Why does a power assist robot system reduce the weight of an object lifted with it? the preliminary results

A power assist robot system reduces the weight of an object lifted with it. However, the root causes of the reduced heaviness as well as the factors affecting the heaviness are still unknown. The knowledge on the root causes and factors could be used to modulate the interactions between the human user and the robot when lifting objects with it. This paper investigated the reasons and factors behind the reduced heaviness of objects lifted with a power assist system. We hypothesized that weight perception due to inertia might be different from that due to gravity when lifting an object with a power assist system because the actual weight and the perceived weight were different. Subjects lifted objects manually and with power-assist separately. We compared load forces and motion features for the manually lifted objects to that for the power-assisted objects and found that the load force and its rate, velocity and acceleration for the powerassisted objects were lower than that for the manually lifted objects. We noticed that there were time delays in force sensing, position sensing, servomotor etc. for the power-assisted objects, but not for the manually lifted objects. We assumed that the delays were responsible for the reduced heaviness of objects lifted with power-assist. Finally, we proposed to use the findings to develop human-friendly power assist devices for manipulating heavy objects in industries that would help improve/modulate interactions between users and robots.