Control of a self moving tube driven by shape memory alloy coils

This article describes the control algorithm of a tube made from silicone rubber incorporating a large number of distributed shape memory alloy coils (SMA). The basic driving principle is the antagonistic operation of SMA and silicone: the tube is made up of several equal sections. Measurement of position or length of the driving elements is too complicated because of their large number. Therefore it is recommended to use a driving principle that works without measurement. A precise thermo-mechanical model has thus been developed for using it in a microcontroller. It considers both the hysteresis behaviour of SMA and the nonlinear behaviour of the silicone. The three-dimensional force balance between the silicone body and the imbedded SMA-coils is calculated. The material properties used in the physical models were determined experimentally. A water cooling system improves the response time. A prototype with an outside diameter of 25 mm was constructed. The paper describes theoretical and experimental results of research.