Piezoelectric buckling actuators : form reduction, bidirectional control, and optimal switching

Abstract

Piezoelectric stack actuators are generally described as having large force density, high bandwidth response, and limited yet precise displacement properties. As a result, these actuators have been widely applied to precision positioning devices, acoustical and optical instruments, and within vibration control mechanisms. Techniques to efficiently amplify this limited displacement have been central to recent piezo-actuator research. One such technique exploits structural buckling to achieve displacement amplification gains greater than 100 while limiting energy transmission loss into the amplifying mechanism. This thesis first surveys the recently developed piezoelectric buckling actuator and identifies critical design elements that may be further optimized to reduce the mechanism's form factor. Focus is directed towards simultaneously reducing structural compliance and mass in the actuator's frame and rotational joints. Use of carbon fiber and new geometry improves structural efficiency while increased joint stiffness is shown through design and material changes. Discussion then shifts to the nondeterministic output of a standalone buckling actuator and methods to address it. A design is presented which couples the buckling actuator to an energy storing mechanism that alternates output direction by enforcing hysteretic force-displacement behavior using a closed loop cam-follower path. Finally, a dual buckling actuator mechanism is discussed which exhibits both quasi-static and dynamic motion properties through asynchronous activation control. Through the use of phase-plane analysis, an optimal switching control law is described. Prototypes of single and dual buckling actuator mechanisms are shown, and experimental performance is presented.