Submitted by Intelligrated and Intralox
The process of fulfilling an order can have many levels of automation depending on factors such as the product being shipped, rate requirements and investment levels. There is a broad range of conveyors and sortation technologies that can be mixed and matched to engineer order fulfillment solutions based on the level of automation desired. As an introduction to conveyor and sortation, this overview will discuss the vast technologies available by function. Note – this overview will discuss case conveyor and sortation technologies only, and the wide range of pallet handling technologies will not be covered.
Conveyors are equipment that transports items, cases, totes or bulk material from one position to another. Conveyor technologies are typically grouped into three sub-categories: transportation, accumulation and system conveyors.
Transportation Conveyor Technologies
This category represents the high volume of straight conveyors used to transport a product. In general, these specific conveyors are not intended to be used to accumulate product.
Non-powered conveyors consist of a frame and gravity rollers or wheels. With no power transmission, they are the least expensive conveyor type in this group. They are often used in order fulfillment areas to stage items or containers during the picking process. They are also often installed at a slight pitch to transport items. In this application, the conveyor can accumulate items, but not to the sophistication as the technologies in the next category.
Belt conveyor is one of the most commonly used conveyor types because it is a very cost effective option for moving an item from one point to another. Belt conveyor is also the most effective way to change elevation in a conveyor system due to the high friction provided between the carrying belt and the item.
Belt conveyor (Image courtesy of Intelligrated)
Belt Driven Live Roller Conveyor
Belt driven live roller conveyor is similar in construction to a belt conveyor, but with rollers on top of the belt. The belt drive underneath the rollers is typically a flat belt, round belt or v-belt. The roller conveying surface is better suited when items are loaded from the side of the conveyor. Rollers can also provide “skewing” functionality to help keep items aligned on the conveyor. Belt driven live roller conveyors are not well suited for elevation changes and are typically more expensive than belt conveyors.
Modular Plastic Belt Conveyor
Constructed of plastic modules and hinge rods, and driven and tracked by plastic sprockets, modular plastic belts have the following qualities: high strength, low and high friction options, abrasion resistance, corrosion resistance, easy to clean, positive drives, and the ability to be built with a variety of flights and other accessories. It is a safe, low maintenance option effective in case handling. It can offer some unique functionality, but is also the most expensive of the transportation conveyors described in this paper.
Modular plastic belt (Image courtesy of Intralox)
Accumulation Conveyor Technologies
This category represents conveyors designed to transport items with the ability to build up a queue of products as the conveyor waits for downstream equipment to become available for further product flow. Accumulation conveyor is critical to achieving high rates through a system while keeping equipment speeds as slow as possible. There are several types of accumulation conveyor as described below.
Minimum Pressure Accumulation Conveyor
The term “minimum pressure” refers to the amount of driving force the conveyor puts on an item that has been accumulated. A minimum pressure accumulator has some level of driving force on cartons at all times. These conveyors are typically belt-driven roller or modular plastic conveyor belts and are more cost effective than the other accumulating conveyor types. This technology is typically not applied for higher rate systems or with items that can be damaged due to excessive pressure. This is the least expensive technology in this group as it requires no accumulation zone activation.
Minimum pressure accumulation conveyor (Image courtesy of Intelligrated)
Zero Pressure Accumulation Conveyor
The term “zero pressure” means that once an item has accumulated, the driving pressure beneath the item is completely removed. By definition, this requires some “activation” process of the drive engagement to the carrying rollers. Zero pressure accumulation allows an item to be easily removed from the middle of an accumulated conveyor. Zero pressure accumulation conveyor is typically made up of photo-electric sensors and on-board zone logic to control the drive actuation. The on-board zone control will be directed by a system level control when it is time to release the items accumulated on the conveyor. The rollers are typically driven by a belt or a padded chain. This technology is typically more costly than minimum pressure accumulation, but a lower cost than zero contact accumulation.
Zero Contact Accumulation Conveyor
Zero contact accumulation conveyor stops items in accumulation mode before they contact the next downstream item. The conveyor is typically built with a small motor and photo-electric sensor controlling each “zone” and often referred to as motor driven roller (MDR). The speeds of the rollers must be lower to keep the conveyor operating with only one item per zone.
Additionally, since there are gaps between every item, the maximum throughput is much lower than a zero pressure accumulator. Zero contact accumulators are typically quieter, safer and easier to install than other conveyors because they are modular and use low voltage components. Since each zone only runs on demand, this technology can provide significant operating energy savings, but this usually comes at the cost of a higher initial purchase price.
System Conveyor Technologies
This represents conveyors that have a unique purpose which is applied to make the transportation and accumulation conveyors function as an integrated system. These specific conveyors are not typically “high volume” as the transportation and accumulation conveyors, but they are essential to any automated order fulfillment system.
Unscramblers / Singulators / Pallet Layer Descramblers
This technology is used to ensure there is a single file stream of items on a conveyor prior to some consolidation of flow in the system (a merge) or a decision point of re-direction in the system (a sorter). Unscramblers and singulators are typically used to separate occasional side-by-sides in a conveyor system or to consolidate bulk items into a single stream of product in a conveyor system. A pallet layer descrambler is another variation of this technology that is used to descramble, singulate, edge align, and sometimes correctly orient full pallet layers of product into single file.
Pallet Layer Descrambler (Image courtesy of Intralox)
Brake Metering Conveyors
This technology is typically used prior to merges and sorters in a conveyor system. Individual lanes which consolidate to a single takeaway would be controlled by turning on and off the brake metering conveyors as the control point in the merge. Brake metering conveyors also typically separate items by a fixed speed change between two belts. As items move from the slower first belt, to the faster second belt, a gap is pulled and photo-electric sensors can measure the item length. This data is used in the system control. Often brake metering conveyors are used to ensure a certain minimum gap prior to induction onto a sorter.
Curves and Junctions
The technology used to articulate a conveyor line around a curve is often similar to the technology used to create a junction conveyor. Used often in a conveyor system when products are changing direction and it is desired to maintain the orientation of the item (i.e. the long dimension of the item is in the direction of travel).
While a merge is really comprised of an entire system including hardware, control devices and software, the technology used to consolidate the conveyor lines and take-away the items away in a single line of flow is often referred to as the merge. There are several types of merge technologies.
One of the more popular technologies is sometimes referred to as a “sawtooth” merge where the perpendicular take-away conveyor would be a roller or belt transportation conveyor. A sawtooth merge may be controlled with “space available” logic where the merging conveyor looks for a window of opportunity large enough to fit the next carton. It may also be controlled with a “timed release” of each merging lane to balance the flow of materials from several conveyor lines.
Another popular technology is a “combiner” merge where parallel conveyor lines feed a wide merge which combines the items prior to discharge. The take-away conveyor will typically be parallel to the infeed lines. Very high rates can be achieved with a combiner if products are released one at a time (or “zippered” together).
At first glance, a staging type merge may look very similar to a sawtooth merge. However, a staging merge can achieve much higher rates by building long slugs of gapped product from a conveyor line on a staging belt. The staging belt then awaits its turn in the upper control merge priority before ramping up to a higher speed and delivering a dense packed stream of product.
Once the conveyor system has collected and consolidated items, there are several technologies used to automate the distribution of these items. One of the more common uses of a sorter in an automated order fulfillment process is to sort items to packing stations. Another common use is sorting finished orders to specific destinations or shipping dock doors. There are several technologies available and should be chosen based on a variety of factors such as item type, item size and throughput requirements just to name a few.
Maintained Orientation Line Sortation
The term “line sortation” refers to the layout and induction of the sorter. A “line” sorter is a single line of conveyor with items inducted at the infeed end of the machine. Items that are not diverted off the sorter go to a downstream conveyor typically referred to as a “recirculation” line. “Maintained orientation” sorters do not rotate products in their respective direction of travel. In other words, if an item enters this sorter with the long dimension in the direction of product travel, it will exit the sorter in the same orientation.
A deflector is a mechanical device that will redirect an item off a belt conveyor onto an aftersort lane. The deflector could have a vertical belt or it may have a low friction static face. Deflectors are typically best applied for a small number of diverts at a low rate. Items to be deflected must be capable of withstanding the impact of the deflector.
Wheel Divert Motor Driven Roller Sorter
In a motor driven roller (MDR) system, wheel diverts which rotate to redirect items can be added. In some cases, it is beneficial to use the same MDR technology for all conveyors in a small compact system. The single item per zone and run on demand technology can provide great benefits, but also limit the throughput to approximately 30 items per minute.
Wheel Divert Sorter (Image courtesy of Intelligrated)
Pop-Up Wheel in Belt Sorter
Wheels set at a fixed angle will lift at the appropriate time and divert items to an aftersort lane. In some cases, wheels will not lift, but rotate to initiate the divert. There are several unique solutions that have been developed which fit into this category. Wheel divert sorters are not considered “positive” sortation because the divert operation is dependent on good friction between the item and the wheels. They are typically best applied when the sorter must handle approximately 20 divert locations or less and at rates of about 100 items per minute or less.
Pop-Up Wheel in Strip Belt Sorter
Similar to the pop-up wheel in belt, the strip belt sorter uses wheels that lift to sort items. The continuous strip belt carrying surface eliminates the transitions that occur at every divert point on a pop-up wheel in belt sorter. This can provide better tracking from a sorter control perspective resulting in higher throughput rates.
Activated Roller Belt Sorter
With an activated roller belt (ARB) sortation system, products are conveyed on rollers embedded in a plastic belt and engaged from below enabling sorts at 30-degree divert trajectories. Moving parts are contained below the conveying surface providing gentle product handling and operator safety. ARB sorters are bi-directional capable and have a small footprint even when there are many diverts. The system effectively sorts a wide range of products from corrugated boxes to loosely packed polybags with throughput rates of up to 350 packages per minute.
Activated roller belt sorter (Image courtesy of Intralox)
Sliding Shoe Sorter
As an item is inducted onto a sliding shoe sorter, corresponding shoes (or pushers) are assigned to each item. When the item reaches its intended aftersort lane, the assigned shoes are “switched” to follow a track inside the sorter, thereby pushing the item off the machine. Sliding shoe sorters are capable of rates up to the 400 per minute range and usually yield the best ROI when applied over 10 to 50 divert locations.
Belt Slat Sorter
Similar to the sliding shoe sorter, the belt slat sorter replaces the sliding shoes with articulating belts. This can be beneficial for sorting bags with straps or buckles that may get caught in sliding shoe sorters.
Belt Slat Sorter (Image courtesy of Intelligrated)
Right Angle Line Sortation
“Right angle” sorters will change the items orientation as the width dimension becomes the items length and vice versa. In some applications, there is a significant benefit to changing an items orientation. This can simplify the aftersort conveyor system and can maximize item storage density in the aftersort lane.
Padded paddles “push” items off a belt conveyor perpendicular to the direction of travel. This technology typically requires a relatively low capital investment, but has the potential to cause damage upon impact with the item and requires gaps large enough for the paddle to activate and return.
Right Angle Transfers
The term “right angle transfer” usually applies to the lifting and diverting of products by belts between rollers in a motorized driven roller system. Right angle transfers are usually limited to about 30 items per minute.
Right Angle Transfer (Image courtesy of Intelligrated)
Pop-Up Roller in Strip Belt Sorter
This is very similar to the pop-up wheel in strip belt technology, however the pop-up roller diverts the product at a right angle changing item orientation. The continuous contact of the strip belts helps throughput rates, but gaps between items must be large enough to compensate for the lift-divert-lower process of the rollers.
Dual Activated Roller Belt
With a dual activated roller belt 90-degree sorter, products are conveyed on rollers embedded in a plastic belt and engaged from below enabling 90-degree divert trajectories. This type of sorter is capable of very high rates for right angle sorting and maximizes floor space by diverting on very tight centerlines.
Dual Activated Roller Belt Sorter (Image courtesy of Intralox)
In contrast to the previous two sortation categories, a “loop” sorter is a continuously rotating machine with the opportunity for multiple induction points. The ability to induct manually or automatically at several locations gives this technology a higher throughput capacity. The carrying surface of the sorters is well suited to handle a wide variety of items and sort individual items in an order consolidation process.
This sorter uses trays mounted to carts on the continuous loop conveyor. The trays tilt and transfer items down into a chute when an item reaches its destination. A tilt-tray sorter can have a high volume of chutes which can each be used as temporary order consolidation locations.
Tilt-Tray Sorter (Image courtesy of Intelligrated)
This sorter is very similar to the tilt-tray technology, but it uses articulating belts on the carts instead of tilting trays. The belts can provide a more positive and predictable divert operation with certain item types.
This sorter is deposits items into locations directly under the carts rather than diverting them off to the side of the machine which can save floor space in some applications.
Sortation Application & Rate Charts
The following charts help explain the best applications and rate capabilities for each of the sortation technologies discussed. Please note that the data in these tables represent typical rule of thumb industry specifications and in most cases do not specifically pertain to a specific manufacturer. If you need help with a specific application, please contact an MHI OFS member organization.
Fig. A - Typical Item Type/Sortation Technology Fit Chart
The chart below represents typical “best fit” practices when it comes to matching the best technology with varying item types.
Fig. B - Typical Technology Specifications Chart
The chart below illustrates other considerations for item type, including size, weight and minimum gapping requirements.
Fig. C - Typical Technology Specifications Chart
The chart below represents typical “rules of thumb” rates by sortation technology. These rates assume average item sizes.