Minimum and Zero Pressure Accumulation Conveyor
Accumulation conveyors are typically used to transport and accumulate cartons and unit loads so that they efficiently queued up and fed into sorting, palletizing, strapping, wrapping or many others processes in a distribution or manufacturing operation. They are used to provide a buffer zone where a steady supply of product can be oriented or held back when downstream processes are not ready for additional product. In addition, accumulation conveyors can be used to smooth out fluctuations in production line rates caused by stoppages or machines operating at different speeds.
Depending on the process that the accumulation conveyor feeds into, the products will release in singulation or slug fashion. A singulation release method is when the conveyor zones are controlled such that the product is discharged from one zone only when the immediately adjacent downstream zone is empty. This release method is typically found for most in-process accumulation and release applications, such as packing, weighing or shipping lines.
Slug release method is when multiple adjacent zones are simultaneously ran in order to provide a large quantity of products to discharge in rapid succession. This is typically done in a merge zone where several parallel accumulation conveyors are feeding into a single higher throughput takeaway conveyor.
There are two types of accumulation conveyors; minimum pressure and zero pressure. A minimum pressure accumulation conveyor does not eliminate the driving force while the products accumulate whereas on zero pressure accumulation conveyors, the driving force is completely eliminated.
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Zero Pressure Accumulation Conveyor
In order to ensure that products do not touch each other while they accumulate, zero pressure accumulation conveyor is used. In zero pressure accumulation conveyor, each zone has a photo-eye sensor sending a product presence signal to a zone controller. If there is a product present in the adjacent downstream zone, then the zone controller keeps the drive rollers from activating. Once the zone controller receives a signal indicating that the next zone is clear of product, then the drive rollers are activated thereby conveying the product to the next zone.
Zero pressure accumulating conveyors are commonly found in distribution centers where there is a wide variety of product width and weight. Here are two of the most common zero pressure accumulation case conveyors:
Motorized Driven Rollers - Now known as "Green Conveyors" because of their energy efficiency and other environmental advantages over traditional 230/460V AC conveyor, these conveyors use 24V DC technology to drive the motor housed inside the roller that powers its zone.
Belt Driven Liver Roller with Photoeye Sensors - Belt Driven Live Roller (BDLR) with photoeye sensors typically divides the 10' or 12' conveyor section into three or four zones. Each zone has a photoeye that senses product presence within the zone. A belt under drive rollers, or carrying rollers, is raised up to engage the drive rollers or lowered to disengage them by pressure rollers that are air or mechanically actuated. The signal to actuate the pressure rollers is provided by a programmable logic controllers (PLC) or a local zone controller mounted on the conveyor frame.
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Minimum Pressure Accumulation Conveyor
Minimum pressure accumulation conveyor allows products to lightly come into contact with each other as they accumulate on the conveyor line. An effective minimum pressure accumulation conveyor keeps the product stopped, even with the cumulative back pressure of the products behind it, until the appropriate signal is given to release the product. Great consideration and understanding of all of the static and dynamic forces must be accomplished in order to effectively apply minimum pressure accumulating conveyors in your material handling system
Minimum pressure accumulating conveyors are commonly found in manufacturing facilities where there is more uniformity in the product dimensions and weights. Here are two of the most common minimum pressure accumulation case conveyors:
Belt Driven Live Rollers with Pressure Rollers - The operation of a minimum pressure accumulating conveyor using BDLR with pressure rollers is very basic and often a good economic decision. The conveyor uses standard BDLR except that each of the 3 or 4 zones in a 10' or 12' section contains a pressure roller mounted in a spring adjusted carrier. The pressure rollers senses the required driving friction required to between the drive belt and the carrying rollers in order to conveyor and accumulate without too much back pressure.
Line Shaft Conveyor - Line shaft, or spool conveyor can be altered just like BDLR in order to make it minimum pressure accumulation conveyor. Each zone in a 10' or 12' section has a pneumatically operated break to be applied to the drive rollers in each zone. When a photoeye senses product presence in the adjacent downstream zone, the break is activated and accumulation occurs. When the zone is cleared, the break releases causing the product to convey to the next zone.
View Video of Hytrol's Gen3 Accumulation Conveyor and Controls Technology |
