Glossary · Motion control and drives
Following error
Also known as: Lag error, Position deviation
German: Schleppfehler
In motion control, following error is the difference between the commanded position of an axis and its actual position measured by the feedback device during motion; drives monitor it against a limit and signal a fault when the axis can no longer follow the command.
- Motion control
In one sentence
Following error is the gap between commanded and actual axis position during motion; exceeding its limit triggers a drive fault.
Example
When a guide rail sticks, the following error of the servo axis exceeds the 2 mm window, and the drive stops the axis with a following error fault.
How it applies
- Engineering: Following error exists only where position is measured, in servo axes and closed-loop steppers. Its size depends on controller tuning, feedforward and acceleration.
- Commissioning: The following error window and time are set so that normal dynamics stay inside and mechanical problems trigger the fault. Too wide a window hides collisions.
- Operation: A following error fault usually means mechanical blocking, overload, a wrong tuning or a feedback problem.
- Documentation: In the fault list, give possible causes and checks in a sensible order (mechanics, load, parameters, encoder). Explain that an open-loop stepper has no following error monitoring; its equivalent problem is Step loss.