Locomotion control of legged robots is nowadays a field in continuous evolution. In this work a bio-inspired
control architecture based on the stick insect is applied to control the hexapod robot Gregor. The control
scheme is an extension of Walknet, a decentralized network inspired by the stick insect, that on the basis of
local reflexes generates the control signals needed to coordinate locomotion in hexapod robots. Walknet has
been adapted to the specific mechanical structure of Gregor that is characterized by specialized legs and a
sprawled posture. In particular an innovative hind leg geometry, inspired by the cockroach, has been considered
to improve climbing capabilities. The performances of the new control architecture have been evaluated in
dynamic simulation environments. The robot has been endowed with distance and contact sensors for obstacle
detection. A heading control is used to avoid large obstacles, and an avoidance reflex, as can be found in stick
insects, has been introduced to further improve climbing capabilities of the structure. The reported results,
obtained in different environmental configurations, stress the adaptive capabilities of the Walknet approach:
Even in unpredictable and cluttered environments the walking behaviour of the simulated robot and the robot
prototype, controlled through a FPGA based board, remained stable.
KEYWORDS: Sensors, Cognitive modeling, Modulation, Systems modeling, Cognition, Animal model studies, Neural networks, Artificial intelligence, Kinematics, Control systems
Even so called "simple" organisms as insects are able to fastly adapt to changing conditions of their environment. Their behaviour is affected by many external influences and only its variability and adaptivity permits their survival. An intensively studied example concerns hexapod walking.1,2 Complex walking behaviours in stick insects have been analysed and the results were used to construct a reactive model that controls walking in a robot. This model is now extended by higher levels of control: as a bottom-up approach the low-level reactive behaviours are modulated and activated through a medium level. In addition, the system grows up to an upper level for cognitive control of the robot: Cognition - as the ability to plan ahead - and cognitive skills involve internal representations of the subject itself and its environment. These representations are used for mental simulations: In difficult situations, for which neither motor primitives, nor whole sequences of
these exist, available behaviours are varied and applied in the internal model while the body itself is decoupled from the controlling modules. The result of the internal simulation is evaluated. Successful actions are learned and applied to the robot. This constitutes a level for planning. Its elements (movements, behaviours) are embodied in the lower levels, whereby their meaning arises directly from these levels. The motor primitives are situation models represented as neural networks. The focus of this work concerns the general architecture of the framework as well as the reactive basic layer of the bottom-up architecture and its connection to higher level functions and its application on an internal model.
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