I've had what seems like good success calibrating a home-brew parallel robot.
The general method is:
1) add a bunch of error variables into your kinematics equations to
represent the major error contributors. This are typically the x, y,
&z positions of the base and platform joints, the minimum leg length
(at "0" position reference), and possible the actuator scale error.
2) move the platform to a series of known orientations, including all
6 axes being varied. I'll do something like a gird measuring every 6
to 12 inches, with Pitch, Roll, and Yaw at -30, 0, +30 for many of the points.
3) use simulated annealing to adjust (hill climb) the error variables
for the closest fit.
4) look for measurements whose final error falls 3 standard
deviations away from the mean, and either remeasure those points or
discard them from the data set.
5) repeat steps 3 & 4 as necessary until the process converges.
Steps 4 & 5 are necessary only if you (as I do) sometimes mess up the
measurements.
-- Carl
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At 01:20 PM 8/29/2006, Anders Wallin wrote:
did you check out
<>
one of the few DIY hexapods I have seen on the net. click screenshots
and download a video at the bottom of the page.
there's a cnczone thread about the machine at:
<>
If you just find the kinematics interesting and want to play around, you
could suspend the moving platform from strings. I remembers seeing
pictures of a couple of these kind of machines but I can't find the
links now...
If someone can come up with a smart way of calibrating home made
parallell robots, then I'm very interested too - until then I'm sticking
with a simple cartesian mill...
I'm curious about the Stewart platform, and what kind of actuators might be
salvaged to create a small one - like meter or less in dia? I suppose just
some salvage steppers with threaded rod, but if others might have better
ideas, I'd love to hear. One of these "sandtables" would be cool to build.
