Stability Analysis for a Force Augmenting Device Considering Delays in the Human Model

This paper presents a stability analysis of the interaction between a human and a linear moving Force Augmenting Device (FAD). The analysis employs the mathematical models of the human, the FAD and their interaction. As a depart from past works, this article presents a stability analysis considering time-delays in the human model. A key ingredient in the analysis is the use of the Rekasius substitution for replacing the time-delay terms. It is proved that the human machine interaction is stable when the human model has no delays. The analysis provides an upper bound for the time-delays preserving a stable interaction. Numerical simulations allow to assess the human-FAD interaction. An experiment is performed with a laboratory prototype, where a human operator lifts a load. It is observed that the human machine interaction is stable and the human operator is able to move the load to its desired position by experiencing very little effort.