Bistable Actuation in Multi-DoF Soft Robotic Modules Driven by Rolled Dielectric Elastomer Actuators

In this work, we propose a novel design methodology to magnify the displacement of a soft robotic system driven by dielectric elastomer actuators (DEAs). The system consists of a 2-degrees of freedom (DoF) module, in which pairs of antagonist rolled DEAs are used to induce a bidirectional bending in a flexible backbone. In the context of 1-DoF DEAs, bistable biasing mechanisms have been extensively used to increase the actuation stroke. In case of multi-DoF DEA systems such as soft robots, however, displacement magnification via bistable concepts has not been investigated so far. Motivated by the need of designing high-performance DEA soft robots, in this paper we present a method to integrate bistable concepts within the considered 2-DoF module. The key element is represented by the flexible backbone of the structure, whose buckling instability can be properly triggered via the DEAs and exploited to achieve large bending angles. Based on a physical model of the device, we first derive an energy-based criterion which permits to to differentiate between monostable and bistable configurations. The developed design rule is then exploited to perform a parameter optimization of the structure geometry. Extensive simulation studies are finally conducted to demonstrate the effectiveness of the novel design.