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servo couplings

Jason H

Stainless
Joined
Mar 29, 2006
Location
Los Angeles, CA.
I am mating a servo to a sewing machine. I have a 17/32 shaft on the sewing machine and the servo is a 5/8 shaft. The misalignment will be very slight as my machinist skills are in the B to B+ range. The servo shaft is keyed, but the sewing machine shaft is dimpled for a set screw only ( it is hardened ). I am not too sure what RPM range will be yet.

What are the recommended manufacturers for couplings? Any direction will help

Thanks

Jason
 
I am assuming by posting that you are saying these will work. I have some here i can play with but not seeing any key ways on them I did not know if they were suitable.

Thanks

Jason
 
Some have keys, others just a set screw depending on the torque requirements. A key way could always be added as you will likely have to bore for the slightly odd 17/32" Ø anyway.
 
A Lovejoy coupling, generic name is spider shaft coupling, would work.

A search through McMaster Carr leads to many options.
McMaster-Carr

Kyle posted what I was going to.

We have a half dozen machines that use the couplings linked to (Flexible Spider Shaft Couplings) in a servo-to-ballscrew application. I don't see why you can't use them, unless you are going really high speeds.
 
Jason,
I think you may want to look at a clamp type coupling, if you have questions about the single set screw holding the torque, over a long term of a dynamic load like a sewing machine.
Also, is it possible that the one shaft is a 13.5mm ?

McMaster, Misumi, MSC all should have couplers in the clamp on style.
 
Be aware that if you use lovejoy couplings, you can have positioning issues due to the flexibility of the spider. Typically use a servo-specific zero backlash type connector for servo applications. These are either metal bellows, double-disk, or spiral cut type connections.
 
re: Flexibility: there is a rotary knife after the machine feeding off an encoder, but I only need +/- 1/16th. Still an issue? No real need for positioning other than that. Off the encoder I will also have some camming going on with a different servo that is feeding material. ( little man has grown up since his first project a few months ago )

Speed is actually at the very low end, but the torque requirements change significantly as the needles have to overcome a large amount of material to go through on the down stroke. I have everything ready to go so I will bore the spiders I have and see.

The shaft mics out at .5312. I think one down fall of the industrial sewing machine maker is that they tried to make everything NOT interchangeable. every part has just the wackiest specs. The machine was US made in the late 40's.

Thanks guys. Will let you know.
 
agree with 3t3d and Tony - backlash is a concern with jaw style couplings.

We use GAM keyless couplings - and if properly bored they simply do not slip even under extreme torque / crash induced shock loading.

They are not cheap - but if you have a time varying torque for motion control - your system response will suffer if you have compliance of any kind in the coupling, especially of the load inertia is much higher than the motor inertia.

look on this page - not a single coupling uses a keyway or setscrew. We do have customers that insist on using a keyway and we often broach a keyway for them - but in my experience with a large number of inadvertent machine crashes under incredibly high loads - the coupling has never slipped.

Servo couplings including bellows couplings and elastomer couplings plus safety couplings from GAM
 
Good luck with this project. Automating things different than a machine tool ball screw is always a nice change.

Here is another vote for staying away from jaw couplings. They just add backlash.

It sounds like the application has all sorts of non-constant loading, so the small backlash may just be dwarfed by other effects. Let us know how it works.
 








 
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