SEW-Eurodrive 1821 2492, Manual, Page: 38 / 68

38
Manual – XFE24A EtherCAT Fieldbus Interface
7
EtherCAT introduction
Motion Control via EtherCAT
While in control intervals 1 to 3 only a slightly inaccurate speed (v = dx/dt
S
≈
dx/dt
G
) is
determined, in the fourth control interval, a significant error (v = 2dx/dtS) occurs when
calculating the velocity. This incorrect speed calculated in one sample interval results in
violent responses of the control algorithms in the controller and can even trigger error
messages.
The problem described above caused by discreet sampling in different systems will usu-
ally only be a problem in motion control applications when the cycle time of the controller
is short or similar to the internal processing cycles of the servo inverter and external en-
coders.
As a rule, EtherCAT is designed for bus and control cycles to be synchronous.
The
Distributed Clock mechanism also enables synchronization of the internal process-
ing time slice of the servo inverter.
In MOVIAXIS
®
, the synchronization of time slices and the data transfer is controlled via
the dual-port RAM of the XFE24A option.
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