The throughput capacity of a conveyor system, as expressed in Cases Per Minute (CPM), is dependent on the slowest speed mainline conveyor and the length of product being transported. While this statement is mathematically true, there are also various operational complexities that impact on throughput. These issues tend to be broad in scope and are for the most part separate from the transportation capacity of the conveyor system.

Aside from the operational issues, conveyor system capacity is based on the speed at which cases are flowing through the system. For example:

In a typical picking and sorting system, the metering belt conveyor (located in the mainline feeding the shipping sorter) determines the maximum case feet per minute that the system is capable of delivering. The metering conveyor is usually feed from several production accumulation conveyor lines via a central merge conveyor.

Holste Says: Most conveyor system engineers agree that the actual system CPM throughput should be within 10% of the maximum allowing for normal system losses. What Do You Say? Click Here to Send Us Your Comments Click Here to See Reader Feedback

The function of the metering conveyor is to limit the case throughput rate to that which can be safely processed by the downstream conveyor equipment. The induction conveyor, which is located between the metering belt and the sorter, is designed to establish sufficient space between individual cases so that the sorting mechanism can divert them into their assigned lanes. The metering conveyor is the slowest speed conveyor in the main transportation line and therefore, determines the maximum case feet per minute the system can produce.

If, for example, the speed of the metering belt is 60 feet per minute, then it will transport (60) 12 inch long cases per minute; or (45) 18 inch long case per minute; or (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 the maximum CPM throughput capacity of the conveyor system.

Most conveyor system engineers agree that the actual system CPM throughput should be within 10% of the maximum allowing for normal system losses. If losses are greater than 10%, then an in-depth operations analysis is recommended.

Some conveyor 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 underlining operational issues.

In older systems, conveyor system efficiency can often be improved by installing new merge logic that will reduce the gap between slugs/trains from the typical 3 to 5 feet to just a few inches regardless of line release sequence. We will continue with more information on this approach in next week’s Sorting-it-Out article.

Final Thoughts

No doubt there are a lot of logistics companies, both large and small that are considering improving the throughput performance of their system operations going forward into the next business cycle. For these companies it is important that they focus on maximizing the efficiency of the equipment and system operations they currently have in-place.