Profile’s memory. For the material used in this example the parameters will be set to the
following values:
a) Pattern is
set to Lt-Dk-Lt (Light-Dark-Light) because the registration line is darker than
the surrounding background.
b) Scan Directio
n is set to R-to-L (Right-to-Left) so that the sensor will evaluate objects in its
field of view beginning with those on the far right. As it scans from right to left, the first
line it encounters that satisfies the Min/Max width rules (described in the next step) will be
the narrow line closest to the right edge of the web – the line we want to track.
c) Max Cente
r is set to 12 and Min Center is set to 9. These parameters define the
maximum and minimum acceptable widths of the registration line. To accommodate
some variation in line width the Max Center value is set 12.5% larger than the nominal
width and the Min Center value is set 12.5% smaller than the nominal width.
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) Min Left and
Min Right are both set to 36. These parameters define the minimum widths
of the white areas covered by the selection window adjacent to the registration line. To
accommodate some variation in these widths they are both set 12.5% smaller than their
nominal widths.
e) Max Left a
nd Max Right are both set to 255. These parameters define the maximum
widths of the white areas adjacent to the registration line. 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.
f) LED Col
or is set to Red. Auto-calibration will select the lighting color that produces the
greatest contrast between the registration line and background. For black and white
patterns (like the one in this example) any LED color will work well, but for colored lines
and backgrounds there will often be one particular LED color that produces a significantly
greater contrast.
g) LED Angl
e is set to Diffuse. This lighting angle provides the best contrast between the
registration line and background on dull, non-glossy materials like the one used in this
example. To track a dark line printed on metallized film or to track the edge of glossy film
material, the best angle would be Reflective. For certain holographic materials the Side
setting may work best.
h) Filter is
set to 4. 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 edges of the
registration line without totally obscuring it. Generally, higher settings will be selected only
for wider registration lines.
i) Thre
shold is set to 10 - 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
67
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