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On–off and proportional–integral controller for a morphing wing. Part 1: Actuation mechanism and control design

The main objective of this research work is the development of an actuation control concept for a new morphing actuation mechanism made of smart materials, which is built from a shape memory alloy (SMA). Two lines of smart actuators were incorporated to a rectangular wing to modify the upper wing surface, made of a flexible skin, with the intention to move the laminar-to-turbulent transition point closer to the wing trailing edge. After a brief introduction of the morphing wing system architecture and requirements, the actuation lines' design and instrumentation are presented. The integrated controller controls the SMA actuators via an electrical current supply, so that the transducer position can be used to eliminate the deviation between the required values for vertical displacements (corresponding to the optimized airfoils) and their physical values. The final configuration of the integrated controller is a combination of a bi-positional (on–off) controller and a PI (proportional–integral) controller, due to the two heating and cooling phases of the SMA wires' interconnection. This controller must behave like a switch between the cooling and the heating phases, situations where the output current is 0 A, or is controlled by a PI type law. The PI controller for the heating phase is optimally tuned using integral and surface minimum error criteria (Ziegler–Nichols). The controller is numerically tested on the linear identified system in terms of time response, Bode diagram, amplitude and phase stability margins, and root-locus.