Today’s manufacturers have started looking downstream more and more for automation opportunities. And when they do, more are choosing robotic systems. According to a 2009 PMMI study on packaging machinery, shipments of robotic palletizers rose by more than 3% in 2008, one of the few categories to show growth during this recessionary period. And shipments of palletizing machinery topped $500 million in 2008.
Designing a robotic palletizing cell has become more complicated as companies continue to invest in sustainable packaging. To reduce dunnage, standard corrugated cardboard cartons are being replaced with thinner-walled pressboard, shrink-wrapped bundles of product on corrugated pads and even loose product in trays. Add increased demand from club stores and marketing changes to the mix, and manufacturers need to account for a much wider range of packaging sizes, shapes and materials.
Choosing the correct end-of-arm tooling helps ensure that a new robotic palletizing or depalletizing system can effectively handle a company’s full range of packaging types. End-of-arm tooling is a highly project-specific component that represents a large percentage of the overall cost of the system. The following five questions will help you design a system that maximizes performance, speed, uptime and return on investment.
1. What kinds of product are you handling?
The first step in choosing robotic tooling is analyzing the full range of products and packaging types running on your line. Take some time to determine how each item should be handled. For example, can the packaging support its own weight during transfer? Or will it need to be supported from underneath?
Here are some important factors to consider:
• Size, shape and weight;
• Stability and construction;
• Sealing, wrapping and/or taping;
• Secondary packaging.
2. What rates do you require on your packaging line?
The throughput capabilities of your robotic system can vary greatly depending on which tool you use and the product you are palletizing. A good starting point is to determine an acceptable range of line speeds (cases per minute), which can help you better evaluate your tooling options.
3. How important are the aesthetics of your packaging?
Certain tooling types enable more pallet configurations than others. This flexibility may be needed to orient graphics for full-pallet displays and meet the demands of club stores. Some tools can cause dimpling in shrink wrap or marking on packaging, which may be unacceptable for items ending up on display.
4. Will the robot be handling slip/tier sheets or pallets?
Don’t forget to take into account tooling for robots that handle tier sheets or pallets. Also keep in mind that peripheral tooling may be required, and that handling tier sheets or pallets will reduce line palletizing rates. Reduction in secondary packaging around the product may necessitate sheets between layers to keep the palletized load stable.
5. Will your system be able to adapt to future packaging changes?
Whenever possible, design flexibility into your system to handle changes in your current product line and the addition of new packaging types in the future. Partner with an experienced palletizing integrator to help you make informed choices and specify the equipment best suited for your application.
Tooling types for palletizing include vacuum, side clamp, fork style and layer handling.
Vacuum tooling is the most popular, yet most misapplied, tooling type. It uses pneumatically actuated cups or foam to lift products, depending on the availability of the surface. As only the top surface of the case comes in contact with the tooling, the vacuum option enables a large range of pallet patterns and is the most prevalent type used for depalletizing. Vacuum tooling is suitable for sturdy, traditional packaging, such as sealed corrugate cases that can bear the total weight of the product during transfer. This method is not recommended for many types of packaging, including tall cases with a low center of gravity. As the robot accelerates, inertia can cause the cases to peel away from the vacuum carrying surface. If not planned for during the design phase, this issue can cause a lot of trouble when it is time to run production.
Fork-style tooling uses a row of forks that comb through conveyor rollers to lift product from the bottom. Forkstyle tooling is useful for handling irregularly shaped cases and bags, cases with lids, fan-fold cartons and any packaging that cannot support its own product weight. On the downside, fork style requires additional space for pattern formation. A large amount of mechanical motion makes this the slowest method, and it is not suitable for depalletizing.
Side-clamp tooling is often used for packages that cannot be handled with a vacuum tool. A robotic palletizer equipped with side-clamp tooling permits shrink-wrapped product in trays or on pads, for example, to be manipulated efficiently. It also enables higher robotic arm speeds than vacuum tooling and provides greater control and confidence when holding and transferring product. Side-clamp tooling works well with thinner-walled sustainable packaging, and can offer flexibility for packaging lines that run a variety of products. For example, a small beverage line is able to clamp a six pack differently than a three-pound box of syrup. However, this type may not be suitable for palletizing fragile items or packaging materials with less tear strength than breach strength (think of a bowling ball in a plastic bag).
Some operations may require complete layer handling for palletizing, which is expensive due to the ancillary material handling equipment needed to form each layer. This application is suitable for cases without sealed tops.
Sometimes, a combination of two separate robotic tooling types is used to help constrain motion along both the x and y axes. Hybrid tooling can also include peripheral tooling for handling pallets or tier sheets. When clamps cannot transfer force to the center of the layer due to overpopulation of product or varying patterns, vacuum tooling can be used to hold the layer in place vertically. Vacuum-assisted layer handling is suitable for patterns that include voids for cooling purposes in pasteurization or heat-curing operations.
With vacuum-assisted fork style, forks support the packages from underneath, while vacuum tooling along the back row of the cases keeps them in place.
Clamping-assisted vacuums are used for tall and light packages. The vacuum tool lifts and moves the product, while the clamps keep it from moving horizontally and peeling away from the vacuum.
Finally, cylinder-mounted vacuum cups can be used as peripheral devices to pick up tier sheets. A set of pick arms swings into position to pick the pallet and then swings back out of the way during the palletizing operation.
Earl Wohlrab is operations manager for Intelligrated’s robotics group and is responsible for the engineering and estimating of all systems featuring Alvey robotic palletizers and depalletizers. He is an expert in developing palletizing systems for consumer, food and beverage markets.