Disk storage device having a radial magnetic yoke feature

Abstract

A disk memory drive includes a brushless drive outer rotor motor having an internal space and a stator with windings. The outer rotor coaxially encircles the stator and a substantially cylindrical air gap is defined between the stator and the rotor. The rotor includes permanent magnets and a hub fixedly connected with the magnet. A disk mounting section is provided on the hub for accommodating at least one storage disk positioned in a clear space, the mounting section being adapted to extend through a central aperture of the storage disk. The windings and the magnets interacting with the windings are disposed for at least half of the axial longitudinal dimension thereof within a space surrounded by the disk mounting section of the hub. Bearings rotatably mount the rotor and the hub.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The disk storage drive illustrated in FIG. 1, having an extremely shallow construction, has a brushless direct current motor 45 having a rotor casing 47 fixed to and coaxial with a rotor shaft 46. A stator lamination 48, carrying a stator winding 49, is mounted on a bearing tube 50. The rotor shaft 46 is rotatably mounted within the bearing tube 50 by means of two bearings 52 and 53. These are kept axially spaced by a pair of retaining rings 54. A cup spring 55 is supported on the underside of the bearing 53 by a retaining ring 56 resting on the rotary shaft 46, so that the bearings 52, 53 are axially braced relative to one another. The bearings 52, 53 are pressed into the bearing tube 50 at the time of assembly. Together with an assembly flange 24, the bearing tube 50 forms a one-piece die casting.

The rotor casing 47 comprises a storage disk receiving part 25 and a shielding can 26, which are joined together, for example, by riveting. The storage disk receiving part 25 is made from a non-ferromagnetic material, preferably lightweight metal. The rotor shaft 46 is pressed into a central opening of the storage disk receiving part 25. As an alternative, the shaft can be cast into the receiving part.

The shielding can 26 is made from a ferromagnetic material and can in particular be constructed as a soft iron deep-drawn part. A plurality of permanent magnetic segments or a one-part permanent magnet 69 are fixed to the inner face of shielding can 26 radially facing the stator lamination 48. The permanent magnet 69 preferably comprises a mixture of hard ferrite, for example, barium ferrite, and an elastic material. Thus, it is a so-called rubber magnet. The latter is trapezoidally or approximately trapezoidally radially magnetized via the pole pitch in a motor construction having a relatively small pole clearance. At the same time, the shielding can 26 forms the magnetic return path for magnetic 69. The shielding can 26 surrounds the magnetically active parts 48, 49, 69 of the driving motor 45 on the periphery thereof, as well as on one thereof. The bottom 28 of shielding can 26 is adapted to the shape of the coil winding heads 27 of the stator winding 49 and contains a central opening 29, whose edge is in the immediate radial vicinity of the circumferential surface of the bearing tube 50. In this way, the shielding can effectively prevents the magnetic flux from straying towards the outside of the storage disk receiving part 25.

The storage disk receiving part 25 has two stepped stages 74 and 75, each of whose circumferential surfaces in the present embodiment carry a plurality of radially distributed and projecting bearing webs 79 or 80. The outsides of bearing webs 79, 80 are ground in a dimensionally true manner to accommodate the internal diameter of the hard storage disks to be placed on the receiving part 25. The stepped stages 74, 75 form shoulders 81, 82 and are provided respectively with an annular recess 83 and 84 at the foot axially of bearing webs 79, 80. This structure ensures that storage disks mounted on the bearings webs 79, 80, and having either one of two opening diameters, will cleanly engage against either the shoulder 81 or 82.

The assembly flange 24 is provided with a recess 85 in which is housed a printed circuit board 86. This printed circuit board carries a rotary position detector, for example a Hall IC, as well as other circuit components for the control and regulation of the driving motor 45. The Hall IC 63 extends up axially from the circuit board 86 to the immediate vicinity of the stator lamination 48. The permanent magnet 69 projects axially over the stator lamination 48 in the direction of circuit board 86 until it partly overlaps the Hall IC 63. In this way, the Hall IC 63 or, if desired, some other magnetic field-dependent semi-conductor component, determines the rotary position of the rotor of the driving motor 45.

In the illustrated embodiment, the two bearings 52, 53 are spaced approximately the same axial distance from the axial center of the permanent magnet 69 and the stator lamination 48.

Disk storages are most usually operated in "clean chamber" environments to protect them against contaminants. By means of the assembly flange 24, the storage drive is arranged on a partition (not shown) which separates the ultra-clean area for receiving the storage disks from the remainder of the interior of the equipment. Dirt particles, grease vapors and the like from bearing 52 and parts of the driving motor 45 are prevented from passing into the storage disk receiving area by labyrinth seals 90 and 91. The labyrinth seal 90 is formed in the end of the bearing tube 50 away from the assembly flange 24 that projects into an annular slot 87 on the inside of the storage disk receiving part 25, accompanied by the formation of sealing gaps. Similarly, for forming the labyrinth seal 91, the end of the shield can 26 projects into the annular slot 88 of the assembly flange 24. The labyrinth seals 90, 91 are preferably dimensioned in the manner described in the aforementioned U.S. Pat. No. 4,438,542.

The embodiment of FIG. 3 differs from the arrangement according to FIGS. 1 and 2 in that storage disks having the same opening diameters are placed on bearing webs 79 of a storage disk receiving part 89, which surrounds the majority of the axial dimension of the magnetic shielding can 26. In other words, the magnetically active parts 48, 49, 69 of the driving motor 45 are partially located within the central opening of the storage disk. A bush-like hub 98 is pressed or cast into the storage disk receiving part 89. The rotor shaft 46 is then pressed into the hub 98. The edge of the central opening 29 in the bottom 28 of the shielding can 26 extends up to the portion 99 of the receiving part 89 which received the hub 98.

The bearing tube 50 projects in the axial direction on the side of the assembly flange 100 remote from the stator lamination 48. As a result, a particularly large axial spacing between the two bearings 52, 53 can be achieved. Axially, bearing 52 is in the vicinity of the axial center of the permanent magnet 69 and of the stator lamination 48. The axial spacing between bearings 52 and 53 is equal to or larger than double the bearing external diameter. To prevent electrical charging of the rotor which in operation rotates at high speed and which would disturb the operational reliability of the disk storage device, the rotor shaft 46 is electrically conductively connected to the equipment chassis by means of a bearing ball 78 and a spring contact (not shown). The printed circuit board 101, carrying the rotary position detector 63 and the other electronic components, is supported on the end of a spacer ring 102 facing an assembly flange 100 and is located between the flange and the stator lamination 48. An annular slot 103 is formed in assembly flange 100 and is aligned with the annular circuit board 101. The annular slot 103 provides space for receiving the wire ends and soldered connections projecting from the underside of the circuit board 101.

FIG. 4 shows an embodiment in which a storage disk receiving part 105 is axially extended in order to be able to house a larger number of storage disks than in the arrangement of FIG. 3. The bearing tube 50 is correspondingly axially extended in order to be able to use the existing installation space with a view to a maximum axial spacing between the bearings 52 and 53. The end of the bearing tube 50, remote from an assembly flange 106, embraces the hub 98 connecting the receiving part 105 and the shaft 46, accompanied by the formation of a labyrinth seal 107. The edge of the central opening 29 of shielding can 26 extends up close to the outside of the bearing tube 50. The free end of the shielding can 26 engages a recess 108 in the assembly flange 106. As a result, a further labyrinth seal 109 is formed. This embodiment otherwise corresponds to the structures already described herein.

In FIGS. 5 and 6, a brushless drive motor, designated as 110 as a stator 111 with a stator lamination stack 112. The stator lamination stack 112 is arranged radially and symmetrically with respect to a central axis of rotation 113 and forms six stator poles 114A to 114F in an essentially T-shaped configuration as seen from above in accordance with FIG. 5, which poles are positioned at regular angular intervals of 60'. Instead of one lamination stack, for example, a sintered iron core can also be provided. Pole shoes 115A to 115F, together with a permanent magnetic rotor magnet 116 define an essentially cylindrical air gap 117. The rotor magnet 116 is radially magnetized in four poles around its periphery as indicated in FIG. 5; that is to say, it has four sections 118A to 118D, and, on the internal side of the annular rotor magnet 116 toward the air gap 117 there are positioned, in alternating sequence, two magnetic north poles 119 and two magnetic south poles 120. The poles 119, 120 have, in the example depicted, a width of substantially 180-el (corresponding to 90 mechanical). Thus, in the circumferential direction of the air gap 117, an approximately rectangular or trapezoidal magnetization is obtained. The rotor magnet 116 is mounted, typically by bonding, in an outer rotor casing or bell 121 of soft magnetic material, preferably steel, which serves both as a magnetic return path and as a magnetic shield. The casing 121 and the magnet 116 together form an external rotor 122. The rotor magnet 116 can include in particular a rubberized magnetic unit, or a plastic-bound magnet. Instead of a single-piece magnetic ring, curved magnetic segments can also be bonded or otherwise attached in the casing 121. Magnetic materials made from synthetic bonding compounds, a mixture of hard ferrite and elastomers, ceramic magnetic materials or samarium cobalt are all particularly suitable as materials for the magnetic ring or segments.

The stator poles 114A to 114F abut a total of six stator slots 123A to 123F. A three-phase stator winding is inserted into these slots. Each of the three phases comprises two 1200°C-el fractional pitch windings or coils 124, 125; 126, 127; and 128, 129, each of which is wound around one of the stator poles 114A to 114F. Both of the coils of each phase, which are connected in series, lie, as depicted in FIG. 5, in a diametrically opposed manner and are preferably bifilar wound. As can be seen from the schematic depiction in FIG. 5, any overlapping between the coils 124 to 129 is avoided. This arrangement allows the end turns of the windings 130 (FIG. 6) to be kept as short as possible. In this embodiment of the present invention, optimal filling of the stator slots 123A-123F by the windings is achieved. Fasteners are generally not required to close the slot openings.

A hub 132, not depicted in FIG. 5, is provided with a cylindrical disk mounting section 131 and preferably is made of a light metal, especially aluminum or an aluminum alloy. It is mounted on the outer rotor casing 121. One or more storage disks 134, preferably magnetic or optical fixed storage disks, are provided on the disk mounting section 131, whereby the disk mounting section 131 extends through the conventional central aperture 135 of the storage disks. The lowest storage disk in FIG. 6 is located on a flange 133 of the hub 132 projecting radially outwardly. The data storage disks 134 can be maintained at an axial distance from each other by suitable spacers 136 and are secured to the hub 133 by means of a tightening device, not depicted, of a known type. In the embodiment shown in FIG. 6, the stator 111, the stator stack 112 and the stator winding (coils 124 through 129) as well as the rotor magnet 116 and the outer rotor casing 121 forming the iron shield, are all completely encompassed within the space occupied by the storage disk stage 131 on the hub 132.

In a central aperture 137 of a frontal wall 138 of the hub 132, which is relatively heavy for reasons of stability, are a ball bearing 139 and a magnetic fluid seal 140 on the side of the support which is axially oriented away from the drive motor 110. The seal 140 consists of two annular pole pieces 141, 142, a permanent magnet ring 143 located between both these pole pieces, and a magnetic fluid (not shown), which is inserted into an annular gap 144 between the magnetic ring 143 and a stationary shaft 145. Seals of this type are known under the designation of "Ferrofluidic Seal". An internal space 146 is located within the motor and is sealed on the side of the space oriented away from the frontal wall 138 by means of a motor cover 147, which is inserted into the outer rotor casing 121 and the hub 132, by means, for example, of adhesion. The internal space 146 includes the internal parts such as the stator 111 and permanent magnet 116 as well as bearings 139 and 149. The motor cover 147 abuts with its cylindrical outer edge 247 the lower edge of the rotor casing 121. This allows a particularly easy assembling of the cover 147 within the hub 132. For sealing purposes, adhesive material 190 is placed in a circumferential groove 191 between the cover 147 and the hub 132.

The motor cover 147 is supported on the shaft 145 by means of an additional ball bearing 149. On the side of the ball bearing 149 away from the drive motor 110, there is a magnetic fluid seal 150, which has a construction corresponding to the seal 140. The seals 140, 150 ensure an effective sealing of the motor internal space 146, including the bearings 139, 149, relative to a clean chamber 148 which accommodates the storage disks 134.

The motor cover 147 is provided on the frontal side facing away from the drive motor 110 with an annular groove 151 receiving a control magnet ring 152. The control magnet ring 152 has four sections of alternating circumferential magnetization corresponding to the rotor magnets 116, which run in sequence in the circumferential direction and extend over 90°C, so that alternating north and south poles, aligned with poles 119, 120 in the circumferential direction, are provided on the bottom side of the control magnetic ring 152.

A stationary flange 154 is disposed on the lower end of the shaft 145 in FIG. 6. The flange 154 is provided with threaded bores 192 for receiving fastening screws by which the disk storage drive may be connected to the disk drive frame, for example, over a wall delimiting the clean chamber 148, or the like. The flange 154 supports a printed circuit board 155 on its frontal side relative to the motor cover 147. Three rotational position sensors 156, 157, 158 are mounted on the printed circuit board 155. In the embodiment shown, these magnetic field sensors may be Hall generators, Hall-IC's, magnetically controlled photocells, magnetic diodes, or the like, which interact with the control magnet ring 152. The rotational position sensors 156, 157, 158 are suitably positioned in the circumferential direction with regard to the coils 124 to 129 so that the changes of the sensor switching conditions essentially coincide with the zero passages of current in the correspondingly positioned coils. This is attained, in accordance with the embodiment shown in FIG. 5, through the fact that the rotational position sensors are displaced by 15-mech with respect to the center of the apertures of the stator slots 123A to 123F. The rotational position sensors 156, 157, 158 may be supported by a common molded part 159 (see, for example, FIG. 14), preferably a plastic injection molded part. By using a common molded part 159 as the support for the rotational position sensors, their relative positioning with respect to one another can be maintained and reproduced in a particularly precise manner. The printed circuit board 155 is fixed to a ring 193 and is tightly pulled against the flange 154 by screws 194 screwed into a ring 193. An upwardly projecting outer rim 195 of flange 154 defines a hollow cylinder extending into an annular groove 196 provided in the bottom side of the flange 154. Thereby a labyrinth gap 197 is formed which provides for additional sealing between the stationary flange 154 and the rotary motor cover 147.

The connection of the rotational position sensors 156, 157, 158 and/or commutational electronics likewise positioned on the printed circuit board are conducted through one or more apertures 161 of the flange 154 which open into peripheral cutouts of the ring 193. The connections of the stator winding coils 124 to 129 of the drive motor 110 are, on the other hand, conducted outwardly through bores 162, 163 of the stationary shaft 145 out of the internal space of the disk storage drive, which is sealed off by means of the magnetic fluid seals 140, 150. The bores 162, 163 can be dimensioned relatively narrowly, because they only have to accommodate the connections of the stator winding but not the connections of the rotational position sensors and/or the commutation electronics (not shown). Furthermore, the rotational position sensors 156 to 158 located outside of the sealed space 146 can be closely adjusted. An excessive weakening of the shaft 145 is thereby avoided.

In a further modified embodiment shown in FIG. 7, the rotor magnet 116 is located directly within the hub 132', which itself forms the magnetic shield, and is made of magnetically conductive material, preferably soft iron. The control magnet ring 152' is located on the frontal side of the flange 133 facing away from the disk mounting section 131 of the hub 132', and alternately magnetized in the axial direction. In this embodiment, the rotational position sensors 156, 157, 158 are axially opposed to the control magnet ring 152'. The magnetic fluid seal 150 ensures, together with a labyrinth seal 165 which replaces the magnetic fluid seal 140 of the embodiment in FIG. 6, the sealing of the internal space 146, including the bearings 139, 149 relative to the clean chamber 148. The connections of the stator winding 166 are conducted through the bores 162, 163 of the stationary shaft 145. It should be understood that, even in this embodiment, the rotational position sensors 156, 157, 158, can, if desired, be accommodated by a common support corresponding to the molded part 159 (FIG. 14), which support is attached to the printed circuit board 155.

If it is desirable to manufacture the hub 132' from magnetically non-conducting, or poorly conducting, materials, such as light metal or alloy, a separate iron shield can be provided. This can be seen in the embodiment in FIG. 8. There, the rotor magnet 116 is accommodated in an iron shielding ring 167. The flange 169 supporting the storage disk 134 forms a part, separated from the hub 132", of the cover 170 which accommodates the ball bearing 140. The hub 132" and the cover 170 are closely connected with one another, so that the axial end section of the hub 132", which extends towards the cover 170, engages in an annular groove 171 of the cover 170.

In both embodiments of FIGS. 9 and 10, the control magnet ring 152' is located in a groove 173 of a bearing support ring 174 on the end of the hub 132. The hub 132 itself forms the magnetic shield, and is accordingly made from conductive material, particularly steel. The control magnet ring 152' interacts, as shown in FIG. 7, with the rotational position sensors 156, 157, 158, which are not shown in FIGS. 9 and 10. In the embodiment in FIG. 9, the internal space 146 is sealed off by means of the magnetic fluid seals 140, 150, but in the embodiment in FIG. 10, labyrinth seals 175 are provided in their place. The embodiment of FIG. 10 further differs from that of FIG. 9 by the stationary shaft 145' in the area where it supports the stator lamination stack 112, and the area directly adjoining the same axially, being axially thickened so that the shaft 145 forms shoulders 176, on which the ball bearings 139, 149 are supported.

In the embodiments shown in FIGS. 8, 9, and 10, the connections of the stator winding are, in a manner preferably corresponding to the embodiments shown in FIGS. 6 and 7, brought out externally through recesses of the shafts 145 and 145'.

FIG. 11 depicts an embodiment similar to that of FIG. 11 of copending U.S. Ser. No. 733,231, in which a soft magnetic yoke ring 167 is inserted in the hub 132, the latter forming a disk mounting section 132 and preferably being made of light metal. Both the rotor magnet 116 and the control magnet 152' are accommodated in the inner circumference of the yoke ring 167. In this embodiment, the printed circuit board 155 together with the rotational position sensors 156, 157, 158 are located within the space 146 sealed by the magnetic fluid seals 140, 150. The circuit board 155 may be suspended from the stator lamination stack 112 by supports 178. A bearing support ring 180 is provided for bringing outwardly the connections 180' of the stator winding as well as the connections 180" of the rotational position sensors 156, 157, 158 and/or of the electronic commutating means which likewise may be mounted on the printed circuit board 155. The support ring 180 is made of the soft magnetic material, preferably ferromagnetic metal, and surrounds and is firmly fixed to shaft 145". The ball bearing 149 and the magnetic fluid seal 150 are disposed between the cover 147' and the support ring 180. At least one and preferably a plurality of axially extending apertures 181 are provided in the support ring 180 for receiving the aforementioned connections. After introduction of the connections therein, which together are indicated at 182, the apertures 181 are sealed, e.g. by a potting compound or a mastic. This embodiment completely avoids bores in the stationary shaft 145" and therefore the solid shaft retains its full strength. The provision of a bearing support ring 180 provides for a particularly small eccentricity or run-out of the rotating members. A soft magnetic shield ring 184 is provided on the inside of the frontal wall 183 of the hub 132.

The embodiment of FIG. 12 corresponds to that of FIG. 7 with the exception that a connection 166 of the stator winding extends through a bearing support ring 185 rather than through the bores in the stationary shaft 145. The ring 185 surrounds the lower portion of the shaft 145. The ball bearing 149 and magnetic fluid seal 150 are disposed in the annular space between the support ring 185 and the ferromagnetic ring 153, which is inserted into hub 132'.

In an embodiment where the rotary position sensors are located externally, the winding leads can also be brought out through an inner bearing support ring encompassing the bearing 149, corresponding to the support ring 180 in FIG. 11. Furthermore, in an embodiment provided with an inboard rotary position sensing arrangment similar to that shown in FIG. 11, a bearing support ring 185 according to FIG. 12 mounted on the stationary shaft 145 and supporting the ball bearing 149 on the inside can be used to bring the connections out to the exterior.

The metal support ring 185 according to FIG. 12 ensures that the rotating parts will display particularly limited runout. The magnetic field of the magnetic liquid seal 150 can be contained in either the ferromagnetic support ring 185 or the ferromagnetic ring 153.

Instead of providing the bearing support rings 180 or 185 with apertures through which the connections can be brought out, the connections can also be potted in the bearing support ring directly.

FIG. 13 shows an embodiment similar to that shown in FIG. 6, of which it is only a further development in many respects.

A particular feature of this further embodiment is the provision of a flat air gap between rotational position indicator or magnetic control ring 152 and the rotational position sensor 156. The printed circuit board 155 is firmly fastened to a stationary flange part 154 with the screw 194. The outside edge of this flange 154 engages in a disk-shaped ring member 147", which may be the motor cover 147 (FIG. 6) in an axial direction like a hollow cylinder, so as to provide a labyrinth gap 197 acting as an additional seal between the stationary flange 154 and the disk-shaped ring member 147". The lower edge of the soft iron outer rotor casing 121 bears on the rotating ring member 147" whose cylindrical outer edge 244 is more easily inserted in the hub body 132 than the arrangement shown in FIG. 6. A mastic 190 is used as the sealant in a peripheral groove between the ring member 147" and the hub 132.

From the user's point of view, the entire motor assembly is fastened by use of appropriate fasteners in the hole 192. The connecting leads from the printed circuit board 155 to the rotational position sensor 156 are brought out through the passage or bore 161 shown with the disked lines, which extends outwardly from an oblique channel 161' until it terminates in the peripheral apertures in the ring 193 which is brought to bear on the flange 154 by a screw 194.

The ring member 147" corresponds to the elements described in the various embodiments and examples as the covers 170, 147, 147' and the rings 53, 74. Preferably, therefore, only 2 parts are needed to completely enclose the inner space 146 of the motor other than the stationary shaft 145 and the bearings 139, 149; namely, the rotor casing 132 and the disk-shaped ring member 147".

FIG. 10 shows a ring 175, somewhat L-shaped in section, which rotates together with the outer rotor of the hub, whereby the ring 175 encompasses an inner, essentially complementary mating part 165, so that the longer leg of the outside part 175 is only separated from the stationary shaft by a narrow gap 275. In combination with the inside mating part 165, this arrangement provides an effective labyrinth seal. This is referenced item 175' in the lower part of FIG. 10, where the basic L-shaped section of the seal is indicated by a solid line and the complementary mating section is referenced 165'. The effectiveness of the labyrinth seal can be enhanced if a projection 175" on the part 175 is provided to project into a recess 165", of the complementary part 165'. The arrangement may be seen also in the upper part of the drawing. In this way, the need to use a substantially more costly magnetic liquid seal of the type shown in FIG. 9 as items 140 and 150, can be avoided. Of course, the incorporation of a labyrinth seal of this type provided with these two interlocking L-shaped leg profiles has an independent significance in connection with data storage disk drives and is not required by the other design features of this motor. As already mentioned, the additional recesses 165"' provide further enhancement of the sealing action of the labyrinth seals. Elements of this type are manufactured as large volume extrusions or deep drawn die pressings and their cost hardly bears comparison with that of magnetic liquid seals. They provide a good low-cost means of the sealing of the clean chamber, because they can be installed at the points of access to the space inside the motor, either in an axial direction or otherwise.

FIG. 14 is a variant of FIG. 6 primarily in the provision of the groove 151 in the motor cover 147 which receives the magnet ring 152 and allows the rotational position sensor 156 to face the magnet ring across a cylindrical air gap vis-a-vis a planar gap in the embodiment shown in FIG. 6.

This invention is not restricted to the use of magnetic field-sensitive rotational position sensors. It can also be used, for example, with optical sensors.

Although the invention has been described in connection with a preferred embodiment and certain alternatives, other alternatives, modifications, and variations may be apparent to those skilled in the art in view of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and scope of the appended claims.