Jellyfish robot

The biggest draws at Festo’s Hannover Fair exhibits have been biologically inspired robotic creatures that show off cutting-edge automation technologies. Turning once again to nature for inspiration, the company’s engineers this year came up with robotic jellyfish that either swim or fly.

They may look whimsical, but the waterborne AquaJelly and airborne AirJelly make use of mechatronic design practices, control strategies and actuation methods that could have serious engineering implications. According to Markus Fischer, Festo’s head of corporate design, these robots have a degree of autonomy and adaptive behavior that “will be very useful in the factory of the future.”

Both the AquaJelly and AirJelly share a basic construction that consists of a sphere-shaped body with eight electrically driven tentacles for propulsion. Both run off rechargeable lithium-ion batteries and are powered by 3V coreless motors. Given the differing mediums in which they travel, the two robots do have different bodies — a laser-sintered pressure vessel for the AquaJelly and a helium balloon measuring 1.35m across for the AirJelly.



Their tentacle construction takes its cues from the functional anatomy of some fish fins. These bio-inspired tentacles consist of two flexible external surfaces connected by a series of internal ribs. When one of the surfaces is put under tension, the entire tentacle bends in the direction of the applied force — a phenomenon that Festo calls the “fin ray effect.”

Festo uses an electric drive, geared power transmission and linkages to actuate the tentacles. Alternating tension between the two external surfaces creates a wave-like motion that propels the robots through the water or air. Fischer describes the resulting movement as “peristaltic” since the waving tentacles seem to move by something like muscle contractions.

Whether they swim or fly, these two types of jellyfish steer themselves by carefully controlled weight shifts. As Fischer explains, their bodies contain a servo-driven swash plate connected to a four-armed pendulum that changes their center of gravity. “The pendulum shifts their weight, and they move in a new direction,” he says.

And for the AquaJelly in particular, that new direction is determined autonomously. This underwater robot guides itself with the help of a sensor array, communications systems and control software based on robotic swarm-intelligence. Fischer notes, for example, multiple AquaJelly robots can avoid each other in the water, using light sensors to pick up the presence of their tank mates. They also have pressure sensors that allow them to gauge their depth within a few mm.

AquaJelly robots also manage their own battery-charging behavior. They communicate with an in-tank charging dock wirelessly via ZigBee, for example, to make sure the dock isn’t occupied when they need to charge.

According to Fischer, giving these robots such a high degree of autonomy required a mechatronic approach in which the mechanical design, sensor engineering and control software were all developed concurrently. “Even simple autonomy is not so simple,” he says.

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