We found out in Wichita that the Pico drives can't handle a high enough voltage for these servos. So that is why the decision to get the the AMC BE25A20 drives when some became available. The 'E' in the part number is because they will accept encoder input for running in velocity mode, so in this case we can use that instead of a tach.
More generally though, I still haven't found the reason that AMC has always recommended to use current mode when using their amps for CNC control. Judging from the responses so far, it seems to contradict what most are saying in respect to having an inner velocity loop makes things much easier to tune. ???? On 03/01/2017 12:08 PM, Jon Elson wrote: > On 03/01/2017 07:46 AM, dragon wrote: >> I have a project coming up soon that involves a retrofit of a Cel-Con >> HMC. The owner has a bunch of AMC BE25A20 drives to use on it. The servo >> motors are Fanuc red caps and we have some of Pico Systems' converters >> that give us the hall and encoder signals from the motors. >> >> I have been doing a bunch of reading trying to figure out if it is >> better to run the servo amplifiers in velocity mode or torque mode. > Do you have DC tachometers in the motors? If not, then the > only way to run the servo amps in velocity mode is to > provide a synthetic tach signal to the drives, derived from > the encoder. Using it with any of the Pico products, you > will only get one update of the velocity every servo period, > and the PPMC incurs a whole servo period delay between > position sampling and DAC update (The DACs update at the > next sampling of the encoder position). Also, this would > take two DAC channels per axis (one for tach, one for > velocity command). > > So, there would be very little advantage to running in > velocity mode, without real tachs (unless you get one of the > encoder to tach converters that some people have built.) > There used to be a great chip to do this, it hasn't been > made in about 15 years. > > Jon > > ------------------------------------------------------------------------------ > Check out the vibrant tech community on one of the world's most > engaging tech sites, SlashDot.org! http://sdm.link/slashdot > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users >
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