I am having some issues with genserkins running a robot arm (this is
the ST R-17 I brought with me to Wichita running LinuxCNC with
joints-axis running on Debian Wheezy with RTAI).

Coordinated moves in XYZ seem to work as expected.  All the joints
working together to keep the end of the arm moving properly in XYZ,
with the tool perpendicular to the XY plane.

The problem comes when I try to use the A and B axis for 5-axis
movement.  My first problem was that A moves pivot around the Y axis
and B moves pivot around X (at least in what I've chosen as the
default pose for the robot).  I thought this was something wrong with
my configuration, so I double and triple-checked everything (it's
super easy to get confused about the reference frame as you go from
joint to joint), but that all looks good.  Then I tried rotating the
arm around the base by 90 degrees, and suddenly A pivots around X and
B pivots around Y.

Further investigation shows that the A and B coordinates are being
applied to something relative to the end of the robot arm.  Regardless
of the XYZ position of the arm, A and B moves always do the same thing
relative to the robot arm.  I would have thought the A and B
coordinates would be relative to the work-piece, just like XYZ, or is
that not how it works?

Anyway, either I'm confused about 5-axis machining, there's something
odd with genserkins, or both.  Any suggestions on where to look for
enlightenment (other than the genserkins code which I'm already
reviewing) would be appreciated!

Is anyone else doing 5-axis machining with genserkins?

-- 
Charles Steinkuehler
[email protected]

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