| 20100165343 | REGISTER MARK DTECTION APPARATUS - A register mark detecting apparatus detects a transparent register mark printed on a conveyed transparent web. The register mark detecting apparatus includes a light source, a parallel light flux irradiation optical system, a collective optical system, a knife-edge, and a light receiving element. The parallel light flux irradiation optical system converts a light flux from the light source into a parallel light flux to irradiate a transparent web with the parallel light flux. The collective optical system collects the light flux transmitted through the transparent web. The knife-edge is disposed near a back focus of the collective optical system. The knife-edge interrupts the light flux going straight in the transparent web and causes only the light flux refracted by being transmitted through the transparent register mark to pass by. The light receiving element receives the light flux transmitted through the knife-edge. | 07-01-2010 |
