21 March 2009

Robo-octopus: under construction

The world's first entirely soft robot is being attempted.
By replicating the muscular structure of an octopus, scientists hope to make a robot with no rigid structure to better explore the seabed. The trouble with today's remote-controlled subs is that their large hulls and clunky robot arms cannot reach into nooks and crannies.

Robot octopus will go where no sub has gone before
Paul Marks, New Scientist 21 Mar 09;
INVEST €10 million in a robotic octopus and you will be able to search the seabed with the same dexterity as the real eight-legged cephalopod. At least that's the plan, say those who are attempting to build a robot with arms that work in the same way that octopuses tentacles do. Having no solid skeleton, it will be the world's first entirely soft robot.

The trouble with today's remote-controlled subs, says Cecilia Laschi of the Italian Institute of Technology in Genoa, is that their large hulls and clunky robot arms cannot reach into the nooks and crannies of coral reefs or the rock formations on ocean floors. That means they are unable to photograph objects in these places or pick up samples for analysis. And that's a major drawback for oceanographers hunting for signs of climate change in the oceans and on coral reefs.

Because an octopus's tentacles can bend in all directions and quickly thin and elongate to almost twice their length, they can reach, grasp and manipulate objects in tiny spaces with extraordinary dexterity.

"So we are replicating the muscular structure of an octopus by making a robot with no rigid structure - and that is completely new to robotics," she says.

The team will have its work cut out. The octopus has evolved a beguilingly manoeuvrable muscle architecture. Each tentacle has four independent muscles running along its length. These longitudinal muscles are separated by transverse muscles which span the width of the limb with an axial controlling nerve that passes through its centre.

This arrangement keeps the tentacle's volume constant, so when it extends a limb by elongating the longitudinal muscles and contracting the transverse ones, it also becomes narrower.

The nearest engineers have come to mimicking this before is with a snake-like tentacle whose segments inflate with compressed air. But while this machine could move well, it did not become narrower when stretched - nor could it work underwater because of the buoyancy of air.

So Laschi and colleagues in the UK, Switzerland, Turkey, Greece and Israel are testing artificial muscle technologies that will more accurately mimic tentacles (Biomimetics and Bioinspiration, DOI: 10.1088/1748-3182/4/1/015006). The team plans to mimic the longitudinal muscles with soft silicone rubber interspersed with a type of electroactive polymer (EAP) called a dielectric elastomer. Apply an electric field to this material and it squeezes the silicone, making it shorter (see diagram).

While Laschi has high hopes for the robot, others are more sceptical. Claire Little, a cephalopod expert at Weymouth Sealife Centre in Dorset, UK, thinks the researchers have underestimated the magnitude of the task. "Don't they realise how flexible an octopus is? They can squeeze through the smallest of holes. This plan sounds a bit crazy," she says.

But Laschi is undeterred. The team has yet to build a tentacle but have built a mechanical simulator that mimics the forces that the EAPs produce. This has proved that the peculiar motions of an octopus tentacle can be copied, she says.

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