A Comparison between Virtual Constraint-Based and Model Predictive-Based Limit Cycle Walking Control in Successful Trip Recovery

Falling is one of the main causes of the injuries among healthy adults. The foremost causes of the falls are: slipping and tripping. Understanding the phenomenon of human balance recovery against these disturbances is a very important issue in the field of biomechanics as well as in the robotics. Previous studies have shown that human movements can be reproduced using engineering techniques and computational facilities. The prediction of movements can be related to an optimization problem. In the present study, control and prediction of human movements in successful trip recovery are addressed.To formulate the optimization problem, a hybrid dynamic model of the human body with seven degrees of freedom is considered. The tripping perturbation is modeled as an instantaneous contact of the swing leg with an obstacle and the dynamics of impact are derived. Two optimization based methods are used to control and predict the gait: (i) virtual constraintbased limit cycle optimization (ii) model predictive based limit cycle optimization. The simulated results are compared with the humanobserved experimental data from the literature. The results show that the second method provides more humanlike predictions than the first method in the kinematic level. The second method can predict proper actions to keep away violating constraints in the future. The theoretical results are in agreement with the aresults of experimental studies on movement adjustments during trip recovery.