Moving coil (or voice coil) actuators work on the same principle
as an audio loudspeaker. They consist a moving carriage with an
attached coil surrounding a powerful permanent magnet. Current
passing through the coil induces an electro-magnetic force, according
to Fleming's
left-hand rule. Varying the direction and amplitude of the
current varies the induced force, allowing us to control the motion.
The result is a device with few moving parts, low friction and
zero backlash with excellent dynamic properties.
Other voice coil manufacturers give no provision for postion
feedback, but all SMAC actuators include a precision, non-contact
linear encoder. This allows closed-loop servo control of motion
in position and velocity modes and real
time monitoring of position in all operating
modes.
These unique features allowed SMAC to develop the "Softland"
routine, which has permitted applications
simply not possible with other technologies.
Operating modes
Using SMAC controllers all of our products are programmable using
3 different modes independently controlling position, velocity,
and force, allowing their performance characteristics to be tightly
monitored. Pass/fail windows for any of these parameters can be
set - useful for error reporting and testing applications.
Position mode
Position mode will allow the actuator to be moved to any position
along the stroke using a given acceleration, velocity and force.
It is possible to make absolute, relative and "learned position"
moves. The force necessary to hold a given position can also be
measured - this is called "holding force" and is used
in applications such as switch testing.
Velocity mode
Velocity mode allows the actuator to be moved with a given velocity,
acceleration, force and direction. Velocity (i.e. position vs.
time) is closed-loop using feedback from the encoder, giving precise
velocity control. Position and position error (the difference
between actual position and desired position at a given time)
can be interrogated in real time during motion. Typically used
for constant speed scanning applications and "softland"
routines.
Force mode
In Force mode, current in the coil is controlled to give a programmed
force output. Position and velocity are open loop, using no feedback
from the encoder, but actual position can still monitored in real
time. Used in applications such as tensile and compression testing
