WO2008061076A2

WO2008061076A2 - X-ray tube bearing assembly with tapered bearing

Info

Publication number: WO2008061076A2
Application number: PCT/US2007/084484
Authority: WO
Inventors: Mark E. Mcilrath
Original assignee: The Timken Company
Priority date: 2006-11-15
Filing date: 2007-11-13
Publication date: 2008-05-22
Also published as: WO2008061076A3

Abstract

An improved bearing assembly (100) incorporating a bearing sub-assembly (108) having a tapered bearing outer diameter (114) and an associated tapered receiving sleeve (106) for installation within a housing bore (102). The bearing sub-assembly (108) seats within the associated tapered receiving sleeve (106), and a axially directed preload is applied to the bearing sub-assembly (108) by a preload member. As temperature increases during operation, the bearing sub-assembly (108) moves axially relative to the housing (104) within the bore (102) in sliding contact between the inner and outer tapered surfaces (112, 114) to accommodate the lowest energy state condition while the desired preload condition is maintained by the preload member.

Description

X-RAY TUBE BEARING ASSEMBLY WITH TAPERED BEARING

Cross-Reference To Related Applications

The present application is related to, and claims priority from, U.S. Provisional Patent Application Serial No. 60/865,875 filed on November 15, 2006, and which is herein incorporated by reference.

Statement Regarding Federally Sponsored Research

Not Applicable. Background of the Invention

The present invention is related to bearing assemblies, and in particular to an improved bearing assembly for use in supporting moving components in large medical imaging devices, such as X-ray tube bearing applications.

Large scale imaging medical devices in which bearings are incorporated, such Computed Tomography (CT) scanners, mammography devices, X-ray tube devices, and other medical detection and assessment applications are demanding mechanical applications for bearings. The bearings utilized to support the large moving components of the medical devices, such as the X-ray tube, may be required to endure high g-levels, operate in a vacuum, or under extreme thermal conditions while providing the ability to maintain precise position control, produce low levels of noise, and provide thermal and electrical conductivity. The low vibration and noise requirements for medical device bearing applications are driven by the need to maximize patient and medical practitioner comfort during a medical scan of the often nervous or traumatized patient, as well as the need for stability to enable the moving components of the medical device to produce high quality images or scans. A source of vibration in traditional medical device bearing assemblies, such as a conventional X-ray tube bearing assembly supporting a target (T) on a shaft (S) shown in Figure 1 , is the presence of a spatial gap (G) between the outer diameter of the bearing subassembly (B) and the inner diameter of the axial bore (AB) in the housing (H) within which it is disposed. This gap (G) is a result of the need for ease of manufacturing assembly (often achieved by a slip fit) and for the ease of repairs -?-

and rebuilds, as well as machining tolerance limitations which may be present during the manufacturing the bearing (B) and the housing (H). Further, thermal expansion rate differences between the materials of the bearing subassembly (B) and the housing (H) can produce changes in the size of the gap (G) as temperatures fluctuate during operation of the medical device. Gaps (G) of this nature have a tendency to produce vibration signatures which are particularly disruptive in medical imaging applications, often vibrating at multiple frequencies which can lead to nonlinear, high amplitude conditions of resonance within the bearing assembly (B) and supporting structures (H). Accordingly, it would be advantageous to provide an improved bearing assembly for use in medical bearing applications and operating environments which eliminates or significantly reduces the presence of any gaps between the bearing subassembly and the housing bore, and which has an improved vibration signature during operation. Brief Summary of the Invention

Briefly stated, the present disclosure provides an improved medical device bearing assembly incorporating a bearing sub-assembly having a tapered bearing outer diameter and an associated tapered receiving sleeve for installation within a cylindrical housing bore. The bearing sub-assembly seats within the associated receiving sleeve, and a continuous axial loading is applied to the bearing subassembly by a preload means. As temperatures vary during operation of the medical device, the bearing sub-assembly moves axially relative to the housing by sliding along the tapered interface between the bearing outer diameter and the receiving sleeve to accommodate the lowest energy state condition while a desired preload is maintained on the bearing sub-assembly by the preload means.

In an embodiment of the present disclosure, the medical device bearing assembly is particularly adapted for use as an X-ray tube bearing assembly.

In an embodiment of the present disclosure, the preload means includes one or more springs secured in place adjacent an end of the housing bore by means of an end cap secured to the housing structure. The preload springs maintain a desired axially directed preload on the bearing sub-assembly.

The foregoing features, and advantages set forth in the present disclosure as well as presently preferred embodiments will become more apparent from the reading of the following description in connection with the accompanying drawings. Brief Description Of The Several Views Of The Drawings

In the accompanying drawings which form part of the specification:

Figure 1 is a cross-sectional illustration of a prior art medical device bearing assembly supporting a rotating target; and Figure 2 is a cross-sectional illustration of an improved medical device bearing assembly of the present disclosure supporting a rotating target.

Corresponding reference numerals indicate corresponding parts throughout the several figures of the drawings. It is to be understood that the drawings are for illustrating the concepts set forth in the present disclosure and are not to scale. Description of the Preferred Embodiment

The following detailed description illustrates the invention by way of example and not by way of limitation. The description enables one skilled in the art to make and use the present disclosure, and describes several embodiments, adaptations, variations, alternatives, and uses of the present disclosure, including what is presently believed to be the best mode of carrying out the present disclosure.

Turning to Figure 2, an improved bearing assembly 100 of the present disclosure for supporting a rotating component 10 axially within a cylindrical bore 102 of a housing 104 having at least one open end is shown. The bearing assembly 100 consists of two main components, a conically tapered sleeve 106 which is installed within the cylindrical bore 102 in the housing 104, and a conically tapered bearing sub-assembly 108 which seats within the conically tapered sleeve 106 and supports a rotating component or shaft 1 10. The conically tapered sleeve 106 is preferably installed within the cylindrical bore 102 of the housing 104 by means of a press-fit or heat shrink process, and defines a tapered or conical inner surface 1 12 having an inner diameter which decreases in relation to an axial distance from an open end of the cylindrical bore 102.

The bearing sub-assembly 108, in turn, is configured with a conically tapered outer surface 1 14 having an outer diameter taper which matches the taper of the inner diameter of the installed tapered sleeve 106, such that the bearing sub- assembly 108 is axially disposed within the cylindrical bore 102 of the housing 104 and establishes a positive contact between the tapered inner surface 1 12 and outer surface 1 14. The positive contact between the inner and outer tapered surfaces 1 12, 1 14 is maintained by an axially directed preload applied to the bearing sub-assembly 108 by a preload element disposed adjacent the large diameter end of the bearing sub-assembly 108, which is retained by means of an end cap 1 16 secured over the cylindrical bore 102. Preferably, the end cap 1 16 includes an axial passage 1 18 through which the rotating component 1 10 passes, and is secured directly to the housing structure 104. The preload element is preferably a spring means 120 which acts to direct an axial load on the bearing sub-assembly 108, either directly or indirectly, maintaining a positive contact between the inner and outer tapered surfaces 1 12, 1 14. However, those of ordinary skill in the art will recognize that any of a variety of suitable preload elements may be utilized to achieve the stated result. For example, the end cap 1 16 may be secured to the housing 104 by a plurality of threaded bolts 122 passing through suitable bores 124 in the end cap 1 16. A spring means 120 may be installed between a head of each bolt and the exterior surface of the end cap 1 16, thereby exerting an axially directed preload on the end cap 1 16, which in turn, abuts against the large-diameter end of the bearing sub-assembly 108, and establishes the desired preload setting. Alternatively, a spring means 120 may be installed directly between the inner surface of the end cap 1 16 and the large-diameter end of the bearing sub-assembly 108, such that the spring member directly applies a desired preload to the bearing sub-assembly 108.

It will be recognized that the design of the conically tapered configuration of the inner and outer surfaces 1 12, 1 14, combined with the preload element, maintains a positive contact between the bearing assembly 100 and the housing structure 104, minimizing vibrations during operation. As operating temperatures increase, the bearing sub-assembly 108 may move axially relative to the housing 104 to accommodate the lowest energy state condition while maintaining surface contact between the inner and outer tapered surfaces 1 12, 1 14 to further maintain the desired preload setting.

Eliminating the gap between the bearing assembly 100 and the inner surface of the cylindrical bore 102 in the housing 104, as is found in conventional medical imaging bearing applications may reduce thermal flux from the bearing which exits through the housing.

As various changes could be made in the above constructions without departing from the scope of the disclosure, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

Claims:

1 . An improved bearing assembly (100) for supporting a rotating component (1 10) axially within a cylindrical bore (102) of a housing (104) having at least one open end, the improvement comprising: a conically tapered sleeve (106) adapted for placement within the cylindrical bore (102) of the housing (104), said conically tapered sleeve (106) having a cylindrical outer surface and a conical inner surface (1 12) having a diameter which decreases in relation to an axial distance from an open end of the cylindrical bore of the housing; a bearing sub-assembly (108) axially supporting the rotating component (1 10) within said cylindrical bore (102) of the housing (104), said bearing sub-assembly (108) seated within said inner diameter of said conically tapered sleeve (106) and having an conical outer surface (1 14) tapered to match the taper of the conical inner surface (1 12); and a preload means disposed to exert an axially directed preload on said bearing sub-assembly (108) to maintain contact between said conical outer surface (1 14) of said bearing sub-assembly (108) and said conical inner surface (1 12) of said tapered sleeve (106).

2. The improved bearing assembly of Claim 1 further including an end cap (1 16) secured to the housing (104) about said at least one open end of the cylindrical bore (102), said end cap (1 16) including an axial passage (1 18) for the rotating component (1 10).

3. The improved bearing assembly of Claim 2 wherein said preload means is disposed between said end cap (1 16) and an axial end surface of said bearing sub-assembly (108).

4. The improved bearing assembly of Claim 2 wherein said preload means is disposed to exert an axially directed preload on said bearing sub-assembly (108) through said end cap (1 16).

5. The improved bearing assembly of Claim 4 wherein said preload means includes a plurality of spring members (120), each of said plurality of spring members (120) disposed between an associated retaining bolt head (122) and a surface of said end cap (1 16), whereby said axial directed preload is exerted on said bearing sub-assembly (108) through said end cap (1 16).

6. The improved bearing assembly of Claim 1 wherein said bearing assembly (100) is an X-ray tube support bearing assembly.

7. The improved bearing assembly of Claim 1 wherein said bearing sub- assembly (108) is adapted for a range of axial movement within said cylindrical housing bore (102).

8. The improved bearing assembly of Claim 1 wherein said conically tapered sleeve (106) is secured within said cylindrical housing bore (102).

9. The improved bearing assembly of Claim 1 wherein said conical inner surface (1 12) of said conically tapered sleeve (106) and said tapered bearing outer surface (1 14) are maintained in positive contact by said preload means.

10. The improved bearing assembly of Claim 1 wherein said preload means includes at least one spring means (120).