On Mon, 30 May 2016, Gene Heskett wrote: > Date: Mon, 30 May 2016 12:47:26 -0400 > From: Gene Heskett <[email protected]> > Reply-To: "Enhanced Machine Controller (EMC)" > <[email protected]> > To: [email protected] > Subject: Re: [Emc-users] PID tuning 7i92 stepper > > On Monday 30 May 2016 09:19:25 Peter C. Wallace wrote: > >> On Mon, 30 May 2016, [email protected] wrote: >>> Date: Mon, 30 May 2016 7:07:14 +0000 >>> From: [email protected] >>> Reply-To: "Enhanced Machine Controller (EMC)" >>> <[email protected]> >>> To: "Enhanced Machine Controller (EMC)" >>> <[email protected]> Subject: [Emc-users] PID tuning >>> 7i92 stepper >>> >>> So I never did get to tuning the PID for the 7i92, now that other >>> things are working sensibly, this is next on my list. >>> >>> So I tried to follow: http://gnipsel.com/linuxcnc/tuning/servo.html >>> >>> Plotted .ferror, .joint-vel-cmd, .motor-pos-fb >>> >>> I see the .joint-vel-cmd, but .motor-pos-fb never moves from 0, even >>> if the scale is tiny. Axis move just as intended. .ferror is just >>> noise under 10u. Looks like quanitization noise. >>> >>> Am I missing something? Is there a different procedure for the >>> unique 7i92 PID loops? >>> >>> 1KHz servo thread, and: >>> >>> # PID tuning params >>> DEADBAND = 0 >>> P = 1000 >>> I = 0 >>> D = 0 >>> FF0 = 0 >>> FF1 = 1 >>> FF2 =0.00013 >>> BIAS = 0 >>> MAX_OUTPUT =0 >>> MAX_ERROR =0.0005 >>> >>> Danny >> >> axis.N.motor.pos-fb has to be changing with a move or you would get a >> following error >> >> Note that HalScope has a bug that causes it to not look at new signals >> until you stop and start the DAQ ( this means you must set the run >> mode to stop and back to the desired display mode after adding a new >> pin,signal, or parameter trace ) Maybe this is whats happening >> >> >> There's really no tuning involved, those values are fine >> >> P= 1/servo period in seconds >> >> FF1=1 >> >> FF2=seconds between position read and velocity write > > I have been using the servo-thread loop time, eg for a 4 kilohertz > servo-thread, FF2 = 0.00025, or for a 1 kilohertz servo-thread, 0.001. > But by this definition I just realized that this figure would not change > with the servo-thread rate as long as the machine can do it, and it > appears the machine in question isn't the least pushed by 4 KHz rate. > glxgears runs ok on another workspace, as does konversation or firefox, > none display any lags while LCNC is running, and moving the machine. > > So, how is this "time thru the loop from read to write" to be measured > Peter? Is there a timer that we can reset and start at the read, and > snapshot at the write that could be displayed on a halmeter to give us > an elapsed nanoseconds "swag" display on this?
Its possible with DPLL based configs but not currently implemented in the driver (also the time is so short with PCI/PCIE cards that its really not important) > > I am thinking this might be one of the reasons I can't use very much > Pgain with either spindle. I have enough Pgain for a good "stiff" drive > but its nowhere near 1/servo period in seconds, else it oscillates, on > the lathe, hard enough to break drive parts. > The 1/servo-period P gain applies only to perfect 1st order control loops (the hardware stepgen is a nearly perfect 1st order system). A P gain of 1/servo-period means that any detected error is corrected in the next period. This does not work with general servo or spindle controls as they have way too much phase lag to allow that much P gain >> (FF2 is not very important and could just be set to 0 for the majority >> of machines ) >> >> >> >> Peter Wallace >> Mesa Electronics > > Thanks for some insite on this, Peter > > 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> > > ------------------------------------------------------------------------------ > What NetFlow Analyzer can do for you? Monitors network bandwidth and traffic > patterns at an interface-level. Reveals which users, apps, and protocols are > consuming the most bandwidth. Provides multi-vendor support for NetFlow, > J-Flow, sFlow and other flows. Make informed decisions using capacity > planning reports. https://ad.doubleclick.net/ddm/clk/305295220;132659582;e > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > Peter Wallace Mesa Electronics (\__/) (='.'=) This is Bunny. Copy and paste bunny into your (")_(") signature to help him gain world domination. ------------------------------------------------------------------------------ What NetFlow Analyzer can do for you? Monitors network bandwidth and traffic patterns at an interface-level. Reveals which users, apps, and protocols are consuming the most bandwidth. Provides multi-vendor support for NetFlow, J-Flow, sFlow and other flows. Make informed decisions using capacity planning reports. https://ad.doubleclick.net/ddm/clk/305295220;132659582;e _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
