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Problem:

I have a rod on a linear rail system. This rod can be pushed forward or backwards. There is air blowing out of the front of the rod (~2 lbf) causing it to move to the back position by default. I am wondering if a mechanism exists that will allow the rod to be moved, but when the rod is let go of, remains where it is despite the force from the air. Something similar to a cordless blind system.

Does a device like this exist that can be bought as an individual mechanism?

Possible solutions:

  1. The most feasible solution (that I am not fond of) is a friction brake. Just a rubber collar that will go around the rods near the bearings. It would work, but I am worried about long term wear, operator fatigue, and possible joltyness when breaking static friction.

  2. An overly complicated "solution" could be to have a constant force spring powered motor assembly to be continuously pulling the rod forward with 2 lbf. The problem with this is that once the air is turned off, the rod will fly forward (not acceptable). I could set it up so that to turn off the air, the spring motor assembly must be braked in some way. That just gets complicated though and interferes with emergency shut off.

  3. My third solution would be to replace the linear rail system that the rod slides on with threaded rods. The air rod could then be moved by spinning a hand wheel that would in-turn spin the threaded rods. I see some friction problems here and would not like the speed restraint of this system, but it could possibly work.

Closing Statement:

If you have any other possible solutions, alternative designs, or comments about my solutions, I would appreciate the input. Thank you.

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  • $\begingroup$ There is a friction based equivalent of a ratchet mechanism. Not sure what it's called, wil look up. Basically a brake pad on a hinge. the angle is such that when going "forward", the hinge lifts and there is little force normal to the rod, thus little friction. When going backwards, the brake pad is jammed into the rod and it stays in place. Typically has a manual release lever to allow backwards motion. $\endgroup$ – Pete W Feb 3 at 22:50
  • $\begingroup$ Machinery's Handbook is AWOL :-( Anyway hope you get the idea. It's the equivalent of a clutch for axial motion. There is a very compact and elegant version of this using ferrules, somewhat similar to compression fittings on tubing. But the release might be more complex $\endgroup$ – Pete W Feb 3 at 23:42
  • $\begingroup$ Ball bearings in tapered grooves can have a similar one-way locking effect. $\endgroup$ – Dave Tweed Feb 5 at 12:29

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