Psychophysical relationships between actual and perceived weights for lifting objects with power-assist: Consideration of constrained and unconstrained lifting

We conducted two experiments. In the first experiment, we made two objects with identical appearance. One was lifted by humans in constrained condition, another was lifted in unconstrained condition, and human's weight perception was compared between the two conditions. The results showed that weight perception for constrained lifting of objects was not too much different from that for unconstrained lifting. In the second experiment, we developed a power assist system for lifting objects and psychophysical relationships between actual and perceived weights for the objects lifted with the system were determined. The results showed that perceived weights were 40% of actual weights. However, the objects lifted with the system were constrained objects that might affect the accuracy of the relationships. The results of the first experiment confirmed the accuracy of the psychophysical relationships derived in the second experiment. Finally, we proposed to use the findings to develop power assist systems for manipulating heavy objects in industries that would improve interactions between the systems and their users.