Time delay and integration imaging for inspection and profilometry of moving objects

Dynamic inspection of moving objects is a significant task in industrial machine vision systems. A CCD camera operating in time delay and integration (TDI) mode is equivalent to a digital drum camera, providing possibilities for dynamic inspection of moving objects (either rotating or translating on industrial platforms). We report some advances in the application of TDI cameras for the inspection and profiling of moving objects. The method is based on conventional light projection systems that are widely used in industry. The TDI system generates an on-line scanning moire´ display that could assist operators to identify defects on objects such as dents. Conventional projection systems use mechanical or interferometric types of fringe projections, which is not desirable in the industrial environment. The TDI system makes use of temporal modulation of a laser diode, which could be easily controlled by a PC or by the output ports in vision systems. In addition to the details of system implementation, we also describe two algorithms for unwrapping the deformation or shape profile of the test object based on the fast Fourier transform and sinusoidal fitting of the recorded patterns.