Question 1:
What is the advantage of running a vision inspection system on a press over using it on an inspection rewinder?
Answer to question 1:
Most of the waste is produced during printing. Installing a vision inspection system on the press can therefore greatly reduce the waste if used properly. In general, a vision inspection system on the press will influence process control as it will have a direct impact on the production. Installing the vision inspection system on the inspection rewinder, however, will have an impact on quality assurance as you are in control of the outgoing quality of your product.
This is what theories tell us so far. In practice, the printing press is a much better place to install a vision inspection system. The web is much more stable and the press does not start and stop all the time. This intermittent operation is what makes using an inspection system on the rewinder so difficult. Web stretch effects force us to set the inspection tolerances very loose, thus making the system very insensitive. Catching a defect in a text area with types smaller than 10 pt will therefore be a random event.
What can we conclude from this? It is possible to run a vision system on a press using much tighter tolerances. This system will therefore be able to find very small defects. But how can these defects be prevented from going into the finished roll? A roll map feature creates a database of all roll defects (we call this a virtual roll) and is then used to control the rewinder. Only this concept results in significant waste reduction, while eliminating all defects during the finishing process.
A word on FDA requirements: The existing rules require 100% print inspection on the inspection rewinder in order to eliminate manual inspection. Due to the above mentioned problems we believe that such systems should be validated very carefully. The critical question to ask is: "How many defects went into the finished roll" which cannot be answered immediately. Instead operators proudly show what their inspection system found...
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