Pallet conveyors transfer discrete products on carriers referred to as pallets typically transported by belt, roller chain, flat-top chain, or for extremely high loads, powered rollers.
Pallet sizes are for the most part standardized among manufacturers in metric dimensions (240 x 240 mm for example) although some manufacturers offer pallets in inch or non-standard metric dimensions.
Here, pneumatic cylinders are used to stop and lift the pallet. Precise locating is achieved by pins that mate to bushings on the pallet.
Image credit: mk North America Inc.
In many cases, conveyor pallets are tooled with custom fixtures to locate and secure the product on the pallet. So not only can the pallet be accurately positioned on the conveyor, but the product can be precisely located on the pallet. This makes pallet-based conveyors the ideal solution for high-precision assembly, machining, inspection, and positioning tasks.
Note that the pallets discussed here are different from the pallets used for storing and handling bulk goods, which are often made of wood or plastic. Similarly, some roller and chain-driven conveyors are marketed as “pallet conveyors” for the transportation of these wooden or plastic pallets through a factory or warehouse.
Pallet conveyors are suitable for transporting products in two dimensions, but can accommodate small elevation changes. Curved sections — typically from 15° to 180° — allow conveyors to change the direction of transport while maintaining pallet orientation.
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Pallets can be transported around corners without changing the pallet orientation.
Image credit: Dorner Mfg. Corp.
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Although they’re typically offered in standard sizes, pallets can be tooled with custom fixtures to locate and secure the product on the pallet.
Image credit: Glide-Line
Conveyor modules referred to as lift and rotate units allow the orientation of the pallet to be changed while maintaining the direction of transport. Pallets can also be lifted and precisely located, for positioning at a workstation or inspection area, where pallet conveyors allow access to the workpiece from more than one side. For access to the bottom of the workpiece, pallets can be made with an open center.
For the heaviest loads, in applications such as appliance assembly and automotive manufacturing, pallets are transported by rollers.
Image credit: Bosch Rexroth Corp.
The use of pallets to move individual products allows non-synchronous movement, so each product can be transported and routed independently. Because the pallets are precisely machined, they can be accurately positioned and located via sensors, and RFID tags or other data carriers can be attached to each pallet to track and document individual product movements. Pallets can be diverted and merged for offline operations, and accumulation allows products to be buffered, smoothing the flow of downstream operations.
Most pallet conveyors — especially those used in automation applications — are modular, based on standard conveyor sections, legs, and lift/transfer/rotate modules that can be easily reconfigured or expanded as needs change. And because components are standardized, pallet-based conveyors can be configured to meet a wide range of environmental requirements, including cleanroom, dry room, washdown, and ESD-compatible applications.
This SPU recirculating pallet conveyor from mk North America is suitable for accumulating applications. This version shown here is a single-wide variation that excels in buffering areas that compensate for different cycle times — both upstream and downstream.
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