Effect of Grasp Height and Inspection Posture on Upper Limb Load during Single-handed Visual Inspection of Objects

Abstract

Automated systems based on image processing have been introduced into the visual inspection process. However, owing to persisting technical and cost issues, human visual inspection still plays a major role in industrial inspections. When workers inspect small items (e.g., digital camera lenses or containers of liquid cosmetics) with one hand, which leads to an awkward posture, they experience upper-limb loading because of high loads on the upper extremities. This upper-limb loading may damage their hands, arms, and shoulders. There are a very limited number of studies that investigate the effects of upper-limb loading on humans during visual inspections; therefore, we conducted experiments on subjects where they used one hand to handle small objects for visual inspections. Using electromyography, joint angle measurements, and subjective evaluations, we investigated the effects of the grasp height and the subject’s inspection posture on the load applied to the upper limb. The results showed that the effects of upper-limb loading varied depending on the inspection posture because of variations in the locations where the loads acted on the body. Therefore, when evaluating upper-limb loading during such tasks, it was necessary to consider not only the muscle load but also the posture, the posture duration, and the subjective metrics.