(143c) Integrated Product and Process Control of Multi-Input-Multi-Output Systems

Product quality control (QC) has been commonly practiced through post-process quality inspection in many manufacturing systems. Statistical analysis of the identified quality problems is then utilized to adjust process operation, so that the quality problems can be prevented from further appearance. This type of reactive quality control (QC) is necessary, but 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, during which the quality problems will continuously occur in manufacturing. Furthermore, the derived solutions for problem solving are mostly heuristic in nature.

This paper introduces a proactive product QC approach, which is 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 control of both process performance and product quality. IPP control is realized by resorting to a classical control scheme, cascade control. With this scheme, the IPP control problem for Multiple-Input-Multiple-Output (MIMO) systems is formulated rigorously, which is the extension of the author's early work for IPP control for Single-Input-Single-Output (SISO) systems (Xiao et al., 2007). The control system is synthesized to meet the preset targets of process performance and product quality. To demonstrate the efficacy and attractiveness of the IPP control design methodology, two practical case studies are illustrated. The first is the control of both the coating quality and process performance of an automotive polymeric coating curing system, and the second investigates the workpiece cleaning and rinsing quality as well as operational performance in an electroplating system. It is shown that closed-loop process control alone is not sufficient at all for product quality assurance. It is found that even if process dynamic performance is satisfactory, product quality may still have even a serious problem when the system experiences different disturbances. By contrast, the synthesized IPP control system can effectively reject a variety of disturbances on the process and the product, and achieve superior set-point tracking capability.