Sercos Slave - Connections to the sensor/actuator level

VIPA technical report

Sercos stands for Serial Real Time Communication System and is worldwide established with numeric controls. Beyond the classic CNC machines this-technique has proved its worth for fast and pre motion control in the whole automation branch.

Sercos, also called "Sercos interface", is a normed digital drive interface basing on fibre optic transmitter technology.
The high real-time needs and the interference-free fibre optic transmitter technology are the main characteristic of this bus system.
In the Sercos System the central controller (NC) usually communicates with the driver.
The data transfer with these peripheral devices happens cyclically.
The master reads the input information of the slaves (drive telegram) and sends the output information to the slaves (master data telegram). A maximum of 254 slaves can be connected to one bus. Sercos manages the communication via three telegram types:
The Master-Sync-Telegram is received from all drives simultaneously and serves the synchronization of all time triggered events in the numeric control (NC) and drives.

The Master-Data-Telegram is like the Master-Sync-Telegram received from all drives simultaneously. It contains the cyclic and the service data for all drives.

Configurable data field

The real-time data are completely transferred at every communication cycle via the so called configurable data field. The drives are sending their telegrams in sequence within assigned time windows. By means of an Ident-No-System, you may define at initialization what real-time data are sent. Besides of numeric values like set point and effective value this may also be bit lists with in- and output commands.

Sensor/actuator level

The Sercos coupler is developed for the fast data transfer at the sensor/actuator level. Central control devices like e.g. the PLC communicate with the decentral in- and output devices via a fast serial connection. The integration of an l/O-slave into the Sercos bus system, which actually had been developed for drives, was solved by VIPA as follows:

  • Basic configuration: (baud rate, light intensity etc.) is being done via the address switches of the IM 253SC.
  • Parameters of analog multifunctional modules: get to the modules via P-O-xxx identifier
  • Input data: are tuned in by S-2xxx identifiers
  • Output data: are tuned in by S-3XXX identifiers

The communication happens cyclically during operation as a master-slave communication. The cycle time is defined at initialization and is between 62 ns and 65 ms.
Minimum times of 1 ms are possible with the Sercos coupler VIPA IM 253SC. Short bus cycles can be kept with larger I/O amounts as well since each module can be configured to take part in the cyclic telegramm traffic or to be reached only acyclic via the service channel.

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