System description
SERCOS is an open, fast bus system that has been the international standard (IEC 61491) for numerically controlled machines since 1995. Meeting high real-time requirements and interference-proof transfer in optical fiber technology are important features of this bus system, which is widely used for drive technology applications. The bus consists of a master and of a number of slaves. In a SERCOS system, the servo drives or the BK7500 SERCOS Bus Coupler represent the slaves.
The bus topology is a ring system, in which it is possible to operate up to 254 stations. The data transfer rate is 2, 4, 8 or 16 Mbit/s. There are basically three types of telegram:
- 1.
- The master-sync telegram is received by all the slaves, and is used for synchronization.
- 2.
- The master data telegram is also received by all the slaves, and contains the cyclic data and the service data.
- 3.
- The slaves send their data in the form of a drive telegram.
PC Fieldbus Cards for SERCOS Interface
Beckhoff specially developed the fieldbus cards FC7501 (single-channel) and FC7502 (double-channel) with PCI interface for the SERCOS interface. The driver integrated in the TwinCAT automation software ensures optimum performance of these passive master cards, so that compared with an active solution there are no unnecessary restrictions with regard to the number of devices or the data length. This also enables larger SERCOS projects with more than 50 axes to be realized. To do so several PCs are precisely synchronized via SERCOS, whereby one PC is defined as the master and all the others as slaves. For these applications it is interesting that the FC7502 double-channel card can handle one master ring and one slave ring. The parameterization of the master/slave mode is carried out simply through the software.
Bus Coupler for SERCOS interface
A further advantage results from the use of Beckhoff Bus Terminals with the BK7500 SERCOS Bus Coupler, which enables the high data rate, short cycle time and high deterministic features of SERCOS also to be used for classic I/O technology. Up to 64 the Bus Terminals for different analog or digital signals can be coupled to a single Bus Coupler. Machine manufacturers with a high drive consumption and low I/O consumption no longer have to install an additional I/O bus.
SERCOS control system
With TwinCAT as software PLC/NC, SERCOS cards, digital servo drives and Bus Terminals as I/O system, Beckhoff thus provides a complete PC-based control system for the SERCOS interface.