Sortation basics

Automatically sorting products as they move through your facility reduces the manual labor needed to prepare for palletizing, packing, shipping and other industrial operations. Today, a variety of automated sorters are available, from basic pushers and diverters that sort fewer than 30 cartons per

Lower speed sorters often work in conjunction with standard roller or belt conveyor, while high-speed sortation requires a specialized system.

A key component of most modern sortation systems is a fixed-position bar code scanner. The scanner identifies each carton on the conveyor and sends that information to the sortation system controls. The controls have been pre-instructed about the destination of each product and can activate the sortation mechanism when the product arrives at its designated divert point.

Slow-speed sortation

The slowest and least expensive sorters work in conjunction with a standard belt or roller conveyor line. These sorters typically handle fewer than 30 cartons or totes per minute.

One example of a slow-speed sorter is a deflector arm. In this design, an arm or paddle sits alongside a conveyor line, opposite a divert point. As a carton approaches, the arm swings out across the conveyor, catching the carton and channeling it off at an angle.

A generous amount of space is needed between cartons to avoid traffic jams behind a deflector arm sorter, says Mark Wossum, an engineer for systems integrator Vargo (877-876-6384, www.vmhi.com ).

These deflectors can be used in “slug mode,” Wossum says, with the arm staying in place to divert a string of cartons down the same divert point.

Another example of a slow-speed sorter is a pusher. A pusher is mounted at the side of a conveyor line, directly across from a divert point. When a product reaches the divert point, the pusher springs out across the conveyor, pushing the product off at a right angle.

Pushers are faster than deflector arms because they don't require as much space between cartons. But fast pushers can be violent, so they aren't recommended for fragile products.

Medium-speed sortation

Several styles of sorters are available for sorting cartons or totes at moderate rates (approximately 30 to 150 cartons per minute). Among the most popular are pop-up sorters. These linear sorters usually move products down the line on belt conveyor. When the product reaches its divert location, wheels or rollers pop up under the product, lift it slightly above the conveyor surface, and power it off the conveyor, usually at a 30 to 45 degree angle.

A common style of pop-up wheel sorter uses a wide conveyor belt that ends at a divert point and begins again right after the divert point, creating a gap in the conveyor. The gap is filled with several rollers that extend the width of the conveyor. Between those rollers are powered, angled wheels that sit below the level of the conveyor.

When a carton reaches the gap in the conveyor, one of two things happens:

1. The angled wheels remain in place and the carton continues moving forward—across the rollers and onto the next section of conveyor, or

2. The angled wheels rise up under the product, lifting it slightly off the conveyor. The wheels then rotate, diverting the carton off the line.

An alternate style of pop-up sorter uses multiple narrow conveyor belts instead of one wide belt. At each divert point, angled wheels are positioned in the gaps between the narrow belts. These wheels sit below the level of the conveyor until they're needed to divert a carton. When a product reaches the divert point, the angled wheels can rise up under the product and divert it.

Pop-up style sorters work best for sorting cartons or other items with firm, flat bottoms, says Jerry Vink of systems integration firm Forte Industries (800-796-5566, www.forte-industries.com ).

Poly bags or other items with inconsistent surfaces, he says, are better handled by more expensive sliding shoe sorters. (The shoe sorters can be run at slower speeds if high throughput isn't necessary.) Sliding shoe sorters may also be a better choice for fragile items. “Shoe sorters can be very gentle, while pop-up wheels can jostle products,” Vink says.

High-speed sortation

High-speed sorters divert approximately 150 to 400 items or cartons per minute. Products can be inducted to the sorter manually or automatically using induction conveyor.

There are four common types of high speed sorters. Tilt tray, crossbelt and bomb bay sorters are typically chosen to sort individual items to workstations such as packing stations or returns processing stations. The fourth type of high-speed sorter, a sliding shoe sorter, usually handles larger cartons and totes.

Item sortation

Tilt tray, crossbelt and bomb bay sorters operate under similar principles, and each type of sorter has the same foundation: a looped track with individual carriages riding on the track.

In a tilt tray sorter, each carriage holds a wooden or plastic tray. Items arrive at the sorter and are released one at a time onto the trays. An item moves around the track until it reaches its intended divert location. Its tray then tilts to one side, and gravity pulls the item off the tray. Items usually slide onto a chute or onto a takeaway conveyor positioned at the side of the sorter. The tray then rights itself and is ready to accept another item for sorting.

A crossbelt sorter works on the same basic principle, except instead of a tray, each carriage in the system holds a 2- to 3-foot cell of belt conveyor powered by a small motor. When an item reaches the divert location, the motor moves the conveyor, discharging the item sideways off the sorter into a chute or onto a takeaway conveyor.

In a bomb bay sorter, each carriage on the track holds a flat tray that has a split down the middle. When an item reaches its intended location, the two sides of the tray swing down and apart, dropping the item into a chute or container positioned directly below the sorter.

Bomb bay sorters are generally less expensive than tilt tray or crossbelt sorters, but they also have the lowest throughput, according to Ken Flick of Sedlak (216-206-4700, www.jasedlak.com ), a systems integration firm. And while tilt tray and crossbelt sorters can accommodate long items by allowing one item to span across two trays or two belts, bomb bay sorters are limited to small items.

“The bomb bay sorter does have benefits when there is a space constraint,” Flick adds. Bomb bay sorters can fit into very narrow spaces, he says, because sort locations are positioned directly below the sorter track.

While crossbelt sorters are the most expensive of these high-speed options, says Flick, they also offer the most product control because they use their own power to divert products rather than relying on gravity. This means the sorter can go faster, he says, and the divert locations can be placed closer together.

A tilt tray sorter requires more space between divert locations than a crossbelt sorter, but it also has fewer moving parts, making it less expensive and easier to maintain.

Carton sortation

Sorting cartons at high speeds usually requires a sliding shoe sorter. Instead of being configured in a loop, a sliding shoe sorter is linear: products enter at the beginning of the line and are diverted before they reach the end of the line.

The bed of a sliding shoe sorter is essentially a length of metal slat conveyor with a small rubber block (called a shoe) mounted on each slat. In most designs, the shoes line up along the side of the conveyor opposite the divert locations. The conveyor carries a carton along the line, and when the carton reaches its divert location, several shoes are activated. The shoes slide across the slats and push the carton off the side of the sorter, usually at a slight angle.

An alternate design places shoes down the center of the conveyor and sorts cartons in either direction.

A sliding shoe sorter usually sorts 200 to 300 cartons per minute, depending on the characteristics of the product and on how closely the induction system spaces the cartons.