Closed-loop shape control of a roll-bending process

This paper describes a shape control system for a three roll bending process. The objective of this process is to impart a desired curvature to a workpiece at each point along the length of the part. Since final part shape is determined by theshape to which the workpiece is loaded and the amount of elastic springback, and since the latter is a strong function of the material properties of the workpiece, a truly closedloop controller must account for these properties to insure consistent process performance. The scheme presented here accomplishes shape control by measuring both the loaded shape, the loading moment, and the effective beam rigidity of the material in real-time. As a result, a very accurate prediction of unloaded curvature can be made and an unloaded curvature control system can be designed. A series of experiments were performed to test this scheme by bending thin sheets of different materials to constant radii, specifying only the desired radius. The results indicate that the controller responds to the different material properties and produces accurate shapes regardless of variability in these properties.