As product and manufacturing specifications tighten, imaging for industrial quality control (QC) faces challenges. For one thing, the tolerances that parts
must be inspected to are more exacting. For another,
specifications for layer composition, subsurface features,
surface roughness and other characteristics also are more
stringent. At the same time, required throughput often is
Industry experts are turning to optical engineering as
well as employing silicon advances and new architectures that boost performance to meet these challenges.
They also are exploiting new wavelengths and other
properties of light to reveal what before was difficult or
impossible to see.
In Laval, Quebec, Canada, Synergx Technologies Inc.
is using a combination of techniques to produce automated optical inspection equipment for the glass industry. In the case of the tens of millions of car windshields manufactured annually, the goal is to catch chips,
scratches, bubbles and other defects that measure less
than 300 microns, with complete inspection of an entire
glass surface taking less than two seconds.
“We have a proprietary optical element, lighting sys-
tem and algorithm to combine multiple levels of focus
range images into a full 100- or 200-millimeter-deep
single focused image,” said Stéphane Baldo, chief tech-
nology officer. Because windshields are becoming cur-
vier, he added, the company will soon have to increase
its imaging depth of field to 300 mm, without sacrificing
cycle time or defect-detection capabilities.
Synergx uses cameras from Teledyne Dalsa Inc. The
company, which is based in Waterloo, Ontario, Canada,
provides products to many QC imaging systems and is a
leading supplier to producers of inspection systems for
flat panel displays, said Xing-Fei He, senior product manager.
The shrinking dimensions of display components
means that critical defects are also getting smaller and
harder to spot, said He. Widely available commercial
high-resolution displays have a pixel size of 60 to 80
microns, with each of these composed of three primary
color subpixels. An inspection system must catch defects
that are significantly smaller than the size of pixels.
Traditionally, detection via imaging has been based on
intensity, said He. A more sophisticated and alternative
approach is detection by wavelength. This works for defects that interact more strongly with specific colors such
as red, green, blue or perhaps the near-infrared. Shorter
wavelengths, for example, may reveal details about the
Getting the Picture on Quality Control
BY HANK HOGAN, CONTRIBUTING EDITOR
The shrinking dimensions of display components means that critical defects
are also getting smaller and harder to spot.
Imaging colorimeters measure light and color to evaluate the quality of illuminated displays in-line. Using high-resolution CCDs, these imaging systems capture an entire display in
a single image and quickly apply software tools to enable real-time QC during production.