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Swarming motor-driven `jellyfish` could lead to automation innovations

28 May, 2008

In recent years, Festo has established a tradition for developing attention-grabbing mechanical creatures that swim around a large tank on its stand at the Hannover Fair. In the past, these have included lifelike sharks and rays that move around under remote control in an uncannily fishlike manner.

This year, the company created an even more impressive display, using electrically powered "jellyfish" which could not only swim autonomously, but could also communicate with each other to act as a "swarm" and to co-ordinate their visits to charging stations at the top of the tank.

Festo developed the bionic jellyfish, called AquaJellies, in conjunction with a German display technology specialist, Effekt-Technik. Festo believes that by extending the principles of swarming behaviour to automation, autonomous or semi-autonomous intelligent systems could work together to solve large-scale problems through strategic co-operation.

AquaJelly with hand

Each AquaJelly (shown above) consists of a translucent hemisphere, a central watertight body, and eight tentacles used for propulsion. The hemisphere houses an annular control board with integrated pressure, light and radio sensors. The orientation of the propulsion system is monitored constantly by one of three on-board microprocessors. The other two control communications by short-range radio signals at the surface, and by light signals from infrared LEDs when submerged.

On its outside, each AquaJelly has two concentric silver rings coated with a conductive metal paint. These are connected to a charging controller that supplies the jellyfish with energy. When a jelly approaches a charging station located above the water surface, it is drawn towards it and supplied with electricity. The charging station consists of a Festo vacuum generator with integrated contact points for transferring the charging energy. A full recharge takes about three hours. The AquaJellies communicate with the charging station to ensure that each is supplied with sufficient energy.

The core of each AquaJelly is a watertight, laser-sintered body housing a 3V coreless electric motor, two 4.2V, 4,000mAh lithium-ion polymer batteries, the charging controllers, and two actuators that help the creatures to move in three dimensions. The motor powers drive plates attached to the top and the underside of the watertight body via two cranks at a 60-degree angle to each other. Eight rhombic joints, connected to the drive plates, set the tentacles in a wavelike motion.

The tentacles are based on the FinRay Effect – a construction derived from the functional anatomy of a fish`s fin. Two alternating tension and pressure flanks are connected by ribs. lf a flank is put under tension, the geometrical structure bends automatically in the direction of the applied force. The delayed activation of the eight tentacles via the rhombic joints produces a regular wavelike motion, which generates a peristaltic forward motion similar to that of a real jellyfish. Festo is exploring the possibility of using this principle for automation tasks such as fast, efficient divert systems, and novel gripper fingers.

The AquaJelly’s movement in three dimensions is achieved by weight displacement. The two actuators in the central body control a swash plate which, in turn, operates a four-armed pendulum that can be moved in four directions. When the pendulum moves in a particular direction, it displaces the jellyfish`s centre of mass, making it move in that direction. This allows the AquaJellies to move in any direction.

A pressure sensor determines the AquaJelly`s depth in the tank to within a few millimetres, allowing the machine to position itself within a specific pressure zone. The pressure sensor is also used to help the fish swim to the surface for recharging.

At the surface, the AquaJellies use the low-energy ZigBee short-range radio system for communications, enabling them to exchange data with the charging station and to signal to each other that the station is occupied.

Underwater, the main communication medium is light. Each AquaJelly is fitted with 11 infrared LEDs (light-emitting diodes) located on a ring inside its dome. These LEDs have a 20-degree aperture angle and use pulsed infrared signals. They allow the jellies to communicate within an almost spherical surrounding space, to a distance of about 80cm.

When a jelllyfish receives a positional signal from another approaching fish, it can take evasive action. As well as the sensors that monitor its surroundings, each AquaJelly is also fitted with an internal sensor system that monitors its energy condition, and a solenoid switch that registers the orientation of the propulsion system.

AquaJelly swarm

Each fish decides autonomously what action to take, based on the prevailing conditions, which can depend on the charge condition, the propulsion system`s orientation, or the proximity of other AquaJellies. A swarm of AquaJellies (shown above) behaves without predetermined control; it results solely from simple rules of behaviour and represents a collective behaviour pattern that maximises the number of "living" jellyfish.

To maximise the number of living jellyfish in a swarm, they must strive for an ideal, evenly distributed utilisation of the charging stations. To secure the existence of the swarm inside the tank, the jellyfish need to make maximum use of the space available, avoiding collisions with others, and using the charging stations in a well co-ordinated manner.

A video of the AquaJellies in action can be seen on Festo`s Web site.

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