Industries
Inc.®
Ph.
(661) 257-4995
Fax (661) 257-4993
ELECTROMAGNETIC LINEAR ACTUATORS FOR ACTIVE
VIBRATION CONTROL.
F. T. van Namen
Abstract.
Electromagnetic linear force
transducers produce a shaft output force proportional to the input current
and nearly independent of the position of the armature. Inertial
force transducers use action and reaction forces in a sealed package to produce
forces over a wide range of frequencies. Low inductance and flux
modulation is achieved by linking the flux of multiple coils. Customizing
for specific output and environmental requirements is facilitated by
the use of computer simulation in combination with FEA.
Introduction.
Since the invention and publication of the virtues of active
noise and vibration control, significant progress has been made in signal
processing and technical implementation into industrial
applications. All major obstacles seem to be scaled except for one: the
force producing element.
Availability of transducers which produce a force via a linear output shaft are
known in the form of solenoids and shakers. The well known shaker tables
are mainly used in experimental settings, they are bulky and expensive, not
suitable for large scale commercial application. The less expensive,
widely available solenoid has major disadvantages for the use in servo
controlled systems. The force output of a solenoid is not constant over
the stroke and only one directional; the armature must be returned with a
spring. The large amount of iron in the changing magnetic field creates a
high inductance and electrical time constant, making them virtually
useless at high frequencies. Alternative actuator materials like piezo
and magnetostrictive alloys produce very high linear forces, but at extremely
small amplitudes.
In essence there are very few electro magnetic transducers available off the
shelf that can be used in an active controlled system. The requirements
for this kind of transducer are slowly being developed. A specification
should provide the following:
Force rating for maximum continuous power at room temperature.
Force per ampere to be independent of stroke, current and frequency.
Operating amplitude and total shaft amplitude.
Operating frequency range.
Internal spring constant and no-load resonance frequency.
Mechanical impedance.
Coil resistance (to be customized).
Electrical time constant.
Maximum distortion.
Linearity vs. stroke or frequency.
Duty Cycles.
Environmental conditions, high and low temperature, chemical resistance.
Dimensions.
Mounting features.
Stray magnetic field.
Two types of transducers were developed and are being applied in
widely varying industries ranging from automotive to household appliances.
Transducers with a linear shaft output apply a direct force between a mounting
surface and a driven element often parallel with passive elements.
Inertial transducers use the reaction forces on an internal mass and
spring to produce a force on the mounting surface. These units are
completely sealed with no external moving parts. They can be mounted on
any surface and produce mass reaction forces onto that structure, they
can be placed in series or in parallel with passive elements, they can be
placed tangential on rotating equipment in order to create torque reaction.
A wide variety of these transducers can now be produced using the standard
production techniques of the loudspeaker industry. Computer
simulation and FEA assist in the customization for special applications.
Contact Motran Industries Inc.
Last revised 7/28/03 11:40:49 AM