Glossary · Motion control and drives
Position loop
Also known as: Position control loop
German: Lageregelkreis
In motion control, the position loop is the outer control loop of a cascaded drive control that compares the commanded position with the measured position and outputs a velocity setpoint to reduce the following error.
- Motion control
In one sentence
The position loop is the outer drive control loop; it compares commanded and actual position and outputs a velocity setpoint.
Example
When a positioning axis overshoots, the commissioning engineer lowers the position loop gain and adds velocity feedforward.
How it applies
- Engineering: The position loop can run in the drive or in the controller. Feedforward of velocity and acceleration reduces following error without raising gain.
- Commissioning: Loops are tuned from inside out: current, velocity, position. Following error limits are set to detect blocked or runaway axes.
- Operation: A following error alarm indicates mechanical problems, overload or wrong tuning.
- Documentation: In fault lists, explain the following error alarm with likely causes and checks. Don't describe the following error monitoring as a safety function unless it is implemented and validated as one.
Position loop vs. velocity loop
The position loop corrects position deviations and commands velocity. The Velocity loop corrects speed deviations and commands current (torque).