AC servo is nonstable at very low speed?
06 Dec 2018 18:00 #121976
by andypugh
Replied by andypugh on topic AC servo is nonstable at very low speed?
It is possible to alter the PID tuning parameters depending on commanded speed.
In fact this was the main motivation for writing the "lincurve" component.
It is quite often useful to be able to alter the PID terms in the fly. For reference, this is the I-gain map for something related to my day-job:
You can see that it is asymmetrical around the zero-error point, and varies with temperature.
And this is only one of 10 that can be chosen dependant on gear.
Compared with this, lincurve is very limited (though you could multiply several together)
I can see it being useful to have large I-gain at zero velocity command, for example, but low P-gain to avoid instability on encoder dither.
In fact this was the main motivation for writing the "lincurve" component.
It is quite often useful to be able to alter the PID terms in the fly. For reference, this is the I-gain map for something related to my day-job:
You can see that it is asymmetrical around the zero-error point, and varies with temperature.
And this is only one of 10 that can be chosen dependant on gear.
Compared with this, lincurve is very limited (though you could multiply several together)
I can see it being useful to have large I-gain at zero velocity command, for example, but low P-gain to avoid instability on encoder dither.
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11 Dec 2018 06:57 - 11 Dec 2018 06:58 #122181
by thang
Replied by thang on topic AC servo is nonstable at very low speed?
Sorry for the late replay,
Here is my config:
+ This is an arm robot.
+ AC servo mrj3-A (mitsubishi) + driver is using auto-tunning to close velocity loop
+ 5i25-7i74-7i83 combo for analog control
+ linuxcn config is using pid to close position loop with 5khz at servo-thread
Here is how system work:
+ At high speed, everything seem work OK
+ joint 1 sometime happen this after move done, change Kp doesnt fix it
+ At very low speed, the joint 0 sometimes vibrate heavy but not happen at all position this happen so random that i can understand it
I also wonder, is there any gain that can eliminate slight vibration at low speed?
Here is my config:
+ This is an arm robot.
+ AC servo mrj3-A (mitsubishi) + driver is using auto-tunning to close velocity loop
+ 5i25-7i74-7i83 combo for analog control
+ linuxcn config is using pid to close position loop with 5khz at servo-thread
Here is how system work:
+ At high speed, everything seem work OK
+ joint 1 sometime happen this after move done, change Kp doesnt fix it
+ At very low speed, the joint 0 sometimes vibrate heavy but not happen at all position this happen so random that i can understand it
I also wonder, is there any gain that can eliminate slight vibration at low speed?
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