We developed a 1 DOF power assist robot for lifting objects. We hypothesized that human's perception of weight due to inertial force might be different from the perceived weight due to gravitational force for lifting an object with a power assist robot. We established psychophysical relationships between the actual weights and the power-assisted weights for the objects lifted with the robot, and also determined the excess in load forces that the subjects applied for three independent lifting schemes or grasp configurations: (i) unimanual lift, (ii) bimanual lift, and (iii) cooperative lift. We also compared the weight perceptual and load force features for the unimanual lifts to that for the bimanual and cooperative lifts. We then modified the power-assist control using a novel control strategy based on the weight perceptual and load force features. The control modification reduced the excessive load forces applied by the subjects in each lifting scheme and thus enhanced maneuverability, naturalness, ease of use, stability, safety etc. of the robot system significantly. Finally, we proposed using the findings to design human-friendly power assist robots for carrying heavy objects in various industries.
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