Electrical generator or motor structure – Dynamoelectric – Linear
Reexamination Certificate
2001-03-27
2004-03-30
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Linear
C381S412000, C381S414000
Reexamination Certificate
active
06713904
ABSTRACT:
TECHNICAL FIELD
The present invention is directed generally to linear actuators, and more particularly to compensating magnetic flux generated by the current in the moving coil of voice coil actuators.
BACKGROUND ART
Voice coil actuators are electromagnetic devices which provide force proportional to current applied to a coil. U.S. Pat. No. 5,677,963, assigned to the assignee of the present application, is a example of such voice coil actuators, and incorporated by reference herein in its entirety.
Different configurations of linear voice coil actuators can provide different shapes of the Force vs. Stroke curves. However, these shapes cannot be changed without increasing the power level in the moving coil. But even this measure achieves only limited results due to a given distribution of the primary magnetic field and the armature reaction.
In a servo system, it may be necessary to maintain constant force or constant speed within a certain stroke. U.S. Pat. No. 5,177,383, entitled “Voice coil motor,” discloses coils with shorted turns employed in an attempt to achieve such characteristics. Because the turns in those coils are shorted, however, current in those turns cannot be adjusted when the moving coil moves from one position to another.
SUMMARY OF THE INVENTION
In accordance with the present invention, one or more separate compensating coils are employed to alter the distribution of the magnetic flux density in the air gap to produce a constant force throughout as much stroke as possible. Current in the separate compensating coils can be adjusted with the stroke using separate power supplies and a position feedback.
These and other features of the present invention will be more readily appreciated upon consideration of the following detailed description and accompanying drawings.
REFERENCES:
patent: 3619673 (1971-11-01), Helms
patent: 3863082 (1975-01-01), Gillott et al.
patent: 3867675 (1975-02-01), Kitz et al.
patent: 5177383 (1993-01-01), Sim
patent: 5521774 (1996-05-01), Parks et al.
patent: 5677963 (1997-10-01), Morcos et al.
patent: 5777403 (1998-07-01), Yuan
patent: 1308349 (1973-02-01), None
patent: 224363 (1997-08-01), None
patent: 308325 (2000-11-01), None
BEI Technologies Inc.
Dougherty Thomas M.
Gray Cary Ware & Freidenrich LLP
Jones Judson H.
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