What is an End of Arm Tool?

            If you are new to molding automation, sometimes the terminology, function and requirements can be confusing. Even those who have years of experience in the industry can be confused by unfamiliar jargon and technical talk. I had a manager who sat through a 45 minute meeting about an end of arm tool problem and at the end, he pulled one of the engineers aside and asked in a whisper, "What is EOAT?" In this post I hope to clear up this question as well as provide a basic understanding of what and end of arm is.
            When I tell friends and family about my business of designing and building end of arm tooling I often get blank stares. I used to try to clear up the situation by delving into what a molding machine does, and why it needs a robot. Then I have to tell them how the molds are all different and that each mold needs its own end of arm tool to take out the parts and runner and put them on conveyors, cut the gates, throw the runner in the grinder, etc. 
          My wife is usually very patient when I talk to her about work, but after this explanation, even she shook her head and said, "I literally understood none of what you just said." With my wife's coaching, I now tell people I build the hands for robots and leave it at that.
             Although my friends and neighbors may still be a bit in the dark about what I actually do. A hand is  a good way to describe what an end of arm tool is. The end of arm acts as the hand of the robot, allowing it to grab onto parts. Robots come from the manufacturer with a flat mounting area at the bottom of the arm called the wrist. The wrist usually has tapped holes, pneumatic air lines, vacuum lines, and electrical connections. Think of these as the nerves, muscles and tendons that extend from your wrist to your hand which allow you to move your fingers, and receive feedback as they experience their environment. The same goes for an end of arm tool, the lines from the wrist allow it to operate its fingers in the form of pneumatic grippers, suction cups, and gate cutters. The electrical connections allow the robot to receive feedback from its hand in the form of sensors and switches to make sure that the parts have all been grabbed by the hand.
              Ironically, though the robot parts are commonly called the arm and wrist, the term robot hand is not often used. The most common name in the molding world is end of arm tool and is usually abbreviated to EOAT; pronounced ee-oh-ay-tee, not ee-oat. Other terms used include end arm effector, end effector, and head tool, though these are more common in the automated assembly world. 
                 
 There are 3 sections to EOAT:

                        -Body
                        -Part Handling
                        -Part Detection

​Body

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The EOAT body is the base that everything else is attached to. It acts as the bridge between the robot wrist and the part handling and part detection sections of the end of arm. There are many common materials used to build the body, including extruded aluminum, stamped steel plates (which remind me of the Erector Set), machined aluminum plate, etc. At Savage Automation we manufacture our bodies using 3D printed Nylon 12. The body needs to have some way to connect the part handling sections. This is usually done with tapped holes, or pre-manufactured mounting clamps. There are many companies that sell framing kits to build your own end of arm tool bodies. Some work better than others.  ​


Part Handling

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Part handling is the fingers of our robot hand. There are thousands of options when is comes to pneumatic grippers, but almost all come in one of 3 flavors: normally open, normally closed, or double acting. Normally open and normally closed grippers only act one way when air is applied, they have a spring that keeps them either open or closed when not actuated. Double acting grippers have no spring and require 2 separate air circuits to operate. Grippers are not really the fingers yet, grippers are the action driver, and they have mounting holes to mount fingers to. 

Fingers are usually custom. Fingers can be machined from aluminum, delrin, HDPE, acrylic and many other materials, and are shaped to match the part they will grab. The key is to try to choose a material that will not damage your part. Grippers are not delicate like your fingers. There is no pressure sensitivity; they actuate when they are told, regardless of weather they will damage the part or not.

Another option for part handling is vacuum suction cups. Most robots are equipped with a vacuum generator, and when used correctly suction cups can be fantastic for part handling. When selecting a suction cup, it is important to chose the right, size, shape and material depending on what your part handling requirements are. The larger the diameter of the cup, the higher the pulling force will be. Vacuum cups come in multiple materials including those for high heat, anti-static, non-marking, and many shapes making it easier to select a cup that will meet the needs of the part. 

Part Detection

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The part detection is the eyes of your robot. A robot's job is to remove the parts and runner from the mold. It should do this every cycle, but sometimes things don't work out that way. If you have a short shot, irregular ejection, or your end of arm does not grab the parts repeatably, the robot may leave the part in the mold. Without some way for the robot to know this, it will do the same thing it always does. It will send a signal to the machine that the mold can close and it will head off to the drop area to release the parts, whether or not it has them. Depending on the mold, closing on a part could cost weeks of downtime and thousands in repair costs. This is why a good end of arm needs part detection. 

Just like grippers and suction cups, there are many choices when it comes to part detection. There are proximity switches, fiber optics, photo electric, and many more. If you are using suction cups, you can hook up an in-line vacuum monitor to detect changes in the amount of vacuum you are pulling and compare it to the set value to determine if the EOAT has all the parts. When part detection works properly, the robot will not allow the machine to close the mold if it has missed one of the parts and will activate an alarm. 

Is it Clearer Now?​

Hopefully this post has made end of arm tooling a little more approachable. Molding automation can benefit molders of all sizes, lowering labor costs, speeding up cycle times,  and making less scrap. 

If you found this article useful, please share it with others. If you didn't find it useful, or you still have questions, leave me a comment below and I'll do my best to answer!

Check out my post next month to find out how what differentiates a good EOAT from a bad one, and how the end of arm can make or break your automation.


​This is the first of a 3 part series on end of arm tooling:
1.  What is an End of Arm Tool?
2. What an EOAT Should Be
3. Mold Design with the End of Arm in Mind