Question:
Why is it recommended to use a master value structure with a 'virtual master' instead of a cascaded master value selection for an electrical shaft for 3200C servo controllers with EtherCAT?
Answer:
The cyclic, synchronised telegram transmission process under EtherCAT implemented in the servo controllers of the 3200C series allows a jitter which cannot be compensated by the EMF2192IB EtherCAT communication module. As a result, the transmit data of a slave drive cannot always be provided in time for telegram transfer. Thus, the following slave drive of the master value cascade will not receive any new data for one cycle. This leads to discontinuities in the torque characteristic. Torque jumps appear (usually in the form of audible 'clicking noises') and have corresponding effects on the behaviour of the machine.
Short-term measures/recommendations:
We recommend to use a master value structure with a 'virtual master' for the electrical shaft. In this way, the master values for the slave drives will be generated in the virtual master and simultaneously transmitted to the slave drives.
Assessment:
The described behaviour with torque jumps caused by the jitter in the telegram transmission can be avoided by using a structure with a virtual master.
If the actual values of a slave drive are used for a chart in a visualisation, they should be smoothed before, if necessary.
Search terms: Sync telegram, synchronisation, master value cascade, jitter
