Closed-Loop Control for High Bandwidth, High Curvature Post-Buckled Precompressed Actuators

The closed-loop dynamic behavior of post-buckled precompressed (PBP) piezoelectric elements is in-vestigated in this paper. PBP actuators have been shown to be capable of generating significantly larger deflections than traditional piezoelectric actuators, up to a factor of three, without compromising applied end force. Due to an axial force close to the perfect-column buckling load they have displayed reduced stability and even instability around zero deflection. Therefore, a closed-loop control system was created to stabilize the PBP actuator over its entire range of deflections. The dynamic response of this system was compared with the open-loop response of the PBP actuator and with the dynamic characteristics of a traditional elec-tromechanical servoactuator. It was found that a pure integrative (I) controller was able to stabilize the PBP actuator over its entire range of deflections. To maintain stability, the gains had to be decreased for higher axial loads, reducing the bandwidth of the system, but still outperforming a traditional servoactuator by 40%. Furthermore, the influence of actuating an aerodynamic control surface was investigated by adding an inertial mass to one of the supporting axes of the PBP actuator. It was shown that a PBP actuator was capable of rotating these masses, although this slightly reduced the speed of the response. Nomenclature a Initial spring compression m b Actuator width m B Distributed coupling stiffness coefficient N d31 Piezoelectric charge constant m/V D Distributed bending stiffness coefficient Nm e Error between measured and commanded signal V E Young’s modulus N/m2 E3 Electric field (through-the-thickness) V/m f Frequency H