Re: [CAD_CAM_EDM_DRO] Re: A "simple" Hexapod project - calibration

>
>
>To cut through all the theory and such, you model the hexapod including
>variables for everything that may not be fixed. This includes the
>locations of the joints, the minimum leg length, the screw pitchs. You
>carefully measure the extension of the legs at several (many)
>positions. The challenge with a hexapod is to be sure you have measured or
>fixed all six degrees of freedom. You now have a set of actuator lengths
>required to reach a number of fixed positions, distributed through the
>range of the machine.
>

This is purely theory, but it seems as if it should work.

On a traditional 3-axis machine, it's calibrated/zeroed by sending the
units towards the home position, till they activate a limit switch. Why
could something similar not work for a Hexapod?

The traditional design (extensible legs) has 6 points to indentify home
-- reel in the legs (or extend them) until they hit a limit switch built
into the leg...then stop. That would give you an identifiable "home"
position, with an excellent degree of accuracy, would it not?

Something similar would be even easier to include on the glide-type
designs -- simply raise or lower the leg assembly till it hits the
switch...simplicity itself.

As for the initial calibration, this is a MUCH more difficult
proposition. Anyone have any practical ideas about how this could be
done? Modelling it in software is one thing, but making theory into a
physical model is something else.

-- Chuck Knight

P.S. A practical question. How are Hexapods interfaced with your
computer? If my count is right, you need 12 lines to control the motors
(6 step + 6 direction), plus a few miscellaneous connections. If limit
switches for each leg are included, that's another 6 as well. We're
really pushing the limits on a parallel port, since it has only a
guaranteed 8 data lines, and a few more if we get creative with the
pins. How is this handled, on a practical level?