A 3D-Printed Worm-Like Robot for Corrugated Pipes Using Anisotropic Fins

In this paper we propose the design of a novel 3D-printed soft robot capable of traversing corrugated pipes, which are widely employed in subsurface agricultural drainage systems. The robot adopts an inchworm-like peristaltic motion for its bellow-structured body, and it utilizes a self-locking mechanism, realized by exploiting the anisotropic interaction of its reconfigurable fins with the pipe ridges, to achieve the desired locomotion. A feature of the design is that the robot robustly moves by an integral multiple of the ridge-to-ridge distance per actuation cycle, allowing the robot to self-localize within the pipe. Experiments are conducted to characterize the stress-strain relationship of the 3D-printed compliant material (thermoplastic polyurethane (TPU)). The results are used in finite element analysis (FEA)-based design of the bellows structure and the fins for achieving the desired compliance and stiffness anisotropy, respectively. Experiments on a robot prototype inside a four-inch drainage pipe have confirmed the utility of the FEA-based design in achieving sound anisotropic fin stiffness, and the robot's capability to travel a fixed number of ridge-to-ridge distances per actuation cycle, determined by the contraction/expansion stroke. The robot also demonstrates robust locomotion in curved or vertical pipes.