Problem

Clarifications

• This article provides basic guidelines to allow an unexperienced user to tune the motion loops of his/her motor. The instructions will be very basic and there will be no stability or control theory explanations.
  

Steps

Torque loop

• Start by setting both Kp and Ki to 0 in case they are not already.

• Start increasing Kp in order to increase the amplitude of the actual value signal wave. you can do this by typing the value directly, moving the slider or using the arrows. Once you start increasing Kp you will see something similar to the following:

• Keep increasing Kp until it reaches its maximum amplitude. There will be a point in which the amplitude of the signal does not change, that is when you need to stop increasing Kp. If you keep doing it you will only introduce additional unstable oscillations into the signal. The maximum amplitude reached will usually fall short of the amplitude of the demand value signal but that is normal. In the example case, the maximum amplitude looks like the following:

• Start increasing Ki until the amplitude of the actual value signal equals the demand signal. Increase Ki just enough to reach the required amplitude, beyond that point you will only introduce more oscillations and initial overshoot to the signal. In our example, the final result is:
  

Velocity loop

• Start by setting all the gains besides the Integral Limit to 0 (you can leave the latter one at 1000 for example to start with):

• Start increasing Kp and sooner or later you will see the motor starting to move:

• Increase the proportional gain until the demand speed signal is reached. Normally with Kp you can get to the maximum speed but if in your case it is not possible, try increasing Ki until the target is reached. However, in systems without load it is rare to use integral gain when tuning velocity.

• First of all, check the current performance of the velocity loop with the gains that you got when tuning the motor without load. In the case of our example it looked like the following:

• Increase Kp and check if both the acceleration and maximum reachable speed increase. Increase it until there are no significant changes or when unstable oscillations are introduced in the system. If the performance is still not enough, start increasing Ki as well until you get the desired behavior. It should get to the point that you reach the required speed following the desired profile accelerations/decelerations. In the case of our example, only Kp was needed:

Position loop

• Start by setting all the gains besides the Integral Limit to 0 (you can leave the at its default value of 32768 for example to start with):
  

• Increase slightly both derivative and proportional gain so that you can get the system to start moving (even though it might be slow and not precise yet). Start with the derivative gain and the add the proportional gain. Be careful if you are tuning a VCA since these actuators seem be sensitive to the derivative gain which you might only need to increase the smallest amount possible in order to stabilize the motion. You can use some reference values like the following in order to get you started:

• From this starting point, start increasing the proportional gain until the target is reached or a steady state value is reached which might usually be under the target value.
  

• Once that steady state is reached, proceed to add some integral gain so that the target value is properly reached in the fastest time possible. Watch out to not over-increase the integral gain too much or you might introduce overshoots and steady oscillations around the target.
  

1. Stable motion turns to unstable motion but the target is reached --> in this case, what you will most likely need to do is increase the derivative gain of the PID controller in order to soften the oscillations and overshoots that are now present in the system once the load is added. If after increasing the derivative gain the system's response is too slow, you will need to increase back the proportional and integral gains so that you get the response as fast as you need it to be.
   
2. Target is not reached directly --> in this case, you will need to work first mostly on the integral gain of the PID controller so that you are able to fully reach the target. If you need the response to be faster you can add some proportional gain for the startup as well. In addition to this, just like in the other case, if overshoots and oscillations are introduced, you need to increase the derivative gain later in order to ensure the most stable motion possible.
   

• Check performance of the PID controller tuned without load once the load is added to the motor.

• Increase derivative gain in order to reduce overshoot and oscillations around the target.