Newbie advice on step response and bode plot


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    Default advice on step response and bode plot

    Hello,
    I'm currently moving to Velocity control with analog +/- 10 Volts and CL feedback.
    System:
    Kflop
    Kanalog
    Konnect
    Sanyo Denki BL Super PY2 Amps
    Sanyo Denki BL Super P5 Servo motors

    System worked with just Kflop in STEP/DIR mode.
    Attached I hope is a screen shot of current settings.

    advice on step response and bode plot-ac-servo-response-jpg

    Similar Threads:


  2. #2
    Gold Member TomKerekes's Avatar
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    Default Re: advice on step response and bode plot

    Hi eng101,

    Do you have any specific questions?

    Can you tell us about your background and what parts you understand?

    Have you read any of our on-line help or wiki articles?

    The first step is usually to determine (or tell us) your axis resolution so we know what kind of speeds, errors, etc, we are talking about. See:
    Dynomotion

    Here are some general comments on what I see:

    Jerk: you have very low Jerk relative to your allowed acceleration (if I can read the tiny numbers in your image). Dividing A/J = 4 seconds. Even in a large machine like a car it wouldn't makes sense to apply the brakes over a 4 second time span. For most machines less than 0.1 seconds it slow enough to avoid shock and disturbances.

    Velocity: Your test only achieves about 1/4 of your allowed velocity even for the fairly large move size because of the limiting Jerk limits applies acceleration so gradually. See:
    Dynomotion

    The Velocity plot is not very useful to judge servo performance. Plot Position Error also. If you attach the raw data we can replot in all different ways ourselves and zoom in. A smaller and quicker move is usually better for judging performance.

    Output Gain: Change back to 1.0 to be less confusing and to avoid outputting more than 2047 to the DACs and causing overflow. (then double P gain to have the same response)

    Filters: you forgot to show us what filters are being used.

    P Gain: have you tried higher gain?

    Bode Plot. The stimulus is too low for your system. The Encoder (red plot) is only changing about +/- 2 counts so quantization error will be large and result in a poor measurement. Similarly the Output (green) is only about +/- 1 DAC count. Please read:
    Dynomotion

    HTH
    Regards

    TK
    http://dynomotion.com


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    Default Re: advice on step response and bode plot

    Hello Tom,

    Thank you for your reply.

    I have very little knowledge in this area.
    I had this working well in Step/Dir, decided to close the loop and fully utilize the function of these servos.
    I have many questions, even after reading.
    First, In the attachment from my previous post, Is the scale on the right vertical axis RPM?
    If it is my servo drive software is stating the servo motor is running at least twice the RPM Posted on the graph. Any thoughts on why this would be the case.
    Second, In the axis window, if I the roll the servo motor one revolution the Position value reads about 1000. Is this the output from the encoder.
    thanks again for any help you can provide.



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    Gold Member TomKerekes's Avatar
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    Default Re: advice on step response and bode plot

    Hi eng101,

    First, In the attachment from my previous post, Is the scale on the right vertical axis RPM?
    The right scale is for the DAC Output (green plot) which has a range of +/- 2047 DAC Counts which corresponds to +/- 10V which corresponds to +/- full speed of the amplifier.

    Second, In the axis window, if I the roll the servo motor one revolution the Position value reads about 1000. Is this the output from the encoder.
    Yes. You might get a more accurate measurement by rotating 10 or more turns and then dividing by the number of turns. Also measure the distance the axis actually moves. This will allow you to determine the Resolution of the axis as described in the link I sent earlier.

    HTH
    Regards

    TK
    http://dynomotion.com


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    Default Re: advice on step response and bode plot

    Hello Tom,

    I feel I have good response now from the servo. Had a few unknown variables to figure out. encoder pulse/rev was incorrect as RPM/1V in amp settings.
    Have to be careful with servos taken from other machines. Part number do not match catalog specs.

    Last edited by eng101; 11-12-2017 at 11:37 AM.


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advice on step response and bode plot
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