On Tue, 8 May 2012, gene heskett wrote: > Date: Tue, 8 May 2012 15:45:11 -0400 > From: gene heskett <[email protected]> > Reply-To: "Enhanced Machine Controller (EMC)" > <[email protected]> > To: "Enhanced Machine Controller (EMC)" <[email protected]> > Subject: [Emc-users] PID controller Q's > > I currently have the commanded spindle velocity, NDI if it is supposed to > be rpms or what, essentially being fed thru the abs function directly into > the pid.0.command input. > > I am sending the encoder.0.velocity thru the abs function also then into > pid.0.feedback. This voltage on the hal meter is noisy but visually > averages someplace in the 3 to 5 range, which I believe is about 2x the > real speed it is turning in rps, and is not majorly modifiable by the plus > and minus buttons on the gui, which issue 1 to 1101 numbers in 100 > increments and that i what I see with the halmeter at the pid.0.command > input. The whole range of numbers presented to pid.0.command in can modify > the spindle speed by perhaps 20%. Running like this, the spindle speed is > extremely stiff, responding to an increased load in a small fraction of a > second. > > If and when I wire up a reverse, it will be done with a dpdt relay > controlled the .rev command from motion module. > > But 2 things, one being that in the halscope, the pid.0.output is > oscillating rail to rail, according to the scope at several hundred volts > peak to peak, and of course the pwmgen is outputting little trains of > pulses at the oscillation speed which is something in 100 hz range. > > I am getting the impression that the gain of the pid.0.feedback pin is many > decades higher than the gain of the command pin. > > Presently from the hal file: > > setp pid.0.Pgain 0 > setp pid.0.Igain 1 > setp pid.0.Dgain 1 > setp pid.0.maxoutput 401 # to keep it from running away > > Those values are straight from the Closed_Loop_Spindle_Speed page of the > wiki, and obviously I don't know enough about PID controls to make > intelligent adjustments. > > I sure could use some help in taming this beast. > > Thanks everybody. > > Cheers, Gene > -- > "There are four boxes to be used in defense of liberty: > soap, ballot, jury, and ammo. Please use in that order." > -Ed Howdershelt (Author) > My web page: <http://coyoteden.dyndns-free.com:85/gene> > "For three days after death hair and fingernails continue to grow but > phone calls taper off." > -- Johnny Carson >
With only D and I you have setup a second order differential equation whose solution is a sine wave :-) I'd start with P only (D and I = 0)and adjust P upwards till it becomes unstable then try adding a small (much less than 1) amount of D. Peter Wallace Mesa Electronics ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
