US2130020A - Cathode filament control for x-ray tubes - Google Patents

Description

sept. 13, 1938.

H. B, MCEUEN cATHoDE FILAMET coNiBoLFoR X-RAY TUBES '2 sheets-sheet 1 Filed March 13, 1934 gmc/whoa',

Sept. 13, 1938.

l H. B. MCEUEN CATHODE FILAMENT CONTROL FOR X-RAY TBES Filed Maron 13, 1954 2 sheetssheet 2 45.y stem. forward and backward with adjustment of the 45 Patented Sept. 13, 1938 CATHODE FILAMENT CONTROL FOR X-RAY TUBES Harry B. Mannen, Jacksonville, F1a.

Application March 13, 1934, Serial No. 715,340

s claims. (o1. 25o- 35) This invention is directed to an improvement Serial Number 702,989, and while such construcin X-ray apparatus, and particularly to the cathtion is preferable, 'or at least desirable, it is to ode thereof to provide for focusing and concenbe understood that the details hereinafter detration of the cathode-filament stream relative to scribed are applicable to any construction of tube the anode. or of cathode stem. 5"

It is well understood that the input energy is To facilitate an understanding of the present limited by the heat of the anode in the predeterinvention, the X-ray tube may be briefly stated mined focal area, and that provision has been toinclude atube or casing I,in whichisarrangeda heretofore made for permissible increase of such cathode stem and assembly 2, and an anode stem j energy by mechanical cooling of the anode. While 3. The tube proper vis made in sections, assembled 10- such cooling is of material benefit in the desired in a manner to permit the interior of the tube direction, it obviously does not and cannot perto be subjected to the necessary vacuum, and the mit the me of the ultimate amount of energy percathode stem, with which the present invention missible for a given focal area of the anode. is more particularly concerned, is formed adjaf I5 If, in addition to a proper cooling of the anode, cent the filament or anode end with an insulatl5 the cathode stream is focused for focal area and ing and seal-off section 4, preferably of glass, as at the same time distributed equally over such in Fig. 1. area, to avoid undue heat at any one part of In connection with the details of the present such focal area, the input energy may be ininvention, the cathode assembly includes a cath- 2o creased toward the permissible maximum without ode stream distributing cup 5, having a wall 6, 20 liability of objectionable heat effects on the anode. of any desired or appropriate outline, such wall The primary object of the present invention is, being shown as of square outline in Fig. 2. This therefore, the provision of means whereby the wall is arranged substantially parallel to the cathode stream may be controlled mechanically axis of the stem, and is connected to a rear Wall and selectively for focusing and concentration or l, substantially at right angles to the stem axis. 25 distribution. The rear wall "l is provided with a rearwardly- A further object is the provision of the adextending sleeve B, which slidably fits on and justing means for control and operation at any is guided by a conforming extension 9 projecttime without in any way affecting or interfering ing forwardly from the insulating and seal-off 3o, with the vacuum condition of the tube. section 4. The distributing cup is thus mounted 3o A further object is the provision of adjusting for sliding movement longitudinally of the stem, means arranged wholly within the tube and norand while the type of mounting described is demally locked against operation, together with sirable, it will be ,understood that any convenmagnetic means arranged wholly outside of the tional or preferred Slidingly-gllided and Supporttube and selectively operable to withdraw the ing mounting may be used. 35 lock of and operate the adjusting means. Arranged within the cup 5 is a cathode com- The invention is illustrated in the accompanyprising a series of filament cups I0, one for each ing drawings, in which: filament. The lament cups are formed by par- Fig. l is a broken longitudinal section of the allel flat sections II, spaced apart and connected cathode tube, illustrating particularly the adjustat their rear ends, as at I2, all as shown in Figs. 40

ing means for the laments. 2 and 3. These cups are connected to high po- Fig. 2 is a face View of the cathode. Y l tential bar IIbut are not connected electrically Fig. 3 is a section on the line 3--3 of Fig. 2. to either of the filament bars I8 or I9, but sup- Fig. 4 is a longitudinal section of the cathode port these bars on insulators and carry Vthem Fig. 5 is a broken elevation showing a modicafilament cups. The auxiliary cup-s are movable tion. as a unit within the main cup and are sup- Fig. 6 is a diagrammatic view showing the relaported forv such movement and to avoid undue tion of the improved cathode and the anode to friction by rollers or like elements I3, arranged illustrate the control of the cathode stream. between the distributing and auxiliary cups. 50

Fig. A7 is a detail View showing adjustment IThe filament cups have a rearwardly-extending nder. bar-like member I4, which passes through the The X-ray tube illustrated is of the general rear wall 'I of themain cup and is xed at `its construction described and claimed in my corear end in an insulating disk I5, slidable in an 55,v pending application filed December 18, 1933, insulating sleeve I6, connected to the sleeve 8 55 of the main cup. A high potential rod extends transversely of and across all auxiliary cups ID, being arranged near the rear of such cups. Similar filament rods I3 and I9 are carried by the lament cups near the upper and lower ends thereof, the rods I8 and I9 being directly supported in insulators I8' carried by the cups. 'I'he high potential lead 20 leads from the rear end of the stem to and through the seal-off section 4, thence through and fixed in disk I5, then through and fixed in bar I4, and is electrically connected to the high potential rod I1. The filament leads 2I and 22 extend in parallel relation to the high potential lead, being secured in the disk I5, and are connected to the rods I8 and I9. In the preferred form all leads are fixed or embedded in the seal-olf section 4. in the disk I5, .and preferably pass through insulating bars I5', to prevent possible short circuit between the leads. The leads throughout an appropriate portion of their lengths are, in the preferred form, of sinuous or convolute form, as at 20 in Fig. 1, to permit longitudinal adjustment of such leads without interfering with current flow. It will be noted that just beyond the sinuous formation toward the filament cups, all leads .are fixed or embedded in the insulator disk I5, and that after passing through this disk the high potential lead 20 terminates at rod I1, While the filament leads 2I and 22 terminate at rods I8 and I9, respectively.

The rods I1, I8, and I9 carry the laments 23, there being one such filament in each filament cup, as shown in Fig. 2. The axial length of the wall 6 of the distributing cup is greater than the similar dimension of the lament cups, and it will be obvious that the spread of the cathode stream may be varied by the axial relation of the distributing and filament cups. also, the adjustment of the filament cups relative to the anode will serve a focusing function. If, therefore, means are provided by which movement of the distributing and filament cups can be selectively controlled, the focusing and also the spread or concentration of the cathode stream can be governed. It must be remembered, however, that the cath-ode stream is in a vacuum, which must not be disturbed, and also, to be commercially effective, the selective adjustments must be available at all times. This provision forms one of the essential features of the present invention.

To provide for the selective adjustment of the filament cups for focusing, the bar member I4 is formed with rack-teeth 24, and supported in bearings 25, carried by the main cup 5, is a shaft 26, on which is fixed a pinion 21 for cooperation with such rack. The shaft is either of insulating material, or is made in sections, connected by an insulating sleeve. The lower end of the shaft terminates adjacent the wall of the tube I.

It is desirable that means be provided for locking the shaft against rotation when not in use, for which purpose the lower bearing 25 is formed on its lower surface with teeth 29, and the shaft below the bearing is provided With a disk 3D having similar teeth. 'I'he shaft is mounted for limited vertical movement, and on the side above the bearing is provided with a fixed collar 3I, between which and the bearing is a spring 32. The shaft, when free of other inuence, will be moved by the spring 32 to interiit with the teeth on the disk and the teeth 29, thus holding the shaft against rotation.

The sleeve 8 or equivalent projection from the Obviously,v

distributing cup is also provided with a rack 33, with which cooperates a pinion 33', carried on a shaft 34, supported in bearings from the extension 9 of the seal-ofi' section 4. This shaft, if made in sections has an insulating connection at 35', and the shaft may, and preferably is, provided with locking means similar to that described in connection with shaft 26, though such is not illustrated.

'I'he shafts 26 and 34 terminate at their lower ends in a bar or disk 36 of magnetizable material. Arranged for cooperation with the disks 36 are operators, including rotatable shafts 38, having an operating handle 39 at the lower end. The upper end of each shaft is provided with a magnet 40, either permanent or electromagnet, which will, if appropriately positioned and operated, compel movement of either shaft 26 or 34, as selected, and thus compel the desired adjustment of the parts described. The magnets are preferably mounted for appropriate cooperation with the selected disk 36, and are designed to be turned out of inliuencing relation on the disks. The manually-operable rods for turning the magnets are of course to be of properly insulating construction,y in order to protect the operator against shock during operation. Each disk is appropriately marked with edge markings at 36', which cooperate with a mark 31' on the tube I, to permit successive adjustments of identical range, or initial adjustment according to predetermined requisites. The mark 31' for the disk 36 on the shaft 26 is of sufficient length to cooperate with the markings of that disk in any position assumed incident to the adjustment of the main cup 5.

When it is desired to adjust the filament cups for focusing the cathode stream on the anode, the operator will move the magnet 40, or the appropriate magnet if more than one is used, into magnetizable influence on the disk 36 of the shaft 26. The initial effect is to move the shaft longitudinally and thus release the lock. The magnetic iniiuence then fixes the shaft and operating shaft, and Vby turning the latter the filament cups may be moved in either direction. A similar operation in connection with shaft 34 will adjust the main cup.

The rack and pinion connection between the shafts 26 and 34 and the controlled parts, is intended to be a conventional illustration of any and all appropriate means for accomplishing this result, it being understood that the purpose is to provide a minute and easily controlled cooperation, and any means to this end is contemplated. Furthermore, the locking means may be in any conventional or desired form, so long as it is automatically serviceable when the operation is not desired and releasable when initiating such operation.

If desired the glass insulating and seal-olf section 4 of the cathode stem may be provided with embedded metallic sleeves 4I, and the leads, filament and high potential, divided to permit adjustment, as indicated in Fig. 5. These leads, indicated in Fig. 5, at 42, 43, and 44, may thus be of usual wire construction, and to insure electrical continuity at all times, each sleeve 4I is additionally connected to the movable portion of the lead thereinV by a spring conductive strip 45.

'Ihe general construction of the cathode assembly will be to avoid any sharp edges, except possibly in or on the anode-facing edges of the filament cups, Where it may be found that needle-like, short points will be formed to point directly toward the anode and project but a very slight distance beyond the main surface of the cup edges. This detail of the filament cups is an optional construction of the present invention, but if used it will help electron emission at the higher voltages and yet be controllable in being directed at the focal area on the anode by the focusing cups. In providing a construction to avoid coronal discharge, it being understood that at the higher voltages electron emission will take place from all rough, sharp surfaces, the edge of wall 6 of the distributing cup 5 will be rounded, and a skirt portion 46 will be extended rearwardly in line with such wall 6 for the full length of the sleeve 8. This skirt will of course be formed with slots to provide for shafts 26 and 34, this skirt providing an electrostatic shield covering all sharp points and edges otherwise and necessarily present. A11 exterior surfaces, particularly of the shield will be highly polished and rounded to prevent electron emission from undesired portionsof the cathode.

With the construction described it is apparent that any predetermined or required adjustment of the filament cups or of the distributing cup, or both, may be readily and easily secured at any time, without loss of vacuum or disconnecting any of the parts, and also while the X-ray tube is in actual use. The capability of adjustment provides for a very fine focus or a large focal area on the anode. By the use of the scaled disk and fixed line, any previous adjustment can be subsequently obtained without difculty. Thus one tube can be used for the lowest, highest, or any intermediate milliamperage, with selected points of adjustment for a predetermined energy.

Through ,the described control the cathode stream is evenly distributed homogeneously over the face of the anode throughout the selected focal area, thus avoiding any centralization of the heat.

The invention, while described in connection with a cathode of an X-ray apparatus with multiple filaments, is equally applicable to other vacuum tubes, as for example, rectifier tubes and the like, and is also equally effective with one or any number of filaments.

The essential results of the construction described is the ability for adjusting in a tube yof this character the size of the focal area on the anode and the distribution of the cathode stream relative to the selected focal area. Thus no small area is forced to carry practically all the wattage employed, but a more or less even distribution of the heat is secured over the selected focal area, and the more perfect this distribution the more possible the use of the ultimate amount of energy allowable for a given focal area on the anode.

While the cathode proper is shown as comprising the filament cups with their filaments, it is obvious that the invention may be practiced with the use o-f other types of cathodes. However, the construction of the cathode disclosed herein is preferred, and results in outstanding advantages.

Having thus described the invention, what is claimed as new is:

1. In a device of the character described, a casing sealed from the surrounding atmosphere, an anode in said casing, a cathode distributing cup mounted within said casing for longitudinal movement with respect thereto toward and from said anode, means within said casing for moving said cup longitudinally thereof toward and from said anode to selected positions with respect thereto, said means including amagnetizable member positioned adjacent the inner wall of said casing, a cathode carried by and within said cup, whereby said cup controls the distribution of the cathode stream, and means wholly eX- ternal of said casing including a magnet located adjacent the outer wall thereof in alignment with said member for actuating said first named means, whereby said cathode is simultaneously moved to said selected positions with said cup.

2. In a device of the character described, a casing sealed from the surrounding atmosphere, an anode in said casing, a cathode mounted within said casing for longitudinal movement with respect thereto toward and from said anode, means within said casing for moving said cathode toward and from said anode to selected positions with respect thereto, said means including a magnetizable member positioned adjacent the inner wall of said casing, and means wholly eX- ternal of said casing including a magnet located adjacent the outer wall thereof in alignment with said member for actuating said first named means.

3. In a device of the character described, a casing sealed from the surrounding atmosphere, an anode in said casing, a cathode distributing cup mounted within said casing for longitudinal movement with respect thereto toward and from said anode, means within said casing for moving said cup longitudinally thereof toward and from said anode to selected positions with respect thereto, said means including a magnetizable member positioned adjacent the inner wall of said casing, actuating means wholly external of said casing and operable therethrough for actuating said rst named means, said actuating means including a magnet located adjacent the outer wall thereof in alignment with said member for actuating said first named means, a cathode mounted within said cup for movement independently thereof toward and from said anode, means within said casing for moving said cathode independently of said cup toward and from said anode to selected positions with respect thereto, said last named means including a second magnetizable member positioned adjacent the inner wall of said casing, and actuating means for said last named means located wholly externally of said casing and operable therethrough, said last named means including a magnet located adjacent the outer wall thereof in alignment with said second named member.

HARRY B. MCEUEN.

Images