Feb 2, 2018
Choosing the Right End-of-Arm Tool for Robotic Palletizing
By: Stephen Gandy, Applications Engineer, Brenton Engineering, part of the ProMach family of brands
End-of-arm tools (EOATs) for robotic palletizing come in all shapes, sizes, and price tags. Knowing what to look for in an EOAT speeds the specification process and leads to correct sizing and lowest overall cost. There are three basic categories of robotic EOATs for palletizing:
Before talking with the palletizing original equipment manufacturer (OEM) about the best EOAT, develop an accurate estimate of how fast cases will come down the line and what the average number of pallets per hour will be. Inflated case and pallet counts can lead to ordering a more expensive tool than needed, while counts that underestimate might result in an inadequate purchase, creating bottlenecks on the line.
For regular slotted cases (RSCs), test the top and bottom seal strength and make those measurements available to the OEM. No one wants ruined products splattered across the plant floor because tops or bottoms gave way due to too much weight. Provide a list of pack patterns required as patterns have an impact on the type of EOAT selected. Give the OEM sample cases and let its engineering team run tests, including the porosity of the corrugated board. Porosity impacts vacuum EOAT effectiveness.
Vacuum There are two kinds of vacuum-based EOATs – Venturi and dense array. Venturi are ideal for lighter, yet sturdy RSCs weighing up to 30 pounds. Gripping one or two cases at a time, Venturi tools are idea for low to moderate speed palletizing and simple pack patterns. Venturi systems utilize the plant’s compressed air system, which means air hoses and air prep systems will have to be in place. Venturi systems are the least expensive of the options.
Dense array vacuum tools rely on a matrix of many small vacuum cups. Dense array tools have their own compressed air generator for greater air flow. Specifying a more powerful air system increases vacuum. Dense array tools are typically used on RSCs reaching up to 50 pounds. They can palletize multiple rows of cases per cycle. The matrix of vacuum cups supports variation in pack patterns with different combinations – zones – of cups programmed to operate during any given lift. Dense array tools are larger and carry a higher price tag than Venturi systems. Running larger pack patterns requires more equipment on the front end creating a pattern for the robot. This approach involves greater overall system footprint and cost.
Frequent cleaning of corrugated dust off the vacuum cups is part of routine maintenance. Occasionally, even with clean vacuum heads and a vacuum that is operating perfectly, cases simply fail to lift or detach from the tool. In these instances, determine whether the porosity of the corrugated board has changed. Another fact to be aware of is that high acceleration does not work well with vacuum tools. If high speed and acceleration are needed, then investigate clamp-based EOATs.
Clamp Clamp-based tools can be operated by either pneumatic actuators or servo electric actuators. One end of the clamp is stationary, while the other end moves in and out. Clamps lift by exerting side pressure, which means they can be used for packaging other than RSCs, including shrink-wrapped bundles such as cases of bottled water and display ready cases. Clamp-based systems accelerate faster than vacuum tools for higher overall speed. Servo-based clamps open and close faster than pneumatic-based clamps, but pneumatic clamps cost less. Work with the OEM to determine whether the speed differential is worth the uptick in price.
Pneumatic clamps are used when cases are all about the same size. Because servo systems can be programmed, they are better for applications where mixed sizes will be handled and for cases that require enough side pressure to hold the packaging without damaging it, for a gentle yet strong grip. One set of clamps can lift a row of cases. Adding clamps increases the number of rows per lift. It’s common to see a set of clamps loading a half pallet each cycle. Clamping tools require more overall space than vacuum. If the packaging in question will require bottom support during palletizing, then investigate fork-style tools.
Fork Fork tools are utilized for packaging that requires bottom support and packaging such as bags or display cases for which neither vacuum or clamps may be suited. In addition to having a fork support the bottom of the load, these tools provide load stability with gentle support on the top and sides as well. Forks are the largest, heaviest, and priciest of the palletizing EOATs. They may also be the fastest as they can palletize an entire row per cycle and some can cycle many times a minute. Fork EOATs require the most space to operate, which may or may not be a problem, depending on the plant space available. Due to their weight and size, these tools may require a heftier robot than either vacuum or clamp EOATs, adding to cost.
Other than making sure these EOATs are properly lubed, forks and clamps are basically maintenance free. Complex pack patterns are not suitable for clamps or forks. For complex patterns, a conventional palletizer is the best option.
Work with OEMs that offer the full range of EOATs, including Venturi and dense array vacuum, pneumatic and servo clamping, and fork solutions. An OEM with limited solutions might push a particular EOAT regardless of whether it is the best fit.