Acceptance criteria for Automatic Visual Inspection: Everything you need to know about the Knapp Test
Visual inspection of pharmaceutical packaging integrity should always comply with international standards, such as USP <1790>, to ensure the quality of the packaged product.
Visual inspection is a non-destructive test method that facilitates the inspection of 100% of products ready for sale. It is particularly effective at identifying items with characteristics that do not conform to standards while also reducing the number of false rejects.
This test method detects various types of defects by analyzing a series of images of the product, either stationary or in motion, captured by high-definition cameras. These images must then be reviewed and evaluated by a trained operator or a properly programmed machine to identify non-conforming products and remove them from the production line.
For a long time, human operators were indispensable in this type of assessment. However, in recent years, technological advancements have introduced solutions that automate and accelerate the process without compromising accuracy. To replace human inspections with automated systems, it is essential to demonstrate that the machine can deliver equal or superior results compared to human operators. To achieve this, the instrument undergoes a specialized evaluation known as the Knapp Test, which objectively measures its performance quality.
The Knapp Test for Automatic Visual Inspection Operators and Machines
The Knapp Test is a protocol approved by international regulations to evaluate the effectiveness of instruments used for visual inspections. In this test, a set of samples is inspected by both qualified human operators and the machine. The results are then compared to determine whether the machine performs better than or at least as well as the operators, enabling its validation.
It’s important to note that the Knapp Test compares the machine’s performance to that of operators who themselves had to pass the Knapp Test to earn the qualification of “inspector.” According to USP standard <1790>, operators must correctly identify a certain percentage of defective products while generating a limited number of false rejects to qualify for performing manual visual inspections. To achieve qualification, the operator undergoes three tests on three different sample sets, achieving the required performance in each round. Operator qualification is valid for one year, after which the operator must retake the Knapp Test. Additionally, qualification is specific to a product category—for instance, qualification for inspecting transparent liquids differs from that for gels or suspensions. Operators inspecting multiple product types must obtain the relevant qualifications for each.
Characteristics of the Knapp Test
The Knapp Test for Automatic Visual Inspection machines compares the machine’s performance to that of several qualified operators. To ensure realistic and comparable results, the standards specify the test procedures, sample characteristics, environment for photo capture, and more.
The samples used in the test must closely resemble the products the machine will analyze in terms of shape, color, size, and internal product characteristics. These samples must also include a predefined set of defects selected from a repertoire of common and uncommon faults. Defects may include the presence of foreign particles inside the container, cosmetic flaws such as cracks or inclusions in the packaging, inadequate fill levels, or changes in the product’s color.
Additionally, the time allocated for inspection and the handling of products must be comparable to ensure a realistic performance comparison between the machine and human operators.
Results and Applications of the Knapp Test
This type of testing is essential for ensuring compliance with international regulations and safeguarding consumer safety. Furthermore, it enables pharmaceutical companies to adopt increasingly advanced Automatic Visual Inspection technology.
By analyzing the Knapp Test results, companies can identify defect types that human operators detect more effectively than machines and take steps to enhance the machine’s performance in those specific areas.
In its commitment to collaboration and continuous improvement, Bonfiglioli Engineering not only provides Automatic Visual Inspection machines but also offers technical assistance with Knapp Tests. This includes support in producing sample sets for testing, conducting the test itself, and evaluating the results.
What Are the Acceptance Criteria for Vision Inspection Technology?
In the video below, Davide Luisari, Design Manager at Bonfiglioli Engineering, addresses this question.
Citations
This article is inspired by information from Bonfiglioli Engineering.
- Bonfiglioli Engineering. “Acceptance criteria for Automatic Visual Inspection: Everything you need to know about the Knapp Test” – Bonfiglioli Engineering, BONFIGLIOLI ENGINEERING S.r.l