JPH0421300B2 - - 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, which rotates at high speed while supporting an anode target in a non-contact manner with a magnetic bearing, 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. 3 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 cup 3 containing a cathode filament for emitting 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 2 . This anode target 4 provides a high potential difference between it and the cathode 2 , accelerates electrons emitted from the cathode filament, causes them to collide, and generates X-rays by bremsstrahlung radiation, as well as a large amount of radiation generated at that time. It is designed to store and dissipate 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. In addition, the support column 5 and the rotor 6
are united. 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 6 and the rotor 6, and one end 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. Bearings 12 and 13 are provided between the stator 9 and the rotating shaft 8.
is interposed so that the rotating shaft 8 can freely rotate. Now, during operation, the power when the electrons emitted from the cathode filament reach the target 4 reaches 1kW when the anode voltage is 50kV and the current is 20mA. 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 transmitted to the rotor 6 and rotating shaft 8, making them high temperature. When the rotor 6 becomes high in temperature, thermal radiation increases and thermal equilibrium is reached as described above. Under the above conditions, supporting column 5
The upper point reaches thermal equilibrium at 800°C approximately 15 minutes after the start of energization, the point at the rotor 6 reaches 550°C 30 minutes after the start of energization, and the point near the bearing 13 reaches thermal equilibrium at 400°C 50 minutes after the start of energization. If the heat conduction of the bearing 13 deteriorates, the temperature at the point will be the same as the point, 550℃
It will also reach. 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. or,
If bearings 12 and 13 reach a temperature of 500°C or higher,
This will cause a decrease in the hardness of the ball, causing damage to the tube such as stopping rotation. Furthermore, it has been found that when the rotor 6 and target 4 are rotated via the bearings 12 and 13 in a vacuum, if the rotational speed is increased, the rotational life is extremely reduced. The rotational speed of X-ray tubes actually used 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 because a special high voltage power supply and voltage cable are required. [Problems with Background Art] The conventional X-ray tube as described above has the following drawbacks. That is, as mentioned above, the inner rings of the bearings 12 and 13 tend to reach high temperatures, but the outer rings are at a low temperature, and the temperature at this point ranges from 60°C to 60°C.
The temperature varies between 550°C depending on the rotational conditions of the balls in the bearings 12 and 13. When the temperature of the balls increases, not only will there be insufficient clearance between the balls and the inner and outer rings, but the lubricant existing between them will evaporate, causing damage to the bearings 12 and 13.
may be damaged. For these reasons, there is a drawback that rotation stoppage accidents tend to occur frequently. To prevent this, the degree of blackening of the target 4 is increased, the degree of blackening of the surface of the rotor 6 is increased, and the degree of blackening of the target 4 and the rotor 6 is increased.
Although it has been considered to install a heat shield plate between the two, the effect of these is relatively small, and the reality is that the input power to the target 4 is too small. Furthermore, when this structure is rotated at high speed, the rotational life becomes extremely poor. When the heat capacity of the target 4 is increased, the weight of the target 4 increases, so
The rotation 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 U.S. Patent No. 4417171, Japanese Patent Publication No. 58-43860, and Japanese Patent Application Laid-open No. 59-63646, as mentioned above. has been done. 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, high-speed rotation with low vibration is possible, and the rotation life is extremely long.The target is set to a positive high voltage, the cathode is set to a negative high voltage, and the rotor and A rotating anode type that significantly improves reliability by keeping the stator essentially at ground potential, which reduces the magnetic gap and increases rigidity, and prevents noise from entering the position sensor that detects rotor displacement. An object of the present invention is to provide an X-ray tube. [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 separated position on the outer periphery 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. This housing 1 includes an endothermic container section 101 that absorbs heat from the anode target 4 for generating X-rays.
, vacuum partitions 102 and 103 in the magnetic bearing, vacuum partitions 104 and 105 in the position sensor, auxiliary bearing support plates 106 and 107, and an end insulating container 108,
It consists of 109. The above-mentioned parts of the housing 1 form a vacuum container as described above, and the inside of the housing 1 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. Further, the rotor 114 for the radial magnetic bearing,
At the ends of 115, low temperature operation cathodes 120, 121 made of heat-resistant metals 118, 119, such as barium imprecathode, are attached . 125 is formed. Furthermore, fixed cathodes 126 and 127 are provided outside the rotating heat-resistant metals 118 and 11.
9, the current-carrying diode 124 ,
Current-carrying diodes 128 , 129 with opposite characteristics to 125
is formed. These diodes keep both the magnetic bearing rotors 114 and 115 substantially at ground potential, and the magnetic bearing internal vacuum bulkhead 10
It has substantially the same potential as 2,103. Therefore, the gap between them can be kept at a small gap of 0.5 mm or less, and the stators 110 and 111 for the radial magnetic bearing and the rotor 11 for the magnetic bearing can be kept at a small gap of 0.5 mm or less.
4, 115 can be reduced to within 1 mm. As a result, bearing rigidity can be extremely increased. Furthermore, metal rings 130 and 131 are fixed to the outer peripheries of the magnetic bearing rotors 114 and 115 following the laminated plates 116 and 117, and a copper ring 132 is attached to the outer periphery of one rotor 115 following the metal ring 131. , a non-magnetic ring 133 is fixed. A stator 134 for rotor rotation is provided outside the copper ring 132,
These form an induction motor that rotates the rotor at high speed. A ring 10 is provided on the outside of the metal ring 130 and the non-magnetic ring 133, respectively.
4,105 through the radial sensor 135,
136 are provided, and magnetic bearing rollers 114 ,
115 deviation is detected. 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. An end surface 137-a of this electrical insulator 137 on the target 4 side
A metal plate 138 made of molybdenum or the like is bonded to. Experiments have shown that this joining can be achieved by brazing or the like. and,
An anode target 4 for generating X-rays is mechanically and tightly fixed to this metal plate 138 by bolts 139. A withstand voltage portion 137-b is formed between the end of the magnetic bearing rotor 114 and the metal plate 138 , and the diameter of the electric insulator 137 is larger than that of the other portions.
14 high withstand voltage (e.g. 80kV or more). In this case, the withstand voltage portion 13 of the electrical insulator 137
7-b has a longer creepage distance by making the surface uneven. A conductive path 14 is provided in the center of the electrical insulator 137.
0 is provided and the target 4 of the electrical insulator 137
A heat-resistant metal 142 is provided on the other part of the conductive path 140, which is electrically connected to the target 4 via a conductor 141 attached to the side end face by metallization or the like. A thermionic emission cathode 143 is attached to the part, and the cathode 143 is heated by a heater 144 attached to the outside.
It is heated to a high temperature of around 1000℃. The heater 144 is supplied with a high voltage (for example,
75 kV), heated as described above, and electrically coupled with low impedance due to the inflow of thermoelectrons from the cathode 143. Therefore, high voltage can be supplied to the target 4 from outside the tube without contact. 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 resistant material. The voltage 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 withstand voltage portion 145-a is provided with an uneven portion to increase the creepage distance. Further, a negative high voltage (for example, -75 kV) is supplied to the cathode 3 by a conductor (not shown), and the thermoelectrons collide with the target 4 kept at a positive high voltage (for example, +75 kV), causing X Generate line 146.
The X-rays 146 are transmitted through an X-ray emission window 147 made of, for example, beryllium and attached to the heat-absorbing container 101.
It is irradiated to the outside of the tube through. Further, secondary electrons (not shown) emitted from the target 4 are shielded by shielding plates 148 and 149 provided inside the tube.
Withstand voltage portion 137- of electrical insulators 137, 145
b, preventing it from flying to 145-a. Furthermore, auxiliary bearings 150 and 151 are firmly supported by support plates 106 and 107 on the outer sides 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. [Modification of the Invention] In the above embodiment, a non-contact current path is employed to maintain the rotors 114 , 115 at substantially ground potential, but a structure in which one or both of them are brought into mechanical contact may be used. It's okay. Similarly, 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. 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 may be moved to the 0 side to form a so-called cantilevered structure. Next, another modification will be explained using FIG. 2, where the same parts as in FIG. 1 are given the same reference numerals. That is, the electrical insulators 137 and 145 are columnar,
If the withstand voltage portions 137-b and 145-a are made to have a high voltage by increasing the creeping distance, the same effect as in the above embodiment can be obtained. Furthermore, withstand voltage portion 13
Of course, the creeping distance may be increased by providing uneven portions on 7-b and 145-a. Alternatively, a conventional mechanical bearing may be used for the bearing portion. [Effects of the Invention] According to this invention, the following excellent effects can be obtained. In other words, since the rotating body is completely non-contact,
It is capable of ultra-high-speed rotation of approximately 30,000 rpm, and can increase the peak input value of the X-ray tube by 1.7 compared to conventional tubes. In addition, since the rotating body is completely non-contact, it is possible to provide an X-ray tube with low vibration and low noise.
Furthermore, since no mechanical ball bearings are used, the rotational life is extremely long. Also, the target 4 is set to a positive high voltage, and the cathode 12 is set to a positive high voltage.
Since 0,121 is maintained at a negative high voltage, a so-called neutral point grounded type high voltage power supply can be used.
In other words, since a conventional X-ray tube power source can be used, the rotating anode X-ray tube of the present invention can be used in a conventional X-ray generator. Furthermore, since the rotors 114 and 115 are substantially at ground potential, the magnetic gap of the magnetic bearing can be made small and strong rigidity can be obtained. ), it is possible to provide an X-ray tube with an extremely large capacity (for example, 6MHU).Furthermore, the rotor 114 ,
Since 115 is substantially at ground potential, noise entering the position sensor 152 can be reduced and stable operation is possible. Further, the structure of the rotors 114 and 115 is simple, and as a result, a compact and low-cost X-ray tube can be provided. As explained above, the present invention has an electrical insulator that mechanically connects a bearing rotor and an anode target that constitute a part of a magnetic bearing, and has a substantially T-shaped longitudinal section, and has an anode in its large diameter portion. A shielding plate to which the targets are connected, a magnetic bearing rotor is fixed to the outer periphery of the small diameter part, and a hole having an inner diameter smaller than the outer diameter of the target is provided between the large diameter part of the insulator and the anode target. This arrangement increases the rigidity of the entire rotating body, and prevents stray electrons from the anode target from colliding with the large diameter part of the insulator and causing it to become charged, maintaining stable operation. be done.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a rotating anode X-ray tube according to an embodiment of the present invention, FIG. 2 is a sectional view showing a modified example of the invention, and FIG. 3 is a sectional view showing a conventional rotating anode X-ray tube. FIG. 1 ...Housing, 4 ...Anode target, 1
10,111... Stator for radial magnetic bearing,
112, 113... Stator for thrust magnetic bearing, 114 , 115 ... Rotor for magnetic bearing, 12
0,121...Cathode, 137,145...Electric insulator.

Claims (1)

[Claims] 1. An electron beam emitting cathode placed in a vacuum container, and a rotatable X provided opposite to this cathode.
A rotating anode comprising a line-generating anode target, a magnetic bearing rotatably supporting the anode target, a bearing rotor forming a part of the magnetic bearing, and an electrical insulator mechanically connecting the anode target. In the X-ray tube device, the electric insulator has a substantially T-shaped longitudinal section, the anode target is connected to the large diameter part, and the magnetic bearing rotor is fixed to the outer periphery of the small diameter part. A rotating anode type X-ray tube device, further comprising a shielding plate having a hole having an inner diameter smaller than the outer diameter of the target, and disposed between the large diameter portion of the insulator and the anode target.