Holste Says: |
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| The key objectives of any picking method should always be speed, efficiency, and accuracy. |
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What Do You Say?
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Previous Columns by
Cliff Holste |
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Companies that are considering migrating from a pick-to-cart order picking process to a more efficient pick & pass zone picking model are often concerned about maintaining picker productivity and order accuracy. With their current operation, order pickers are responsible for picking complete orders assigned to them, usually a cluster of 2 to 6 orders in each tour of the DC. But, in the more mechanized zone picking method, order pickers pick only a portion of each order. The concern is that while this process will improve order picking productivity, order accountability will be lost leading to more picking errors.
While these are legitimate concerns, they are unfounded. The following will provide insight as to why pick & pass zone picking is one of the most preferred methods.
Understanding the Picking Process and Flow
The Single Picker per Order Method:
In the typical pick-to-cart operation, picking is for the most part restricted to the warehouse floor where active pick locations are easily accessible. Pickers are tasked with moving horizontally throughout the warehouse gathering all of the products required to complete the cluster of orders on their pick cart. The pick route they take is usually based on a quick assessment of the orders and knowing where product is stored.
Depending on “hit density” (the distance between picks and number of picks per stop) a very high percentage of the picker’s time is spent moving from one location to another. It would not be unusual for a picker to spend half or more of his/her time moving about the DC. It can be difficult to manage activities that take place in the deep dark recesses of a large warehouse. Some companies try to estimate times for completing each picking assignment. But that’s usually nothing more than a guess that does not take into account anomalies such as inventory and slotting errors, which occur more frequently than most DC managers would care to admit.
Oftentimes, for efficiency purposes, the pickers are picking directly into shipping containers. While accountability is high, without an audit procedure prior to shipping, picking errors can go undetected. Generally, only shorts are reported by the customer.
In this type of operation a paper pick list is most often used to drive the picking function. As an alternative, RF or Voice Directed technologies are used. While these technologies have been proven to increase productivity and reduce errors, picker travel time remains for the most part unchanged.
The Mechanized or Automated Zone Picking Method:
Among the first advantages of the zone picking method is being able to manage the process incrementally in both the horizontal and vertical plane. Because pickers are working within a specific zone, that zone can be on a mezzanine. Orders can be started in any zone where a pick is required. A continuous loop conveying system equipped with automated zone transfer technology will insure that order picking containers (tote box or shipping carton) will visit all zones where picks are required.
Picking within the zone is computer directed. Cluster picking allows a half dozen or more orders to be sequentially picked in one pass through the zone. Hit density (as defined above) is optimized thereby increasing picker productivity. Based on the relativity short pick path and a highly predicable pick sequence, the time required to complete the order can be accurately calculated. And, management visibility to the operation is greatly enhanced.
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