Reconfigurable soft pneumatic actuators with metamaterial reinforcements: Tunable stiffness and deformation modes

Abstract

Soft pneumatic actuators are ideal for interacting with fragile objects, food, and humans due to their inherent compliance. Modulating stiffness and deformation is crucial for adapting to diverse applications. However, achieving non-uniform stiffness and deformation remains challenging, as most methods provide only uniform stiffness or limited deformation modes. This study proposes embedding metamaterial beams within the inextensible layer of soft pneumatic actuators to enable both uniform and variable stiffness and deformation control. Beams with hexagonal, reentrant, and rectangular honeycomb topologies were investigated across three relative densities. Experiments revealed up to 26.6% stiffness and 43% curvature shifts, by changing the employed reinforcements, validated with finite element models. A kinematic model incorporating a multi-curvature approach effectively approximated the bending behavior of actuators with segmented meta-reinforcements. The actuators demonstrated the ability to grasp objects weighing over 11.9 times their weight with a two-actuator gripper and to apply forces of up to 2.25 N individually. Additionally, varied reinforcements enabled non-bending deformations, further expanding the actuators' functionality. The actuators were evaluated in fruit-handling scenarios, demonstrating their ability to manipulate objects of varying sizes and weights. This work underscores the potential of metamaterials in soft robotics, enabling tailored mechanical properties and expanded functionality for complex applications.