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Computer-aided 3D tolerance analysis of disk drives

Disk drives are multicomponent products in which product build variations directly affect quality. Dimensional management, an engineering methodology combined with software tools, was implemented in disk drive development engineering at IBM in San Jose to predict and optimize critical parameters in disk drives. It applies statistical simulation techniques to predict the amount of variation that can occur in the disk drive due to the specified design tolerances, fixturing tolerances, and assembly variations. This paper presents statistics describing the measurement values produced during simulations, a histogram showing the measurement values graphically, and an analysis of the process capability, C pk , to ensure robust designs. Additionally, it describes how modeling can determine the location(s) of the predicted variation, the contributing factors, and their percent of contribution. Although a complete 2.5-in. disk drive was modeled and all critical variations such as suspension-to-disk gaps, disk-stack envelope, and merge clearances were analyzed, this paper presents for illustration only one critical disk real estate parameter. The example shows the capability of this methodology. VSA®-3D software by Variation Systems Analysis was used.