FB1.OFFSET Recalculation After Feedback Unwind
On a rotary application with an absolute multi turn feedback it's possible to run over the feedback unwind. If the gear between motor and application is binary nothing happens. If the application has a non binary gear ratio, the position after a restart of the drive may not be same. To readjust this situation the FB1.OFFSET needs to be corrected. On a producing machine it's not usable if, after every power cycle, an electrician has to recheck the position of the axis. For this situation the following auto correction has been implemented in the PLC code.
This correction calculation is used in connection with the TIA Modbus Interface for the AKD. If using this code, pay attention to the fact that software is only capable of reading the correct position if the communication between the drive and the PLC is up and running. What ever happens while not connected can not be detected and is therefor not take into account recalculating the correct offset position.
The code attached in the AP_AutoOffsetCalcFB_010_en.txt is written in STL with the Siemens TIA Portal V13.
This code is used to manually set the FB1.OFFSET and can be triggered after the startup of the PLC to reset the FB1.OFFSET according to the data stored in the retain memory of the corresponding data bloc.
The MN_AKDModbusAutoOffset_0A0_en.pdf gives a more detailed instruction of how to use.