Rockwell Automation 5370-CVIM2 Module - Manual (Page 285)

5 Chapter Chapter 7
Inspection Tools
7–47
Circularity –– Circularity is a measure of how close the basic shape of an
object is to being a perfect circle, and it is expressed in percentages, with 100
percent being a theoretically perfect circle. Circularity measurement is
especially useful when the perimeter of an otherwise circular object is fuzzy
or convoluted. The formula that the CVIM2 system uses to calculate
circularity in percent is . . .
. . . where A is the area value and I is the inertia value.
For example, in Figure 7.41, the two shapes are both basically circular and
have similar areas (12,377.0 for the circle vs 12,330.0 for the “flower”
shape). The circle has a regular, smooth perimeter, which results in a
roundness of 96.2%, while the flower shape has a convoluted perimeter, and
therefore has a roundness of only 67.8%. Note, however, that the circle has a
circularity of 100.0%, and the flower has a circularity of 98.4%. This
indicates the ability of the circularity measurement function to ignore the
effects of a convoluted edge.
Figure 7.41 Example: Comparing Circularity to Roundness
ǒ
A 2
2
p I
Ǔ
x 100