Delta RMC151 - Manual (Page 926)

RMC70/150 and RMCTools User Manual
RMC70 Address: %MDn.3, where n = 12 + the axis number
RMC150 Address: %MDn.3, where n = 24 + the axis number
System Tag: _Axis[n].ActVelFilter, 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: 100
Description
This parameter specifies the cut-off frequency of the Actual Velocity input filter in hertz.
The filter is applied to the Actual Velocity before it is used in the control algorithm. The
filter is a low-pass fourth order Butterworth filter.
For most position or velocity control applications, there is no need to change this
parameter from its default setting. If you are using the velocity of a reference input, you
may wish to decrease this value if the velocity is noisy.
Setting the Actual Velocity Filter to zero (0) disables the filter. If the Velocity Filter
Type parameter is set to Model, the Actual Velocity Filter will not be used (see below).
How the RMC Uses the Filtered Velocity
The Velocity Filter parameter specifies how the Actual Velocity Filter is used in the
RMC:
• Status Only (default setting)
The Actual Velocity Filter is applied to the Velocity value used for status and for
plots, but it is not applied to the value used for control. This is the default setting
because the filtering introduces phase that negatively affects control. This option
should be selected for systems that need to react to quick changes.
• Low-Pass
The Actual Velocity Filter applies to both the Actual Velocity status register and the
velcoity value used by the control algorithm. If you want the filter to apply to the
control, choose this option.
• Model
The Actual Velocity Filter is not used. Instead, the Model is used to calculate the
Actual Velocity. This value is then used for both the Actual Velocity status register and
the control algorithm.
Filtering increases the phase delay in the filtered value. By default, filtering is applied to
the Velocity and Acceleration values used for status and for plots, but it is not applied to
the values used for control because of the phase delay filtering introduces. Therefore,
filtering should be left out of systems that need to react to quick changes. You can select
to use filtered values for control with the Velocity Filter Type and Acceleration Filter Type
parameters.
Notice that this Actual Velocity filter is independent of the Actual Position 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?
906 Delta Computer Systems, Inc.