JPS6196639A - Rotary anode x-ray tube - Google Patents

Abstract

PURPOSE:To reduce change in clearance of ball bearing due to thermal expansion of X-ray tube in the axial direction, stabilize rotation and reduce noise level by using a material having a thermal expansion coefficient smaller than that of stationary side as the cylindrical material which specifies interval of bearing device in the rotating side material. CONSTITUTION:An anode target 1 is coupled to the one end of a drive motor rotor 3 and two ball bearings 4 are fixed in the specified interval with the cylindrical member 6 in the outer ring (rotating) side and the cylindrical member 7 in the inner ring (stationary) side. The compositions of cylindrical member 6 in the outer ring side is, for example, Fe-40Ni-0.45Mn, while the cylindrical member 7 in the inner ring side is SUS316. The cylindrical member 9 of the outer ring has the thermal expansion of about 1/4 the thermal expansion of the cylindrical member 78 in the inner ring side. Since the thermal expansion difference is generated even in the radius direction when the outer ring side becomes longer than the inner ring side, elongation in the axial direction can be eliminated sufficiently by the groove at the running surface of ball bearing and the clearance in the axial direction which is equal to the initial condition or more can be assured.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to the improvement of rotating anode X-ray tubes, and particularly to the improvement of rotating anode X-ray tubes.
Related to improving the rotational performance of ray tubes and large-capacity X-ray tubes.

[Background of the invention]

Traditionally, rotating heavy metal disks (tungsten.

A rotary anode X-ray tube (hereinafter referred to as an X-ray tube) is known that generates X-rays by bombarding a target such as molybdenum with thermoelectrons. The X-ray tube mainly consists of a rotating anode containing the above-mentioned target, a cathode that generates thermionic electrons, and a glass container in which these are housed. There is. When thermoelectrons hit a target, X-rays are generated.
Since 99 or more of thermionic energy is converted into heat, the temperature instantly becomes high and easily reaches the melting point of the target metal, so the target metal is rotated to prevent this. Due to the rotation, the heat generation point moves moment by moment, and at the heat generation point where the electron beam hits, heat is diffused by conduction, which allows the target metal to maintain its temperature below the allowable temperature and generate X-rays continuously. . A bearing device is required to rotate it, but
The usage conditions are high vacuum (10-6 torr or less) as above.
, solid (silver) due to the harshness of high temperatures (up to 500 tl').

A special ball bearing lubricated with Mo8K, lead, etc.) is used. These bearings have an extremely long lifespan under load and speed conditions that would not cause any problems with equipment used with normal oil lubrication. However, because they are lubricated with solid under the vacuum and high temperature conditions mentioned above, rotational noise may occur. However, not only do they produce large vibrations, but they also have short lifespans. In particular, high-speed, high-brightness X-ray tubes are indispensable for advanced diagnosis.
This becomes an important problem in large-capacity X-ray tubes for CT and the like.

The special feature of the Xg tube as a rotating machine is that the temperature of the viewing section rises to 5ooc. Moreover, the rolling elements (balls) of ball bearings
300 transiently on the rotating body side and stationary body side with
degree or more, a temperature difference of around 100 to 200 degrees occurs in a steady state. Temperature differences in ball bearings cause changes in the bearing clearance, and if the bearing is incorrectly designed, the clearance will disappear and the inner and outer rings will tighten on the rolling elements, creating an excessive load and making it impossible to rotate.

In addition, to avoid this situation, the bearing clearance should be increased to 4.
A method of setting the temperature to a large value of 0 to 50 μm is sometimes adopted, but until a large temperature difference occurs, the bearing clearance is large, causing the entire rotating body to move irregularly.
This has the disadvantage that the target deflection increases. If the target shakes too much, the X-ray image will become unclear, and dynamic loads will be generated on the rotating body, increasing the risk of problems such as damage to the bearing and increased imbalance.

On the other hand, when the bearing clearance changes due to a rise in temperature, a structure is recommended that always eliminates the bearing clearance by applying preload using a coil spring or the like, as shown in, for example, Japanese Patent Laid-Open No. 52-55395. FIG. 9 shows a general coil spring preload structure, but as a result of various experiments and studies to date, it has been found that this structure cannot maintain a stable rotational state for a long period of time. As mentioned above, the bearings of the X-ray tube must be lubricated with a solid material, and as compared to oil lubrication, the bearings of the X-ray tube must be used with roughened transfer surfaces. As a result, the rollers vibrate as they rotate, creating a large vibration load between the balls and the inner and outer ring raceway surfaces.Furthermore, since there is no vibration absorption effect due to oil, the rollers are pressed against each other by a preload spring (inner ring in the figure). is prone to slight vibration in the axial direction. As a result, the preloaded sliding portion suffers fretting wear, easily becoming locked, unable to maintain an appropriate preload force, and often resulting in excessive preload, making it impossible to rotate. Furthermore, since the rolling wheels vibrate minutely in the axial direction, the rolling path of the balls is not determined, and damage to the balls and the inner and outer ring raceway surfaces progresses rapidly. As a result of step 7, the damage progresses → the axial micro-vibration of the rolling wheels increases → the damage progresses, and the bearing is damaged in a chain reaction, making it unable to rotate.

US Pat. No. 3,634,870 is a measure to fundamentally solve the problem of steering caused by fretting wear of preloaded sliding parts. In this structure, since the rolling surface to be pressed by the preload spring is mounted on a bearing support having a spring action, there is no preload sliding part, and problems caused by galling can be completely solved.

However, since the rolling wheels are supported by spring bodies, their degree of freedom increases, making them susceptible to minute vibrations not only in the axial direction but also in the radial direction. The problem of making progress is unsolvable.

[Purpose of the invention]

The present invention was made in view of the drawbacks of the above-mentioned prior art, and
Rotating anode
The purpose is to provide wire tubes.

[Summary of the invention]

A feature of the present invention is that the amount of thermal expansion of a member is determined by the product of temperature and coefficient of thermal expansion. By understanding the temperature rise at each point in the vicinity of the bearing, and reviewing these comprehensively, we were able to reduce the bearing clearance to a level that does not pose a practical problem even if there is a temperature difference.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. An anode target 1, which is an anode member, is fastened to one end of a drive motor rotor 3, which is a rotating member, and is rotatably supported by two ball bearings 4 spaced apart from each other.

The two ball bearings are an outer ring side (rotating side) cylindrical member 6 and an inner ring side (rotating side) cylindrical member 6.
Stationary side) It is fixed at a prescribed interval with the cylindrical member 7.

The material composition of the outer ring side cylindrical member 6 is Fe-4ONi-0,4
5Mn.

The inner ring side cylindrical member 7 is made of SUS 316 (J'IS standard), and the thermal expansion coefficients from room temperature to 300C are 9 x 10''/r and 2.3 x 10-', respectively.
/c, the amount of thermal expansion of the outer ring side cylindrical member 6 is about 1/4 that of the inner ring side cylindrical member 7. The ball bearing 4 is a bearing support member 5
The entire rotation is covered in a vacuum by a part of this bearing support member 5 and a glass tube 8 which is a tube container, and a cathode body 2 which is a cathode member is provided on the opposite surface of the anode target. , this cathode body 2 is fixed within a glass tube 8. The glass tube 8 having such a structure is called a rotating anode X-ray tube (hereinafter referred to as an X-ray tube). A motor stator 9 serving as a magnetic field generating device is provided on an insulating frame 10 around the outer periphery of the glass bulb 8, and the insulating frame 10 is fixed to an envelope (not shown). The interior of the routing container is filled with insulating oil (
(not shown) is enclosed.

In this configuration, the number of thermoelectrons generated in the cathode body 2 is 3
When it hits the anode target 1 rotating at a high speed of 00 to 10,000 r-, X-rays are generated from the surface of the anode target 10 in the direction of the arrow in the figure, but as mentioned above, the anode target 1 is rapidly heated and It may even reach C. Since the inside of the glass tube 8 is kept airtight in a high vacuum, most of the heat is radiated to the outside, but some of it is transferred to the drive motor rotor 3, ball bearing 4, and bearing support member 5 by conduction. As a result, the ball bearing 4 is heated to a maximum of 550C.

FIG. 2 shows the results of actual measurement of an example of the temperature rise characteristics of the anode target 1 and the ball bearing 4 when thermoelectrons impinge on the anode target 1 to generate X-rays.

Temperature measurements were carried out by attaching thermocouples to the back surface near the center of the anode target 1, the outer ring and inner ring of the ball bearing (high temperature side) near the target, and the outer ring on the side opposite to the target (low temperature side).

In addition, we have devised a way to heat the measurement without rotating it. From Figure 2, 1) Anode target, rotating side of the bearing,
Heat is conducted from the stopped side of the bearing, and there is a short time delay in temperature rise. 11) Therefore, there is a maximum distance of 350 d between the outer ring (rotating side) and inner ring (stationary side) of the bearing during transient periods.
eg, there is a temperature difference of about 100 deg at steady state.

iii) The temperature difference between the outer rings of the two bearings (high temperature side and low temperature side) is approximately constant at approximately 50 degrees. This has also been confirmed for the inner ring side. etc. can be seen.

In this way, there is a large temperature difference between the rotating side and the stationary side of the ball bearing, and the reason why it changes from moment to moment is because the contact area between the balls and the inner and outer ring raceway surfaces is small, making it difficult for heat to conduct. It is.

FIG. 3 shows the results of calculating the difference in thermal expansion between the outer ring side cylindrical member and the inner ring side cylindrical member of the X-ray tube according to the present invention using the temperature difference between the two members as a parameter. For comparison, FIG. 4 shows the difference in thermal expansion in a conventional example, in which both members are made of SUS316. As is clear from Figure 4, 350 d
When there is a temperature difference in eg, the amount of thermal expansion differs by 250 μm, and the outer ring side becomes longer than the inner ring side. The inner and outer ttS = running surfaces of a ball bearing have grooves formed with a curvature slightly larger than the diameter of the balls, and the degree of freedom in the axial direction (axial clearance) is closely related to the radial clearance. In other words, even if the drive motor rotor heats up first and the distance between the outer rings of the two bearings becomes longer, a thermal expansion difference equal to the temperature difference will also occur in the radial direction, resulting in an increase in the degree of freedom in the axial direction. .

However, it is impossible to eliminate the entire difference in thermal expansion described above only by the groove shape of the bearing raceway surface, and for this reason, conventionally, it has been necessary to provide an extra 100 μm or more in the initial value of the axial clearance. As mentioned above, it is desirable for the ball bearing of the X-ray tube to firmly and rigidly fix the inner and outer rolling wheels from both sides, and in this state, ensure a slight degree of freedom for the balls, that is, a clearance in the axial direction.

In the present invention, since the high-temperature rotating side cylindrical member is made of a material with a small coefficient of thermal expansion, even if there is a temperature difference of 350 degrees, the difference in thermal expansion amount can be reduced to 90 μm, 1/3 compared to the conventional one. The elongation in this direction can be sufficiently eliminated by the shape of scrap on the raceway surface. In other words, the axial clearance increases due to the expansion of the bearing clearance i (radial direction) due to thermal expansion in the radial direction.
This maintains an axial clearance equal to or greater than the initial one.

The groove curvature of the raceway surface is expressed as a ratio to the soil spacing, and the closer it is to the soil spacing, the higher the load capacity, but it also causes an increase in friction torque, and also increases the bearing inclination and the ratio of the axial clearance to the radial clearance. becomes smaller. In other words, the degree of freedom decreases. When the groove curvature is larger than that of a soil shovel, the load capacity decreases, but the ratio of the axial clearance to the radial clearance also increases in cases where the friction torque is small. According to research, analysis, and experiments to date, the friction torque of solid-lubricated ball bearings for X-ray tubes is too large due to the groove curvature of ball bearings used in normal oil lubrication, and conversely, even if the load capacity is slightly small, Good things are clear. Therefore, it is common practice to increase the groove curvature of at least one of the rolling wheels. In this case, the amount of increase in the axial clearance relative to the increase in the radial clearance is greater than that of a normal ball bearing, and the amount of axial elongation due to thermal expansion that can eliminate the groove shape increases. Such a ball bearing 4
In the X-ray tube that uses
Even better characteristics can be obtained if the thickness is set to 45 μm.

FIG. 5 shows the difference in thermal expansion when the rotating cylindrical member 6 is divided into two halves and the respective materials are 5US316 and pe-4ON i -0.45 μm. The temperature difference is 350 de
Although the difference in thermal expansion at g is slightly large at 20 μm, this amount can be sufficiently eliminated by the groove shape.

Furthermore, it can be seen that when the steady state is reached and the degree difference becomes 100 degrees, the amount of thermal expansion becomes almost zero and returns to the initial state.

The method of dividing the outer ring side cylindrical member 6 and the selection of the material should be determined based on the shape of the drive motor rotor 3, thermal design, groove shape of the ball bearing 4, etc., and are not limited to the embodiments. . Furthermore, the cylindrical member that is divided and combined with different materials is not limited to the outer ring side, but may be divided and combined on the inner ring side.

In the above embodiment, the outer ring of the bearing 4 is attached to the drive motor rotor 3, and the outer ring rotates while the inner ring remains stationary.
The temperature on the outer ring side increases.

FIG. 6 shows an embodiment in which the present invention is applied to an X-ray tube with a rotating inner ring, and the general structure is the same as that in FIG. 1. The rotating cylindrical member 6 is attached to the shaft 3 a attached to the other end of the drive motor rotor 3 , and the stationary cylindrical member 7 is in contact with the bearing support member 5 to define the spacing between the ball bearings 4 . In this example, the temperature rise characteristics of each part of the anode when thermionic electrons are bombarded with the anode target 1 are different from those of the X-ray tube shown in the example of Fig. 1, and the maximum temperature difference is 300 degrees, steady state. at 150 degrees
It became. However, the application method of the present invention remains unchanged in principle, and the rotating side cylindrical member 6 is l;"e-4ONi -0,
45 μm, and the stationary side cylindrical member 7 is made of 5US316. I will avoid explaining the effect as it overlaps with that of an X-ray tube with a rotating outer ring. Depending on the groove curvature of the inner ring or outer ring raceway surface and the anode design, the rotating cylindrical member 6 or the stationary cylindrical member 7 may be divided and different materials may be combined.

FIG. 7 shows another embodiment of the present invention, in which the outer ring side cylindrical member 6
A slit 6a is made in the. By processing the slit 6a as shown in the figure, the axial spring constant is 204/ltr.
The depth, number, and depth of the slits 6a can be reduced to m.
It is possible to set any desired spring constant by pinching. As mentioned above, in X-ray tube solid lubricated ball bearings, the balls and inner and outer rings are rotated in a rough state with unevenness of around 1 μm on the raceway surfaces, so a high-frequency riser is generated between the balls and the inner and outer rings. sharp dynamic loads are likely to occur. The slitted cylindrical member exhibits the effect of absorbing this high frequency dynamic load through spring action, thereby reducing noise and extending the life of the bearing.

Note that the spring action of the slitted cylindrical member according to the present invention and [
The spring preload structure described in the section ``Background of the Invention'' differs in the following points, and the above-mentioned problem does not occur.

That is, in a preload structure using a coil spring or the like, the spring constant is as low as 2 Ky/w at most, and therefore the rolling wheel pressed by the spring can easily move in the axial direction. As a result, 7renote/g wear occurs on the sliding parts,
This had the drawback that it caused the ball to spin and the rolling path of the ball became unstable. In the present invention, the spring constant is set to several tens to hundreds of times the spring constant, and the amount of axial movement of the rolling wheel fixed to the slitted cylindrical member is suppressed to a negligible several μm. Therefore, there is no occurrence of fretting wear, and there is no adverse effect on ball rolling, and only high frequency dynamic loads are absorbed.

FIG. 8 shows an example of the result of actually measuring and comparing the vibration acceleration of an X-ray tube incorporating a cylindrical member with slits and a cylindrical member without slits at the end of the bearing support member 5.

Vibration acceleration is often used as a simple and effective method of measuring the strength of high-frequency dynamic loads, and can also be used as a measure of the strength of noise. The strength of the high-frequency dynamic load is strongly influenced by the surface condition of the ball bearing, so even if you test the same ball bearing, it is difficult to maintain the same surface condition, but we repeated it four times with and without slits. When the samples were recombined and measured and the results were averaged, the results were as shown in Figure 8.

The slitted cylindrical member has the above main effects, but
When the difference in thermal expansion becomes unexpectedly large and the balls are pressed between the inner and outer raceway surfaces, the cylindrical member deflects in the axial direction, reducing the thrust load caused by the pressing. It has the effect of

Since the stress acting on the slitted cylindrical member is extremely weak, there is no problem with a member with low allowable stress, such as 5US316 or Fe-4ONi-0,45Mn alloy.
There is no difference in performance depending on the material. Hot work tool steel does not reheat up to 500C and can be easily processed precisely, so it is suitable for high-performance X-ray tubes that require rotational precision. In addition,
There are several methods for machining Surin) 6a, such as high-speed cutters and electrical discharge machining, but high-speed cutters are faster and have better accuracy.

Ru.

〔Effect of the invention〕

According to the present invention, focusing on the fundamental physical phenomenon that the amount of thermal expansion of a member is determined by the product of temperature and coefficient of thermal expansion, the present invention focuses on the fundamental physical phenomenon that the amount of thermal expansion of a member is determined by the product of temperature and coefficient of thermal expansion. By actually measuring and analyzing the temperature rise of A rotating anode X-ray tube can be provided.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view of an embodiment of the rotating anode X-ray tube according to the present invention, FIG. 2 is an explanatory diagram showing an example of the actual measurement results of the temperature rise of each part of the anode, and FIGS. 3 and 5 are according to the present invention. An explanatory diagram showing the effect of reducing the amount of thermal expansion. FIG. 4 is an explanatory diagram showing the amount of thermal expansion of a cylindrical member in a conventional X-ray tube. FIG. 6 is an explanatory diagram showing the amount of thermal expansion of a cylindrical member in a conventional X-ray tube. 7 is an enlarged view of the cylindrical member according to the present invention; FIG. 8 is an explanatory diagram showing the vibration reduction effect of the rotating anode X-ray tube according to the present invention; FIG.
The figure is a schematic diagram showing a general constant pressure preload structure. DESCRIPTION OF SYMBOLS 1... Anode target, 2... Cathode body, 3... Drive motor rotor, 4... Ball bearing, 5... Bearing support member, 6... Rotating side cylindrical member, 7... Stationary Side cylindrical member, 8...Glass tube, 9...Motor stator, 10
・・・Insulating film V-frame, 3a... 咄, 6a... slit.

Claims (1)

[Scope of Claims] 1. An anode member arranged to face the cathode member, a rotating member integrally formed with the anode member, a bearing device that rotatably supports the rotating member, and a bearing that fixes the stationary body side of the bearing device. In a rotary anode X-ray tube configured in a vacuum state by covering the above member with a support member, a part of the bearing support member, and a container, the cylindrical member defining the spacing between the bearing devices is different on the rotating side and the stationary side. A rotating anode X-ray tube characterized in that it is a member. 2. In the rotating anode X-ray tube, the cylindrical member on the rotating side is a member having a smaller coefficient of thermal expansion than the cylindrical member on the stationary side.
wire tube. 3. In the rotating anode X-ray tube, the cylindrical member on the rotating side or the stationary side is divided into two or more parts, and the coefficients of thermal expansion of these members are made different.
Rotating anode X-ray tube as described in . 4. In the rotating anode X-ray tube, the cylindrical member on the stationary side is made of a steel material such as stainless steel, and the cylindrical member on the rotating side is made of F.
The rotating anode X-ray tube according to claim 1, characterized in that the material has a coefficient of thermal expansion smaller than that of the stationary cylindrical member, such as an e-Ni alloy or a Mo alloy. 5. In the rotating anode X-ray tube, 1/2 or more of the cylindrical member on the rotating side is made of a low thermal expansion coefficient material such as Fe-Ni alloy or Mo alloy, and the rest is made of steel material. A rotating anode X-ray tube according to scope 4. 6. In the rotating anode X-ray tube, a plurality of slits are made in the cylindrical member, and the axial spring constant is set to 20 to 200K.
The rotary anode X-ray tube according to claim 1, characterized in that the rotary anode X-ray tube has a diameter of 100 g/mm. 7. The rotating anode X-ray tube according to claim 6, wherein the cylindrical member having a plurality of slits is made of hot work tool steel.