| 摘要 |
PURPOSE:To exactly execute an optical detection of a picture pattern area rate of a press plate by providing a roughly rectangular slit on a light intake of a light shielding box so that the short side direction width of the surface to be measured of a reflected light going into the short side of its slit becomes a size being below the same direction width of a calibration mark. CONSTITUTION:A detection area of a press plate 13 is irradiated by a light beam from a fluorescent lamp, a reflected light therefrom is guided to the inside of each light shielding box 19 through a slit 20 and photodetected by a light receiver S1, and a picture pattern area rate of a press plate detection area is detected instantaneously. A slit 20A of light intake of a box 19A opposed to a calibration mark 21 is a roughly rectangular shape having a short side (a) in the parallel arrangement direction X2 of a light shielding box group 18 and as for this short side (a) has a size being below width f0 of the mark 21, therefore, the incident light quantity is made sufficient by taking enough length of the long side in the scanning direction X1. In such a way, a light beam can be received in a state that it is suppressed that a reflected light goes into the box 19A and an undesirable influence of light beam from the periphery has been eliminated, a light beam from the mark 21 is detected with high accuracy and an optical detection of the picture pattern area rate of the press plate 13 is executed exactly. |
