Suspension Assembly for Mechanically Retaining a First Article by Bracing it Against a Second Article
A suspension assembly for mechanically retaining a first article by bracing it against a distant second article, includes a tensile rod that extends between first and second articles. At least one first surface is mechanically linked to the tensile rod, and at least one second surface mechanically linked to the first article. The first surface and said second surface are braced against one another by tension in the tensile rod, and have at least three separate points of contact between them. At least one of the first and second surfaces is non-planar, and at least one of the points of contact is provided by a part of the surface which is convex and non-planar.
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This application is related to co-pending U.S. patent application Ser. No. ______, filed concurrently herewith, and entitled “Suspension assembly for mechanically retaining a first article by bracing it against a second article”.
This application is a continuation of PCT International Application No. PCT/GB2007/050248, filed May 10, 2007, which claims priority under 35 U.S.C. §119 to British Patent Application No. 0609247.2, filed May 10, 2006, the entire disclosure of which is herein expressly incorporated by reference.
BACKGROUND OF THE INVENTION Summary of the InventionThe present invention relates to a suspension assembly and a suspension system for supporting a first article by bracing it against a second article. While the suspension assembly and suspension system of the present invention is of general application, and may find use in many constructions, it is considered to be particularly useful in retaining containers one inside the other, with precisely defined separation between the respective walls of the containers. An example of such use is in retaining cryogen vessels within outer vacuum containers in cryostats, for example those used for accommodating magnets for MRI imaging systems. Another application lies in the retaining of a cryogen vessel within outer vacuum container in cryostats used for cryogenic storage of liquefied gases. The present invention is particularly advantageous when an intermediate article must be suspended between the first and second articles. In the example of cryogen vessels within an outer vacuum container, the intermediate article will typically be a thermal radiation shield, located concentrically with the cryogen vessel and the outer vacuum container, and intermediate between them.
Known systems comprising a cryogen vessel and radiation shield/s suspended within a vacuum vessel are commonly suspended using tensile elements with a low thermal conductivity and small cross-sectional area to reduce the heat flow to the cryogen vessel. These tensile elements are made as long as is possible to maximise their effectiveness by reducing their thermal conductivity. In certain configurations the design of the vessels is not conducive to long, tensile elements and a shorter, more compact element would be more suitable. The present invention addresses this need, and in certain embodiments aims to provide a suspension system suitable for cryogen vessels wherein placement of long tensile elements is not possible, or not desirable.
The present invention relies on the use of hard materials in certain shapes to ensure a minimum contact area between articles, so minimising thermal conduction between the articles. The suspension system of the present invention is also very compact, requiring only a small separation distance between the articles. The suspension system of the present invention is also particularly robust and simple to adjust.
Accordingly, the present invention provides suspension systems as defined in the appended claims.
The above, and further, objects, characteristics and advantages of the present invention will become more apparent from consideration of the following description of certain embodiments thereof, in conjunction with the accompanying drawing, wherein:
The present invention advantageously employs the minimal contact area between two hard surfaces, of which at least one is non-planar, in order to provide a rigid suspension system which is easy to adjust and which has minimal thermal conductivity. In preferred embodiments, spherical or spheroid surfaces are employed, as described below, but other surfaces could be used.
In the illustrated embodiment, the suspension assembly 20 comprises a central spherical element 16 retained against the first article 12 by a group of at least three outer spherical elements 18. The opposing side of the central spherical element 16 is preferably retained against the second article 14 in an identical manner.
A housing 22 for the outer spherical elements 18 between the central spherical element 16 and the second article 14 could be threaded 19 on its outer periphery and retained within a threaded carrier 24, thereby allowing rotation of the housing 22 to apply preload to the suspension assembly 20. After suitable adjustment, the position of housing 22 within the threaded carrier 24 may be locked and sealed by welding the housing 22 to the threaded carrier 24. Alternatively for an adjustable system an ‘o’ ring style seal could be used. It is generally sufficient for only one side of the suspension assembly to be adjustable, since preload applied from one side will preload the whole assembly. A housing 26 for the outer spherical elements 18 between the central spherical element 16 and the first article 12 could be fixed, as shown in
While the described adjustment 22, 24 is useful in providing a preload on the suspension assembly 20, the same adjustment method may be applied to adjust the relative position of the cryogen vessel, first article 12, within the outer vacuum container, second article 14.
In the illustrated embodiment, an intermediate article 30, in this example a thermal radiation shield, is retained between the first article 12 and the second article 14. This intermediate article is, in the illustrated embodiment, restrained by a retainer 32 mounted on the central spherical element 16. The suspension assemblies 20 typically serve to hold first and second articles at a predetermined separation d, and to retain the intermediate article 30, if any, at predetermined distances e, f, from the first and second articles. As may be appreciated from consideration of
A particular feature of the suspension system of the present invention is that only minimal surface area of physical contact is present between the central element 16 and the outer elements 18. This ensures a correspondingly low thermal conduction between first and second articles. In the embodiment illustrated in
Suitable hard materials may be: hardened steels (e.g. tool steels or bearing steels); ceramics may be preferable being harder and having lower thermal conductivity; silicon nitride; tungsten carbide; zirconium oxide; boron nitride; diamond. Coated or surface modified materials may also be appropriate, such as nitrided steels, case hardened steels, or ion implanted surfaces. Other surface treatments such as laser glazing for promoting hard and preferably wear resisting surfaces may be used to provide surfaces for use in the present invention.
Another particular feature of the suspension system of such embodiments of the present invention is that it is particularly low profile. As in the embodiment illustrated in
The suspension arrangement of the present invention allows a relatively small, adjustable suspension assembly 20 to resist loads in all three xyz axes due to the central spherical element 16 being trapped between the two sets of outer spherical elements 18. This could allow a minimum number of these suspension assemblies 20 to fully constrain a typical cryogenic vessel within an outer vacuum container. A possible system configuration is shown in
The suspension assembly 20 illustrated in
The embodiment of
In addition to these variations on the sizes and placing of the spherical elements, other general variations may be provided within the scope of the present invention. For example, the various spherical elements may be replaced by spheroid elements, or indeed elements of any shape provided that they contact each other at only a single point. Examples may include oblate spheroid, prolate spheroid, cone or truncated cone, pyramid or truncated pyramid, or part surfaces of any of these shapes.
In all of the embodiments disclosed with reference to
Suitable hard materials may be: hardened steels (e.g. tool steels or bearing steels); ceramics may be preferable being harder and having lower thermal conductivity; silicon nitride; tungsten carbide; zirconium oxide; boron nitride; diamond. Coated or surface modified materials may also be appropriate, such as nitrided steels, case hardened steels, or ion implanted surfaces. Other surface treatments such as laser glazing for promoting hard and preferably wear resisting surfaces may be used to provide surfaces for use in the present invention.
The above-described embodiments each provide a compression suspension assembly, in that a central member is provided, which is retained in compression by outer members respectively attached to first and second articles. A further set of embodiments of the present invention will now be described. The following embodiments provide tensile suspension assemblies, in that a central member is held in tension between two outer members respectively attached to first and second articles.
Suitable hard materials may be: hardened steels (e.g. tool steels or bearing steels); ceramics may be preferable being harder and having lower thermal conductivity; silicon nitride; tungsten carbide; zirconium oxide; boron nitride; diamond. Coated or surface modified materials may also be appropriate, such as nitrided steels, case hardened steels, or ion implanted surfaces. Other surface treatments such as laser glazing for promoting hard and preferably wear resisting surfaces may be used to provide surfaces for use in the present invention.
In a variation of this embodiment, illustrated in
Further variations on the embodiment of
As already described with reference to certain embodiments, it is preferred that the suspension assembly be provided with a means for applying a preload. In the context of the embodiments of
The second article 102 is preferably also provided with a suspension assembly 100 according to any of the described embodiments, although the invention covers suspension arrangements which employ a suspension assembly 100 at one end only of the tensile rod, with a conventional mounting arrangement at the other end of the tensile rod.
Although many variations on shape are possible, in a preferred embodiment, the surface of the larger element 106 is at least part of a sphere. Such a surface allows the tensile rod 102 to be directed in any direction available, which is constrained at least by the dimensions of the through-hole between the contacting surfaces 104, without difficulty, and without the length of the tensile rod 104 requiring adjustment, which may not be the case with larger elements 106 of other shapes.
In further embodiments, as illustrated by way of example in
The above described example embodiment each comprise either a single compression suspension assembly, in which a central object is compressed between first and second surfaces, each braced between the central object and a respective one of first and second articles; or a single tensile suspension assembly, in which a tensile rod is linked to a first surface, which bears on a second surface, which is itself mechanically linked to a first article. However, further embodiments of the present invention include further sets of contact points, arranged in series in the thermal path between first and second objects to further increase impedance to thermal conduction through the suspension assembly. For example,
While the present invention has been described with reference to a limited number of particular embodiments, one skilled in the art will understand that numerous variations may be made within the scope of the claimed invention.
Claims
1. A suspension assembly for mechanically retaining a first article by bracing it against a distant second article, said suspension assembly comprising:
- a tensile rod extending between first and second articles;
- at least one first surface mechanically linked to the tensile rod, and
- at least one second surface mechanically linked to the first article; wherein
- said at least one first surface and said at least one second surface are braced against one another by tension in the tensile rod;
- said at least one first surface and said at least one second surface have at least three separate points of contact between them;
- at least one of said at least one first surface and said at least one second surface is non-planar; and
- at least one of the points of contact is provided by a part of the surface which is convex and non-planar.
2. The suspension assembly according to claim 1, wherein:
- at least one of the points of contact is provided by respective opposing portions of said at least one first surface and said at least one second surface; and
- each of said opposing portions comprises a convex non-planar surface.
3. The suspension assembly according to claim 2, wherein the at least one convex non-planar surface is one of a sphere and a spheroid.
4. The suspension assembly according to claim 1, wherein one of said at least one first surface and said at least one second surface comprises a set of at least three objects retained together in fixed relative positions, which objects are one of spherical and spheroidal.
5. The suspension assembly according to claim 1, wherein one of said at least one first surface and said at least one second surface comprises an article having at least three surfaces retained together in fixed relative positions, said at least three surfaces being one of part spherical and part spheroidal.
6. The suspension assembly according to claim 1, wherein one of said at least one first surface and said at least one second surface comprises by an interior surface of a cup having a corresponding at least three protrusions on said interior surface.
7. The suspension assembly according to claim 1, wherein:
- one of said at least one first surface and said at least one second surface has the form of an interior surface of a cup; and
- said interior surface comprises one of a hollow pyramid or hollow truncated pyramid.
8. The suspension assembly according to claim 6, wherein:
- an interior surface of the cup is in the form of one of a hollow hexagonal pyramid and a hollow hexagonal truncated pyramid; and
- alternate sides of the hexagonal pyramid are larger than intervening sides therebetween.
9. The suspension assembly according to claim 1, wherein at least one of said at least one first surface and said at least one second surface comprises a substantially planar backplate having a number of protrusions thereon.
10. The suspension assembly according to claim 1, wherein one of said at least one first surface and said at least one second surface is one of spheroidal and spherical.
11. The suspension assembly according claim 10, wherein an other one of said at least one first surface and said at least one second surface comprises at least three objects retained together in fixed relative positions, which objects are one of spherical, spherioidal, part spherical and part spheroidal.
12. The suspension assembly according to claim 1, wherein at least one of the at least one first surface and the at least one second surface is braced against a corresponding one of the first or second articles through an adjustment device which may be adjusted to apply a mechanical tensile preload to the tensile rod.
13. The suspension assembly according to claim 1, wherein an intermediate object is provided, held in compression between first surface and second surface.
14. A suspension assembly comprising:
- a tensile rod which passes between at least three rounded surfaces attached to an article; and
- a rounded element attached to one end of the tensile rod, so as to bear on the rounded surfaces attached to the article.
15. The suspension assembly according to claim 14, further comprising a corresponding structure provided on a second article, at the other end of the tension rod.
16. A suspension assembly for mechanically retaining a first article by bracing it against a second article, said suspension assembly comprising:
- a tensile rod which passes through a rounded surface attached to the first article; and
- an element comprising a set of at least three rounded surfaced attached to an end of the tensile rod;
- wherein each of the set of rounded surfaces bears on the rounded surface attached to the first article.
17. A suspension assembly for mechanically retaining a first article by bracing it against a second article, comprising:
- a tensile rod which passes through a set of at least three rounded surfaces attached to the first article; and
- an element comprising a rounded surface attached to an end of the tensile rod;
- wherein the rounded surface bears on each of the set of rounded surfaces attached to the first article.
18. A cryostat comprising a cryogen vessel retained within an outer vacuum vessel by a suspension system comprising at least one suspension assembly according to claim 1, wherein the first article is the cryogen vessel and the second article is the outer vacuum vessel.
Type: Application
Filed: Oct 1, 2008
Publication Date: Jan 22, 2009
Applicant: Siemens Magnet Technology Limited (Witney)
Inventor: Peter Gore (Abingdon Oxfordshire)
Application Number: 12/243,515
International Classification: F25B 19/00 (20060101); A47G 29/00 (20060101);