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Taking inspiration from the ocean

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Festo, in conjunction with the specialist display technology company, Effekt-Technik GmbH, has developed a bionic jellyfish – known as AquaJelly – to demonstrate swarming behaviour. Each AquaJelly is able to sense various aspects of its environment and to function completely autonomously, but is also endowed with communicative faculties that enable it to cooperate with other members of the group, and thereby behave as a system with a higher order of development.

Festo has created the AquaJelly as part of its ongoing research programme into advanced automation. The company believes by extending the principles of swarming behaviour to automation, many small autonomous or partly autonomous intelligent systems could work together to solve large-scale problems through strategic cooperation. The AquaJelly also provide a visually arresting demonstration of state-of-the-art animatronic technology.

AquaJelly is an artificial autonomous jellyfish with an electric drive unit and an intelligent adaptive mechanism that emulates swarming behaviour. It consists of a translucent hemisphere, a central watertight body and eight tentacles for propulsion. The AquaJelly's translucent hemispherical dome houses an annular control board with integrated, pressure, tight and radio sensors. The orientation of the propulsion system is constantly monitored by a processor. The control board also contains 8 white and 8 blue LEDs, which together with the sensors allow communication between several AquaJellies.

On the outside, AquaJelly has two concentric silver rings coated with conductive metal paint; connected to these is a charging control unit that supplies the jellyfish with energy. When AquaJelly approaches a charging station located above the water surface, it is drawn towards it and supplied with electricity. The charging station itself consists of a Festo vacuum generator with integrated contact points for transferral of the energy for charging. The AquaJelly communicate with the charging station to ensure each jellyfish is supplied with sufficient energy.

The central component of AquaJelly is a watertight laser-sintered body that houses a central electric motor, the two lithium-ion polymer accumulator batteries, the charging control unit and the actuators for the swash plate. A full recharging procedure takes around three hours. Via two cranks, the electric motor powers drive plates attached to the top and the underside of the watertight body; the cranks are configured at a 60-degree angle. Connected to the drive plates are eight rhombic joints which set the tentacles in wavelike motion. The tentacles are designed as structures based on the FinRay Effect® – a construction derived from the functional anatomy of a fish's fin. The actual structure consists of two alternating tension and pressure flanks connected by ribs. lf a flank is put under tension, the geometrical structure automatically bends in the direction of the applied force. The delayed activation of the eight tentacles via the rhombic joints gives rise to a regular wavelike motion, which generates propulsion. The tentacles together produce a peristaltic forward motion similar to that of their biological model. Festo are exploring using this principle for automation tasks including a very fast and efficient divert system and a novel gripper finger.

Controlling AquaJelly's motion in three-dimensional space is effected by weight displacement. For this purpose, two actuators integrated into the central watertight body control a swash plate, which in turn operates a four-armed pendulum that can be moved in four spatial directions. When the pendulum moves in a particular direction, AquaJelly's centre of mass is displaced accordingly – the jellyfish then moves in the direction of the pendulum's displacement. By means of this peristaltic motion, AquaJelly can move in any spatial direction.

The jellyfish's sensor system comprises three components that use different media. A pressure sensor makes it possible to determine AquaJelly's depth in the tank to within a few millimetres. AquaJelly is thus aware of its precise position at all times and can position itself within a specific pressure zone. It also relies on the pressure sensor for recharging, since this is the only way it can strategically swim to the surface. For communication at the water's surface AquaJelly uses the energy-saving ZigBee® short-range radio system, which enables it to exchange data with the charging station and to signal to other AquaJellies at the surface that the station is occupied. The radio waves penetrate to a physically determined minimal depth, and AquaJelly must decide within a narrowly defined range which charging station it will approach.

Nevertheless, the principal communication medium under water is light. AquaJelly is fitted with eleven infrared light-emitting diodes (LEDs) located on a ring inside its dome. These LEDs have a 20 degree aperture angle and use pulsed infrared signals. AquaJelly can communicate within an almost spherical surrounding space to a distance of about 80 cm. When it receives a positional signal from another approaching jellyfish, for example, AquaJelly can thus take evasive action in good time. In addition to the sensors that monitor its surroundings, AquaJelly is also fitted with an internal sensor system that monitors its energy condition and a solenoid switch that enables it to register the orientation of the propulsion system.

Each jellyfish decides autonomously on the basis of the prevailing conditions – which for example can depend on the charge condition, the propulsion system's orientation or the proximity of another AquaJelly – what action is to be taken. Although the overall behaviour of a swarm of AquaJellies is emergent, i.e. arises without predetermined control, it results solely from a suitable choice of simple rules of behaviour for individual AquaJellies and represents a collective behaviour pattern that maximises the number of living jellyfish.

AquaJelly exists within a spatially bound scenario with only a limited number of charging stations. In order to survive, the various AquaJellies must thus strive for an ideal, evenly distributed utilisation of these stations, in order to maximise the number of living jellyfish in the swarm. To secure the existence of the swarm in the water tank it is crucial to make maximum use of the space available, avoiding collision with other jellyfish and utilising the charging stations in a well-coordinated manner.

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