Vision Systems Engineering Ltd.
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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 images?
Comparison 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 my products?
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 similar applications.

What is the most important aspect?
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 lighting.

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 system measure?
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 before purchasing.

What is meant by sub-pixel measurement?
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 vision system.

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 system?
Calibration should 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 are moving?
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.

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Last Updated February 2002

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