How to configure a motor with an unbalanced vertical load

How to configure a motor with an unbalanced vertical load

Problem

I have an application in which my motor has to move an unbalanced vertical load and I am wondering if there are some additional steps that need to be done after properly configuring my motor and feedback devices and when tuning the motor. What do I need to do?

Clarifications

  • Systems with unbalanced vertical load are systems that depending on the nature of the load might not be properly controlled from the drive. In this particular article, we focus on the type of unbalanced vertical loads that we can handle: constant loads (weights that go against gravity).

Steps

Systems with unbalanced constant vertical loads don't add any additional steps in the configuration process of the system. Actually, the only difference with a system with a regular balanced load is the introduction if the following parameter: torque offset. This leads to the following required steps after the motor has been configured and tuned properly:
  • Open the Move and Scope window at the same time. In the Move window proceed to the Position window and perform a position movement inside the allowed motion range. Once the target position has been reached (and the drive is correctly holding the position in a stable way), proceed to plot the torque actual value register in the Scope and note the value at which it stabilizes. Write down this value since it will be the value that you need to set for the torque offset. An example of this torque actual value could be the following:

  • Once you have the torque actual value written down, you can proceed to write this same parameter as the torque offset in the Torque Control window:

After this, you should be able to control in a better way the whole system and especially both velocity and position loops. However, if you want to fine-tune the torque loop, you will need to set the torque offset back to 0 or otherwise it will be impossible for you to tune it correctly due to the offset that you will see in the Tune window.