> > Its good to remember that both step/dir systems and most servo systems are > running in velocity mode (effectively linear extrapolation from each way > point) so that the actual errors caused by a lower update rate are only > second > order errors. What I consider a fast CNC machine may machine at 600 IPM > with > 400 IPS/S acceleration (1/40 sec to full speed) Even with these extremes, > its > possible to keep within 1/5000" of a acceleration limited profile with 1 > KHz > position (and velocity) update rate. If the TP provided forward differences > for velocity and higher derivatives a much slower update rate is feasible > if the underlying hardware has a simple extrapolator.
That's a good point. Out of curiosity, how do you arrive at the 1/5000" error figure? My calculations for sample rate are based on the limitations of the algorithm, more than the absolute accuracy. The current method I'm using to handle tangents requires that each segment be "touched" at least twice, implying that each segment needs to take at least 2 cycles. This creates an upper bound on the velocity we can achieve for a given update rate and segment size. The 8kHz (not 12kHz, oops) figure is also due to the fact that blend arcs split up segments, so there are in general up to twice as many segments as the original program. We can cheat the speed limitation by increasing the update rate, though there are obvious limits in terms of performance here. Hitting each segment is a safe assumption, and much easier algorithmically. However, it means we can't take advantage of the "close-enough" accuracy we'd get by skipping over short segments. In the long term, I'm sketching out a small change that will only need to touch each segment once instead of twice. If it works, it should offer a big performance boost on short segments. ------------------------------------------------------------------------------ Rapidly troubleshoot problems before they affect your business. Most IT organizations don't have a clear picture of how application performance affects their revenue. With AppDynamics, you get 100% visibility into your Java,.NET, & PHP application. Start your 15-day FREE TRIAL of AppDynamics Pro! http://pubads.g.doubleclick.net/gampad/clk?id=84349351&iu=/4140/ostg.clktrk _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
