stepgen dir signal

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17 May 2018 18:48 #110818 by billykid
stepgen dir signal was created by billykid
hi, I have a closed loop system with 4 pwmgen plus a stepgen for axis a.
mesa 5i23. looking at the oscilloscope I saw that the pin direction of the stepgen is sometimes a square wave with 50% duty cycle. Is this normal?
however it works everything was just a curiosity.
thank you
Mauro
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18 May 2018 03:35 #110830 by PCW
Replied by PCW on topic stepgen dir signal
The stepgen is basically a servo system so can dither somewhat. if you use the PID setpup you can usually
rid of this behaviour with proper tuning
The following user(s) said Thank You: billykid
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18 May 2018 12:25 #110840 by billykid
Replied by billykid on topic stepgen dir signal
I do not have the pid for axis A. better to put it?
I found a mini itx industrial iei kino dh610 with i5 4 GB memory I'm going to 8khz with the 5i23 and the servos DC work perfectly.
when I have finished I can post all the details because it seems to be a 'great card
fast and very little latency even with rt-preempt.
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18 May 2018 14:16 #110842 by PCW
Replied by PCW on topic stepgen dir signal
The PID based stepgen control works somewhat better then the built in position mode control in the driver, though I doubt you would notice any real difference
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19 May 2018 16:30 - 19 May 2018 16:38 #110890 by billykid
Replied by billykid on topic stepgen dir signal
at least now the signal seen at the oscilloscope is perfect and dir no longer oscillates.
how did P = 125 being an 8khz okay? I'm a donkey doing the calculations :-)
Thank you
Mauro
Last edit: 19 May 2018 16:38 by billykid.
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19 May 2018 18:14 #110895 by PCW
Replied by PCW on topic stepgen dir signal
You can use up to P=8000 at a 8 KHz servo thread
( P= servo thread rate means correct any position error by the next thread time)

Anything higher will result in overcorrection

You may not want to go as high as 8000 without DPLL firmware, as servo thread jitter
will cause random bogus velocity corrections and the magnitude of these corrections is proportional to P
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