An artificial reflex improves the perturbation-resistance of a human walking simulator

Most walking assist systems reported are not available for real-world environment, where frequent perturbations are caused by slips, uneven terrain, slopes and obstacles. On the other hand, it is evident that human beings cope with those perturbations, especially when the perturbations cannot be predicted or perceived in advance, with reflexes, which cause relatively fixed muscular responsive patterns to perturbations unconsciously within a short period of time ranging from several 10 to 200 ms. Our ultimate goal is to realize artificial reflexes in real-world walking support systems for those paralyzed people, whose afferent and efferent neural pathways are usually weakened, so that the reflexive system is also impaired to a certain degree. This goal needs both qualitative and quantitative understanding of human reflexive mechanism during walking. However, except for some hypotheses about the underlying neural mechanisms of the reflexes during walking, there is no widely accepted unified theory, nor are there clear experimental results that could be directly quoted in the disciplines of physiology and motor control. Our approach includes (1) acquiring muscle activity profiles during normal walking and slip-perturbed walking by recording and processing Electromyographic (EMG) signals of several walking-related muscles, in human gait experiments; (2) developing a central-pattern-generator (CPG) based neuro-musculo-skeletal simulation model; (3) comparing joint trajectories of the simulation model with those of a human subject during normal walking to verify the simulation model's conformity with human walking; (4) using muscle activity profiles of reflexive responses to slip-perturbation during walking to construct a rapid responding pathway. The results showed that, (1) The simulation model could show behavior resembling that of normal human walking; (2) in the case of occurrence of slip-perturbation, the rapid responding pathway could improve the perturbation-resistance and maintain the balance for the walking; (3) using the simulation model, several hypotheses on underlying neuro-mechanism were investigated. These reveal the possibility to realize the artificial reflex for the paralyzed people.