This study explores the traditional equipment maintain or replace decision under scenarios of increasing customer expectations, loss due to process deviation, and process drift. Customer expectations are operationalized by tighter product specifications. The Taguchi loss function is employed to estimate the loss due to target deviation. In this paper we characterize the machine drift, uncertainty about future technological change, and the learn-and-break-in process by a generalized Brownian-Motion-Ito-Process. The photolithography process is analyzed in numerous scenarios varying demand, rejection levels, and quality losses.
Marsh, Robert and Seong-Hyun Nam. "The Impact of Increasing User Expectations on Machine Replacement." IIE Transactions. 35.5 (2003): 457-466.