A biomechatronic overall concept 2 Penguins are survival artists that brave the icy Antarctic storms to rear their young on land, where they move rather staidly and at times even somewhat clumsily. They feed mainly on small shrimplike creatures – krill – which they hunt in the depths of the ocean. The penguins’ swimming and diving behaviour has been studied in Antarctica for many years. Using state-of-the-art methods, researchers have succeeded in revealing the secrets of the underwater “flight” of this unusual order of birds. Nature as a laboratory for efficient processes In their search for food, penguins often travel more than a hundred kilometres per day; Adélie penguins dive to depths of up to 350 metres, and their larger cousins, the emperor penguins, to as much as 700 metres. In the water they are fast, have a great deal of endurance and are astoundingly agile: they can reach a top speed of almost 30 kilometres per hour, although their speed of travel in the more energy-efficient migratory mode is around 10 to 15 kilometres per hour. Penguins prove robust and crashproof when landing on an iceberg after an audacious leap or making their way through the pack ice. After 40 million years of evolution, they are perfectly contoured. Their artless elegance is matched by the highest levels of energy efficiency and a streamlined body design. Haulage tests with cast models of the spindle-shaped penguins’ bodies show a flow resistance 20 to 30% lower than the hydrodynamically most favourable known technical bodies (cd-values <0.02, with Reynolds numbers in the order of 106). The elastically deformable wing surfaces also make for high thrust efficiency. These two factors combine to yield a surprisingly low energy consumption level. Investigations of the metabolism of living penguins in a specially built swimming tunnel in Antarctica have revealed that Adélie penguins, for example, can swim more than 180 kilometres on a full stomach (approx. 1 kilogram of krill). If the penguins’ bodies were operated with petrol, they would thus be able to travel some 1,500 kilometres through the icy Antarctic waters on just one litre of fuel. These phenomenal feats from the animal kingdom provided the inspiration for the bionic realisation of the AquaPenguin. Bionic penguins – technology-bearers as autonomous underwater vehicles The bionic penguins are designed as autonomous underwater vehicles (AUVs) that independently orient themselves and navigate through the water basin and develop differentiated, variable behaviour patterns in group operation. The penguins’ hydrodynamic body contours and elegant wing propulsion principle were adopted from their natural archetypes. The wings comprise a skeleton of spring steel elements embedded in an elastic matrix of silicon that gives them their profile; they can thus twist to an optimal angle in interaction with the hydrodynamic forces in each stroke, whereby the pitch angle can also be regulated interactively. The robotic penguins can thus manoeuvre in cramped spatial conditions, turn on the spot when necessary and – unlike their biological archetypes – even swim backwards. An entirely new feature in robotics is the torso that can move in any direction. To make such an “organic” change of shape possible, the head, neck and tail segments were based on a new 3D Fin Ray®structure. This structure, derived from the tail fin of a fish, has thus been extended into three-dimensional space for the first time. In the realisation selected here, the bending structure consists of flexible longitudinal struts with circumferential connecting elements that maintain the shape of the elastic skin. Steering is effected via the longitudinal struts and mechanically linked draw lines, with small actuators for horizontal and vertical movement. The actuators and control electronics are housed in the dry chamber of the torso. The shoulder joints are spherical; the wing axes pass through the joints and are also fitted with separately rotatable bearings within the sphere. The additional axis of rotation is controlled by one actuator per wing, which adjusts the wings’ pitch angles. This mechanism is used for steering in various manoeuvring situations. A special flapping mechanism acts on the wing axes directed toward the torso, in order to operate the two wings synchronously and to provide the strong up-and-down motion for propulsion. Wing drive mechanism
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