Motion Estimation by Optical Flow and Inertial Measurements for Dynamic Legged Locomotion

Dynamic legged locomotion entails navigating unstructured terrain at high speed. The discontinuous foot-fall patterns and flight phases, which are pivotal for its unrivaled mobility, introduce large impulses and extended free-falls that serve to destabilize motion estimation. In a nod to biological systems, visual information, in the form of optical flow, is used with a hybrid estimator tuned to the principal phases of legged locomotion. This takes advantage of the ballistic nature of the flight phases to vary optical flow calculation methods and estimator parameters. Experimentation on a single-leg shows a reduction in inertial drift. In tests with 6g impulses, pose was recovered within 5 deg rms with angular rate errors limited to 10 deg/sec at frequencies up to 250 Hz. This compares well with angular rate recovery by vision only and traditional inertial techniques.