How Palletizers Stack Up

It’s hard to imagine a modern distribution system without pallets and palletized loads. With the exception of single parcel shipments, just about everything shipped in any quantity is placed on a pallet and unitized into a compact high-density load for transport. Pallets are stacked, placed on racks (shelves) and handled in many different ways with the goal to deliver products quickly and efficiently. Pallets have made bulk handling of product extremely simple and the fork lift truck that moves pallets is common in stores, warehouses and any area where product is moved.

PORTABLE PLATFORMS
Describing a pallet and the product it contains is straightforward. A pallet is a raised platform upon which goods are placed for transport. Typically, the palletized items – cases, bags, cans, bottles, etc. – are smaller than the pallet. The pallet becomes a space efficient, easily handled transport mechanism for all of the smaller items. It may be made of wood, plastic, metal or corrugated kraft board and is usually rectangular in shape with the standard size of 40 in. x 48 in. The product is arranged on the pallet in an orderly and compact pattern permitting efficient handling throughout the distribution system. Patterns conform to the pallet shape and produce the optimized load in the pallet dimensions while maintaining structural strength forthe load.

Pattern design is dictated by how the pallet is handled in the distribution system. Pallets with a pattern designed for a shipping container may be different than those that move through a trucking system and a racked warehouse in a distribution center. The cases are not stacked the same on each layer on most pallets. Rather, an interlocked arrangement of cases is used to stabilize the load. Cases are arranged by length and width against each other to form a layer of the multiple layers in the unit load. Unless the cases are heavy or large, the tiers or layers are changed, normally rotated 180 degrees, to maintain structural strength in the stack of the load and to keep the layers from breaking apart in transit. Many pallet patterns deliberately produce small gaps or openings within the layers. This gap is a result of how the positioning of the cases end up creating a uniform outside cube on the pallet.
In determining how to palletize product, the packaging engineer must have an overview of the distribution system, the method of transport and the storage requirements of the product to determine the pallet load design. Originally hand palletization was used to stack the product in the pattern specified. While it is the most versatile way to stack product on a pallet, this method is only effective when the rate of product being palletized is slow. Automated single product palletization with a single pallet pattern evolved from hand palletization. High-level palletizers were developed to handle high-speed production operations that produced product at 50 to 60 (or more) cases per minute. The machines quickly placed and stacked cases on a pallet for shipment. Most high-level palletizers can handle six layers or tiers of product per minute. This modest beginning of one type of machine from the mid 20th Century has now evolved and expanded into a variety of methods for placing and arranging products on a pallet.

PUTTING PRODUCT TO PALLET
There are four basic designs or types of palletizers widely used in the industry today. These are high-level palletizers, low level palletizers, articulated arm robots and gantry palletizers. (Gantry type palletizers may use a robot arm or crane arrangement to pick and place the product on the pallet.)
Beyond the four basic units there are a number of other palletizer types with very specialized designs. These designs address unique products or situations including bulk palletizers for empty cans or bottles, and miscellaneous palletizers designed to palletize products packed in bags, drums and kegs. These are a small part of the overall market.

Of the four basic designs or types of palletizers the high-level or low-level are used most often for high-speed operations. This is sometimes referred to as fixed automation (the machine does not move). The difference between the two designs is how the tiers are first organized and then stacked on the pallet.
The name “high-level palletizer” describes, in general, the operation of the machine. A high level palletizer receives the product being palletized at an elevation or level considerably above the pallet. The pallet is fed into the palletizer from a magazine or accumulation station. As the pallet enters the palletizer it is raised and positioned under a bed or tray. The product moves onto the bed or tray and is organized into a single layer or tier of product. The pallet is below the level of the assembled tier and the entire layer of product is gently placed on the pallet. The equipment then begins organizing the second tier of product, modifying the arrangement of the cases to match the requirement of the pallet pattern. A slip-sheet, a heavy sheet of paper or paperboard, is sometimes used to separate the layers. The pallet and the first layer of product is lowered to the height of one layer and the second layer is placed on top of the first. This lowering of the pallet, layer by layer, is repeated until the correct number of layers is in place. The full pallet then lowers slowly to floor level and moves by conveyor or forklift to any banding or stretch wrapping operation employed prior to shipment. A second pallet is moved into position, raised to the level just below the forming bed and the process is repeated.

“Placement of the first layer on the pallet and placement of subsequent layers is critical in all palletizing operations,” says Ted Yeigh, Columbia Machine Inc., Vancouver, Wash. Products may not fit the standard dimensions of a pallet and when placed on the pallet they may “overhang,” or “underhang” the pallet edge. (Overhang means the cases stick out beyond the edge of the pallet, while underhang means the product does not reach to the edge of the pallet.) The palletizer must place each layer of product on the pallet in precisely the right position to minimize problems created when there is too much overhang or underhang.

Low level palletizers have the advantage of smaller footprints than high-level machines. A pallet in a low level machine is neither raised nor lowered and the tier or layer is formed at a level closer to the floor. Each layer is formed on a bed and then raised and lowered to transfer the load to the stationary pallet. The bed then returns to the starting position and the next layer is formed. After the pallet is completely loaded, it is discharged from the palletizer and another pallet is positioned and the process is repeated. Low-level palletizers normally move two and possibly three layers per minute onto a pallet.

Robotic palletizers, both articulated arm and gantry type, have begun to appear in increasing numbers in the last decade. Usually considered pick and place systems, robotic palletizers can pick up a single case or multiple cases of product from one or more locations and place them at pre-programmed spots on the pallet bed. Basic computing capability, combined with sensors to identify product variations, make robots intelligent systems that can identify and separate multiple product or package outputs. Robots also offer the ability to automate multiple production lines with one machine. By placing the discharge of multiple lines near a robot location, one robot has the capability to identify and handle multiple products. Robotic palletizers can also produce multiple pallet loads based on the size, shape or other identifying characteristics of the packaging line output, on multiple finished pallets. This is accomplished by the robot’s ability to rotate or move—a capability not available in fixed position high- or low-level conventional palletizers. Robot palletizers are generally slower than conventional systems because they may handle one case at a time or because they manage multiple functions at the same time. They typically handle 15 to 30 cases per minute.
Like all robots, those used in palletizing are described by the type of arm they use. Smaller, lighter products or applications use an articulated arm with multiple axis capability. Heavy weight products rely on a heavier arm or a gantry arm that typically has a limited number of axes of movement. This distinction is not absolute, however, and one can find cross examples with many variants in different robot palletizer operations.

The last group of machines are specialized palletizers designed for unique products or material handling opportunities. Bulk palletizers are the most common of these specialized units. A typical packaging application for a bulk palletizer would be building loads of empty cans for shipment from the canmaker to the filler. The unfilled package is palletized at the manufacturing location using a minimum of packaging and then transferred to the filler. Cans fit well in this bulk handling process, given their high inherent column strength. Metal cans are assembled in layers on a pallet with a slip-sheet between the layers. Each palletized tier of cans is banded to secure the load and then transported to the can filler where the process is reversed and the bulk cans are depallitized onto a filling line.

PICKING A PALLETIZER

Palletizing equipment has been undergoing major changes in the past decade to keep up with different demands from different parts of the supply chain. “New Human Machine Interface (HMI) controls are transforming both conventional and robotic palletizers,” says Yeigh. “These controls permit the machines to be quickly reconfigured to handle different case sizes, pallet patterns and layers of product on the same machine.”

The computerized controls also provide improved data gathering and reporting. Real time reporting of production, alarm reports and downtime reports are some of the common capabilities customers need to refine their operations, along with other pieces of information important to the supply chain, like hourly output. Many of the new machines also contain complete schematics and operation manuals making them simpler and easier for people to troubleshoot and repair equipment without a call to the equipment supplier.

In many cases, the computer interfaces walk the operator or mechanic through troubleshooting or preventative maintenance. These interfaces are permitting palletizer makers to produce higher speed machines that can handle smaller case sizes.
“Many of the big box stores are moving to smaller cases and in some instances from traditional cases to shrink-wrapped product bundles increasing the capability and handling demands required on the machines,” says Yeigh. Both manufacturers and retailers are attempting to reduce waste and packaging, to deliver the largest amount of product to the consumer with the least amount of packaging.

HMIs are also making palletizers extremely versatile. “One robotic cell can handle four or five manufacturing lines because they can be adapted to multiple product variations, and because they typically handle only one or two units per movement,” says Harry Horni of Priority One, Bel Air, Md. “This gives them maximum flexibility in building different pallet patterns at the same time.”

Robotic palletizers, particularly gantry type palletizers, are moving into many distribution centers. These robots can handle a large number of lines and SKUs. “. . . (a gantry) can handle a large number of lines, sometimes 15 or more, and can produce the layered ‘rainbow pallet’ that makes distribution more efficient. A rainbow pallet is one where different layers may contain different products,” Horni says. “These systems can completely automate case picking operations for products like soft drinks, where different flavors in different quantities are needed at different stores.”

Ergonomics are a big advantage palletizers are bringing to smaller manufacturers. “A palletizer, either a conventional low level or robot, will minimize ergonomic issues associated with repetitive motion, lifting and rotation by employees doing hand palletizing,” says Dave Mathews, sales channel and new product development manager, Brenton Engineering Company, Alexandria, Minn. Small manufacturers are becoming aware of these advantages and in many cases are installing machines in operations that were not considered for a palletizer based on ergonomic improvements for employees alone.

Palletizers still have much room for improvement. The ability to organize at the case or unit level has started but still requires more refinement. Today’s supply chain, with its speed and intricacy, is a very new animal. The challenge facing palletizers is taking an old idea and keeping it new and useful to the new ways of handling and distributing product.

Columbia Palletizing provides expert palletizing equipment for manufacturing, shipping and receiving.

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