Marine robotics' future lies in undemanding arms
Tethered ROVs have been fitted with grabs for some while, but there's a rising demand for kitting out remotely controlled and autonomous underwater vessels with manipulators.
For example, the US Navy is looking into an alternative to putting ordnance disposal divers in danger, as a remote system could locate and deal with improvised explosive devices. However, many other marine sectors are interested in carrying out regular inspections without needing a surface ship hanging around to provide a tether.
But here you hit a snag. These AUVs usually don’t have a big onboard power source and tend to be restricted in size; more, access can be hampered around harbours or marine structures. Therefore the necessary manipulation kit also has to be scaled to suit.
“You want something that’s only about the size of a human diver – which means you can get into a more cluttered environment,” RE2 Robotics CEO, Jorgen Pedersen told MJ. “And as you don’t have a tether to bring power from a surface ship, you need a system that will work within what’s available.”
These twin requirements have resulted in an important switch from the more traditional, hydraulically operated actuators to an electromechanical system. “Hydraulic solutions are effective on larger devices, but you lose efficiency on smaller versions,” he said. And on an untethered AUV, efficiency is everything.
Therefore RE2 has developed a pair of electromechanical arms which sit either side of something akin to a chest, especially for AUVs roughly between 20kg and 40kg. These AUVs are capable but still allow launching from a RIB or other small craft without much ancillary equipment.
The Dexterous Maritime Manipulation System (or DM2S) is also able to operate from a very constrained power supply. “Our unit will run off a small 12V battery, typically drawing less than 25W on each arm, so these are really very power efficient devices,” said Pedersen.
Despite this, the DM2S has a very high strength-to-weight ratio; he added that while only coming in at around 5kg “each arm will be able to lift around 6kg at full extension”.
The shell has been designed to be neutrally buoyant, this is important to reduce the effect of the manipulators on vehicle dynamics. While it can take on fairly shallow waters as it is, “it can also be filled with oil for greater depths - it can be used either way” he explained. This is a useful attribute: while the first naval contract will see the system tailored for depths of up to 150m, deep-sea roles could mean it’s deployed a kilometre below sea level.
It could be further adapted for various tasks: for example, the DM2S currently has five degrees of freedom, (DOF) but given the modular design, it’s possible to add or subtract joints. The hands, presently akin to lobster claws can grasp objects, turn valves, pinch wires and so on, but again, there’s the potential for further finesse.
However, the move into an electromechanical design has a knock-on effect “as you have to think again about extremely corrosive salt water, sealing, pressures and so on” he said. All this entails extreme attention to detail. As Pedersen explained: “For example, beyond a certain depth, you can’t have anything with air inside or material that could easily get crushed... actually we have had to think about every single electronic component.”
More, although this first version will have a one-way interface, following generations may well benefit from haptic feedback. This will allow the sense of touching an object to be transmitted back up to the user.
While the initial interest (including a US$2.5m development and commercialisation contract) comes from the US Office of Naval Research “there is an awful lot more this equipment can do,” concluded Pedersen: "It's exciting technology for multiple markets."
By Stevie Knight
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