An interesting mechanism:

[www.designnews.com]

Edited 1 time(s). Last edit at 12/08/2008 06:46PM by nophead.

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[www.hydraraptor.blogspot.com]

Cool!

That actually looks startlingly simple... I'm surprised it hasn't been done before. It seems like the hardest part would be getting the spacing of the wheels and the drive pulley right for the belt to mesh properly...

nophead Wrote:
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> An interesting mechanism:
>
> [www.designnews.com]
> Belt_Drive.php?nid=2337&rid=1696394

Yeah I saw that a while back and was thinking of a repstrap design based on a simple square frame for the x & y using the belt on each side with the stepper motor in the center.

The stepper motor in the center could be geared down with another belt to a common axle going to both sides. Also using skate bearings with U shaped bracket to bind it the frame so that is in tension.

The thing about it is that it could be scaled up easily by simply using more belt for each axis.

... i used the 'opposite' concept for micropositioning:
- one belt fixed to a plate, the second belt stretched, so it would elongate 2% and positioned 2 centimetres above the bottom belt and connected to a moving stage.
- then a slider with a roll which presses a fraction of the upper belt on the bottom one.
- when moving the slider you have a linear 'harmonic-drive' with the difference of the stretched belt against the bottom as resulting displacement.

So for a bottom belt of 1m length and a complete run you would displace the moving stage exactly 2mm - or when pushing the slider 10cm you'll have 0,2mm or you'll get 2 microns when pushing 1mm.

For higher accuracies you need better surfaces and stiffer materials - so with an etched and polished steel-toothbelt you can rise this concept to the accuracy of the teeth-geometry ...

Viktor

Edited 1 time(s). Last edit at 12/09/2008 03:27AM by Viktor.

ive been thinking of a positioning system using a flat gear that would be printable on the reprap itself. havent made a stl or anything but plan on it,
making it about 6" long per section so there can be several placed in a line for the entire lenght of the stroke. and have a gear on the stepper attached to the axis being moved.

but again cant prove the concept till i get my strap finished

If by flat gear you are talking about a rack and pinion system I wrote a script to generate racks in the Art of Illusion open-source 3D modeling system some years ago. You can download it at...

[3dreplicators.com]

There is also a script that designs involute profile gears that you can download at...

[3dreplicators.com]

There is a tutorial on how to use the gear script at...

[3dreplicators.com]


Hopefully, these will make your task a little easier.

Edited 1 time(s). Last edit at 01/20/2009 11:49AM by Forrest Higgs.

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Hell, there are no rules here - we're trying to accomplish something.

Opportunity is missed by most people because it is dressed in overalls and looks like work.

Thomas A. Edison

Thanx forest. these will probably make this a whole lot easyer

Edit: after looking at the instruction im not sure if were talking about the same thing but havent actualy dl the files (im at work). I believe that the normal name for a linear gear is a rack so i will assume were still talking about the same thing.

Edited 1 time(s). Last edit at 02/08/2009 05:37PM by RBisping.

Yeah, I have a rack script and a gear script which generates gears which fit with the rack. I gave you the links for both.

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Hell, there are no rules here - we're trying to accomplish something.

Opportunity is missed by most people because it is dressed in overalls and looks like work.

Thomas A. Edison