Route overlap metrics to batch orders

In this study different metrics to perform order batching for a unidirectional cyclical picking system are investigated. Batches must be formed to minimise walking distance that is measured as the total number of cycles traversed by pickers.Route overlap metrics are developed to approximate walking distance before picker routing. Thereby, information about route similarity is added to identify orders that are compatible for batching.A span is the length of a section of picking line that a picker walks to collect the items in an order. Three metrics based on the concept of a span are developed, namely the stops non-identical spans, the non-identical stops-spans and the stops-spans ratio metric.Numerical experiments are carried out to determine the best combination between route overlap metric and batching method. A prominent South African retailer's distribution centre provides \(50\)~sample picking waves for an experimental set up with real-life data. The stops non-identical spans metric used together with greedy smallest entry heuristic to perform the batching consistently leads to a low number of cycles traversed to complete a picking wave relative to the other methods.