Drive motor for information-storage-disk devices

A drive arrangement for signal-processing devices, especially storage-disk devices, of the type including a motor whose rotor is used for direct-drive,

• the arrangement comprising:
• a brushless dc motor comprising an internal stator and an external permanent-magnet rotor,
• the stator comprising a carrier structure accommodating at least one roller bearing unit, the carrier structure being provided with a mounting portion for mounting the motor as a whole,
• the rotor including a rotor shaft journalled within the roller bearing unit accommodated in the carrier structure, the rotor comprising a rotor magnet arrangement which is of predetermined axial length and has a general inner periphery,
• the stator furthermore comprising a packet of stator plates radially outward of the carrier structure, the stator plate packet having two opposite axial end faces,
• the stator plate packet having cut-outs forming salient poles and being provided with a stator winding to produce a periodic stator field,
• the axial length of the stator plate packet being substantially smaller than the axial length of the rotor magnet arrangement,
• the stator plate packet being provided at at least one of its axial end faces with at least one flux-conducting element having an overall peripheral outline which as viewed axially of the rotor is substantially the same as the peripheral outline of the stator plate packet,
• the flux-conducting element having a peripheral skirt portion which extends generally parallel to the general inner periphery of the rotor magnet arrangement and is of substantially constant axial length along at least the major part of its circumferential extent,
• the skirt portion forming with the rotor magnet arrangement a useful air gap which is a continuation of the air gap formed between the outer periphery of the stator plate packet and the inner periphery of the rotor magnet arrangement,
• the skirted-rim flux-conducting element being provided with cut-outs in the regions of the cut-outs of the stator plate packet for generation of a reluctance torque component which during rotor rotation is shifted in time relative to the electromagnetic torque component resulting from said periodic stator field,
• the portions of the stator plate packet constituting the salient poles having leading ends and trailing ends considered with respect to the direction of rotor rotation,
• the overall outline of the stator plate packet being such that the leading end of each salient pole portion of the stator plate packet is initially of reduced radius and, proceeding circumferentially, is of increasing radius towards the trailing end of the salient pole portion,
• the skirt portion of the flux-conducting element consisting of a circumferential succession of skirt portion segments corresponding to the salient pole portions,
• the cut-outs of the flux-conducting elements being cut-outs from the leading ends of the skirt portion segments thereof, each cut-out having a surface area equal to about 10-30% of the surface area which the respective skirt portion segment would have if the cut-out were not present,
• the overall peripheral outline of the skirted-rim flux-conducting element corresponding to that of the stator plate packet and accordingly being of initially reduced radius at the portion thereof corresponding to the leading end of a salient pole and, proceeding circumferentially towards the trailing end, being of continuously increasing radius,
• the cut-outs from the skirt portion segments being so shaped that, at the leading end of a salient pole the skirt portion is entirely absent for a first predetermined circumferential extent, then for a second predetermined circumferential extent increases in axial length to a predetermined value, and then for the remainder of its circumferential extent has a substantially constant axial length substantially equal to the predetermined value.

A drive arrangement for signal-processing devices, especially storage-disk devices, of the type including a motor whose rotor is used for direct-drive,

• the arrangement comprising:
• a brushless dc motor comprising an internal stator and an external permanent-magnet rotor,
• the stator comprising a carrier structure accommodating at least one roller bearing unit, the carrier structure being provided with a mounting portion for mounting the motor as a whole,
• the rotor including a rotor shaft journalled within the roller bearing unit accommodated in the carrier structure, the rotor comprising a rotor magnet arrangement which is of predetermined axial length and has a general inner periphery,
• the stator furthermore comprising a packet of stator plates radially outward of the carrier structure, the stator plate packet having two opposite axial end faces,
• the stator plate packet having cut-outs forming salient poles and being provided with a stator winding to produce a periodic stator field,
• the axial length of the stator plate packet being substantially smaller than the axial length of the rotor magnet arrangement,
• the stator plate packet being provided at at least one of its axial end faces with at least one flux-conducting element having an overall peripheral outline which as viewed axially of the rotor is substantially the same as the peripheral outline of the stator plate packet,
• the flux-conducting element having a peripheral skirt portion which extends generally parallel to the general inner periphery of the rotor magnet arrangement and is of substantially constant axial length along at least the major part of its circumferential extent,
• the skirt portion forming with the rotor magnet arrangement a useful air gap which is a continuation of the air gap formed between the outer periphery of the stator plate packet and the inner periphery of the rotor magnet arrangement,
• the skirted-rim flux-conducting element being provided with cut-outs located at least partly outside the angular intervals occupied, at the air gap, by the salient-pole-forming cut-outs of the stator plate packet, to thereby produce a reluctance torque component which during rotor rotation is shifted in the relative to the electromagnetic torque component resulting from said periodic stator field.