Multi-Objective Lead Time Control in Multistage Assembly Systems

In this paper ve develop a multi-objective model to optimally control the leadtinle of a ltiultistage assembly system. the multistage assembly system is 1110deled as anopen queueing network, whose service stations represent manufacturing or asseltiblyoperations. '[he arrival processes of the individual parts of the product, which should beassembled to each other in assembly stations, are assull1ed to be independent poissonprocesses with equal rates. in each service station, there is one machine with exponentiajlydistributed processing time, such that the service rate is controllable. the transport timesbetveen the service stations are independent random variables with exponentialdistributions. by applying the longest path analysis in queueing networks, we obtain thedistribution function of time spend by a product in the system or the manufacturing leadtime. the decision variables of the ltiodel are the number of servers in the service stations.l~he problem is formulated as a multi-objective optimal control problelti that involves threeconflicting objective functions. the objective functions are the total operating costs of thesystelti per period (to be minitnized), the average lead time (min). and the probability thatthe lnanufacturing lead tilne does not exceed a certain threshold (nlax). the goalprogranlming method is used to solve a discrete-time approximation of the originalprobleln.