GB2562261A

GB2562261A - Motor Rotor

Info

Publication number: GB2562261A
Application number: GB1707460.0A
Authority: GB
Inventors: Lee Harkin Richard; Kailasam Sivabalan; Martina Skinner Ulrike
Original assignee: Edwards Ltd
Current assignee: Edwards Ltd
Priority date: 2017-05-10
Filing date: 2017-05-10
Publication date: 2018-11-14
Also published as: GB201707460D0; KR20180003246U; TWM570559U; JP3217140U; CN208723644U; KR200497518Y1; DE202018002207U1

Abstract

A motor rotor 10 comprising a magnet carrier 20; a magnet 40 carried by the magnet carrier; a sleeve 60 surrounding the magnet; and first and second circumferential seals 52 located to seal the magnet within a void between the carrier and the sleeve. The seals are located to hermetically seal the magnet at axial ends 30 of the magnet, wherein the magnet extends between the first and second seals. The magnet carrier and sleeve may extend axially beyond the first and second seals. The carrier may have an annular shoulder 27B positioned to locate the magnet at an axial position on the carrier, where the seal is located proximate to the shoulder. The shoulder may also have a circumferential recess 27C to receive the first seal and the carrier may also be dimensioned to receive the second seal. The seals may comprise of a potting compound or an O-ring, where the seals comprise a synthetic rubber and fluoro-polymer elastomer compound. The magnet may comprise a ring magnet that comprise a plurality of C-shaped magnet segments, where the magnet comprises a rare earth magnet, or one of a group comprising iron boron and samarium cobalt. The motor rotor may be used in a vacuum pump.

Description

MOTOR ROTOR

FIELD OF THE INVENTION

The present invention relates to a motor rotor and method.

BACKGROUND

Motors are known. In an electrical motor, a rotor assembly is provided which rotates with respect to a non-rotating part or stator. In one arrangement of motor, the stator contains one or more coils which surround the rotor assembly having one or more magnets. Activation of the coils causes the rotor assembly to spin within the stator.

Although motors are useful, their operation can have unexpected consequences. Accordingly, it is desired to provide an improved rotor.

SUMMARY

According to a first aspect, there is provided a motor rotor comprising: a magnet carrier; a magnet carried by the magnet carrier; a sleeve surrounding the magnet; and first and second circumferential seals located to seal the magnet within a void between the magnet carrier and the sleeve. The first aspect recognises that when operating a motor in a challenging environment, such as would occur when operating a motor in an aggressive chemical environment where chemicals in the environment can attack or degrade the performance of the rotor, it may be desirable to seal off the magnet from that environment in order to maintain its performance.

Accordingly, a rotor is provided. The rotor may be for an electric motor. The rotor may comprise a magnet carrier or holder. The rotor may also comprise one or more magnets carried by or fixed to the magnet carrier. The rotor may also comprise a sleeve or housing which may surround or receive the magnets therewithin. The rotor may also comprise at least one, and preferably a pair of, circumferential or annular seals. The seals may be located to seal the magnet within a void or opening created between the magnet carrier and the sleeve. In this way, the magnet is encapsulated by re-using the magnet carrier and the sleeve in conjunction with the seal, in order to fluidly-isolate or protect the magnet from chemicals in the environment within which it operates. This helps to prevent damage to the magnet caused by adverse chemicals in the environment.

In one embodiment, the first and second circumferential seals are located at axial ends of the magnet. Accordingly, the seals may be located or positioned at either end of the magnet.

In one embodiment, the magnet extends axially between the first and second circumferential seals. Accordingly, the magnet may be provided between the seals.

In one embodiment, the magnet carrier and the sleeve extend axially beyond the first and second circumferential seals. Accordingly, the magnet carrier and/or the sleeve may extend in the axial direction past the seals in order to retain the seals.

In one embodiment, the magnet carrier has an annular shoulder positioned to locate the magnet at an axial position on the magnet carrier. Accordingly, the magnet carrier may have a shoulder or protrusion which upstands radially from its outer surface, against which the magnet may abut to locate the magnet at a selected position axially on the magnet carrier. This helps to align the magnet with the coils.

In one embodiment, the first circumferential seal is located proximate the annular shoulder. Accordingly, the annular shoulder may be positioned adjacent the first seal to help to locate the first seal.

In one embodiment, the annular shoulder defines a first circumferential recess dimensioned to receive the first circumferential seal. Accordingly, the annular shoulder may at least partially define or provide a portion of a circumferential groove on the outer surface of the magnet carrier into which the circumferential seal may be seated.

In one embodiment, the magnet carrier defines a second circumferential recess dimensioned to receive the second circumferential seal. Providing a further circumferential groove on the outer surface of the magnet carrier helps to retain the seal in place.

In one embodiment, the sleeve is retained by the first and second circumferential seals. Accordingly, the sleeve may be located on, or held in place by, the circumferential seals in order to hold the sleeve, the magnet and the seals in place.

In one embodiment, the sleeve and the magnet carrier are dimensioned to compress the first and second circumferential seals. Accordingly, the seals may be compressed or squeezed between the sleeve and the magnet carrier in order to hold them in place and to improve the sealing of the magnet.

In one embodiment, the first and second circumferential seals comprise at least one of a potting compound seal and an O-ring seal.

In one embodiment, the first and second circumferential seals comprise a synthetic rubber and fluoropolymer elastomer compound.

In one embodiment, the magnet comprises a ring magnet.

In one embodiment, the ring magnet comprises a plurality of C-shaped magnet segments.

In one embodiment, the rotor comprises a fixing operable to fix the magnet to the magnet carrier.

In one embodiment, the magnet comprises a rare earth magnet.

In one embodiment, the magnet comprises one of a group comprising iron boron and samarium cobalt.

In one embodiment, the first and second circumferential seals are located to hermetically seal the magnet within the void between the magnet carrier and the sleeve.

According to a second aspect, there is provided a vacuum pump comprising the motor rotor of the first aspect.

According to a third aspect, there is provided a method, comprising: providing a magnet carrier; providing a magnet carried by the magnet carrier; providing a sleeve surrounding the magnet; and locating first and second circumferential seals to seal the magnet within a void between the magnet carrier and the sleeve.

In one embodiment, the method comprises locating the first and second circumferential seals at axial ends of the magnet.

In one embodiment, the magnet extends axially between the first and second circumferential seals.

In one embodiment, the magnet carrier and the sleeve extend axially beyond the first and second circumferential seals.

In one embodiment, the method comprises locating the magnet against an annular shoulder on the magnet carrier to locate the magnet at an axial position on the magnet carrier.

In one embodiment, the method comprises locating the first circumferential seal proximate the annular shoulder.

In one embodiment, the method comprises receiving the first circumferential seal in a first circumferential recess defined by the annular shoulder and dimensioned to receive the first circumferential seal.

In one embodiment, the method comprises receiving the second circumferential seal in a second circumferential recess defined by the magnet carrier.

In one embodiment, the method comprises retaining the sleeve with the first and second circumferential seals.

In one embodiment, the method comprises dimensioning the sleeve and the magnet carrier to compress the first and second circumferential seals.

In one embodiment, the first and second circumferential seals comprise one of a potting compound seal and an O-ring seal.

In one embodiment, the magnet comprises a ring magnet.

In one embodiment, the method comprises fixing the magnet to the magnet carrier.

In one embodiment, the magnet comprises a rare earth magnet.

Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.

Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

Figures 1A to 1D illustrate a motor rotor, generally 10, according to one embodiment.

DESCRIPTION OF THE EMBODIMENTS

Before discussing the embodiments in any more detail, first an overview will be provided. Embodiments provide an electrical motor rotor assembly which is less susceptible to chemical attack in harsh chemical environments. In particular, embodiments provide an arrangement whereby the magnet of the motor rotor and any adhesives used to fix the magnet to a magnet carrier is hermetically sealed against chemicals present in the environment in which the motor operates. The magnet typically comprises a surface ring permanent magnet which may be unitary or formed from C-shaped components and is received on a magnet carrier. The magnet carrier forms part a hermetically sealing enclosure to protect the magnet from chemical attack from chemicals present in the environment in which the motor rotor is placed. In some embodiments, the magnet is fixed to the magnet carrier using an adhesive. A cylindrical sleeve is coaxially located to surround the magnet, which protects the radially outer surface of the magnet from mechanical damage during assembly, helps retain the magnet in place under strong centrifugal forces and provides part of the hermetically sealing enclosure. At either end of the magnet, a circumferential seal is provided which also provides part of the hermetically sealed enclosure, seals each axial end of the magnet and fully encloses the magnet within an annular void defined by the motor carrier, the sleeve and the circumferential seals themselves. Such hermetic sealing protects the ring permanent magnet from chemical attack during operation of the rotor motor and protects any adhesive, when present.

Rotor Assembly

Figure 1A is a side view illustrating a motor rotor, generally 10, according to one embodiment. Figure 1B is a sectional side view of the motor rotor 10. Figure 1C is a perspective view of the motor rotor 10. Figure 1D is another perspective view of the motor rotor 10. The motor rotor 10 comprises a magnet carrier 20. In this example, the magnet carrier 20 is formed from C45E carbon steel, which provides a good magnetic circuit for the magnet. The magnet carrier is an elongate cylinder with a profiled inner and outer surface, as will now be explained. The magnet carrier 20 defines a radially inner bore 25 which is shaped to receive a rotor shaft (not shown). The magnet carrier 20 has a radially outer surface 27 which is profiled. A first portion 27A of the outer surface 27 is cylindrical and extends from an axial end 30 to a first shoulder 27B which upstands radially from the first portion 27A. A second shoulder 27D upstands radially from the first portion 27A, is located axially away from the first shoulder 27B and, together with the first shoulder 27B, defines a circumferential groove 27C. The second shoulder 27D upstands radially by a height which is greater than that of the first shoulder 27B.

The motor rotor 10 also comprises a surface ring permanent magnet 40 which is a cylindrical annular ring having a radially inner surface 43, a radially outer surface 47 and annular ends 41,49. In this embodiment, the surface ring permanent magnet 40 is made from neodymium iron boron or samarian cobalt.

The motor rotor 10 also comprises O-ring seals 52, 50, located proximate the axial end 30 and within the groove 27C, respectively. In this embodiment, the Ci-ring seals are made from Viton (trade mark). The first portion 27A can optionally be provided with a slight groove proximate the axial end 30 in order to help assist retention of the O-ring seal 52.

The motor rotor 10 also comprises a sleeve 60 which is coaxially located and circumferentially surrounds the surface ring permanent magnet 40 and the O-ring seals 50, 52. In this embodiment, the sleeve 60 is grade 303 stainless steel formed into a cylinder having an inner surface 63 and an outer surface 65.

Assembly of the rotor motor 10 will now be described. The magnet carrier 20 is provided and the surface ring permanent magnet 40 is moved from the axial end 30, along the axial length of the first portion 27A until it abuts against the first shoulder 27B. Any adhesive placed between the outer surface 27 and the inner surface 43 adheres the surface ring permanent magnet 40 to the magnet carrier 20 so that the magnet carrier 20 rotates when the surface ring permanent magnet 20 is urged by a surrounding coil (not shown) ofthe motor.

The O-ring 50 is received in the groove 27C and the O-ring 52 is moved over the axial end 30 and abuts against an axial end of the surface ring permanent magnet 40 and retained by the slight groove proximate the axial end 30 (if provided).

The sleeve 60 is then moved from the axial end 30 over the O-ring 52 (which is held in place by the surface ring permanent magnet 40), over the surface ring permanent magnet 40 (which is retained in place by the first shoulder 27B) and over the O-ring 50 (which is retained in place by the second shoulder 27D).

The relative dimensions of the magnet carrier 20, the sleeve 60 and the O-rings 50, 52 compress the O-rings 50, 52 to form a hermetic circumferential seal at both axial ends of the surface ring permanent magnet 40.

Accordingly, it can be seen that the surface ring permanent magnet 40 is hermetically sealed from ingress by chemicals which could degrade the surface ring permanent magnet 40 itself or any adhesive used to fix the surface ring permanent magnet 40 onto the magnet carrier 20.

Although the embodiment mentioned above uses O-ring seals, it will be appreciated that potting compounds may also be utilised and that the profile of the outer surface 27 could be changed accordingly. It will also be appreciated that the application of such potting compound would typically occur under vacuum conditions.

Previously, permanent magnet motor solutions have tended to be on benign I light-duty vacuum applications. Such permanent magnet motor solutions have predominantly been surface-ring permanent magnet motor designs due to their cheap and simple construction. However, as mentioned above, both the magnet and glue in these designs are vulnerable to chemical attack especially in medium and harsh-duty vacuum applications.

Embodiments improve the robustness and reliability of surface-ring permanent magnet motor designs with a hermetically sealed carrier that has been designed to extend the application suitability of surface-ring permanent magnet motors from light-duty load-lock applications to medium and harsh vacuum applications.

The use of rare earth magnets and glues, especially neodymium iron boron, are vulnerable to long-term chemical attack during certain vacuum applications, e.g. high concentration levels of hydrogen and fluorine. Over time the glue and the magnet assemblies can weaken resulting in poor performance and ultimately motor failure. As a consequence of this failure mode induction motor technology has typically been used in medium and harsh vacuum applications, with surfacering permanent magnet motor technology only being used on light-duty load-lock applications specifically within semiconductor processing applications.

Embodiments provide a hermetically sealed magnet arrangement which protects both the rare earth magnet and the glue from chemical attack. This provides a more reliable motor arrangement for medium and harsh vacuum applications therefore enabling the use of high efficiency synchronous motors in more semiconductor processing applications.

Embodiments include the following components: 1. C45E carbon steel magnet carrier - this provides a good magnetic circuit for the magnet; 2. Two O-ring grooves machined on the carrier - this provides a reliable location for the two sealing O-rings; 3. Two VITON (trade mark) O-rings - VITON (trade mark) is a proven material for medium and harsh vacuum applications; 4. Neodymium iron boron (Nd Fe B) magnet ring - this provides a cost effective magnet solution with excellent magnet strength; 5. Grade 303 Stainless steel protective sleeve.

The use of VITON (trade mark) O-rings to provide a hermetic seal for the magnet and the glue. The O-ring compression also holds the protective stainless steel sleeve in place therefore removing the need for glue on the outer sealing surface.

Embodiments enable use of surface-ring permanent magnet motors in semiconductor vacuum applications. However, the approach could be used in other industrial applications.

Although illustrative embodiments ofthe invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

REFERENCE SIGNS motor rotor 10 magnet carrier 20 inner bore 25 outer surface 27 first portion 27A first shoulder 27B groove 27C first shoulder 27D axial end 30 permanent magnet 40 inner surface 43 outer surface 47 annular ends 41,49 O-ring seals 52, 50 sleeve 60 inner surface 63 outer surface 65

Claims

1. A motor rotor comprising: a magnet carrier; a magnet carried by said magnet carrier; a sleeve surrounding said magnet; and first and second circumferential seals located to seal said magnet within a void between said magnet carrier and said sleeve.

2. The motor rotor of claim 1, wherein said first and second circumferential seals are located at axial ends of said magnet.

3. The motor rotor of claim 1 or 2, wherein said magnet extends axially between said first and second circumferential seals.

4. The motor rotor of any preceding claim, wherein said magnet carrier and said sleeve extend axially beyond said first and second circumferential seals.

5. The motor rotor of any preceding claim, wherein said magnet carrier has an annular shoulder positioned to locate said magnet at an axial position on said magnet carrier.

6. The motor rotor of claim 5, wherein said first circumferential seal is located proximate said annular shoulder.

7. The motor rotor of preceding claim 5 or 6, wherein said annular shoulder defines a first circumferential recess dimensioned to receive said first circumferential seal.

8. The motor rotor of any preceding claim, wherein said magnet carrier defines a second circumferential recess dimensioned to receive said second circumferential seal.

9. The motor rotor of any preceding claim, wherein said sleeve is retained by said first and second circumferential seals.

10. The motor rotor of any preceding claim, wherein said sleeve and said magnet carrier are dimensioned to compress said first and second circumferential seals.

11. The motor rotor of any preceding claim, wherein said first and second circumferential seals comprise one of a potting compound seal and an Ci-ring seal.

12. The motor rotor of any preceding claim, wherein said first and second circumferential seals comprise a synthetic rubber and fluoropolymer elastomer compound.

13. The motor rotor of any preceding claim, wherein said magnet comprises a ring magnet.

14. The motor rotor of claim 13, wherein said ring magnet comprises a plurality of C-shaped magnet segments.

15. The motor rotor of any preceding claim, wherein said magnet comprises a rare earth magnet.

16. The motor rotor of any preceding claim, wherein said magnet comprises one of a group comprising iron boron and samarium cobalt.

17. The motor rotor of any preceding claim, wherein said first and second circumferential seals are located to hermetically seal said magnet within said void between said magnet carrier and said sleeve.

18. A vacuum pump comprising the motor rotor of any preceding claim.

19. A method, comprising: providing a magnet carrier; providing a magnet carried by said magnet carrier; providing a sleeve surrounding said magnet; and locating first and second circumferential seals to seal said magnet within a void between said magnet carrier and said sleeve.