Session: 04-13 SS: Active Hybrid Composites

Paper Number: 171489

171489 - Soft Robotic Octopus Tentacles Actuated by Scalable Coiled Artificial Muscles 

Soft robotic arms inspired by the octopus tentacles are of technological interest owing to their gentle interactions with the environment and their extremely rich kinematics. Despite their low modulus, they can be useful for applications like underwater exploration where gravity is almost canceled by density matching. The slim geometry of the octopus arm robot provides great flexibility, allowing biomimetic motions such as grasping by bending the tentacles. The softness and deformability of the octopus arm could enable manipulation in tortuous paths, as it can pass through tight obstacles.

Here, we explore two new design motifs which leverage two key features developed in our group: a logarithmic spiral soft tentacle spine and hierarchical supercoiled polymer muscles for actuation arranged in antagonistic pairs. Our design focuses on minimizing the internal resistance from the antagonist muscles which enable the two-way reversible actuation strokes. We realize this by using twisted and coiled polymer actuators (TCPA) which have a hierarchical supercoiled architecture. These muscles have a J-shaped nonlinear force-displacement curve when stretched. The J-shaped behavior results from the supercoiled morphology where three fibers are plied around an embedded electrical wire to enable joule heating. These supercoiled TCPAs are fabricated by an automatic TCPA manufacturing machine that can continuously produce TCPA from nylon fishing lines and electrical wires. The machine plies three nylon fishing lines together with an electric wire embedded in the center and twists them to have sufficient internal twist. Another thicker nylon fishing line is adopted to serve as a mandrel, which has plied nylon lines coiling on it to make the supercoiled TCPAs. We compared the tensile properties and actuation performance of machine-made muscles and human-made muscles to mark their differences. A theory was established to relate the machine manufacturing parameters with the twist density of muscles and to predict the geometric properties of muscles (such as coil angle and pitch).

The logarithmic spiral design motif enables the arm to achieve larger bending angles because the contraction of one muscle group is not significantly resisted by the stretching of the antagonist. The spiral design mimics the morphology of the biological octopus arm and reduces the bending rigidity. The soft structure of the octopus arm is made of low modulus silicone units with a central silicone rib, which are manufactured in 3D printed molds. We study the kinematics of the arm motion actuated by cables attached to constant force mechanisms. This sheds light on the role of friction between the cables and the arm on the kinematics. A key contribution of this work is to unravel the impact of various design parameters on the arm kinematics. Finally, the limitations of the current design and future improvements will be described.

Presenting Author: Liuyang Cheng University of Illinois at Urbana Champaign

Presenting Author Biography: Liuyang Cheng received the B.S. degrees in mechanical engineering from Zhejiang University in 2021. He is currently pursuing a Ph.D. degree in mechanical science and engineering at the University of Illinois Urbana-Champaign under the supervision of Prof. Sameh Tawfick. His research interests include biomimetic materials and robotics, focusing on artificial ligaments, artificial muscles, and the soft octopus arm.