Closed-Loop Tuning

The Closed Loop Tuning tool commands the selected axis to do a predefined sinusoidal motion profile. The tool automatically measures the motion that occurred and calculates a set of servo gains based on the information that you specified. The function of the Closed Loop Tuning algorithm is to translate a set of tuning specifications, based on the open-loop magnitude crossover frequency and the phase margin, into a set of servo gains.

IMPORTANT: Before you use the Closed Loop Tuning tool, the axis that you select must be stable.

  1. In the Axes category of Automation1 Studio, select the Servo topic. Then make sure that you are in the Basic Editing mode.
  2. In the Classical Tuning module, select the Closed Loop Tuning tab at the top of the application.
  3. At the top of the module, click the drop-down arrow to select the axis that you want to configure.
  4. In the Oscillation Options toolbar, configure the oscillation Amplitude (primary units) and Frequency (Hz).
  5. In the Calculation Options toolbar, enter a target Crossover Frequency (Hz) and Phase Margin (deg).

    6. Tip: For information about applicable target values for a range of mechanical devices, refer to the Selecting a Maximum Target Crossover Frequency section of this guide. A phase margin in the range of 32 degrees to 45 degrees is permitted for most conditions.

  6. Click the Start Closed Loop Tuning button .
  7. If the axis cannot complete the motion because the controller generates a Position Error Fault, divide the oscillation amplitude or excitation frequency by 2. Then click the Start Closed Loop Tuning button to do Closed Loop Tuning again.
  8. If the Closed Loop Tuning tool tells you that an invalid inertia was calculated, multiply the oscillation Amplitude (primary units) or Frequency (Hz) by two. Then click the Start Closed Loop Tuning button to do Closed Loop Tuning again.
  9. If the quality estimate is less than 50%, do not apply these changes. Increase the values of the oscillation Amplitude (primary units) and the Frequency (Hz). Then click the Start Closed Loop Tuning button to do Closed Loop Tuning again.
  10. To apply the servo parameter values to the controller, click the Apply Changes button.
  11. If the axis is stable when the new servo parameter values are applied and if it is necessary for you to have higher dynamic performance, do one of the options that follow:
    • Increase the value of the Crossover Frequency (Hz). Then click the Start Closed Loop Tuning button to do Closed Loop Tuning again.
    • Decrease the value of the Phase Margin (deg). Then click the Start Closed Loop Tuning button to do Closed Loop Tuning again.

      • Tip: If you start Closed Loop Tuning again with the same Oscillation and Calculation options after applying the servo parameter values to the controller, it is typical to get a higher quality estimate and more accurate gains. This occurs because the axis shows a higher dynamic performance during the measurement.

  12. If the axis is unstable when the new servo parameter values are applied, do the steps that follow:
    1. Reset the controller to go back to the previous servo parameters that are stable.
    2. Lower the value of the Crossover Frequency (Hz) or Phase Margin (deg).
    3. Click the Start Closed Loop Tuning button to do Closed Loop Tuning again.
  13. When the performance of the selected axis is satisfactory, click the Save All button on the bottom-left corner of the application. This makes sure that the updated parameters will have an effect after the next controller reset.