Visual Inspection of pharmaceutical packaging integrity should always comply with international standards, such as USP <1790>, in order to guarantee the quality of the packaged product.

Visual Inspection is a non-destructive test method that makes it easy to check 100% of products ready to be sold, and is particularly effective in identifying items having characteristics that do not conform to standards, while also reducing the number of false rejects

This test method identifies many types of defects by examining a series of images of the product while stationary or in motion that are collected from high-definition cameras. To do this, the images collected from the cameras must be viewed and evaluated by a trained operator or by a properly programmed machine to detect non-conforming products and remove them from the production line.

For a long time, human operators were irreplaceable in this type of assessment. However, in recent years, technological solutions have been developed that automate and speed up the process without affecting its accuracy. However, to replace human inspections with automatic inspections, it is necessary to demonstrate the machine’s ability to produce better—or at least the same—results as humans. So, the instrument undergoes a special test called the Knapp Test, which objectively assesses the quality of its performance.


The Knapp Test for Automatic Visual Inspection operators and machines

The Knapp Test is one of the protocols approved by international regulations to assess the effectiveness of an instrument in performing visual inspections. In this type of test, a set of samples is inspected by both qualified human operators and the machine. Then, the results are compared to determine whether the machine performed better than, or at least as well as, the operators, and therefore whether it can be validated.

It is important to remember that the Knapp test compares the performance of the machine to that of operators who had to pass the Knapp Test themselves to receive the qualification of “inspector”. USP standard <1790> requires operators to be able to correctly identify a certain percentage of defective products and generate a limited number of false rejects to be considered able to manually perform Visual Inspection. To be qualified, the operator performs three tests on three different sets of samples, and must achieve the expected performance in every round of testing. Operator qualification is valid for one year, after which the operator takes the Knapp Test again. Qualification is also valid only for a specific category of products. This means that qualification for inspection of transparent liquids is different from gels or suspensions, and an operator inspecting different types of products must obtain all the specific qualifications.


Characteristics of the Knapp Test

So, the Knapp Test for Automatic Visual Inspection machines compares the machine’s performance with that of several qualified operators. And, to obtain as realistic and comparable results as possible, the standards also establish precisely how the tests are to be performed, the characteristics of the samples, the environment in which the photos are to be taken, etc. 

The samples used for the test must be as similar as possible in terms of shape, colour, size, and characteristics of the internal product to those that will be analysed by the machine, and they must have a specific set of defects chosen from a repertoire of both common and less common faults. These include the presence of foreign bodies or particulate matter inside the container, cosmetic defects such as cracks or inclusions in the packaging, inadequate fill level or change in the sample’s colour.

The time assigned to the inspection and the way in which the products are handled must also be comparable, so that the performance of the machine and the human operator can be compared realistically.


Results and applications of the Knapp Test

This type of testing is essential to ensure product compliance with international regulations and to guarantee consumer safety. However, it also allows pharmaceutical companies to equip themselves with increasingly technologically advanced Automatic Visual Inspection machines.

By assessing the results of the Knapp test, it is possible to identify the types of defects that human operators identify better than the machine and take appropriate steps to improve the machine’s performance in the specific areas where it is most lacking.

That is why, in its commitment to collaboration and continuous improvement, Bonfiglioli Engineering provides not only Automatic Visual Inspection machines, but also technical assistance in conducting Knapp Tests, providing its customers support in producing the sets of samples to be tested, in the actual testing phase and in evaluating the results.


To learn more about our inspection solutions and how they can benefit your processes, contact us today

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