A robotic worm for tight spaces

Researchers of the Adolphe Merkle Institute's Polymer Chemistry and Materials group and their collaborators at Case Western Reserve University (Cleveland, USA) have developed a soft, worm-like robot that can wriggle itself through spaces that are considerably smaller than its cross-section. The electrically activated robot can also move across sticky or slippery surfaces in any direction.

Soft earthworm-like robots that exhibit mechanical compliance can, in principle, navigate through uneven terrains and constricted spaces that are inaccessible to other robots. Such devices are potentially useful for applications that include search and rescue operations, underground exploration, pipe inspection, and even biomedical procedures. However, unlike the living species that they mimic, most of the previously reported worm-like robots contain rigid components that limit their mechanical compliance, such as motors and other actuators, which limit how they can adapt or deform to various environments or obstacles. “To address this limitation, our major goal was to demonstrate a fully soft robot that capable of deformations that would not be possible with traditional rigid-bodied robots,” says Prof. Christoph Weder, AMI chair of Polymer Chemistry and Materials.

Weder and his US partners developed and investigated a highly flexible robot with a fully modular body almost entirely based on soft polymers. The device contains segments that are assembled from bilayer actuators, which reversibly change their shape when heated and cooled, respectively. “The trick for achieving a high bending deflection, and to generate large blocking forces was to use a new class of high-thermal-expansion polymers that we combined with a commercial low-thermal-expansion polyimide film,” explains Dr. Livius Muff, who worked on the project as a PhD student. The possibility to individually activate the bilayer actuators through electrically powered heating elements allows for highly precise control of the robot’s movements. Mimicking the locomotion principle exploited by earthworms, the robot is propelled by the sequential contraction and expansion of the various segments. This operating principle also allows the robot to access spaces that are much smaller than its cross-section in the resting state might suggest.

Limitations of the first embodiment of the new robot design are that its movements are quite slow, and that its motion requires a considerable amount of energy. The researchers believe, however, that the robot’s modular architecture will allow for improved performance by using faster and more energy-efficient bending actuators, without changing the overall design. Moreover, the current version is externally powered and controlled, but it could be become autonomous with the incorporation of soft batteries and independent control systems. “The robot can overcome narrow constrictions, and explore hollow spaces while suspended in mid-air,” points out Muff. “These skills make future iterations of the worm potential candidates for underground exploration of cave systems, subterranean infrastructure inspection, or surveillance operations. “Furthermore, the worm robot’s hollow tubular structure could be used to deliver cargo such as medication or emergency supplies to trapped individuals in collapsed buildings or rubble.”

The results of this research project were published in the leading scientific journal Advanced Materials. This work was carried out with joint funding from the US and Swiss National Science Foundations as part of the Partnerships for International Research and Education (PIRE) program Bio-inspired Materials and Systems.

Reference: Muff, L. F.; Mills, A. S.; Riddle, S.; Buclin, V.; Roulin, A.; Chiel, H. J.; Quinn, R. D.; Weder, C.; Daltorio, K. A. Modular Design of a Polymer-Bilayer-Based Mechanically Compliant Worm-like Robot. Advanced Materials 2023, 34, 2210409. https://doi.org/10.1002/adma.202210409.