User guide

7-8 Programming Basics
Table 7 -1 Fiducial Ratings
Shape Characteristics
£ donut Excellent. Immune to rotation. Inner and outer diameters allow for further
definition.
# pound Good. Uniqueness maintained under rotations.
l circle Good. Immune to rotations.
m hole/gap Poor. Requires machining accuracy to match definition. Not repeatable
between different workpieces.
: cross Poor. Single axis identification does not allow for poor quality printing of the
shape.
Uniqueness: While a fiducial must be a unique feature on the workpiece, the fiducial must
appear the same on all similar workpieces. The fiducial includes the feature and the
background. This means that the same shape on two workpieces with different backgrounds
will not be identified as the same. See Figure 7 -3 for examples of good fiducials.
The uniqueness of a fiducial is often defined by its proximity to other elements on the
workpiece. A circle might be a repeated pattern on a workpiece, but a circle next to
rectangle might be unique to the location you are trying to define. This type of identification is
more common when defining nested pattern fiducials, rather than workpiece alignment
fiducials.
Contrast: The ability to enhance the contrast of the fiducial to the background can be
optimized by Vision System parameters. However, you should choose a fiducial that has good
natural contrast from the background.
While the selection of a fiducial is unique to a workpiece, the following figures show good
fiducials as far shape, background, size and contrast.