Best belt drive ever! (If I do say so myself)

Hi Mike-
I'm very familiar with your innovative designs for your stages - I recall seeing a prototype of your super Z a couple years ago. I was the engineering manager at Danaher Precision up until 9 months ago, hence the NEATman name... I'm having much more fun at my current job though.

Anyway, I was thinking that this same belt drive technology could be used to create a KAOS style XY stage. Is that a configuration that you will develop in the future? I don't have a specific application for it, I just thought it's a really cool design.

For anyone who dosen't know what a KAOS stage is, check out Mike's home page.

Regards,
Keith
NEATman

Am I right in thinking that the KAOS stages only have actuators for one axis, but the distance between the two set the second axis due to the angled slides ? Very clever.

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Originally Posted by NEATman

snip...
Anyway, I was thinking that this same belt drive technology could be used to create a KAOS style XY stage. Is that a configuration that you will develop in the future?

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Hi Keith, thanks for the kind words.
Yes, KAOS is a natural for the type of packaging aps that this could go in.
I haven't got it on a front burner, though. Early adopters of this are large format printing, cnc laser cutting and water jet.

Where are you working now? If you want to tell me privately, it's everman at bell-everman dot com
Glad to hear you like it more.

Devil's advocate question: What is the benefit of the bottom belt? Seems to me it would all work with just the belt that's wrapped around the pinion via the idlers.

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Originally Posted by jamma

Devil's advocate question: What is the benefit of the bottom belt? Seems to me it would all work with just the belt that's wrapped around the pinion via the idlers.

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I'll give it a shot. Mike, feel free to correct me if I am off base...

It effectively shortens the free belt length. Because the top belt is locked by the rollers into the fixed bottom belt, which is bonded to the frame, the effective length of the belt that is subject to dynamic stresses ie stretching, is only the part between the pressure rollers. If you only had the top belt, the entire belt is subject to stretching and whipping.

This is the innovation in Mike's system. Looping a free belt/chain over a drive motor with a couple of idlers on either side is common but bonding a belt to the frame and using it to effectively shorten the belt length is new. This increases repeatability and reduces backlash.

bob

Excellent idea especially for wide gantrys where racking is a problem.

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Originally Posted by jamma

Devil's advocate question: What is the benefit of the bottom belt? Seems to me it would all work with just the belt that's wrapped around the pinion via the idlers.

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Good question. That works, but has a stretchy belt in the load path. For my robotics business, I need a very stiff drive so that I can move fast and settle a heavy payload in tens of milliseconds, not whole seconds. When you drive something with a ten foot long rubber band, the performance is bunk, and yes, arguably at a certain level it doesn't matter.
A belt fixed at both ends (without our lower rack feature as you suggest), is much better than a standard continuous belt run, so for a lot of DIY'ers, it's a step up, but stiffness wise, not as good as a rack and pinion.
ServoBelt gets you zero backlash, high stiffness and high speed.

Apologies, Bob, I saw after I posted that you'd done a good job of replying already!

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Originally Posted by Mike Everman

Apologies, Bob, I saw after I posted that you'd done a good job of replying already!

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No problem Mike. I wasn't thinking in terms of stiffness and the high G loads so you have clarified that for me.

A few friends of mine worked on a similar linear stage but is much stiffer take a look here:
http://stuff.mit.edu/people/kripa/HP...racktrack.html

and here
http://library.mit.edu/item/000934811

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Originally Posted by mapex99

A few friends of mine worked on a similar linear stage but is much stiffer take a look here:
http://stuff.mit.edu/people/kripa/HP...racktrack.html

and here
http://library.mit.edu/item/000934811

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That is similar. I see they used belting with teeth on both sides. There was a patent like that which came up in the search; we labeled it "tractor tread". Faaaascinating.

Why do you say it's stiffer? Clearly all the hardware is heavier duty than anything I've done with this, if my sense of scale is working. Oh, I think I see.

I threw out this approach early because the tooth clearance couldn't be removed without either huge tension in the tractor belt, or interfering toothform of the rack, making it a special form, not off-the-shelf. In the latter case, as the belt wears, clearance is created that you can't deal with.

Looks like some nice work in any case!

The MIT setup is a bit stiffer because the belt is engaging an aluminum rack instead of a second belt. Even if you scale the MIT stage down to the NEMA23's you're using I think you'd get about double the bandwidth with the MIT stage (think of the belt teeth as cantilevered beams, two cantilevered beams in series are 1/2 as stiff as one cantilevered beam everything being equal).

You mentioned tooth clearance, that wasn't much of an issue with the MIT machine. I believe the tooth form in the AL track was essential toleranced line-to-line and since it is engaging many teeth at any given moment, you get a nice elastic averaging effect across the teeth...hence no backlash.


Also the motor in the MIT system doesn't move which is much easier to deal with cabling wise and you can get a really big motor on it without taking part of the stage payload.

I do like your design, I think it is very inexpensive and will be quite robust.

good luck
Andrew

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Hi guys,
I'm not ready for a full release of this, so I'm starting a thread here for discussion. This summer, I'll put a complete product release thread up in the proper place.
This is called ServoBelt. The vid is (almost) self explanitory.

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I like your ideas mike and I had a similary one. only I went the Mit way which was new for me. Instead of the milled toothed track I used the lower belt, only I used as a core to pour a fixed track from glassfilled epoxy its much faster then milling and you still have the belt.
I want to use it for the X axis of a shopbot like contraption. The idea was that it was much cheaper than an acme or ballscrew and possibly as acurate, I could drive both sides of the X axis with one motor which axis would drive both beltwheels.
The problem with this system is that motor axis has to be placed fairly high to still have a reasonable Z axis and the problem of a long free flapping belt returns, unless of course you raise the X axis tracks as in a U type table.

I did like your differential ball bearing, I never saw something like it, great!

Keep going on Berend Veen
From the netherlands.

Hi Mike

It's really intersting to see that what I was thinking of doing on my DIY router looks likes it works! I came to the same conclusion as you have that a belt drive could act as a flexible rack and pinion and the down side of belt stretch could be minimised if you locked the stationary part of the belt into a matching "rack" along the length. I was planing on casting an epoxy mate for the belt as described by Berend.... so once again its nice to see that this idea is shared by others.

What I am stuck with in my design (still in CAD ) at present is the fact that I havent got any adjustment from the the idlers to the pinion so getting the belt in sync with the rack is a bit of an issue.

Do you know or can you point me in the right direction on how to determine the pitch length of a belt passing over back idlers and a driven sprocket is calculated so as the teeth ar in sync (at a multiple of the belt pitch where they exit the idlers)

Or am I making this too hard for myself and should allow for adjustment?

Very nice setup BTW and I really like your Kaos design... very elegant.


Cheers

Mark
PS heres a post of my present X-axis drive. http://www.cnczone.com/forums/showthread.php?t=53824

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Originally Posted by mhasting2004

What I am stuck with in my design (still in CAD ) at present is the fact that I havent got any adjustment from the the idlers to the pinion so getting the belt in sync with the rack is a bit of an issue.

Do you know or can you point me in the right direction on how to determine the pitch length of a belt passing over back idlers and a driven sprocket is calculated so as the teeth ar in sync (at a multiple of the belt pitch where they exit the idlers)

Or am I making this too hard for myself and should allow for adjustment?

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Shoot! I responded to this and it didn't take somehow. The short answer is that all you need is movement on the motor up and down 1 tooth pitch, so you can tension it. The mesh below takes care of itself.

I just posted elsewhere, and realized I've forgotten to update the info here. Some good illustrations.

Our site hasn't been updated yet, but here is the current state of info available on the net.

www.bell-everman.com/ServoBelt_Techsheet_web.pdf
www.bell-everman.com/servobelt%20x-sect.jpg
www.bell-everman.com/ServoBelt%20Q%20and%20A.doc
http://www.bell-everman.com/SERVOBEL...NEMA_34%20.jpg
http://www.bell-everman.com/SB232-90...33-180-520.jpg

And a video:
www.bell-everman.com/ServoBelt.wmv

neat belt design... so can somebody answer this...
the lower half of belt is stationary or is it in motion... how is it attached on the ends... or is it in motion to reduce friction also... do have a slower speed video to show this movement...?

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Originally Posted by markus_detroy

neat belt design... so can somebody answer this...
the lower half of belt is stationary or is it in motion... how is it attached on the ends... or is it in motion to reduce friction also... do have a slower speed video to show this movement...?

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If you look to the end of the linked video, you'll see it moving by hand without the motor attached. the lower belt is bonded down and acts as a rack. Nothing special on the ends. The upper dynamic belt is just held down on the ends without tension.

Hi Mike

Did you choose to use the T5 profile only based on its ability to mesh with itself or did you find it better for other reasons over say a GT style profile?

I can find info on how the GT profile or a trapazoidal profile comes into mesh with a pulley however I am uncertain how it works in reverse as the idler back bends it out of the "rack"

Have you considered casting the "rack" as an alternative to using two facing belts?

I originally was planning on using T5 in my project but started to think a GT 8 would provide better backlash etc over the trapazoidal tooth profile.


Cheers

Mark

Yes, the mesh quality was my main concern. That being said, the Gates GT meshes well, but has line contacts vs. face. Not a big deal, as the preload makes the contact more rectangular, as does drive loads.
The mesh "unmating" or rolling off of the track is a non-issue, I think.
As to molding the rack, yeah, that's an approach, but labor intensive. I don't want to get into the rack business. ha

Hi Mike,
Very nice design for your stated applicatiion. I like it!

Bud