Efficient material handling is crucial in optimizing factory automation. Choosing the right pallet conveyor can maximize productivity, maintainability, and overall ROI.
By Dan Toynton | Motion Automation Intelligence
Because conveyor types abound — especially small asynchronous conveyors— choosing the optimal solution for a specific application can be challenging. Informed decisions depend on well-defined design requirements and evaluation of different conveyor types.
In fact, a wide range of factory-automation applications can benefit from the use of pallet conveyors, and the pallets of such systems can be modified to fit application needs. The general purpose of such pallet conveyors is to safely and securely transport assemblies or end products to designated positions. Many end products are manufactured in stages and move from station to station as assembly and inspection progress.
Accurate product positioning at workstations is vital, and all conveyor styles to be discussed in this article can accurately lift and locate products to manufacturer specifications. However, certain pallet styles may be more advantageous than others depending on the product type and complexity. So to begin, determine the pallet conveyor’s intended purpose.
Technical factors when selecting pallet conveyors
After identifying a conveyor’s main purpose, consider operations attributes such as zoning, speed, position repeatability, pallet size, load limits, and the ability to create low back pressure. Zoning is an essential consideration for conveyors. Independently controlled zones (each with its own drive motor) enable smooth stops and starts for queued products to the next station without physical stopping mechanisms. Accumulation, the grouping of products or pallets, benefits from zoning. With smooth stops and starts, zoning helps relieve back pressure (when pallets stack up behind a stopped lead pallet) in turn reducing wear and damage.
Sometimes applications need sections with curves or the ability to change direction in a small radius or at a right angle. Fortunately, there’s likely a conveyor and pallet style that can help meet these specific needs.
Some systems can benefit from access to the assembly’s bottom for inspection. To facilitate this, the pallet can be modified to allow for the inspection from beneath using automated vision inspection equipment. This requires an open-center-style conveyor.
Another factor is system preference. For example, conveyors increasingly use low-voltage drive motors and networked control modules for simple setup and reduced wiring. These features may be advantageous for integration with existing systems.Additional items to consider regarding the application include:
- Any pallet leading-edge requirements.
- Elevation changes.
- Cleanroom requirements.
- Ease of maintenance and reliability factors.
- Jam prevention — for example, ensure the design accommodates small assembly parts.
- Environmental health and safety (EHS) guidelines.
Pallet conveyor type one:
Flexible plastic chain
This pallet conveyor type uses a modular flexible chain (tabletop) system. Pallets travel along the top of a single chain and are typically halted by a pneumatic pallet stop, held in position while the conveyor continues to run beneath the pallet.
Lift-and-locate modules along the conveyor path lift the pallet into an accurate and repeatable position for the assembly process to occur.
Advantages: Sweeping turns or tight wheel turns allow uninterrupted flow of the pallets during transit. This conveyor type accommodates elevation changes where necessary, using inclines and declines. Generally, the flexible chain can be a standard low-friction material or electrostatic discharge (ESD) rated where needed. Various modules include lift-and-locate or lift-and-rotate, plus merge-and-divert for creating parallel transit paths. Typically, flexible chain pallet conveyors are the least expensive option.
Disadvantages: Due to the frame design, the bottom of the pallet is unexposed, preventing access for inspection or other processes. There are also width restrictions because of the relatively narrow span of the conveyor typically being used. The general load limit of about 20 pounds per pallet may be an issue for certain applications. This conveyor style is generally not cleanroom-rated due to the shedding that occurs when its specific chain wears. However, wet and dry-cleaning modules are available to help reduce contamination from normal chain material wear.
Typical applications include those in automotive components assembly, medical-device manufacture, life science, health and beauty products, consumer goods manufacture, and manufacturing and assembly.
Pallet conveyor type two:
Dual timing belt
This type of pallet conveyor features two parallel timing belts exposed along rails on which the pallets ride.
Advantages: This conveyor style is typically easy to maintain, although ease of main belt replacement varies by brand. Another key feature is the relatively low cost point, which is slightly more than the flexible chain style while still below the other styles we will discuss. The open-center design allows access to the bottom of the pallet for inspection or other tasks. Finally, a larger range of pallet sizes is available (typically up to 320 mm) plus a higher load rating for both individual pallets and overall conveyor load.
Disadvantages: Dual timing belt conveyors are not suitable for pallet accumulation, especially with heavier pallet loads exceeding 50% of the rated capacity. This conveyor style is generally unsuitable for high-level cleanroom use due to dust caused by the pallets riding on the belt surface, particularly in accumulating applications. This weakness can be reduced by creating zoning sections.
Zoning can be set up for dual timing belt conveyors when initially designed and installed. This involves using multiple conveyors positioned end-to-end, creating a completed system that allows for the starting and stopping of each section. Some might argue that this isn’t technically zoning, but from a practical standpoint, it causes a similar result: The pallet doesn’t need to stand still on the conveyor as the belts run beneath it, so wear and shedding belt debris is reduced. However, costs rise with each added section, so considering roller-style conveyors for accumulation may be warranted.
Typical applications include those in automotive assembly, appliance manufacturing, medical products, electronics, and consumer goods.
Pallet conveyor type three:
Dual slip roller
Two distinct styles of slip roller conveyors are manufactured today: small timing belt-driven and gear train-driven. Both have rollers on each side of the conveyor on which the pallets run.
The drive motors turn a series of smooth drive axles, equipped with slip-fit wheels.
Advantages: When a pallet applies a load to the top of the rollers, slight pressure is put on each wheel. The resulting friction causes the wheels to exert gentle forward pressure on the pallet. This relatively low force allows for excellent accumulation conditions. The surface finish and materials in the axle and wheel contact areas minimize environmental contamination, making this conveyor type suitable for cleanroom applications. Like the dual timing belt style, the dual slip roller type features an open-center design.
These conveyors come in multiple sizes and are typically driven by timing belts, which are easy to maintain and work extremely well in some applications. Certain manufacturers use a small timing belt to drive each row of rollers.
Also available in the market is a patented design driven by an enclosed gear train that allows zoning — in other words, running only target sections of the conveyor. The zones or activated sections are changeable by removing or replacing gears in the drive train. This innovative feature is significant for those wanting extremely long drive train life, flexibility in design and potential redeployment. Gear train-driven models’ low-voltage design and the typically networkable drives improve safety and need less wiring.
Disadvantages: The single disadvantage of the dual slip roller conveyor is a higher cost compared to the other types.
Applications for this conveyor type generally have cleanroom requirements and include those related to medical devices, life sciences, consumer electronics, and assembly — especially where open-center access to allow for bottom inspection or marking is required.
Pallet conveyor type four:
Dual flexible or modular chain-driven
Using two parallel modular chains, this conveyor style features an open-center design and supports various pallet sizes and loads.
Advantages: This conveyor style is typically cost-effective given the higher loads and larger pallet size ranges supported. The open-center design allows for inspecting or marking the underside or the pallet where access is available. In addition, some larger assemblies need physical access for testing or hand tools to access the product being built.
Disadvantages: This product type isn’t typically cleanroom rated; it isn’t suitable for those applications due to dual modular chains that shed debris in the form of dust, especially following initial startup. The speed rating is more limited than the timing belt style mentioned above.
This conveyor style is typically engineered to order and may be costlier than predesigned product solutions. Designers should be aware that small parts, such as screws, can cause chain damage when dropped into dual plastic chain conveyors used in small-part assembly.
Applications include the manufacture of larger automotive products and appliance assembly.
Final pallet conveyor considerations
Various choices are tied to the features and benefits of each conveyor choice discussed, as summarized in Table 1. As pallet conveyor selection is a critical and potentially difficult decision, collaborating with a qualified partner may help sort out the best solution rather than trying to make a given style work for a given application. When choosing an expert partner, consider their ability to provide installation or field service on conveyors on a local, regional, national, or even international level. Ask about configuration tools that provide quick access to CAD drawings to streamline the process and expedite design revisions.
Design teams familiar with the features and limitations of various pallet conveyor types are more likely to find good solutions and avoid pitfalls. When searching for the suitable pallet conveyor solution, remember that a single manufacturer may have a limited selection of pallet conveyor styles and may not offer the optimal choice for the specific application. Keep options open and explore solutions from different manufacturers for the best fit.
Most of all, include the appropriate safety specialists to meet all safety guidelines.
Selecting the right pallet conveyor for specific needs requires some important considerations, but it’s well worth the cost-effectiveness.
Motion Automation Intelligence | ai.motion.com
Dan Toynton is a Conveyor Specialist for Motion Automation Intelligence. He has been involved in industrial manufacturing and automation for more than 25 years. For the past six years, Toynton has focused his efforts full-time on the proper application of conveyors for automation, including pallet conveyors. Through his years of automation experience, he has become familiar with various industries and product solutions.
Filed Under: Motion Control Tips
