5 End of Arm Tool Design
Elissa Ledoux
1) “The Claw” Introduction
A robot cannot pick up objects or perform operations on its own – it needs a claw suitable for the operation. This “claw,” as it is called colloquially, is known as an “end-of-arm tool” (EOAT) or just “tool” in industry, and an “end effector” (EE) in academia. These are used to:
- pick and place objects
- draw, weld, glue, or cut,
- insert or poke things
- other applications
A typical EOAT consists of:
- a flange that mounts to the robot’s wrist,
- an angled block to avoid singularities when aligning the tool tip with the approach vector,
- a standoff that offsets the tool tip from the robot’s wrist to allow reaching into tight spaces, and
- an endpiece that enables interaction between the tool and the workpiece or part to pick.
Different EOATs are used for different applications, but the most common ones for pick-and-place operations are:
- magnet tools
- suction tools
- gripper tools
The following video explains end-of-arm tools in more detail.
Video: Robotic End-of-Arm Tools
Quick Quiz
2) Magnet Tools
A magnetic EOAT is used to pick smooth, ferrous objects. This EOAT has a magnetic endpiece, so this must be designed with enough surface area contacting the part – easy if the part has a flat surface, not so easy if the surface is curved or oddly shaped. This video by HVR Magnetics Co. shows a large gantry robot lifting steel sheets with magnets:
Video: Loading Steel Sheet onto Cutting Table with Lift Magnets on Gantry Robot System
This next video by CKD Corporation demonstrates a Yaskawa robot picking and placing ferromagnetic billets using different magnetic EOATs.
Video: Pick & place with Yaskawa robot using CKD magnetic attraction hand & free position pad unit
Common magnetic EOAT suppliers are Industrial Magnetics and Magswitch. The magnets are selected based on force, but the max force listed on the spec sheet is often not enough to lift a part of the same weight due to accelerations or contacting lines instead of planes (i.e. on curved surfaces). The following video shows how to calculate the required strength of a magnet for pick-and-place tasks.
Video: Magnet EOAT Example
Quick Quiz
3) Suction Tools
Suction cups are the most generic, widely applicable end-of-arm tools. They are used for anything with a smooth surface. Suction cups are specially made for different surfaces, including plastic, wood, films, and glass. Piabb and Schmalz are common suction cup suppliers. The number of suction cups used depends on the size of the cups, weight distribution of the object, and smooth surface area for contact. For small objects, a single suction cup is often used, while for larger objects, an EOAT may consist of an array of cups or a vacuum pad. This video by Southie Autonomy shows a beverage packing robot on a production line using a vacuum pad to lift packs of drinks.
This video by Universal Logic of a Neocortex G2R cell shows robots that use AI and computer vision combined with suction EOATs to perform order fulfillment, picking and placing a variety of smooth objects.
The following video shows how to calculate suction cup size and number for an EOAT based on part weight, acceleration, and available vacuum pressure.
Video: Suction EOAT Example
Quick Quiz
4) Gripper Tools
Gripper EOATs are often part-specific, so a certain gripper would be used for a certain part to pick. Grippers are more complicated to design and manufacture, but they also allow finer control. They are the best type of gripper for squishy or irregular objects, but they can be used for almost anything. Common robotic gripper manufacturers are Schunk, Onrobot, and Robotiq. The following video by ceylon CAD shows close-up animations of various types of angular and parallel grippers, revealing how they work:
Video: Gripper Designs
Robotic grippers can be either pneumatically or electromechanically actuated. Pneumatic grippers are binary, either fully open, or fully shut, and are high-strength and simple to design and operate. Electromechanical grippers are more complex, allowing slower and finer motion control for lighter objects. The following video demonstrates an electromechanical Robotiq gripper with a Universal Robot for a machine tending operation.
Video: Machine Tending with Robotiq Dual Gripper Demo at Automate 2017
This video by FANUC America Corporation demonstrates a robotic assembly system for electrical wire harnesses:
Sometimes soft robotic grippers are used for picking delicate objects, like fruit. Soft robotic grippers are typically pneumatically actuated, with bellows that curve the fingers as they inflate, to morph softly around the object. These videos by the University of Sydney and Rochu show soft robotic grippers picking fruit and vegetables:
Video: Robotic Arm Picking Apples
Video: Rochu Soft Robotic Gripper for Food Industry Automatic Solution
The gripper is also the most complicated EOAT to calculate, because its grip force is proportional to friction between the gripper fingers and the object as well as the number of fingers on the gripper. Often, a kinematic linkage is used to transmit force from the actuator to the tip, further complicating the mathematics. The following video shows how to calculate grip tool force for a simple parallel gripper based on part weight, acceleration, and friction.
Video: Gripper EOAT Example
