We hypothesized that weight perception (WP) due to inertia might be different from WP due to gravity for lifting an object with a power assist robot (PAR). Objects were lifted with a PAR independently under three different lifting schemes-unimanual, bimanual, and cooperative lift. Then, psychophysical relationships between actual and power-assisted weights (PAWs) as well as excess in load forces (LFs) were determined for each scheme separately. A novel control strategy was introduced to reduce the excess in LFs for each scheme. Finally, we proposed to use the findings as design guidelines to design PARs for lifting heavy objects in industries that would improve HRI in terms of human, robot and system.

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.

An object lifted with a power assist robot is always perceived lighter than its actual weight. But, the human operator cannot differentiate between the power assisted weight and the actual weight and eventually applies load force (vertical lifting force) according to the actual weight of the object. This faulty force programming (excessive load force) gives faulty motions to the power assist robot and jeopardizes its operability, maneuverability, ease of use, naturalness, human-friendliness, safety etc. In this paper we assume that these problems still exist with the power assist robots because human's weight perception is not included in the design and control of the conventional power assist robots .We hypothesize that human's perception of weight due to inertial force may be different from the perceived weight due to gravitational force for lifting object with a power assist robot. Based on this hypothesis, we designed a 1 DOF power assist robot and established a psychophysical relationship between the actual weights and the power assisted weights for the objects lifted with the robot. We also determined the excess of the load forces that humans applied. Then, we modified the control system of the power assist robot based on the psychophysical relationship and the load force characteristics. The modification of the control system reduced the peak load forces applied by humans 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.

In this paper, we designed a 1DOF power assist system for lifting objects. Human's vertical lifting force, comprises of inertial force and gravitational force, was considered as the desired dynamics of the system. We hypothesized that human's perception of object weight due to inertial force might be different from the perceived weight due to gravitational force for lifting object with the power assist system. The hypothesis meant that the mass parameter of the inertial force might be different from the mass parameter of the gravitational force. We then designed the control system of the power assist system based on the desired dynamics and simulated the system using MATLAB. We then psychophysically determined the optimum mass parameters for the inertial and the gravitational force components of the desired dynamics of the power assist system on the basis of human's perception of object weight. The results showed that human's weight perceptual consideration with the dynamics (control system) of the power assist system enhanced maneuverability, stability, naturalness, ease of use, safety etc. when lifting objects with the system. Finally, we suggested using the findings to design human-friendly power assist systems for manipulating heavy objects in various industries.