US2222549A - X-ray tube - Google Patents

Description

Nov. 19, 1940. A, VERH DEFF 2,222,549

X-RAY TUBE Filed Dec. 17, 1938 2 Sheets-Sheet 1 nun lNVE/VTOR AOR/ANL/ VERHOZTF Nov. 19, 1940.

A. VERHOEFF X-RAY TUBE Filed Dec. 17, 1938 2 Sheets-Sheet 2 Patented Nov. 19 1940 UNITED STATES PATENT OFFICES X-RAY TUBE Conn, as trustee Application December 17, 1938, Serial No.'246,451 In Germany December 22, 1937 11 Claims.

My invention relates to 'X-ray tubes having a rotary anode and particularly to tubes of this type which are enclosed within a protective hous- In practice the rotation of the anode of an X- ray tube is usually effected by means of a ro- *ating magnetic field set up by a stationary, and preferably three-phase, stator which surrounds the tube. Although this method is very simple and satisfactory it is difiicult to insulate the stator, which must be located close to the tube, against a high voltage with respect to the anode. Furthermore the stator increases the diameter of the protective housing of the tube, and if it is desired to control the speed of rotation of the anode a frequency changer must be used. In addition, if three-phase current is not available, it is necessary to provide phase-displacement means for starting the rotation of the anode.

The object of my invention is to overcome the above difiiculties and for this purpose I rotate the anode by means of a driving rotor which is located outside the Vacuum space of the X-ray tube and which may be either an electro-magnet 25 or a permanent magnet. Alternatively the rotatable anode may carry a permanent magnet cooperating with a driving rotor consisting of a body of ferromagnetic material, which body may be provided with poles. I drive this rotor from an electric motor, and effect this drivethrough a shaft of insulating material so that the rotor can have the potential of the anode.

The motor is located at one end of the tube so that it does not cause any increase in the diameter of the protective housing, and may be of a variable speed type, for instance a single-phase commutator motor.

According to one embodiment of the invention, I locate the driving rotor within a glass or me- 40 .tallic reentrant portion of the tube envelope, and provide the anode with a cylindrical extension which extends into the annular space formed between this reentrant portion and the outer wall of the tube envelope. This cylindrical extension forms the point of application of the driving torque and is provided with a cylinder-of magnetic material of high permeability or with a 55; mg medium, such as air, or 'a' stirrerfor a cooling' i means surrounds the tube, and as a result the liquid, such as oil, is provided Within the protective housing, I prefer to connect the driving rotor to the means for driving the fan or stirrer. This gives a simple construction and at the same time an increase in the speed of rotation of the anode will be accompanied by an increase in the cooling capacity, which is very desirable.

The driving rotor may also serve to circulate a cooling fluid and for this purpose may be formed as an impeller of a fan or as a rotor of a pump, or an impeller or pump rotor can be arranged adjacent the driving rotor so that they are also at high potential. The driving shaft may be made hollow so that it can serve as a passageway for the cooling fluid, and under some conditions this improves the cooling of parts of the tube in the vicinity of the anode.

In order that the invention may be clearly understood and readily carried into effect, I shall describe the same in more detail with reference to the accompanying drawings in which:

Figure l is a sectionized view of a portion of an X-ray'tube embodying the invention,

Fig. 2 is a sectional View along line II-II of Figure 1,

Fig.3 is a sectionized view of a portion of an X-ray tube according to another embodiment-of the invention, and

Fig. 4 is a plan view of the driving rotor of Fig. 3.

Fig. 5 is a plan view of a driving rotor in a modified form.

Fig. 6 shows a modification of the construction represented by Fig. 3. I

The X-ray tube partly shown in Figure 1 has an envelope comprising acentral metal cylinder 3, for instance of chrome iron, to the ends of which are hermetically sealed two vitreous mem-- bers l and 2. Member I has a reentrant portion 1 whose lower end is hermetically sealed to a cup-shaped member 6 of metal, for instance of chrome iron. Supported by member 6 is ashaft 5 upon which is rotatably mounted acylindrical anode 4 having an annular portion 8 extending into the annular space formed by vitreous member l and carrying an iron cylinder 9. Instead of being solid, the cylinder 9 may be made up of axially-extending sections each forming a separate magnetisable body. A cylindrical body 43 is fixedly secured to member 6 and has a large surface closely spaced from the inner surface ofanode 4 so as to facilitate the removal of heat from the anode.

Metal cylinder 3 is provided with a Window 36 for the exit ofthe X-rays, and is surrounded,

except at window 36, with alead sheath 29. Acathode 35 located within a concentrating device 34 is shown near the target surface ofanode 4.

The X-ray tube is enclosed within a protective housing I! of metal, or of insulating material having a metal coating, provided with a filter holder 31, and having a cup-shaped end portion [6 provided with several apertures 33. Supported in a suitable manner from housing I! is a moulded body 23 of insulating material which serves to prevent flash-over between the parts of the tube which are at high potential and the housing I! which is usually grounded. Body 23 surrounds the vitreous member I with an intermediate annular space !0 and is provided with a central bore in which is moulded a metal tube 22 provided at its lower end with a plurality of apertures 32.

Supported from an apertured portion 50 of body 23 is a motor I5, preferably of the variable speed type, having a shaft l9 carrying a fan 21. A rod 26 of insulating material is secured at one end to shaft l9. During operation the housing and the windings of motor l5 have substantially the potential of housing 11.

Within the space formed by reentrant portion 1 and aligned with ring 9 is a driving rotor II] in the form of a permanent magnet which, as shown in Figure 2, has four poles l l to [4 of which poles II and 12 may be north poles and poles l3 and I4 may be south poles, as indicated. Rotor I0 is fixedly mounted on a metal shaft [8 which shaft has one end supported in abearing 5| secured to member 6, and its other end extending through a bearing 2| secured to tube 22, and connected to the lower end ofinsulating rod 20. Thus, because of its metallic connection to member 6, rotor I0 is at a very high potential with respect to the housing I! and the motor l5. However, the use of theinsulating rod 20 completely insulates the motor and housing against this high voltage.

As rotor I0 and portion 8 are at the same potential, the intervening part of glass portion 1 will not be electrostatically loaded, and consequently the spacing between the peripheral surface of rotor l0 and the inner surface of portion 8 can be as small as is possible from a mechanical standpoint. In view of this small spacing there will be very little slip between rotor l0 andanode 4, and the anode can be rapidly accelerated to the desired rotational velocity.

Tube 22, to which rotor 10 and thusanode 4 is electrically connected, is engaged by a contact rod 26 forming part of a terminal piece 24 of insulating material secured to housing I! by a nut 52. An insulated cable 25 for the supply of anode current is secured to terminal piece 24 with its conductor connected to rod 26.

To eliminate the passage of current throughbearing 5|, member 6 may be made longer so as to extend between rotor l0 and portion 8 and form a direct metallic connection with tube 22. Such a construction is illustrated by Figure 3.

During operation the cooling air travels a course indicated by the arrows. More particularly the air passes from the cathode end of the tube through the annular passageway formed betweencylinder 29 and thecentral portion 28 of housing H. The air then passes upwardly through the space 10, downwardly through the space formed between the portion 1 and an extendingportion 3| of member 23, through apertures 32, through the annular passageway formed between tube 22 andshaft 20, and out of the tube through apertures 33. With such a circulation of air the vitreous member I as well as the metal to glass seals of the tube envelope are effectively cooled.

Figure 3 is a sectionized view of a portion of an X-ray tube which, in other respects, is similar to that shown in Figure 1. In Figure 3 the reentrant part of member I terminates at apoint 53 at which it is hermetically fused to aring 39 of chrome iron. Secured to the lower end ofring 39, for instance by solder, is a cup-shaped metal member 54, hereinafter more fully described, to which is fixedly secured the metal member 43 of Figure 1.

Mounted in member 43 is a bearing 42 carrying ashaft 55 to which is secured ananode 56 similar to theanode 4 of Figure 1 and having an extending portion 51 surrounding a portion ofmember 54 and provided with an iron ring 9.

A moulded member 58 of insulating material, whose upper portion (not shown) is similar to that of member 23 of Figure 1, surrounds the tube envelope with an intermediate space H. Moulded within the central part of member 58 is a metal tube 59 having a flared end portion 40 extending into the space enclosed within the cup-shaped member 54.

Tube 59 has an inner coating 12 of insulating material to prevent flashing-over from the inner surface of the metal tube through the space between this tube andshaft 60 to grounded parts at the end of the housing.

Within the bore of tube 59 is ashaft 60 which is similar torod 20 of Figure 1 and is driven in a similar manner by the motor l5 of this figure. F'ixedly secured to the lower end ofrod 60 is a coupling 6| connected to a bushing 64 secured to adriving rotor 62.Rotor 62 rotates on a ball bearing 38 mounted on ashaft 63 carried bymember 54. As shown more clearly in Figure 4,rotor 62 is similar to rotor [0 of Figure 1 except that it has a grooved inner surface which forms with the bushing 64, four openings 44.

Ametal spring 4| has one end secured tomember 54 and its other end bearing the flared end of tube 59 to form a direct electrical connection therebetween. V

Theanode 56 is rotated in the same manner as in Figure 1, by the rotating magnetic field produced .by rotating thedriving rotor 62. I have found that eddy currents produced inmetal member 54, through which the magnetic lines of force pass, greatly reduce the speed of rotation of the anode, and to avoid this, I make this member of a non-magnetic material which has a high resistivity, for example more than 0.4 ohm per cubic centimeter cm. length and 0.01 cm. section). By using such metals the reaction caused by the eddy currents is extremely small, because these currents will be much smaller than in the case of a metal of high conductivity. As a result the anode will be readily carried along. I have found that particularly good results are obtained by using constantan, which is an alloy consisting of equal parts of nickel and copper and has a specific resistivity of about 0.5, but other non-magnetic alloys of high resistivity can be used.

During operation the cooling air is circulated by means of the fan 21 of Figure 1 and follows a course which is somewhat similar to that described in connectionwith Figure 1. However, in Figure 3 the air flows downwardly around the periphery ofrotor 62, along the bottom ofmember 54, and upwardly through the openings 44 to the annular space formed between tube 59 androd 60. Due to the passage of air along the bottom of member '54 a very effective cooling of the anode is obtained.

Instead of using thefan 21 of Figure 1, therotor 62 can be formed as an impeller as shown in Fig. or a fan can be mounted above this.

rotor on member 6!. With the rotor shown in Fig. 5 the magnet poles 14 form the Wings of a fan and are so positioned as to draw the air from the rear side to the side from which the rotor is shown, which is the side facing the bottom ofmember 5 1 of Fig. 3. Again the spokes 15 are disposed with a reversed inclination, so that theyform a blower propelling the air from the space between the rotor andmember 54 to the space enclosed between shaft 611 and tube 59.

Fig. 6 shows a portion of the arrangement of Fig. 3 with a modified construction of the shaft. In this construction the shaft 16 is hollow.

Through holes 73 provided in the thickened end portion of the shaft the air is permitted to penetrate into the duct Tl by which it is be sucked away. Because the space between the shaft and the tube 59 does no longer serve as an air conduit, it may be narrower than in the structure of Fig. 3. The insulating coating of the inner side of tube 59 is omitted, as there is no danger for flashingover across the long narrow gap between the metal tube 59 and the insulating shaft 16.

While I have described my invention in connection with specific examples and constructions, I do not wish to be limited thereto but desire the appended claims to be construed as broadly as'is permissible in What I claim is:

1. An X-ray apparatus comprising an X-ray tube having a cathode and a rotatable anode, a protective metallic housing enclosing said tube, and means for magnetically rotating said anode including a driving rotor, a motor supported from said housing, and a shaft of insulating material connected between said motor and rotor, said rotor being in magnetic relationship with said anode.

2. An X-ray apparatus comprising a protective housing, and an X-ray tube within saidhousing and comprising an envelope having a reentrant portion forming an annular space with the envelope, a cathode, and a rotatable anode supported from the reentrant portion and having a portion extending into said annular space, and means to magnetically rotate said anode including a driving rotor within said reentrant portion, said rotor being in magnetic relationship with the extending portion of said anode.

3. An X-ray apparatus comprising an X-ray tube having a cathode and a rotatable anode, and

' protective housing enclosing said tube, a fan, a

motor for driving said fan and supported from said housing, and means to magnetically rotate said anode including a driving rotor in magnetic relationship with said anode, and a shaft of insulating material connecting said rotor to said motor.

4. An X-ray apparatus comprising an X-ray tube having a cathode and a rotatable anode, a,

view of the prior art.

for circulating a fluid around the X-ray tube including a member arranged adjacent said rotor.

5. An X-ray apparatus comprising an X-ray tube having a cathode and a rotatable anode, a protective housing enclosing said tube, and means for rotating said anode and for circulating a fluid around said tube including a motor supported from said housing, a driving rotor, and a shaft of insulating material connecting said rotor and motor; said rotor being in magnetic relationship with said anode and being shaped as an impeller.

6. An X-ray apparatus comprising an X-ray tube having a cathode and a rotatable anode, a protective housing enclosing said tube, and means for rotating said anode and for circulating a fluid around said tube including a motor supported from said housing, a driving rotor, and a hollow shaft of insulating material connecting said rotor and motor, said rotor being in magnetic relationship with said anode and being shaped as an impeller.

7. An X-ray apparatus comprising an X-ray tube having a cathode and a rotatable anode, a protective metallic housing enclosing said tube,

tube, and means to rotate said anode including a driving rotor in magnetic relationship with said anode, a motor, and a shaft of insulating material connecting said motor and rotor, said envelope having a non-magnetic metal portion bf a resistivity at least .04 ohm per cubic centimeter extending between said rotor and a portion of said anode.

9. .AnX-ray apparatus comprising an X-ray tube having an envelope, a cathode and a'rotatable anode, a protective housing enclosing said tube, and means to rotate said anode also enclosed by said housing, said means including an electric motor, a rotor and a shaft of insulating material connecting said motor and rotor, said rotor comprising radially extending magnet poles andsaid anode comprising a ring of ferromagnetic material, surrounding said rotor, a reentrant portion of said envelope extending between said rotor and ring, said shaft projecting from said reentrant portion.

10. An X-ray tube comprising an evacuated envelope having a reentrant portion, a cathode within said envelope, a rotatable anode within said envelope and at one end thereof, and means to magnetically rotate said anode including a driving rotor in magnetic relationship with the anode, and a driving device connected to said rotor, said rotor being located within said reentrant portion and outside the evacuated space of the tube.

11. An X-ray tube comprising an evacuated envelope having a reentrant portion, a cathode within said envelope, a rotatable anode near said reentrant portion, and means to magnetically rotate said anode, said means including a driving rotor in magnetic relation with the anode, and a motor connected to said rotor, said rotor being located within said reentrant portion and outside the evacuated space of the tube.

1 ADRIANUS VERI-IOEFF.

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