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  1. #1
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    Closing the loop and controllers

    Hi guys,

    I have been researching a controller upgrade for my mill (Novakon Pulsar) for a pretty long while, and I have a question regarding servos and controllers. It seems that there are several different controller options out there that handle servos differently - some still send step/dir information to the servo drivers which close the loop internally, some can send analog outputs to drives and receive the encoder input in the controller, and some are in between. I apologize that this question is a bit vague, but when selecting a controller for servos, is there a performance increase for closing the loop in the controller vs the drive? And does a controller that sends step/dir vs analog basically negate the advantages of using servos? My goal is to choose a controller that will get the best performance out of the servos.

    Thanks for your advice!

    Micah

  2. #2

    Re: Closing the loop and controllers

    Closing the loop in the controller and using an analog signal has been the industry standard for the last 30 years or so. Today the highest performance systems use an all digital system over a network, using one of a few communication protocols.

    I still use the analog method and close the loop in the controller, and it's my preference to put the feedback device directly on the load for maximum positioning accuracy.

    With the hobby class servos that use step & direction signals and close the loop in the drive, there is still some advantage in that the torque curve is much better than a stepper.
    Jim Dawson
    Sandy, Oregon, USA

  3. #3
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    Re: Closing the loop and controllers

    Thanks for your input Jim. Do you have recommendations on analog hardware/software controllers?

  4. #4

    Re: Closing the loop and controllers

    Quote Originally Posted by burbingus View Post
    Thanks for your input Jim. Do you have recommendations on analog hardware/software controllers?
    My pleasure to help out.

    Edit: I need to work on my reading comprehension.

    Centroid products would deserve a hard look.
    Jim Dawson
    Sandy, Oregon, USA

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    Re: Closing the loop and controllers

    I had looked at the Oak - I was a little put off that the software add ons weren't included and seemed pretty expensive, but I need to learn more about it. Thanks again!

  6. #6

    Re: Closing the loop and controllers

    I finally looked at what a Novakon Pulsar is.

    For a budget upgrade DMM Tech servos/drives, Mesa or Dynomotion Kflop/Kanalog products, and Mach3 or LinuxCNC might be good options.

    Another good but more expensive option for a controller is Galil Motion Control products, the 18x6 or 40x0 product lines. Compatible with Mach3 and DMM products. I use Galil and DMM products, along with my own CNC software, on my machines.
    Jim Dawson
    Sandy, Oregon, USA

  7. #7
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    Re: Closing the loop and controllers

    I would second linuxcnc and mesa.. Probably the least expensive solution. (software is free and interface hardware is inexpensive)

  8. #8
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    Re: Closing the loop and controllers

    Thanks guys. I think at the top of my list are LinuxCNC/Mesa, Mach3or4/Galil, KMotion/KAnalog. I'm trying to look at the hardware specs and the other pros and cons of each. Thanks for your recommendations - your previous posts have also been extremely helpful in trying to figure this all out.

  9. #9

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    Re: Closing the loop and controllers

    Quote Originally Posted by burbingus View Post
    I had looked at the Oak - I was a little put off that the software add ons weren't included and seemed pretty expensive, but I need to learn more about it. Thanks again!
    For what you are doing closing the loop in the servo drive is all you would need to do, you would not notice any difference if you closed it in the control, just the headache of setting it up and the extra cost for no gain

    Dmm and Acorn you won't get any better, other than free software like Linux CNC
    Mactec54

  10. #10
    Super Moderator Al_The_Man's Avatar
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    Re: Closing the loop and controllers

    Quote Originally Posted by burbingus View Post
    Thanks guys. I think at the top of my list are LinuxCNC/Mesa, Mach3or4/Galil, KMotion/KAnalog. I'm trying to look at the hardware specs and the other pros and cons of each. .
    Like Jim I use mainly ±10vdc analogue control and use a controller that closes the loop rather than just handing positioning over to the drives alone, there are a few advantages, the likes of electronic gearing of axis allowing the for accurate synchronized threading or any other method where axis synchronization is reqd.
    This helps in placing the controller on par with the higher end Industrial versions
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

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

  11. #11
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    Re: Closing the loop and controllers

    Hi,
    I use an open loop controller and Step/Direction to closed loop servo drives (Allen Bradley) and it works very well indeed.

    Using the controller to close the loop is a venerable technique but is slowly fading away as closed loop servo drives become ever smarter and smarter
    and at cheaper prices.

    Increasingly in industrial practice distributed motion control is becoming the norm. In that circumstance each servo drive not only closes the loop with its own
    servo but handles limits, homing and generates its own motion commands under synchronous communication with other drives/servos connected
    to the machine via the likes Ethercat or Profibus.

    Bang for your buck I would go for Delta or DMM servos/drives. In which case a wider range of cheaper open loop controllers than the more traditional closed loop controllers.

    Craig

  12. #12
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    Re: Closing the loop and controllers

    Quote Originally Posted by mactec54 View Post
    For what you are doing closing the loop in the servo drive is all you would need to do, you would not notice any difference if you closed it in the control, just the headache of setting it up and the extra cost for no gain

    Dmm and Acorn you won't get any better, other than free software like Linux CNC
    Hey Mac, why wouldn't there be a noticeable difference in closing in the driver versus the controller?

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