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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

February 22, 2012

Automated Sorting - Improves Eaches Picking Efficiency

Automating Pick-&-Pass Zones Drives-up Picking Efficiency and System Throughput

“Piece picking”, “eaches picking”, “loose case picking”, “broken case picking”, and “split case picking” are the most common terms used to describe the picking of individual items. Typically, these items are picked directly into a corrugated shipping container or perhaps a captive plastic tote box used as a material handling transport container for moving items through the picking operation.

Holste Says:

One example of how sortation is being deployed to increase individual item picking throughput performance and productivity can be found in the pick & pass environment.
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Individual item picking often is the cause of much consternation among distribution managers. It can be aggravatingly slow and inefficient. In some operations it drives down system productivity and throughput. With the exception of a very narrow choice of automatic dispensing machines (suitable for small items like pharmaceuticals, cosmetics, CDs, etc.) item picking in the DC is largely a hands-on event and typically involves lot of walking.

The Material Handling Industry has over the years develop and refined technologies such as: RF, Pick/Put-to-Light, and Voice Directed along with item picking strategies like Product-to-Person all of which have proven benefits for a broad spectrum of the market.

That being said, the most common practice still involves the use of some form of the push pick cart. However, driven by the ever increasing level of eCommerce, even pick cart technology has become more sophisticated (see – “GNC Uses In-House Developed Pick Carts to Turbocharge Piece Picking”).

The use of sortation systems certainly has provided relief in many circumstances. One example of how sortation is being deployed to increase individual item picking throughput performance and productivity can be found in the pick & pass environment.

The Pick & Pass Automated Zone Option

Without going into too much system design/operational detail, let’s first look at a typical non-automated pick and pass system configuration.

As shown in Example “A”, a powered takeaway conveyor line is centered between a case flow rack and static shelves. Dead roller conveyor is located along both sides of the powered conveyor line leaving enough aisle space for picking between the face of the picking rack and the edge of the roller conveyor. All picking must begin in the first zone.

In a paper based operation, a preprinted pick list is attached to an empty container, and the container is placed on the roller conveyor. The picker working that zone pushes the container (sometimes 2 or 3 at a time) thru the zone, picking the required product (for each container) along the way. The picker is required to check off each product picked. If there is insufficient product to complete the order, the container is set aside and held in that zone until the needed product is replenished. The alternative is ship the order incomplete and backorder the missing product.

At the end of the zone the container is either complete (no more items required) or it requires items from downstream zones. If the container is complete, it is put onto the powered takeaway line where it is transported to order checking, packing, and shipping. If more items are required the container is passed onto the next downstream zone and the picking routine is repeated. The container is passed thru each consecutive zone until all items on the order have been picked. All orders start in the first zone even if no picks are required in that zone. If the order requires a pick in the first and last zones, it must be pushed thru all of the in-between zones.

In the above example, a simple paper pick list is used to drive item picking. RF, Pick-to-Light, or Voice technologies are commonly used to drive the physical picking operation and improve picker performance. While these methods have been proven to increase productivity and reduce errors the flow of containers within the non-automated pick and pass operation remains the same, i.e., sequential.

Unfortunately, pick & pass operations of this type are plagued with throughput problems brought about by frequent and, in some extreme cases, near perpetual gridlock.

With the above in mind we can now look at how automated zone routing sortation works to improve the performance of the split case pick and pass method.

To meet its heavy split case picking requirements, in 1998 totes-Isotoner became the first major company to deploy an Automated Zone Picking system in its new DC, see (Looking Back on 10 Years of Distribution Center Automation at totes Isotoner”).

Innovative in 1998, Automated Zone Picking has become more commonplace now in-part due to newly designed and configured sortation and conveyor equipment such as motor driven roller (MDR). This technology is now providing relief in many split case Pick & Pass environments.

Example “B” above, and the picture below, shows a right angle transfer popup sorter imbedded in the mainline powered conveyor that is capable of automatically scanning and transferring containers to either the left or right side picking zones. Containers traveling on a conveyor system so equipped are routed only to the pick zones where a pick is required. If the zone is full (blocked), the system control can direct the container to:

  • go to the next available zone requiring a pick,
  • continue to re-circulate through the system until a zone becomes available,
  • transfer to opposite side even if pick not required,
  • or, based on priority rules wait at the transfer for the picker to clear the full condition.

In this type of operation, pickers use RF terminals connected to the WMS and a printer network. When the WMS downloads a wave, shipping compliant labels are printed in each container’s originating zone. The label indicates what size shipping container is required (based on the total cubic volume of the required items) and the labels are manually applied to the side of the appropriate shipping container. This label is then used to drive item picking, convey and automatically sort partially picked containers to downstream zones for additional picks, and for shipping sortation on the conveyor system.

In each zone, the picker has the option of taking one or multiple containers (cluster picking). In cluster picking mode, the picker scans each container in the “train”. The WMS then directs the picking in location sequence for that train in that zone, indicating how many of each SKU are required for each of the containers in the train. The cluster picking option is key to optimizing split case picking productivity.

When the last pick to a shipping container is confirmed via RF scanning, a container contents label is printed and manually applied to the side of the container. The container is then manually closed, sealed and put back onto the powered conveyor system. An alternative to manually closing/sealing is to send the open containers to an automated closing/sealing station.

As a result, congestion and buffering problems are greatly reduced (if not eliminated entirely). Another benefit of the automated zone routing and sortation function is that it greatly reduces the number of times a container is “touched” as it moves throughout the picking process. In addition to increasing throughput the pick zones can be significantly larger and therefore, fewer of them are required.

In addition to the WMS, it should also be noted that an integrated Warehouse Control System (WCS) is key to optimizing all of the potential benefits.

In addition to routing containers within a pick module the same technology can be used to rout containers to more highly automated areas of the DC such as “A” frame dispensers, horizontal carousels, vertical lift modules, mini-load ASRS, etc.

Final Thoughts

As evidenced by the growing adoption rate of these systems, automated zone sorting, when combined with zone routing/skipping logic, and cluster picking, definitely increases throughput performance and productivity of the split case Pick & Pass operation.

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