On 7/4/23 13:31, Marius wrote:
Hi
I have been trying to get a rotary fourth axis setup going with the help
of regular and knowledgable contributors to LinuxCnc. We came up against
a brick wall as many other project developers have done.
The problem seems to be that our trajectory planner lack the ability to
look ahead for any rotary axis. This means that a coordinated move that
includes a rotary move will be dysfunctional at best.
Not true Marius, if you are having problems, something about your config
is wrong. I am presently carving a 2 start screw in wood with my B axis
on the 6040 gantry mill. And its accurate to a fraction of a degree
anyplace in the 400mm length of that screw. With no PID's in use on
that machine. All you should have to do is calculate the end points
related to where it starts for the b axis and issue the two end points
in the same command line. I carve a two start buttress thread by pre
positioning at the shape point of the tooth, and carve that position for
the length of that screw. That rotates the b axis in perfect sync with
the y motion. At the far end of the screw, I add 180 degrees to the b,
move it that addition 180, then come back to the y starting point with b
coming bavk to 180, which is about 6mm off the end of the screw, then I
move b back to zero, reposition the tool for the next pass, and do it
again till its done. The 7 degree angle of the load bearing face of
that thread is established by a wedge under the motor, an angle
duplicated in the tooths shape. The nuts are printed on a 3d printer in
PETG, with a dozen teeth engaged in the length of the nut.
There are no PID's and my B axis is a 3NM, 3 phase stepper/servo driving
a 5/1 worm which is driving a square socket that turns a 2x2 stick
nearly 600 mm long.live center at the other end of the stick, shimmed to
reduce the z motion required to do as close to a true cylinder the
length of that thread. And it all Just Works. My Z axis is also driven
by a 1NM version of that stepper/servo.
Start by checking your .ini file. under:
[DISPLAY]
you should have something like this:
GEOMETRY = XYZA
then down file a ways:
[TRAJ]
AXES = 4
COORDINATES = XYZA
Now, that's wrong but my i/o channels are limited to 4 axis so my B axis
is actually wired to what would be the A terminals in the interface as I
am using a 5i25 and a 7i76 plus a std breakout for other functions. A
7i90HD would fix that but bring another wagon load of shekels for
7i42TA's, takes 3 of them as the 7i90 has no buffers to protect the fpga
used from 5 volt stuff. I've forgotten how, but on screen in axis it
does show as B.
Check the above, the rest of my .ini has it as A and JOINT_3.
Digging thru my .hal file will get more complex as its been a couple
years since I first rigged a different B axis.
So start with the above.
And have a happy 4th Marous.
I understand that there is a free trajectory planner on offer to
LinuxCnc but it has not been integrated. It would seem that some lack of
skills or time has a role to play in getting it integrated.
I unfortunately do not have the skills nor the time to tender to assist
with this however, someone made the suggestion that maybe the community
could embark on a fund raising project to enable us to pay for someone
to get the trajectory planner integrated. I am sure that many would
stand to benefit from this and other users that I have spoken to has
indicated that they would gladly contribute.
I would at least want to start a discussion around the idea.
Regards
Marius
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Cheers, Gene Heskett.
--
"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
Genes Web page <http://geneslinuxbox.net:6309/>
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