Modular Volumetric Actuators Using Motorized Auxetics

Volume change has become a critical actuation method in robotics. However, the need for fluid flow or thermal processes to generate volume changes limits the durability, speed, and efficiency of these actuators. In this paper, we develop a new electromechanical actuator that volumetrically expands. By combining auxetic materials with a servo, we produce a simple isotropically expanding actuator that can be modularly composed. We discuss the symmetry considerations in selecting an appropriate auxetic framework for our actuator, eventually choosing a double-layered polyhedral auxetic design. Characterization shows that a single actuator can expand in radius to 119% of the original size and generate 90N of force, while maintaining a small package and a speedy expansion / contraction cycle. Finally, we demonstrate the modularity of our actuators by linking three actuators to create a vertical tube-crawling robot. The small package and fast cycle time of our system highlight how viable these electromechanical volumetric actuators can be as an important actuator modality.