JP2006261096A - Radiation emitting apparatus with bearings and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve ball bearings for supporting a rotary anode of an X-ray tube. <P>SOLUTION: An X-ray tube equipped with a cartridge with a bearing and its production method are provided. The tube includes a sealed container in which X-ray radiation is generated. A cathode, an anode which is opposed to the cathode and rotates on a shaft (7), and a fixed anode-shaft support (11) having a holding chamber (12) in which an anode shaft is held are prepared in the container. The support in the form of a detachable cartridge has ball bearings (26, 28). The chamber of the support is filled with gallium-indium-tin alloy and sealing arrangements (18, 19) are prepared in the place of exits of the shaft in order to prevent the alloy from leaking. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  Embodiments of the present invention are a radiation emitting apparatus such as an X-ray tube in which a cartridge is provided with a rotary anode having a bearing, and a manufacturing method thereof. Embodiments of the present invention can be used for medical imaging and can be used in the field of non-destructive testing and control when using high power radiation emitting devices.

  For example, in a radiological examination, X-rays are generated by an electron tube provided with an anode that rotates on a shaft. The strong electric field formed between the cathode and anode allows electrons emitted by the cathode to impinge on the anode and generate x-rays. For this x-ray emission, a positive polarity is applied to the anode by the shaft of the anode and a negative polarity is applied to the cathode. This unit is insulated, in particular, by a dielectric part or a sealed container of electron tubes. This sealed container may be partially made of glass.

  When using a tube at high power, the impact of electrons on the anode has the effect of abnormally heating the anode. If the power is too high, the trajectory of the anode discharge may be damaged and a collision hole may be opened. To prevent such overheating, the anode is rotated so that a constantly updated and constantly cooled surface is directed to the electron stream. Thus, the tube motor freely drives the anode shaft with a mechanical bearing. The shaft is disposed in the anode chamber. The anode chamber itself is formed as an anode support. The bearing is held on the one hand by the anode support and on the other hand the anode shaft.

  In practice, when manufactured on an industrial scale, the bearings include conventional ball bearings as opposed to rarely used magnetic bearings. The problem presented by the rotary anode arises from the rapid wear of the ball metal film during shaft rotation in the bearing. Then, the practical life is about 100 hours, and the service period of the pipe is about 6 months to 1 year. In order to overcome this problem, the balls can be coated with a thin layer of metal, lead or silver.

In order to suppress fast wear of the metal layer, a lubricant film is placed between the bearing and the anode shaft at the interface between the ball surface and the shaft surface. The inside of the chamber is filled with a liquid mainly composed of gallium-indium-tin. The reason for choosing such a liquid is that it improves the coefficient of friction, reduces collision noise between balls, and enhances heat transfer to the stationary member by heating the anode, either by convection or conduction. Other lubricant liquids are generally not selected because of their low degassing properties.
Japanese Patent Laid-Open No. 5-258691 US Pat. No. 6,125,168 US Pat. No. 6,160,868 US Pat. No. 6,377,658 US Pat. No. 6,192,107 U.S. Pat. No. 4,943,889 U.S. Pat. No. 3,719,847 US Patent Application Publication No. 2003/0165217

  It has been found that the use of alloys based on gallium-indium-tin contributes to the difficulties. In fact, the alloy is liquid at ambient temperatures (10 ° C. and above) and oxidizes very rapidly on contact with air. This oxide is solid and takes the form of a surface film within a very short time of about 1 to 2 minutes. This means that any industrial scale handling of this liquid must be done in a neutral atmosphere or under vacuum with some precautions. In addition, the thin film has no lubricity and is actually far from lubricity. Furthermore, gallium is highly corrosive. When handling this mixture, even in the laboratory, liquid can spill, leak, or overflow, and can cause puddles or deposits on the surface being handled. Then, it is very difficult to remove all of these puddles or deposits in the white room, that is, the clean room, particularly in the production system (in the closed vessel of the pipe). Even if the contamination is wiped off, the contamination will reappear within a few seconds in the form of another brownish contamination at the location just cleaned (but not completely cleaned). The condition of the clean room will then not meet the requirements for high quality manufacturing.

  These difficulties then have two forms. That is, the handling of the alloy itself in the laboratory or plant and the manner of insertion into the bearing under vacuum during the manufacture of the tube. In addition, the purity of this liquid can be lost over time despite the contribution to the lubrication of the bearing in the association with the ball of the bearing, and can eventually be as ineffective as with the ball coating. There is.

  In order to improve diagnosis at present and in the future, the power required by electron tubes is increasing. This increase in power increases the anode weight from 6 kg to 8 kg. As a result, the effect inside the bearing is becoming important. Furthermore, when used in computed tomography with continuous rotation at 2 revolutions per second, the bearing receives an acceleration of approximately 8G. A rotational speed of 3-4 revolutions per second is predicted. As a result, the service life of bearings with balls and liquids, and thus the service life of tubes, can be limited in time. In fact, if heating and friction occur inside the bearing, the liquid will lose its properties as it occurs, and thus quality may be impaired.

  Furthermore, the use of a rotating anode must meet three main constraints. First, the anode rotation must be as free and complete as possible, and a simple solution for dynamic equilibrium must be designed to prevent the tube from vibrating when the anode rotates. Second, the anode must be capable of being raised to high voltages (usually steel ball bearings serve this purpose). Third, the heat generated by the impact of the electrons on the anode target and propagating through the shaft must be dissipated efficiently.

  Japanese Patent Laid-Open No. 5-258691 (Patent Document 1) describes an assembly in which a ball bearing is lubricated with a gallium alloy. However, this assembly does not meet the above constraints. In fact, the balance in this publication is difficult due to the large rotor diameter, heat dissipation is performed by a small fixed shaft, and no design to improve thermal and electrical conduction has been found.

  US Pat. No. 6,125,168 (Patent Document 2) discloses an X-ray tube having improved heat conduction only by using a gallium alloy. US Pat. No. 6,160,868 (Patent Document 3) also improves the thermal conductivity with a gallium alloy. US Pat. No. 6,377,658 (Patent Document 4) has the same format, and US Pat. No. 6,192,107 (Patent Document 5) also has the same format. US Pat. No. 4,943,889 (Patent Document 6) cools the anode itself. For thermal reasons, US Pat. No. 3,719,847 provides a liquid metal that returns to a liquid state after evaporation. US Patent Application No. 2003/0165217 (Patent Document 8) is provided only with a heat shunt.

  One embodiment of the present invention is a radiation emitting device such as an X-ray tube that includes a sealed container in which radiation is generated. In the sealed container, there are disposed a cathode, an anode disposed opposite to the cathode and rotating on the shaft, and a fixed anode / shaft support. The support includes a holding chamber, and the anode shaft is held in the chamber. The support is in the form of a removable cartridge. The support part has a ball bearing. The chamber of the support is filled with a liquid lubricant such as a gallium-indium-tin alloy. The chamber is provided at the shaft outlet with means such as a sealing arrangement to prevent the alloy from leaking out of the chamber.

  One embodiment of the present invention is a method of mounting a rotating anode on a radiation emitting device such as an x-ray tube. The method includes providing an anode shaft that is mounted within an anode support chamber. A vacuum is set in the chamber. The anode chamber under vacuum is filled with a liquid lubricant such as a gallium-indium-tin alloy, thus producing a cartridge. The cartridge is fixedly attached to a radiation emitting device such as an X-ray tube.

  Embodiments of the present invention will be more clearly understood from the following description and the accompanying drawings. These drawings are provided for illustrative purposes only and are not intended to limit the scope of the invention in any way.

  In order to solve the above problems and meet the above constraints, embodiments of the present invention provide a cartridge for an x-ray tube. In an embodiment of the present invention, the anode support includes a cartridge that can be easily removed and replaced. The cartridge includes an anode shaft mounted by ball bearings in the chamber of the fixed support. Such bearings are well suited for the large centrifugal acceleration forces that a tube receives, for example when mounted on a computerized tomography machine. In order to improve the rotation, the bearing balls are no longer necessarily made of steel and may be made of a ceramic (in one example silicon nitride) with a very low rolling resistance coefficient. And the power supply and heat dissipation that is no longer provided by the ball is provided by a liquid lubricant such as a gallium-indium-tin liquid metal alloy. The anode shaft is embedded in the alloy in the cartridge chamber. The chamber is completely filled with alloy. For filling, the chamber is first placed under vacuum before alloy injection. When attached to the tube, a removable anode is attached to the end of the anode shaft.

  Embodiments of the invention provide that the entire shaft is immersed in an alloy that is a liquid material, and the chamber seal is formed by a sealing device located at the shaft outlet.

  FIG. 1 shows an X-ray tube 1 according to an embodiment of the invention. The tube 1 has a sealed container 2. For example, the sealed container 2 is defined by the wall 3 of the tube 1. The tube 1 also has a rotating anode 4. The rotary anode 4 is disposed so as to face the cathode 5. A motor 6 for rotationally driving the anode 4 is provided inside the sealed container 2 of the tube 1. The anode 4 has an anode shaft 7. The cathode 5 is disposed so as to face the anode track 8. When a high voltage is supplied to the anode 4, electrons are emitted from the cathode 5 by the effect of a strong electric field and collide with the anode track 8. As a result of this collision, the anode orbit 8 formed of the X-ray emitting material emits X-rays 9. X-rays 9 pass through a window 10 provided in the wall 3 and exit from the tube 1. The window 10 is made of, for example, glass or X-ray transmissive material. The window is airtight. The sealed container 2 formed in this way is conventionally placed under vacuum, specifically, placed under vacuum via a suction port (not shown), and the suction port is subsequently sealed (stemming). ).

  In order to keep the anode 4 rotating, the tube 1 is provided with an anode support 11. The support 11 is hollow and has a chamber 12. Inside the chamber 12, a bearing or sliding part 13 holds the anode 4 by the support part 11. In order to solve the problem of lubrication and heat transport during the rotation of the anode 4, the chamber 12 is filled with a liquid lubricant such as a gallium-indium-tin liquid alloy. The chamber 12 can be filled by adding the flow path 14 guided to the outside from the chamber 12. This filling is possible after placement of the anode shaft and before or after dynamic balancing of the shaft 7. If the dynamic balance of the shaft 7 is performed before filling, the balance is much better controlled. It is then possible to use a bottle that fills the chamber 12 by gravity or injection. Sealing the flow path 14 with a simple plug or stopper or placing a plug or stopper in the flow path 14 provides a fill-side seal.

  FIG. 2 shows that the shaft 7 is held in the chamber 12 by bearings. The outlet 15 of the shaft 7 is provided with a receptacle 16 which is designed to accommodate the anode, or generally a fixing or mounting device. Subsequently, the anode can be mounted, for example, just before closing the wall 3. At the outlet 15, the fixed support portion 11 is fixed to the assembly ring 17 by, for example, a screw. The ring 17 may include an O-ring groove 18 to provide a seal. Sealing can be achieved in two complementary ways. First, for vacuum sealing, a space is defined between the inner diameter of the ring 17 and the outer diameter of the shaft 7 perpendicular to the ring 17 at position 19 when the anode shaft is no longer rotating. . The boundary of this space is fixed by the surface tension on the material of the shaft 7 and the ring 17 of gallium-indium-tin liquid metal alloy. This alloy has low wettability, a surface tension of approximately 1 / 100th of a millimeter clearance, suitable for efficient rotation of the shaft 7, and easily adaptable to industrial scale conditions . The ring 17 is fixed when the shaft 7 rotates.

  As the shaft 7 rotates, the pressure of the liquid alloy increases. The alloy tends to escape from the chamber 12 and contaminate the sealed vessel of the tube. In this case, in order to confine the alloy to the interior of the chamber 12, a spiral relief feature on the surface of the ring 17 on the side of contact or perpendicular to the ring 17 in the region 19 or on the surface of the shaft 7. Is provided. The pitch of the helix is oriented so that for a given direction of rotation of the shaft 7, the helix relief behaves like a scraper in front of the surface facing towards the relief. Such a scraper serves to push the alloy back into the chamber 12.

  In the illustrated embodiment, the support has a pair of concentric surfaces arranged in a pair at opposite positions in this space. The surface attached to the shaft is the surface 19 and the other surface is attached to the support by the ring 17. The surface 19 is attached to the shaft and is arranged inside the surface attached to the support. The shaft 7 may be provided with a surrounding shape 20 as shown in FIG. A very important clearance is obtained at the position of the surrounding shape 20. It is also possible to equip the radial surface 21 of the two opposing rings 17 and the radial surface 22 of the shaft 7 with a spiral relief feature having the same effect of pushing the alloy back into the chamber 12.

  The removable cartridge shown in FIG. 2 is more suitable for industrial scale operation in cartridge design and includes a shaft 7. The shaft 7 is provided about an axis 23 and has a series of bores as a retracting shoulder or step starting from the receptacle 16. The first lumen 19 has the largest diameter and is disposed opposite the ring 17. During assembly, the ring 17 is thus mounted around the shaft 7. At the boundary 24 of the ring 17, the shaft 7 has a first shoulder 25. Starting from the retraction feature 25, the shaft 7 has a main holding part with a smaller diameter than the surface 19. From above the main holding portion, the first ball bearing 26 and the second ball bearing 28 are preferably fitted by pressure fitting. The two bearings 26 and 28 are separated from each other by a cylindrical spacer 27 along the shaft 7. The spacer 27 enters exactly the free part of the chamber 12. The spacer 27 leaves a free space in the center (the space is subsequently filled with an alloy). The bearings 26 and 28 each have a race, such as reference numerals 29 and 30, which are designed to be arranged on one side firmly against the shaft 7 and on the other side firmly against the support 11 respectively. . The races 29 and 30 are supported by relative rotation by the shaft 7 and the support 11 respectively.

  A mounting nut 31 is screwed from above the thread 32 of the shaft 7. The thread 32 is disposed at one end 36 of the shaft 7. The end 36 is opposite to the end where the receptacle 16 is disposed. The thread 32 can be arranged after the last shoulder 33 of the shaft 7. This last shoulder 33 is not essential. The nut 31 carries a support ring 34. The ring 34 presses the race 30 toward the ring 17. The race 30 presses the spacer 27 in the same direction by a fixed ring 35 (preferably having the same diameter and cross section as the spacer 27). The spacer 27 presses the race 30 of the bearing 26 in the same direction. At the inner end portion 36 of the shaft 7, a helical spring 37 is supported on the back surface 38 of the support portion 11. A hole 14 is open from this back side 38.

  In this way, the shaft 7 provided with the spring 37 in particular is arranged in the chamber 12. Once the shaft 7 is arranged in this way, the ring 17 is fixed to the support portion 11 with the two screws 39 and 40. Preferably, the widths of the races 29 are slightly smaller than the widths of the races 30, so that these races 29 are arranged without being pressed against the shoulder 25 or the support ring 34. In this way, the shaft 7 can rotate freely. When the screws 39 and 40 are screwed in, the spacer 27 is held by the ring 17 and the ring 32.

Preferably, the balls of the bearings 26 and 28 are made of a hybrid alloy known as ceramic rather than steel, for example silicon nitride Si ₃ N ₄ or Rex20 / Si ₃ N ₄ . Such balls have a feature that the rolling resistance coefficient is extremely large. If desired, the races 29 and / or 30 of the bearings 26 and / or 28 are also made of ceramic. It is also possible to use cage bearings, especially with balls as described above. Thus, dynamic balance of the cartridge shaft is ensured before the chamber 12 is placed under vacuum and filled with alloy. This balance is desirable for rotating the shaft 7 at high speeds and is possible without the use of lubricants by the choice of ball material. In other cases, a balance may be ensured after placing an intermediate lubricant and then cleaning, but it is not practical. Preferably, the balancing is performed in the presence of an anode mounted on the shaft 7.

  Once equilibrium has been achieved, a vacuum is set in the chamber 12 by suction through the holes 14 under a neutral atmosphere if necessary. When three-way valves each provided with a cock are used, it is possible to inject a gallium-indium-tin liquid alloy into the chamber 12 through the holes 14 or to make it flow by gravity when setting a vacuum. Next, the chamber 12 is closed by, for example, a valve provided in advance. The assembly is sealed as a result of negative capillary tension. If necessary, the amount of alloy injection corresponds exactly to the volume of the chamber 12 (reduced by the presence of the shaft 7, bearings 26, 28 and spacer 27). The liquid alloy completely embeds the assembly and the bearings 26 and 28 are immersed in the alloy. The alloy occupies the entire space between the spacer 27 and the shaft 7 and the housing of the spring 37.

  Once the cartridge is manufactured, the anode 7 can be attached to the cartridge and attached to the wall of the tube 1 by means of screws, for example. Alloys are good conductors of heat and electricity, so all constraints are met.

  In addition, while embodiments of the present invention have been described with reference to example embodiments, those skilled in the art may make various modifications to the actions and / or methods and / or results without departing from the scope of the present invention. It will be appreciated that equivalent arrangements may be substituted for, and substituted for, elements of the present invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Accordingly, the invention is not limited to the specific embodiments disclosed as the best mode contemplated for carrying out the invention, but is intended to encompass all embodiments belonging to the scope of the claims. Furthermore, the terms first, second, etc. are used, but do not imply order or importance, but are used to distinguish one element or feature from another. Furthermore, the use of the singular indefinite article does not imply a limit on quantity, but that there is at least one referenced element or feature.

It is typical sectional drawing of the X-ray tube by embodiment of this invention. It is sectional drawing of the cartridge by embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 X-ray tube 2 Sealed container 3 Wall 4 Rotary anode 5 Cathode 6 Motor 7 Anode shaft 8 Anode track 9 X-ray 10 Window 11 Anode support part 12 Chamber 13 Bearing 14 Flow path 15 Shaft outlet 16 Receptacle 17 Assembly ring 18 Groove 19 Surface 20 Surrounding shape 21 Radial surface of ring 22 Radial surface of shaft 23 Shaft 24 Boundary 25, 33 Shoulder 26, 28 Bearing 27 Spacer 29, 30 Race 31 Nut 32 Thread 34 Support ring 35 Fixed ring 36 End 37 helical spring 38 back 39, 40 screw

Claims (13)

A sealed container (2) in which radiation is generated;
A cathode (5) disposed in the sealed vessel, an anode (4) disposed opposite the cathode and rotating on the shaft (7), and a fixed anode shaft support (11);
A radiation emitting device (1) comprising:
The support includes a holding chamber (12) in the form of a removable cartridge,
The shaft (7) of the anode (4) is held in the chamber (12);
The support has ball bearings (26, 28),
The chamber (12) is filled with a liquid lubricant;
A radiation emitting device (1), wherein the chamber is provided with means (18, 19) for preventing the liquid lubricant from leaking out of the chamber.   The apparatus of claim 1, wherein the liquid lubricant is a gallium-indium-tin alloy.   The apparatus of claim 1, wherein the ball bearing comprises a ceramic ball.   The apparatus according to any one of claims 1 to 3, wherein the ball bearing comprises a ceramic bearing.   The apparatus according to claim 1, wherein the ball bearing includes a cage.   6. At the position of the anode shaft outlet from the support, the support has a clearance that is less than the natural flow clearance of the liquid lubricant due to the surface tension of the lubricant. The apparatus as described in any one of.   At the position of the outlet of the anode shaft from the support, the support is a spiral type whose pitch orientation is such that the liquid lubricant is pushed back to the chamber as the anode rotates. Or an apparatus according to any one of the preceding claims having a vortex relief feature.   At the position of the outlet of the anode shaft from the support portion, the support portion is concentrically arranged in a pair of oppositely arranged surfaces with one surface attached to the shaft and the other surface attached to the support portion. The device according to claim 6 or 7, wherein the device has a surface and the surface attached to the shaft is arranged inside the surface attached to the support.   At the position of the outlet of the anode shaft from the support portion, the support portion is concentrically arranged in a pair of oppositely arranged surfaces with one surface attached to the shaft and the other surface attached to the support portion. The apparatus according to any one of claims 6 to 8, wherein the apparatus has a surface and the surface attached to the shaft is arranged outside the surface attached to the support. A method of mounting an anode on a radiation emitting device,
Providing an anode shaft mounted within the anode support chamber;
Providing a vacuum in the chamber;
Filling the anode chamber under vacuum with a liquid lubricant to form a cartridge;
Attaching the cartridge to the device in a fixed manner;
With a method.   The method of claim 10, wherein the step of attaching the anode shaft to the chamber includes balancing prior to filling the chamber with the liquid lubricant.   12. A method according to claim 10 or 11, wherein the step of attaching the anode shaft to the chamber comprises balancing without using a lubricant.   13. A method according to any one of claims 10 to 12, wherein the anode is attached to the shaft before the cartridge is attached to the device.

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