EtherCAT Redundancy Island (ERI)
The "EtherCAT Redundancy Island" realizes highavailability within EtherCAT. The island consists of two CPUs which behave as master and slave. If one CPU fails the other CPU resumes the process.
Highavailibty is used in applications which must not be interrupted, in applications where loss of production causes huge costs and to guarantee continuous operation without survey and without maintenance personnel.
The “EtherCAT Redundancy Island” shortly called “ERI” offers the possibilty to create highavailable systems within the EtherCAT fieldbus. Two CPUs are the core of this architecture. One CPU behaves as a master, the other as a slave. In respect to the EtherCAT fieldbus the CPUs work as EtherCAT slaves. The EtherCAT cable redundancy is used to keep the communication to the EtherCAT master running in case of a fault in ERI master or ERI slave.
Master and slave contain the same application program. After startup of the highavailable system the master regulates the process, the slave only does some I/O signal checks. In case of a master fault, a redundancy switch is done. The detected fault and the redundancy switch will be reported to the EtherCAT master. The process will be continued.
ERI master and ERI slave can have their own I/O devices, but can also possess switched devices. This architecture allows to connect sensors and actors as one channel or on two channels. Using two channels allows redundant periphery. An actor can be switched, a sensor can be read by both CPUs. Feedback input channels can be used to check whether the output channel has been set properly.
The hardware basis of the ERI is an industrial version of the Raspberry PI from the Kunbus corporation. As operating system an adapted version of the Raspberry PI operating system “Raspian” is used, which is a Linux distribution containing a realtime patch.
The CPUs are programmed using a standard C,C++ compiler. Important IIoT protocols like MQTT and OPC UA can be used to connect the CPUs to the cloud.
Of course “ERI” can also be used as normal Soft PLC without highavailability.