Method for Supporting Decision-Making in Rescheduling for Lean Flexible Manufacturing

Abstract

In high-mix low-volume manufacturing and agile manufacturing, flexibility to cope with fluctuations in production conditions is a key for competitive production. To realize the flexible manufacturing, it is required to immediately generate, evaluate, modify and determine a production schedule which is suitable for the new condition. Decentralized methods of scheduling and simulation for the immediate generation and evaluation have been developed based on a concept of highly-distributed manufacturing systems in which each machine is computerized and can communicate with other machines. Although these methods are useful for performing the flexible manufacturing, it is possible that the original schedule is good even for the new production condition and performing rescheduling is in vain. This research aims at supporting decision-making on rescheduling for realizing lean flexible manufacturing in which rescheduling is performed only when it is effective. In this paper, delay in operation due to inaccurate estimation of processing time is considered, and the following method is proposed: When it turns out completion of an operation delays and the amount of the delay is estimated, the original schedule is repaired by the right-shift policy. The repaired schedule is then analyzed using simple criteria for judging whether rescheduling should be executed or not. Several criteria focused on critical path were given, and the effectiveness of this support method was shown by numerical experiments. NomenclatureJ total number of jobs O j total number of required operations of job j O jo the o-th operation of job j M jo the set of machines which can process O jo S jo starting time of O jo F jo finishing time of O jo P jo required processing time of O jo EST jo the earliest starting time of O jo LST jo the latest starting time of O jo