A GERT Model for Calculating the Production Buffering of Critical Equipment with Urgent Jobs Considered

Liu Yuan; Hao Jing-jing; Ying Hong-bin

doi:10.3969/j.issn.1007-7375.2014.02.005

Abstract：In order to reduce the negative fluctuation of unexpected urgent jobs on the normal production of critical equipment and assure the consistency of production schedule , a novel method for determining the production buffering of critical equipment in a manufacturing system containing unexpected urgent jobs is developed .The production manager can confirm the proper reserved capabilities according to the research result .Specifically , the procedures of urgent job arrival and manufacturing are discussed based on the queuing theory with a negative exponential distribution , and the transferring rules and realistic conditions are revealed.Additionally, a kind of graphic evaluation and review technology (GERT) model is utilized to describe the operation of urgent jobs in critical equipment and the transfer between adjacent nodes is studied.In doing so, the node transferring parameters and the moment generating functions are calculated . Furthermore , by the Mason rule , the probabilities of the stable states are determined to provide support for obtaining the buffering capacity of critical equipment .Finally, a group of machining centers in a research institution is used as a case study .It is shown that the average reduction of adjusted situations of monthly production plan of critical equipment group reaches to 14.6%.Thus, the fluctuation of production sched-ule can be effectively controlled and the feasibility and practicality of the proposed method are verified .