Actual Position Filter

Type:	Axis Parameter Register
RMC70 Address:	Fn:2, where n = 12 + the axis number
RMC150 Address:	Fn:2, where n = 24 + the axis number
System Tag:	_Axis[n].ActPosFilter, where n is the axis number
How to Find:	Axes Parameters Pane, All tab: Feedback → Filtering/Modeling
Data Type:	REAL
Units:	Hz
Range:	0 (Off) or greater than 0.01
Default Value:	0

Description

This parameter specifies the cut-off frequency of the Actual Position input filter in hertz. The filter is applied to the Actual Position before it is used in the control algorithm. The filter is a low-pass fourth order Butterworth filter. Setting this value to zero (0) disables the Actual Position filter.

Filtering of the Actual Position is not recommended on position control axes. The control algorithms use the filtered Actual Position. If filtering is enabled, it will slow the response of the system. The lower the cut-off frequency, the slower the system will respond.

Notice that this Actual Position filter is independent of the Actual Velocity Filter and Actual Acceleration Filter. If the Actual Velocity and Actual Acceleration filters are being used on the controlled values (Velocity Filter Type or Acceleration Filter Type are set to Low-Pass or Model), then you should make sure to always set the Actual Position filter, Actual Velocity Filter, and Actual Acceleration filter to the same values.

Limits

The filter is limited to greater than 0.01 due to inaccuracies in the calculations for lower values. The filter is disabled (without notice to the user) when the frequency is set above 1/4 the sample frequency (500Hz for 500us loop, 250Hz for 1ms loop, 125Hz for 2ms loop, 62.5Hz for 4ms loop).

Why Bother?

Filtering the input can reduce noise in the feedback. It also makes the plots look cleaner. Filtering of the position should not be done on control axes.