Question 5:
Some people say that using a line scan cameras is less robust than using an area scan camera. Is this true?
Answer to question 5:
In fact an inspection system that utilizes line scan cameras is more complicated to develop as the technology is more complex and it is harder to obtain images. Nevertheless, once the system is developed it offers even a higher degree of simplicity to the user. Why is this:
The line scan system generates its image from scanning a line across the web as the web moves by. The web can therefore easily be stabilized by running it around an idler roll, thereby avoiding wrinkles or loose areas.
The systems resolution is optimally adapted to the system’s requirements. The width of the web processing equipment is always fixed. Therefore it is simple to select a line scan camera in order to obtain the resolution required. The second dimension along the web, however, depends on the product that is run on the machine. An area scan camera is truly limited as it can only provide a fixed frame size, whereas the line scan camera as it builds-up the image in its memory is flexible in this respect.
The following two images illustrate how the two basic principles work:
All manufacturers of web inspection systems are working towards using line scan cameras or have already made this step. The most important factor that has influenced this process is that line scan cameras are available up to extremely high resolutions. Today, area cameras are limited to about 2000 pixels square while line scan cameras today can cover up to 8000 pixels (At this moment the largest line scan camera features even 12000 pixels).
But this question was also about robustness: In our experience robustness is very much related to the quality of the inspection algorithms. As the computing power has improved significantly it is now possible to provide more robust algorithms. The PixelRegistration technology from Nyquist Systems is setting new standards regarding robustness and accuracy of web inspection.
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