Alternative to Ball Screw or Rack-n-Pinion

[samualt]

Saw this and thought it might be interesting to some people. Its a kinky kind of rack-n-pinion, only different. They say it's Zero-Backlash! Check out Roller Pinion from Nexen. I may have to try one of these sometime just to see how well they work. Very unique!

[arvidb]

Hey that thing is really cool! If you try it, be sure to report on it here. Any idea on the cost?

Arvid

[samualt]

They don't have their prices listed. Does anyone? I call these "Stealth Products". Like so many other motion control specialists they don't list prices and want you to play phone/email tag with their sales staff before you find anything out. They said in their brochure it costs more than a rack system but less than a ball screw. Whatever that means.

Here is a brochure they gave me:
Roller Pinion Brochure, PDF - Adobe Acrobat Format

Revised:
The Linear Distance Per Revolution of the thing is 6.3" for the smallest model - RPS16. That is about twice the length of a regular pinion gear, assuming you chose the smallest regular pinion. This just means you have some more stepping-down to do.

[samualt]

Well, I got a reply from them on their smallest model. If you were going to make an axis that is around 60" long it would cost you about 1500 US after taxes and shipping. Around 3K for an 8 foot long x-axis (racks on both sides).
Is is definitely out of my league. But, it's still interesting even if I can't afford it.

[blurrycustoms]

Anybody else have any experience with this system? Seems pretty expensive.

[RICHARD ZASTROW]

This is a bit off-subject but Nexen has other interesting products as well. I have no connection with Nexen, I'm not their promoter.

Linear rail brakes, rotary brakes, the above roller gears among others.

Neat stuff but I haven't used any yet.

Dick Z

[Zumba]

Is this new technology (as in last few years)? Seems like putting rollers on a pinion is something that engineers probably thought of decades ago. Does anyone else offer a roller pinion design?

Regardless, it is a very cool system. Ballscrews are impractical for large routers on low to medium budgets. Companies like Thermwood require support arms to prevent whip. Komo uses helical R&P. Bridge mills use massive ballscrews that probably cost more than high end routers.

Roller pinion... relatively inexpensive, easy to manufacture, lube-free. Pretty much the perfect linear drive system for woodworking IMO.

[smannn]

I know there is a very smiliar gear in use, since 1999, at a General motors plant which is in use to stamp quarter panels in a linear motion application. I'm not a liberty to cast judgement but Nexen's technology is very similar to what is used in the GM plant. Infrindgements on current patents? But to answer you question, yes there are others out there that have this technology.

[yamaha_r6m]

Joseph Ives used roller pinions in clocks. I'm not sure if the nexen rollers rotate on a shaft like Ives pinions did or not.

[BillTodd]

It's the inverse of a chain and sprocket (imagine a short length of chain wrapped in a circle as the pinion and a linear 'sprocket')

It would be interesting to experiment with a fixed chain laid flat (or held rigid in a U shaped channel, or even upside-down in a suitable T slot) with a sprocket on the motor. It could give similar performance to the roller pinion at a fraction of the cost.

[RICHARD ZASTROW]

There were similar designs made a few years back b some guy named Leonardo DaVinci. He also mated the roller pinion against face gears. Clever fellow eh?

Dick Z

[yamaha_r6m]

Originally Posted by BillTodd It's the inverse of a chain and sprocket (imagine a short length of chain wrapped in a circle as the pinion and a linear 'sprocket') It would be interesting to experiment with a fixed chain laid flat (or held rigid in a U shaped channel, or even upside-down in a suitable T slot) with a sprocket on the motor. It could give similar performance to the roller pinion at a fraction of the cost.

Not exactly. If you use a chain sprocket curve then the line of motion of the of the drive pinion will not stay parallel to the line of motion of the rack. Say that three times fast. Here's what I mean:



The sprocket profile looks more pointy than it really is. The export kind of lost something. The tooth profile is actually convex. Here's a better look:



Note how the center line of the pinion follows a cycloidal path.

The pinion is in rotation about its center axis and in translation; also; the pinion path and the line of motion along the rack must be parallel. With those constraints I simulated the motion of the pin through rotation and translation. The actual rack profile should look like this:



Both profiles above used the same pinion configuration: 3/8" rollers, 10 rollers per pinion, 2PI length of travel per rotation.

Compare the last profile with that used by Nexen:



The Nexen profile is more triangular and less like a sprocket profile.