JPH0457063B2 - - 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, such as X-ray diagnosis, but in cases such as stomach examinations,
Conventionally, an X-ray tube as shown in FIG. 5 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 50KV current
For 20mA, it reaches 1KW. 99 of this power
% or more 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. And the heat of target 4 is rotor 6,
It is transmitted to the rotating shaft 8 and makes 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, the point on the support column 5 reaches 800 in about 15 minutes after the start of energization.
℃, 550 at the point of rotor 6 30 minutes after the start of energization
℃, thermal equilibrium is reached at a point near the bearing 13 at 400°C approximately 50 minutes after the start of energization. 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.

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 as a special high voltage power supply and high voltage cable are required.

[Problems with background technology]

However, the conventional X-ray tube as described above has the following drawbacks. That is, when the temperature of the balls of the bearings 12, 13 increases as described above, not only does the clearance between the balls and the inner and outer rings become insufficient, but also the lubricant existing between them evaporates, causing the bearings 12, 13 to become hot. 13 may be damaged. For these reasons, there is a drawback that rotation stoppage accidents tend to occur frequently. To prevent this, it has been considered to increase the degree of blackening of the target 4, increase the degree of blackening of the surface of the rotor 6, and install a heat shield plate between the target 4 and the rotor 6, 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
The rotation life becomes shorter and shorter. In order to eliminate these problems, a rotating anode type X-ray tube using a magnetic bearing has been developed as described in U.S. Pat.
It was proposed in No. 58-43860 and Japanese Unexamined Patent Publication No. 59-63646. However, each of these has drawbacks as described above.

[Purpose of the invention]

The purpose of this invention is to rotatably support a large-capacity X-ray generation target using a magnetic bearing without contact, maintain the rigidity of the magnetic bearing sufficiently high, and increase the rigidity of the rotating part to reduce the resonance frequency. It enables ultra-high speed rotation with low vibration, extremely long rotation life, and high positive voltage to the target.
By keeping the cathode at a high negative voltage and the vacuum vessel and the rotor and stator of the magnetic bearings substantially at 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]

In this invention, an insulator is inserted and fixed inside a rotor for a magnetic bearing, and an X-ray generating target is mechanically fixed to a separated position on the outer periphery of the insulator via the insulator. and the magnetic bearing rotor are electrically insulated by the separated insulator, the magnetic bearing rotor is maintained at substantially ground potential, and at least one conductor is provided penetrating through the inside of the rotor. A positive high voltage is supplied to the target from outside the tube through 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 possible to rotate targets with large weight and external dimensions at ultra-high speeds, extremely long life, low vibration,
This is a low-noise rotating anode type X-ray tube device.

[Embodiments of the invention]

The rotating anode type X-ray tube device of the present invention is constructed as shown in FIGS. 1 to 3, and the conventional example (FIG. 5)
The same parts are given the same symbols.

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 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, magnetic bearing rotors 114, 1
15 are arranged. The rotors 114 and 115 for magnetic bearings are made of a magnetic material such as pure iron, and on the outer periphery there are laminated plates 116 and 11 made of 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.

Now, at each end of the metal cylindrical member of the magnetic bearing rotor 114, 115, there are heat-resistant cylinders 118, 119 made of a thin heat-resistant metal such as tantalum, which has a small heat capacity, or a ceramic such as Si3N4 with a metalized surface. Connected and fixed electrically and mechanically. A part of the outer periphery of these heat-resistant cylinders is provided with a rotating cathode 120, 1 for thermionic emission, which emits thermionic electrons at a relatively low temperature, such as a barium imprecathode.
21 are attached to each. Furthermore, rotating anodes 124 and 125 for inflowing electrons are constructed in the vicinity of the rotating cathodes 120 and 121 of these heat-resistant cylinders, and these rotating cathodes and rotating anodes are rotated integrally with the rotor. There is.

On the other hand, fixed anodes 122 and 123 for electron inflow are disposed around rotating cathodes 120 and 121 in close opposition to each other on the inside of end insulating containers 108 and 109 coaxially surrounding heat-resistant cylinders 118 and 119 of the rotor. ing. Also, close to this, a rotating anode 1
Fixed cathodes 126 and 127 for thermionic emission, which have a heater function and are closely opposed to each other around 24 and 125.
are placed respectively. In this way, the fixed anode and fixed cathode form a diode pair 128 and 129 with opposite polarity to the rotating cathode and rotating anode, which are electrically short-circuited by the heat-resistant cylinder, and their operation causes the metal on the outer periphery of the rotor to The cylindrical member is maintained at approximately ground potential.

These fixed cathodes 126 and 127 are made of metal that can be heated to high temperatures, such as tungsten wire, and when heated to, for example, 2250°C, they not only operate as cathodes for generating thermionic electrons, but also emit strong thermal radiation from their surfaces. The heat-resistant cylinders 118 and 119 facing each other are heated to a high temperature. and,
The cathodes 120, 121 attached to these are heated to approximately 900° C. and operate as cathodes as described above.

A diode anode 12 facing these cathodes
2, 123 is made of a filament, such as a tungsten wire, and is heated by being energized from outside the vacuum envelope, and is connected to the opposing cathode 12.
0.121 is heated auxiliary. Fixed cathode 1 above
26 and 127 are grounded, and the fixed anode 12
2 is connected to a positive voltage, for example 50V, through a resistor 153.
is applied. Therefore, although the current value is limited to a low value, the potential of the rotors 114, 115 is substantially always at ground potential. In Figure 1, another
The connection of the two grounding diodes is omitted.
Furthermore, since the outer diameters of the heat-resistant cylinders 118 and 119 are smaller than the outer diameters of the magnetic bearing rotors 114 and 115, the centrifugal force is reduced despite the high temperatures, making it possible to withstand high-speed rotation. .

These diodes keep both the magnetic bearing rotors 114 and 115 substantially at ground potential, and have substantially the same potential as the vacuum partitions 102 and 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. Above copper ring 1
32 has a stator 134 for rotating the rotor.
are provided and these form an induction motor to rotate the rotor at high speed. Radial sensors 135 and 136 are provided outside the metal ring 130 and non-magnetic ring 133 via rings 104 and 105, respectively, to detect the displacement of the magnetic bearing rotors 114 and 115.

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. Experiments have shown that this joining can be achieved by brazing or the like. 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
It is electrically coupled to the target 4 via a conductor 141 attached to the side end face by metallization or the like. A heat-resistant cylinder 142 is provided at the other end of the conductive path 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), heated as described above, and electrically coupled with low impedance due to the inflow of thermoelectrons from the cathode 143. 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 have a large diameter and a withstand voltage. The portion 145-a provides high withstand voltage (e.g.
80KV). As described above, the rotor 115 is kept at 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 creeping 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, 115 are operating normally, they are not in contact with the rotors 114, 115, but before operation or in the case of abnormal operation, the rotating parts are supported by the auxiliary bearings 150, 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.

[Modified example of the invention]

In the above embodiment, a non-contact current path is used to maintain the rotors 114 and 115 at substantially ground potential, but a structure may be adopted in which one of the rotors 114 and 115 is brought into mechanical contact.

Moreover, the rotor 114 or 115 and the insulator 137
or 145 are bonded over the entire surface, but it goes without saying that 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 cantilever structure.

Next, another modification will be explained using FIG. 4. Note that FIG. 2 shows only the left end portion of FIG. 1, and the same parts as in FIG. 1 are given the same reference numerals.

That is, the insulator 13 in the rotors 114, 115
7 and a heat-resistant cylinder 118 attached to the end of the rotor.
A shield plate 160 is attached in the middle. This shield plate 160 is mechanically supported by the end insulating container 108, and its potential is maintained at a lower potential than the ground potential or the potential of the target 4.

During operation, the cathode 12 of the current-carrying diode
6, 120 are heated to a high temperature, the metal evaporates, but it is captured by the shield plate 160, so the surface of the electrical insulators 137, 108 is not contaminated, high withstand voltage is maintained, and reliability is improved. A highly rotating anode type X-ray tube device can be provided.

Furthermore, the radiant heat from the heat-resistant cylinder 118 heated to a high temperature is shielded by the shield plate 118,
Since the electrical insulator 137 is not heated, the reliability of the electrical insulator 137 is increased.

It goes without saying that the same concept holds true for other current-carrying diodes (not shown).

〔Effect of the invention〕

According to this invention, the following excellent effects can be obtained.

In other words, since the rotating body is strong against centrifugal stress,
It is possible to rotate at an ultra-high speed of about 30,000 rpm, and the peak input value of the X-ray tube can be increased to about 1.7 compared to conventional tubes. Furthermore, since the rotating body is completely non-contact, it is possible to provide an X-ray tube with low vibration and low noise, and 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 type X-ray tube device 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 reduced and strong rigidity can be obtained, allowing the target 4, which is extremely heavy (for example, 4 kg), to be moved at high speed (for example, 30,000 rpm). Since it can be rotated, it is possible to provide an X-ray tube with an extremely large capacity (for example, 6 MHU). Furthermore, the rotors 114, 11
5 is substantially at ground potential, noise entering the position sensor 152 can be reduced;
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.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing one embodiment of the present invention, FIGS. 2 and 3 are enlarged views of the main parts, and FIG.
The figure is a sectional view of a main part showing another embodiment of the present invention, and FIG. 5 is a schematic sectional view showing a conventional structure. 1...Housing (vacuum container), 4...Target, 3...Cathode for electron beam emission, 110,1
11, 112, 113... Stator for magnetic bearing,
114,115...rotor, 118,119...
... Heat-resistant cylinder, 120, 121 ... Rotating cathode, 12
4,125...rotating anode, 122,123...fixed anode, 126,127...fixed cathode.

Claims (1)

[Scope of Claims] 1. An anode target for generating X-rays provided in a vacuum container, a cathode provided opposite to the anode target and emitting an electron beam toward the anode target, and an anode target including the anode target. The rotor includes a rotor to support and a magnetic bearing to rotatably support the rotor in a non-contact manner, and the rotor has a metal plate on its outer periphery that forms part of the magnetic bearing and is electrically insulated from the anode target. A cylindrical member and a heat-resistant cylinder with a small heat capacity electrically connected to this metal cylindrical member are connected, and a rotating cathode for thermionic emission and a rotating anode for electron inflow are located close to each other in a part of the heat-resistant cylinder. A fixed anode for electron inflow and a fixed cathode for thermionic emission having a heater function are provided in close opposition to the rotating cathode for thermionic emission and the rotating anode for electron inflow of the heat resistant cylinder. A rotating anode type X characterized by being provided inside a surrounding vacuum container.
wire tube device.