User Manual

Programming Basics 7-7
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.
❍
❍❍
❍ 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 dependent on the workpiece, the following figures show
good fiducials as far shape, background, size and contrast.