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Author Topic: PID tuning for MR-J2S Servos  (Read 2215 times)

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Offline tcustom

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PID tuning for MR-J2S Servos
« on: April 16, 2016, 09:32:51 PM »
Hello,
Hope that somebody can understand my poor english.
I use Mr-J2s servos for my machine. I think my servos are well tuned, but I can't find any reasonable values for PID in DSPMC.
I already read DSPMC integration manual several times, and tried many times to make it stable. But I can't yet.

This is what I did.

1. First of all, I tuned servo drivers through Mitsubishi servo tuning program.
2. Open DSPMC  plugin window, then set velocity 10000, acceleration 1000, distance 0.1, P : 100, D and I : 0, lowpass filter : 5.
3. Execute move and increase P gain until axis can move.
4. Add D and I gains  gradually. (status graph doesn't change properly.)
5. After I make graphs (red and blue) as close as possible, then I put larger value for distance (ex: 1~3mm) and execute.
6. Motors are vibrate and make loud noise like grinder when they moving.

I already did this a dozen times. So I add Accel,Decel and S-pattern constants in MR-J2S drivers.(parameter 11,12,13)
After I add this, motor looks stable but it can't follow commands quickly.

Isn't there anybody use Mitsubishi servo motors?
Please give me a guideline.

Thank you.

P.S. What is the purpose of 'velocity feed foword'?

Offline Vital System Support

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Re: PID tuning for MR-J2S Servos
« Reply #1 on: April 16, 2016, 09:47:55 PM »

Torque command input work best with analog control.   make sure 0 to +-9v produce 0 to max torque (or speed) on the motor.

you can verify this by putting 5 volts on the analog command input and this should produce 1/2 max power (or speed) at the motor.

you can then make all PID param to zero and then start adding P until you have good motion.  do not put too much P, as it may produce grinding noise.  Set low pass filter to 5.  Set I to 10 and Max Error I to 250.  You can add D to reduce oscillations.

Velocity feed forward produce more power at high speed and less power at low speed.  this helps to reduce following error at high speeds.

hope this helps.

Offline tcustom

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Re: PID tuning for MR-J2S Servos
« Reply #2 on: April 16, 2016, 09:59:13 PM »
Hello,

Thanks for your answer.

You mean that I need to set my servo amps to 'torque control mode'?

If then I also change wiring.

Mitsubishi servos use +-8v for torque command.




Offline Vital System Support

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Re: PID tuning for MR-J2S Servos
« Reply #3 on: April 16, 2016, 10:09:06 PM »
yeah 0 to +-8v is ok too.  I dont think applying +-10v will do any damage.  if you command accel/velocity within the servo drive/motor limits, dspmc will not put out more than +-8volts.  

If changing wires too much trouble, you can try velocity mode first.
« Last Edit: April 16, 2016, 11:45:54 PM by Vital System Support »

Offline tcustom

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Re: PID tuning for MR-J2S Servos
« Reply #4 on: April 17, 2016, 02:03:24 AM »
I already did it with velocity control mode.

There is nothing I can do anymore with velocity mode?

If I change to torque mode, I need to change wiring of servo drivers connector.

I want to do everything I can do in speed control mode first.

Thank you.