Electricity: motive power systems – Positional servo systems – With stabilizing features
Patent
1998-02-24
2000-10-31
Ro, Bentsu
Electricity: motive power systems
Positional servo systems
With stabilizing features
310 51, G05B 501
Patent
active
061407909
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates generally to motors and the vibrations or resonances which are set up within such motors; particular applications or examples will be given with respect to spindle motors used in disc drive assemblies, but the application of this invention is not limited to these specific examples.
BACKGROUND OF THE INVENTION
Most motors, indeed most rotating systems that are spinning about a fixed axis, have vibrations or harmonics which are set up and become part of the system, disturbing the overall stability and smooth operation of the system. Such problems are particularly acute in the disc drive industry, where a spindle motor mounts and supports a disc or disc pack for high speed rotation. The disk drive industry is continually seeking to obtain a head disc assembly (HDA) capable of operating with an increased track density which requires greater resistancy to shock and vibration.
As the operating demands on the HDA increase, problems associated with conventional HDA systems become performance limiting factors: for example non-repetitive run-out (NRR) associated with conventional ball bearings limits track spacing and thus, reduces the track density at which the HDA can reliably operate. NRR is associated with the highly complex dynamic behavior of the hard disk drives: mechanical modes of the motor and the disc pack correspond to predicted mechanical resonance, which are in turn excited by ball bearing vibration. To reduce NRR magnitude, the vibrational characteristics of the drive have to be modified.
In the prior art, a number of efforts have been made to electronically damp vibration associated with a motor or with a transducer in a disc drive. The prior art to damp vibrations in a moving transducer in order to more quickly center it on a track includes U.S. Patents to Song, U.S. Pat. No. 4,414,497; Sidman, U.S. Pat. No. 5,459,383, and Ravizza, U.S. Pat. No. 4,080,636. Each of these comprise elaborate circuitry for adding feedback loops to more quickly damp out the vibrations or movements in a moving transducer. All of these are not associated with problems of damping out vibrations in a motor or the disc itself, and also add considerable complexity and cost to the system.
Other patents have added mechanical or electromechanical elements to the motor itself in an effort to damp out vibrations in the motor. These patents include Hasigawa, U.S. Pat. No. 5,317,466; Bartec, U.S. Pat. No. 4,198,863; and Clancey, U.S. Pat. No. 4,286,202. These patents are especially directed to the addition of mechanical or electromechanical elements to motors to detect and damp out vibration. Again, these prior art approaches have not proven to be effective in detecting the resonance modes which can exist in rotating motors and particularly disc drive spindle motors, and damping out such resonances. Further, they add considerable cost and complexity to the motor design.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to damp out the resonances which occur in a rotating system.
A related objective is to stabilize the spin axis of a rotating system in a given position.
It is a further objective of this invention to accurately simulate the undamped resonant movements of the rotating system, and then to apply an out of phase force to the rotating system to damp out the resonant movements.
It is a further objective and a related objective of the invention to apply an out of phase force which accurately and repeatably damps or attenuates the resonant movements and thereby stabilizes the system.
In this invention, the term "attenuation" is directly related to the fact that the force applied is out of phase with the resonant movements within the system. This is as opposed to the idea of adding a force which directly opposes the resonances which are occurring within the system, which would thereby add stiffness to the system, and constitutes the approach taken by the prior art. This would be the approach taken by an electromagnetic bearing, or the like, bein
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Fleury Christian
Heine Gunter K.
Leuthold Hans
Ro Bentsu
Seagate Technology LLC
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