Lenze E94P PositionServo with MVOB - Manual (Page 60)

58 L S94H201E_13426446_EN
Parameters
5.9.10 Set Default Gains
Click the [Set Default Gains] button to access the Default Gains parameter. Selecting [Set Default Gains] will
reset the gains to the default values in the motor file.
5.9.11 Feedback and Loop Filters
Hardware Version 2 provides for the use of 1 feedback filter and 2 cascaded loop filters. Loop filters are
identical in structure and operation.
The feedback filter is a low-pass first order filter used primarily to filter noise from the feedback device.
The time constant of the filter is settable and from 2mS and up. Values of 2 – 8mS are generally adequate
for most applications.
The Loop filter can be configured as a Low-Pass, Notch or Resonant type filter.
The Low pass filter is used to lower noise in the system produced by control and feedback signal disturbances
and quantization noise. The Low-pass cut off frequency is usually set at 5-10 times the desired velocity
loop bandwidth.
If enabled, the loop filter is installed between the velocity and current loop.
The Loop filter can be configured as a Notch or Resonant type filter. Both configurations implement
band-stop filtering for solving certain mechanical compliance problems. A common problem is torsional
resonance due to mechanical compliance between load inertia and motor inertia. Consider a motor coupled
with a long load shaft with an inert load at the opposite end. Such a system will have a resonant frequency of
f
r
=
π
2
1
J
p
K
s
[Hz]
where
JL = load inertia [kgm^2]
JM = motor inertia [kgm^2]
Ks = total stiffness of coupling and shaft [Nm/rad]
Jp = (JL * JM) / (JL + JM)
p = 3.1416
Applying the loop filter at this frequency in the configuration “Resonant Filter” will cancel the resonant pole
effectively allowing higher overall loop gain without losing stability.
The Resonant filter setting allows the user to set the resonant frequency, the bandwidth of the filter as well
as maximum attenuation gain in dB.
The Notch filter serves a similar purpose as the resonant filter. It has programmable bandwidth and center
frequency. The Gain in the center frequency point is not programmable and depends on the bandwidth of
the filter which is programmable. The resonant filter is a second order bi-quad filter with -20dB/dec roll-off.
This resonant filter is good for applications where resonances have a wide bandwidth rather than in those
that have a big amplitude and narrow bandwith.