Do you really need screw correction AND backlash comp? I'm not so sure you do.
I would turn off any backlash comp and screw comp and setup the feedback loop with the linear scales and try and tweak the position loop to get what you want. Use a velocity mode stepgen and feed that with a PID loop. The machine I have setup with a position loop is pretty forgiving. I could post the hal file if you would like to see the configuration. Who really cares where your motors are at if you can accurately control the actual position via the scales? Backlash will not be compensated but the velocity mode stepgen won't care. The PID loop will try and compensate. Does anyone know if Stuart is using screw or backlash comp on that big horizontal mill that is setup with a dual loop and direct reading scales? I would bet that he is not. Dave On 8/8/2010 2:35 PM, Brian wrote: >> The motion controller copies feedback to command while in the machine >> off state. The stepgen also updates its internal command position while >> it is disabled (which it should be in machine off). The motion >> controller shouldn't do anything when it's enabled (it might, and that >> would be a valid bug), and it should only apply screw correction when it >> starts moving, since it doesn't know any direction until then. >> >> Of course, this will be a problem if the magnitude of screw compensation >> is larger than your following error setting. >> >> - Steve >> > This is why feeding the scale position into axis.N.joint-pos-fb would > be so elegant. Because everything else would work correctly. > > The only thing that would make it better is if the screw comp 'sensed' > direction change rather than taking a que from the motion controller. > Then if you move the machine manually, and re-enable the motors, the > screw comp will know what side of the screw it is on to start with. > Even without doing that, I suspect that the secondary feedback loop > would be sufficient to cover up that problem, and get things going > again. > > Brian > > ------------------------------------------------------------------------------ > This SF.net email is sponsored by > > Make an app they can't live without > Enter the BlackBerry Developer Challenge > http://p.sf.net/sfu/RIM-dev2dev > _______________________________________________ > Emc-developers mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-developers > > ------------------------------------------------------------------------------ This SF.net email is sponsored by Make an app they can't live without Enter the BlackBerry Developer Challenge http://p.sf.net/sfu/RIM-dev2dev _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
