Characteristics of the human weight perception when lifting objects with a power assist system

Power assist devices are meant to be used in cooperation with humans. However, there are several variables that influence the human response and the actual systems rarely take into account the human features, hence failing to fulfill their potential. In this paper, the way that constraining and applying different lifting schemes affect the perceived weight of the lifted object is presented. The results of the experiment showed a correlation between the perceived weight and the restrained condition leading to a second experiment to determine if the grip force applied was related to the perceived weight. These results were applied in the creation and the experimental methods of the presented one-degree of freedom power assist device for lifting objects and its control algorithm. The objective of the aforementioned device was to enlighten the factors behind the difference in the perceived weights, found in a previous research, between lifting an unconstrained object and lifting it with a power assist device. As a result, a correlation was established between the reaction force and the perceived weight, focusing in the timeframe in which the object lost all contact with the support surface.