Integrating machine scheduling and self-healing maintenance by job-mix pull control

In general, machines degrade with use. But, for some manufacturing processes machine ageing can be reversed by processing alternative types of jobs. In the latter case, machines can run longer without breakdowns if job types are balanced and scheduling is optimised. However, when job arrivals are stochastic, even short-term fluctuations in job mixes can increase the risk of breakdown. This paper presents a proof of concept study on job-mix pull control to exploit the age-reversing, healing effect. Because adding pull control will impact the architecture of factory scheduling, three issues are addressed in the proof. First, it is shown that the new architecture would have a better performance than the existing dispatching approach. Second, a method of pulling jobs from upstream to reduce the probability of machine breakdown is developed. The condition of workload imbalance in which job mix control (JMC) should or should not be activated is analysed. Finally, the benefit of JMC is evaluated by using simulation to demonstrate potential improvements that can be achieved. Besides the proof of concept, this study produces an important finding. A lingering cumulative influence of the self-healing effect is discovered, pointing out a new direction for future maintenance scheduling research.