User Manual

7-6 Programming Basics
Fiducial Detection
The Vision System has three tools or methods to find fiducials as described below. The
exercises that follow will teach you how to use these tools. The first exercise will use the
Model Finder method to define Workpiece fiducials. The second exercise will use the
Corner Finder method to define a pattern fiducial. Defining Workpiece and pattern fiducials
is the crucial first step to creating accurate dispensing programs.
Since the Manual Finder method is only used under special circumstances, and is taught
exactly like a Model Fiducial, you will not perform a Manual Fiducial exercise.
Model Finder
This method uses pattern recognition to find a previously defined gray-scale model, which is
the defined fiducial in the field of view. This type of detection is used with model fiducials
as described in the section “Model Fiducials”.
Corner Finder
This method uses edge detection algorithms to find the corner of a previously defined part in
the field of view.
Manual Finder
This method is used mainly on dispensing systems equipped with the AV-700 Vision
System. Manual Finder prompts the operator to manually target the fiducial location every
time a fiducial search is performed.
Model Fiducials
Fiducials can be used to define the position and orientation of the workpiece, or identify the
location of parts on a workpiece. Part of the programming process is to determine which
fiducials should be defined to achieve the accuracy and speed required for your dispensing
process. Model fiducials are usually letters, dots, or silk-screened marks on a circuit board.
Selecting Good Model Fiducials
In order to be effective indicators of workpiece location, fiducials must be unique and easily
distinguished from all other features and artifacts on the workpiece. The must also be
consistently placed in the same location from one workpiece to another. Fiducials are
selected according to shape, position and use.
Size and Shape: The shape of a fiducial determines whether the fiducial is recognizable
under translation or rotation. Fiducials should be recognizable as the same shape, even if
rotated or translated. Below in Table 7 -1 are some types of fiducials and their rating.
The maximum size of the Model Window in FmNT is 200 x 200 pixels (approx. 100 x 100
mils on the part). Fiducials must be smaller than that in order to be used, unless a portion of
the fiducial element can be used to represent the whole fiducial. Large fiducials take longer
to find. However, if the fiducial is too small, other artifacts or contamination in the Search
Window on the workpiece might be misinterpreted as a fiducial.