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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.

November 9, 2016

Sorting It Out : Conveyor System Capacity Constraints Impact Productivity

The Fix may be Easier than you Think!


During peak volume periods, shipping demand may exceed the incremental (case per minute) capacity of the conveyor system. When this happens order picking and shipping operation are less efficient which leads to overtime and/or forces a second shift.

The case per minute rate of a conveyor 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). Conveyor speed can easily be determined using a hand held tachometer that is calibrated in feet per minute.

Holste Says...

There may be other problems that impact on capacity and productivity such as frequent bottlenecks which may also be eliminated by increasing conveyor speed.

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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 shipping lines. The slow speed side of this conveyor determines the maximum case feet per minute the system can produce. For example if the speed is 60 feet per minute (FPM) then it will handle (60) 12 inch long cases per minute; (45) 18 inch long case per minute; and (30) 24 inch long cases per minute.

Once you determine the length of the average case, based on the speed of the metering belt, you can calculate what the system is capable of delivering. If that amount is less than what is required, consider increasing the speed of the metering belt 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 and productivity such as frequent bottlenecks which may also be eliminated by increasing conveyor speed.

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 relatively costly approach 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 operations. A system operations audit done by a trusted advisor or independent consultant would be a good first step.

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