surface.

2. The rotating anode X-ray tube according to claim 1.

5. The third bearing portion has a third fixed-side bearing surface that protrudes from the peripheral surface of the fixed shaft.

2. The rotating anode X-ray tube according to claim 1.

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