The Magazine for Underwater Professionals
Soft robotic grippers improve ability to collect delicate u/w specimens
During a 2014 talk on his exploration of deep-sea coral reefs, marine biologist David Gruber showed a video of clunky robotic hands collecting fragile specimens of coral and sponges from the ocean floor. Harvard University, USA, engineer and roboticist Robert J. Wood was in the audience – the two scientists were being recognised as emerging explorers by the National Geographic Society – and a lightbulb went off.
“They were using rigid Jaws of Life-type grippers designed for the oil and gas industry that were totally overpowered and were destroying things,” recalls Wood, who is a professor at the Harvard School of Engineering and Applied Sciences (SEAS) and faculty member at the university’s Wyss Institute for Biologically Inspired Engineering. “It immediately clicked that there was a soft robotics solution that may be viable.”
In the months that followed, the pair collaborated to design, fabricate and test soft robotic grippers for deep-sea collection of fragile biological specimens. Their 2015 expedition to the Gulf of Eilat in the northern Red Sea, a unique marine ecosystem that houses one of the world’s largest and most diverse coral reefs, marked the first use of soft robotics for the non-destructive sampling of fauna from the ocean floor.
Gruber, an associate professor at Baruch College, City University of New York, USA, explores deep-ocean ecosystems with a particular focus on organisms that display bioluminescent and biofluorescent traits. When he wants to visit a coral reef below the maximum depth that human divers can tolerate, Gruber relies on a remotely operated vehicle.
But there was a problem: the standard-issue robotic “hands” of underwater ROVs are ill-suited to collecting delicate coral, sponge and other samples because the equipment was designed for undersea construction and to install and repair submerged pipelines. In contrast, manipulating and grasping fragile organisms from the seafloor requires something that can mimic the dexterity and soft touch of a human diver’s hand. Wood recognised that soft robotics were tailor-made for the task.
As described in a paper published in the journal Soft Robotics, the team successfully developed two types of grippers and in the process demonstrated a new fabrication technique that allows for the rapid creation of soft actuators. The new technology could enhance researchers’ ability to collect samples from largely unexplored habitats thousands of feet beneath the ocean surface, areas that scientists believe are biodiversity hotspots teeming with un-known life. The soft grippers could also be useful in underwater archeology.
Wood and Kevin Galloway, a mechanical engineer at the Wyss Institute, set about designing two types of hands to replace the ROV’s factory-furnished metal gripper, each capable of gently recovering objects of different sizes and shapes. One, inspired by the coiling action of a boa constrictor, can access tight spaces and clutch small and irregular shaped objects. The other, a bellows-style model, features opposing pairs of bending actuators.
To facilitate rapid in-field modification and repair, the team emphasised simple construction, inexpensive materials and a modular design. This meant they could try multiple configurations and make them in quantity. Harvard’s Office of Technology Development has filed a patent application on the team’s method for the manufacture of bellows-type soft actuators. The method is scalable, opening up a wide range of commercial, biomedical and industrial applications for this type of actuator.
The biggest design challenge, Wood says, was a lack of precise specifications. They weren’t designing a robotic arm to repetitively attach doors to car bodies in a motorcar assembly plant. The team had no way of knowing the size, shape or stiffness of the objects they would be sampling on the ocean floor. To approximate likely specimens, they visited the produce aisle and brought back an assortment of vegetables – celery, radishes, carrots, bok choy – and tied them to a metal grate that was then dropped into a test tank at the University of Rhode Island (URI), USA. After exhaustive tank tests, the grippers were put through their paces at depths greater than 800 metres off the Rhode Island coast.
Field testing took the team to Israel’s Gulf of Eilat in May 2015. There they conducted more than a dozen dives ranging from 100 to 170 metres. Most dives involved “catch and release” manoeuvres to test system performance. But they did manipulate the grippers to retrieve samples of delicate (and relatively abundant) red soft coral, as well as difficult-to-snag coral whips, bringing them to the surface undamaged in the ROV’s cargo tray.
But simply collecting hard-to-harvest samples isn’t the end-game. Researchers like Gruber hope to apply these techniques to conduct in situ measurement of organisms, and eventually, gene expression and transcriptomic analysis.