182050 User manual - 第68页
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Video Model The video model is an alternative to using fiducials for board alignment. Video
model uses the correlation between the image of an area of the stencil and the
image of the same area of the board to align the two. This is useful if the board
has no fiducials or the condition of the fiducials does not allow satisfactory
recognition (see optimizing a video model).
Image Quality The vision system is able to accept a wide variation of quality of fiducial,
therefore any variation in lighting normally causes no problems with fiducial
recognition. However the image quality can be optimized by ensuring the
lighting levels are correct. Changing the intensity of the vision illumination is
achieved by the adjustment of the software controlled lighting during Fiducial
setup.
X Y Reference
Video Model Fiducial
Mono Monitor Fiducial Box
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Histogram The histogram gives a graphical representation of the grey scale values within
the box set around the fiducial. As can be seen there are two peaks which
represent the light and dark areas of the picture. Ideally there should be two
distinct peaks, the separation of which can be changed by varying the lighting
levels.
Experience of changing these parameters, while viewing the histogram, dem-
onstrates their effects.
Optimizing a Video
Model
When using a Video Model, selection of a good image shape is critical. The
following are some basic guidelines for selection of an optimum image.
Fine and Course
Features
As with fiducials, areas of a board selected as a Video Model should have
shapes with a solid consistent tone within the boundaries (course features) and
not shapes with inner lines or lettering (fine features).
Black
% Area
Within Box
Mid Grey White
Model with Fine Features Model with Course Features
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Positional
Information
When selecting a Video Model, if the image shapes have edges all in the X
direction or all in the Y direction, not enough positional information exists for the
camera system. An image with good X and Y information is necessary for
accurate positioning:
Preparing the
Vision System
The vision system learns the fiducial during a board setup. The fiducial
coordinates are entered into the product file during the editing of a default file.
This enables the camera to find the fiducials initially. The setup needs to be run
in step mode from the status page.
The following procedure is typical for all fiducial shapes, although in this
instance a circle fiducial shape is referred to throughout.
1. Select Mode (F1) until Step is indicated in the mode option on the screen.
2. Select Exit (F8).
3. Place the board onto the rails.
No Positional information
in the X direction
No positional information
in the Y direction
Equal positional information
in the X and Y directions.
Video Model
The procedure for creating a Video Model is very similar to that for creating a
Fiducial, throughout the following fiducial procedure, boxes like this contain
alternative procedure steps, to allow the setup of a Video Model.
Mode
Load
Data
Edit
Data
Setup
Squeegee
Change
Screen
Change
Tooling
Change
Language
Exit
Mode
Load
Data
Edit
Data
Setup
Squeegee
Change
Screen
Change
Tooling
Change
Language
Exit