Trying To Mix A Power Drive Screw With Vibration?

[1BrickShort]

I have a 1/4-20 ACME thread power drive screw that is exposed to high amounts vibration, and right now it keeps back driving on me.

There is a spring loaded mass that is "bouncing" off of the face of the nut and causeing the screw to back drive. The efficiency of the threads is -.625ish, and it would make scense mathematcally that these threads should not back drive, but they are. My gut tells me it is the "hammering" effect of the mass that cause the threads to back drive, but my mind says no, that is linear motion that should be locked tight, due to the thread efficiency.

Is there anyone out there who has run into the same problem? Can I change thread type or # of threads per inch to solve this problem? I am in need of some good ideas...

 

[GregLocock]

I agree that the vibration is probably causing the unwanted back drive, although I'd be hard pushed to calculate why exactly.

Can you add axial compliance to the system?

Can you add friction to the drive?

Can you reduce the pitch of the thread?





Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[1BrickShort]

Well, unfortunately I can not add friction due to my power consumtion and operating time requirements of the system, but I could change the pitch of the thread. That is a good idea.


What do you mean when you say axial compliance?

I am not very familiar with vibration experiments or termanology

Thanks for the ideas...

 

[GregLocock]

What do you mean when you say axial compliance?
=
Can you mount the system so that there is some elastic component in the mounting of the motor/gearbox, or the screw? That will help to abosrb the shock of the vibration and may prevent back-driving.


Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.