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Multimodal sensor fusion for foot state estimation in bipedal robots using the Extended Kalman Filter

Towards enhancing the dynamic locomotion and manipulation abilities of bipedal robots in real-world scenarios, a key problem lies in the accurate estimation of the dynamic state of the feet of the robot. In this paper, an approach is presented for estimating the dynamic pose and the internal (body) and external (ground contact) wrenches acting on the individual feet of a bipedal robot fusing haptic (compliant skin), inertial, and force/torque (F/T) measurements. Assuming rigid body dynamics on an individual foot, an Extended Kalman Filter (EKF) is used to combine ankle F/T sensor readings, contact forces computed from a compliant tactile array on the foot sole and accelerometer plus gyroscope measurements, thereby estimating both the state and the external wrenches affecting a foot through a method of state augmentation. Moreover, covariance estimation of the measurement noise was carried out for all sensors, in particular, for the skin, a bayesian-network-based regression method was chosen. The framework was implemented with the iCub humanoid robot under a toppling scenario; the estimated augmented foot state was then used to compute the Foot Rotation Indicator (FRI) trajectory as a validation through prediction of the onset of toppling and instability.