absolute encoders with dual axis

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30 Apr 2024 09:56 - 10 May 2024 10:16 #299380 by zmrdko
Hi,

i am wondering how would behave and if its possible to have dual axis with absolute encoders. Lets say you power off machine and one joint of dual axis moves a little, but the other one not (gantry gets skewed). What will happen on powering on machine again? Will the one moved joint go back so that gantry is squared as before?
Last edit: 10 May 2024 10:16 by zmrdko.

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30 Apr 2024 10:25 #299383 by tommylight
Probably yes, but a bit fuzzy on this as it was quite a while back, depends on how far it moved and the tolerance set in the ini file.
Usually for metric machines, that is set to 1mm.
LinuxCNC cam be set to jog individual joints in joint mode, so if it moves more you can use that to jog near that tolerance and enable the drives, then LinuxCNC will keep them in position.
I did this with normal incremental encoders to prove the rails vere skewed on a long machine, but never with absolute encoders, although i think it should work.
Give it a try if you can, and report back, it might be some time till i get a chance to confirm this.
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30 Apr 2024 15:31 #299406 by zmrdko
Thanks for quick response. I am about to order absolute encoder motors for my delta b3 drives, so I wanted to check first.
What about feedback position? Doesn’t it have to be set from encoder? Lets say I have mesa 7i95t with step/dir control and feedback is set from stepgen. This might be an issue, right?
I had delta ethercat servos set up on my table a while back, using encoder feedback. I think it worked nice even with incremental encoders, even though you had to home once after launching linuxcnc, but after that it keeped positions well. After power off, i moved one motor from dual axes and when re-powered, motor quicky rotated back to correct position.

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06 May 2024 02:16 #299873 by zmrdko
Worked well even with incremental encoders. The position is kept even after reopening linuxcnc. So basically you have to home once after powering up servo drives.
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