On Tuesday 07 November 2017 13:22:44 Jon Elson wrote: > On 11/06/2017 11:37 PM, Gene Heskett wrote: > > Greetings; > > > > Some things in the man 9 pid page are too well hidden in the > > mathematical "jargon". > > > > So can we clarify a few things? > > > > like: > > pid.N.command-deriv float in > > The derivative of the desired (commanded) value for > > the control loop. If no signal is connected then the derivative > > will be estimated numerically. > > > > What for instance, would/should be connected here, and what would be > > the desired result of such a connection? And in this context, what > > is a derivative? > > In a positioning servo, if you have a way of sensing > velocity (such as a tach + ADC, or derive velocity from > encoder timestamps) this can provide less noise than > deriving velocity by subtracting current position from > previous position. > A number of encoder systems (software encoder, Mesa and Pico > System UPC and PPMC) can provide this. > Coarse and noisy velocity gets multiplied by the D parameter > and adds a lot of noise to the velocity command output. > > With nothing connected to this HAL pin, then actual velocity > is derived from subtracting position, and you get all the > noise of quantized position plus quantized sample time. > > > Like: > > pid.N.error float out > > The difference between command and feedback. > > > > This, on my G0704 seems to be a constant zero at any gain setting of > > the halscope. What is this trying to tell me? And yes, its > > suitably addf'd. :) > > Well, on a positioning servo, this definitely gets a > non-zero value, although it SHOULD be quite small. I have > following error fault set to .005", so I know it is less > than that, and I tune to try to get all unloaded moves down > to 200 uInch or so. > > I have no idea what it would do on a speed servo, such as > when used for the spindle. > > Jon
After I was forced to restart lcnc, by tripping the breaker it was running on with some alu dust in a heater, the error outputs started working, and looked like about what I expected. Around 2 volts peak at an m3-m4 event, and mirrored that waveform on an m4-m3 transition. Reminds me of Bob Pease and his flooby dust. :) 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> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
