driving a screw with a flat belt

I want to drive a 15mm diameter screw with a motor on a fixed mount at a very low speed, maybe 1 rev/min. The 800mm long screw will be turning through some fixed nuts so will be moving in its axial direction as it rotates. I am planning to try using a 25mm wide flat belt that goes over a pulley on the motor shaft and directly on the screw threads. The pulley will have a center hump to help keep the belt on the pulley. I am concerned that the movement of the screw might be enough to pull the belt off the motor pulley.

Does anyone have any idea if this sort of drive can be made to work? I would not be so concerned if I were driving a smooth shaft with the belt, but the threads in the screw may cause problems as the screw moves axially...

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Fix another pulley with a nut in the center for the screw to be driven with.

That won't work. I need to turn the screw and have it move in the axial direction. This isn't linear positioning in the traditional sense...

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Not sure I have my head wrapped around your project yet... So forgive me if I'm thinking wrong...

If you had a round screw nut... Let's say like a round lead screw nut. Now on your motor mount bracket you have 2 arms that come off it like a C channel. A hole threw the arms for the screw to pass through but smaller then the round nut. Thrust washers on either side of the round nut. So the screw would pass through one arm of the C channel then a thrust washer then round nut with belt then thrust washer then second arm and out the other side. The motor spins the belt around the round nut and since the nut is constrained between the two arms the screw moves axially? Is that kinda what your looking for?

Edited 1 time(s). Last edit at 07/25/2015 01:15AM by madmike8.

Hmm, I smell chocolate extrusion here?
I believe the belt in your setup will follow the screw for a bit, but the axial forces will out balance at some point. But then the tension on the belt will be uneven and the sharp threads of the screw will eat the belt pretty fast. Not to mention, that greasing the screw is a noGo.

Could you fix a pulley on the far end of the screw and mount the motor on a linear slide? This way both pulleys would be aligned at all times.
Or, if you want the motor being fixed, extend the shaft with a square shaft and let the motor pulley slide on the square shaft.

I had a similar approach on my extended shaft extruder here:


-Olaf

This is what I am talking about:



The nuts and motor are fixed, the screw is free to rotate and move axially. The screw and nuts are standard hardware store stuff. This is not intended to be a high precision mechanism.

I am a bit concerned about the screw chewing up the belt, but not too concerned about lubrication. My biggest concern is how far the belt may shift up or down along the screw as it turns.

This is NOT for the chocolate extruder- that design is now finished/workable.

Edited 1 time(s). Last edit at 07/25/2015 07:59AM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

How about something like this:

Splined shaft (slippery) tied to threaded shaft
Shaft moves up / down in pulley with spline insert
via fixed nut on threaded rod
keeping motor pulley fixed.






Edited 1 time(s). Last edit at 07/25/2015 10:02PM by cozmicray.

That might be workable but doubles the length of the whole thing. I have more thinking to do....

Thanks!

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Put the nut inside pulley.

Can your end effector limit threaded rod rotation?