Contour tracking of specularly reflecting surfaces

The aim of the presented work is to develop an ultrasonic imaging system for contour detection of specularly reflecting sheet metal surfaces and surface contour tracking during a continuous hydroforming process. Based on certain design considerations in context with hardware limitations to obtain on-line information about the state of forming during the whole process a sparsely filled ultrasonic 1D transducer array has been used with a limited number of transducer elements, operating at 2 MHz. It has been shown before, that "2.5D-geometries" (surface areas with curvatures independent of one direction) could be detected and tracked with a sufficient accuracy (linear aperture, 10 cm width, 21 transducers, error in sound propagation direction less than 1 mm). We now present the design and results of an imaging system for automated detecting and consecutive tracking of sheet metal surface contours during the forming process by means of an active contour model. To achieve a sufficient accuracy, a priori in process information, e.g., starting and final positions of the sheet metal, forming velocity, preceding instantaneous contour geometries are incorporated into the active model.