Design and Closed‐Loop Motion Planning of an Untethered Swimming Soft Robot Using 2D Discrete Elastic Rods Simulations

Abstract

Despite tremendous progress in the development of untethered soft robots in recent years, existing systems lack the mobility, model‐based control, and motion planning capabilities of their piecewise rigid counterparts. As in conventional robotic systems, the development of versatile locomotion of soft robots is aided by the integration of hardware design and control with modeling tools that account for their unique mechanics and environmental interactions. Here, a framework for physics‐based modeling, motion planning, and control of a fully untethered swimming soft robot is introduced. This framework enables offline co‐design in the simulation of robot parameters and gaits to produce effective open‐loop behaviors and enables closed‐loop planning over motion primitives for feedback control of a frog‐inspired soft robot testbed. This pipeline uses a discrete elastic rods (DERs) physics engine that discretizes the soft robot as many stretchable and bendable rods. On hardware, an untethered aquatic soft robot that performs frog‐like rowing behaviors is engineered. Hardware validation verifies that the simulation has sufficient accuracy to find the best candidates for sets of parameters offline. The simulator is then used to generate a trajectory library of the robot's motion in simulation that is used in real‐time closed‐loop path following experiments on hardware.

Recent Advances on Underwater Soft Robots

“…Compared with the open‐loop control system, one of the advantages of the closed‐loop control system is that it is more robust and more suitable for the online control requirements in the actual environment. The representative one is the bionic frog‐shaped robot designed by Huang [ 273 ] through DERs. Under the premise of ensuring the overall smooth operation through the streamlined structure design, the frog robot completes the closed loop of the overall control system through attitude perception.…”

Recent progress on underwater soft robots: adhesion, grabbing, actuating, and sensing

“…Moreover, on this basis, Huang et al (2022) studied a completely cordless soft frog swimming robot framework based on physical modeling, motion planning, and control. They used the discrete elastic rods (DERs) physics engine to disperse the soft robot into many stretchable and flexible rods.…”

“…The square-shaped robot is used in the simulation pipeline so that 2D simulations can be performed. The streamlined robot is intended to show the potential performance of such swimming robots with a design that minimizes drag [reprinted with permission from Huang et al (2022) ].…”

Gecko adhesion based sea star crawler robot

“…Marine creatures have evolved multiple gait and motion techniques along with flexible structures, that allow them to move in different and efficient ways (Gemmell et al, 2015;Mo et al, 2020;Wereley, 2021). These techniques have been widely studied and have served as inspiration for different kinds of underwater mobile soft robots like swimmers (Patterson et al, 2020;Ulloa et al, 2020;Shen et al, 2020;Huang et al (2022;2021), walkers (Corucci et al, 2015;Wu et al, 2021), crawlers (Tan et al, 2021) or a combination of these gaits like swimming and crawling (Arienti et al, 2013;Giorgio-Serchi et al, 2017). Inspired by the sea star locomotion (Figure 1A) which includes crawling and grounded bouncing (Heydari et al, 2020), many attempts have been made to create a sea star crawler (Youssef et al, 2022).…”