GB2244762A - Bearing assembly with magnetic seal - Google Patents

Abstract

In a xerographic cassette, an auger which is used to transport developer material is driven from outside the cassette and, to that end, the auger shaft 11 extends through a bearing assembly 13 in the cassette wall. To prevent leakage of developer material from the cassette through the bearing assembly, the latter includes at least one magnet 17 which serves to attract and retain material from within the housing to form a seal around the shaft. Two magnets 17, 18 with opposed faces of the same polarity may be provided; alternatively, the magnet may provide a plurality of axially spaced poles, alternate ones of which are of opposite polarity. <IMAGE>

Description

Bearinq Assembly for a Rotatable Member The present invention relates to a bearing assembly for a rotatable member for use, particularly, in a housing containing magnetic material. The assembly is especially useful in a housing containing developer material in a xerographic reproduction machine.

In xerographic copying/printing machines, it is known to supply/transport developer material within a housing by using a rotating member, for example an auger or a paddle wheel, which is driven from outside the housing. To that end, the shaft of the rotating member may extend outside the housing through a bearing in the housing wall. Care must then be taken to ensure that developer material does not leak from the housing through the bearing of the shaft and, usually, that involves the provision of some form of seal for the bearing. A contact seal can be used but has a limited life and may generate heat which can have an adverse effect on the developer material within the housing in that it can result in the formation of agglomerates in the material and those, in turn, can affect the quality of copies/prints produced by the machine.

The developer material within the housing may be ferromagnetic (or include a ferromagnetic component) so that a magnetic brush developer roll can be used to transport developer material to an electrostatic latent image to develop the latter in known manner. US-A-3 788275 describes an arrangement which makes use of the nature of the developer material to prevent the material from contaminating a roller bearing in the development apparatus of an electrostatographic printing machine. The roller bearing supports the hub of a paddle wheel which is used to transport developer material comprising toner particles and magnetizable carrier granules.

Permanent magnets are provided around and within the hub to entrap carrier granules which are then impelled away from the roller bearing, as the paddle wheel rotates, by threaded portions on the internal and external surfaces of the hub.

A linear magnetic seal for preventing leakage of developer material in the region where a moving photoreceptor surface enters the development station of a xerographic copier is described in US-A-3 906 899.

Outside the fieid of xerographic reproduction machines, the use of magnets to prevent the escape of magnetic material from magnetic clutches and similar devices has been described in US A-2 809 733, -2 863 538, -2 996 162 and -3 254 745. In addition, magnetic seals for rotatable shafts are available under the name "Ferrofluidic" (Trade Mark): those seals typically comprise a permanent magnet and two pole pieces which surround the shaft, and a ferromagnetic liquid which is contained in the gap between the shaft and the pole pieces.

It is an object of the invention to provide a bearing assembly for a rotatable shaft suitable for use more especially but not exclusively in a housing containing magnetic material, which assembly is comparatively simple in construction and is also effective to prevent leakage of material from the housing.

The term "magnetic" as used herein refers to a material that is capable of being attracted by a magnet.

The present invention provides a bearing assembly for a non-magnetic rotatable member which is mounted in a housing for powdered magnetic material, the assembly comprising a stationary bearing member which provides a bearing surface for the rotatable member, and a magnet which is mounted in the bearing member and surrounds the rotatable member, the magnet serving to attract and retain magnetic material from within the housing to form a seal preventing leakage of material from the housing between the bearing surface and the rotatable member. The magnet may be located adjacent a second magnet which is mounted on the rotatable member within the housing, the magnets having opposing faces of the same magnetic polarity.Alternatively, there may be a plurality of annular magnets mounted side-by-side in the bearing member, each magnet being magnetized in the radial direction and adjacent magnets being magnetized in opposite directions.

The present invention further provides a bearing assembly for a rotatable member which is mounted in a housing for magnetic material, the assembly comprising a stationary bearing member which provides a bearing surface for the rotatable member, and two magnets which surround the rotatable member and are located adjacent one another, one magnet being mounted in the bearing member and the other being mounted on the rotatable member, the magnets having opposing faces of the same magnetic polarity whereby magnetic material from within the housing is attracted and retained by at least one of the magnets and forms a seal preventing leakage of material from the housing between the bearing surface and the rotatable member.

The present invention also provides a bearing assembly for a rotatable member which is mounted in a housing for magnetic material, the assembly comprising a stationary bearing member which provides a bearing surface for the rotatable member, and a plurality of annular magnets positioned side-by-side in the bearing member and surrounding the shaft, each magnet being magnetized in the radial direction and adjacent magnets being magnetized in opposite directions, the magnets serving to attract and retain magnetic material from within the housing to form a seal preventing leakage of material from the housing between the bearing surface and the rotatable member. The plurality of annular magnets may be provided by a single member having a plurality of magnetized regions, each of which constitutes one of the magnets.

The, or each, magnet may be a ring magnet.

The magnetic material in the housing may be in powdered form: it may, for example, be developer material for a xerographic reproduction machine.

The rotatable member may be a shaft which is supported in the housing wall by the bearing assembly. The shaft may be formed of a plastics material.

In an embodiment of the invention described herein1 the housing is in the form of a cassette which is locatable in, and removable from, the main body of a xerographic reproduction machine.

By way of example, embodiments of the invention will now be described with reference to the accompanying drawings, in which: Fig. is a diagrammatic cross-section of a xerographic cassette including developer apparatus; Fig. 2 is a perspective view of one end of an auger assembly which forms part of the developer apparatus in Fig. 1; Fig. 3 is a longitudinal cross-section, at the same end, of one of the augers of Fig. 2, and Figs. 4 and 5 are similar to Fig. 3 but show other embodiments of the invention.

Fig. 1 shows a xerographic cassette 1 which is designed to be removably-mounted in the main body of a xerographic copying/printing machine. The casette 1 comprises a housing 2 which contains the principal process elements of the machine, namely a photoreceptor 3 in the form of an endless belt with a photosensitive surface, developer apparatus 4, a transfer corotron 5, a cleaning device 6 for the photoreceptor and a charging corotron 7. The function of each of those process elements is well known.

The developer apparatus 4 includes a magnetic brush developer roll 8 and two counter-rotating augers 9, 10 which transport powdered developer material from a hopper and deliver it to the developer roll. The developer material, which may be either a single-component material (i.e.

toner only) or a two-component material (i.e. toner and a carrier), forms a magnetic brush around the developer roll 8, in well known manner, and is transported by the developer roll to the photoreceptor 3 to develop a latent image on the latter.

Each auger shaft 11 (Figs. 2 and 3) extends through the rear wall (not shown) of the cassette housing 2 and the projecting portion of the shaft is splined as indicated at 12 (Fig.2). When the cassette 1 is inserted into the main body of a xerographic copying/printing machine, the splined shaft portions 12 engage in coupling members (not shown) in the machine body and are thereby coupled to a rotational drive member. The rear wall of the cassette housing 2 is a plastics moulding which provides support for the auger shaft bearing assemblies 13 and hence for the auger shafts 11. Each of the augers 9, 10, including its shaft 11, is formed from a non-magnetic material (for example, glass-filled polypropylene).

Each bearing assembly 13 comprises a sleeve 14 which has a radiaily-enlarged portion 15 at its innermost end (i.e. the end that extends into the housing 2), in which a ring magnet 17 is housed.

The internal surface of the sleeve 14 provides a bearing surface for the shaft 11. Projecting outwardly from the sleeves 14 is an integral flange 16 (Fig. 2) which, in turn, is supported in the rear wall of the cassette housing 2.

Mounted on each of the auger shafts 11, within the cassette housing 2, is another ring magnet 18 which faces the magnet 17 in the enlarged portion 15 of the respective bearing assembly 13 The facing surfaces of the rings 17, 18 are of the same magnetic polarity, resulting in an axial force on the shaft 11 in the direction away from the bearing assembly and in a small gap 19 being formed between the faces of the magnets.

At their other ends (not shown), the auger shafts 11 are rotatably supported by thrust washers against a wall of the cassette housing. The thrust washers provide an axial force on each shaft in the opposite direction to that due to the magnets 17, 18.

When the auger shaftsare rotating there will be an axial force on each due to the action of the developer material on the auger. For one of the augers, rotating in one direction, that force will be opposed by the force due to the magnets 17, 18 and for the other auger, rotating in the other direction, it will be opposed by the force due to the thrust washer.

The magnetic field in the gap 19 due to the magnets 17, 18 causes a small bead of the magnetic material from within the cassette 1 to become trapped and to remain in the gap 19, the magnetic field then being located substantially outside the respective shaft 11. The bead of material surrounds the shaft 11 and effectively forms a seal preventing leakage of developer material from inside the cassette housing 2 into the bearing assembly 13. Because the seal is comparatively noncontacting, attendant frictional forces are low and, as a result, comparatively little heat is generated so that the formation of agglomerates in the developer material can be avoided. The seal can also be expected to have a comparatively long life The ring magnets 17, 18 can be formed from any suitable material, for example a ferrite-ioaded polymer.

The ring magnet 18 on the auger shaft 11 can be omitted although it will then be necessary to provide some alternative arrangement to provide an axial force on the auger in the opposite direction to that due to the thrust washer at the other end. For example, a thrust washer could be provided outside the cassette housing 2 at the end of the shaft adjacent the bearing assembly 13 or, as illustrated in Fig. 4,a reaction surface 20 could be provided within the bearing assembly 13.

In the embodiments shown in Figs. 3 and 4, the rings 17 of the bearing assemblies are magnetized axially (i.e. in a direction parallel to the axis of the respective auger shaft 11). As an alternative, a radially-magnetized or, preferably, several radially-magnetized rings could be utilized. An arrangement in which several radially-magnetized rings 21 are employed, is illustrated in Fig. 5 from which it can be seen that the direction of magnetization alternates from one ring to the next. Such an arrangement can be provided by a plurality of separate ring magnets or by a single member having a plurality of radially-magnetized regions (i.e. an integral multipole). Although three ring regions 21 are shown in Fig. 4, this is for illustration only and the number of rings can be varied as required.Depending on the number of rings there may be more than one bead of magnetic material trapped by the rings to form a seal. In this arrangement, like that of Fig. 4, a thrust surface 20 is provided within the bearing assembly to counteract the axial force on the auger.

It will be appreciated that, although the bearing assemblies described above with reference to Figs. 2 to 5 are for use in a xerographic cassette, this is not essential. A similar assembly could be used in any form of developer apparatus in a xerographic printer/copier (for example, apparatus which employs a paddle wheel rather than rotatable augers to transport developer material) and could also be used in other locations in which there is a need to exclude magnetic material from a rotary bearing. The magnetic material that forms the seal need not be taken from within the housing and, in certain circumstance, could be a liquid rather than a powder material.

Claims (18)

Claims:

1. A bearing assembly for a non-magnetic rotatable member, the assembly including a stationary bearing surface for the rotatable member, and at least one magnet which surrounds the rotatable member and retains, between the magnet and the rotatable member, a seal of powdered magnetic material preventing leakage of material between the rotatable member and the bearing surface.

2. An assembly as claimed in claim 1, including a stationary bearing member which provides the said stationary bearing surface and which also provides a mounting for the magnet.

3. An assembly as claimed in claim 1 or claim 2, in which the magnet is located adjacent a second magnet, with opposing faces of the magnets being of the same magnetic polarity.

4. An assembly as claimed in claim 1 or claim 2, in which the said at least one magnet provides a plurality of magnetic poles, alternate ones of which are of the opposite magnetic polarity, lengthwise of the rotatable member.

5. A bearing assembly for a rotatable member, the assembly including a stationary bearing surface for the rotatable member, two magnets which surround the rotatable member and are located adjacent one another with opposing faces of the magnets being of the same magnetic polarity, and a seal of magnetic material which is retained between one at least of the magnets and the rotatable member and prevents leakage of material between the rotatable member and the bearing surface.

6. A bearing assembly as claimed in claim 5, including a stationary bearing member which provides the said stationary bearing surface and which also provides a mounting for one of the magnets, the other magnet being mounted on the rotatable member.

7. A bearing assembly for a rotatable member, the assembly including a stationary bearing surface for the rotatable member, a magnet assembly which surrounds the rotatable member and provides a plurality of magnetic poles, alternate ones of which are of the opposite magnetic polarity, lengthwise of the rotatable member, and at least one seal of magnetic material which is retained between the magnet assembly and the rotatable member and prevents leakage of material between the rotatable member and the bearing surface.

8. An assembly as claimed in claim 7, including a stationary bearing member which provides the said stationary bearing surface and which also provides a mounting for the magnet assembly.

9. A bearing assembly as claimed in any one of claims 5 to 8, in which the magnetic material is a powdered material.

10. An assembly as claimed in any one of the preceding claims, in which the seal prevents leakage of powdered material from within a housing in which the rotatable member is mounted.

11. An assembly as claimed in claim 10, in which the powdered material within the housing is magnetic and in which the said magnet attracts material from within the housing to form the seal.

12. An assembly as claimed in any one of the preceding claims, substantially as described herein with reference to, and as shown in, Figs. 2 and 3, or Fig. 4, or Fig. 5 of the accompanying drawings.

13. A housing containing powdered magnetic material, including a rotatable shaft which is supported in the wall of the housing by a bearing assembly as claimed in any one of the preceding claims.

14. A housing as claimed in claim 13 when incorporated in developer apparatus for a xerographic reproduction machine, wherein the magnetic material is, or is a component of, developer material.

15. A housing as claimed in claim 13 or claim 14, in which the shaft is the shaft of a rotatable member for transporting the material within the housing.

16. A housing as claimed in any one of claims 13 to 15, in the form of a cassette which is locatable in, and removable from, the main body of a xerographic reproduction machine.

17. Developer apparatus for a xerographic reproduction machine, including means for transporting developer material, said means including a non-magnetic rotatable shaft supported by a stationary bearing surface in a bearing assembly which also includes a seal of magnetic material preventing leakage of material between the shaft and the bearing surface, the seal being retained in position by a magnet which surrounds the shaft.

18. A xerographic cassette substantially as described herein with reference to, and as illustrated by, Figs 1 to 3, or Figs. 1 to 3 as modified by Fig. 4 or Fig. 5, of the accompanying drawings.