Fraunhofer Institute for Machine Tools and Forming TechnologySMA-based drives have continuously opened up new markets in recent years and can now be found in a wide variety of applications, such as smartphone cameras or valves in the automotive sector. Compared to conventional drives, SMA-based systems offer significant advantages: higher power density, electromagnetic compatibility, high efficiency thanks to simple design, noiseless operation and easy integration into compact installation spaces. As they also consist of few mechanical components, wear is minimal. Thanks to the so-called intrinsic sensor effect, these materials not only act as actuators but also as sensors, which enables them to provide information about external loads, actuating strokes and temperatures. The result is compact, technically simple but highly functional lightweight actuators, which have recently been used in the Grabbit G7 drone from Vectorbirds.
The developed actuator system is used to lock the drone's battery slide and prevent unintentional release during operation. It consists of a spring-loaded slider and an SMA wire. When cold, the wire, which is only 76 micrometers thick, is pretensioned by the spring force. When electrically heated, the wire contracts as it wants to return to its original load-free shape and thus pulls the slider back. As soon as the wire cools down, the return spring moves the slider back to its original position and pretensions the wire again.
SMA actuators are also easy to scale in terms of stroke, installation space, force range and service life. Longer wires provide more stroke, thicker cross-sections enable more force. This facilitates their use in a wide variety of application scenarios.