AU761353B2

AU761353B2 - Magnetic repulsion bearings for electricity meters

Info

Publication number: AU761353B2
Application number: AU51931/00A
Authority: AU
Inventors: Stephen Donnelly
Original assignee: Email Ltd
Current assignee: EMWEST PRODUCTS Pty Ltd
Priority date: 1999-08-24
Filing date: 2000-08-10
Publication date: 2003-06-05
Anticipated expiration: 2020-08-10
Also published as: AU5193100A

Description

1

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Magnetic Repulsion Bearings for Electricity Meters The following statement is a full description of this invention, including the best method of performing it known to me:- FIELD OF THE INVENTION o The following invention relates to magnetic bearings. More particularly, though not S.exclusively, the invention relates to magnetic repulsion bearings, typically provided in pairs where the rotational axis of one bearing substantially coincides with the :10 longitudinal central axis of the other bearing.

It is known to provide concentrically aligned bearings having flat faces, each defining o a like magnetic pole facing one another such that the bearings repel each other. An application of such known bearings is in the suspension of the disk of an electricity meter. In such installations, the disk is affixed to a rotary shaft, one end of the shaft having a mild steel cup within which a flat faced ferrite magnet is received. The e "rotational centre line of the shaft coincides with that of a lower bearing housing which ooooo supports a magnet within a ferrous cup. The magnets face each other such that like poles (either N or S) face each other. The upper bearing is suspended as a result of magnetic flux forces generated parallel to the axis of the rotating shaft. However, when the bearings become misaligned, the radial forces applied to the suspended bearing can cause that bearing to shift sideways such that the bearings become nonconcentric. Moreover, the radial force profile (ie. a plot of radial force versus axial displacement) of such known bearings is non-linear. This is most probably due to the ferrous components which cause localised and high flux densities. As the surfaces slide past each other they cause a rapid increase in force. This type of non-linear force behaviour is not desirable and would be greatly improved by the removal of the ferrous cup.

OBJECT OF THE INVENTION It is the object of the present invention to overcome or substantially ameliorate the above problem and/or more generally to provide an improved magnetic bearing assembly, typically for use in electricity meters.

DISCLOSURE OF THE INVENTION There is disclosed herein a bearing assembly for an electricity meter, the assembly ooooi comprising: S.a lower housing formed of non-ferrous material, 15 a lower magnetic bearing having a substantially upwardly presented face mounted within the housing, a lower pin mounted within the housing and passing through the lower magnetic bearing, a moving element shaft substantially co-linear with the lower pin and 20 including means cooperative therewith, and an upper magnetic bearing mounted to the moving element shaft and including a face presented downwardly toward the upwardly presented face of the lower magnetic bearing, said faces having like magnetic polarity so as to repel one another oooeo 0 so as to suspend the moving element shaft.

Preferably the faces of the upper and lower magnetic bearings are frusto-conical.

Preferably said face of one of the magnetic bearings, typically the upper magnetic bearing, is frusto-conically convex.

Preferably said face of the other of the magnetic bearings, typically the lower magnetic bearing, is frusto-conically concave.

3 Preferably the means cooperative with the lower pin include a rotor bush fitting with an end opening of the moving element shaft and bearing against an outer surface of the lower pin.

Preferably the rotor bush is made of a material having a low coefficient of friction.

Preferably both the upper and lower magnetic bearings having one or more annular planar surfaces.

Preferably one or each of said annular planar surfaces is/are disposed at an outer periphery of the respective magnetic bearing.

Preferably one or each of said annular planar surfaces is/are disposed at an inner S•periphery of the respective magnetic bearing.

Preferably the upper and lower magnetic bearings are manufactured by injection moulding.

Preferably the lower bearing includes a plurality of longitudinal ribs disposed at its *20 periphery, the ribs serving to tightly engage the bearing within a recess formed in the lower bearing housing.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings wherein: Figure 1 is a schematic cross-sectional elevational view of part of an electricity meter incorporating a magnetic bearing assembly; Figure 2 is a schematic plan view of a lower magnetic bearing; Figure 3 is a schematic cross-sectional elevational view of the lower magnetic bearing of Figure 2 taken at A-A in Figure 2; Figure 4 is a schematic diagram indicating lines of magnetic flux about a portion of a pair of opposed magnetic bearings within the assembly of Figure 1; Figures 5A, 5B and 5C are schematic partial elevational views of alternative bearing geometries; and Figure 6 is a schematic cross-sectional elevational view showing alternative magnetic field alignments.

DESCRIPTION OF THE PREFERRED EMBODIMENT In Figure 1 of the accompanying drawings there is schematically depicted a bearing assembly 10. Assembly 10 includes a lower bearing housing 15 typically fabricated from free machining aluminium rod to AS1864 (alloy 2011 However, any non- .ooooi ferrous, hard, strong material might be used. Within the lower bearing housing there is received a lower pin 16 typically fabricated from wire grade stainless steel 15 (typically 302 stainless steel). However, any strong, rigid material might be used. The lower end of the pin 16 is firmly affixed within a lead alloy 17 which is diecast in the lower end of the lower bearing housing 15. The pin 16 might typically include a flattened portion which, when embedded within the lead alloy 17, prevents spinning of the lower pin therein.

The lower bearing housing 15 includes a recess within which there is received a lower magnetic bearing 18. The lower magnetic bearing 18 is generally disk shaped and has its magnetic north pole pointing upwardly. As shown in Figure 2, the lower magnetic "bearing 18 includes a number (typically 8 or 10) of longitudinal ribs 21 by which the bearing is tightly received within the recess at the upper part of the housing 15. As shown in Figure 3, the lower bearing 18 includes an outer edge 20 (from which the ribs 21 extend). The bearing 18 also includes a central aperture 25 through which the lower pin 16 extends.

The upper surface of the lower bearing 18 includes a frusto-conically concave surface 22 surrounded by an annular peripheral flat surface 24. A frustoconically concave surface 22 would typically extend at an angle from the horizontal of between 0' and 900. A similar annular flat surface extends from the central aperture 25 to the conical surface 22. The bearing 18 also includes a flat bottom surface 19.

Suspended by magnetic repulsion of the lower magnet 18 is an upper magnet 12 fitted about the lower end of a moving element shaft 11. Shaft 11 typically supports a rotary disk of an electricity meter. Shaft 11 is typically a microfinished round drawn aluminium wire. The lower end of moving element shaft 11 includes a recess within which there is received a rotor bush 13. Bush 13 is typically manufactured from a low coefficient of friction material such as Vespel SP-211D manufactured by DuPont or Torlon 4301 manufactured by Amoco Chemicals Corporation. The rotor bush 13 bears lightly against the outer surface of the lower pin 16 to assist centralising the bearing 12 relative to the bearing 14.

ooo i The bearing 12, part of which is shown in detail in Figure 4, includes an upper surface 25, an outer edge 27, an inner aperture 28 (which receives the lower end of moving 15 element shaft 11), a frusto-conically convex surface 29 and a pair of annular flat '•surfaces 30 and 31. The upper bearing 12 is disposed such that its north pole faces downwardly toward the upwardly facing north pole of the lower bearing. As an alternative, the south poles of bearings 12 and 14 might face one another.

The upper bearing 12 might be injection moulded about the lower periphery of the moving element shaft 11.

As an alternative to the provision of the frusto-conical surfaces 22 and 29, the upper •and lower bearings might be provided with flat planar surfaces.

In an assembly like that shown in Figure 1 but with flat planar facing magnetic bearing surfaces, a linear radial force profile is achieved. That is, the behaviour of the system is linear unlike previous systems which have employed a ferrous cup.

Furthermore, the system exhibits a much lower radial force for a given out of concentricity as a result of this cup removal.

It should be appreciated that modifications and alterations obvious to those skilled in the art are not to be considered as beyond the scope of the present invention. For example, simple axial magnetisation of the bearings 12 and 14 might be changed by using partial radial fields. Furthermore, the pair of magnetic bearings can be inverted such that the downwardly facing surface of the upper bearing is concave and the upwardly facing surface of the lowermost bearing is convex. Furthermore, the geometry of the bearings themselves might be changed as for example as shown in Figures 5A, 5B and 5C, that is, the facing surfaces can be circular, parabolic or stepped. The stepped arrangement of Figure 5C adopts a constant field method whereby the resultant force vector of the vertical and horizontal magnetic force components is angled.

•A further change might be in that of the magnetisation pattern. The magnetisation pattern shown in Figure 4 might be improved upon to provide better alignment results.

That is, instead of the North to South pole centre lines of each of the magnetic bearings extending generally vertically through the centre of the aligned cross-sections as shown in Figure 4, the centre lines might be angularly offset so as to provide a component of resultant force between the two bearings in the horizontal plane. This is .000illustrated in Figure 6 where the angle 0 represents the centre line of the magnetic 20 force as it passes through the lower bearing cross-section. Where the angle 0 is less 00* than 450, the vertical component of force between the facing bearings is greater than the horizontal force component between the bearings at that point. Where 0 is less than 450 the vertical force component is less than the horizontal force component.

The angle 0 might be varied both for the upper and lower bearings to fine tune alignment properties.

Another change might be in the materials chosen for forming the magnetic bearings themselves. Also, the method of forming the bearings can be changed. For example, the method might be injection moulding, compression bonding or sintering. The materials might be ferrite, NdFeD, FdB, SmCo or AlNiCo, for example. Furthermore, the internal structure of the bearings might be isotropic or anisotropic.

Claims

1. A bearing assembly for an electricity meter, the assembly comprising: a lower housing formed of non-ferrous material, a lower magnetic bearing having a substantially upwardly presented face mounted within the housing, a lower pin mounted within the housing and passing through the lower magnetic bearing, a moving element shaft substantially co-linear with the lower pin and including means cooperative therewith, and an upper magnetic bearing mounted to the moving element shaft and including a face presented downwardly toward the upwardly presented face of the lower •magnetic bearing, said faces having like magnetic polarity so as to repel one another so as to suspend the moving element shaft.

2. The bearing assembly of claim 1 wherein the faces of the upper and lower magnetic bearings are frusto-conical. *SSS

3. The bearing assembly of claim 1 or claim 2 wherein said face of one of the .20 magnetic bearings is frusto-conically convex.

4. The bearing assembly of claim 3 wherein said one of the magnetic bearings is the upper magnetic bearing.

5. The bearing assembly of claim 3 wherein said face of the other of the magnetic bearings is frusto-conically concave.

6. The bearing assembly of claim 5 wherein said other of the magnetic bearings is the lower magnetic bearing. 8

7. The bearing assembly of any one of the preceding claims wherein the means cooperative with the lower pin include a rotor bush fitting with an end opening of the moving element shaft and bearing against an outer surface of the lower pin.

8. The bearing assembly of claim 7 wherein the rotor bush is made of a material having a low coefficient of friction.

9. The bearing assembly of any one of the preceding claims wherein both the upper and lower magnetic bearings having one or more annular planar surfaces.

The bearing assembly of claim 9 wherein one or each of said annular planar surfaces is/are disposed at an outer periphery of the respective magnetic bearing. :O Oi

11. The bearing assembly of claim 9 wherein one or each of said annular planar 15 surfaces is/are disposed at an inner periphery of the respective magnetic bearing. got 0

12. The bearing assembly of any one of the preceding claims wherein the upper and lower magnetic bearings are manufactured by injection moulding.

13. The bearing assembly of any one of the preceding claims wherein the lower bearing includes a plurality of longitudinal ribs disposed at its periphery, the ribs serving to tightly engage the bearing within a recess formed in the lower bearing *to housing.

14. A bearing assembly substantially as hereinbefore described with reference to the accompanying drawings. DATED this 10th day of August 2000 EMAIL LIMITED By its Patent Attorneys: HALFORD CO