Sheet property sensor with sheet wrinkle remover

摘要

Apparatus is provided for sensing a property of a sheet (18). A sensor element (32) is adapted to be placed alongside the sheet path, and a base member (34) is adapted to be positioned on one side of the sheet and in sliding contact with one surface thereof. The sensor element is enabled to produce a sheet property sensing interaction with the sheet in a limited region of the sheet path, the interaction region being movable to any one of a plurality of sensing locations spaced across the width of the sheet. The base member has a pair of groove portions (44, 46) forming gas conducting channels with open sides exposed to the sheet surface in contact with the base member. Each of the groove portions has a part (40, 40A) extending upstream of the interaction region. The groove portions diverge from each other as they extend in a downstream (20) direction. A source of subambient gas pressure communicates with the groove portions for reducing the gas pressure therein so that the contacting surface of the sheet is at least nominally depressed into the groove portions to such an extent that the divergence of the grooves and the longitudinal movement of the sheet exert thereon a transverse tension. This tension is sufficient to substantially smooth out longitudinally extending sheet wrinkles. Typically a plurality of gas removal devices are provided for minimizing the introduction of gas between the base member and the sheet.