Actuators are key elements in almost every production plant and machine. Depending on the application, there are a variety of established solutions, such as hydraulics, pneumatics, electrodynamics and piezoelectrics. Different requirements result from the respective applications, such as force, stroke, dynamics, stiffness and installation space. Due to the enormous energy density and the ability to take over structural and geometric functions, shape memory alloys represent an interesting alternative to conventional actuator technologies. For wire-based actuators, the performance and application limits are already known due to extensive research and the technology can be found in various commercial applications. However, especially in industrial machine technology, many applications require short strokes (smaller than 1 mm) and large forces (bigger than 1 kN) with minimal space requirements. In order to qualify SMA-actuators for these applications, new challenges regarding design, construction, simulation and system integration must be overcome.

The paper first describes relevant application cases. These include fine positioning during the production and assembly of workpieces or the active influencing of the mechanical stiffness of tools during forming processes. The basis of the actuator design is the characterization of a shape memory alloy under compressive load, which is suitable for actuator application at room temperature. The focus of the investigations is on the running-in and stability behaviour in order to guarantee the lifetime of the actuator. Thus, the cyclic thermo-mechanical load can lead to a degradation of the shape memory material and consequently to a reduction of the actuator usable range. Accordingly, the material must be sufficiently stable over the required number of cycles and shortening during the operational lifetime must be taken into account when designing the actuator.

Based on this, the actuator development is realized, whereby the extrinsic two-way effect is used to implement a control of the actuator. The temperature of the shape memory component must be set in a defined manner by heating or cooling devices. Due to the higher thermal mass of the SMA‑components, the heating and especially the cooling behavior must be taken into account with regard to the required switching times and positioning speeds. Based on the described boundary conditions, a scalable actuator concept and a systematic approach is presented in order to design the active components involved according to the requirements. The applicability and functionality of the concept is demonstrated by investigations on a concrete actuator. Finally, optimization potentials and a roadmap for further development are presented and discussed.


Development Approach of Actuators for High Loads Based on Shape Memory Alloys

Division / Sponsors: 
Aerospace Division

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2020/volume/84027

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