Tablets are the most common pharmaceutical dosage form of today. Their advantages are simplicity, low production and packaging cost and their relative stability. Tablets with less than three millimeters of diameter are called minitablets. The production of tablets and minitablets involves a series of sequential process steps during which the incoming raw materials in form of powders are formulated into a final dosage form. Tablets and minitablets are nowadays often film coated.
The thickness and the uniformity of the film coating represent an important quality attribute of the coating. Its suitability is particularly important in cases where the coating serves to achieve the modified release of the active ingredient. Despite this, the appropriate final thickness of the coating is still mostly ensured empirically and on the basis of unreliable theoretical calculations, while the success of the coating processes often depends on the competence and experience of the operator managing the process.
Different approaches for in-line and on-line film coating thickness estimation have been proposed in the past by the U.S. Food and Drug Administration through the good manufacturing practices guidelines, what encouraged the pharmaceutical industry to develop and use new techniques for in-line and on-line measurement of the critical process parameters and properties of the incoming raw materials. The proposed approaches rely on different technologies, which are either limited to specific types and minimum and maximum coating thicknesses or require the construction of complex calibration models.
Machine vision can be defined as a field focused on the realization of computer vision systems intended to be used in industrial environments, often for the purpose of automated visual inspection. We believe that despite its rare up-to-date use for such purposes, machine vision represents a promising approach for in-line and on-line monitoring of coating processes that can overcome all the shortcomings of techniques proposed in the past.
The contributions of this dissertation therefore combine the development and the evaluation of machine vision systems and approaches for in-line and on-line monitoring of pharmaceutical tablets and minitablets film coating processes. The work focuses on the estimation of the coating thickness, which as such can represent a critical quality parameter for coated tablets and minitablets. The contributions are briefly presented below.
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