JP3754512B2 - Rotating anode X-ray tube - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rotary anode X-ray tube.
[0002]
[Prior art]
As is well known, a rotating anode type X-ray tube supports a disk-shaped anode target with a rotating body and a stationary body having a bearing portion, and while energizing an electromagnetic coil of a stator disposed outside a vacuum vessel, An electron beam emitted from the cathode is applied to the anode target surface to emit X-rays. The bearing portion is a rolling bearing such as a ball bearing, a spiral groove formed on the bearing surface, and a liquid metal lubricant such as gallium (Ga) or gallium-indium-tin (Ga-In-Sn) alloy. It consists of a hydrodynamic slide bearing filled with a gap.
[0003]
As a rotary anode X-ray tube using the latter dynamic pressure type slide bearing, a radial direction dynamic pressure type slide bearing has a small diameter portion, and a thrust direction dynamic pressure type slide bearing has a large diameter portion. For example, JP-B-3-77617, JP-A-2-244545, JP-A-2-227947, JP-A-2-227948, JP-A-4-363845, JP-A-5-290770, or USP5504797. It is disclosed in the specification etc.
[0004]
In the rotary anode X-ray tube disclosed in each of the above-mentioned publications, the bearing surfaces of all the hydrodynamic sliding bearing portions in the radial direction and the thrust direction, which are spiral grooves of a herringbone pattern, maintain a bearing gap of, for example, 20 μm. The helical groove and the bearing gap are filled with a liquid metal lubricant. The spiral groove of each bearing has a depth of about 20 μm.
[0005]
By the way, in the rotary anode type X-ray tube provided with this kind of dynamic pressure slide bearing, since the rotational resistance of the bearing is considerably larger than that of the ball bearing, the anode target is rotated at a relatively low rotational speed of about 3000 rpm. Operate to perform X-ray exposure.
[0006]
However, if the rotation speed of the anode target is low, it is natural that the input load to the anode target cannot be increased, and the solution is to use a large heat capacity, that is, a large and heavy anode target. In addition, for example, in an X-ray imaging apparatus equipped with a rotating anode type X-ray tube, there are not a few cases in which an object is imaged by changing the position from various directions and speedily. Thereby, a large acceleration is applied to the anode target, and thus a large load in various directions and a large load is applied to the hydrodynamic bearing irregularly.
[0007]
Thus, it is necessary to stably support a large load in each direction with the bearing. X-rays in which radial and thrust hydrodynamic bearings are configured between a simple columnar fixed body and a rotating body fitted therein as described in, for example, JP-A-4-363845 As the diameter of the fixed body is increased, the tube can have a bearing performance that can sufficiently withstand the load in each direction. Further, as described in the above USP5504797 specification, a structure in which a fixed portion is provided with a large-diameter portion and a dynamic bearing in the thrust direction is formed here has an advantage that the diameter of the thrust-direction bearing can be arbitrarily increased. Has become practical.
[0008]
[Problems to be solved by the invention]
By the way, the conventional rotary anode X-ray tube using this type of hydrodynamic bearing has bearing performance that can sufficiently withstand a large load in each direction. However, the larger the diameter of the fixed body that fits the rotating body, and the longer the axial length, the greater the rotational resistance of the bearing. Requires a very large rotational drive power.
[0009]
On the other hand, if the axial length of the fixed body fitted to the rotating body is shortened, the rotational resistance can be reduced accordingly, but the rotational center axis of the rotating body is likely to be displaced. That is, as shown in FIG. 6, the rotation center axis R of the anode target 11 and the rotator 12 is likely to be shifted or inclined with respect to the center axis C of the fixed body 15, and precession is likely to occur. In such a state, the fixed body and the rotating body come into contact at various places, or the bearing gap becomes uneven at each place, so that a normally balanced dynamic pressure is not generated in the bearing. In this figure, the bearing gap and the inclination of the rotating body are exaggerated, but the fixed body large diameter portion 15b in which the thrust direction bearing in the conventional rotary anode type X-ray tube is constructed. The axial length L of the small fixed-body diameter portion in which the radial bearing with respect to the diameter D is configured has a dimensional ratio of less than 1.2 times.
[0010]
In the figure, reference numerals 18 and 19 denote two sets of radial dynamic pressure bearings and a herringbone pattern helical groove formed in the fixed body, 15b denotes a fixed body large diameter portion, 15c denotes an anode support portion, and 23 and 24 denote Two sets of thrust direction dynamic pressure bearings with the upper and lower surfaces of the large fixed body diameter as one bearing surface, and a circle-shaped herringbone pattern helical groove formed in the large fixed body large diameter portion, 12b is a copper cylinder of the rotating body Appears. The spiral groove and the bearing gap of each bearing are filled with a liquid metal lubricant (not shown).
[0011]
According to the conventional structure, as described above, the fixed body and the rotating body may be brought into contact with each other, or the bearing may not operate normally due to unevenness or fluctuation of the bearing gap. In particular, such inconvenience becomes more pronounced as the rotational speed increases. Further, if the diameter D of the fixed body large-diameter portion 15b constituting the thrust direction bearing is large, the rotational resistance between the large-diameter portion and the rotating body becomes particularly large, and high-speed rotation becomes difficult.
[0012]
The present invention provides a rotating anode type X-ray tube that eliminates the above-mentioned disadvantages, is less likely to cause a shift or inclination of the rotation center axis, and that can be rotated at a high speed, for example, exceeding 6000 rpm with a low rotation resistance. The purpose is to do.
[0013]
[Means for Solving the Problems]
In the rotary anode type X-ray tube of the present invention, the axial length of the fixed body small diameter portion where the radial direction dynamic pressure type slide bearing is formed is the fixed body large diameter portion where the thrust direction dynamic pressure type slide bearing is formed. The average bearing gap of the thrust direction dynamic pressure type sliding bearing is set to be larger than the average bearing gap of the radial direction dynamic pressure type sliding bearing. It is characterized by that.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The embodiment will be described below with reference to FIGS. The same parts are denoted by the same reference numerals. A disk-shaped anode target 11 made of heavy metal is integrally fixed to a rotating shaft 13 projecting from one end of a substantially bottomed cylindrical rotating body 12 by a nut 14. The rotating body 12 has an inner cylinder 12a made of an iron alloy and an outer cylinder 12b made of copper double fitted and fixed. Inside the rotating body 12, a substantially columnar fixed body 15 made of an iron alloy is inserted.
[0015]
The fixed body 15 has a small diameter portion 15a having a small diameter Dr in the upper part of the figure, a large diameter part 15b having a large diameter Ds in the lower part thereof, and an anode support part 15c at the lower end. In addition, the fitting portion between the rotating body 12 and the fixed body 15 is configured with a dynamic pressure type spiral groove sliding bearing in the radial direction and the thrust direction as shown in the above-mentioned publications. That is, two pairs of herringbone pattern spiral grooves 16 and 17 are formed on the outer peripheral bearing surface of the small-diameter portion 15a, and the hydrodynamic slide bearings 18 and 19 in the radial direction together with the inner peripheral bearing surface of the inner cylinder 12a of the rotating body. Is configured.
[0016]
Further, a herringbone pattern spiral groove 20 is formed in a circle on the illustrated upper bearing surface of the large-diameter portion 15b of the fixed body. The thrust ring 21 is screwed so as to substantially close the lower end opening of the inner cylinder 12a of the rotating body. On the upper bearing surface of the thrust ring 21 that is in contact with the lower bearing surface of the fixed body large diameter portion 15b, a herring phone pattern spiral groove 22 is also formed in a circle shape. The two sets of spiral grooves 20 and 22 and the bearing surfaces of the fixed body or the rotating body that are close to each other constitute dynamic pressure type plain bearings 23 and 24 in the thrust direction.
[0017]
Thus, for example, in the case of a rotating anode X-ray tube for circulatory imaging where the input heat capacity of the anode target is about 2.5 MHU, the fixed body small diameter portion 15a in which the radial direction dynamic pressure type slide bearings 18, 19 are formed is The axial length Lr is set to 100 mm, and the diameter Dr is set to 20 mm. On the other hand, the diameter Ds of the fixed body large diameter portion 15b in which the thrust direction dynamic pressure type slide bearings 23 and 24 are formed is set to 40 mm.
[0018]
In particular, the axial length Lr of this small fixed body diameter portion is set to a dimensional ratio in the range of 1.2 times or more, more preferably 1.5 to 5 times the diameter Ds of the large fixed body diameter portion. If the dimensional ratio (Lr / Ds) of these two is less than 1.2 times, the above-mentioned rotation axis of the rotating body is likely to be displaced or inclined, and if it is too large, the rotational resistance at the small diameter portion is undesirable. Will become bigger.
[0019]
Moreover, it is desirable to set the diameter Dr of the large fixed body diameter to a dimensional ratio in the range of 1.5 to 5 times the diameter Ds of the small fixed body diameter. If these dimensional ratios are less than 1.5 times, the dynamic pressure of the thrust direction bearings cannot be obtained sufficiently compared to the dynamic pressure of the radial direction bearings. It becomes too large and it becomes difficult to rotate at high speed.
[0020]
Further, the bearing gap of the hydrodynamic slide bearing portion constituted by the respective bearing surfaces of the rotating body and the fixed body is such that the average bearing gap Gs of the thrust direction hydrodynamic slide bearings 23 and 24 is the radial direction hydrodynamic slide bearing. The dimension is set to be larger than the average bearing gap Gr of 18,19. The average bearing clearance is an overall average value in the axial direction and the circumferential direction of the bearing portion in the radial direction dynamic pressure type slide bearings 18 and 19, and the diameter is large in the thrust direction dynamic pressure type slide bearings 23 and 24. This is the average value of the bearing gaps at both the upper and lower parts. In other words, it does not represent a part of the bearing gap when it is offset in a specific direction.
[0021]
In the case of the rotary anode X-ray tube as described above, the average bearing gap Gr of the radial slide bearings 18 and 19 is set in the range of 10 μm to 20 μm, for example, 15 μm. On the other hand, the average bearing gap Gs of the thrust slide bearings 23 and 24 is set in a range of 30 μm to 60 μm, for example, 45 μm. Each of the spiral grooves 16, 17, 20, and 21 has a depth of about 20 μm.
[0022]
The fixed body 15 is provided with a lubricant accommodating chamber 31 formed of a hole having a diameter of 3 mm, the central axis portion of which is cut out in the axial direction. The upper end opening 31a shown in the figure of the lubricant accommodating chamber 31 communicates with the radial dynamic pressure type slide bearing 18 via a space Sa in the upper part of the drawing. Further, four radial passages 32 extending from the lubricant accommodating chamber 31 to the circumferential space Sb are formed symmetrically at intervals of 90 degrees. As a result, the lubricant containing chamber 31 communicates with the circumferential space Sb through the radial passage 32, and further communicates with the two sets of radial hydrodynamic slide bearings 18 and 19 on the upper and lower sides in the drawing.
[0023]
A liquid metal lubricant L such as a Ga alloy is supplied into the spiral groove of each bearing portion, the bearing gap, the lubricant accommodating chamber, the radial passage, and each space. The filling amount of the lubricant is preferably in the range of 20% to 80% of the space volume including the bearing portions and the bearing gaps, the lubricant accommodating chamber, the radial passage, and the internal spaces, for example, approximately 50. It is an amount of volume corresponding to%.
[0024]
Since the rotating anode X-ray tube having such a configuration can obtain a relatively small rotational resistance, the rotating body and the anode target can be rotated at a rotational speed exceeding 6000 rpm continuously or at the time of X-ray exposure. it can. That is, for example, when imaging is waited for, it is always continuously rotated at an arbitrary rotational speed between 3000 and 6000 rpm, and when performing X-ray imaging by X-ray exposure, the rotational speed is increased to 9000 to 10000 rpm and X-ray imaging is performed. be able to. As described above, X-ray imaging can be performed by increasing the rotation speed to a high-speed rotation speed that allows instantaneous X-ray exposure when necessary. Even in such a high-speed rotation, the occurrence of displacement and inclination of the rotating shaft of the rotating body is suppressed, and a stable operation can be obtained.
[0025]
In the embodiment shown in FIG. 4, the outer peripheral wall surface 15d of the fixed body large diameter portion 15b in which the thrust direction dynamic pressure type slide bearings 23 and 24 are formed is made a surface which is not wetted at all or with a liquid metal lubricant. . Therefore, a lubricant wetting prevention layer 35 made of a material that repels this lubricant with little or no liquid metal lubricant, such as a ceramic thin film made of titanium oxide, is attached to the outer peripheral wall surface 15d of the large diameter portion. It is formed. Of course, the lubricant wetting prevention layer 35 is not formed on the bearing surface of the hydrodynamic slide bearing including the spiral grooves 20 and 22. It should be noted that the lubricant wetting prevention layer may be made of a material other than those described above, or any material that does not wet the surface of the base material itself having a large fixed body diameter with the lubricant. However, the bearing surface on which the spiral groove is formed must be a surface that gets wet with the lubricant.
[0026]
According to this embodiment, the rotational resistance between the fixed body large diameter portion and the rotating body can be reduced by the lubricant wetting prevention layer 35. That is, in the absence of the wetting prevention layer 35, the space Q between the outer peripheral wall surface 15d of the large fixed body diameter located farthest from the center axis of rotation and the peripheral wall surface of the rotating body that is in close proximity to the outer peripheral wall surface. Contact resistance due to wettability with the intervening liquid metal lubricant acts relatively large as rotational resistance. However, according to this embodiment, since the lubricant wetting prevention layer 35 is formed here, the contact resistance between this surface and the liquid metal lubricant present in the space Q is reduced. As a result, the rotational resistance is reduced, which is advantageous for high-speed rotation.
[0027]
In the embodiment shown in FIG. 5, the lubricant wetting prevention layer 35 is provided on the inner peripheral wall surface of the rotating body 12 surrounding the outer peripheral edge portion of the fixed body large diameter portion 15 b formed by the thrust direction dynamic pressure type slide bearings 23, 24. It is formed by adhesion. The lubricant wetting prevention layer 35 may also be formed on the outer peripheral wall surface 15d of the large fixed body diameter as shown in FIG. The lubricant wetting prevention layer 35 is preferably not formed in a region functioning as a dynamic pressure type sliding bearing so as not to impair the bearing performance of the dynamic pressure type sliding bearings 23, 24. According to this embodiment, the rotational resistance can be reduced as described above, which is advantageous for high-speed rotation.
[0028]
【The invention's effect】
As described above, according to the present invention, the rotating body can be rotated at a high speed without causing a shift or inclination of the rotating shaft.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of an essential part showing an embodiment of the present invention.
FIG. 2 is a side view showing a part of the fixed body in FIG. 1;
3 is a top view showing the thrust ring of FIG. 1. FIG.
FIG. 4 is a longitudinal sectional view of an essential part showing another embodiment of the present invention.
FIG. 5 is a longitudinal sectional view of an essential part showing still another embodiment of the present invention.
FIG. 6 is a longitudinal sectional view showing a conventional structure and operation.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Anode target 12 ... Rotating body 15 ... Fixed body 15a ... Fixed body diameter small part 15b ... Fixed body diameter large part 16, 17, 20, 22 ... Spiral groove 18, 19 ... Radial direction dynamic pressure type slide bearings 23, 24 ... Thrust direction dynamic pressure type slide bearing 35 ... Lubricant wetting prevention layer M ... Liquid metal lubricant Lr ... Axial length Dr of small fixed body diameter ... Outside diameter Ds of small fixed body diameter ... Outside of large fixed body diameter Diameter Gr: Average bearing clearance Gs of radial direction dynamic pressure type sliding bearing Gs: Average bearing gap of thrust direction dynamic pressure type sliding bearing

Claims (3)

A small diameter portion and the large-diameter portion fixing member closed by end becomes the anode supporting portion, a rotating body anode target is fixed to a portion fitted and keeping the bearing gap on the outer periphery of the fixed body, the A radial dynamic pressure type slide bearing configured between the small diameter portion of the fixed body and the rotating body, and a thrust direction dynamic pressure type slide bearing configured between the large diameter portion of the fixed body and the rotating body; In the rotary anode type X-ray tube comprising the above-described sliding bearings and the liquid metal lubricant supplied to the bearing gap,
The fixed body diameter large portion is provided on the anode support portion side, and the axial direction of the fixed body small diameter portion on which the radial dynamic pressure type slide bearing is formed is the small diameter portion side of the fixed body large diameter portion thrust hydrodynamic length from the slide bearing is a 5 times or less of the dimensional ratio 1.5 times the outer diameter of the fixed body large-diameter portion of the thrust direction dynamic pressure type sliding bearing is formed, and the above A rotary anode type X-ray tube characterized in that an average bearing gap of a thrust direction dynamic pressure type slide bearing is set to a size larger than an average bearing gap of the radial direction dynamic pressure type slide bearing. 2. The rotation according to claim 1, wherein an average bearing gap of the thrust direction dynamic pressure type slide bearing is in a range of 30 μm to 60 μm, and an average bearing gap of the radial direction dynamic pressure type slide bearing is in a range of 10 μm to 20 μm. Anode X-ray tube. The outer peripheral wall surface of the fixed body large diameter portion and at least one wall surface of the rotating body peripheral wall adjacent to and opposed to the fixed body large diameter outer peripheral wall surface are surfaces that are not or hardly wetted by the liquid metal lubricant. The rotary anode type X-ray tube according to claim 1.

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