JP3149449B2 - X-ray tube - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a cathode of an X-ray tube.

[0002]

2. Description of the Related Art The structure of a conventional rotary anode X-ray tube having two focal points, a large focal point and a small focal point, is schematically shown in FIG. FIG. 3B shows the case of three focal points. As described above, a plurality of cathodes (A and B in FIG. 3A, A in FIG.
In the form of obtaining multiple focal points by separately providing B and C), the filaments at different positions (FIG. 3)
12A and 12-2 in FIG. 3A, and 12- and 12- in FIG.
The electron lens system must be designed so that electrons emitted from 1, 12-2 and 12-3) focus on the same point T on the anode 13. In such an electron lens system, there is a problem that the electron lens system is complicated because the electron trajectory needs to be largely bent.

[0003] Another method for changing the size of the focal point is to apply a bias voltage 14 to the focusing electrode 11 of the cathode as shown in FIG. By applying the bias voltage 14 in this manner, the focus becomes smaller (C), and by turning off the bias voltage 14, the focus becomes larger (D).

[0004]

FIG. 4B is a plan view of the cathode of the above-mentioned X-ray tube of the bias voltage application type viewed from the direction in which electrons are emitted. The electrode 11 is parallel to the axial direction of the filament coil 12 (the vertical direction in FIG. 4B). For this reason, the size of the focal point on the anode 13 changes only in the direction (width direction) perpendicular to the axial direction of the filament coil 12, and in the axial direction (length direction) of the filament coil 12.
The size of the focal point hardly changes. That is, when the size of the focus is changed by changing the size of the bias voltage 14, the resolution differs between the width direction and the length direction, which is not preferable in practical use.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an X-ray tube capable of changing the size of a focal point not only in the width direction but also in the length direction. Is to provide.

[0006]

According to the present invention, a bias voltage is applied between a focusing electrode of a cathode and a filament so that a focal point in a direction perpendicular to a winding axis of a filament coil is adjusted. An X-ray tube whose size can be changed is characterized in that a filament coil is divided into a plurality in the direction of its winding axis so that current can be independently supplied to each partial filament coil.

[0007]

[Action] Each partial filament coil is turned on independently,
Alternatively, the size of the focal point in the length direction of the filament coil can be changed by controlling not to light. By using both the change of the focus in the length direction and the change of the focus in the width direction by changing the bias voltage applied to the focusing electrode, the focus is changed in a well-balanced manner in the length and width on the anode. be able to.

[0008]

FIG. 1 shows the structure of an X-ray tube according to a first embodiment of the present invention. FIG. 1A is a diagram viewed from the axial direction of the filament coil 2, and FIG. 1B is a diagram viewed from a direction perpendicular to the axis. As shown in FIG. 1A, a bias voltage source 4 is provided on the focusing electrode 1 of the cathode of this embodiment, and a switch 5 is provided in series with the bias voltage source 4. When the switch 5 is OFF, the bias voltage 4 is not applied to the focusing electrode 1, and the electrons emitted from the filament 2 form a relatively large focal point B 2 on the rotating anode plate 3 due to the shape of the focusing electrode 1. On the other hand, when the switch 5 is turned on and the bias voltage 4 is applied to the focusing electrode 1, the electron beam is narrowed down and a relatively small focal point B 1 is formed on the anode plate 3. However, FIG.
As shown in the above, the size of the focal point changes like B1 and B2 only in the width direction of the filament coil 2, and depending on the application / non-application of the bias voltage 4 as described above, Length direction (Fig. 1
The size of the focal point hardly changes in the direction perpendicular to the paper surface in FIG. 1A, and in the horizontal direction in FIG. 1B.

For this reason, in this embodiment, as shown in FIG. 1B, the filament coil 2 is divided into three portions 2-1, 2-2 and 2-3 in the longitudinal direction, and the filament coil 2 is independently formed. A current can be passed. When the switch 5 in FIG. 1A is turned off, current flows through all of the three filaments 2-1, 2-2, and 2-3, and when the switch 5 is turned on. The current is applied only to the central filament 2-2 and the other filaments 2-2
The current is not supplied to the filaments 2-1 and 2-3. As a result, when the bias voltage 4 is not applied to the focusing electrode 1 of the cathode, the size of the focal point on the anode plate 3 is as large as L2 × B2 in both length and width, and when the bias voltage 4 is applied, the focus is L1 × B1. In addition, both the length and width are reduced, and the balance of the resolution in the vertical and horizontal directions when the size of the focal point is changed is maintained.

In the above description, three filaments 2-1,
The example in which two types of focus sizes are divided into two cases, that is, the case where all of 2-2 and 2-3 are turned on and the case where only one central portion is turned on, has been described. 2
By adding the case where the individual is turned on, the size of the focal point can be set to three types. In this case, it is necessary to provide two types of bias voltages 4 (three types including the case where no bias voltage is applied) accordingly. Also,
Dividing the filament coil into three or more pieces (in the longitudinal direction) can also increase the kinds of focal spot sizes. Further, by applying the present invention to the multiple cathode type X-ray tube shown in FIG. 3, more types of focal points can be formed (FIG. 2).

[0011]

The size of the focal point of the electron beam on the anode can be changed not only in the width direction but also in the length direction of the filament coil, so that the balance of the resolution in the vertical and horizontal directions is maintained. The size of the focus can be changed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a rotating anode X-ray tube according to an embodiment of the present invention, in which (a) is a side view as viewed from an axial direction of a filament coil, and (b) is perpendicular to an axis of the filament coil. The side view seen from the direction.

FIGS. 2A and 2B are schematic configuration diagrams of another embodiment of the present invention, where FIG. 2A is a side view as viewed from the axial direction of the filament coil, and FIG. 2B is a direction perpendicular to the axis of the filament coil. FIG.

FIG. 3 is a schematic configuration diagram of a conventional rotary anode X-ray tube having a plurality of focal points by providing a plurality of cathode focusing electrodes.

FIG. 4 is a schematic configuration diagram of a conventional rotary anode X-ray tube in which a plurality of focal points are provided by applying a bias voltage.

[Explanation of symbols]

1, 11 ... cathode focusing electrode 2, 2-1, 2-2, 2-3, 2A, 2A-1, 2A-
2, 2A-3, 2B, 12-1, 12-2, 12-3 ...
Filament 3, 13… Anode plate 4, 14… Bias voltage source 5… Switch

Claims (1)

(57) [Claims] An X-ray tube capable of changing a size of a focal point in a direction perpendicular to a winding axis of a filament coil by applying a bias voltage between a focusing electrode of a cathode and the filament. Is divided into a plurality in the direction of the winding axis so that current can be independently supplied to each of the partial filament coils.