To enhance efficiency and ergonomics, processors are turning to high-speed mechanical and flexible robotic systems to stack their boxes, bags or pails onto pallets and slipsheets.

The robots are coming! The robots are coming!

Automatic palletizers - robotized and otherwise - are used in all industries to unitize loads of boxes, bags, pails and even discrete parts prior to shipping. Manual pallet loading works all right for some applications, but when loads get heavier and production rates increase, manual labor becomes a cost burden - not just in wages paid out, but in workman's compensation claims resulting from repetitive motion and lower back injuries.

In contrast, mechanically and electronically automated lines can reduce labor expenses and eliminate injuries. Palletizers - including systems that handle slipsheets - can provide sufficiently gentle product handling for most products while surpassing manual operations in speed and uniformity. And anyone who has spent time at the dock knows that pallets not stacked uniformly are less stable and are a chief cause of product damage.

How big is the market? According to Tom Carbott, managing executive at the Material Handling Industry of America (Charlotte, N.C.), upwards of 40 mechanical palletizer suppliers exhibited at the ProMat 93 materials handling show in Chicago this past February. As for robotics, MHIA's 1992-93 Material Handling Product Directory lists 17 robot suppliers. (Copies of the directory are offered at no charge.) The FP Resource also lists approximately 30 palletizer sources and 20 robotic companies serving material handling needs.

Types of palletizers

A step from manual palletizing is the use of arm-like vacuum grabbers, such as a pneumatic hose with suctions, installed above the work area. Instead of heavy lifting, the user's job is to guide the item onto the pallet. But manual operations are still slow and labor-intensive. Higher throughput applications require automated systems.

Processors may turn to automatic palletizers with equipments as low as 10 cases per minute. Systems are available that can handle 100 or more per minute. It is difficult to generalize about a typical palletizer application because the food industry is anything but monolithic - even applications within a given product category can vary widely.

Factors that influence your choice in palletizers include package/case weight, the variety of products that need to be palletized, system capacity, ability to handle multiple stacking patterns, changeover time, the speed and elevation of infeed and discharge conveyors, and cost. Cost can range from under $40,000 to hundreds of thousands of dollars for a single high-capacity palletizer, plus extra costs for accumulators and other material handling considerations at the infeed or discharge.

Mechanical systems begin with vacuum head palletizers, which use pneumatic suction cups to lift and stack layers of boxes, bags or pails onto a pallet. For high-speed stacking of regular-shaped rectangular boxed products, newer row-stripping palletizers are the norm. These machines arrange boxes on a stripper plate that transfers completed layers onto the pallet load. Floor-level units increase accessibility for maintenance and correcting line jams; elevated models require mezzanine access but may better match the height of a plant's conveying systems. While palletizers generally form layers, row-assemblers ad accumulation conveyors are added at the infeed for multi-line applications.

Most palletizer suppliers offer control packages based on programmable logic controllers (PLCs) and, increasingly, operator interface computers to further increase the productivity at the end of your packaging line conveyors. Automated controls with pre-programmed logic and memory provide quick and easy storage of pallet patterns, production rates and other parameters specific to each product being handled. By installing bar-code labels and scanners on the infeed conveyor, these parameters can be automatically uploaded to the palletizer without operator intervention.

Peanut butter palletizing

Dick Schulhaffer, plant manager for Louisville-based Allgood Foods, told Food Processing, "If the industry didn't have palletizers, labor costs would be catastrophic. It's no longer just the bottling companies who find that it's economically beneficial to use palletizers.

"We run three shifts, and the palletizer has eliminated at least one person per shift. It's not just a matter of cost savings - you can't put a price on injuries. I can give you figures, but there definitely has been a reduction in workman's comp claims in the production area."

Allgood is one of the largest private label manufacturers of peanut butter, producing products for customers ranging from retail chains to national brands. The plant uses a case stripper (from Alvey, St. Louis) to palletize packed cases coming off two production lines in as many as 16 patterns, which are pre-programmed into the palletizer's local computer control station.

The current palletizer was up and running in early 1990. Total installation cost at the time was about $135,000, which included integration of automated conveyors. Actual palletizer cost was under half the total cost. As far as benefits, Schulhaffer explained that "although there is some added maintenance cost, actual maintenance is very low."

According to Schulhaffer, "With both lines running, we'll run up to 1,200 cases an hour. Without an accumulator, we can run both lines together, but only if we're running the same case through ... To run two different case sizes simultaneously, we would need an accumulator, and right now, our floor space is at a premium."

Robotic palletizers

Robotic palletizers may provide solutions to issues such a floor space and flexibility. Depending upon the application, a robot may take up as little as five square feet of floor space, compared with the hundreds of square feet its more conventional cousins typically take.

The small footprint can be deceiving, however, because components such as moving arms require areas to be fenced off for safety. And by the time conveyors are added, the installation may occupy the same amount of spaces as any case stripper. But installations can be more easily custom-fitted to a particular floor plan, and are more easily modified, broken down or moved to suit future changes.

In addition to sharing general benefits with all palletizers, robots provide greater flexibility, beyond the floor space issue. While it is generally agreed that case strippers are better than robots for high-speed installations, robots are a viable option when multiple products and rapid product changeovers are required. Changeover can be reduced from several minutes to literally instantaneously for installations integrated with bar-code readers and full computer control.

There are a few different varieties of robots, which increase in cost along with load capacity and versatility of machine "hand-eye" coordination, Some require only two axes of motion, others four. Some are designed around self-contained frames, others are free-standing with articulated arms instead of fixed masts.

Robots can be equipped with vacuum or mechanical grippers to pick up one or more packages/cases, pails or bags at a time. A robot might make five or 15 trips per minute between infeed conveyor and pallet, depending on factors such as package type, number of cases being picked at a time, laod weight and pallet pattern complexity.

For instance, a robot capable of making 10 trips from infeed conveyor to pallet might be considered to have 10-case-per-minute capacity. But it the same robot is equipped with a gripping tool that picks up a complete 10-case layer at a time - as is being done at a U.S. yogurt processing facility - capacity becomes 100 cases per minute. Therefore, speed and capacity consideration are best determined on case-by-case basis.

Tony's robotic pizza packers

The Salina, Kan., facility of Tony's Pizza Service, which packs about 100 SKUs, is one of the larger frozen pizza operations in the United States. Products include Red Baron brand frozen pizza and other frozen ethnic foods. Cases weigh 10 to 30 lbs with dimension from 8 to 30 inches.

The plant uses both high-speed case strippers (Columbia Machine, Vancouver, Wash.) as well as robots. According to Don McCain, business systems planning manager for Tony's, "We use Columbia palletizers in some areas where we have long runs of the same types of products, and where a 10- to 15-minute changeover is adequate. Typically, we'll run one of these lines for an entire eight-hour shift. They have a very large footprint, but they just run and run."

For shorter-run products, six robot stations have been installed to pack up to 12 products simultaneously. "Conventional palletizers weren't flexible enough to handle the number of products and chageovers for these products."

Prior to the robotic installastions, pallestizing for these items was done manually in a refrigerated staging room outside the freezer. Cold temperature compounded the diffulty of repeatedly picking and placing cases weighing up to 30 lbs each. As McCain put it, "Palletizing in a near-freezing environment is not really something you want your human beings to be doing."

To implement the robotic installation, McCain called an independent robotic systems integrator (Robot Aided Manufacturing Center, Red Wing, Minn.) to specify robotic and conveyor mechanicals as well as electronic integration. The resulting turnkey system involved conveyor upgrades, robots, custom case-grabbers, bar code scanners and computer control installations.

The same medium-capacity robot (GMFanuc Robotics, Auburn Hills, Mich.) is installed at each of three robotic work cells. Each is fed by a main converyor that breaks into four "spur" conveyors. Two robots are stationed at each work cell between two spurs. Barcode scanners and conventional switches and sensors make it possible to assign each products its own spur. Having six robots able to palletize up to 12 products simultaneously gives Tony's all the flexibility it needs for the foreseeable future.

Average capacity is about 30 cases per minute, based on a robot making 10 palletizing trips per minute carrying three cases at a time. (Arm capacity is 110 lbs.) A custom-built end-of-arm tool consists of about 20 vacuum-grabbing suction cups on a welded frame.

What makes it all work is the programming. Automation begins with the initial bar-code scan. Bar-code scanner data are transmitted to a DOS-based desktop computer, running customized cell control software. The computer then downloads all the necessary parameters to a PLC, which holds the programs for everything from sequencing the robots' servo-motors, actuating the pneumatic gripper cups and executing the interlocking stacking programs. (PLC ladder logic and computer software programming were handled by RAM.) After a pallet is completed, a discharge conveyor sends it on its way, making room for a new to be loaded.

One divert conveyor is still maintained to handle unexpected situations, in which case manual palletizing may be required. This is the exception to an otherwise automated unitizing system.

Two control rooms host cell-controlling computers and video screens of key areas in the operation, and help identify problems such as line jams. According to McCain, "It makes a whole lot of difference that the application is user-friendly - it has made all the customization worthwhile."

McCain cites a robotic payback period of less than two years.

Maintenance and training

What kind of palletizer should you choose? It's common for processors to use both robotic and mechanical palletizers for various requirements within the same plant. In additions to the cost and operational considerations in justifying your decision, consider training and maintenance.

For instance, robots are quite reliable, but what if something goes wrong? Are your engineers up to snuff on machine vision? Do you have a local service organization lined up?

Even conventional palletizers need "TLC." As with any heavily automated system mechanical or electronic, you cannot just install a palletizing system and walk away from it. One engineer at a pet food company told Food Processing, "When you have hydraulics you cannot get away from dealing with leaks. And the components are not always visible or easily reached, which makes it tough for the maintenance department to deal with." Even mostly electric systems may use hydraulics for their powerful hoisting capability.

For installations that are heavily automated, companies should make sure their operators are property trained. The costs may be minimal for plants using several of the same types of controller or computer systems throughout the plant, because users can be migrated from station to station.

Remember that pallets stacked high are subject to the same laws of physics as low loads. Pallets stacked high may be unstable and damage the product. While machines provide uniform high-speed loading, they cannot "finesse" each pallet like a human being who pays individual attention to the details.