On 12/6/24 16:48, Viesturs Lācis wrote:
Hello!
One of the Biesse retrofits I have been working on lately is finally
receiving some of its intended final shape:
https://photos.app.goo.gl/cKi8pysM3Tnb9Egh6
That wood box on top of it contains 600W laser CO2 tube (some pics of
it also included). Since I have no idea how to lift it without braking
I decided to mount it with all the box and encapsulate the tube in
foam.
But still I believe that crucial for this project is jerk-limited
motion to avoid the bumps at start and end of motion not only to keep
the components in place but I also think (have no experience with
laser tubes and did not find too much info on the web) that laser tube
itself might not like it (I have to put PSUs and chillers up there as
well - chillers might appreciate it as well). Customer already knows
that the accelerations will be way lower than previously when this
machine still had all the spindles but I am still worried about the
jerk.
So the question for 10K is: what is the current status of jerk
limitation? Searching mailing list and forum shows quite a few
discussions but I did not see anything about it being implemented (in
separate branch or whatever). I do recall discussion that it would be
hard to make it work with spindle synchronized moves. I do not need
that here, motion only with G0, G1 and G2/G3.
Is there any alternative trajectory planner to try? I found this
script (unfortunately python is the code that I totally do not
understand so I have no idea what does this script do):
https://github.com/cnc-club/linuxcnc/blob/master/devshit/s-curve.py
AFAIK cnc-club is a group of LinuxCNC users in russia that have done
some development (including translations etc) but I do not recall that
they would merge their stuff back.
I am fine with workarounds as well. I did find discussion from 3 years
ago here on mailing list with a suggestion of putting limit3 component
before pid component. That machine has 8i20 servo drives, if that
changes anything. pid.n. command is connected to joint.n.motor-pos-cmd
at the moment.
Oh and once I mentioned 8i20 drives in that Biesse - PCW I still would
like to get an answer about the implementation of those Yaskawa
encoders with bizarre C channel. If that is too much effort then it is
fine, "NO" is also totally valid (and pretty expensive for me) answer
so I would hope for something positive, but getting any answer at all
would be better. AFAIK there are some convertors that cost quite a few
hundreds per piece and can do the trick but I have lots of questions
and doubts about them (but I could try to get one and send over to you
if that seals the deal).
Viesturs
I'm far from an expert on that but a limit3 has done what I needed
several times. And IIRC it has always been applied prior to the pid its
controlling,, preferably in such a position as to shape it all in one
module.
Cheers, Gene Heskett, CET.
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
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