Steve,
Pardon me for jumping into this discussion between you and Art. I
don't know anything about Art's code but my experience with large
mills is that about 10 PPR for a spindle speed sensor will give the
controller a much better idea of what the machine is doing.
As I understand his algorithm he is not trying to control spindle
speed but rather to measure it and it's absolute position so as to
make the carriage motion correct for the thread in question. A 10 PPR
spindle pulse with an index pulse for each revolution would seem to be
ideal for this operation.
The software can then make a very accurate determination of actual
spindle speed and the index pulse will tell where it is relative to
the cartridge. The best of both worlds.
If you look at this from 20,000 feet (or meters for Art) it's a
classic type 1 open loop servo. Feedback from the spindle sensor
controlling the carriage motion to produce a desired result but no way
of knowing if it did.
I these cases the best one can do is get the most accurate feedback
from the rotation sensor and hope the other axis did what is was told
to do. This is a very reasonable assumption with modern stepper or
servo controls.
Regards;
Ken
