Need help with MESA hardware

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04 Aug 2022 21:26 #249069 by bassti
Hi,

im planning my new mill. I use JMC Drives + Motor. The motor`s encoder has 2500 lines per rev. The ballscrews have 10mm pitch.The gear ratio is 1:1, so i got 1 micron accuracy. 

I can use the drive in torque (analog) , velocity (analog) or position mode (step / dir).
I want linuxcnc to close the loop (linuxcnc should know where the axis/joint is)
Now i figured aut 2 configurations for my machine but im not sure about loosing accuracy.
My favorite is to use a Mesa 7i95 so i can easy use a stepper for my toolchanger.
But i think ithat the drive acts like a stepper with 2500 lines per rev - so its maybe not possible to position the axis with the same accuracy like a system with a 7i97 ? 

maybe somebody can help me


 
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04 Aug 2022 22:17 #249071 by tommylight
Pretty sure that both those will work the same as far as precision is concerned, LinuxCNC can drive steppers in velocity mode so i do not think there is any difference.

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05 Aug 2022 07:54 #249100 by bassti
Replied by bassti on topic Need help with MESA hardware
i think when i use the 7i79/7i95 i can use 4x mode to read the encoder (i got 10000) - so i have a scale of 1000.
but the encoder just can 2500 - so i got a scale of 250 (in position mode)
the drive allows torqe and velocity only with analog setpoint

this is why im think that i need the Mesa with analog setpoint :(

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05 Aug 2022 21:45 #249163 by andypugh
If the only feedback is at the motors then you might as well close the position loop in the drives.

But it's up to you, you can close it in LinuxCNC if you prefer. It is easier to see what is happenign during tuning that way. Though the tuning might be less effective than the tighter loop at the drive.

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