Synthesis and Experimental Validation of Two-Step Variable-Structure Control of a Micro-Actuated Flow Effector

To achieve fast and agile missile flight, carefully designed micro-actuated flow effectors relying on smart structures is a promising technology thanks to their compactness and lightweight properties. Indeed, micro-actuated flow effectors are ideal candidates to carry out active flow control. Such effectors can be mounted on a compliant mechanism and be actuated by means of antagonistic shape memory alloy (SMA) wires. This paper proposes a variable-structure control law for such micro-actuated flow effectors which is designed with the objective of controlling flow effector positions over a range of 1 mm and within a bandwidth of [0.1 Hz, 1 Hz]. A bang-bang controller is used to guarantee fast decaying transients and performance robustness with respect to modeling uncertainties. When the tracking error is less than a prescribed threshold, stabilization without chattering is achieved by switching from the bang-bang control law to a linear digital control law, whose design is based on the parametric identification of the entire mechanical device composed of the antagonistic actuation, of the compliant mechanism, and of the micro-actuated flow effector. The rate independent hysteresis, which is typical of SMA, is represented as an input-output phase lag and is thus taken into account in the control design. Experimental results show that the control law is capable of providing effective control up to 1.0 Hz.