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  1. #1
    Join Date
    Oct 2012
    Posts
    87

    Dual AC Servo Tuning

    Hi All,
    I'm about to buy my last two AC servos for my Cnc router and was just wondering how you go tuning twin ac servos with the granite vsd-e drives. So two motors on the one axis. Any input would be good. Ps using Mach 3 as the final drive system.
    Alan

  2. #2
    Join Date
    Dec 2003
    Posts
    24214
    Not sure how you can synchronize two servo's with Mach, it has been done with steppers of course.
    It is typically done in systems that use a motion card that close the loop for ALL axes, this way a type of electronic gearing is used where one or more slave axes are slaved off of a master encoder.
    Galil Motion cards are an example, or Dynomotion.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  3. #3
    Join Date
    Jun 2011
    Posts
    72
    Alan,
    This is something I have wondered myself. (I'm using Samsung Faracon Servo Drives)

    In Samsung drives (and I assume all servo drives) the commanded position is compared to the actual position to determine drive output. As the commanded position is effectively being drip fed to the drive, the errors shouldn't really get too big.

    The servo drives normally have an encoder passthru, so you can get the position of each drive. What to do with it, I am not sure yet.....

    Initially I was planning on doing this part open loop, and just tuning the servo error trip down from a big number to a much smaller number (from 8000 pulses to something like 10-250 pulses, on a 2048ppr encoder), and making the drive fault output cause an e-stop in Mach3. Obviously some tuning and careful observation would be required.

    Also you need to make sure that if 1 drive has a fault, that the other drive sees it and stops trying to move. I've been thinking about doing this as an output1->input2, output 2-> input1 crossover link (using the enable inputs), or alternately feeding the 2 drive outputs into mach3 e-stop to stop everything

    The only other thing I have been contemplating is whether the 'move complete' output can be utilised, given that the steps are being drip feed.

    Cheers
    Paul

  4. #4
    Join Date
    Sep 2004
    Posts
    1207

  5. #5
    Join Date
    Oct 2012
    Posts
    87
    Thanks Tero.

    Alan

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