A Study on the Effect of Luminance of Inspection Surface on Defect Detection in Visual Inspection utilizing Peripheral Vision

Abstract

This study focuses on differences of luminance of an inspection surface due to inspection environment, and considers experimentally the effect of luminance of inspection surface on defect detection in visual inspection utilizing peripheral vision. In the experiment, the luminance of inspection surface, defect locations, and defect characteristics (luminance contrast and size) are designed as experimental factors, and their effect on defect detection rate is evaluated. As a result, it is clarified that the defect detection rate is low in a case that the luminance of the inspection surface is 50 cd/m 2 and the rate increases in a case that the luminance is between 100 cd/m 2 and 250 cd/m regardless of the viewing area where the defect exists. In particular, it is found that the tendency is remarkable in a case that the surface luminance of defect (evaluation index of visibility of defects that was proposed in previous study) is between 0.21 and 0.34. From the above, in order to realize highly accurate visual inspection, it is necessary to control appropriately inspection environment according to the surface luminance of acceptable limit of defect. 本研究では，周辺視野を活用した目視検査において検査環境の違いによる検査対象面の明るさの相違が欠 点検出に及ぼす影響について検討するため，検査対象面の輝度と欠点の配置，および欠点の特徴(輝度コ ントラストと大きさ)を変動要因とする実験を考案し，これらが周辺視野での欠点検出に及ぼす影響につい て実験的に評価した．その結果，欠点検出率は欠点が存在する視野領域にかかわらず検査対象面の輝度が 50 cd/m 2 で低くなり，100～250 cd/m 2 間であれば同程度に高くなることが明らかになった．特に，先行研究 で提案されている欠点自体の視認性を評価する指標である欠点の面光度が0.21～0.34の場合，その傾向が顕 著にあらわれることがわかった．以上のことから，実際の目視検査工程で精度の高い目視検査を実現するた めには，欠点の許容限度の面光度に合わせて検査対象面の輝度が低くならないように検査環境を適切にコン トロールすることの必要性が示された． (キーワード：目視検査，検査環境，輝度，周辺視野，欠点検出)