JP2007115552A - Filament for x-ray tube and x-ray tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To greatly improve uniformity of temperature distribution of a filament in a length direction by changing a winding pitch of a coil. <P>SOLUTION: A coil-like filament is structured of a center part having a plurality of turns with the same winding pitch and two end parts having a plurality of turns with a smaller winding pitch. A winding pitch of the plurality of turns of the end parts is decreased gradually by the same varying quantity from the turn nearest to the center part toward the outermost turn. If a winding pitch at the center part is expressed in p, a varying quantity of the winding pitch is expressed in Δp, the number of windings of the filament as a whole is expressed in n, and the total number of windings of the two end parts is expressed in k, Δp/p is to be within a range of 0.015 to 0.1, and k/n is to be within a range of 0.3 to 0.8. A value of the k/n is preferred to be within a range of the following formula: k/n=0.72-4.66(Δp/p)±0.12. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a filament for an X-ray tube, and more particularly to a filament characterized by a device for making the temperature distribution in the longitudinal direction of a coiled filament uniform. The present invention also relates to an X-ray tube comprising such a filament.

  It is desirable that the coiled filament for the X-ray tube has a temperature distribution as uniform as possible over the entire length of the coil. A normal filament for an X-ray tube has a uniform wire diameter and winding pitch, so the temperature near the center is highest and the temperature near both ends is low. On the other hand, when the temperature distribution of the filament is made uniform, the intensity distribution of the electron beam emitted from the filament becomes uniform, and the electron beam is formed by irradiating the target (anti-cathode) of the X-ray tube. The brightness distribution of the X-ray focal point is also uniform. In addition, when the coil temperature distribution is uniform, the coil wire diameter decreases uniformly and the life is prolonged as compared with a filament having a nonuniform temperature distribution. Furthermore, when the temperature distribution of the coil becomes uniform, the maximum temperature of the filament can be lowered even when the same tube current is obtained, as compared with a filament having a nonuniform temperature distribution, and the life of the filament can also be extended. .

The present invention relates to changing the winding pitch of the coil of the filament for the X-ray tube, and the following patent document 1 is known as the technology most closely related to this. Note that even a utility model document will be referred to as a broad patent document.
Japanese Utility Model Publication No. 6-9047

  In this patent document 1, the coil winding pitch of the X-ray tube filament is made dense at the center and roughened at both ends, so that the temperature near the center of the coil is raised and the electron density distribution is made Gaussian. Yes. Therefore, the temperature distribution is not made uniform, but rather the temperature at the center is considered to be higher than that of a normal coil having a uniform winding pitch. For example, the coil filament of Patent Document 1 has a pitch of 80 turns / inch at the center and 50 turns / inch at both ends.

On the other hand, in technical fields other than the X-ray tube, it is known that the coil has a uniform pitch distribution in the length direction of the coil by roughening the central pitch of the coiled filament and increasing the pitch at both ends. For example, there are the following Patent Document 2 and Patent Document 3.
Japanese Patent Laid-Open No. Sho 63-232264 Microfilm of Japanese Utility Model No. 63-57323 (Japanese Utility Model Application No. 1-161547)

  Patent Document 2 relates to a coil filament of a halogen bulb for an electronic copying machine. By making the coil pitch of the end portion denser than that of the intermediate portion, temperature drop at the end portion is prevented, and The illuminance at the center is the same as at the center. For example, the pitch of the middle part is 26.3 turns / cm and the end part is 33.8 turns / cm.

  Patent Document 3 relates to a coil filament of a light bulb used in a vehicle or the like. By making the winding pitch of the central portion sparser than the winding pitch of both ends, the temperature distribution in the longitudinal direction of the filament is made uniform. ing. Further, this document also discloses that the outermost winding pitch is made the most dense, and the winding pitch is gradually made sparse from the outermost side toward the center.

  According to the above-mentioned Patent Document 2 and Patent Document 3, it can be understood that the temperature distribution in the longitudinal direction of the filament becomes uniform if the winding pitch in the vicinity of both ends of the coil filament is made denser than the central portion. Therefore, the present inventors have developed a filament for an X-ray tube based on such an understanding, and it has been found that the uniformity of temperature distribution is insufficient only by such a device. .

  The temperature distribution of the filament of the X-ray tube affects the density distribution of the electron beam generated from the filament, which is reflected in the luminance distribution of the X-ray focal point on the target. If the filament life is simply extended, the techniques disclosed in Patent Document 2 and Patent Document 3 described above may be used. However, considering the uniformity of the brightness of the X-ray focus, the uniformity of the temperature distribution is more strict. Sex is required.

  Accordingly, an object of the present invention is to provide a filament for an X-ray tube capable of extremely improving the uniformity of temperature distribution in the longitudinal direction of the filament. Another object of the present invention is to provide an X-ray tube having such an X-ray tube filament.

  The filament for X-ray tube of the present invention is a coiled filament, and has a central portion having a plurality of turns having the same winding pitch, and a winding pitch that is smaller than the winding pitch of the central portion on both sides of the central portion. And two ends having a plurality of turns. The winding pitch of the plurality of turns at the end portion is sequentially decreased by the same amount of change from the turn close to the central portion toward the outermost turn. When the winding pitch of the central portion is represented by p, the amount of change is represented by Δp, the total number of turns of the filament is represented by n, and the total number of turns of the two end portions is represented by k, Δp / p Is in the range from 0.015 to 0.1, and k / n is in the range from 0.3 to 0.8.

  The value of k / n is preferably within the range of the following mathematical formula. k / n = 0.72-4.66 (Δp / p) ± 0.12.

  The X-ray tube of the present invention includes an X-ray tube filament having the above-described characteristics.

  According to the present invention, by devising the winding pitch as described above, the temperature distribution in the longitudinal direction of the coiled filament becomes uniform. For example, when the filament is heated to a temperature of about 2500 ° C., the temperature distribution in the longitudinal direction of the filament falls within a range of 50 ° C. or less except for the outermost two turns.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a front view of a filament according to an embodiment of the present invention. The filament 10 is obtained by winding a wire 12 having a wire diameter d in a coil shape with a winding number n (that is, n turns) so as to have an outer diameter D. Lead wires 14 are integrally connected to both ends. In this example, the number of turns n is 20. In the figure, the leftmost turn is referred to as the first turn. Hereinafter, the second turn and the third turn are designated, and the rightmost turn is the twentieth turn. Winding pitch of the first turn is p _1, the winding pitch of the second turn is p _2, the same applies hereinafter. The winding pitch of the most right-hand side of the 20-turn is a p _20. Generally expressing this, the winding pitch of the i-th turn is p _i , i = 1 to n. Hereinafter, the winding pitch is simply abbreviated as pitch.

In the illustrated filament, the pitch from turn 6 to turn 15 has the same value. A portion composed of a plurality of turns having the same pitch is called a central portion, and the pitch is represented by p. That is, p ₆ = p ₇ =... = P ₁₅ = p. From the first turn to the fifth turn, the pitch is smaller than the central pitch. That is, the pitch is denser than the central portion. The same applies from the 16th turn to the 20th turn. Thus, the part where the pitch is smaller than the center part is called an end part. The pitch p ₅ of the fifth turn is smaller by Δp than the pitch p at the center. Further, the pitch p ₄ of the fourth turn is smaller by Δp than the pitch p ₅ . Similarly, the pitch decreases in order until the first turn. That is, at the left end of the figure, the pitch decreases sequentially by Δp from the fifth turn (turn near the center) to the first turn (outermost turn). When this is expressed by a mathematical formula, p−p ₅ = p ₅ −p ₄ = p ₄ −p ₃ = p ₃ −p ₂ = p ₂ −p ₁ = Δp. The same applies to the right end portion shown, a _{p-p 16 = p 16 -p} 17 = p 17 -p 18 = p 18 -p 19 = p 19 -p 20 = Δp.

FIG. 2 is a graph showing a change in pitch in the filament of FIG. The horizontal axis is the turn number, and the vertical axis is the pitch of each turn. In this example, in the central portion from the sixth turn to the fifteenth turn, the pitch p is constant at 0.65 mm (650 μm). The pitch p ₅ of the fifth turn is smaller than the central portion pitch p by Δp = 30 μm, and therefore, p ₅ = 0.62 mm. Hereinafter, similarly, the same change amount Δp is decreased. That is, p ₄ = 0.59 mm, p ₃ = 0.56 mm, p ₂ = 0.53 mm, and p ₁ = 0.50 mm. Similarly, at the right end of the figure, p ₁₆ = 0.62 mm, p ₁₇ = 0.59 mm, p ₁₈ = 0.56 mm, p ₁₉ = 0.53 mm, and p ₂₀ = 0.50 mm.

  At the left end, the number of turns i in which the pitch is changed as compared with the central portion is five. Even at the right end, the number of turns j in which the pitch is changed as compared with the central portion is five. Their total k is 10. Therefore, in the example of this filament, the number of turns included in the center portion is 10, and the total number k of turns (number of turns whose pitch changes) included in the two end portions is 10.

  FIG. 3 is a graph of the temperature distribution of the filament different from FIG. This filament has 22 turns, d = 0.4 mm, D = 3 mm, p = 0.65 mm, Δp = 0.03 mm, i = 5, j = 5 (ie, k = 10). This filament was obtained by actually measuring the temperature distribution in the longitudinal direction of the filament when it was heated to around 2500 ° C. by passing an electric current. The horizontal axis is the turn number, and the vertical axis is the temperature. The temperature at each turn was measured with an optical pyrometer at the apex 16 of each turn as shown in FIG. Since this filament has a dense pitch at the end, the temperature at the center does not become higher than at both ends. Rather, in this example, the temperature at the center is slightly lower. And in the range from the 3rd turn to the 20th turn, the temperature distribution is within the range of 50 ° C. Only the first turn, the second turn, the 21st turn and the 22nd turn are out of the range of 50 ° C.

  Such temperature distribution was calculated by theoretical calculation in addition to the actual measurement values shown in FIG. In the theoretical calculation, the temperature distribution is calculated using the finite element method with the current and thermal radiation as variables, and the values of Δp and k (= i + j) are determined so that the temperature distribution is as uniform as possible. The calculated temperature distribution at that time showed almost the same tendency as the actually measured temperature distribution shown in FIG. Therefore, in the following examination, the values of Δp and k are obtained by theoretical calculation so that the temperature distribution is as uniform as possible.

  FIG. 4 is a list of analysis results. In this list, for filaments with various coil specifications, the pitch variation Δp is used as a parameter so that the temperature distribution in the longitudinal direction of the filament falls within the temperature range of 50 ° C (however, at both ends) (Except for the temperature of each two turns), the optimum value of k was obtained. As coil specifications, there are a wire diameter d, a coil outer diameter D, the number of turns n, and a pitch p at the center. The analysis results are obtained by using the pitch change amount Δp as a parameter and determining how much the value of k is to achieve a good temperature distribution as described above when Δp.

  For example, for a filament with a coil specification of d = 0.2 mm, D = 1.13 mm, n = 20, and p = 0.65 mm, when the pitch of the end of the filament is changed under the condition of Δp = 20 μm, i + j = When k = 8-10, the temperature distribution is within the range of 50 ° C. “Average” on the right side of the column k in FIG. 4 is an average value for the optimum range (for example, 8 to 10) of k. When the optimum value of k is 8 to 10, the pitch is sequentially reduced from the side closer to the center for 4 turns or 5 turns on both sides.

  FIG. 5 is a graph showing the analysis results shown in FIG. The horizontal axis is the pitch change amount Δp, and the vertical axis is the value of the number k of turns at which the pitch changes. Data for all coil specifications are shown in the same graph. This graph shows that the relationship between Δp and k tends to be the same regardless of the coil specifications. When the pitch change amount Δp is increased, the optimum value of k tends to decrease. A straight line 20 passing through the center of the distribution of each data, more specifically, a straight line 20 obtained by the least square method is expressed by the equation “k = 13.7−0.136Δp”. Using this straight line 20, for example, when [Delta] p = 25 [mu] m is selected, it can be seen that the optimum k at which the temperature distribution is most uniform is 10-11.

  Lines 22 and 24 are obtained by adding 2 to the k value of the straight line 20 and subtracting 2 from it. Each data is almost within the range of the straight lines 22 and 24. Therefore, if Δp and k are selected so as to satisfy the equation “k = 13.7−0.136Δp ± 2”, a filament having a uniform temperature distribution can be obtained.

  FIG. 6 is a graph showing Δp and k normalized after p and n. The horizontal axis is obtained by dividing the pitch change Δp by the central pitch p, and the vertical axis is obtained by dividing the number k of turns in which the pitch changes by the total number n. By normalizing in this way, a relationship independent of the number of turns n and the pitch p, that is, a more general relationship is obtained. Each data has Δp / p in the range of 0.015 to 0.1 and k / n in the range of 0.3 to 0.8. For data within this range, a filament was obtained that had a temperature distribution around 2500 ° C. within 50 ° C. Therefore, it is preferable that Δp / p and k / n be within this range first. .

  Then, when a straight line 26 passing through the center of the distribution of each data is obtained, the straight line 26 becomes a mathematical expression “(k / n) = 0.72−4.66 (Δp / p)”. When the straight lines 28 and 30 of plus 0.12 and minus 0.12 are drawn above and below the straight line 26, each data is almost within the range of the straight lines 28 and 30. Within this range, the equation is “(k / n) = 0.72−4.66 (Δp / p) ± 0.12”. If Δp / p and k / n are selected so as to satisfy this mathematical expression, a filament having a uniform temperature distribution can be obtained.

  FIG. 7 is a perspective view of an essential part of an X-ray tube including a filament that has been devised as described above. When a current is passed through the filament 10 and a high voltage is applied between the filament 10 and the rotating cathode 32, an electron beam 34 is generated from the filament 10. The electron beam 34 is applied to the outer peripheral surface of the rotating counter cathode 32, and an X-ray beam is generated therefrom. For example, the point focus X-ray beam 36 or the line focus X-ray beam 38 can be extracted.

  The filament of the present invention can be applied not only to the above-described rotating cathode X-ray tube but also to a fixed target (stationary target) X-ray tube.

It is a front view of the filament of one Example of this invention. It is the graph which illustrated the change of the pitch in the filament of FIG. It is a graph of the temperature distribution of the longitudinal direction of a filament. It is a list of analysis results. It is a graph of an analysis result. It is another graph of an analysis result. It is a perspective view of the principal part of the X-ray tube provided with the filament of this invention.

Explanation of symbols

10 Filament 12 Wire 14 Lead wire 16 Vertex 32 Rotating anti-cathode 34 Electron beam 36, 38 X-ray beam

Claims (3)

In coiled filament for X-ray tube,
A central portion having a plurality of turns with the same winding pitch, and two ends on both sides of the central portion and having a plurality of turns with a winding pitch smaller than the winding pitch of the central portion;
The winding pitch of the plurality of turns at the end portion decreases sequentially by the same change amount from the turn near the center to the outermost turn,
When the winding pitch of the central part is represented by p, the amount of change is represented by Δp, the total number of turns of the filament is represented by n, and the total number of turns of the two end parts is represented by k, Δp / p is 0. A filament for an X-ray tube, characterized in that it is in the range of .015 to 0.1 and k / n is in the range of 0.3 to 0.8. The filament for X-ray tubes according to claim 1, wherein the value of k / n is within the range of the following formula.
k / n = 0.72-4.66 (Δp / p) ± 0.12   An X-ray tube comprising the filament for an X-ray tube according to claim 1 or 2.

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