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  1. #1
    Join Date
    Oct 2006

    Bridgeport Interact 2 -- tachometer mode vs. voltage mode?

    I am converting a Bridgeport Series II Interact 2 CNC mill to EMC.

    I am currently using Advanced Motion 30A8T drives for all axes.

    The drives give me a selection of tachometer mode (with feedback from motor's tachometer) or voltage mode (which means output the asked voltage without any regard for motor feedback).

    The question is what mode to use. Voltage mode seems to be safer, in that if a tachometer breaks or stops sending signals, it would not go into a runaway mode.

    Am I losing anything such as accuracy, by not using tachometer feedback?

  2. #2
    Super Moderator Al_The_Man's Avatar
    Join Date
    Dec 2003
    You should have torque or current mode option, if so this is the one I use and is the method recommended by AMC for CNC application.
    Also it is easier to tune as there is no 'inner' loop the gain is normally turned to max and the feedback to min.
    Voltage is just an open loop speed control.
    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
    May 2007
    Tachometer feedback gives you smoother motion at very slow speeds if you are stuck with lower resolution encoders. Without it the control has no idea if or how fast the axis is moving until the next pulse from the encoder and at very slow speeds that can be a significant period of time.

    On newer machines part of the reason you see very high count encoders is so they can get smoother movement at slow speeds without haveing tachometers.

    On a machine like this the benifits of tachometers would be minimal.

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