Process control

Many quality control problems are multivariate in nature since multiple process or product variables are measured and monitored in modern industry. Occasionally a multiple population, multi-variable scenario is encountered in parallel line manufacturing system. This work deals with the analysis of such system using multivariate techniques such as Canonical Analysis, MANOVA and Mahalanobis Distance. Using such techniques, the significant differences between the populations and the magnitude and directions of the variations within and between the populations were determined. Also, elimination/reduction of such variations using multivariate techniques led to a drastic improvement of the production system. A methodology for application of such multivariate techniques for the purpose of quality assurance and improvement was developed here. The application of this methodology was performed on a pager production line and the results obtained show the benefits and the feasibility of the use of multivariate techniques for on-line monitoring and quality control.

In certain applications, one needs to control physical plants that operate in hazardous conditions. In such situations, it is necessary to acquire access to the controller from a different (remote) location through data communication networks, in order to interconnect the remote location and the controller. The use of such network linking between the plant and the controller may introduce network delays, which would affect adversely the performance of the process control. The main theoretical contribution of this thesis is to answer the following question: How large can a network delay be tolerated such that the delayed closed-loop system is locally asymptotically stable? An explicit time-independent bound for the delay is derived. In addition, various practical realizations for the remote control tasks are presented, utilizing a set of predefined classes for serial communication, data-acquisition modules and stream-based sockets. Due to the presence of a network, implementing an efficient control scheme is a not trivial problem. Hence, two practical frameworks for Internet-based control are illustrated in this thesis. Related implementation issues are addressed in detail. Examples and case studies are provided to demonstrate the effectiveness of the proposal approach.