Shape-Memory-Alloy (SMA) as actuator

Shape-Memory-Actuators overview

Why is SMA interesting for actuators?

  • Very high power density
  • Low weight
  • Electrically controllable
  • Intrinsic sensor effect ("self-sensing")
  • Large force range up to kN
  • Shortening up to 5% (relating to the length of the SMA)
  • Achievable switching times of a few milliseconds
  • Lifetime up to several million switching cycles
  • No noise emission
  • High availability of the basic material in form of wires
  • Proven a million times
SMA compared to conventional technologies
Shape memory alloy compared to other actuator technologies
  • The above diagram clearly shows the superior power density of SMA actuators. Also in terms of power-to-weight ratio, no other actuator technology is able to realise such high forces in minimal installation space.
Shape memory effect: What is it based on and how is it used actuatorially?
  • The name itself describes the property of being able to deform back into a previously imprinted shape even after severe deformation.
  • The shape memory effect is based on a reversible phase transformation at the crystal level, which is triggered thermally or mechanically.
  • The so-called transformation temperatures are typical for each SMA and can be adjusted via the alloy proportions.
  • Through targeted heating, e.g. by passing an electric current through an SMA wire, it shortens and can perform work. If the SMA wire cools down afterwords, it can be mechanically stretched back to its original length and the cycle starts again.
Self-sensing and closed-loop control
  • The strain state of the SMA can be determined directly via resistance measurement and thus be used for control. If the temperature of the SMA is also known, even a force/displacement control can be realised.
Shape memory effect: example applications
  • Industry: clamping, tensioning, locking technology; electrification of drives
  • Medical technology: ultra-light actuators in wearables
  • Consumer: Toy actuators, tool drives
  • Automotive: locking technology, valve technology
  • And much more

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