Research on Work-in-Progress Control System of Integrating PI and SPC

Taking unfinished parts, that is, parts' work-in-progress (WIP), as the background, the PI control algorithm is proposed to apply for WIP control in discrete production systems and the cascade control of PI controllers is suggested. Designing of PI controllers is transformed into an optimization problem on the frequency domain, so as to guarantee the stability and robustness of PI controllers' parameters. Effective measures are taken to resolve the situations where WIP is beyond control limits, that is, two kinds of controllers, the backlog controller and the input rate controller, are devised to stabilize WIP, which correspond with the "I controller" and the "P controller" in the PI algorithm respectively. By such doing, the engineering implementation of PI controllers is well performed. For the permanent performance improvement, the SPC&PI integration control scheme is being used for WIP control. An integrating WIP control system (I-WipCS) is set up. Based on the above research, the implementation of the I-WipCS system is carried out in the production line of certain motorcycle engines' crankcases. Subjects such as its components, the principle of integrated controllers, and the dynamic scheduling strategies are analyzed. Then the control effect of I-WipCS system is assessed through simulation under dynamic environments.