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Integrated Stepper Motor with encoder - Problem maintaining target position

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  • #16
    Originally posted by RockB View Post
    I did a simple experiment to test this out. I set the motor resolution to 25000 ppr and changed multi move to a simple relative single move. It looks like motor has problem staying stable at a target position of 2000 counts. It oscillates slowly around target value. However, when to motor is connected to a small load, it reaches target position and comes to complete stop. Do you think this is common behaviour in steppers with encoders or a cade of mechanical lash?
    The axis is closed loop. It's a simple proportional loop, but once you set a target position, it is trying to hold it. Since there is a disconnect between the pulse output position and the encoder position, if there is slop in the linkage, this can happen. The tradeoff is between larger deadbands vs tighter control. If the linkage is sloppy, your really can't do both.


    Originally posted by RockB View Post
    Do you have any alternative methods to implement multi move? Your next release sounds very promising. I would be happy to test out your beta release.
    The entire purpose of multi-move was to approximate the behavior of the original CTRIO's Dynamic Positioning mode, and the purpose of DynaPos was to simulate an axis in the old module where there wasn't such. None of that is really required in BRX. The basic AXPOSTRAP can move to a variable relative or absolute position, so multiple moves is just setting the position variable and turning it on. When it's done, it turns on the Success bit or jumps to the Success stage. You can do basically the identical logic that you were doing with .AtPosition.

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    • #17
      Originally posted by BobO View Post

      Once we release the AXSCRIPT instruction here very soon, there will be even less reason.
      Bob O can you share details on what AXSCRIPT is capable of and how it is different from AXPOSTRAP or AXPOSSCRV?

      Also do you do you have a release date for DMD 2.4?

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      • #18
        Originally posted by RockB View Post
        Bob O can you share details on what AXSCRIPT is capable of and how it is different from AXPOSTRAP or AXPOSSCRV?

        Also do you do you have a release date for DMD 2.4?
        Almost too much to list. AXSCRIPT is a motion sequence, where you can execute moves, set axis properties, do looping, wait for events, etc. You can use it to construct blended moves, custom home routines, or even things like flying saw apps. It's quite powerful. As for availability...soon.


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        • #19
          Originally posted by BobO View Post

          Almost too much to list. AXSCRIPT is a motion sequence, where you can execute moves, set axis properties, do looping, wait for events, etc. You can use it to construct blended moves, custom home routines, or even things like flying saw apps. It's quite powerful. As for availability...soon.


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          Bob O Thank you for the info. Does any of the axis positioning commands have "Look Ahead" capability? In my application, the stepper motor is used to dispense a semi-viscous liquid. Frequent velocity changes can cause liquid to be incorrectly dispensed (too little or too much as start and end points). Is there a way to programmatically look ahead stepper target positions and adjust the velocity?

          In other words, I have seen that a stepper motion fully decelerate after the first move and then fully accelerate at the start of the next move, but that is not ideal as all that acceleration and deceleration would result in the poor flow of the liquid.

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          • #20
            Originally posted by RockB View Post
            In other words, I have seen that a stepper motion fully decelerate after the first move and then fully accelerate at the start of the next move, but that is not ideal as all that acceleration and deceleration would result in the poor flow of the liquid.
            You are describing what some call a "blended move". AXSCRIPT will do that very nicely.

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