Browse Prior Art Database

Linear Magnetic Actuator

IP.com Disclosure Number: IPCOM000109174D
Original Publication Date: 1992-Aug-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 2 page(s) / 66K

Publishing Venue

IBM

Related People

Goldowsky, M: AUTHOR [+2]

Abstract

Disclosed is a method to focus radial magnetic flux in a surrounding coil by using axially magnetized magnets in the bucking mode. No iron is used in the magnetic circuit which results in a small diameter voice coil actuator of low cost. Force amplification may be obtained using more than one stage of magnets and coils.

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Linear Magnetic Actuator

       Disclosed is a method to focus radial magnetic flux in a
surrounding coil by using axially magnetized magnets in the bucking
mode.  No iron is used in the magnetic circuit which results in a
small diameter voice coil actuator of low cost.  Force amplification
may be obtained using more than one stage of magnets and coils.

      Fig. 1 shows two opposed polarity magnets separated by an air
gap.  The opposing fluxes cause the total resulting flux to go
radially outward (or inward) at the center of the gap.  This flux
returns back to the magnets through the air.  A coil surrounding  the
gap produces an axial force on the magnets in proportion to coil
current.  The coil does not extend beyond the gap (axially), as the
field becomes rapidly non-radial outside the gap.  Thus, the magnet's
gap determines the actuator's maximum stroke which is generally
limited to short-stroke applications.

      A two-stage actuator is shown in Fig. 2.  Three magnets are
used instead of two.  This gives a higher force to mass ratio as two
coil forces are obtained with three  magnets instead of one coil
force with two magnets.  The flux is outward in one coil and inward
on the other, so coil current must be reversed in one coil for the
forces to add.

      As more stacks are employed, the force to weight ratio
increases; asymptotically approaching a 1.00 ratio (n/n+1), where n =
number of coils.  This will give higher accelerations wh...