Calzavara, Martina

Persona, Alessandro

Sgarbossa, Fabio

English

Georgia Southern University: Digital Commons@Georgia Southern

6. Conclusions and Future Research2018 International Material Handling Research ColloquiumSavannah, Georgia USA, July 23‐26, 2018Economic and performance analysis ofdual bay Vertical Lift Modules  Fabio Sgarbossa, Martina Calzavara and Alessandro PersonaUniversity of Padova2. Objective of the Research1. Small Objects Order Picking Solutions3. Compared Warehousing SolutionsIn this paper, dual-bay VLMs, compared to a carton racks warehouse, havebeen analysed from an economic point of view.Some mathematical formulations have been developed,to estimate the total annual cost and the respectiveapplicability limits of both systems, according to theirproductivity.Moreover, some useful guidelines for practitioners are derived.Vertical Lift Modules (VLMs)• Higher throughput (dual tray)• Picking errors reduction• Ergonomics improvement• Safe products storage4. Cost ModelsCarton racks warehouse (W) Dual-bay Vertical Lift Module (V)•Picker-to-parts solution•Picker travels within the aisles (traveltime lower than case-pick-from-pallet warehouse)•Parts-to-picker solution• In a dual-bay system, picker works inparallel with the crane, standing inthe picking bayThe total annual cost ௏ or ௐ includes a fix cost term (space & equipment) and a variable one (operators)Carton racks warehouseDual-bay Vertical Lift Moduleௐ ௦௣ ௐ ௐ ௢௣ ௐ ௬௏ ௏ ௦௣ ௏௏௏ ௢௣ ௏ ௏ ௬5. Economic & Performance Comparison்஼௏ௐ 𝑽 𝑽∗𝑽𝑸 𝑸∗∗௏௦௣௏ ௏௏ௐௐ௢௣ ௬ ொொ∗௦௣௏ ௏௏ௐௐ௢௣ ௬்஼௏ௐTrend of ∗ ௏ and VLM applicability region for ௏=24,000 €/year, ௬=3,600 h/year, ொ=1.5and (a) ௦௣=80 €/m2 or (b) ௦௣=120 €/m2, while (c) has ௏=18,000 €/year and ௦௣=80 €/m2Trend of ொ∗ varying ௏ for ௏=24,000 €/year, ௬=3,600 h/year and (a) ௦௣=80 €/m2 or (b)௦௣=120 €/m2 and for (c) ௏=18,000 €/year, ௬=3,600 h/year, ௦௣=80 €/m2Conclusions on ∗ 𝑽 and 𝑸∗ :• they are not very sensible to the total volume of the stockeditems• they depend on the annual floor space cost per square meterand on the annual cost of the VLM• Generally, the required throughput and the number of workinghours per year 𝒚 can affect the applicability of the VLMModelling of the Refilling activity:• since it is different for the two systems and it has an impact on thestorage allocation, on the travelled distances and, then, on theoverall timeExtension of the comparison to other systems:• Development of a complete tool for their evaluation andcomparison. This could help the choice of their most properapplication in real warehouse picking contextsNotation Description𝑄 [picks/h] Total hourly required throughput, 𝑄 ൌ ∑ 𝑄௜௡௜ୀଵ𝑉 [m3] Total storage volume, 𝑉 ൌ ∑ 𝑉௜௡௜ୀଵ𝐻 [m] Plant height𝑆𝐿௦ Storage volume utilization level, 𝑠 ∈ 𝑊, 𝑉𝑄௦ [picks/h] Storage system hourly throughput, 𝑄௦ ൌ 3600 𝑡௟௦⁄ , 𝑠 ∈ 𝑊,𝑉𝑅ொ ൌ 𝑄௏ 𝑄ௐ⁄ Throughput ratio between the two solutions𝑡௟௦ [s] Average cycle time per line 𝑠 ∈ 𝑊, 𝑉𝑉௏ [m3] Storage volume of one VLM𝐴௏ [m2] Operating area of one VLM, including the VLM area and the space for the operator𝐶௏ [€/year] VLM annual cost𝑘௦ Storage system space cost coefficient, 𝑠 ∈𝑊, 𝑉𝐶௦௣ [€/(m2year] Annual space cost per square meter 𝐶௢௣ [€/h] Hourly operator costℎ௬ [€/year] Number of working hours in a year 𝑇𝐶௦ [€/year] Annual storage system total cost, 𝑠 ∈ 𝑊,𝑉𝐶௙௜௫௦ [€/year] Annual storage system fix costs, 𝑠 ∈ 𝑊, 𝑉𝐶௩௔௥௦ [€/year] Annual storage system variable costs, 𝑠 ∈𝑊, 𝑉number of VLMs to install to perform the picking ofitems and to stock the total storage volume

Economic and Performance Analysis of Dual-Bay Vertical Lift Modules

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Economic and Performance Analysis of Dual-Bay Vertical Lift Modules

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