Integrated Product and Process Control of Single-Input-Single-Output Systems

In many chemical and allied manufacturing systems, product quality is controlled based on postprocess quality inspection on sampled final products. Statistical analysis of the identified quality problems is then utilized to improve process operation, and thus the quality of succeeding products. Although this type of reactive quality control (QC) is necessary, it is not only inefficient because it ‘‘waits for’’ the occurrence of product quality problems, but also ineffective due to usually a significant time lag from problem identification, through solution derivation, to action taking. Furthermore, the derived solutions for problem solving are mostly heuristic in nature. This paper introduces a proactive product QC approach, which is established based on the concept of integrated product and process (IPP) control. Aiming at simultaneous dynamic control of process operation and product manufacturing, this approach ensures all-time systematic control of both process performance and product quality. From the view point of both process control and product control, it is shown that IPP control can be realized by resorting to a well known scheme, cascade control. The IPP control problem for Single-Input-Single-Output systems can be formulated rigorously, and the control laws can be identified readily. A synthesized IPP control system can effectively reject disturbances on the process and the product, and have excellent set-point tracking capability, regardless of the type of interaction between the process and the product. The efficacy and attractiveness of the IPP control system design methodology are demonstrated through two types of case studies. 2007 American Institute of Chemical Engineers AIChE J, 53: 891–901, 2007