Abstract
Non-traditional warehouses rise as effective solutions to shorten the travelled distances to store and retrieve unit loads, adding aisles crossing the parallel racks. Multiple warehouse configurations are proposed by the literature discussing the enhancements toward standard layouts. In previous contributions, the authors introduced the diagonal cross-aisle model, concluding about its positive impact on the handling performances under single command operations. This paper extends the previous works, integrating dual command operations, through an original analytic model supporting the design of non-traditional warehouses with a couple of symmetric straight diagonal cross-aisles and random storage assignment strategy. The closed-form expressions to compute the expected cycle travel distances are provided, optimising the aisle position. An industrial case study applies the model, getting distance savings ranging from 11 to 17%, compared to standard layout and further considering the loss of storage space due to the presence of the additional aisles.
Highlights
Warehouses represent a capstone of supply chain management [1]
This paper extends the previous design model proposed by Bortolini et al [19], integrating single and dual command operations for the UL storage and retrieval (S/R)
Single and dual command cycle distances are minimised, separately, using Eqs. 5 and 12. The former leads to a minimum travel distance of about ESoCpt 1⁄4 1:70 per single command cycle, in the dimensionless normalised non-traditional warehouses (NTWs) space when αSoCpt 1⁄4 34:85°, the latter allows getting a minimum travel distance of about EDopCt 1⁄4 2:91 per dual command cycle, in the dimensionless normalised NTW space when αDopCt 1⁄4 30:80°. These results suggest to optimally positioning the couple of symmetric straight diagonal cross-aisles according to the best angles, slightly different for single and dual command cycles
Summary
Warehouses represent a capstone of supply chain management [1]. Unit-load (UL) storage systems are the most diffuse solutions to receive, store and ship products into single units moved using pallets [2]. & The automation level of the S/R system; & The shape factor, i.e. ratio between the two plant area dimensions; & The number of vertical levels; & The number and the position of the pickup and delivery (P&D) points; & The aisle number and positioning; & The assignment policy of the items to the bays These cross-dependent features univocally define the warehouse configuration, i.e. layout, and they constitute the input of mathematical models to predict the warehouse operation performances [10]. In 2015, Bortolini et al [19] introduced the diagonal cross-aisle model based on the inclusion of one or multiple couples of straight aisles crossing the racks diagonally with no changes in the rack positioning respect to the standard reference layout, i.e. parallel vertical racks (Fig. 1) Adopting this layout, this paper extends the previous design model proposed by Bortolini et al [19], integrating single and dual command operations for the UL S/R.
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