The right gripper for bin picking depends on the part you are picking and where it has to go next. Across the bin picking systems we deploy, three grippers cover most applications:
- Suction cup: our preferred choice for parts with a flat surface. It is fast, simple and easy to integrate.
- Two-finger gripper: when suction does not work and the part has a few good pick points, such as a bore, an edge or a flange.
- Magnetic gripper: for ferromagnetic steel parts, especially oily or perforated ones that are hard to pick with suction.
When none of those works, we may use an adaptive or three-finger gripper, or design a custom one. Those are edge cases.
Suction cups
Suction is our default. It needs only one face the cup can seal on, it is fast, and simple to integrate. Typical parts are sheet metal blanks, moulded plastic housings, plastic pouches, or castings with a machined face.
Use flat cups on smooth, flat faces. Use bellows cups on curved or uneven faces: their compression also absorbs height error from the vision system.
Suction fails on holes, porosity, deep texture or ribs under the cup. For porous parts, size the vacuum generator for the leak rate or place pick points on solid material. Oily parts still seal, but they can slide off the cup on fast or tilted moves.
Fit every suction tool with a vacuum switch, so a failed pick is caught before the robot moves, and a check valve, so the part does not drop on air or power loss.
The UR5e application shows the approach on a dark perforated part: the pick points sit on solid material between the holes, so the cup always has a surface to seal against.
Two-finger grippers
When there is no face to seal on, grip a feature instead: a bore, an edge or a flange. Two-finger parallel grippers are robust and place parts accurately.
Grip inside a bore where you can. Expanding fingers need less room than closing ones and centre the part as they open, which matters in machine tending, where parts go into a chuck or fixture.
Design the fingers for the part: long and slim to reach into the bin, with tapered tips that slide between parts. 3D-printed fingers make it cheap to try a few versions.
The limits: fingers need clearance on two sides of the feature, and every pick adds an open and close compared with suction.
Magnetic grippers
A magnet holds steel through one face, regardless of holes, oil, rust or rough surfaces. That makes it the fix for perforated stampings, oily machined parts and rough forgings.
Check the grade first. Austenitic stainless holds only 1 to 3 percent of what low-carbon steel does, and aluminium and copper not at all.
Thin sheet is the other limit: below the magnet's de-stack thickness, it lifts the part underneath too. Magnets with built-in sensing handle this. Magswitch's smart grippers, for example, detect a second part on the face, lower the field until only one part stays attached, then return to full force for the move.
Switchable permanent and electro-permanent magnets hold without power, so a power cut does not drop the part.
Magnetic vs vacuum gripper for metal parts
For steel parts both can work. The surface and the thickness decide.
| Suction cup | Magnetic gripper | |
|---|---|---|
| Holes, oil, rust, rough surface | Struggles: leaks or slides | Not affected |
| Material | Any, including aluminium and stainless | Ferromagnetic steel only |
| Thin, stacked sheet | Can lift two if parts are nested | Lifts two below the de-stack thickness |
| Power or air loss | Drops the part without a check valve | Switchable magnets keep holding |
| Part surface | Leaves no mark, little residue | Can attract chips, may leave the part magnetised |
If the part has a clean flat face, use suction: it is simpler and works on any metal. If it is oily, perforated or rough steel, use a magnet.
Edge cases: adaptive, three-finger and custom grippers
A small share of parts need something else.
- Three-finger centric grippers centre round and hexagonal parts, such as shafts and billets going into a chuck. They are larger than two-finger grippers, which limits how far they reach into a bin.
- Adaptive and soft grippers conform to irregular or delicate parts. Payloads are low, and the part's position in the gripper is less certain, which costs placement accuracy.
- Custom grippers combine principles when one part lies in the bin several ways: suction for a part lying flat, fingers for the same part wedged against a wall with only an edge exposed. On one complex metal part we built a single tool with two gripping principles because no standard gripper handled every position.
Decision factors
The part
Start with the part in your hand and its drawing. Is there a flat face at least as large as a cup? Is it ferromagnetic, and how thick? Is there a bore or an edge with clearance around it? How heavy is it, and is it oily, porous or textured where you would grip it?
Where the part goes next
A part dropped into a tote tolerates several millimetres of error. A part loaded into a fixture or a machine may tolerate less than one, and any movement in the gripper adds to that error. Precise placement favours fingers that locate the part, or a regrip station or second camera look before placing.
The bin
The gripper has to work inside a box. Keep the part that enters the bin slim and about as long as the bin is deep, with anything bulky up near the robot flange. Make it rigid, because deflection at the tip is an error calibration cannot correct. Route hoses and cables out of the top of the tool, since a snagged hose is a common cause of downtime. A tool that tolerates angled picks reaches more parts near the walls and in the corners.
Holding force
Size the gripper for the worst load in the move, not for the part's weight. For a vertical lift, the required force is mass times gravity plus acceleration, times a safety factor. If the load acts sideways on the grip, divide by the friction coefficient as well. Use a safety factor of at least 1.5 for smooth, dense parts, 2 or more for oily, porous or rough parts, and 2.5 or more when the part is rotated during the move, which bin picking usually does. EN 13155 covers vacuum and magnetic lifting devices.
Cycle time
Suction is the fastest. Fingers add an open and close to every pick, and electro-permanent magnets add their switching time. If the cell is cycle-time critical, that alone can decide between two grippers that both work.
Test the gripper on your parts
The gripper choice is only settled once it has picked your real parts from a real bin, including the last few parts in the corners. Check four things: whether the tool reaches parts against the walls without colliding, whether it lifts exactly one part, whether the part stays put during the move, and whether it arrives within the placement tolerance.
The gripper is one half of the decision. For the other half, see the 3D camera comparison, and for choosing a supplier, bin picking companies compared.
Send us a bin of your parts and we return a pick video and a written verdict within 72 hours, gripper recommendation included. For more examples by part and industry, see our applications.
