Abstract
The robustness of biped walking in unknown and uneven terrains is still a major challenge in research. Traversing such environments is usually solved through vision-based reasoning on footholds and feedback loops—such as ground force control. Uncertain terrains are still traversed slowly to keep inaccuracies in the perceived environment model low. In this article, we present a ground force-control scheme that allows for fast traversal of uneven terrain—including unplanned partial footholds—without using vision-based data. The approach is composed of an early-contact method, direct force control with an adaptive contact model, and a strategy to adapt the center of mass height based on contact force data. The proposed method enables the humanoid robot Lola to walk over a complex uneven terrain with 6 cm variation in ground height at a walking speed of 0.5 m/s. We consider our work a general improvement on the robustness to terrain uncertainties caused by inaccurate or even lacking information on the environment.
Highlights
The research on biped robots is often motivated by their theoretical ability to traverse uneven and unstructured terrain—a scenario in which wheeled robots may fail
While that contribution focuses on the generation of the center of mass (CoM) trajectories and balancing with such narrow support regions, our work focuses on how to realize already planned contact wrenches when there is an unplanned partial foothold
The results show a significant reduction in the maximum sagittal inclination angle (% À28 %) for the combination—that is, with the early-contact concept, changing contact model, and CoM dynamics in the force controller
Summary
The research on biped robots is often motivated by their theoretical ability to traverse uneven and unstructured terrain—a scenario in which wheeled robots may fail. The resulting desired forces/torques l f ;d for each foot f are fed into corresponding instances of a hybrid position/force-control scheme.[12] The included force controller tracks the desired ground reaction forces based on the measured forces l f ;m by modification of the task-space trajectories These newly modified trajectories w mod; w_ mod are passed to a velocity-level inverse kinematics. Modified force/position control blending factor bf (blue), and the planned (black) and modified (red) desired, relative load for the impacting foot in an early-contact scenario. The direct force-control scheme (first part of (5)) is activated immediately in an early-contact situation by increasing the blending factor bf of the corresponding foot (see section on the previous work).
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