Abstract
In this work we research the role of body dynamics in the complexity of kinematic patterns in a quadruped robot with compliant legs. Two gait patterns, lateral sequence walk and trot, along with leg length control patterns of different complexity were implemented in a modular, feed-forward locomotion controller. The controller was tested on a small, quadruped robot with compliant, segmented leg design, and led to self-stable and self-stabilizing robot locomotion. In-air stepping and on-ground locomotion leg kinematics were recorded, and the number and shapes of motion primitives accounting for 95% of the variance of kinematic leg data were extracted. This revealed that kinematic patterns resulting from feed-forward control had a lower complexity (in-air stepping, 2–3 primitives) than kinematic patterns from on-ground locomotion (νm4 primitives), although both experiments applied identical motor patterns. The complexity of on-ground kinematic patterns had increased, through ground contact and mechanical entrainment. The complexity of observed kinematic on-ground data matches those reported from level-ground locomotion data of legged animals. Results indicate that a very low complexity of modular, rhythmic, feed-forward motor control is sufficient for level-ground locomotion in combination with passive compliant legged hardware.
Highlights
The overlapping fields of functional leg anatomy, leg and body compliance, and neuro-control in legged locomotion are intensively researched
In this study we reported on the interplay between a modular, feed-forward locomotion controller, and the mechanical entrainment of a quadruped, self-stably walking and trotting compliant legged robot
We measured the complexity of the feed-forward controller, and the complexity of the resulting leg kinematics through the number of basic patterns accounting for a certain variance of kinematic data from in-air leg motions and on-ground locomotion, respectively
Summary
The overlapping fields of functional leg anatomy, leg and body compliance, and neuro-control in legged locomotion are intensively researched. Though intrinsically limited (Webb, 2001), robots are beginning to be used as proof-of-concept platforms (Raibert et al, 1984; Raibert, 1990; Full and Koditschek, 1999; Ijspeert et al, 2007; Umedachi et al, 2010; Zhou and Bi, 2012) In this experimental work we present results by comparing basic patterns measured from kinematic leg data from in-air stepping movements of a suspended legged, compliant robot, and from on-ground locomotion of the same robot during lateral sequence walk and trot. The robot was designed such that its leg’s compliance and cable-driven actuation were the medium of change of kinematic complexity between feed-forward-sent and observed kinematic joint patterns, through emerging mechanical entrainment during level-ground (flat ground) locomotion. The robot would stumble, fall, or move only very poorly, i.e., very slowly or even backwards
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