WO2008058267A2

WO2008058267A2 - X-ray tube bearing assembly with c-spacer

Info

Publication number: WO2008058267A2
Application number: PCT/US2007/084246
Authority: WO
Inventors: Martin Scott Galehouse
Original assignee: Timken Co
Current assignee: Timken Co
Priority date: 2006-11-10
Filing date: 2007-11-09
Publication date: 2008-05-15
Anticipated expiration: 2009-05-10
Also published as: WO2008058267A3

Abstract

The bearing assembly (100) includes an axial shaft (102) supported on front and rear bearing sub-assemblies (104, 106), each of which has an inner raceway (108) and an outer raceway (110). The outer raceways (110a, 110b) for each of the bearing sub-assemblies (104, 106) are carried on cylindrical outer members (112, 114) coaxially disposed between the supported shaft (102) and the housing within which the bearing assembly (100) is disposed. A spring element (116) is disposed coaxially about the supported shaft (102) medially between each of the cylindrical outer members (112, 114). An axial preload force is applied on each of the cylindrical outer members (112, 114) by wedging engagement of contact surfaces (120) of the spring element (116) with associated contact surfaces (122) of the outer members (112, 114), applying an axial outwardly directed preload force to each of the front and rear bearing sub-assemblies (104, 106).

Description

X-RAY TUBE BEARING ASSEMBLY WITH C-SPACER

Cross-Reference to Related Applications

The present application is related to, and claims priority from, U.S. Provisional Patent Application Serial No. 60/865,202 filed on November 10, 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, such as for use in X-ray tube bearing applications, which utilizes a combination of a centrally disposed C-spacer and front and rear outer members to apply a desired preload to associated front and rear supporting raceways. 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 traditional spring-loaded X-ray tube bearing assembly is a complex assembly consisting of a shaft supported on front and rear bearing sub-assemblies. The outer raceway of the rear bearing is maintained in a preload condition by means of a spring disposed coaxially about the shaft, and maintained within the bearing housing by a sleeve member which is coaxially disposed about the shaft adjacent the front bearing sub-assembly and which is secured to the bearing housing. Since only the rear raceway experiences the preload force from the spring, a measurable amount of end-play is present in the supported shaft during operation. End play may produce vibration signatures which are particularly disruptive in medical imaging applications, as they produce vibration at multiple frequencies and can lead to nonlinear, high amplitude, conditions of resonance within the bearing assembly and supporting structures. Accordingly, it would be advantageous to provide an improved bearing assembly for use in X-ray tube bearing applications and operating environments which provides a uniform preload force on both front and rear bearing sub- assemblies, and which eliminates or significantly reduces the presence of any end play in the supported shaft, improving the vibration signature of the bearing assembly during operation. It would further be advantageous to provide an improved bearing assembly which requires fewer components than existing bearing assemblies, and which may be utilized in constrained space applications in medical imaging devices and elsewhere. Brief Summary of the Invention Briefly stated, the present disclosure provides a bearing assembly for use in medical imaging equipment which provides a uniform preload force on both front and rear bearing sub-assemblies, and which eliminates or significantly reduces the presence of any end play in the supported shaft. The bearing assembly includes an axial shaft supported on front and rear bearing sub-assemblies, each of which has an inner and an outer raceway. The outer raceways for each of the bearing sub- assemblies are carried on cylindrical outer members coaxially disposed between the supported shaft and the housing within which the bearing is disposed. A C-spacer spring element is disposed coaxially about the supported shaft medially between each of the cylindrical outer members. An axial preload force is applied on each of thθ cylindrical outer members by contact surfaces of the C-spacer spring element, applying a preload to each of the front and rear bearing sub-assemblies.

In an embodiment of the bearing assembly of the present disclosure, the C- spacer spring element includes a plurality of tapered contact surfaces which engage

5 matching tapered contact surfaces on each of the cylindrical outer members. Radial compressive forces exerted by the C-spacer spring element are transferred into axial preload forces at the tapered contact surfaces.

The foregoing features, and advantages set forth in the present disclosure as well as presently preferred embodiments will become more apparent from the 10 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 an exploded view of the bearing assembly of the present disclosure; Figure 2 is an axial cross-sectional view of the bearing assembly of Fig. 1 ; 15 Figure 3 illustrates a C-spacer spring half-section with exemplary dimensions; Figure 4 illustrates an end-view of the C-spacer spring half-section of Fig. 3; Figure 5 illustrates an inner end view of a cylindrical outer member; Figure 6 illustrates a cross-sectional view of the cylindrical outer member of Fig. 5; and

20 Figure 7 illustrates the interaction between the contact surfaces of the C-spacer spring and cylindrical outer members of the present invention.

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. 25 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

30 presently believed to be the best mode of carrying out the present disclosure. -A-

Turning to the Figures, and to Figure 1 and 2 in particular, a bearing assembly 100 of the present disclosure is shown for use in medical imaging equipment. The bearing assembly 100 includes an axial rotating shaft 102 supported for rotation about a longitudinal axis X on a front bearing sub-assembly 104 and a rear bearing sub-assembly 106, each of which has a respective inner raceway 108a, 108b and a respective outer raceway 1 10a, 1 10b. The bearing assembly 100 is configured to provide a uniform preload force on both the front and rear bearing sub- assemblies 104, 106, and to eliminate or significantly reduces the presence of any end play in the supported rotating shaft 102. The outer raceway 1 10 of each of the bearing sub-assemblies 104, 106 is carried on an associated cylindrical outer member 1 12, 1 14 coaxially disposed between the supported shaft 102 and the housing (not shown) within which the bearing assembly 100 is disposed. A C-spacer spring element 1 16 is disposed coaxially about the supported shaft 102 medially between each of the cylindrical outer members 1 12, 1 14. An axial preload force is applied on the annular ends 1 12a, 1 14a of each of the cylindrical outer members 1 12, 1 14 by edges 1 18 of the C-spacer spring element 1 16, applying a preload to each of the front and rear bearing sub-assemblies 104, 106.

Preferably, as best seen in Figures 3 through 6, the edges 1 18 of the C- spacer spring element which are adjacent to the inner annular ends 1 12a, 1 14a of the cylindrical outer members 1 12, 1 14 includes a plurality of tapered contact surfaces 120. These tapered contact surfaces 120 are configured to engage matching tapered contact surfaces 122 on the inner annular ends 1 12a, 1 14a of each of the cylindrical outer members 1 12, 1 14. In an embodiment of the present disclosure, the taper angle is selected to be 40.0 degrees, as shown in Figure 4 for both the contact surface 120 and the matching contact surfaces 122. Radial compressive forces exerted by the C-spacer spring element 1 16, which urge the opposite ends of the C-spacer spring element 1 16 circumferentially towards each other are transferred into axial preload forces acting on the cylindrical outer members 1 12, 1 14 at the interface between tapered contact surfaces 120 and 122, essentially acting as wedge surfaces. The axial preload forces are carried through thθ cylindrical outer members 1 12, 1 14, to the respective outer raceways 1 10 disposed adjacent the outer ends of each of the cylindrical outer members 1 12, 1 14, maintaining a desired uniform preload force on each of the bearing sub-assemblies

104, 106. By maintaining a uniform preload force on each of the bearing sub- assemblies 104, 106 during operation, the bearing assembly 100 has improved acoustical properties and experiences uniform loading, extending useful service life.

Depending upon the specific application in which it is utilized, various configurations for the C-spacer spring element 1 16 in a bearing assembly 100 of the present disclosure may be used, which differ by spring thickness, taper angle of the contact surfaces 120, initial axial displacement, and final axial displacement. The initial and final axial displacements may be selected in order to achieve a desired preload setting on the bearing sub-assemblies 104, 106 when the rotating shaft 102 expands during operating due to thermal effects. Those of ordinary skill in the art will recognize that various design variables operative to provide benefits and liabilities to the C-spacer spring configurations. Based on the manufacturing tolerances and of the bearing assembly 100, the required axial displacements and an acceptable stress level for a C-spacer spring element 1 16 may be optimized for each application.

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 . A bearing assembly (100) for use in medical imaging equipment, supporting a rotating shaft (102) within a bearing housing, comprising: a front bearing sub-assembly (104) including a first outer member (1 12) supporting a first outer raceway (1 10a) disposed coaxially about the rotating shaft (102) within the bearing housing; a rear bearing sub-assembly (106) including a second outer member (1 14) supporting a second outer raceway (1 10b) disposed coaxially about the rotating shaft (102) within the bearing housing; a spring element (1 16) disposed coaxially about the rotating shaft (102), medially between an inner annular surface (1 12a) of said cylindrical outer member (104) and an inner annular surface (1 14a) of said cylindrical outer member (1 14), said spring element (1 16) in engagement with said inner annular surfaces (1 12a, 1 14a) of each of said cylindrical outer members (1 12, 1 14); and wherein said spring element (1 16) is configured to apply an outwardly- directed axial preload force to each of said front and rear bearing sub-assemblies (104, 106) through said cylindrical outer members (1 14, 1 16).

2. The bearing assembly (100) of Claim 1 wherein said spring element (1 16) is a C-spacer spring element having a plurality of contact surfaces (120) in sliding wedge engagement with associated contact surfaces (122) on said inner annular surfaces (1 12a, 1 14a) of each of said cylindrical outer members (1 12, 1 14); and wherein said C-spacer spring element (1 16) is configured to apply said axial preload force to each of said front and rear bearing sub-assemblies (104, 106) through said cylindrical outer members (1 14, 1 16) at interfaces between said contact surfaces (120, 122).

3. The bearing assembly of Claim 2 wherein said plurality of contact surfaces (120) on said C-spacer spring element (1 16) and said associated contact surfaces (122) on said annular inner ends (1 12a, 1 14a) of said cylindrical outer members (1 12, 1 14) are angled.

4. The bearing assembly of Claim 3 wherein an angle of said contact surfaces (120) on said C-spacer spring element (1 16) and said associated contact surfaces (122) on said annular inner ends (1 12a, 1 14a) is selected to achieve a desired preload setting.

5. The bearing assembly of Claim 3 wherein said contact surfaces (120) on said C-spacer spring element 1 16 have an inward taper of approximately 40 degrees relative to an axial side surface (1 18) of said C-spacer spring element; and wherein said associated contact surfaces (122) each have an outward angle of approximately 40 degrees relative to said inner annular surfaces (1 12a, 1 14a); and whereby said contact surfaces (120) and said associated contact surfaces (122) engage in sliding wedge contact.

6. The bearing assembly of Claim 2 wherein said C-spacer spring element (1 16) is configured to exert a radial compressive force; and wherein said plurality of contact surfaces (120, 122) are configured to transfer at least a portion of said radial compressive force axially into each of said cylindrical outer members (1 12, 1 14) to apply said axial preload force to said front and rear bearing sub- assemblies (104, 106).

7. The bearing assembly of Claim 2 wherein a spring thickness of said C- spacer spring element (1 16) is selected to achieve a desired preload setting.

8. A method for applying a preload to a bearing assembly (100) having a rotating shaft (102) supported by an inner bearing sub-assembly (104) and an outer bearing sub-assembly (106), comprising: disposing an annular spring element (1 16) medially between said inner bearing assembly (104) and said outer bearing sub-assembly (106); and applying, from said annular spring element (1 16), an axial outwardly directed preload force to each of said bearing sub-assemblies (104, 106).

9. The method of Claim 8 wherein said annular spring element (1 16) is a C-spacer spring element having a radially compressive spring force urging contact surfaces (120) on first and second ends of said C-spacer spring element toward each other; and engaging said contact surfaces (120) with matching associated contact surfaces (122) on inner annular surfaces (1 12a, 1 14a) of said bearing sub- assemblies (104, 106), whereby said radially compressive spring force exerts said axial outwardly directed preload force to each of said bearing sub-assemblies (104, 106).