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Author Topic: PID tuning for MR-J2S Servos  (Read 4752 times)

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PID tuning for MR-J2S Servos
« on: April 16, 2016, 09:32:51 PM »
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'?
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.
Re: PID tuning for MR-J2S Servos
« Reply #2 on: April 16, 2016, 09:59:13 PM »

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.

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 »
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.