Controlling VFD's with your PC?
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  1. #1
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    I was wondering if anyone knows how this is done? Would there be a way to wire and program a VFD to respond to step/direction signals?
    What I am trying to do is convert an old CNC to respond to G-code and control spindle speeds.

    Thoughts?

    Sean S

  2. #2
    D. Thomas Guest

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    Although posted by me, John Kasunick actually wrote the following response--

    I'm not sure what you want to do. Direction should be no problem, most VFDs have a forward/reverse input that changes the direction of rotation.
    Using the step signal on the other hand would be complicated. Steps control position, not speed. A VFD cannot rotate the shaft a small amount (a step) at a time, and cannot be used to control position. (Actually they can, but only the most sophisticated ones can do it, and usually only as part of a complete system that is too complicated to get into here.) I am guessing that you want to control the spindle with the VFD, not one of the machine axis. In that case, I doubt that step and direction would be used.

    I don't know G-code, so I don't know what codes are used for spindle control. I assume there are codes for spindle stop and start, and possibly for spindle reverse. Those could be handled by connecting the corresponding outputs of the CNC controller to the start/stop and fwd/rev inputs of the VFD. Speed is another story. If the controller has an analog output (like 0-10V) that can be set by a G-code, then that output could be connected to the VFD speed
    reference input. I don't know enough about CNC & G-codes in general and the specific controller you have to be much help with your project. All I can suggest is read the manuals for your controller and VFD, and try to figure it out.

    John Kasunich

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    Thanks John and Don.
    What I've learned in the meantime is you need an analog board for your PC and of course a VFD that will accept voltage as a means of adjusting the frequency.
    Both seem reasonable but finding a developer who will write the code to control the PC board via g code may be a bit harder.

    Many Thanks again.
    Sean

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    Every thing you need to control a VFD from a PC and a LOT more is available from Anilam.

    http://www.anilam.com/

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    Mate that link didn't work for me

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    Most VFDs can also be controlled via Modbus. You can get USB to RS485 converters and control them that way, although the specific registers that need to be controlled differ between manufacturers.

    Many higher end units also have ethernet and or USB support either natively or via add-in boards, although the USB is generally only for commissioning with proprietary software.

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    For motion control, a Servo Controller is much the better choice. and to the average person. the control "box" looks a lot alike.

    Open or closed loop, there are many options. speed torque position... etc.

    Servo motors are not costly on the used market. nor are the " boxes" that run them. and there is a connector for a PC cable on every one!

    Oh! I forgot.. What initiated my response...
    All the SERVO controllers I have encountered accept "step and direction" input!

    So there is that...

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    Quote Originally Posted by Sean S View Post
    I was wondering if anyone knows how this is done? Would there be a way to wire and program a VFD to respond to step/direction signals?
    What I am trying to do is convert an old CNC to respond to G-code and control spindle speeds.

    Thoughts?

    Sean S
    I think you are going to get a lot of confusing input, based on the Step and Direction question.

    You just want the VFD to be controllable by the CNC control, for spindle speed, yeah?

    Hit up the VFD manual. Most will accept a 0-10v input and a direction(maybe +10v to -10v?)signal for the speed control.

    IIRC, I was reading here on PM that MotionGuru was actually using some VFDs to control motion on a very large mill, a while back.

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    Hmm 2002 and 2020.

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    Was gonna say... Dude is surprised that the link didn't work 18 YEARS later?!

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  14. #11
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    Quote Originally Posted by CarbideBob View Post
    Hmm 2002 and 2020.
    Whups!

    Indeed!

  15. #12
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    Go easy on him... Australia is in a different time zone...


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