Soft stop type device for gravity Fixture 2

[Bflo]

I'm designing a fixture that's using a small Deltron slide that's mounted to slide with/against gravity. I'd like to prevent it from crashing due to gravity when/if the operators hand slips off of the handle. I'd also like full travel of the slide, but somehow to slow down the travel if it's either dropped or pulled down hard. The idea would be like one of those soft close drawer slides but much smaller as the Deltron slide is tiny (

https://deltron.com/search/Slides_Ball_Crossed_Roller_Model.aspx?pkid=2980).

My initial thoughts were a piston actuator with an accumulator chamber, but that sounds more complicated than necessary. My 2nd thought would be a spring that stops the slide 1/4-1/2" from the bottom and the operator would just have to push down to overcome that action. It seems this approach would still allow for jarring of the fixture when it comes to a quick stop.

 

[MintJulep]

Eddy current brake.

https://m.youtube.com/watch?v=uh0bbW6S3BY

 

[3DDave]

Traditionally an air dashpot would be used. However there are viscous damper devices available.

For example (just from searching)

https://www.toyoudamper.com/rotary-damper/gear-dampers.html

would be used with either a wheel or gear rack. The one's I've seen are unidirectional - freely turning one way and damping the other.

Eddy current devices are also very widely used, and are quite impressive - they offer a no-static friction resistance to motion.

 

[Bflo]

Thanks so much. Apparently McMaster has the gear dampers (

https://www.mcmaster.com/dampers/shaft-type~geared/)

but I don't see small eddy current brakes for sale on the web at all. I guess I can just make one pretty easily, although I'm guessing there's a balance between magnet & tube dia., what type of magnets, etc...It looks like after searching a bit, I found a video/link that explains it a bit (axially magnetized, works with copper or aluminum, etc.)

https://www.kjmagnetics.com/blog.asp?p=eddy-currents

Unless I'm not thinking straight, the problem with a gear damper is that I'd have to have the gear not engaged with a rack until the lowpoint, and then for the gear to have the teeth engage the rack correctly without crashing.

 

[3DDave]

Typical magnetic dampers are a flat strip/vane that lies between two magnets. This is used to damp precision mass balances, such as pan-beam balances. It's not an item one would buy.

 

[Bflo]

So I'm trying to have a backup if the eddy current idea doesn't work and I'm wondering if there's a way to machine or allow a rack to always engage correctly with a gear damper as the damper effect isn't wanted until the near end of travel. I obviously don't want them to bind when they meet, especially if the fixture is dropped. I'm not sure yet if the rack should be on the slide and the gear should be stationary but I'm guessing that doesn't matter.

That's why I don't have a mount yet for the gear there in the pic.

 

[3DDave]

It's probably better to make a choice that will reduce the weight that might be dropped.

 

[Compositepro]

A counter-weight will solve all your problems, and add perceived value to your device.