Electro-Magnetic Gripper Design Problems

Secure and lock the status in the grip position with some or other mechanical method. The power can then safely be turned of and a power failure wont have any effect.

A normally locked lock must be used. That is power or force is required to unlock.

More info may help.

How are you controlling the speed of the grip action?

Is it a positive or friction grip?

I agree with the mechanical locking device; some sort of strap or clamp for safety's sake.

You might also consider using an independent power source for the magnet, i.e., an inverter similar to a computer power supply/back-up.

We have used a seperate Normally Open pneumatic valve with an end effector attached to a small cylinder to mechanically lock a large cylinder attached to the upper half of a mold in place. So, when power/air pressure was lost (and yes, it happened!), the upper mold remained in position. Something along this line may work for your application.

Something else is to have a spring loaded pin or mechanical lever to rotate into place when your cylinder block goes up. When it is time for it to come down, another mechanical device (depending on your application) pulls/pushes it out of the way.

What about attaching a set of jaws to hold the cylinder block in place as along as there is weight on the magnet, in the event of sudden loss of power, the jaws catch the cylinder block, to release the jaws it would require the magnet to push the cylinder bock against a stop, such as a pallet or a conver belt.. to release the jaws.

Hi Labyguy,

Sounds too complex to me. Such magnets don't typically have a guidance system to orient the pushing effect in order to release the jaws.

How about using the same magnet that picks up the block to also pull a hinged set of forks (like the kind on a forklift) underneath the block. The forks would latch themselves automatically via a spring loaded ratchet tooth mechanism, thus if power fails the forks stay under the block. In order to release the forks the operator would energize an actuator to disengage the ratchet lock. Springs would then retract the forks.

John

Use compression springs on the pads that grip. Allowing the gripper to close with a electro-mechanical latch. Latch would hold gripper arms closed holding part instead of coil of gripper. Tension to hold the part will be applied by the springs. Open gripper by unlatching. This will solve power failure problem.

These other suggestions seem like they'd require a lot of re-engineering and new mechanical designs as well. Maybe they LIKE the electromagnet because it's strong and easy, just disastrous under loss of electric power.

I like mareng's suggestion of independent power source or UPS to safeguard against power loss. Surely a UPS has enough capacity. Electric door locks are awful strong and don't require much power once they are seated. ( Although I surely hope there aren't people underneath these things when they're being picked.)

Hello,

You didn't say what you were using to lift the load. In the USA, all cranes with a mag on them must have a back-up battery system that holds up the load for a 90 second minium and be able to lower the load to the ground on battery.

I'm an industrial electrician for a company that has a 50 ton mag crane and once a mounth tests ours, with a load on, it for both operation of the main hoist and length of time.

Suggest you contact your hoist manufacturer to see if they have anything available.

I don't suggest a do it yourself approach because of liability if the load drops.

I agree! I made the assumption you were working on a much, much smaller scale. It would be a good idea to at least list a few parameters when asking for suggestions. Roughly, what is your load weight? What is picking this up?

"We are designing a electro-magnetic gripper for cylinder block, but problem is if electric supply fails, cylinder block falls down. what can be done?"

Look at a self locking lifting cam on the block hoist/holder. When block is set in place and load on hoist/holder is relieved a magnetic release operates the cam to disengage.

I have used a screw clamp in a similar situation. when the motor driving the screw fails the statusquo is of course maintained. It is simple, though slower than an electromagnetic grip.

Hi There, there are elecro/permanent magnetic chucks available. these units need power only to energise or de-energise. they are Bi-Stable either on or off in the event of power failure. They were developed for Machining using magnetic chucks on lathes and milling machines were power failure = loss of hold is dangerous. check them out.