On Thu, 20 Dec 2012, Viesturs L?cis wrote: > Date: Thu, 20 Dec 2012 21:05:25 +0200 > From: "[UTF-8] Viesturs L?cis" <[email protected]> > Reply-To: "Enhanced Machine Controller (EMC)" > <[email protected]> > To: "Enhanced Machine Controller (EMC)" <[email protected]> > Subject: Re: [Emc-users] Pid saturated, was: Servo error > > 2012/12/20 Peter C. Wallace <[email protected]>: >> >> The 7I39 is a voltage output device. You should not limit the maximum PID >> value or this will limit the maximum speed (but max PID should be limited to >> about 95% for bootstrap gate drive reasons) > > Could You, please, help me out with little more explanation? > The way I see it: > motor has some fixed resistance in ohms; > since I = U/R, increasing voltage will increase also the current in > motor phases. > Is that correct? Or am I missing something here? > > When I increased max_output to 0.9 for Z axis motor, I got CR11 led > turned on very quickly. I had not yet tuned PID parameters to get the > motor stable, it was still vibrating as I tried to move it. So that is > why I concluded that increasing max_output was the main reason for > that.
If its out of control. current limiting is inevitable Tune first > > Another thing I do not understand is: how can PID get saturated > immediately when I press a jog button? Sometimes I am getting this as > well. Another thing is that joint moves in one direction, HalScope > reports that pid output is below 0.5, but in opposite direction it > reaches the limit of 0.67; I do not believe that there is such a > difference - there are Hiwin rails, size 15, 2 bearing blocks on each > rail, with motor removed I can easily push the whole thing with one > finger. I simply do not understand, what is wrong. If you have assymetrical drive (or high drive and little motion) you likely have a commutation issue > Acceleration is relatively low - 150 mm/s^2. According to my calcs, > with 0.5 Nm rated torque, 16:1 planetary reducer and 27 teeth module 1 > gear in a rack, I get more than 400 N linear force. Since the weight > of gantry bridge is less than 40 kg, motor should be able to move it > with acceleration of 1G, which is 9800 mm/s^2. Of course, I have not > accounted for friction, efficiency of planetary reducer etc, but I am > asking even less than 2% of its rated capabilities, I am not even > thinking about the fractions of percent from a peak torque. > >> Overcurrent and fault conditions should be handled by having a reasonable >> ferror setting (a motor in current limit will cause a stall thats is >> detectable as a ferror) > > I agree, that is the best thing to do, when overcurrent fault has > already happened. What I would like to do is to tune the motors so > that they do not cause drive to exceed current limit. Even if it means > reducing max velocity and acceleration that motors can achieve. If commutation is wrong, you will have a lot of current that does not generate torque. I suspect this is whats happening. General flakey behaviour also points to incorrect commutation. I would first verify with motors unconnected to load, that you can get symmetrical torque in both directions for the same amount of drive. Then I would spin the motor for a number of minutes and retest the torque to make sure you are not gaining/losing encoder counts (which will throw the commutation off) > > -- > Viesturs > > If you can't fix it, you don't own it. > http://www.ifixit.com/Manifesto > > ------------------------------------------------------------------------------ > LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial > Remotely access PCs and mobile devices and provide instant support > Improve your efficiency, and focus on delivering more value-add services > Discover what IT Professionals Know. Rescue delivers > http://p.sf.net/sfu/logmein_12329d2d > _______________________________________________ > 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. ------------------------------------------------------------------------------ LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial Remotely access PCs and mobile devices and provide instant support Improve your efficiency, and focus on delivering more value-add services Discover what IT Professionals Know. Rescue delivers http://p.sf.net/sfu/logmein_12329d2d _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
