Nonlinear, large-strain PZT actuators using controlled structural buckling

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 tiny displacement in the axial direction of the beam may lead to a large defection in the middle of the beam. This paper presents a novel large-strain piezoelectric actuator exploiting the buckling of a structure with imbedded PZT stacks. Although the free displacement of a PZT stack is only 0.1% of the stack length, the buckling mechanism, controlled with an effective algorithm and strategically placed redirecting stiffness, can produce a large bi-polar 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.