Alignment of an Unmarked Deformable Sheet Like Object Based on NURBS Fitting

In this paper, we proposed a method to realize automatic labeling task of a flexible sheet like object. It is a demonstration to the similar operations widely adopted in industrial production line such as those in flexible printed circuits assembly. In these operations, it needs to precisely position a specific part within a deformable sheet to a predefined position. In many applications involving such operations, the usage of artificial markers are not allowed and the target may lack enough features for tracking. Thus 3D position of the alignment reference has to be estimated from its contour. The task of aligning an unmarked paper sheet considered in this paper well demonstrates these situations. In this paper, Non-uniform rational B-Splines (NURBS) fitting is utilized for tracking the shape variation of the paper. It is proved that for an unstretchable sheet like object, the fitted NURBS plane can be used in the way of servo control for regulating the shape. It provides a simple way to track the featureless points described with the paper undeformed generally as a sketch. The advantage of the proposed method is verified by successful alignment experiment in which a certain line defined on an undeformed paper sheet is aligned to the predefined position on a box.