01/2007
8.1 General
8-177
© Siemens AG 2007 All Rights Reserved
SINUMERIK 840Di sl Manual (HBIsl) – 01/2007 Edition
8.1.4 Description of a DP cycle
At time T
I
, the current actual position values are read from all isochronous DP
slave drives. In the next DP cycle, the actual values are transferred to the DP
master in the time T
DX
.
The NC position controller is started at the time T
M,
with T
M
> T
DX,
and com-
putes the new speed setpoint for each axis on the basis of the position setpoint
and the transferred actual position value.
At the start of the next DP cycle, the speed setpoints are transferred from the
DP master to the DP slave drives in the time T
DX
.
At time T
O
, the speed setpoints are taken as new specified values for all drive
controllers.
DxDxDxGC DPV1 DxDxDx
Speed
control cycle
Drives:
DP slaves: 1 to 3
NC:
Master or position
controller
T
I
T
M
T
O
T
MAPC
=
T
DP
GC
T
DX
R
PROFIBUS DP
communication
1
2
T
DX
R R RRRRRRRRRR RRRR
DPV1
T
O
T
I
G T R
G T R
Fig. 8-2 Example: Optimized DP cycle with 3 DP 611U slaves
Key to Fig. 8-2:
T
MAPC
Master application cycle: NC position control cycle
The following always applies for SINUMERIK 840Di sl: T
MAPC
= T
DP
T
DP
DP cycle time: DP cycle time
T
DX
Data exchange time: Sum of transfer times of all
DP slaves
T
M
Master time: Offset of the start time for NC
position control
Actual values
Position controller
Setpoints
8 PROFIBUS DP Communication
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