US 3591821 A
Description (OCR text may contain errors)
United States Patent Inventors AppL N0.
Filed Patented Assignee Priority Yosllltlka Seki Yokohama-shi;
Tlkeshi Muraki, Kawasaki-shi, both of, Japan 721,243
Apr. 15, 1968 July 6, 1971 Tokyo Shibaura Electric Co., Ltd. Kawasaki-obi, Japan Apr. 19, 1967 ROTARY ANODE TYPE X-RAY GENERATOR HAVING EMITTING ELEMENTS WHICH ARE VARlABLY SPACED FROM THE CENTRAL AXIS Primary ExaminerRoy Lake Assistant ExaminerE. R. LaRoche Attorney-Stephen H. Frishauf ABSTRACT: An X-ray generator comprises a cathode and a rotary anode mounted in opposite ends of an envelope. The cathode is provided with an electron emitting source in a desired doughnut-shaped region which is bounded by a minimum diameter circle and a maximum diameter circle, both of these circles being concentric with the rotary axis of said anode. The anode projects X-rays upon impingement thereof by an electron beam emitted from said electron emitting source. The electron emitting source is arranged on a line which connects the minimum and maximum diameter circles, whereby the electron beam from said electron emitting source is projected to the entire part of said X-ray radiating re- 'gion by rotating said anode.
PATENTEU JUL 6197i (:1, 591 821 FIGQ1 ROTARY ANODE TYPE X-RAY GENERATOR HAVING EMITTING ELEMENTS WHICH ARE VARIABLY SPACED FROM THE CENTRAL AXIS OF CATHODE This invention relates to a rotary anode type X-ray generator and, more particularly, to a rotary anode type X-ray generator suitable for emitting X-rays from the entire circumferential surface of an anode in the directions of the radius of said anode.
In a known X-ray tube capable of emitting X-rays from the entire circumference or from more than three desired point sources thereon, it is possible to inspect conveniently and efficiently, for example, scratches and nests on the inner surface of a cylindrical metallic tube and faulty portions of the junction between tubes. Furthermore, if a bulb, viz. the emitting source, is arranged at the center and an object to be irradiated thereabout in the case of coloring a jewel such as a crystal and of the X-ray irradiation treatment of living creatures and processed goods, many things can be irradiated at the same time thus widening the use of said X-ray tube.
In X-ray tubes of this type heretofore used, a fixed anode type has generally been in use. Namely, in such tubes, in a hermetically sealed bulb is arranged an anode in the shape of a truncated cone upon the slanting slope of which is formed a target which is spaced from and yet concentrically with a cathode consisting of a spiral filament formed concentrically with the central axis thereof in a focusing groove provided in a head portion of said cathode. Electrons emitted from the filament are focused by said focusing groove and become hollow cylindrical-shaped electron beams, thereby to generate X-rays from a focal area taken by the impingement of the electron beams to the entire surface of said target.
However, in such an X-ray tube electron beams projected from the cathode always impinge upon a single portion or X- ray radiating region over the whole circumference of the target since the anode is a fixed, as above mentioned. Therefore the impinged portion is heated to extremely high temperatures, causing a gradual emersion of gas from the anode. This greatly shortens the life of the X-ray generator and is a fatal impediment to the functioning thereof, which prevents the X- ray generator from being employed when high output X-ray radiation is required.
Next, X-ray tubes utilizing the concept of rotating the anode were developed. However, since in the aforementioned cathode a filament constituting part of the cathode is formed concentrically with the central axis, electron beams emitted collide against part of the circumference of the target, as in the case of a fixed electrode type, irrespective of rotating the anode of the X-ray tube. Thus the above-mentioned defects can not be removed by such a tube.
An object of the present invention is to provide an 'X-ray generator capable of receiving impingement of electron beams by the entire X-ray radiating region of its anode when the anode is rotated.
Another object of the invention is to provide an X-ray generator of a compact type and with high output.
In order to achieve these objects, an electron emitting source, viz. a filament, is positioned on a curve whichcorresponds to a virtual curve connecting a minimum diameter circle and a maximum diameter circle, these circles having the rotating axis of the anode as their centers in said X-ray radiating region. The position of the filament is continuously or intermittently varied. Other objects and advantages of the present invention will be more fully understood from the fol lowing description when taken in conjunction with the appended drawings in which:
FIG. 1 is a side elevation partially in section of one embodi ment of a rotary anode type X-ray generator of the present invention; 1
FIG. 2a is a plan view of the bottom ofan electron emitting plane of a cathode of said generator;
FIG. 2b shows the upper plane of said anode to explain the operation of an X-ray radiating region of the anode which corresponds to the cathode in FIG. 20,"
FIG. 3a shows the upper plane of the cathode, illustrating another embodiment of the invention;
FIG. 3b shows the upper plane of said anode to explain the operation of an X-ray emitting region of the anode which corresponds to the cathode in FIG. 3a;
FIG. 4a is a perspective view of the cathode to show still another embodiment of the invention; and
FIG. 4b illustrates the upper plane of the cathode, explaining the operation of the X-ray radiating region of the anode which corresponds to the cathode in FIG. 4a
Referring first to FIGS. I to 3, inclusive, the X-ray genera tor shown therein comprises an envelope 1 of glass or other suitable material having a cathode 2 mounted at one end thereof and ananode 3 mounted at the other end. The anode 3 is of a rotary type and comprises a rotor body 4 suitably supported by a bearing structure (not shown) upon a stem or spindle 5 which extends outwardly of the envelope through a conventional glass-to-metal seal structure 6. Extending from the rotor 4 towards the cathode 2 is a shaft 7 which supports a target member 8 secured to the shaft by a cap nut 9. The target 8 is preferably made of tungsten or other metals of high atomic number and the nut 9 and shaft 7 are preferably made. of molibdenum or other suitable metals having high strength at high temperatures. As will be noted, the target 8'if. formed with a peripheral frustoconical target surfaceportion l0 and a fiat center portion 11 which extends at right angles to the shaft 7.
The cathode 2 is provided with a head portion 12 having a focusing volute or spiral groove 13 provided therein in which is mounted an electron emitting source 14, viz. a'filament, adapted to be energized through leads -15 from a sourceof electrical energy. The filament 14 and groove 13; are designed to generate and focus a beam of electrons,-as illustrated at 16 in FIG. 1, upon the target portion 10 of the anode target .8. The beam 16 is preferably of rectangular cross section with its longeraxis extending vertically as shown in FIG. 1. The beam 16 is further focused to impinge upon the ,targetarea 10 over a focal area 17. Preferably, the angle of inclination of thetarget portion 10 is such that as viewed at right angles to the beam 16, the focal area 17 is of a volute or spiral shapeas may be covered in a suitable X-ray radiating region 18 of the target portion 10, said volute being preferably of the same, shape as the groove 13. In other words, one end portion of the focal area 17 should be positioned at a desiredminimum diameter circle 19 in an X-ray radiating region 18, while the other end portion should be located in a maximum diameter circle 20 of said region 18.
There will now be explained the operation of the X-ray generator of FIGS. 1-3. When the filament 14 is energized an electron beam 16 is irradiated upon the focal area 17 on the target 8, and consequently X-rays are radially projected outwardly from said focal-area. If the electron beam 16 continuously impinges upon only the'area 17 for a longperiod of time (that is, if the anode is stationary), this portion will become heated to very high temperatures. As a result, various unfavorable influences as described at theintroductory part of this specification will occur. However, according to the present invention the shaft 5 is rotated by a suitable means from the outside of the envelope 1, the target member 8 is rotated with the rotation of said shaft 5, and a region bounded by a dot and chain line as shown in FIG. 2b whichcorresponds to the focal area 17 is utilized for impingement by electron beams so that the electron beam always impinges upon dif ferent parts of the X-ray radiating region (a region bounded by dotted lines '19 and 20 in FIG..2b).
When the target 8 is rotated as described above, the focal area 17 is situated over substantially the whole areaof the X- ray radiating region, and the region efficientlyacts to project X-rays. It is possible to rotate saidtarget 8=before the region has been heated to high temperatures, vwhereby'makingit possible to lengthen the life of the X-ray generator and to provide an X-ray generator of a small size having a high output.
The cathode need not only comprise a single filament of such a spiral shape as is illustrated in FIG. 2a but alternatively it may be made as shown in FIG. 3a. In FIG. 3a the filament is divided into four filament sections 24 and the divided fila ments 24, made in the shape of conical arcs, are received in four respective focusing grooves 29 provided in the head por' tion 12 of the cathode 2. In this case, the radius from the central axis of the cathode to one end of each filament 24 may be made a little different from that to the other. The same effect can be obtained when divided filaments of a circular arc are so arranged. As shown in FIG. 3b, the target surface upon which an electron beam impinges always varies within the X- ray radiating region, as illustrated by dotted lines, due to the rotation of the anode 3. Scanning of electrons on the same target portion does not occur. Furthermore, the scanning width and area are widened accordingly. Since each focal area 27 is formed to be a circular arc similar to a filament 24, X-rays are radiated outwardly from almost the entire circumference of the target, without changing the positions of said area 27 and the filament 24 irrespective of the rotation of the anode.
As another embodiment, the cathode, as illustrated in FIG. 4a may comprise a supporting member 42 attached to the head portion of a base member 21 fixed in a body in an envelope. Filaments 45, each of which is a point source are received in focusing cup recesses 44 provided at the end portions of respective four arms 43 of a cross-shaped member,
1 each of the arms having different lengths. As shown in FIG. 4b
, an electron beam from the filaments 45 impinges upon a with respect to each other. However, the angles therebetween can be varied according to the particular use. Further, the
I electrical connection of each of said filaments 45 may either focal area 46 which is capable of being positioned over the enbe in series or parallel. In the case of a parallel connection, it is convenient if only a single filament is made capable of being energized at a time by a suitable means. The X-ray tube of the present invention, in comparison with the X-ray generator of a whole circumference projection type in FIGS. 1 to 3, is capable of providing higher outputs and is convenient for use when whole circumference radiation is not necessary.
While the invention has been described in connection with some preferred embodiments thereof, the invention is not limited thereto and includes any modifications and alterations which fall within the scope of the invention.
1. An X-ray tube comprising:
a cathode mounted in said envelope;
a rotatable anode mounted within said envelope facing said cathode, said anode having a substantially frustoconical target surface;
electron emitting means disposed adjacent the entire periphery of the cathode, said electron emitting means including at least one electron emitting element having two ends, one end of each of said at least one electron emitting element being spaced at a different distance from the central axis of said cathode; than the other end; and
means coupled to said anode for rotating said anode.
2. An X-ray tube according to claim 1 wherein said electron emitting sources extend over overlapping distances from the axis of rotation of the anode.
v 3. An X-ray tube according to claim 1 wherein said electron emitting means comprises a filament located in a focusing spiral groove in the cathode.