Time response: overshoot, settling time, steady-state error
Control performance is described by the shape of the response to a step input. What the numbers written in a specification mean.
Measures
| Measure | Meaning |
|---|---|
| Rise time | From 10% to 90% of the final value |
| Overshoot | The largest fraction by which it exceeds the final value (%) |
| Settling time | The time from which it stays within ±2% (or 5%) of the final value |
| Steady-state error | The error left after enough time has passed |
Relation to a second-order system
- The smaller the damping ratio ζ, the larger the overshoot (about 5% at ζ = 0.7)
- The larger the natural frequency ωn, the faster
A specification such as "overshoot 5% or less, settling time 200 ms or less" fixes targets for ζ and ωn, and the gains are chosen to match.
3D labRun what you have read so far→Steady-state error
With P control alone, a loaded motor stops a little below the target speed, because output only exists while there is error. The integral (I) term accumulates error and removes this gap.
Measuring
On a real board, change the target as a step, log the output (telemetry) and plot it. Overlaying it on the simulated response shows the difference between model and reality.