3.1.8.3.10 Command smoothing and
Interpolation
3.1.8.3.10.1 Overview
Commands are sent to the slaves with a step size that depends on the master’s update rate. In EtherCAT,
these steps are usually in intervals of 250 µs to 8 ms while other protocols may have even slower rates.
These steps may cause audible noise or even instability when a controller is tightly tuned.
Fast command changes and slow update rates increase the negative effects on control performance.
To improve the quality of the trajectory, the input command can be shaped with a finite impulse response
filter.
This filter somoothes the control values from the previous to the current target, smoothing out the input and
preventing spikes in the derivative around the target changes.
This feature can be used in all position and velocity control modes:
Cyclic synchronous position mode
Cyclic synchronous velocity mode
Profile position mode
Profile velocity mode
Homing mode
3.1.8.3.10.2 Side Effects
Attention
This feature introduces delay to the control input therefore it’s important to close the control loop in
the servo drive directly. If the control is closed on the master, this feature would introduce a lag that
may affect that controller’s stiffness.
Note
All axes on the chain must be commanded together and should have the same FIR settings.
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