[MrWild]

Why doesn't running a closed loop controller with Mach or EMC make for a closed loop system? What specifically are you missing that you would have with "true" closed loop system?

I've heard this argument before, but I'm not a believer.

The last time we went through it here on the 'Zone, there were no really compelling answers for what the "true" closed loop could do that an "open loop" Mach running a servo drive couldn't accomplish. I think the most compelling thing was you wouldn't have to home the machine after an E-Stop, which wasn't much of an advantage.

Cheers,

BW

Simple answer is tracking error. closing the loop in hardware includes a real time tracking error. A pulse train tells a drive to 'go here." The drive starts moving and moves to "here." There is a slight time delay between commands and execution. because of not knowing exactly. Minor to be sure but there is a reason a hardware derive will fault out if the tracking error becomes too large.

Lets say the Y axis is holding steady while the X axis is plowing along and starts lagging the pulse stream. It won't be much of a lag or it will fault out, yet there is a lag up to several thousandths. While the X is lagging, Y is ordered to move. Suddenly you are not making parts to print.

With EMC, you have a control that flat knows where the Axes are. If something is lagging, EMC knows not to move any other axis until it is where it should be before the move. Mach can't do this by the very nature of how it makes controls work.

If all you are doing is steppers, Mach is just fine. When you go to servos, I think I want a control that doesn't allow for lag. EMC is the smart choice for that picture. Why do I use EMC? I'm cheap and figured as long time ago I only wanted to learn a control once. The only real whines about EMC are that it has a steep learning curve. It isn't that steep. Way less than Pro E. About on par with AutoCAD for dificulty.