Kollmorgen BDS5, Installation And Setup Manual

Page: 72 / 150

C
HAPTER
3 - O
PERATION
BDS5
3-10
ways, such as chain drives (which have load in one
direction but are unloaded in the other) and systems
with excessive backlash (where there is no load when
gear teeth are not touching).
When the inertia changes, the system has the
following characteristics:
•
System performance is excellent when the
motor is in some positions and unacceptable
when the motor is in other positions.
•
Reducing the bandwidth eliminates the
problem.
If the system performance is poor because of
changing inertia, you can make the following
corrections:
•
Correct the system mechanics so that inertia is
constant.
•
Detune (that is, reduce the bandwidth of) the
system. If the times when your system will
have excessively changing inertia are
predictable, you can write your program to
detune your system in these regions.
3.8.4 Resonance
Resonance is a high frequency (> 500 Hz) where the
system mechanics oscillate. Normally, systems with
resonance will be very stable when you tune with
lower target bandwidths. As you increase the target
bandwidth, you will begin to hear a fairly pure, high
pitch. If you want to decrease resonance, use shorter,
larger diameter driving shafts. Often, the low-pass
filter can help you raise the bandwidth 20% or 30%,
but this can be a difficult trial-and-error process: you
slowly lower the low-pass filter frequency (LPFHZ)
and attempt to raise the target bandwidth for tuning.
When your system has a resonance, it will have the
following characteristics:
•
The system will make a clear, high pitch
(>500 Hz). Do not confuse this problem with
compliance, which has a low pitch.
If the system performance is poor because of
changing inertia, you can make the following
corrections:
•
Enable the low-pass filter (LPF) and reduce
LPFHZ, if necessary.
•
Reduce the bandwidth of the system.
•
Shorten the length and increase the diameter of
shafts and lead screws.
3.8.5 Low-Pass Filters
The LPF switch enables the low-pass filter. It can be
turned on and off when the drive is operating. The
frequency of the low-pass filter is stored in LPFHZ in
Hz. It can also be changed when the drive is
operating. For example, if LPFHZ is 200 and LPF is
on, then a 200 Hz low-pass filter is run in the BDS5.
The filter can be modeled as two cascaded, low-pass,
single-pole filters, both with a 3 dB frequency of 200
Hz. LPFHZ should be set as high as possible, since it
degrades the system performance.
For example, the following sequence sets the low-
pass filter to 250 Hz and enables the drive.
LPF ON ;ENABLE LOW_PASS FILTER
LPFHZ 250 ;SET BREAK FREQ. TO 250
;HZ
If the low-pass filter is on, the
TUNE command may not work
well.
NOTE