DEFOCUS DETECTION METHOD OF MICRO THROUGH HOLE INSPECTION DEVICE AND DEFOCUS DETECTION METHOD

PROBLEM TO BE SOLVED: To provide a micro through hole inspection device for imaging a steel plate by arranging the steel plate between a lighting device and a camera in order to detect the micro through hole in the steel plate and to inspect the presence or absence of the micro through hole based on imaged data.SOLUTION: A defocus detection method of a micro through-hole inspection device acquires two-dimensional array image data including a micro through-hole, and extracts one-dimensional array image data on a line traversing the micro through-hole. The secondary differential calculus is applied along the direction where the pixels are arrayed with respect to a gradation value of the one-dimensional array image data, and searches the maximum gradation value h after the secondary differential calculus and a position of the pixel relating to the maximum graduation value h, and calculates an edge width L which is a differential value of the position of two pixels zero-crossing first respectively. When the maximum gradation value h after the differential calculus is equal to or less than a threshold value β1 and the edge width L is equal to or more than a threshold value β2, it is determined that the defocusing occurs in a light reception part of the micro through-hole inspection device.SELECTED DRAWING: Figure 5 【課題】鋼板における微小貫通穴を検出するために、照明とカメラとの間に鋼板を配置して当該鋼板を撮像し、撮像データに基づき微小貫通穴の有無を検査する微小貫通穴検査装置において、合焦外れを検知する。【解決手段】微小貫通穴を含む２次元配列画像データを取得し、この２次元配列画像データから、微小貫通穴を横切る線上の１次元配列画像データを抽出する。１次元配列画像データの階調値について画素が並ぶ方向に沿って２次微分を施し、２次微分後の最大階調値ｈおよびその最大階調値ｈに係る画素の位置を検索し、最大階調値ｈに係る画素の位置の両側でそれぞれ最初にゼロクロスする２つの画素の位置の差分値であるエッジ幅Ｌを算出する。微分後の最大階調値ｈがしきい値β１以下であり、かつ、エッジ幅Ｌがしきい値β２以上であるとき、微小貫通穴検査装置の受光部における合焦外れが生じていると判定する。【選択図】図５