JP2001276049A - Cathode scanning type x-ray generator and x-ray ct scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a very high-speed CT scanner with drastically reduced scanning time and a cathode scanning type X-ray generator for realizing this objective. SOLUTION: The very high-speed CT scanner and the cathode scanning type X-ray generator for realizing this scanner have a cathode-side rotator assembly AR, an electron gun assembly EG, a cathode for emitting electrons, and an annular cathode power supply mechanism SL1 in a doughnut-shaped vacuum vessel VV, and makes a cathode orbit around an examined object while feeding power to the cathode to make an accelerated electron beam incident on the surface of an annular X-ray target TG to generate X-rays orbiting at high speed. The cathode-side rotator assembly is freely rotatably supported by a bearing mechanism CBG consisting of a hydrodynamic slide bearing lubricated by a liquid metal lubricant. There is a path of the liquid metallic lubricant having directivity at the opening part of the hydrodynamic slide bearing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathode scan type X-ray generator for an X-ray CT scanner which is small in size and emits X-rays from an X-ray orbiting at a high speed and can perform ultra-high speed scanning. And an X-ray CT scanner capable of performing ultra-high-speed scanning using the same. By limiting the rotating part for orbiting the X-ray focus to small parts in the vacuum vessel, the X-ray focus can be stabilized around the specimen at high speed without a mechanical rotation mechanism in the atmosphere. Provided is a small-sized X-ray CT scanner capable of obtaining a three-dimensional image by instantaneously photographing a subject by orbiting the subject. Using a hydrodynamic sliding bearing that uses liquid metal as a lubricant, the electron gun assembly is circulated in the vacuum vessel, and the electron gun assembly and other parts circulating in the vacuum vessel are energized from outside the vacuum vessel. I have.

[0002]

2. Description of the Related Art A conventional X-ray CT scanner will be described with reference to FIG. Conventional X
The line CT scanner includes a fixed base 1001 and a bearing 1003.
And a rotating gantry 1002 that rotates through the. The rotating gantry 1002 is rotated in the air by a rotation driving mechanism 1009 controlled using a controller 1008. An X-ray tube 1004 for generating X-rays, a high-voltage power supply (not shown) for supplying a high voltage thereto, a detector 1006 for receiving X-rays, and other electronic circuits 10
07 and the like are attached to the rotating frame 1002. A signal of an electronic circuit attached to the rotating gantry 1002 is transmitted to the fixed gantry 1001 by a slip ring (not shown). For this reason, the sum of the masses of the components attached to the rotary gantry 1002 increases, and if the scanning speed of the X-ray CT scanner is increased, a large centrifugal force acts, and the components mounted on the rotary gantry 1002 and the rotary gantry 100
2 has a drawback that the scanning speed cannot be increased because it cannot withstand excessive stress.

[0003] X-rays used in conventional X-ray CT scanners
The wire tube 1004 is a disk-shaped X-ray target having a diameter of about 10 cm and 3,000 rpm in a cylindrical vacuum vessel.
The X-ray is rotated at a high speed of about m, and collides with electrons emitted from the cathode of the electron gun assembly to emit X-rays 1005 in one direction. The entire structure is cylindrical.
An X-ray tube for an X-ray CT scanner, which needs to generate a large amount of X-rays, requires a cooler, and the sum of both masses is 1
The rotation frame 1002 for attaching and rotating it in the air becomes large, and the entire X-ray CT scanner becomes large, which is not only inconvenient to handle, but also requires a large installation space. And the operating costs were large. Further, in recent years, as the use of X-ray CT scanners has expanded, there has been a demand for instantaneous observation of blood and a contrast agent. In order to respond to this, it is necessary to rotate the X-ray tube 1004 around the subject at a high speed. The highest orbiting speed so far is 2r
ps, which is considered the limit. on the one hand,
There is a demand to increase the X-ray dose to enhance the image quality and enhance the diagnostic performance, and it is necessary to increase the size and mass of the conventional X-ray tube 1004. Simultaneously satisfying these conflicting requirements has been impossible with an X-ray CT scanner having a conventional structure.

On the other hand, an X-ray CT scanner of the electronic scan type has been developed in the past in order to increase the scanning speed. This is done by taking out electrons from an electron gun assembly fixed at the bottom of a vacuum vessel in the shape of a thermos bottle placed on its side, and electromagnetically controlling the position of the electrons while traveling about 100 cm in the vacuum vessel. After orbiting around the subject, the electrons are made incident on an arc-shaped X-ray target to extract an X-ray that makes a half circle. With this structure, high-speed scanning with a scan time of about 0.1 second is possible,
Poor image quality due to insufficient X-ray dose, too large X-ray focus, difficulty in maintaining stable operation, and difficulty in handling because the entire device is large They have disadvantages such as high cost and are used only for special purposes.

[0005]

The problem to be solved is that the scan time of the X-ray CT scanner is greatly reduced to eliminate motion artifacts and to provide a sufficient level of X-ray dose in imaging a fast moving subject. An object of the present invention is to provide an X-ray CT scanner which can obtain a high-quality image with less photon noise by securing the X-ray CT scanner, and which is small in size and easy to handle. In particular, as a bearing mechanism that can be used reliably in a vacuum to achieve this, and a power supply mechanism that can supply power to components rotating in a vacuum, a ring-shaped fluid that uses liquid metal, which is liquid during operation, as a lubricant Developed a pressure-sliding bearing, despite the large diameter of the bearing and the large height drop at the bearing opening, not only does the liquid metal lubricant not leak out of the bearing mechanism, but also temporarily Cathode scan type X-ray generator with improved reliability of the bearing mechanism by providing a mechanism to automatically return the liquid metal lubricant into the bearing even if liquid metal lubricant overflows the bearing opening due to some sudden inconvenience , And X-ray C using it
To provide a T-scanner.

[0006]

SUMMARY OF THE INVENTION In the present invention, all rotating parts of an X-ray CT scanner are mounted in a donut-shaped vacuum vessel so as to be reduced to a minimum, eliminating the need for mechanical rotating parts in air. By doing so, an X-ray CT scanner capable of ultra-high-speed scanning is realized. The vacuum container is formed in a donut shape, and the subject is placed on a bed in the atmosphere near the central axis of the vacuum container. Electrons are emitted from the cathode of the electron gun assembly that orbits in the vacuum vessel, and accelerated electrons collide with an annular X-ray target mounted in the vacuum vessel facing the orbit of the cathode, causing X-rays. Generate. The generated X-ray passes through an X-ray emission window provided on the small-diameter wall of the vacuum vessel, and is applied to the subject in the atmosphere. The X-rays that have passed through the subject are detected by an annular X-ray detector arranged in the atmosphere coaxially with the vacuum vessel, reconstructed into a tomographic image by a computer, and displayed on a display device. The rotating part for rotating the X-ray focal point in the vacuum vessel is limited to a light-weight electron gun assembly and the like, and its volume is small, and it has a substantially symmetrical shape as a whole. Even when rotating at a high speed, the stress applied to the rotating body can be sufficiently reduced, and the high-speed rotation can be stably continued. Also, since about three electron gun assemblies are mounted on the same cathode side rotating body assembly, the scan time is reduced to 0.
Ultra high-speed scanning of about 03 seconds can be performed.

An X-ray CT scanner of the type in which an electron gun is rotated inside a donut-shaped vacuum vessel has been proposed in the past, but has not been realized so far. One of the reasons is that a means for continuing stable rotation in a vacuum and a reliable means for stably setting the potential of the rotating body to a constant value have not been found. In the present invention, as a bearing mechanism that can be used reliably in a vacuum, an annular dynamic pressure sliding bearing using a liquid metal that is a liquid during operation as a lubricant is adopted,
This provides a means for preventing the liquid metal lubricant from leaking out of the bearing mechanism despite the fact that the diameter of the bearing is large and the height drop of the opening of the bearing is large. Further, the potential of the rotating body is set to a constant value via the liquid metal lubricant.

When the bearing rotating body constituting the rotating part of the bearing mechanism is rotating, the liquid metal lubricant is confined inside the bearing by the suction action of the bearing groove provided on the surface of the bearing. Generally, when the bearing rotating body stops rotating, leakage of the liquid metal lubricant is prevented by the surface tension of the liquid metal lubricant generated in the opening at the end of the bearing. However, in the X-ray CT scanner of the present invention, the center of rotation of the bearing rotor is substantially in the horizontal direction, and since the diameter of the bearing is as large as about 100 cm, the height drop around the entire gap at the opening of the bearing is reduced. The liquid metal lubricant, which is large and is located vertically below the opening of the bearing, receives a large static pressure due to gravitational acceleration. In the opening of the bearing, the size of the gap in the opening of the bearing is extremely small so that the pressure effect of the surface tension generated on the liquid metal can overcome the static pressure.
As one means for achieving this, the bearing adjacent to the opening of the bearing is limited to a thrust bearing, and the size of the bearing gap of the thrust bearing is kept small. Due to this effect, the pressure effect of the surface tension in the vertical downward direction becomes larger than the static pressure of the liquid metal lubricant, and the leakage of the liquid metal lubricant to the outside is prevented, and stable operation is guaranteed.

However, inside the bearing mechanism,
For example, it is necessary to prevent the liquid metal lubricant from leaking into the vacuum space outside the bearing mechanism even when a sudden accident such as ejection of internal gas occurs. In the present invention, when the angle formed between the bearing surface and the surface facing the vacuum space from the opening of the bearing is increased, the pressure inside the liquid metal lubricant increases, and the surface of the liquid metal lubricant swells outward. However, since this portion does not contact the surrounding surface, when the pressure returns to normal, the liquid metal lubricant returns into the bearing. In addition, a directional passage leading to the inside of the bearing mechanism is provided in the opening of the bearing, and in the event that the liquid metal lubricant overflows from the opening of the bearing to the vacuum space side, the bearing passes through this directional passage. Automatically returned inside the mechanism. Since the liquid metal lubricant cannot flow backward in the directional passage, the liquid metal lubricant does not leak into the vacuum space through the directional passage. Therefore, the cathode scan type X-ray generator of the present invention can continue stable operation for a long time without the liquid metal lubricant leaking out of the bearing mechanism.

According to the present invention, the bearing surface is in thermal communication with the vacuum vessel, and the vacuum vessel is forcibly cooled from the outside. , The thermal expansion is small, and stable operation can be continued for a long time. Further, components that generate heat, such as an electron gun assembly and an X-ray target, are also forcibly cooled via the liquid metal lubricant present in the bearing gap, thereby suppressing thermal expansion and the like.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A cathode scan type X-ray generator is wrapped in a donut-shaped vacuum vessel, and the vacuum vessel is installed so that its central axis is substantially horizontal. A subject (human body) is placed in the atmosphere, and the vacuum container is arranged so as to surround the subject. The vacuum container is fixed without rotating, and the angle with the subject and the position in the horizontal direction can be changed. X-rays are generated toward the subject while moving the X-ray focus so that the X-ray focal point orbits around the subject inside the vacuum vessel. By using the orbiting X-rays, an X-ray CT scanner having no rotating mechanism in the atmosphere is realized. A cathode scan type X-ray scanner for X-ray CT scanners that can perform ultra-high-speed scanning and obtain a large output, which cannot be realized with an X-ray CT scanner having a conventional structure.
A ray generator and an ultra-high-speed X-ray CT scanner using the same have been realized with a simple structure at low cost and with high reliability.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a cathode scan type X-ray generator according to one embodiment of the present invention and an X-ray CT scanner using the same will be described below with reference to the drawings. FIG. 2 shows a cathode scan type X-ray generator of the present invention and an X-ray using the same.
FIG. 3 is a schematic cross-sectional view of the entire structure of the X-ray CT scanner, FIG. 3 is a principle view, and FIG. 4 is a cross-sectional view of a part of a cathode scan type X-ray generator according to the present invention which is located vertically above at a certain moment. 5 is an enlarged sectional view of a part of a bearing mechanism which is a main part of the cathode scan type X-ray generator of the present invention, and FIG. 6 is an enlarged view of a lower part of FIG. It is sectional drawing.

As shown in FIG. 2, the donut-shaped vacuum vessel VV is installed so that its central axis is substantially horizontal, and is constantly evacuated to a high vacuum state from an exhaust port VC by a vacuum pump (not shown). As shown in FIG. 2 or FIG.
A cylindrical cathode-side rotating body assembly CR is provided in a vacuum space inside the vacuum vessel VV. The cathode-side rotating body assembly CR is a bearing mechanism CBG comprising a dynamic pressure sliding bearing using a liquid metal which is a liquid at room temperature as a lubricant. , Which are rotatably supported in a vacuum, and their central axes coincide with CC ′. Three electron gun assemblies EG are attached to the cathode side rotating body assembly CR separately in the circumferential direction. As shown in FIG. 2, FIG. 4 or FIG. 5, a cylindrical rotor RT2 made of copper is coaxially attached to the cathode side rotating body assembly CR, and a magnetic path made of a magnetic material is coaxial with the cylindrical rotor RT2. A cylinder is attached. An arcuate stator LM2 is mounted along the vacuum vessel wall outside the vacuum vessel VV in a state facing the rotor RT2. The rotor RT2 is disposed so as to be sandwiched between the magnetic path cylinder and the stator LM2. Since the rotor RT2 receives a rotational torque from the stator LM2 through the wall made of a non-magnetic material of the vacuum container and receives a rotational torque, the cathode side rotating body assembly CR rotates. The cathode side rotating body assembly CR is a bearing mechanism CBG comprising a dynamic pressure sliding bearing.
It is electrically and thermally connected to the vacuum vessel VV through the liquid metal lubricant therein.

As shown in FIG. 2 or FIG.
A cathode 1 for emitting thermoelectrons 2 is attached to the tip of G. An annular X-ray target TG is attached to face the orbit of the cathode 1. As shown in FIG. 2 or FIG. 4, the X-ray target TG is mechanically coupled to a cylindrical anode-side rotating body assembly AR. The anode side rotating body assembly AR is rotatably attached to a part of the vacuum vessel VV via a bearing mechanism ABG including a dynamic pressure sliding bearing using liquid metal which is liquid at room temperature as a lubricant. A rotor RT1 made of a copper tube is mounted on the anode side rotating body assembly AR, and a magnetic path cylinder made of a magnetic material is mounted coaxially with the rotor RT1. An arc-shaped stator LM1 is attached to the outside of the vacuum vessel VV along the vacuum vessel wall so as to face the rotor RT1. The rotor RT1 is disposed between the magnetic path cylinder and the stator LM1. Since the rotor RT1 is given a rotational torque by receiving electromagnetic induction from the stator LM1 through a wall made of a non-magnetic material of the vacuum vessel, the anode side rotating body assembly AR rotates. The center axis of rotation of the X-ray target TG coincides with the center axis CC 'of rotation of the cathode 1 included in the electron gun assembly EG, and the cathode 1 is always opposed to the surface of the X-ray target TG. Rotate in opposite directions.

Referring to FIG. 2 or FIG. 4, cathode feeding mechanism SL
1 will be described. In the embodiment shown in FIG. 2 or FIG.
The two cathode power supply mechanisms SL1 are coaxially mounted, and form three independent current paths. In these figures, the internal structure of the cathode power supply mechanism SL1 is simplified. The cathode 1 of the electron gun assembly EG is electrically connected to the high voltage terminal HT through an annular cathode power supply mechanism SL1 having a central axis substantially the same as the orbiting central axis CC ′ of the electron gun assembly EG in a vacuum space in the vacuum vessel VV. It is connected to the. The high voltage terminal HT is connected to a negative high voltage of about -150 KV from an unillustrated high voltage power supply outside the vacuum vessel VV and the electron gun assembly EG.
Is supplied to heat the negative electrode 1. Each cathode power supply mechanism SL1 has a fixed part and a rotating part, and the fixed part holds the vacuum container VV while maintaining electrical insulation via the insulator 220.
It is mechanically fixed to a part of. Cathode feeding mechanism SL1
The rotating part and the fixed part constitute a dynamic pressure sliding bearing using a liquid metal as a lubricant, and electricity is supplied between the two through a liquid metal lubricant. The rotating part of the cathode power supply mechanism SL1 is mechanically connected to the electron gun assembly EG by an elastic rotation torque transmission mechanism 217, and the cathode power supply mechanism SL1 allows a certain degree of eccentricity and axial displacement. Rotates with the electron gun assembly.

The X-ray target TG is an anode side rotating body assembly A
It is electrically and thermally connected to the vacuum vessel VV via the liquid metal lubricant present in the R bearing mechanism ABG. The vacuum vessel VV is at the ground potential and is forcibly cooled with cooling water or the like. Therefore, the X-ray target TG is set to the ground potential, and a large amount of heat generated from the X-ray target TG is efficiently removed by the cooling water flowing through the wall of the vacuum vessel VV via the liquid metal lubricant. Since the thermal resistance between the X-ray target TG and the cooling water is sufficiently small,
Since the temperature of the line target TG is kept low, a large power input is allowed, and an extremely large amount of X-rays can be generated in a short time.

The electron gun assembly EG includes F1 and F shown in FIG.
As shown in F2 and F3, three are mounted at equal intervals around the cathode side rotating body assembly CR. Here, F1, F2, and F3 represent Xs formed by the collision of the electrons 2 with the X-ray target TG.
The three foci of the line are shown. X-ray focus F1, F2, F
3 simultaneously circulates in the same direction as shown in FIG. 3 while simultaneously generating X-rays. The current positions of these X-ray focal points are detected by an angle detection mechanism (not shown) attached to the cathode side rotating body assembly CR. X-ray focus F1, F
2 and 4, the X-rays emitted from F3 are shaped like a fan by an X-ray distribution limiting mechanism inside the X-ray target TG, as shown in FIG.
After the X-ray intensity distribution in the fan direction is optimized by passing through the fan-direction distribution shaper WF (see FIG. 4) attached to the X-ray source, the X-ray emission window XW (see FIG. 4) of the vacuum vessel VV After passing through the external annular slit SLT, it passes through the subject M and reaches the respective opposing surfaces of the two annular X-ray detectors DF and DB mounted coaxially with the X-ray target TG.

As shown in FIG. 3, X-ray focal points F1, F2,
The X-rays emanating from F3 are received by the subdivided detection elements, each of which is in the opposite part D1, D2, D3 of the detector. The irradiation field range and the like are determined so that the detector portions D1, D2, and D3 do not overlap each other. Since the sum of the detector portions D1, D2, D3 occupies almost all of the annular detector, all the detection elements in the X-ray detectors DF, DB are effectively used, and the cost / performance ratio is improved. Each of the annular detectors DF and DB is also divided into a large number of detection element rows in the direction of the central axis CC ′, and a signal detected by each detection element is converted into a digital signal by an electronic circuit (not shown). The image is reconstructed into a tomographic image by a computer (not shown) and displayed on an image display device (not shown) to obtain a multi-slice CT image.

FIG. 4 is an enlarged view of a part of the cross section around the electron gun assembly at a moment when it is positioned vertically above, and the same parts are denoted by the same symbols. In FIG. 4, the internal structure of the bearing mechanism CBG is shown in a simplified manner. The cathode-side rotating body assembly CR has a generally rotationally symmetrical structure as a whole, and the components such as the electron gun assembly EG attached thereto are small and lightweight, so that they can sufficiently withstand high-speed rotation of about 10 rps. In this case, the X-ray focus is 3
Since the number of scans is one, the scan time can be reduced to 0.03 seconds. The X-ray target TG has a large diameter of 120 cm, rotates in the direction opposite to the X-ray focal points F1, F2, and F3, and is forcibly cooled as described above, so that the surface temperature of the X-ray target TG increases. Since it is difficult to input a large amount of power, a sufficient amount of X-rays can be generated in a short time, and a high-quality CT image with little photon noise can be obtained despite ultra-high-speed scanning. In addition, since the multi-slice scan is realized, X-rays can be effectively used, not only can the resolution in the direction parallel to the central axis CC 'be increased, but also a wide range of imaging can be completed in a short time to achieve three-dimensional scanning. Real-time CT image can be obtained.

In order to realize the X-ray CT scanner having the above configuration, it is inevitable to realize the bearing mechanisms CBG and ABG and the cathode power supply mechanism SL which can be practically used in the above-described device configuration.
An object of the present invention is to realize a dynamic pressure sliding bearing that rotatably supports a rotating part in a vacuum. Conventionally, dynamic pressure sliding bearings having a diameter of 5 cm or less and having an opening on only one side have been put to practical use. In this case, the liquid metal lubricant inserted into the dynamic pressure sliding bearing is retained inside the bearing opening by the action of surface tension at the bearing opening. In order to obtain a sufficient bearing pressure of the hydrodynamic sliding bearing, the size of the gap between the rotating part and the fixed part has been limited to several tens of μm. For example, when the size of the gap in the opening of the bearing is 50 μm and the height drop of the liquid metal lubricant exceeds about 18 cm, the static pressure of the liquid metal lubricant due to gravitational acceleration overcomes the surface tension at the opening of the bearing and the liquid Metal lubricant leaks out. This becomes a serious problem when the rotating part of the bearing stops rotating. In particular, as in the case of the present invention, the height drop of the opening of the bearing is 1
A dynamic pressure sliding bearing of about 00 cm was not feasible with the prior art.

Referring to FIGS. 5 and 6, an embodiment of a bearing mechanism CBG comprising a dynamic pressure sliding bearing will be described. FIG.
5 is an enlarged view of a part of the cross section of the cathode side rotating body assembly CR and the cathode side bearing mechanism CBG, and the upper part of FIG. 5 shows a part which is vertically located at a certain moment in actual use. , The lower part indicates the part located vertically below at the same moment. In FIG. 5, the central part is omitted and is shortened and displayed. FIG. 6 is an enlarged view of a lower part of FIG. 5 and shows a cross section of the bearing mechanism CBG. A bearing rotating body 102, which is a rotating part of the bearing mechanism CBG, is coaxially attached to the cathode side rotating body assembly CR. Bearing rotating body 102
The bearing fixed body 101 which is a fixed part of the bearing mechanism CBG
Are fitted with a gap. Bearing fixed body 10
One part is mechanically and thermally coupled to the vacuum vessel VV. The vacuum vessel VV is attached to a support base (not shown) so that an appropriate posture and a horizontal position with respect to the installation floor can be maintained. The bearing fixed body 101 and the bearing rotating body 102 have surfaces facing each other, and the facing surfaces are the first bearing gaps 103 and 108, the second bearing gaps 104 and 109, the third bearing gap 106,
111. At least one of the opposing surfaces forming the bearing gap has a herringbone-shaped bearing groove. In the first, second and third bearing gaps, a liquid metal that is liquid at room temperature, preferably gallium, indium,
Filled with a lubricant made of a tin alloy, each bearing gap is a radial bearing, a first thrust bearing and a second thrust bearing mounted opposite each other with a distance across the radial bearing. Bearing gap. The bearing gaps 103 and 108, the bearing gaps 104 and 109, and the bearing gaps 106 and 111 are the same, respectively, and different numbers indicate different positions. Here, at least one of the surfaces facing the bearing gap has the bearing groove.

When a rotational torque is applied to the cathode side rotating body assembly CR, a dynamic pressure is generated in these bearings, so that the rotating portion can be floated and rotatably supported. When the bearing rotating body 102 is rotating, the liquid metal lubricant in each bearing gap is subjected to the action of being confined inside the bearing, so that it does not leak from the bearing gap to the outside vacuum space.

As shown in FIGS. 5 and 6, first and second end gaps 105 and 110 and second and end gaps 107 and 112 are formed on opposing surfaces formed by the bearing fixed body 101 and the bearing rotating body 102, respectively. Bearing gap 1 for radial bearings
03, 108 and first end gaps 105, 110,
The central axes of the opposing surfaces constituting the second end gaps 107 and 112 coincide with CC ′ in a state where they are substantially horizontal. Bearing gap 10 of first thrust bearing
4,109, and bearing gap 1 of the second thrust bearing
06, 111 are flat, and the bearing gaps 104, 104 of the first thrust bearing are formed.
Reference numeral 109 denotes a bearing gap between the radial bearings 103 and 108 and the first end gaps 105 and 110, and a bearing gap between the second thrust bearings 106 and 111 denotes the bearing gaps 103 and 108 of the radial bearing and the second end gap. 10
7, 112. First end gap 10
The diameter of each of the opposing surfaces forming the second end gaps 107 and 112 is smaller than the diameter of the opposing surfaces forming the bearing gaps 103 and 108 of the radial bearing. The size of the first end gaps 105, 110 and the size of the second end gaps 107, 112 are larger than the size of the bearing gaps 103, 108 of the radial bearing and the first end gaps 105, 110.
And the second end gaps 107, 112 are both in communication with the vacuum space, and have opposing surfaces (not shown) that are not wetted by the liquid metal lubricant described above. Bearing gaps 104, 109 of the first thrust bearing
There is an annular bearing opening 121, 121 'between the first end gap 105, 110 and the second end gap 1 with the bearing gap 106, 111 of the second thrust bearing.
07, 112 between the annular bearing openings 120, 12
There is 0 '. These bearing openings have opposing surfaces that are not wetted by the liquid metal lubricant and a gap sandwiched therebetween. The diameter of the opposing surfaces that form the bearing openings 120 and 120 ′ and the bearing openings 121 and 121 ′ is smaller than the diameter of the opposing surfaces that form the bearing gaps 103 and 108 of the radial bearing. End gaps 105 and 11
0, end gaps 107 and 112, bearing openings 120, 1
The reference numerals 20 ′ and the bearing openings 121 and 121 ′ are the same, and different numbers indicate different positions. Here, at least one of the surfaces facing the end gap has the non-wetting surface.

When the bearing rotator 102 stops rotating, the bearing opening 12 which substantially forms a boundary between the region where the liquid metal lubricant is present and the vacuum region in the bearing mechanism CBG.
The surface tension acts on the liquid metal lubricant at 0, 120 'and the bearing openings 121, 121' to prevent the liquid metal lubricant from leaking out of the bearing openings. The static pressure in the liquid metal lubricant due to gravitational acceleration is proportional to the depth of the liquid metal lubricant from the waterline. In other words, the static pressure in the liquid metal lubricant increases as it is positioned vertically downward. On the other hand, the pressure effect of pushing the liquid metal lubricant by the surface tension is inversely proportional to the size of the gap of the bearing opening. Therefore, the bearing opening 1
If the size of the gap between the bearings 20, 120 'and the bearing openings 121, 121' is made sufficiently small, it is possible to prevent the liquid metal lubricant from leaking from the inside of the dynamic pressure sliding bearing having a large diameter. This is because the bearing openings 120, 1
20 'and the bearing openings 121, 121' can be achieved by configuring the end of the first thrust bearing and the end of the second thrust bearing, respectively. The reason is that the diameter of the bearing used in the present invention is as large as about 100 cm, so it is difficult to keep the gap size of the radial bearing at a sufficiently small value, but the size of the bearing gap of the thrust bearing is small. It is easy to keep
Therefore, it is easy to keep the size of the gap of the bearing opening provided adjacent to this small. The reason why the size of the bearing gap of the thrust bearing can be reduced is that the thrust bearing is hardly affected by thermal expansion because the distance between the opposed bearings is short, and is mounted so as to have a horizontal rotation center axis CC '. Therefore, it is hardly affected by gravitational acceleration and centrifugal force, and because the bearing surface is made flat, it is easy to maintain high accuracy,
Even if the size of the bearing gap is small, the bearing loss can be prevented from becoming excessive by reducing the width of the bearing.

However, during the process of evacuating the inside of the vacuum vessel VV to a vacuum state or during a long-time operation, the gas contained in the liquid metal lubricant and the bearing surface are formed. When a problem such as a case where gas remaining in the material to be expanded expands occurs, the liquid metal lubricant is applied to the bearing openings 120 and 120 ′ or the bearing openings 121 and 12.
It may be pushed out of 1 '. Even in this case, it is required that the function of pushing the liquid metal lubricant into the bearing is generated. Furthermore, even if the liquid metal lubricant is irreversibly pushed out of the bearing openings 120, 120 'or the bearing openings 121, 121', the liquid metal lubricant is evacuated to the vacuum space outside the bearing mechanism CBG. Must be prevented. In the present invention, in order to meet these demands, a directional passage for the liquid metal lubricant is installed as described below, and the bearing opening 12 is provided.
The liquid metal lubricant extruded outside the 0, 120 'and bearing openings 121, 121' is automatically returned to the interior of the bearing by the directional passage.

The above will be described with reference to FIG. The description here will be made only for the vertically lower part shown in the figure. The bearing gap 111 forming the second thrust bearing and the bearing gap 109 forming the first thrust bearing are formed in an annular bearing opening 120 and a bearing opening, respectively, which substantially form a boundary with a vacuum space. 12
It is next to 1. The bearing rotor 102 includes
Bearing opening 120, bearing opening 121 and end gap 1
An annular depression 132 and an annular depression 133 are provided at the positions of the respective boundaries with the end gap 12 and the end gap 110. Further, the bearing rotating body 102 is provided with annular recesses 151, 152, and 153 having larger diameters. In these portions, the size of the gap between the rotating surface and the fixed surface is as large as 1 mm or more. And there is substantially no bearing pressure. The annular recess 152 is adjacent to the bearing gap 111 of the second thrust bearing, and the annular recess 1
Reference numeral 53 is adjacent to the bearing gap 109 of the first thrust bearing, and a third annular recess 151 is provided between the annular recess 152 and the annular recess 153. Radial bearings are formed between the annular dent 152 and the annular dent 151 and between the annular dent 153 and the annular dent 151, respectively. In the description so far, the bearing gaps of these radial bearings are collectively indicated by 108. The amount of the liquid metal lubricant is determined so that at least a part of the annular recesses 151, 152, and 153 has a space that is not filled with the liquid metal lubricant in any case.

The annular recesses 132 and 133 adjacent to the bearing opening 120 and the bearing opening 121 are provided with the annular recesses 151, 152 and 153 between the bearings and the directional passages 154, 155 and 156. , 157. Each of the directional passages 154, 155, 156, and 157 is composed of a number of directional passages that are disposed evenly over the entire circumference of the bearing rotor 102. These directional passages include an annular recess 132 and an annular recess 13.
3, the liquid metal lubricant moves in the direction of the annular depressions 151, 152, and 153, but the liquid metal lubricant cannot move in the opposite direction. These directions are obtained by providing small valves (not shown) in or at the outlets of these passages. The inside of the passage is not wetted by the liquid metal lubricant. When the bearing rotating body 102 rotates at a high speed with the liquid metal lubricant reaching the annular recess 132 or the annular recess 133, the liquid metal lubricant receives the centrifugal force and pushes the valve to pass through this portion. Annular recesses 151, 152 with larger diameters
Reaches 153. On the other hand, when the liquid metal lubricant receives a force in the opposite direction, the valve closes and the passage is closed, so that the liquid metal lubricant cannot move.

Next, another embodiment will be described. The surfaces of the directional passages 154, 155, 156, 157 are not wetted by the liquid metal lubricant. For example, it is made of a metal oxide film. In these passages, the effect of the surface tension acting on the liquid metal lubricant in which the liquid metal lubricant is pushed back is greater than the effect of the liquid metal lubricant being pushed out by the static pressure of the liquid metal lubricant. The effect of the surface tension acting on the liquid metal lubricant to push back the liquid metal lubricant is made smaller than the effect of moving the liquid metal lubricant by the centrifugal force applied to the liquid metal lubricant. This can be achieved by determining the diameter of the passage when these passages are formed of holes having a circular cross section, or by appropriately determining the width of the slit when the passage has a slit-like cross section. The centrifugal force applied to the liquid metal lubricant is larger than the static pressure of the liquid metal lubricant, and since the direction in which the centrifugal force acts is determined, the direction in which the liquid metal lubricant can move is determined, and the direction is generated.

For unexpected reasons, the liquid metal lubricant comes out of the annular bearing opening 120 or 121 into the vacuum space side, and the annular recess 132 or the annular recess 13 is formed.
When the liquid metal lubricant reaches the position 3, the centrifugal force causes the liquid metal lubricant to return through the directional passages 154, 155, 156, 157 to one of the annular recesses 151, 152, 153 between the bearings. Will be. In this manner, the liquid metal lubricant that has exited the bearing opening 120 or the bearing opening 121 is returned to the inside of the bearing, so that the liquid metal lubricant can be prevented from leaking out of the bearing mechanism, and stable operation can be performed for a long time. Can be continued.

In the above description, the cathode side rotating body assembly CR
The bearing mechanism CBG composed of a dynamic pressure sliding bearing used in the above has been described, but the bearing mechanism ABG composed of a dynamic pressure sliding bearing used in the anode side rotating body assembly AR is also a rotating part of the cathode power feeding mechanism SL1. The bearing mechanism including the dynamic pressure sliding bearing used in the above has a similar structure.

When the bearing rotating body 102 is rotating at a sufficiently high speed, a relatively large bearing loss occurs in the bearing gap of the above-mentioned hydrodynamic sliding bearing, but the bearing fixed body 101 is forced from the outside. Since it is also thermally coupled to the cooled vacuum vessel VV, it is kept at a low temperature. Since the bearing rotating body 102 is thermally connected to the bearing fixed body 101 via the liquid metal lubricant in the bearing gap of the dynamic pressure sliding bearing, a sufficiently low temperature is maintained. Further, a cathode side rotating body assembly CR is mechanically connected to the bearing rotating body 102, and a heating element such as an electron gun assembly EG is attached to the cathode side rotating body assembly CR. Particularly, in the anode-side bearing mechanism AGB, a large amount of heat flows from the X-ray target TG which generates a large amount of heat. Even in these cases, the temperature of the bearing mechanism can be kept sufficiently low for the above reasons.

Although the present invention has been described with reference to illustrative embodiments, the present invention is not intended to be limited to the structure and form of the embodiments illustrated herein, but to be departed from the spirit and scope of the invention. It is to be understood that various embodiments are possible and that various changes and modifications can be made. For example, in the present invention, three electron gun assemblies are attached, but one or three or more electron gun assemblies may be used. Further, in the present invention, a structure in which both the cathode side rotating body assembly CR and the X-ray target TG are rotated is shown. However, a cathode scan type X-ray having a structure in which the X-ray target TG and a portion connected thereto are fixed. It includes a generator and an X-ray CT scanner using the same. Needless to say, the bearing fixing body 101 may be configured as a part of a vacuum vessel. Also,
In the above embodiment, an example is shown in which a liquid metal that is liquid at room temperature is used as a lubricant.However, even if it is a solid at room temperature, it has a slightly higher melting point and is heated and liquefied before operation. Of course, the same effect can be obtained by operating. Further, the X-ray emission window for taking out the X-rays generated from the X-ray target outside the vacuum vessel may be integrated with the vacuum vessel or may be configured as a part of the vacuum vessel. If the X-ray attenuation rate at a portion is small, it can be regarded as an X-ray emission window. Vacuum container V
It is needless to say that V need not have a rotationally symmetric shape. It goes without saying that the center axis of the vacuum vessel VV and the center axis of the cathode side rotating body assembly CR or the anode side rotating body assembly AR may be shifted to some extent. It is needless to say that the X-ray target TG is configured to be divided, and there may be a gap in each divided portion. The rotating part of the cathode power supply mechanism SL1
It goes without saying that the bearing rotating body itself constituting the bearing mechanism of the cathode power feeding mechanism SL1 may be used. Of course, the cathode power supply mechanism SL1 may be integrally formed with the bearing mechanism CBG. In the present invention, the size of the gap means the shortest distance from an arbitrary point on one of the opposing surfaces constituting the gap to the other surface of the opposing surface constituting the gap. .

The present invention realizes an X-ray CT scanner capable of performing ultra-high-speed scanning as described above. The present invention can be applied to an electron beam irradiation device for irradiating an electron beam from a device. That is, the X-ray target and the parts related thereto, the X-ray X-ray distribution limiting mechanism, the fan direction distribution shaper WF, and other X-ray related parts are omitted from the device configuration described in the above embodiment, and the X-ray The emission window XW is changed to an electron beam emission window made of a thin titanium plate, and the direction of emitting electrons from the electron gun assembly EG is changed to the direction of the electron beam emission window. When this is used, it is possible to provide an electron beam irradiation apparatus which can be used for plastics, glass, and other modification treatments and has a large industrial effect.

[0034]

As described above, when the cathode scan type X-ray generator of the present invention is employed, the rotating part can be formed into a structure in which light parts are attached to a substantially rotationally symmetric structure inside the vacuum vessel, so that centrifugation is performed. Ultra-high-speed scan type X-ray C with less influence of force, for example, a scan time of 0.03 seconds
The T scanner can be realized at a low cost with a simple structure. In particular, a large amount of X
Lines can be generated, and a sufficiently high-quality image with little photon noise can be obtained. The generated X-rays are effectively received by the annular surface detector, and a large number of cross-sections in a wide area can be instantaneously photographed. Using this data, the three-dimensional internal structure of the subject can be instantaneously obtained. Be able to inspect. For this reason, it is possible to provide an X-ray CT scanner capable of faithfully and immediately imaging even a portion that moves quickly, such as a human heart, inside the subject. The bearing mechanism uses a hydrodynamic sliding bearing that uses liquid metal as a lubricant, so it can be used stably in a vacuum for a long time, and can keep the potential of the rotating part constant, and it is very small. The occurrence of unstable phenomena such as discharge can be prevented. Further, the heat generated inside through the dynamic pressure sliding bearing can be effectively guided to the outside of the vacuum vessel and cooled. Even if the liquid metal lubricant leaks from the opening of the bearing, it is returned to the inside of the bearing again, so that the bearing mechanism can operate stably with high reliability in a high vacuum environment. Since there is no external mechanical rotation mechanism and the related power supply and electronic circuits can be used in a stationary state, the overall reliability is high and the whole X-ray CT scanner is compact.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic cross section of a conventional X-ray CT scanner.

FIG. 2 is a cross-sectional view of a main part of an overall structure of a cathode scan type X-ray generator according to the present invention and an X-ray CT scanner using the same.

FIG. 3 is a diagram illustrating the principle of a cathode scan type X-ray generator according to the present invention and an X-ray CT scanner using the same.

FIG. 4 is an enlarged view of a cross section of a part of the cathode scan type X-ray generator according to the present invention, which is located vertically above at a certain moment.

FIG. 5 is an enlarged sectional view of a bearing mechanism, which is a main part of the cathode scan type X-ray generator according to the present invention.

FIG. 6 is a further enlarged sectional view of a part of FIG. 5, which is a main part of the cathode scan type X-ray generator of the present invention.

[Explanation of symbols]

ABG Anode-side bearing mechanism AR Anode-side rotating body assembly B Bed CBG Cathode-side bearing mechanism CR Cathode-side rotating body assembly DB Rear detector assembly DF Front detector assembly D1 Part of detector DF, DB D2 Detector DF, Part of DB D3 Detector DF, Part of DB EG Electron gun assembly F1 X-ray focal point F2 X-ray focal point F3 X-ray focal point HT High-voltage terminal LM1 Arc-shaped stator LM2 Arc-shaped stator M Subject RT1 Rotor RT2 Rotor SL1 Cathode feeding mechanism SLT Slit TG X-ray target VC Exhaust port VV Vacuum container WF Fan direction distribution shaper XW X-ray emission window 1 Cathode 2 Electron beam 101 Bearing fixed body 102 Bearing rotating body 103 Vertical upper part of radial bearing gap 104 Vertically above the bearing gap of one thrust bearing 105 Vertically above the end gap Part 106 Vertical upper part of the bearing gap of the second thrust bearing 107 Vertical upper part of the end gap 108 Vertical lower part of the radial bearing gap 109 Vertical lower part of the bearing gap of the first thrust bearing 110 Vertical lower part of the end gap 111 Vertical lower part of the bearing gap of the second thrust bearing 112 Vertical lower part of the end gap 120 Bearing opening 120 'Bearing opening 121 Bearing opening 121' Bearing opening 132 Annular depression 133 Annular depression 151 Annular depression 152 Annular depression 153 Annular recess 154 Directional passage 155 Directional passage 156 Directional passage 157 Directional passage 217 Rotating torque transmitting mechanism 220 Insulator 1001 Fixed gantry of conventional X-ray CT scanner 1002 Conventional gantry of X-ray CT scanner 1003 Conventional X-ray CT scan Journal bearing 1004 X-ray tube of conventional X-ray CT scanner 1005 X-ray of conventional X-ray CT scanner 1006 Detector of conventional X-ray CT scanner 1007 Electronic circuit of conventional X-ray CT scanner 1008 Conventional X-ray Controller of CT scanner 1009 Rotation drive mechanism of conventional X-ray CT scanner

Claims (10)

[Claims] 1. A donut-shaped vacuum container for forming a vacuum space by maintaining a vacuum state inside the vacuum container, and supported in the vacuum space inside the vacuum container so as to be rotatable coaxially with a center axis of the vacuum container. A cathode side rotating body assembly, an electron gun assembly attached to a part of the cathode side rotating body assembly, a cathode attached to the electron gun assembly and emitting electrons, and A rotating portion of a cathode power supply mechanism for externally supplying power, an annular X-ray target attached to a surface including the orbit of the cathode, and an X-ray generated on the surface of the X-ray target. An X-ray emission window for taking out of the vacuum vessel, a rotation drive mechanism for applying a rotational force to the cathode-side rotating body assembly, and a bearing rotatably supporting the cathode-side rotating body assembly in the vacuum vessel. Mechanism and the cathode And a bearing mechanism for rotatably supporting a rotating part of the power supply mechanism in the vacuum vessel. At least one of these bearing mechanisms is a part for fixing the bearing mechanism. It includes an annular bearing fixed body and an annular bearing rotating body which is a rotating part. Between these bearing fixed body and the bearing rotating body, dynamic pressure sliding using liquid metal, which is liquid during operation, as a lubricant. A cathode scan type X-ray generator, wherein a bearing is formed, and the bearing rotating body is provided with a directional passage through which the liquid metal lubricant can move in only one direction; and X-ray CT scanner using. 2. A donut-shaped vacuum vessel for forming a vacuum space by holding the inside of the vacuum state, and supported so as to be coaxially rotatable in the vacuum space inside the vacuum vessel with the center axis of the vacuum vessel. An anode-side rotator assembly, an annular X-ray target attached to the anode-side rotator assembly, and an electron gun assembly attached to orbit around an X-ray target in a trajectory facing the surface of the X-ray target. A cathode mounted on the electron gun assembly and emitting electrons,
A cathode power supply mechanism for supplying power to the cathode from outside the vacuum vessel, and X-rays generated on the surface of the X-ray target.
An X-ray emission window for taking out the radiation outside the vacuum vessel;
A rotating drive mechanism that applies a rotational force to the anode-side rotating body assembly; and a bearing mechanism that rotatably supports the anode-side rotating body assembly in a vacuum space in a vacuum vessel. The bearing mechanism includes an annular bearing fixed body that is a part for fixing the bearing mechanism, and a bearing rotating body that is a rotating part, and a liquid is formed between the bearing fixed body and the bearing rotating body during operation. A hydrodynamic sliding bearing using a certain liquid metal as a lubricant is formed, and the bearing rotating body is provided with a directional passage through which the liquid metal lubricant can move in only one direction. Scan type X-ray generator and X-ray CT scanner using the same. 3. The cathode scan type X-ray generator according to claim 1, wherein the directional passage has a valve, and an X-ray generator using the same. Line CT scanner. 4. The cathode according to claim 1, wherein the directional passage moves the liquid metal lubricant only in one direction by the action of centrifugal force. A scan type X-ray generator and an X-ray CT scanner using the same. 5. The directional passage is configured to prevent the liquid metal lubricant from flowing back due to the surface tension of the liquid metal lubricant on the surface of the directional passage. A cathode scan type X-ray generator according to claim 1 or 2, and an X-ray CT scanner using the same. 6. A cathode scan type X-ray generator according to claim 5, wherein said directional passage produces a pressure effect of surface tension greater than the static pressure of said liquid metal lubricant. , And an X-ray CT scanner using the same. 7. The dynamic pressure sliding bearing has opposing bearing surfaces with a gap, and at least one of these bearing surfaces is provided with a herringbone-shaped bearing groove. In the pressure sliding bearing, a first thrust bearing that generates a dynamic pressure in the rotation axis direction, at least one radial bearing that generates a dynamic pressure in the rotation radial direction, and a face facing the first thrust bearing with a distance. A second thrust bearing provided, a low pressure portion having a low bearing pressure is provided between any two of these bearings, and the low pressure portion communicates with the low pressure portion. The cathode scan type X-ray generator according to any one of claims 1 to 6, and an X-ray CT scanner using the same. 8. At least one of said first thrust bearing and said second thrust bearing is connected to a first bearing opening which is a substantial boundary with said vacuum space, The bearing rotor has an annular recess which is recessed in the rotation axis direction in the bearing rotating body, and the annular recess communicates with the low-pressure portion through the directional passage. The cathode scan type X-ray generator according to claim 7, wherein the X-ray CT scanner uses the same. 9. A method according to claim 7, wherein said directional passage is mounted such that said liquid metal lubricant moves in a direction to enter said low pressure portion. And an X-ray CT scanner using the same. 10. A donut-shaped vacuum container for forming a vacuum space by maintaining the inside of the vacuum state, and supported so as to be coaxial with the center axis of the vacuum container in the vacuum space inside the vacuum container. A cathode-side rotating body assembly, and an electron gun assembly attached to a part of the cathode-side rotating body assembly,
A cathode attached to the electron gun assembly for emitting electrons, a rotating portion of a cathode power supply mechanism for supplying power to the cathode from outside the vacuum vessel, and electrons accelerated by the cathode are emitted. An electron beam emission window for taking out, a rotation driving mechanism for applying a rotation force to the cathode side rotating body assembly,
A bearing mechanism for rotatably supporting the cathode side rotating body assembly in the vacuum vessel; and a bearing mechanism for rotatably supporting the rotating part of the cathode power supply mechanism in the vacuum vessel. At least one of these bearing mechanisms includes an annular bearing fixed body that is a part for fixing the bearing mechanism, and an annular bearing rotator that is a rotating part. A dynamic pressure sliding bearing using liquid metal, which is liquid during operation, as a lubricant is configured between the body and the bearing rotating body, and the liquid metal lubricant moves in only one direction to the bearing rotating body. An electron beam irradiation apparatus, wherein a directional passage is provided.