In - Process Measurement of Bending Angles Based on the Principle of Light Sectioning

This paper presents an industrial application of optical 3-D sensing based on the principle of light sectioning. The presented project aims at an in-process measurement of the bending angle in a commercial bending machine. Air bending is a valuable manufacturing method in a flexible and computer integrated manufacturing system, because it allows forming of sheet metals with a great variety of bending angles. But achieving high working accuracies requires adaptive control strategies to overcome deviations from the desired bending angle caused by material tolerances. The investigations comprise fundamentals of system design for integrating such a measuring system in any commercial bending machine. System design considerations about the choice of the components and synchronization of illumination and detection system are described. Furthermore, the different steps for achieving 3-D data are sketched. First step is evaluating the position of the profile on the CCD sensor with subpixel accuracy due to interpolation algorithms. Next step is the calculation of 3-D coordinates which correspond to these sensor positions. The bending angle can be evaluated with statistical deviations of about 1 angular minute. But measuring absolute values of bending angles presupposes knowledge of the correspondence between camera and workpiece coordinates. The basic equations to describe this correspondence and the application of photogrammetric calibration methods for a simple model of the detection system are presented. First experimental results prove the derived equations and show promising results even for the simple model of the detection system.