Fuzzy approach in psychophysical modeling of human operator-manual lifting system

A fuzzy representation of the human operator decision-making process of selecting the maximum acceptable weight of manual lift is developed. Measures of acceptability are expressed in terms of membership functions which describe the degree to which the combined effect of biomechanical and physiological stresses is acceptable to the human operator. It is assumed that the combination of these two stresses has a synergistic effect on the individual's performance, and that the perception of this effect is reflected in an operator's choice when selecting the preferable weight of lift. The combined acceptabilities of a lifting task are compared to the subjective capacity norms established by the subjects in a psychophysical experiment. The conditions under which the distance between acceptability measures of the combined and the psychophysical stresses can be minimized are established. It is concluded that at a certain level of similarity between the acceptability measures of these stresses, a decision is made, and the preferred weight of lift selected.