Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2000-10-16
2002-12-31
Vidovich, Gregory M. (Department: 3726)
Metal working
Method of mechanical manufacture
Electrical device making
C310S051000
Reexamination Certificate
active
06499209
ABSTRACT:
FIELD OF THE INVENTION
The present invention provides internally damped stators, rotors, and transformers having improved vibration damping performance and the internally damped cores from which they are made.
The internally damped stators are useful, for example, for various electric or magnetic motor applications, specifically electric motors used for disk drive spindle motors and electric motors used for automobiles and power generating equipment. The internally damped stator improves the vibration damping properties of the motor with which it may be used.
The internally damped rotors are useful, for example, for various electric or magnetic motor applications, specifically electric motors used for disk drive spindle motors and electric motors used for automobiles and power generating equipment. The internally damped rotor improves the vibration damping properties of the motor with which it may be used.
The internally damped transformers are useful, for example, for various electric or magnetic applications, specifically power supplies in computers and stereo equipment. The internally damped transformer core improves the vibration damping properties of the transformer in which it may be used.
Methods of making the internally damped cores, stators, rotors, and transformers of the invention are also provided. The preferred method is cost effective and particularly good for manufacturing at high volumes. The internally damped stators, rotors, and transformers can optionally be made in such a manner as to reduce cut and shorted wires.
BACKGROUND OF THE INVENTION
Periodic or random vibrations or shocks can excite the induction core of a stator, rotor, or transformer to vibrate at its resonant frequencies. These can be problematic due to the resultant formation of undesirable stresses, displacements, fatigue, and sound radiation. Such undesirable vibrations or shocks are typically induced by the interaction of the stator and rotor. The resulting magnetic flux interactions of the stator and rotor can lead to vibration in either of the components.
Flux build-up and flux fields interacting with each other at high rates can lead to a flux field force being applied to the stator or rotor, causing it to vibrate at resonant frequencies resulting in sound radiation, fatigue, and vibrations that can be transmitted to other portions of the motor or items attached to the motor leading to degraded performance (such as in a disk drive where the excessive vibrations transmitted by the stator can cause read and write errors and reduced drive performance) and/or excessive heat build-up from frictional movement. A quiet motor is important to many applications. For example, disk drives often require a motor to operate at less than 30-45 dBA so that when the drive is used in an application, it does not bother the end user of the drive.
Typical stators, rotors, and transformers have many magnetic layers. These layers are stamped or otherwise cut in single individual layers, typically a ring pattern with “poles” extending from the ring. The magnetic layers are stacked by hand or by automated assembly to the desired stack height of the stator, rotor, or transformer. The layers are then joined in a number of ways, such as, for example, by pressing the layers together with a die and using a punch to crimp the layers together, coining, embossing, encasing or coating the outer surfaces of the assembled layers with a rigid non-vibration damping polymeric material (such as an epoxy), applying heat and pressure to form a hydrostatic bond, or combinations of the aforementioned.
Various techniques have been used to reduce vibrational and shock effects (stresses, displacements, etc.) on stators. Three basic techniques include:
1) adding stiffness or mass to the stator so that the resonant modes of the stator are not excited in operation;
2) isolating the stator so that the vibrational or shock energy does not excite other items in the motor construction or items connected to the motor; and
3) damping the stator core by “potting” or encasing the stator core exterior, or portions of the stator core exterior in a polymeric potting material. Typically a polymeric potting material, which optionally may have some damping benefit and/or stiffness benefit, may be used to encase all or a portion of the stator core exterior, thereby reducing the vibration excitation levels and the harmful effects.
Katakura et al., U.S. Pat. No. 5,241,229 discloses a magnetic disc drive motor comprising a hub for carrying magnetic discs on its outer periphery, a drive magnet rigidly fitted to the inner periphery of the hub, a stator core having a coil wound around it and juxtaposed with the drive magnet, and a motor frame having a substantially cylindrical holder for rigidly holding the stator core, wherein the space between the stator core and the motor frame is filled with a resin material. A compact and simply configured magnetic disc drive motor can thus be realized, which is capable of rotating magnetic discs in a very stabilized manner. With such an arrangement, since the space between the stator core and the motor frame, which was not used for any particular purpose, is filled with a resin material, the space within the motor is effectively utilized to enhance the rigidity of the motor frame.
The aforementioned design provides for a stiffer stator thereby reducing some vibration levels. In addition, the resin material can also provide some vibration damping. This design, however, is difficult to manufacture as filling between the poles is difficult. The design can also reduce the heat flow away from the stator increasing the temperature of the windings and creating various problems related to high temperatures of the motor.
This design would also be expensive to manufacture as each stator with windings in place would need to be potted, requiring fixturing, cure ovens, and potential long manufacturing cycles. Variability between stators being potted would be expected as each would have variations due to tolerances of the windings, etc. The potted design would also require a significant amount of organic resin material to be used inside the motor and disk drive assembly. The organic resin material would be largely exposed to the internal motor and drive atmosphere which could lead to outgassing concerns when the drive operates at elevated temperatures (typically greater than 45° C., most typically greater than 60° C.). The outgassing could lead to corrosion or outgassed material build-up on various parts inside the motor or drive, such as on a disk, read/write heads and other exposed surfaces leading to drive performance reductions or drive failure.
Von Der Heide, et al., U.S. Pat. No. 4,647,803 discloses an electric motor with a substantially cylindrical air gap between the stator and the rotor, the stator being fitted to a bearing support for the rotor shaft bearing. In order to reduce noise emissions, the stator is connected to the bearing support by means of an elastic damper and the stator and bearing support are separated from one another by an air gap adjacent at least part of their facing faces. This design adds damping and isolation, but would be costly to manufacture and also requires additional manufacturing steps to make the motor and precise alignments of parts.
Maughan et al., U.S. Pat. No. 5,365,388 discloses a disk drive that has a stator positioner disposed on a shoulder of a drive shaft housing which is part of a spicule. The positioner secures the stator against movement and references the motor to the spicule which engages and guides the cartridge. An open cell urethane gasket between the printed circuit board and the stator absorbs vibrational forces. This design offers isolation, but does not offer direct damping of the stator, thus its overall effectiveness is limited.
Dunfield et at., U.S. Pat. No. 5,619,389 discloses a spindle motor for rotating at least one disc in a data storage device which includes a base, a shaft, a rotor and a stator. According to the patent a bearing interconnects the rotor with the s
Hilderbrand Larry S.
Johnson Gordon G.
Landin Donald T.
McCutcheon Jeffrey W.
3M Innovative Properties Company
Harts Dean M.
Kenny Stephen
Vidovich Gregory M.
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