Engineering or mechanical device terminology

Can’t find the right terminology to search for this.

It’s for a machine at work. A linear actuator moves a gripper back and forth loading parts. If the machine’s power is cut at the wrong time in the cycle, the grippers drop and when the power comes back on as everything goes to its home position, sometimes the grippers impact other components, and their shaft gets bent.

I’m thinking there has to be some sort of coupler, that goes on a shaft, and if that shaft impacts something, it separates before the shaft gets bent. Then to get operational you just re-attach the coupler and proceed. But I can’t seem to hit upon the correct terminology to search for this someplace like McMaster-Carr.



A limit switch ?

No, it’s got to be purely mechanical to protect the shaft with no power to the system.

Then a torque limiter ?

Like these

No, not a torque limiter either. The force comes from perpendicular to the shaft. Also the isn’t even rotating at the time.


A pic or diagram would help.

You would think, but using breakaway as a search term has yielded nothing.

Search for “flexible shaft couplings” on McMaster

There is

  1. Connection-Severing Flexible Shaft Couplings
  2. Splined Flexible Shaft Couplings
  3. U Joints

All potential candidates

I’ve heard such devices described with the term “mechanical fuse” - and Googling this produces some results.

I’ve seen this done with rubber bands, bungee cord, velcro, contact cement, and magnets.

I tried Googling “Lateral Force Breakaway Coupling” and came up with a few candidates.

This one is probably not exactly what you are looking for, but it demonstrates the concept of what you need, right?

How much force do the gripper have to endure during normal operation?

I’m thinking that you might be able to fabricate something that will work:

Sever the gripper attachment and glue very strong magnets to the ends of the severed section. You would also need to account for the attachment’s alignment so that when magnets break apart, the attachment can be re-assembled in its correct position.

Just a thought.

I would look at changing the programming for the way it homes. So that it homes in one axis first which ever axis is safest usually up. I have limited experience with PLCs but was a long time CNC mill programmer. Rule #1.1.3 is home in Z first then X and Y plus whatever else axis’s. Otherwise you are bound to crash.

I was thinking the same thing last night. PLCs are easy to program and should be a snap to insert a delay in the gripper channel.

Yes the programming is the first line of defense against this happening. A mechanical solution is just a redundant protection.

None of the over torque protections are what is needed. I would have guessed something off the self existed but if it does I can’t find it.

Thanks for all the input.

I’m an industrial engineer in a manufacturing facility with a lot of automated equipment, and we have a lot of ‘pick and place’ and other robots that have a similar design to what OP described (machines in which there is a potential for collisions when machines don’t ‘home’ in the proper sequence after a stoppage). Our first solution would be to modify programming to prevent collisions.

We would probably not consider a mechanical solution without addressing the underlying programming/sequencing issue. Is the mechanical solution reliable? Will it ‘break-away’ at unintended times? Even with the breakaway, is it acceptable for those collisions to occur every time the machine gets ‘out of sequence’? Its another component that can wear out and take care of (increases complexity). It another spare to keep in stock.

If we received equipment that crashes or collides after a stoppage, our machine supplier or engineer would be getting a very angry phone call to please come re-program the machine right away.

This type of thing is common enough that it is a part of our specifications and pre-acceptance checklist to test machines (prior to shipment to our facility) by E-stopping mid-cycle or cutting power, and making sure the machine can be recovered by an operator (i.e. not an engineer or programmer) and that various machine parts don’t collide with one another during the recovery.