Split case picking is often the bane of DC managers. It can be slow, tedious, and prone to errors. Except for very high end automated picking machines used in specialty applications (pharmaceuticals, H&BA, CDs, etc.), it can’t really be well automated. RF, Pick-to-Light, and Voice Directed picking technologies, combined with picking carousels and other product-to-person methods, have been widely adopted to increase picking accuracy and productivity.

The Pick & Pass concept, which has its roots in the manufacturing production line, offers a practical and relatively low cost order fulfillment solution especially for split case picking where thousands of SKUs can be involved. Still, Pick & Pass operations are plagued with throughput problems brought about by frequent and, in some extreme cases, near perpetual gridlock.

Understanding the Notorious Buffering Problem Associated with Pick & Pass Operations

As anyone who manages a Pick & Pass operation knows, the major problem is the inherent lack of buffer space for WIP (work-in-process) order picking containers. The process of picking multi-line orders begins in the first zone requiring a pick. The picking/shipping container(s) is then “passed” along to each consecutive zone where a pick is required. Often the containers must pass through zones where no picks are required. This results in non-productive handling and loss of time while the containers sit idle waiting to be moved through the zone(s).

Dr. Tom McNamara, Assistant Professor, Rennes School of Business (tom.mcnamara@esc-rennes.fr ) in a recent trade journal paper entitled, “Smart Buffering In Unreliable Production Line Performance” describes this situation as being similar to an “Unpaced” production line where each operator is free to work at their own speed, passing their work pieces (picking containers) to the next station (pick zone), usually by hand. Storage space byway of a “buffer” is provided in between (or in this case in-front of) each pair of work stations in order to temporarily hold work in process (WIP) items. The function of the buffers is to help avoid production stoppage when a worker is deprived of having a work piece (container) to process (known as “starving”), or is unable to pass an item on to the succeeding station due to lack of space (known as “blocking”).

Dr. McNamara goes on to say – “There are of course several issues to consider in the design and management of these lines, such as; where to place workers who complete tasks at different rates, or where to store WIP along the line, are just some of the challenges to be faced. Another problem that needs to be taken into account is when a station breaks down (or in this case depletes a SKUs on-line stock) and production (picking) stops temporarily. This is a key feature of so-called “unreliable” lines, and also has to be taken into account.”

The focus of his article is on the decision of how much buffer space is needed, and where to place this storage space along the production line, while taking into consideration unreliability factors. While the associated buffering problems of a production line are very similar to that of a Pick & Pass operation an alternative solution is available.

Automation Improves Pick & Pass Performance

With the above in mind, we can now look at how automated zone routing sortation works to improve the performance of the Pick & Pass operation.

In recent years, newly designed and configured sortation and conveyor equipment is providing relief in many split case picking circumstances. One example of how this equipment is being deployed to increase throughput performance and productivity can be found in the automated pick and pass environment.

The picture below shows a right angle transfer Pick & Pass 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 picker to clear the full condition.
  
  

Automated Zone Pick & Pass System

(Picture courtesy of Forte Industries)

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. It should also be noted that a well designed flexible Warehouse Control System (WCS) is key to maximizing these as well as other 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 carousels, vertical lift modules, mini-load ASRS, etc.

Applying New Conveyor Technology to Pick & Pass System Design

A major development within the conveyor industry known as MDR (Motor Driven Roller) technology provides both the flexibility and adaptability to enable automated zone sorting within the Pick & Pass system configuration. With this unique design, low voltage (24 or 48vdc) motors for driving product are actually contained within individual rollers, or, as in the case of Hytrol, mounted on the outside of the conveyor frame, allowing for much greater design flexibility, as the power and intelligence are self-contained within small conveyor sections.

Although MDR equipped conveyors hardware cost is more than conventional live roller conveyors, according to various industry sources, they are less expensive to install and maintain. From an operational perspective, MDR offers many unique benefits – the following are but a few:

• the design eliminates the need for pneumatic piping with most manufacturers,
• majority of the wiring is 110 volt AC to power supplies rather than 480v to many motors,
• MDR rollers run on demand rather than all the time reducing noise levels and energy consumption.

Pick & Pass Automation Metrics

Robert (Bob) Babel, VP of Implementation Services at Forte (www.forte-industries.com), reports Pick & Pass systems in operation achieve between 200 & 1200 units/hour per associate or 50 to 150 lines/hour per associate. Babel points out that these metrics will vary based on units per line, units per carton, lines/zone, module configuration, pick zone size, pick methodology, etc. According to Babel, Forte has implemented automated pick & pass operations in the apparel, medical, home goods, and hardware industries. The following is a recent example:

Forte Industries worked with Kurt Jacob, Director of Distribution at Holloway Sportswear to take them from a garment-on-hanger (GOH) storage and picking operation, which was admittedly slow and cumbersome, to a more efficient flat goods automated zone Pick & Pass operation that incorporated (8) zones with walk-back aisle configuration.

Holloway has mostly medium and slow moving SKUs. Orders range from a single tee shirt in a mailer bag to multi-carton orders. The average order consists of 4 lines with 3 units per line. All orders are picked into bar coded shipping containers that are sized based on the total cubic volume of the required item(s). Pickers are equipped with RF terminals connected to the WMS.

According to Holloway’s productivity reports the pick rate is about 70 lines per picker per hour. Kurt points out that the key to facilitating this flow is slotting the nearly 15,000 SKUs. High velocity items are slotted closest to the conveyor, reducing the pickers travel time. Kurt believes that an important criteria to accent the ABC analysis of products is considering companion picks (when customer buys a garment, then purchases a matching accessory) and family grouping (when selecting the SKU, customer will buy same style and color in all sizes).

At Holloway, picker productivity is further enhanced by grouping containers together so that batch picking methods can be utilized. The system also facilitates VAS by automatically routing orders requiring embellishment operations (embroidery and screen printing) to the appropriate WIP area.

It’s interesting to note that at Holloway the Pick & Pass conveyor and sorting system is also used to efficiently distribute cases of products for replenishment to the pick zones. Another added feature is a corrugate removal conveyor mounted directly above the Pick & Pass routing conveyors.

Enhancing the Pick & Pass Operation

Regardless of the Pick & Pass layout configuration or level of automation, the manual split case order picking operation itself can be substantially improved (as mentioned above) through the adoption of “Golden Zone” SKU slotting techniques. There are many such programs available through a variety of providers. One such program that got our attention recently can be found at the following Google site link: https://sites.google.com/site/slottingtoaconveyorpicking/

Final Thoughts

Split case picking is fraught with many performance and productivity robbing challenges. The problem has been exacerbated by SKU proliferation and the explosion in small Internet orders. That explains why automated zone routing sortation has rapidly become an industry standard solution for Pick & Pass systems.

No doubt getting split case picking “right” will continue to be challenging. Therefore, companies should take full advantage of recently developed conveyor technologies in addition to automated picking and sorting methods to increase system flexibility, agility, and performance.

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