| 摘要 |
PURPOSE:To let the worker to know a drill is broken, by detecting the drill being broken through a change of electrostatic capacity between copper foils on upper and bottom surfaces of a printed circuit board. CONSTITUTION:An electrostatic capacity between copper foils on both surfaces of a printed circuit board 3 is decreased in proportion to a decrease of area of the copper foils 6, 7. Accordingly, in accordance with an increase of number of holes drilled in the board, the electrostatic capacity between the copper foils tends to decrease. If a drill 22 is in a normal condition, as a number of the drilled holes increases the electrostatic capacity between the copper foils decreases, and if the drill is broken during its drilling work, the electrostatic capacity no more decreases after the drill is broken, and this fact enables a position of the borken drill to be detected. Dividing the range of drilling into some blocks, the broken drill is detected for every block. |
