Split-belt Adaptation Model of a Decerebrate Cat Using a Quadruped Robot with Learning

K. Kodono and H. Kimura

Abstract

We propose a model connecting body dynamics and sensor feedback to investigate gait adaptation mechanisms of decerebrate cats in split-belt waking. In our previous studies, we proposed a leg controller using leg loading/unloading for the leg phase transition of a quadruped robot:``Kotetsu.'' The purpose of this study is to make a model of split-belt gait adaptation in spinal cats and decerebrate cats referring to biological knowledge and to evaluate the validity of those models using Kotetsu. We construct the spinal cat model integrating our leg controller with Frigon's spinal cord model. In addition, we employ motor learning in the cerebellum by long-term depression for the decerebrate cat model. As the results of experiments, we show that early adaptation in split-belt walking is obtained by the stance-to-swing leg phase transition mechanism in the spinal cat model. We also show that late adaptation in split-belt walking is obtained motor learning as the step distance adjustment in the decerebrate cat model. The validity of those models are evaluated by comparing durations of forelegs bisupport phases and duty ratios in the transition from tied-belt to split-belt walking between decerebrate cats and Kotetsu with the decerebrate cat model.

Constructing the model of the gait adaptation mechanism of decerebrate cats in split-belt walking using a quadruped robot

• We are using our original phase modulation methods based on leg loading/unloading as the basis of the controller.
• We modified the condition for lift-off by leg unloading while referring to the spinal cord half-center CPG model proposed by Frigon et al. (J. Phys. 2017).
• We added the adaptation mechanism as the model of the motor learning by long-term depression in cerebellum.
• As a result of experiments of split-belt walking using a quadruped robot "Kotetsu", we successfully obtained similar gait adaptation patterns as those of a decerebrate cat in split-belt walking. There are two adaptations, those are early adaptation at the spinal cord level and delayed adaptation at the cerebellum level.
• In order to emulate the head constraint in decerebrate cat experiments, Kotetsu is tethered by two strings with springs at the top of the body in order to constrain forward/backward motion and rotation in the horizontal plane. But side-way motion and rolling motion is not disturbed (experimental setup:tethered)

Results of experiments


• split-belt walking using the spinal cat model (MPG 7M)
  (All belts speed is 13.2cm/s at beginning. Around 8 sec., the belt speed of left fore is increased to 22.3cm/s.)
• split-belt walking using the decerebrate cat model (MPG 8M)
  (All belts speed is 13.2cm/s at beginning. Around 14 sec., the belt speed of left fore is increased to 22.3cm/s.)