Introduction To The SERCOS interfaceâ¢ - Sercos N.A.

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SERCOS I and II Topology SERCOS III communicates over industrial Ethernet and offers both a line and ring logical structure within the cable. The double ring structure offers the possibility of redundant data transfer. With SERCOS III, in case of a break at any point in the ring, the protocol automatically switches over to the line structure, so that the communication and manufacturing will continue while the integrated diagnostics tool signals the break, which can be repaired without interfering with the plants’ performance. SERCOS III doesn’t use the star topology of the standard Ethernet. No hubs or switches are needed. Ring structure (double ring) M1 Master M2 Line structure (single ring) M1 Master M2 Slave 1 Slave 2 Slave n Slave 1 Slave 2 Slave n With hardware redundancy SERCOS III Topologies Without hardware redundancy Introduction to the SERCOS interface -- Sept. 2006 -- Page 6
B. Communications Structure In order to ensure strict synchronization of multiple axes and a predictable update time at each axis, the SERCOS interface utilizes a master/slave communication structure, where the motion control acts as a master, the drives act as slaves. SERCOS I and II drives are only permitted to respond to queries from the motion control, so direct communication between slaves isn’t possible. However, this feature is advantageous in some motion control applications and the Ethernet physics enable such a slave-to-slave data transfer, so SERCOS III supports this feature. C. Physical Layer With SERCOS I and II one fiber optic ring is used to exchange full 32-bit data between controllers, drives, I/O and sensors. This includes commands, status, parameters and diagnostics. In SERCOS III, standard industrial Ethernet is used for this purpose. Note that Ethernet fiber optics can be used for communication with SERCOS III. D. Communications Controllers ASIC (SERCOS I & II) or FPGA or GPCC (SERCOS III)-based SERCOS interface controllers are normally integrated into master motion controls as well as drives, amplifiers and I/O modules. They simplify the task of the designer by automatically handling most SERCOS interface communication functions. E. Timing Timing is critical in serial networks because motion controls cannot accurately reconstruct the state of the machine unless everything is precisely synchronized – measurements, transmissions and replies. Many of the messages that controls and drives send each other are for timing and synchronization. In CNC position loop software, the position error is determined in a software routine that takes time. The system works because the position error updates are designed to occur at predictable points in time. The same logic is applied in the SERCOS interface. Methods are specified to keep the jitter on the serial link down to a low level, then an internal timing sequence is used to ensure that all drives in a loop act upon their command signal at the exact same moment, and all acquire their feedback information at the exact same moment. The result is transparent to the user. F. SERCOS interface IDNs All motion control and drive communication is performed via a set of SERCOS interface telegrams, which each have an identification, or “Ident” (IDN) number. All parametric data, such as scaling and loop gains, and real-time loop closure information is set up this way. This allows the SERCOS interface to standardize the most common interface data. Over 500 IDNs are presently used to define a comprehensive set of motion control and I/O commands. All SERCOS interface products must incorporate a subset of these, but do not necessarily need to include all IDNs. Introduction to the SERCOS interface -- Sept. 2006 -- Page 7
Page 1 and 2: I. General Description Introduction
Page 3 and 4: III. Three Generations of the SERCO
Page 5: the motion bus, and use Ethernet ha
Page 9 and 10: VIII. Differences and Similarities
Page 11 and 12: X. Ideal for Distributed Multi-axis
Page 13 and 14: Typical applications for such a pro

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Introduction To The SERCOS interfaceâ¢ - Sercos N.A.