Siemens SIMOVERT MASTERDRIVES Manual page 733

05.2006
9.4.30 Real master with deadtime compensation [833]
Siemens AG 6SE7087-6QX70 (Version AG)
SIMOVERT MASTERDRIVES
Preferably, the virtual master axis should be used as the master value
source for synchronization ([832] or [790]+[791]). In principle, this
results in the most calm control behavior and the highest possible
accuracy – also in dynamic operation – due to identical deadtimes for
all axes during master value and position actual-value sensing.
However, it is often not possible to use a virtual master axis as the
master value has to be read in via an external master value generator
attached to an upstream machinery component, which already exists
(motor encoder or built-on encoder).
In this case, the "Real master with deadtime compensation" function
block is used − both on the drive in which the master value generator is
evaluated and in the downstream drives to which this master value is
forwarded via SIMOLINK.
First of all, the input position value from the position encoder (or from
SIMOLINK) is limited to the axis cycle length, which can be set via
U425. The position actual value normally reaches the position controller
via the signal path of the synchronization block later than the position
actual value of the dedicated axis generated directly in the fast position
controller cycle. The deadtime resulting in this case is normally
particularly large for such drives, which receive this master value via
SIMOLINK. The deadtime compensation U424 ensures that this
deadtime is compensated for by adding a corresponding "advance
distance lead" to the master value. The distance lead is speed-
dependent: the higher the speed, the greater the distance the material
covers within the deadtime.
The speed value on which this is based can be gained by differentiating
from the master value or can be directly picked up from the position
sensing of the external master value generator, whereby preference is
given to the latter signal. An unsmooth speed signal can be smoothed
via U427, whereby the set smoothing time constant results in a higher
deadtime to be compensated.
For this purpose, the drive is accelerated to two different speeds. The
positional change is calculated through measurement of zero pulses or
printing index.
=
s s
Positional change 2
=
v v
Change 2
s
Positional
→ =
t
Deadtime
v
Compendium Motion Control
− =
s
1
− =
v
1
[LU]
change
=
1 -
Change [LU/ms]
Technology Option F01
[ LU ]
LU / min
[ms]
9-85