A Variable Stiffness PZT Actuator Having Tunable Resonant Frequencies

A new approach to a variable stiffness actuator with tunable resonant frequencies is presented in this paper. Variable stiffness actuators have become increasingly important to meet safety requirements and achieve adaptive manipulation or locomotion. For cyclic motion, exploiting dynamic resonance can lead to high power transmission, high energy efficiency, and large motion amplitude. Resonance and variable stiffness characteristics have yet to be incorporated into a single actuator design. In this paper, a cellular artificial muscle actuator that achieves both variable stiffness and variable resonance capabilities is presented. The design is based on piezoelectric stack actuators. First, the principle of variable stiffness and variable resonant frequencies is described. The static and dynamic performance are then quantified with theoretical models. Theoretical analysis reveals that the proposed actuator can be tuned over a broad range of resonant frequencies by selectively turning specific units on or off. Initial prototypes are tested experimentally and exhibit 15% static strain, over 300% static stiffness tunability, and over 100% dynamic resonance tunability.