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Is using Position Control on its own okay?

RichB
Intellectual 585 points

Hi forum members

I wish to use Position Control on its own, i.e. without Position Move and Position Plan.

Is this a good idea? It has the right control system that I want which is a position setpoint and feedback, bandwidth to tune how to get there, and a velocity maximum.

The reason I ask is that, AFAIK, only lab 13a uses position control raw and that is only to hold it at 0 position for bandwidth tuning. I intend to expand upon this to build my position control application.

Thanks

Rich

  • 0
    TI__Guru** 119680 points
    you can use the controller and feed in your own references. You don't have to use the move or plan.
  • 0
    Guru 12800 points

    Rich,

    You can do this.  We have a number of customers who opt to only use the controller.  They key trick will be to make sure that your profile generation works with the windowed position system that our controller expects.  I've attached a document that shows an example of what the curves coming out of our profile generator look like.  

    6523.SpinTAC_Position_Move_Rollover.pdf

    Your profile generator will need to create this sawtooth position reference in order for it to work with our controller.

  • 0 in reply to Adam D. Reynolds
    Intellectual 585 points
    Cheers both.

    Yes I was aware of this windowed system. Ok I shall continue with this then.

    The main reason I wanted this was because I want to continually (but not periodically) update the position setpoint and not have any hastle with Position Move needing to cancel a movement and then restart a new one (at least, that's how I thought it works - can you confirm?)

    Many thanks
    Rich
  • 0 in reply to RichB
    Guru 12800 points
    Rich,

    Position Move does not support updating to a new setpoint in the middle of a movement. You would need to reset it and it would need to go into a halt state before beginning the next transition.
  • 0 in reply to Adam D. Reynolds
    Intellectual 585 points

    Adam

    Thanks for that PDF. I see how there's 130 revs travelled according to the "position" top trace.

    Please can you explain the rollover concept a bit more? I get the PosErrMax_mrev term but not so much ROMax_mrev.

    For example, starting at zero mrev and ignoring PosErrMax_mrev for the moment, if ROMax_mrev was 20, how would I get to 25?

    Sorry to load this post with more questions - does one really need to feed in a velocity and accel references as well as the position? Is it an advised thing to do? Could you recommend using position reference only?

    Cheers

    Rich

  • 0 in reply to RichB
    Guru 12800 points

    Rich,

    The ROMax_mrev configuration sets how many mechanical revolutions of the motor before the position signal has a rollover.  So this establishes the upper and lower bound for the mechanical position signal.

    If the ROMax_mrev was set to 20, once the motor has rotated through 20 revolutions, the position signal would rollover to -20 then begin to increment up to -15 where it would stop.

    You don't need to use the velocity and acceleration references if you don't want to.  You will lose some dynamic performance since there won't be any feedforwards provided to the controller.  But you will still be able to control your system.