linear scale and AC servo set up - sanity check

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10 Oct 2022 14:18 #253885 by chienMouille
No worries at all, I hope you had a good week-end!

I tried to change the enable signal as you say but that doesn't bring us to a moving servo. remains still on jogs. (it does move with the open-loop config, so it's about this setup for sure)

Yes, the scales have index marks. Would be great to use them to home.

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10 Oct 2022 14:49 #253889 by andypugh
If you start the system then attempt to jog the X axis, then open a terminal window and run
halcmd show pin > pins.txt

Then that should create a text file with the current values of all the pins,
can you create and attach that file and we can see where the data path is broken.
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10 Oct 2022 16:29 #253893 by chienMouille
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10 Oct 2022 22:48 #253923 by andypugh
OK, first thing I see is
29  float IN              0  pid.x.command <== x-ext-output
...
 29  float OUT  -5.570936e-18  pid.x_external.output ==> x-ex-output

So you have two separate signals, x-ex-output and x-ext-output and I think that they should be the same signal (ie, same name)

How far did you jog before doing the print? It is claiming 1e-18, which isn't very far at all.
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10 Oct 2022 22:51 #253924 by andypugh
Also:
 29  float OUT             0  pid.x.output

I think that a connection of this to x-output is missing too.
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11 Oct 2022 07:04 #253935 by chienMouille
Arf. The ext is definitely a typo. Sorry to waiste your time on that.

What would you connect the pid.x.output to? We connected the feedback of it nut not the output. Should this output be connected to the velocity command and the scale pid output connected to the position command?

I will be away from the shop until this weekend unfortunately. So won't be able to test it further until then. I'll try then and keep you updated. Thanks a lot!

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11 Oct 2022 10:07 #253947 by andypugh

What would you connect the pid.x.output to? We connected the feedback of it nut not the output. Should this output be connected to the velocity command


Yes, the pid.x.output should drive the stepgen velocity input. That input is already linked to x-output so you just need
net x-output pid.x.output
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15 Oct 2022 12:00 #254165 by chienMouille
Hi!

After the config corrections, the motor moves!

How should I go about tuning it now?

So far, with P(int) at 1000 and FF0(ext) at 1, all the rest to 0, it behaves as open loop (no backlash comp), though the DRO shows the scales feedback and not just the command anymore.

If I put any value to I(ext), the axis moves contiunuously (runs away) in the last commanded direction, the higher the number the faster the move.

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15 Oct 2022 12:42 #254166 by andypugh
Can you do another pin-value readout? My guess is that something needs to be done to make the servo encoder and the linear scale agree about where zero is. (I think you will need to do this _before_ the f-errror trips and zeros the commands)

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15 Oct 2022 13:46 - 15 Oct 2022 14:09 #254169 by chienMouille
yes, here, I jogged 5mm right then back then again prior to the readout.

EDIT: the servo encoder is not fed back to linuxcnc, in case.
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Last edit: 15 Oct 2022 14:09 by chienMouille.

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