09.2008
Communication / PROFIBUS
Siemens AG
6SE7087-6QX70 (Version AK)
SIMOVERT MASTERDRIVES
Compendium Motion Control
8.2-99
With DSC the actual position calculated inside the drive is also fed back
directly:
Path
Interpolation
n
cmd
x
cmd
–
x
act,NC
K
pc
T
pc
Zero Offset
and
Compensation
Master Controller (NC)
Drive Controller
x
act
Transmission
delay
n
cmd
Interpolation
(T
pc
)
Speed filter
Speed
calculation
Speed control
2
Position
control
n
Drive
–
T
pc
T
sc
–
x
act,NC
x
act, Drive
3
4
1
A
B
n
cmd
: speed command
T
sc
: speed controller sampling time
x
cmd
: position command
T
pc
: position controller sampling time (= T
MAPC
)
x
err
: position error command
K
pc
: position controller gain
x
act
: actual position
Fig. 8.2-33
Structure of the LR circuit based on the speed setpoint interface with DSC
For this to be possible, the control error calculated in the master is
transmitted as well as the speed setpoint. The additional feedback
network can use the internal formats in the drive for position presentation
and is thus independent of the position presentation in the master. The
above presentation assumes that the network is calculated in the speed
controller sampling time T
SC
which will be possible in many cases. In this
way the maximum possible dynamic improvement is achieved. However,
greater clock times T are also possible, if the calculation time is short
(T
SC
≤
T
≤
T
PC
).
The structure contains a total of three feedback branches for the actual
position value (No. 1, 2 and 3). Feedback branch no. 2 compensates fully
for the action of no. 1 in respect of the actual value transmitted by the
drive x
act
, so that the dead time in branch no. 1 no longer has to be
considered for the stability of the position control circuit. As a result, the
position control circuit is initially open. Feedback branch no. 3 closes the
circuit again, but with a shorter delay, so that greater gains can be set.
Operation
