Collision-free swimming with ultrasound

Underwater robot BionicFinWave manoeuvres through a pipe system

Dolphins and pilot whales can even find their way in murky and dark waters thanks to their natural echo sounder. Submarines also use ultrasound technology for locating purposes. Ultrasound sensors can calculate distances, even to transparent materials and underwater. The BionicFinWave uses these characteristics to its benefit. Thanks to ultrasound sensors, the bionic underwater robot swims collision-free through a pipe system made of acrylic glass.

Ultrasound sensors transmit sound waves in a high frequency range towards their target object, which reflect the sound waves as an echo. The sensors receive these signals and are able to calculate the distance using the time interval until the echo is returned. Distances can be measured and one’s own position can be determined using this measuring principle.

The underwater robot BionicFinWave with its undulating fin motion uses the technology to swim collision-free through a transparent pipe system. Five ultrasound sensors on its head and the inertial sensor technology constantly measure the distances to the walls and its actual direction through the water. A processor analyses this data and uses it to work out when there is a curve in the pipe system. It controls the fins in such a way that the BionicFinWave swims as centrally as possible and does not hit the walls.

Undulating fin motion

The BionicFinWave uses its two side fins to move along. They generate a continuous wave, the so-called undulating fin movement. The wild marine flatworm, the cuttlefish and the Nile perch move through the water in the same way. With the wave-shaped movement of the fins, the fish push the water backwards, thus creating a forward thrust.

Flexible silicone fins

The fins on the BionicFinWave are completely made from silicone and do not require any struts or other support elements. This makes them extremely flexible and enables them to implement the fluid wave movements of their biological role models. They are attached on the left and right to nine small lever arms that have a deflection angle of 45°. The lever arms in turn are driven by two servo motors located in the body of the underwater robot. Two attached crankshafts transfer the force to the levers so that the two fins can be moved individually. This enables them to generate different wave patterns.

To swim in a curve, for example, the outer fin moves faster than the inner fin, similar to the chains on a digger. A third servo motor at the head of the BionicFinWave controls the bending of the body, enabling it to swim up and down. The crankshafts and joints are made from a single piece using the 3D printing process, and are thus flexible and supple.