Chris Radek wrote: > On Wed, Sep 15, 2010 at 09:07:28AM -0500, Chris Radek wrote: > >> It looks like the axes can't accelerate as fast as you are requesting. >> > > After looking at it again, this comment is wrong. > > > The problem is that your tuning is completely wrong for velocity > mode. With P only, you're commanding a velocity proportional to the > position error. This is not at all what you want. > > Setting this up is a little tricky. Your amps probably have their > gain set so that something around 9v is the rapid speed for the axis. > You need to set your ppmc dac scaling so a commanded rapid velocity > (in inches/second) gives this 9 volts. > > Umm, yeah, I didn't even look at the PID, P=10 is pretty low. Here's the PID, etc. settings from my Bridgeport, which is a velocity servo machine.
P = 150 I = 0 D = 0.3 BIAS = 0 FF0 = 0 FF1 = 8.17 FF2 = 0.005 What I did was work P up in modest increments, with all other settings at zero, until the following error was as small as I could get without instability. I added a little D to improve stability, and then increased P a little more. > Looks like on ppmc, duty cycle = value / scale. So with value 8 > (rapid speed from your ini) if you want duty cycle 0.9 your scale > should be 8.89. > Duty cycle? Are you talking about the DAC output? The OUTPUT_SCALE is a divider, so OUTPUT_SCALE = 8.89 would divide the output of the PID signal by 8.89. If PID output was capped at +/- 1.0, then the DAC would only get 11% of full scale. The PPMC driver takes a +/- 1.0 value and multiplies it by 10 to give a +/- 10 V output range. > Then you should set FF1 = 1 to make the pid output equal to the > commanded velocity (plus or minus the adjustments that will come > from P and D as you settle on a good tuning.) > I'm not sure a blanket 1.0 works that well here, but you can try that for a start, after you get the P term set for much tighter control of velocity. Jon ------------------------------------------------------------------------------ Start uncovering the many advantages of virtual appliances and start using them to simplify application deployment and accelerate your shift to cloud computing. http://p.sf.net/sfu/novell-sfdev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
