Current robotic control strategies are mainly based on trajectory plans that adjust the movements based on the next desired state. These control policies do not efficiently perform where the dimensionality of the control problem increases or disturbances are perturbing the system from the external environment. These issues are critical in locomotion tasks and the need for different control methods arises. To make autonomous robots able to move in a real and dynamic environment, the research has focused on biologically inspired controller, such as neuro-controller.
The interaction among different bio-inspired motion controllers whose communication represents a simplified model of the neural locomotion control in vertebrates is possible in the Neurorobotics Platform.
The presented solution combines classical control strategies with reservoir computing and spiking neural networks (Reservoir computing with spiking populations by Alex Vandesompele) to obtain a scalable and adaptable controller by taking advantage of the different learning properties of neural networks. To reflect the scalability of the controller, the experiments are performed on the simulated modular Fable Robot. In the experiment, it is built in a quadruped configuration so that the control architecture is composed of 4 cerebellar microcircuits, called Unit Learning Machines (ulm).
The use of a spiking neural network with reservoir computing as a trajectory planner (Central Pattern Generator, cpg) allows the learning of complex periodic trajectories for the movements of the robotic modules, whose frequency modulation is possible by just changing the frequency of the input signal to the network. Not optimally tuned PIDs give to the robot early stability during the first part of the simulation and provide a torque command for each module. Thus, a cerebellar network composed of 4 micro complexes computes and provides corrective effort contributions based on the inverse dynamics model of each robotic modules.
In the video below, it is possible to appreciate the locomotion improvements of the robot in an experimental simulation. The recording shows the simulation around second 100-130 when the position error is decreasing and stabilizing. The brain visualizer shown the spiking activity of the input population of the Central Pattern Generator (the higher groups) which are reflected in the blinking of one population of the reservoir (lower group). The spike train window (on the left) shows the periodicity of the spike trains which generate the trajectories for the modules (starting from the bottom, the activities of the input populations and one reservoir population are displayed).
The feed-forward cerebellar effort contribution decreases the mean of the position error of 0.3 radiant and its variance of 0.01 radiant compared to the case when just the effort command from the cpg is provided to the robot (the plot concerning the behavior of the second module is shown below). Moreover, the trend of the error is decreasing along the simulation time and the distance covered by the robot with the cerebellar-like neural network contribution is 9.48 m while the cpg controller contributes to have the robot walk for 1.39 m.
The modular configuration of the Fable Robot makes easier to test the control strategy for different configurations of the robot and patterns of locomotion, having the cerebellar-like neural network compensate the error after a short learning phase, since it has previously learned the internal model of the module.
This work was done in collaboration between DTU, Ghent and SSSA teams.