| 摘要 |
A flying spot is used to scan a web completely across the web from a leading to a trailing edge plus an additional distance on each side with the apparatus being initiated automatically as the leading edge is reached and ceasing an output when the trailing edge is reached. The web might be a paper web, for example, being scanned to determine the two edges, and also to determine defects including holes and wrinkles in the web. The flying spot is rectangular with the length of the rectangle parallel to the moving direction of the web and this flying spot rectangle traverses from one side to the other of the web. A hole in the web gives less than average reflected illumination to a detector, whereas a wrinkle gives increased illumination to the detector. The circuit differentiates the raw signal so that a hole or dark signal, gives a positive and then a negative going pulse, whereas a wrinkle, or lighter signal, gives a negative going pulse followed by a positive pulse. The circuit discriminates between the leading web edge, which is a negative going pulse after differentiation, and the negative initial pulse of a wrinkle. The circuit also discriminates between the positive going pulse of the trailing web edge and the positive initial pulse of a hole in the web. The foregoing abstract is merely a resume of one general application, is not a complete discussion of all principles of operation or applications, and is not to be construed as a limitation on the scope of the claimed subject matter. |
