As markets reach their saturation limits for many products and as customers grow more demanding, it becomes necessary for manufacturing industries to produce customized products of high quality at lower cost and quicker pace. Modern manufacturing industries are trying to achieve these goals with the help of technologies such as flexible manufacturing systems, computer-aided manufacturing, and computer-integrated manufacturing, and with information and communication systems. As a key component of these technologies, on-line process monitoring makes it possible to build integrated, adaptive, and high-speed manufacturing systems capable of operating with minimal human supervision to produce high-quality products at reduced cost.