Expert Insight: Sorting it Out
  In this regular column/blog, SCDigest Material Handling System Editor looks at a variety of design, system, technology and ROI issues related to material handling automation systems in distribution and manufacturing.  
  By Cliff Holste  
  February 14, 2008  

When is a Sortation System Right for Distribution Operations?


If you Handle 10,000 Cartons or more per Shift, you are a Good Candidate, Holste Says; Understanding True Cases Per Minute

Holste Says:
Once the decision to automate the sorting function has been made, the obvious questions of how much, and what kind of equipment and control needs to be answered! 

What do you say? Send us your comments here

One of the first and most frequent questions I receive is: “Do we have enough volume to justify an investment in sortation technology?”

My answer: If your operation ships at least 10,000 cases in a single shift you are probably a candidate for an entry level automated sorting system.  Sorting cases manually at or above this volume is not productive. In addition, depending on the employee’s physical capability and endurance level, as well as ergonomic and safety factors, this level of manual processing can cause serious operational complications. 

At 10K and above, there can be no doubt that an effective marriage of finely tuned mechanical equipment and the appropriate application of PC/PLC software control will yield high levels of productivity.  In the somewhat limited space available here, I will endeavor to explain a few of the more important fundamentals you will need to know to get a good start on Sorting it Out.

The actual sorting function, when closely analyzed, can be very complex.  Done poorly, sorting could cost considerably in wasted manpower, delays, shipping errors, and worse – lost orders.  Done right, it adds to a company’s productivity, profitability, and enhances customer service factors.  Once the decision to automate the sorting function has been made, the obvious questions of how much, and what kind of equipment and control needs to be answered.

In order to be sorted, a carton must be conveyable and must carry some identifiable address or code to distinguish it from any others.  The most common practice is placing a coded label on the top, the front, or the side of the carton.  Typically, this is done manually; however, automatic print and apply equipment can be a cost effective alternative.  RF tags are available and are coming down in price, but the cost differential may still be too much to justify.  The code must be capable of being scanned by fixed-beam or moving-beam scanners.  For high velocity sorting applications, high resolution, omni-directional camera scanning equipment is available.  The information contained in the code is then used by the sort control system to track the case and sort it at the proper location.

Just knowing the basic facts can sometimes be misleading.  For instance, one of the fallacies that should be avoided in planning and budgeting for a sortation system is to base your equipment choices on actual required case-per-minute (cpm) sort rate.  Let’s say you require a yield of 50 or 60 (cpm), which could be handled by a simple, low cost belt sorter equipped with pop-up wheel diverters.  However, In order to achieve this yield, you will need a sorter that can handle 75 to 80 cpm to make up for the possible lag in active inventory replenishment, order picking, or whatever else could happen upstream of the sorter in the conveying system.  This bump up in cpm will require a more expensive higher capacity sorter.

No order fulfillment distribution center system operates at an absolute constant throughput.  So, the best policy is to design in buffers, like accumulating conveyors at merge points, and at case scanning/sorter induction.  Also, larger-capacity after-sort chutes or longer shipping conveyor lines can reduce sorter shutdowns.  For example, if an after-sort chute or conveyor line becomes full, cases assigned to that location are going to be automatically re-circulated, via an accumulating conveyor loop, back to the sorter for re-induction.  If the re-circulation line is allowed to accumulate cases until there is no more space left, the sorter will shut down.  Every time this happens, it reduces sorter throughput capacity and system productivity.  Most, if not all of these delays and shutdowns are caused by operational conditions outside of the sorting systems’ ability to control the action.

With good operating practices and preventative maintenance programs, today’s automated sorting systems will provide many years ofaccurate, reliable service.  So be sure to plan for future growth.  Upgrading the sorting system in the future, to satisfy changes in customer order profiles, and/or higher throughput requirements, can be a serious and costly proposition if not considered in the initial planning and system design stage.

I’d love to hear your perspective on this.

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  Cliff Holste, is SCDigest Material Handling Systems Editor. He has more than 30 years experience in the materials handing field as an enginer, system designer, consultant and more. He is also president of Holste Material Handling Solutions in Cincinnati. To discuss your materials handling system issue or project, you can contact Cliff at