Answers to frequently asked questions ...
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How do vision systems work?
Vision systems grab
images of each produce to be inspected using electronic cameras. The images
are temporarily stored on the vision system and processed to inspect the
particular features specified for each application. The results of the
inspection are used to automatically decide if the product is good or
bad. The vision system provides outputs to drive reject mechanisms and
quality alarms. Hint: Systems
with everything built into a robust industrial housing are more suitable
for the industrial environment that PC based vision systems.
Do vision systems compare
is not a good technique. It tends to highlight natural variations in the
product rather than the faults that the system should be looking for.
The most common approach is to inspect particular areas of each image
for the specific features that have been specified as being critical to
the quality of the product. Each image is inspected from first principles.
A good part is usually used as a reference for initially setting up the
system. Hint: Try out the vision system with
a range of good and bad products before purchasing.
Can vision systems inspect
Vision systems are
now used throughout manufacturing industry. It is almost inevitable, that
someone, somewhere, is already using vision to inspect products like yours.
Hint: Ask your vision supplier about solutions they have supplied for
What is the most important
Get the lighting right
and your installation will be effective and reliable. Click on "Lighting"
and "More lighting" to find out more.
Hint: Make sure the operation of the vision system is not affected by
small changes in lighting levels and by the effects of variations in ambient
How fast will it go?
As vision systems become
ever more powerful, speed is becoming less and less of an issue. Systems
are readily available that will inspect up to 50 products per second.
Very few production lines run faster than this.
Hint: Make sure the system you are purchasing has some spare capacity,
it is almost inevitable that you will want to do some extra inspections
in the future.
How accurately can the vision
Vision systems tend
to be used more for feature checking than high accuracy measurement. For
very high accuracy, vision may not be the most appropriate technology
to use. As a general rule, most systems can measure about 1 part in 250-500
of the field of view of the camera. As the field of view of the camera
is reduced, so the accuracy goes up. To measure a large object accurately
it may be necessary to use a number of cameras, or take a number of views
with a single camera. Hint:For
measurement applications, check the repeatability of the vision system
What is meant by sub-pixel
Some image processing
can produce results that are calculated to a theoretical accuracy that
is greater than the size of individual pixels in the image. Great care
should be taken to ensure the validity of such measurements.
Hint: Small variations in lighting may make the apparent size of an object
change. That change may not be detected by sub-pixel resolution of the
What is the
smallest defect that can be detected?
By selecting the correct
lens the vision system can be set up to have the magnification required
to detect virtually any defect however small. As the magnification increases,
the field of view of the camera reduces.
Hint: Make sure the smallest defect can be found
everywhere within the field of view.
How do I calibrate the vision
be simple. You replace the product you are looking at with a ruler, measure
the field of view and enter the result into the vision system.
Hint: Check that the vision system presents all measurements in real dimensional
units rather than pixels.
Does it matter if the products
No it doesn't. Modern
cameras have special electronic shuttering that means clear images of
fast moving products can be captured without strobe lighting being required.
Hint: Strobe lighting systems often need extensive
screening to prevent adverse health effects on people working in the area.
Can I inspect colored products?
The vast majority of
vision applications do not require color processing. Most vision applications
inspect monochrome, grey-level images of the products to be inspected.
In some instances color vision systems can be very useful, such as when
features in an image can only be isolated on the basis of their color
Hint: It is common for monochrome systems to be used for color inspection,
with colored lighting or colored filters being used to increase the contrast
between different colors.
Would you like
further information? Then
Last Updated February 2002
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