Bipolar Piezoelectric Buckling Actuators

A nonlinear piezoelectric amplification mechanism utilizing structural buckling is presented, and its static and dynamic properties are measured and analyzed. Buckling is a pronounced nonlinear effect that occurs at a structurally singular point. A small piezoelectric displacement on the order of $10 mu$m results in a large buckling displacement on the order of millimeter. Furthermore, the usable stroke is doubled if both sides of the singular point can be reached resulting in bipolar motion. Despite the large gain, buckling is an erratic, singular phenomenon; the side on which deflection will occur is unpredictable. In this paper, multiple design concepts are presented for regulating the buckling direction as well as for extending its usable stroke to bipolar motion. Nonlinear force--displacement relationships are modeled and measured. Nonlinear dynamic analysis using phase planes reveals that the buckling actuator can generate bipolar motion above a specific amplitude. Below this amplitude, it generates only monopolar oscillation. The proposed design concepts are implemented on monolithic flexure mechanisms, and prototype buckling actuators are tested to verify the concepts. Experiments show promising results: 20 N of peak-to-peak output force, and 6.2 mm of bipolar displacement generated by piezoelectric actuators with free displacement of $42 mu$m.