Modelling, simulation and experiments of novel planar bending embedded SMA actuators

The new type of structure named planar bending embedded shape memory alloy actuator is developed. Two SMA wires are embedded in parallel with the axis of the elastic rod. The recovering wire, which is superposed along rod’s axis, is set to obtain “U” memory shape and the restoring wire, with straight memory shape, is placed off-axially. The differential strain gauges are located at suitable position in corresponding to the actuator’s bending direction in order to measure the signal of displacement. The mathematic model obtains both for simulation and control system analysis of the actuator, inherently non-linear device exhibiting significant major and minor hysteresis loops. The model calculates martensite fraction using two exponential equations, one for heating and the other for cooling. By making use of continuity, common origin and common limit conditions and adjusting martensite fraction coefficients appropriately, the model can adequately account for the presence of minor hysteresis loops. Finally, the experimental and simulated results of step response using two-stage hybrid controller prove the validity of the non-linear model.