Electronic Leadscrew

[sconisbee]

Ok so i've heard these talked about a bit, never seen one in action before, and have read alot of the stuff i can find on it but...

Has anyone here actually made/used one?

With an electronic lead screw granted the gear train will be made redundant but what about the threading indicator?, and the keeping half nuts closed while doing a metric thread with an imperial lead screw issue?

[oldtiffie]

There was a thread or post from Germany or someone that was German - I forget - some months ago.

It was all electronic and was based on pulses and synchronisation as I recall. The full process and diagrams were there.

I though I had it book-marked but can't find it.

Evan has a similar system for speed control of his lead-screw on his South-Bend lathe. Perhaps he might re-post the article or the link. It was quite clever.

Perhaps this link might be of use:
http://www.stellar-international.com/lathe.html

[Ryobiguy]

I built one using a custom "ELS" software module for EMC^2 that I wrote.

http://server.fricktion.net/~mfrick/...mcEls_v0_1.pdf
(URL updated 1-28-2011)

Works great - totally synchronized like it's got gears.
I don't have a threading dial, but using a carriage stop, returning the leadscrew to home position, and ignoring spindle until it passes it's home position, I don't need a threading dial, nor do I need to keep the half-nut closed.
Sure, I have to stop on each threading pass, but it works for any possible thread pitch within the limits of resolution. 4 is the lowest TPI I've tried.

[oldtiffie]

Thanks ryobiguy.

That seems to be far and away better than the "German" item I referred to.

Do you build the item for sale? I have a 230/240v 1ph 50Hz supply in Australia. If so please PM me.

Electronics is pretty well a complete mystery to me as I am from the era/age of steam radio!!

My lathe has no power feed or quick-change gear-box.

Your solution would seem to fit in with me very well.

I have a full set of changes gears but never use them unless screw-cutting.

[bob_s]

or join the Yahoo group

http://tech.groups.yahoo.com/group/E-LeadScrew/

[Ryobiguy]

You can have my software for free once I package it up and release it.
It's tuned for my system, so it would take some tweaking to get it running on someone else's setup.

Once you get a spindle encoder and stepper motor on the leadscrew and get those both wired up to a PC parallel port, you can at least try it out, and if you don't like it you haven't lost anything.

Once it's hooked up to a PC, you could also hook up to EMC^2 and use a real CNC controller too. I haven't actually tried it out myself, I just wrote my own program that runs parasitically in EMC^2 'cuz I'm not yet ready for full CNC, and I don't quite have the hardware it needs. I don't have a quadrature encoder with index pulse (not totally necessary, could hack around that,) I don't have a second axis, nor do I even have the stepper's direction signal hooked up to the PC.


Also, the Yahoo ELS group (mentioned above) is also developing a ~$150 standalone ELS controller based on the PIC microcontroller. It's almost in the production phase. It's got a LCD display (20x4 characters I think), a keypad, a stepper driver (somewhere around 2 amps?,) an MPG (or at least a hookup for one using inexpensive encoder,) can drive a second axis (with external driver) to do tapers and fully automated threading. I think I also heard something about a nice metal case for it too. Join the group for ask for details if you can't find them in the archive.

-Matt

[oldtiffie]

Thanks bob-s and Ryobiguy.

Very sound advice and very much appreciated.

[Mcgyver]

Matt - that was a great write up....i need more time to read it properly but wanted to say thanks for taking to time on it, great content

[John Stevenson]

I joined the e-leadscrew group when it first started and the idea's for what was needed were being thrashed out.
Most just wanted threading but not go to full CNC.

I advocated just using one axis of TurboCNC and a spindle encoder to do the threading but was told that was CNC.

So three years down the line they have come up with a single axis CNC that can be extended into a 2 axis CNC admittedly in a smaller case and no screen.

No sour grapes but once you start using a stepper motor, spindle encoder and driver you have re-invented CNC.

.

[rantbot]

I was disappointed by the discussion in that Yahoo group. I saw no consideration anywhere of the errors which all of classical control theory is devoted to dealing with. Steady-state offset error is, obviously, the big one in a leadscrew-driving system. Damping of oscillation is another biggie. (Fixing those are what the "integral" and "derivative" portions of a P-I-D feedback loop do.)

This is typical of the digital guys, who too often seem to think that simply counting pulses is all that's involved in control of moving parts. The phase-locked loop is a good way to generate a proportional error signal, albeit of limited resolution. But that's just the start of the control problem. Is a simple proportional feedback control system good enough for the application? What are the numbers?