Motion Analysis of the Torso and the Elbow During Picking and Placing Heavy Object on Shelf

In recent years, labor shortages and workforce aging have become problematic. One solution to this problem is introducing humanoid robots to perform human tasks. This research is aimed at analyzing the posture and preparation posture of the torso and elbow in human motions for improving the motion planning of humanoid robots utilizing the redundant part. We analyze the frontal tilt angle of the torso, time of backward bending the torso, and lateral tilt angle of the elbow when humans apply force. In the experiments, we focused on picking and placing heavy objects on the shelf, which requires maintaining balance and exerting force, and confirmed the differences in movements by changing the weight of the objects. An optical motion capture system and a six-axis load cell were used for measuring the motion. The subjects were asked to approach the shelf from a distance of 1 m and move a heavy object from the upper to the middle height of the shelf. As a result, the heavier the object, the earlier the preparation posture of a backward bending of the torso before grasping. The heavier the object, the larger the tilt angle of the torso forward. Significant differences were observed between the time of backward bending and picking the object, distances from the shoulder to wrist joint, and tilt angle of the torso. We identified the posture and time required to bend the torso for holding a heavier object in front of the shelf, considering the dynamic stability of the Zero-Moment Point.