Effect of Object Size and Grasp Position on Upper Limb Load during Visual Inspection(Theory and Methodology)

本研究では,立位姿勢で検査対象物の取り回しを伴う目視検査作業を想定した実験を行い,そのときの上肢負担を明らかにすることを目的とした.被験者は視力が0.7以上であり,筋骨格系の罹患歴および愁訴のない健常成人男性10名,実験条件は検査対象物の大きさが3水準,検査対象物の把持位置が2水準,検査速度が3水準とし,これらを組み合わせた計18条件で実験を行った.評価項目は,筋電図を用いた筋負担,関節角度を用いた関節モーメント,被験者の主観による評価の3項目とした.実験の結果,検査対象物の大きさは検査対象物の取り回し作業,作業姿勢の維持および主観評価に影響を与える,上肢負担に対する主要な要因であることが明らかとなった.Visual inspection by workers plays a major role in industrial inspection processes. There are many studies on the inspection speed or the visual fatigue of the inspectors but few on the upper limb load caused by maintaining posture and grasping objects, which are also problems in visual inspection. If the object to be inspected is light in weight but large in size (e.g., a plastic part), the workers tend to take an awkward posture because it is difficult for them to handle such an object. In this study, we therefore aim to clarify the effects of the object size, grasp position and inspection speed on the upper limb load. In this experiment, ten healthy male subjects were asked to inspect objects using combinations of three object size conditions (A1, A3, and A5 paper sizes), two grasping position conditions (lateral and bottom sides of the objects) , and three inspection speed conditions (1.5s per inspection point, 1.0s per inspection point and the maximum effort speed). The muscle activity and the joint moment were used as the evaluation indices. We also investigated the subjective indices of the burden and the difficulty of the task. Electromyography was performed at the sternomastoid muscle, the upper part of the trapezius muscle, the clavicular part of the pectoralis major muscle, the sternocostal part of the pectoralis major muscle, the biceps brachii muscle, the middle part of the deltoid muscle, the flexor carpi radialis muscle and the extensor carpi ulnaris muscle. The joint moment was calculated using the angle of the neck joint, shoulder joint, elbow joint and wrist joint. The results revealed that the object size was the dominant factor affecting the upper limb load