Custom homing - without back-off, keep in one direction

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21 Apr 2017 08:54 - 21 Apr 2017 09:00 #91758 by plmicia
plmicia created the topic: Custom homing - without back-off, keep in one direction
Dears,
I am retrofitting Brother TC-225 milling machine with LinuxCNC 2.7.8.
I would like to keep as much original behavior as possible, including homing sequence.
This milling machine is equipped with separate limit+, limit - and home switch.
Original homing is specific, without changing direction of the move. Home switch is someway "overpassed".

I will try to describe below original Brother homing process (in Liniux CNC nomenclature :-):
- search for home switch in "+" direction (@ home_search_vel). There is no back-off! after home switch trip
- final detection of switch home (@ home latch_vel), still in the same direction, home switch "overpassed" until release
- index pulse (@ home latch_vel), still in the same direction
Hope you understand what I mean :S .

Is it possible at all to interfere LCNC homing sequence so deep?

I am not sure why Brother engineers made such homing algorithm. Only backlash issues comes in to my mind...
Anyway, it is not a big deal to use homing sequence served by Linux, but I am jut curious if such modification is possible at all.
Last Edit: 21 Apr 2017 09:00 by plmicia.
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25 Apr 2017 13:51 #92057 by andypugh
andypugh replied the topic: Custom homing - without back-off, keep in one direction
All things are possible when you are talking about software, but it might be more trouble than you want to go to.

The home sequence code is here:
github.com/LinuxCNC/linuxcnc/blob/master...motion/homing.c#L362

You are interested in changing what happens at the end of HOME_SET_COARSE_POSITION and the states it goes to based on various velocities.
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05 May 2017 12:06 #92697 by plmicia
plmicia replied the topic: Custom homing - without back-off, keep in one direction
Wow!
This is impressive :-).
Anyway I will leave this as it is for now. It is to risky for me to perform any LCNC source code changes.
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05 May 2017 12:25 #92699 by andypugh
andypugh replied the topic: Custom homing - without back-off, keep in one direction

plmicia wrote: Wow!
This is impressive :-).


Certainly some of our better code, being clearly written and well-commented.

If only it was all like that.
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05 May 2017 13:32 #92703 by rodw
rodw replied the topic: Custom homing - without back-off, keep in one direction

plmicia wrote: Wow!
This is impressive :-).


I also said that about the homing sequence documentation. Very clear. I remember when wading through it the first time how well it had been put together. It answered every question I had about the process.:cheer: :cheer:
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