How can I do position maintenance using a digital input to capture an encoder count and adjust the move profile on the fly.

I have a rotary table (45:1 ratio) being driven by a stepper motor. I am using a 7344 motion controller. I want to be able to do position maintenance on the move. I have a home input on the table. My thoughts were to capture the position when the table goes by the home input and compare it with the previous time and make the adjustment in the next move. I am just not sure what the best way to do this is. I am thinking that I want to tie the home input to one of the trigger inputs as well as the home.

Hello,
Your best option will be to use an encoder for feedback in your system. If you use an encoder then at the end of the move, the controller will compare your trajectory position with the position the encoder reads (the actual position) and make the necessary adjustments. Also, this is all handled transparently so you won't have to worry about any complicated programming issues.
Regards,
Andy Bell
Applications Engineer
National Instruments

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  • ***Resubmitted for further review*** How can I do position maintenance using a digital input to capture an encoder count and adjust the move profile on the fly.

    I have a rotary table (45:1 ratio) being driven by a stepper motor with an encoder attached to the motor. I am using a 7344 motion controller. I want to be able to do position maintenance on the move. The problem is that I am always moving in the same direction and the table has mechanical error. I have a home input on the table, which I have wired to the trigger input for the corrosponding axis. My thoughts were to capture the position when the table goes by the home input and compare it with the previous time and make the adjustment in the next move. I am just not sure what the best way to do this
    is.

    Hello,
    So when you say that the table has mechanical error you mean that the number of steps per table revolution will vary from revolution to revolution? I apologize that I misunderstood this initially. What you could do is use high speed capture to read the position of the stepper every time the home switch (or some other mechanical switch) is hit for each revolution of travel. Then when the high speed capture lined is toggled you can read the current position and modify your next move accordingly. To get details about High Speed Capture please search for High Speed Capture from our Developers Zone at: zone.ni.com
    There are examples programs on our website and examples available with the FlexMotion driver.
    Please let me know if you have any further questions.
    Re
    gards,
    Andy Bell
    Application Engineer
    National Instruments

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