BRIEF DESCRIPTION OF THE DRAWINGS
In order that the manner in which the above recited and other useful aspects and objects of the invention are obtained, a more particular description of the invention briefly described above will be given by making reference to a specific embodiment that is illustrated in the appended drawings. These drawings depict only one embodiment of the invention and are not to be considered limiting of its scope.
FIG. 1 illustrates a simplified cross-sectional illustration of an exemplary x-ray tube showing a window positioned in the side of the x-ray tube housing;
FIG. 2 is a cross-sectional illustration of a first exemplary embodiment of a bond layer;
FIG. 3 is a cross-sectional illustration of a second exemplary embodiment of a bond layer;
FIG. 4A is a cross-sectional illustration of a third exemplary embodiment of a bond layer;
FIG. 4B is a partial cross-sectional perspective illustration of the third exemplary embodiment of the bond layer of FIG. 4A;
FIG. 5 is a partial cross-sectional perspective illustration of an exemplary embodiment of a support flange; and
FIG. 6 is a top view of the outline of a window frame depicting an exemplary window frame configuration.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION
Reference will now be made to the drawings to describe exemplary embodiments of the invention. It is to be understood that the drawings are diagrammatic and schematic representations of these embodiments, and are not limiting of the invention, nor are they necessarily drawn to scale.
In general, embodiments of the invention are directed to an improved apparatus and method for bonding of an x-ray tube window to an x-ray tube window frame. Further, embodiments of the invention are directed to a method and apparatus for reducing mechanical and thermal stresses on a window used in an x-ray tube. Moreover, the window is designed to allow x-rays generated within the x-ray tube to exit the x-ray tube without undue attenuation of the x-rays by the window.
I. Exemplary X-Ray Tube
In order to describe the various methods of the invention, attention is directed to FIG. 1 which illustrates a simplified cross-sectional illustration of a typical x-ray tube 10 having a window 12 disposed in a window frame 14 positioned in the side of a housing 16. Housing 16 cooperates with window 12 and window frame 14 to define an evacuated enclosure 18 that encloses a cathode 20 and an anode 22. Window frame 14 is illustrated as being structurally integrated within housing 16. Window 12 separates the vacuum of evacuated enclosure 18 of x-ray tube 10 from the normal atmospheric pressure found outside x-ray tube 10, and yet enables x-rays generated from anode 22 to exit x-ray tube 10 and strike an intended target 24.
Although x-ray tube 10 is depicted as a rotary anode x-ray tube, exemplary embodiments of the invention can be utilized in any type of x-ray tube that utilizes an x-ray transmissive window formed in the housing of the x-ray tube that permits x-rays produced within the x-ray tube to be emitted from the housing.
II. First Exemplary Bond Layer
Directing attention now to FIG. 2, details are provided concerning a first exemplary embodiment of a bond layer. An x-ray tube 200 includes a housing 202, as well as a window assembly 201 that includes a window frame 204 that is connected to housing 202. Window frame 204 comprises an outer annular rim 205 and a support flange 206 supporting a window 207 of the window assembly 201. In the exemplary illustrated embodiment, the window 207 of the window assembly 201 can be considered to comprise two portions, particularly, a first portion 208 which does not overlap support flange 206, and a second portion 209 which overlaps support flange 206. Second portion 209 of window 207 is affixed to support flange 206 using a bond layer 210 of the window assembly 201. Specifically, second portion 209 of window 207 is in direct contact with an upper surface 212 of the bond layer 210 of the window assembly 201. The exemplary bond layer 210 of FIG. 2 can be implemented in the x-ray vacuum environment of FIG. 1.
In the illustrated embodiment, outer annular rim 205 of window frame 204 is connected to housing 202. Support flange 206 of window frame 204 is formed along the inside surface of outer annular rim 205, and extends toward the center of the ring formed by window frame 204. The cross-section of window frame 204 is illustrated as generally L-shaped, with support flange 206 extending generally parallel to housing 202 and perpendicular to outer annular rim 205. However, other shapes are possible, including angling support flange 206 upward or downward with respect to housing 202. Exemplary embodiments of support flanges angled downward with respect to a housing are illustrated in FIGS. 3-5 described below.
With continuing reference to FIG. 2, the bond layer 210 is interposed between support flange 206 and window 207. In some embodiments, bond layer 210 is between about 0.001 and about 0.003 inches thick, but the bond layer 210 can be thinner or thicker depending on the particular application. The area of a support flange that is overlapped by a window is defined herein as the bonding area of the support flange, though the bond layer may not, in every case, completely cover the bonding area. Thus, the area of support flange 206 overlapped by window 207 is known as the bonding area of support flange 206. In the exemplary embodiment illustrated in FIG. 2, the bond layer 210 substantially covers the bonding area of support flange 206.
Upper surface 212 of bond layer 210, in contact with second portion 209 of window 207, has a substantially smooth finish. A substantially smooth finish as defined herein includes any surface finish of about 64 microinches or less, which may also be expressed in terms of a surface finish value ‘Ra’ of about 64 or less. One example of a substantially smooth finish is a surface finish of about 32 microinches or less, or a surface finish value Ra of about 32 or less. Another example of a substantially smooth finish is a surface finish of about 8 microinches or less, or a surface finish value Ra of about 8 or less. The substantially smooth finish of upper surface 212 of bond layer 210 can be achieved by cold rolling bond layer 210 after the bond layer 210 is attached to the support flange 206. However, any other method of forming upper surface 212 of bond layer 210 with a surface finish of about 64 microinches or less is contemplated as residing within the scope of the invention.
With continuing reference to FIG. 2, window 207 is diffusion bonded to support flange 206. Several forms of diffusion bonding techniques can be utilized in connection with embodiments of the invention. One exemplary form of diffusion bonding that can be utilized is sometimes referred to as solid-state joining and serves to join two parts together using heat and pressure, but without melting the associated bond layer. This type of solid-state joining process is suitable for joining window 207 to bond layer 210, and for joining bond layer 210 to support flange 206. Diffusion bonding is performed in order to form a vacuum-tight seal between support flange 206 and window 207. This vacuum-tight seal enables a vacuum to be maintained in the interior of the evacuated enclosure 216.
When second portion 209 of window 207 is diffusion bonded to upper surface 212 of bond layer 210, the shape of second portion 209 conforms closely with the shape of upper surface 212. Particularly, the substantially smooth finish of upper surface 212 of bond layer 210 permits window 207 to be diffusion bonded to bond layer 210 and bond layer 210 to be diffusion bonded to support flange 206 with no material deformation of window 207. Thus, the substantially smooth finish of upper surface 212 of bond layer 210 results in an extended operational life of x-ray tube 200 because deformation induced cracking and leaking of window 207, and consequent loss of vacuum from housing 202, is avoided.
III. Second Exemplary Bond Layer
Directing attention now to FIG. 3, details are provided concerning a second exemplary embodiment of a bond layer. An x-ray tube 300 includes a housing 302 and a window assembly 301 that includes a window frame 304 that is connected to housing 302. Window frame 304 comprises an outer annular rim 305 and a support flange 306 supporting a window 307 of the window assembly 301. In the exemplary illustrated embodiment, the window 307 of the window assembly 301 can be considered to comprise two portions, particularly, a first portion 308 which does not overlap support flange 306, and a second portion 309 which overlaps support flange 306. Second portion 309 of window 307 is affixed to support flange 306 using a bond layer 310 of the window assembly 301. Specifically, second portion 309 of window 307 is in direct contact with an upper surface 312 of the bond layer 310 of the window assembly 301. The exemplary bond layer 310 of FIG. 3 can be implemented in the x-ray vacuum environment of FIG. 1.
In the illustrated embodiment, support flange 306 is formed along the inside surface of outer annular rim 305, and extends toward the center of the ring formed by window frame 304. Further, support flange 306 is oriented at a predetermined angle α at its juncture 314 with outer annular rim 305 such that the support flange 306 is oriented toward the interior of an evacuated enclosure 316, as indicated in FIG. 3. Support flange 306 and bond layer 310 each generally comprise a frustoconical section. In this exemplary embodiment, the window 307, which may be preformed, has a generally bowl-shaped configuration in order to fit snugly within window frame 304. The bowl-shaped configuration of window 307 can be, for example, generally parabolic, elliptical, or spherical. Examples of an angled support flange and a preformed bowl-shaped window are disclosed in U.S. Pat. No. 6,459,768, entitled “X-Ray Tube and Window Frame,” which is incorporated herein by reference.
In the embodiment illustrated in FIG. 3, the bond layer 310 is interposed between support flange 306 and window 307. In some cases, bond layer 310 is similar in thickness to bond layer 210 of FIG. 2, however, any suitable thickness may be employed. Bond layer 310 substantially covers the bonding area of support flange 306. Upper surface 312 of bond layer 310, in contact with second portion 309 of window 307, has a substantially smooth finish, as indicated earlier herein in connection with upper surface 212 of the bond layer 210 disclosed in FIG. 2. Window 307 is diffusion bonded to bond layer 310 and bond layer 310 is diffusion bonded to support flange 306 in order to form a vacuum-tight seal between support flange 306 and window 307. When second portion 309 of window 307 is diffusion bonded to upper surface 312 of bond layer 310, the shape of second portion 309 conforms closely with the shape of upper surface 312. The substantially smooth finish of upper surface 312 of bond layer 310 permits window 307 to be diffusion bonded to bond layer 310 and bond layer 310 to support flange 306 with no material deformation of window 307. Among other things then, the substantially smooth finish of upper surface 312 of bond layer 310 results in an extended operational life of x-ray tube 300 because deformation induced cracking of window 307, and the consequent loss of vacuum from housing 302, is avoided.
IV. Third Exemplary Bond Layer
Directing attention now to FIG. 4A, details are provided concerning a third exemplary embodiment of a bond layer. An x-ray tube 400 includes a housing 402 and a window assembly 401 that includes a window frame 404 that is connected to housing 402. Window frame 404 comprises an outer annular rim 405 and a support flange 406 supporting a window 407 of the window assembly 401. In the exemplary illustrated embodiment, window 407 can be considered to comprise two portions, particularly, a first portion 408 which does not overlap support flange 406, and a second portion 409 which overlaps support flange 406. Second portion 409 of window 407 is affixed to support flange 406 using a bond layer 410 of the window assembly 401. Specifically, second portion 409 of window 407 is in direct contact with an upper surface 412 of bond layer 410 of the window assembly 401. The exemplary bond layer 410 of FIG. 4A can be implemented, for example, in the x-ray vacuum environment of FIG. 1.
In the illustrated embodiment, support flange 406 is formed along the inside surface of outer annular rim 405, and extends toward the center of the ring formed by window frame 404. Support flange 406 is oriented at its juncture 414 with rim 405 toward the interior of the evacuated enclosure 416. Further, at least the upper surface of support flange 406 has a generally arcuate cross-section. Additionally, the support flange 406 and bond layer 410 each comprise a frustoconical section. In this exemplary embodiment, the window 407, which may be preformed, has a generally bowl-shaped configuration in order to fit snugly within window frame 404.
In this exemplary embodiment, the bond layer 410 is interposed between support flange 406 and window 407. Bond layer 410 is similar in thickness to bond layer 210 of FIG. 2, but other thicknesses of bond layer 410 may be employed also. Bond layer 410 substantially covers the bonding area of support flange 406. Upper surface 412 of bond layer 410, in contact with second portion 409 of window 407, has a substantially smooth finish, as indicated earlier herein in connection with upper surface 212 of the bond layer 210 disclosed in FIG. 2. Window 407 is diffusion bonded to bond layer 410, and bond layer 410 is diffusion bonded to support flange 406 in order to form a vacuum-tight seal between support flange 406 and window 407. When second portion 409 of window 407 is diffusion bonded to upper surface 412 of bond layer 410, the shape of second portion 409 conforms closely with the shape of Z upper surface 412. The substantially smooth finish of upper surface 412 of bond layer 410 permits window 407 to be diffusion bonded to bond layer 410 and bond layer 410 to be diffusion bonded to support flange 406 with no material deformation of window 407. Thus, the substantially smooth finish of upper surface 412 of bond layer 410 results in an extended operational life of x-ray tube 400 because deformation induced cracking and leaking of window 407, and consequent loss of vacuum from housing 402, is avoided.
Directing attention now to FIG. 4B, further details are provided concerning the exemplary embodiment of bond layer 410 which connects window 407 to window frame 404 of FIG. 4A. Particularly, FIG. 4B illustrates support flange 406 and bond layer 410 as generally defining a frustoconical shape. Similarly, FIG. 4B illustrates support flange 406 having a generally arcuate shape. Also, FIG. 4B illustrates window 407 as generally bowl-shaped.
V. Exemplary Support Flange
Directing attention now to FIG. 5, details are provided concerning an exemplary window assembly 500 that includes a window frame 504 configured to be connected to an x-ray device housing (not shown). Window frame 504 comprises an outer annular rim 505 and a support flange 506 that supports a window 507 of the window assembly 500. In the exemplary illustrated embodiment, window 507 can be considered to comprise two portions, particularly, a first portion 508 which does not overlap support flange 506, and a second portion 509 which overlaps support flange 506. In contrast with the windows depicted in the exemplary embodiments of FIGS. 2-4B, however, second portion 509 of window 507 in the embodiment disclosed in FIG. 5 is not affixed to support flange 506 using a bond layer, but rather is affixed directly to the surface of support flange 506. Specifically, second portion 509 of window 507 is in direct contact with an upper surface 512 of support flange 506.
In the illustrated embodiment, support flange 506 is formed along the inside surface of c outer annular rim 505, and is oriented and shaped in similar fashion to support flange 406 of FIGS. 4A and 4B. As in the case of other exemplary embodiments disclosed herein, the window 507 may be preformed, and has a generally bowl-shaped configuration in order to fit snugly within window frame 504. Of course, other window shapes and configurations may be employed as well.
Unlike the embodiments disclosed in FIGS. 2-4B, the embodiment disclosed in FIG. 5 does not include a bond layer between support flange 506 and window 507. Instead, the upper surface 512 of support flange 506, in contact with second portion 509 of window 507, has a substantially smooth finish, as described in connection with upper surface 212 of FIG. 2. Window 507 is diffusion bonded to support flange 506 in order to form a vacuum-tight seal between support flange 506 and window 507. When second portion 509 of window 507 is diffusion bonded to upper surface 512 of support flange 506, the shape of second portion 509 conforms closely with the shape of upper surface 512. The substantially smooth finish of upper surface 512 of support flange 506 permits window 507 to be diffusion bonded to support flange 506 with no material deformation of window 507. Thus, the substantially smooth finish of upper surface 512 of support flange 506 results in an extended operational life of x-ray tube 500 because deformation induced cracking and leaking of window 507, and consequent loss of vacuum from housing 502, is avoided.
VI. Exemplary Window Frame Configuration
FIG. 6 is a top view of the outline of an exemplary window frame 604. It is recognized that the shape of the window frame is not limited to a circle as described in the previous embodiments. Rather, the window frame 604 can be any shape. For example, the window frame of FIG. 6 comprises a hexagonal shape. Accordingly, the shape of the x-ray tube window of the exemplary embodiments depicted in FIG. 2-5 may comprise any shape that is consistent and compatible with the purposes of the device in which the window frame is disposed. Exemplary frame shapes could include, for example, polygonal shapes or elliptical shapes or some combination of the two.
VII. Other Exemplary Embodiments
It is appreciated that, while the exemplary embodiments illustrated in FIGS. 2-5 utilize a window comprising beryllium, the principles described in these exemplary embodiments can also be applied to windows composed of different materials. For example, x-ray transmissive window materials including titanium, nickel, carbon, silicon, aluminum, biaxially-oriented polyethylene terephthalate, and polyethylene could be employed.
It is also appreciated that, while the support flanges of the exemplary embodiments shown in FIGS. 2-4B illustrate smooth surfaces to which the bond layer is applied, this surface may be roughened to assist in the adhesion of the bond layer thereto. Support flange surfaces have varying degrees of roughness are contemplated as residing within the scope of U exemplary embodiments of the invention illustrated in FIGS. 2-4B.
The support flanges of the window frames shown in FIGS. 2-5 are comprised of stainless steel, nickel-copper alloy, nickel, or any other metals or alloys having suitable characteristics. Also, the outer annular rims of the window frames shown in FIGS. 2-5 are comprised of a metal or metal alloy that can be affixed to the housing of the x-ray tube. However, it should be understood that in some embodiments the window frames shown in FIGS. 2-5 could be integrally formed as part of the housings of the x-ray tubes shown in FIGS. 2-5. Likewise, in some embodiments, the outer annular rims shown in FIGS. 2-5 are omitted.
The bond layers in FIGS. 2-4B are comprised of copper or a copper silver alloy which is soft and has good diffusion characteristics, or any other metal or alloy having suitable characteristics. Likewise, the edges of the bond layers in FIGS. 2-4B that are not in contact with either the support flange or the window can be fillet shaped or curved, instead of generally flat as illustrated in FIGS. 2-4B.
The invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.
Patent Application
20070291901
