Abstract
Visual inspection is one way to ensure product quality, and although automated visual inspection has been introduced, it is costly and associated with technical issues. Thus, human visual inspection still plays a major role in visual inspection in the industry. Many studies have focused on the visual fatigue of the inspectors. However, upper limb load caused by handling objects and maintaining a specific posture is also considered a problem in visual inspection. If the inspection object is lightweight but large in size (e.g., a plastic part), the inspectors tend to maintain an awkward posture due to difficulty in handling the object. Despite these findings, few studies have elucidated the effect of upper limb load. In this study, we intended to assess the effect of inspection side and object size on upper limb load. Ten healthy male subjects were instructed to inspect objects using a combination of six inspection side conditions (i.e., the sides of front with horizontal LED, top, under, front with vertical LED, right, and left) and two object size conditions (i.e., big: a square, 450 mm each side, and small: a square, 150 mm each side). Muscle activity and joint moment were the evaluation indices. We also investigated subjective indices for burden and task difficulty. Electromyography was performed on the subjects' sternomastoid muscle, the upper part of the trapezius, the clavicular part of the pectoralis major, the middle part of the deltoid, the biceps brachii, the extensor carpi radialis, and the flexor carpi ulnaris muscle. The results showed that the muscle load of the upper limb is highest when the inspection side condition is under side. Additionally, if the object is big, the muscle load of the neck and upper limb is greater.
