Different Types of Gap Generation in Sortation
When it comes to sortation, one of the most important design considerations that can impact rate and reliability is the gap established between the products at induction (or entry) to the sortation machine.
It might be hard to believe that something as seemingly insignificant as the distance between products can be so critical to the sorting process, but without proper gap, sorters won’t function as designed. And beyond sortation, gap can influence all levels of warehouse automation.
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Gap generation begins at induction, which is the point at which an item enters your sorter. At the point of induction, two tasks are performed.
The first is that the item or carton, as well as its destination, are identified. This can be achieved through some method of data capture which can be either traditional scanners or cameras. Camera systems can not only read and decode barcodes but can also detect human readable information on the case. This information can then be communicated to higher level systems such as a WES (Warehouse Execution System) which will then assign the appropriate destination for sortation.
The second task accomplished at induction is the generation of gap, which is the proper spacing between the cartons or parcels on the sortation.
Factors Impacting Required Gap
Though gap may refer to either distance or time between product, distance is the more common designation. A certain amount of gap is required in any sorter so that the system can divert product to its destination without error.
The amount of gap that your system needs to operate efficiently is highly dependent on a number of different factors including, but not limited to: The type of sorter being used, the width of the sorter, the speed of the sorter, the maximum sorter rate (products per minute), etc.
Proper gap is required for your sortation system to work at its designed maximum sort rate. Required gap varies across each type of sortation systems. For example, pop up wheel sorters can require a gap of approximately 18 inches to sort reliably, whereas a shoe sorter can sort down to as little as one shoe of gap. This reduced gap, along with the greater speed of the shoe sorter, attributes to its greater rate capability.
The weight distribution in the product being handled can also be of concern; if an item is top heavy, it may topple over during sortation as the system accelerates or decelerates to create gap. Gapping algorithms need to take into account the g forces placed upon conveyable items so that items don’t get toppled when gap is being generated.
Types of Gap Generation
Gap can be generated in your sortation system in a number of ways, but the three basic methods are blow through, start/stop, and gap optimization. At its most basic, creating a gap between items is done by using two conveyors running at different speeds. This difference in operating speed is what creates the gap between items as they enter the sorter.
Blow Through Gap Generation
Blow through gap generation utilizes gapping conveyors that operate at fixed speeds. Because of this, the distance between items (gap) is also fixed. If the sorter handles both large and small items or cartons, this can result in wider gaps between items, which translates as wasted space and lowered sorter throughput.
Blow through gap generation offers the least control when it comes to creating gap. It is very much a “set it and forget it” kind of system, most ideal for operations that handle a limited variety of products.
Start/Stop Gap Generation
Start/stop gap generation is more or less exactly what it sounds like. Once the first conveyor (the infeed unit) releases the first item onto the second conveyor, it will momentarily pause or stop. This holds back subsequent packages which were previously back to back or almost touching on the first conveyor. The length of the pause will allow the first carton to pull away and create a gap between the next carton in line. Once this gap is achieved the next carton will release.
Gap Optimization
In gap optimization, the primary goal is ensuring that gap remains consistent between items, regardless of item size. This is done through the use of sensors, which determine the distance between items entering the sorter and then accelerate or decelerate the conveyor to achieve the desired gap. This method of gap creation ensures that all items have enough gap to allow for proper scanning/sorting, while minimizing wasted space so that throughput remains high.
Compared to blow through and start/stop gap generation, gap optimization offers the most control over gap creation and is ideal for operations that handle a wide variety of products. While gap optimization requires a higher investment than other alternatives, it can be applied when required to ensure the required system throughput performance is achieved.
Bridging the Gap
When selecting a new sortation system for your distribution center or warehouse, there are numerous critical factors that need to be considered and factored into the system designs. While things like sorter cost and type are obvious, it’s easy to overlook the impact of gap generation on your operation’s efficiency. A skilled systems integrator can help you ensure that your system utilizes the best technology for your needs.
