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Ideas for motorizing old micron-screws wanted ...

Posted by VDX 
Ideas for motorizing old micron-screws wanted ...
October 03, 2007 05:07PM
Hi all,

... how can i best motorize the micron-screws in an oldstyle measure-microscope?

Two images are applied - the screws goes in and out, when turned, so i have to deal
with this too ...

My first idea was to fix belt-gears at the outer ends of the screw-heads and simply drive them with a tooth-belt and a stepper-motor, so the belt can swoop over the disposition, but maybe someone has a better way?

If it works, then it should be a very good and stable basis for a repstrap smiling smiley


Edited 1 time(s). Last edit at 10/03/2007 05:16PM by Viktor Dirks.
open | download - Messmikroskop1.jpg (265.4 KB)
open | download - Messmikroskop2.jpg (256.7 KB)
Re: Ideas for motorizing old micron-screws wanted ...
October 04, 2007 12:27AM
I may be speaking from a misconception, but here goes.
Give the thing a toothed rod "gear", long enough to be engaged for the total distance of travel of the screw. Fit a second, more typical gear, to this. As it travels, it continues to be engaged.

If the travel is not too much, and you have room to play, you might consider a belt or chain that's long enough that the travel of the screw isn't enough... Think of a triangle. The long side would be the chain or belt. The short side would be the travel of the screw. If the long side is sufficiently larger than the short side, the difference between it and the hypotenuse shouldn't be enough to cause a problem with the belt or chain. Add a tensioner spring to the back end and most of that goes away too, (leaving the angle between the sprocket or pulley and the belt or chain, as a potential problem area.)

A third method. Attach a fixed guide rod, (or two,) to the frame. Place the motor so it turns the screw directly, but is held at a single orientation by the guide rods. This would necessitate a bracket on the motor that engages the guide rods.

I hope this is useful to you. Good luck.
Re: Ideas for motorizing old micron-screws wanted ...
October 04, 2007 02:40PM
Hi Sean,

... a longer belt-drive was my first thought too, but this isn't the optimum yet ...

If i use the original micron-screws, then i have the higher accuracy with 1 millimeter per revolution, but only 25 millimeters maximum way for X and Y (Z has two rails, both a bit harder to turn, so i have to insert a complete new axis).

When i remove the 25-mm-micron-screws and insert a linear-stepper, then i would have 130 millimeters in X and 70 millimeters in Y - with the costs and the accuracy of the linear drives (~350 Euros for two 1-micron-steppers).

So it's actually the selection of alternative A = 25mm way in XY with a cheap and easy workaround, or B = buy two expensive linear steppers and have a bigger working area.

Or a brand-new alternative C with a better idea ...

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