Accumulation conveyors are used to transport and accumulate cartons and unit loads. These conveyors are used to hold product for release to another work station or for induction into sortation conveyors. Accumulation conveyors are available in either "Minimum Pressure" or "Zero Pressure" configurations. Zero Pressure Accumulation conveyors prevent cartons or unit loads from contacting each other, while Minimum Pressure conveyors allow for slight touching and line pressure buildup. Four different types of accumulation conveyors are discussed here: Minimum Pressure Conveyor or MPC, Control Flow Conveyor or CFC, Motorized Roller Conveyor, and Chain Driven Live Roller Conveyor.

Motorized Roller Conveyor

Motorized roller conveyor utilizes 24-Volt powered rollers instead of a long driving belt. Each zone has one or two powered rollers (the motor is actually built into the roller) with short O-ring belts connecting to the non-powered rollers to provide the driving force.

This type of conveyor is becoming very popular for a number of reasons:

Control Flow Conveyor

This type of belt driven live roller conveyor provides accumulation of product in zones without buildup of line pressure. By using sensor bars or photo-eyes, each zone is activated by air pressure pushing up a snub roller to cause contact of the driving belt with the carrying rollers. When the belt contacts the carrying rollers, the product moves forward. When the belt loses contact with the carrying rollers, the product stops, or accumulates in the zone and prevents the next package from moving forward until that zone is cleared. As more products accumulate, additional zones are also deactivated until the leading zones have been cleared. Photo-eye CFC is best used when cartons are light or do not have uniform bottoms. This design also will accommodate empty boxes, since the photo-eyes sense the presence of a package and provides more exact spacing of accumulated cartons. Sensor bar CFC is best when cartons are fairly uniform and have firm, flat bottom surfaces.

Control Flow Conveyor
Minimum Pressure Conveyor Minimum Pressure Conveyor

This type of accumulating conveyor uses a unique concept. The carrying rollers are designed to be slightly eccentric so that they will alternately engage and disengage the driving belt as the conveyor rollers rotate. When cartons are stopped manually or mechanically or when scheduled accumulation is taking place, the rollers continue to rotate until they lose contact with the driving belt. When this happens, almost all driving force on the packages ceases and minimum pressure is achieved, and the conveyor is idling. To reactivate movement, an exciter pad laced into the belt passed under the carrying rollers supporting the stopped load and the rollers again start turning, moving the product along the conveyor path. This type of accumulation conveyor provides a lower cost since no air compressor is used and no air piping is required in the installation or operation of the conveyor. However, there is slight pressure exerted against the packages which requires careful consideration in design for carton sizes and weights.

Chain Driven Live Roller Conveyor

Chain Driven Live Roller Conveyor, or CDLR, is used when accumulating large, heavy loads such as pallets, drums or steel without any line pressure.

Chain Driven Live Roller Conveyor

The rollers in each zone are connected roller to roller by sprockets and chains. An air clutch is attached to one roller in each zone. Each zone is connected clutch to clutch by sprockets and chains As product moves and accumulation is to begin, the load is transported through the preceding zones and onto zone 1 at the discharge end and either depressed a sensing roller or triggers a photo-eye, removing the air pressure to the clutch in that zone which stops the carrying rollers. A signal is sent to zone 2 so that when its sensing device is activated, the carrying rollers in that zone stop.

This process continues for all the remaining zones and product is accumulated until the preceding zone is available, which triggers the movement of product to begin. Standard zone length is 5'-0" and the maximum length of the product being conveyed should be 12" less than the zone length. This product is used extensively in manufacturing applications to stage product for the next work cell and in Distribution centers to handle pallets and drums.

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