Analysis of weight perception, load forces, and objects' motions in lifting objects with a power assist robot system to modify the control

Abstract

We developed a one-degree-of-freedom (1-DOF) power assist system (PAS) for lifting objects. Load force (vertical lifting force, LF) consisting of inertial and gravitational forces was derived as the dynamics of motion of the system. We hypothesized that the inertial mass (mass parameter constituting the inertial force) would be different from the gravitational mass (mass parameter constituting the gravitational force) when lifting an object with the PAS. The PAS was simulated and objects were lifted with the PAS during the simulation. We critically analyzed human's weight perception, load forces and objects' motions, and identified several control parameters such as we derived the LF magnitudes and rates for various inertial and gravitational mass conditions and also determined the relationships between (i) inertial mass and LF rates, (ii) gravitational mass and LF magnitudes, (iii) gravitational mass and LF rates etc. We also analyzed the relationships among LF, object's displacement and acceleration time trajectories. We then elucidated how to modify the power-assist control based on the findings (control parameters) that would enhance maneuverability, stability, safety etc. of the PAS. The results can be used to develop PASs for carrying heavy objects in various industries.