Weight-Perception-Based Model of Power Assist System for Lifting Objects

Abstract

This paper deals with the design and control of a power assist system for lifting objects based on weight perception. We considered vertical lifting force (load force) as the desired dynamics for lifting objects with the power assist system. Load force consists of inertial force and gravitational force. We hypothesized that weight perception due to inertial force may differ from perceived weight due to gravitational force for lifting objects with a power assist system. Based on this hypothesis, we designed a 1-degree-of-freedom (DOF) (vertical up-down) power assist system and determined a psychophysical relationship between actual weights and power-assisted weights for lifted objects. We also determined the excess in the load forces that subjects applied when lifting objects with the system. The excessive load force causes problems such as sudden high acceleration of the lifted object, user safety and other concerns while lifting the object, loss of system maneuverability and stability, and possibly fatal accidents. We modified the power-assist control based on the psychophysical relationship and the load force characteristics. Modifying control reduced the excess in load forces and significantly enhanced maneuverability, naturalness, ease of use, stability, and safety. We proposed using the findings to design industrial power assist systems for transporting heavy objects in various industries such as assembly and manufacturing, mining, logistics and transport, construction, disaster management and rescue, and military operations.