mill moves when powered on
15 Nov 2016 20:11 #82845
by an92626
mill moves when powered on was created by an92626
Have a 3 axis mill but only x axis hooked up at this time. When I power linuxcnc on (press F2), the table immediately starts to move. using mesa 5125 / 7177 boards and ocilloscope on analogout0 for x axis does show positive voltage as soon as linuxcnc powers on, so something in linuxcnc is telling the table to move. attached are my ini and hal files. Can anyone tell me why linuxcnc is telling the table to instantly move? My plan is to manually home machine so I did not plan on any auto home feature. Did I accidentally install a auto home feature?
thank for the help.
thank for the help.
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15 Nov 2016 20:41 #82848
by PCW
Replied by PCW on topic mill moves when powered on
Are the servos tuned?
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15 Nov 2016 23:06 #82851
by an92626
Replied by an92626 on topic mill moves when powered on
The initial mill had manuals which included set up procedures for the servo amplifiers. I went through the set up procedures to adjust the servo pots both statically and dynamically. Not sure how I can do more to tune the servos when they instantly move as soon as linuxcnc is powered on and as soon as the servo moves I get a following error.
I read about tuning and adjusting pid ff0, ff1,etc, but I think I need to stop the servo from instantly moving before I can do anything else. With the servos powered up and enabled, they do not move as long as there is no voltage in the analog input wires. When linuxcnc is powered on (F2) and analogout is not connected to servo amp, halscope and oscilloscope shows no voltage on analogout. When linuxcnc is powered on (F2) and analogout is connected to servo amp, halscope and oscilloscope shows voltage on analogout and the table move and then gets a following error. Why does connecting analogout affect whether linuxcnc applies voltage to analogout?
I read about tuning and adjusting pid ff0, ff1,etc, but I think I need to stop the servo from instantly moving before I can do anything else. With the servos powered up and enabled, they do not move as long as there is no voltage in the analog input wires. When linuxcnc is powered on (F2) and analogout is not connected to servo amp, halscope and oscilloscope shows no voltage on analogout. When linuxcnc is powered on (F2) and analogout is connected to servo amp, halscope and oscilloscope shows voltage on analogout and the table move and then gets a following error. Why does connecting analogout affect whether linuxcnc applies voltage to analogout?
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15 Nov 2016 23:43 #82852
by PCW
Replied by PCW on topic mill moves when powered on
It should be pretty much expected that some axis will runaway as soon as LinuxCNC enables the drives
This is because on a first startup there is a 50% chance that the encoder --> motor feedback is reversed
which will cause an instant runaway.
I would suggest looking at JTs servo tuning guide:
gnipsel.com/linuxcnc/tuning/servo.html
Note the order of the "Prepare to Tune" items, there's no point in
trying to tune or fiddle with polarities until the encoders read properly (on the DRO)
with proper scaling and direction.
Once the encoder setup has been done, and you still get runaways when you enable the drives.
you need to change the analog output polarity. This is done be changing the sign of the OUTPUT_SCALE
INI file constant for the affected axis
This is because on a first startup there is a 50% chance that the encoder --> motor feedback is reversed
which will cause an instant runaway.
I would suggest looking at JTs servo tuning guide:
gnipsel.com/linuxcnc/tuning/servo.html
Note the order of the "Prepare to Tune" items, there's no point in
trying to tune or fiddle with polarities until the encoders read properly (on the DRO)
with proper scaling and direction.
Once the encoder setup has been done, and you still get runaways when you enable the drives.
you need to change the analog output polarity. This is done be changing the sign of the OUTPUT_SCALE
INI file constant for the affected axis
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16 Nov 2016 01:31 #82853
by an92626
Replied by an92626 on topic mill moves when powered on
Thanks for the response. I tried your suggestion and tested the x encoder by hand and the direction was reversed. I tried negating the output_scale value in the ini file and it did nothing, but when I negated the encoder_scale value, the encoders worked right and when I powered linuxcnc (F2), the table did not move on its own and give a following error. I tried moving table within linuxcnc and it did move right. Should it really have been the output_scale value and do I have other problems I need to figure out, or since negating the encoder_scale works am I good to proceed with figuring out the other axis? Could this have also been fixed by reverse some of the wiring, and if so which wires?
Thanks for help.
Thanks for help.
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16 Nov 2016 01:58 - 16 Nov 2016 01:59 #82854
by PCW
Replied by PCW on topic mill moves when powered on
This is why you must get the encoders working first (since this determines LinuxCNC's directions)
and then set OUTPUT_SCALE so you get negative feedback, that is feedback that acts to reduce the error
(positive feedback is what results in a runaway)
if you have a runaway either reversing the INPUT_SCALE or OUTPUT SCALE will fix the runaway
but reversing both will still result in a runaway (and INPUT_SCALE _MUST_ be right for the axis direction to be right)
Instead of changing the sign on INPUT_SCALE You can reverse the encoder direction by swapping the A and B wires (or pairs if they are differential) Buts that's more work than just adding or deleting a single - sign in a file
Likewise if (and only if) your drives have differential analog inputs ( a +IN and a- IN ) you can swap those to
reverse the analog output scale, again I think its better to do this in the INI file
and then set OUTPUT_SCALE so you get negative feedback, that is feedback that acts to reduce the error
(positive feedback is what results in a runaway)
if you have a runaway either reversing the INPUT_SCALE or OUTPUT SCALE will fix the runaway
but reversing both will still result in a runaway (and INPUT_SCALE _MUST_ be right for the axis direction to be right)
Instead of changing the sign on INPUT_SCALE You can reverse the encoder direction by swapping the A and B wires (or pairs if they are differential) Buts that's more work than just adding or deleting a single - sign in a file
Likewise if (and only if) your drives have differential analog inputs ( a +IN and a- IN ) you can swap those to
reverse the analog output scale, again I think its better to do this in the INI file
Last edit: 16 Nov 2016 01:59 by PCW.
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