Originally Posted by
HimyKabibble
Pete,
The Geckos will keep you where you command as long as they are properly tuned, and you operate them within their capabilities. The "closed loop" boards are of value only when you push *too* hard, and exceed the capabilities of the drives and motors. The *only* times I've ever lost position on my machine was when I did something stupid, and ran the tool into an immovable object, like a vise or clamp. Now that I know what I'm doing, that's rare, and even when it does occur, it only takes about two minutes to re-reference the machine, and get back to work. These things will not help with "accuracy", unless you're willing to accept a HUGE loss in performance. If you believe you can "close the loop" and start operating with zero following loss, get ready to run VERY slow accelerations, and start running your jobs at a snails pace. Following error is a fact of life, and under any remotely realistic operating conditions, it is not a problem at all. PID control loops were developed to give the best performance over a wide range of operating conditions, and you cannot have a PID loop without following error *and* get reasonable performance. The I term will always ensure you end up where you should, which is all that matters. Under light loads, the following error will be very small. In fact, Geckos are often criticized for faulting with such a small following error. Larger, more powerful servos controllers often allow following errors in the thousands, or tens of thousands, of counts, yet they work just fine on large VMCs delivering the kind of performance and precision we can only dream of. Keep in mind too that as long as you're running CV mode, you're not necessarily *exactly* following the programmed path anyway, because Mach will modify the path as necessary to maintain CV. This probably has a far greater effect on "accuracy" than any following error.
Regards,
Ray L.