17 January 2010

Central Pattern Generators Out of the Gait

Animals with 4 or more legs tend to utilise various gait patterns of locomotion, shifting from one to another effortlessly to save energy. Now, scientists at Max Planck Institute and Bernstein Center for Computational Neuroscience Göttingen, the Physics Department of the Georg-August-University of Göttingen are using central pattern generators (CPGs) in robots, to allow similar gait-shifting. In fact, they have managed to control multiple gaits using just one CPG!
In humans and animals, periodically recurring movements like walking or breathing are controlled by small neural circuits called "central pattern generators" (CPG). Scientists have been using this principle in the development of walking machines. To date, typically one separate CPG was needed for every gait. The robot receives information about its environment via several sensors - about whether there is an obstacle in front of it or whether it climbs a slope. Based on this information, it selects the CPG controlling the gait that is appropriate for the respective situation.

One single pattern generator for many gaits

The robot developed by the Göttingen scientists now manages the same task with only one CPG that generates entirely different gaits and which can switch between these gaits in a flexible manner. This CPG is a tiny network consisting of two circuit elements. The secret of its functioning lies in the so-called "chaos control". If uncontrolled, the CPG produces a chaotic activity pattern. This activity, however, can very easily be controlled by the sensor inputs into periodic patterns that determine the gait. Depending on the sensory input signal, different patterns - and thus different gaits - are generated.

The connection between sensory properties and CPG can either be preprogrammed or learned by the robot from experience. The scientists use a key example to show how this works: the robot can autonomously learn to walk up a slope with as little energy input as possible. As soon as the robot reaches a slope, a sensor shows that the energy consumption is too high. Thereupon, the connection between the sensor and the control input of the CPG is varied until a gait is found that allows the robot to consume less energy. Once the right connections have been established, the robot has learned the relation between slope and gait. When it tries to climb the hill a second time, it will immediately adopt the appropriate gait. _MaxPlanckSociety

 Even simple insects use different gaits to conserve energy.  Being able to program such energy-saving hacks into multi-legged robots should lead more quickly to autonomous roving robots capable of "living off the land" while achieving extended missions.  Living off the land might mean operating on solar energy or even eating forms of carbon such as plants, coal, or peat.

Central pattern generators are useful circuits, only algorithmic in a definitional way.  CPGs are generally seen as automatised motor controls for muscles, but it is likely that similar circuits contribute to cognitive functions at a low level.

Rodney Brooks must be loving this.


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