Order allocation, rack allocation and rack sequencing for pickers in a mobile rack environment
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In this paper we investigate the problem of simultaneously allocating orders and mobile storage racks to pickers. Here storage racks are allocated to pickers to enable them to pick all the products for the orders that have been allocated to them. In situations of this type the pickers remain at fixed locations and racks are brought to them by robots, e.g. as in Amazon fulfilment centres that use Kiva robots. We also consider the problem as to how to sequence the racks for presentation to each picker to assist in order picking. Problems of the type considered here arise in facilities operating as robotic mobile fulfilment systems. We present a formulation of the problem of allocating orders and racks to pickers as an integer program. In addition we present a heuristic for the problem based upon our formulation. We also consider the problem of how to sequence the racks for presentation at each individual picker and formulate it as an integer program. Computational results are presented for randomly generated test problems, that are made publicly available, involving up to 500 products, 100 orders, 100 racks and 10 pickers.
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