On 8/14/23 15:53, John Dammeyer wrote:
This thread has some good information about this
https://sourceforge.net/p/emc/mailman/message/34363029/
For interest sake I set my mill up to turn 1 RPS with my 60 tooth
non-symmetrical encoder (4mm slots, 2.5mm teeth) and then ran the power
tapping G-Code to see what the knee Z axis would do.
What I found is that it moved in short spurts. Putting my finger on the
knee and against the column it still appeared to move rather slowly with
less of a jerk. All this makes sense of course.
Something might be off in the quadrature accuracy. Do you have a dual
trace triggered scope? That will likely be quite helpful. 60 teeth,
non-symetrical is going to generate a horrific amount of quantization
noise because neither waveform is going to be a 50/50 ratio in the time
domain. I got rid of all signs of that by putting my $20 Omron encoder
encoder on the rear of the spindle MOTOR, making and index pulse
generator on the spindle with a glued on screw and an ATS-667 hall
device, and tally switches on the heads gearshift knob to electronically
change gears. So the SCALE changes with the gearshift knob. And I can
run the pid's Pgain above 20.
My servo period is 1000000 nanoseconds or 1 ms. At 1 RPM that's one tooth
every second or 4 encoder edges per second meaning one edge every 250mS.
That's 250 servo periods. What I think I'm seeing is that every 250 servo
periods the system detects the encoder edge and knows it's moved 1/240th of
the 20 TPI thread. (0.000208333") So it tells the Z axis to move that same
distance and I suspect the velocity setting of 0.0002083333/250mS.
Does that make sense? Is there a way to log each Z axis speed/distance
command so I can see what it's doing?
Or have I misunderstood how the power tapping synchronized motion is done.
Thanks
John
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Cheers, Gene Heskett.
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