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XPS-Q8 Controller
14.2
Filtering and Limitation
In addition to the various PID correctors and calculations, filtering and limitation
parameters also have the same structure for all the correctors (PIDFFVelocity,
PIDFFAcceleration and PIDFFDualVoltage, etc).
The first section of the above diagram shows the succession of two digital notch filters.
Each filter is defined by its central frequency (NotchFrequency), its bandwidth
(NotchBandwidth) and its gain (NotchGain).
The gain, usually in the range of 0.01 to 0.1, is the value of the amplification of a signal
at a frequency equal to the central frequency and the bandwidth is the range about the
central frequency for which this gain is equal to a -3 db reduction.
Notch filters are typically used to avoid the instability of the servo loop due to the
mechanic's natural frequencies, by lowering the gain at these frequencies. When they
are implemented, these filters add some phase shift to the signal. This phase shift
increases with the filter bandwidth and must remain small in the frequency range where
the servo loop is active to maintain stability. The result is that notch filters are only
effective at avoiding instabilities due to excessive and constant natural frequencies.
The last section of the diagram shows the limitation and scaling features. Scaling is used
to transform units of position, speed or acceleration to a corresponding voltage. The
Limitation factor is a safety that is used to limit the maximum voltage that can be
applied to the driver to protect against any runaway or saturation situations that may
occur.
14.3
Feed Forward Loops and Servo Tuning
14.3.1
Corrector = PIDFFVelocity
The PIDFFVelocity corrector should be implemented into applications where the
positioner driver requires a "speed" input (constant voltage to the driver provides
constant speed output to the positioner), using MotorDriverInterface = AnalogVelocity.
Figure 54: Filtering and Limitation.
Figure 55: Corrector = PIDFFVelocity.
177
XPSDocumentation V1.4.x (EDH0301En1060 — 10/17)
Motion Tutorial
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