Horizon UserManualV6.pdf - 第89页
Fiducial Parameters There are a number of parameter values which need to be adjusted when setting up a fiducial. Fiducial Type This refers to the shape and dimensions of the fiducial. Background The vision system needs t…
STAGE 6
Vision System Setup
Introduction
The printer uses a vision system to carry out the following:
•
Stencil/Board Alignment
•
2Di Inspection (optional)
•
Board Identification - Selective Print/Pass Through (optional)
After the board is fed to the board stop position, the camera moves into position
to view the relative board and screen features. The information from these
camera images is used by the vision system to identify the board, if selective
print/pass through is enabled and to calculate the screen correction needed to
align the screen to the board. The camera and vision system is also used for 2Di
inspection, if enabled, for further information refer to the 2Di chapter in this
manual.
Fiducials A fiducial is an alignment mark which is produced as a part of the artwork of the
board and the screen. There are normally several of these marks on each board,
some of which are used for board alignment and some for alignment when
placing components on the board. These marks, therefore, should be in the same
relative position on both board and screen.
The vision system has a library of synthetic fiducials of the most commonly
found shapes. The dimensions of these fiducials can be tailored by the operator
to fit the fiducials on the board and screen. After the vision system has been
taught these fiducial parameters, it is able to search the field of view of the
camera and recognize any features which resemble these fiducials. The centre of
the fiducial is calculated and used as the point of location.
The vision system conducts a search in the field of view of the camera looking
for any shape that resembles the programmed fiducial. After finding a shape it is
assigned a score comparing its shape and size to the shape and size of the fiducial
in the vision system memory. This score is set between 1 and 999, the better the
fit the higher the score.
NOTE
However, this does not mean that a fiducial score of 900 for example aligns more
accurately than a fiducial score of 700 for example.
This score is used, in conjunction with acceptance parameters set by the
operator, to recognize the fiducial. The available fiducial shapes are:
•
Circle
•
Rectangle
•
Diamond
•
Triangle
•
Double Square
•
Cross
1.72 User Manual Software Version 6
MACHINE PROGRAMMING
STAGE 6
CIRCLE CROSS DIAMOND TRIANGLE RECTANGLE DOUBLE SQUARE
Fiducial Parameters There are a number of parameter values which need to be adjusted when setting
up a fiducial.
Fiducial Type This refers to the shape and dimensions of the fiducial.
Background The vision system needs to know if the fiducial is surrounded by a dark or light
background compared to the fiducial colour.
Acceptance Score After the vision system has located a screen or board fiducial, it assigns a level of
match of that fiducial compared to the fiducial strategy set in the vision system.
This is given a score, the better the match the higher the score. The acceptance
score is the minimum level, set by the operator, above which the vision system
accepts the recognition of the fiducial.
Minimum 0
Maximum 999
Increment 10
Default 700
There are various dimensions of each fiducial shape which have to be set by the
operator. As an example, here, the circular fiducial is described.
Fiducial Diameter This needs to be set to the exact diameter of the fiducial to achieve a satisfactory
score.
Inner and Outer
Contours
These are set to eliminate any defects that may occur in the surface of either the
fiducial or the background. The vision system ignores anything inside the inner
contour and outside the outer contour. Increasing the distance between the inner
and outer contour can, if the fiducial and background surfaces are variable,
drastically affect the score level.
Select Mark A select mark is an identification mark, placed only on the board, to differentiate
between boards to be printed and boards to be passed through the printer without
printing. A select mark has the same properties and parameters as a fiducial, as
described above. A select mark is only used with the selective print/pass through
option, where different product boards are fed through the printer.
Software Version 6 User Manual 1.73
MACHINE PROGRAMMING
STAGE 6
GEOMETRIC CENTRE
(USED AS LOCATION POINT)
FIDUCIAL DIAMETER
INNER CONTOUR
OUTER CONTOUR
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 screen 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.
1.74 User Manual Software Version 6
MACHINE PROGRAMMING
STAGE 6
Mono Monitor
X Y Reference
Fiducial Box
Video Model Fiducial