Reassessment of COM-ZMP model for the identification of lateral standing controller of a human

This paper reports the result and discussion about our second experiment of standing motion measurement and analysis. We aim at identifying the standing controller of a human. In order to tackle the dynamical complexity of the human body, the COM-ZMP (the center of mass and the zero-moment point) model, which is widely used for designing the whole-body controller of humanoid robots, and a piecewise-linear controller is applied. In the previous experiment, the authors proposed a method to collect a sufficient number of loci of COM in a phase space for the identification of a controller, and showed that the human's standing behavior qualitatively has a similar property with the COM-ZMP model. It was also found, however, that the collected loci had large variability due to the uncertainty of convergence point and were partially inconsistent with the model, so that it was still difficult to identify the controller. Then, the authors reassessed the model and measurement protocol, and conducted the second experiment in order to improve the reliability of the measurement by visually presenting the referential point to subjects and by redesigning the protocol. As the result, more reliable loci to be processed of identification were obtained. It was also found that the effect of variation of the COM height due to the limitation of leg length, which was thought to be another source of the inconsistency, certainly existed but was not critical to model the human behavior.