Application of trained NiTi SMA actuators in a spatial compliant mechanism: Experimental investigations

This contribution presents the experimental investigations on the open loop behavior of a spatial compliant mechanism using trained NiTi Shape Memory Alloy (SMA) actuators. The mechanism consists of a central superelastic pillar on which a moving platform is mounted and actuated by three SMA wires. The SMA actuators have been trained by thermal cycling with constant bias force before fixing them on to the mechanism. The optimal power requirements of the actuators have been determined experimentally. Open loop time responses have been obtained by applying various voltage inputs and duty cycles to the actuators for establishing a suitable working point. Models representing the reverse transformation (heating) and forward transformation (cooling) have been obtained from experiments. The relationship between the actuation force and the tilt of the moving platform obtained with trained and untrained SMA actuators are compared. The experiments demonstrate that the results obtained with trained actuators are in close agreement with the analytical results.