Dynamic actuators Printed shape memory alloys make actuators more dynamic

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Many applications - in toolmaking and mechanical engineering, for example - require actuators to convert electrical signals into mechanical movements. Experts at Fraunhofer are simplifying this process ...

When it comes to converting electrical signals into movements, so-called actuators made of thermal shape memory alloys (SMA) are ahead of the game, especially when it comes to large forces and small installation spaces, as researchers from the Fraunhofer Institute for Physical Measurement Techniques (IPM) explain. The only problem is that such actuators cool down poorly, which slows down the dynamics of such transformation processes. To overcome this problem, a team from Fraunhofer IPM, Fraunhofer IWU and Fraunhofer IFAM has developed compact, highly dynamic high-load actuators based on thermal shape memory alloys (SMA), as part of the recently completed “HochPerForm” project, according to a report.

Innovative actuator lifts half a tonne

With a diameter of just 15 millimetres and a length of 16 millimetres, these innovative actuators are capable of lifting up to 500 kilograms by up to 200 micrometres. Thanks to an innovative Peltier temperature control system, the actuators can be controlled at a frequency of over 0.3 Hertz. Only two cables are required for control, which are connected to decentralised and relatively inexpensive control electronics. In order to achieve this, individual partial function models were first developed to answer the three central questions of the project.

• How can the installation space of a SMA high-load actuator be minimised?

• How can the fast temperature control of the developed actuator be achieved?

• Can the required SMA components be additively manufactured?

Building on the knowledge gained, the team developed a SMA high-load actuator that has a significantly improved property profile thanks to an additively manufactured SMA component and high-performance temperature control. Using a functional demonstrator, it was possible to show that the new high-load actuators are very well suited for the fine positioning of components in production machines, for example, and are predestined for applications that require high holding or clamping forces.

A team from Fraunhofer IPM has pursued two approaches for the rapid cooling of a SMA high-load actuator. Firstly, they investigated the use of switchable heat pipes and secondly, round thermoelectric modules. According to the researchers, the second system in particular makes it possible to achieve high dynamics with a small system size. This opens up completely new application possibilities for SMA actuators in terms of compactness, controllability and simplicity. The basic SMA high-load actuator was then developed at the Fraunhofer IWU. It consists of the SMA component, which acts as an energy converter, and a sophisticated preload system.

During development, a modular system was created that allows SMA high-load actuators to be customised to meet specific requirements. The lack of geometrical freedom and availability of shape memory components was previously a shortcoming of SMA high-load actuators. However, Fraunhofer IFAM has now succeeded in solving this problem by additively manufacturing customised SMA components. This was made possible by the IFAM team's extensive experience, which has also significantly improved functional properties such as hysteresis and degradation through powder bed-based laser beam melting (L-PBF).

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