Large-strain piezoelectric actuators using controlled structural buckling

Abstract

Buckling is a highly nonlinear and singular phenomenon in thin beams, and is usually an undesired characteristic that must be prevented from occurring in engineered systems. Buckling, however, can be a useful mechanism for gaining extremely large displacement amplification, since a infinitesimal displacement in the axial direction of the beam may lead to a large deflection in the middle of the beam. This thesis presents a novel large-strain piezoelectric actuator exploiting the buckling of a structure with imbedded piezoelectric stack actuators. The realization of this buckling actuator began by rethinking the paradigm of where PZT stacks are placed in traditional flexure-based displacement amplification mechanisms. Although the free displacement of a PZT stack is only 0.1% of the stack length, the buckling mechanism can produce a large bipolar displacement that is approximately 150 times larger than the original PZT displacement. Furthermore, the structural buckling produces a pronounced nonlinearity in output impedance; the effective stiffness viewed from the output port varies as a function of output displacement, which can be a useful property for those applications where actuator stiffness needs to vary. Buckling is controlled with phased activation of the input units and either 1) a strategically placed redirecting stiffness or 2) multiple buckling units working in parallel.