Effect of Speed and Scanning Direction on Upper Limb Load during Visual Inspection

Abstract

Human visual inspection is still considered to play a major role in industrial inspection processes. Many studies have focused on the inspection accuracy or visual fatigue of the inspectors. However, upper limb load caused by maintaining posture and grasping an object is also considered a problem in visual inspection. If the inspection object is light in weight but large in size (e.g., a plastic part), the inspectors tend to take an awkward posture because of the difficulty in handling the object. Despite this, few studies have elucidated the effect of upper limb load. In this study, we therefore intend to clarify the effect of speed and scanning direction on upper limb load. In this experiment, ten healthy male subjects were asked to inspect objects using combinations of four speed conditions and two scanning direction conditions. For the speed conditions, speeds of 1.25, 1.00, and 0.75 s per inspection point, and a maximum effort speed were considered, and for the scanning direction conditions, the vertical and horizontal directions were considered. Muscle activity and grasp force were used as evaluation indices. We also investigated subjective indices for burden and task difficulty. Electromyography was performed in the sternomastoid muscle, the middle part of the deltoid muscle, the anterior part of the deltoid muscle, the clavicular part of the pectoralis major muscle, the biceps brachii muscle, the flexor carpi radialis muscle, the extensor carpi ulnaris muscle, and the flexor digitorum superficialis muscle. The results showed that the burden on muscles operating the cervical joint and wrist joint is high, and that the maniphalanx load due to grasping motion is different depending on the hand region.