Laser scanning and camera-based automatic inspection systems were developed to
deliver 100%, on-line, real-time, defect detection for a wide range of
materials. Inspection systems must perform better than the best
inspector, and must do so on-line, consistently and reliably, without
false hits. Successful application of the technology requires
a firm understanding of the nature of the optical challenge and selection of
the correct optical solution.
Get the Optics Right!
An automatic inspection system displaces or augments human inspection. The two
inspection processes are very similar. A survey of manual inspection
techniques, utilized in display, coated/metallized/base film, glass,
photosensitive media, paper, storage media and metals revealed a common manual
inspection algorithm, below:
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1.The product and defects are
illuminated. Companies expend
considerable effort to define a
light source, which will interact
with the defect to make the
defect “stand out” against the
substrate. The universal goal is
to provide a light source, which
is safe for human use, which
allows an inspector to detect the
visual defects, while acceptable
product can be easily ignored.
However, as human eyes can
tolerate only very limited lighting
conditions (wavelength and
intensity), these systems are
usually sub-optimal.
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2.The trained inspector focuses on the visual anomalies, highlighted by the
light source,
ignoring the balance of the product; 99.9999% of the product is not inspected.
Defects
are sized and classified based upon agreed specifications.
Automating this inspection task requires a
fundamental understanding of the optics of defect detection, for a given
application. The algorithms for human and machine inspection are very
similar, with one notable exception. The
light source, which can be employed in an automatic inspection system, does
not have to be viewed by a human. This means that the best light source
can be employed; the constraint of “human-safe” can be removed.
Rule #1, for both manual and machine inspection, is simply, “Get the optics right!”
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