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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 28, 2018

Sorting It Out: Automatic Conveyor Speed Control – Speed Varies to Accommodate Carton Flow

Flexible Speed Control Improves Conveyor System Performance


Carton handling conveyor speeds have been steadily increasing. Some types of conveyors are approaching speeds of 500 plus feet per minute, with conveyor sorters actually attaining blazing-fast speeds up to 700 feet per minute. At these speeds the system would be handling and sorting cartons in the 200 to 250 per minute range. We are quick to point out however, that requirements for ultra high rates above 150 cases per minute are rare. High speed conveyors are not an advantage if the rest of the operation is unable to keep up. If you can't pick, pack and load at those rates, ultra-fast conveying and sortation speed may create bottlenecks that offset any gains achieved through greater speed.


In the typical picking/packing and shipping system operation there are extended periods of slow or even no volume followed by peak volume periods. Conveyor equipment that runs at a constant speed is often running too fast or too slow. In response to these highly fluctuating volume patterns, conveyor manufacturers are being pressured by their customers to better accommodate this operational reality. As a result conveyor systems can be equipped with automatic speed control through innovative solutions such as more responsive servo and VFD (variable frequency drive) control.


While conveyor manufactures have different solutions – a typical solution calls for the anticipated case volume to be entered into the Warehouse Control System (WCS). This then allows the conveyor system to automatically slow down or speed up to more closely match volume demand within system design parameters and constraints. For example – daily demand may typically peak a few hours ahead of order cut-off time when maximum speed would be most beneficial.

Holste Says...

Speed control and gap optimization initiatives have been made possible due to the continued increase in relatively cheap computing power and faster processing capability.

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Automatic Speed Control is a solution that automatically adjusts the speed to predetermined settings (low, medium, high) of the entire sortation system from merge through the sorter take-away conveyors to accommodate current throughput volume. Automatically adjusting the sorter speed reduces energy use, wear on equipment, sound levels and maintenance requirements. Automatic Speed Control extends the life of the sorter and conveyors, improves carton transportation control, while reducing operating cost.


The sorter automatically adjusts to the throughput demand as it changes throughout the day. If there is a surge or decline in flow, the sorter automatically speeds up or slows down to efficiently accommodate the variable rate. With Automatic Speed Control, the sorter does not run continuously at full speed throughout each shift of operation since actual demand fluctuates in most warehouse operation. This is how the energy savings is accomplished while allowing less stress on the conveyors and sorter. In a typical system, the speed will vary from Low to Medium to High depending on the rate of carton flow.


There are multiple applications for Automatic Speed Control in most operations. In a typical configuration, electronic sensors on the upstream conveyor network detect inbound volume. For a shipping application, electronic sensing monitors downstream availability. If the shipping operation is waiting for more truck trailers, or is temporarily under staffed, the sorter can slow down to accommodate. In this example, the Automatic Speed Control functionality allows the system to refrain from sorting high volumes of throughput to shipping when only a moderate flow can be accepted.


Another approach to higher capacity is through gap optimization where the population of cartons on the sorting system is increased by reducing the gap between cartons as they are being merged and inducted onto the sorter. Smaller gaps serve to increase the population of cartons on the conveyor, producing higher throughput volume.


To a large degree these speed control and gap optimization initiatives have been made possible due to the continued increase in relatively cheap computing power and faster processing capability. Thus allowing software engineers to develop more sophisticated logic based programs that optimize conveyor speed while minimizing carton gaps at critical merge and sorter induction points.


Final Thoughts


Conveyor speed control and carton gap optimization are not new technologies. Shippers who require more flexible conveying and sorting speed and/or higher shipping volume should first have an assessment done by a trusted conveyor system provider. A good place to start looking would be at MODEX 2018 in Atlanta, GA April 9-12. You can check it out and register at

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