On Sunday 25 September 2016 08:47:13 Robert Ellenberg wrote: > Hi All, > > Recently, I found a way to reduce the acceleration / velocity jitter > during threading and tapping motions (see this issue on github > <https://github.com/LinuxCNC/linuxcnc/issues/164> and the > feature/spindle-sync-jiiter-fix branch > <https://github.com/robEllenberg/linuxcnc-mirror/tree/feature/spindle- >sync-jitter-fix>). The effect looks significant on the HALscope, but > I'm not sure how much of a difference it would make on a real machine. > Is anyone interested in doing a before and after test on real > hardware? > I am in the middle of converting a Sheldon 11x36, and finding I need to make everything but most of the bolts. Otherwise I'd be up for it in a heartbeat.
> Thanks! > Rob I hadn't seen the github posts, but will look. And the 1st link is exactly what I've been fighting with. Enough Pgain to be usefull and its hammering the headstock gears. Fiddling with the opto spacings helps, as does a brghtness pot to each opto's led. But there is no true null point, ever. What I've now done is a bit of filtering on the two, soon to be 3 machines that have a spindle encoder, but it does so at the cost of 2 to 4 edges worth of delay of the encoder output fed back to the PID. I am running the position data thru a 4 stage fifo I've constructed out of hal modules, with the feedback to the PID being the unity gain sum of those 4 fifo buckets. Timing and sequencing being controlled by the addf order such that its output is available without any additional delays caused by miss-ordering in the servo-thread period. At low spindle speeds, the update of the fifo is done only if an edge has been detected, fifo update triggered by an unequal from a comp module, looking at the last data and the current data. It works well, reducing that noise by /4, allowing more Pgain, and hasn't seemed to have affected rigid tapping operations unless thats why a peck cycle cuts a looser tap. I have noted that using cheap taps that I have to back out, clean and anoint about every turn. But I have blamed the majority of those problems on the fact that cheap taps aren't straight. Cheap, straight and sharp, pick any 2. :( Thank you very much for taking a look at this Robert. Are you running a buildbot, the output of which is available to apt-get etc? That would make it much easier tested here. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
