Abstract
Interlimb coordination plays an important role in adaptive locomotion of humans and animals. This has been investigated using a split-belt treadmill, which imposes different speeds on the two sides of the body. Two types of adaptation have been identified, namely fast and slow adaptations. Fast adaptation induces asymmetric interlimb coordination soon after a change of the treadmill speed condition from same speed for both belts to different speeds. In contrast, slow adaptation slowly reduces the asymmetry after fast adaptation. It has been suggested that these adaptations are primarily achieved by the spinal reflex and cerebellar learning. However, these adaptation mechanisms remain unclear due to the complicated dynamics of locomotion. In our previous work, we developed a locomotion control system for a biped robot based on the spinal reflex and cerebellar learning. We reproduced the fast and slow adaptations observed in humans during split-belt treadmill walking of the biped robot and clarified the adaptation mechanisms from a dynamic viewpoint by focusing on the changes in the relative positions between the center of mass and foot stance induced by reflex and learning. In this study, we modified the control system for application to a quadruped robot. We demonstrate that even though the basic gait pattern of our robot is different from that of general quadrupeds (due to limitations of the robot experiment), fast and slow adaptations that are similar to those of quadrupeds appear during split-belt treadmill walking of the quadruped robot. Furthermore, we clarify these adaptation mechanisms from a dynamic viewpoint, as done in our previous work. These results will increase the understanding of how fast and slow adaptations are generated in quadrupedal locomotion on a split-belt treadmill through body dynamics and sensorimotor integration via the spinal reflex and cerebellar learning and help the development of control strategies for adaptive locomotion of quadruped robots.
Highlights
Humans and animals change their locomotor behaviors depending on the environment and situation
During the split-belt treadmill walking of humans, when the treadmill speed condition is changed from the tied configuration to the split-belt configuration, the relative phase between the leg movements rapidly changes to break the antiphase relationship and the stride length and duty factor differ between the two legs (Reisman et al, 2005)
When the treadmill speed condition is returned to the tied configuration, the stride length and duty factor quickly return, whereas the relative phase rapidly diverges from antiphase and slowly returns to antiphase to reduce the asymmetry
Summary
Humans and animals change their locomotor behaviors depending on the environment and situation. During the split-belt treadmill walking of humans, when the treadmill speed condition is changed from the tied configuration (belts move at the same speed) to the split-belt configuration (belts move at different speeds), the relative phase between the leg movements rapidly changes to break the antiphase relationship (i.e., asymmetric interlimb coordination appears) and the stride length and duty factor differ between the two legs (Reisman et al, 2005). When the treadmill speed condition is returned to the tied configuration, the stride length and duty factor quickly return, whereas the relative phase rapidly diverges from antiphase (i.e., asymmetric interlimb coordination appears even in the tied configuration) and slowly returns to antiphase to reduce the asymmetry. The quick divergence of the relative phase upon return to the tied configuration has been suggested to be the after-effect of learning
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