Dynamic magnetic information storage or retrieval – Record transport with head stationary during transducing – Disk record
Reexamination Certificate
1998-04-01
2001-02-27
Letscher, George J. (Department: 2652)
Dynamic magnetic information storage or retrieval
Record transport with head stationary during transducing
Disk record
Reexamination Certificate
active
06195226
ABSTRACT:
The present invention relates to a disk storage device according to the characteristic clause of claim
1
and a process for production of such a disk storage device. The invention relates especially to disk storage devices with one or several disk-like information carriers that are fixed or fixable to a rotatable hub and housed in an operation chamber of a device chassis, which is enclosed from the surroundings so as to write or read data by means of optical or magnetic write/read heads that can be moved across the information carriers.
Disk storage devices have an operation chamber with a reduced contamination, where at least one disk rotates. This invention relates especially to hard disk drives with a spotlessly clean operation chamber, as there the silence in operation of the motor is especially sensitive to the function of the device.
Because of the compactness that is required to an extreme extent, driving motors with flat air gaps would be desired for such a type of device. However, a “Pan-Cake-Motor” with a flat air gap and with a given small axial size and a large diameter in a way has a mechanical softness in the axial direction, through which it is very susceptible for vibrations in this region. That particularly disturbes, in combination with magnetic motor forces, the operation of the write/read heads. This is the main reason, why direct drive motors with a flat air gap have not got a chance in hard disk storage devices, yet. The cylindric air gap motor has a natural precedence because of the extreme requirements of compactness, accuracy, silence in operation and noise.
A corrective measure is not given yet, when the magnetic yoke is allowed to co-rotate. This is better, of course, than when the magnetic yoke disk would be stationary. In this case, the axial forces that act between the fixed and the rotating magnetic yoke would also be added. Moreover, a stationary magnetic yoke means eddy current losses (that are considerable, when the number of revolutions is up to 10.000 rpm for hard disk drives), and these eddy current losses cause braking. To suppress these eddy current losses one could use for instance a core of coiled up layers that is configured as a stationary magnetic yoke, but that would be extravagant An alternative to the suppression of the eddy current would be ferritic magnetic yoke portions. A ferritic magnetic yoke means also reduced eddy current losses. By this, on the contrary, the losses due to the hysteresis cannot be avoided, however, they may be relatively low in case of materials that are suitable to ferritic sintered components.
There is a force action between the winding and the rotor, which has an effect on the winding or the winding support (stator side) and the rotating permanent magnet, respectively, the magnetic yoke—but in a reduced manner also in that case, when the latter co-rotates on both sides of the air gap, and these forces go into the bearing in any case. The bearing seat of a disk storage device is disadvantageously loaded against these partly considerable axial forces. A main source of these forces are the pulse-like commutation currents in the winding coils.
Therefore, according to the invention, it is proposed to design the stator /rotor symmetrically in relation to a plane perpendicular to the rotation axis. Then, these forces cancel each other and do not load the bearing.
By further embodying this invention, variants are proposed that are suitable to product engineering, i.e. at a relatively reasonable price, which have, together with a symmetric construction as far as possible in the above mentioned sense, respectively, together with a cheaper asymmetric construction, possibilities to avoid or substantially reduce these pulse-like axial forces, which generally originate from the current pulses in the windings and which are transmitted to the bearing.
For this purpose it is planned to make the magnetic yoke portions stiff against axial deformations in such a manner, that the ocurring, disturbing exciting forces will be damped, also, if it is possible, compensated, respectively, prevented.
The following measures serve for this purpose alternatively or cumulatively:
a) to provide an edge that is bent up in the axial direction into the hub radially at the inner edge of the upper rotating magnetic yoke (steel) plate, so that the upper magnetic yoke of the rotor, if it is formed as a deep-drawn portion with an outer edge directing to the bottom, has preferably an S-shaped cross section between the rotation center and the outer circumferential edge. This would be the rotor portion of the permanent magnet, Oil whose flat ring shaped disk middle part at its bottom the axially magnetized rotor magnet is provided;
b) if the lower flat disk shaped magnetic yoke is allowed to co-rotate, it should be supported on the bent down outer edge of this rotor pot, however the disk shaped winding should be supported radially on the inner edge;
c) on the lower magnetic yoke radially at the inner edge also a bent up collar should be provided;
d) the inner collar at the lower magnetic yoke is bent up into the region of the stator disk winding, perhaps over and above it.
e) If the lower magnetic yoke rotates according d), then it is supported on the inner edge of the collar and the disk winding is mounted on its outer edge.
REFERENCES:
patent: Re. 34412 (1993-10-01), Elsaesser
patent: 3845339 (1974-10-01), Merkle et al.
patent: 4519010 (1985-05-01), Elsaesser
patent: 5424887 (1995-06-01), Schuh
patent: 5446610 (1995-08-01), Elsaesser et al.
patent: 5774302 (1998-06-01), Elsaesser et al.
patent: 42 38 886 (1994-05-01), None
Letscher George J.
Papst Licensing GmbH & Co. KG
Welsh & Katz Ltd.
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