JP3730297B2 - Rotating anode X-ray tube - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rotary anode X-ray tube having a plurality of filament cathodes that emit an electron beam, and in which the positional deviation of an electron beam incident on a rotary target from each filament cathode is reduced.
[0002]
[Prior art]
A rotary anode type X-ray tube is an apparatus that generates X-rays, and is used in an X-ray CT apparatus or the like. Here, a schematic structure of the rotary anode X-ray tube will be described with reference to FIG. Reference numeral 21 denotes a glass vacuum vessel constituting a rotary anode type X-ray tube, and a cathode 22 for emitting an electron beam is disposed inside the vacuum vessel 21. Further, a rotating target 23 that constitutes the anode is disposed opposite to the cathode 22. The rotation target 23 is fixed to a rotation shaft 24, and the rotation shaft 24 is connected to a rotor 25. In addition, a stator 26 is provided outside the vacuum vessel 21 so as to surround the rotor 25.
[0003]
The stator 26 is configured to rotate the rotor 25 when current flows therein, and to transmit the rotation to the rotation target 23 through the rotation shaft 24 to rotate the rotation target 23. An electron beam is incident on the rotating target 23 to be rotated from the cathode 22 and X-rays are generated.
[0004]
Here, the structure of the cathode and the rotating target portion in the conventional rotating anode X-ray tube will be described with reference to FIG. A is a rotating target portion that generates X-rays and constitutes a part of the anode. A cathode B is located in front of the rotating target portion A. Reference numeral 31 denotes a substrate constituting the cathode B, and a focusing electrode 32 having a circular periphery is brazed onto the substrate 31 using the back surface thereof. The surface of the focusing electrode 32 is inclined so that the center is lowered, and first and second focusing grooves 33a and 33b are formed on the inclined surface. Spaces 34a and 34b are formed on the back side of the focusing electrode 32 corresponding to the focusing grooves 33a and 33b. The focusing electrode 32 is fixed to the substrate 31 by welding or the like.
[0005]
A large-focus filament cathode 35a is disposed in the center of the first focusing groove 33a. The filament cathode 35 a is supported by a cathode support member 36 a, and the cathode support member 36 a extends below the substrate 31. An insulator 37a is fixed to an intermediate portion of the cathode support member 36a. The upper surface of the insulator 37a is joined to the lower end cylindrical portion of the upper fixing member 38a, and the upper end flange portion of the upper fixing member 38a is welded and fixed to the upper surface of the space 34a. The lower end of the insulator 37a is fixed by a lower fixing member 39a.
[0006]
In the center of the second focusing groove 33b, a small focus filament cathode 35b is arranged. The filament cathode 35 b is supported by a cathode support member 36 b, and the cathode support member 36 b extends below the substrate 31. An insulator 37b is fixed to an intermediate portion of the cathode support member 36b. The upper surface of the insulator 37b is joined to the lower end cylindrical portion of the upper fixing member 38b, and the upper end hook-like portion of the upper fixing member 38b is welded and fixed to the upper surface of the space 34b. The lower end of the insulator 37b is fixed by a lower fixing member 39b.
[0007]
In the structure described above, an electron beam is incident on the rotating target portion A from the filament cathode 35a for large focus and the filament cathode 35b for small focus. The rotating target portion A that has received the electron beam generates X-rays. At this time, the electron beams radiated from the large-focus filament cathode 35a and the small-focus filament cathode 35b are focused so as to be incident at the same position in the rotating target portion A as indicated by arrows ea and eb in the figure. The shape and dimensions of the electrode 32 and the focusing grooves 33a and 33b are determined.
[0008]
[Problems to be solved by the invention]
In the rotary anode X-ray tube having the above-described structure, when a voltage is supplied to each electrode and the device is in an operating state for a long time, the temperature of the X-ray tube and each electrode rises, and the focusing electrode 32 and the rotary target portion A expand. . At this time, the focusing electrode 32 expands in the lateral direction indicated by the arrow X. Accordingly, the positions of the electron beams incident on the rotating target portion A from the large focus filament cathode 35a and the small focus filament cathode 35b move away from each other.
[0009]
Further, the surface of the rotating target portion A moves in the direction of the cathode B as indicated by the dotted line D due to the thermal expansion of the rotating target itself or the thermal expansion of the rotating shaft to be connected. When the surface of the rotating target moves in the direction of the cathode B, the positions of the electron beams incident on the rotating target portion A from the filament cathode 35a for large focus and the filament cathode 35b for small focus also act in directions away from each other. To do.
[0010]
For this reason, when thermal expansion occurs in the electrodes of the X-ray tube or the like, the positions of the electron beams incident on the rotating target portion A from the two filament cathodes 35a and 35b are shifted in directions away from each other. For example, when focusing on a small focal point, the position of the tube moves due to the thermal history of the tube, which is one of the causes of artifacts in the CT apparatus. The technique disclosed in Japanese Patent Application Laid-Open No. 6-290721 has a complicated structure and is considered to be impractical.
[0011]
The present invention solves the above-described drawbacks, and an object of the present invention is to provide a rotary anode X-ray tube in which the positional deviation of an electron beam incident on a rotary target from a plurality of filament cathodes is reduced.
[0012]
[Means for Solving the Problems]
Rotating anode X-ray tube of the present invention, arranged an anode having a rotating target, and the substrate provided on the front of the rotating target, the filament cathode for emitting an electron beam to said rotating target in the current Tabamizo The first and second focusing electrodes are separated from each other by a gap , and the first and second focusing electrodes are opposite to the other focusing electrode with respect to the position of the filament cathode of one focusing electrode, respectively. And a vacuum vessel containing the anode and the first and second focusing electrodes fixed to the substrate.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to FIG. A is a rotating target portion and constitutes a part of the anode. A cathode B is disposed in front of the rotating target portion A. Reference numeral 11 denotes a substrate, and two focusing electrodes 12 a and 12 b are fixed on the substrate 11. The two focusing electrodes 12a and 12b have a structure separated from each other by a gap G located in the middle, and have a substantially symmetrical structure with respect to the gap G.
[0014]
For example, the surfaces of the focusing electrodes 12a and 12b are inclined so as to become lower toward the other direction, and first and second focusing grooves 14a and 14b are formed on the inclined surfaces. Further, on the back side of the first and second focusing electrodes 12a, 12b, first and second spaces 15a, 15b are formed at positions corresponding to the first and second focusing grooves 14a, 14b, and The lower ends of the spaces 15a and 15b are lifted from the substrate 11. The two focusing electrodes 12a and 12b are brazed or welded to the substrate 11 at, for example, the rearmost fixed portions 16a and 16b that are separated from the counterparts.
[0015]
Further, a large focus filament cathode 17a is disposed in the first focusing groove 14a. The filament cathode 17a is supported by a cathode support member 18a. The cathode support member 18a extends below the substrate 11, and an insulator 19a is fixed in the middle thereof. The upper surface of the insulator 19a is joined to the lower cylindrical portion of the upper fixing member 20a, and the hook-shaped portion at the upper end of the upper fixing member 20a is welded and fixed to the upper surface of the space 15a. The lower surface of the insulator 19a is fixed by a lower fixing member 21a.
[0016]
A small focus filament cathode 17b is disposed in the second focusing groove 14b. The filament cathode 17b is supported by a cathode support member 18b. The cathode support member 18b extends below the substrate 11, and an insulator 19b is fixed therebetween. The upper surface of the insulator 19b is joined to the lower cylindrical portion of the upper fixing member 20b, and the hook-shaped portion at the upper end of the upper fixing member 20b is welded and fixed to the upper surface of the space 15b. The lower surface of the insulator 19b is fixed by a lower fixing member 21b. The anode constituted by the rotating target portion A and the like, the two focusing electrodes 12a and 12b, and the like are hermetically housed in a glass vacuum container (not shown).
[0017]
In the above-described structure, for example, consider a case where the X-ray tube enters an operating state and the anode, the cathode, etc. expand due to a temperature rise. Since the two focusing electrodes 12a and 12b are opposite to each other in the portions 16a and 16b fixed to the substrate 11, the two focusing electrodes 12a and 12b are thermally expanded so as to narrow the gap G between them. Accordingly, the two filament cathodes 17a and 17b come close to each other, and the position of the electron beam incident on the rotating target from the filament cathodes 17a and 17b almost overlaps with the position of the target D as indicated by the dotted line.
[0018]
That is, the surface of the rotating target moves in the direction of the cathode B as indicated by the dotted line D due to thermal expansion of the rotating shaft to be connected. By this movement, the position of the electron beam incident on the rotating target from the two filament cathodes 17a and 17b acts in a direction away from the target.
[0019]
However , the positional deviation of the electron beam incident on the rotating target due to the thermal expansion of the two focusing electrodes 12a and 12b becomes small.
[0020]
In the above-described embodiment, the two focusing electrodes 12a and 12b are brazed to the substrate 11 by the most fixed portions 16a and 16b that are farthest from the counterpart. However, it is not necessary to be the farthest end portion, and it may be a portion located on the opposite side of the counterpart with respect to the position of the filament cathodes 17a and 17b. At this time, when the two focusing electrodes 12a and 12b are expanded due to the temperature rise, the position of the thermal electrons incident on the rotating target from the large-focus filament cathode 17a and the small-focus filament cathode 17b are incident on the rotating target. The positions of the electron beams to be moved move toward each other, and the effect of the present invention is realized.
[0021]
【The invention's effect】
According to the present invention, it is possible to realize a rotary anode type X-ray tube with a small positional deviation of electron beams incident on a rotary target from a plurality of filament cathodes.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing an embodiment of the present invention.
FIG. 2 is a diagram illustrating the structure of a rotary anode X-ray tube.
FIG. 3 is a schematic cross-sectional view illustrating a conventional example.
[Explanation of symbols]
11 ... Substrates 12a, 12b ... Focusing electrodes 14a, 14b ... Focusing grooves 15a, 15b ... Spaces 16a, 16b ... Focusing electrode fixed portions 17a, 17b ... Filament cathodes 18a, 18b ... Cathode support members 19a, 19b ... Insulator 20a, 20b ... Upper fixing member 21a, 21b ... Lower fixing member A ... Rotating target part B ... Cathode G ... Gap

Claims (1)

An anode having a rotating target, and the substrate provided on the front of the rotating target, the filament cathode for emitting an electron beam to said rotating target placed in the collecting Tabamizo, first structures which are separated from each other by a gap Each of the first and second focusing electrodes is fixed to the substrate at a portion opposite to the other focusing electrode with respect to the position of the filament cathode of the one focusing electrode, Furthermore, a rotary anode type X-ray tube comprising the anode and a vacuum vessel containing the first and second focusing electrodes fixed to the substrate.

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