Optical detection system for features on a sheet or web

An optical detection system for detecting a feature located at a predetermined lateral position on a sheet or web fed along a flow path, comprising:

• a source of light on one side of the plane of the flow path and at a first margin of the flow path;
• a detector on one side of the plane of the flow path and at the second margin of the flow path;
• a first set of fibre optics, one end of the first set of fibre optics forming a first row of fibre optic ends extending transversely to the direction of feed at the first margin of the flow path and on the side of the plane of the flow path opposite the source, for receiving light from the source, the other ends of the first set of fibre optics being arranged in a second row parallel to the first row and providing light for illuminating elements of the sheet or web and crossing the path of the feature which is required to be sensed;
• and a second set of fibre optics, one end of which forms a row of fibre optics parallel to the first row for receiving light from the elements of the sheet or web illuminated with light from the first set of fibre optics, the other ends of the second set of fibre optics forming a row of fibre optic ends parallel to the first row at the second margin of the flow path, to provide light for the light detector;
• the passage of the sheet or web blocking the passage of light from the source to selected ones of the first set of fibre optics and the passage of light toward the detector from selected ones of the second set of fibre optics, according to the lateral position of the web relative to the nominal flow path, whereby when the said feature crosses the transverse rows of fibre optic ends, the detector will receive light only from the element of the sheet or web containing the required feature, irrespective of lateral error in the web or sheet position.

An optical detection system for detecting a feature located at a predetermined lateral position on a sheet or web fed along a flow path, comprising:

• first, second and third sources of light, the first source being located on one side of the plane of the flow path and at a first margin of the flow path, the second source being located on one side of the plane of the flow path and at the second margin of the flow path, and the third source being located on one side of the flow path in a position such that the required feature of the sheet or web will be illuminated during its passage past the light source;
• first, second and third sets of light sensors each located on a side of the plane of the flow path opposite a corresponding light source, each set comprising a number of equally spaced sensors arranged in a row extending transversely tothe direction of feed;
• whereby light from the said feature will reach one of the sensors of the third set, depending on the lateral position of the web or sheet relative to the nominal flow path and the passage of light to sensors of the first and second sets will be selectively blocked by the respective margins of the web or sheet, according to its said lateral position;
• and gating means responsive to the outputs of the first and second sets of sensors to gate the outputs of the third set of sensors so that only the output of that sensor receiving light from the required feature will be transmitted.