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Robotic Appendages Inspired by Tentacles

These soft manipulators, driven by air pressure, can grab and manipulate soft objects, finding wider applications in robotic grippers and wearable devices.

It is no doubt that traditional robots can be rigid and if we want them to be able to hold and manipulate soft objects, we need their manipulators to be as flexible in the way elephant trunks, octopus tentacles, and human fingers are. While elephant trunks and octopus tentacles exhibit complex 3D spatial trajectories, the design of soft manipulators with a mathematical model that can follow a particular 3D spatial trajectory remains a challenge.

Inspired by these biological organisms, scientists from Shanghai Jiao Tong University in China have designed a type of multiple-segment soft manipulator with these animal appendages in mind. These multi-segment soft manipulators have a tentacle-like shape and consist of a series of connected internal chambers that can be inflated pneumatically, blowing them up like a balloon. With one highly flexible side on one end of the tentacle and a stiffer side on the other end, increasing air pressure to the chambers will cause the structure to bend towards the stiffer side.

Author Dong Wang commented, “Our soft manipulator consists of multiple segments where each segment shows a different actuation mode — twisting, in-plane bending, or helical actuation — by choosing different chamber orientations.”

To inverse design the soft manipulators with trajectory matching, the team developed an analytical framework that takes into account geometric, materials, and loading parameters. With this, the spatial trajectory can be reconstructed by combining it with a 3D rod theory. By varying the parameters, they can inverse design a manipulator that would follow a trajectory.

“The key advance of this work is the development of a mathematical methodology that can automatically design soft manipulators matching complex 3D trajectories upon single pressurisation,” said Wang.

Furthermore, the team’s proposed methodology is also said to be more cost-efficient than conventional computational models. With their mathematical model, they confirmed that their technique produced manipulator designs with behaviours comparable to ones from computational models, and validated their results with simple experiments, showcasing the grasping of complex objects with their designed manipulators.

“To achieve truly versatile applications of the designed soft manipulators, more work is needed,” said author Guoying Gu.

The team envisions that future work would involve applying this approach to systems with multiple actuators and perhaps automating the inverse design process with machine learning as currently, the first stage of the process still requires a human operator to select the regions of the curve that are to be twisted, bent, or deformed.

Their work is expected to find broader applications in robotic grippers, implantable and wearable devices, and robots that have to navigate through rough terrains. [APBN]

Source: Jiang et al. (2021). Modeling and inverse design of bio-inspired multi-segment pneu-net soft manipulators for 3D trajectory motion. Applied Physics Reviews, 8(4), 041416