Optical Fibers Weave Illumination for Web Inspection
Daniel C. McCarthy
Datacube Inc. designed its Black Widow web inspection system to detect, measure and classify defects in rolled products ranging from aluminum to paper to plastic film. Its ability to stitch and process data from the edges and overlaps of adjacent cameras and sensors enables it to capture defects in extremely wide webs. The system's accuracy relies on the company's pipelined image processing technology, supported by illumination from a fiber optic line array produced by StockerYale Inc. in Salem, N.H.
The arrays have been part of the system since its commercialization in 1996. They were selected because their cost fit Datacube's budget constraints, but their uniform, structured illumination also enabled the Black Widow system to detect smaller flaws, such as holes and pits, across wider surfaces.
Optical fibers deliver high-intensity halogen light along the length of a rod lens in this fiber optic line array. The uniform, structured light makes it the light source of choice for one integrator of high-end web inspection systems. Courtesy of StockerYale Inc.
More than 600,000 50-µm-diameter optical fibers are fanned along the 112-in. length of the array. The fibers each have a 0.66 numerical aperture and deliver light from four halogen bulbs at either end. A rod lens focuses the light into a line roughly 0.25 in. wide. StockerYale can customize the rod lens to vary both its length and the width of its focus.
This type of array can also use LEDs, but these light sources don't deliver the same intensity as halogen. The added intensity not only highlights smaller details in a web, but also allows the line-scan cameras used by Datacube to integrate light more quickly, enabling them to inspect faster-moving webs.
Illumination can make or break web inspection systems, which meld images from multiple cameras. The fiber arrays' uniform illumination ensures that defects detected by the camera are in fact defects, and not variations in one or more light sources.
"You have to do an awful lot of things to compensate for poor illumination," said Larry Taitelbaum, director of Datacube's business development. "That makes illumination the easiest thing to fix or replace." He also noted that loyalty plays a role in an integrator's selection of components. Datacube continues to integrate StockerYale's arrays in each new generation of the Black Widow because it has met the integrator's cost and performance windows.
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