Grippers, explained with a kitchen drawer
Open the drawer next to your stove. Tongs, a spatula, a ladle, a magnet on the fridge, a rubber jar opener. You already own every kind of robot gripper there is. Here is what each one is called in a quote, what it picks, what it drops, and why the drawer matters more than the arm.
The short answer
A robot arm is a very precise way of moving a tool to a place. The tool is the gripper, and the gripper decides what the cell can and cannot do. Every gripper in an industrial quote has a cousin in your kitchen, and thinking about them that way will make you a better buyer than most of the people quoting you.
Tongs: the two finger gripper
Two jaws that close on a part. Electric or pneumatic, with fingers machined to fit what you are picking. It holds anything with two parallel faces it can reach, which is most machined parts, and it is the default for machine tending. It fails on things that are round and slippery, things that vary in size beyond the finger stroke, and things with nowhere to grab. Like tongs on a meatball, it works until it does not.
The spatula: the vacuum gripper
A flat pad with suction cups, or a foam pad with hundreds of tiny holes. It picks anything with a flat, sealed, reasonably clean surface: cases, cartons, sheet metal, glass, panels. It is the gripper of palletizing. It fails on vented cartons, dusty surfaces, porous materials and anything whose top is smaller than the pad. Zoned vacuum, where only the cups over the part switch on, is the version that picks a small box and a large one with the same tool, and is what made mixed-case work possible.
The jar opener: the soft gripper
Rubbery fingers that wrap around a part and conform to it. Great for produce, bakery, bags and anything delicate or irregular. Herbs, as in the Danish greenhouse in this site's casebook, where a wide, force limited gripper handled cut herbs without custom tooling per product. It fails on heavy parts and on precision, because conforming to the part means not knowing exactly where it is.
The fridge magnet: the magnetic gripper
Picks ferrous sheet and parts, including stacked blanks where a vacuum would pick two. It fails on aluminum, stainless that is not magnetic, and anything near electronics that would rather not be magnetized. Sheet destacking cells use it with a fanner that separates the top sheet.
The ladle: custom and special tooling
Hooks, pins, needle grippers for textiles, tray grippers that lift a whole layer of egg cartons, which is how one plant in the casebook case packs 1.5 million eggs a day as the vendor published it. Custom tooling is where the engineering money goes, and it is also where the clever ideas live: pick the unit load the product is already stable in, not the fragile thing inside it.
The tool changer: the whole drawer
A coupling on the wrist that lets the arm swap grippers in seconds. The right answer for a shop with several part families, and an added cost and failure point for a shop with one. A cell with a tool changer is a cell that admits the parts vary, which is honest.
Why the drawer matters more than the arm
Arms are mature, reliable and similar across makers at a given payload. The matrix on this site lists 755 of them and the differences between the top candidates for your job are usually smaller than the difference between the right gripper and the wrong one. A mis-specified gripper drops parts, double picks, marks surfaces and jams at four in the afternoon, and no amount of robot fixes it. R2-D2 was useful on the Death Star not because he was fast, but because he had the right tool for the data port.
How to specify yours
Bring the seller your worst three parts: the lightest, the heaviest and the one that is always slightly wrong. If the gripper handles those on the demo, it will handle your average. If the seller only wants to see the average, you have learned something about the seller.
Describe the part and how it arrives to Joe, the concierge on this site, and he will tell you which drawer to open before he tells you which arm to look at.
Related on this site
- The gripper is the project
- Pick and place
- Palletizing
- Tray denesting
- Mixed-case depalletizing wasn't automatable until 3D vision could find a box it had never seen
Pick the gripper for your worst part, not your average one. The arm will do whatever the gripper can hold, and nothing it cannot.
Put it to the test on your own job
Tell Joe what you are running and he will apply this to your numbers, including telling you when a robot is the wrong answer.
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