02. October 2019

We congratulate Arathi Pai to her doctorate

Arathi Pai has successfully passed her doctoral examination. She received her doctorate for the topic „Computationally Efficient Modelling and Precision Position and Force Control of SMA Actuators“ under Prof. Dr. Ansgar Trächtler.

Shape Memory Alloys (SMAs) are metallic alloys that display shape recovery after deformation through an increase of temperature. These shape recovery mechanisms can be exploited to create SMA-based position or force actuators. However, due to their inherent nonlinear and hysteretic behaviour, the control of such actuators is non-trivial.

The development of control strategies for SMA actuators is alleviated by the use of models incorporating these nonlinearities. In this thesis, a novel phenomenological model to predict the behaviour of SMAs for varying temperature and stress is presented. The model shows outstanding correlation with experimental data. In order to use the models within a control loop, computationally efficient inverse models are also developed.

A novel control strategy for precision control of SMA actuators is then developed by using a combination of large and small signal controllers. The large signal controller, responsible for course positioning, is a temperature controller that gets its desired temperature value online from the inverse SMA model. The small signal controller is responsible for fine positioning. The control results show robust and precise tracking control with exceptional disturbance rejection for various loads.

The control strategy is then used for force control in an industrial SMA-based clamping vice to clamp a thin-walled test tube. While the large signal controller remains unchanged, the small signal controller is used for force control rather than for position control. The control unit of the vice is an embedded processor, on which the control algorithms run in real-time. The vice shows accurate force tracking and good disturbance rejection.

The doctorate will be published soon at the HNI-press. Congratulations.

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