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

alenz2002 wrote:

>--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
>
>
>>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, having personally used this system for special projects over the
>past several years I concur that gimbal lock isn't an issue since it
>involves two rotational axes pointing in the same direction and the
>case in point is about a single rotational axis (the C-axis) along
>with the X and Z linear axes. And while the 0-0 crossing does have to
>be treated as a special case, it is but one of many.
>

OK, maybe my use of the term "gimbal lock" was wrong, but you confirm
that working right over the center of the rotary axis needs special
attention.

Jon