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SMA-Snapper - a bi-stable actuator activated by shape-memory alloy wires


By utilizing shape-memory alloy wires in a smart way, the new actuator design allows for lightweight and space-saving construction of bi-stable actuation solutions.


Common applications for bi-stable actuators are, e.g., electrically powered switches, relays or locks. Nowadays widely used servo-motors or electromagnets implicate several disadvantages, such as non-lightweight construction and/or high power consumption. Actuators based on shape-memory alloys (SMA) offer several advantages, e.g. due to the high actuation energy density of SMA materials. A common example of SMA-actuators that are already in series production is the spoiler adjustment of sports cars.

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A new actuator design has recently been developed at Saarland University and ZeMA – Zentrum für Mechatronik und Automatisierungstechnik. The sketch shows the construction principle including a bi-stable spring. In particular, the main movable part turns downwards when the blue wire is heated, as indicated by the central arrow. In this way, a switch or other bi-stable applications can easily be realized. Other configurations have also been developed (not shown here).



Due to its novel design, the proposed SMA technology offers a number of advantages:

  • Very small weights and sizes possible due to minimalistic and simple construction form
  • High forces, in particular high energy density (force/weight)
  • Frequencies: at least 10 Hz possible
  • SMA has no noise emission (snap can “click” but does not have to)



The technology is suitable in particular for electric switches, relays or locks as well as other bi-stable actuation applications.

Preliminary technical data as derived from the prototypes:

  • Minimum size: allows micro scale construction, e.g. 10x10x5mm3 or below
  • Temperature range: up to +60-70ºC as tested; above requires further assessment
  • Power needed for activation: depending on wire diameter and length (resistance of wire), e.g. between 0.05 – 2 W for common applications
  • Actuation characteristics: very fast actuation for 1 time actuation possible (in the ms-range)
  • Durability: several million cycles

Related publication available on request.

Universität des Saarlandes Wissens- und Technologietransfer GmbH

Dr. Frank Döbrich
0681 302-3508
Universität des Saarlandes Wissens- und Technologietransfer GmbH Starterzentrum | Gebäude A1 1
66123 Saarbrücken




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SMA, shape-memory, Formgedächtnislegierung, Formgedächtnisdraht, bi-stable, actuator, bistabil, Aktuator, snapper, Schnapper, Schnappmechanismus

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