Re: [CAD_CAM_EDM_DRO] Re: A Z80 guy needs help!

I'm not quite sure what you want to end up with, but wouldn't fixed, time
dependent, moves that might not get to where you want them to be before feeding
new positional data be self defeating? Wouldn't a closed loop system be better?
In other words a:

go to start point
move to XY (wait till arrival is announced by encoder)
continue

sort of sequence.....

Bill

On Sun Jan 20 09:43:15 2002, ccs@..., <ccs@...> wrote:

>> This is a for a "G-Code in, step/direction out" project that will
>> take about a year to complete. All motion is vector based and works
>> on the assumption that position is the running sum of precise
>> velocities, each applied for a precise period of time (1/1,024 of a
>> second).
>
>That is an interesting approach. I think you would have to be very
>carefull to prevent accumulation of roundoff error - ie, you will have
>to round the velocity to whatever precision you can express it in, and
>then recalculate the move time so that the move total comes out
>exactly right. You may still have trouble getting circles to return
>to their starting point.
>
>> For circular interpolation this would be:
>>
>> Xv = R sin (theta + delta) - R sin (theta)
>> Yv = R cos (theta + delta) - R cos (theta)
>>
>> This requires solving for sin/cos in the shortest time possible to a
>> 24 bit accuracy. I am using a Chebysheff polynomial expansion
>> coefficients to converge the series in the fewest possible terms. For
>> this I have a "roll your own" math package in assembly to do it.
>
>If it were my project, I would implement circular moves as a sort of
>on-the-fly preprocsssor which segmented the arcs into short linear
>moves. Many programs use a cubic spline interpolator in their finest
>trajectory planning loop, which means that the executed path is
>actually a lot more rounded thea the segments because it is fit to a
>simpler-to-caluclate curve through several points.
>
>In other words, because sine and cosine are expensive, you can
>calcualte them accurately at a few points and use a less expensive
>approximation to interpolate between those points.
>
>Chris Stratton
>
>PS - if it were me, I'd prototype the algorithm on a PC, plotting the
>output on screen or as postscript or something to verify that it all
>works, before trying to get it running on the z80.
>
>-------------------------------------------------
>Christopher C. Stratton
>Engineer, Instrument Maker, and Horn Player
>ccs@... 617 628 1062
>http://web.mit.edu/~stratton/www/brassbuild.html
>
>Addresses:
>FAQ: http://www.ktmarketing.com/faq.html
>FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/

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