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Computers & Chemical Engineering, Vol.23, No.S, S1011-S1014, 1999
Vehicle Routing Problem (VRP) formulation for continuous-time packing hall design/operations
Detailed scheduling of a packing hall consisting of a number of packing lines is a problem encountered in many process industries. The scheduling problem is complicated by the presence of sequence dependent changeovers of different lengths. Vehicle routing problems (VRP) arise in many distribution, product inventory, and mobile repair industries. A common objective is to find a route for a vehicle, which satisfies a variety of constraints, and so as to minimise the total vehicle operating cost. In other applications, it may be important to minimise the total time. Little work has been done on the solution of the large-scale design/scheduling/sequencing problems using VRP type formulations. A model for this problem has been presented and its computational performance is compared with other classical disjunctive formulations. The approach presented here is based on a continuous-time formulation in that all events (packing and changeovers) are allowed to start and end at any time. The proposed approach has excellent integrality property, as it does not contain any 'big M'. type of constraints encountered in these problems. This problem is formulated as a mixed integer program and solved using a standard solver, which makes the proposed approach attractive commercially. The details of the formulation and the results of a large-scale commercial packing hall problem are given.