Pallet-Transfer Conveyors Position Parts for Assembly
In asynchronous assembly systems, modular pallet-transfer conveyors get the right parts to the right spot, at the right time
The most common pallet-transfer conveyor carries pallets on twin strands of belt or chain. Each strand rides in a track within an extruded aluminum profile. The profiles are separated by space, and only the edges of the pallet are supported. The strands provide just enough friction to move the pallet. But, if the pallet encounters a gate or another pallet, it stops and the strands slide freely beneath it. Typically, pallets can be positioned with an accuracy ±0.02 millimeter.
The strands can be belts, roller chain or flat-top chain. Belts are made from static-dissipative rubber, and generate the most friction for moving pallets. They are used when pallets must be positioned precisely. With thick belts made from low-durometer rubber, the product may be able to ride directly on the conveyor, without a pallet. One drawback of belts is that they are more difficult to repair or resize than roller chain or flat-top chain.
As its name implies, roller chain consists of steel and plastic rollers linked together in a chain. Roller chain can carry heavy loads with minimal chain tension and power consumption. With roller chain, starts and stops have a low impact. The chain moves forward, but the rollers can spin. So, pallets accelerate slowly after stopping, which is good if you have a sensitive product or a heavy product, and you don’t want to jerk it too much on the conveyor.
Flat-top chain is a roller chain topped with flat caps of low-friction plastic or steel. Because it can flex from side to side, flat-top chain is used for carousel and serpentine layouts. An advantage of both roller chain and flat-top chain is that individual links can be removed for easy repair or resizing.
Pallet-transfer conveyors are available for handling products as small as cosmetics cases or as large as kitchen appliances. The conveyors can be arranged in many ways: side-by-side, rectangular, carousel, serpentine or even one atop the other.
Because the conveyors are built with extruded aluminum framing, they are like tracks for a model train: Engineers can easily add new sections. And, because their motion is asynchronous, these conveyors can be used on assembly lines that blend manual and automated operations.
Many options are available for moving pallets from one conveyor to another. Transfer modules lift and shift pallets from one conveyor directly across to another. They can be used at the end of a line or in the middle of one. Elevator modules are used in over-and-under conveyor setups, or to transfer pallets to another level of the factory. Curved modules or turntables transfer pallets between parallel conveyor sections.
There are also many options for stopping pallets. Cushioned stops bring pallets to a gentle halt. Lift-and-tilt and lift-and-rotate modules facilitate manual assembly operations. Lift-and-locate units raise pallets off the conveyor for automated processes. Dowel pins in the stops engage holes in the pallet for precise positioning. If the process exerts downward force on the pallet, such as a pressing operation, cams can be used to lift the pallets instead of pneumatic cylinders.
Hold-down rails can be attached to the sides of the tracks to prevent pallets from tipping. These rails are used at stations where screwdriving, pressing or other operations might tilt the pallet. Another way to provide additional locating accuracy is with guide rails. Located below the conveyor track, the rails match corresponding slots underneath the pallet. The rails are tall enough to slide into the slots and stabilize the pallet, but not so tall that they lift the pallet off the strands.
Bosch Rexroth offers a variety of pallet-transfer conveyors to match a range of pallet sizes, payloads and applications:
- TS 1 conveyors for payloads to 3 kilograms.
- TS 2plus conveyors for payloads to 240 kilograms.
- TS 4plus conveyors for payloads to 250 kilograms.
- TS 5 conveyors for payloads to 400 kilograms.
- TS 2pv conveyors for transport of solar panels.
The latter is designed to directly transport photovoltaic modules (both thin-film and silicon cell technologies). Based on the TSplus conveyor, the TS 2pv has been customized to suit the specific demands of solar panel manufacturing.
Thanks to its closed surface and a special treatment, the conveyor’s toothed belts feature particularly low friction and wear. The TS 2pv fulfills the requirements for clean room Class 6 and is static-safe. As accumulation of solar components is not permitted during transport, each section element has its own drive. Frequency converters enable soft stopping and gentle acceleration of sensitive solar products. Depending on the module size, engineers can select from various conveyor sections with multiple tracks and lengths of up to 6 meters.
Lift and transfer units are also available to move panels from longitudinal to transverse conveyors. And, a special heat-resistant conveyor version is available for applications such as transporting hot glass plates with temperatures of up to almost 200 C.
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