GB2075240A - Disk storage drive - Google Patents

Abstract

A storage disk having a centre hole is driven by an electric motor which extends coaxially through the hole. The motor has a rotor and a stator and the disks are secured to the rotor so that they rotate therewith. Preferably a seal, especially a labyrinth seal, is provided to eliminate or reduce the escape of contaminants from the motor into the environment of the disk. <IMAGE>

Description

SPECIFICATION Disk storage drive The present invention relates to disk storage devices in general, and to a disk storage drive in particular.

In disk storage devices bits representing data are stored in circular tracks on rigid or flexible disks which are rotated at relatively high speeds. Bits are inscribed or read by a read/write head which must be accurately positioned relative to the particular track which is being inscribed or read. This means that the disks must rotate absolutely true, or as close to it as possible.

To impart rotation to such disks it is known to arrange the electric drive motor axially below the disk and to connect the disk via suitable connecting elements to the motor shaft for rotation therewith.

This, however, is disadvantageous because the upper of the two motor shaft bearings is subjected - not the least because of the high-speed rotation -- to greater stresses than the lower one. As a result, the disk will soon no longer rotate true and reading and writing errors will develop.

According to another proposal the motor is lo cated somewhat higher, so that the disk is posi tioned in a plane which is axially adjacent (i.e., as considered with reference to the axis of rotation) to the upper bearing of the motor. The connecting elements are shaped differently than in the first mentioned construction, but they still connect the disk with the motor axis. This means that although the disadvantages of the first-mentioned construc tion are somewhat alleviated in this second propos al, they still do exist.

Still another proposal, contained in US Patent No.

4101945, also connects the disk to the motor shaft above the motor, but arranges the bearing system intermediate the disk and the motor.

Common to all this prior art is the connection of the disk to the motor shaft, which requires relatively complicated connecting structure without, however, being able to assure optimum uniformity of load distribution to all bearings of the motor-shaft bear ing system.

Accordingly, it is an object of the invention to provide an improved disk storage drive wherein the connection between the disk (or disks) and the drive motor is simpler than in the prior art.

Another object is to provide such a drive in which the foces (load) acting during the operation of the drive are distributed as uniformly as possible to all bearings of the motor-shaft bearing system.

A concomitant object is to provide a drive of the type in question in which the escape of contaminant particles from the interior of the motor, is wholly or substantially precluded. This is important since such particles --e.g., lubricant, metal particles and the like-- may cause operating difficulties and/or dam age to the disks, heads and other sensitive elements located in the "clean-room" environment in which disk storages are generally operated.

Still a further object is to provide such an im proved drive which is considerably more compact than those heretofore proposed.

An additional object is to reduce the "out-of-true" running of the disk or disks driven by the drive.

In pursuance of the above objects and of still others which will become apparent hereafter, one aspect of the invention resides in a disk storage drive which, briefly stated, may comprise at least one storage disk having a centre hole; an electric motor extending coaxially through the hole and having a stator and a rotor; and means connecting the disk to the rotor for rotation with the same.

By resorting to the invention a direct connection of the disk(s) to the rotating component of the motor is obtained, rather than to the motor shaft and, moreover, the need for connecting elements extending outwardly away from the motor shaft is eliminated. As a result, a very compact and rigid unit of drive motor and disk(s) is obtained. The centre of gravity of the disk(s) is located between the two motor bearings, so that the disk oscillating tendency is substantially reduced; the disk(s) can therefore run truer than in the prior art and this eliminates the objectionable prior art disadvantages.

Different types of motors may be used for the inventive drive. A currently preferred type is a collectorless D.C. motor of the type disclosed in US Patents No. 1873897 and 3840761 as well as in German Allowed Application AS 2225442. Using a motor of this type and having e.g., a single-strand winding, it is possible to obtain a practically constant torque. This is possible in other motors only by using two separate windings which are electrically offset by 900 and through which usually pulses of opposite polarity must be fed. A motor of the type outlined above is thus substantially simpler and less expensive since multiple windings and their associated electronic controls are omitted.Moreover, this type of motor is of excellent operating quality and can be made more compact than other motors of similar ratings, so that the motor can be mounted within the centre holes of the disks and the bearing system can be made sufficiently robust to assure a prolonged service life. In connection with this latter aspect it must be remembered that the disk hole diameter is standardized, so that overall smaller dimensions of the motor leave more room for larger bearings to be used.

In one preferred arrangement, the stator has an at least single-strand stator winding which produces an alternating field, an angular-position detector, and means for connecting said winding to a D.C. current source in dependence upon signals received from said detector, the magnetic resistance in the statorpart of the magnetic circuit being variable in dependence upon the angular position of the rotor and the motor producing an auxiliary reluctance moment which is offset in time relative to the electromagnetic torque produced.

In another preferred arrangement, the stator forms part of the magnetic resistance, and the stator winding, rotor and stator are so co-ordinated that an auxiliary reluctance moment which develops in operation at least during periods during which electromagnetic torque produced by the motor is interrupted, combines with the electromagnetic torque to form therewith a substantially constant total torque.

It is preferred that the device of the invention comprises a two bearings journalling the rotor on the stator and being spaced from one another lengthwise of the axis of rotation of the rotor, the rotor and disk having a joint centre of gravity which is intermediate said bearings.

It is also preferred that the device of the invention comprises means for at least reducing the escape of contaminants from said motor into the environment of the disk. Suitably the contaminants-reducing means comprises a labyrinth seal in an airgap between the stator and the rotor.

Further, it is preferred that the device of the invention comprises means for expelling contaminants from the motor in a direction away from a contaminant-free environment in which the disk is located.

A second aspect of the invention relates to a driving mechanism for a magnetic fixed plate store with a driving motor, having a stator and a rotor for driving a hub for receiving a least one fixed storage plate and housed within a first space of the fixed plate store.

Fixed storage plates are suitable for storing large data quantities, which are written or read out with the aid of a magnetic head arrangement if the storage plate is rotated with respect to the magnetic head arrangement. When writing or reading out data it has been found that problems sometimes occur due to dirt particles.

The problem of this second aspect of the invention is to provide a driving mechanism for fixed plate stores, which obviate such problems during data input and output.

The second aspect of the invention is based on the finding that the cause of the aforementioned problem can be due to dirt particles emanating from the drive. The dirt may come not only from the bearings, but also from the winding with its highly structured surface. In particular, grease or dust particles can escape from the bearing system. In general, the dirt particles from the bearing system have been held back by complicated and expensive seals, e.g.

Ferrofluidic seals, which bring about a sealing action between fixed and rotary parts as a result of a combined action of magnetic fields acting there, together with lubricant emulsions containing magnetically conductive particles.

According to the second aspect of the invention, the problem is solved in that labyrinth packings or seals are arranged between the drive parts supplying the dirt particles and the area intended for housing the fixed storage plate. Such labyrinth packings make it possible to completely prevent or at least considerably reduce the risk of dirt particles passing from the inside of the motor into the area of the fixed storage plate, so that no problems occur when writing or reading out data.

Preferably, a labyrinth packing is placed in the vicinity of one axial end of the bearing tube which coaxially receives the bearing, whilst another labyrinth packing is placed adjacent to the other axial end of the bearing tube in the vicinity of the flange. Thus, parts of the driving motor from which dirt particles escape are separated from the substantially dirt particle-free area for housing the fixed storage plates.

The driving motor is preferably constructed as a commutatorless direct current motor of the external rotor type with a permanent magnetic rotor, the rotating rotor casing advantageously containing a one-part permanent magnetic ring or a permanent magnetic tape bent in annular manner with approximately trapezoidal radial magnetization via the pole pitch. The permanent magnet can in particular be amagnet combined with plastics or a so-called rubber magnet. Such magnets are formed from mixtures of hard ferrites and elastic material, particularly barium ferrite combined with elastomers.

The hub can be part of the rotating rotor casing. In this case, the magnetic shield is appropriately housed within the casing. The permanent magnet of the external rotor is preferably surrounded in bellshaped manner by the magnetic shield, so that no magnetic stray fields can be propagated in the direction of the hub and the fixed storage plates located on the latter. In order to obtain magnetic shielding which on the one hand requires a relatively small amount of shielding material, but on the other hand provides an inexpensive construction thereof for suppressing stray fields, the magnetic shield appropriately forms part of the magnetic yoke for the permanent magnet and is constructed as a soft magnetic, cup-shaped, deep-drawn member, whose base has a coaxial recess in the core.

A driving mechanism of the aforementioned type generally comprises a speed control circuit and/or driving electronics which, in the case of a commutatorless direct current motor more particularly ensures the necessary commutation. If the motor includes a shield ring connected to the stator, it is also possible to use the same for cooling the speed control circuit and/or the drive electronics, particularly if the semi-conductor components are kept in thermally conductive contact with the sheild ring.

On the end face remote from the hub, the rotor preferably has a fan for forming the ventilation area.

Such a construction is not only particularly simple but also leaves the circumferential surface of the rotor free as a braking surface for the brake which is frequently provided with such driving mechanisms.

The following is a description, by way of example only and with reference to the accompanying draw ings, of presently preferred embodiments of the invention. In the drawings: Figure 1 is a fragmentary view, in vertical section, illustrating a first embodiment of the invention; Figure 2 is an enlarged fragmentary detail view, showing a modification of the embodiment in Figure 1; Figure 3 is a view analogous to Figure 1 but illustrating still another embodiment of the invention; and Figure 4 is a view analogous to Figure 1 but illustrating yet another embodiment of the invention.

In the embodiment of Figure 1, the drive comprises a collectorless D.C. motor according to one of the two previously mentioned US motor patents or the previously mentioned German Allowed Application.

This motor has a permanent magnetic rotor 1 which surrounds a stator 2 (i.e., the motor is of the external-rotor type). Stator 2 has a one-strand winding 3 which produces an alternating field and an auxiliary reluctance moment which, in co-operation with the electromagnetic torque, produces a total torque of high constancy. Rotor 1 is journalled in stator 2 via a shaft 4 and a bearing system composed of two anti-friction bearings 20 and 21 which are spaced from one another axially of the shaft 4. The axis of rotation of the rotor 1 is designated with reference character A.

Mounted directly on the outer periphery of the rotor 1 (i.e. not on the shaft 4) are two disks 5,6 of the disk storage (there could be a single disk or more than two). Mounting is effected via rings 7,8 and 9 which surround the motor 1; disks 5 and 6 are slipped over the rotor 1 (they have the usual centre holes) and retained between the rings 6,8 and the rings 8, 9, respectively. Ring 7 is secured in suitable manner (e.g., via screws, welds or the like) to the rotor 1; ring 9 has a flange portion 9a which overlaps the upper side of the rotor 1 and is secured thereto via a plurality of screws 10 (only one shown) which are spaced circumferentially about the axis A. Ring 9 presses against disk 6 and via the same presses ring 8 against disk 5 which in turn is pressed against ring 7; thus, disks 5 and 5 can rotate only with, but not relative to, the rotor 1.

In view of this direct connection of the disks 5, 6 to the rotor, and the position of the disks relative to the bearings in such a manner that the centre of gravity of the rotor 1 is located between the two bearings 20, 21, forces are transmitted substantially uniformly to both bearings and the disks 5, 6 rotate true and without, or substantially without, any vibrations or oscillations.

As mentioned before, disk storages are most usually operated in "clean-room" environments to protect them against contaminants. The drive according to the invention is particularly well adapted for such an application, because it can offer an anti-contaminant feature.

Motors, no matter how carefully manufactured, are inevitably a source of contaminant particles since lubricant, abraded metal particles are the like escape from the motor into the ambient atmosphere.

In most applications this presents no problem, but it does do so under "clean-room" conditions. Under such circumstances, therefore, the motor and disks may be mounted on a base plate or surface 11 constituting a part of the wall or walls which bound the "clean-room" environment CR. Such mounting is effected in any manner known perse and requires no illustration. Attached to the rotor 1 and/or the ring 7 (or else integral with either of these) is another ring 12 of generally L-shaped cross-section, having a portion 12a which extends parallel to the plate 11 and defines therewith a narrow gap 13 which communicates with the environment CR and with the air gap of the motor. The upper surface of portion 12a carries an annulus (one blade shown of radially extending blades 14 which are arranged circumferentially of the ring 12.An intermediate annular plate 15 is mounted above the plate 11, between the same and the lower disk 5; its radially inner edge portion overlaps but is upwardly spaced from the blades 14. Plate 15 is provided with one or more openings (one shown) in which a filter 16 is installed. The air-flow produced by the ring 12 and its blades 14 (acting as an impeller) causes a constant circulation of air through the filter or filters 16, so that any contaminants released by the motor become entrapped in filter(s) 16 and can do no harm in the environment CR.

Two overlapping annular baffles 17, 18 on the stator 2 and rotor 1 are interposed in the airgap between stator and rotor, defining with one another their own airgap which serves to further retard the escape of contaminants from the motor to the environment.

The embodiment of Figure 2 is the same as the embodiment of Figure 1, with the exceptions to be described, and therefore an illustration and discussion of the already familiar elements is not needed.

Figure 2 differs from Figure 1 in the more elaborate seal which replaces the baffles 17, 18. This seal, arranged in the same location as the baffles in Figure 1, is a labyrinth seal formed by a plurality of annular grooves 22 in the inner surface of rotor 1 into which a plurality of ribs 23 project from the stator 2. There is no contact of the ribs with the material bounding the grooves and the arrangement serves as a highly effective seal against the escape of contaminants to the motor. Incidentally, it goes without saying that although the seal is shown radially outwardly of the winding 3, it could be located radially inwardly of the same or it could be located both radially inwardly and radially outwardly to improve the effect still further.

The embodiment of Figure 3 is also particularly suited for "clean-room" applications. Here, the rotor 30 is mounted in stator 31 via shaft 32 and antifriction bearings 33, 34. The winding 35 of stator 31 is heavily potted, i.e., embedded in one of the electrically insulating materials 36 which are known perse in the art, to prevent the escape of contaminant particles. The potting material 36 may in turn be surrounded by a jacket of heat-shrinkable synthetic plastics 37 (also known perse) which, when shrunk onto the material 36, surrounds the same extremely tightly and further prevents the escape of contaminant particles. A cupped inverted cover 38 of electrically insulating material may surround the winding, being connected to the stator 31, and have an upper free circumferential edge 39 which extends into an annular groove 40 of the stator 31 to provide still another seal against the escape of contaminants.

The groove 40 could be omitted and the edge 39 simply abut the stator 31.

The disks 5 and 6 are shown only diagrammatically here; their mounting on rotor 30, although not shown, may be analogous to that shown in Figure 1.

Stator 31 is mounted beneath a supporting plate 41 and the "clean-room" environment CR is also below this plate.

Within the hub of the stator 31, intermediate the bearings 33,34, the shaft 32 carries a set of blades 42 which, on rotation of shaft 32, cause an axial airflow in the direction indicated by the arrows. Thus, air is drawn from the environment CR through the bearing 33 and expelled via the bearing 34 and the opening in plate 41, into the non-controlled ambient atmosphere. Any contaminant particles which may be liberated in the path of this airflow -- e.g., dust, abraded bearing metal particles -- will be expelled from the motor to the ambient atmosphere and cannot enter the environment CR.

The invention is susceptible of a variety of modifications. For example, if desired a shielding element could be used to surround the rotor, being connected thereto for rotation with the same. The disks could then be mounted on this shielding element.

The element connecting the upper end of shaft 4 to rotor 1 (see Figure 1) could be constructed as a radial-flow impeller in lieu of or in addition to -- and to perform the function of -- the impeller 12, 14. The drive according to the invention is suitable for use with all types of disk storages and irrespective of the diameter of the centre hole of the disks. It is also conceivable to use an A.C. motor instead of a D.C.

motor and to use an internal rotor motor; only slight modifications would be necessary in the latter case to mount the disks in the desired manner.

Referring now to Figure 4, a driving mechanism 10 has a commutator-less direct current motor 11 with a rotor casing 14 fixed to rotor shaft 12 and concentric to the latter. A group of stator plates 58 carrying a stator winding 29 forms part of the stator of motor 11. The stator plates 58 surround a bearing tube 44, which is part of a central support 22. Rotor shaft 12 is mounted in the bearing tube 44 with the aid of two bearings 48, 48', which are held in place by spaced retaining rings 50. A cup spring 52 bears against the bottom of bearing 48' and a retaining ring 54 is located on rotor shaft 12, so that bearings 48,48' are axially spaced relative to one another. Together with an assembly flange 30 bearing tube 44 forms a one-piece die casting.As an alternative, the bearing tube 44 can be force fitted into a hub joined to flange 30.

Rotor casing 14 not only surrounds the group of stator plates 58, whilst forming a cylindrical air gap 15, but on the side remote from the assembly flange 30 is axially extended, providing a hub 70. Hub 70 is used for mounting and driving one or more (not shown) fixed storage plates having a central bore, whose diameter corresponds to the external diameter of hub 70. These plates can be commercially available 5-" or 8" plates. The illustrated construction makes it possible to adapt the diameter of hub 70 to the central bore of the storage plates without taking account of the necessary drive power of motor 11 and the resulting most favourable diameter of air gap 15. A printed wiring board 20 is housed in the free space 26 within hub 70. Wiring board 20 is circular and is connected to the central support 22.

Wiring board 20 carries the drive electronics and a speed control circuit, which includes interalia a Hall IC 35 serving as a rotation position detector, output stage transistors 61 and a potentiometer 64. The soldered joints of the circuit components of the drive electronics and the speed control circuit, which are preferably produced in one operation, e.g. in a dip soldering process, are indicated at 65. Potentiometer 64 can be used inter alia for setting different operating points or for compensating component tolerances. It can be adjusted by means of a screwdriver via a not shown bore in flange 30 and one of the slots in stator plates 58. A line 31 leading to the printed wiring board 20 is connected to a d.c.

voltage source. The side of wiring board 20 carrying the soldered joints 65 faces the base 40 of the rotor casing 14.

In this embodiment, rotor casing 14 is made from a magnetically non-conducting or poorly conducting material, e.g. an aluminium alloy die casting. A plurality of continuous segments or a one-part permanent magnet 56 is fixed to the inner surface of rotor casing 14 facing stator plates 58. The permanent magnet preferably comprises a mixture of hard ferrite, e.g. barium ferrite, and elastic material and thus forms a so-called rubber magnet. It is trapezoidally or approximatelytrapezoidally radially magnetized via the pole pitch with a relatively small pole clearance. A magnetic yoke 57 is positioned between rotor casing 14 and permanent magnet 56. Magnetic yoke 57 also forms part of the magnetic shield.

It is in principle also possible to produce the rotor casing 14 from magnetically conductive material, particularly soft iron, it being constructed e.g. in the form of a deep drawn part. In such a case, there is no need for a separate soft iron yoke.

Magnetic yoke 57, including rounded portion 157 and shield ring 60 surround the magnetically active part of the driving mechanism 10 in bell-shaped manner. This effectively prevents the propagation of magnetic stray fields in the area of the fixed storage plates located on hub 70. The stray field cannot pass to any significant extent through the annular clearance between rounded portion 157, shield ring 60 and the recesses of shield ring 60 for the passage of the one or more Hall IC 35, because the soft magnetic shield rings draw said field towards them.

In the represented embodiment, the fixed shield ring 60 is simultaneously used as a cooling plate for the output stage transistor 61 thermally conductively connected to shield ring 60 by full surface engagement. If necessary, the cooling bodies of output stage transistor 61 can be electrically insulated from the shield ring 60, e.g. by means of a mica washer or the like. It is also possible to subdivide shield ring 60 as the function of the number of output stage transistors 61 in order to avoid such an electrical insulation.

Assembly flange 30 makes it possible to fit the driving mechanism 10 in a way not shown in Figure 1 to a partition 72 of the not illustrated fixed plate store. Partition 72 separates the ultra-clean area for receiving the fixed storage plates from the remainder of the interior of the apparatus. Any dirt particles, grease vapours or the like which may escape from bearing 48 are held back by labyrinth packings 90, 91. The labyrinth packings are formed by fixed and rotary parts, which coaxially interengage within the driving mechanism.

With respect to bearing 48, base 40 is constructed as a cylindrical bus 92 and extends into bearing tube 44. There is only a small gap 94, with a maximum axial extension for the escape of dirt particles from bearing 48, the action of labyrinth packing 90 being reinforced by the gap 95 formed by ring 93 and bearing tube 44.

In the same way, magnetic yoke 57 forms a further labyrinth packing 91. Due to the fact that yoke 57 engages in an all-round recess of flange 30 the small, but axially extending gaps 96, 97 prevent the escape of dirt particles from the inside of the motor.

To increase the action of the labyrinth packing when holding back the dirt particles, the axially directed gaps 94, 95, 96, 97 are in each case kept as narrow as possible, i.e. they are radially small being approximately 1 to 2mm, but they have a maximum axial length, e.g. S to 20mm. The gap size or thickness in the radial direction cannot be randomly small, because this means high manufacturing costs and in particular high windage losses. Depending on the characteristics of the adjacent surfaces, the latter can be considerable. Such direct store drives are in fact operated at e.g. 5000 r.p.m. However, the radially driven gaps are axially e.g. 3 or Smm "thick" and radially preferably below 100 mm "long".

(These values relate to a motor size, whose diameter is half that shown in Figure 1). Further gaps are also possible.

Thus, labyrinth members can additionally or alternatively pass e.g. from a coil end cover in comb-like manner into recesses of opposing matching shape formed in the bottom of a bell-shaped outer rotor casing. In principle, the dimensioning rules of claims 15 to 17 apply here.

A fan 32 with fan blades 33 is fixed to the free end of rotor shaft 12 remote from hub 70. Fan 32 leads to an intense air movement in the vicinity of the assembly flange 30, so that the flange is cooled. By means of bearing tube 44 and flange 30 dissipated heat from motor 11 is effectively conducted to the outside in this way.

To prevent an electrical charging of the rotor bell which would be prejudicial to the operating reliability of the plate store, rotor shaft 12 is appropriately connected in electrically conductive manner to the apparatus chassis via a bearing ball 36 and a not shown spring contact.

The commutator-less d.c. motor 11 can advantageously be a single-phase electronic motor with an auxiliary reluctance moment (single or two-pulse) (US Patent 3873897) or a three-phase electronic motor as described in earlier-dated German application P30 21 328.6.

The idling speed of motor 11 can be 5,800 r.p.m.

and the rated speed e.g. 3,600 r.p.m.

The stator advantageously has four distinct wound poles, whose pole tips are so deformed that the width of air gap 15 is modified in the vicinity of the tips and consequently the auxiliary reluctance moment is produced.

While the invention has been illustrated and described as embodied in a disk storage drive, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the present invention as defined in the following Claims.

For example, ring 7 of Figure 1 could be integral with rotor 1.

Claims (21)

1. A disk storage device comprising at least one storage disk having a centre hole; an electric motor extending coaxially through said hole and having a stator and a rotor; and means connecting said disk to said rotor for rotation with the same.

2. A device as claimed in Claim 1, wherein the motor is an external-rotor motor, and the connecting means connect the disk to an outer circumferential wall of the rotor.

3. A device as claimed in Claim 1 or Claim 2 wherein the motor is a collectorless D.C. motor having a permanent magnetic rotor.

4. A device as claimed in Claim 3, wherein the stator has an at least single-strand stator winding which produces an alternating field, an angularposition detector, and means for connecting said winding to a D.C. current source in dependence upon signals received from said detector, the magnetic resistance in the stator-part of the magnetic circuit being variable in dependence upon the angular position of the rotor and the motor producing an auxiliary reluctance moment which is offset in time relative to the electromagnetic torque produced.

5. A device as claimed in Claim 3, wherein the stator forms part of the magnetic resistance and the stator winding, rotor and stator are so coordinated that an auxiliary reluctance moment which develops in operation at least during periods during which electromagnetic torque produced by the motor is interrupted, combines with the electromagnetic torque to form therewith a substantially constant total torque.

6. A device as claimed in any one of the preceding claims which further comprises two bearings journal led the rotor on the stator and being spaced from one another lengthwise of the axis of rotation of the rotor, the rotor and disk having a joint centre of gravity which is intermediate said bearings.

7. A device as claimed in any one of the preceding claims which further comprises means for at least reducing the escape of contaminants from said motor into the environment of the disk.

8. A device as claimed in Claim 7, wherein the contaminants-reducing means comprises a labyrinth seal in an airgap between the stator and rotor.

9. A device as claimed in any one of the preceding claims which further comprises means for expelling contaminants from the motor in a direction away from a contaminant4ree environment in which the disk is located.

10. A device as claimed in Claim 1 and substantially as hereinbefore described with reference to and as illustrated in Figure 1.

11. A device as claimed in Claim 1 and substantially as hereinbefore described with reference to and as illustrated in Figure 2.

12. A device as claimed in Claim 1 and substantially as hereinbefore described with reference to and as illustrated in Figure 3.

13. A driving mechanism for magnetic fixed plate stores with a driving motor having a stator and a rotorfordriving a hub for receiving at least one fixed storage plate and located within a first space of the fixed plate store, according to German application P30 45 972.4, wherein labyrinth packings are arranged between the drive parts from which emanate the dirt particles and the area of the first space intended for housing the fixed storage plate.

14. A mechanism as claimed in Claim 13, wherein one labyrinth packing is arranged adjacent to the axial end of the bearing tube coaxially receiving the bearing oriented approximately towards the centre of the first space and a second labyrinth packing is provided in the vicinity of the other axial end of the bearing tube, in the vicinity of the flange.

15. A mechanism as claimed in either of Claims 13 and 14, wherein the axial extension of the labyrinth gaps parallel to the rotor axis is greater than the radial extension thereof.

16. A mechanism as claimed in Claim 15, wherein the thickness of the labyrinth gap is small over its axial extension and large over its radial extension.

17. A mechanism as claimed in either of Claims 1Sand16,whereina/d > 10andr'd#2.

18. A mechanism as claimed in any one of the preceding claims, wherein on the stator side comblike members are introduced into the base or edge of the rotor bell in such a way that comb-like projections on the rotor side project between the comb-like members on the stator side.

19. A mechanism as claimed in Claim 18, wherein the comb-like projections have unequal spacings.

20. A mechanism as claimed in Claim 19, wherein the projections on the stator side and the rotor side are of different thickness.

21. A mechanism as claimed in any one of the preceding claims, wherein the rotor and/or stator parts are themselves constructed as labyrinth packing parts.