Linear Rail design
Linear Rail design
(OP)
I'm mocking up a linear rail that is part of a "lift" system.
I would like to use the type of linear rail Pacific Bearing sells that is self lubricating and suitable for "harsh environments" as this system will be used outdoors.
The linear rail slider itself is "pulled and pushed" by a ball-screw actuator. The slider on the rail is attached to a linkage system that does the lifting.
The question I have is that the linear rail itself does not support any moment about is sliding axis, and I would not like to introduce any lateral forces to the linkage system. Hence, two parallel rails would solve this problem.
Are there accepted layouts for the rails and the number of sliders to minimize the chances of bending/binding of the sliders? I.E. two rails, three sliders? Two rails, four sliders? Two rails, two sliders?
How about mounting of the slider itself? Do I need to design in some degrees of freedom? Or will this depend on the tolerance of the rail/linear bearing?
I'm primarily concerned with robustness and ease of manufacture/setup and maintenance. I.E. the ability to field repair the unit without needing $10k worth of metrology tools.
Axial force seen by the ball screw will potentially be upwards of 10,000 lbf.
I would like to use the type of linear rail Pacific Bearing sells that is self lubricating and suitable for "harsh environments" as this system will be used outdoors.
The linear rail slider itself is "pulled and pushed" by a ball-screw actuator. The slider on the rail is attached to a linkage system that does the lifting.
The question I have is that the linear rail itself does not support any moment about is sliding axis, and I would not like to introduce any lateral forces to the linkage system. Hence, two parallel rails would solve this problem.
Are there accepted layouts for the rails and the number of sliders to minimize the chances of bending/binding of the sliders? I.E. two rails, three sliders? Two rails, four sliders? Two rails, two sliders?
How about mounting of the slider itself? Do I need to design in some degrees of freedom? Or will this depend on the tolerance of the rail/linear bearing?
I'm primarily concerned with robustness and ease of manufacture/setup and maintenance. I.E. the ability to field repair the unit without needing $10k worth of metrology tools.
Axial force seen by the ball screw will potentially be upwards of 10,000 lbf.
Beat to fit, paint to match.





RE: Linear Rail design
But ... this was for special-purpose pick-and-place machinery and occasional special-purpose machining operations, in an indoor industrial environment. I don't know if those components would last outdoors, and they certainly aren't meant for sloppy loose-tolerance operations.
RE: Linear Rail design
To answer your question, under your axial force requirements, I think you should contact a Pacific Bearing rep because it is not directly stated on their website or the phamplet that I have.
RE: Linear Rail design
TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering
www.bluetechnik.com
RE: Linear Rail design
Whammett, does your system use any kinds of seals or wipers on the sliders? The catalog for the linear rails claims that operation in "harsh environments" is acceptable, but I was wondering just how harsh they had in mind.
Tygerdawg, I found the Pacific Bearing application section that has basically everything I was looking for! I'll take a look at some other mfg's to expand my horizons.
Thanks for the replies.
Beat to fit, paint to match.
RE: Linear Rail design
The only thing we were worried about was withstanding hurricanes, but we seemed to get lucky this year with no large hurricanes making landfall in South Louisiana.
"I came, I saw, I made it better."
-Ode to Industrial Engineers
Will ChevronTexaco Corp.
RE: Linear Rail design
Look at the vertical lift applications.
ht
RE: Linear Rail design
one rail mounted against a datum adge, as mentioned before, the other one adjustable.
Bearings are positioned using a similar system.
The holes in the rails for the screws are plugged shut.
Wipers (scrapers) are mounted in front of, and after every sliding bearing. They withstand very harsh environment: cooling oil, which is aggressive, and metal chips and particles are all wiped away. Wipers/scrapers are to be replaced regularly.
Renewing the rails/bearings is relatively easy done, but needs a millimess for alignment. And quite some time, and an operator who knows what he's doing.
Ball-screw actuators usually aren't designed for sloppy fits, so maybe you should consider another way of driving the thing?
Bronze threaded housings for the lead screw? Like old-skool mills?
RE: Linear Rail design
Would shields/covers help in this situation, or is it pointless to use them?
If so, you could have some made of SS....perhaps make a "labyrinth" arrangement to minimize the effects of the environment, and make the seal replacement less frequent.
RE: Linear Rail design
I would really like to stay away from linear ball bearings in this application since it will be outdoors in sand, ice, etc. I'm worried that telescopic shields will have the same problems as the slider in regards to needing sliding bearing surfaces and their own set of seals.
I wont be designing the pivoting part of the mechanism, so the whole thing needs to fit into a specific "envelope", which is making this challenging! I'll see if I can post some sketches to give a better idea of what I'm trying to do.
Beat to fit, paint to match.
RE: Linear Rail design
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i use these in a very abbrasive enviorments.. those frelon bearings require a pretty tight tolerance and i know junk can get cought in there and tear them up
RE: Linear Rail design
It looks like we didnt get the contract anyway, so I've stopped all work on the mock-up.
Thanks for the all the replies.
Beat to fit, paint to match.
RE: Linear Rail design