Nitinol Actuators by Miga Technologies LLC

We design SMA wire products.

Shape memory alloy wires (SMA) or “muscle wires” are known to produce motion with the highest force-to-weight ratio of any known actuator. But they are also notoriously difficult to control outside of very slow actuation speeds because the wires are easily overheated: destroying the ‘memory’.

SMA wire is ideal for electrical actuation because it is ‘resistive.’ That is, it obeys Ohm’s law: V=I*R, where V is the input voltage, I is the required current, and R is the wire resistance. But how long does it take to actuate at a given voltage? How much power do I need to provide, and for how long? How long can I energize the wire so that it contracts fully, but does not overheat?

Common SMA Actuation Questions:

How much current will it draw if my application requires a 9-volt battery, and I need 0.2″ of stroke with 1 pound of force?

What wire diameter, length, and voltage do I need to provide 0.125″ of stroke in 0.150 seconds, and to be ready to actuate again in 5 seconds?

How many cycles will I get from a 3.7 volt 200mA-hr lithium-ion cell?

How will my SMA actuator perform in low ambient temperature conditions? Does it require more time to energize? Can I still use a 6-volt power supply if the device needs to operate at 0˚C? How warm can the ambient temperature be?

I don’t need a million cycles, so how much force can I get out of my actuator if I only need it to operate 100 times?

The Answer:

Over the past 18 years, we have developed and exhaustively proven a highly sophisticated model that we use to predict every single aspect of SMA behavior: allowing us to quickly hone in on certain design parameters, while holding others fixed.

Given a desired stroke and force, or desired operating speed or voltage, we can predict all other aspects of the actuation.

Some type of stroke or force amplifying leverage may be suggested if hard requirements exist for one or the other design parameters.

In other cases, longer wire sections may be required to meet speed or voltage requirements.

There are complex space and volume constraints for every actuator design, in addition to the more common force, stroke, or voltage requirements.

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