MPG causing axis oscillations.
30 Mar 2016 13:29 #72388
by eman5oh
MPG causing axis oscillations. was created by eman5oh
I finally have my machine fully configured and everything working as it should except for my MPG pendant. Sometimes but not all the time when I jog the machine with the mpg the axis I am jogging oscillates at the end of the move. It acts like a servo motor with too much P gain. I am running stepper motors on my machine with a MESA 5i25 connected to a 7i76 card. The machine moves fine when jogging with the keyboard and I ran the 3d tux file several times with no issues. As I was setting up the machine the following error was set .500 in and now is set to .010. With .010 I get a small oscillation then the axis will fault with a following error. I have tried the MPG with and without debounce with the same result. I have also tried the standard jog mode and velocity mode. It still happens on occasion. I am running 2.7.4 and have tried the 2.7.4 with build bot fixes. What should I be looking for to track this down?
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30 Mar 2016 14:36 - 30 Mar 2016 15:46 #72389
by PCW
Replied by PCW on topic MPG causing axis oscillations.
It would help to have the .ini file included as this has all the parameters
This sounds like a tuning issue of some kind so the parameters are needed to
discover what's wrong
in general I do know that larger jog increments can cause troubles and this is often fixed by
running the jog signal through the ilowpass component
This sounds like a tuning issue of some kind so the parameters are needed to
discover what's wrong
in general I do know that larger jog increments can cause troubles and this is often fixed by
running the jog signal through the ilowpass component
Last edit: 30 Mar 2016 15:46 by PCW.
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30 Mar 2016 16:26 - 30 Mar 2016 16:28 #72391
by eman5oh
Replied by eman5oh on topic MPG causing axis oscillations.
ini file below
I will try to use the ilowpass and see if it fixes this.
I will try to use the ilowpass and see if it fixes this.
Last edit: 30 Mar 2016 16:28 by eman5oh.
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30 Mar 2016 17:06 #72399
by PCW
Replied by PCW on topic MPG causing axis oscillations.
Jog inputs should not violate acceleration and velocity constraints
but it does seem like this is happening.
The filter should help (and make larger jog increments a lot more pleasant)
but it still does not explain why you are getting this violation
one thing I am suspicious of is the trajectory planner not running
at the servo thread rate so you might try changing the TRAJ
cycle time to match:
[TRAJ]
AXES = 3
COORDINATES = X Y Z
LINEAR_UNITS = inch
ANGULAR_UNITS = degree
CYCLE_TIME = 0.001 -- changed from .010
DEFAULT_VELOCITY = 0.17
MAX_LINEAR_VELOCITY = 1.67
but it does seem like this is happening.
The filter should help (and make larger jog increments a lot more pleasant)
but it still does not explain why you are getting this violation
one thing I am suspicious of is the trajectory planner not running
at the servo thread rate so you might try changing the TRAJ
cycle time to match:
[TRAJ]
AXES = 3
COORDINATES = X Y Z
LINEAR_UNITS = inch
ANGULAR_UNITS = degree
CYCLE_TIME = 0.001 -- changed from .010
DEFAULT_VELOCITY = 0.17
MAX_LINEAR_VELOCITY = 1.67
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30 Mar 2016 17:38 #72405
by eman5oh
Replied by eman5oh on topic MPG causing axis oscillations.
Thanks for the help, I will try both and report back.
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31 Mar 2016 01:08 #72429
by eman5oh
Replied by eman5oh on topic MPG causing axis oscillations.
I tried both of your suggestions and I still the issue, if I set ilowpass.0.gain to .5 the osilatiosn stop but I get the axis fault with following error. I seems to only happen when I have the jog incement set to .100 in per click and turn the mpg slowly. Any more ideas?
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31 Mar 2016 01:31 #72430
by PCW
Replied by PCW on topic MPG causing axis oscillations.
0.5 is way too high (1/2 in 1 ms, 3/4 in 2 ms etc)
I would try .005 or so as a start
I would try .005 or so as a start
The following user(s) said Thank You: eman5oh
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31 Mar 2016 01:53 #72431
by eman5oh
Replied by eman5oh on topic MPG causing axis oscillations.
I found .050 seems to be what the machine likes. This is a lot better than it was but it still oscillates a little form time to time while jogging. I have the following error set to .010 is that a reasonable setting for steppers?
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31 Mar 2016 02:00 #72433
by PCW
Replied by PCW on topic MPG causing axis oscillations.
Thats still pretty high, why not lower?
( the example here suggests 0.01 )
linuxcnc.org/docs/html/examples/mpg.html
(scroll down to "jog.hal with ilowpass" )
what is the ilowpass scale?
I have 0.0001, 0.0002 as FE setting on a 1G accel/2400 IPM test config
( the example here suggests 0.01 )
linuxcnc.org/docs/html/examples/mpg.html
(scroll down to "jog.hal with ilowpass" )
what is the ilowpass scale?
I have 0.0001, 0.0002 as FE setting on a 1G accel/2400 IPM test config
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31 Mar 2016 17:16 #72483
by eman5oh
Replied by eman5oh on topic MPG causing axis oscillations.
I tried .01 and lower but it seems to make the oscillations worse, .05 was the result of tring a bunch of different settings and seeing what worked best. It seems lowpass masks the problem but does not make it go away. I will try to lower the ferror to .001 and do some more testing. ilowpass scale is set to 1 so my jog steps are .001, .010, and .100 per click of the mpg.
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