Miniaturized and Motorized: Fast, Architected Soft Robotic Actuators via Molded Thermoplastic Elastomers

Handed shearing auxetics, or HSAs, are a class of architected materials increasingly used as electrically-driven soft actuators. HSAs are directly driven by servo motors, resulting in architected soft robotic actuators that enable capabilities spanning manipulation and locomotion. However, the material properties and form factors available to HSAs are limited. Thus, fabricating miniaturized HSAs from robust, durable materials is difficult. Moreover, scaling HSAs to smaller form factors is also complicated by the need to miniaturize the motors driving them. Here, we present a method for fabricating miniaturized, robust HSA actuators via molding from thermoplastic polyurethane (TPU) powders. Our method produces soft HSA actuators with low torque requirements that can be actuated with DC micromotors. We describe the overall fabrication process for our actuators, characterize the free displacement and blocked force generated by single HSAs, and demonstrate the performance of a multi-DoF platform comprising a 2x2 assembly of HSAs. We find that our new HSAs produce actuation strains and forces of 40% and 1.2N, respectively, with servo motors; with DC micromotors, they can actuate to at least 20Hz. Altogether, the use of micromotors and thermoplastic elastomers enables us to achieve extremely robust and fast actuation with HSAs. We expect our new approach to HSA design, fabrication, and actuation will open up new opportunities in the use of architected soft robotic actuators that operate with the actuation bandwidths found in both rigid robots and living organisms.