Rockwell Automation 5370-CBPK Color CVIM BLISTER-PAK Option - Manual (Page 25)

Chapter 5
Auto Setup
5–5
NOTE 1: Changing the minimum area tolerance value after completing the
auto setup process will have no effect on the calculated area tolerance values.
You can, however, alter the calculated area tolerance values as explained on
page 6–10 under the Area Tolerance heading.
NOTE 2: Under some circumstances, a tablet may appear larger or smaller
than it actually is. Minor variations in lighting or tablet orientation may result
in identical objects presenting larger or smaller areas of a trained color. In
rare cases, slight differences in the actual size of a tablet or capsule may be
acceptable. Most often, however, you will seek minimum area tolerance
values that minimize false rejects and, at the same time, fail blisters
containing broken or malformed objects, and pockets containing multiple
objects.
Minimum Shape Tolerance
The minimum shape tolerance parameter sets the minimum value to which
the shape tolerance will be set during the “teach–in” process, even if the
observed shape variation is less. The default value is 10%.
During inspection, the system attempts to match the camera image of objects
with the stored image of those objects. In an ideal world, every object in
every pocket of every blister would appear to have exactly the same shape.
However, in the real world of production inspection, at least some variation
in shape is almost certain to occur.
For purposes of the Color CVIM BLISTER-PAK option, the shape of a
previously learned color (along with its area and relative position) determines
the definition of a tablet or blister. Shape is determined by examining the
area of a learned color and calculating
1 its “circularity.” This is a measure of
how circular an object is, with a perfect circle having a shape of 1.0 and less
circular objects having lower circularity values.
During the auto setup process, the Color CVIM BLISTER-PAK option
accommodates shape fluctuations by evaluating the variation in the
circularity of the sample objects and, on the basis of that evaluation,
automatically calculating shape tolerance values for each blister. These are
expressed as percentages.
It is possible, however, that a very small range of circularity values may be
encountered during the carefully controlled conditions of an application
“teach-in.” This could result in calculated tolerance values that are be much
lower than the actual circularity variations expected during production
inspection operations.
1 The formula used to calculate circularity has the effect of ignoring fuzziness or convolutions in the perimeter of
an object. Instead, the calculation measures how close the basic shape of the object is to being a perfect
circle, irrespective of variations in the perimeter.