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About the Author

Cliff Holste is Supply Chain Digest's Material Handling Editor. With more than 30 years experience in designing and implementing material handling and order picking systems in distribution, Holste has worked with dozens of large and smaller companies to improve distribution performance.

Logistics News

By Cliff Holste

May 13, 2015

Logistics News: Hit Density Drives Picker Productivity

Zone Picking Method - Best Alternative for Increasing DC Performance

Holste Says:

The key objectives of any picking method should always be speed, efficiency, and accuracy.
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Previous Columns by Cliff Holste

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Sorting It Out: For Shippers - Benefits Of Real-Time Control In The DC Are Huge!

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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.

Another benefit is that each pick zone can be specifically designed and optimized for the different types of picking activity (full case or split case) and each pick module can accommodate different configuration (double deep pallet flow, case flow, static shelving, horizontal and/or vertical carousals, etc). Paperless picking technologies such as RF, Pick-to-Light, and Voice Directed can be easily adopted to increase productivity and accuracy. And, integrated software based slotting programs can be deployed to further enhance picking performance.

Note: Picture courtesy of Forte Industries

If you are considering adopting a pick & pass zone picking system, the question of how many picking zones are needed can best be addressed with a list of things to consider, such as:

How will the system direct the pickers? Can the number of pick faces within a zone be increased or decreased? (Here you are looking for flexibility in zone configuration relative to SKU slotting)
Can the system support more than one picker in a zone – working together on the same order or on different orders? (In this case you are looking for the ability to handle peak volume periods)
Can the zone boundaries be changed easily? Every once in a while, by wave or by order? (Is zone size dynamic or static?)

Are the pickers picking one order at a time or a cluster of several orders?
Can zones overlap?

Breaking up orders into picking zones requires a robust WMS order processing and SKU slotting optimization functionality. These capabilities and a whole lot more are available from most WMS providers.

Final Thoughts

The key objectives of any picking method should always be speed, efficiency, and accuracy. However, in today’s fast changing business environment, flexibility and adaptability are not only desirable but essential to being able to make quick adjustments in sales strategy, order SKU mix and volume. If your current order fulfillment operation can no longer satisfy these objectives, perhaps it has out lived its functional life and it’s time to adopt more up-to-date methods.

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