Hi all, I have a VMC with low inertia servos and 25 amp 270 volt velocity mode servo amps. It has tachometers and 1/25400 inch (micron) resolution rotary encoders on the motors.
I have been struggling with a bad tachometer on Y for a while now - it would come and go - and when people started talking again about generating tach signals for retrofitting Fanuc setups that don't have real tachometers, I got interested. I was out of DAC outputs, so I got a second servo interface board (7i48, which is a Mesa product that has six DACs and six differential encoder inputs, and is newly supported in EMC2/git-master). The hostmot2 Mesa driver has a high quality encoder velocity output that it generates based on high resolution timestamps on encoder edges. In HAL, I hooked this velocity output directly to a new DAC and set the DAC scaling so that rapid speed will give an output around 9 volts. I wired the DAC output directly to the servo amp in place of the tachometer. This voltage is a lot lower than the real tachometer generates, but the servo amp has a gain control and it was very easy to set the amp accordingly. I'm happy to report that the motion on Y is smoother than I have ever heard it. This machine rapids (I have it set conservatively) at 7.5 inch/sec and 30 inch/sec2 acceleration. Adjusting the tunings (amp and EMC) just a bit, I was quickly able to get following errors within about 10 encoder counts (0.0005 inches) during accelerations to rapid speed, and virtually nil (a count or two) during cruises/cuts. I think this is awesome and send thanks to Peter W for his cool products and hostmot2 work and Seb K for his hostmot2 driver work. I have every reason to believe that machines with these generated velocity signals and "missing" tachs are not a problem for EMC2 + Mesa. Chris ------------------------------------------------------------------------------ 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-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
