Most engineers in the medical device industry are familiar with process capability measurement terms Cp, Cpk, Pp, and Ppk. A small subset of us uses these metrics to generate process validation reports claiming to meet our customers’ capability requirements.
But how many OEMs and suppliers have gone to the next level by providing the empirical evidence necessary to prove that the measured data and calculated capability index is trustworthy? Why aren't we equally as familiar with terms like “percent study variation,” and “precision to tolerance?”
Medical device suppliers and OEMs alike will benefit by discovering one of the lesser-known keys to world-class manufacturing: measurement systems analysis (MSA). This article starts by presenting a basic understanding of histograms and capability metrics (see Figure), and then discusses the benefits of MSA. It uses a hypothetical process and measurement system to help explain the concepts.
By definition, a Measurement System is the collection of instruments or gauges, standards, operations, methods, fixtures, software, personnel, environment, and assumptions used to quantify a unit of measure. In other words, it’s the complete process used to obtain measurements. In theory, a perfect measurement system will give you the same answer for repeated measurements. However, measurement systems in the real world seldom act like that due to the abundance of variables involved.
Note that MSA ties to FDA regulations. If your company produces medical devices that require FDA approval via the 510(k) application, then your company and its suppliers are subject to the FDA Quality System Regulation and must comply with the 21st volume of the Code of Federal Regulations (CFR) Part 820 of US federal law, also referred to as the FDA GMP or Good Manufacturing Practice. This law states, “The QS regulation requires you to validate processes whenever the results of a process cannot be fully verified by subsequent inspection and test methods.” This is the technical definition of a “special process.”
To read the article, which originally appeared in Medical Electronics Design, click here.
About the author
John Rokusis the vice-president of continuous improvement at Micro Power Electronics, responsible for training and coaching Micro Power employees in lean deployment, and applying Six Sigma problem-solving methodologies. He is accredited by the American Society for Quality as a certified Six Sigma Black Belt. Rokus earned his BS degree in Industrial/Manufacturing Engineering from Oregon State University.