JP2001276038A - Cathode scan type x-ray generator and x-ray ct scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small and highly reliable cathode scan type X-ray generator for a very high speed X-ray CT scanner and the very high speed X-ray scanner using it, by which the inside of a subject is stereoscopically and instantly inspected and an excellent CT image is obtained. SOLUTION: The cathode scan type X-ray generator for the very high speed X-ray CT scanner is provided with a doughnut shape vacuum vessel VV, a cathode side rotary body assembly CR inside the vessel and a ring-shape cathode power supply mechanism SL1 to be operated in vacuum for energizing the cathode. The generator is used for the very high speed X-ray CT scanner. Then the rotary part of the cathode side rotary body assembly or the cathode power supply mechanism is supported by a bearing mechanism consisting of a hydrodynamic slide bearing lubricated by liquid metal so as to be freely rotatable. The rotary part inside the vacuum vessel is thermally and electrically connected to the outer part of the vessel via the liquid metallic lubricant and kept in low temperature and fixed potential.

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 focal point to small parts inside the vacuum vessel, the X-ray focal point is stabilized at high speed around the specimen without a mechanical rotating mechanism in the atmosphere. The present invention provides a small-sized X-ray CT scanner capable of obtaining a three-dimensional image by taking an image of a subject instantaneously 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. The signals of the electronic circuit mounted on the rotating gantry 1002 are transmitted to the fixed gantry 10 via a slip ring (not shown).
01 is transmitted. For this reason, the sum of the masses of the components attached to the rotary gantry 1002 increases, and if an attempt is made to increase the scanning speed of the X-ray CT scanner, a large centrifugal force acts, and the components mounted on the rotary gantry 1002 and the rotary gantry 1002 It has the drawback that the scanning speed cannot be increased because it cannot withstand excessive stress itself.

[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. Furthermore, in recent years, as the applications of X-ray CT scanners have expanded, there has been a demand for instantaneous observation of blood and a contrast agent that move rapidly. 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 2 rps, which is considered the limit. On the other 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 in the imaging of a fast-moving subject, and that a sufficient level of X-rays is obtained. An object of the present invention is to provide an X-ray CT scanner that can obtain a high-quality image with a small amount of photon noise while securing a sufficient dose and that is small in size and easy to handle. In particular, to achieve this, a bearing mechanism that can be used reliably in a vacuum and a power supply mechanism that can supply power to components circulating in a vacuum are used. A sliding bearing has been developed, and the position of the rotating part constituting the dynamic pressure sliding bearing in the direction of the rotation center axis is limited to a predetermined range, and the rotation part moves in the direction of the rotation center axis within this range. Even if the rotational speed of this rotating part changes, the dynamic pressure at the bearing opening is kept constant, and despite the fact that the bearing diameter is large and the height difference in the circumferential direction of the bearing opening is large, An object of the present invention is to provide a cathode scan type X-ray generator and an X-ray CT scanner using the same, in which a liquid metal lubricant does not leak out of a bearing mechanism.

[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 to minimize the size of the rotating parts, 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-rays are applied to the subject in the atmosphere through an X-ray emission window provided on the small-diameter wall of the vacuum vessel. 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 orbiting the X-ray focal point in the vacuum vessel is limited to a lightweight electron gun assembly, etc., and its volume is small and its shape is almost symmetrical as a whole. Even when the high-speed rotation is performed, 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 0.0%.
An ultra-high-speed scan of about 3 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 liquid metal that is liquid during operation as a lubricant is employed, and a liquid metal lubricant is used for the dynamic pressure sliding bearing. Thrust bearings have a variable gap size mechanism to prevent leakage out of the bearing mechanism.This thrust bearing changes the size of the bearing gap so as to generate a small constant value of dynamic pressure in the direction of the rotation center axis. However, it is configured not to adversely affect the dynamic pressure of other thrust bearings.

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. When the bearing rotor stops rotating, the leakage of the liquid metal lubricant is generally prevented by the surface tension of the liquid metal lubricant generated at the opening of the bearing. However,
In the X-ray CT scanner of the present invention, the rotation center axis of the bearing rotating body is substantially horizontal, and the diameter of the bearing is about 10 mm.
Since it is as large as 0 cm, the height drop in the circumferential direction of the bearing opening is large, and the liquid metal lubricant in the portion located vertically below the bearing opening receives a large static pressure due to gravitational acceleration. In the present invention, the size of the gap of the bearing opening is made extremely small, and the bearing opening has a surface that is not wetted by the liquid metal lubricant. Therefore, the pressure of the surface tension of the liquid metal lubricant at this portion is reduced. The effect is large enough to overcome the static pressure described above. As a means for keeping the size of the gap in the bearing opening small, the bearing adjacent to the bearing opening is limited to a thrust bearing so that the size of the gap in the thrust bearing can be changed. At least one of the opposing surfaces constituting the thrust bearing adjacent to the bearing opening is a bearing fixed body that is a fixed part of the bearing rotating body or the bearing via an elastic part so that its position can be moved. It is connected to the. Due to the action of this part, when the bearing rotating body stops rotating, the size of the bearing gap decreases, the surface tension at the bearing opening increases, and when the bearing rotating body rotates at high speed, In addition, the bearing gap of the thrust bearing is widened, and the generation of excessive dynamic pressure is prevented. Therefore, when the bearing rotating body is rotating at a high speed, no excessive bearing loss occurs, and the liquid metal lubricant is sucked into the bearing by the effect of the bearing groove. Even when spread, the liquid metal lubricant does not leak from the bearing mechanism into the vacuum region.

However, if it is desired to increase the bearing pressure in the direction of the rotation center axis, another thrust bearing is provided, and this thrust bearing bears a substantial bearing in the direction of the rotation center axis.
The thrust bearing adjacent to the bearing opening has a main function of preventing the liquid metal lubricant from leaking from the bearing opening. That is, the present invention has a thrust bearing for rotatably supporting the rotating body in the rotation axis direction and a thrust bearing for preventing the leakage of the liquid metal lubricant. Is characterized by being substantially constant irrespective of the rotation speed.

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. , Heat expansion is small, and stable operation can be performed for a long time. Furthermore, electron gun assembly and X
Components that generate heat, such as a line target, are also forcibly cooled via the liquid metal lubricant 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 in the vacuum space inside the vacuum vessel. An X-ray CT scanner that does not have a rotating mechanism in the atmosphere is realized using the orbiting X-rays. A cathode scan type X-ray generator for an X-ray CT scanner capable of performing an ultra-high-speed scan and obtaining a large output, which cannot be realized with an X-ray CT scanner having a conventional structure, and an ultra-high-speed X-ray using the same The CT scanner was 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 diagram, and FIG. Is an enlarged view of a part of a cross section around the electron gun assembly in a state of being located vertically above at a certain moment. The same parts have the same symbols. FIG. 5 is an enlarged sectional view of a bearing mechanism which is a main part of the cathode scan type X-ray generator of the present invention.
FIG. 6 is an enlarged sectional view of a lower part of FIG.

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 or FIG. 4, a cylindrical rotor RT2 made of copper is provided on the cathode side rotating body assembly CR.
Are mounted coaxially, and a magnetic path cylinder made of a magnetic material is mounted coaxially with the shaft. Rotor RT2
An arc-shaped stator LM2 is attached to the outside of the vacuum vessel VV along the vacuum vessel wall in a state facing the vacuum vessel VV. The rotor RT2 includes the magnetic path cylinder and the stator L.
It is arranged in a state sandwiched by M2. The rotor RT2 receives a rotational torque from the stator LM2 through the wall made of the non-magnetic material of the vacuum vessel VV and receives a rotational torque, so that the cathode side rotating body assembly CR rotates. The cathode side rotating body assembly CR electrically and thermally passes through the vacuum vessel V through a liquid metal lubricant in a bearing mechanism CBG including a dynamic pressure sliding bearing.
Connected to V.

As shown in FIG. 4, a cathode 1 for emitting thermoelectrons 2 is attached to the tip of the electron gun assembly EG. An annular X-ray target TG is attached to face the orbit of the cathode 1. As shown in FIG. 2, the X-ray target TG is a cylindrical anode-side rotating body assembly A.
It is mechanically coupled to R. 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. Anode rotating body assembly AR
Is equipped with a rotor RT1 made of a copper tube.
A magnetic path cylinder made of a magnetic material is mounted coaxially with the magnetic path cylinder. An arc-shaped stator LM is formed along the vacuum vessel wall outside the vacuum vessel VV in a state facing the rotor RT1.
1 is attached. The rotor RT1 is disposed between the magnetic path cylinder and the stator LM1. The rotor RT1 is connected to the vacuum vessel VV from the stator LM1.
The anode-side rotating body assembly AR rotates because the rotating torque is given by receiving electromagnetic induction through the wall made of the non-magnetic material. 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 drawings, the internal structure of the cathode power supply mechanism SL1 is schematically shown in a simplified manner. The cathode 1 of the electron gun assembly EG is connected to the orbiting center axis CC ′ of the electron gun assembly EG in a vacuum space in the vacuum vessel VV.
Annular cathode feeding mechanism SL1 having substantially the same central axis as
Is electrically connected to the high voltage terminal HT. To the high voltage terminal HT, a negative high voltage of about -150 KV and power for heating the cathode 1 of the electron gun assembly EG are supplied from a high voltage power supply (not shown) provided outside the vacuum vessel VV. The cathode power supply mechanism SL1 has a fixed part and a rotating part, and the fixed part is mechanically fixed to a part of the vacuum vessel VV via an insulator 220 while maintaining electrical insulation. The rotating part and the fixed part of each of the cathode power supply mechanisms SL1 constitute a dynamic pressure sliding bearing using liquid metal as a lubricant, and electricity is supplied between the two via the liquid metal lubricant. The rotating part of the cathode power supply mechanism SL1 is provided with a rotational torque transmission mechanism 217 that is resilient to the electron gun assembly EG.
The cathode power supply mechanism SL1 rotates together with the electron gun assembly EG while allowing a certain degree of eccentricity and axial displacement.

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 indicate three focal points of X-rays that are generated when the electrons 2 are accelerated and collide with the X-ray target TG. X-ray focus F
1, F2 and F3 simultaneously rotate 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. The X-rays emitted from the X-ray focal points F1, F2, F3 are shown in FIG.
As shown in the figure, the fan is shaped like a fan by the X-ray distribution limiting mechanism inside the X-ray target TG, passes through the fan direction distribution shaper WF (see FIG. 4) attached to the cathode side rotating body assembly CR, and the fan X-ray emission window XW of the vacuum vessel VV after the X-ray intensity distribution in the direction is optimized (see FIG. 4)
, And after passing through an external annular slit SLT, passing through the subject M, and opposing surfaces of two annular X-ray detectors DF and DB mounted coaxially with the X-ray target TG. To reach.

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, and D3 occupies almost all of the annular detector, all the detecting elements in the X-ray detectors DF and 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 detecting element rows in the direction of the central axis CC ′, and a signal detected by each detecting element is converted into a digital signal by an electronic circuit (not shown). The multi-slice CT image is reconstructed into a tomographic image by a computer which is not shown, and is displayed on an image display device (not shown).

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 schematically shown in a simplified manner, and the internal structure is shown in FIGS. 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, since there are three X-ray focal points, 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 of the bearing 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 dynamic pressure of the dynamic pressure 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 at the opening of the bearing is 50 μm, when 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 Lubricant leaks out. This becomes a serious problem when the bearing rotating body stops rotating. Particularly, a dynamic pressure sliding bearing having a height drop of about 100 cm in the circumferential direction of the opening of the bearing as in the case of the present invention cannot be realized by the conventional technology.

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 is a part located vertically above at a certain moment in actual use. , And 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 part located below 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. A bearing fixed body 101 which is a fixed part of the bearing mechanism CBG is fitted to the bearing rotating body 102 with a gap. A part of the bearing fixing body 101 is mechanically and thermally connected 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. Bearing fixed body 10
1 and the bearing rotating body 102 have surfaces facing each other, and the facing surfaces have first bearing gaps 103 and 108, second bearing gaps 104 and 109, and third bearing gaps 106 and 111. ing. At least one of the opposing surfaces forming the bearing gap has a herringbone-shaped bearing groove. The first, second, and third bearing gaps are filled with a liquid metal that is liquid at room temperature, preferably a lubricant made of an alloy of gallium, indium, and tin, and each of the bearing gaps has a radial gap. The bearing gaps correspond to the bearing gaps of the first thrust bearing and the second thrust bearing which are mounted to face each other with a distance therebetween with respect to the bearing. Bearing gaps 103 and 10
8, bearing gaps 104 and 109, bearing gap 106
And 111 are the same, and different numbers indicate differences in the indicated 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 gap is subjected to the action of confining the inside of the bearing, so that the lubricant does not leak from the bearing gap to the outside vacuum space. Even when the bearing rotating body 102 stops rotating, it is necessary to prevent the liquid metal lubricant from leaking from the inside of the bearing mechanism to the vacuum space of the vacuum container. This will be described below.

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.
109 is adjacent to the bearing gaps 103 and 108 of the radial bearing, and is the bearing gap 10 of the second thrust bearing.
6, 111 are bearing gaps 103, 10 of radial bearings.
8 and adjacent. The bearing gaps 104, 109 of the first thrust bearing are first end gaps 105, 110
In addition, the bearing gaps 106 and 111 of the second thrust bearing
Is connected to the second end gaps 107 and 111.
As shown in FIG. 6, both end gaps are 121 in the bearing opening, which substantially delimits the liquid metal lubricant, and the bearing gap 208 of the third thrust bearing adjacent the bearing opening 120, and the fourth gap. Thrust bearing gap 2
07 respectively. Hereinafter, these thrust bearings will be described with reference to FIG. Here, FIG.
However, it is to be understood that the structure is to be rotated with respect to the rotation center axis CC ′.

The bearing rotating body 102 is formed in a thin plate shape at a portion having a smaller radius than a portion constituting the bearing gap 109 of the first thrust bearing and the bearing gap 111 of the second thrust bearing. In this state, the third thrust bearing and the fourth thrust bearing are configured. The third thrust bearing has a bearing gap 208 formed between the surface of the thin plate portion of the bearing rotating body 102 and the movable ring plate 202 attached so as to have a surface facing the thin plate portion. . At least one of these surfaces has a herringbone shaped bearing groove. The movable ring plate 202 is connected to the bearing fixed body 101 by a connection mechanism 200 composed of an annular structure having a small rigidity in the direction of the rotation center axis CC ′. The bearing gap 208 is the first end gap 110
Is in communication with The third thrust bearing has a bearing opening 121 defining a substantial existence boundary of the liquid metal lubricant, a portion having a smaller radius has a surface which is not wetted by the liquid metal lubricant, and has a vacuum state. It has become.

Similarly, the fourth thrust bearing has a bearing gap formed by being sandwiched between the surface of the thin plate portion of the bearing rotating body 102 and the movable ring plate 201 having a surface facing the thin plate portion. 207. At least one of these surfaces has a herringbone shaped bearing groove. The movable ring plate 201 is connected to the bearing fixed body 101 by a connection mechanism 195 formed of an annular structure having a small rigidity in the direction of the rotation center axis CC ′. The bearing gap 207 communicates with the second end gap 112. The fourth thrust bearing has a bearing opening 120 that defines a substantial existence boundary of the liquid metal lubricant, a portion having a smaller radius has a surface that is not wetted by the liquid metal lubricant, and has a vacuum state. It has become.

Further, the bearing fixed body 101 of this embodiment has a mechanism for arbitrarily adjusting the rigidity of the connection mechanisms 195 and 200. The movable ring plates 201 and 202 are provided with variable gap size mechanisms 204 and 2 provided on the bearing fixed body 101.
06, which are movable ring plates 201, 202 via pressure transmitting mechanisms 203, 205 made of, for example, springs.
Is connected to. Variable gap size mechanisms 204, 20
Reference numeral 6 is made of, for example, a screw, and the pressure applied to the movable ring plates 201 and 202 is adjusted by inserting and removing the screw. Further, as another embodiment, a variable gap size mechanism 2 is provided.
04 and 206 are formed of, for example, electromagnets, and are electrically connected to a controller (not shown) outside the vacuum vessel VV;
With this controller, the pressure applied to the movable ring plates 201 and 202 can be adjusted remotely. In this case, since the rotation characteristics can be adjusted from the outside so as to be optimal, a preferable state can be achieved. Further, an AC current is supplied from the controller, and the movable ring plate 20 is supplied from the gap size variable mechanisms 204 and 206.
When a minute vibration is applied to the shaft 1, 202, the liquid metal lubricant is easily supplied to the bearing gap, and the rotating torque at the time of starting the bearing rotating body 102 is reduced, so that a more preferable state is obtained.

Next, the operation of the thrust bearing adjacent to the bearing opening will be described with reference to FIG. First, the reason why the bearing opening is mounted adjacent to the thrust bearing in the thin plate portion of the bearing rotating body 102 will be described. In the bearing opening 120 and the bearing opening 121, surface tension acts on the liquid metal lubricant on a surface that is not wetted by the liquid metal lubricant, and the liquid metal lubricant is supplied to the outside even when the bearing rotor 102 stops rotating. To prevent leakage. 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 becomes higher as it is located vertically downward. On the other hand, the pressure effect of the surface tension is inversely proportional to the size of the gap in the bearing opening. Therefore, the bearing opening 120 and the bearing opening 121
If the size of the gap 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.

However, since the diameter of the bearing used in the present invention is as large as about 100 cm, it is extremely difficult to keep the size of the gap of the radial bearing at a sufficiently small value. One reason is that the rotating part of the bearing mechanism is 10 rps
When the rotor is rotated at a high speed of about 20 μm, the expansion of this part due to centrifugal force occurs about 20 μm.
It is extremely difficult to keep it at about μm. The second reason is that, because the diameter is large, the difference in thermal expansion between the rotating parts becomes large, and it is difficult to accurately keep the size of the bearing gap at a small value. Therefore, if the radial bearing has a bearing opening, it is extremely difficult to generate a large surface tension because the size of the gap of the bearing opening becomes large, and the liquid metal lubricant in the bearing leaks from the bearing to the vacuum space. Is extremely difficult to prevent.

The distance between the third thrust bearing and the fourth thrust bearing used in the present invention is as small as about 1 cm, the influence of thermal expansion can be kept small, and the size of the bearing gap of the thrust bearing is reduced. Can be kept small enough. Further, since the surface constituting the bearing gap is perpendicular to the direction of the rotation center axis CC ′, the influence of the centrifugal force can be ignored. Further, since the bearing surface of the thrust bearing is flat, it is easy to sufficiently increase the machining accuracy, and the bearing gap 2
It is easy to keep 07,208 small values with high accuracy. For example, when the size of the bearing gap is maintained at 17 μm, the size of the gap of the bearing opening can be also set to 17 μm, so that a pressure effect of surface tension that overcomes the static pressure of the liquid metal lubricant having a height drop of 120 cm or more is generated. Can be. Therefore, the area where the liquid metal lubricant is present in the bearing mechanism is provided in the bearing opening 121 at the end of the third thrust bearing having such a small gap size.
And the bearing opening 120 at the end of the fourth thrust bearing, the liquid metal lubricant can be easily confined inside the bearing mechanism. It is possible to provide a bearing mechanism that does not leak.

As described above, when the bearing rotating body 102 is stationary, the bearing gaps 208 and 2 of the thrust bearing are provided.
07 can be reduced to about 17 μm, so that the liquid metal lubricant can be prevented from leaking to the vacuum space side from the bearing openings 120 and 121. However, when the size of the bearing gap is constant, On the other hand, when the bearing rotor 102 is rotating at a high speed, the size of the bearing gap is too small, so that the rotational torque becomes excessive and the bearing loss may become excessive. In order to avoid this, if the size of the bearing gap of the thrust bearing is fixed to a large value such as about 50 μm in advance, the pressure effect of the surface tension of the liquid metal lubricant in the bearing openings 120 and 121 is reduced. The pressure becomes smaller than the static pressure in the liquid metal lubricant, and the liquid metal lubricant leaks from the bearing openings 120 and 121 to the vacuum space side. Since the dynamic pressure of the bearing is greatly affected by the rotational speed of the bearing rotating body, if the size of the bearing gap is fixed, high precision control of the size of the bearing gap is required, which is not only expensive, but also, for example, A change in the size of the bearing gap caused by a reaction with the liquid metal lubricant or thermal expansion adversely affects the rotational characteristics of the bearing mechanism.

When the present invention is adopted, one of the bearing surfaces constituting the bearing gaps of the third and fourth thrust bearings easily changes in the direction of the rotation center axis CC 'as described above. Even if the rotation speed of
The dynamic pressure in these thrust bearings depends only on the rigidity of the resilient connection mechanisms 195, 200 in the direction of the rotation axis CC '. If the rigidity of the connection mechanisms 195 and 196 in the direction of the rotation center axis CC ′ is reduced, the dynamic pressure of the third and fourth thrust bearings can always be set to a substantially constant value. When the rigidity of the connection mechanisms 195 and 200 is adjusted, the dynamic pressures of the third and fourth thrust bearings can be set to arbitrary values. X-ray C of the present invention
In the T-scanner, the bearing stiffness in the direction of the rotation center axis CC 'is maintained by the first and second thrust bearings, and the third and fourth thrust bearings leak liquid metal lubricant from the bearing openings. Playing a role in preventing
Therefore, while maintaining sufficient bearing rigidity, the bearing openings 121, 1
The bearing pressure of the third and fourth thrust bearings 20 can always be kept at a small value. Even when the bearing rotating body 102 moves in the direction of the rotation center axis CC ′, the movable ring plates 201 and 202 automatically follow the movement, thereby preventing the bearing gaps 208 and 207 from changing. When the rotation speed of the bearing rotor 102 decreases, the size of the bearing gaps 208 and 207 becomes small, and when the bearing rotor 102 is stationary, the bearing gaps 208 and 207 become about 17 μm. There is no leakage from 120 to the vacuum space. When a dynamic pressure is generated in the third and fourth thrust bearings, the liquid metal lubricant is drawn into the bearing, and the liquid metal lubricant does not leak from the bearing openings 121 and 120.

As described above, when the present invention is adopted, when the diameter of the bearing opening 120 and the bearing opening 121 communicating with the vacuum space exceeds 100 cm, when the bearing rotating body 102 is stationary, It is possible to provide a dynamic pressure sliding bearing that operates stably without the liquid metal lubricant leaking into the vacuum space outside the bearing mechanism CBG even during rotation. The bearing mechanism ABG used for the anode side rotating body assembly AR has the same structure. Also,
Cathode power supply mechanism SL1 essential for implementing the present invention
The bearing mechanism composed of a dynamic pressure sliding bearing used in a vehicle has a similar structure.

Since the bearing fixing body 101 is thermally connected to the vacuum vessel VV which is forcibly cooled from the outside, this part can be kept at a low temperature. Bearing rotating body 102
The bearing fixed body 10 via the liquid metal lubricant in the bearing gap of the radial bearing, the first and second thrust bearings.
1 and can be kept at a sufficiently low temperature. Further, a cathode 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 rotating body assembly CR. In particular,
In the bearing mechanism AGB on the anode side, 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 portion can be sufficiently reduced for the above-described reason.

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. Further, it goes without saying that the bearing fixing body 101 may be configured as a part of the vacuum vessel.
Further, in the above embodiment, an example is shown in which a liquid metal that is liquid at room temperature is used as a lubricant, but 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 afterwards. Further, the X-ray generated from the X-ray target
The X-ray emission window for taking out the radiation outside the vacuum vessel may be integrated with the vacuum vessel or may be configured as a part of the vacuum vessel, provided that the X-ray attenuation rate at this part is small. Of course, it can be regarded as an X-ray emission window. Needless to say, the vacuum vessel VV does not have to 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. Needless to say, the rotating part of the cathode power supply mechanism SL1 may be the bearing rotating body itself constituting the bearing mechanism of the cathode power supply mechanism SL1. 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.

[0036]

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 to be cooled. Since the rigidity of the bearing is maintained at a sufficient value without leakage of the liquid metal lubricant from the hydrodynamic sliding bearing, the rotating portion in the vacuum vessel can maintain high-precision rotating characteristics for a long time. 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 schematic 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 partially enlarged sectional view of FIG. 5 showing a main part of the cathode scan type X-ray generator according to 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 Forward 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 Cylindrical Rotor RT2 Cylindrical 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 Radial bearing gap Vertical upper part of the bearing 104 Vertical upper part of the bearing gap of the first thrust bearing 105 Vertical upper part of the cap 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 Vertically lower part 111 Vertically lower part of the bearing gap of the second thrust bearing 112 Vertically lower part of the end gap 120 Vertically lower part of the bearing opening (may also represent the entire bearing opening) 121 Vertically lower part of the bearing opening (bearing opening) 195 connection mechanism 200 connection mechanism 201 movable ring plate 202 movable ring plate 203 pressure transmission mechanism 204 variable gap size mechanism 205 pressure transmission mechanism 206 variable gap size mechanism 207 bearing gap 208 bearing gap 217 rotation torque transmission mechanism 22 Insulator 1001 Fixed mount for conventional X-ray CT scanner 1002 Rotary mount for conventional X-ray CT scanner 1003 Bearing for conventional X-ray CT scanner 1004 X-ray tube of conventional X-ray CT scanner 1005 For conventional X-ray CT scanner X-ray 1006 Detector of conventional X-ray CT scanner 1007 Electronic circuit of conventional X-ray CT scanner 1008 Controller of conventional X-ray CT scanner 1009 Rotation drive mechanism of conventional X-ray CT scanner

Claims (8)

[Claims] 1. A donut-shaped vacuum vessel for forming a vacuum space by maintaining the inside of the vacuum state, and supported so as to be able to circulate coaxially with the center axis of the vacuum vessel in the vacuum space inside the vacuum vessel. 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 supplying power from the outside, an annular X-ray target attached to face the rotating trajectory of the cathode,
An X-ray emission window for extracting X-rays generated on the surface of the X-ray target to the outside of the vacuum vessel, a rotation drive mechanism for applying a rotational force to the cathode-side rotating body assembly, and the cathode-side rotating body assembly A bearing mechanism for rotatably supporting the inside of 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 fixes this bearing mechanism. A bearing fixed body, which is a part, and a bearing rotating body that is fitted into and rotated by the bearing fixed body, and a liquid metal that is liquid during operation is lubricated between the bearing fixed body and the bearing rotating body. A plurality of hydrodynamic sliding bearings, each of which has opposing bearing surfaces with a gap, and at least one of these bearing surfaces has a herringbone-shaped bearing groove. Is provided on the dynamic pressure sliding bearing, a first thrust bearing that generates a dynamic pressure in the rotational axis direction, and the first thrust bearing is opposed to the first thrust bearing at a distance and the dynamic pressure is generated in the opposite direction. The resulting second thrust And a third thrust bearing provided adjacent to a bearing opening which substantially forms a boundary between the region where the liquid metal lubricant is present in the bearing mechanism and the vacuum space. A cathode scan type X-ray generator, wherein the size of a bearing gap forming the third thrust bearing is configured to be variable;
And an X-ray CT scanner using the same. 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;
It has a rotary 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 vessel. A bearing fixed body that is a part for fixing the bearing mechanism, and a bearing rotating body that is fitted to and rotated by the bearing fixed body. Liquid is present between these bearing fixed body and the bearing rotating body during operation. A plurality of hydrodynamic sliding bearings using a liquid metal as a lubricant, each of the hydrodynamic sliding bearings has an opposing bearing surface with a gap, and at least one of these bearing surfaces Is provided with a herringbone-shaped bearing groove, the dynamic pressure sliding bearing, a first thrust bearing that generates a dynamic pressure in the rotational axis direction, facing the first thrust bearing with a distance. Generates dynamic pressure in the opposite direction A second thrust bearing, and a third thrust bearing provided adjacent to a bearing opening substantially forming a boundary between a region where the liquid metal lubricant present in the bearing mechanism is present and the vacuum space. A cathode scan type X-ray generator characterized in that the size of a bearing gap constituting the third thrust bearing can be changed, and an X-ray CT scanner using the same. 3. The bearing according to claim 1, wherein the third thrust bearing has a smaller change in bearing pressure than any of the first thrust bearing and the second thrust bearing. A cathode scan type X-ray generator according to any one of the above, and an X-ray CT scanner using the same. 4. The third thrust bearing according to claim 1, wherein when the bearing rotor stops rotating, the gap of the bearing opening adjacent to the bearing is narrowed, and the liquid metal lubricant in the bearing opening is closed. The cathode scan type X-ray generator according to any one of claims 1 to 3, wherein a pressure effect due to surface tension is maintained larger than a static pressure of the liquid metal lubricant. X-ray CT scanner using this. 5. When the rotation speed of the bearing rotator is high, the size of the bearing gap constituting the third thrust bearing increases, and when the rotation speed of the bearing rotator is low, the size of the bearing gap increases. 5. The cathode scan type X-ray generator according to claim 1, wherein a size of a bearing gap constituting the third thrust bearing is reduced, and an X-ray CT using the same. Scanner. 6. A position of the bearing rotating body in a rotation center axis direction is substantially determined by the first thrust bearing and the second thrust bearing, and rotation of the bearing rotating body is performed. When the speed is constant, the size of the bearing gap constituting the third thrust bearing is substantially constant irrespective of the position of the bearing rotor in the direction of the rotation center axis. A cathode scan type X-ray generator according to any one of claims 1 to 5, and an X-ray CT scanner using the same. 7. The bearing mechanism has a gap size variable mechanism capable of changing the size of a bearing gap constituting the third thrust bearing, and the third thrust bearing is provided by the gap size variable mechanism. 6. The cathode scan type X-ray generator according to claim 1, wherein a size of a bearing gap forming a bearing can be controlled, and an X-ray generator using the same.
Line CT scanner. 8. A donut-shaped vacuum container for forming a vacuum space by holding 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, 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 electron beam emission window for extracting electrons emitted from the cathode and accelerated, and a rotation drive mechanism for applying a rotating force to the cathode side rotating body assembly And 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. Have these axes At least one of the bearing mechanisms of the receiving mechanism has a bearing fixed body that is a part for fixing the bearing mechanism, and a bearing rotating body that is fitted into and rotated by the bearing fixed body. A plurality of hydrodynamic sliding bearings using liquid metal, which is liquid during operation, as a lubricant are configured between the bearing rotating body and each of the hydrodynamic sliding bearings has an opposing bearing surface with a gap. A herringbone-shaped bearing groove is provided on at least one of these bearing surfaces, and the dynamic pressure sliding bearing includes a first thrust bearing that generates a dynamic pressure in the rotation axis direction, A second thrust bearing facing the one thrust bearing at a distance and generating a dynamic pressure in the opposite direction, and a region between the liquid metal lubricant existing in the bearing mechanism and the vacuum space. Bearing opening that forms a substantial boundary To have a third thrust bearing disposed adjacent an electron beam irradiation apparatus characterized by being configured to change the size of the bearing gap which constitutes the third thrust bearing.