DE3528200A1 - X-ray tube having a rotating anode - Google Patents

Abstract

For expansion compensation during the mounting of a rotating anode of an X-ray tube on the end of an insulating shaft of the drive rotor, the anode (12) and the shaft (15) (which cannot have the same linear coefficient of expansion) are installed by means of a component such as a screw (29) whose useful length is calculated as a function of all the expansion coefficients of the assembled materials such that the expansion difference between the anode and the shaft is compensated for, and a constant stress is ensured at all the temperatures which occur. …<??>Used for medical X-ray technology. …<IMAGE>…

Description

PRINZ, LEfSER: BUNKE '- & PARTNER

Patent Attorneys "· European" PaVeYit Attorneys OC 00 OD η

Emsbergerstrasse 19 8000 Munich 60

-3-

August 5 T985

THOMSON - CGR

13, Square Max Hymans

75015 Paris / France

Our reference: T 3818

X-ray tube with rotating anode

The invention relates to an X-ray tube with a rotating anode, in particular the fastening of the disk forming the anode on the axis of the rotor that makes it rotate.

The invention is preferred to an X-ray tube with magnetic Suspension applicable in which the rotor is electrically powered by the high voltage applied to the anode should be isolated.

A known X-ray tube consists of an electron generator forming the cathode, which opposite a Target is arranged, which forms the anode and is connected to a high voltage source. This disc-shaped Anode is arranged on the axis of the rotor of a motor to be rotated. Because of the high in operation occurring power and the small surface of the impact zone of the electrons on the anode target.

HD / bl

equips the rotational movement of the anode an increase in performance by the electron bombardment against a relative cold matter takes place. Such X-ray tubes have recently been through the use of rotors with magnetic Suspension improved. The rotor no longer rests on ball bearings during operation. When using a Such a suspension, it is very advantageous to electrically isolate the anode disk from the rotor. This will avoided that the magnetic bearings and the various

jO which electronic systems for control and regulation, which ensure the magnetic suspension must be put on high voltage. Obviously a simple one The solution is to manufacture the rotor axis from a highly electrically insulating material. at In such an arrangement, only the disk is placed on a positive high voltage, and the current is derived from the anode via any suitable device known per se, so that the rotor is at a potential remains, which is close to the ground potential.

The manufacture of such a rotor with an isolating axis, however, encounters considerable difficulties, which are based in particular on the high temperature differences that occur and which have so far not been satisfactory could be solved.

This is because the anode disk and the rotor axis can have temperatures of the order of magnitude of 1,500 ^° C. during operation

achieve gO. This will allow you to choose from among those available Materials considerably restricted, because the material of the axle must be both electrically insulating and heat-resistant be. The anode disk itself must consist of a heat-resistant material that has a high degree of

Q5 has voltage number in the periodic table. Due to the restricted Choice of material for both the anode disk and the axis, it is practically impossible to

• ο-Ι aren expansion coefficients of the materials for the anode disk and axis to adapt to each other. The difference in expansion between the axle and the anode disk in normal Operation of the X-ray tube is too great to have good mechanical strength at all temperatures that occur to ensure.

The invention is based on the object of solving this problem.

The basic idea of the invention consists in the expansion coefficient completely disregarded for the choice of material for the axle and the anode disk (in particular the best insulating and heat-resistant materials are used for the common axis, for example a ceramic or aluminum dioxide), and during assembly to provide an element which has a given expansion coefficient and its dimensions are designed so that the various coefficients of linear expansion of the assembled materials must be taken into account.

The invention thus creates an x-ray tube, one with a rotor axis through a suspension system having connected rotating anode and is characterized in that of the assembled components at least some are formed from materials having different coefficients of linear expansion, wherein at least one element of the suspension system has a useful length which is designed such that the axial dimensions of the suspension system essentially the axial dimensions of the anode parts and the Compensate axis which are under the effect of this suspension system.

The suspension system usually works with axial Restraint; the compensation element can then at the

Arrangement according to the invention the most varied of shapes exhibit. For example, a strut or strut system (or more of them) can be used with the suspension system.

According to a preferred embodiment, the element of predetermined useful length consists of the screw a mechanical unit of screw and nut, which is mounted between the anode and an inner shoulder of the axle is, the position of the inner shoulder relative to the anode determines the said useful length of the screw.

It should be noted that the invention is not limited to use in an x-ray tube with a magnetic suspension is (although it is the preferred area of application), but can be applied to any X-ray tube where the anode is to be electrically isolated from its propulsion system.

Further features and advantages of the invention emerge from the following description of exemplary embodiments and from the drawing referred to. In the drawing show:

1 shows a schematic partial view of an X-ray tube with magnetic suspension;

2 shows a partial section of such an X-ray tube, the fastening system according to the invention between the anode disk and the insulating axis

is shown;

FIG. 3 is a view similar to FIG. 2, but showing a variant of the fastening system; FIG.

FIG. 4 is a view similar to FIG. 2, but showing a further variant of the fastening system; FIG. and

FIG. 5 is a view analogous to FIG. 4, but which shows a further variant of the fastening system.

The X-ray tube 11 shown in the drawing with a rotating anode 12 operates with a magnetic suspension. The rotating anode 12 is disk-shaped and is bombarded on its surface 14 with an electron beam emanating from the cathode (not shown). The anode is attached to the end of an axis 15 of a rotor 16 equipped with magnetic bearings. The rotating anode 12, the axis 15 and the rotor 16 are housed inside a shell 18, for example made of glass. The positive pole of a high voltage is applied to the anode via the device shown. The rotor is driven via a stator 19 which is located on the outside of the shell 18. The magnetic suspension takes place via two pairs of poles 20 and two pairs of poles 21, which are arranged on the outside of the shell 18 in the vicinity of the two axial ends of the stator. In Fig. 1, a pair of poles 20 and another pair of poles 21 are i- the plane of the figure shown ^n; the other two pole pairs are each rotated by 90 ° and are not shown in the drawing so as not to overload them. The rotor is hollow and provided with safety bearings 24, which are mounted on a stationary axis 25 connected to the shell 18 inside the rotor so that it can be supported on the stationary axis when it is not under the action of the pole pairs 20 and 21 is kept in equilibrium.

According to one feature of the invention, there is axis 15 the rotor made of a heat-resistant and insulating material, for example aluminum dioxide or ceramic, and therefore has a linear expansion coefficient, which is considerably different from that of the anode disk 12, which is made of graphite.

As Figures 2 and 3 show, the anode 12 is one of a kind

• σι axial bore 26 pierced, and the axis 15 is with a bore 28 provided "which opens out at the free end of the axis and through a diameter graduation with a straight shoulder 27 is provided. An assembly of screw 29 and nut 29a is between surface 14 of the Anode disk and the shoulder 27 arranged. This assembly of screw and nut forms an assembly system with axial restraint, as mentioned above. An axial bore 26 in the anode disk corresponds to the final diameter the axis 15, so that this anode disk rests against a straight shoulder 30 of the axis.

According to the invention, the material from which the screw 29 is made and the position of the shoulder 27 (which their useful length determined) chosen such that the axial extent of the mounting system the axial extent the anode parts and the axle parts, which are under the action of this mounting system, essentially compensated.

In the embodiment shown, the screw fulfills even the function of the compensation system mentioned the mounting arrangement. The determination of the usable length L of the screw (i.e. the distance between the shoulder 27 and the surface 14 of the anode disk) happens as follows:

Let L ₁ be the length to be taken into account for the axial expansion of the anode; in the example of Figures 1 and 2, L _{1 is} just the thickness of the anode disk near the axis;

L- be that for the axial extension of the end part of the Axis 15 length to be considered; in the example shown in FIGS. 1 and 2, this is the distance between shoulders 27 and 30;

Let a ₁ , a "and a ₃ be the linear expansion coefficients of the materials, from which the anode disk 12 or the axis

15 or the screw 29 exist. If it is assumed that in the operation of the X-ray tube these three elements always have the same temperature increase At compared to the ambient temperature experience, the following condition must be met so that the expansions between the holding Parts (the axle and the assembly of screw and nut) and the held part (anode washer) the same are:

a.L..At

Since L = L. + L "

^a 1 " ^a 2
one obtains: L = L ₁

^{1 a} 3 " ^a 2

Thus, if L is chosen in the manner indicated above, the cold state is directed towards the anode disk the clamping force exerted on the longitudinal axis is maintained over the entire operating temperature range, see above that the anode disk remains properly attached to the insulating shaft.

In the example shown in Fig. 1, for which a .. = 5.5 · 10 ~ ⁶ m / ° C (graphite) and a ₂ = 7 · 10 ~ ⁶ m / ° C (aluminum dioxide), the screw 29 is made selected a material whose temperature coefficient lies between these two values, namely TZM with a., = 6 · 10 m / ° C). The ratio LZL ₁ is therefore 1.5. The useful length of the screw 29 is therefore greater than the thickness of the anode disk 12 (typically 30 mm for a 20 mm thickness of the anode disk).

The embodiment shown in Fig. 2 corresponds to a combination of materials, where the expansion coefficient of the screw is greater than the expansion coefficient of the other two materials. This is particular the case when the axis 15 is made of ceramic

* '/ Ο ι (a ₂ = 3 · 10 m / ° C), while the coefficients a and a are unchanged compared to the previously described embodiment. The corresponding calculation results in:

^a 1 " ^a ?

^{L = L} 1

ι a ₂ a ₃

The ratio L / L results for the figures given above. = 0.83. The usable length of the screw is therefore less

than the thickness of the anode disk.
10

In the two embodiments described above, the radial expansion difference is calculated by the Difference values between the diameter of the hole 28

and diameter at the end of the axis 15 compensated. 15th

In the embodiments according to FIGS. 5 and 6, compensation is provided both in the radial direction and in Reached longitudinal direction. To this end, the axial opening of the anode disk 12a and the end part of the axle are

15a with frustoconical, cooperating with one another Contact surfaces 35, 36 are provided. The other elements of the arrangement are as in those previously described and therefore denoted by the same reference numerals as in Figures 1 and 2. It can be shown that the for the

axial expansion of the anode disk expansion to be taken into account is the distance between the apex of a cone 38, in which the frustoconical contact surfaces 35 and 3 6 are inscribed, and the surface 14 of the anode disk is on which the nut 29a rests.

In the same way, the length to be taken into account for the axial extension of the axis is the distance between the apex of the cone 38 and the shoulder 27.

If the expansion coefficient of the screw is less than or is greater than the expansion coefficients of the anode disk and the axis, the embodiment is obtained

according to Figure 4, in which the apex of the cone 38 on

^a 1 ~ ^a 2

the outside of the anode disk, with L = L ₁

1 a - a

In the opposite case, the embodiment according to FIG. 5 is obtained, in which the apex of the cone 38 opens the inside of the anode, with:

L = L.

^a 1 - ^a 2

In all of the cases described above, the effective length of the clamping screw 29 is determined using the following relationship:

^a 3 " ^a 2

Claims (1)

PRINZ, LEISER, BbNKE & PARTNER - Patent Attorneys European Patent Attorneys ^ R 9 Q 9 Γ) Π V Ernsbergerstraße 19 8000 Munich 60 \ 5th August 1985 THOMSON - CGR 13, Square Max Hymans 75015 Paris / France Our reference: T 3818 Claims X-ray tube with a rotating anode (12), which with
the axis (15) of a rotor (16) is connected by an assembly system (29, 29a), characterized in that at least certain of the assembled components are made of materials that are different linear
Have expansion coefficients, and that at least
an element (29) of the assembly system has a useful length which is determined such that the axial expansions of the assembly system, the axial expansions of the anode and axle parts, which under the action of this
Mounting system stand, essentially compensate. 2. X-ray tube according to claim 1, characterized in that said element of a predetermined useful length Screw (29) in an assembly consisting of screw and nut, which is between the anode (12) and a Inner shoulder (27) of the axle is mounted, the position of the inner shoulder relative to the anode being said useful length certainly. HD / bl 3. X-ray tube according to claim 2, characterized in that that the specified usable length at least approximately fulfills the following relationship: ^a 1 " ^a 2 L = L ₁ , where L is the specified usable length, 1 a ₃ - a ₂ L. is a length which is necessary for the axial extension of the Anode is to be considered, and a .., a ~, a_. the respective linear expansion coefficients of the materials, from which the anode (12), the axis (15) and the screw (29) are formed. 4. X-ray tube according to claim 3, characterized in that said rotating anode of an axial cylindrical Hole is perforated, which corresponds to the diameter at the end of the axis, and that the rotating anode is in contact is arranged on a straight shoulder (30) of the axle, said length to be taken into account being the thickness the anode (12) is near said axis (15). 20th 5. X-ray tube according to claim 3, characterized in that the anode has an axial opening and that the axial opening and the end part of the axis are provided with frustoconical contact surfaces (35, 36) which cooperate with each other, the length to be taken into account being the distance between the apex of a cone (38), in which the frustoconical contact surfaces are inscribed are, and the surface (14) of the anode against which a clamping device is supported. 30th 6. X-ray tube according to one of the preceding claims, characterized in that the axis consists of ceramic. 7. X-ray tube according to one of claims 1 to 6, characterized in that the axis consists of aluminum dioxide.