US 4,701,653 A · Disk drive with internal brake and static discharge

Abstract

A drive unit for direct drive of an information-storage disk comprises a collectorless D.C. external-rotor motor having a permanent-magnet rotor magnet arrangement of considerably reduced axial length. Electrostatic charge is removed from the rotor shaft by a metallic spring element which engages the shaft periphery from within the interior of the rotor housing. An electromagnetic braking arrangement is located interiorly of the housing. The packet of stator plates for the stator has an axial length shorter than that of the rotor magnet arrangement, but is provided at its axial end faces with skirted-rim flux-conducting elements whose peripheral skirt portions form useful-air-gap extensions in cooperation with the rotor magnet arrangement. The stator plate packet and associated skirted-rim flux-conducting elements may have cut-outs defining salient-pole structure; the skirt portions of the flux-conducting elements are provided with cut-outs at their leading ends serving to produce a reluctance torque component which, during rotor rotation, is shifted in time relative to the electromagnetic torque component attributable to the salient-pole configuration. The portion of the rotor structure which supports an information-storage disk has an annular recess accommodating a disk-holding magnet whose upper surface is slightly recessed relative to an annular magnetically conductive disk-supporting ridge of the rotor, the cross-sectional shape of the ridge being such as to establish a magnetic disk-holding force of exactly predetermined character despite tolerance-range variation of the coercive force of the holding magnet employed.

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

a brushless D.C. motor comprising
(a) an internal stator,
(b) an external permanent-magnet rotor, and
(c) a motor shaft defining the rotation axis of the rotor,
(d) wherein the stator includes a carrier structure comprising an axially extending carrier pipe portion which encircles the motor shaft and accommodates at least one roller bearing unit, said motor shaft extending axially through the interior of said carrier pipe portion and being journalled within said at least one roller bearing unit, and wherein the carrier structure furthermore includes a radially outward extending mounting portion for mounting the motor as a whole,
(e) the stator further comprising a packet of stator plates radially outward of the carrier pipe portion, and a stator winding wound upon said packet of stator plates,
(f) the external permanent-magnet rotor including a rotating generally pan-shaped rotor housing comprising a peripheral wall portion having two axial ends, one axial end being located close to said radially outward extending mounting portion, the other axial end being located remote from said radially outward extending mounting portion,
(g) the rotating pan-shaped rotor housing further comprising a generaly planar, generally radially extending base portion located at said other axial end of said peripheral wall portion of said rotating generally pan-shaped rotor housing,
(h) the external permanent-magnet rotor further comprising an annular arrangement of permanent-magnet material located at the interior side of said peripheral wall portion and spaced radially outward from and encircling said packet of stator plates, and
(i) electrically conductive discharge means in electrically conductive engagement with at least one of said rotor and said stator, and operative for maintaining said rotor and said stator at equal electric potentials,
(j) the drive arrangement furthermore comprising an electromagnetic braking arrangement located axially between said stator winding and said generally radially extending base portion of said generally pan-shaped rotor housing,
(k) said electromagnetic braking arrangement comprising:
(k1) a braking surface portion,
(k2) means mounting the braking surface portion
for axial displacement in a first direction towards said generally radially extending base portion of said generally pan-shaped rotor housing into an operative position in which said braking surface portion frictionally engages the interior surface of said base portion and applies to the latter frictional braking force braking the rotor housing and thus braking the rotor, and
for axial displacement in an opposite second direction away from said base portion of said generally pan-shaped rotor housing into an inoperative position not frictionally engaging the interior surface of said base portion so as not to apply braking force to the latter,
(k3) electromagnetic deactivating means operative when energized for axially displacing said braking surface portion in said second direction, and
(k4) biasing means operative when said deactivating means is not energized for axially displacing said braking surface portion in said first direction,
(k5) said braking surface portion and the interior surface of said base portion of said generally pan-shaped rotor housing, at the zone at which said braking surface portion applies braking force to said base portion, both extending at least chiefly in the purely radial direction of the motor.

16 more elements

Disk drive with internal brake and static discharge

Life of this patent

Disk drive with internal brake and static discharge

Life of this patent

Abstract

Claims31