Higher throughputs, fewer injuries, more consistent stacking, improved accuracy. These are just a few of the benefits automated palletizing systems have over manual stacking of pallets.

"I think the biggest benefits are ergonomic," says Mike Ehr of Fanuc Robotics (www.fanucrobotics.com ). "They eliminate the risk of stress-related injuries."

"One serious back injury can easily pay for a palletizer," adds Dick Sampson of Columbia Machine, Inc. (www.palletizing.com ). "Plus it is hard to find quality people who are willing to do hard physical kind of work anymore."

When labor savings and injury reductions are factored in, it is easy to see economic justification for automation for those companies that build a large number of pallets daily. Most can see paybacks on systems in a short amount of time.

Another advantage is reliability.

"Machines are going to be more reliable day in and day out than a person doing manual palletizing is going to be," says Ken Thouvenot of Alvey (www.alvey.com ).

As with any materials handling project, the key is to match the right equipment to the job. Palletizers should be considered as a part of the overall materials handling system, as they must be able to easily integrate with other systems and maintain the same rate of throughput as equipment feeding them. They must also integrate well with conveyors and lift trucks that will pick up the loads that they build.

There are two primary types of palletizing systems – in-line and robotic.

"With a dedicated in-line system you get speed. With robotics, you get flexibility," says Michael Hernan of Horizon Automation (www.horizon-automation.com ).

In-line systems move a layer of product, one stock keeping unit (SKU) at a time. Row strippers and vacuum heads are the most widely used systems. These systems build pallet loads the fastest, but are also the most expensive. They are typically chosen for high-flow needs.

Robotics systems build the load several cartons at a time. While slower, they are very versatile.

"Their biggest claim to fame is that they do mixed SKU handling," says Kurt Lloyd of HK Systems (www.hksystems.com ). "They allow you to customize pallets to the customer's needs."

Typical robotic systems include SCARA, articulated arm, and gantry.

Here is a brief look at each type of system.

Row stripper palletizers are the most commonly installed in-line systems and possess very high stacking speeds. They typically consist of a central staging area that accumulates one row at a time of an individual product SKU. It is here that pushers rotate, slide, or grab each carton until it is aligned with other cartons into a tight load layer. The group of cartons are then pushed or "stripped" onto the base of the pallet or onto other layers already on the pallet. Some units build from the bottom up while others form loads from the top down.

There are basically two types of row stripper designs, high-level and low-level.

High-level row strippers are faster, usually topping out at 160 cartons/ minute, and build from the top down. After being accumulated, a transport mechanism vertically lifts the cartons, moves them over the pallet, and then lowers the newly built layer so it can be slid into place. These units occupy less floor space than low-level row strippers since they accumulate and build the load overhead at 7-12 feet above floor level.

Low-level units spread out their accumulation and load building over a greater footprint at or near floor level. These palletizers build bottom up and tend to run slightly slower with peak rates of 140 cartons/minute. The unit builds an initial layer, which is held in place while another layer is built below it. The process is repeated until all layers have been built.

Vacuum head systems use a similar system of pushers and mechanical devices to accumulate and build layers. Instead of pushing the load onto a pallet, however, this system uses a vacuum head to pick up the cartons together as a row and place them upon the stack. These units typically use suction, though clamshell grippers may also be used for grabbing and placement duties.

Vacuum head palletizers are good for loading pails, drums, bags, and other odd shaped items that may not slide easily in row strippers. Vacuum heads are slower, typically handling between 10-25 cases/minute, but cost about one-third of the price of a row stripper.

SCARA arm (selective compliant articulated robot arm) palletizers consist of a single, fixed-mast robot with an arm able to rotate at the knuckles. This provides a wide range of movement along an X/Y radius. It is also designed for a high amount of flexibility, and can build as many as six pallets at a time. Unlike in-line systems which typically handle only one incoming line composed of one SKU, robotic systems can palletize multiple lines feeds and mixed SKUs. Built in bar code readers define incoming SKUs and determine how loads should be built on each of the surrounding pallets.

Speeds tend to be about 10-30 cases/minute, but they can handle a box 5x5x5 inches one moment and then lift and deposit a load that is 36x24x12 inches in the next move. The end effectors that lift the load vary among various vacuum and gripper types.

Articulated arm systems are similar to SCARA palletizers except that the arm is jointed, offering a wider range of motion and flexibility. Of course, this means that they are more expensive.

"When you desire flexibility, you have to reach for more dollars," adds Hernan. "If you have a complicated intermix load situation, then articulated arm is the robot of choice."

As with SCARA systems, there are a variety of end effectors available, including grabbers, vacuum, clamp, and units that offer dual combinations of the above. Articulated arm robots have greater reach and are good for palletizing complex mixed SKU loads. Stacking speeds are generally about 10-30 cartons/minute.

Gantry palletizers are comprised of a robot attached to a moving carriage that rides suspended from an overhead I-beam. Typically, a central conveyor line feeds into the system. The robot picks up a carton with an end effector. Then the gantry slides along cells of in-process pallets and stops at the chosen cell to add the carton upon the load. Following deposit, it returns to the pick-up station to retrieve another carton.

Robots feature from two to four rotating axis and are ideal for heavier loads, supporting cartons up to 900 lbs. Speed is somewhat sacrificed for flexibility, as systems typically achieve rates of 10-30 cartons/minute.

Gantry systems can easily build mix SKU loads and offer support to flexible manufacturing and specialty packaging needs. Up to 40 pallets can be served at one time per robot, making them ideal for building loads to customer specifications.