Human Operator's Weight Perception of an Object Vertically Lifted with a Power Assist System

This paper attempts to design a power assist system for maneuvering heavy objects in industries based on human operator's perception of object weight. The perceived weight of an object maneuvered with a power assist system is always very much less than the actual weight of the object. But, the human operator cannot differentiate between the perceived weight and the actual weight and eventually applies forces in accordance with the actual weight of the object. This faulty force programming gives faulty motion to the power assist system and jeopardizes its maneuverability, ease of use, human-friendliness, safety etc. The research presented herein, firstly, subjectively determines the optimum maneuverability conditions for lifting objects with a power assist system, secondly, establishes a psychophysical relationship between the actual weights of objects and the perceived weights of the same objects by human operators when the objects are vertically lifted with the power assist system as well as analyzes human's manipulative force characteristics for lifting objects with the system, thirdly, compares human's manipulative force characteristics for lifting power assisted objects with that for lifting actual objects, and finally, attempts to use these findings to design the feedback position control law for the power assist system. This type of psychophysical considerations with power assist system enhances maneuverability, operability, ease of use, human-friendliness, safety etc. of the system in an optimal fashion.