Gantrykins with HM2 Servo in closed Loop
I have a homebuild CNC actually driven by 2 Granite devices and 2 Dugong Drives in step/dir mode by emc softstepper. I am planning to rebuild it using AC Servos with Stoeber Posidyn SDS AC Servo Controllers, with 5i25/7i77.
I have two things I don't understand quite good for now. First, I have two independent Y-Axis Motors. If the are getting out of synchronous running, it would probably screw the machine. The Portal weighs ~180kg, so even one Motor just doing nothing would be harmful to the geometry.
If I understood correctly, the Gantrykins are just virtually bind the joints to an axis? I read I cannot jog in Intervals (1mm, 10mm) anymore after that, is a MPG with switchable stepwidth affected by this problem?
Second, the SDS AC Drive has a velocity controller that can be configured using integral and proportional term plus a lowpass (set to zero as stated here in the forum)
Both P- and I-Term can be set in percent, what would make sense or do I have to tune both of them?
Actually they are set to 60% proportional and 30% integral. Wuold it be wise to set the drive only to integral and leave the rest to linuxcnc?
Thanks in advance!
julian
PS: early Video of the machine:
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Can you take the X-axis off and decouple the Y sides during the tuning process (perhaps add some dummy mass). Servo runaway/oscillation could be as unpleasant as you fear.I have two things I don't understand quite good for now. First, I have two independent Y-Axis Motors. If the are getting out of synchronous running, it would probably screw the machine. The Portal weighs ~180kg, so even one Motor just doing nothing would be harmful to the geometry.
I am not sure. You could try modifying the sample gantry config to test it.If I understood correctly, the Gantrykins are just virtually bind the joints to an axis? I read I cannot jog in Intervals (1mm, 10mm) anymore after that, is a MPG with switchable stepwidth affected by this problem?
I think you would need to tune both to give the best velocity command following behaviour. This would be best done in a configuration where a tuning error won't wreck the machine.Second, the SDS AC Drive has a velocity controller that can be configured using integral and proportional term plus a lowpass (set to zero as stated here in the forum)
Both P- and I-Term can be set in percent, what would make sense or do I have to tune both of them?
I don't think so. LinuxCNC will be issuing velocity commands to the drive, and the velocity-to-current loop in the drive needs to be working properly.Actually they are set to 60% proportional and 30% integral. Wuold it be wise to set the drive only to integral and leave the rest to linuxcnc?
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That is doable, as I am moving to my now hobbycellar soon the machine will be "parted"... Is there a possibility (a real, not a theoretical) that combining the axes after tuning leads into new harmonic interactions between the two drives?
Can you take the X-axis off and decouple the Y sides during the tuning process (perhaps add some dummy mass). Servo runaway/oscillation could be as unpleasant as you fear.[...]me wimpering about shearing machine to death...[...]
Ok. Ill try this and perhaps our wisdom will increase
I am not sure. You could try modifying the sample gantry config to test it.If I understood correctly, the Gantrykins are just virtually bind the joints to an axis? I read I cannot jog in Intervals (1mm, 10mm) anymore after that, is a MPG with switchable stepwidth affected by this problem?
Anyway I am wondering how in such beautiful an mighty software such a "on top" Kinematic is needed for a gantry config This doesnt look "right"...
I would offer my humble programming abilities if this will be helpful?
I think you would need to tune both to give the best velocity command following behaviour. This would be best done in a configuration where a tuning error won't wreck the machine.Second, the SDS AC Drive has a velocity controller that can be configured using integral and proportional term plus a lowpass (set to zero as stated here in the forum)
Both P- and I-Term can be set in percent, what would make sense or do I have to tune both of them?I don't think so. LinuxCNC will be issuing velocity commands to the drive, and the velocity-to-current loop in the drive needs to be working properly.Actually they are set to 60% proportional and 30% integral. Wuold it be wise to set the drive only to integral and leave the rest to linuxcnc?
I feared that. Ok, this WILL take time, but I'll try.
Thanks a lot,
Julian
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Anyway I am wondering how in such beautiful an mighty software such a "on top" Kinematic is needed for a gantry config This doesnt look "right"...
it isn't completely necessary. You can simply connect axis.1.motor-pos-cmd to both PID modules in the HAL.
The only reason to run Gantrykins is to allow the two sides to home independently to individual home switches for auto-squaring. If you never want the two sides to move independently then you can just use trivkins.
Note that gantrykins isn't "on top", it replaces trivkins.
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juwi wrote:
Anyway I am wondering how in such beautiful an mighty software such a "on top" Kinematic is needed for a gantry config This doesnt look "right"...
it isn't completely necessary. You can simply connect axis.1.motor-pos-cmd to both PID modules in the HAL.
The only reason to run Gantrykins is to allow the two sides to home independently to individual home switches for auto-squaring. If you never want the two sides to move independently then you can just use trivkins.
Note that gantrykins isn't "on top", it replaces trivkins.
Ahh, I understand. Ok, using brakes and absolute encoders on the servos there is no need for Gantrykins, except as a "second machine" for time-to-time rehoming...
Wonderful That made my day and sounds like a perfeect match
Thanks a lot!
yours,
Julian
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[...]
it isn't completely necessary. You can simply connect axis.1.motor-pos-cmd to both PID modules in the HAL.
[...]
Is that still the way with SSI absolute position feedback devices?
Best regards,
julian
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[Is that still the way with SSI absolute position feedback devices?
It ought to be, yes, but I can't claim to have tried it.
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