Hi,
From my experience a board like ESS based FPGA could be able to monitor the pulse train read by the encoder.
I'm talking about a passive comparator (no PID control).
You are correct, the ESS COULD be a feedback controller but Warp9 have expressed no interest in doing so. A major part
of that thinking is because each servo and servo drive is a feedback loop. Thus all an ESS need do is provide open
loop step/direction commands and allow the servo and drive to follow. The servo/drive have an following error window
and can monitor if the loop gets out of whack with respect to the input commands.
You need to imagine a situation where the ESS commands pulses but the signal is lost before reaching the servo drive input.
Imagine what situation? Are you talking a faulty breakout board?
My ESS has never lost any pulses in the four years I've been using it. As an example I have a PCB
program that I run from time to time, it is a largish but detailed board and it takes 10-12 hours to run. At the end of the
program I can drill a 0.4 mm through hole EXACTLY through the hole I drilled at the start of the job. If Mach, or the ESS,
or my BoB's, or my stepperdrives, or my stepper lost a step that would not be the case.
If the ESS board monitored the encoder it would be possible to detect the error (pulses commanded - pulses executed).
What I have proposed is that the servo drive monitor the commanded position (the cumulative step/direction position) by
Mach/ESS and the machines actual current and live position which achieves exactly what you are proposing.
There are controllers that can do as you wish, but they start at six and more times the cost of an ESS. In addition those
controllers are suffering a shrinking share of the market because of the to trend smart servo drives, the motion controllers
don't need it any more, in fact Ethercat does away with the motion controller altogether and 'distributes motion control'
amongst its Ethercat slaves.
Craig