SEW-Eurodrive DFE24B EtherCAT - Page 70

70
Manual – Fieldbus Interface DFE24B EtherCAT®
8
EtherCAT
®
introduction
Motion Control via EtherCAT
®
As a rule, EtherCAT
®
is designed for bus and control cycles to be synchronous.
Velocity mode
In velocity mode, a speed (or velocity) setpoint is transferred from the controller to the
inverter and the actual position value is read from the inverter or a separate encoder.
In velocity mode, the inverter is a simple speed actuator. The control time-slices of the
controller, bus transfer, the internal processing cycle of the inverter and the encoder
must be synchronized.
Position referencing, monitoring of permitted travel ranges or limit switches, load-depen-
dent ramp specification, and lag error monitoring are realized in the higher-level control-
ler, not MOVIDRIVE
®
B.
To prevent unwanted excessive acceleration during longer control intervals (>1 ms), in-
stead of adopting the speed setpoint directly, MOVIDRIVE
®
B uses linear interpolation.
This means that for a setpoint cycle of 5 ms, the controller in MOVIDRIVE
®
B does not
INFORMATION
The Distributed Clock mechanism also makes sure that the internal processing time-
slice of the inverter is synchronized too.
In MOVIDRIVE
®
B, the time-slices and data transfers are synchronized via the dual-
port RAM of option DFE24B
6823492875
M
V
X X
X
ref
v
ref
t
ref
X
act
v
act
[3]
[2][1]
[4]
[5]
[C]
[A]
[5] [6]
[B]
x
ref
Position setpoint [1] Position controller [A] Control
x
act
Position actual value [2] Speed controller [B] Fieldbus interface
v
ref
Speed setpoint [3] Output stage of the inverter [C] Inverter
v
act
Actual speed value [4] Driven machine
t
ref
Torque setpoint [5] Encoder (V = speed; X = position)
[6] Optional encoder
00
I