Instruction Manual

Programming Basics 7-5
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 the
Model Finder method, you will not perform a Manual Finder 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” below.
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. They 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 256 x 256 pixels (approx. 120 x 120 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.