German Researchers Build a Grapple Mini-Sub to Remove Trash

Ocean litter tech projects generally focus on visible, floating trash that drifts on the surface and washes up on shore. But a team with Technical University Munich (TUM) has taken a different tack and devised an unmanned grapple robot to pick up trash from the bottom, where pollution may be out of sight but not out of the ecosystem.

In harbors and along busy waterfronts, the seabed typically contains an abundance of sunken trash. In one study in the port of Dubrovnik, researchers counted up 1,000 pieces of manmade debris in an area of just over 1,000 square feet. Cleanup currently depends on professional divers, if it is attempted at all, and there are fiscal and practical limits to how much by-hand waste disposal on the bottom can accomplish.

In a bid to address this problem, the TUM team devised a robotic surface vessel that supports a miniature ROV, which can maneuver underwater and grab objects with a four-pronged grapple mounted beneath it. When it grabs something with this grip, the surface vessel hoists the submersible up, and the object is deposited in a second, accompanying autonomous skiff.

The idea is to make the process autonomous and self-driving so that the team of robots can clean up a harbor without much human input. That means training a neural network (AI model), which requires lots of example images of the target - in this case, underwater trash, which is not often photographed intentionally. To build a database, the researchers hand-tagged about 7,000 images and used it to train up an AI model to run the operation. It is capable of creating a 3D model of trash on the bottom and determining where best to grab hold of it, according to Dr. Stefan Sosnowski, Chair of Information Technology Control at TUM.

The grapple itself is capable of lifting more than 500 pounds in one hoist, and is equipped with sensors to determine the limits of the force it applies. This helps it pick up more fragile debris (like glass) without crushing it. The whole assembly is interconnected with a power and data cable in order to give the ROV grapple a meaningful amount of runtime; the cable also doubles as the hoisting line for ROV deployment and recovery. Other applications for this system can be readily envisioned, from shipwreck debris removal to explosive ordnance disposal.