On 12/9/20 8:21 AM, Jon Elson wrote:
On 12/08/2020 10:53 PM, Gene Heskett wrote:
What does that 22mv mean in folllowing error since I have that set
for about half an inch at the moment?
It is not milli VOLTS, it is milli-units. Generally inches or mm,
depending on your preference.
so 22m means 0.022" assuming that's what you use. Or, if this is a
rotary, then it could be
0.022 degrees.
My method of tuning is to first increase MIN_FERROR to prevent
following error trips, then reduce
P to a small value, just enough that error doesn't creep up. Adjust
FF1 until error is small at moderate speed, less than 50 encoder
counts, perhaps. Then, assuming a real axis with encoder feedback,
add a LITTLE FF2 to reduce the error spikes on accel/decel. (Don't
bother on stepper-simulated axes.)
Then, increase P to drive the error down to a small fraction, add a
little D to improve stability.
It takes practice and experience to know what to adjust based on the
Halscope trace.
Jon
Tuning seems to be a highly individualized endeavor. Hopefully a damped
(in following error) search. :-)
I start with a classic ZN ... increase P until you get un-dampened
oscillation. Make starting P .6 of that value.
Set FF1 equal to one and then adjust as necessary to minimize following
error.
Adjust FF2 to minimize spikes on accel and decel. Adjust FF0 if needed
for zero crossing. Try small amounts of D and I although I usually leave
them a zero. Following error is < 1e-3 and can get down as good as 5e-4.
The values in PID, etc do seem to interact so going thru the loop a few
times can't hurt. As always YMMV.
The major error on my machine is backlash. Adding a glass scale to X and
Y might help. (future project).
I suspect that having tach feedback makes tuning much easier. I've never
had much success with torque mode.
If I had the skill in linuxcnc internals I'd would try a well
constrained Monte Carlo. No chance of my doing that. ;-(
Dave
Be careful, stay safe.
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