Measuring curl of thin papers.

A method to measure curvatures (curl) of thin papers is examined. The method is based on measurement of the out-of-plane deflection of a curled sheet with a noncontact laser distance meter. The specimen is arranged so that its plane is vertical to minimize additional deflections caused by gravity. A cylindrical shell was used to evaluate the method. The classical relation between evaluated curvature and inverse radius of the shell was verified, and the utility of transformation equations for the curvatures was demonstrated by rotation of the cylinder. The influence of gravity on the curvature was investigated using finite element analysis. The error in the evaluation of curvature due to gravity is estimated to be less than 4% for sheets with basis weights larger than 40 g/m 2 .