Open-Loop Tuning

The Open Loop Tuning tool moves the selected axis by injecting open-loop current into the axis when it is not under closed-loop control. This tool automatically measures the motion that occurred and calculates a set of servo gains based on the information that you specified. If you use this tool, it is not necessary for the selected axis to be stable or enabled. The function of the Open 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.

WARNING: Because this is an open-loop tool, use it only when the axis that you are tuning is free from external forces. For example, if an axis moves in the vertical direction and uses closed-loop control to counteract gravity, then the axis will free-fall if you try to tune it with the Open Loop Tuning tool.

  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 Open 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 Tuning Options toolbar, configure the Excitation Time (ms) and the Percent Average Current.
  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 Open Loop Tuning button .
  7. If the Open Loop Tuning tool tells you that an invalid inertia was calculated, multiply the Excitation Time (ms) or the Percent Average Current by two. Then click the Start Open Loop Tuning button to do Open Loop Tuning again.
  8. If the quality estimate is less than 50%, do not apply these changes. Increase the values of the Excitation Time (ms) and the Percent Average Current. Then click the Start Open Loop Tuning button to do Open Loop Tuning again.
  9. To apply the servo parameter values to the controller, click the Apply Changes button.
  10. If the axis is stable when the new servo parameter values are applied, Aerotech recommends that you use a different tuning tool that keeps the axis under closed-loop control, such as Closed LoopClosed A broad term relating to any system where the output is measured and compared to the input. Output is adjusted to reach the desired condition. Tuning or the Frequency Response module.