Estimating and Validating Relationships between Actual and Perceived Weights for Lifting Objects with a Power Assist Robot: The Psychophysical Approach

A power assist robot reduces the perceived weights of objects lifted with it. However, the relationships between actual and perceived weights have not been estimated yet that result in inappropriate force programming, improper interactions between robots and human users in terms of safety, maneuverability, motion etc. In this paper, we present the development of a power assist robot system for lifting objects. We estimated relationships between actual and perceived weights for the objects lifted with the system by comparing the perceived weights of the power-assist-lifted objects to some reference weights following psychophysics. The results showed that the perceived weights were 40% of the actual weights. However, the power-assist-lifted objects were constrained objects as they were tied to the force sensor and the objects for reference weights were unconstrained objects, which might affect the accuracy and reliability of the relationships. This is why, we conducted another experiment where we made two objects with identical appearance. One was lifted by humans in constrained condition, and another was lifted in unconstrained condition, and weight perception between the two conditions was compared. The results showed that weight perception for constrained lifting was not much different from that for unconstrained lifting. Results of this experiment validated the psychophysical relationships between actual and perceived weights for the power-assistlifted objects, and also confirmed the accuracy of the relationships. Finally, we proposed to use the findings to develop power assist robots for manipulating heavy objects in industries that would improve interactions between robots and their users.