An integrated approach for the vending machine replenishment problem

[[abstract]]販賣機能夠普及的原因在於其對於消費者的便利性，尤其在人口密集、店面租金昂貴設置不易的地點，自動販賣機就成為一種便利的消費方式，但是自動販賣機因為存貨有容量的限制，需要經常性的執行補貨作業，若是因為補貨作業的缺失，而造成經常性的缺貨問題，將會使消費者失去信心，造成自動販賣機原本擁有的優勢消失。因此建立有效率的配送模式，在適當的時間將正確的商品數 量，以較低的成本運送至自動眅賣機所在的地點，可以將自動販賣機的優勢發揮到極致。 過去曾有學者提出類似週期性車輛途程問題(PVRP)為基礎的週期性存貨途程問題(IRP)的補貨作業模式，然而此法可能會因為販賣機每日銷售量波動過大而造成補貨作業的效率不彰，所以本研究提出一個非固定間隔天數的補貨作業模式，以彌補固定週期補貨模式的不足。由於在模式中包含了車輛途程問題，此類問題有NP-Hard 的特性，不易以最佳化軟體在合理時間內求出最佳解，因此本研究應用模擬退火法來求解此組合最佳化問題，以得到最佳的補貨途程模式。 實例測試結果顯示，本研究所提之非固定週期之補貨模式，在各週的規劃都能有效的改善週期性補貨模式補貨的相關作業成本，對於不同型態的需求量資料，也都能有所改善。在需求量波動較大的資料最高有20%的改善幅度；而在波動較小的資料雖然改善幅度較小，但也能有近10%左右的改善幅度。[[abstract]]In this paper we present a model and solution procedures for the vending machine replenishment problem encountered in vending machine supply chains utilizing vendor-managed inventory (VMI) scheme. The model is a modification of the existing Periodic Vehicle Routing Problem (PVRP). Our model is different from from previous research in that the replenishment period is not fixed and its objective is to minimize the sum of the shortage cost and traveling costs during a given time period. The proposed model belongs to the class of NP-hard problems since it includes the vehicle routing problem as a subproblem. It is difficult to solve this problem to optimality within a reasonable time period. Thus,we developed a Simulated Annealing (SA) heuristic for this problem by. The SA treats the replenishment frequency of each vending machine as a decision variable instead of a fixed parameter. It optimizes the replenishment frequencies of vending machines and vehicle routes simultaneously in order to find the best trade-off between the shortage and transporataion costs. This new approach can reduce the total shortage and transporation cost by 10 to 20%, as indicated by the computational study