Smoothstepper step problem

[cv580]

I have a smoothstepper on a large mill with stepper drives and what ever code that is being run through the smoothstepper it will not make the whole stepping distance ie: if the code is X-1.250, Y1.250, Z-.750 the actual distance the smoothstepper will make is X-1.2499, Y1.2502, Z-.7499. Can anyone explain why this happens and what the fix is? If I run the machine thru a parallel port this does not happen. The drives are being run in step and direction mode. I have used a dial gauge on the axis and it confirms the over travel and under travel with the smoothstepper.

cv580

[Hood]

What are your steps per unit?

Hood

[cv580]

Steps per unit are 10,000 (ball screw makes 5 turns to 1 inch of travel), I have tried different step per unit settings but then distance travelled becomes incorrect in a big way. The undertravel or overtravel remains constant until the axis passes thru 0.000 and then the change of plus or minus a step will happen.

cv580

[Hood]

I cant remember exactly what it is but Greg did explain it to me a few years back, its something to do with the way things are calculated but it doesnt accumulate. In fact I cant even remember if its just a display thing or actually a real value but either way 0.0001 is an insignificant value. I agree  it is f a visual nuisance but you soon forget about it when you realise how small it is


Hood

[cv580]

It is actually .0002" as it will go plus or minus .0001" and it can be more than a nuisance especially when you look at the DROs while running code and see a bunch of 9's because it has rolled back .0001", also I have been doing some very small engraving of serial numbers and losing a .0001 step makes for some difficulties also so it does depend on what you are doing will make it a small or big issue.
Does Warp9 still support the smoothstepper as I have tried to send them e-mails about this problem but never receive a reply?

cv580

[MillMaster]

Hey cv580
I have the exact same problem with my smoothstepper, I have been told that it is no big deal as it is such a small step and there is more back lash in the axis than what travel the smoothstepper cannot make but I disagree with that thought as we are now working with electronics that can be super super accurate, basically I see what the smoothstepper doing here is a form of electronic backlash. I have talked to other people that are having this issue with the smoothstepper and it is only happening in the step and direction mode, I know one shop that have this issue and they were talking to Warp9 about this and the explanation came back something along the line about it being a problem with the algorithm not being right for the step and direction mode and using a hysteresis for the step and direction mode which is not used for the quadrature mode, from this I gather the smoothstepper is not really designed for step and direction mode. I do hear a lot of comments of it is just a small step and not to be concerned about it, which I do not agree with because here is a product with great potential but it is put on the market as is with no feedback from the machining community then it will remain a half built product that is not right, I do not know of another motion controller on the market today with this sort of lead and lag. I gather that the designer of the smoothstepper is not a machinist and if everyone in the machining world comes across with the attitude of plus or minus .0001" is not a big deal then nothing will be done by Warp9 and you will be stuck with a motion controller that has lead and lag. He has to know what is not working properly, so yeah + or - .0001" steps is a concern for some of us chipmakers. As for support for the smoothstepper from Warp9 I am not sure what their take is on this issue, I understand they are a moderater on this forum maybe they could let us know what their thoughts are! 

millmaster

[RICH]

Your steps per unit are 10000, so if all was perfect ( which it is never true ) the very best you can hope for in
position is 0.0001" plus or minus. To do better than the 0.0001" the mechanical axis needs a required steps per unit
at 20000. 

It's an emotional issue to see say 1.9999 instead of 2.0000.
I never had a display problem with any of the machines, SS or PP,  if the steps per unit was reasonable above 10000.

Do small engraving and say it makes a difference on small engraving of letters.......how small and how deep and what is your runout at the tip of the point. Best i could ever do is 0.0005" tip radius which won't even last in scribing butter.  And you will not scribe a single point / line width of 0.001" since there will be spindle runout and ovality of the point. Sorry, just don't buy a practical impact on lettering because of the .0001" . FWIW my engraving
machine requires  253000 steps per unit , slow,  but accurate as can be in positioning. Small quality letters or numbers .010" high are a real challenge, almost not practical.

RICH

   

 

[Hood]

can I ask the specs of your machine please?

Hood

[MillMaster]

Hey Rich
I think we are looking at a electronic issue here, you are thinking of a mechanical issue with the machine. What mode are you running your machines in? Step and direction or quadrature? The mode will make a difference in what the display shows.

millmaster

[Hood]

millmaster
 what machine do you use the SS on?

Hood