ORDER PICKING OPTIMIZATION

Chapter eight RightPick RightShip: Order Picking and Shipping

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Table 8.3 Zone Picking Costs and Control Complexities

Zone Picking Costs and Control Challenges

Notes and Comments

Order assembly

The major difficulty and cost factor in zone picking is the need to assemble the order across order picking zones. The two methods for order assembly—progressive assembly by passing the contents of the order from zone to zone and wave picking with downstream sorting—can be excessively expensive. They can also reduce the operating flexibility of the warehouse and significantly increase the level of sophistication of warehouse control systems. It is nearly impossible to perfectly balance the workload between zones on a daily basis. To do so requires advanced slotting techniques or, as is the case with highly sophisticated zone picking schemes, dynamic floating zones are used. In those operations, the size of the zone varies as a function of the associated workload. In either case, the controls are an order of magnitude more complex than those used in free form picking.

Workload imbalances can create bottlenecks,

gridlock, and low worker morale.

decision is whether the order picker should work on a single order (single order picking) or multiple orders during a picking tour.

Single-Order Picking In single-order picking, each order picker completes one order at a time. For picker-to-stock (PTS) systems, single-order picking is like going through a grocery store and accumulating the items on your grocery list in your cart. Each shopper is only concerned with his or her list. The major advantage of single-order picking is that order integrity is never jeopardized. The major disadvantage is that the order picker is likely to traverse a large portion of the warehouse to pick a single order. Consequently, the travel time per line item picked is high if the order does not contain several line items. (For large orders, a single order may yield an efficient picking tour.) In addition, in some systems, response-time require ments do not allow orders to build up in queue to create efficient batches for order picking. For an emergency order, the customer-service motivation should override the efficiency motivation, and we should pick the single emergency order without batching.

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