Servo homing

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12 May 2021 14:56 #208627 by parmitt
Servo homing was created by parmitt
Hi,

I'm looking to see if anyone has any ideas of how to best integrate the inbuilt homing cycle of my servo drives into linuxcnc?

As an experiment to give me maximum performance at minimum cost I am running chinese CANopen drives in velocity mode (standard CiA402 profile), bridged to LinuxCNC via an ethercat board of my own design.

The actual motion control side of things works beautifully, with a nice low following error, and the absolute encoders mean that the drives retain their position regardless of power status. I can also easily switch the drives into homing mode & command a homing cycle via ethercat., which is highly repeatable due to the use of both limit switches & an encoder index mark.

However for the life of me I can't figure out the best way of integrating the inbuilt homing cycle of the drives into LinuxCNC - there are a couple of vague posts alluding to people having done this, but I'm struggling to follow what has been done amongst all the other noise in 100+ page forum threads.

Classic ladder, modifying homing.c & other options have all been discussed - but I don't know if this is already a solved problem? I'd be amazed if no reliable solution to homing servo drives already exists!

Cheers,
Paul

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12 May 2021 14:59 #208628 by andypugh
Replied by andypugh on topic Servo homing
I would propose not trying to integrate the inbuilt homing, if you have absolute encoders.
Home the drives once, possibly outside of LinuxCNC, then use the absolute encoder feedback and the HOME_ABSOLUTE_ENCODER INI file option.

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12 May 2021 21:50 #208661 by parmitt
Replied by parmitt on topic Servo homing
Thanks Andy - this is pretty much what I'm doing at the moment to be honest.
I just wondered if there was a way I could integrate it better, as I do periodically re-home to check things & it's a bit painful how I have things set up.

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12 May 2021 22:00 #208663 by andypugh
Replied by andypugh on topic Servo homing
My lathe has almost-absolute encoders. With a power failure or similar the position.txt file is not written, and I need to re-home.

For that purpose I have a copy of the normal config which is set up to not use the absolute encoder option.

You can have as many INI files in the config folder as you want. They can share HAL files, tool table etc.

(In fact they can share large portions of INI file text too, though I have not bothered doing it that way)

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