JPH0515028B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a rotating anode type X-ray tube device, in which an anode target is supported in a non-contact manner by a magnetic bearing and rotates at high speed, and furthermore, the anode target is , a negative high voltage is supplied to the cathode, the vacuum vessel and the magnetic bearing rotor are kept at substantially ground potential, the distance between the stator and rotor of the magnetic bearing is maintained at 4 mm or less, and the compact The present invention relates to a rotating anode type X-ray tube device with a structure. [Technical background of the invention] Generally, X-ray tubes are used for medical purposes, for example, for X-ray diagnosis, but in cases such as gastric examination,
Conventionally, an X-ray tube as shown in FIG. 7 has been used. This X-ray tube is of a so-called rotating anode type, and a cathode 2 is disposed on one side of an envelope 1.
A cathode 3 containing a cathode filament that emits thermoelectrons and a focusing electrode is provided eccentrically.
Further, near the center of the envelope 1, a substantially umbrella-shaped anode target 4 is arranged opposite to the cathode structure 2 . This anode target 4 provides a high potential difference with the cathode structure 2 , accelerates electrons emitted from the cathode filament, causes them to collide, and generates X-rays by bremsstrahlung radiation. It is designed to store and dissipate large amounts of heat, and is designed to rotate at high speeds to effectively expand the heat generation area. Such an anode target 4 is connected to a covered cylindrical rotor 6 via a support column 5. The rotor 6 generates rotational force by receiving a rotating magnetic field generated by a stator 7 disposed outside the envelope 1, and together with the stator 7 forms an induction motor. Note that the support column 5 and the rotor 6 are integrated. A rotating shaft 8 is disposed inside the rotor 6 along the axis, and one end of the rotating shaft 8 is fixed to the rotor 6 with a screw or the like (not shown). A bottomed cylindrical stator 9 is coaxially disposed between the rotating shaft 8 and the rotor 6, and one end thereof is fixed to the envelope 1 via sealing rings 10 and 11. . A portion of the stator 9 is exposed outside the tube, and also serves to support and fix the entire X-ray tube to the outside. A bearing 1 is provided between the stator 9 and the rotating shaft 8.
2 and 13 are interposed so that the rotating shaft 8 can freely rotate. Now, during operation, the power when the electrons emitted from the cathode filament reach target 4 is as follows: anode voltage: 50 kV, current: 20 m
In case of A, it reaches 1kW. Since more than 99% of this power is converted into heat, the target 4 is heated to a high temperature with heat radiation to the outside and heat conduction to other parts. Thermal radiation increases in proportion to the fourth power of temperature, so as the temperature rises, heat radiation increases significantly and thermal equilibrium is reached in a short time. For example, under the above conditions, equilibration occurs at 1100°C after 5 minutes. On the other hand, when heat is transferred by thermal conduction, if the other end of the conductive medium is thermally free, the end gradually becomes hotter over a long period of time. The heat of the target 4 is then transferred to the rotor 6 and rotating shaft 8, making them hot. When the rotor 6 becomes high in temperature, thermal radiation increases and thermal equilibrium is reached as described above. Under the above conditions,
The point on the support column 5 reaches 800℃ approximately 15 minutes after the start of electricity supply.
At the point of rotor 6, 550℃ 30 minutes after the start of energization,
At a point near the bearing 13, approximately 50
Reach thermal equilibrium at 400℃ in minutes. If the heat conduction of the bearing 13 deteriorates, the temperature at the point will be approximately the same as that at the point, reaching 550°C. Depending on the rotational conditions of the balls in the bearings 12 and 13, thermal expansion may cause poor clearance between the outer ring and the inner ring, resulting in problems such as damage to the bearings. Furthermore, if the temperature of the bearings 12 and 13 exceeds 500° C., the hardness of the balls will decrease, causing damage to the bulbs such as stopping rotation. In addition, the rotor 6 is connected via bearings 12 and 13 in a vacuum.
When rotating the target 4, it has been found that increasing the rotational speed significantly reduces the rotational life. X-ray tubes actually used
The rotational speed is about 10,000 rpm, but even in this case the rotational life is not sufficient. Furthermore, when the heat capacity of target 4 increases,
The disadvantage was that the weight of the target was increased and the rotational life was shortened. In order to solve this problem, US Pat.
Magnetic levitation type X-ray tubes have been proposed, as described in Japanese Patent Laid-Open No. 59-63646, but these have the following drawbacks. i.e. U.S. patent specifications
In No. 4417171, the outer diameter of the rotor is extremely large, which not only increases the size of the entire X-ray tube, but also requires a high voltage to be applied to the central column, making it difficult to maintain it. In Special Publication No. 58-43860,
The disadvantage is that the rotor and target have low rigidity, the resonance frequency is low, and high speed rotation is not possible.
In Japanese Patent Application Laid-Open No. 59-63646, the anode must be kept at ground potential, which is inconvenient as a special high voltage power supply and high voltage cable are required. [Problems with Background Art] The conventional X-ray tube as described above has the following drawbacks. That is, bearings 12, 13
The inner ring tends to become hot, but the outer ring has a low temperature, and the temperature at this point is between 60℃ and 550℃.
It changes depending on the rotation status of the balls in the bearings 12 and 13. Bearing 12,1 as described above
If the temperature of the ball 3 rises, not only will there be insufficient clearance between the ball and the inner and outer rings, but
The lubricant that exists between these evaporates,
Bearings 12 and 13 may be damaged. For these reasons, there is a drawback that rotation stoppage accidents tend to occur frequently. In order to prevent this, increasing the degree of blackening of the target 4, increasing the degree of blackening of the surface of the rotor 6, and installing a heat shield plate between the target 4 and the rotor 6 have been considered, but these effects are limited. The actual situation is that the input power to the target 4 is relatively small. In addition, when this structure is rotated at high speed, the rotational life becomes extremely short. When the heat capacity of the target 4 is increased, the weight of the target 4 increases, so
Rotational life becomes shorter and shorter. In order to eliminate these problems, a rotating anode type X-ray tube using a magnetic bearing was proposed in US Pat. ing. However, each of these has drawbacks as described above. [Objective of the Invention] The object of the present invention is to support a large-capacity X-ray generating target in a contactless and rotatable manner using a magnetic bearing, to maintain the rigidity of the magnetic bearing sufficiently high, and to reduce the rigidity of the rotating part. By increasing the resonant frequency, it enables ultra-high speed rotation with low vibration, extremely long rotation life, and a high positive voltage for the target.
By keeping the cathode at a high negative voltage and the vacuum vessel and the rotor and stator of the magnetic bearings at substantially ground potential, the magnetic gap is reduced, increasing rigidity, and noise is removed from the position sensor that detects the displacement of the rotor. An object of the present invention is to provide a rotating anode type X-ray tube device in which the reliability is significantly improved by preventing the intrusion of [Summary of the Invention] This invention involves inserting and fixing an insulator inside a rotor for a magnetic bearing, and mechanically fixing an X-ray generating target at a position separated in the axial direction of the insulator through the insulator. The target and the magnetic bearing rotor are electrically insulated by the separated portion of the insulator, the magnetic bearing rotor is maintained at substantially ground potential, and at least one of the magnetic bearing rotors is penetrated into the inside of the rotor. A positive high voltage is supplied to the target from outside the tube through a conductive path provided in the tube. A negative high voltage can be applied to the cathode, and it can be used with the same high voltage power supply with the same neutral point grounding as a conventional rotating anode X-ray tube, and the same level of power as a conventional X-ray tube. It is a rotating anode type X-ray tube device that can rotate a large-capacity target at an ultra-high speed, has an extremely long life, and has low vibration and noise. [Embodiments of the Invention] A rotating anode type X-ray tube device of the present invention is constructed as shown in FIG. 1, and the same parts as in the conventional example (FIG. 3) are given the same reference numerals. That is, the central portion of the housing 1, which is a vacuum container, is made of metal and is maintained at ground potential. The housing 1 includes a heat absorbing container part 101 that absorbs heat from the target 4 for generating X-rays, vacuum partitions 102 and 103 in the magnetic bearing, vacuum partitions 104 and 105 in the position sensor, and an auxiliary bearing support plate. 106, 107 and end containers 108, 10
It is made up of 9. Housing 1 like this
The above-mentioned parts form a vacuum container as described above, and the inside of the container is maintained at a high vacuum. Radial magnetic bearing stators 110 and 111 that generate an attractive force in the radial direction are provided outside the vacuum partition walls 102 and 103 within the magnetic bearings. This radial magnetic bearing stator 11
Next to each of 0 and 111, there is a stator 1 for a thrust magnetic bearing that generates an attractive force in the thrust direction.
12 and 113 are provided. Inside each of these stators are rotors 114 , 1 for magnetic bearings.
15 are arranged. The magnetic bearing rotors 114 and 115 are made of a magnetic material such as pure iron, and on the outer periphery thereof are laminated plates 116 and 11 made of a magnetic material.
7 is coated, and a suction force is generated between the laminated plates 116, 117 and the stators 110, 111 for the radial magnetic bearing to constitute a radial magnetic bearing. In addition, heat-resistant cylinders 118 and 119 made of a thin heat-resistant metal such as tantalum or a ceramic such as Si ₃ N ₄ with a metallized surface are connected to the ends of the magnetic bearing rotors 114 and 115, for example. Low-temperature operation cathodes 120, 121 such as barium imprecathode are attached, and current-carrying diodes 124, 125 are formed between them and heaters 122, 123 for heating. Furthermore, fixed cathodes 126 and 127 are provided in the vicinity thereof, and current-carrying diodes 128 and 129 having characteristics opposite to those of the current-carrying diodes 124 and 125 are formed between the fixed cathodes 126 and 127 and a portion of the rotating heat-resistant cylinders 118 and 119 . are doing. These diodes keep both the magnetic bearing rotors 114, 115 substantially at ground potential, and at substantially the same potential as the vacuum partitions 102, 103 within the magnetic bearings. Therefore, the gap between them can be kept within 0.5mm,
Stator 110, 11 for the above radial magnetic bearing
1 and the magnetic bearing rotors 114 , 115 can be reduced to within 1 mm. As a result, bearing rigidity can be extremely increased. Further, metal rings 130 and 131 made of non-magnetic metal are fixed to the outer periphery of the magnetic bearing rotors 114 and 115 following the laminated plates 116 and 117, and metal rings 130 and 131 made of non-magnetic metal are fixed to the outer periphery of the rotor 115 . Subsequently, a copper ring 132 and a non-magnetic ring 133 are fixed. The above copper ring 13
A stator 134 for rotating the rotor is provided on the outside of the rotor 2, and these form an induction motor to rotate the rotor at high speed. Radial sensors 135 and 136 are provided on the outside of the rotor ends via rings 104 and 105, respectively, to detect the deflection of the magnetic bearing rotors 114 and 155 . Furthermore, a penetrating electrical insulator 137 is mechanically and rigidly fixed to the inside of the magnetic bearing rotor 114 by shrink fitting or the like. A metal plate 138 made of molybdenum or the like is bonded to an end surface 137-a of the electrical insulator 137 on the target side of the rotor 114 . This joining can be achieved by brazing or the like. The end flange 4a of the cylindrical support of the anode target 4 for generating X-rays is attached to this metal plate 138 by bolts 139 to a heat insulating ring 138 made of ceramic or the like.
It is mechanically and tightly fixed via a. At an intermediate portion between the end of the magnetic bearing rotor 114 and the metal plate 138, an insulating cylindrical portion 137-b in which the diameter of the electrical insulator 137 is larger than that in other portions.
is formed to maintain a high withstand voltage (for example, 80 kV or more) of the target 4 and the magnetic bearing roller 114. In this case, the insulating cylindrical portion 137-b of the electrical insulator 137 has a bent surface to increase the creepage distance. A thin conductive sleeve 140 is provided on the inner peripheral surface of the central hole of the electrical insulator 137.
The conductive film 141 and the member 13 attached to the end surface of the target 4 side of the conductive film 141 by metallization treatment or the like.
It is electrically connected to the target 4 via 8,139. A heat-resistant cylinder 142 is provided at the other end of the conductive sleeve 140, and a thermionic emission cathode 143 is attached to a part of the cylinder.
is heated to a high temperature of around 1000℃. The heater 144 is supplied with a high voltage (for example,
75 kV) is applied, and the inflow of thermionic electrons from the heated cathode 143 as described above results in electrical coupling with low impedance. This cathode 14
Since the perveance of the diode composed of the cathode 3 and the heater 144 is greater than that of the diode composed of the cathode 3 and the target 4 , the voltage drop in this portion is smaller. Therefore, high voltage can be supplied to the target 4 from outside the tube in a non-contact manner. An electrical insulator 145 is also inserted and fixed into a part of the inside of the other magnetic bearing rotor 115 by shrink fitting, etc. Similarly to the above, the target mounting metal plate 138 and the rotor 115 are connected to a large diameter insulator. The cylindrical portion 145-a provides high withstand voltage (e.g.
80kV). As described above, the rotor 115 is kept at the ground potential, and the target 4 is kept at a high positive voltage. Note that the insulating cylindrical portion 145-a has a bent structure portion to increase the creepage distance. Further, a negative high voltage (for example, -75 kV) is supplied to the cathode 3 from outside the tube through a pushing 148 and a conductor (not shown), and thermionic electrons are supplied to the cathode 3 through a positive high voltage (for example, (+75 kV)). The X-ray beam 146 is maintained at a constant temperature and collides with the target 4 to generate an X-ray beam 146.
The X-ray radiation is irradiated to the outside of the tube through an X-ray emission window 147 made of, for example, beryllium and attached to the tube. In addition, secondary electrons (not shown) emitted from the target 4
is shielded by shielding plates 148, 149 provided inside the tube, and is prevented from flying into the insulating cylindrical portions 137-b, 145-a of the electrical insulators 137, 145. Further, a heating voltage and a high voltage are supplied to the heater 144 from outside the tube via a pushing 145. Furthermore, auxiliary bearings 150 and 151 are firmly supported by support plates 106 and 107 on the outside of the ends of the rotors 114 and 115 , respectively. When the rotors 114 and 115 are operating normally, they are not in contact with the rotors 114 and 115 , but before operation or in the case of abnormal operation, the rotating parts are supported by the auxiliary bearings 150 and 151. Further, a position sensor 152 for detecting deviation in the thrust direction is attached to the end of the rotor 115 , and the output thereof controls the thrust magnetic bearing stators 112 and 113 to perform position control in the thrust direction. In addition, as the material of the electrical insulators 137 and 145,
It is preferable to use ceramics such as silicon nitride (for example, Si ₃ N ₄ ) because of its increased mechanical strength. Next, a method of joining the magnetic bearing rotor 114 and the electrical insulator 137 will be explained using FIGS. 2 and 3. Note that the electric insulator 137 is made of ceramics, preferably silicon nitride (for example,
We will discuss the case using Si ₃ N ₄ ). That is, as described above, the magnetic bearing rotor 114 includes the laminated magnetic plate 116, the cylinder 130, the bearing cylinder 114-1, and the mechanical elastic body 11.
4-2, the bearing cylinder 114
-1 is fixed to the outer periphery of the electrical insulator 137 via the mechanical elastic body 114-2. The mechanical elastic body is made of pure iron, for example, and the third
It has a shape as shown in the figure. That is, it is made into a cylindrical shape, and a plurality of, preferably eight, slits 114-2-a are provided at the end thereof. Furthermore,
An inwardly convex portion 114-2-e is provided at the end thereof, and is in contact with the outer diameter of the electrical insulator 137. The outer diameter of the central portion of the mechanical elastic body 114-2 is gently tapered, and is mechanically and tightly joined to the inner diameter of the bearing cylinder 114-1, which is tapered in the opposite direction. ing. During this time, it is firmly fixed by brazing, for example. Tapered portions 114-2-b, 114-2 are provided at both ends of such mechanical elastic body 114-2.
2-c is formed, and the electrical insulator 137
Tapered portions 137-c and 137-d are formed on the outer periphery, and these tapered portions are in close mechanical contact. Further, the central portion of the mechanical elastic body 114-2 has a gap between it and the electrical insulator 137, which is equal to or larger than the difference in thermal expansion between the two. Further, on the outside of the portion of the mechanical elastic body 114-2 having the slit 114-2-a, the bearing cylinder 114-1
There is a gap greater than the thermal expansion difference between the electrical insulator 137 and the electrical insulator 137. Further, the tapered portions 137-d, 137-c
, at least one of which is the bearing rotor 114
An angle that can absorb the difference in thermal expansion in the radial and axial directions is determined according to the inner diameter and length of the tube. Furthermore, the length, number, and wall thickness of the slits 114-2-a are determined so that no mechanical stress is applied to this portion. At the time of assembly, the magnetic bearing rotor 114 is assembled in advance and inserted into the electrical insulator 137 from the outside (in the direction of the smaller diameter) under high temperature and pressure. At this time, another tapered part 114-2-d is provided inside the mechanical elastic body 114-2, and a tapered part 137-f is formed outside the protruding part 137-e of the electrical insulator 137. For,
Does not cause excessive resistance during insertion. When the insertion is completed, the mechanical elastic body 1
14-2 having the slit 114-2-a receives a stress within the elastic limit, and the electrical insulator 13
It is mechanically firmly fixed between the tapers of 7. Now, during operation, due to the inflow of heat from the target 4 , the electric insulator 137 and the magnetic bearing rotor 1
14 becomes high in temperature, the outer bearing rotor 114 made of iron, for example, has a larger thermal expansion than the electrical insulator 137 made of ceramic, for example, on the inside, but the mechanical elastic body 114-2
There are slits 114-2-a at both ends of the slits 114-2-a, and since these portions act as so-called firmness, they are displaced with an appropriate stress and can absorb this difference in thermal expansion. Since they are joined at the tapered part, the difference in thermal expansion in the axial direction can be absorbed by elongation within the elastic limit in the radial direction. It can be joined with high mechanical strength. Furthermore, since it has a sufficiently strong spring constant, the resonance frequency of this part can be increased to 1 kHz or higher, and it has been demonstrated that there is no adverse effect on rotation at 30,000 rpm. or,
The rotational balance did not change significantly even when the temperature changed. By creating such a structure, the difference in thermal expansion is equivalent to 0.1 mm, and the stress reaches 80 kg/mm ² , so it was thought that the external metal would yield and joining would be impossible. We were able to create a rotor that can withstand practical use even at temperatures above ℃. This made it possible to realize a large-capacity magnetically levitated X-ray tube device, which had previously been considered impossible. Note that the other bearing rotor 115 can also be made in the same manner. [Modification of the invention] In the above embodiment, a non-contact current path is employed to maintain the rotors 114 and 115 at substantially ground potential, but it is possible to employ a structure in which one or both of them are brought into mechanical contact. Also good. Similarly, it goes without saying that the non-contact conductive parts 143 and 144 for supplying voltage to the target 4 from outside the tube may be changed to a conductive mechanism using mechanical contact. Also, the rotor 114 (or 115 ) and the insulator 1
37 (or 145) is joined on the entire surface,
Of course, the bonding surface may be limited to a portion. Moreover, the target 4 and the electrical insulators 137, 145
Although the two are connected via metal plates 138 between them, they may be directly joined. Further, in the above embodiment, the target 4 is supported on both sides, but the stator 111 for magnetic bearing is supported on both sides.
Of course, it is also possible to move it to the 0 side and create a so-called one-sided holding structure. Alternatively, a conventional mechanical bearing may be used for the bearing portion. Furthermore, it goes without saying that the bearing cylinder 114-1 and the mechanical elastic body 114-2 may have an integral structure. Further, the electrical insulator 137 and the mechanical elastic body 11
The contact portion with 4-2 is not limited to both ends, but may also be in contact with the center portion. Further, the mechanical elastic body 114-2 may have a multi-segmented structure. Next, a fourth modification of the method of fixing the bearing rotor 114 to the electrical insulator 137 will be described.
This will be explained with reference to FIGS. First, FIG. 4 shows an example in which the outer periphery of the electrical insulator 137 is cylindrical, and a part of the inner diameter of the mechanical elastic body 114-2 is shrink-fitted or press-fitted without having a taper. It is convenient if either one of the contact parts with the electrical insulator 137 is fixed by brazing or the like. The inner diameter of the central portion of the mechanical elastic body 114-2 is set to a size larger than the outer diameter of the electrical insulator 137 by adding a gap equivalent to the difference in thermal expansion. FIG. 5 shows that the inner surface of the mechanically elastic body 114-2 is cylindrical, and a part of the electrical insulator 137 has a portion with a small outer diameter corresponding to the difference in thermal expansion. This is an example in which the electric insulator 137 is held elastically. FIG. 6 shows the mechanical elastic bodies 114-2, 11
This is an example where two 4-2s are used. One mechanical elastic body 114-2 has a fitting portion 114-2-f, and the electrical insulator 137
It is fitted into a recess provided on the outer periphery of the shaft, so that it does not move in the axial direction. [Effects of the Invention] As explained above, the present invention provides an arrangement in which the rotor has a shaft between the cylindrical or columnar electric insulator made of ceramics and the magnetic bearing rotor made of a ferromagnetic metal at least in part. This is a rotating anode type X-ray tube device in which cylindrical mechanical elastic bodies having a plurality of slits formed along the direction are interposed and are fitted and fixed to each other. As a result, even if a difference in thermal expansion occurs between the electrical insulator and the magnetic bearing rotor during operation, the cylindrical mechanical elastic body absorbs the difference and maintains the strength of the fit and fixation between the two. . In this way, a highly reliable magnetically levitated rotating anode X-ray tube device can be realized.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a rotating anode type X-ray tube according to an embodiment of the present invention, FIGS. 2 and 3 are sectional views and perspective views showing an enlarged main part of FIG. 7 to 6 are cross-sectional views showing modified examples of the present invention, and FIG.
The figure is a sectional view showing a conventional rotating anode type X-ray tube. 1 ... Housing, 110, 111... Stator for radial magnetic bearing, 112, 113... Stator for thrust magnetic bearing, 114 , 115 ... Rotor for magnetic bearing, 120, 121... Cathode of grounding diode, 137, 145...Electrical insulator,
4...Target, 3...Cathode.

Claims (1)

[Scope of Claims] 1. An electron beam emitting cathode provided in a vacuum container, a rotatable anode target provided opposite to the cathode, and an anode target supporting the anode target and extending in the direction of the rotation axis. and a magnetic bearing stator coaxially surrounding the rotor and provided outside the vacuum vessel, the rotor being made of cylindrical or columnar ceramics mechanically coupled to the anode target. A rotating anode type comprising an electrical insulator and a magnetic bearing rotor that is coaxially fitted around the outer periphery of the electrical insulator, cooperates with the magnetic bearing stator, and has a ferromagnetic metal at least in part. In the X-ray tube device, the rotor has a cylindrical mechanical elastic body having a plurality of slits formed along the axial direction interposed between the electric insulator and the magnetic bearing rotor, so that the rotor is mutually interconnected. A rotating anode type X-ray tube device characterized by being fitted and fixed.