A Soft Ring-Shaped Actuator for Radial Contracting Deformation: Design and Modeling

Bioinspired movements such as elongation/shortening and bending are extensively studied in the field of soft robotics. However, radial contracting deformation has been overlooked, another typical deformation in nature, such as the constrictive deformation in the human esophagus and bladder. We present a novel soft ring-shaped actuator that generates radial contraction and examine its quasi-static performance under pressurization. This actuator consists of a soft ring-shaped body and a rigid casing. A single circular air chamber embedded concentrically inside the actuator is created through the lost-wax method. A theoretical model of the quasi-static state of the actuator's contracting deformation was formulated in light of the minimum total potential energy principle. Meanwhile, a finite-element method (FEM) model was constructed to stimulate the radial contraction of the actuator. In addition, experiments were conducted to identify the maximum input pressure and measure the deformations at the specific input pressure. When the actuators were pressurized under 20.0 kPa, axisymmetric contractions were achieved. The theoretical model and FEM models produced the predictions in good agreement with experimental results, with slight mean relative differences regarding peak points, 3.4% and 5.4%, respectively. In addition, pilot tests suggest that the ring-shaped actuator can achieve the key tasks of robotic manipulators, such as gripping and holding.