a) Pattern is set to Lt-Dk (Light-Dark) because the metallized area to the left of the edge is
lighter than the yellow stripe to the right of it.
b) Scan Directio
n is set to L-to-R (Left-to-Right) so that the sensor will evaluate objects in its
field of view beginning with those on the far left. As it scans from left to right, the first
edge it encounters that satisfies the Min/Max width rules (described in the next step) will
be the left edge of the yellow stripe – the edge we want to track.
c) Min Left and
Min Right are both set to 53. Min Left defines the minimum width of the
metallized area to the left of the edge and Min Right defines the minimum width of the
yellow stripe to the right of the edge. To accommodate some variation in these widths
they are both set approximately 12.5% smaller than their nominal widths.
Note: Refer t
o page 70 for more information about the Min/Max parameters.
Note: The
settings for the Min/Max parameters range from 0 to 255 and are scaled in
units of “half-pixels”, or 0.0024” [0.062mm].
d) Max Left a
nd Max Right are both set to 255. These parameters define the maximum
widths of the Left and Right areas described in the previous step. Setting them to 255
removes any restriction on the maximum width of these areas, so either one could extend
beyond the edge of the sensor’s field of view.
e) Max Cente
r and Min Center are set to their default values of 255 and 0, respectively.
These parameters are not used for edge tracking.
f) LED Col
or is set to Blue. Auto-calibration will select the lighting color that produces the
greatest contrast between the registration edge and background. For yellow markings
(like those in this example) blue typically produces a significantly greater contrast than
other lighting colors.
g) LED An
gle is set to Reflective. This lighting angle provides the best contrast between the
registration line and background on highly reflective or mirror-like materials like the one
used in this example.
h) Filter i
s set to 16. This parameter helps the sensor ignore scratches, smudges, and other
stray marks by deliberately blurring the image. Higher settings create more blurring, so
the auto-calibration routine will select the highest setting that blurs the edge of the
registration stripe without totally obscuring it. Generally, higher settings will be selected
only for wider registration stripes.
i) Thre
shold is set to 12 - a value that is approximately 50% of the contrast value of the
registration line’s edges. This will filter out other edges in the sensor’s field of view that
fall below this value.
AccuBeam 3 Digital Line Guide Sensor
69
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