Re: [CAD_CAM_EDM_DRO] Re: Is this a silly idea

Tony Hursh wrote:

>On Wed, 2003-12-10 at 06:04, Jon Elson <elson@...> wrote:
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>
>
>>No, you should be able to write a simple kinematics routine for
>>EMC, and use the rest as is. The only thing you have to worry
>>about is the "gimbal lock" problem. If you ever drive the machine
>>through the 0 - 0 point, the results are unpredictable at the center
>>of rotation of the rotary axis.
>>
>>
>
>Computer graphics guys avoid the gimbal lock problem by using
>quaternions rather than Euler transformations. A quick Google shows that
>the International Space Station is using quaternions also (movie fans
>may recall the "gimbal lock" incident in Apollo 13).
>
>Maybe quaternions could be applied here?
>
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>

No, we were talking about a physical machine with one rotary axis
and one (or two) linear. If the programmer runs a straight line right
over the (0,0,0) point, the rotary axis doesn't have any defined position
to be in. I have no idea what EMC's reverse kinematics will do in
that case. NaN problems seem quite likely, but it might behave
fine, too. I don't know. But, it could be a serious problem.
This type of machine (Rho-Theta) has another problem. When far
from the center of the rotary axis, extremely small movements of
the rotary axis cause very large movements of the workpiece.

Jon