ENGINEERING JOURNAL CHIANG MAI UNIVERSITY

Volume 26, No. 03, Month DECEMBER, Year 2019, Pages 184 - 196

Heuristic based scheduling for tablets film coating process

Chutamas Pontrakul and Pisit Jarumaneeroj

Abstract Download PDF

The main objective of this research is to determine tablets film coating sequences on parallel machines such that both the completion time (makespan) and the number of tardy jobs are minimized. The underlying tablets film coating problem investigated in this paper is one of production planning problems that requires considerably long periods of cleaning and setup whenever production orders,i.e. drugs, have been changed. As these times vary and depend on the previously coated drugs, inefficient planning may eventually lead to delivery delay. We show that this problem could be transformed into the Vehicle Routing Problem with Time Window (VRPTW), where a variable arc exchange heuristic is devised to solve such a problem. Our proposed heuristic is a 2-phase one, where the initial solutions are constructed from easy-to-implement dispatching heuristics, i.e. Earliest Due Date (EDD) and Longest Processing Time (LPT); and, once completed, they are then iteratively improved by a series of improvement operators – 2OPT, RELOCATION, and SWAP – mimicking the concept of Variable Neighborhood Search (VNS) until no improvement could be found. The results from our proposed heuristics are comparatively good, when compared to those of the optimization model, in terms of solution quality as the gap is less than 2% for instances of 10-30 orders; but, they require much less computation time, which is crucial from a practical point of view. Though the optimizer fails to provide the optimal solution when the number of orders increases to more than 40, due to run-out-of-memory error, the proposed heuristics are still be able to provide acceptably good solutions within an acceptable period of time.

Keywords

Job scheduling, Vehicle Routing Problem with Time Window, Heuristic

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