Monitoring sheet length.

摘要

A method of detecting the acceptability of sheets comprising a) monitoring the length of a sheet at two laterally spaced positions; b) determining the difference between the monitored lengths; c) comparing the difference with a predetermined threshold to determine whether the difference is large or small; d) i) if the difference is large, comparing each monitored length with predetermined reference values to determine the acceptability of the sheet; or ii) if the difference is small, determining the average of the two lengths, and comparing the average with one or more predetermined reference values to determine the acceptability of the sheet.