For handling ferrous parts like steel blanks and billets, an electro-permanent magnetic (EPM) gripper is the default choice for our machine tending cells. Unlike permanent magnets that are always on, or electromagnets that need constant power, an EPM uses a single pulse of electricity to activate and another to deactivate, making it failsafe and energy-efficient. This technology provides high holding force, averaging 10 to 50 kg, even on oily or dusty surfaces where vacuum grippers would fail.
What is a magnetic gripper for a cobot?
The grippers we integrate are exclusively EPMs, not simple electromagnets. A standard electromagnet needs continuous power to hold a part, which generates heat and drops the part during a power loss. An EPM avoids both problems entirely.
An EPM contains both a permanent magnet and an electromagnet coil. A short electrical pulse aligns the magnetic fields to turn the gripper on, and a reverse pulse cancels them to release the part. Between these pulses it consumes zero power while maintaining 100% of its holding force, making the operation intrinsically failsafe.
For cobot integration, EPMs are typically controlled via a URCap. This lets operators manage the gripper directly from the Universal Robots teach pendant. Instead of complex I/O wiring and programming, setup becomes a plug-and-play process that takes minutes.
Gripper magnet technology comparison
We select the gripper technology that guarantees process stability. This table shows why EPM is the standard for safe, energy-efficient robotic handling of ferrous materials.
| Attribute | Permanent magnet | Electromagnet | Electro-permanent magnet (EPM) |
|---|---|---|---|
| Failsafe? | Yes (always on) | No (drops part on power loss) | Yes (holds state on power loss) |
| Power use | None | High (constant current) | Very low (pulse on/off only) |
| Controllable? | No (always on) | Yes (on/off) | Yes (on/off) |
| Heat generation | None | High | Negligible |
| Typical cobot use | Not used | Rare; unsafe | Standard choice |
Source: Olympus Technologies internal engineering standards and supplier datasheets.
Key operating attributes
Holding force is the headline metric, but residual magnetism and response time are what determine success in a real application. A gripper specified on holding force alone will often fail to meet cycle time or quality requirements. At Olympus Technologies, we model the entire part-handling sequence.
Response times for EPMs are typically under 500 milliseconds for both activation and deactivation, including the demagnetisation pulse. This speed ensures the gripper does not become the bottleneck in a fast machine tending cycle, which often runs between 15 and 45 seconds.
Residual magnetism is the small magnetic field left on the part after release. While modern EPMs actively cancel the field with a reverse pulse, a tiny amount can remain. This matters for applications like welding, where arc blow can be an issue, or when parts might attract metal shavings in a later process.
Common machine tending applications
We deploy magnetic grippers most often for three applications where they outperform other EOAT. Their ability to handle imperfect materials makes them ideal for the realities of a shop floor.
Press brake tending. Magnetic grippers are perfect for picking flat or slightly curved steel blanks to feed a press brake. They are indifferent to the dust, cutting oils, and perforation patterns that cause vacuum systems to fail. This reliability is key to consistent throughput in sheet metal work.
CNC machine loading. For loading and unloading steel billets from a CNC mill or lathe, a magnetic gripper offers a simple, robust solution. It grips raw, heavy blocks securely without the precise finger positioning a mechanical gripper would require.
Stamping and forming. In stamping operations, a magnetic gripper can securely pick a part from a die, even if it is still warm. The distributed force prevents damage to newly formed components. This is a common application we deliver for the automotive sector.
When standard grippers fail and magnets excel
A vacuum gripper is often the first choice for its versatility, but its performance falls off a cliff with even minor surface imperfections. A single hole in a sheet metal part or a light film of machine oil can render a suction cup useless, causing dropped parts and downtime. This is the exact point where we specify a magnetic solution.
Mechanical grippers face a different set of constraints. They struggle to pick very thin sheets without buckling them, and have difficulty with parts that lack parallel gripping surfaces. For many common machine tending scenarios, a mechanical gripper simply cannot get a reliable hold.
The challenge of oily or perforated sheets
When a press brake needs to bend a perforated steel sheet, a vacuum gripper is not an option, because the air leaks through the holes and no vacuum forms. Likewise, machine oil or coolant on a billet being loaded into a CNC breaks the seal a suction cup needs.
A magnetic gripper is unaffected by these conditions. Its holding force depends only on the material being ferrous and on its thickness. We have implemented magnetic grippers that handle oily sheets with a lift capacity exceeding 25 kg without a single slip.
Are you handling non-ferrous materials?
The obvious limitation of a magnetic gripper is that it works only on ferromagnetic materials like steel and iron. It will not work on aluminium, copper, titanium, or most grades of stainless steel (such as 300 series). For these materials a different approach is needed.
In these cases we look at either vacuum or mechanical grippers. Vacuum grippers are excellent for smooth, flat, non-porous sheets of aluminium or plastic. Mechanical grippers are better for grabbing cast or forged parts with defined features. The choice depends entirely on part geometry and surface.
What if residual magnetism is unacceptable?
For some processes, even a tiny residual field on a part spells disaster. After being handled by an EPM, a steel part might slightly attract metallic dust or, more seriously, interfere with TIG welding by causing arc blow, where the magnetic field deflects the welding arc.
In these situations the gripper's programming becomes critical. We implement a specific demagnetisation cycle within the robot program, a series of diminishing and reversing pulses that neutralise the field. Where even this is insufficient, the part must pass through a separate demagnetising tunnel, which adds cost and complexity. Understanding this downstream impact is a core part of our design process.
Frequently asked questions
How do you deal with residual magnetism?
Modern EPM grippers have built-in demagnetisation cycles. The control unit runs a short, multi-step electrical sequence to actively cancel the magnetic field on release. For highly sensitive applications, we can integrate a secondary demagnetising station into the cell.
Can a magnetic gripper pick one thin sheet from a stack?
Yes, with the right technology. Standard EPMs struggle with this and often lift two or three sheets at once. We use special dual-zone or shallow-field magnetic grippers designed to generate a field that only penetrates the top 0.5 mm to 1.0 mm, ensuring a single sheet is picked.
Are magnetic grippers safe in a power cut?
Electro-permanent magnets are intrinsically failsafe. Because they only use power to change state, they hold the part securely with zero power input. If power fails mid-move, the cobot stops but the gripper will not drop the part.
What is the typical cost of a magnetic gripper for a cobot?
The hardware for a cobot-ready EPM gripper typically costs between £2,000 and £6,000, varying with the required holding force, special features like shallow-field control, and the included URCap integration. The complete integrated solution cost will be higher.
Related guides
- Comparison: vacuum vs mechanical grippers for cobots.
- Flexibility: quick-change tool changers for cobots.
- Press brakes: how to choose a press brake cobot tending cell.
Talk to an automation engineer
If you are handling ferrous parts and struggling with inconsistent gripping, a magnetic solution could be the answer. Our engineers can assess your parts and process to determine the right end-of-arm tooling for the job.
Contact Olympus Technologies to book a free, no-obligation consultation and see if magnetic grippers can make your machine tending process more reliable.
