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Cliff Holste

Supply Chain Digest
Material Handling Editor

Logistics News - Sorting It Out

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.

February 21, 2018

Sorting It Out: Increasing System Throughput Capacity – The Fix Maybe Easier Than You Think


Many of the Typical Throughput Problems can be Solved by Adjusting Conveyor Speed

 

During peak shipping seasons, if demand exceeded the capacity of the material handling system, resulting in shipping delays, overtime hours and/or a second shift, there may be a few relatively simple upgrades that will solve the problem.

 

The case per minute rate (CPM) of a material handling system is dependent on the slowest speed mainline conveyor. In a batch picking and sorting system, this is usually going to be the metering belt conveyor (also referred to as the induction conveyor) located in the mainline feeding the shipping sorter. This particular conveyor is typically located just upstream of the sortation conveyor and is usually feed by one or more accumulation conveyor line(s). The speed of this conveyor (or any other conveyor) can easily be determined using a hand held tachometer that is calibrated in feet per minute.

 

Note: The function of the metering/induction conveyor is to insure that there is sufficient space between cases so that the sorter can divert individual cases into the shipping lines. The slow speed metering side of this conveyor determines the maximum case feet per minute the sorting system can produce. For example if the speed is 60 feet per minute (FPM) then it will produce (60) 12 inch long cases per minute; (45) 18 inch long case per minute; and (30) 24 inch long cases per minute. The high speed induction side “pulls” a gap between the cases.


Holste Says...

A system operations audit done by the original conveyor vendor, a trusted advisor or independent consultant would be a good first step.

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By determining the length of the average case you can calculate what the system is capable of delivering based on the speed of the metering belt. If that amount is less than what is required, consider increasing the speed of the metering/induction conveyor by simply changing the ratio of the drive sprockets. However, the conveyor provider should be consulted prior to making any such changes as this may require re-calibrating the sorter tracking controls.

 

There may be other problems that impact on capacity such as frequent bottlenecks which may also be eliminated by adjusting conveyor speeds.

 

Some problems appear to be obvious and easily fixed such as adding accumulation conveyor between picking and sorting operations to smooth out the surges without shutting down picking. However, while this may provide some temporary relief, it may not fix the underlining system problem.

 

Digging deeper will sometimes reveal the hidden or less obvious problems that sap system performance.

 

A good example of this can often be found at the central merge. Here cases of product from multiple picking lines are buffered and automatically merged into a single conveyor line that feeds product to the induction conveyor and on to the sorter. Even when the merge is operating at peak performance, the gaps between slugs of cases being released from the accumulation lines can reduce system capacity by 10 to 15 percent. Installing new merge logic can reduce the gap between slugs from the typical 3 to 5 feet to just a few inches regardless of line release sequence. Your conveyor system provider can advise if this control upgrade would be applicable in your operation.

 

Final Thoughts

 

No doubt there are shippers, both large and small that need to increase the throughput performance of their conveyor system. This is a case where a system operations audit done by the original conveyor vendor, a trusted advisor or independent consultant would be a good first step.


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