A multi-cell piezoelectric device for tunable resonance actuation and energy harvesting

Variable stiffness actuation and energy harvesting have been important yet separate challenges in robotics. Both functions are needed, however, for mobile robots on extended missions when actuators and generators must be used together. In this paper, we present a unique piezoelectric cellular system that combines motion generation and energy harvesting capabilities into a single, scalable device. Each of the discrete cellular units provides linear, contractile motion at 10% strain using the converse piezoelectric effect. These units may also be back-driven from environmental loading and thereby generate energy using the direct piezoelectric effect. Furthermore, each cell has the capability to toggle between a low stiffness ON state and a high stiffness OFF state, which allows an assembly of individual cells to tune both their static stiffness and structural resonant frequencies online. We demonstrate the effectiveness of our device for tuning both locomotion speed and the harvested power of an underwater flapping fin system.