Pipe inspection and maintenance are necessary to prevent economic and casualty losses due to leakage of fluids from damaged pipes. In-pipe soft robots made of highly deformable materials have been proposed to meet the needs, yet most of those comprise multiple segments and require multiple actuators controlled independently, resulting in less compact structures and more demanding control schemes. In this study, we harness the highly nonlinear buckling of elastic ribbons and bioinspired artificial muscles to significantly enhance the crawling capability of a single-actuator soft robot. Our prototype robot consists of a McKibben pneumatic actuator surrounded by three longitudinally arranged elastic ribbons. These tailored ribbons are three-dimensional (3D) printed and can be buckled into highly deformed 3D shapes upon inflation of the actuator. First, we show that the robot exhibits strong anisotropic friction when fully buckled. Then, we demonstrate that by simple open-loop on/off control, our robot achieves robust crawling in horizontal, vertical, bent pipes and even wet pipes partially or filled with water. It can also adapt to pipes with some variations in diameter. Using only one actuator lowers the complexity of robot structure and pneumatic system, offering high potential for new applications at different scales.
Keywords: McKibben artificial muscles; buckle; elastic ribbons; pipe crawling; soft actuator; soft robots.