I guess you have start calculation from the encoder counters each time and then there will be no problem with add up over time.
Nicklas Karlsson On Thu, 30 Jul 2015 09:44:02 -0400 John Kasunich <jmkasun...@fastmail.fm> wrote: > > > On Wed, Jul 29, 2015, at 09:35 PM, richsh...@comcast.net wrote: > > I am adapting a version of the "little hobber" and want to use linux-CNC to > > do the ratio division between the hob and the work spindles. Additionally, > > a third axis that is actually the feed needs to be incorporated. Any > > thoughts. > > The "encoder-ratio" HAL component was invented with this specific use in mind. > http://linuxcnc.org/docs/html/man/man9/encoder_ratio.9.html > > It is a software based encoder counter (like the regular software encoder > counter), but it does the math differently to avoid some problems that can > happen if you use a more "normal" approach. > > The normal approach would be to use either software or hardware encoder > counters to measure the position of each axis, then scale the positions based > on the tooth ratios, and eventually compare them to determine how to drive > the slave axis. The problem is that if you run long enough you start running > out of accuracy. Imagine that your hobber has been running for hours. You > might find yourself subtracting 100,000,000.03 revolutions of the master from > 100,000,000.05 revolutions of the slave. If the math doesn't have enough > significant digits, the 0.02 revolution difference gets lost in the noise. > > The encoder ratio component uses a different approach to the math, and will > never run out of accuracy no matter how long it goes. > > -- > John Kasunich > jmkasun...@fastmail.fm > > ------------------------------------------------------------------------------ > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
